ECT and Functional Connectivity Between Hippocampus and DMN: New Study From Denmark

Out on PubMed, from researchers in Denmark, is this study:

Electroconvulsive therapy disrupts functional connectivity between hippocampus and posterior default mode network.

Gbyl K, Labanaukas V, Lundsgaard CC, Mathiassen A, Ryszczuk A, Siebner HR, Rostrup E, Madsen K, Videbech P.Prog Neuropsychopharmacol Biol Psychiatry. 2024 Feb 17:110981. doi: 10.1016/j.pnpbp.2024.110981. Online ahead of print.PMID: 38373628

The abstract is copied below:

Background: The mechanisms underlying memory deficits after electroconvulsive therapy (ECT) remain unclear but altered functional interactions between hippocampus and neocortex may play a role.

Objectives: To test whether ECT reduces functional connectivity between hippocampus and posterior regions of the default mode network (DMN) and to examine whether altered hippocampal-neocortical functional connectivity correlates with memory impairment. A secondary aim was to explore if these connectivity changes are present 6 months after ECT.

Methods: In-patients with severe depression (n = 35) received bitemporal ECT. Functional connectivity of the hippocampus was probed with resting-state fMRI before the first ECT-session, after the end of ECT, and at a six-month follow-up. Memory was assessed with the Verbal Learning Test - Delayed Recall. Seed-based connectivity analyses established connectivity of four hippocampal seeds, covering the anterior and posterior parts of the right and left hippocampus.

Results: Compared to baseline, three of four hippocampal seeds became less connected to the core nodes of the posterior DMN in the week after ECT with Cohen's d ranging from -0.9 to -1.1. At the group level, patients showed post-ECT memory impairment, but individual changes in delayed recall were not correlated with the reduction in hippocampus-DMN connectivity. At six-month follow-up, no significant hippocampus-DMN reductions in connectivity were evident relative to pre-ECT, and memory scores had returned to baseline.

Conclusion: ECT leads to a temporary disruption of functional hippocampus-DMN connectivity in patients with severe depression, but the change in connectivity strength is not related to the individual memory impairment.

Keywords: Electroconvulsive therapy; Hippocampus; Major depressive disorder; Resting state fMRI.

The paper is here.

And from the text:

CONCLUSION Our study provides evidence of a reduced functional connectivity between the hippocampus and the posterior DMN after a series of ECT, but this effect was not correlated with ECT-induced memory deficits in our sample. We propose that future research focuses on reproducing these findings and investigating their potential link with memory impairment. We recommend the future studies (1) ensure optimal definition of the hippocampal seeds, (2) employ a comprehensive assessment of episodic memory, including retrograde amnesia for autobiographical information, and (3) incorporate task-based fMRI to examine connectivity during the retrieval of episodic memory

Here is a sophisticated fMRI study showing decreased functional connectivity between hippocampus and the DMN after ECT, but no correlation with memory impairment. Perhaps the most important finding is that both the connectivity decrease and memory impairment are temporary. The anti-ECT crowd needs to learn that ECT causes temporary deficits in episodic memory.

Kudos to Dr. Gbyl and colleagues for this useful contribution to the neuroimaging ECT literature.