Loud noises affect how brain processes speech

Blasting music doesn’t just hurt your hearing—it may actually affect your brain. A new study suggests that listening to sounds above 85 decibels not only increases a person's risk for hearing loss, but also appears to change how their brain processes speech.

It's long been known that frequent exposure to loud noises, such as music, can permanently damage hair cells in the ear. These hairs receive sound and convert the energy into sound signals to the brain. Eventually, the hairs don’t regrow, causing permanent hearing loss.

Researchers from University of Texas at Dallas analyzed the effects of hearing loss on rats. One group of rats was exposed to high-frequency noise at 115 decibels. The second group was exposed to low-frequency noise at 124 decibels. The first group suffered moderate hearing loss. The second group, however, suffered severe hearing loss.

A month after the initial experiment, the researchers found that both types of hearing loss affected brain circuits in the auditory cortex and how the animals processed speech sounds. This area of the brain is tied to understanding and processing sound. It’s similar to a piano scale—brain cells at one end respond to low-frequency sound and brain cells on the other end respond to high-frequency sound.

In the group of rats with severe hearing loss, fewer than one-third of the auditory cortex sites reacted to sound. When the brain cells did respond to noise, it was slowly and with loud sounds in narrow frequency ranges. This group of rats also had difficulty distinguishing a speech task that they had performed before the experiment.

The same results were not seen in the group of rats with moderate hearing loss. They did complete the speech task, although they did react to sounds more slowly and need more stimulation to hear high-frequency sounds than rats with normal hearing.

The study results were published in Ear and Hearing.

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