Beginnings:
Chapter 2 of “Beyond Biology”
By Charles S. Yanofsky, M.D.
Some years ago as I set out to describe what I felt was the
simplest of higher cognitive functions I
began to appreciate its true complexity. Memory is who we
are.
Contents
Our birth is but a sleep and a forgetting:
The Soul that rises in us, our life's Star,
Hath had
elsewhere in its setting,
And commeth from afar:
Not in entire
forgetfulness,
And not in
utter nakedness,
But trailing clouds of glory do we come
From God, who
is our home:[1]
-William Wordsworth
“Where
have I read that at the end, when life, surface upon surface, has become completely encrusted with
experience, you know everything, the secret, the power, and the glory, why you were born, why you are dying, and how it
all could have been different? You are
wise. But the greatest wisdom, at that
moment, is knowing your wisdom is too late.
You understand everything when there is no longer anything to understand.”
[2]
-Umberto
Eco
Memory is simple, deceptively
simple. It is like a single beguiling facet of crystal seen in an uncut stone. Should you cut carefully
through the rock that hides the crystal,
you will marvel at its
complexity. So it is with memory. On the
surface there is nothing to it. Human
memory is easily assessed. Storage in
devices from notepads to computer disks, is second nature. But explore memory completely, as an element
of cognition, and you will find it to be more complex than is appreciated by
the average neuro or computer scientist.
Ask a person to recall three
simple objects after a couple of minutes say, "hammer, three and
yellow", as doctors do in a mental status exam. People look askance when I
ask this type of question. What does it prove? It's an entrée into memory
function. Memory is the easiest cognitive function to assess. I used to wonder
how memory batteries became part of I.Q. tests. What does a person's memory
tell you about their intellect? We all know people who do well in school
because they memorize easily and regurgitate verbatim what is taught with
little mental processing. People who don't think seem to get the best grades in school.
Nowadays we have less regard for
simple memory. Schools claim to teach
students how to think, eschewing rote
memorization. Students are given open
book or take-home tests trying to to de-emphasize
memory tasks. Why should a student
depend on his memory when we have so many recording devices? Educators tend to lose sight of the fact that
creativity is drawn from a storehouse of internal memory, images,
words, combinations of words, melodies that are part of us. Creative persons recombine accumulated memory
elements in novel ways.
I always admired the way my fathe
Clinically speaking, it is quite
easy to tell when someone is having trouble with their memory. They complain of
losing objects, forgetting names and appointments more than in the past, going to anothe
Schematically we break memory
into three components, immediate recall -- the ability to repeat what has been
said, recent memory -- what can be reproduced a few minutes after a stimulus,
and remote memory -- recollection of one's distant past. You may be surprised
to learn that remote memories are harder to erase than recent memories. Old
memories are difficult to conjure up, it is true. They tend to pop up when not interfered with by the laying down of
new memory traces (engrams), something familiar to us from conversing with
older persons who do not register new memories well. Old memories are stored
differently than new ones. Well
established engrams arewidely available throughout
the brain. Memories that have circuited through the brain often enough become overdetermined, and reside in multiple locations to
interact richly with other memories. Few of us will ever forget how to tie a
shoelace. On the other hand we have only newly been exposed to recent events
which are just now assimilating into memory pathways.
It's still useful to think of new memories as
beating a path through a set of neurons and synapses as the process of learning
takes place. This is the point of departure of the old theory of Donald Hebb who in 1949 suggested that the physical substrate of
memory was a strengthening of connection between neurons, more efficient
transmission across the synapse, where nerve cells communicate with each
other. The average human brain contains about
100 billion neurons and perhaps one to ten thousand as many connections
between neurons, synapses. A memory is laid down when the connectedness between
neurons is increased, when a message
passes more easily from one neuron to the next across a synapse.
We usually associate the
hippocampus in the brain with new memory traces. Hippocampus means "sea
horse" since it looks like one
under low power of the microscope stuck in the middle part of the temporal lobe.
If the hippocampus is removed on both sides or is affected by a disease, a
person will no longer be able to learn.
New memories cannot be formed. There is some evidence that some simple
learning takes place by strengthening connections between hippocampal neurons,
that learning can be thought of mechanically as the strengthening of
connectedness or facilitation of transmission between nerve cells rather than,
or supplemental to, a change within a
nerve cell. This involves a pre and post-synaptic neuron. One
process that strengthens connectedness between neurons is Long Term Potentiation.
This process utilizes excitatory transmitter Glutamate. This creates a situation in the post-synaptic
neuron where it can be more easily stimulated by chemical signals coming from
the terminals of a neuron synapsing with it.
It happens because of the influx of Calcium into the cell. The marine
snail Alplysia serves as an experimental model for this process. Calcium affects an intracellular enzyme, Calmodulin. Eric Kandel and
colleagues worked extensively with this instructive animal model years ago.
There is a complex interaction here in that the
post synaptic neuron secretes a chemical messenger that makes the
presynaptic neuron more likely to secrete its transmitter. There is some new
evidence that what is made by the postsynaptic neuron to affect its partner is
the simple molecule nitric oxide (NO).
So what is involved is communication that goes in both directions
between the pre and postsynaptic neurons, communication that ends up
strengthening their interdependence and connectedness. The sum total of
increased connectedness between neurons is reflected in a change in the
behavior of the animal that is learning.
The hippocampus is involved with more advanced and rapid kinds of learning
that enters consciousness.
Figure 1: The hippocampus[3] of the temporal lobe. This seahorse shapedstructure controls the initial stages of memory formation.
You detect learning takes place
by observing a change in behavior. This is true for humans and experimental
animals. A snail can learn to withdraw a
body part, or a rat can learn a maze after a small number of exposures in order
to efficiently find a food reward, probably by the very same subcellular mechanisms as a child learns to
spell. His teacher seeks to observe a
change in behavior on a spelling or other test.
Whereas the child had not been able to spell a word before, she is able
to write it perfectly now. She has
learned and the test looks at an alteration of behavior.
Scientists have
looked at how these learning processes take place within the individual cell on
the microscopic level. In order to do this they generalize from a simplest
case. After a first exposure, memory
needs to consolidate if it is to
result in a reasonably permanent effect on the brain. Memory consolidation is
expressed in molecular and then in structural alterations in neurons and other
brain cells. Recent work has shown
unequivocally that protein synthesis is necessary for memory
consolidation. Other proteins modulate
production form the RNA templates. The chemistry inside the neuron utilizes
chemical messengers[4] , the very same messengers involved in a host
of other cellular functions, such as
cyclic AMP. Why does the individual cell
start to make proteins? The goal is to
create new connections between cells,
new synapses and parts of synapses, perhaps divided synapses, and the
like. Rats learning to navigate mazes
require production of specific proteins in the hippocampus. If this process is interfered with, the animals will not be able to navigate the
mazes. For the first time we are able to correlate
protein production and alteration of the untrastructural microscopic change,
with the laying down o
The laying
down of explicit memory is accompanied by ultrastructural changes in the
hippocampus and other areas. The brain is not a static structure. It is
changing, rebuilding, forming proteins
and synapses constantly as it is used. We cannot speak of the brain as having
only a static anatomical structure. The anatomy changes as it is used much like
a muscle or any other organ of the body.
In the brain this change in structure is easiest to see in memory
circuits, especially the hippocampus and the mechanism for structural change
involves gene products and proteins but is ultimately expressed in formation of
synapses or connections between neurons. Disuse and stress may lead to
atrophy. Hormones particularly cortisone
like hormones and estrogens have been shown to influence this process.
It is easy to
see that as soon as we learn which
specific molecules aid learning
then we may some day be able to influence them.
We will know how they are affected by disease, and, even more
importantly, we may be able to enhance
memory function by altering these molecules.
The memory we
think of most of the time, recalling words or methods, is explicit that is, mostly
verbal memory. Humans want to be able to
recall most of the time in task utilizing their language: names, dates, places,
methods of operation and the like. Implicit
or non-verbal memory is at least as
important as explicit memory however.
Implicit memory is the second
type of learning that happens on a nonconscious level.
It uses a different mechanism and
anatomic substrate. For example you
learn motor skills like playing the piano or basketball subliminally and many
aspects of this learning which involves practice do not enter consciousness.
The anatomical pathways for implicit memory are quite different, especially
memory which enhances motor skill. There
are a number of different types of implicit memory.
For example, in addition to
memory that enhances motor performance at a piano or in athletic
competition, there is undoubtedly a
similar kind of sensory implicit
memory. What allows emotions to surge
with recognition, resonate in a fashion,
well after a rhythmic figure or theme has been introduced in a symphony, is undoubtedly a subconscious implicit memory
mechanism. You hear a brief rhythmic
figure in the Berlioz Symphonie Fantastique
as he is being led to the scaffold which is "drummed" into the head
over and over again. Much later, a similar figure picked up as the Finale closes, has emotion reaching a fever pitch. Most listeners don't even notice it. They just feel the high emotion. Perhaps the composer himself is not aware
that he's used this technique because the music being on his mind, he will tend to use the same themes again in any case, much as the writer will, if he doesn't watch out, use the same words or even phrases again in
very different contexts. Much of this
occurs without a conscious thought, on
the part of the composer, or the listener.
It happens on a much more primitive level, of course, in popular music,
as themes are repeated, often interminably,
in a short song that lasts perhaps one or two minutes. What happens a good deal of the time in
popular music especially, is that there is such an abundance o
In classical music there is the
sonata form, consisting of
exposition, development and
recapitulation. One or more themes
present themselves in the exposition.
The development sees new expressive territory being claimed and finally
in the recapitulation, the listener is
transformed in a certain way, that
is, he hears the same or similar themes
differently. Jazz pieces use the same
basic form, incidentally, with a statement,
embellishment ( improvisation) and restatement of a melody. Since this process seems to be so
universal, this may hint at somet basic physiological mechanism. We
have a mutual maturation process involving composer and listener
alike. Otherwise stated, repetition alters the brain's response. Memory has to be there for past to alter the
future. The memory could just as well be
subconscious, unnoticed, yet it heightens subsequent response.
The hippocampus has vigorous
connection to areas responsible for consciousness and emotion# .
Emotion areas of the brain the Papez Circuit,
or limbic system, physically connect to
memory pathways. James Papez published his
observations in 1937 which makes him ancient as far as biomedical literature is
concerned. But many of his basic
observations are still extremely useful.
He noted that the brain could be broken into medial and lateral
sections. Medial parts connect most
strongly to the hypothalamus which is involved in basic bodily (visceral
functions) and is a structure that also helps organize emotion. The lateral
parts connect to the dorsal thalamus that is a way station for sensory inputs.
The structure of the medial of inner part of the hemispheres is intimately
involved with emotion and also memory.
Early anatomists connected many of these structures with the sense of
smell as this was considered to be one of the most primitive senses in animal
evolution (phylogenetics). In particular
olfactory (smell) pathways connect very intimately with the hippocampus. Thus memory, olfaction, and emotion are
closely allied anatomically. Since many
other animals, especially reptiles and mammals, are capable of expressing rage,
but only man shows evidence for advanced thought, with these medial brain structures being
relatively older in evolution, and with simpler cellular architecture, they are
considered to be more primitive, hence emotion is more primitive than cognition
or thought. We now have a much better
understanding that all of these functions interact, so as to be all part of a larger conscious
whole that includes both thought and emotion[6]. The individual structures and details about
their connections may be interesting to some readers but are not at all
necessary for purposes of discussion here.
At about the same time, new work
was published dealing with another brain structure, the amygdala (for almond,
an almond shaped structure in the temporal lobe). Animals that lacked an amygdala were docile,
hypersexual, and hypervi
Figure 2: The Papez circuit. Mamillary body to midbrain (1) and anterio-ventral nucleus of thalamus (mamillothalamic tract) (2), thalamus to cingulate gyrus (3), cingulate to hippocampus (4), hippocampus to mammillary bodies via fornix (5)[8].
The connectedness of the memory
circuit to the limbic system or emotion centers of the brain is neither
coincidental nor insignificant. The
post-traumatic stress syndrome links memory to high emotion.
PET scans show that the amygdala
is extremely active in forming memories. One may ask why this is so, since the
amygdala is viewed as an emotional center oft the brain. We have seen that it
is intimately connected with memory and emotional circuits. Perhaps this is why in sleep when we are
working to consolidate memories which closely tied to emotion and emotional expression
. Memory and emotion are closely linked.
Emotion that goes along with
memory is an integral part of it. I rarely recall dreams but was able to remember and record
most of what turned out to be a very complex dream because of a musical theme
that seemed to be playing through the dream sequence, much as music plays in a
movie. It was a theme played by the high
strings and flutes of Prokofiev's Romeo and Juliet that I'd been listening to
the day before. The music was supposed
to be portentous telling you that something fateful would happen in scenes to
follow. In the dream it evoked a totally
different emotion, one of ghostlike eerie fear that I hadn't appreciated while
listening to the piece. The day after
the dream, recalling the music and its attendant emotion, I was able to
reconstruct the complex dream surprisingly well, all through the process using
the melody and emotion as a sort of mnemonic device. Moreover there since sensory experiences from
the day prior are frequently used for dream material it may be that one
function of sleep and dreaming is a dry run rehearsal of the previous days
events that leads ultimately to the permanent laying down of memory
traces. The hunter dreams of catching
his prey, re-rehearsing experiences of
the day before, reshuffling images, recreating scenes that will enhance his
performance the day after. In fitful
sleep you rehash yesterday's argument with your boss, etc. Dreams place
memories in an emotional context, are intimately tied to the emotional valence
of memories. Perhaps this is why the
Forgetting is at least as
important as remembering. There must be
active processes that aid in forgetting,
some of which will someday be described on the cellular and biochemical
level, just as active memory is
described. This would serve obvious housekeeping functions. For one thing you
could picture that it would be impossible to function if all of our memories
old and new were constantly competing for our limited attention. Imagine if all of your old memory stores
kept creeping into consciousness. You wouldn't be able to handle current
tasks. You are taking an exam in biology
which asks specific questions. Think what would happen if you were unable to keep out of your mind's
eye for at least a while what you had learnt in physics the day before. Some other memories, might be more difficult to exclude, from your
current attentions, but the point is,
some active adaptive process pushes even recent memories out of
consciousness, mostly unclutters
awareness. Older memories are
pushed even further away. Somewhere in
our brain (this turns out to be all over our brain and is difficult to
localize) is a memory attic which contains relics of our past.
Dynamically trained psychiatrists
still talk about repression as a defense
mechanism, an active process, pushing old memories out of awareness. This is still a useful concept, but contrary
to psychodynamic renderings of the process,
it is almost always a healthy, not a pathological process.
It is easiest to conceptualize repression as an uncluttering
mechanism. As we have seen, dreams from the previous night are actively
pushed back into unconsciousness where they belong. For most of us dream content can almost never
be retrieved or is brought to the surface only with great difficulty (and very
questionable authenticity). This is
universal for most healthy functional individuals.
I recall a conversations with a
very troubled man in his mid 50's who was plagued with numerous memories of his
childhood and unresolved conflicts mostly revolving about his relationship with
a now deceased father. Time and again he'd
mention to me with great emotion, how
his father could never tell him he loved or approved of him, something which obviously hurt him
deeply. But it was apparent that he was
trapped in a web of old memories.
Trapped or fixated in his past,
he was incapable of handling the challenges of the present. Some
therapists might talk about how important it is to revisit these childhood
conflicts with the rational retrospectiscope of a
grown adult. The only problem is that in
many cases there seems to be a total entrapment or fixation on the thought
processes of childhood. Plain repression
of these memories would seem to be much more adaptive. Perhaps old painful memories which we push
away have subtle and unsubtle effects on our present lives as they influence
attitudes and behavior. And so the
debate goes on.
Through years of scientific
research there have been many theories of how learning takes place. Some of
these theories stress what happens inside instead of between cells. They
implicate synthesis of chemicals such as nucleotides and proteins. Neurons are analyzed for these chemical
constituents after an animal is exposed to certain experiences that change
behavior. These older theories are in not incompatible with synaptic theories
and there is every reason to suspect that our explanations regarding how
memories are formed are very incomplete.
Memory function is certainly a
composite of many biochemical processes within and between neurons. Even the simplest discussion of memory, the
most rudimentary of cognitive functions, reveals that we are trying to deal with many separate
processes. We have already mentioned
immediate, recent, and remote memory, conscious and subliminal motor
memory. The chemical and anatomic
substrates for these different processes
are not the same. For example, verbal and conscious memory is the type we talk
about classically being mediated initially by the hippocampus. For words and
symbols that usually require conscious awareness, the hippocampus is the portal
of entry into the brain until the memory engram becomes firmly established and
destroying the hippocampus will affect short term memory, blocking the initial establishment of a
foothold in the brain. But non-verbal
performance memory, is mediated by motor
systems such as the cerebellum and it is more than likely that performance
learning, basketball and piano playing among other things takes place directly
within these systems. It is likely that
there are other forms of learning as well, but the basic breakdown is into
conscious vs unconscious processing.
Figure 3:Types of memory. Retrieval brings memories into
awareness. For the most part, emotions, motor and sensory engrams, though not
subject to voluntary retrieval, may still affect behavior and performance.
Clinically a decline in mental
function seems manifest first in a loss of ability in recent memory. This corresponds to neuropathological
changes that occur first in the hippocampal
and parahippocampal areas of the brain,
especially in Alzheimer's disease.
We all know elderly persons who lose their ability to remember. In some
of these persons other spheres of mental effort remain relatively unaffected
and they are said to have a benign forgetfulness of aging. In others, loss of
recent memory function signals a global decline in cognition termed dementia.
This is what happens in Alzheimer
disease which is frequently presents with a loss of memory function.
The transmitter Acetylcholine is
most closely associated with this disease, and intimately tied with recent
memory. A diffusely projecting nucleus in the brain, the nucleus basalis of Meynart shows the most change. The output of this group of
neurons is primarily cholinergic and largely to the hippocampus.[10] A lot of people have tried to help failing
memory by increasing this neurotransmitter much as one does in Parkinson's
disease with dopamine that is deficient because of loss of Dopamine producing
neurons in the brain. All kinds of substances have been used to retard the
degradation of Acetylcholine, or to replace this transmitter, some of these
dripped directly into the ventricles of the brain to improve memory, all with
a very minor effect. The first of these
to be FDA approved is called Tacrine or Cognex but it has little lasting benefit and significant
toxicity, affecting the liver mostly. The minimal benefit can best be
appreciated by sensitive measures such as psychological tests.
It's just because memory is so
easy to get at that it seems to have so much philosophical relevance. Computers
and libraries have vast stores of information as bundles of bits appropriately
labeled, which can be retrieved when asked for. Named bundles of engrams are
stored in isolation, retrieved, and operated on in ways defined by a user. It
is reasonable to ask whether the brain functions as a repository of information
in the same way as a computer or library.
Surprisingly, The answer is that
it does not.
