Cochlear Implant History (AB)

Cochlear implant history

Two-hundred years ago, a scientist by the name of Alessandro Volta inserted metal rods attached to an active circuit into his ears. He described the sensation as similar to the sound of boiling water. This was the first documented attempt to provide electrical stimulation directly to the auditory system.

Although additional attempts continued throughout the next 50 years, by the mid 1800's the thought of using electrical stimulation as a therapeutic method was rejected. It wasn't until the 1930's that the effects of electrical stimulation on hearing were studied again. Two independent research teams, one from the United States and one from the Soviet Union, found that hearing sensations were achieved by individuals who were deaf when they received electrical stimulation to the middle ear. Neither of these investigations, however, resulted in a practical application for a hearing implant primarily because the technical difficulties encountered at the time could not be overcome.

By the late 1950's, scientists in France reported the first successful electrical stimulation of hearing nerves by inserting an electrode in a deaf subject's inner ear. The patient perceived the rhythm of speech and reported that the stimulation provided assistance in lipreading. This was the beginning of the development of modern-day cochlear implants.

Throughout the 1960's tremendous energy was devoted to studying and developing cochlear implants, and by 1970 the first wide-spread clinical application was underway. These early generation cochlear implants were single-channel devices that sent coded information to only one electrode site in the inner ear. These devices provided patients with speech and sound awareness and enhanced lipreading ability, but generally did not provide auditory-only speech recognition.

The introduction of multichannel devices in the 1980's represented a major advance in cochlear implant technology. Multichannel devices stimulate hearing nerve fibers at multiple locations along the length of the cochlea and where all electrodes are stimulated at once, or sequentially, where electrodes are stimulated one at a time.

Stimulating nerve fibers at multiple locations is important because each nerve fiber in the inner ear is "tuned" to a different pitch depending on its location. Hearing nerves are organized so that high frequencies are picked up at the base of the cochlea while low frequencies are picked up at the center or apex. This arrangement is referred to as the "tonotopic" organization of the ear. With the introduction of multichannel systems, the ability to understand speech without lipreading was achieved.

Source: Advanced Bionics