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Tinnitus: Tinnitus Association
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According to the American Tinnitus Association over 50 million Americans are affected to some degree. Of these, about 12 million have tinnitus which is severe enough to seek medical attention. Of those, about two million patients are so seriously debilitated by their tinnitus, they cannot function on a "normal," day-to-day basis.
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The following scenario of the emergence of tinnitus perception has been proposed (Neurosci.Res. 8:221-254, 1990). A weak imbalance of neuronal activity within the auditory system, most frequently related to damage of the inner ear, is detected at low levels in the auditory system, and being a new signal it is further enhanced by subcortical centers, transferred to the auditory cortex and perceived as a sound - tinnitus, and is subsequently evaluated. In the majority of cases the continued presence of tinnitus combined with a lack of any positive or negative association results in habituation of the reaction to the tinnitus signal. Although tinnitus perception may still be possible, there is little or no annoyance or discomfort. This situation is typical for children, or those leaving a loud concert, who tend to treat tinnitus as a natural event, and tinnitus typically does not annoy them.
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Many people write to the American Tinnitus Association asking if a one-time exposure to loud noise experienced many years ago can cause tinnitus. Noise is damaging if you must shout to be heard, if your ears hurt, or if your hearing is lessened immediately following noise exposure. The noise exposure could occur just one time or over months or years. The level of noise can affect the degree of hearing loss. For example, sounds of 100 decibels experienced for more than 15 minutes can cause hearing loss. Sounds of 110 decibels experiences for more than a minute can cause hearing loss.
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Other recent imaging studies link cases of tinnitus to irregular activity in the auditory cortex and other related parts of the sound processing pathway, termed auditory association areas. Additional areas, including those that process emotion and may underlie a person's annoyance with the ringing... sometimes appear involved. The researchers identified the areas by examining how varying degrees of tinnitus loudness influenced brain activity. Some work examined patients who can alter their tinnitus with an eye movement, a jaw clench or a touch of the skin. Other studies examined patients with tinnitus that increased or decreased when they received a dose of the drug lidocaine.
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This form of tinnitus may occur anywhere in the auditorysystem and is much less understood, with the causes being many and open to debate. Anything from the ear canal to the brain may be involved. The sounds can range from a metallic ringing, buzzing, blowing, roaring, or sometimes similar to a claanging, popping, or nonrhythmic beating. It can be accompanied by audiometric evidence of deafness which occurs in association with both conductive and sensorineural hearing loss. Other conditions and syndromes which may have tinnitus in conjunction with the condition or syndrom, are otosclerosis, Menier's syndrome, and cochlear or auditory neve lesions.
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Loud noise is the most common cause of preventable tinnitus. A study of 1,687 people with tinnitus revealed that noise exposure accounted for one out of four cases of tinnitus. Tinnitus from noise exposure and hearing loss generally go together. The American Tinnitus Association reports that up to 90% of all people with tinnitus have some level of noise-induced hearing loss. If you are around loud sounds for a while, perhaps you've noticed that your ears rang for a while after. This is tinnitus.
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Tinnitus Association