Electroconvulsive therapy (ECT) demonstrates favorable outcomes in the management of severe depressive
disorders. ECT has been consistently associated with volumetric increases in the amygdala and hippocampus.
However, the underlying mechanisms of these structural changes and their association to clinical improvement
remains unclear. In this cross-sectional structural MRI study, we assessed the difference in amygdala subnuclei
and hippocampus subfields in n = 37 patients with either unipolar or bipolar disorder immediately after eighth
ECT sessions compared to (n = 40) demographically matched patients in partial remission who did not receive
ECT (NoECT group). Relative to NoECT, the ECT group showed significantly larger bilateral amygdala volumes
post-treatment, with the effect originating from the lateral, basal, and paralaminar nuclei and the left corticoamydaloid transition area. No significant group differences were observed for the hippocampal or cortical volumes. ECT was associated with a significant decrease in depressive symptoms. However, there were no
significant correlations between amygdala subnuclei volumes and symptom improvement. Our study corroborates previous reports on increased amygdalae volumes following ECT and further identifies the subnuclei
driving this effect. However, the therapeutic effect of ECT does not seem to be directly related to structural
changes in the amygdala