Most of us can remember feeling dizzy--after a roller coaster ride, maybe, or when looking down from a tall building, or when, as children, we would step off a spinning merry-go-round. Even superbly conditioned astronauts have had temporary trouble with dizziness while in space. In these situations, dizziness arises naturally from unusual changes that disrupt our normal feeling of stability.

But dizziness can also be a sign that there is a disturbance or a disease in the system that helps people maintain balance. This system is coordinated by the brain, which reacts to nerve impulses from the ears, the eyes, the neck and limb muscles, and the joints of the arms and legs. If any of these areas fail to function normally or if the brain fails to coordinate the many nerve impulses it receives, a person may feel dizzy. The feeling of dizziness varies from person to person and, to some extent, according to its cause; it can include a feeling of unsteadiness, imbalance, or even spinning.

Disease-related dizziness, whether it takes the form of unsteadiness or spinning, is fairly common in the older population. Today, both older and younger people with serious dizziness problems can be helped by a variety of techniques--from medication to surgery to balancing exercises. Such techniques have been developed and improved by scientists studying dizziness.

Much of today's research on dizziness is supported by the National Institute Of Neurological and Communicative Disorders and Stroke (NINCDS). This Institute is a unit of the National Institutes of Health. It is the focal point within the Federal Government for research on the brain and central nervous system, including studies of the senses through which we interact with our surroundings.

With NINCDS support, scientists are searching for better ways to diagnose and treat dizziness, and are investigating the mechanisms that help us maintain our normal sense of balance. These studies, along with basic research on how the ear, the brain, and the nerves work, hold the best hope for relief for dizziness sufferers.

A delicate balancing act

To understand what goes wrong when we feel dizzy, we need to know about the vestibular system by which we keep a sense of balance amid all our daily twisting and turning, starting and stopping, jumping, falling, rolling, and bending.

The vestibular system is located in the inner ear and contains the following structures: vestibular labyrinth, semicircular canals, vestibule, utricle, and saccule. These structures work in tandem with the vestibular areas of the brain to help us maintain balance.

The semicircular canals and vestibule of the inner ear contain a fluid called endolymph that moves in response to head movement.

The vestibular labyrinth is located behind the eardrum. The labyrinth's most striking feature is a group of three semicircular canals or tubes that arise from a common base. At the base of the canals is a rounded chamber called the vestibule. The three canals and the vestibule are hollow and contain a fluid called endolymph which moves in response to head movement.

Within the vestibule and the semicircular canals are patches of special nerve cells called hair cells. Hair cells are also found in two fluid-filled sacs, the utricle and saccule, located within the vestibule These cells are aptly named: rows of thin, flexible, hairlike fibers project from them into the endolymph.

Also located in the inner ear are tiny calcium stones called otoconia. When you move your head or stand up, the hair cells are bent by the weight of the otoconia or movement of the endolymph. The bending of the hair cells transmits an electrical signal about head movement to the brain. This signal travels from the inner ear to the brain along the eighth cranial nerve--the nerve involved in balance and hearing. The brain recognizes the signal as a particular movement of the head and is able to use this information to help maintain balance.

In the inner ear, rows of hairlike fibers project from tiny patches of nerve cells called hair cells.

These tiny calcium stones called otoconia are part of the inner ear's balance system.

A thorough exam reveals the cause of most dizziness.

The senses are also important in determining balance. Sensory input from the eyes as well as from the muscles and joints is sent to the brain, alerting us that the path we are following bends to the fight or that our head is tilted as we bend to pick up a dime. The brain interprets this information--along with cues from the vestibular system--and adjusts the muscles so that balance is maintained.

Dizziness can occur when sensory information is distorted. Some people feel dizzy at great heights, for instance, partly because they cannot focus on nearby objects to stabilize themselves. When one is on the ground, it is normal to sway slightly while standing. A person maintains balance by adjusting the body's position to something close by. But when someone is standing high up, objects are too far away to use to adjust balance. The result can be confusion, insecurity, and dizziness, which is sometimes resolved by sitting down.

