Cellular discharge in the dorsolateral prefrontal cortex of the monkey in cognitive tasks

Single-unit activity was recorded in the prefrontal cortex of monkeys performing two visual short-term memory tasks: delayed matching-to-sample and delayed response. The animal had to retain a color (sample) in the first task and a positional cue in the second. Cells reacting to the sample or the cue were found throughout the dorsolateral prefrontal cortex, some cells differentiating colors (red and green) and others positions (right and left). About one-half of all cells showed altered discharge during the retention period (delay). In some of them that discharge differed depending on the sample or cue. One cell type showed descending firing frequency in the course of the delay. Another showed the opposite, that is, increasing firing as the delay progressed. Cells with altered delay-period discharge were more common in the cortex of the sulcus principalis and the inferior convexity than in other prefrontal areas. The findings are viewed as reflecting the participation of prefrontal neurons in the temporal structuring of behavior.