What is a Cochlear Implant?
What is a cochlear implant?
A cochlear implant is a surgically implanted device which enables sound to be delivered to the individual with severe to profound hearing impairment. The device is available to adults and children.
Research in the area of cochlear implants dates back to 200 years ago when a scientist named Alessandro Volta inserted metal rods attached to an active circuit into his ears. The research continued and in 1950, scientists in France reported the first successful electrical stimulation of hearing nerves by inserting an electrode in a deafened subject's inner ear. The patient was able to perceive rhythm of speech and this stimulation assisted in lip-reading.
Since that time, research in this area has continued and the implant has evolved from a single electrode (channel) device to multiple electrode (multi-channel) devices with a variety of speech coding/processing strategies available. Speech processing strategies are the ways by which the sound is converted into electrical signals that are sent to the brain and interpreted as sound. Today, multi-channel, multi-strategy cochlear implant systems are available. In addition, with improved technology, miniaturization has become possible with a behind- the- ear speech processor (similar to behind-the-ear hearing aids) which is currently available.
The implant procedure involves surgical implantation of the internal receiver and an array of electrodes in the cochlea. External equipment includes a headset (which consists of a microphone and a transmitter) and a speech processor (body-worn or ear-level).
In order to understand how the cochlear implant provides access to hearing, one must first understand how the normal ear works. The hearing mechanism is a complex system made up of three parts; the external ear, the middle ear and the inner ear. In most cases of profound hearing loss, the inner ear does not function normally.
The outer ear consists of the pinna (which collects sound waves) and the ear canal (which delivers the sound towards the eardrum). Once the sound waves reach the eardrum (or tympanic membrane), they cause the eardrum to vibrate, which in turn causes a chain reaction in the three tiny bones (malleus, incus and stapes) in the middle ear. The motion of these three tiny bones generates movement of the fluid in the cochlea. Inside the cochlea there are tiny sensory receptors (hair cells) which are arranged tonotopically -- the cells near the base are most responsive to high pitched sounds and the cells at the apex (in the centre) are most sensitive to low pitched sounds. As the fluid in the cochlea begins to move, these tiny sensory receptors convert these mechanical vibrations into electrical impulses. These impulses are sent to the hearing nerve which are sent to the brain and interpreted as sound.
In most cases of profound hearing loss, the hair cells are damaged or depleted although there are usually surviving nerve fibres. A cochlear implant stimulates the surviving nerve fibres with electrical signals by way of an array of electrodes implanted in the inner ear. Depending upon the information received, certain electrodes will 'fire' -- the basal electrodes providing the sensation of high pitched sounds and the apical electrodes providing the sensation of low frequency sound, much in the same way that the hair cells in a normal cochlea are arranged. The stimulated nerve fibres then carry the electrical signals to the brain where it is interpreted as sound.
A thorough evaluation is necessary in order to determine candidacy for a cochlear implant. This involves a medical evaluation by a physician, a thorough audiological evaluation, speech and language assessments, social assessments and may include psychological assessment. Children must undergo an intensive period of therapy with hearing aids, focusing on teaching the child to learn to listen so that one may determine the benefit received from traditional hearing aids.
Clinical studies to date as well as experience with children who have received a cochlear implant indicate that many profoundly hearing impaired children (even those with no previous auditory experience) can learn to process the speech patterns made available by the implant, and through therapy and teaching, become competent spoken language communicators who function independently in both the educational and social mainstream.
Cochlear Implant Programming
The Clinic is equipped with the equipment for the programming of a number of cochlear implant speech processors from Cochlear Americas, Advanced Bionics and Med-El. The programming of the speech processor is done by an audiologist. The programming involves determining the amount of electrical stimulation necessary for each electrode (or electrode pair) in order to elicit a response to sound. There are several parameters that must be programmed in order for the individual to begin to interpret the information provided by the implant.
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