Age-related hearing loss is often blamed on the ear, but new research suggests the culprit may be the brain itself.
Researchers at the University of Rochester have found the cause of some cases of hearing loss – a common problem in the elderly – is located in the brain stem, the first stop that acoustic information makes after it leaves the ears. Their findings were reported last month at the Association for Research in Otolaryngology.
“We are finding more and more subtle problems in the way the brain processes information as we age,” said Robert Frisina, a professor of otolaryngology at the university’s medical center. He and his colleagues have studied people of all ages with normal inner-ear function and found that aging leads to more difficulty processing auditory information. “Many of these older people, even with normal ears, may have trouble understanding a conversation. And we think we have figured out why. Their brains are aging,” Frisina said.
About half of people in their 60s suffer noticeable hearing problems, and that number increases substantially as the decades progress. Three-quarters of people in their 80s can’t hear as well as their younger counterparts. The majority of older people with hearing loss have moderate to severe impairments, Frisina said.
People lose the ability to decipher high-pitched acoustic information. But Frisina said that the chief complaint is that they don’t understand speech when background noises are present.
The scientists invited adults into the laboratory, identified those with normal inner-ear processing and selected only those people for the study. They were hooked to brain scanning machines as sounds were fed into their ears.
That’s when the researchers found that younger people could block out background noise and interpret speech much better than older people. And the brain showed evidence of this age-related deficit. In the brain stem, Frisina explained, there is an area that sorts out speech from noise. This region shows signs of wear and tear as people age, starting as early as the 30s and 40s.
Brain centers involved in “timing,” or how the brain processes speech and background noise, also have been identified in animals. And researchers recently found that a “feedback” system that normally limits background noise by turning the volume down doesn’t work as well in old people.
Frisina suspects that these timing and feedback problems may account for many complaints of hearing loss among older people. If he’s right, hearing aids do very little to help with this kind of problem.
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