Institute explains how cochlear implants work

From: Times Picayune - New Orleans,LA,USA - Mar 21, 2004

East Jefferson bureau

The following is some general information on cochlear implants from the National Institute on Deafness and Communication Disorders, or NIDCD.

-- Destruction of cochlear hair cells and the related degeneration of auditory nerve fibers result in the type of hearing loss that accounts for most of the 250,000 people in the United States with profound deafness.

-- The cochlear implant is an electronic device that provides the function of the damaged or absent hair cells by electrical stimulation to the remaining nerve fibers. The implant conveys weak electric stimuli to the vicinity of the auditory nerve.

The electric stimulus activates the nerve, which then transmits a signal to the brain. The brain recognizes this signal and a person then can hear.

-- The cochlear implant has the same function as the hair cells, in that it transforms sound into an electric current that stimulates the auditory nerve.

-- The procedure for the cochlear implant involves two components, internal and external.

-- The internal component or implant package contains an induction coil and an electrode array. With surgery, this implant package is implanted in the temporal bone behind the ear.

-- The electrode array is introduced into the inner ear, the cochlea. An electric current across the electrode array activates the auditory nerve and the result is the person can hear.

-- The external part converts sound waves into electric signals. That part consists of a microphone, a small speech processor and an external coil. The microphone picks up the sound waves and transforms them into weak electric signals. The speech processor modifies these electric signals. They are then sent to the external coil via a cable.

-- When the external coil is placed over the internal coil, signals will be transmitted through the intact skin to the implant and electrode array. The auditory nerve is stimulated, which results in acoustic sensations.

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