Tinnitus Study Offers Hope for Treatment
Researchers have for the first time identified the source of tinnitus, the constant and debilitating ringing in the ears that afflicts as many as 50 million Americans.
The discovery could lead to the first effective treatment for the disorder, Buffalo researchers report today in the journal Neurology.
Tinnitus results from damage to the inner ear caused by loud noises, medications, blows to the head and other factors. But researchers have never known precisely which parts of the ear are generating the disturbing sounds.
Using positron emission tomography scans to image the brains of a small group of tinnitus patients, Dr. Alan H. Lockwood of the Buffalo Veterans Affairs Medical Center concluded that the noise originates not in the ear, but in the auditory cortex, a portion of the brain in the temporal lobe opposite the affected ear.
When the ear is damaged, he said, the brain rewires itself, perhaps in an attempt to compensate for the loss of function. That rewiring generates electrical signals that the brain interprets as noise.
Intriguingly, other researchers report today in the journal Nature that a similar type of rewiring occurs in people who have lost a limb. That rewiring produces the phantom pain suffered by many amputees.
The tinnitus report “is very important, because we really haven’t known the mechanisms responsible for tinnitus,” said Gloria Reich, executive director of the American Tinnitus Assn. “We’re terribly pleased.”
Lockwood’s study is “a seminal finding,” said Kenneth Gruber of the National Institute on Deafness and Other Communications Disorders. “People have not wanted to work on tinnitus because it is so difficult to study. Alan has shown us that you can be productive using modern techniques. . . . And this will attract more people into the field.”
Estimates vary, but between 20% and 35% of Americans suffer tinnitus at some time in their lives, particularly in their later years. It may appear as buzzing, roaring, whistling, hissing, high-pitched screeches or other sounds, and is often accompanied by hearing loss. The condition is usually permanent.
It can be caused by exposure to loud noises, wax buildup in the ear canal, certain medications--especially high doses of aspirin--ear or sinus infections, jaw misalignment, heart disease, tumors, an underactive thyroid and head and neck trauma.
About 10% of the elderly suffer tinnitus so severe that it disrupts their lives, producing depression, anxiety, sleep disorders and other emotional problems.
The only current treatments are special hearing aids that amplify normal sounds to overcome the ringing, or so-called maskers that use white noise to hide the sounds. Drugs may be employed to treat emotional side effects, but there are none that affect the disorder directly.
Lockwood and his colleagues at the VA and the University of Buffalo studied a small group of tinnitus sufferers who can vary the loudness of the ringing by clenching their jaws. Fewer than 1% of patients have this ability, although some others can do it with eye movements or other facial tics.
As the patients alternately clenched and unclenched their jaws, the researchers used PET scans that allowed them to measure activity throughout the brain when the tinnitus was loud and when it was barely discernible. Differences between the two readings, especially when compared to scans from people without the disorder, allowed researchers to identify the site responsible for the tinnitus, a portion of the auditory cortex that processes signals from the ears.
Scans showing the response to actual sounds demonstrated that the perceived noise was originating in the auditory cortex and not in the ear.
They also found that tinnitus activated the hippocampus, a portion of the brain that controls the limbic system--which is associated with emotions and feelings. That link to the hippocampus, Lockwood said, may explain why people with severe tinnitus also have emotional problems.
The discovery opens a door into new research on tinnitus, Lockwood said. “Without objective information on how and where the condition originates, developing effective treatments has been difficult. By identifying the sites in the brain that mediate tinnitus, we have taken a critical step down the road toward a cure for this disabling condition.” Researchers might, for example, develop drugs to change the activity of neurotransmitters in the affected area.
Lockwood said the phantom noises heard by tinnitus sufferers are similar to phantom limb pain, a phenomenon in which amputees often feel excruciating pain that seems to originate in the missing limb. “Tinnitus may be the auditory counterpart to phantom limb pain,” he said.
Researchers from the University of Toronto and Toronto Hospital report in Nature today on the causes of phantom limb pain. They found that in at least some amputees, the brain is reprogrammed in the same fashion that was observed for tinnitus--but in the thalamus, a walnut-sized part of the brain that is the center for sensory information flowing into the brain.
The thalamus contains a map of the body, with different sites on the body’s surface linked to specific areas of the thalamus. When a limb is amputated, they found, the portion of the thalamus previously associated with that limb makes new connections to other locations in the thalamus. It is electrical signals from this rewiring, they found, that generate the pain.
Dr. Andres Lozano and his colleagues were able to map the linkages while they were surgically implanting microelectrodes to control the phantom pain. The finding should give patients “a sense of reassurance in knowing that there is a biological basis for phantom pain,” said Dr. Karen Davis, who was part of the team.
One possibility arises from the inadvertent pairing of the two studies, experts said. If implanted electrodes can control the pain of phantom limbs, perhaps they might also be able to control the intensity of phantom noises.
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The Buzz of Tinnitus
What is it? A constant and debilitating buzzing or ringing in the ears.
Where Does the Noise Come From? The auditory cortex opposite an affected ear. When an ear is damaged, researchers say, the brain rewires itself, generating electrical signals that the brain interprets as noise.
What Causes It? Loud noises, medications such as aspirin and blows to the head.
Who Is Affected? A least 20% of the population, 50 million people, at some time in their lives. Severe tinnitus disrupts the lives of 10% of the elderly. It has grown more common as a result of people playing music too loud. It frequently affects rock musicians, including Pete Townsend of the Who, Jeff Beck and Ted Nugent.
What’s Next? Many hope the discovery of tinnitus’ cause will lead to an effective treatment.
Sources: Neurology