Some scientists believe that motion sickness, a malady that affects sea, car; and even space travelers, occurs when the brain receives conflicting sensory information about the body's motion and position. For example, when someone reads while riding in a car, the inner ear senses the movement of the vehicle, but the eyes gaze steadily on the book that is not moving. The resulting sensory conflict may lead to the typical symptoms of motion sickness: dizziness, nausea, vomiting, and sweating.

Another form of dizziness occurs when we turn around in a circle quickly several times and then stop suddenly. Turning moves the endolymph. The moving endolymph tells us we are still rotating but our other senses say we've stopped. We feel dizzy.

Diagnosing the problem

The dizziness one feels after spinning around in a circle usually goes away quickly and does not require a medical evaluation. But when symptoms appear to be caused by an underlying physical problem, the prudent person will see a physician for diagnostic tests. According to a study supported by the National Institute of Neurological and Communicative Disorders and Stroke, a thorough examination can reveal the underlying cause of dizziness in about 90 percent of cases.

A person experiencing dizziness may first go to a general practitioner or family physician; between 5 and 10 percent of initial visits to these physicians involve a complaint of dizziness. The patient may then be referred either to an ear specialist (otologist) or a nervous system specialist (neurologist).

As part of a research study, this NINCDS physician tests a patient's balance. Tests that make the patient feel dizzy help establish a diagnosis.

The patient will be asked to describe the exact nature of the dizziness, to give a complete history of its occurrence, and to list any other symptoms or medical problems. Patients give many descriptions of dizziness-depending to some extent on its cause. Common complaints are light-headedness, a feeling of impending faint, a hallucination of movement or motion, or a loss of balance without any strange feelings in the head. Some people also report they have vertigo--a form of dizziness in which one's surroundings appear to be spinning uncontrollably or one feels the sensation of spinning.

The physician will try to determine what components of a patient's nervous system are out of kilter, looking first for changes in blood pressure, heart rhythm, or vision--all of which may contribute to the complaints. Sometimes dizziness is associated with an ear disorder. The patient may have loss of hearing, discomfort from loud sounds, or constant noise in the ear, a disorder known as tinnitus. The physician will also look for other neurological symptoms: difficulty in swallowing or talking, for example, or double vision.

Tests and scans

After the initial history-taking and physical examination, the physician may deliberately try to make the patient feel dizzy. The patient may be asked to repeat actions or movements that generally cause dizziness: to walk in one direction and then turn quickly in the opposite direction, or to hyperventilate by breathing deeply for 3 minutes.

In another test, the patient sits upright on an examining table. The physician tilts the patient's head back and turns it partway to one side, then gently but quickly pushes the patient backward to a lying down position. The reaction to this procedure varies according to the cause of dizziness. Patients with benign positional vertigo may experience vertigo plus nystagmus. rapid, uncontrollable back-and-forth movements of the eyes.

In a new caloric test to diagnose dizziness, air or water is injected gradually into a patient's ears. The eye movements that result are recorded.

One widely used procedure, called the caloric test, involves electronic monitoring of the patient's eye movements while one ear at a time is irrigated with warm water or warm air and then with cold water or cold air. This double stimulus causes the endolymph to move in a way similar to that produced by rotation of the head. If the labyrinth is working normally, nystagmus should result. A missing nystagmus reaction is a strong argument that the balance organs are not acting correctly.

NINCDS-supported scientists at The Johns Hopkins University in Baltimore observed that not all patients can tolerate the traditional caloric test. Some become sick when the ear is irrigated with the standard amount of water or air before physicians can measure their eye movements. So the scientists are designing a method of conducting the test more gradually by slowly adjusting the amount of water or air reaching the inner ear. Their goal is to reduce patient discomfort while allowing the test to proceed.

Balance disorders are often accompanied by hearing loss.

Some patients who cannot tolerate the caloric test are given a rotatory test. In this procedure, the patient sits in a rotating chair, head tilted slightly forward. The chair spins rapidly in one direction, then stops abruptly. Depending on the cause of dizziness, the patient may experience vertigo after this rotation.

