Listening to iPod may no longer risk hearing-loss

Fearing that listening to your iPod at high volumes could damage your hearing? Worry not, for scientists have now found the key to protect your ear from the deafening noise of music players and those high sound levels in rock shows and dance clubs.

By tweaking a system in the ear that limits how much sound is heard, the researchers have discovered one alteration that shows that the ability of the ear to turn itself down contributes to protecting against permanent hearing loss.

"There's some uncertainty in the field about what this sound-limiting system is used for. Now we've definitively shown that this system functions in part to prevent acoustic trauma," said Dr Paul Fuchs, professor of otolaryngology-head and neck surgery.

For their study, the researchers focused on the nAChR protein found on so-called sensory hair cells in the ear. Nerve cells from the brain release signals that are picked up by nAChR and turn down these sensory hair cells.

The researchers genetically altered a single building block in the nAChR protein and tested mice for their ability to hear.

"This point mutation was designed to produce a so-called gain of function in which the inhibitory effect of ACh should be greater than normal," said Fuchs.

It was found that altered mice were less able to hear soft sounds than normal mice, which indicated that the genetic alteration made in the nAChR protein did indeed further "turn down" the ear.

Later, the researchers asked if the alteration in nAChR, and hence the improved sound-blocking ability of these altered mice, also had the potential to protect from sound damage.

The team blasted 100-decibel sound at mice and again measured their ability to hear.

"One hundred decibels, for me, is painfully loud, and conversation is impossible. But sound levels in night clubs or rock concerts can be that high, and extended exposure to sound at that volume can cause hearing loss," said Fuchs.

And it was discovered that mice with the altered, gain-of-function nAChR suffered less permanent hearing damage compared to normal mice.

"We think this pathway could be a therapeutic target for protecting from sound damage. So far, there is little or no specific pharmacology of hearing. We're still learning how the inner ear works. The encouraging news is that molecular mechanisms like the hair cell's nAChR frequently involve unique gene products, so there is a real chance of finding ear-specific drugs in the future," said Fuchs.

Meanwhile, Fuchs recommended that one should limit the time spent at rock concerts, and wear earplugs to protect hearing.

The study has been published in PLoS Biology.