Development of a novel eighth-nerve intraneural auditory neuroprosthesis

Cochlear nerve stimulation using a linear array of electrodes, the cochlear implant, has become an accepted treatment for profound deafness. Major limitations of this technology are high threshold of stimulation, poor performance in a noisy background, cross-talk between electrodes, unsatisfactory channel selectivity, and variable reconstruction of frequency space. A novel auditory neuroprosthesis is proposed that is expected to overcome these problems by implanting an array of three-dimensional microelectrodes, the Utah Electrode Array, directly into the cochlear nerve.

We have conducted acute, extending for up to 12 hours and semichronic, extending for up to 52 hours, electrophysiological experiments, radiologic and histologic studies in 12 cats.

The electrically evoked auditory brainstem response was used as a means to characterize the threshold, dynamic range, and stability of cochlear nerve stimulation through the implanted Utah Electrode Array neuroprosthesis. Plain film, computed tomographic, and histological studies were conducted to determine the result of the implant.

The electrically evoked auditory brainstem response thresholds were approximately one to two orders of magnitude lower than those evoked with conventional cochlear implants. We were able to close the cochleostomy, bring the cat into normal anatomical position, and obtain stable electrically evoked auditory brainstem responses for up to 52 hours. Plain film and computed tomographic studies indicated that the Utah Electrode Array neuroprosthesis was in the intended position in the nerve. Histological studies did not reveal hemorrhage or significant damage to the nerve.

Because the presented stimulation paradigm appears to significantly mitigate some of the problems of conventional cochlear implants, it may offer a new therapeutic approach to profound deafness.