Recurrent circuits encode visual center-surround computations in the mouse superior colliculus

Center-surround interactions underpin visual saliency computation, yet debate persists over whether subcortical visual circuits actively contribute or passively access this via descending cortical projections. To address this, we developed an optogenetic approach delineating visual center and surround zones of individual neurons in the superficial layer of the superior colliculus (SCs) solely using synaptic input arising from retinal ganglion cells (RGCs). Surround network activation of whole-cell recorded SCs neurons induced suppression of their RGC-driven center responses regardless of their cell-type. Notably, this modulation occurs through decreases in excitation rather than increases in inhibition. Cell-type-specific trans-synaptic and functional mapping in conjunction with large-scale modeling revealed a SCs-based circuit defined by two key motifs, highlighting the central role of local recurrent excitatory networks in generating surround inhibition. We propose that recurrent-based subcortical and cortical visual circuits have evolved to independently perform center-surround modulatory interactions, thus enabling parallel saliency computations across multiple levels.