OPTOGENETIC STIMULATION OF GABAERGIC NEURONS IN THE SUPERIOR COLLICULUS EVOKES CONTRALATERAL OROFACIAL MOVEMENTS AND INHIBITION IN THE CONTRALATERAL SUPERIOR COLLICULUS

Orofacial movements such as eye, whisker, and nose movements are essential for active sensing and orienting behavior. The superior colliculus (SC) is a key midbrain structure controlling orienting movements, yet its contribution to orofacial motor control remains poorly understood. Here, we combined optogenetic activation of GABAergic neurons in the SC, large-scale electrophysiological recordings using Neuropixels probes, and high-speed multi-camera tracking to examine how inhibitory SC circuits influence orofacial movements in mice. We tracked eye position, as well as nose and whisker movements during optogenetic stimulation. Activation of SC GABAergic neurons reliably evoked eye, whisker, and nose movements. Notably, these movements were directed contralaterally to the site of stimulation. This contrasts with previous findings showing that optogenetic inhibition of the SC with eNpH3.0 shifts eye movement in the ipsilateral direction (Zahler et al., 2021), suggesting distinct circuit mechanisms for suppressing collicular activity versus activating inhibitory populations. To probe the underlying circuitry, we recorded neural activity in the SC contralateral to the stimulation site. Optogenetic activation of GABAergic neurons produced a rapid and robust suppression of firing rates in the opposite SC. These results indicate that stimulation of SC GABAergic neurons preferentially inhibits the contralateral colliculus rather than exerting purely local inhibition. Together, our work identifies an intercollicular inhibitory mechanism by which GABAergic neurons in the superior colliculus shape orofacial orienting movements. This circuit architecture provides a functional substrate for lateralized control of orienting behavior and highlights a previously underappreciated role for inhibitory SC neurons in coordinating bilateral motor outputs.