Multielectrode intracochlear implants. Nerve survival and stimulation patterns.

A series of neurophysiological and anatomical experiments have been performed on cats implanted on a long-term basis with scala tympani electrodes. Auditory nerve survival was assessed for both neomycin sulfate-deafened and previously normal-hearing cats three weeks to 30 months after electrode implantation. Acute neurophysiological experiments were performed on nearly all of the cats and the spatial response to electrical stimulation was determined. The results of these experiments suggest that the auditory nerve can withstand surgical implantation and the long-term interface with scala tympani electrodes. In addition, restricted portions of the auditory nerve can be discretely excited with bipolar stimulation. Monopolar stimulation produced a very broad excitation pattern. These findings have important implications for the application of multielectrode prosthetic devices to the profoundly deaf.