Toward New Generation Auditory Brainstem Implants: Electrical and Optogenetic Stimulation of the Cochlear Nucleus

Abstract

Auditory brainstem implants (ABIs) help provide some hearing to patients with non-functional auditory nerves or ossified cochleae. ABIs bypass the cochlea and electrically stimulate the surface of the cochlear nucleus (CN). Performance of ABI users in speech reception tasks is usually poor. One of the possible explanations for their limited performance is the poor spatial selectivity of electrical stimulation that limits frequency resolution. In this project, we show that spatial selectivity of electrical stimulation was usually poor in a rat model, as stimulation in one point of the CN surface led to activation of most of the tonotopic axis in the inferior colliculus (IC). These results point to the need for new stimulation strategies to improve frequency representation in the central auditory system of ABI users. An optogenetic approach is promising, as light may be more easily focused than electrical current. To test the feasibility of optogenetic control of the CN, we transfected the CN of mice with AAV2/8-Channelrhodopsin-2 (ChR2). We found a significant increase in activity in IC and primary auditory cortex during blue light stimulation in mice with successful ChR2 expression in the CN. Overall, these results lay the groundwork for a new generation opto-electronic ABI.