Retinal ganglion cell input to superior colliculus encodes salient information

The superior colliculus (SC) is critical in detecting and responding to salient stimuli. However, it is unknown whether salience signals are inherited from external sources such as retina and cortex, or arise from the intrinsic circuitry within SC. We used in vivo 2-photon calcium imaging with adaptive optics to examine the activity of retinal ganglion cell (RGC) axon terminals in superficial SC (sSC). We found that RGC boutons exhibit similar saliency-related activity as sSC neurons. A majority of boutons respond more strongly to salient discontinuities of visual features, and change their orientation preference depending on stimulus properties such as the orientations of edges of drifting gratings. We furthermore demonstrate that these effects arise from the center-surround receptive field structure of RGCs. Our results show that the orientation tuning of RGCs is highly flexible, and that saliency encoding originates in retina rather than sSC.