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PROBLEM: We're always told that turning the volume up too high or standing too close to speakers is going to permanently damage our hearing, and that once there's ringing or temporary hearing loss it means we've done permanent damage. Why does that happen, really?

METHODOLOGY: Australian researchers interested in ways our ears may have adapted to accommodating loud sounds bred mice lacking a specific gene receptor thought to be involved in protecting the inner ear. They then exposed them to sustained periods of moderately loud noise while measuring their loss of hearing sensitivity (by monitoring brain responses).

RESULTS: The regular mice, like humans, had worsened hearing for about 12 hours after hearing the high-decibel sound. The genetically modified breed meanwhile experienced far less temporary hearing loss. However, in the experiments where the sound was loudest, the latter experienced more permanent damage to their ears.

IMPLICATIONS: The researchers were able to demonstrate that when sound levels rise, the inner ear releases a hormone that binds to a receptor that was missing in the genetically modified mice. In normal circumstances, this reduces the amount of sound transmitted by the ear's hair cells, causing our hearing sensitivity to worsen for a while. During that time, we might be less able to hear a pin drop, but we are more able to tolerate louder-than-usual sound without damaging our ears. The mechanism appears to be "otoprotective" (oto meaning ear). Loud music can be damaging, but having temporary ringing or deafness tells us the damage could be worse.

"ATP-gated ion channels mediate adaptation to Q:4 elevated sound levels" is published in Proceedings of the National Academy of Sciences.

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