Research ArticleNEUROTECHNOLOGY

Multichannel optogenetic stimulation of the auditory pathway using microfabricated LED cochlear implants in rodents

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Science Translational Medicine  22 Jul 2020:
Vol. 12, Issue 553, eabb8086
DOI: 10.1126/scitranslmed.abb8086

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Honing hearing restoration

Cochlear implants provide the brain with auditory information as a treatment for hearing impairment, but electrical implants suffer from channel cross-talk, which can limit the quality of hearing. Keppeler et al. developed multichannel LED cochlear implants that use optogenetics to stimulate spiral ganglion neurons. Testing in rats and gerbils demonstrated improved spectral selectivity and hearing restoration. This study provides the groundwork for further design optimization and scaling of LED-based optical cochlear implants toward clinical translation.

Abstract

When hearing fails, electrical cochlear implants (eCIs) provide the brain with auditory information. One important bottleneck of CIs is the poor spectral selectivity that results from the wide current spread from each of the electrode contacts. Optical CIs (oCIs) promise to make better use of the tonotopic order of spiral ganglion neurons (SGNs) inside the cochlea by spatially confined stimulation. Here, we established multichannel oCIs based on light-emitting diode (LED) arrays and used them for optical stimulation of channelrhodopsin (ChR)−expressing SGNs in rodents. Power-efficient blue LED chips were integrated onto microfabricated 15-μm-thin polyimide-based carriers comprising interconnecting lines to address individual LEDs by a stationary or mobile driver circuitry. We extensively characterized the optoelectronic, thermal, and mechanical properties of the oCIs and demonstrated stability over weeks in vitro. We then implanted the oCIs into ChR-expressing rats and gerbils, and characterized multichannel optogenetic SGN stimulation by electrophysiological and behavioral experiments. Improved spectral selectivity was directly demonstrated by recordings from the auditory midbrain. Long-term experiments in deafened ChR-expressing rats and in nontreated control animals demonstrated specificity of optogenetic stimulation. Behavioral studies on animals carrying a wireless oCI sound processor revealed auditory percepts. This study demonstrates hearing restoration with improved spectral selectivity by an LED-based multichannel oCI system.

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