| Cochlear nerve stimulation using a linear array of electrodes, the Cochlear Implant, has become an accepted and effective treatment for profound deafness. Major limitations of this technology are high thresholds of stimulation, poor performance in a noisy background, cross talk between electrodes, unsatisfactory channel selectivity and limited reconstruction of frequency space. In this research, animal and cadaveric human experiments were conducted to develop a novel auditory neuroprosthesis that is expected to overcome these problems by using the Utah Electrode Array (UEA) to effect direct intraneural stimulation of the cochlear nerve. Three specific issues were investigated:; First, the possibility of UEA implantation was investigated in cadaveric human temporal bone studies and an appropriate animal model was developed. Nerve viability was demonstrated in the animal model using serial Auditory Brainstem Responses during the surgery.; Second, acute and semichronic animal experiments were conducted via implanted UEA's to determine the electrophysiological characteristics of the implanted arrays. Plain film x-ray, computed tomographic and histologic studies were also conducted in the animal model to demonstrate the postimplant position of the UEA in the nerve.; Third, the focal nature of intraneural stimulation was examined in the animal model using fiber excitation overlap studies between pairs of electrodes. The overlap of stimulated fibers was explored as a function of latency, electrode separation and current levels of the stimulated electrodes.; In conclusion, this dissertation has demonstrated the surgical feasibility, the electrophysiological parameters and encouraging levels of electrode independence in this piece of work. We expect these results to provide an entrée into chronic feline experiments to demonstrate the biocompatibility and long-term viability of the implant. The successful experiments of which will set the stage for human experiments, making the proposed auditory neuroprosthesis a clinical reality. |
