Background: The efficacy of electroconvulsive therapy (ECT) is determined by stimulus electrical intensity and electrode placement. Three theories offer different accounts for why increasing the stimulus dosage of right unilateral ECT enhances antidepressant effects. This study examined the effects of ECT on interictal quantitative electroencephalograms (EEGs), contrasting these theories in their predictions regarding global, lateralized, and topographic changes in ECT-induced slow-wave activity. The time course of EEG changes and associations with efficacy were also determined.
Methods: Sixty-two inpatients with major depressive disorder were randomized to ECT conditions that differed in stimulus intensity (low vs high dosage) and electrode placement (right unilateral vs bilateral). Resting, eyes closed, 19-lead EEG recordings were obtained at pretreatment, following a single treatment, following an average of 7 treatments, during the week following the ECT course, and after a 2-month follow-up period.
Results: Electroconvulsive therapy produced a marked short-term increase in delta and theta power. At a 2-month follow-up, there were no significant alterations in any frequency band. The ECT treatment conditions differed markedly in efficacy. Global and lateralized EEG effects did not distinguish effective and ineffective forms of treatment. Effective forms of ECT resulted in increased delta power in prefrontal regions, and this change was associated with the magnitude of symptomatic improvement.
Conclusion: The induction of slow-wave activity in prefrontal cortex is linked to the efficacy of ECT.