Tags: hearing | loss | brain

If You Can't Hear at Parties, Blame Your Brain

Wednesday, 31 Dec 2008 10:35 AM

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NEW YORK — It's almost New Year's Eve, a time for plunging into boisterous crowds bathed in loud music. And for some of us, that means turning to an old friend and hearing things like this:

"Did you know (BOOM-da-da-BOOM) went over (Bob! You look wonder-) so she said (clink-clink) and then I (Here, have another one) what would you do?"

Huh? Too noisy to hear! But wait — how come these younger people understood what she said? What's wrong with your ears?

Actually, part of the problem may be your brain.

In fact, it may lie in your brain's dimmer switch for controlling the input from your ears. That bit of brain circuitry appears to falter with age, and scientists are getting some clues about why.

If you have trouble understanding conversation in a noisy room, you're experiencing what's sometimes called the cocktail party problem.

That can be one of the first signs of an age-related hearing loss — a more general problem that can creep in during middle age, and affects one-third of adults ages 65 to 75.

Scientists are still trying to piece together why our hearing goes downhill with age, with the goal of trying to slow it or even reverse it.

When it comes to the cocktail party problem, the dimmer switch is a piece of that story, though it's not clear just how big a factor.

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

Scientists have long known that the brain not only receives signals from the ears, but can also talk back to them. And when there's too much noise, this dimmer-switch brain circuitry tells the ears to reduce their flow of signals to the brain.

This helps the sensitive auditory system handle loud sounds that otherwise would overwhelm it and become distorted, as when a radio is turned up too loud for the speaker to handle. In addition, 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, Frisina said.

The brain has an added trick for focusing on a particular person's speech rather than competing conversations, Frisina said. Since you're probably facing the person you want to hear, his words arrive at both your ears at the same time and at the same volume. The brain can use that, along with the dimmer switch, to home in on that person's speech, Frisina said.

Frisina and colleagues published evidence in 2002 that the dimmer switch effectiveness declines with age. The drop-off showed up in middle-aged people (ages 38 to 52) and was even worse in people past age 62.

Then they showed the same thing happens in mice, which meant they could study those animals to get clues to what's going on in people. Just last year, they found a possible cause in mice for the decline: reduced supplies of a key structure on the surfaces of the nerve cells in the dimmer-switch circuitry.

Now 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.

The hope, of course, is to understand the details of the problem and find a way to intervene to slow down the age-related hearing problem, 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.

Another crucial element lies within the inner ear, where sound is converted to nerve signals. That's accomplished by cells that use delicate hairs to detect sound waves. These hair cells can be damaged by aging and by long hours in loud environments like rock concerts.

Loss of those cells makes it harder to understand speech in noisy rooms. For example, it can hinder one's hearing of high sound frequencies, like those of certain consonants. Losing those consonant sounds can make words hard to understand in noisy situations.

"What you're hearing is more of a mumbling sensation than actual clear speech," said Anne Oyler of the American Speech-Language-Hearing Association.

While scientists continue to study hearing problems, people who have trouble understanding their fellow partygoers can take some steps to help themselves. Oyler suggests facing the speaker directly to get facial cues that might fill in some blanks. And don't be shy about admitting the problem and suggesting a move to a quieter place.

"A lot of people, even some people with normal hearing, have trouble hearing with background noise," Oyler said. "You can say, 'I'm sorry, I'm having trouble hearing you. I want to know what you have to say.'"

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