Distributed and causal influence of frontal operculum in task control.

It has been suggested that the frontal operculum (fO) is a key node in a network for exerting control over cognitive processes. How it exerts this influence, however, has been unclear. Here, using the complementary approaches of functional MRI and transcranial magnetic stimulation, we have shown that the fO regulates increases and decreases of activity in multiple occipitotemporal cortical areas when task performance depended on directing attention to different classes of stimuli held in memory. Only one region, the fO, was significantly more active when subjects selectively attended to a single stimulus so that it determined task performance. The stimuli that guided task performance could belong to three categories--houses, body parts, and faces--associated with three occipitotemporal regions. On each trial, the pattern of functional correlation between the fO and the three occipitotemporal regions became either positive or negative, depending on which stimulus was to be attended and which ignored. Activation of the fO preceded both activity increases and decreases in the occipitotemporal cortex. The causal dependency of the distributed occipitotemporal pattern of activity increases and decreases on the fO was demonstrated by showing that transcranial magnetic stimulation-mediated interference of the fO diminished top-down selective attentional modulation in the occipitotemporal cortex, but it did not alter bottom-up activation of the same areas to the same stimuli when they were presented in isolation. The fO's prominence in cognitive control may stem from a role in regulating the level of activity of representations in posterior brain areas that are relevant or irrelevant, respectively, for response selection.