Positron emission tomographic (PET) studies of normal humans undergoing specific cognitive activation paradigms have identified a region of the anterior cingulate cortex as a component of an anterior, midline attentional system involved in high-level processing selection. However, deficits in attention have not been demonstrated in patients following bilateral anterior cingulotomy, a procedure that results in lesions of adjacent anterior cingulate cortex. Task paradigms used in PET studies that recruit the anterior cingulate cortex were applied to normal, control subjects and to a patient before and after cingulotomy to provide highly sensitive and functionally targeted reaction time measures of attentional performance. In contrast to unchanged performance in several neuropsychological measures, this patient demonstrated specific deficits in attention during the subacute postoperative period, which resolved spontaneously several months after surgery. Such impairment is consistent with the evolving view of the anterior cingulate's involvement in high-level processing selection. These data show the feasibility of using information from PET activation studies of normals in the design of novel chronometric tasks useful for probing abnormalities in specific cognitive operations associated with discrete cortical regions.