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Presented By:

Charles S. Yanofsky, M.D.

Susquehanna Physician Services

699 Rural Avenue, Ste. 205

Williamsport, PA 17701

(570) 321-2820

 

You are about to view one of our most popular web publications. Feel free to use it as you wish, short of copying it without proper attribution. I have a number of other publications on at the website: www.susqneuro.com on various topics including question and answers, motivational publications, papers on general medical concerns and neurology. To avail yourself of these, just click on the "publications" section above.

Dizziness Explained

If you've been to doctors but feel frustrated over your dizziness, this booklet is for you. Dizziness is a thorny problem for doctors and patients alike, the chief complaint in over 8 million physician visits a year, almost as common as headache and back pain, major causes of disablity, yet the cause is unspecified in over half the cases. Chronic cases average 5 physician visits without resolution. Imbalance can lead to loss of livelihood, falls and injuries. Some form of dizziness affects up to 10% of adults, most often with incomplete diagnosis and imperfect resolution.

Dizziness is one area where doctors and patients fail to see eye to eye. People are seen by multiple specialists and end up with different opinions. You may have the impression that no one is listening to or cares about your problem. After a while you wonder if you're imagining things. Lots of dizzy persons express great relief once a diagnosis is firmly in place, even if they can't be cured, just at the prospect of understanding a little bit of what's wrong.  Dizziness is not different from any other problem. It can be solved by a systematic approach. I will analyze the problem and tell you what can be done. Hopefully, you will find your particular situation described in these pages.

Dizzy Guy

Kinds of Dizziness - The History

The first part of a medical evaluation is the history. Dizziness is an uncomfortable inner feeling of confusion. Because the word is used to describe so many different sensations, we need to have a firm grasp of exactly what a person means when he or she complains of dizziness. Our first task then, is to extract a personal description.

We need to determine if dizziness is vertiginous or not. Vertigo is a specific spinning sensation, an illusion of motion. You may remember as a child spinning like a top and the sensation you would have when you stopped. It was fun then but it can be disconcerting when it happens on its own. You may recall nausea, veering and staggering. You tended to veer a certain way depending on your direction of spin. If you had spun around with a friend you may have seen his eyes jiggle at the time he had vertigo. This is nystagmus and it goes with vertigo. You can observe nystagmus if you watch a person look out the window in a train or car. As they move past telephone poles or trees you see a repeating jumping eye movement. The eye slowly goes in one direction and quickly back to its original position in the opposite direction.

Is the dizziness vertiginous or non-vertiginous?? This is a basic question we spend considerable time trying to nail down. Lots of people won't commit themselves. True vertigo is like love. When it's there you know. If you can’t say whether you have vertigo, chances are you don’t have it. We put non-vertiginous dizziness in a separate category. If you have vertigo and veer in a one direction or spinning seems to be in one direction (clockwise/counterclockwise) that is consistent. For many people vertigo is worse when they move are in a particular position, laying supine, for example, or with one ear down. Nausea and vomiting often accompany severe vertigo, especially when it is prolonged.

So what if you have dizziness but not vertigo? Then things get more hairy. You may suffer from common lightheadedness. This is what you feel when you get up too fast, as if not enough blood is getting to your brain. A certain small amount of transient lightheadedness is normal, but sometimes lightheadedness is more persistent. This occurs with anemia from blood loss, volume loss from sweating, when you are short on fluids. Medicines that affect blood pressure regulation include antihypertensives, diuretics and antidepressants. Some persons experience visual darkening or near fainting when they stand. Lightheadedness with near fainting is common in the frail elderly, and in adolescents in a growth spurt. It is part of diabetes when it affects peripheral nerves responsible for blood pressure, and Parkinson's disease. It is usually worst in the morning or after a long period of recumbency.

When you stand your circulation has to make adjustments. Your body is a fluid filled container. Blood naturally gravitates to your legs. When you stand, automatic responses mediated by the sympathetic nervous system (adrenaline), the heart, veins and arteries come into play. Blood suddenly needs to be shunted up to the head. Arteries, have muscle in their walls, which constricts, maintaining blood pressure, and the heart beats faster and harder. As you get older or if you're sick or affected by drugs, this response tends to be less brisk. This is what is meant by orthostatic hypotension. One criterion for orthostatic hypotension is a systolic (upper) blood pressure drop of more than 20 mm in the lying vs. the standing position.

When a lightheaded dizziness leads to Syncope or an actual loss of consciousness we look for a problem with blood circulation, mainly heart, blood vessels and problems that affect their function. The Carotids and Vertebral arteries supply blood to the brain and partially clog and harden from atherosclerosis. One interesting problem is the subclavian steal syndrome. The subclavian artery carries blood both to the arm and the brain. It gets blocked in such a way that blood actually flows from the brain into the arm(!!), and this causes dizziness and problems with circulation to the head. Many processes impairing peripheral nerve function alter blood pressure regulation.

A lot of people say they feel dizzy but what they are really feeling unsteady on their feet. They may be afraid to walk or even to drive. Usually these fears are well-founded and these persons may fall. Something may have affected their balance mechanisms or coordination when they try to walk. A stroke in the brain, multiple sclerosis, or in the elderly, accumulation of multiple separate problems over time (multi-sensory deficit) may be the cause. The sense of dysequalibrium can also come from burnt-out chronic vertigo.

It's important to talk about any ancillary symptoms. You may experience a certain numbness and tingling in the fingers, toes, and around your mouth. Nervousness or agitation accompanies this and air hunger. a feeling that you can't get your breath. These symptoms are associated with hyperventilation or anxiety. In hyperventilation syndrome you breathe more than you need to. It's a physical problem connected to a drop in Carbon Dioxide in the blood, a gas that your lungs try to get rid of. When Carbon Dioxide goes down blood vessels in head and extremities automatically constrict. The smaller blood vessels don't deliver enough blood to the brain and you feel dizzy. Hyperventilation usually occurs when you're nervous. Very often you will have trouble putting your finger on specifically what is aggravating you. And over breathing may not be apparent to you or another observer because you're simply breathing more than your body needs to. A test called a blood gas will show low carbon dioxide concentrations during the attack. The problem is very recurrent. It helps to be aware that it won't do any permanent harm or have profound physical consequences. Occasionally similar symptoms occur in young women with Mitral Valve Prolapse an anomaly of a heart valve. This problem usually isn't serious either. Sometimes there are palpitations or a racing, irregular or strong heartbeat.

Diplopia or double vision warns of a more serious problem. A lot of people equivocate but it is easy to tell whether you have it or not. The problem is quite dramatic. You're seeing two of things where you should be seeing one. If you cover one eye it goes away. In diplopia there is a subtle imbalance in the tiny eye movement muscles. When you look at an object with two eyes it is focused or thrown on the same exact spot on your two retinas. When one eye is turned slightly the wrong way the image is thrown onto a very different area. Your brain will fuse these images when they are a little off but at a certain point the two images are too far apart for the brain to fuse them and you see double. Diplopia is more serious symptom that may point to diseases affecting the brainstem, a warning of a serious stroke and other processes.

