Stimulus-response incompatibility activates cortex proximate to three eye fields

We used functional magnetic resonance imaging (fMRI) to investigate cortica l activation during the performance of three oculomotor tasks that impose i ncreasing levels of cognitive demand. (1) In a visually guided saccade (VGS ) task, subjects made saccades to hashed targets. (2) In a compatible task, subjects made leftward and rightward saccades in response to foveal presen tation of the uppercase words "LEFT" or "RIGHT." (3) In a mixed task, subje cts made rightward saccades in response to the lowercase word "left" and le ftward saccades in response to the lowercase word "right" on incompatible t rials (60%). The remaining 40% of trials required compatible responses to u ppercase words. The VGS and compatible tasks, when compared to fixation, ac tivated the three cortical eye fields: the supplementary eye field (SEF), t he frontal eye field (FEF), and the parietal eye field (PEF). The mixed tas k, when compared to the compatible task, activated three additional cortica l regions proximate to the three eye fields: (1) rostral to the SEF in medi al frontal cortex; (2) rostral to the FEF in dorsolateral prefrontal cortex (DLPFC); (3) rostral and lateral to the PEF in posterior parietal cortex. These areas may contribute to the suppression of prepotent responses and in holding novel visuomotor associations in working-memory. (C) 2001 Academic Press.