[Functional plasticity of frontal neurons in rhesus monkeys during performing visual discrimination go/no-go task]

We previously reported that frontal neurons in monkeys may be essentially responsive to the biological meanings of the stimuli in a task, rather than to their physical attributes. To examine this hypothesis, activity of single neurons was recorded from the frontal cortex of monkeys (Macaca mulatta) while performing a visual delayed discrimination GO/NO-GO task (task I, n = 2) and a visual discrimination response GO/NO-GO task (task II, n = 2), respectively. A green or red light presented in the period 2 of task I and in the period 4 of task II was used as a cue to guide the monkeys' behaviour. The same green/red light was presented in the period 2 of task II as well, but this was not a cue and had no definite meanings in the task. The monkeys were trained to watch attentively the panel in period 3 of both tasks. A total of 163 task-related neurons were recorded: 98 in task I and 65 in task II. Although neuronal responses appeared in all periods of both tasks, the majority of the responses (70% of the total) were in the periods 2 and 3 of task I, and in the periods 3 and 4 of task II. Furthermore, in the period 2 of task I and period 4 of task II, but not in the period 2 of task II, most of neurons were responsive exclusively to either green or red light. The results support the hypothesis stated above, and suggest that the responses of the frontal neurons to signal stimulation are gradually established in the course of learning, and possess highly developed functional plasticity.