In one variation of this test, the chair is placed in a tent of striped cloth. As the chair rotates, electrodes record movements of the patient's eyes in response to the stripes. The physician evaluates these eye movements, a form of nystagmus, to determine if the patient has a disorder of the balance system.

Because disorders of balance are often accompanied by hearing loss, the physician may order a hearing test.

Hearing loss and associated dizziness could also be due to damaged nerve cells in the brain stem, where the hearing and balance nerve relays signals to the brain. To detect a malfunction, the physician may order a kind of computerized brain wave study called a brain stem auditory evoked response test. In this procedure, electrodes are attached to several places on the surface of the patient's scalp and a sound is transmitted to the patient's ear. The electrodes measure the time it takes nerve signals generated by the sound to travel from the ear to the brain stem.

Patients with dizziness may undergo a computed tomographic (CT) scan to see if the problem is a tumor or a cyst.

If there is reason to suspect that the dizziness could stem from a tumor or cyst, the patient may undergo a computed tomographic (CT) scan. In a CT scan, x-ray pictures are taken of the brain from several different angles. These images are then combined by a computer to give a detailed view that may reveal the damaging growth.

Sometimes anxiety and emotional upset cause a person to feel dizzy. Certain patients may be asked to take a psychological test, to try to find out whether the dizziness is caused or intensified by emotional stress.

The many tests administered by a physician will usually point to a cause for the patient's dizziness. Disorders responsible for dizziness can be categorized as:

* peripheral vestibular, or those involving a disturbance in the labyrinth.

* central vestibular, or those resulting from a problem in the brain or its connecting nerves.

* systemic, or those originating in nerves or organs outside the head.

Confused signals

When someone has vertigo but does not experience faintness or difficulty in walking, the cause is probably a peripheral vestibular disorder. In these conditions, nerve cells in the inner ear send confusing information about body movement to the brain.

Meniere's disease. A well-known cause of vertigo is the peripheral vestibular disorder known as Meniere's disease. First identified in 1861 by Prosper Meniere, a French physician, the disease is thought to be caused by too much endolymph in the semicircular canals and vestibule. Some scientists think that the excess endolymph may affect the hair cells so that they do not work correctly. This explanation, however, is still under study.

The vertigo of Meniere's disease comes and goes without an apparent cause; it may be made worse by a change in position and reduced by being still.

In addition to vertigo, patients have hearing loss and tinnitus. Hearing loss is usually restricted at first to one ear and is often severe. Patients sometimes feel "fullness" or discomfort in the ear, and diagnostic testing may show unusual sensitivity to increasingly loud sounds. In 10 to 20 percent of patients, hearing loss and tinnitus eventually occur in the second ear.

Patients suspected of having Meniere's disease commonly undergo electronystagmography, an electronic recording of the caloric test.

Meniere's disease patients are often helped by drugs or surgery.

Meniere's disease patients may undergo electronystagmography, an electrical recording of the caloric test, to determine if their labyrinth is working normally.

Attacks of Meniere's disease may occur several times a month or year and can last from a few minutes to many hours. Some patients experience a spontaneous disappearance of symptoms while others may have attacks for years.

Treatment of Meniere's disease includes such drugs as meclizine hydrochloride and the tranquilizer diazepam to reduce the feeling of intense motion during vertigo. To control the buildup of endolymph, the patient may also take a diuretic, a drug that reduces fluid production. A low-salt diet--which reduces water retention-is claimed to be an effective treatment of Meniere's disease.

When these measures fail to help, surgery may be considered. In shunt surgery, part of the inner ear is drained to reestablish normal inner ear fluid or endolymph pressure. In another operation, called vestibular nerve section, surgeons expose and cut the vestibular part of the eighth nerve. Both vestibular nerve section and shunt surgery commonly relieve the dizziness of Meniere's disease without affecting hearing.

A more drastic operation, labyrinthectomy, involves total destruction of the inner ear. This procedure is usually successful in eliminating dizziness but causes total loss of hearing in the operated ear--an important consideration since the second ear may one day be affected.

