Optical cochlear implants: a promising treatment tool for hearing loss

Abstract

Hearing loss affects more than 1.5 billion people worldwide. The main means of rehabilita­tion used are hearing aids and cochlear implants (CI). The electrical CI converts sound into electrical impulses that directly stimulate neurons in the spiral ganglion to provide auditory sensation; it has the disadvantage of a wide spatial dispersion of the current, limiting the spectral resolution and the dynamic range of sound coding, which leads to a poor understan­ding of speech in noisy environments and a poor appreciation of music. In recent years, the use of optical stimulation instead of electrical stimulation have been studied since it emits stimuli with greater spatial selectivity. Optical CIs have been described using infrared light and others using optogenetic methods, the latter requiring the expression of photosensitive proteins induced by adeno-associated viruses. The spectral selectivity of optogenetic stimula­tion has been found to be indistinguishable from acoustic stimulation and allowed near-phy­siological firing rates with good temporal accuracy up to 250 Hz stimulation. Studies compa­ring an optical and an electrical CI system conclude that the use of optogenetics would allow hearing restoration with improved spectral selectivity compared to an electrical CI.