New research on tinnitus could lead to treatment HEALTH

Dennis Brody, now retired, was a firefighter with the city of Alameda and has suffered for years with severe tinnitus. He still occasionally visits the Station 4, where he spent most of his time. Dennis Brody, now retired, was a firefighter with the city of Alameda and has suffered for years with severe tinnitus. He still occasionally visits the Station 4, where he spent most of his time. Photo: Special To The Chronicle Photo: Special To The Chronicle Image 1 of / 7 Caption Close New research on tinnitus could lead to treatment 1 / 7 Back to Gallery

UC Berkeley scientists believe they've found a new avenue for treating tinnitus, an often debilitating ear and brain condition that causes people to hear a constant ringing or buzzing sound - and that in most cases is untreatable.

Doctors have known for several years that the cause of tinnitus is not in the ear alone, but in the brain. In research released last week, the UC Berkeley team found that tinnitus may be similar to the "phantom limb" syndrome that amputees sometimes experience - neurons continue firing in the parts of the brain associated with hearing, even though they're getting no input from the ear.

If scientists can find a way to rewire the brain so that those areas are receiving input again, the neurons could be better regulated. Or scientists may be able to find a drug that turns off the firing mechanisms.

Either way, the result could be peace and quiet for the millions of people who suffer from tinnitus, said Shaowen Bao, an adjunct assistant professor with UC Berkeley's Helen Wills Neuroscience Institute.

"We still need more research to gradually resolve this question of tinnitus," said Bao, co-author of the tinnitus study, which was published online in the Proceedings of the National Academy of Sciences. "But in a lot of ways, the bits and pieces are all there. People are just trying to put together a theory that explains it all. We did the same thing, and we think our conclusion is important."

Range of ringing

Bao is a tinnitus sufferer himself, although his case is relatively mild, he said, and he's able to ignore the hum in his ears most of the time. But there's a broad range of tinnitus severity, from a dull buzzing in one ear, like static on a phone, to a loud, distracting ringing in both ears that can keep people from sleeping or even thinking clearly.

Nearly 50 million people in the United States have tinnitus, according to the American Tinnitus Association, although most of them either have it temporarily or never seek help for the condition.

Roughly 2 million people have serious enough symptoms that they are disabled by tinnitus - they may not be able to work and their quality of life is seriously affected. There's no cure for tinnitus, and most of the available treatments aren't very effective, doctors and patients say.

"The tinnitus was so severe that I did not sleep more than two or three hours in a month," said Dennis Brody, 53, who retired from the Alameda city fire department three years ago when his back problems and tinnitus had gotten so bad that he couldn't work. "I went suicidal. I couldn't eat. My anxiety level was through the roof."

His tinnitus, he said, is like hearing a "high voltage electrical buzzing" in his head all the time. He's been able to relieve the worst of it with hearing aids that mask the sound, and therapy to deal with anxiety - a common problem among tinnitus sufferers. But he's hopeful for a cure someday, especially for people who can't get any relief from treatment.

Tinnitus is always associated with hearing loss, often from sustained exposure to loud noises. Usually high frequencies are lost - sometimes the frequency is so high that patients don't notice, even though they can hear the ringing or buzzing sound.

Theory upended

Scientists figured out a few years ago that the root of tinnitus is in the brain, and in particular, how the auditory cortex receives and interprets sensory input from the ear.

The prevailing theory at first was that after hearing loss, the brain remapped itself so that neurons that used to "hear" at a certain frequency instead started responding to different, closely related frequencies. But the neurons weren't precisely fit to respond to those frequencies, and that somehow left patients hearing odd sounds in their heads.

Bao's theory, which he tested in rats with induced hearing loss, is that the problem is exactly the opposite - the brain doesn't remap itself, and so the affected neurons aren't receiving any sensory input. In someone with normal hearing, input controls how the neurons fire, or communicate with one another, Bao said. Without the input, the neurons fire constantly, creating the "phantom" sound associated with tinnitus.

"This research is a substantial correction of how we think about tinnitus," said Dr. Michael Merzenich, professor emeritus of otolaryngology at UCSF, who was not involved in the UC Berkeley research. "We really need to sort out how to engage this disengaged area of the brain."

Training the brain

Merzenich has studied brain remapping for years, and through his work at the company Posit Science he's been trying to train the brains of patients with hearing loss to better interpret sounds. He said that even before he saw Bao's research, he'd heard from several patients who reported that their tinnitus improved after their brain was trained, or remapped - a result that surprised him, given the earlier theories on the cause of tinnitus.

Doctors previously assumed that exposing tinnitus patients to frequencies near the ones they were no longer able to hear would actually cause more damage, by further exciting the neurons that were already reaching for new sensory input. Now, Bao is suggesting that such exposure may actually be helpful, by coaxing neurons to accept input from frequencies similar to the ones they lost.

It may also be possible to relieve tinnitus symptoms by preventing the neurons from constantly firing. That could be accomplished with drugs - in the rat studies, at least two drugs were found to stop the neuron activity, but both of them had serious side effects, including blindness, that make them unsuitable for use in humans.