Towards optogenetic approaches for hearing restoration.

Hearing impairment (HI) is the most frequent sensory deficit in humans. As yet there is no causal therapy for sensorineural HI - the most common form - that results from cochlear dysfunction. Hearing aids and electrical cochlear implants (eCIs) remain the key options for hearing rehabilitation. The eCI, used by more than 0.7 Mio people with profound HI or deafness, is considered the most successful neuroprosthesis as it typically enables open speech comprehension in quiet. By electrically stimulating the auditory nerve, eCIs constitute a brain-machine interface re-connecting the patient with the auditory scene. Nonetheless, there are short-comings resulting from the wide spread of electric current inside the cochlea which limit the quality of artificial hearing. Since light can be better confined in space than electric current, optogenetic stimulation of the auditory nerve has been suggested as an alternative approach for hearing restoration, enabling higher resolution of artificial sound encoding. Future optical CIs (oCIS) promise increased spectral selectivity of artificial sound encoding, and hence might improve speech recognition in background noise as well as processing of music.