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 made parallel arm movements within different parts of space in an instructed-delay reaching task. In this task: (1) extrinsic variables, such as the direction of movement, were dissociated from intrinsic ones, such as the joint configuration used to perform the movements; and (2) the early neural events related to the presentation of the visual stimulus concerning movement direction were dissociated in time from the later events linked to the execution of movement. Under these experimental conditions, cell activity in area 5 changed so that the population of 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 interval 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 reflects not only the composition of the direction signal for reaching but also the spatial configuration of the arm.