Anterior Cingulate Cortex: Error Monitoring or Conflict Monitoring?

Abstract:
A controversial issue in the literature on the function of the anterior cingulate cortex (ACC) is whether this region is primarily responsible for error monitoring functions or for the detection of response conflict, such as that observed in Stroop interference tasks. Two patients with focal ACC lesions (D.L. - right mid-caudal ACC, R.N. - left rostral-mid ACC) and 3 patients with bilateral orbitofrontal (OF) and ventral ACC damage were tested in an event-related potential (ERP) study designed to investigate processing associated with error detection and response competition. A word-arrow Stroop task required button press responses to either the word "left" or "right" or an arrow pointing to the left or right. Stimulus displays were either congruent or incongruent. On error trials, control subjects generated an error-related negativity (ERN) component peaking about 60 ms after incorrect responses. OF patients failed to generate an ERN, D.L. showed a significant reduction, and R.N. showed a modest reduction in ERN amplitude. A smaller negative component observed on correct conflict trials was intact in R.N. but reduced in D.L. All patients showed behavioral evidence of error correction and compensation. These results suggest that distinct subregions of the ACC contribute differentially to error monitoring and conflict monitoring.