Positional vertigo. People with benign positional vertigo experience vertigo after a position change. Barbara noticed the first sign of this disorder one morning when she got up out of bed. She felt the room spinning. Frightened, she quickly returned to bed and lay down. After about 30 seconds the vertigo passed. Fearing a stroke, Barbara went to the emergency room of a hospital for a medical evaluation, which failed to show a problem. She had no symptoms for several days, then the problem returned. At this point, Barbara was referred to an otoneurologist, a physician who specializes in the ear and related parts of the nervous system.

Viral infections may lead to vestibular neuronitis

Like Barbara, most patients with benign positional vertigo are extremely worried about their symptoms. But the patients usually feel less threatened once the disorder is diagnosed.

The cause of benign positional vertigo is not known, although some patients may recall an incident of head injury. The condition can strike at any adult age with attacks occurring periodically throughout a person's life.

In one type of treatment, the patient practices the position that provokes dizziness until the balance system eventually adapts. Rarely, a physician will prescribe medication to prevent attacks.

Vestibular neuronitis. In this common vestibular disorder, the patient has severe vertigo. Jack experienced his first attack of this problem at 2 a.m. when he rolled over in bed and suddenly felt the room spinning violently. He started vomiting but couldn't stand up; finally, he managed to crawl to the bathroom. When he returned to bed, he lay very still--the only way to stop the vertigo. Three days later, he was able to walk without experiencing vertigo, but he still felt unsteady. Gradually, over the next several weeks, Jack's balance improved, but it was a year before he was entirely without symptoms.

Unlike Meniere's disease, vestibular neuronitis is not associated with hearing loss. Patients with vestibular neuronitis first experience an acute attack of severe vertigo lasting for hours or days, just as Jack did, with loss of balance sometimes lasting for weeks or months. About half of those who have a single attack have further episodes over a period of months to years.

The cause of vestibular neuronitis is uncertain. Since the first attack often occurs after a viral illness, some scientists believe the disorder is caused by a viral infection of the nerve.

Other labyrinth problems. Inner ear problems with resulting dizziness can also be caused by certain antibiotics used to fight life-threatening bacterial infections. Probably the best-known agent of this group is streptomycin. Problems usually arise when high doses of these drugs are taken for a long time, but some patients experience symptoms after short treatment with low doses, especially if they have impaired kidneys.

The first symptoms of damage to the inner ear caused by medication are usually hearing loss, tinnitus, or unsteadiness while walking. Stopping the drug can usually halt further damage to the balance mechanism, but this is not always possible: the medicine may have to be continued to treat a life-threatening infection. Patients sometimes adapt to the inner ear damage that may-occur after prolonged use of these antibiotics and recover their balance

Balance can also be affected by a cholesteatoma, a clump of cells from the eardrum that grow into the middle ear and accumulate there These growths are thought to result from repeated infections such as recurrent otitis media. If unchecked, a cholesteatoma can enlarge and threaten the inner ear. But if the growth is detected early, it can be surgically removed.

Brain and nerve damage

The vestibular nerve carries signals from the inner ear to the brain stem. If either the nerve or the brain stem is damaged, information about position and movement may be blocked or incorrectly processed, leading to dizziness. Conditions in which dizziness results from damage to the brain stem or its associated nerves are called central causes of dizziness.

Acoustic neuroma. One central cause of dizziness is a tumor called an acoustic neuroma. Although the most common sign of this growth is hearing loss followed by tinnitus, some patients also experience dizziness.

An acoustic neuroma usually occurs in the internal auditory canal, the bony channel through which the vestibular nerve passes as it leaves the inner ear. The growing tumor presses on the nerve, sending false messages about position and movement to the brain.

The hearing nerve running alongside the vestibular nerve can also be compressed by the acoustic neuroma, with resulting tinnitus and hearing loss. Or the tumor may press on other nearby nerves, producing numbness or weakness of the face. If the neuroma is allowed to grow, it will eventually reach the brain and may affect the function of other cranial nerves.

These benign cells from an acoustic neuroma were grown in tissue culture. If diagnosed early, acoustic neuromas can be removed completely with no neurological damage.

