The Science and Theory behind Cochlear Implants

By Hugh Darrow

Excerpt from a paper in NeoNature, February 2010.

A cochlear implant is a small electronic device implanted into the cochlea which aims to restore a very basic level of hearing to the deaf or severely hard of hearing. They are the most widely used neuroprosthetics in the U.S.

In order to understand how a cochlear implant works, one must first understand the how the human ear works. Sound waves travel through the air and are funneled into the auditory canal by the pinna - the outer part of the ear that we can see. The sound waves travel down the auditory canal and put pressure on the tympanic membrane -- also known as the eardrum -- causing vibration of the ossicles on the other end of the eardrum. This vibration continues through the ossicles and puts pressure on the oval window attached to the cochlea.

The cochlea is where the sensation of hearing occurs. It is a fluid-filled space that spirals like a sea shell. Within the spirals of the cochlea are small hair cells called the organ of Corti. When pressure is put on the oval window, the fluid within the cochlea moves, and some hair cells are pressed down. When this happens, the hair cells become activated and transmit this information to the brain. Different perceptions of sound are based on the different combinations of sound waves pressing down various hair cells in the organ of Corti within the cochlea. People who are deaf or hard of hearing may have an ineffective cochlea or damage to that area. They may also have damage to the ossicles that transmit sound vibration.