Reward modulates visual responses in the superficial superior colliculus of mice

Abstract

The superficial layers of the superior colliculus (SC) are highly visual and receive direct input from the retina. Nonetheless, neural activity in the superficial SC (sSC) is modulated by locomotion and pupil-linked arousal. Here we show that visual responses of neurons in the sSC are additionally modulated by reward delivered prior to the visual stimulus. We trained mice to perform a visual detection task and recorded the activity of neurons in the SC using two-photon calcium imaging and electrophysiological recordings using high-density silicone probes (Neuropixels). Neurons across all layers of the SC responded to various task events, including reward delivery. However, responses to events like licking or movements did not explain the visual response modulation by reward. Electrophysiological recordings showed that most of the reward modulation occurred in the superficial rather than the deeper layers of the SC. Neurons also exhibited modulation by pupil-linked arousal, which was independent of the reward modulation. Performance of a population decoder to detect visual stimuli improved significantly by reward modulation but not by pupil-linked arousal modulation. Our results indicate that behavioural factors other than locomotion and arousal modulate visual activity in the SC.