Slurred speech or Dysarthria points to a process affecting the brain itself, especially when associated with dizziness and vertigo. Any numbness on one side of the face or body is of more concern. Here we exclude numbness and tingling connected with hyperventilation. A lot of people have a vague diffuse weakness when they are dizzy. This matters less. Nervous people tend to be weak in the knees. Clumsiness or unsteadiness can be a problem. Nausea and vomiting, Tinnitus, a very annoying ringing or roaring in one or both ears, and hearing loss, best appreciated when it occurs on one side as in listening to the telephone receiver with one ear and having trouble understanding speech, frequently accompany dizziness. Sometimes you may have a generalized pressure or full sensation associated with sinus problems. This clues us in to a problem with the balance organs in your ears rather than elsewhere in the brain.

The last kind of dizziness is vaguely described. It isn't a lightheadedness, not a near fainting episode exactly nor is there true vertigo. The person just figures there is something wrong but can't describe it. Memory for the dizzy events may be affected leading us to suspect partial alteration of consciousness as can occur with some kinds of epileptic seizures. Dizziness can be a premonitory sensation before a seizure or an epileptic aura. This is rare. Another possibility is that the subject is not very verbally adept as often happens in children who are dizzy or with someone with poor verbal skills or even being nervous in a doctor's office.

The majority of persons with vague dizziness they can ill describe have an anxiety equivalent. They are just nervous. This may seem ridiculous at first glance but a number of good studies have shown this to be true and laboratory tests are almost always negative. When a vague nondescript headache accompanies dizziness this is nearly always indicates anxiety. Dizziness, especially vertigo, can sometimes also occur as part of a migraine headache syndrome. Lastly dizziness may be a panic attack equivalent, a kind of agoraphobia, fear of being outside in a public place. Subjects report severe dizziness often accompanied by other symptoms, palpitation, anxiety, sweating, on leaving the safety of their own home, perhaps in going out in a car or in a supermarket or being out in a public place where they may not be able to get into safety, so that they feel there is no escape, should an episode happen to occur. This sensation is most often described as "dizziness", though it is truly a form of phobia or anxiety. So as you can see, we use the history of the complaint to point us in a certain direction. It's the first step in helping you with your problem.

TYPES OF DIZZINESS:
I. Vertigo
II. Light-headedness
III. Imbalance-disequilibrium
IV. Psychic change

The Examination

You are entitled to a neurological examination in our office. For dizziness the exam is designed to answer certain specific questions. Some authorities suggest that dizzy patients be subjected to what is known as a "dizziness battery". In other words if a person mentions dizziness he or she goes through a routine rote set of maneuvers. The history directs what we will do. One problem: you may not be symptomatic at the time we see you. Some findings that would otherwise clue us in to the problem may be normal.

First is the gait exam. Many people who have an unsteady gait, particularly older folks, complain of dizziness. Your gait yields a global picture of your movements. Obvious problems such as weakness on one side or with both legs reveal themselves so we can focus on them later. Normal gait is one of the miracles of biology, the result of convergence and associative processing of a barrage of inputs from many areas in the nervous system. Have you ever watched those complex robotic walking machines on TV or in the movies?? You never see true two legged walkers. The best man-made machines walk on perfectly level surfaces in an extremely ungainly manner, unacceptable for human or animal. The stability, coordination and integration just aren't there. These walking machines utilize the biggest, best, and fastest modern computers, yet they haven't perfected human gait patterns.

.

Dancer

Walking Gait
Figure 1: Amazing feats of balance and grace in human dance, even ordinary gait, have never been reproduced by any machine, and won't be any time soon.

Motor systems, including the frontal lobes of the brain responsible for initiation and planning of movements, the basal ganglia deep structures in the brain that add control and fluidity to movements, and the computer-like cerebellum, degenerate with age. This diminishes athletic prowess in younger people. Once it happens we can't affect it much except with therapy, exercises and the use of assistive devices. We try to maximize unaffected systems to make up for the deficit. You can slow down these aging processes by getting regular exercise and taking care of your general health. We may diagnose a fixable problem in one of these systems. In Parkinson's disease we use specific medicines. Hydrocephalus affects higher brain areas controlling gait and can be treated surgically. Arthritis causes bone overgrowth that can press on the spinal cord, or affect weight-bearing joints like the hips and knees. Older folks walk flexed or leaning forward. They walk slowly and carefully and worry about falling. They have problems initiating gait (termed gait ignition) and once they get going can walk at the same velocity for awhile until presented with any change which they cannot adjust for. They take small tentative shuffling microsteps, part of a gait apraxia. A primitive stereotyped motor scheme for gait is hard-wired into the spinal cord. The pattern involves extension of one lower extremity and partial flexion of the other. Pick up your right leg when you stand. Your spinal cord will strengthen the extensor muscles in your left leg to support your weight. Suppose you get a splinter in your right foot or burn it on a boardwalk. Then you will withdraw or flex the right leg and the spinal cord automatically commands the left leg to support your weight. Your weight will shift to your left leg slightly stretching the weight-supporting muscles in very same way that the doctor hitting your knee with a hammer stretches the quadriceps muscle to get a reflex. A reflex is nothing more than an automatic muscle tightening mediated by the spinal cord. Normal gait is a basic alternation and repetition of a flexion and extension pattern. This and many other basic motor patterns are wired into the lower levels of the nervous system but then we have layer upon layer like veneers perfecting motor outputs from systems above, the frontal lobe (pyramidal), basal ganglia (extra-pyramidal), and cerebellum. The very highest motor levels are the most volitional but always these systems thoroughly integrate before exerting their influence on the spinal cord's basic motor pattern.

We have simultaneous sensory inputs from three main systems:

1. Position sensation comes from joints and stretch receptors in muscles of your legs and neck. This information travels to the cerebellum and higher brain centers via pathways in the spinal cord. Most of this information works below our level of awareness, controlling balance automatically.

2. Vision enters consciousness but it also controls posture in subtle ways.

3.The most important system related to dizziness is the Vestibular Apparatus. Did you know about fluid-filled balance organs in the ears, separate from hearing organs? They send impulses to the brainstem and spinal cord. The vestibular apparatus is an evolutionary modification of the "lateral line" balance organs found in fish.

Sensory control of balance is largely redundant. You can do just fine if you cut any of the three systems. Most of us have no problem standing when we shut our eyes.

The most important interaction between vision and the ear is the maintenance of visual fixation. While our ancient forebears were running away or chasing other animals, the most pressing need was to maintain a visual fix on the predator or prey, this despite running and bouncing over irregular terrain, even swinging through trees in three dimensions.

Maintenance of visual fixation - Keep your eyes on the prize - this is how the vestibular apparatus and the eyes interact. If you're normal, you'll have no trouble reading this text as you quickly shake your head back and forth or up and down at a comfortable reading distance. The image remains steady and readable. Now try shaking the booklet back and forth. It's a blur. You can't keep the image steady. Take away the total inner ear on both sides and a person may complain of oscillopsia. Objects seem to oscillate back and forth when you move your head because the mechanism for keeping objects in view has been obliterated. This happens with destruction of the inner ear on both sides. Antibiotics like gentamycin can cause extensive damage to the inner ear and produce this very disabling symptom. So can surgical destruction of both labyrinths. The vestibular system of the inner ear keeps your eyes on the prize. The connection between ears and eyes is the vestibulo-ocular reflex (VOR) the basis for all discussion about how the ears and head movements affect the eyes.

