Thalamocortical boutons cluster by ON/OFF responses in mouse primary visual cortex

In higher mammals, the thalamic afferents to primary visual cortex cluster according to their responses to increases (ON) or decreases (OFF) in luminance. This feature of thalamocortical wiring is thought to create columnar, ON/OFF domains in V1. We have recently shown that mice also have ON/OFF cortical domains, but the organization of their thalamic afferents remains unknown. Here we measured the visual responses of thalamocortical boutons using two-photon imaging and found they also cluster in space according to ON/OFF responses. Moreover, fluctuations in the relative density of ON/OFF boutons mirrors fluctuations in the relative density of ON/OFF receptive field positions on the visual field. These findings indicate that there is a segregation of ON/OFF signals already present in the thalamic input, a result that may reflect the spatial organization of retinal ganglion cell mosaics themselves.