Prefrontal neuronal activity during gazing at a light spot in the monkey.

We trained monkeys to make rapid key-release when a tiny light spot dimmed, so that they gazed at the spot until it dimmed. While the animal was performing the gaze task, we recorded unit activity in the prefrontal cortex and found that many neurons increased in discharge rate during the gaze trial (G neuron) with a variety of discharge patterns: many units were activated continuously during the gaze period; others were activated phasically only in an earlier portion of the gaze period. The activation of the G neurons was little influenced by stimulus parameters, such as the size, intensity and position of the light spot. However, it was dependent on behavioral state of the animal: error trials with delayed key-release showed a weak activation while extinction procedure induced enhanced activation in the initial several trials. The dependence of the activation on the behavioral state may suggest that the activation is at least involved in attentional process during gazing at a behavioral cue.