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Brain Affects Hearing

December 30, 2008

New Year’s Eve is marked by constant celebration and time spent with friends, but if you find yourself straining to hear, it’s your brain – not your ears – that could be to blame.

Scientists are now learning why and how age affects the brain’s dimmer switch for controlling the level of input from your ears.

Researchers say if you have trouble understanding conversation in a noisy room, you’re experiencing what’s sometimes called the cocktail party problem.

It’s just one of the first signs of an age-related hearing loss; it affects one-third of adults ages 65 to 75.

Scientists want to slow down or reverse hearing loss, and are trying to discover why our hearing goes downhill with age.

Researchers say they’re still trying to determine what else besides the dimmer switch contributes the cocktail party problem.

“I think it’s a significant player,” said Robert Frisina of the University of Rochester in New York, who is studying it.

Scientists understand that the brain can receive signals from the ears, and also talk back to them. So, when there’s too much noise, the dimmer-switch brain circuitry tells the ears to reduce their flow of signals to the brain.

Frisina said since background noise at a party tends to be lower-pitched than speech sounds, the dimmer switch probably can block out that distracting noise more than it does the speech.

In 2002, Frisina and colleagues published evidence that the dimmer switch effectiveness declines with age.

They noted the same trends occur in mice, which meant they could study those animals to get clues to what’s going on in people.

Frisina hopes to use genetically altered mice to focus his studies on particular parts of the dimmer switch circuitry. There is some evidence that shortcomings in this wiring harm the inner ear as well, he said.

While it is not yet clear how big a role the dimmer switch plays in the cocktail party problem, Frisina’s work “makes a good case that it’s got to be one of the important factors,” said Charles Liberman, who directs a research laboratory at the Massachusetts Eye and Ear Infirmary.

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