For humans the laying down of
memories is equivalent to maintaining the continuum of consciousness. Time is
continuous and we reckon and follow it on the basis of stored past and newer
experiences. Our past serves as a basis for comparison but it also colors
perception and action. This is what we
mean when we talk about learning or memory.
We expect the laying down of a memory engram will make some enduring
change in thought, emotion or behavior that we will be able to measure. If there is no way to determine that a
difference has somehow been wrought, then the effect of memory is imperceptible. On the basis of what has been laid down
before we are made to see things in different ways. Each old memory trace may be more or less
critical. For example, a traumatic childhood sexual experience not only changes
adult sexual encounters but colors all subsequent experience. Much of the work
of classical psychotherapy is breaking a traumatic or maladaptive link between
emotions and current events, and
re-establishing connections with previous repressed memories. What is truly fascinating is that this seems
to occur whether or not specific memories can be specifically retrievedf . This continuity of experience is perhaps the
most important determinant of personality structure. A human life is a chain
of experiences encoded in memory that is a continuous flux of maintained
consciousness.
It is undoubtedly true that
experience alters our personality, ou
This has implications concerning
the meaning of life and death. Consider the possibility that a soul or
personality is reincarnated after death, not just discarded by posterity, but
simply transmigrates into a different vessel, a different body. Typically
persons who believe in such a doctrine reason that we are not aware of this
because memories of our past lives are inaccessible. At first blush this seems
to be an absurd notion. After all, a soul with no access to its past is a new
creation. But the past may not be entirely cut off from the present. It may be
difficult to get at, especially for those of us unskilled at the proper
technique. More importantly, it may come
out in subtle ways and may still color
present experience in much the same way that our own living memory does. Even
so reincarnation of the soul is hard to swallow at least for Westerners
because memory is for us the contiguity of existence. When continuous formation
of memory traces stops a new line of
experience, in essence, a new being, emerges. In one sense, life and death,
creation and destruction may be defined this way, a break in sequential memory.
But here lies an even more critical point.
There is more to human memory than simple retrieval of information bits
in storage. Memories, meaning our past,
even if not specifically retrieved, change present and future experience.
Memory, arguably the simplest of all cognitive functions, may take on an
almost mystical significance. Some persons claim that they can bring back
memories of a previous life through extreme hypnotic regression, that memories
inaccessible to our waking existence can be brought back via hypnosis. There is as yet no scientific evidence that
hypnosis improves retrieval under any circumstances and none to support the
notion that hypnosis causes the true elicitation of childhood and other
forgotten memories. Observing hypnotic
sessions, one comes away with the impression that the hypnotized subject is
manipulating the therapist but under the best of circumstances no one has ever
proved the veracity of a hypnotic regression into childhood or into past
life.
Most supposed hypnotic
recollections are really works of the imagination. This is especially apparent to
scientifically-minded folks who look with a jaundiced eye at recollections of
infancy and past lives. Where does
memory end and imagination begin? This
is a most difficult question to answer for the subjects of hypnosis, assuming that they are not out-and -out
malingerers or fakes.
False memories have been subject
of a lot of attention in recent years.
There are celebrated cases of child abuse and sexual misconduct such as
one involving the Catholic Archbishop of
Memory and imagination[12] are both abstract non-material entities
comprised of pure thought. Some of this
manipulation of ideas may be non-verbal and subconscious. How do we know, when we are creating
something, that we're not simply
reaching down into our memory stores and placing ideas in a new
juxtaposition? A good deal of creativity
and synthesis involves bringing up memories in a new light. An inspiration, or solution to a difficult question hits us
when we least expect it, most
often when we are not even working on a problem that is consuming our attention
at the time, but more often during random activity. This sudden inspiration, has been noted by a number of creative
persons. For example in the words of
mathematician Henri Poincare[13]:
"Most striking at first is this appearance of sudden
illumination, a manifest sign of long,
unconscious prior work. The role of this unconscious work in
mathematical invention appears to me incontestable, and traces of it would be
found in other cases where it is less evident.
Often when one works hard at a
hard question nothing good is accomplished at the first attack. Then one takes a rest, longer or shorter, and
sits down anew to the work. During the first half-hour, as before, nothing is
found, and then all of a sudden the decisive idea presents itself to the
mind. It might be said that the
conscious work is more fruitful because it has been interrupted and the rest
has given back to the mind its force and freshness. But it is more probable that this rest has
been filled out with unconscious work
and that the result of this work has afterward revealed itself to the geometer
just as in the cases I have cited; only the revelation, instead of coming
during a walk or a journey, has happened during a period of conscious work, but
independently of this work which plays at most a role of excitant, as if it
were the goad stimulating the results already reached during rest, but
remaining unconscious, to assume the conscious form."
All of us have experienced the
same process so well described above. It
happens when we lose something and suddenly,
never when we are looking for it,
remember where it was. This
recollection comes to us in a flash. And we just know that what we have
recollected is accurate. Isn't it
exactly the same when we have been working on some puzzle or problem, that we
experience a sudden flash and the solution is ours. These points are so inspiring because in an
instant we just know we have come upon the right solution; all of it just works out so perfectly we
almost need no verification. You can
observe this for yourself in hearing people solve puzzles on TV o
Some people lose the ability
temporarily to store new memories. A
condition known as Transient
Global Amnesia, is most probably caused by blocking the blood supply to specific regions of
brain. We know that if only one side of the brain is
affected memory registration will not be affected. The problem has to affect
both sides of the brain at once. The
subject with TGA loses the ability to form memories for a
few hours. During that time, he is
exceedingly uncomfortable and feels disoriented as if in a cloud, asking
questions pertaining to time and place time and again, forgetting
answers given almost immediately and is concerned about this. After the episode
there is no recollection at all for the period of time for which memory was
affected. Sometimes this seems to occur after some kind of exertion or trauma
just as if a blow or concussion has
occurred. In one case TGA was occurred
repeatedly in relation to sexual intercourse[14].
Another condition that breaks the
stream of awareness of life is syncope, or
simple faint. Of course any epileptic seizure that disturbs
consciousness will do the same thing. But syncope is interesting for one
reason. Interrupt the blood supply to the brain and a faint occurs. It happens
with a drop of blood pressure. If the heart, for any reason stops pumping blood
to the brain efficiently, you will faint. How long does it take to lose
consciousness once brain stops getting blood?
Almost immediately!! This is quite
remarkable and one wonders why this is so.
The brain metabolizes glucose and
needs oxygen continuously in order to make energy. It is one of the most
voracious consumers of energy in the body. Other tissues can switch into
alternative energy sources when necessary. When you exercise for a while
muscle, sensing a diminishing supply of energy, with the liver overwhelmed in
its ability to supply constant amounts of glucose, switches to the consumption
of fats and can also depend (briefly) on anaerobic glycolysis
so that energy can be utilized without a constant high concentration of
oxygen. Not so the brain.
The brain requires a constant
blood supply. Otherwise it will stop functioning right away and a person will
faint. If left for just a few more
minutes there will be irreparable damage or even brain death. This underlines a
certain fact about the brain. It is an information storage and manipulation
device needing to be constantly connected to its power source. The brain
resembles a computer that is on and storing and manipulating data. Cut power for even an instant and the thing
shuts down. Whatever program you were working on is lost. One wonders why the brain couldn’t have been
designed in a different way, perhaps with the ability to switch immediately to
its own “battery” or energy supply for just a few moments when necessary. It
seems when awake, the organ is revved up and utilizing to the hilt immediate
sources of energy, glucose and oxygen.
After one or two minutes or so without any blood, the old informational
content can still be gotten back. When consciousness returns after this short
length of time, you are still the same person.
Also in the brain, as everyone
knows, neurons are, as a general rule not replaceable. This is in
contradistinction with other organ systems, the liver, the gut, skin, blood and
so forth where cells are replenished constantly and rapidly. Injure the
intestine, kill cells by the millions and they will grow back very fast. Why not in the brain? Of course that is because every brain carries
information built into its anatomy and transmitter and electrical
patterns. Nerve cells are not
replaceable because new nerve cells will not have the same informational
content. Information and experience, life in other words has a certain immediacy.
The same holds for instruments which store changes in time or even
keep time. A constant source of energy
is required. That is the reason for that little battery in your clock radio why
everything is lost when your computer’s power supply gets interrupted.
The chain of recollections that
defines continuity of consciousness is broken, but the situation is still
different from that of reincarnation in that it is still possible to reach back
and recall experiences of the just slightly more remote past and also to
continue to record future experiences in a stream of mental awareness. Even
so, the person with TGA is very troubled
by the void in memory long after this temporary process is over. This is so
even when as usually happens, family and friends inform him of events relating
to the specific time frame that these events occurred. Other's recollections of
events in one's own life aren't satisfactory. A vacuum or discontinuity,
however short, must be filled.
Diversion:
why time travel is not possible:
Memory
determines a stream of awareness.
Breaking this stream of awareness is very uncomfortable. An hiatus is difficult to deal with. It is
only memory that changes us as we
journey through our lives from our past into our future. History gets recorded in our mind. I think that's why it's so difficult to
fathom, why for nuclear physics, time can stretch and contract and just as
easily flow backward as forwards in some instances. The best example is the Feynman diagram in
which nuclear particles collide and create other nuclear particles, for example a neutron will split into a
proton and electron liberating some energy.
This process can just as easily flow backward as forward as long as
conservation laws are respected. This is
intuitively impossible for us in ou
Figure 4:Typical Feynman diagram[15] in which two pion
particles are formed from the collision of
proton and antiproton particles. This could just as well go the opposite
direction in time with the pions forming the proton
and antiproton.
For humans there is an immense
difference between the past and the future.
In the past something occurred,
it alone and of itself. But the
future is unknown and filled with alternative possibilities, only one of which will actually happen. This is particularly true if we introduce
free will into the equation. The past
and future are asymmetric and not interchangeable, for the past is one hundred percent
determined but the future is at best probabilistic often chaotic. As the future is subjected to time's arrow
and becomes part of the past, it is recorded in conscious and unconscious
memory (it becomes history) and the
uncertain turns into certainty. The flow
of time is thus asymmetric, and the past is recorded in our mind, altering forever future experience. The Second Law of thermodynamics seems so
theoretical and flimsy, not good enough an explanation for what we all know to
be true for all of us. Time travels in
one direction, forward. The most important explanation, has to do
with how our mind's work, consciousness
and human intuition about time's irreversibility. Even if the backward flow, the undoing and
redoing of events is theoretically possible, it is not possible as a mental
event, not unless we can fundamentally alter mental processing, which some day
we may be able to do. Time travel may
thus depend as much on changing mental processes as it does in manipulating
physical laws.
Figure 5: Time's arrow. As the past blends with the future in our present, one becomes many possibilities, so that one can't turn back. Free will, exacerbates this process, expanding alternatives unpredictably.
Figure 6: History diagram. At each branch point
only one of a number of possibilities actually occurs.
Let us suppose for a moment that
one could go back in time. One of the
major problems that a lot of people pick up on is that the act of going back
and reporting on the past has to alter the future. The reporter who does go back then returns to
the future is sure to alter the course of events. This is so even if he is a fly on the wall,
invisible to those experiencing their present.
When the time travele
But that is not the biggest worry
with time travel. Every moment in time,
as the figures show, is a branch point
of alternative possibilities. Only one
of these possibilities actually occurs.
Then events continue until almost immediately another branch point with
alternatives again occurs. At any point
it is just about as likely that things could have turned out a different way.
Biologists have noted that life
on earth as we know it is due to specific developments as branch points. Scientists have to admit that even on the
earth, life and sapient life probably would never have existed but for a very
improbable chain of events. Preplanetary gases had to
have coalesced into what we know as the earth just the right distance from the
sun making our planet like Goldilocks'
porridge, neither too hot nor too cold.
Floes of molten rock inside the earth had to have created a magnetic
field which blocked the lethal effects of radiation to make life possible. Specific conditions perhaps heat and
lightening had to have existed to juxtapose and give sufficient energy to
simple organic compounds in order to make
life which at any event had to eventually become self-replicating. The cell had to have evolved the way we find
it today, with the aid of prokaryotic
parasitic invaders which carried with them mitochondria and chloroplasts,
remnants of simpler forms that make the cell and cellular energy handling
possible. Photosynthesis had to have
served as a chemical process that freed oxygen to make an atmosphere for aerobic life to survive. Cells had to have gotten together and
specialized to make more advanced complex animals and plants come into
being. Explosions and extinctions of
groups of organisms had to have taken place in highly specific ways. Dinosaurs
and not mammals could well have ruled the earth but for the accident of an
enormous meteorite impact upon the
planet etc etc.
In other words, biologists sensing that life as we know it on earth is
the result of highly improbable
alternatives are less sanguine than physicists and astronomers about life as we
know it especially sapient life, existing on other worlds. Even if you look upon life as some kind of
self-organizing complexity, still one has admit that life as we know it on the
earth, is the resultant of a specific chain of happenstances. Things might well
have ended up a whole lot different even on our beloved earth, in other words,
without us!!
We begin to appreciate an
indeterminacy. If you can look back and
you see that things could just as well have turned out different or you begin
to see the future in the same way, all of a sudden you realize why time travel
is impossible. You will not be able to
travel along the precise path of possibilities you were on; you will be sure to
lose your way among different alternatives.
You may get stuck on a different time line or, put differently,
alternate universes. Maybe you will end up in a different world that only has
prokaryotes or lacks a magnetic field and has no life at all. If you ever travel in time you can be
virtually certain, you cannot go home again.
This implies that the inability
to travel in time is tied to the uncertainty, the indeterminacy of the
universe. For time travel to be possible
the universe must be deterministic, alternatives at branch points need to be
fixed, established. Our lack of
conception of time travel is thus as strong an argument as there could be,
against determinism.
Dream memories are
stored, affect us subliminally, but are difficult to bring to any form of surface
awareness. Most of us can't recall them in any detail and we are hard-pressed
to attach any specific meaning or context to them. Even so, they affect at the
very least, the feeling tone of subsequent experiences and color perceptions.
I've often had the experience of acting and feeling as if a dream event were
true while in reality, it was a mental fabrication. Only after noticing that
what I'd assumed couldn't possibly be true did I realize that I must have in
fact dreamt it. Certainly thought involves a kind of simultaneous
layering. A lot of times we find
ourselves trying to manage even juggle feelings. Feelings come to us from contradicting
forces-- present reality, manifest thought content, and dreams that lurk in the background of
thought. We are handling simultaneous realities, our present conscious stream of reality and a
subliminal illogical dream-driven thought stream. The incompleteness of recollection of active thought processes of
sleep shroud them in mystery. Ancient dream interpreters were accorded supernatural powers and even in modern
society are held in high esteem from Joseph to Daniel and Freud to Jung. Still,
there is every reason to believe that at least two continuous streams of
consciousness interact and operate upon each other even though the memories are
not made manifest. We know that details of immediate past experience form the
previous day, often apparently inconsequential details, are incorporated into
the content of dreams. Conversely, dreams imperfectly remembered while awake influence mood and beliefs. Your
wife or your child having appeared in a dream experience at night may color
your interaction with your family the next morning. Mental engrams may be
operated upon and may interact without even being specifically recalled.
Memories of events from actual
experience are difficult to reach. Details inscribed in certain portions of
our brain may still be inaccessible. Perhaps you've experienced this while at a
gathering introducing a person whom you know and anxiety momentarily blocks a
recollection. Tests in school engender
the same kind of anxiety that blocks recall. The answer may enter your mind
only after you've left the room. Details of earlier life become inaccessible
merely because events are too distant to be pertinent to our current situation.
This is a service that are brain provides
for us, the sorting or packing away of memories, an uncluttering
of immediate experience. Old useless memories are almost irretrievable.
The difference between
people with super memories as opposed to the rest of us seems to be a matter of
memory retrieval, not storage. To
utilize a memory you have to have done two things: It has to have been written down somewhere
which in the brain means there has to have been some structural alteration in
the brain that results in the memory's having been stored. Next you have to use some mechanism to
retrieve the stored memory. The reason
why you can't recall something is frequently a matter of getting at, retrieving,
the stored memory trace. Storage
involves lower brain structures such as the hippocampus and some other areas
adjacent areas too, the thalamus, entorhinal area
that lie beneath the highest levels of the brain, the cerebral cortex. But retrieval, recruits cortex
especially. Consequently it is retrieval
that is most vulnerable to changes in level of consciousness.
Thus we have an anatomic model
for a memory engram or any thought or sensation reaching consciousness. In order for us to be aware of anything, a memory,
a sensation, pleasure or pain, it has to stimulate the highest areas of the
brain, the cerebral cortex, responsible for consciousness. The stimulus has to have caught our
attention, that is aroused the gray colored cell bodies at the surface of the
brain. Example: an unconscious person is unconscious because
the lower brainstem levels have failed to arouse the cerebral cortex which is
not awake or aroused. You squeeze a
finger on the hand of the subject. He
withdraws the hands and winces in discomfort.
But he is not awake and aware.
Does he "feel" the
pain? The answer is that he does not
feel it. In order to experience or
feel, one must be conscious to the
stimulus, awake and aroused. If the
stimulus does not reach consciousness
and despite intact automatic behavioral responses, withdrawal and wincing,
there is no painY . The
anatomical substrate of conscious awareness is the cerebral cortex. In order for us to be aware of something, it
must take hold of cortical neurons,
something needs to direct our attention to that particular thing. This is what we mean by retrieval. Here widespread cortical excitation, attention, is directed to a specific memory
engram dredged up from the past. It is
taken out of storage, comes to our attention and is thus retrieved.
It's been demonstrated time and
again that memories are very well recorded. They can be elicited with certain
techniques such as hypnosis, the use of certain inhibitory drugs such as short
acting barbiturates and by electrical stimulation. Some of these methods relax a person, help
him get past any anxiety or distraction impairing retrieval# How are our memories ordinarily
retrieved? One model assigns to each
memory a specific anatomical location. You
Another far more useful model for
memory retrieval is described by the great Russian psychologist A.R. Luria in his classic book about a subject with a
superlative memory, The Mind of a Mnemonist. This person was described to retrieve
memories through synesthesia, the merging and connecting of various sensory
modalities such as sight, and sound. Certain specific recollections might be
connected with an explosion of vivid colors, for example. One might ask what does
this accomplish? Doesn't the mnemonist now have to remember even more than he
would otherwise in order to extract a specific memory? The answer is that this
is not a factor because the most difficult aspect of remembering has mostly to
do with retrieval, not storage.
Synesthesia has a definite psychedelic quality and
as one might imagine is a common event in drug users. It is probable that the editorial, inhibitory
or excluding properties of the brain are impaired and especially by opiates and
sedatives that may impair the more advanced or controlling areas of the brain
preferentially compared to lower areas.
Dr Ober in his very interesting study Boswell’s Clap and Other Essays goes
into marvelous detail in his study of literary figures and medical impairments
and their influence on literary production.
