Light delivery using a tapered optical fiber for optogenetic stimulation in mouse auditory midbrain

Electrical stimulation is the state-of-the-art method to restore hearing in deaf patients. However, the method offers limited frequency resolution due to the unavoidable electric field spread in the neural tissue. To overcome this limitation, we performed precise optogenetic stimulation in the murine inferior colliculus (IC) using a tapered optical fiber. Tapered fibers permit switching of light output which enables stimulation at various depths in the IC. Both the light-sensitive pump, channelrhodopsin-2 (ChR2) and archaerhodopsin-3 for neuronal activation and inhibition, respectively were co-expressed in the murine IC. We demonstrate that ChR2 stimulation at spatially separated regions can elicit distinct changes in the local field potential recorded at the auditory cortex. Furthermore, inhibition of neuronal activity by optical perturbation of Arch-T neurons between the stimulated regions increases the sensitivity of the IC to the ChR2 activation.