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

Area of Science:

• Neuroscience
• Psychiatry
• Medical Imaging

Background:

• Mechanisms of memory deficits post-electroconvulsive therapy (ECT) are not fully understood.
• Altered functional interactions between the hippocampus and neocortex are implicated in ECT-induced memory impairment.

Purpose of the Study:

• To determine if ECT reduces functional connectivity between the hippocampus and posterior default mode network (DMN).
• To investigate the correlation between altered hippocampal-neocortical connectivity and memory impairment.
• To assess the persistence of connectivity changes six months after ECT.

Main Methods:

• Resting-state functional MRI (fMRI) was used to measure hippocampal connectivity in 35 patients with severe depression undergoing bitemporal ECT.
• Connectivity was assessed before ECT, immediately after, and at a six-month follow-up.
• Memory was evaluated using the Verbal Learning Test - Delayed Recall, with seed-based connectivity analyses performed on hippocampal regions.

Main Results:

• Following ECT, three of four hippocampal seeds showed reduced connectivity to posterior DMN nodes (Cohen's d: -0.9 to -1.1).
• Patients experienced group-level memory impairment post-ECT, but individual memory changes did not correlate with reduced hippocampus-DMN connectivity.
• At six-month follow-up, hippocampus-DMN connectivity returned to baseline levels, as did memory scores.

Conclusions:

• Electroconvulsive therapy causes a transient disruption in functional hippocampus-DMN connectivity in patients with severe depression.
• The degree of connectivity change following ECT does not correlate with the severity of individual memory impairment.