Vision, with the help of the inner ear, helps us maintain an upright, 2-legged stance. In karate, he who maintains his balance and fixation takes the match!!.

Sensory and Motor Inputs
Figure 2: Sensory and motor inputs in balance.

Many older folks have multiple faulty sensory inputs. Diabetes is common in older Americans. It damages nerves carrying messages from the feet and can cause blindness. Joints may be stricken with arthritis. Eyes and ears muscles may all be dysfunctional. Loosely we speak of Multi-sensory deficit involving sensory motor and non- nervous components. It is best to maximize residual abilities using feedback from a cane, hearing aid, glasses stimulation and therapy.

The brain integrates data on the current position of the head in relation to the ground or gravity, movements and acceleration and any perturbation or change in order to maintain upright posture. Just imagine what's involved in playing basketball. You need quickly to respond to moves of players and the ball. Suppose you're suddenly fouled. You need to make split second adjustments to right yourself. Recall that the basic patterns maintaining weight bearing and balance reside in the spinal cord and lower levels of the nervous system but are perfected by higher centers. As you age it gets harder to respond to novelty. As long as you are walking a constant rate there is no problem, but a sudden stimulus will cause a fall and affect righting reflexes that maintain your upright posture. Acceleration or change in speed, even turns, lead to falls.

Inner Ear
Figure 3: Schematic of the Inner Ear

Link to Benign Positional Vertigo:

On this website!

 

Back to the physical exam. Note the three semicircular canals in the diagram. Most of this is a fluid filled tubular structure. The nerves from the hearing part of the ear, the cochlea and the balance portion of the ear the semicircular canals are separate divisions of the vestibulo-cochlear nerve. Unlike auditory input destined to for conscious experience, information from the semicircular canals is processed by lower brain centers, perfecting movements. These data go to the spinal cord, brainstem and cerebellum. The brain receives input from each ear. The utricle and saccule (see diagram) respond to gravity and linear movement while the semicircular canals inform the brain about angular acceleration (turns). Suppose you move quickly. You make every effort to maintain your bearings. If you're looking at something and someone slaps you hard on the back, or if you're running and dribbling a ball or are running and suddenly jump over a big obstacle, you need to keep your eyes peeled. The maintenance of balance and posture is reflected in the eyes. When your head turns to the right, you automatically preserve your gaze. Your eyes will reflexively turn leftward in their sockets. In order to maintain visual fixation, to keep your eye on the ball, signals have to reach the tiny eye muscles. This comes from the vestibular apparatus (also termed labyrinths because it is constructed of winding twisted tubes). The vestibular input is widespread exerting a profound effect on balance and coordination but it is most conveniently examined by looking at eye movements.

One ear can sometimes affected by trauma, infection, fluid accumulation, a virus, or sinusitis. If the labyrinth on one side stops working the brain will have a tough time trying to decode contradictory inputs. This mix-up is felt as dizziness or vertigo. As crazy as this may seem the first thing we will want to examine is your eyes. Nystagmus is a to-and-fro tremor of your eye movements. Here is how it works. Each ear exerts an influence that makes the eyes turn away from it. - the left ear pushes both eyes to the right. In each ear the three semicircular canals each exert a force on eye movements (and on your body) in the opposite direction along their plane. Note that the orientation of each semicircular canal is in a different plane. Between the two ears there are six of them. Imagine your head placed about 30 degrees from the horizontal so that two of these six canals are oriented in the approximate horizontal plane. If something affects the function of one ear the other ear will still be working and push both eyes toward the affected ear. When the right ear ceases to function the left ear wins out and the eyes end up being pushed rightward. You start to veer to the right when you walk, to point to the right when you try to reach for objects (as long as there is no other sensory input such as your vision to set things straight). You do this automatically because as far as the labyrinths are concerned, you are turning to your right. As far as you are aware, the environment seems to be spinning in the opposite direction (to your left). When you're examined we test for these tendencies by examining eye movements. While your eyes slowly try to go rightward, the higher brain areas correct this movement and throw the eyes rapidly and repeatedly to the left. What the observer sees then is a slow movement of the eyes to your right, followed by rapid corrective movement to your left. This cycle of slow right eye then rapid leftward movement occurs repeatedly, and voilà, we have nystagmus. (The nystagmus described is left beating named for the direction of rapid movement.) You may be as sick as anything, confused, sweaty, wanting to vomit and veering as you walk. You may also appreciate movement in your eyes. Objects in the environment may seem to move as your eyes do and this subjective sensation of movement is vertigo. All of these terrible things come from problem in your ears or the connection of the vestibulo-cochlear nerve to the brainstem. We try to describe the nystagmus precisely, which direction it goes, what brings it on, how long it takes to come on (latency), whether it goes away or not after repetitions (fatigues). We induce it by having you turn and move around fast and tilting you on an exam table or bed with your head tilted something called the Nylen-Baràny or Dix-Hallpike maneuver. When the ear is involved the slow phase of the nystagmus will be toward the diseased ear.

We observe quick turns, tandem or balance walking with one foot placed directly in front of the other like the police do when checking for drunkenness. Balance is looked at as you stand on one foot. You stand with your eyes closed and open, arms crossed over your chest, the Romberg test to look at the influence of vision. There are some interesting techniques to bring out abnormalities such as a forceful side-to-side head shake and watching you walk as you turn your head. You may be stood on a foam pad and a lot of times we try to push you over, disturbing your center of gravity to see how you right yourself.  You may have your blood pressure taken laying and standing to see if there is a change and be checked for past pointing or a tendency for your arms and hands to drift in a particular direction. You can be made to hyperventilate, have ears and eyes and sinuses checked. We need to get an idea about your hearing, whether there is a conductive or high frequency nerve type hearing loss. And the rest of the neurologic exam is important to be sure there isn't a more widespread process that dizziness may be a small part of, such as multiple sclerosis or a problem with circulation to the brain (a stroke). We do all of this to localize the problem. The main question we are asking is if the problem is in the ear or the brain. If it is in the ear we say the process is peripheral if in the brain central. Peripheral labyrinthine dizziness is a lot of times more severe, apt to be associated with wilder vertigo vomiting and imbalance. On the other hand it is less serious because it does not threaten the brain and will not cause death paralysis or a permanent problem. All the while I'm trying my level best to localize the problem, to determine what parts or systems are responsible for your complaint.

Schwannoma near the cerebellum
Figure 4: Schwannoma near the cerebellum.

 

Causes of Dizziness

For some reason doctors and patients think first about brain tumors when dealing with dizziness. In fact, serious problems like this are very rare. One rare benign tumor that everyone seems to worry about is an acoustic neuroma or schwannoma (pictured above). Almost everyone ends up getting an MRI or CT brain scan to look for this rare entity which most of the time causes hearing loss in one ear.

I've included some of the more common causes of vertigo in the table below. One of the more instructive and common problems is Benign Paroxysmal Positional Vertigo (BPPV). If you look at the picture of the inner ear you see semicircular canals and a utricle and saccule. The utricle and saccule have small stones called otoliths that move in response to gravity. Some of these stones can come loose or dislodge especially where there is a force or trauma, then travel into the semicircular canal where it does not belong. BPPV is a peripheral kind of vertigo that is now thought to happen because of the dislodgment otoliths ("oto"-ear, "lith"- stone) from the utricle. The hallmark feature is that vertigo will happen when a person lays on the side with the affected or bad ear down, so that the problem is often intensely positional. And the problem can sometimes be cured by the so-called Epley maneuver designed to move the otoliths back into position.

