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Restoration of acoustical triggered avoidance behavior via optogenetic cochlear stimulation
18 April 2018 (online)
Electrical cochlea implants (CIs) represent the state of the art concerning hearing restoration in profoundly hearing impaired enabling open speech comprehension in most patients. The current spread, caused by electrical stimulation of spiral ganglion neurons (SGN), generates wide electrical fields leading to activation of large subsets of SGNs, which limits the number of separate channels and thus limits frequency and intensity resolution. Optogenetic modification of SGNs – expression of light-gated ion channels in the cell membrane of SGN via gene transfer – allows stimulation by light. Focusing light to activate small subsets of SGNs could then increase frequency and intensity resolution of optical CIs.
As already shown, SGNs of adult Mongolian gerbils could be equipped with the channelrhodopsin-2 variant CatCh via an intracochlear injection of adeno-associated-viruses (AAVs), which provided activation of the auditory system by optical cochlear stimulation. In this study an optical fiber was implanted via the round window in the cochlea of those animals. Using a shuttlebox paradigm animals learned avoidance behavior triggered by optogenetic cochlear stimulation with hit rates up to 95% and low irradiance thresholds (2µV). This acquired avoidance behavior could be directly linked to acoustic stimulation. A different set of animals was deafened ototoxically after successful acoustical shuttlebox training. Following appropriate intracochlear AAV-injections, avoidance behavior could be restored by optical cochlea stimulation.
In conclusion, this study demonstrates the possibility of learning behavioral tasks via optogenetic cochlear stimulation. Direct transfer of optical triggered to acoustical triggered avoidance behavior and vice versa suggests similarity of percepts.