Left: 3D microscopic image of an optical LED-based cochlear implant. Right: optical cochlear implant in the basal turn of the marmoset cochlea. (Credit: Daniel Keppeler, UMG)

The development of optical cochlear implants is complex. One factor is the complicated structure of the cochlea, which is poorly accessible for investigation, even by imaging because it is deeply embedded in the temporal bone. However, detailed knowledge of the structure of the cochlea is critical for the development of innovative therapy of deafness. Researchers rely on animal studies to develop the gene therapy and optical cochlear implants and to test their efficacy and safety.

With the data obtained on the anatomy of the different cochleae, a team was able to design an implant with LED emitters for common marmosets. The implant was then inserted by an experienced ear, nose and throat surgeon in a manner analogous to surgery in humans. The researchers used imaging data to simulate the propagation of light generated by the emitters of the optical implants in the cochlea of nonhuman primates.

The simulations indicate spatially limited optogenetic excitation of auditory neurons and thus higher frequency selectivity than with previous electrical stimulation. According to these calculations, optical cochlear implants lead to significantly improved hearing of speech as well as of music. Optical stimulation would lead to a much more differentiated auditory impression than the electrical stimulation used so far.

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