TACTILE PROCESSING IN THE MOUSE INFERIOR COLLICULUS

The inferior colliculus is a crucial auditory midbrain processing center. The lateral cortex of the inferior colliculus (LCIC) also receives non-auditory inputs; LCIC neurons respond to high frequency vibrations in isolation and concurrent sound enhances their responses further. The question remains if this is specific to vibrotactile stimuli or if simple pressure to the skin is also processed by the LCIC. To answer these questions, we performed in vivo electrophysiological recordings in the LCIC of anesthetized mice using multi-electrode silicon probes while presenting a variety of auditory and tactile stimuli, both separately and simultaneously. A subset of recorded units (n = 26/107, 6 mice) robustly spiked to on- and offset of pressure stimuli to the hind paw with short latencies (20-30ms), even when the hearing thresholds were elevated by blocking the ear canals. Increasing stimulus strength increased the onset response rate and decreased the response latency. The response to repeated (10-50Hz) pressure stimuli followed the stimulation frequency with high fidelity, often showing stimulus adaptation. The tactile response was often suppressed by sustained sound presentation, but persisted in a subset of units. Ongoing experiments examine how stimulus onset asynchrony and relative stimulus strength shape multisensory responses. Our finding already showed that low frequency, repeated pressure steps are robust somatosensory stimuli that drive multimodal LCIC neurons with high temporal fidelity. We hope our and other’s findings will resolve the LCIC’s non-auditory role and help understand the function of pre-thalamic sensory processing centers in multisensory integration.