Exactly how does a cochlear implant work? Do you just put it on and hear magically? Not quite. Some things have to happen before you can actually hear with the implant.
To understand how a cochlear implant works, you have to look first at how we normally hear. Normally, sound transmissions will cause the eardrum and middle ear bones to vibrate. Those vibrations then get converted into electrical impulses when they reach the cochlea. Then those impulses are transmitted to the brain via the auditory nerve.
However, in a deaf person, this does not happen. So a cochlear implant, which is considered a prosthesis for health insurance purposes, takes over those functions. The electrodes in a cochlear implant are a substitute for damaged hair cells in the inner ear.
External Parts and Internal Parts
A cochlear implant consists of external parts and internal parts. The external parts are the parts that are outside of the body. There is a microphone on the sound processor (or speech processor). The microphone collects the sounds from the environment. The speech processor is similar to a behind-the-ear hearing aid in shape and design. A transmitter that goes on the head is connected to the speech processor. The speech processor takes the sound and converts it to digital (not yet electrical) signals. The processor then feeds these signals to the transmitter through a cable.
The internal parts are inside the body. Under the skin behind the ear is a receiver that has been implanted surgically. The receiver takes in the digital signals generated by the speech processor and changes them to electrical signals (pulses). The receiver sends those electrical signals to the inner ear via a wire that is connected to the receiver.
Inside the wire are tiny electrodes. The wire threads its way into the cochlea. Inside the cochlea is an electrode array that is part of the wire. That electrode array sends the signals to the auditory nerve that then transits them to the brain. The brain knows that the signals are sound, but the implant user has to learn how to interpret that sound.
Sometimes something goes wrong and some of the electrodes may go bad. I personally discovered this soon after my own surgery. I can still use my implant, but the loss of those electrodes means I have lost some hearing ability. I described that experience in the blog post, "Sorry, your electrodes are dead."
The sensation when I turn on my cochlear implant and "snap" the magnetic transmitter into place on top of the receiver, takes getting used to. I find myself plunged instantly in and out of silence as I turn my implant on and off.
Lifespan of a Cochlear Implant
Cochlear implants do not last forever, nor are they immune from failure. A cochlear implant can fail and have to be removed and a new one implanted. In fact, there have been recalls of cochlear implants by manufacturers. About.com readers have also shared their experiences with implant failure. In addition, a question about the expected lifespan of a cochlear implant is answered by an implant manufacturer here at About.com.Sources:
Animation: Normal Ear, Ear with Hearing Loss, and Cochlear Implant Procedure. U.S. Food and Drug Administration. http://www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/ImplantsandProsthetics/CochlearImplants/ucm133345.htm. Accessed December 2010.
Cochlear Implant. Medline Plus. http://www.nlm.nih.gov/medlineplus/ency/article/007203.htm. Accessed December 2011.
Cochlear Implants. National Institute on Deafness and Other Communication Disorders. http://www.nidcd.nih.gov/health/hearing/pages/coch.aspx. Accessed December 2011.
