POSTERIOR PARIETAL CORTEX - FUNCTIONAL-PROPERTIES OF NEURONS IN AREA-5 DURING AN INSTRUCTED-DELAY REACHING TASK WITHIN DIFFERENT PARTS OF SPACE

The activity of single neurons was recorded in area 5 while monkeys ma de parallel arm movements within different parts of space in an instru cted-delay reaching task. In this task: (1)extrinsic variables, such a s the direction of movement, were dissociated from intrinsic ones, suc h as the joint configuration used to perform the movements; and (2) th e early neural events related to the presentation of the visual stimul us concerning movement direction were dissociated in time from the lat er events linked to the execution of movement. Under these experimenta l conditions, cell activity in area 5 changed so that the population o f preferred direction vectors of parietal neurons rotated in space in a way which predicted the rotation of the arm necessary to perform the task. This rotation occurred both during the ''instructed-delay time, '' when the monkey waited for the ''go-signal,'' and during the time i nterval surrounding the onset of movement. This suggests that reaching to visual targets in area 5 is coded by a mechanism combining somatic and visually derived information within a shoulder- or body-centered coordinate system and that instructed-delay time activity in area 5 re flects not only the composition of the direction signal for reaching b ut also the spatial configuration of the arm.