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

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