Functional dissociation of attentional selection within PFC: response and non-response related aspects of attentional selection as ascertained by fMRI.

In this experiment using a color-word Stroop task, we explored whether different regions of prefrontal cortex bias selection of response-related processes as compared with non-response-related processes. To manipulate demands at the level of response selection, we varied the degree of overlap between stimulus-response mappings in a manual Stroop task. To vary demands at a non-response level, we compared activation for incongruent trials (e.g. the word 'purple' in blue ink) that contain two color representations, one in the word and one in the ink color, to neutral trials (e.g. the word 'drawer' in blue ink), which contain only one color representation, that in the ink color. These manipulations had differential effects within prefrontal cortex. Both a region of right inferior frontal cortex and caudal regions of the cingulate were sensitive to the selection demands at the response-level and insensitive to demands at the non-response level. In contrast, a more anterior region of left dorsolateral prefrontal cortex was sensitive to the number of color representations (i.e. incongruent versus neutral trials), but not to the overlap in stimulus-response mappings. Therefore, this study indicates a functional differentiation for implementing attentional control within prefrontal cortex.