Distribution and size of GABAergic neurons in area 7b and the retroinsular cortex of the monkey.

The distribution of gamma-aminobutyric acid (GABA) neurons was examined in the retroinsular cortex (Ri) and area 7b of the monkey. GABA-immunoreactive somata and puncta were observed in all layers of Ri and area 7b. The densest concentration of these neurons was located in layers I and II. The vast majority (98.9%) of GABA-immunoreactive somata were less than 15 microns in major diameter. These data demonstrate that high concentrations of GABAergic neurons are located in those cortical layers that have been shown to receive afferent projections from corticocortical fibers.