Activation of a Visual Cortical Column by a Directionally Selective Thalamocortical Neuron.

The retinas of rabbits and rodents have directionally selective (DS) retinal ganglion cells that convey directional signals through the lateral geniculate nucleus (LGN) of the thalamus to the primary visual cortex (V1). Notably, the function and synaptic impact in V1 of these directional LGN signals are unknown. Here we measured, in awake rabbits, the synaptic impact generated in V1 by individual LGN DS neurons. We show that these neurons make fast and strong connections in layers 4 and 6, with postsynaptic effects that are similar to those made by LGN concentric neurons, the main thalamic drivers of V1. By contrast, the synaptic impact of LGN DS neurons on superficial cortical layers was not detectable. These results suggest that LGN DS neurons activate a cortical column by targeting the main cortical input layers and that the role of DS input to superficial cortical layers is likely to be weak and/or modulatory.