Objectives: We aimed to characterize the effect of electroconvulsive therapy (ECT) on mismatch negativity (MMN), an event-related potential suggested as a biomarker of cortical dysfunction and illness progression in psychosis, and its association with improvement in positive symptoms.

Methods: MMN was calculated from electroencephalogram recorded during a passive auditory oddball paradigm before and after ECT in psychosis patients receiving both ECT and medication, at matched intervals in patients receiving medication only, and at baseline in healthy controls (HCs). In patient groups, group-time interaction on MMN amplitudes was analyzed using mixed models for repeated measures. In the ECT group, correlations between MMN amplitude and Positive and Negative Syndrome Scale (PANSS) subscales were assessed.

Results: Data from 26 ECT-treated patients, 23 medication-only patients, and 50 HCs were analyzed. At baseline, MMN amplitude and latency differed among groups. A significant group-time interaction indicated differential MMN amplitude change between the ECT group and the medication-only group. In the ECT group, a positive repeated-measure correlation was observed between MMN amplitude and PANSS positive score.

Conclusion: Our results demonstrate a normalizing effect of ECT on MMN amplitude and its relationship with improvement of positive symptoms. They imply that ECT modulates neurophysiological mechanisms underlying MMN generation.

Keywords: Electroconvulsive therapy; Mismatch negativity; Event related potentials; Psychosis.