Regional cerebral blood flow, an index of local neuronal activity, was measured using positron emission tomography (PET) during the performance of the classic Stroop color/word task in eight healthy right-handed subjects.In the first condition of this paradigm, subjects name the color of the words presented on a video monitor. All the words are the color names congruent to the color presented (e.g., the noun "red" displayed in red color). In the second condition, subjects also name the color of the words presented on the monitor. However, during these trials all words are color names incongruent to the color presented (e.g., the noun "red" displayed in green color). The difference in brain activity between these two conditions (i.e., incongruent minus congruent) could reveal brain systems involved in the attentionally mediated resolution of the conflict between the habitual response of reading words vs. the task demands of naming the color of the words-i.e., the Stroop interference effect. The most robust responses occurred in the anterior cingulate cortex. Other responses noted were in the left premotor cortex, left postcentral cortex, left putamen, supplementary motor area, right superior temporal gyrus, and bilateral peristriate cortices. These data provide support for the role of the anterior cingulate cortex in attentional processing through the selection and recruitment of processing centers appropriate for task execution. Furthermore, the extensive distributed network of activated regions suggests that the Stroop interference effect cannot be explained simply in terms of stimulus encoding or response interference.The Stroop task (1, 2) is a classic experimental paradigm used in behavioral neuroscience in both clinical and research settings. Subjects note the strong interference of word reading upon color naming, called the Stroop interference effect, when a noun presented is a color name displayed visually using a different color (see Fig. 1 What are the likely anatomical loci and associated cognitive operations involved in attentional conflict paradigms such as the Stroop task? Two general areas are suggested on the basis of data from several sources: the prefrontal cortex and the anterior cingulate. The prefrontal cortex, based on experimental evidence from both monkeys as well as humans (4, 5), has been demonstrated to be important not only for memory buffering to permit "on-line" processing but also for inhibition of "prepotent" habitual, albeit sometimes inappropriate, responses. Lesions of the left prefrontal cortex result in impaired performance in the Stroop task (6). Linguistic tasks requiring the inhibition of reading a noun and the generation of a verb appropriate to the noun result not only in activation of the left prefrontal cortex but also the anterior cingulate (7,8). Some human diseases, such as schizophrenia, involving prefrontal (9) and anterior cingulate abnormalities (10) result in impairments in attentional conflict paradigms (11).Recent technological advances in nuclear medi...

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.

Studies of speed of cognitive processing in Parkinson's disease (PD) have yielded mixed results. This may relate in part to a differential effect on cognitive speed by the type of information to be processed. In the present study, we compared medication fasted, nondemented individuals with mild idiopathic PD (N 5 26) with age-matched controls (N 5 12) on a test requiring easy and hard same-different discriminations for verbal, quantitative, and spatial information, as well as on a traditional memory scanning paradigm. A voice-activated relay rather than a key press was used to eliminate the need for limb and finger movements. Simple reaction time and movement time were also measured in a task requiring subjects to move a hand held stylus to a designated target. The PD group performed as fast as the control group across all tasks except movement time. Thus, in our paradigm, the presence of PD alone does not predict cognitive slowing in the presence of motor slowing. (JINS, 1998, 4, 584-592.)