Early treatment of acoustic neuroma helps patients regain balance.

Computed tomography has revolutionized the detection of acoustic neuromas. If an early diagnosis is made, a surgeon can remove the tumor. The patient usually regains balance.

Stroke

Dizziness may be a sign of a "small stroke" or transient ischemic attack (TIA) in the brain stem. TIA's, which result from a temporary lack of blood supply to the brain, may also cause transient numbness, tingling, or weakness in a limb or on one side of the face. Other signs include temporary blindness and difficulty with speech. These symptoms are warning signs: one should see a physician immediately for treatment. If a TIA is ignored, a major stroke may follow.

Systemic diseases: underlying illness

Dizziness can be a symptom of diseases affecting body parts other than the-brain and central nervous system. Systemic conditions like anemia or high blood pressure decrease oxygen supplies to the brain; a physician eliminates the resulting dizziness by treating the underlying systemic illness.

Damaged sensory nerves. We maintain balance by adjusting to information transmitted along sensory nerves from sensors in the eyes, muscles, and joints to the spinal cord or brain. When these sensory nerves are damaged by systemic disease, dizziness may result.

Multiple sensory deficits, a systemic disease, is believed by some physicians to be the chief cause of vaguely described dizziness in the aged population. In this disorder several senses or sensory nerves are damaged. The result: faulty balance.

People with diabetes, which can damage nerves affecting vision and touch, may develop multiple sensory deficits. So can patients with arthritis or cataracts, both of which distort how sensory information reaches the brain. The first step in treating multiple sensory deficits is to eliminate symptoms of specific disorders. Permanent contact lenses can improve vision in cataract patients, for example, and medication or surgery may ease pain and stiffness related to arthritis.

Symptoms of damaged sensory nerves may be relieved by a collar to eliminate extreme head motion, balancing exercises to help compensate for sensory losses, or a cane to aid balance. Some patients are helped by the drug methylphenidate, which can increase awareness of remaining sensations.

Systemic neurological disorders such as multiple sclerosis, Alzheimer's disease, Parkinson's disease, or Creutzfeldt-Jakob disease may also cause dizziness, primarily during walking. However, dizziness is rarely the sole symptom of these nervous system diseases.

Low blood pressure. One common systemic disease causing dizziness is postural or orthostatic hypotension. In this disease, the heart does not move the blood with enough force to supply the brain adequately. Symptoms include sudden feelings of faintness, light-headedness, or dizziness when standing up quickly.

Because the muscles in aging blood vessels are weak and the arteries inadequate in helping convey blood to the head, older people are particularly susceptible to this condition. Older persons who do not sit or lie down at the first sensation of dizziness may actually lose consciousness.

Postural hypotension is easily diagnosed. The patient's blood pressure is checked before standing abruptly and immediately afterward.

Anxiety can trigger attacks of dizziness

People who have undetected anemia or those who are taking diuretics to eliminate excess water from their body and reduce high blood pressure are also at risk of developing postural hypotension.

A physician can easily diagnose postural hypotension: the patient's blood pressure is measured before standing abruptly and immediately afterward. Treatment is designed to eliminate dizziness by reducing the patient's blood volume.

A secondary symptom

Dizziness may also be a secondary symptom in many other diseases. Faintness accompanied by occasional loss of consciousness can be due to low blood sugar, especially when the faint feeling persists after the patient lies down.

A common cause of mild dizziness--the kind described as light-headedness--is medicine. A number of major prescription drugs may produce light-headedness as a side effect. Two types of drugs that can cause this problem are sedatives, which are taken to induce sleep, and tranquilizers, which are used to calm anxiety.

When anxiety strikes

Tranquilizers may cause a type of dizziness referred to as light-headedness--but so may anxiety. Cynthia is a young woman who becomes light-headed under a variety of stressful circumstances. The light-headedness sometimes is accompanied by heart palpitations and panic. She can produce these symptoms at will by breathing rapidly and deeply for a few minutes.

