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How does a cochlear implant work?
Hearing loss is usually the result of damage to sensory cells in the inner ear (called “hair cells”) which send signals to the brain via the auditory nerve resulting in the perception of sounds. Even though deaf individuals have damage to these hair cells, there are many usable nerve fibers within the auditory nerve that can be stimulated by the cochlear implant’s electrical signals. A cochlear implant is different from a hearing aid. A hearing aid makes sound louder – called amplification. A cochlear implant bypasses the normal outer and middle ear and directly electrically stimulates the nerve responsible for hearing. Because the insertion of the cochlear implant can cause damage to the sensory cells of the inner ear, it is typically reserved for those with severe sensory hearing loss who do not benefit from hearing aids.
There are two main components to a cochlear implant:
1. The internal receiver/stimulator (implant) which is surgically placed under the skin and in the ear.
2. The external speech processor (headpiece) which is not implanted and is worn either behind the ear (ear-level speech processor) or on the belt (body-worn processor).
Sound is picked up by the microphone on the speech processor, which converts the sound into an electrical signal. This signal is then “encoded” or converted to specific patterns or pulses that is then sent to the transmitting coil of the speech processor. The signal is then sent across the skin inductively (i.e. there is no direct connection with the implant) to the receiving coil of the internal receiver/stimulator (the implant). The implant then sends the encoded electrical signal to the electrode array which has been implanted into the cochlea (inner ear). Multiple channels and points of stimulation now fire in a pattern that the cochlea can recognize stimulating the auditory nerve. The auditory nerve picks up these signals and transmits them to the brain (auditory cortex) where they are perceived as sound.