Objectives/hypothesis: Although cochlear implants have been successfully used by many individuals with profound hearing impairment, limitations still remain with this approach to hearing restoration, including poor stimulation selectivity because of cross-talk between electrodes and poor low-frequency percepts. These limitations may be mitigated by direct intraneural stimulation of the auditory nerve by way of an array of penetrating microelectrodes. Such an approach should provide focal stimulation and selective activation of the nerve fibers, thereby minimizing cross-talk among implanted stimulating electrodes and evoking narrow-band frequency percepts.
Study design: We investigated the activation of primary auditory cortex evoked by such direct intraneural electrical stimulation of the auditory nerve.
Methods: We implanted 11 penetrating microelectrodes in the cat auditory nerve, simulated the nerve by way of these electrodes, and recorded the evoked neuronal activity patterns in cat primary auditory cortex. We compared these activation patterns with acoustically evoked cortical activity patterns obtained in a different animal.
Results: Our results showed that direct stimulation of the auditory nerve evoked localized activity patterns in primary auditory cortex similar in spatial extent to those evoked by acoustic stimulation and that the extent of cortical activation by both acoustic and electrical stimuli was graded with stimulus intensity. These results suggest that the implanted electrodes can excite independent and small populations of nerve fibers.
Conclusion: This study demonstrates the functional feasibility of direct intraneural auditory nerve stimulation with an array of penetrating microelectrodes and that such an approach could form the foundation for an auditory prosthesis with improved frequency coding.