Performance of multisite silicon microprobes implanted chronically in the ventral cochlear nucleus of the cat

A central auditory prosthesis based on microstimulation within the ventral cochlear nucleus (VCN) offers a means of restoring hearing to persons whose auditory nerve has been destroyed bilaterally and cannot benefit from cochlear implants. Arrays of silicon probes with 16 stimulating sites were implanted into the VCN of adult cats, for up to 314 days. Compound neuronal responses evoked from the sites in the VCN were recorded periodically in the central nucleus of the contralateral inferior colliculus (ICC). The threshold and growth of most of the responses were stable for at least 250 days after implantation of the arrays. The responses evoked from the deepest and shallowest electrode sites did exhibit some changes over time but none of the thresholds exceeded 10 microA. The thresholds and growth of the compound responses from most of the stimulating sites were very stable over time, and comparable to those of chronically implanted single-site iridium microelectrodes. Multiunit neuronal activity evoked from the stimulating sites in the VCN was recorded along the dorsolateral-ventromedial (DLVM) axis of the ICC. The distribution, span and degree of overlap of the multiunit activity demonstrated the utility of the multisite, multishank array configuration as a means of accessing the neuronal populations in the VCN that encode various acoustic frequencies. These findings are encouraging for the prospects of developing an auditory prosthesis employing multi-site silicon microprobes.