In-silico Framework for Benchmarking Optogenetic Hearing Restoration

Authors: Lakshay Khurana1, Lukasz Jablonski1, Petr Nejedly1, Tobias Moser1

1Institute for Auditory Neuroscience

Background: Optogenetic cochlear implants (oCIs) represent a promising means to better restore hearing in individuals impacted by severe sensorineural hearing loss than possible with electrical cochlear implants (eCIs). The wide spread of current and channel interactions in eCIs limit comprehension of speech in noisy environments and the enjoyment of music. By reducing the spread of neural activation, oCIs promise a greater number of independent stimulation channels.

Methods: A computational framework for the evaluation of oCIs in the human cochlea was developed using four main modules. First, a generic n-of-m sound coding strategy was implemented, which could be easily adjusted to evaluate various parameters. Second, a three-dimensional ray-tracing model of a reconstructed human cochlea was used to investigate light propagation. Third, a biophysical model of spiral ganglion neurons (SGNs) was built to simulate optogenetically evoked firing. Fourth, a similarity measure was developed to compare the input sound spectrograph to the output spikes pattern. Finally, these stages were integrated to generate a comprehensive model capable of processing an audio files dataset and computing a similarity score.

Results: The major findings indicate that the spatial spread of light using μLED- and waveguide-based oCIs is narrower than the electrical current spread. Moreover, the impact of variables such as emitter-to-SGN distance, emitter rotation, and scar tissue formation on the irradiance at SGNs was evaluated. The improved spectral resolution of oCIs compensates for the currently lower temporal fidelity of optogenetically driven firing.

Conclusion: The computational framework provides a valuable resource for researchers to explore the complex interplays of sound processing, light delivery, and optogenetic stimulation. This study supports the notion that optogenetic stimulation of the cochlea could improve the speech understanding of CI users.