Air Date: Week of February 25, 2005

Living on Earth's Jennifer Chu reports that hearing loss could be all in the brain.

Transcript

CURWOOD: It's Living on Earth. I'm Steve Curwood. And coming up: the violent history of humans and wolves. First, this Note on Emerging S cience from Jennifer Chu.

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CHU: If you've been hard of hearing lately it may not be your ears that are failing, but your brain.

According to studies at the International Center for Hearing and Speech Research in Rochester, what people consider loss of hearing as we age has to do with our brain's decreased ability to organize information, not with our inability to hear.

Generally, the brain is a master at sorting through many noises in order to concentrate on one voice, for example. But as we age our brain's filter system, located in the brain stem in the back of the neck, gets overwhelmed with information, making it harder to pick out key sounds or phrases.

Scientists proved this by testing the hearing capacity and the brain's feedback system of 30 subjects in a noisy room. They played sounds into one ear and measured how much of the sound was processed. They then administered hearing tests to these same subjects. They found even those with excellent hearing still had difficulties picking out sounds in a crowded room. Although the reason behind this distinction is unclear, researchers think it may have something to do with a breakdown in the calcium regulation in the brain stem.

These findings may help to counter what's called "the destructive feed back loop." That happens when people compensate for another person's hearing loss by speaking louder to them and doing real damage to otherwise healthy ears. That's this week's Note on Emerging Science, I'm Jennifer Chu.