Functions of the medial frontal cortex in the processing of conflict and errors

A principal function of the medial frontal cortex, in particular the anteri or cingulate cortex (ACC), is to monitor action. The error-related negativi ty (ERN, or NE), an event-related brain potential, reflects medial frontal action-monitoring processes. Specifically, the error-detection theory of th e ERN states that the ERN reflects ACC processing that is directly related to detecting the error. This theory predicts that ERN and ACC activity shou ld increase directly with the dissimilarity of the error from the correct r esponse, with similarity defined with respect to the common movement featur es of the responses. In contrast, the conflict-detection theory claims that ACC and ERN activity represent the detection of response conflict. This th eory predicts that the activity should increase directly with the similarit y of the error and the correct response. To test these theories, we investi gated the effects of response similarity and conflict on the ERN, using a t ask that involved hand and foot movements. ERN activity was largest under c onditions of high response conflict, where the error was similar to the cor rect response. This finding favors the conflict-detection theory over the e rror-detection theory, although the ERN was not associated with posterror s lowing, as predicted by proponents of both theories. Discrepancies between our results and those of past studies may stem from the use in previous stu dies of four-finger response tasks which are subject to unique physiologica l and biomechanical constraints. We conclude that the ERN reflects medial f rontal activity involved in the detection or affective processing of respon se conflict.