Schematic diagram of layer 3 circuitry in monkey dorsolateral prefrontal cortex. (A) The principal axon of layer 3 pyramidal neurons (P) gives rise to local axon collaterals that arborize within the same cortical column, intrinsic collaterals that spread horizontally and arborize in distant columns, and associational projections to other cortical regions either within the same or within the contralateral hemisphere. (B) Innervation of the layer 3 pyramidal neuron in panel A by different classes of GABA neurons. (C) Perisomatic (proximal dendrites, soma, and AIS) GABA inputs to the same layer 3 pyramidal neuron. Abbreviations: AIS, axon initial segment; CB1R, cannabinoid 1 receptor; CCK, cholecystokinin; CR, calretinin; G, GABA; P, pyramidal; PVB, parvalbumin-containing basket neuron; PVCH, parvalbumin-containing chandelier neuron; SST, somatostatin; WM, white matter.