Biophysical design considerations of the cochlear prosthesis [Abstract]

Abstract

In order for the cochlear prosthesis to transfer sufficient information to primary auditory nerve fibres for recognition of speech-like sounds, it is necessary to electrically excite discrete fibre populations at several points along the cochlear spiral (Tong et al., 1979). In addition, because of the large number of stimulus electrodes and the small volume of the scala tympani in which the electrodes are usually implanted, current transfer must derive from "passive" electrochemical processes in order to preserve the normal biochemical environment of the nerve fibres. From measurements made in the human cochlea during implantation of the cochlear prosthesis, it has been shown that the longitudinal ground current distribution arising from a multielectrode system incorporating a common intracochlear ground electrode is accurately replicated by measurements made in a saline-filled uniform tube of diameter 3-5 rom. Further measurements in such tubes are described which investigate the possibility of improved current localisation by reduction of the ground electrode impedance and the possibility of producing greater electrochemical "passivity" by the use of voltage sourcing in preference to current sourcing.