Vestibular neuronitis, we believe, is due to inflammation in the ear's balance organ. Another theory is that it is caused by an interruption of the blood supply to one branch of the vestibular nerve that goes the labyrinth. It is hard to find anything on a laboratory test or x-ray, though there may be definite abnormalities on the ENG test discussed elsewhere. There is nothing to be seen in the ear. Most of the time there is no hearing loss. It can occur after a cold or virus infection and usually goes away and is forgotten about. Some doctors may call it a viral labyrinthitis, indicating some vague inflammation of the nerve or labyrinth. There is some good information that many cases may be due to the ubiquitous (just about everyone has been exposed) Herpes simplex virus. You may feel fine, then the problem appears out of the blue with frightening suddenness. A person with this entity gets so sick so fast that most of the time they end up in the Emergency room. There is severe vertigo with vomiting and unsteadiness. Vertigo always comes on when you change position but at first it may be so bad that even if you are still you will feel you are whirling. Viral labyrinthitis we now know, usually leaves some at least subtle imbalance or dizziness long after it's occurred.

Eventually the problem may happen only when you move or turn or only when you are in a certain position. Then it may cause unsteadiness for a while and go away, perhaps even be forgotten. But you can still attack of full blown vertigo years later. What we can do is treat the more serious problem when there is an attack or recurrence. There should not be any sequelae or permanent damage. That's why it's also considered "benign" or not life-threatening or serious. This is not to minimize the discomfort from the problem. Sometimes the vertigo will degenerate into a less explicitly vertiginous more constant imbalance or lack of sure-footedness.

Another problem you may hear about is Mé niè re's disease. This is a symptom triad of vertigo, tinnitus, and fluctuating hearing loss, but you also have a fullness in the ear. The tinnitus is a sound a roaring or more often a ringing usually in one ear. Tinnitus alone is often very disturbing. Doctors like it for localization because it tells which ear is the culprit. When it is mild it is usually noted in the quiet when there is no other noise to mask or overwhelm the sound. Some people are bothered by it night and day. If you have ever been exposed to loud noise, the kind that injures the ear at a rock concert, using power tools, firearms or subway noise, when the injurious sound is finished, you will have a tinnitus. You should protect your hearing in such environments!! In Ménière's disease, the tinnitus is loud during an attack of vertigo and persons with it always have recurrent often severe attacks of vertigo and tinnitus. In this case the tinnitus is a sign that hearing is being injured and this is what happens most of the time over years. Hearing is diminished on the side with tinnitus but this is gradual. Meniere's is thought to be due to fluid (endolymph) accumulation in the ear canals so it is more properly called endolymphatic hydrops. There are some therapies for decreasing this fluid accumulation. The first line of therapy is avoiding salt which helps to accumulate fluids and diuretics which get rid of salt. There are operations that drain fluid (Endolymphatic sac surgery) and in bad cases procedures to cut the vestibular nerve. Sometimes the disorder runs in families and it also can affect both ears. Since Ménière's is due to fluid buildup in the ear, it is somewhat analogous to glaucoma in the eye.

You can have a more serious infection or labyrinthitis due to bacteria in the ear. Even Syphilis can affect the ear. This can spread from an ordinary middle ear infection. Nowadays few ear infections go untreated. Even so (or possibly because of profligate use of antibiotics), a lot of people develop chronic or very recurrent otitis media. Trauma is a common cause of vertigo. Some persons have a labyrinthine concussion or slight injury that will improve on its own. It is certainly true that the labyrinth can be damaged by a blow to the head. But where imbalance due to head injury is analyzed we may find that there is a brain injury as well as an ear problem that slows recovery. Some doctors feel the ear may be traumatized by high impact sports such as the wrong type of aerobics, running in the wrong way, so that the ear is jarred repetitively. This may cause a very subtle or mild imbalance. Occasionally there may be leaking of the perilymph, a so-called perilymph fistula which seems to arise from a sudden change in pressure such as in scuba-diving or mountain climbing. Straining as in sneezing, causes increased symptoms including vertigo and hearing loss. Some antibiotics used less now, called aminoglycosides may injure both the cochlear and vestibular parts of the ear (These drugs kill hair cells.) and there are some other drugs, especially aspirin and quinine if used in very large quantities that affect the ear but usually causes tinnitus more than anything else. Other drugs including sedatives and anti-seizure medications can cause imbalance and vertigo. It is very common to see people taking many drugs at once which in combination may make them dizzy.

Cupulolithiasis is a condition in which the otoliths break off and directly weigh down and stimulate the sensitive part of the semicircular canals, the cupula, that contains the sensitive hair cells. The otoliths come from Utricle which mostly send signals to the brain about gravity and side to side movement to preserve balance and posture. So in a lot of ways cupulolithiasis is very similar to BPPV described above. The sensory cells of the inner ear are all hair cells. In these delicate single cells, the electrical charge changes when something tickles or moves hairlike extensions (cilia). The same kind of cell responds to vibration of membranes caused by sound waves and motion of endolymph in the semicircular canals that occurs with acceleration. The otoliths can be moved utilizing a special procedure so that very often this condition is easy to treat.

CAUSES OF VERTIGO:

PERIPHERAL (ear)

CENTRAL (brain)

Vestibular Neuronitis
Benign Positional Vertigo Link
Meniere's Disease
Ear Trauma
Labyrinthitis
Drugs (aminogycosides, quinine, ASA)
Perilymph fistula
Degenerated Otoconia
(cupololithiasis)
Autoimmune ear disease
cholesteatoma

Stroke in Brainstem
Tumor in brainstem
Multiple Sclerosis
Encephalitis
Migraine (rare)
Drugs (esp. sedatives)
Seizures (rare)
Anxiety and Panic
Motion Sickness
Acoustic Neuroma
Head trauma

Central Nervous System processes are much more of a worry. One less serious cause of vertigo is Motion sickness. This is much more common in women who tend to be sensitive to movements as when they are on a cruise or in a car. One theory is that the inner ear is supersensitive to movement because the central nervous system does not modulate (control, dampen out) inner ear sensitivity like it should. Nervousness or jitteriness may contribute. Vertigo can be the first warning of a stroke. Usually vertigo is associated with other symptoms and signs that tip us off we are not dealing with an ear problem. There is loss of sensation or motor function or clumsiness and often a problem with speech, swallowing or double vision. One common stroke with a good prognosis is called a lateral medullary syndrome. It affects the medulla and cerebellum causing severe dysequalibrium, swallowing, voice and speech problems and a peculiar numbness over one side of the face and the opposite side of the body. When these problems occur there is brain dysfunction. Some of these problems also occur in the other disorders listed but they usually don't come on so suddenly as a stroke. These other symptoms can be subtle or even on rare occasions, not be present at all. That is why we have always to be careful in older persons at risk for arteriosclerosis. Dizziness and vertigo very frequently are symptoms of multiple sclerosis in young persons. With multiple sclerosis the vertigo is associated with signs such as problems with eye movements or speech and it almost always occurs episodically and goes away. Only rarely will a brain tumor cause vertigo although this can happen in young children with brainstem or cerebellar tumors.

