Cortical excitation/inhibition ratios in patients with major depression treated with electroconvulsive therapy: an EEG analysis

TL;DR

This study investigates how electroconvulsive therapy affects brain excitation/inhibition ratios in depressed patients, finding that frontal brain changes correlate with treatment success.

Contribution

A novel method based on critical dynamics is used to estimate cortical excitation/inhibition ratios during ECT treatment.

Findings

Frontal fE/I ratios in frequencies 12–28 Hz increased significantly in responders to ECT.

No changes in fE/I ratios were observed in non-responders or healthy controls.

Frontal fE/I ratio modulation may be a key mechanism of ECT effectiveness.

Abstract

Electroconvulsive therapy (ECT) is an effective treatment for major depression, but its working mechanisms are poorly understood. Modulation of excitation/inhibition (E/I) ratios may be a driving factor. Here, we estimate cortical E/I ratios in depressed patients and study whether these ratios change over the course of ECT in relation to clinical effectiveness. Five-minute resting-state electroencephalography (EEG) recordings of 28 depressed patients were recorded before and after their ECT course. Using a novel method based on critical dynamics, functional E/I (fE/I) ratios in the frequency range of 0.5–30 Hz were estimated in frequency bins of 1 Hz for the whole brain and for pre-defined brain regions. Change in Hamilton Depression Rating Scale (HDRS) score was used to estimate clinical effectiveness. To account for test–retest variability, repeated EEG recordings from an independent sample of 31 healthy controls (HC) were included. At baseline, no differences in whole brain and regional fE/I ratios were found between patients and HC. At group level, whole brain and regional fE/I ratios did not change over the ECT course. However, in responders, frontal fE/I ratios in the frequencies 12–28 Hz increased significantly (pFDR < 0.05 [FDR = false discovery rate]) over the ECT course. In non-responders and HC, no changes occurred over time. In this sample, frontal fE/I ratios increased over the ECT course in relation to treatment response. Modulation of frontal fE/I ratios may be an important mechanism of action of ECT.

Figures