{Reference Type}: Journal Article
{Title}: Analyzing fractal dimension in electroconvulsive therapy: Unraveling complexity in structural and functional neuroimaging.
{Author}: Denier N;Grieder M;Jann K;Breit S;Mertse N;Walther S;Soravia LM;Meyer A;Federspiel A;Wiest R;Bracht T;
{Journal}: Neuroimage
{Volume}: 297
{Issue}: 0
{Year}: 2024 Jun 18
{Factor}: 7.4
{DOI}: 10.1016/j.neuroimage.2024.120671
{Abstract}: <B>BACKGROUND: </B>Numerous studies show that electroconvulsive therapy (ECT) induces hippocampal neuroplasticity, but findings are inconsistent regarding its clinical relevance. This study aims to investigate ECT-induced plasticity of anterior and posterior hippocampi using mathematical complexity measures in neuroimaging, namely Higuchi's fractal dimension (HFD) for fMRI time series and the fractal dimension of cortical morphology (FD-CM). Furthermore, we explore the potential of these complexity measures to predict ECT treatment response.<BR><B>METHODS: </B>Twenty patients with a current depressive episode (16 with major depressive disorder and 4 with bipolar disorder) underwent MRI-scans before and after an ECT-series. Twenty healthy controls matched for age and sex were also scanned twice for comparison purposes. Resting-state fMRI data were processed, and HFD was computed for anterior and posterior hippocampi. Group-by-time effects for HFD in anterior and posterior hippocampi were calculated and correlations between HFD changes and improvement in depression severity were examined. For FD-CM analyses, we preprocessed structural MRI with CAT12's surface-based methods. We explored group-by-time effects for FD-CM and the predictive value of baseline HFD and FD-CM for treatment outcome.<BR><B>RESULTS: </B>Patients exhibited a significant increase in bilateral hippocampal HFD from baseline to follow-up scans. Right anterior hippocampal HFD increase was associated with reductions in depression severity. We found no group differences and group-by-time effects in FD-CM. After applying a whole-brain regression analysis, we found that baseline FD-CM in the left temporal pole predicted reduction of overall depression severity after ECT. Baseline hippocampal HFD did not predict treatment outcome.<BR><B>CONCLUSIONS: </B>This study suggests that HFD and FD-CM are promising imaging markers to investigate ECT-induced neuroplasticity associated with treatment response.