cal practice over the past 10 years has generated renewed interest in the etiology and the methods of assessment of individuals with profound hearing loss. In this section we review the hardware and software components of a cochlear implant, present patient selection criteria for an implant, and discuss speech perception results in postlingually deafened adults with multichannel cochlear implants. The same cochlear implants are used for management of profound deafness in children deafened prelingually (before age 2) and postlingually. The indications and results for children are discussed in Chapter 7.
Cochlear implants attempt to replace the transducer function of damaged inner ear hair cells. Most causes of sensorineural deafness result in injury to the hair cells rather than to auditory nerve fibers. Prolonged deafness eventually affects the auditory nerve, as its neurons rely on neurotrophic factors (proteins produced by hair cells) for their survival. It has been shown that electrical stimulation provided by cochlear implants can prevent neural degeneration (Leake, Hradek, and Snyder, 1999). The devices are continually undergoing modification and upgrading; however, the basic components of the systems have not changed.
The early pioneers of cochlear implants include William House (1976), Blair Simmons (1965, 1966), and Robin Michelson (1971). These individuals were the first to describe the clinical benefits of electrically stimulating the inner ear. House and Michelson described the placement of single electrodes within the scala tympani of the inner ear, while Simmons introduced multiple electrodes directly into the auditory nerve. Their reports in the 1960s were strongly criticized by the scientific community.
The first commercially available implants were produced in 1972 as the House-3M single channel implant. This device was an aid to speechreading and provided an awareness of environmental sounds to several thousand postlingually deafened adults and a few hundred children. Graeme Clark (Clark et al., 1977) and his research team in Australia focused on multichannel stimulation. A commercially available (Cochlear Corporation) multichannel implant with 22 separate channels began clinical trials in 1983. The University of California at San Francisco implant team also began clinical trials in 1985 with a multichannel implant. A variant of this device is now manufactured by Advanced Bionics (the Clarion cochlear implant). Major advances in microcircuitry and speech coding algorithms have been developed over the past 20 years.
In 2003, there were three companies that made commercially available cochlear implants for use in the United States—Cochlear Corporation, Advanced Bionics, and Med El. Each has a slightly different elec-