Music for Deaf Ears

A magnified image of the U-M electrode array that transmitted sounds to the brain when it was implanted in the auditory nerves of research animals. Initial results suggest the device could have advantages over cochlear implants, the technology currently used to restore partial hearing in people with profound to severe hearing loss. The array has 16 stimulating sites spaced 100 micrometers apart — about the width of a human hair.

Scientists at the Kresge Hearing Research Institute have shown in animals that a tiny, ultra-thin electrode array implanted directly in the auditory nerve can transmit a wide range of sounds to the brain. U-M scientists believe the new hearing-assist technology could one day be a superior alternative to current cochlear implants.

Electrode array implants could improve the ability of profoundly and severely deaf people to hear low-pitched sounds common in speech, hear conversation in a noisy room, identify high and low voices, and appreciate music — areas where current cochlear implants have significant limitations, says John C. Middlebrooks, Ph.D., a professor of otolaryngology and of biomedical engineering.

Middlebrooks explains that cochlear implants are designed to stimulate the auditory nerve and other cells to produce a sensation of hearing. But their location, separated from auditory nerve fibers by fluid and a bony wall, is a limitation.

“Access to specific nerve fibers is blunted,” Middlebrooks says. “The effect is rather like talking to someone through a closed door. Because the electrode array is in intimate contact with nerve fibers, it achieves more precise activation.”

The next step will be testing the device over time to see if it is safely tolerated by the auditory nerve, according to Middlebrooks. If the initial success in animals is borne out in further tests, he says that a human auditory nerve implant is probably five to 10 years away.

—Anne Rueter

For an expanded version of the story:
www.med.umich.edu/opm/newspage/2007/hd.htm