Spatial organization of precentral cortex in awake primates. III. Input-output coupling.

Abstract

Experiments involving sensory inputs to loci in the forelimb region of precentral cortex and motor outputs from these same loci were performed in awake monkeys [Macaca arctoides]. The sensory inputs involved extracellular unit responses of single neurons to cutaneous stimulation or to passive rotations of limb parts about joints. Motor outputs were determined in terms of movement of limb parts about joints in response to low-current (< 30 .mu.A) intracortical microstimulation (ICMS) with the same electrode used for recording. With only extremely rare exceptions, a homonymous relationship existed between input and output. A negative correlation existed between direction of ICMS effect and direction of effective passive joint rotation. ICMS of cortical sites induced movement either toward or away from the cutaneous receptive field of that site, with about equal frequency. Vertical aggregates of cells with similar input-output properties existed in a direction parallel to the radial fibers and orthogonal to the cortical surface. The conjugation of all clusters functionally related to single joints produces ring or crescent-shaped zones. Specific sensory inputs can apparently assist the central facilitation of neuronal clusters in precentral cortex, thereby playing a role in the sequencing of movement vectors during execution of behavioral action.