A dedicated circuit links direction-selective retinal ganglion cells to the primary visual cortex

Using a combination of viral-tracing and in vivo imaging techniques, the authors show that there are several parallel pathways in the mouse visual system and that directional and orientation selectivity in the cortex may arise from the specialized tuning of retinal circuits. How the eye observes directional change The motion-detecting cells of the retina, called direction-selective ganglion cells (DSGCs), have been known about and studied for more than half a century but their precise role in visual processing has remained unclear. Using a combination of genetic, anatomical and imaging techniques, Andrew Huberman and colleagues investigate the connections made by DSGCs in the mouse brain and find that they link specifically to neurons in the superficial layers of primary visual cortex. Inputs from several different DSGC types are combined to convey both directional and orientation information to the cortex. In addition, non-direction-tuned information from the retina is sent to deeper layers of cortex. This reveals that the mouse visual system contains several functionally distinct parallel pathways and that directional and orientation selectivity in the cortex may arise from the earliest stages of visual processing involving motion-detecting cells in the retina. How specific features in the environment are represented within the brain is an important unanswered question in neuroscience. A subset of retinal neurons, called direction-selective ganglion cells (DSGCs), are specialized for detecting motion along specific axes of the visual field 1 . Despite extensive study of the retinal circuitry that endows DSGCs with their unique tuning properties 2 , 3 , their downstream circuitry in the brain and thus their contribution to visual processing has remained unclear. In mice, several different types of DSGCs connect to the dorsal lateral geniculate nucleus (dLGN) 4 , 5 , 6 , the visual thalamic structure that harbours cortical relay neurons. Whether direction-selective information computed at the level of the retina is routed to cortical circuits and integrated with other visual channels, however, is unknown. Here we show that there is a di-synaptic circuit linking DSGCs with the superficial layers of the primary visual cortex (V1) by using viral trans-synaptic circuit mapping 7 , 8 and functional imaging of visually driven calcium signals in thalamocortical axons. This circuit pools information from several types of DSGCs, converges in a specialized subdivisi