A Comparative Research On Characteristics Of Dynamic Brain Networks Between Depressed State And Euthymic State In Bipolar Disorder

Background: Many studies showed that bipolar patients have abnormal brain neurological activity,there is a dysfunctional connection in multiple brain networks such as the Default mode network(DMN),the Central executive network(CEN),the Salience network(SN).However,the manner by which these abnormal functions change across the different phases of BD is still unclear,and the mechanism of mood switching between different mood states in bipolar disorder remains unclear.Most of the current studies on neuroimaging of brain function changes in different phases of bipolar disorder are focused on the comparison of manic mood state and euthymic mood state,and few researches explored the biological mechanism of mood switch between depressed and euthymic mood states.However,the duration and quantity of depression in patients with bipolar disorder were more than manic phase,and about 60% of BD patients were first affective attack by depression.In addition,the existing studies have mostly used static function connectivity method to analyze the brain networks activity,and rarely consider the dynamic time domain characteristics of patients in MRI scanning.Therefore,this study will analyze the dynamic brain network characteristics of bipolar disorder patients with the first episode of depression and those in the euthymic phase,and compare the differences between bipolar disorder patients and healthy controls,so as to further clarify the biological mechanism of mood switch in bipolar disorder.Method: We recruited 20 bipolar depressed patients whose first episode is depression,25 bipolar euthymic patients and 32 healthy controls according to the inclusion and exclusion criteria,all the participates underwent resting-state functional magnetic resonance imaging(rs-f MRI)scans.According to the quality of the MRI data,excluding the influence of head movement,20 bipolar depressed patients,23 bipolar euthymic patients,and 31 healthy controls were included for analysis.Using an existing parcellation of the whole brain,we measured dynamic functional connectivity(d FC)between brain regions and identified the different patterns of brain network connections between groups.Then,we changed the parameters of d FC analysis to conduct a second d FC analysis verification,and detected the dynamic functional connectivity density(d FCD)between the three groups and the brain networks of the different d FCD,and again identified the different brain network connectivity patterns between the groups.Results:In whole-brain d FC analysis,we found d FC abnormalities in multiple brain regions in multiple brain networks between bipolar patients and healthy controls.The same conclusion was obtained in d FC secondary validation analysis and d FCD analysis.Further analysis showed that the connectivity between the left superior temporal gyrus(STG)in the somatomotor network(SMN)and the right middle temporal gyrus(MTG)and bilateral posterior central gyrus(Po G)in the DMN was increased in bipolar depressed patients than in euthymic patients.However,the connectivity in these brain regions did not differ significantly between bipolar euthymic patients and healthy controls.In addition,compared with HCs,the d FC in the frontal-striatal-thalamic(FST)circuit was abnormal in the bipolar euthymic patients.In the d FC secondary validation analysis and d FCD analysis,we also found that there were abnormal neural activities in multiple brain regions of the SMN,DMN and FST circuit between the three groups.Conclusion:There were extensive differences in d FC and d FCD in multiple brain networks involving DMN and SMN and FST circuit between bipolar depressed patients,bipolar euthymic patients and healthy controls.Differences in d FC within and between DMN and SMN can be used to distinguish depressed and euthymic states in bipolar patients.The hyperconnectivity within and between DMN and SMN may be a state feature of depressed BD.The abnormal connectivity of the FST circuit can help identify euthymic BD from HCs.Even with clinical symptoms remission,patients with bipolar disorder may not fully recover their brain functional activity.