Synaptic connectivity of the visual thalamocortical circuit. (a) Excitatory inputs carrying visual information from the dorsal lateral geniculate nucleus (dLGN, green) in the thalamus innervate pyramidal (PYR, blue box) neurons and Parvalbumin (PV, red box) interneurons in thalamorecipient layers of the visual cortex (red box). PV interneurons receive inputs from neighbouring PYR neurons across cortical layers. Astrocytes (AST) express molecules that can act as synaptic bridges between thalamocortical axons and their postsynaptic targets (Hevin, blue box). (b) Red box: the synaptic immunoglobulin SynCAM 1 organizes thalamic inputs onto PV interneurons. Presynaptic interacting partners of SynCAM 1 at thalamocortical synapses are currently unknown, but other SynCAMs (2 and 3) are candidates. Blue box: Neuroligin 1 on PYR cells interacts with Neurexin-1α via the astrocytic Hevin (brown) to organize thalamic inputs onto PYR cells. Astrocytic process is depicted in orange. Presynapse (Pre) and postsynapse (Post) are indicated.