Spatial Organization of the Primate Precentral Cortex

Within the framework of the global description of somatotopical organization of the primate precentral cortex by Woolsey and his coworkers (16), studies were undertaken to examine the detailed motor and sensory organizations for the control of the forelimb. The techniques of single unit recordings in behaving primates after Evarts (6), and intracortical microstimulation (ICMS) of Asanuma and Sakata (5) were used. In these studies, we observed that within a cortical zone, which receives input from a joint at the periphery, or controls movements about a joint, neurons with similar input and output properties are organized in vertically arranged aggregates (8,9,15), an observation in agreement with previous reports (see ref. 1 for review). Each possible movement about a joint is in general represented multiply by clusters of aggregates in different regions within a joint zone. When zones from all joints were examined, we observed that a cortical zone controlling a more distal joint was partially enclosed by a zone controlling a more proximal joint, resulting in a nested organization with the finger zone in the middle, successive enclosures by the wrist and elbow zones and a shoulder zone at the perimeter (8). This same nested pattern was observed for sensory inputs as well (15). Further, we found a tight coupling between sensory inputs and motor outputs, with the coupling conforming to the same nested organization (9)