Disturbed action monitoring has been demonstrated in Major Depressive Disorder (MDD). A well-known marker for performance monitoring is the error-related negativity (ERN), an event-related potential (ERP) generated in the anterior cingulate cortex following erroneous responses. The aim of the current study was to explore the mood state dependency of the ERN in MDD.

Behavioural and ERP measurements were obtained during performance on a speeded two-choice reaction task in 15 patients with MDD and 17 matched controls. Measurements took place during the early stages of a depressive episode and again following 7 weeks of antidepressant treatment. The healthy volunteers also participated in both sessions.

Whereas speed of response had substantially increased at session 2 in both groups with larger increases in the MDD group, equal ERN amplitudes were demonstrated between both sessions for the controls as well as the patients. The equal amplitudes in the MDD group might be attributable to the great variance in mood symptom remission rates in our sample. Nevertheless, strong correlations between inter-session changes in symptom severity and ERN amplitudes did emerge in the patient group.

The present ERP results indicate that performance monitoring in MDD is affected by mood state with only totally remitted patients demonstrating increased ERN amplitudes. The observed behavioural performance adjustments in all patients might mainly be attributable to a practise effect and the (partial) remission of depressive symptoms. Future longitudinal studies that include only patients with total symptom remission should corroborate and refine the current findings.