Brain Network Mapping For Major Depressive Disorder Receiving Electroconvulsive Therapy

Major Depressive Disorder(MDD)is a common mental disorder with continuous feelings of sadness as its primary feature,and severe depression even leads to suicide.Electroconvulsive therapy(ECT)is one of the most potent and rapid antidepressant treatments for depression,particularly for severe and treatment-resistant depression.Under general anesthesia,small electric currents passes through the brain,intentionally triggering a brief seizure,which rapidly improves some psychiatric symptoms.The functional abnormalities of default mode network(DMN)have been well documented in MDD.However,the association of functional reorganization of DMN with antidepressant effect and gene expression is unclear.Moreover,many studies have reported brain network abnormalities in MDD patients,however,how ECT affects functional network topology to improve clinical symptoms in MDD patients remains to be studied.Therefore,this thesis aims to elucidate the antidepressant effect of ECT by using the functional and gene expression characteristics of DMN,and topological characteristics of the whole brain network.Here,we investigated the link of treatment response with functional alterations of DMN and gene expression in individuals with MDD after ECT.Then,the functional brain network for each subject was mapped using Brainnetome Atlas and graph-theory was applied to measure topological properties for both binary and weighted network.Static and dynamic functional connectivity analyses showed increased intrinsic/static but decreased dynamic functional couplings of inter-and intra-subsystems and between nodes of DMN.The changes of static functional connectivities of DMN were spatially correlated with human brain gene expression data.Moreover,static and dynamic functional connectivities of DMN before treatment as features could predict the changes of depressive symptoms after ECT.And the results of graph theory show that ECT can significantly increase shortest path length and decrease global efficiency in MDD patients.In addition,significant alterations in nodal degree,nodal efficiency as well as between nodal functional connectivity strength were found in MDD patients after ECT.The network nodes showing changed degree,efficiency and connectivity were primarily distributed in default mode network(DMN),fronto-parietal network(FPN),and limbic system.Taken together,these results shed new light on the underlying neural and genetic basis of antidepressant effect of ECT.ECT improves depressive symptoms by reorganizing disrupted network topological architecture or the functional connectivities of DMN in MDD patients.Moreover,DMN has the potential to serve as prognostic biomarkers to guide accurate personalized treatment.Meanwhile,the thesis highlights the important role of functional reorganization of DMN,FPN,and limbic network contributing to depression remission.