Elizabeth Gudrais in Harvard Magazine:
In the human ear, it takes only a few millionths of a second from the time a sound wave vibrates the receiving “hair cells” to the time the cells generate a neural response. The equivalent process in the human eye, from photon absorption to cellular response, takes a thousand times longer. Hearing “is fast because it’s simple,” says professor of neurobiology David P. Corey of Harvard Medical School.
Well, yes and no. On a basic level, it’s easy to explain how we hear: sound waves, traveling through the air, vibrate the eardrum at certain frequencies and magnitudes, which the brain interprets to identify the sound’s pitch and volume. Betwixt vibration and human perception, though, lie several intermediate steps. Hair cells in the inner ear convert sound waves — a form of mechanical energy — into electrical signals. In the brain, those messages make several transformations between electrical and chemical signals and back again, bouncing from neuron to neuron until they reach a final resting point where we perceive them as sound.
It was 30 years ago when Corey, as a graduate student at the California Institute of Technology, began applying his undergraduate background in physics — and his childhood drive to take things apart and figure out how they work — to the mystery of hearing. In a recent article in Nature, he and his colleagues describe a protein they believe adds a crucial piece to this intricate puzzle.
Scientists have long known that the eardrum vibrates and transmits the vibration to the inner-ear bones, touching off a mechanical process in the cochlea, the snail-shaped organ containing hair cells with bristly cilia that vibrate back and forth in response to sound waves — the greater the cilia vibration, the louder the sound. (A video clip on this magazine’s website, www.harvardmagazine.com/av/hearing.html, shows these cilia vibrating in response to a piece of music.)