How the ear protects your hearing


earCall it a natural earplug: Your ears appear to be able to automatically turn down certain frequencies to protect your hearing, and a new study provides more details about how this mysterious process works.

Although it’s too early to know for sure, the research could lead to drugs that protect the ear from dangerous noise, said study author Paul Fuchs, co-director of the Center for Sensory Biology at the Institute for Basic Biomedical Sciences at Johns Hopkins School of Medicine. “We don’t really know how things work in the ear at a cellular and molecular level. We’re just starting to make those discoveries.”

At issue is the ear’s ability to inhibit one frequency band while leaving another

intact, Fuchs said. “Say you’re in a factory where there’s lots of loud, low-frequency noise from the machinery,” he explained. “It’s conceivable that this could turn down

the part of the cochlea hit by low frequencies.”

The system is somewhat akin to a stereo system that allows listeners to adjust the treble and bass, Fuchs said. Research has shown that this can help protect the ear from permanent damage caused by loud sounds, he said.

The system can also “help us to more clearly hear sounds in a noisy background” by allowing us to distinguish between sounds, said John J. Guinan Jr., a professor of otology and laryngology at Harvard Medical School.

In the new study, Fuchs and colleagues in the United States and Argentina genetically engineered mice to have a greater ability to turn down certain frequencies. The findings appear in the Jan. 20 online issue of PLoS Biology.

The researchers found that the mice were better able to withstand 100-decibel sound that was blasted at them. That level of sound, which can cause permanent hearing damage, is akin to the noise from a chain saw or a loud rock concert.

“These animals were less sensitive to traumatic sound,” Fuchs said, although they could still suffer hearing loss. But might information about the ear’s volume control system in mice hold potential benefit for humans?

“One possibility,” Guinan said, “is that we can predict who is likely to have their hearing damaged by loud sounds and who is resistant.” He called the research “a well-done study with believable results.”

The findings might also lead to drugs that could “prevent noise-induced hearing loss, one of the most common forms of acquired, permanent hearing loss, as can occur in recreational activities, such as hunting or shooting, and from occupational settings, including factory or military work,” said Robert D. Frisina, associate director of the University of Rochester’s International Center for Hearing and Speech Research.

— HealthDay News

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