MPIDS Colloquium: Hearing the light: Optogenetic Stimulation of the Auditory Nerve

When hearing fails, speech comprehension can be restored by auditory prostheses. However, sound coding with current prostheses, based on electrical stimulation of audito-ry neurons, has limited frequency resolution due to broad current spread. We aim to im-prove frequency and intensity resolution of cochlear implant coding by establishing spa-tially confined optical stimulation of spiral ganglion neurons (SGNs). We have estab-lished optogenetic stimulation of the auditory pathway in rodents using virus-mediated expression of channelrhodopsins to render SGNs light-sensitive. Optogenetic stimulation of spiral ganglion neurons activated the auditory pathway, as demonstrated by physiolog-ical recordings and behavioral analysis. Fast opsins enabled SGN firing at physiological rates (hundreds per second). The spatial spread of cochlear excitation was lower for opto-genetic than for monopolar electrical stimulation suggesting improved frequency resolu-tion of coding. In summary, optogenetic stimulation of the auditory nerve is feasible and bears substantial potential for future application in research and hearing restoration.