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The ear's amplifier

Yale Medicine Magazine, 1998 - Winter/Spring


Using sound and music to study the delicate workings of hair cells may provide answers about hearing loss.

The body's musical sense might go all the way down to the cellular level.

Well, maybe it isn't music in the traditional sense. But Joseph Santos-Sacchi, Ph.D., professor of surgery (otolaryngology) and of neurobiology, is studying cells in the inner ear that seem to dance in response to music. He even has a videotape of the cylindrical cells dancing to the sound of the William Tell Overture.

"This cell movement is unique. It's unlike any other movement found in the body." says Dr. Santos-Sacchi (who denies any real musical talent but has a saxophone, clarinet and keyboards at home.) Since hair cells allow us to hear, understanding how this unusual dancing movement relates to cell function could be a key to eventually unlocking treatments for certain forms of hearing loss.

When hair cells in the inner ear detect a mechanical disturbance–a sound wave–they respond by sending information about the sound to the auditory nerve and on to the brain. There are two types of hair cells: inner and outer.

"Most of the information you hear comes from the inner hair cells," he says. But Dr. Santos-Sacchi studies the outer hair cells, which have very few direct connections to the auditory nerve but still play a role in sound reception.

The outer hair cells seem to actually change their length–by changing the surface area of their cell membranes–in response to sound. "Presumably, they start jumping up and down," he says. "At least, that's what happens in vitro."

Dr. Santos-Sacchi takes the outer hair cells from guinea pigs and studies the electrical signals that correspond to the cells' motion. If the researchers can figure out how to modulate that motility, it may be a step towards understanding how the outer hair cells work.

That's important because the outer hair cells seem to be part of a sort of "cochlear amplifier" that uses a mechanical feedback mechanism to boost the vibration of the basilar membrane of the cochlea.

Outer hair cells tend to be the first to go in response to any insult, such as disease or loud noises. They don't regenerate in mammals, so the result can be hearing loss.

"Presumably, the way that works," Dr. Santos-Sacchi says, "is that the inner hair cells are no longer getting that boost."