MRI ECT Changes in the Hippocampus: New Study from Switzerland

Out on Pubmed, from researchers in Switzerland and Germany, is this paper:

Gradient of electro-convulsive therapy's antidepressant effects along the longitudinal hippocampal axis.

Gyger L, Regen F, Ramponi C, Marquis R, Mall JF, Swierkosz-Lenart K, von Gunten A, Toni N, Kherif F, Heuser I, Draganski B.Transl Psychiatry. 2021 Mar 29;11(1):191. doi: 10.1038/s41398-021-01310-0.PMID: 33782387

The abstract is copied below:

Despite decades of successful treatment of therapy-resistant depression and major scientific advances in the field, our knowledge about electro-convulsive therapy's (ECT) mechanisms of action is still scarce. Building on strong empirical evidence for ECT-induced hippocampus anatomy changes, we sought to test the hypothesis that ECT has a differential impact along the hippocampus longitudinal axis. We acquired behavioural and brain anatomy magnetic resonance imaging (MRI) data in patients with depressive episode undergoing ECT (n = 9) or pharmacotherapy (n = 24) and healthy controls (n = 30) at two time points 3 months apart. Using whole-brain voxel-based statistical parametric mapping and topographic analysis focused on the hippocampus, we observed ECT-induced gradient of grey matter volume increase along the hippocampal longitudinal axis with predominant impact on its anterior portion. Clinical outcome measures showed strong correlations with both baseline volume and rate of ECT-induced change exclusively for the anterior, but not posterior hippocampus. We interpret our findings confined to the anterior hippocampus and amygdala as additional evidence of the regional specific impact of ECT that unfolds its beneficial effect on depression via the "limbic" system. Main limitations of the study are patients' polypharmacy, heterogeneity of psychiatric diagnosis, and long-time interval between scans.

The pdf is here.

And from the text:

Discussion 

Our study provides empirical evidence for a gradient of ECT-induced behavioural and brain anatomy changes along the longitudinal hippocampal axis, with predominant effects on its anterior portion and the amygdala. We observed a steeper rate of volume change in the anterior hippocampus in ECT-treated patients compared with individuals on pharmacotherapy only and HC. There is a similar gradient linking the longitudinal hippocampal axis and amygdala anatomical characteristics with ECTs antidepressant effects, such that large anterior hippocampus and amygdala at baseline correlates with better clinical outcome after ECT, while stronger ECT-induced volume change is associated with less improvement.

This is a well-written and presented neuroimaging study that may move the needle of knowledge of mechanism of action of ECT a bit in the forward direction. The finding of correlation of baseline anterior hippocampus and amygdala with better clinical outcome is straightforward, but the second finding, that there was less clinical improvement with greater volume change, seems puzzling. Remember, this study only had only n=9 ECT patients, so we should not devote too much of our own cortical space to remembering the specifics of the results. But the reminder that the hippocampus is a complex and multi-faceted brain region, with "emotional memory" located more anteriorly ("limbic" hippocampus) is a good learning point.

I recommend a full read only for devoted neuroimaging fans, ~20 minutes.