He points up the synesthesia in Francis Thompson’s “Ode to the Setting
Sun”:
From: ODE TO THE SETTING SUN By Francis Thompson
ODE
Alpha and omega, sadness and mirth
The springing music, and its wasting breath--
The fairest things in life are Death and Birth,
And of these two the fairer thing is Death,
Mystical twins of Time inseparable,
The younger hath the holier array,
And hath the awfuller sway:
It is the falling star that trails the light,
It is the breaking wave that hath the might,
The passing shower that rainbows maniple,
Is it not so, O thou down-stricken Day,
That draw’st thy splendours round thee in thy fall?
High was thine Eastern pomp inaugural;
But thou dost set in statelier pageantry,
Lauded with tumults of a firmament:
Thy visible music-blasts make deaf the sky,
Thy cymbals clang to fire the Occident,
Thou dost thy dying so triumphally:
I see
the crimson blaring of thy shawms!
Why do those lucent palms
Strew thy feet’s failing thicklier than thy might,
Who dost but hood thy glorious eyes with
night,
And vex the heels of all the yesterdays?
Lo! This loud, lackeying praise
Will stay behind to greet the usurping moon,
When they have cloud-barred over the West
Oh, shake the bright dust from the parting shoon!
The earth not paeans thee, no serves thy hest
Be godded not by Heaven! Avert they face,
And leave a blank disgrace
The oblivioius world! Unsceptre thee of state and place![16]
There are many other techniques
employed to increase retrieval so that subjects appear hypermnestic. Ancient Roman orators connected individual memories with rooms and
parts of rooms in a type of topological memory system, of a mansion or structure already familiar to
themF . A related technique is to assign each
specific memory to a wall, corner or ceiling of a familia
Most other memory techniques work
to strengthen associations between two
or more objects. One may be considered the known or "given", to be
associated with an unknown or "data".
For example, a lot of us have trouble associating a name with a
face. We may see a person to whom we've
recently been introduced and forget the name.
The face is the given, the name the data. Or, we may have trouble
connecting a state with its capital.
There are many common sense techniques employed to strengthen these
associations. These ordinarily appeal to
other senses, especially vision, in the making of the memory. To reinforce
Many people find the simultaneous
recall of memories by two individuals mysterious. Two people may suddenly blurt
out a recollection at the same time. Perhaps this means they are sympatico or really
in love or that they know each other so well there is an undercurrent of deep
subsurface communication. They fail to realize that both of them have been
subject to the same stimuli. A more
parsimonious explanation for their simultaneous verbalization is that the same
memory is tied in their mind, with the same stimulus. This is much the same as
our ability to recognize and extract the memory of a certain song after the
opening bar, sometimes just a single chord, is played. All this means that
there are myriad ways of getting to memories once they are firmly imprinted on
the brain.
The purely anatomical model which
proposes that each separate memory resides in a specific anatomical location
is appealing. Electronic devices such as records, laser disks and floppy disks
store information this way. You retrieve a memory by finding its address. Penfield's electronic probe may easily be likened
to a phonograph needle. (Recall that Penfield was the neurosurgeon who tried
stimulating brain gyri during brain surgery and found that electrical
stimulation would elicit specific memories some of the time.) Stimulate the proper gyrus and you will
elicit (play back) a specific memory.
But it has not been possible to erase specific
memories in the brain merely by cutting
certain anatomical regions out. In
humans who have specific lesions caused by stroke, penetrating injuries, or the
like, that destroy specific regions of
the brain, it has never been possible to show specific memories are lesioned as
well. Rather it is most likely that specific memories are not lost. The brain
seems to be unlike electronic data recording systems. You can't pin down
specific engrams to certain tracks, locations or addresses. In fact, as you cut
areas of the brain out, even temporal lobes (as is occasionally done for
epilepsy) you get the impression in seeing these patients, that their basic
personality and memory structure is intact.
How do we explain the fact that memories can be brought out by an
electrical probe, by topiographic stimulation of the
brain and yet cannot be lesioned?
An engram is a single unit of
memory that makes an impact on the brain. One popular theory of memory is that engrams are stored widely rather than
at specific addresses. The entire brain or large portions of the brain may
store memory traces conspiratorially. Perhaps engrams are stored widely over a
large volume of brain. This would fit with the experience of clinicians that it
is not possible to connect specific focal brain lesions with the loss of
specific memories, also with the fact that older memories are easy to retrieve
and more resistant to loss. Perhaps repeated exposure (as in learning, studying
and then experiencing a certain fact, produces widespread anatomical
(synaptic) or biochemical cerebral changes.
When holograms (three dimensional pictures)
first came into existence, cognitive and physical scientists were intrigued
with the technique. Bits of information were widely distributed over the entire
picture so that far flung regions of the hologram contained information about
other distant regions. The hologram lived up to its name and recorded data not
in an analytical fashion as most electronic devices and even regular
photographs seem to do, but saw information as a complete unanalyzed package.
Data about a single point in three dimensional space was widely distributed on
the photograph. Another feature of a hologram is that data from the whole
picture is contained in a small part and thus a good portion of a hologram
would have to be damaged before the picture would be lost. These are features
that holograms have that seem to fit the model of memory driven by lesion
experiments[18].*
As it turns out, computer
scientists are actively studying holographic storage. There are all kinds of
possibilities here. Two beams of laser light will work to retrieve information
stored by comparing their transmission in what is called an interference
pattern. Information is stored in three, rather than in two dimensions and
mechanical contrivances such as disk drives would be replaced by non-moving
electronic devices. Retrieval of specific pieces of information would be much
quicker. Rather than retrieving a single bit of information at time, a whole
image of thousands of bits could be retrieved at once making video image
storage more of a possibility and also parallel rather than serial or sequential
information processing[19].
Another slightly contrasting
theory, is that engrams are overdetermined or, in
other words specific memories are multiply stored in various regions about the
brain rather like having a record with a song stored over and over again or a floppy disk with the
same file stored in multiple locations. Apart from the sheer inefficiencies
involved, this explanation doesn't make sense. Why should memories be stored
multiple times merely for the purpose of not losing them in the unlikely
instance of a brain lesion. Perhaps just to fool the neuroscientist? However this picture turns out to be closest
to the truth.
At one time I had visions of neurosurgeons extracting specific
memories in their operations. When you went under the surgeon's knife you
never knew what you were going to lose. In one patient he'd extract memories of
married life, in another, records of childhood, perhaps a high school diploma
here, a Ph.D. there. We now know (from experience) how ridiculous this notion
is. By whatever means (and it is most probably quite different from a hologram
model) specific memories are widely distributed in the brain.
Memories seem to be are stored,
then attached by certain handles
tugged upon during the process of retrieval. Some of these handles aren't
adequate in and of themselves to extract memory engrams. Perhaps these may even
break off under the weight holding a memory down. Certain forces that keep a
memory from coming to the surface impai
To Review (Please see figure
below): As memory gets established it is embedded, dug into, the brain,
(signified by the spade in the picture).
A single memory or engram is
multiply represented over the cortex, and stored in different cortical regions
through use of such techniques as synesthesia (multiple sensory involvement)
and visualization. A primarily auditory engram or single memory can be
visualized and is thus represented an additional time in a visual association
area. That way the memory is, in a sense, reproduced over the cortex and is
over-represented as visual reproductions and auditory associations accrue. The engram is thus acquiring various handles
by which it can be brought to the attention of a person o
Thus a single memory engram is
subject to: FOCUSING OF ATTENTION,
RECORDING, CONSOLIDATION, CORTICAL SPREAD (Reproduction, overdetermination), RETRIEVAL
Figure 7:Model for
Storage and Retrieval of Explicit Memory
When you cut out a specific area
of the cortex, you do not destroy a memory.
What may happen is that you will extirpate a specific way of getting the
memory out. Let's say you stored
recollections of a hammer among many other tools. If some process comes along, typically a
stroke, that destroys the small language region to which you've assigned
tools, then you will not be able to
extract a recollection of a hammer by appealing to it as a tool. That particular handle, for that specific
engram, the hammer, will be affected.
Since a hammer is otherwise quite a familiar object, you will still be able to appeal to a
recollection via other modalities, say a
tactile or a visual association. Recent
research, especially by the neurologist
Antonio Damasio, mentioned previously, shows that exactly this type of
categorization and anatomic compartmentalization of concepts takes place in the
brain. The handle determines the
anatomic locale in the brain. In other words,
visual associations are likely to be stored in visual brain areas, language categories in the language portions
of the brain and so forth. Individual
memories, long established, are stored
in multiple brain regions.
Computers store memory in files
and register them once typically, unless there are multiple copies in the hard
disk, CD ROM or other storage
device. Computers can bring up ideas
fast because they can search text for any occurrence of a word, looking through their various files. They perform these whole file searches at
enormous speed, that brains aren't
capable of. The age of the filing
typically does not matter to a computer either.
Ancient o
Nine times out of ten when a
young person complains of a poor memory one can assume that the memory is
grounded too strongly and cannot be removed, or that this person is distracted
from the business of storage by some process that distracts his attention, i.e.
anxiety or preoccupation. Anxiety
affects memory in two ways. It blocks
attention so that the original memory cannot be laid down. The original stimulus isn't noticed because the subject was paying
attention to other things. Then he
wonders why he didn't remember it. Or,
anxiety can weaken the association that helps us to extract memory. Often anxiety is a force that keeps a memory
buried so that it just cannot be extracted. This is one mechanism for the
phenomenon of repression.
On the other hand older
individuals are much more likely to suffer from a disease that impairs the
original storage and registration of memory engrams. Older individuals can just as well have
problems that younger ones do, but in
addition are more likely to have degenerations that preferentially affect the
hippocampus like Alzheimer disease. Strokes and seizures and many drugs which
older folks are much more likely to be taking can also block attentional processes
instrumental in laying down and consolidating engrams. In other words older individuals are more
likely to have an organic neurological problem that impairs memory formation
and retrieval, yet old and young may
present with the same complaint.
Certain unpalatable recollections
of childhood are actively suppressed,
particularly the ones attached to high
emotions. The inability to recall details of our past or conversely aberrant
recollections may be the cause of serious psychiatric derangements. On the
other hand, when a person is helped to bring such recollections to the surface
an explosion may well occur. A war veteran may have suppressed horrible
recollections of the battlefield or his participation in human slaughter.
While specific memories cannot be recalled guilt or other emotion attached to
these memories may impair this person's ability to function in his current
situation. He may feel unworthy to participate in normal life, suppressing his
normal aggressivity that he needs in order to compete in real life situations;
he may drop out of life entirely until he has worked these problems out perhaps
becoming addicted to alcohol or another substance, compounding his sense of
worthlessness. Memories that are essentially irretrievable may thus affect our
present life in profound ways.
Unacceptable recollections of
childhood such as participation in a sexual act may be actively suppressed may
cause symptoms that can ruin lives. One woman afflicted with a variety of
apparently psychosomatic ills including among others chronic neck pain with
losses of consciousness also apparently prone to a variety of drug addictions
recalled that she'd been sexually abused as a child. Other life circumstances
include in psychiatric hospitalizations, her son's tragic suicide by hanging
pointed to pervasive maladaptation in this highly intelligent and articulate
woman, a remarkable illustration of the biblical observation that the sins of
the fathers are visited upon the children.
But I noted, the abuse that this woman had suffered as a
child was relegated to the very end of her history. This often underlines its
importance pointing to its basic role in her life circumstances and symptoms.
Indeed there seems to be a subliminal realization in many people of the
fundamental importance of certain life events that are not at first brought to
the surface in a conversation or in a medical history. Very often, these come
to light at the very end of a history with appropriate probing or these details
may finally make their way through at the end of an interview as if they
somehow are of critical importance and just have to come out. Sometimes such
critical details literally come out just as a person is about to leave. It is
as if this person can't leave the room without first telling you what is really
on their mind.
When dark volatile memories
finally do reach the surface, there is often an emotional explosion that
profoundly alters a person's world view. In immunology we know of a mechanism whereby an organism having once been exposed to an
object, which has excited his immune system is exposed to it again. On the
second exposure, immunity which may have brought but a slight reaction on the
first exposure is poised to react with great force, almost as if frustrated at
inaction on the first encounter. A
person given a Tuberculin skin test, may have a mild swelling in his
skin. That is how to determine that he
has had some exposure to the Tuberculosis bacillus. But give him the skin test
a second time and his reaction may be extreme and can literally (on rare
occasions) cause him to slough his entire arm. This quite appropriately is
called an anamnestic response. It is analogous to one's mental reaction to
certain memories.
Immunity is highly
analogous to learning on many levels.
The immune response is altered by repeated exposure to an antigenic
stimulus just as our behavior is altered by repeat exposure. As we saw in
chapter one, antibody production is
combinatorial. Plasma cells are capable
of producing an enormous variety of antibody molecules that fit molecules on
microbes capable of causing infection. On first exposure to a microbe a
particular clone of plasma cells producing antibodies against the invader is
called into action. The antigen is displayed on the surface of activated
t-cells and macrophages that attack
and incorporate and digest the
invader. The initial immune response is
limited, but continued o
What we see in the immune system is
an altered response based on experience,
learning in other words. Learning takes place in the immune system, learning - a change in behavior based upon
experience. It is possible that similar
mechanisms control an alteration of responses in the central nervous
system, although this remains to be
elucidated. For example the CNS may well
be capable of generating a large array of molecules via combinatorial
techniques analogous to antibody production in the immune system. Learning may then be induced on the molecular
level afte
Human awareness is a continuous
thread of memory wending its way through time. More accurately, it is a whole
multidimensional fabric with complex interweaving of recollections, patterns
and trends. Our brain is capable of looking at this fabric in a wide variety of
ways gazing at individual threads delineating simple chains of events in normal
time, or stepping slightly farther away to look upon how events are interwoven
or even further still, to examine patterns or mosaics of patterns that comprise
a life. Details and the big picture are hard to appreciate simultaneously but
describe the recording of experience that is human life.
Korsakov's syndrome
happens with destruction of areas of brain responsible fo
Remote memories are more resistant to
processes that affect mental function. By the time remote memory is affected
we observe a more profound and global deterioration in personality
structure. By referring to our memory
model it is easy to see why this is so.
Most old memories are multiply determined and stored according to large
numbers of handles in widespread brain
regions. For a basic remote memory to
be lost, a lot of the brain has to be affected. A person who unable to recall
even remote events, or who is unable even to recreate his own methods and
habits and ways of performing simple acts has nothing lost his entire
personality. Yet many of us are oblivious to our own personal past and also to
the history which allows us to place our own lives and daily events in true perspective. We may be blinded to the
context of events in our own lives and a feeling of orientation of lives in
human history. Without some appreciation of history we are lost in an amnesiac
limbo.
We have seen how memory in living organisms
differs from information storage and retrieval in machines. Living things have a history and memory that
affects them. It is part of a complex
fabric interacting with current experience and continuing registry of
experience. But from the human perspective, memories are tied to an emotional
valence, memories mean something, they
aren't just stored.
Humans aren't manufactured like
machines. They develop. Humans contain within themselves a record of their
history and as such history is indelibly embedded in the present. Each stage of
development bears upon all later stages as the fully formed adult human, still
an evolving creature, emerges. This happens not through any noncontiguous
quantum process wherein all past forms are rejected in turn in favor of a final
finished perfect product, but rather as the obverse of this process, through
continuity, modification and reworking of past forms. It is true that we see
many examples in human development where children and adults appear to make
quantum leaps. Suddenly, or so it seems a baby who has been crawling begins to
walk, sometimes quite well. An adult may rarely make certain sudden changes in
his life, perhaps giving up alcohol or cigarettes. Of course there may be signs
of a more continuous process that are difficult to appreciate at first blush.
This continuity or inability to forget is the basis of all biology. Evolution
is inscribed in the development of every embryo and our mental development over
the course of our lives contains within it a history of past ideas that are reworked
and reshaped over time. Ontogeny recapitulates phylogeny, as was first
enunciated by the German evolutionist Ernst Haekel. The evolution of an animal is replayed in its
embryology. The same holds for mental development. Hence, the understanding of
a person's present is imperfect without appreciation of his past. As we observe
a person's behavior, we can only see very little of what he is about. If only
we could live his life as he has lived it, developed as he has and still
function as an objective outside observer of his behavior and experience. Our
actual powers of human observation are so limited.
All of this information is
recorded in our genetic endowment which unfolds to make a final organism. This unfolding programme
is given by the genetic machinery of the cell. This is how the living differs
from the inanimate.
"Organisms
are unique at the molecular level because they have a mechanism for the storage
of historically acquired information, while inanimate matter does not. Perhaps
the was an intermediate condition at the time of the origin of life, but for
the last three billion years or more this distinction between living an
nonliving matter has been complete. All
organisms possess a historically evolved genetic program, coded in the DNA of
the nucleus (or the RNA in some viruses). Nothing comparable exists in the
inanimate world, except in man-made machines. The presence of this program
gives organisms a peculiar duality, consisting of the genotype and a phenotype.
The genotype (unchanged in its components except for occasional mutations) is
handed on from generation to generation, but, owing to recombination in ever
new variations. In interaction with the environment, the genotype controls
the production of the phenotype, that is, the visible organism which we
encounter and study.
The
genotype (genetic program) is the product of a history that goes back to the
origin of life, and thus it incorporates the "experiences" of all
ancestors, and Delbrück said so rightly. It is this which makes organisms historical
phenomena. The genotype also endows them
with the capacity for goal-directed (teleonomic) processes and activities, a
capacity totally absent in the inanimate world"
-Ernst
Mayr[20]
This is well-taken but seriously
underestimates the ability of humans to store information and evolve. Our own
information storage capacity, indeed our very evolution is increased and
accelerated by our ability to store data in the brain and in recent human
history to store engrams extra-cerebrally, through the invention of writing and
more recently with the aid of ever- more efficient and information-dense
storage devices such as hard disks and CD-Roms. All
this makes possible change that occurs faster than by biological methods alone
which occurred first through acculturation and dependence on ordinary
mechanisms for memory storage utilizing language, and later through use of
writing and ever more sophisticated storage devices.
Physicist Frank J. Tipler gives a cogent argument in his book, PHYSICS AND IMMORTALITY, that the brain is nothing more than a
"finite state machine[21]", that is, if you had extraordinary knowledge
about the state of all of the neurons and synapses in the brain, the connections between neurons, the current
status of all the huge number of elements,
say 10 to the 10th neurons each with up to 10 to the 5th synapses in
various states, all of these states,
both of neurons and of synapses can be assigned a numeric value, and although as we can see there is a very
large number of neurons and synapses, even so,
this number is finite. Given the
numeric description of the brain's state at any time, and a description of
input or influence on the brain, the
outcome will always be known which is an alteration of the brain's state at
time (t+1). This model ignores the effect
of history, experience and memory on the brain's response, or at the very least, it de-emphasizes it and
gives history diminished importance. Tipler would probably say that the brain's or a neuron's
history and development can also be expressed as some numerical descriptor of
the current status of neurons and synapses.
