Prefrontal neurones sensitive to increased visual attention in the monkey.

Single units were recorded in the prefrontal cortex of two monkeys performing a simple visual detection task. Task difficulty was manipulated in consecutive blocks of trials to increase the degree of attention towards the stimulus. Fifteen percent of the neurones sampled exhibited a systematic change in the average preparatory discharge rate in relation to task difficulty. Behavioural data (changes in reaction time and error ratios, 'difficult' probe trials presented in the 'easy' context) suggested that increased attention was actually induced. These results show the sensitivity of a population of prefrontal neurones to the behavioural context which determine the level of attention. The preparatory nature of the observed changes may be of special functional significance for the control of effortful attention.