 

Testing

Patients often come to us after they have had a lot of tests. As a general rule, laboratory and X-ray tests don't add very much to the evaluation of dizziness. Tests should be done with some specific idea in mind and not just because a person is still symptomatic. Logic should always dictate what tests are done.

The audiogram is one of the most useful tests if we suspect ear disease. Infections and inflammatory processes often affect hearing. The Audiogram tests hearing of pure tones and graphs each tone against the hearing level in decibels, a measure of loudness. Persons with nerve deafness tend have a problem with high tones. Air and bone conduction (sounds placed right over the bone) are compared. We are trying to figure out whether the nerve or hair cells are damaged or whether hearing loss is due to a problem conducting sound vibrations to the hearing apparatus. This separates so called conductive from sensori-neural hearing loss, giving a good idea about whether the nerve is involved in the problem. Conductive loss is due to problems ranging from wax buildup to otosclerosis that affects the ossicles or little bones that conduct sounds inside the ear. Speech discrimination is also tested. You may hear tones without a problem but be unable to understand speech in which case the problem is not just in the middle ear. Then there are fancier things that can be done such as reflex testing to figure out if the cochlea is involved or something closer to the brain (retrocochlear). A good audiogram helps us to localize a problem a little better.

For the ENG, or electronystagmogram, electrodes are placed about the eye and the head is tilted and cold and warm water or air is placed in the ear canal. Warm water stimulates and cold inhibits the ear so that if you put cold water in one ear canal the eyes will want to rove toward that ear (see discussion on nystagmus above). What it does is watch and quantify the nystagmus and other eye movements. You can judge if there is a reduced response to stimulation of one or both ears. We can see how the eyes move as they are watching a moving object (tracking), and with change in body position as well. Nowadays eye movements can be watched utilizing infra-red tracking devices instead of electrodes and put on videotape. With the MRI scan we can see a structural problem and it is good at finding problems with blood vessels and multiple sclerosis as well as some tumors. It is sensitive for sinus disease too but we have cheaper easier tests to look for that such as sinus x-rays or the Head CT scan. Occasionally a Carotid Doppler or Transcranial Doppler are useful to examine arteries. Some persons who nearly faint or have certain types of lightheadedness may need to have certain heart tests such as an EKG or an echocardiogram. Persons complaining of vague dizziness, lightheadedness should have certain blood tests done including tests for the thyroid gland. This is pretty much the gamut of tests that are done. More sophisticated computerized balance and movement tests are being developed all the time and are used in some centers. Evoked Responses follow electrical signals through the nervous system and are occasionally useful to diagnose a problem in the spinal cord, hearing system or the brain.

Eye
Graph of Eye Motion
Figure 5: The ENG: Above is a view of the eye, which is an electrical dipole or battery. Eye movements can be recorded on a chart using electrodes. Below is a diagram of nystagmus followed by eye following or tracking. Eye position is on the vertical axis, time, on the horizontal axis.

 

Therapy

One of the most eminently treatable conditions which here is treated as a separate entity is BPPV, Benign Positional Paroxysmal Vertigo Please click here for special link to this section!

By now you've learned about a basic strategy: Diagnose what's wrong and then do something about it. Vertigo is often the most acutely troubling kind of dizziness. Often there is imbalance, vomiting and inability to eat. We have to attack all of these problems at once. And we'll need to be sure the vertigo is not part of a life-threatening process such as a stroke. If there is something like an infection threatening hearing and permanent disability, we have to take care of that too.

A variety of medicines decrease vertigo. Antihistamines decrease vertigo by affecting mechanisms in the inner ear. Sometimes they help for sinus related problems along with decongestants. The most frequently used drug is meclizine or Antivert. This has some limited effect but also causes drowsiness. Diminhydrinate is a similar drug related to Benedryl (diphenhydramine) that is also used; hydroxyzine or Atarax is another. These inhibit Acetylcholine one of the best known signaling or transmitting chemicals in the brain. Scopolamine an anticholinergic drug, can now be given in low dosage in the form of an ear patch so the drug is absorbed through the skin (Transderm-Scop). Like antihistamines this can cause drowsiness, dry mouth, and even memory disturbances, especially in older folks and it can increase the heart rate. It has the side benefit of inhibiting intestinal movements so that it may help with nausea. Anti-vomiting medicines are also effective particularly a drug called Phenergan or Compazine that can also make you sleepy. Low doses of Valium or Xanax can be helpful for vertigo. If a person is vomiting too much and is unable to keep up with fluids he may have to be admitted to the hospital temporarily to get fluid intravenously.

Over the long term the vertigo fatigues, particularly if it comes from the inner ear. The good news is that the brain can usually be trained to do this. As far as the vestibular system and connections, the brain's response is very plastic and adaptive. If one system such as the vestibular system is out of commission, the functions of other systems are redundant and can be trained to work take over for the damaged labyrinth. The brain's response to sensory systems contributing to gain stability will diminish over time and with training. This is habituation. The brain has mechanisms that make it respond less to persistent sensory stimuli. We can take advantage of this phenomenon with vestibular exercises. When you have vertigo particularly the kind exacerbated by certain movements or positions, you naturally avoid these positions. You shouldn't. The exercises are designed to put you into just the postures you find most uncomfortable. They retrain the brain to respond to signals from the healthy ear that give a truer picture of reality, while fatiguing the diseased ear's response.

Many persons benefit from vestibular rehab programs for retraining. The three methods by which therapy helps are: Adaptive Plasticity, (learning within the central nervous system to accommodate deficits), Sensory substitution (learning to use the eyes to compensate for damage to the peripheral nerves or the ear for example), and habituation (lessening of the brain's response when you repeat stimuli over and over again). In other words rehab programs and exercises help you in a number of ways. They either dampen out inner ear responses that cause vertigo, teach you how to use other redundant sensory or visual systems if you have damage, or help you adapt to the damage. Below is a set of exercises that are very useful for a variety of conditions that affect the ear and brain connections. Most apply to certain specific clinical conditions, such as BPPV Link here for discussion, or bilateral peripheral vestibular dysfunction, or multi-sensory deficit, for example and it is best to have supervision in a program designed just for you. A general principle is that you should practice maneuvers where there is a problem, so that you can learn how to accommodate and get around a deficit. If you have positional vertigo, you need to put yourself right into the most uncomfortable position repeatedly so that you can habituate quickly, that is, decrease the vertigo that comes with that particular position. These exercises are not a one size fits all situation. Ideally a program needs to be designed for you and you should work with a therapist familiar with balance disorders and vertigo.

Here is what you should do:

Seated:

1. Move your eyes through their full range both up and down and to the right and left.

2. Follow (track) an object with your eyes.

3. Practice fixation. One good technique is to look at print on a page while moving your head side to side. Another is to watch your finger moving to your left while at the same time moving your head to the right. Then reverse the process.

4. Move your neck through its full range forward, back, and to the right and left with your eyes open and closed.

5. Watch your hand by rotating your neck as it moves to the right and left.

6. Sit on the edge of a bed and tilt your head back to the right if you can, then lay flat. Repeat this on the left with your eyes open and closed.