The past is expressed as a numerical alteration of present status that
admittedly may alter the response to a stimulus. Perhaps.
In the embryo,
our nervous system starts out inauspiciously as
thin tubular structure. The brain, spinal cord and peripheral nerves are
modifications of this basically tubular design with all the major components
being well formed by the fifth or sixth week after conception.
Figure 8:Early Embryonic Disk.
How is this accomplished? In the embryo the a flat structure the
embryonic disc, forms a central neural groove.
Cells well up and proliferate next to this groove to form 2 neural
crests that rise beside the groove and then finally join at their center (see
figure) eventually forming the primordium of the
nervous system the neural tube. So the
nervous system ultimately comes from a basic tubular formation. From there all else is a modification, a reworking
of forms.
Only the spinal cord retains its
basic tubular form by the time at birth. It is a rather flattened ovoid
structure, especially in the neck when the originally hollow center has been
filled in by the growth of neurons
composing its gray matter. The brain's structure which also is ultimately
derived form a simple tube, is a much
more elaborate. But he brain's development involves the proliferation and
growth of neurons and other supporting elements. The circular hollow structure
eventually becomes the four fluid filled chambers (ventricles) of the brain.
Nervous system formation from a a tiny streak that begins to form in an embryo only three
millimeters long depends on the presence of notochord, a semirigid
structure that is present in some of our evolutionary forebears. The notochord
keeps an animal rigid, but the notochord is given by vertebrates including
humans in favor of a bony vertebral column. This acts as a structural support
for animals with an elongated architecture that is symmetric about a single
axis. The notochord degenerates by the time our development is complete.
Cartilaginous discs are remnants of notochord between bony vertebrae. Yes, these the same disks that herniate to
cause back pains, nerve root
disease, so that people lose work and
wages and otherwise cause other mischief.
Notochord remnants may even be present in a mature animal as tumors
called chordomas that can compress the spinal cord.
The notochord is the first use of
an endoskeleton to maintain rigidity of body form, specially useful for forward
swimming. Cartilage often matures into bone. Bone is more complex, more rigid
and requires calcium. Evolutionary development mirrors maturation. Cartilage
precedes bone in more immature animal forms.
Moreover the presence of
notochord cells prefigures and causes
first segmentation, the breaking of an elongated body form into segments and
then for the laying down of bone that forms a
repetitive structure that is composed of
vertebrae. These simila
But the notochord plays an even
more important role. It induces or creates the proper signals to bring about
the earliest formation of the nervous system. Were it not for the development
of the notochord the primitive nervous system could not commence formation. In
more basic animals such as Amphioxis a nervous system forms above or dorsal to
its notochord just as it does in the human embryo. This illustrates two basic
embryologic principles. Firstly a structure once formed gives signals for the
formation of other structures. Embryologic experiments in which such structures
are cut away show that development depends on preexisting parts. It is likely
that preexisting embryologic structures send out chemical signals to adjacent
cells that cause these cells to develop
in an exact way. This is a process of induction.
We now know what some of these
chemicals are, proteins, specified by
certain genes called homeobox genes. These genes are remarkable for a number of
reasons. First, much of their D.N.A. pattern appears to be preserved virtually
throughout the entire animal kingdom even in such disparate species as worms,
insects, mammals, and in humans, virtually all animals that have an elongated
back to front structure. Second, the
genes lie in an order on chromosomes, that is exactly the same as the
front-to-back order on the animal! One can only speculate that the original
zygote, the one fertilized cell that is present at conception, is already
oriented in a certain way to bring about cell divisions that will dictate the front to back development of
the final animal, depending on the orientation of its homeobox genes. The
proteins specified by these genes appear in specific foci on the developing
embryo. Around these foci, there is a gradually decreasing concentration
gradient that also signals specific development. One chemical might signal that
a forelimb should develop at a specific place, while still another homeobox
protein might center about the hand so that there will be two opposing
concentration gradients of proteins, from the shoulder down and another from
the hand up that each serve to signal specific anatomical developments. Homeobox proteins determine differentiation
of embryonic cells from front to back along the longitudinal axis, from head to tail or in anatomic lingo, in
the rostro-caudal direction, the first most basic factor that
distinguishes developing cells in different locales.
Early in life the embryo is a
totally noncommitted ball of
like-appearing cells. Later a certain group of these cells
differentiates into a flat sheet that will eventually form the animal itself
and another group of cells responsible for the environment and nourishment of
the developing animal including the yolk sac, placenta, and amnion. The flat
disc of cells that develops into the actual living animal cannot be distinguished on any basis
from the cells that form the rest of the embryo, yet the process of differentiation happens
with perfect fidelity as if by magic. These cells at this stage have not yet
committed themselves on the question of the exact part of the animal that they
will form. Experiments in which these first primitive cells are moved to
different locations within the embryo show that these first cells are
multipotential, that is are capable of forming any of various parts of the
nascent animal. If a few of these cells are cut away, chances are the
developing animal will not miss them at all at an early stage because the
others will just fill in, or, otherwise stated the same cells that are cut off
can at this stage form a whole new organism.
Slightly later in development
three germ layers form designated mesoderm, ectoderm and endoderm. The mesoderm forms structural elements, bone
cartilage and muscle including the primitive notochord. Mesodermal cells seem
to signal adjacent cells to differentiate into ectoderm which in turn, forms
the nervous system and the skin, while the endoderm eventuates in the viscera
or internal organs especially the gut.
At this stage cells are
multipotential still. The cells that are descendants of a single cell may form
any of a wide variety of organs, only their options are somewhat more limited
than at the previous stage of differentiation. Some ectodermal cells in a given
location may be capable of forming any of various parts of the nervous system.
For example at this still relatively early stage a whole wide area in the front
of the animal may contain cells capable of forming part of the eye, cells in
this particular area designated as "the frontal eye field". The frontal eye field becomes smaller in
relation to the size of the animal as many of its cells make commitments to
form other organs. This commitment of cells is determined at every stage by
location. It is as if each cell determines what it will become by asking where
it is. Although the exact mechanism
responsible for this commitment is imperfectly understood, it is only
reasonable to assume that the process has something to do with concentration
gradients of proteins, some of these
homeobox proteins.
Even after birth parts of the
brain become committed to serve certain functions as localization of abilities
develops. In most people, the left hemisphere performs the bulk of language
functions; this is what we mean by left hemisphere cerebral dominance.
Certainly the left hemisphere is responsible for the bulk of language function
in most right handers. This hemispheric preference is preordained and mostly
genetically determined. Left handedness does tend to run in certain immediate
families. Very early in life, though, it is possible for a person who was
originally destined to be right handed and left brain dominant to instead
become left handed and have language function predominate in his right
hemisphere. This happens in the event of an early cerebral injury. In these
persons who may have had a devastating event in utero
or a brain injury during or shortly after birth there may be weakness,
sometimes profound, on the right side of the body. Scans may show atrophy or
damage to the left side of the brain and they will also presumably be right
hemisphere dominant for language function (though this is difficult to prove.)
Presumably this also occurs in persons originally intended to be left handers
but this is harder to diagnose because of the relative infrequency of left
handers. If a person is left handed and has no family history for left
handedness, an early cerebral injury may
be the mechanism.
This altered pattern of cerebral
dominance will not occur unless a brain injury occurs very early, especially
before the person's first year of life. Later, different portions of the brain
are much more committed to perform their specialized function - committed in
the same way as embryologic anatomy described above. In a younger person it is
easier for non-damaged parts of the
brain to assume function for damaged parts, a property known as plasticity within the human brain. It is
clear plasticity partly depends on the degree of commitment of function and
that this depends on the age of the organism, one good explanation for why
younger brain-injured persons may have better prognosis that older persons.
Development is in part about
commitment. Every cell which gives rise
to other cells must at some time decide upon its destiny, commit itself to play a certain role that is
determined by its relative position in the embryo. Some will hold the exalted function of a
neuron, others will have a more modest
existence as liver or gastrointestinal cell.
Once totally committed, there is no turning back. Once a cell commits
itself, its descendants, other cells, products of cell divisions, differentiate
on the basis of this decision. Early in
embryo's life specific cells are committed to be endoderm cells, those that comprise the viscera. Some of these endoderm cells separate off and
give rise to cells of the liver, others the stomach, still others, the gut and
so forth. Some of the liver cells will
break away and form the hepatic ducts that transport fluids inside the liver,
others hepatocytes that mediate chemical reactions, others supporting cells and
so forth. Sometimes other specialized
cells actually migrate into an organ from afar as is the case with certain
glandular tissues. The process is
commitment of the ancestral cell or anlage in German, then differentiation or
specialization of its descendants. Once
committed, and especially once differentiated, the cell has embarked upon a
process that cannot easily be reversed.
The cell can not turn back and perform another function. It is no longer plastic.
Notice here that in making this
commitment the predicament of the individual cell is not too different from the
individual neuron described in the last chapter, which at a certain point,
given multiple inputs, mostly from adjacent cells has to make a decision to
fire or not to fire. Here in development
an individual cell is made to commit itself to play a specific role, to give
rise perhaps to a line of cells that will eventually form a certain organ or
perhaps even degenerate.
If you begin with the observation
that the single zygote cell gives rise to cells committed to perform every
function in the body then you have to conclude that the zygote cell and hence
every cell in an animal's body which has exactly the same genes, is multiply capable. Every somatic cell contains all the genetic
machinery necessary to become any type of cell in the animal's body. What happens, of course, is that
many genes are turned off, not
expressed. The liver cell does not
produce the neuron's specific proteins, assume the shape of the neuron; the
neuron does not make proteins specific to the hepatocyte and so forth.
Therefore commitment, differentiation, specialization mostly are mostly
about inhibition, masking of certain
genetic elements. Only some of a cell's
full genetic potential is expressed and that is how cells become what they are
going to be. If scientists could learn
all about the processes that control gene expression, that could be every bit as useful as mapping
out all of our genes, the current focus
of research.
Well after all of our chromosomes
and genes are mapped, researchers will
be trying to unravel the mysteries of gene expression. Just as one example, as we have seen with
the plasma cells and likely many other cells create proteins in a mix and match
process combining information, pieces of
information from different genes in novel ways.
New plasma cell clones compete for survival and a license to reproduce in a Darwinian fashion right in our own
bodies. Those whose antibody products
match the antigens displayed on the foreign invader, divide and make more of their own kind, thus
increasing their fitness. This is but one unusual mechanism of gene expression
and there are likely to be many others.
It is clear also that this is
only one example of natural selection that occurs inside an animal's own body
among its very own cells. In the embryo
certain cells are selected to divide for a few generations just to form a
supporting matrix, then targeted for mass destruction. These cell lines are necessary for
development only for a while, then
sculpting takes place as organs take their final form. This happens to many cells of neural origin
in the brain, whose precise form is so
critical to final function. Precise
neuronal connectivities will determine exactly how the brain will eventually
perform.
Certain cells in development are
destined to be destroyed. A perfect
example is tail cells in animals that are not destined to have a tail, as in
tadpoles that mature into frogs. Lately
scientists have discovered that cells go through a specific cycle before they
die. These cells literally sacrifice themselves for the good of the adult
intact organism in a process termed apoptosis
[22]. This is a
preprogrammed cell death cascade. The
interesting thing is that it appears that embryonic processes that sculpt the
final form of the organism in which cells are programmed to die, resemble cell death in disease as well. An
entire cascade of events is set up both in the embryo and in certain diseases
such as degenerative neurological conditions or in the immune response to an
attack from an outside organism. If you
can define the cascade of cell death,
then it should be possible to intervene in conditions where programmed
cell death is pathological. For example
in stroke we know that neurons die thorugh a course
of events that involves the chemical Glutamate, a so-called excitotoxin. Stoke therapies are aimed at inhibiting
Glutamate and excitotoxins or in otherwise
intervening in the cascaded of events that occurs when cells die during a
stroke to save brain cells a process termed neuroprotection.
It is characteristic of a mature
differentiated cell line, that cells reproduce slowly in controlled
fashion. During development in the
embryo, on the other hand, cells may reproduce like crazy. In total considering
the final number of cells that make up a person, there is only the equivalent
of perhaps 50 doublings of cell numbers from zygote to mature person. The differentiated cell has a limits its
repertoire of what it will become, what
descendants will be. The uncommitted
cell is pluripotent. Its descendants may
do anything. Occasionally a committed
cell will regress and act like a more primitive progenitor cell. That is how cancer happens in most instances. A mature cell line will give rise to a
renegade immature pluripotent cell line.
These cells may even produce chemicals that are characteristic of other
very different cells. Internal
mechanisms that control cell reproduction and growth, no longer work and the cells start to
reproduce wildly. In very young children
some solid cancerous tumors called neuroblastomas
form from neuronal cell elements when some cells fail to mature and
differentiate. Neuroblastomas are
swiftly growing lethal tumors.
Neuroblastomas are quite different from ordinary tumors that develop
typically in older adults. Most tumors
in adults come from immature cell lines that have dedifferentiated from mature
cells. In the case of neuroblastomas, cells that give rise to the tumor have
failed to differentiate in the first place.
In some cases their chromosomes are defective. They have a deletion in part of the first
chromosome. However some
Neuroblastomas having a better prognosis
have more normal chromosomes In some of these advanced cases of
neuroblastoma, the tumors will
miraculously regress. How? The involved cells will suddenly
differentiate giving rise to a mature
cell line.
The neuroblastoma cells, immature forebears of sympathetic
ganglia, send a signal that causes
immature Schwann cells to migrate into
the area. Schwann cells are the elements
that add the myelin covering to a nerve.
Neuroblastomas with a good prognosis,
those that will eventually regress and mature, have abundant Schwann cells. Evidently there is an exchange of chemicals,
between the neuroblastoma tumor cells and Schwann cells in the area. The neuroblastoma sends out signals that call
in the Schwann cells, and then the
Schwann cells send signals that hasten the maturation the embryonic
normalization of development in the tumor and it regresses and matures rather
than kills the tiny patient. Here we
have an excellent example of the constant crosstalk that is the exchange of
chemical signals that causes maturation and differentiation of cells in the
embryo[23].
The best example of cells that
have partly determined the destiny of their descendants is the stem cell. Blood is produced in the bone marrow by
various mesoderm cells destined to give rise to different blood cell lines, the
red corpuscles that carry oxygen, the white cells, polymorphs and lymphocytes
that fight infection, and platelets that aid in clotting. Stem cells are the partially committed
immature, not yet differentiated cells that will give rise to all of these cell
lines. Harvesting, growing, finding and
using the chemical signals that control the differentiation along these
individual cell lines, has become a major industry. Stem cells may turn out to
have all kinds of uses. One would be
when it becomes necessary to destroy the bone marrow that makes blood cells as
a treatment for cancer, reimplanting
stem cells will provide new blood cells and save the life of the patient. Knowing about chemicals that control blood
cell production will help in a host of
diseases where blood cells become deficient.
For example, erthropoetin a protein that encourages the production of
red blood cells, has been synthesized and is in wide use in sick patients who
are not making their own blood cells.
Some of these persons have had
chemotherapy for cancer, some are
otherwise chronically ill and anemic, some have severe kidney failure and the
kidneys are the main source of erythropoetin. Other proteins signal the
production of white cells, others platelets,
making cell transfusions a thing of the past.
The cell line that is
differentiated, the specialist, has a hard time turning back and into multipotentiality even if called upon to do so; it is less
plastic. Plasticity, the ability to
assume a different function, to fall into the breach in the case of a lesion or
injury, is the opposite of differentiation in the sense that a cell which is
more plastic is less specialized. In
most healthy animals in which no pathological process occurs, differentiation is the key to success. It determines how well specialized cells will
work l together. For the whole organism,
maturity is largely a matter of increased specialization among elements of its
structure which develops from a single pluripotent generic undifferentiated cell.
The organism develops from this
finite inauspicious beginning, a singularity,
that is, from a single perfectly pluripotent cell, one that can give
rise to everything within the organism.
Over time the organism is in a constant state of developmental flux
determined by previous less differentiated states. The anatomy reflects this continuous
embryologic development. A final
structural integrity is exactly analogous to the contiguity of memory. The intact integrated person is a composite
of continuous memory as the organism is determined by its complex
development. The present is a product of
the past.
Systems are built on the basis of
preexisting parts. the organism forms on the principle of adjacency. If not for the notochord the central nervous
system would fail to materialize. The
notochord, which came from the need for an elongated body to swim forward in an
aqueous medium, now induces adjacent
cells to become a part of a segmented structure. Some differentiate into bony vertebae, others
into nerves, and vessels. These
components would not "know" thei
On the sides of the primitive
notochord along the axis of the developing animal, segmentation occurs as
individual nerve roots innervate their own specific segment. Vertebrae and ribs
are also mark animal segments. I recall as a student being overwhelmed by the
sheer wealth of anatomic detail and especially the precise choreography of
cellula
Figure 9: The embryologic branchial
arches evolve from
Still it is remarkable that
biological patterns unfold repeatedly
with so few mistakes. What we witness in the embryo is repetition and
amplification of basic processes. There are modifications and remodifications
of primordial patterns. Vertebrae and discs are such repetitive structures so
are the branchial (=
Figure 10: A surface view of what
becomes of the branchial arches which govern the
making of both deep and
superficial structures. The first forms
the chin and jaw area.[25]
Talk to most people who have never appreciated embryology and it is not at all obvious to them that there is a plan or pattern that relates all life forms. Embryology proves the point. We can see over time what has been grafted onto previous structures. It is as if we have a video replaying an unfolding of form. Most people have little to no perception of this. People who advocate for animals haven't heeded many lessons from biology, mainly that life fits into a larger plan or pattern. They tend to treat all living things as equivalent and to lose sight of their differences. Well-educated persons either haven't thought about this subject or aren't convinced either that biology culminates in humankind. I learned a long time ago that some things that I accept as almost axiomatic, aren't so obvious to others.
I was talking to one of my physician colleagues who is interested in this topic. He'd just read some work by Stephen Gould, the evolutionary biologist. It was late at night and both of us were rather exhausted from having made rounds all that day. We stood in the intensive care unit, under the eyes of all, and debated the topic. Even lowly bacteria whose cells lack a true nucleus may be by his account, considered to be as biologically advanced as us. I could see some of his arguments but couldn't believe my ears, as we stood under the light created by human invention, without that light we'd be in the dark, perhaps relegated to sleep by that time, in a warm building on a winter's night, also the product of an human invention--bacteria are as advanced as us!! By what system of reckoning? In the bugs' favor they have modified themselves in a milieu of natural selection well after humans had. In other words some bacterial strains are much "newer" than the human species. Many of them were in that very intensive care unit, having adapted to the newest antibiotics we could use on them. As a group, hominids, apes similar to humans had been on the scene only very recently, for perhaps 4 million years, the genus Homo having arisen some two million years ago in Homo habilis. Primitive bacterial species had already evolved over 3 billion years ago.
