When the hair cells of the cochlea have been damaged or destroyed and therefore incapable of converting mechanical energy from the middle ear into electrical impulses, a cochlear implant can create impulses in the cochlea that the brain can learn to interpret as sound.
CIs were developed in the 1960s to assist those with profound deafness due to sensorineural hearing loss; they have been FDA-approved since 1985. While the CI will not restore normal hearing, it can give a person with severe to profound hearing loss an enormous benefit by providing auditory stimulation that was unachievable with hearing aids alone. This provides an enhanced understanding of his/her environment and can greatly help the understanding of speech.
The device consists of a microphone and speech processor worn outside the body, similar to a traditional hearing aid, as well as a transmitter that is surgically placed below the skin behind the ear. This transmitter sends impulses to electrodes implanted in the cochlea, which then travel up the auditory nerve to the brain.