Cynthia's light-headedness is due to hyperventilation: rapid, prolonged deep breathing or occasional deep sighing that upsets the oxygen and carbon dioxide balance in the blood. The episodes are typically brief and often associated with tingling and numbness in the fingers and around the mouth. Hyperventilation is triggered by anxiety or depression in about 60 percent of dizziness patients.

Research offers new insights into the basis of balance

Once made aware of the source of the symptoms, a patient can avoid hyperventilation or abort attacks by breath-holding or breathing into a paper bag to restore a correct balance of oxygen and carbon dioxide. If hyperventilation is due to anxiety, psychological counseling may be recommended.

Some patients who report dizziness may be suffering from a psychiatric disorder. Generally these persons will say that they experience light-headedness or difficulty concentrating; they may also describe panic states when in crowded places. Tests of such patients reveal that the inner ear is working correctly. Treatment may include counseling.

Demystifying dizziness through research

Scientists are working to understand dizziness and its sources among the complex interactions of the labyrinth, the other sense organs, and the brain. The research is offering new insights into the basis of balance, as well as improvements in diagnosis, treatment, and prevention of dizziness.

Innovative surgery. Delicate surgical instruments and operating microscopes have made possible new methods to help patients with dizziness. The symptoms of benign positional vertigo, for example, may be relieved by a microsurgical ear operation called a singular neurectomy in which a tiny portion of the vestibular nerve is divided and cut.

Patients with Meniere's disease may benefit from a microsurgical operation called the cochleosacculotomy. In this procedure, a small curette or wire loop is used to reach into the vestibule of the inner ear and remove the fluid-filled saccule. An investigator at the Massachusetts Eye and Ear Institute in Boston has found that this operation relieves symptoms of vertigo in about 80 percent of patients.

Space biology. Research also promises to help astronauts who suffer from dizziness or space sickness. In one study, a scientist aboard a space shuttle conducted experiments to find out why half the astronauts who have space sickness at the start of a flight overcome this problem before the end of the mission. The investigator, from the Massachusetts Institute of Technology, found that the space traveler's brain no longer relies on the gravity-sensitive inner ear structures for information about position and motion. Instead, the astronaut's brain realizes that the inner ear is sending false information and starts to depend more on the eyes to find out about the body's movements. This finding may enable space biologists to train astronauts before launch to avoid space sickness.

During that same space mission, a German scientist performed experiments that raised questions about the theory behind the caloric test. According to that theory, alternate heating and cooling of the endolymph causes the fluid to form wave-like swirling patterns called convection currents. These currents make the brain think the head is moving. The result is nystagmus.

In space, however, lack of gravity should prevent convection currents from forming, so the eyes were expected to remain still. Instead, they moved just as though the test was being done on Earth in normal gravity. These experiments indicate there is more than one explanation for why the caloric test works: when the endolymph is warmed, the fluid expands and moves the cupula, the top of the cochlear duct. The movement of the cupula cues the brain that the head is moving and the eyes respond.

This research helps scientists interpret methods used to test vestibular function. It also promises to increase our understanding of the balance system.

Currently, scientists at the Johnson Space Center in Houston and at the Good Samaritan Hospital in Portland are preparing to study space sickness and vestibular function in a microgravity (near zero gravity) laboratory. The astronauts' vestibular function will be analyzed in a series of experiments, including studies to test whether visual input becomes more important in maintaining balance as weightlessness increases. The scientists anticipate that this research will help all sufferers of motion sickness, not just astronauts.

Scientists are developing better diagnostic tests for dizziness

Improved diagnosis. Back on Earth, improvements are being made in measuring precisely the eye movements of patients undergoing diagnostic tests for dizziness. Investigators at the NINCDS-funded research center at the University of California at Los Angeles have developed a computer-controlled chair in which a patient is shifted into a variety of body positions to stimulate the labyrinth. Eye responses are measured with newly designed computerized instruments. To further stimulate eye movements, a set of computer-generated visual patterns can be moved with the chair or independently. of it.

These instruments will extract much information about a patient's ability to integrate information from the eyes and the inner ear, and will help distinguish patients with different disorders of the balance system.

