Previous work has suggested that human subjects engaged in tasks, like
the Stroop task, that require response selection utilize the medial f
rontal cortex. We used positron emission tomography to measure blood f
low changes in a stimulus-response compatibility task designed to maxi
mize the demand on response selection processes. We report significant
activation in the cingulate sulcus (Brodman's area 32) and a correlat
ion of activity in this region with faster response time for an incong
ruent stimulus-response task.