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Cochlear Implants

This entry describes what a cochlear implant is, how it works, and who may benefit from it. The chapter then discusses limitations of cochlear implants and solutions to overcome these limitations in the future. Finally, the chapter discusses issues related to cochlear implant simulation, accessibility, and impact on Deaf culture. The cochlear implant is a medical device used to restore functional hearing by electrically stimulating the auditory nerve in the damaged inner ear (the cochlea). It is an invasive device, requiring surgery to drill a hole in the skull behind the ear to access the cochlea and an additional hole in the cochlea to place the implant electrodes.

Since the Federal Drug Administration’s (FDA’s) approval of the first commercial device in 1984, more than half a million people have received cochlear implants worldwide, with roughly one half being adult users and the other half being pediatric users. Except for the first FDA-approved 3M/House cochlear implant system that had a single electrode contact in the cochlea and had about 1,000 users, all contemporary devices have multiple electrode contacts ranging from 12 to 24. In 2017, there were five cochlear implant manufacturers, with three having their products available globally (Cochlear, MED-EL, and Advanced Bionics) and two available regionally (Neurelec in Europe and Nurotron in Asia, Europe, and South America).

The contemporary cochlear implant has allowed its average user to carry on a conversation on the telephone. But more important, it has allowed prelingually deafened users to develop relatively normal language, with many of them attending regular schools. The cochlear implant has been considered a medical and technological wonder and is without question the most successful neural prosthesis that has been developed to restore a major human function.

The Cochlear Implant System

A typical multielectrode system consists of an external part and an internal part. The external part includes at least a microphone, a hearing-aid-like sound processor with batteries, and a coil that transmits radio frequency signals to the internal part. The internal part includes at least a coil that receives the radio frequency signals, a receiver and stimulator case, and an electrode array. The transmitting and receiving coils are aligned by magnets across the skin to form an efficient transcutaneous radio frequency transmission link. The receiver and stimulator case is hermetically sealed so that the electronics inside the case are protected from erosion by body fluids and moisture.

Except for earlier versions of the cochlear implant systems that used a ceramic case, all available commercial systems use a titanium case that improves mechanical protection of the enclosed electronics. The intracochlear electrode array consists of 12 to 24 small contacts typically made of 90% platinum and 10% iridium alloy for its low reactive electrical property and high resistance to corrosion. The electrode array may be straight or curved, similar to the snail-like cochlear shape. A return or reference electrode made of the same alloy is placed outside the cochlea as either a peripheral part of the intracochlear array, as a plate attached to the surface of the case, or as an independent array.

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