Standing:

1. Repeat as many of above maneuvers as possible.

2. Stand up and sit down repeatedly with your eyes open and closed.

3. Just stand still with the eyes open and closed.

Walking:

1. Walk across the room with eyes open and closed.

2. Practice tandem walking. (Police drunk test)

3. Walk up and down a hill.

4. Practice walking in a place where there are contradictory visual stimuli, such as a long hall or in a supermarket where there are lots of carts and people moving in different directions.

5. Practice walking daily while looking in shop windows etc. Do not just keep your eyes glued to the ground. Walk naturally. Try to walk naturally without really thinking about it.

At first, you should do these exercises very often, perhaps three times a day.

Very Important: As you do the exercises you should be reducing the medicines we use to treat acute vertigo, Antivert, Valium, Phenergan etc. These drugs suppress the vestibular system in the inner ear and we aim to use this system in retraining. You can't be trained with an unnatural type of system suppression.

Studies have proven that these exercises are effective for a lot of people. One problem in evaluating any therapy is the high probability of spontaneous recovery. Try to keep this in mind. The prognosis is pretty good most of the time.

Vestibular Rehabilitation is a whole new field in which these exercises and many others techniques are done by specially trained physical therapists. As we have seen, a person can function very well even if one system is diseased or not functioning. The most important aim of therapy is to train other redundant systems to take over when there is a problem. This is especially beneficial with a problem in one inner ear. The good ear plus other systems are more than sufficient for balance and eye movements even on an advanced level. Unfortunately many persons, especially older folks and people with multiple sclerosis and Parkinson disease, have multiple deficits. These persons might not have a remediable problem. The emphasis in rehab will not be so much retraining for these people, but teaching ways to get around their problem and maintain mobility and especially falls prevention. Determining which braces and assistive devices are needed, and teaching techniques of standing, attention and walking that prevent falls is the major thrust of therapy. Studies have shown that targeting even healthy older folks and emphasizing training in this high risk group, is cost effective and health-promoting.

For BPPV a technique called the Epley maneuver see discussion  can cure the problem!! Recall that in BPPV an otolith stone is lodged where it shouldn't be, traveling from the utricle to the posterior canal. An Epley maneuver is basically a simple tilt and turn technique which repositions the otolith, taking it out of the position where it creates abnormal currents in the posterior canal altering the response of the inner ear. Patients who've been symptomatic for years can go home cured. There are good home therapies as well that effect canalith repositioning such as the Brandt-Daroff exercises.

Surgery is done for intractable ear problems and vertigo, but some surgeries, done as a last-ditch effort, do not help symptoms. There are a lot of different procedures and the details cannot be given here. Some surgeries are reconstructive such as for otosclerosis and to correct holes or fistulas. Other procedures are destructive aimed at taking out a diseased labyrinth or cutting the vestibular nerve.

For non-vertiginous dizziness the therapy depends on what is wrong. Much of this is outlined in my first section. For example, if we find a heart or circulation related problem, we will try to address that. If there is a problem primarily with gait unsteadiness physical therapy can help. Occasionally we find that prescribed medicines are causing harm. Then of course, we will try to identify this problem and discontinue them as possible.

This is the story of dizziness. Like any other area of endeavor, dizziness responds best to a logical objective reasoned approach. I don't claim to be able to solve every problem and there is a lot we don't know, but we can help most people. I hope you have found a description of your own problem in this booklet or at least have an idea about how medical doctors evaluate and treat dizziness and disturbances of balance. We are eager to be of help and answer any questions you may have.

 

Psychiatric Aspects of Dizziness

Among patients I see with Panic Disorder, a striking number have symptoms in specific situations. Persons with Panic Disorder have spontaneous attacks of intense fear and discomfort that begin abruptly, almost like an adrenaline rush or flight or fight reaction, like palpitations, sweating, shaking, intense fear, tremor, inability to catch one’s breath. These sensations occur on spontaneously or when in specific situations such as a car or supermarket. Sensitivity to a car or market is so typical, it bolsters the diagnosis of a panic attack. Whenever I suspect panic disorder, I always ask specifically about reactions to being in a car or supermarket. Most of the time the person will mention it on their own. It is enough to make you wonder what’s so unusual about these particular situations?

I used to think that markets and automobiles engendered so much fear because you can't readily escape these situations and feel trapped, but a number of patients have told me this is not so. What seems to happen is that in both circumstances you are having to deal with bodies moving toward or away from you in a narrow passageway. You are expected to make numerous split-second decisions (computations) about moving objects if you plan to avoid a mishap or accident and you have to depend on vision alone. For most of us this is second nature and we have no problem. When we walk around a supermarket balance and walking come to us automatically. A lot of this mediated by vestibular and proprioceptive systems.

The supermarket or highway may disproportionately affect persons who have subtle abnormalities with vestibular or proprioceptive systems. Under such conditions a person may become visually dependent. He or she depends abnormally on visual systems in order to stand, walk, and maintain balance. Now if you ask them to go into a supermarket and begin to try to avoid obstacles and moving persons and to shop at the same time, their visual computation apparatus goes into overload and anxiety occurs. The theory then, about why anxiety attacks are so common under specific circumstances, is that in some patients at least, there may be a vestibular component to anxiety disorders. You’re asking their visual systems to do too much. The frequent occurrence in relation to these specific stimuli may also explain why panic disorder is so frequent now in the age of fast moving cars on freeways and elaborate supermarkets, as opposed to previous times, when anxiety and neurosis expressed itself in its own special circumstances.

Furman and Jacob introduced the term space and motion discomfort (SMD) which loosely describes this scenario. There is a definite overlap of vestibular abnormalities and anxiety. The greatest number of persons have vestibular abnormalities with few psychiatric symptoms or psychiatric disease without dizziness or vestibular problems but there is also a great deal of overlap and interaction between vestibular function and anxiety.

I’m not trying to say here that anxiety or panic disorders are caused by vestibular dysfunction. If that were the case, persons with inner ear disease and the aged would all have panic disorder. Instead what seems to happen is that persons who have a certain tendency to have panic disorder, and I’m not prepared to discuss here what makes some persons have this tendency, may find they become symptomatic under specific circumstances that tax the computation capacity of their visual systems. This explains some characteristics of panic disorder and may even play into the common symptom of agoraphobia, fear of going out into strange places. Subjects may simply not wish avoid overloading their brainstem computers. If we can put our finger on this aspect of panic attack disorder, it is possible we may be able to intervene in some cases with vestibular training and rehabilitation. More than that, panic and anxiety disorders may be thought of as physical syndromes i.e. disorders of sensory systems rather than psychiatric symptoms of unknown etiology.

Visual dependence and computational overload may explain dysfunction in a number of other situations. Persons who are afraid of heights (acrophobia) also overuse their eyes. Watch one sometime. The eyes are wide open and they are looking around and down while normal folks walk about hardly using their eyes, confident they won't fall even at the edge of a cliff or atop a mountain. Acrophobics don’t have this confidence and are overly dependent on their eyes. Acrophobics try to use their eyes in a conscious effort to maintain balance while walking continues to be automatic for normals. With visual systems overwhelmed, anxiety is compounded. Makes you wonder whether persons with a fear of height might benefit from vestibular retraining as well.

