IPSILATERAL CORTICAL PROJECTIONS TO AREA-3A, AREA-3B, AND AREA-4 IN THE MACAQUE MONKEY

In the macaque monkey area 3a of the cerebral cortex separates area 4, a primary motor cortical field, from somatosensory area 3b, which has a subcortical input mainly from cutaneous mechanoreceptive neurons. T hat each of these cortical areas has a unique thalamic input was illus trated in the preceding paper. In the present experiments the cortical afferent projections to these 3 areas of the sensorimotor cortex monk ey were visualized and compared, using 4 differentiable fluorescent dy es as axonal retrogradely transported labels. The cortical projection patterns to areas 3a, 3b, and 4 were similar in that they each consist ed of (a) a ''halo'' of input from the immediately surrounding cortex, and (b) discrete projections from one or more remote cortical areas. However, the pattern of remote inputs from precentral, mesial, and pos terior parietal cortex was different for each of the 3 cortical target areas. The cortical input configuration was least complex for area 3b , its remote input projecting mainly from insular cortex. The pattern of discrete cortical inputs to the motor area 4, however, was more com plex, with projections from the cingulate motor area (24c/d), the supp lementary motor area, postarcuate cortex, insular cortex, and postcent ral areas 2/5. Area 3a, in addition to the proximal projections from t he immediately surrounding cortex, also received input from the supple mentary motor area, cingulate motor cortex, insular cortex, and areas 2/5. Thus, this pattern of cortical input to area 3a resembled more cl osely that of the adjacent motor rather than that of the somatosensory area 3b. Contrasting with this, however, the thalamic input to area 3 a was largely from somatosensory VPLc (abbreviations from Olszewski [1 952] The Thalamus of the Macaca mulatta. Basel: Karger) and not from V PLo (with input from cerebellum, and projecting to precentral motor ar eas). (C) 1993 Wiley-Liss, Inc.