(3/3) Here, we show that some L5 interneurons receive powerful monosynaptic input from the lateral geniculate nucleus (LGN) and have visual response properties more similar to L4 interneurons than those receiving little direct LGN input.

(2/3) In Layer 4 (L4), they are known to receive potent synaptic input from the thalamus and generate fast, local feedforward inhibition. In Layer 5 (L5), they are thought to receive less direct thalamic input and be strongly dominated by intracortical input.

(1/3) Fast-spike GABAergic interneurons are found across the entire depth of the visual cortex but may have very different response properties and functions in each cortical layer depending on a host of factors that are specific to the different layers.

We found that LGN-DS neurons do target L4 DS simple cells and that the targeting is highly selective. We conclude that this highly selective thalamocortical connectivity of LGN-DS neurons contributes to the sharp directional selectivity of cortical simple cells.

We used spike-train cross-correlation analysis of pairs of LGN-DS and L4 simple cells to address two important questions: do LGN-DS neurons synaptically target DS simple cells in L4, and, if so, do they contribute to the directional preferences of these V1 DS neurons?