A cochlear implant (CI) is an electronic medical device that does the work of damaged parts of the inner ear (cochlea) to provide sound signals to the brain. A National Institute on Deafness and Other Communication Disorders (NIDCD) fact-sheet on cochlear implants says in 2012, the FDA estimated that 324,200 people had received implants worldwide. Currently in 2017, around 45,000 CIs are sold worldwide each year, which brings the total number of CI-users worldwide close to 500000, of which 60% are adults and 40% children.
When there is a very severe to total sensorineural hearing loss it is usually because the hair cells in the cochlea are so damaged that they do not create these electrical signals, or enough of them, to make use of a hearing aid satisfactory. The cochlear nerve is usually intact.
A cochlear implant helps to restore the sense of hearing for individuals with severe-to-profound sensorineural hearing loss. For individuals with this type of hearing loss, hearing aids provide little or no benefit. A CI is the only medical device capable of replacing a sense. It works by bypassing non-functioning parts of the inner ear and providing electrical stimulation directly to nerve fibres in the cochlea. A CI system consists of two parts: an externally worn audio processor, which sits comfortably behind or off the ear, and an internal cochlear implant, which is surgically placed just under the skin. The speech processor is connected to a headpiece with a microphone to pick up the sound waves. The processor converts them into minute electrical signals. The headpiece has a transmitter, which sends the electrical signals through the skin to the receiver and internal implant. The transmitter is held in place over the internally implanted receiver above the pinna, or outer ear, by a magnet. The electrical signals from the processor are sent to the electrodes. Like the hair cells in the normal ear, the electrodes at the beginning of the electrode array are usually stimulated by the high frequencies and those at the end of the array, near the apex of the cochlea, by the low frequencies. The signals then pass along the cochlear nerve and are decoded in the auditory centre of the brain and the implant user “hears”.
Some cochlear implant users hear very well indeed. They can even use a telephone quite normally and go about their daily life reasonably well. Not everyone is so successful, but most people find conversation easier and more relaxed because their hearing helps them to lip-read better even if they cannot understand speech through hearing alone.
When children with a profound hearing impairment are implanted early enough (< age 2) and bilaterally, their hearing and speech can develop in a manner similar to that of their hearing peers. In these cases, spoken language appears to emerge almost naturally and most of these students attend regular school. But every child is different, and the child’s ultimate level of success will depend on a number of factors which cannot be predicted before implantation. For that reason, it is important to monitor the development of the children very well and multidisciplinary.