Prefrontal unit activity during a color discrimination task with GO and NO-GO responses in the monkey.

The activity of single neurons was recorded in the prefrontal cortex of monkeys performing a color discrimination GO and NO-GO task with a sequenced 3 visual stimuli (starting signal of a trial, discriminanda and command for response selection, respectively). A total of 161 units showed changes in their activity in association with at least one of the 4 events of the task (3 visual events and reward). Three patterns of activity change coupled to event onset (Type A, B nd C) were found irrespective of the kind of events. Type A was a transient activity increase after event onset. Fifty-two units showed the Type A change. Three-fourths of them became active after one particular event, and the remaining one-fourth after more than one event. Type B was a gradual activity increase preceding event onset followed by a decrease after event onset. Sixty-five units showed the Type B change. In two-thirds of them, the activity changes occurred around one particular event, and in the remaining one-third around more than one event. Type C consisted of sustained activity between two different events. Eighty-three units showed the Type C change. This type of change was found in 5 different combinations of events. Four-fifths of the 161 units showed one of 3 patterns, and the remaining one-fifth more than one of these patterns during different periods of a trial. It is suggested that Types A and B are involved in the information processing in relation to a particular event onset, and Type C provides a reference for distinction of events.