Very soon both of us realized
that the discussion hinges on how you define what is more advanced. That's
where the whole argument gets hung up. I
admit from the start that for me this idea of advancement is not a difficult
topic. I "know" which kinds of
animals I consider to be more advanced from the beginning (admitting that such
foreknowledge is anti-scientific--in science you are supposed to
"find" the truth, which can be very surprising, using objective
evidence.) Below would count as some of
my own criteria. This is important n the
sense because in the method that I view evolution, there is a progression from
less advanced life-forms, all the way up
to those who reflect on the nature of
such things. There is a great bulk of creatures who make their own
living and survive some well, some not so well, and others who function on a
level of making a living also but go a step beyond, transcend the mundane every
day business of staying alive to consider something beyond themselves. In this
category I place humans. We've reached a
point that we are not only concerned about immediate survival, but can plan for
the future, not just by making up a nest
and a home under hormonal pressure according to a pre-wired plan but to
influence what is to come according to an inner plan. And then to contemplate about what all of
this means.
From a scientific viewpoint how
reasonable it is to dismiss the concept of evolutionary advancement. Advancement is difficult to define. Depending on what criteria you use you may
come to different conclusions as to which creature is more advanced. And why should anyone care about which
life-form is more advanced anyway? It's
just that we like to think that things progress, improve, evolve. Biologically we have a very hard time
proving that humans are more advanced than other creatures. After all early and simple life forms such
as bacteria exist in much greater numbers than more recently evolved and
complex creatures and in a much wider array of habitats. They are, even today, more successful, judging by their numbers. And we have many examples of more complex
creatures further adapting into a relatively simple state, arthropods and bacteria that evolve into
obligate parasitism, sighted creatures
that lose their lose the ability to see as they adapt to dark
environments. Yet it is possible to
find a few criteria for advancement which come out in our (human's) favor so
that at the end of the day we may continue to see a conventional progression in evolutionary
history from "lower" to "higher" life forms.
What determines whether an
animal will be considered more or less advanced, what are the criteria by which we may state
objectively that one organism is more advanced than another? An organism could be considered more advanced
if it competes more effectively in its ecological niche. But this would be
confusing what is advancement with success.
Lots of species win out by sticking to a simpler strategy. Still another criterion is recency of appearance
of a life form. Certain bacteria in our
hospitals have even more recently evolved antibiotic resistance, insects,
insecticide resistance. Indeed some might argue that lately man has almost ceased to evolve biologically because
the weak survive and the physically strong or most aggressive don't necessarily
make out better in our societies. But
humans and human like creatures have appeared very recently in earth's history
and out-compete every other species of plant and animal in a largest array
ecological niches. Some large groups of
organisms, most importantly bacteria and
insects, are giving us a good run for our money, but humans have been able to
employ certain members of these groups for their own gain, to make antibiotics, proteins, or using certain carnivorous insect
species to eliminate crop eaters, even infecting certain pests with
bacteria; our ingenuity knows no bounds. No other single species is as ecologically
sophisticated or sociologically prolific as humans are. Many animals have evolved advanced social
organizations but no species has the diversity of social interactions that we
have. We aren't so happy that our
efforts have apparently resulted in the extinction of many species of animal
and plant by this time.
Still another criterion, perhaps the main one, is complexity. In order to decide which organism is more
complex we need estimate its informational content, how much information one would need to
reproduce a single individual. This point of view is enhanced by the computer,
which has given insight into recording and expressing information. If as we
have indicated, the human genome contains roughly 1010
bits of information or four thousand 500 page books, we may call man the
crowning achievement of biology on the basis of the amount of information in
each cell, far more than other
organisms. It's also reasonable to ask
the question for a human, how many bits
of information does it take to encode the totality of being, that is including
biological information and brain content, and there are a number of ways making
an estimate. Consider that that brain
has 10 to 100 billion neurons which have up to many thousands of synapses. Each synapse may be considered to carry one
bit of information. As revealed in chapter
one, I maintain that this will also give
us a profound underestimate of the information stored within the brain, mainly because many bits of information are
stored on the subcellular even the subsynaptic level, but for our arguments here, in which we are
only trying to find the life form that most complex this estimate is good enough. Frank Tipler, in
his book THE PHYSICS OF IMMORTALITY uses an estimate of 1015 possible states of the entire brain and this
is close enough for our purposes, though it may in fact be far off.[26] Another disadvantage of this particular
informational state concept, is that as I hope we have seen in the present
argument, the current state of the human
organism, does not tell all about all future behavior which is partly a
function also of its past and past memories as argued in this chapter. One can counter that even in that case, the
one in which we need take the past into our consideration of the present, the current status of the organism as a
function of past events is still expressible in terms of bits of present
information. Fair enough. But it should be clear at all times that the
past does at all times make a difference perhaps seen in alteration of current
expressions of informational status in the present.
The vast majority of living
things are simple (in comparison with
ourselves.). There are far far more things
alive on earth that lack a true cellular form, with nuclei and specific
organelles such as mitochondria, than there are that are composed of true
cells. The technical terms are prokaryotes vs. Eukaryotes, precursors to cells vs. True cellular
organisms. Prokaryotes are blue-green
algae and bacteria mostly and of course there are even more primitive living
forms such as viruses that contain nucleic acids and you might even include
Prions a type of mostly protein parasite that appears to contain no nucleic
acid among the living if you like. There
are many many more of "them", organisms
without true cells or nuclei, than
"us" who are made of cells.
Then we have the one celled animals and plants, and the protozoa. Bacteria in particular, may according to some of our criteria as given
above, be counted as more advanced. They
are, and have been for billions of years, extremely successful, adapting to all kinds of environments form
the hottest sulfur springs, and places deep inside the earth's crust to
ecosystems deep inside other more complex animal's intestines, to the polar
caps, bacteria may be considered as a group to be by far better adapted, and to have
radiated into more biological situations than any more complex creature.
Table 1: Criteria for deciding a species is more advanced.
|
CRITERION |
VICTOR |
|
Numbers |
Many
examples: bacteria, insects, variety
of other organisms |
|
Success
in single niche |
Many
examples, as above |
|
Success
in Multiple Niches (diversity) |
Man |
|
Recency
in Evolution |
Bacteria
and insects acquire new forms most rapidly |
|
Complexity |
Man |
|
Embryology |
Man |
|
Consciousness |
Man |
|
Artifacts |
Man |
|
Transcending
Earth boundary |
Man |
Whole groups of cells got
together only recently in biological history,
by current reckoning only
about 600 million years ago. The earliest life that has left a trace is
estimated to be 3.5 billion years old. Still,
relatives of the earliest life forms far outnumber multi-celled organisms. It
is not at all clear that more complex life forms dominate the earth. Simpler life forms, prokaryotes, have pushed
the life's envelope to the limit, having
been around in time as soon as the earth became earth, that is just as soon as
it had cooled off enough to remain solid, and perhaps well before, and in all habitats on the planet including
deep within the earth's crust. But
multi-celled organisms are more advanced according to a number of criteria.
When cells get together, it gives them a chance to specialize while
maintaining a common identity primarily by virtue of an identical genotype.
Multi-celled creatures are more advanced by virtue of complexity and specialization. Not only information theory, but embryology
argue in favor of these creatures being more advanced forms, as to some extent you can follow their
development through previous evolutionary forms. This is not to say that the complexity of
embryology of an animal is the sole determinant of level of advancement. Otherwise it might be possible to state that
certain insects that metamorphose into quite different forms might be
considered to be more advanced. Here
I'm not just talking about butterflies from caterpillars, but also various insects that go through
complex forms, larva to pupa to adult and various molts in which they take on a
number of different shapes.
The major feature that humans
have of course, is the advance of the nervous system and we are uniquely freed
to some extent, the degree may be
debated for many of us, from pure
biology, adaptation of structure and form and dependence on one niche. As can be seen from the table the criteria
for advancement go from the more to
less purely biological as you go from
top to bottom on the table. The brain
has allowed us to be successful in many environments and at some time in the
future we may expect to live away from our mother planet. Of course we need not evolve
Having made criteria for
biological advancement helps us to see a
trend, a purpose or teleology. It
allows you to state that the "purpose" of nature is the development
of more advanced organisms or involved neurological structures. Simpler creatures such as bacteria and
insects are in some ways much more adapted, numerous, fecund, successful than
are we. Here Stephen Jay Gould contends
that the advent of humans is by no means inevitable in biological
evolution, that we are, in fact, more accidental.
"It is tempting to say that the
victors won by virtue of greater anatomical complexity, better ecological fit
or some other predictable feature of conventional Darwinian struggle. But no recognized traits unite the victors,
and the radical alternative must be entertained that each early experiment
received little more than the equivalent of a ticket in the largest lottery
ever played out on our planet--and that each surviving lineage, including our
own phylum of vertebrates, inhabits the earth today more by the luck of the
draw than by any predictable struggle for existence."[27]
Gould makes a good point. The best example is the great cataclysms
that happened a number of times in the earth's history, that of the Cretaceous period that saw the
sudden extinction of dinosaurs, perhaps
due to a meteor landing on the earth and also the end of the Ordovician and
other mass extinctions, advents of partial clean slates if you will few of
these extinctions being well explained. At these times it wasn't necessarily
the strongest and best adapted creatures that survived. A massive explosion of biological forms
suddenly came to be in the Cambrian period in which all of the known phyla
evolved over a short space of time In an "explosion" of diversity.
This Cambrian explosion is analogous to the inflationary model of the
universe in which, shortly after the Big Bang the universe expanded suddenly in
size. There is no good scientific explanation for the sudden Cambrian expansion
in life forms. And the four or five or
so mass extinctions of biota remain unexplained as well and don't fit well into
any current evolutionary paradigm,
making the earth in its current form, and our own existence, far
from inevitable. There are a good number of scenarios of
worlds of fundamentally different form
that may just as probably exist, and
quite possibly do without we humans gracing them, considering them, writing
about them and these parallel worlds probably do exist right within our own
galaxy (there is no need to invoke parallel universes in this context), only no one is describing them because they
do not included a mechanism of self-awareness. For the same reason, we can say little about countless human
societies that left no written record.
There is no witness.
A number of scientists have
written about this lack of inevitability
of evolution from the less complex or advanced to more complex organized
biological systems and that Darwinian principles would fail to predict a world
such as ours with people and complex biological systems on small and large
scale. They have allowed themselves to
explore if furtively, into teleology or
purpose in their writings, though such
thought is forbidden in the strictest scientific sense. Scientists don't argue teleologically
. They are supposed to consider only the
outcome on the basis of antecedents.
Stuart Kauffman and Michael Behe have noted
that the level of complexity couldn't ever be predicted using our current
understanding of biological and physical laws.
At best, evolutionary theory, is
descriptive of diversity, but doesn't help much in yielding up the
complexity of our world. Levels of
organization we see cannot be predicted or even fully explained with our
current scientific tools. Whether you're
observing microscopically at enzyme systems, or macroscopically at social
organization and human inventiveness, scientific understandings are inadequate
to the task of predicting and explaining and you have to conclude that either
there is a self-organizing principle, or that there is some one who is the
author and controller of this complexity,
teleology.[28] It is important to note that neither author
is a religionist or suggesting a belief in God.
Both would are searching for scientific explanations for their
observations and find them lacking.
Animals develop which means
grafting a present state onto their past. The past is not discarded but
rathe
Anyone who maintains that humans
are the most advanced creatures on earth, endowed with reason and evolutionary
and developmental memory, imposes an
awesome challenge. Our intellectual
endowment, our competitive advancements
do not entitle us to rape the environment,
don't license men as super-competitors.
Quite the opposite. With
intellect, free will comes a burden a
responsibility to care for the earth and everything living.
Each person is made to replay his
evolutionary history in his own development,
and his cells, more specifically the nuclei of these cells, carry the specific information that makes
this journey possible. Evolution is
written into our present form, our
anatomy. But if there is an embryology
of form, there is equally one of ideas.
An unfolding plan in both spheres must be specified somewhere. The more
advanced the animal to human form is,
the greater the need to have this information. The greater the amount of
information needed in the developmental process, the more advanced is the
organism.
As adults we carry not only
primitive atavistic childhood thought processes but also patterns derived from
mythic historical thought processes that are a part of our cultural heritage,
what Jung referred to as archetypes. Succeeding thoughts graft onto older
thought processes. Though ideas are
overthrown, very little is thrown
away. We function with reference and
reverence for the past. It is as if we
have purchased a garment that no longer fits but yet we do not discard it. We
modify it to follow current cognitive topography. Changes in the embryo appear
to be complex and even the final anatomy is difficult to master, yet the blueprint
for development is specified within the
very small volume of a cell's nucleus. Instructions for a ballet are contained
within a small number of pages.
As we have seen, the homeobox
protein products specify front to back, rostro-caudal, development within the embryo. Very soon after it is first formed, the
fertilized egg, or zygote determines its future axis, where will be its head,
and where its rump or tail. At the time that all of this is determined, perhaps
after the very first cell divisions into 2, 4, or 8 cells perhaps, the front to back development of the embryo
will be specified by varying concentrations of homeobox proteins.
The other major direction of
differentiation is dorsal to ventral,
back to soft under belly over the thickness of the body. The embryo starts out essentially as a sheet
of cells, a flat disk of cells hanging over a yolk sac. Future dorso-ventral differentiation will be determined mostly by
induction. Notice that development is
specified along two axes rostro-caudal (head to rump)
and dorso-ventral (backbone to underbelly). A third orthogonal axis is less well known
about from the embryologic standpoint since it is generally symmetricF ,
namely side to side o
The neural tube comes from
ectoderm, the outermost layer of embryo that forms folds. These pile up largely
through some reproduction of cells, and mostly via cell migration. Cells also
elongate and internal skeletal structures within the cell the microtubules and
ensure that they maintain this shape partly determining the ultimate folded
structure within the embryo. Ectodermal folds later meet over the top or dorsal
aspect of the embryo to fuse into a primordial tube from which the central
nervous system will develop. Meanwhile cells lying just above this tube bud off
to form a crest that will be the peripheral nervous system. They form long
nerves that carry signals to and from distal reaches of the body.
Figure 11: Development of a central neural tube
from folds and crests.[29]
The spinal cord remains in the
form of a thin tube, but the brain's development at the head end of the animal
is much more complex. The brain is very
much only a modification of the basic rostro-caudal
tubular structure. Though the spinal
cord remains basically straight the brain will form by taking certain bends,
near the midbrain and again at the pons and at the junction of brain and spinal
cord. Brain formation rostrally occurs as neurons grow and then migrate around
what will become the four spinal fluid filled
ventricles.
Primitive nerve cells find a
resting place a short distance away from the surface lining of the ventricle.
When they reproduce they have a neat way of migrating to the ventricular
surface. Primordial neurons have a tendency to form extensions adumbrating
later axon and dendrite formation. While preparing to divide the nuclei of
these cells begin to travel in down the cell body which changes shape like an
amoeba. Nuclei travel toward the ventricular surface. This movement is aided by glia or supporting
cells and the withdrawal of previously formed neuronal cell processes. The
neuron assumes a smaller form with the nucleus near the ventricular surface and
here divides to form daughter cells. The nucleus again remigrates
back to its resting place remote from the ventricular surface as the neuron
again grows new long processes during maturation.
Figure 12: An MRI (magnetic
resonance) image of the brain showing the fluid-filled ventricles as white
structures in the center of the picture. The image is a horizontal slice
through the skull.
Basic principles of form and
function established during this embryonic stage presage basic principles of
neural function that being now established, will persist throughout the life of
the individual. There is a specific division of labor.
The first general principle of
nervous function is that it can be broken into three divisions, an afferent o
Early in the development of the
embryo separate afferent vs. efferent functions are mirrored in the anatomy of
the embryo. In the spinal cord, afferent or sensory components take on a more
dorsal (toward the hard backbone)
position while motor or efferent components assume a position ventrally
(more toward the soft underbelly). In the adult the dorsal horn in the spinal
cord will receive all sensory impulses from nerves over the body while the
ventral horn will send out motor impulses. The nerve cells that effectuate movements
termed the Alpha Motoneurons, reside
in the ventral gray matter of the cord. The cord's gray matter is shaped like a
butterfly (figure) with the bottom (ventral) portions of the right and left
wings housing motoneurons. In the thoracic spinal cord there is a third horn
(the intermediolateral column) that is just above
(dorsal) to motor neurons, comprised of effectuating cells of the sympathetic
nervous system. Well above (or dorsal) to these cells, the axons carrying
sensory impulses enter the cord. There are sensory neurons that reside in this
general area, the upper portion of the right and left wings of our butterfly.
These modulate or act on sensory impulses beginning the first stage in sensory
processing. Some of these neurons are in the tract of Lissauer. When a sensation is extreme it is felt as
pain. More moderate sensations are just felt without being interpreted as
painful stimuli. In general the more energetic is a stimulus, the more extreme
the sensation, until it reaches a certain threshold that is interpreted as
being painful. The classic example is heat. Your feet might feel comfortable on
a pavement that is 80 degrees, but a 150 degree pavement would be a different
story. There are cells in Lissauer's tract that modulate mild stimuli so that
they do not reach the brain in the same
way that painful stimuli which should initiate avoidance do. Some cells have
axons that have collaterals (branches) that synapse o
Figure 13:Structure of the Spinal Cord. Sensory
neurons are dorsal; motor neruons are ventral[30].
Most sensory nerve cells reside
outside the spinal cord in clusters of neurons, the dorsal root ganglia. These
neurons are bipolar, that is, they have two long axonal extensions. One process
goes out into the periphery to sensory end organs collecting sensory data. The
second process goes into the spinal cord and helps convey sensory information toward the brain. The
Dorsal root ganglia are all derived from neurons that eventually separate from
the neural tube, part of the neural crest. They lie above or dorsal to the
neural tube. The axons that go into the cord conveying pain, synapse or connect
with other neurons within the cord, practically at the same level and then
another neuron takes over to carry the impulse toward the brain. As this neuron
does so, it crosses to the other side of the spinal cord. The axons that convey
non painful (and non-temperature) impulses are thicker and have more myelin,
hence conduct impulses faster entering the spinal cord continuing to travel
toward the head on the same side, in white matter denoted as the dorsal
columns. The dorsal columns carry information about position, touch,
vibration, etc. Not surprisingly, such perceptions arrive at the brain somewhat
faster than does information conveying pain. This explains why when you burn
your toe, for a split second you know what you've done and that your about to
have an extremely painful perception. Then the actual pain is felt. Your foot's
withdrawal however, has already taken place, before you feel the pain, because
much of the mechanism for withdrawal resides within the spinal cord itself and
is carried out on a very basic primitive level.
