Deciding Not to GO: Neuronal Correlates of Response Selection in a GO/NOGO Task in Primate Premotor and Parietal Cortex

Monkeys performed reaching movements in two opposite directionsin a symmetrically rewarded GO/NOGO task with an instmcted-delayperiod. Instructional cues were presented at the target locations.The decision not to move was clearly reflected in cell activityin dorsal premotor cortex, but not in parietal cortex area 5.In premotor cortex, the initial response (<250 msec) of mostcells to the appearance of the instructional cues in GO andNOGO trials was similar. However, by the end of the delay period,the responses of most cells were statistically different betweenthe two trial types, and the population signals were much lessdirectional in the NOGO trials than in the GO trials. In area5, in contrast single-cell and population signals were generallysimilar and strongly directional in both GO and NOGO trials.This result suggests a role for area 5 in visuomotor analysisfor the guidance of limb movements. It further suggests thatseparate representations of potential motor responses to externalinputs and of the intended response to that input can coexistin parietal and premotor cortex, respectively.