What is a Cochlear Implant and How Does it Work?

First and foremost, a cochlear implant is the ultimate achievement in a continuing quest, which has persisted for more than four centuries, to alleviate the difficulties of those who are hard of hearing. During this quest, the fundamental principle of providing various means by which to amplify sounds as the only viable solution has persisted until relatively recently, and it was only the methods by which the amplification was achieved that differed. The ear trumpets and similar devices employed the basic principles of acoustics until, with the invention of the telephone, electrical amplifiers became possible. An evolution culminating in today’s solid state digital electronics has resulted in near-invisible hearing aids with exceptional performance and wireless functionality. Those with profound sensorineural deafness, however, remained condemned to a world of silence until the development of a working cochlear implant in the late 1970s. While conventional amplification aids help to manage hearing loss resulting from reduced conductivity, the delicate hair cells within the middle ear that convert mechanical energy into nerve impulses for transmission to the brain are intact. For subjects in whom these sensory cells are badly damaged or missing, no amount of amplification can result in a nerve impulse. Instead, a device that is designed to stimulate the auditory nerve directly is the only possible means to assist such patients. A typical unit consists of one or more microphones, connected through a speech processor to a transmitter that is positioned behind the ear. The transmitter is tethered magnetically to a tiny receiver implanted beneath the mastoid bone. This, in turn, sends signals to an array of electrodes that terminate in the cochlea and which act then stimulate the auditory nerve. These electrical stimuli are received by the brain as a pattern of signals that closely resembles that produced in hearing subjects by speech and music, and which the patient can quickly learn to understand. The surgery is surprisingly quick, as is the recovery time, and patients can often detect a few words almost at once. Generally, though, a period of rehabilitation, which tends to vary between one individual and another, will be required by the recipient of a cochlear implant before he or she will enjoy the full benefits of the procedure. Implantation, however, is not for everyone and will only be undertaken after a thorough evaluation by an audiologist and the attending surgeon. Primarily intended for those with sensorineural hearing loss who are unable to benefit from a conventional hearing aid, it is also offered to children who are deaf from birth, as well as to those whose conductive deafness has proved far too severe to be managed with a hearing aid.

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