The general structure of the nervous system as
determined early in evolution and also in development is carried forward in the
brainstem where the principle dorsal = sensory, ventral = motor is carried
forward. The brainstem controls many automatic and repetitive activities and
also serves as a conveyance for sensations toward the uppe
Figure 14: The importance of the sulcus limitans in separating
sensory from motor components in brainstem.[31]
In the central nervous system
clusters of nerve cells form nuclei analogous to nerve cell clusters of the
neural crest in the peripheral nervous system, the ganglia. Another basic
principle of nervous function is that there are both sensations and actions
that are carried out automatically
without the intervention of consciousness. You sense, for example, that you
have to breathe more when the carbon dioxide concentration in the blood
increases and when oxygen decreases and both the sensing and the breathing are
done automatically, freeing your mind for higher mental operations. These
totally automatic functions are termed general visceral, referring to basic
bodily functions that have to continue on an automatic basis. There are other
sensations and movements that are semi automatic and under more conscious
control. The best example is movement of facial muscles of expression. You
laugh, smile, and cry semi automatically, effortlessly, though you could exert
more precise control if you wanted to. There is a sort of gradation of volition
and perception involving more or less, as a matter of degree, awareness in
action and perception. This gradient has its foundation in the structure and
development of the nervous system. Swallowing muscles and muscles of facial
expression though voluntary, are homologous with and derived from the
All the afferent (sensory) nuclei are
separated from the efferent (motor) nuclei by the sulcus (fold) limitans. The
major separation to be made is between perception and action. The afferent and efferent
automatic nuclei, sensory and motor i. e. the visceral afferents and visceral efferents,
lie next to each other on either side of the sulcus limitans. These are flanked by the somatic afferent and
efferent motor and sensory nuclei. Thus a structural separation is complete, a
separation that reflects functional
differences. First, afferent nuclei are separate from efferents. Second, there
is a gradation from inside out on both sides flanking the sulcus limitans
(diagram). Progressing farther out from
this major dividing point, the nuclei become more voluntary. A person is more "aware" of sensory
perceptions transmitted; they are more
conscious, and motor activity progressively becomes more voluntary and
deliberate.
The best example of a nerve
serving automatic function is the Vagus which helps regulate such functions as
heart rate, blood pressure, and gut motility. We can't be bothered with
conscious control of such functions. Signals arrive into certain nuclei (for
example the Solitary nucleus which receives data on blood pressure, carbon
dioxide concentration in the blood and taste, a visceral afferent nucleus) and
actions are taken by the dorsal motor nucleus of the Vagus, a visceral efferent
nucleus. Another visceral efferent nucleus controls salivation. Nerve fibers
from each of these nuclei contribute to the Vagus nerve. This means, as in a lot of cases, that a number of different nuclei, way
stations of gray matter within the brainstem,
contribute to a single nerve,
which is nothing more than a cable conveying messages to and from the
periphery.
An example of a nucleus that has
connections with consciousness is the Cochlear nucleus that receives data about
sounds in the environment. Hearing is a special sense that impacts upon consciousness,
hence the cochlear nucleus is a special somatic afferent nucleus. If this weren't an obvious fact considering auditory
functioning alone, we could still know
this by looking at the position of this nucleus in the brainstem. It is one of
the most lateral of brainstem nuclei, establishing its role as a somatic
afferent nucleus. The nuclei controlling
movements of the eyes and of the tongue are under conscious control and are
considered by virtue of their function as well as by their position far away
(medial) to the sulcus limitans, somatic efferents. Thus we see by example the
profound and beautiful organization of even the lower areas of the brain.
Figure 15: Organization of the Medulla: Various
types of motor and sensory nuclei and nerves.[32]
Finally some of the muscles that
control voluntary movements of the pharynx and little muscles in our ears that
protect us from damaging loud sounds
come down to us through evolution as remnants of
The picture of the nervous system
that emerges through all of this anatomic and developmental description is one
of tight organization. It is built upon
the basic structure of a simple hollow tube.
At maturity, only the spinal cord
preserves this general structure. In the
cord we have two divisions of nervous function, afferent and efferent
limbs, which are only minimally
embellished with any but the simplest reflex associative function. Afferent
(sensory-incoming impulses) are generally dorsal, to our back, and efferent
(motor) impulses are sent out ventrally toward the underbelly. Automatic behaviors reside right in the
cord. We have discussed at few, the
stretch reflex, withdrawal with
contralateral extension of the unaffected limb to maintain an erect posture.
The major function of the cord is, as a complex cable, to convey information from the brain down to
the body and limbs and from the limbs and body to the brain. The outer cord (outside the gray butterfly
--see illustration) contains all white matter with fibers that run, for the
most part, from head to tail and tail to
head.
Higher in the brainstem the
nervous system maintains its basic tubular structure but it is somewhat
flattened out so that motor fibers are more medial or more toward the center
and sensory fibers more laterally. The
brainstem is further organized about a central sulcus limitans that separates
afferent (lateral) from efferent
(medial) cell groups. The further
away are these afferent and efferent nuclei from this sulcus limitans, the more they are involved with conscious
action and perception. The closer fibers
have to do with less conscious, more
automatic, action and perception. The types of nuclei (grey matter cell
groups) are designated as somatic
(voluntary, conscious) and visceral (having to do with organs, unconscious and
further by designations special and general,
as in special somatic afferent,
having to do with the special sense of hearing, for example.
The brainstem is thus a tubular more complex, embellished spinal cord retaining a lot of
design features, but modified.
Traveling higher up to the
thalamus, basal ganglia and the
brain, we still retain some design
characteristics of even the by now primitive spinal cord structure. The brain too is afferent, efferent, associative.
Generally the design is that the efferent limb is still more ventral,
the afferent, more dorsal, but there are all kinds of more complex
embellishments to all three components.
The archetypal afferent or sensory component in the brain is vision,
which sends its fibers as dorsal as any fibers can go, all the way to the back of the brain in the
occipital lobes. Vision is the most
precise and highly organized of the senses,
the most logical and developed sense.
Seeing is believing and all that,
all to be discussed in its own chapter.
Also the extreme front (ventral)
part of the brain, the frontal lobes,
get their own chapter later on in this
text. Here the associative limb of
nervous function reaches its peak, with motor plans and schemes, philosophical thought and wonder and
interpretation of high emotion. The associative limb of nervous function is especially overgrown in the brain.
Embellishment of the same tube? Yes only
things have gotten a little out of hand which is why I suppose, you and I are who we are.
We mentioned the function of the Notochord in
organizing the nervous system. It first
separates the cells destined to perform nervous system function then the cell
above the Notochord organize into a tube. Interesting that the notochord at
once defines our phylum, the major
taxonomic division that is right below the level of a kingdom, which is where we are on the evolutionary
scale, and is, embryologically, the
major organizer of the spinal cord and nervous system. This is not an accident, but a sign of a major strategic
departure, in evolution into a rigid
vertical head to toe design plan.
Unfortunately, the notochord
eventually mostly degenerates becoming part of the cartilaginous disks between
vertebrae. The notochord also does
not go through the entire length of the
embryo. Just in front of (rostral) to
this embryo organizing structure neuroectodermal cells organize to form the
brain. The brain also begins very much like a tube but then its development is
a flowering or embellishment upon this structure. Diverticulae
develop, for example for the special senses of sight and vision. There are
bends or folds that occur, and finally the tiny area analogous to the central
canal of the spinal cord becomes the fluid-filled ventricles.
Figure 16:Relation of spine and notochord.[33]
The hindbrain which includes the
medulla and pons, is more or less
similar to the spinal cord in structure. In fact its a little hard to see
exactly where the spinal cord ends and the medulla begins, at first, as you travel slightly toward the head of a
mammal. Later on as you travel closer to the top of the head, it's a different
story as abundant complex structures are added. But the notochord may still be
an organizing principle.
At 28 days of gestation or so for
the human the previously open neural tube is essentially closed. The middle
closes first forming a rostral and caudal residual neuropore, the last open part of the neural tube. Bone
encases neural tissue with cells descended from mesoderm. Some muscle, also of Mesodermal origin,
surrounds the bone, and all of this is covered with fascia and then skin.
Eventually the neuropores too close in turn. But all may not go right. The
embryo is vulnerable at this point.
Spina bifida is one of the most
commonly encountered anomalies. This refers to a failure of fusion or closure,
of elements around the spinal cord. It can be of various degrees. In some cases
only the overlying bone for perhaps one segment doesn't close completely but
the skin, meninges that cover the spinal
cord etc. do make a complete seal. This common finding on lumbar X-rays and
usually causes no symptoms and is termed spina bifida occulta. In other cases elements of bone and skin
fail to close over the spinal cord over a variable length usually leaving the
rear most portion of the cord, and some variable portion in front of that
uncovered and most often not functioning.
It appears closure first of the neural tube is necessary for subsequent
closing and sealing of overlying tissues. In some very severe instances the
neural tube doesn't close and then the overlying tissues also are malformed.
Abnormally formed and nonfunctioning nervous tissue is surrounded by coverings
which do not protect it adequately. The main danger is that the clear spinal
fluid that is contiguous within the nervous system and bathes the brain and
spinal cord, is exposed the outside and bacteria enter it to cause
life-threatening infection. In some
infants all that is present is an oozing bag near the rear end just waiting to
become infected. These defects, meningomyeloceles (Named for the coverings of
the spinal cord, the meninges that are often part of the tissue in the defect +
'myelo', meaning spinal cord. A 'cele',
is a bag or an open space.) should be
closed as quickly as possible.
The other problem is that the
nervous tissue within the defect does not function. Almost always these caudal
(near the back) nerves affect the function of the bladder and there is
incontinence and repeated urine infection later in life. These nerves also go
to muscles in the leg. If the defect is long, it will affect correspondingly
more nervous tissue. To make matters worse there is many times some defect
closer to the head as well termed an encephalocele or sometimes a more minor
misdevelopment in that area. This echoes the embryologic closing of the rostral
neuropore and caudal neuropore at about the same time. Something must happen at
a certain time to affect this particular stage of development but we have no
real clue as to what this may be. Is there a toxin that affects the embryo from
the outside? We now know that giving an
expectant mother extra Folic Acid, a B vitamin, prevents, though not
completely, these defects, called
dysraphisms, in newborns and that some
drugs increase their incidence.
There have been many theories. We
do know that these defects have been for some reason most common in persons of
British descent and there is in some cases an increased incidence in certain
families. Embryological development is a
house of cards the normal formation of one structure leads to normality in
others. Just one little error though will have dire consequences that cause other
malformations because of the mechanism of induction in which the proper
formation induces the development of
other structures.
When the bones lengthen as the person grows the
cord which originally extended past the bottom of the lumbar spine ends
considerably higher up at about L1 or L2 or so. (There are 5 lumbar vertebrae.)
What's left near the tail is a space containing a bag of nerve roots having the
appearance of a horse's tail or cauda
equina. In a lot of cases though with malformations at the bottom of the spine
the nervous structures are bound too tightly (tethered) to the spine and with
growth the spinal cord ends up being stretched and the bottom of the brain can
even be pulled down past the bottom of the bony skull. When the spinal cord is tethered in this way
to the bottom of the spine, function can be compromised, so that surgery may be necessary to untie it
and decrease stretch on the cordY .
At a certain stage the neuron
will stop migrating and dividing. Apparently it receives a chemical signal
that tells it that its time to stop division., or perhaps only a certain fixed
number of cell divisions are programmed into the developmental process. In the
process of repeated division and maturation the cells become committed
determining the location they will assume and ultimately the role to play in
the adult animal. By the time of a human's birth most neurons have lost their
potential for cell division and their anatomic destiny is irreversibly determined
even though the final appearance of each individual neuron is not yet finalized.
Some neurons are destined to die. Those that survive often dramatically change
from growing more (or sometimes less) dendritic processes and changing their
exact pattern of intercellular connection. While connections between neurons,
ultimate microscopic intercellular anatomy is critical to the understanding of
how the brain functions, the process determining how cells are interconnected
is not at all understood, nor are the signals that tell a cell it should
finally cease to divide.
Glia called astrocytes are
critical to the migration of neurons. These essentially star shaped cells share
many characteristics of neurons and also embryologic origin being derived from
neuroectoderm. Glia, like neurons, tend to form long cellular extensions. In
the Embryo these cellular processes serve as scaffolding on which neurons
migrate. In the cerebellum, a complex
structure modulating motor control, small neurons, the granule cells, constantly migrate during development over
the processes of a special type of astrocyte,
the Bergmann glia which pathologists pick out easily in post-mortem
sections of cerebellum in an adult.
Figure 17:Neuronal migration.
Future neurons move, directed by glia from the
shoreline of the
The glia, like their neuronal
cousinsÆ , are long cells. Many of these stretch radially
from the surface of the ventricle or central canal in the case of the spinal
cord, a structure filled with spinal
fluid and lined with ependymal cells that delimit the fluid-filled
ventricle. They stretch from the
ventricle, to the outer surface of the spinal cord, or inside the head, to the
covering of the brain, the pia, from inside to outside, in other words. Neuroblasts, forerunners of neurons,
reproduce like crazy at the inner ventricular surface. All the newborn neurons accumulate in a
mantle layer (see Figure 14) and then
begin to migrate to their final place hugging onto the radial glia as a guide[35]. Their is a general flow of migrating neurons
from the inner ventricular surface to the outer pial surface in both the brain
and spinal cord. The glia guide the
migrating neurons but other chemical substances determine final relationships
and connections. This is how the organization of the brain and layering of
neurons will be determined. The whole
human enterprise, the root or origin of
intelligence and all human endeavors,
lies in this connectedness and layering.
As we have seen with whales and dolphins though their brains are larger
than ours, our mental capacities far
outstrip theirs only by virtue of this cellular layering and architecture.
Once cells have found their final
home the relationships with their fellows are firmed up. These relationships
continue to evolve from a less to a more committed state. The method of growth of interneuronal
connections is best worked out for the visual system. In classic experiments
performed by Roger Sperry, eyes of frogs were
removed then replaced, but rotated
180 degrees from their original position. When the optic nerve connecting the
eyes to the brain and conveying visual signals regenerates the axons grow
exactly into their previous positions. Remarkably, since the eyeballs are
turned around, the frog behaves as if objects are 180 degrees in the wrong
direction and the poor frog will then leap away from a tasty fly. This shows
that by this stage these specific axons have already been committed to grow in
a precise path. Similarly in monkeys the precise projection of each eye upon
alternating stripes of visual cortex in the back of the brain (the occipital
lobe) are well known. There are alternating stripes representing visual
projections corresponding to each eye within the visual cortex. If one eye is
covered or is not used, neurons corresponding to that eye's projection area
develop to a lesser extent. When that eye is then uncovered it is still
virtually blind. The same process occurs in the cortex of cats reared in the
dark. Occipital cells fail to develop properly. Research has linked this
cortical development to changes in a certain cellular protein, microtubule
associated protein 2 (MAP- 2) whose active state has been found to be altered
by the lack of synaptic neuronal input. The alteration in brain function in
dark reared animals only occurs if the animals are placed in the dark during a
critical period, indicating that cellular formation and commitment occur in a
specific time frame. We may be observing the same phenomenon in infants and
children with crossed eyes (strabismus). Because the eyes don't focus together
and visual objects end up falling on different parts of the retina, these children would have double vision.
Ordinarily they adapt by suppressing the image of one eye. When an eye's image
is continuously suppressed neurons within the brain that handle this eye's
visual input likely fail to develop and blindness or low vision in that eye
becomes permanent.
Bell's palsy causes paralysis of
one side of the face due to an inflammatory process that damages the facial
nerve. In the healing process, the axons
that are partly destroyed begin to regrow. They tend to follow a specific
course reinnervating muscles that had been previously deprived of their nerve
supply as functional movement of the face returns. Most likely the muscle sends
out a chemical signal to the damaged nerve telling it to regrow in the muscle's
direction. Actually another scenario
that is even more likely is that the axons of the nerve sprout into the tubular
axon cylinders. Axon cylinders are
empty myelin tubes left after the dead
axons of the facial nerve degenerate. These myelin cylinders very probably send
out a chemical saying, in essence, "Come to me" stimulating the damaged axons of the facial
nerves to regrow. As it happens, the facial nerve also controls
salivary and lachrymal glands and sometimes
axons that had previously innervated one set of glands grows aberrantly
into the other. Thus recovering patients cry "crocodile tears" when
they really should be salivating over food. What is even more common is that
nerve regrows into the wrong muscle so that the muscles of facial expression
are not as easy to control. Closing an eyelid may cause a corner of the mouth
to elevate at the same time, as two muscles that were not initially supposed to
move together do so in a synkinesis.
This is an example of the variable tendency of neuronal extensions to grow
into more or less specific paths. Similar principles may apply for the growth
of nerve processes both in development
and in regeneration after injury. Long after birth and development, some regeneration is possible, utilizing many of the same mechanisms that
applied during embryogenesis. Nerve cell
axons can still sprout even in old age,
depending in many cases, on the very same chemical signals that grew
them in the first place. Both nascent
and damaged nerve axons respond to chemical signals arising their sites of
future innervation muscles, glands, and other structures as if imploring "Come to me, come to
me." Presumably these chemicals are
so-called "nerve growth factors" and other substances and some
perhaps are similar to cytokines as well,
chemicals that call lymphocytes and other immune cells (troopers)
into a battle zone created by bacterial or viral invaders. Identification and utilization of these chemical signals will be crucial for
treating diseases where there is nerve damage and also in finding the cause of
other conditions where nerve components grow uncontrollably in genetic
disorders such as neurofibromatosis and for certain tumors of the nervous
system.
As neurons migrate out to the surface of the
brain and continue to proliferate the surface area of the outer areas
designated as the cortex, increases greatly and there are multiple infoldings.
Gyri or convolutions separated by sulci or folds, form. Some infants have been
born with relatively few gyri or folds Their brains are fairly nonconvoluted
and smooth and they are said to have lissencephaly. This problem produces profound
mental retardation and apparently occurs after the 22nd week of gestation, the
time when folds begin to develop. The problem relates to abnormal neuronal
migration in that the normal layering of the cells of the cerebral cortex is
very abnormal, usually resulting in
severe mental retardation.
In our conception of the human
cortex various portions are demarcated by sulcal folds. For example the frontal
lobe is separated from the parietal lobe by the Central Sulcus. This infolding
or convolution of the brain (sulcation)
adds greatly to the surface area of the cortex. The whole surface, folds and all, architecturally, has the cell layers that we
have been talking about and thus increases the processing power of the
brain. The cerebral cortex of lower
mammals is a great deal more smooth and infolding occurs late both in evolution
and in the embryologic development that reflects it. Neurons proliferate near
the ventricles then migrate up a scaffolding of glial extensions. With more
convolutions and infolding comes more cortical surface and neurons. These also
require more cabling (white matter) as they project downward to effect
sensation and motor control. Whit matter
tracts also connect interacting cortical areas with each other. The highest brain centers in man are very
specialized. We can see this not only clinically when for some reason a
patient destroys certain specific areas of his brain and loses a specific function. You can also see changes
in cellular architecture that define areas of the brain.
