Their finding, published in a recent issue of Nature Neuroscience, could improve the design and programming of hearing aids and cochlear implants by filling in a "black hole" in scientists' understanding of how we hear, say the researchers.
"Sound itself is mechanical, a wave that moves, just like the ripples fanning out from a pebble dropped in a lake," says Paul Fuchs, Ph.D., professor of otolaryngology at the Johns Hopkins School of Medicine. "When the inner ear detects this wave, a burst of chemicals is released and a nerve sends an electrical signal to the brain that carries information about the original sound. But the nature of the chemical burst has been a mystery until now."
With the help of powerful microscopes, the scientists studied individual cells from rat cochleas, tiny coiled structures deep inside the ear where sound is translated into electricity, the language of the brain. Fuchs and research associate Elisabeth Glowatzki discovered that these so-called "hair cells," named for tiny projections that stick up like a spiky haircut, release a barrage of chemical packets to an adjacent nerve in response to sound.
The finding was unexpected, Fuchs says, because hair cells were thought previously only to communicate to nerves by sending a single packet of these chemical transmitters at a time.
"Most cells in the brain normally move one packet to their edges, releasing a single dollop of transmitter that travels the short distance to the nerve," he says. "But hair cells deliver a dramatic burst of packets."
The scientists suggest this means of communication with nerves may help hair cells carefully control the signals they send. "Hearing requires smooth signaling to accurately detect and distinguish a wide range of sound freq
Contact: Joanna Downer
Johns Hopkins Medical Institutions