Cortical activation associated with midtrial change of instruction in a saccade task.

The appearance of a visual stimulus in the peripheral visual field can elicit different saccade responses depending on prior instruction. This flexibility is commonly attributed to differences in motor set. Little is known about how the brain switches between one saccade response and another. To investigate the neural processes associated with switches between saccade motor sets, we recorded event-related potentials (ERPs) in 13 subjects, in three tasks that required subjects to generate prosaccades to a visual stimulus on 75% of the trials. On 25% of the trials, the color of the fixation point (FP) changed 300 ms prior to stimulus presentation. In the "ANTI" task, the change of the FP was the instruction to generate an antisaccade; in the "NOGO" task, subjects were instructed to maintain fixation; and in the "PRO" task, subjects were instructed to generate a prosaccade. The switch in motor set from prosaccades to antisaccades in the ANTI task and the cancellation of the prosaccade motor set in the NOGO task modulated frontal and frontocentral channels. Futhermore, the ANTI task but not the NOGO task was associated with differences at central and parietal channels compared with the PRO task. We hypothesize that the frontal activation in the ANTI and NOGO task reflects inhibition and task-switching processes, whereas the parietal activation reflects the preparation of this area for the sensorimotor transformation process that is necessary for the generation of an antisaccade.