Tinnitus --the false perception of sound in the absence of an acoustic stimulus, a phantom noise--is one of the most common clinical syndromes in the United States, affecting twelve percent of men and almost fourteen percent of women who are sixty-five and older. It only rarely afflicts the young, with one significant exception: those serving in the armed forces. Tinnitus affects nearly half the solders exposed to blasts in Iraq and Afghanistan.
A recent report from the Department of Veterans Affairs estimated that nearly seventy thousand of the 1.3 million soldiers who have served in Iraq and Afghanistan are collecting disability for tinnitus, and more than fifty-eight thousand are on disability for hearing loss. In 2006, the V.A. reportedly spent five hundred and thirty-nine million dollars on payments to veterans with tinnitus.
How our hearing happens
Normally, the outer ear, known as the pinna, collects sound waves and directs them into the ear canal, which carries the sound waves to the eardrum. In turn, the eardrum vibrates, and these tremors are picked up by the three tiny bones in the middle ear: the malleus (resembling a club), the incus (shaped like an anvil), and the stapes (similar to a stirrup). These bones amplify the sound vibrations and transmit them to the inner ear, where the cochlea converts the vibrations into electrical impulses, which travel from the acoustic nerve to the part of the brain that processes sound, the auditory cortex.
Tinnitus can be temporary, caused by excess wax, an infection of the inner ear, or the toxic effects of drugs like aspirin (which appears to weaken the neural signals from the ear to the brain) or those used to treat cancer. But the majority of people with chronic symptoms develop them in conjunction with hearing loss. With the recent proliferation of MP3 players, rates of hearing loss and tinnitus may rise sharply in the coming years.
A recent European Union study has projected that as many as ten million Europeans may be at risk of developing severe hearing loss as they age; and, according to the American Academy of Audiology, noise-induced hearing loss affects about one out of every eight children in the United States.
As part of a standard evaluation, patients are given a series of tests: a typanogram, to determine how the eardrums respond to air pressure; an assessment of the cochlea's response to sound; and a standard audiogram, to test the frequency and intensity of sounds that define the span of hearing.
Why is it that the buzzing in the ear ceases if one makes a sound? Is it because the greater sound drives out the less?
Researchers have only recently begun to explore the neurological basis for tinnitus. Because a real sound will activate areas on both sides of the brain and PET-scan results indicate that tinnitus patients only activate one side of the brain (on either the right or left side) when real sounds are absent, it is suggested that the tinnitus originates in the central nervious system. The brain becomes hyperactive in an effort to compensate for the reduced input, generating phantom sounds. This conclusion was published in the journal Neurology in 1998 and began to change the way that researchers approached tinnitus.