Cochlear Implants:
A Modern Hearing Miracle

For little Alivia Anderson, being able to hear the simple songs that toddlers love is a miracle of modern technology. Alivia, now almost two, was born with a malformation of the cochlea-the snail-shaped part of the inner ear that channels vibrations to the auditory nerve and the brain. Instead of a hollow spiral for sound to travel through, her cochleae are incomplete, preventing or limiting the ear-to-brain communication that makes hearing possible. But a cochlear implant, which Alivia received at 13 months of age as a patient in the U-M Cochlear Implant Program, has given her the gift of hearing. She is among the youngest ever to receive a cochlear implant.

Terru Zwolan

The University of Michigan has been a leader in cochlear implants since the program, one of the nation's first, was established 16 years ago. Since then, 200 adults and 300 children with hearing impairments have received cochlear implants at Michigan. Receiving a cochlear implant at Alivia's age can be a distinct advantage, says Terry Zwolan, Ph.D., clinical associate professor and assistant research scientist in the department of otolaryngology and director of the U-MCochlear Implant Program.

"We're seeing that the sooner a child gets an implant, the sooner we can tap into speech and language development," she notes. Zwolan and Paul Kileny, Ph.D., professor of otolaryngology, recently completed a study of 102 children with cochlear implants showing that children who received their implants at a younger age did better on word and sentence recognition tests.

Whether children like Alivia will lead normal hearing lives remains to be seen, however. "We have great hopes that these children will lead a normal hearing life," Zwolan says. "But it's so recently that we've started to do these really young children that only time will tell if we're able to fully mainstream them into normal hearing classrooms."

Cochlear implants transform speech and sound into electrical signals that the brain can interpret. They bypass the normal function of the outer ear, hair cells and cochlea, using surgically implanted electrodes and digital signal processors worn on the ear or body to do the work that the damaged or malformed ear structures can't do.

The first step is capturing sound: A small magnetic microphone on the outside of the head, held in place by an implanted magnet, picks up sounds and sends them to a processor. After the processor's programming translates the signals, the impulses travel through a coil to a receiver inside the ear. The implant transmits these signals through dozens of electrodes to the auditory nerve and brain, allowing the wearer to detect and understand speech and noise.

The model that baby Alivia was fitted with uses the first miniaturized device worn behind the ear, as well as a second processor the size of a pager worn on the body. It will allow her audiologists to fine-tune the sound she hears and the way speech is interpreted.

The technology of cochlear implants has improved greatly over the past decade. "In the early years, cochlear implants were suitable only for people who had some residual hearing," says Zwolan. "Now we're getting such nice results that criteria have expanded to include adults and children with severe to profound hearing loss."

"Hearing aids and cochlear implants are very different instruments," says Zwolan. "A hearing aid amplifies normal sound and uses the hearing that a person has to let them process that sound. It's simply making sounds louder. A cochlear implant replaces the hearing inside the cochlea -that's why it's reserved for people who can't benefit from hearing aids."

Zwolan can be reached at zwolan@ umich.edu.