Cochlear Implants (CI)

Cochlear implants are surgically-implanted devices that stimulate the hearing nerve using electrical impulses. These devices are typically used to restore hearing in persons with severe to profound sensory losses in both ears, but can sometimes also be used for people with problems with auditory neuropathy / auditory dysynchrony (ANAD). In order for cochlear implants to work effectively, the auditory nerve leading to the brain must be intact and functional.

Unlike hearing aids, which provide the existing hearing organ with amplified sound, cochlear implants create an entirely different form of hearing by directly stimulating the nerves inside of the cochlea by way of a tiny electrodes placed along the membrane that contains the sensory cells (hair cells). The cochlear implant device consists of three primary components, one of which is on the outside of the body, and the other two surgically implanted. The sound processor – which can either sit on the external ear similarly to a the behind-the-ear style hearing aid (BTE) or a body-worn device that can be carried anywhere on the front of a person’s torso – takes in sound through a microphone and processes it into electrical signals. The processor is connected to the receiver/stimulator, which sits beneath the skin in a section of the skull that has been shaped to hold it, with a magnet. These two components communicate using radio-frequency signals sent through the skin. The processed sound is then delivered to the cochlea using a series of electrodes called an “array” which directly stimulates the hearing nerve endings. Each electrode stimulates a region along the above-mentioned membrane, representing specific pitches of sound.

A cochlear implant evaluation comprises of a comprehensive hearing test, a consultation with a physician to obtain medical clearance, a mandatory trial period with hearing aids, specific tests to gauge the effectiveness of hearing aids, and pre-surgical counseling. In order to be fit with a CI, a person must be healthy enough to undergo major surgery, demonstrate the motivation and determination necessary to properly rehabilitate the implanted ear, and must meet minimum criteria for hearing aid ineffectiveness. This entire process is of utmost importance, as the surgery required to implant the device typically destroys all of the natural hearing function that may be left in the cochlea. The exception is with hybrid style implants, which preserves the portion of the hearing organ responsible for detecting low-pitched sounds, but still requires invasive surgery and the destruction of most of the cochlea.

Once the device is implanted into the skull, a short period of time is required before the CI can be activated to allow the surgical site to heal. The area of implantation is then evaluated by the surgeon or physician responsible for the patient, after which the external device can be attached to the implanted portion of the device and turned on. From this point on, an audiologist takes over the duties of maintaining and adjusting the CI to maximize the benefit the patient receives from the device. Because “hearing” with a cochlear implant is so much different than natural hearing, recipients of CIs need to be re-trained how to perceive sound. This process – called aural rehabilitation – is undertaken using specialized speech and listening exercises, along with adjustments called “mapping” to calibrate the CI to the patient’s preferences and needs. Assistive listening devices (ALD) such as FM and induction loop systems can also be used in conjunction to provide better sound quality to the CI user. The external part of the device can be removed at any time, but without it the person with the implant will be completely deaf at least in the ear that the CI was implanted into. Cochlear implants are typically powered by size 675 hearing aid batteries or rechargeable batteries.

Other Links:

• NIDCD.NIH.gov
• FDA on Cochlear Implants
• ASHA.org
• Advanced Bionics
• Cochlear Americas.com
• Medel.com