Signaling the brain. To understand dizziness, scientists must find out how stimuli to the labyrinth are translated into information that the brain can use to maintain balance. How, for example, is information from the inner ear sent to the brain and interpreted? Among the scientists studying this question is an NINCDS grantee at the University of Chicago who is looking at the different ways hair cells react to the movement of inner ear fluid. He has identified a characteristic pattern of electrical response in hair cells. The next step is to discover how these messages are interpreted by the nerve cells carrying information to the brain.

An NINCDS grantee at the University of Minnesota adjusts the controls on an oscilloscope used to monitor patients' eye movements during vestibular testing.

Another NINCDS grantee at the University of Minnesota is studying the activity of the brain when it sends balance-preserving signals from the sense organs to the muscles. In one experiment, healthy persons are rotated in the dark at a constant rate. After a few minutes they no longer think they are moving. This is because the inner ear only senses changes in the rate of movement. If the lights are turned on and both the chair and the room rotate at the same constant speed, again the person doesn't sense movement. Both the inner ear and the eyes are fooled into thinking there is no motion.

But the investigator found that if the chair and the room are accelerated, the patient develops what is described as sensory conflict. The acceleration of the chair tells the inner ear that there is movement. But the eyes tell the brain that the body is stationary. How patients react in these conflict situations reveals how the brain puts together various types of sensory information to maintain balance. The results of this and related experiments will help scientists build a mathematical model of the balance system.

Hope for the future

For those who are healthy, equilibrium is a sense often taken. for granted. People can't see their labyrinth, even though it is as much a sense organ as the ears or the eyes. But when it is injured, an ability vital to everyday living is lost.

Scientists already understand a great deal about the labyrinth's function and the way the brain maintains balance. Further research into this complex system should help those who are incapacitated by dizziness when the balance system goes awry.

Voluntary health organizations

The following organizations provide information on dizziness or on inner ear diseases that cause dizziness:

Acoustic Neuroma Association
P.O. Box 398
Carlisle, PA 17013
(717) 249-4783

American Academy of Otolaryngology-Head and Neck Surgery
Suite 302
1101 Vermont Avenue, N.W.
Washington, DC 20005
(202) 289-4607

Better Hearing Institute
P.O. Box 1840
Washington, DC 20013
(703) 642-0580
(800) 424-8576 (Toll free)

National Hearing Association
721 Enterprise
Oak Brook, IL 60521
(312) 323-7200

Human tissue banks

The study of ear tissue from patients with dizziness and deafness is invaluable in research. Temporal bones willed by people with balance or hearing problems and by people with normal hearing can be used to help research scientists and physicians training to be otolaryngologists. Physicians in training study the basic anatomy of the temporal bone and develop their surgical skills. Scientists use the bones for research on the inner ear and on congenital disorders that cause deafness. Middle ear bones (ossicles) and the eardrum are also used as grafts to surgically correct sound transmission problems of the middle ear.

NINCDS supports four temporal bone banks that supply scientists in every state with tissue from patients who have dizziness or deafness. The donated temporal bone includes the eardrum, the entire middle and inner ear, and the nerve tissues which combine into the brain stem. For information about tissue donation and collection, write to:

National Temporal Bone Bank
Eastern Center
Massachusetts Eye and Ear Infirmary
243 Charles Street
Boston, MA 02114
(617) 523-7900, ext. 2711

National Temporal Bone Bank
Midwestern Center
University of Minnesota
Box 396-Mayo
Minneapolis, MN 55455
(612) 624-5466

National Temporal Bone Bank
Southern Center
Baylor College of Medicine
Neurosensory Center--Room A523
Houston, TX 77030
(713) 790-5470

National Temporal Bone Bank
Western Center
UCLA School of Medicine
31-24 Rehabilitation Center
Los Angeles, CA 90024
(213) 825-4710

Some useful definitions:

acoustic neuroma: tumor of the vestibular nerve that may press on the hearing nerve causing dizziness and hearing loss.

