Parsing executive processes: strategic vs. evaluative functions of the anterior cingulate cortex

Abstract

Event-related functional MRI and a version of the Stroop color naming task were used to test two conflicting theories of anterior cingulate cortex (ACC) function during executive processes of cognition. A response-related increase in ACC activity was present when strategic processes were less engaged, and conflict high, but not when strategic processes were engaged and conflict reduced. This is inconsistent with the widely held view that the ACC implements strategic processes to reduce cognitive conflicts, such as response competition. Instead, it suggests that the ACC serves an evaluative function, detecting cognitive states such as response competition, which may lead to poor performance, and representing the knowledge that strategic processes need to be engaged.

Figure 1

Stimuli were presented for 500 ms, followed by an interstimulus interval of 12 s. Image acquisition was synchronized with stimulus onset and five 2.5-s fMRI scans were acquired during the course of a 12.5-s trial.

Figure 2

The time course of the BOLD response in the ACC during the course of a trial for each trial type. Data are displayed as percent change from the mean activity in the region. Transient activity is seen in the ACC, which varies according to expectancy and trial type. In the mostly incongruent condition, ACC activity is not modulated by trial type. In the mostly congruent condition, a robust modulation by trial type is observed, with greater activation in the incongruent, compared with the congruent condition. In addition, when incongruent trials are contrasted directly across the two expectancies, ACC activity is significantly greater in the low control, high conflict, mostly congruent condition, than the high control, low conflict, mostly incongruent condition.