Volume Increases in the Medial Temporal Lobe Following Electroconvulsive Therapy
Post by Amanda McFarlan
What's the science?
Electroconvulsive therapy (ECT) is recognized as an effective treatment for individuals with severe psychiatric disorders like treatment-resistant depression. Although ECT has been used in psychiatric practice for more than 80 years, the mechanisms that underlie the treatment response remain unclear. Neuroimaging studies have provided evidence of structural changes in the brain in response to ECT, however, the heterogeneity between studies has made it difficult to draw straightforward conclusions. This week in Biological Psychiatry, Janouschek and colleagues performed a meta-analysis to investigate structural changes in the brain following ECT treatment.
How did they do it?
Several limitations including small sample sizes, different statistical approaches, and interstudy inhomogeneity have made it challenging to interpret the findings from neuroimaging studies involving ECT. Therefore, the authors aimed to overcome these limitations by pooling datasets from multiple studies. They searched PubMed and Google Scholar for structural MRI studies that involved ECT. They retrieved a total of 12 studies published between 2014 and 2019 that met the inclusion criteria for their analysis. With these studies, the authors used the statistical approach activation likelihood estimation to perform a quantitative coordinate-based meta-analysis and identify regions of significant convergence within the gray matter of the brain — in other words, the areas most commonly affected across multiple studies. In subsequent analyses, the authors investigated the robustness of their results by performing a jackknife analysis (leave-one-out) on the 10 studies (out of 12) that had reported significant results.
What did they find?
The authors identified 2 clusters within their dataset: a large cluster in the right hemisphere and a small cluster in the left hemisphere. The larger cluster was localized to the medial temporal lobe and mainly comprised the amygdala as well as a small portion of the hippocampus and basal forebrain. The smaller cluster was also localized to the amygdala but included the parahippocampal gyrus, hippocampus, and entorhinal cortex as well. Both clusters represented increases in grey matter volume. Next, the authors found that the cluster in the right hemisphere was mainly driven by studies that exclusively used right unilateral stimulations, with smaller contributions from bilateral and mixed stimulation paradigms. Conversely, the cluster in the left hemisphere was mainly driven by studies that used bilateral and mixed stimulations, which suggests that the position of the electrode during ECT may have a strong influence on the laterality of these findings. Other clinical or treatment parameters, such as age, gender, or treatment response did not have an influence on these brain structural changes. Finally, the authors corroborated their findings using the jackknife analysis and showed that there is evidence of bilateral spatial convergence in the amygdala and hippocampus across the studies involving ECT.
What’s the impact?
This is the first study to investigate brain structural changes during ECT using a coordinate-based meta-analysis of MRI studies involving ECT. The authors found evidence of a bilateral volume increase during ECT that was localized to the medial temporal lobe, particularly in the amygdala and hippocampus. In all, these findings are consistent with previous results from primary research studies and mega-analyses. These findings also help provide insight into the underlying mechanisms associated with treatment response following ECT. Future research is needed to better understand how volume changes might lead to a reduction in depression symptoms following ECT.
Janouschek et al. Meta-analytic Evidence for Volume Increases in the Medial Temporal Lobe After Electroconvulsive Therapy. Biological Psychiatry (2021). Access the original scientific publication here.