The exact effects of electroconvulsive therapy (ECT) on the brain are still not accurately known. Hypotheses considered include the effect of ECT on cortical excitability of the brain. The aim of this trial was to assess the changes in cortical excitability in the brain of a patient with remitted schizophrenia, undergoing maintenance ECT. Three successive ECT applications resulted in significant prolongation of the cortical silent period, which implies augmentation of inhibitory cortical mechanisms in the brain, most likely mediated by the GABAergic (GABA, γ-aminobutyric acid) system with direct involvement of GABAB receptors. The actual therapeutic effect of ECT is therefore probably due to facilitation of cortical inhibitory mechanisms induced by GABAergic neurotransmission.