The technical aspects of cochlear implantation

The historical development of attempts to provide some hearing ability, in totally deaf patients, by electrical stimulation of the cochlear nerve is reviewed to the point at which single channel intracochlear electrodes were tried in patients. The results obtained with this type of prosthesis are described and discussed in terms of the possible physiological mechanisms involved. Results obtained from promontory stimulation are also presented as a means of patient selection and are compared with the results from intracochlear electrodes. Based on these findings, the approaches for the development of multichannel intracochlear electrodes and for a single channel electrode with speech processing are described. The problems involved with materials, coding, electrode isolation and transmission are considered and the current results in these areas are detailed. Such results imply that the long-term prospects of developing a prosthesis that could provide adequate speech intelligibility are good.