Time-related changes in task performance after lesions restricted to the frontal cortex

Behavioural studies in patients and functional neuroimaging studies in norm al subjects suggest that the right frontal cortex plays an important role i n sustaining attention to a task. However, the contribution of different re gions of the frontal lobe to performance changes has not been clearly estab lished. First, the assessment of sustained attention has not been carried o ut in patients with lesions that are restricted to cortical regions of the frontal lobe. Second, although sustained attention is often measured by per formance on a task requiring effortful attention, it may be more meaningful to measure changes in performance as a function of time-on-task. Two studi es were carried out in five groups of subjects: patients with left or right frontal cortical resections, patients with left or right anterior temporal lobe resections, and normal controls. In the first experiment, a brief (4- min) selective attention task was performed. The right frontal group, unlik e the other groups, did not show improved reaction times after the first mi nute on the task. The second experiment involved a long (30-min) shifting a ttention task. Both the left and right frontal groups were slower than cont rol groups: however, reaction times in the right frontal group increased wi th time spent on the task. We conclude that the: right frontal cortex plays an essential role in modulating arousal during performance of a task and m ay also underlie aspects of learning during the early stages of task perfor mance. (C) 2001 Elsevier Science Ltd. All rights reserved.