VOA常速英语:Research Shows Tinnitus May Affect Brain Responses

Have you ever gone to the doctor, complaining of a loud ringing or buzzing sound that no one else seems to hear?  It may be what's called tinnitus, and while it does not matter whether you pronounce it tinn-EYE-tus or TINN-eh-tus, it can be a distressing condition.  This phantom noise affects an estimated 50 million Americans and 250 million people worldwide.  There is no cure for it. 

Retired Air Force Colonel Horace Humphries, Junior says tinnitus can affect your whole life. "I have nights where I can't sleep.  I'm in a situation where it kind of affects your memory.  It affects how you do things. I can't be around any loud noises at all," he said.

Colonel Humphries was in the U.S. Air Force when ear protection was not required around military aircraft.  And even away from the flight line, war is not a quiet business. He describes what happened in Vietnam when a rocket blew up as he was driving back to base. "It was so loud it lifted the side of the Jeep up and I remember my ears ringing real bad," he said.

And they continued to ring, even after he returned home and retired.  Tinnitus affects as many as 20 to 40 percent of returning military.  Then, as they join the elderly population, their condition can get worse. Dr. Jay Piccirillo of Washington University in St. Louis says tinnitus can be very isolating. "Nobody else can see your injury.  Nobody else can see your suffering.  So these patients feel alone and they feel like they're suffering in silence," he said.

Dr. Piccirillo says tinnitus is likely caused by damage to the auditory system that can eventually affect other parts of the brain.  The sound that generated the injury in the first place is gone, but recognition of the sound is still there. "That tinnitus sound, that roaring, clicking, clacking, whatever it is, is constantly being sent up to the cortical part of the brain and the brain is misinterpreting it as meaningful information," he said.

Not every member of the military experiences tinnitus, even after combat.  So why do some suffer and others do not?  To find out, the researchers at Washington University plan to interview and take brain images of  200 U.S. soldiers before they leave for active duty in Iraq or Afghanistan. When they return, they will be reinterviewed and images will be taken again to identify those who have developed tinnitus.

"Is there some preexisting vulnerability in the way the different regions of the brain really don't communicate or communicate ineffectually, that then prohibits the sufferer, the tinnitus sufferer, from overcoming the acoustic injury," he said.

Dr. Thanos Tzounopoulos of the University of Pittsburgh School of Medicine supports the theory that brains of tinnitus patients are different than others. He has been studying the brains of laboratory mice after they have been exposed to loud noise.  "We found that the response to stimulation in tinnitus mouse, in mice, that had behavioral evidence of tinnitus was much larger compared to the responses that we found to [in] normal mice," he said.

The mice were exposed to 116 decibels of sound, equivalent to an ambulance siren, for 45 minutes.  Weeks later, researchers exposed the mice to lower decibels of noise, played for a time, stopped briefly and then resumed in a pulsating pattern.  Normal mice had less reaction while mice with tinnitus heard the ringing noise and were startled when the louder pulsing noise came back.

These images reflect the differences in the hyperactivity in the mice with tinnitus.

The American Tinnitus Association says ringing, buzzing or humming becomes more common as we age.  But the scientists are worried about younger generations who frequently listen to MP3 players and other devices that deliver loud music.  As they grow older, their risk of developing tinnitus is much higher and it may be much harder by then to stop the music.