Magnetic seizure therapy and electroconvulsive therapy increase frontal aperiodic activity.

Major depressive disorder (MDD) is a leading cause of disability worldwide. One of the most efficacious treatments for treatment-resistant MDD is electroconvulsive therapy (ECT). Recently, magnetic seizure therapy (MST) was developed as an alternative to ECT due to its more favorable side effect profile. While these approaches have been very successful clinically, the neural mechanisms underlying their therapeutic effects are unknown. For example, clinical "slowing" of the electroencephalogram has been observed in both treatment modalities. A recent longitudinal study of a small cohort of ECT patients revealed that observed clinical slowing was better explained by increases in frontal aperiodic activity, an emerging EEG signal linked to neural inhibition. Here we investigate the role of aperiodic activity in a cohort of patients who received ECT and a cohort of patients who received MST treatment. We find that across treatments, frontal aperiodic activity better explains increases in delta band power associated with clinical slowing, compared to delta oscillations. Increased aperiodic activity is also linked to therapeutic efficacy, which is suggestive of a potential shared neural mechanism of action across ECT and MST: an increase in frontal inhibitory activity.