The highest brain centers have
six layers of neurons. This pattern is defined late in the embryo. This
association cortex or neocortex is also a marker of our humanity. Going from
the surface of the brain over increasing depths, layers II and IV with smaller
granular shaped cells, are primarily receptive and are most developed in
cerebral areas concerned with special senses, particularly hearing and vision.
Layers III and V are to a large extent, efferent. In some areas of the brain
giant Motor neurons, Betz cells, reside
in layer V, and are concerned with initiating movements. In the visual cortex
of the occipital lobe layer IV has so much input it is broken up into two
separate sections by a Stripe of Gennari. This stripe
is responsible for giving this area its anatomic name, the Striate
(striped) Cortex. As we began to appreciate in chapter
one. It is this multilayered cellular
design, that you begin to appreciate
under the microscope, which
distinguishes the much less
intelligent dolphin and whale
brains (cetaceans) many of which are actually much larger and heavier than
humans from the incredibly greater computational capacity of our own smaller
organs. (For a fuller description see Chapter 1: "Inside the
Neuron".)
Below is a rendering of the famous
Brodmann Area map of the human cerebral cortex.
Regions of the brain, surface were demarcated by Brodmann, a German
Neurologist (1868-1918) who carefully
classified these areas under the microscope. The names and functions of
specific areas need not concern us here. The point is that generally the
functions of each separate area correlate with the cellular architectural
design and layers as seen under the microscope. It should come as no great
surprise that structure affects function in the brain or any anywhere
else. The more advanced areas of the
brain have the most complex cellula
Figure 18: The Brodmann
areas. Regions of the cerebral cortex were classified using cytoarchitecture. We know these areas correlate functionally
with sensory, motor, and association areas[36].
Late in evolution and by
implication late in embryologic
development, we begin to see that brain anatomy becomes more complex. As we have seen this goes with advanced
cerebral function which was late to develop.
The brain of animals and humans have their similarities but human
uniqueness is reflected in anatomy.
Differences may be subtle, may be
missed by a less discerning eye. In
broad terms though, we humans posses certain association areas inside the
brain, or at least our areas are much larger than those of lower animals. Once you begin to see changes in the
architecture of cells under the microscope you can compare similar brain areas
in man and other animals.
This is not to minimize the
primary and secondary sensory and motor areas of the brain that are
eloquent, that do affect, the
neurological exam. These areas too are
architecturally much more complex in humans than in other animals. The areas that has been studied the most in
this regard is the visual cortex, also
explored later on. Suffice it to say here that the general scheme in cortical
structure is a column of cells. This
vertical column may be composed of as much as six layers of cells. One vertical column, sometimes referred to as a barrel, will take on a specific sensory or motor
function. In primary cortices, those
receiving or sending our specific information one column or barrel may receive
information from a specific body part,
say a portion of the tip of the pinky finger. That is this column's receptive field, or, a primary motor column may control of
portion of contraction of the little flexor of the thumb or perhaps a grasping
response of the hand. Specialization and
localization of function is quite specific.
While in the primary sensory
and motor areas there is specific localization of function, in the secondary areas localization is less
exact. This is because secondary cortices are concerned with less
specific, more abstract, higher order
levels of function. Motor wise secondary
areas might control more of a pattern of movement rather than a specific muscle. For example, in the striate, cortex or
primary vision area, many cells have a receptive field. This means that they
will respond only to a stimulus that occurs in a small area of one's vision. A
single cell may respond only to an object within a very small part of one's
visual field. Only in the human brain are such association areas so well
developed. We have just hit upon a whole third limb of human endeavor (in this
case almost specifically human) reflected in development and anatomy,
association. thus we have afferent, efferent, and associative limbs that
together define neural function.
In the human brain the above
breakdown into afferent, efferent and associative gives an incomplete
description. There are regions that are
meta-associative, the areas that are phylogenetically (in evolution, and in development) newest.
Not surprisingly, these are the regions of the brain that make us the
most distinctly human. They are also hardest for the clinical neurologist,
biologist or psychologist to get at.
For example, it has been
relatively easy to define function within most areas of more primitive parts of
the brain, say, the brainstem or areas of the cerebral cortex serving specific
functions. We described such areas. It 's easy for a neurologist to see that a
patient who has a stroke in the right motor cortex has an obvious weakness on
the left side of his body where his arm is weaker than the leg.
Thus we have the typical hemiparesis,
a half body weakness. Moreover,
since analogous areas are present in lower animals, lesioning them or
stimulating them to obtain information about these areas is no problem either.
But there are other areas in the
brain that appeared late in the evolutionary scheme of things. The best example
is the prefrontal areas of the brain. This is a region that is in front of the
motor and speech areas of the frontal lobe. For generations, this area was
considered a clinically "silent"
or "ineloquent" area of the brain, because ostensibly, patients with lesions in
this region did not appear to have any neurological deficit. In fact, patients with schizophrenia and
other severe forms of mental illness were subjected to gross, primitive
neurosurgical procedures during the 1940's and 50's called prefrontal
lobotomies[37] Clinicians and psychologists had trouble
finding specific deficits in such patients especially using such crude measures
of mental function as psychological tests (IQ. tests and so forth). This is
what is meant by the notion that such areas of the brain are hardest to get at,
to get a handle on and assess function.
It's easy to appreciate that our
measurement of human cognitive function must be skewed toward those areas that
are easiest to assess such as memory, and even some forms of simpler arithmetic
and verbal ability (for example vocabulary tests) and away from more complex
abstract areas that really separate the men from the boys. Stephen Jay Gould
has made a study of this fascinating topic [38]. Science and
pseudoscience has naturally focused on quantities that are easiest to measure
such as skull shape and volume (and by the way they haven't always measured
even these quantities accurately) and away from the more difficult less
tangible areas such as acculturation to draw erroneous conclusions. The best
way of proving this is that there happen to be whole huge areas of frontal and
temporal lobe, especially in one's non-dominant hemisphere, whose function is not established and that we
have a devil of a time assessing. I can't say how many patients I've seen whose
neurological function appeared to be intact, with gigantic tumors in one of the
silent areas of the brain, the frontal or temporal lobe especially on the non-
dominant side. These persons usually present late in their disease with
intractable dull headaches or, most commonly, seizures, or their spouse may
notice a vague alteration in mental function that really results from
deformation of the rest of the brain by a large mass or increased pressure
within the skull.
Quite obviously, the prefrontal
areas are not a part of the human brain for no purpose. In fact, being that
these areas are so new, they have to serve an extremely adaptive function for
humans particularly and this area must be critically important for out
biological success. This means that the frontal lobes and all other such newer
area of the brain, the very areas that were so long felt to be clinically
silent, must be the areas most
important. As with a lot of things, what is subtle, not visible to the casual observer, turns out
to be the most important and intriguing.
The prefrontal area, and other parts of parietal and temporal lobe constitute the physiological substrate of our
humanness. The brain is divided then into "silent" or ineloquent
areas and eloquent ones. The eloquent
areas speak the most and the loudest.
When there is a lesion in these areas it's obvious. Because our measures of such things are
crude, the ineloquent regions, namely the huge areas that are
phylogenetically the newest, ones that appear only In humans are barely missed
when diseased. Huge tumors are
found in these areas without an obvious
deficit, that is something gross like a
hemiparesis, yet it is in these quiet
regions that the personality resides,
the frontal lobes, the temporal lobes.
They suffer in silence.
Memory function works this way
too. Whatever is less obvious turns out
to be the most important. Packed into
our being are all kinds of memory engrams,
data from development (that we are not just made as some final product,
but unfold, develop), data passed down from previous civilizations and our own
society, stories, myths legends, information from early childhood and adult
memories as well. All of us function at
this moment t0 on the basis of information incorporated into
our being from all previous time, t
-∞..
The higher areas of the brain
develop and are myelinated (insulated so as to function) last, another example of ontogeny recapitulating
phylogeny. For a long time it was thought
that myelination ends at birth. It has been found that the prefrontal areas are
still being myelinated until the age of 16 or so.
If myelination and other
maturational processes still occur in children, this presents a great
theoretical obstacle in testing young children to determine their intellectual
abilities. Basically you can test a five, six, or seven year old and label him
at that time. You may put him into a gifted, average, or learning disabled
(slow) category as many of our schools do now. But at a young age, you are
testing a not completely developed brain which is still plastic and has not
reached any final plateau. Testing will
successfully stratify five and six year olds.
But the ones who come our on top may merely have matured faster than
their same-age colleagues. Later on,
when developmental processes end, the
slower kids might be superior to the faster ones. What a pity to test kids at a
very young age, then pigeonhole them,
put them on an academic track for
life as has been the practice in
many European countries and
It does no good to classify kids
on the basis of which ones are the fastest myelinators. Some tasks notably some
gross motor and lower extremity tasks,
measured at an early age, steer
you in the wrong direction. For example
its often true that toddlers who walk early and are the best on their
feet, perform more poorly in the classroomY. Lots of kids with Attention Deficit
Disorder function much better than their slower colleagues on the playground,
making much better use of slides and monkey bars than less adventurous
tykes. Look at lower four legged
animals. Many of them can walk on the
first day of life. Humans take a lot
longer to learn to walk, typically
around twelve months. If we were test
such motor abilities in babies and then jump to conclusions about their
ultimate abilities we would be sadly mistaken.
Even after birth humans spend an
inordinate amount of time immature and unproductive. This is the phenomenon of neotony. Kids of a certain age are good for nothing
but learning, and playing (at which time they are learning) and developing. It
goes without saying that their motor and sensory systems and minds are not in
their full adult form for a long while, perhaps 18-20 years. Their faces are so cute and infantile, for a very long time, reflecting how they are on the inside. They are born undeveloped. That's what makes
them so much more advanced! Almost all
other animals make productive citizens of their offspring within a much shorter
space of time. So do all of the
societies where none of us would care to live.
But of course, animals never get to experience the heady the heights of
human performance. Development occurs quite slowly in humans. Some kids will run earlier, some speak o
This is only one of many reasons
why early testing and performance, that
too many schools depend on, is not
predictive of a child's final development (or a measure or future academic or any other
success). The very best thing that can
be said about early testing is that if you have a child with a certain
score, you at least know he will be able
to perform at that level. Even this is
deceptive, since, for a variety of reasons,
performance may later deteriorate.
It can be said that so many child prodigies don't just burn out. The
problem is that although they may be slightly more rapid myelinators or
developers, or may be pushed to perform
to gain their parents love and approval, poor little fellows (sort of like trained circus animals, when
you think about it), this says very
little about their adult capacities. Many of them turn out not to have anything
out of the ordinary. Indeed it is
amazing given all of the advantages that these kids receive in the areas of
attention, expectations, allocation of resources etc., that so few of them seem
to make any marks or to perform outstandingly as adults. Of course there are
always the Mozarts and Mendelsohns
who are really exceptions, but the Einsteins and
The pituitary gland the master
endocrine gland of body controlling secretion of all other ductless gland
hormones, arises by the joining of ectoderm
from two separate sources. Actually
most of the active gland as we know it isn't even derived from brain. Rathke's
pouch consists of a small group of ectodermal cells that originally lie at the
roof of the embryonic mouth at about three weeks of gestation. This group of cells grows upward slowly
toward the brain as a hollow group of cells contiguous with the mouth to
eventually join another group of neuroectoderm derived cells that grow from the
diencephalon (the part of brain laying just beneath the hemispheres). Many of
the mouth- derived cells degenerate or die so that the connection between the
mouth and brain is broken. The cells that are left form the so-called
adenohypophysis, the actual glandular secretory pituitary gland. Since these
cells secrete their chemical product directly into the blood (not into a body
cavity), the pituitary is a ductless or endocrine gland. Follicle stimulating
hormone and luteinizing hormone help to control the testes and ovaries, also
ductless glands. Other hormones include prolactin that helps to control the
breasts' secretion of milk, thyroid stimulating hormone, adrenocorticotropic
hormone that stimulates the adrenal glands, and growth hormone which are all
produced by cells derived from Rathke's pouch in the foregut. The pituitary is
housed in a bony cavity, the sella turcica which is part of the sphenoid or wing shaped bone
of the skull. The nerve cell derived neurohyphophysis cells are connected with
the adenohypophysis cells from behind and hang down below the hypo (=below)
thalamus. These are intimately connected to the adenohypophyseal cells by an
extensive blood vessel network so they can exert their own control. In
addition to two known hormones, oxytocin and vasopressin that have a direct
effect inside the bloodstream this system of capillaries and veins, a portal
system, carries chemical that instruct the anterior pituitary to secrete or not
to secrete hormones. These chemicals are the releasing and inhibitory factors.
What we have in the pituitary gland is the joining of two groups of cells. The
anterior lobe of the gland, the adenohypophysis is not derived from brain and
is really not a part of the brain even though it ends up inside the skull. Only
the neurohypophysis or posterior lobe is truly a part of the brain.
Gland or secretory cells are
little different from neurons. Both neurons and secretory cells liberate
chemicals when excited and both can be excited electrically. The neuron, it is
true, is a specialist in excitation and affecting other adjacent cells. It can
be stimulated as a general rule over a wide portion of its surface and can
affect adjacent cells over a large surface as well. For the secretory cell,
things are only slightly different. When stimulated it will secrete a chemical
not in a very specific region over its surface but instead in order to affect
other cells, ordinarily to send a signal to other cells, not adjacent, but
distant. The message from glandular cells usually has to be carried by the
blood.
In the development of the eye part of the
brain ends up outside the skull. Optic vesicles evaginate from the forebrain
and end up outside the cranial cavity. These vesicles are connected to the
brain by the optic nerves. The hollow tube invaginates to accept the lens and
cornea which are derived from non brain ectoderm while brain derived cells form
the retina. The retina forms in two parts separated by an intraretinal space
that obliterates in later development just as the hollow center in the optic
nerve does. The retina consists of many layers of cells and constitutes the
initial processing station for visual signals that turns light into a language
of electrical impulses. It is easy to see that receptors of sensation of all
types turn various forms of energy into specific electrical input for the
benefit of the brain. This turning of one form of energy into another is the
job of a transducer which all receptors really are. The familia
In the central nervous system
axons invaginate into a glial cell, the oligodendrocyte. This distinction hits
some snags, however. In the spinal cord motor nerves the cell body is within
the spinal cord yet the axons form peripheral nerve. Groups of axons going from
one particular locale to another within the central nervous system are
designated as tracts, not nerves. Therefore the optic nerve is a misnomer. The
optic nerve is really a tract.
The lesson learned from the
pituitary and the eye, is that what is in the skull, is not necessarily a part of the brain. The adenohypophysis is glandular tissue that
is non-neural. On the other hand the
retina, which is outside the skull, is still part of the brain. Examine the
retinal with an ophthalmoscope, and you may learn what is happening in the brain. The retina's blood supply comes from the
brain's and the optic nerve has myelin of the central nervous system, not peripheral nerves. The tiny pituitary
gland is a fusion of brain and body. The
controlling ductless gland is brought up to the brain from the periphery so
that the brain has more intimate control over it. Indeed the entire
hypothalamic-pituitary relationship is a fusion of brain influence and the
periphery. The function of the
hypothalamus is to process information about body temperature, satiety, blood pressure, even emotion, and
other internal functions and wield control over these processes. A retino-hypothalamic
tract that running from the eye to the brain carries information about light to
the hypothalamus' supra-chiasmatic
nucleus. This data entrains the
brain to keep a person in sync with night and day even as this varies when we
travel or the seasons change. Part of
this process implicates the hormone, melatonin.
The culmination of all of this
prenatal development is the birth of electrical activity in the brain. We've witnessed a lot of controversy in
recent years about when human life begins,
when a human fetus becomes human.
There is little controversy about the fact the as soon as the sperm
meets the ovum to form a zygote we have a potential to form a human, but when does the developing baby actually
turn into a human? Arguably, this is
when organized electrical activity begins to occur. More specifically it is
when this activity is organized enough to define separate levels of
awareness as defined electrophysiologically,
when it can be seen on the EEG and other electrical tests. It may be said that a person exists when
darkness is separated from light, when arousal is recognizable as a separate
state, from sleep. It should not come as
a surprise that this distinction is made roughly at the full nine month
gestation. One can at a certain stage of
development see differences in levels of
arousal from waking to slow wave and REM sleep.
This happens at roughly 28-30 weeks conceptual age, that is after conception. When waking activity is defined and sleep is
separate from wakefulness, then a person can be said to be. This makes eminent
sense because that is when we can see arousal in an infant. Arousal is necessary but not sufficient for awareness. This is not that far from natural birth
which is at about 40 weeks of gestation.
Most vocal religionists today, pro-lifers, insist that life starts at
conception. This is by no means a point of view uniformly held by religious
persons. Some maintain that life starts
at the time of birth. From the
scientific point of view the latter position seems closer to correct. When alertness is separated from sleep, satisfyingly the same as when light is
separated from darkness on the first day of the biblical Genesis. Indeed if we consider the time when we can
reliably correlate behavioral signs of levels of arousal with EEG changes, when we can see reliably that baby is awake,
asleep, and in REM sleep and are able to correlate these electrical changes with
behavior, that we are remarkably close
to the normal 40 week's gestational age,
the normal time of birth and also when the breath of life begins. Would it then be reasonable to absolutely
forbid abortion in the third trimester of a pregnancy but allow it to occur
under special circumstances before that time?
Human Cognitive development is
too often presented as an unvarying succession of milestones and so it is
though post -natal development often occurs in fits and starts. There is not
always a smooth continuity. Suddenly an infant who has been only crawling, gets
up and walks, and he may be able to take more than a few steps. Some of the
reasons for this have already been alluded to. The myelin insulation has to
finally cover the tracts descending and
ascending in the spinal cord so that the
brain can finally exert its control and primacy.
What we do know in the
macroscopic sense, is that development is basically unvarying, that humans
have a tendency to build on past
successes, in all spheres of development. There are exceptions to this rule,
but very few. Probably the best example is the infant we all know or hear about
who learnt to walk, but never learned to crawl. Even here, what most likely
happened is that the crawling phase was incredibly short for that particular
infant.
Infants and children also
regress, especially under emotional tension (the best example is with a new
sibling) or when they are sick. This
probably serves also as a mechanism to practice old skills and to build in other ways upon them.
The interesting angle here is that there is an dialog between the new and the
old which neve
Regression is an important
academic tool couched in terms of a review. In September of the third grade,
children who were exposed to multiplication ordinarily come back to problems in
addition and subtraction, something
undoubtedly less threatening to them at
that stage. Also there is forgetting and the need to relearn, but again the
need also to build in different ways upon old knowledge, a dialog with history.
