CORTICAL AREAS WITHIN THE LATERAL SULCUS CONNECTED TO CUTANEOUS REPRESENTATIONS IN AREA-3B AND AREA-1 - A REVISED INTERPRETATION OF THE 2NDSOMATOSENSORY AREA IN MACAQUE MONKEYS

Cortical connections between various body representations in areas 3b and 1 and lateral parietal cortex were examined in 18 macaque monkeys. We injected tracers (Fast Blue, Diamidino Yellow, Horseradish Peroxid ase, and Rhodamine Dextran), alone or in combination, into closely rel ated cutaneous responsive sites, e.g., adjacent digits. Separated patc hes of labeling were found across the parietal operculum and insula fo r all injected locations. On the basis of cytoarchitectural criteria, the labeled regions include the second somatosensory area (SII), retro insular area (Ri) and granular insula (Ig). Assuming the connections a re homotopical from physiologically identified body representations in primary somatosensory cortex, the labeling patterns in SII include co mplete anterior and posterior body maps. The orientation of the body i s erect in the posterior and supine in the anterior SII region. Area 3 b has greater density of connections with anterior SII. The maps are m irror images aligned along the distal extremities. The anterior-poster ior (A-P) length of the ''SII region'' exceeds 7 mm; it extends in the coronal plane from the fundus of the lateral sulcus to surface cortex near the anterior tip of the intraparietal sulcus. Two additional top ographically organized maps are likely in Ri. These are ''worm-like'' body maps oriented along the A-P axis and joined at the head represent ation. Connections with the center of Ig are not somatotopically organ ized. The diversity of somatosensory areas in lateral parietal cortex revealed by the labeled connections was discussed in reference to prio r mapping of SII in monkeys and was compared to reports of multiple ar eas in this region of cortex in other species. (C) 1995 Wiley-Liss, In c.