Afterward, she was surprised and delighted to hear the chirping of birds and the rattling of plastic bags. Jeanne also noted that “no medical doctor ever suggested that I might check into the possibility of an implant. … Please bring this operation to the attention of your hard-of-hearing readers.”

About 15,000 adults and 10,000 children in the United States have had cochlear implants, designed for those with damaged hearing-hair cells in the inner ear. Such damage is the most common cause of hearing loss and can be triggered by congenital disorders, meningitis, drug therapies and other causes. However, because the auditory nerves or neurons remain intact, a surgical implant can be used to compensate for the lost hair cells.

The remarkably complex yet elegant human ear can be divided into three sections: the outer, middle and inner ears. Sound or acoustic pressure waves are guided by the outer ear to the three smallest bones in the human body, descriptively known as the hammer, the anvil and the stirrup. These bones, in the middle ear, mechanically vibrate in response to the external sound waves. The vibrations cause fluid in the cochlea (a snail-shaped organ in the inner ear) to move, in turn displacing the attached basilar membrane in the cochlea.

Some of the 16,000 hair cells on this membrane then move in response, causing an electrochemical firing of auditory neurons, which send electrical impulses to the brain so that the initial sound waves can be identified.

If the hair cells are damaged, the entire process is short-circuited. Unlike hearing aids, which simply amplify sound waves, cochlear implants are meant to serve as an artificial bridge between the remaining working parts of the ear, effectively replacing the hair cells on the basilar membrane.

A cochlear implant is surgically inserted under the skin behind the ear. It essentially consists of four parts: a microphone, a speech processor, a transmitter and a set of electrodes. Sound waves are collected by the microphone and sent to the speech processor, which converts these sounds into a set of signals to the transmitter. The transmitter converts the signals into electrical impulses, which are then used by the electrodes to stimulate the auditory neurons in a manner similar to their natural stimulation by hair cells.

A cochlear surgical implant is costly (about $60,000), but as technology continues to advance, this expense should decrease. For perspective, consider that the estimated life-time cost of special education and other services for a severely hearing-impaired child is $1 million . And as Jeanne Leffers observed when comparing a lifetime of hearing aids to her implant, “the difference in the quality of my hearing was tremendous.”

By Gerard Voland
http://www.fortwayne.com/mld/journalgazette/living/14528270.htm