It's been often observed that a
baby is born with all the 10-100 billion or so neurons he will ever have. There
is some new information that indicates this isn't quite so, that some neurons
will still be formed after birth, but it is basically so. The 350 gram newborn
brain is about one fourth of its adult weight. By the age of three, the brain
is three quarters of its adult weight and by the age of 5, 90%. I've heard some
psychologists say that 90% of our intelligence is determined by the age of
five. This is a meaningless and therefore unprovable assertion when you think
about it. Scientifically it is meaningless since you would be unable to design
an experiment that would prove or disprove the assertion. It therefore should be considered to be
untrue. Most probably though its
been propagated in the literature since it sounds either profound o
As an example, it has always been thought that language
acquisition for one's native tongue needs to happen at a very early age,
certainly before the age of five. The
left hemisphere of the brain in most of us is dominant, being responsible for the generation of
verbal thoughts and language function.
But some information indicates that there is not a "critical
period" for language acquisition.
For example, in a little boy with Sturge-Weber
disease, a malformation of blood vessels
that affected the function of his entire left hemisphere, treatment, the
removal of the affected left side that caused epilepsy, was delayed until he
was almost nine years old. This little
fellow who was virtually mute until that time, finally acquired, essentially
normal language at about the age of nine. We also observe patients with stroke
who relearn language utilizing thei
When
does mental activity truly begin? Some extreme religionists and psychologists agree on certain points - that
mental activity begins early, probably well before birth. The religionist,
especially anti-abortionists, not only maintain, as everyone does, that in the
embryo there is the potential for the eventual emergence of human consciousness as we know it, but also
at a very early stage, perhaps at or
even before conception, the potential human is invested with a soul. This
latter contention, I'm truly unprepared to comment on, but there is the very
interesting open question about when mental activity begins. The
psycho-analysts say, at least some small minority of them, that experiences
occurring early, very early, even prenatally, may
alter a person's development in years to come, even as an adult. You find such
outlandish practices as babies being born under warm water for its gentle
soothing effects, and rushing really without good reason or evidence, for the
newborn baby to be bonded with its mothe
An infant is considered to be
born at term at about 38 to 42 weeks
post conception. Due to the miracle of the neonatal intensive care unit, it is
now possible to record the EEG in infants after their 22nd week of gestation. From a scientific standpoint, it is
reasonable to attribute the beginnings of life to the point where EEG activity
begins to occur in the brain. When is
the embryo a person? When some form of
electrical quickening or activity occurs in the brain. You can still argue that
if there is any awareness at this stage, the start of cerebral electrical
activity, that awareness has to be
minimal and that is a good point, but at any event this is a convenient time to
date the beginnings of mental life.
Some mammals such as a rat and mouse are
normally born premature. In them we can see that they evolve from having
essentially a flat EEG with no discernible activity at birth, to a burst
suppression pattern. Activity begins to emerge but starts to be present alternating
with long periods of flatness or electrical quiescence. This paroxysmal
activity is disorganized but it is the first thing to appear as the brain
matures. We can see the same pattern in premature human infants (figure).
Electrical silence alternates with high voltage paroxysmal activity. This is
the first sign of electrical life in the developing brain.
Later on, at about 30 to 33 weeks
post-conception, there is a general trend for activity to become less
paroxysmal and more continuous regular and organized. There are shorter periods
of electrical quiescence or silence but there are still spikes that mark
initial activity in developing neurons. Faster and rhythmic activity then is
seen including slower waves superimposed by faster more rhythmic activity, so
called spindle delta bursts or delta brushes, possibly the first evidence for
some electrical rhythmicity in the developing brain.
Some short time after birth
different levels of consciousness or sleep wake cycles are noticeable and can
be partitioned off, the forerunners of these same stages as in the adult. Basically,
we are always in one of three basic stages. We are either awake or asleep and
when we are asleep we are either in slow wave restful sleep, or paradoxical=REM
o
Later there is maturation into
patterns of the full term newborn where waking activity is distinguishable
(finally) from sleep and different stages of sleep. One pattern that marks
quiet sleep in the infant is the Trace Alternant pattern in which there are
again some bursts of paroxysmal activity which usually occur in all areas of
the brain at once. This harks back to
the very premature pattern present in the early premature. The infant at term or shortly later, is just
beginning to differentiate or partition off sleep and different stages of sleep
from wakefulness. His partitioning is at first somewhat pathologic. The infant
shows signs of going from wakefulness right directly to REM or dream sleep
instead of going through the stages of
slow wave sleep first as adults do. Sometime after birth at about 44 weeks or
so post conception, the infant will develop the adult sleep stage pattern and
REM sleep will not occur until he has gone through the appropriate stage of
slow wave sleep.
Embryology is emblematic of all
the other historical processes that contribute to our makeup or current
state. My review of this as far as the
brain is concerned is meant to at one blow expose anatomical principles and
give a thumbnail sketch of biological development, to make large patterns more
visible. At the same time there are so
many other developmental considerations packed into our current makeup all of
which influence current behavior:
thought, action, feeling.
Development continues after birth
of course. At birth, an infant can
barely see. Acuity is estimated to be
about 20/800 on a Snellen chart at two weeks, 20/70 at five months, and 20/20 by five years
old. In the famous “visual cliff” studies an infant asked to cross the gulf
between two halves of a table covered with clear glass to reach its mother will
manifest anxiety at about the age of 8-10 months of age.
Infants and children progress
over a well-known and orchestrated series of developmental stages. They acquire a long series of reflexes and
behavioral responses, often casting off
old reflexes such as a Babinski, Moro,
forced grasp, and tonic neck response as they develop and as axons myelinate. What is fascinating is that with destruction
of certain parts of the nervous system and in certain diseases, many of these once cast-off reflexes, are
documented to reappear. It is as if the
nervous system develops by a layering process.
Each new stage of development is
merely added to a former phase,
in just the same way as we have seen, the cerebral cortex modulates the
automatic responses of the spinal cord and lower brain centers. This model carries forward to a myriad of
other developmental processes as we will see below.
Just one is human history. This is less a discussion of history than it
is of embryology, except to say that the
average person seems to have historical conceptions all wrong, which is the reason why most people are
thoroughly bored with it. The man on the
street, if cares one wit about history at all, which usually he does not, will
give George Santayana the credit
for what is worthwhile about studying it,
"Those who do not remember the past are doomed to relive
it.." This standard reason given
for the purpose of studying history is all wrong. We know that the study of the past will
almost never yield up a remedy for our present predicaments, nor prevent us
from making mistakes of the past. Hitler was well aware of Napoleon's failed
attempt to invade
Let us do a quick survey of history in one paragraph. We descend from animals which reproduced
sexually over eons of time. Ancient
hominids ate both meat and vegetable matter and were hunter-gatherers of the
plain. Savage Cro-Magnon men from which
we more closely descend, probably
existed alongside Neanderthals who we now understand, had a primitive religion
as well as reverence for their dead.
Neanderthals may well have been
brutally annihilated by more intelligent Cro-Magnon men. The biggest advance in human history came
with the domestication of animals and the cultivation of crops making it
possible to make a permanent home. Next came the raising of cities and
development of writing, civilization,
roughly 6 or 7 thousand years ago that was so momentous, that the Bible reckons it as the beginning of
time. Writing coincides with a higher
human consciousness or self awareness allowing us, for the first time, to build upon a past permanent record without
relying entirely upon our own imperfect memory and word of mouth. For the first
time, men were able to keep a written record,
outside the limits of the human brain.
After this we have abundant historical accounts of war, though it seems incontrovertible that
organized savage physical struggles took place well before the emergence of
even of our species. When these struggles
occurred and the invaders prevailed, the
city,
What's the point of going into
all of this? It is who we are. Let's say that a religious sect requires male celibacy and sexual abstinence. Then it is denying something human and is
going to have to expect to run into some trouble. Apart from the obvious, that such groups are not
self-propagating, sexuality is quite
basic and may be expected to spill forth in some way whether through fantasy,
masturbation, homo-eroticism, pederasty
or other channels. Such constraints may
bring about much more "sinful"
behavior than the original behavior they were used to minimize, but also increase focus on sexuality which,
naturally expressed, would never have been raised to such a high level of
importance.
Less basic perhaps is meat
consumption. Again, the rule is that vegetarians, while noble in their intentions, end up being much more hung up on food, which
really is quite second nature and not much of a concern to the rest of us who
live in an environment of plenty.
How to handle aggression. Aggression has been part
human nature throughout history. There is no way to deny it and it does
no good to repress it. Groups that
survive today because of successful
plunder. We are not the descendants of sacked cities but mostly offspring
of the sackers. Granted the erecting of cities gave many
groups the possibility of surviving by their own intellectual whiles and
stealth as much as by physical strength.
Numerous well-intentioned utopian experiments in which all persons work
and wealth is evenly distributed have
failed. Perhaps there are a few
short-lived examples that do survive if you count in certain convents,
kibbutzim, and Amish societies. But for the most part, aggression and self-interest have to be
counted in the human equation and dealt with,
not denied. Denying these
tendencies will in the end cause an eruptions of aggression a riot, or a
war. This is one human characteristic
that needs constant management.
Aggression has instead to be channeled in constructive ways. If a persons could be rewarded for self
interest as long as it benefits his society as well, that would be ideal. The enlightened society
is one in which human characteristics are acknowledged and incentivized to work
for the common good and survival of
the whole. It is the way, for the most part, that our capitalist
societies function and the biggest part of the story of the collapse of
communism and failure of socialist regimes. "Enlightened" self-interest, behaviors that benefit
society, need to be rewarded. Repression and loss of freedom may work over the very short term but are not
likely to be successful over long timeframes.
I don't recommend we deny who we
are. We need to study ourselves
more and work effectively with our
discoveries. In the ideal situation we
could then have an opportunity to advance past our immediate predicament to
demand even more from ourselves. That is
part of being born and not
manufactured which means our past is part of our being. We need to know how we came to be to
determine who we are.
Whether or not one looks at
history as a saga of progress into more advanced phases of development of
mankind, and I admit that that is the
way I see it, the lesson from our embryologic origins how the infant unfolds
and morphs from a past state, is applicable to an interpretation of past events
and without this knowledge we know so much less or who we are, because we are the embodiment an unfolding of
our past. That is the real value of a
study of history. That is why we
remember. As conscious wondering beings
we crave a knowledge of who we are. If we have no idea where we come from we
are less alive, less conscious. Our present is a product of our past and how
we came to be. While rare is the occasion where knowledge of history will be of
any practical use, memory places us on a
tapestry of time and space, providing
data about our particular space-time coordinates. It helps us put our lives in the context
of the human experience. Without it we
have disorientation. Historical
distortion yields a kind of vertiginous
disorientation.
There are myriad other
contributors to our memory and our past.
It is not my goal to review development here, only to point out in general terms how these
considerations lead to a fuller appreciation of who we are and where we fit in
the scheme of things. I provide a very
brief summary mainly for purposes of illustration.
Jean Piaget (1896-1960) was one
of the greatest contributors to cognitive development of children. He represented cognitive maturation as a
series of four successive stages,
Sensori-motor (0-2
years), Pre-operational (2-7 years), Concrete Operations (7—12 years), and Formal
operations (12-15 years). The child is held to progress through a
series of intellectual milestones in development. For example,
in the sensori-motor phase he
masters the concept of object permanence between 8 and 12
months of life and is able for the first time to try to find an object
temporarily hidden from view. Before
that time, a hidden object, apparently
disappears forever from the infant’s regard.
Similarly, in the concrete operational phase “object conservation” is mastered. A child realizes that the quantity of clay is
the same no matter what its shape, whether
it be rounded into a ball or elongated in a sausage shape. In the formal operations stage, the youngster is able to handle rational and
systematic meaning about hypothetical problems,
is able for the first time to think mathematically and symbolically. Each stage is a pre-requisite for successive
thinking modes.
Whatever one may think about
Sigmund Freud (1856-1939) and he is not looked at kindly in this day and
age, he did look at emotional
development of the young child,
interpreting this to be essentially sexual. He invented the well-known and worn, oral (1st year), Anal (2nd
year), Phallic (years 3-6), Latent
(6-12), and Genital phases,
proposing that it is possible through incomplete resolution of
conflicts, for a person to be mired or
fixated at one or another of these successive phases.
Freud’s views were enhanced by
Erik Erikson (b. 1902) who identified
developmental stages according to successive life tasks or conflicts viz. Trust vs. Mistrust (infancy- 1st
year), Autonomy vs. Shame and Doubt ((2nd
year), Initiative vs. Guilt
(preschool), Industry vs. Inferiority
(School age), Intimacy vs. Isolation
(young Adult), Generativity vs. Stagnation (Prime or life), Ego integrity vs. Despair (Old Age). These descriptive observation of conflicts
presented by life are at once obvious and bear more than a grain of
truth, but again, reaching successive
stages depends upon success in resolving the conflict presented by the preceding stage and unlike
his predecessors, Erikson rightly
extended development throughout an entire lifetime, instead of restriction to
childhood. Humans experience an entire
lifetime of maturation of thought processes.
Whether or not one agrees with
the accuracy of such specific staging of development, there is little doubt that cognition
continues to morph throughout a person’s lifetime and stages may be represented
according to an anatomic developmental model as successive layers or
laminations.
I am presenting here a layered
or laminate
structure of consciousness based on memory.
Each successive stage is built upon a bedrock or former stages depending
on the underlying stage as a support. and prerequisite. Children either are or
are not ready to learn about a new
concept. Readiness depends on their
biological development. Before
puberty, they may not be able to
understand a lot of concepts about sex.
Or they may be unready for advanced concepts because they have not yet
mastered more elementary ones. It’s very
hard to teach calculus before you have mastered algebra. Or, they may be
unready for information due to a combination of biological and experiential
factors. A 9 year old child was
shown films of comatose patients on ventilators as part of program
teaching them about death at his school then asked to vote whether they
would want to be kept alive under these
terrible conditions. He voted no. Soon thereafter his grandmother died. For some reason he was unable to sleep at night. As it
turned out, he thought he'd killed his grandmother when he voted to
terminate the comatose patient. Young
children whose parents get divorced very frequently feel responsible. Perhaps there were terrible fights and the
child may have wished for an instant that his parents would split apart. At a certain stage of development a wish is
tantamount to making something
happen. A substantial part of evolution
into adulthood is expanding abilitiy to separate
fantasy from reality. We know that well
after adulthood, there are concepts that
can only be dealt with at more advanced state of development. We call this wisdom by which we mean a state
of advanced readiness.
At any given time,
it is possible to reach downward into our personal treasure- trove of
memories, past former stages of development which are very
much still present, to regress, in other
words, into former stages or to just use the information still there and
incorporate it into the engram sediment that is our daily lives. Sometimes this happens after an injury, as in some multilingual stroke victims who
have a tendency to revert to the original language of their childhood. Usually this is not the case, but regression may occur after a psychic trauma or other process.
Examples of regression into pre-logical thought
abound. For example much (by no means
all) religious thought is at once, pre-logical yet so basic and therefore all
the more powerful. The more mythical stories stretch the boundaries of logical
adult thought processes, the greater is
the power driving their belief. The most unbelievable stories bring about the
most resilient belief. This would stand to reason, since a person who believes
strongly in something illogical or disproven by
experience is the most unlikely to be dissuaded from his belief by logical
argumentation. An inverse correlation
exists between reality testing and the power of mythical beliefs, so much so that I hesitate to give specific
examples for fear of violent repercussions.
I do have faith that the reader,
on being exposed to this principle,
or perhaps having already made the same observation, will be able to
come up with abundant examples on his or
her own.
Figure
19: The laminae of Development
(examples).
In summary, I have developed in this chapter a
different, more comprehensive view of
memory, which is far more than the
recollection of details just presented,
much more than the storage of bits on a computer disk. Rather memory in humans is a dynamic
interaction of the past with a
challenging present, the interface of our makeup with life experience. Memory expresses itself In learning by which
we mean the alteration of behavior consequent to experience, behavior comprised
of perception, thought, emotion, action.
Up until now our concept of
memory has been superficial. We have
been mired with overly simplistic models of memory and have failed to see it
for what it is. Consequently, the importance
of memory has been underestimated. When
we view memory in all of its shining glory as
the sum total of what we are at any given moment, interacting with our present to produces all future
experience, the complex depths of
life, then we see ourselves as we really
are not mere biological machines or
automatons. No longer are we fooled into
accepting a simple biological model for the laying down of memory engrams, or influenced by the disk drive or CD ROM
model of memory, as entirely a material.
Memory is in part our innards
and assumes myriad dimensions and
great depths. A better model than a disk
drive might be Jacob’s ladder with hundreds of retrieving angels continuously
climbing and descending from the cortical empyrean to the layered depths of
past conflicts and experience. This is
what makes us who we are, unique beings
whose life will be easily reproduced o
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INPUT (Memory) |
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Evolution |
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Embryology (Developmental anatomy) |
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Childhood
Cognitive Development (à la Freud,
Piaget) |
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Adult Stages (à la Erikson) |
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Cultural History |
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Culture |
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Personal
History |
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Upbringing |
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"Collective
unconscious" (Jung) |
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preverbal
childhood experience |
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dreams |
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Epilogue: What will we leave to our children?
All of this is meant to show that
memory, something superficially very simple, is a whole lot more complex. It is the sum total of our being up until the
point in time we call the present. We
live in the computer age and it is reasonable to see all of this in terms of
information systems. After our lives are
over, and even now, what are we leaving to our children?
Our life span is finite. But parts of us are passed down for a much
longer period of time. Our legacy is quite obviously in part genetic. We will leave certain traits and form and
physiognomy. We will leave certain weaknesses and strengths as well. Perhaps a
tendency to develop heart disease of diabetes o
The most important legacy we will
leave is a record of our own life, well or poorly lived. Our whole life exists
within certain space-time coordinates as we have seen. Certain aspects of our existence may or may
not be discoverable depending on the status of memory and technology used to
extract this information. Most of this data will be unavailable forever, though it will continue to exist of
course. Even the pyramids and the Taj Mahal standing now as witness to the past, will
eventually collapse, and at some future
time there will be no record that they ever were. Certain particularly resilient ideas may well
survive over much longer time frames, even though they are not palpable or
tangible.
If we see this legacy as
information, the next step is to construct tiers of information that become a
record of our life. This information is
remembered, extracted, extractable or not,
as is all information registered or not registered, retrievable or
irretrievable in memory. This discussion
provides little more than a survey of what is possible the tiers of information
recorded. Information in the form of
genetics, development, personal and collective history, events and choices, cultural and personal
ideas and the course of life. Our brain
merely makes possible new forms of information which may be passed down to our
children, culture, events, ideas as well
as the genetic and structural and physiological information that lower animals
pass on to their offspring. We need to be mindful that we are passing down a
good deal more than biological heritage.
Note: This material is copyrighted
and can be reproduced only with written permission of it author, Charles S. Yanofsky