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

Behavioural studies in patients and functional neuroimaging studies in normal subjects suggest that the right frontal cortex plays an important role in sustaining attention to a task. However, the contribution of different regions of the frontal lobe to performance changes has not been clearly established. First, the assessment of sustained attention has not been carried out in patients with lesions that are restricted to cortical regions of the frontal lobe. Second, although sustained attention is often measured by performance on a task requiring effortful attention, it may be more meaningful to measure changes in performance as a function of time-on-task. Two studies 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, unlike the other groups, did not show improved reaction times after the first minute on the task. The second experiment involved a long (30-min) shifting attention task. Both the left and right frontal groups were slower than control groups; however, reaction times in the right frontal group increased with 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 may also underlie aspects of learning during the early stages of task performance.