Clinical EEG slowing induced by electroconvulsive therapy is better described by increased frontal aperiodic activity

Abstract

Electroconvulsive therapy (ECT) is one of the most efficacious interventions for treatment-resistant depression. Despite its efficacy, ECT's neural mechanism of action remains unknown. Although ECT has been associated with "slowing" in the electroencephalogram (EEG), how this change relates to clinical improvement is unresolved. Until now, increases in slow-frequency power have been assumed to indicate increases in slow oscillations, without considering the contribution of aperiodic activity, a process with a different physiological mechanism. Here we show that aperiodic activity, indexed by the aperiodic exponent, increases with ECT treatment. This increase better explains EEG "slowing" when compared to power in oscillatory peaks in the delta (1-3 Hz) range, and is correlated to clinical improvement. In accordance with computational models of excitation-inhibition balance, these increases in aperiodic exponent are linked to increasing levels of inhibitory activity, indicating that ECT might ameliorate depressive symptoms by restoring healthy levels of inhibition in frontal cortices.

Magnetic seizure therapy and electroconvulsive therapy increase aperiodic activity

“…The observation that frontal aperiodic activity increases after a course of ECT supports our recent finding from a smaller, longitudinal study 25 . Furthermore, similar observations after a course of MST identify the increase in aperiodic activity as a potentially informative physiological change shared by both of these seizure-based treatments for depression.…”

“…This conflation occurs even in the absence of oscillations, which are not omnipresent, but rather appear infrequently in short bursts [22][23][24] . So even if there are no oscillations, a large aperiodic signal can appear very similar to slowing in the EEG, as we have recently demonstrated 25 . This effect occurs because the EEG signal is a mix of oscillations and aperiodic activity, where oscillations are defined by concentrated power with a specific, narrow frequency band.…”

“…Electrodes of interest for further analysis were frontal (FP1, FPZ, FP2, AF3, AF4, F7, F5, F3, F1, FZ, F2, F4, F6, F8, FC5, FC3, FC1, FCZ, FC2, FC4, FC6). Further analysis was restricted to these electrodes because previous investigations found strong effects in frontal regions 25 and because both ECT and MST treatments target frontal cortical regions for stimulation. These electrodes were chosen to maintain consistency between the analyses in this study and the exploratory study in REF #25, and because prior research shows EEG effects of MDD treatment are strongest on frontal electrodes 59,60 .…”

“…To test this hypothesis we compare measures of aperiodic activity, oscillations, and canonical band power. For each treatment modality, resting state EEG was collected at baseline and after completing a standard treatment, and analyses were restricted to frontal channels for replicability 25 . We find that in both ECT and MST treatment conditions, aperiodic exponent in frontal regions increases significantly and this change better explains observed delta (1-4 Hz) band power increases than power of a delta oscillation.…”

Changes in electrophysiological aperiodic activity during cognitive control in Parkinson’s disease

“…Literature provided mixed results about correlation between behavior and aperiodic activity. Some studies showed an association between the aperiodic parameters and cognition: Ostlund et al 35 found that a lower exponent during resting state predicted better performance on the dual-task "Stopping task", Smith and colleagues 89 showed that the aperiodic exponent was associated with cognitive performance and Ouyang et al 90 also evidenced that aperiodic activity during resting state was associated with cognitive processing speed. However, a study aiming to investigate aperiodic parameters and their link with cognition didn't show any correlation between aperiodic activity and behavior.…”