The regulation of cognitive control following rostral anterior cingulate cortex lesion in humans

The contribution of the medial prefrontal cortex, particularly the anterior cingulate cortex (ACC), to cognitive control remains controversial. Here, we examined whether the rostral ACC is necessary for reactive adjustments in cognitive control following the occurance of response conflict [Botvinick, M.M., Barch, D.M., Carter, C.S., & Cohen, J.D. Conflict monitoring and cognitive control. Psychological Review, 108, 624-652, 2001]. To this end, we assesed 8 patients with focal lesions involving the rostral sector of the ACC (rACC patients), 6 patients with lesions outside the frontal cortex (non-FC patients), and 11 healthy subjects on a varient of the Simon task in which levels of conflict were manipulated on a trial-by-trial basis. More specifically, we compared Simon effects (i.e., the difference in performance between congruent and incongruent trials) on trials that were proceeded by high-conflict (i.e., incongruent) trials with those on trials that were proceeded by low-conflict (i.e., congruent) trials. Normal controls and non-FC patients showed a reduction of the Simon effect when the proceeding trial was incongruent, suggestive of an increase of cognitive control in response to the occurence of response conflict. In contrast, rACC patients attained comparable Simon effects following congruent and incongruent events, indicating a failure to modulate their performance depending on the conflict level generated by the proceeding trial. Furthermore, damage to the rostral ACC impaired the posterror slowing, a further phenomenon indicating reactive adjustments in cognitive control. These results provide insights into the functional organization of the medical prefrontal cortex in humans and its role in the dynamic regulation of cognitive control.