Let’s suppose you become for one reason or another, be it anxiety or malfunction of vestibular or proprioceptive systems, overly dependent on vision. Then most of the time complicating the visual field by adding even more stimuli will worsen the situation. An interesting case in point is the Parkinson patient with gait and balance disorder. Parkinson’s is a motor disease in which exact motor computations are impaired by a defect in the basal ganglia. Frequently the Parkinsonian festinates, takes tiny steps, and is unable to account for a shift in his center of gravity. Unable to make rapid motor defensive adjustments to environmental perturbations, he falls. He will falter unless he is constantly vigilant, conscious, about his gait and balance, whereas for most normals, this is entirely of second nature.

What do you observe? Most of the time the severe Parkinson patient will fall or freeze, if you complicate visual input by adding more stimuli. If another person suddenly appears in the room, or he has to walk through a turnstile or a doorway, he’ll get overwhelmed festinate, take tiny steps, and topple over. All of this is extraneous noise that overwhelms him. But certain limited visual stimuli will help the Parkinson patient to walk. Paint or tape equidistant lines on the floor, and he will miraculously begin to make perfect strides and will not fall over!! From this we learn that there are two classes of sensory stimuli for patients who are impaired or visually dependent. There is noise, impairing stimuli and likewise there is a smaller category of guidance sensory stimuli.

About the worst thing you can do to an acrophobic is to put him on a high ski slope. The guy will be stuck on the top of the hill scared to death on his skis. Now place him in the middle of the slope with lots of skiers swooshing down the slopes past him. Maybe place another drop on to the right of him, and make him go down a narrow passageway. He’ll be scared to death.

Is their anything you can do to help? The best thing is to expose the acrophobic to vestibular and proprioceptive training before you send him to the slopes. Reduce visual dependence. The most rational approach to anxiety disorders (at least in some cases) would be to unload overburdened sensory systems as much as possible. Teach the subject to use alternative systems (vestibular, proprioceptive) and reduce sensory overload. Alternatively provide guidance sensory stimuli; avoid noise. Vestibular rehab may have a role in treating some forms of anxiety.

The foregoing describes how the vestibular system may interact with anxiety mechanisms. I’ve often heard new mothers observe that their toddler can’t walk yet only because they are afraid. Toddler’s don’t get up on their own and step because of fear. Spouses of Parkinson patients frequently make the same observation. It’s only the fear of walking that’s stopping them. Fear of walking, nine times out of ten, is well-founded. Toddlers and Parkinsonians are afraid of walking because their at risk of falling. The fear of losing one’s balance is a deeply entrenched protective mechanism.

The same very likely is connected with the frequent co-existence of anxiety and dizziness. Anxious persons are frequently dizzy. In a good many instances a person who sees a doctor because of dizziness, anxiety is the primary problem. Some of these have so-called "phobic postural vertigo". There is good evidence from other quarters that these folks have pervasive anxiety. What we don't know and have difficulty measuring and defining, is the component of vestibular dysfunction and the relative roles of psychiatric and physical problem.

There is little doubt that dizziness can occur from anxiety alone. This dizziness tends to be vaguely described or more often it is a light-headedness or giddiness, rarely a discreet vertigo. A dysequalibrium or gait unsteadiness rarely happens just form anxiety although a complaint of sudden weakness of the knees is often encountered. A trial of hyperventilation is used to exacerbate dizziness suspected of coming from anxiety. If dizziness happens after hyperventilation, it's always considered to be strong evidence for a psychological cause. However there are some vestibular conditions where hyperventilation will temporarily increase vertigo. Accurate apportionment of symptoms to psychological vs. Physical or vestibular cause can be very complicated. In order to do so we may have to break old rules.

Described here is the intersection of matters that seem purely mechanical, computations of spatial relationships and motor plans, on one hand, and "psychological" distress, on the other. Complete understanding and successful treatment of panic and anxiety will require attention to physiological and psychological parameters.

Information

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Afterword: The Brain as a Computer

We live in the computer age. Many of our most distinguished scientists accept nowadays, the notion that the brain is nothing more than a complex computer. Nowhere is the picture of brain as computer more applicable than in the vestibular system.

Vestibular function is a fitting model for brain computation for 2 reasons:

1. The inner ear brings about eye movements and positional change automatically, without conscious intervention. We speak of vestibulo-ocular and vestibulo-spinal reflex mechanisms. We can predict that certain movements within the labyrinth cause specific eye movements and postural adjustments.

Three Semicircular Canals
Figure 6: Three semicircular canals are orthogonal and deal with angular turns. The saccule with vertical linear movement, the utricle with horizontal movement.

2. Eye movements and postural linear and turning movements may be described mathematically. So are events within the labyrinth, and over a similar Cartesian coordinate system. Position and movement are translatable to the three familiar Cartesian orthogonal (90 degrees from each other) axes: x,y and z, with x being horizontal, y vertical, and z depth. As it happens the three semicircular canals, designated the superior, lateral and posterior, are also practically orthogonal, and it is thus tempting to postulate that the canals communicate with the brain using some type of Cartesian code. The two ears are mirror images of each other, of course, and the semicircles of the canals of one ear complete full circles in the same planes as the other. Between the two ears the 6 semicircular canals make up 3 full circles in three orthogonal planes.

The canals are round because they are designed to detect turning movements, angular acceleration. A complex of data integrated over the three planes will describe completely any angular acceleration.

The canals, the membranous labyrinth, named for the twisting structure from Greek mythology, sit in an outer casing, the bony labyrinth. These tiny (they are less than the size of a quarter of a dime) delicate transducers of movement, are surrounded by liquid perilymph which dampens random vibratory noise that will contaminate signal transduction. The semicircular canals are filled with a liquid of their own, the endolymph. Inertia holds the endolymph fluid in one place as the head starts to turn (accelerates). The fluid, moving in relation to the membrane, thus exerts a shear force on the tiny hair cells. These cells are sensitive to the movement of the fluid. Two kinds of hair cell cilia, stereocilia and kinocilia, are exposed to fluid shear forces.

Inner Ear (Labyrinth)
Figure 7: A more detailed picture of the position of one labyrinth, showing the semicircular canals in three planes.

Hair cells sensitive to pressure of endolymph are arrayed on a sensitive part of each semicircular canal, the crista or crest on the cupula. When the endolymph applies a shear force on the cilia or hairs of the cell in a specific direction (toward the kinocilium) the hair cell depolarizes, (becomes excited). The cells oriented in such a way as to be sensitive to the direction of these forces. Movement in one direction will depolarize or excite the cell, changing its membrane potential. It communicates this excitation to the next neuron whose firing rate is altered. This second neuron has a slow constant basal firing rate. Stimulate the hair cell and the second neuron will fire faster, inhibit it and it will slow down. That is how direction of the head turning in the labyrinth is converted to the language the brain can understand, firing rates. The position of each cell and the signal derived from it are codes for specific movements which are integrated in the vestibular nuclei and other brainstem structures.

Hair Cells
Figure 8: The level of excitation of the hair cell is directionally determined as seen here. The state of excitation (depolarization) of the hair cell is communicated to a second cell whose firing rate is determined by movement direction and orientation.

