Attention-related unit activity in the frontal association cortex during a go/no-go visual discrimination task.

Unit activity related to a go/no-go visual discrimination task was studied in four rhesus monkeys. We recorded 272 task-related cells from frontal cortex in a region extending from the midprincipal sulcus to the central sulcus, and medially to the cingulate sulcus. Units located in anterior regions (dorsolateral prefrontal and anterior cingulate cortex) were typically related to both go and no-go trials (designated type II units) and showed similar ("symmetrical") activity in both kinds of trials; some of them also showed prestimulus ("anticipatory") activity. Such units were present but less common in posterior regions (postarcuate and precentral and posterior cingulate cortex). Units in these posterior regions were active predominantly in go trials (designated type I units). Also found posteriorly were "asymmetrical" type II cells whose activity was greater in go trials and occurred later in the trial, around the behavioral response. The anterior symmetrical and anticipatory type II units in the frontal association cortex were similar to such units described earlier in the brain stem reticular formation and may have similar functions in supporting focused and preparatory attention. On the other hand, asymmetrical type II units in the posterior frontal regions may have a role in the initiation of visually guided motor behavior.