Local recurrent circuits modulate visual center and surround interactions in the mouse superior colliculus

Abstract Visual saliency is computed through center-surround interactions that initially originate in the retina and are later shaped by extraretinal circuits in the brain. The circuit mechanisms contributing to this modulation remain elusive. Using an optogenetic approach applied to the superficial layers of the superior colliculus (SCs), we demonstrate that the SCs is sufficient to generate surround suppression through patterned sequences between activated visual center and surround zones in individual neurons. Like the primary visual cortex, surround network activation causes decreases in center excitation rather than increases in synaptic inhibition. We reveal the identity of a SCs-based circuit with two interacting circuit motifs, recurrent excitation and feedback inhibition, capable of modulating levels of center excitation when the visual surround is active, using whole-cell recordings, trans-synaptic mapping, and functional approaches with computational modeling. We propose that early subcortical and cortical visual circuits have evolved to independently perform surround modulation, thus enabling parallel saliency computations across multiple levels.