A cochlear implant is an electronic device that partially restores hearing. It can be an option for people who have severe hearing loss from inner-ear damage and who receive limited benefit from hearing aids.
Unlike hearing aids — which amplify sound — a cochlear implant bypasses damaged portions of the ear to deliver sound signals to the auditory (hearing) nerve.
Cochlear implants use a sound processor that fits behind the ear. The processor captures sound signals and transmits them to a receiver implanted under the skin behind the ear. The receiver sends the signals to electrodes implanted in the snail-shaped inner ear (cochlea).
The signals stimulate the auditory nerve, which then directs them to the brain. The brain interprets those signals as sounds, though these sounds won't be just like normal hearing.
It takes time and training to learn to interpret the signals received from a cochlear implant. Within a year of use, most people with cochlear implants make considerable gains in understanding speech.
Mayo Clinic's approach