balance system: complex biological system that enables us to know where our body is in space and to keep the position we want. Proper balance depends on information from the labyrinth in the inner ear, from other senses such as sight and touch, and from muscle movement.

benign positional vertigo: condition in which moving the head to one side or to a certain position brings on vertigo.

brain stem auditory evoked response (BAER): diagnostic test in which electrodes are attached to the surface of the scalp to determine the time it takes inner ear electrical responses. to sound to travel from the ear to the brain. The test helps locate the cause of some types of dizziness.

caloric test: diagnostic test in which warm or cold water or air is put into the ear. If a person experiences certain eye movements (nystagmus) after this procedure, the labyrinth is working correctly.

cholesteatoma: a tumorlike accumulation of dead cells in the middle ear. This growth is thought to result from repeated middle ear infections.

computed tomography (CT) scan: radiological examination useful for examining the inside of the ear and head.

diuretic: drug that promotes water loss from the body, through the urine. Used to treat hypertension, diuretics may bring on dizziness due to postural hypotension.

dizziness: feeling of physical instability with regard the outside world.

endolymph: fluid filling part of the labyrinth.

hair cells: specialized nerves found in the semicircular canals and vestibule. Fibers (hairs) sticking out of one end of the hair cells move when the head moves and send information to the brain that is used to maintain balance.

hyperventilation: repetitive deep breathing that reduces the carbon dioxide content of the blood and brings on dizziness. Anxiety may cause hyperventilation and dizziness.

inner ear: contains the organs of hearing and balance.

labyrinth: the organ of balance, which is located in the inner ear. The labyrinth consists of the three semicircular canals and the vestibule.

Meniere's disease: condition that causes vertigo. The disease is believed to be caused by too much endolymph in the labyrinth. Persons with this illness also experience hearing problems and tinnitus.

middle ear: the space immediately behind the eardrum. This part of the ear contains the three bones of heating: the hammer (malleus), anvil (incus), and stirrup (stapes).

multiple sensory deficits: condition associated with dizziness in which damage to nerves of the eye and arms or legs reduces information about balance to the brain.

neurologist: physician who specializes in disorders of the nervous system.

nystagmus: rapid back-and-forth movements of the eyes. These reflex movements may occur during the caloric test and are used in the diagnosis of balance problems.

orthostatic hypotension: see postural hypotension.

otologist: physician who specializes in diseases of the ear.

peripheral vestibulopathy: vestibular disorder in which the vestibular nerve appears inflamed and paralyzed. Patients may have one or several attacks of vertigo.

postural hypotension (also called orthostatic hypotension): sudden dramatic drop in blood pressure when a person rises from a sitting, kneeling, or lying position. The prime symptom of postural hypotension, which is sometimes due to low blood volume, is dizziness or faintness. The condition can be dangerous in older persons, who may faint and injure themselves.

semicircular canals: three curved hollow tubes in the inner ear that are part of the balance organ, the labyrinth. The canals are joined at their wide ends and are filled with endolymph.

stroke: death of nerve cells due to a loss of blood flow in the brain. A stroke often results in permanent loss of some sensation or muscle activity.

TIA: see transient ischemic attack.

tinnitus: noises or ringing in the ear.

transient ischemic attack (TIA): temporary interruption of blood flow to a part of the brain. Because a TIA may signal the possibility of a stroke, it requires immediate medical attention. During a TIA, a person may feel dizzy, have double vision, or feel tingling in the hands.

vertigo: severe form of dizziness in which one's surroundings appear to be spinning uncontrollably. Extreme cases of vertigo may be accompanied by nausea.

vestibular disorders: diseases of the inner ear that cause dizziness.

vestibular nerve: nerve that carries messages about balance from the labyrinth in the inner ear to the brain.

vestibular neuronitis: another name for peripheral vestibulopathy.

vestibule: part of the labyrinth, located at the base of the semicircular canals. This structure contains the endolymph and patches of hair cells.

While a patient watches a rotating drum, the otoneurologist checks his eyes for signs of any disturbance in neurological function that could cause dizziness.

Information provided by the NIH.