Intracortical circuits of pyramidal neurons reflect their long-range axonal targets

Cortical columns generate separate streams of information that are distributed to numerous cortical and subcortical brain regions1. We asked whether local intracortical circuits reflect these different processing streams by testing if the intracortical connectivity among pyramids reflects their long-range axonal targets. We recorded simultaneously from up to four retrogradely labelled pyramids that projected to the superior colliculus, the contralateral striatum or the contralateral cortex to assess their synaptic connectivity. Here we show that the probability of synaptic connection depends on the functional identity of both the presynaptic and postsynaptic neurons. We first found that the frequency of monosynaptic connections among corticostriatal pyramids is significantly higher than among corticocortical or corticotectal pyramids. We then show that the probability of feedforward connections from corticocortical neurons to corticotectal pyramids is approximately three- to fourfold higher than the probability of monosynaptic connections among corticocortical or corticotectal cells. Moreover, we found that the average axodendritic overlap of the presynaptic and postsynaptic pyramids could not fully explain the differences in connection probability that we observed. The selective synaptic interactions we describe demonstrate that the organization of local networks of pyramidal cells reflects the long-range targets of both the presynaptic and postsynaptic neurons.