Each sensitive region or cupula houses cells that fire all the time at a quantifiable level. The orientation of the semicircular canal of that cupula determines the direction of stimulation. Thus we have a magnitude and direction of force which in physics defines a vector. This vector can be graphically represented on Cartesian coordinate axes whose orientation at any time is determined by the head position at that instant. Under ideal circumstances each of 6 cupulas send the brain a information about a vector, direction and magnitude describing angular acceleration. The six vectors may be added to determine a single vector that influences eye movements. That there are eight vestibular nuclei, four on each side of the brainstem, attests to the complexity of computing movements on the basis of 6 angular acceleration vectors over time. By comparison, visual imaging is taken care of by just one pair of lateral geniculate bodies, though a great deal of complex visual processing is done both right in the retina and also at higher cortical levels.

Suppose the head turns suddenly to the left. Then endolymph fluid will stay still and move against the cupulas, sensitive structures in the right ear. The exact angle of torsion is written into the array of three orthogonal semicircular canals and is computed in the brain. Soon the head turn to the left will stop and the endolymph will then move in the opposite direction, that is, away from the cupulas of the right ear and toward those of left.

When the left ear is stimulated the eyes will be made to move to the right. A stimulated canal generally pushes the eyes in the opposite direction. Thus there is constant push-pull relationship between the labyrinth and the eyes. The left ear canal pushes the eyes to the right, the right canal to the left. There is a balance between these two countervailing forces in our eyes. One canal, the lateral canal, lies practically horizontal, and is most important. The lateral canal is actually horizontal as you lay supine with your head up 30 degrees. Stimulate it in this position and the eyes will move to away in a straight line. You can do this by moving the head or putting cold or warm water in the ear. You can observe the resulting eye movements and quantitate them with an electronystagmograph. Tilt the head up or down from this specific 30 degree position and the horizontal movements will become rotatory due to the combination of vector forces determining the movement of the eyes.

Observe the direction of the arrows on the Cartesian axes represented in figure 6. That axis will be serve as the same axis of nystagmoid eye movement for the eyeball. Stimulate one semicircular canal and the eyeball will rotate directly through that semicircular canal’s axis line. The problem in clinical assessment is that head positions which determine the orientation of these axes, constantly change and so do the positions of the eyes. However, it is possible to assess the semicircular canals individually by keeping the head at a certain tilt, for example 30 degrees forward from the supine position to isolate the lateral semicircular canal and at the same time, control for eye positions.

A second component of eye movement comes from the upper brain and this is corrective. The cerebral cortex, noting deviation of the eyes, will make a rapid corrective movement. Looking at nystagmus there is a slow component induced by vestibular forces, and a rapid component in the opposite direction courtesy of the cortex.

Disease processes usually reduce the influence of one or another canal or labyrinth. (Some diseases cause stimulation. In Ménière's disease the diseased ear is stimulated by the accumulation of endolymph fluid.) As mentioned, the major purpose of all of this is to maintain visual fixation ("eyes on the prize"). One outcome is that absent the influence of the upper cortical brain, the eyes will move much like a doll whose head is turned, a so-called "doll's head response". The eyes will appear to be fixated on a spot despite head movement and will move in a direction opposite to head movement. This is the vestibulo-ocular reflex.

The Utricle and saccule, in the meantime, are primarily concerned with maintenance of posture. Recall that these structures have calciferous otoliths, tiny rocks, inside the ear that are very heavy (specific gravity 2.5) helping to detect the direction of gravity and fall on hair cells in the maculae (sensitive regions) of these small organs. These organs perhaps are descended from ancient statocysts that also function with the aid of heavy particles in much lower animals. Hair cells are the sensitive end organs for the detection of gravity. Hairs (cilia) are deformed and signals sent to the brain. The utricle affects the level of the eyes. In certain patients whose surgery has damaged one utricle, the eyes are on two different levels. Semicircular canal impulses then go more rostrally (higher) to control eye movements and their nerve is mostly the superior vestibular division which goes to the more rostral vestibular nuclei in the brainstem (there are four on each side.) while the utricle and saccule send signals primarily via the inferior vestibular nerve division and to the spinal cord.

One influence of computer technology is how it has influenced our conception of physiology. Brain systems including balance mechanisms have come to be viewed as individual automatous but interacting modules, each computing some function and affecting neighboring processes to perfect sensory and motor function. In the brain, modules are typically bundles of neurons, either nuclei or anatomical structures. The cerebellum is a primary example of an automatous computational device that perfects movements. Cerebellar inputs are multiple simultaneous and complex deriving from such diverse sensory sources as proprioceptors, vestibular apparatus, visual and motor systems. The cerebellum connects through cerebellar nuclei to other structures primarily over white matter tracts, cables, within the central nervous system. The cerebellum has to process diverse data from many different systems all at once, in other words, in parallel. In most modern computers information flows through a single microprocessor sequentially though with many operations per second. The cerebellum and other neuronal systems process large numbers of inputs in parallel, and so there is a fundamental difference in style of processing. The brain is considered a massively parallel device, the computer as sequentially processing device. In recent years, computer scientists understanding this basic difference in data handling and having great admiration for the accomplishments of biological systems (biocomputation of gait and balance is great example), have sought to emulate processing in the brain utilizing parallel arrays of microprocessors in their instruments. We in biology on the other hand, have benefited from computer science by acquiring a modular view of brain processes.

The cerebellum receives information on posture and movement form the vestibular apparatus, and processes this in context with other data it receives from the spinal cord and visual system. Information from the utricle and saccule affect mostly the midline cerebellum (flocculus) and the cerebellum, in turn, uses this to compute instructions on balance and stance. This data is transmitted to the motor output areas in spinal cord via cerebello-spinal connections and there is a reciprocal feedback relation with the cerebellum via large spino-cerebellar tracts that relay information from stretch receptors in muscle. The vestibular apparatus also connects widely with higher brain centers affecting gaze mechanisms through the medial longitudinal fasciculus which also connects with the cord and brainstem to affect balance directly. Vestibulospinal tracts make a direct connection to the spinal cord. Motor systems also modulate the basic function of the vestibular apparatus itself, through up and down regulation of sensory cells, making these cells more or less excitable or sensitive to stimulation. Data from the vestibular and all other sensory systems help determine general arousal levels though the reticular system responsible for general arousal in higher animals. Sensory information finally reaches the conscious cortical levels after processing in the thalamus. The cortex also helps initiate movements directly and with the help of the cerebellum and basal ganglia which perfect the rather crude motor plans of the motor cortex. Hence we have autonomous but intensely interactive modules that comprise motor functions. Underlying all of this, as we have seen are crude hard-wired reflex mechanisms built right into the spinal cord.

We may fully expect an intense cross fertilization of neurophysiology and computer science in the coming decades. Silicon (computer) devices and Carbon based (biological) modules will certainly interact more closely. Not only will communication between brain and computer be easier, but biological and silicon modules will likely mix. There is nothing to prevent Silicon devices being implanted in the brain and biological devices from being embedded in computers.

Vestibular Influence
Figure 9: A Modular view of vestibular influence.

Revised  2004, 4/18/99. © 1999 Charles Yanofsky

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