An FMRI Study Of Functional Connectivity And Brain Network Abnormalities In Hippocampal Subregions Of Depression In Resting State

Major depression disorder(MDD)is a kind of mental illness characterized by persistent depression,attention and memory decline,low personal evaluation and lack of motivation.Every year,350 million people in the world are affected by MDD,and the lifetime prevalence of MDD in China is as high as 3.4%.This seriously affects people's lives and hinders social discovery.However,the pathogenesis of MDD is still unclear.With the discovery of neuroimaging technology,researchers found that functional magnetic resonance imaging(f MRI)can be used to explore the pathological mechanism of MDD.In addition,many f MRI studies do find some functional and structural abnormalities in the brain of MDD patients,but there is still no consistent result,so there is no general conclusion about MDD.However,studies have found that the hippocampus of depression patients often appears abnormal.Specifically,many studies have found that the volume of hippocampus is smaller than that of healthy people,but it is not very accurate to determine whether the hippocampus is a biomarker of MDD only based on the volume of the abnormal.Therefore,this study will focus on functional connections and brain networks,trying to provide evidence for the hippocampus as a biomarker of MDD in terms of resting-state functional connections and brain networks.In this study,the experimental design of case-control group was used,and 80 people were included in the study,including 55 in MDD group and 25 in healthy control group.The demographic data,clinical scale data and f MRI data of the subjects were collected within 48 hours after enrollment.In the study,resting-state f MRI data of the subjects were used.In the first part,the resting state functional connectivity(rsfc)method was used to compare the differences of functional connectivity of the hippocampus between the MDD group and the healthy control group,and the receiver operating characteristic curve(ROC)was used to discriminate MDD patients from healthy controls.In the second part,based on the first part,the differences between MDD group and healthy control group were further compared in the brain network composed of hippocampus subfields and functional connection abnormal brain area.To explore the role of hippocampus in the pathogenesis of MDD through research one and two.The main results are as follows:(1)The results of two sample t-test showed that: Compared to HCs,the cornu ammonis(CA)as seed region exhibited an increased functional connectivity to the left premotor cortex(PMC).(MNI: 45,6,-9;t=3.87).On the other hand,a reduced functional connectivity from the CA to the right insula(MNI:-45,12,36;t=-3.63)was shown.Increased functional connectivity was reported from the DG to the left orbitofrontal cortex(OFC)(MNI:-39,-39,18;t =5.02)and left ventrolateral prefrontal cortex(vl PFC)(MNI:-36,33,3;t =3.8).The subiculum as seed region revealed an increased functional connectivity to the left PMC(MNI:-48,12,36;t =4.64),the right middle frontal gyrus(MFG)(MNI: 39,9,54;t =4.07),and the left vl PFC(MNI:-39,33,6;t =4.0).In addition,a decreased functional connectivity was shown between the subiculum(MNI: 45,3,-9;t =-3.84)and the right insula.ROC curves confirmed that the differences between groups were statistically significant.(2)The results of brain network analysis show that in the first brain network,the hub in the healthy control group is the CA,and there is no hub in the MDD group;in the second brain network,the hub in the healthy control group is the DG,and the hub in the MDD group is the left VLPFC;in the third brain network,the hub in the healthy control group is the left vl PFC,and the hub in the MDD group is the left vl PFC right insula.The connection density of MDD group(9 connections)was lower than that of healthy control group(12 connections).The connection direction of CA and right insula,DG and left vl PFC in MDD group was opposite to that in healthy control group.The connection intensity between the CA and the right insula of MDD group was significantly lower than that of the control group(P < 0.01,t =-3.27)Therefore,this study draws the following conclusions:(1)There are some functional differences between the three subregions of hippocampus,but the three subregions are not completely independent but cooperative.It is mainly due to the abnormal functional connection between the hippocampus and the cognitive related brain area that leads to the disorder of emotion regulation and cognition in MDD patients.Therefore,the abnormal functional connection of hippocampus is related to the clinical symptoms of MDD.(2)The emotional network of MDD patients is not closely connected which may lead to the abnormal mood of MDD.Therefore,the abnormality of brain network in hippocampus plays an important role in the pathogenesis of MDD.In conclusion,the abnormal functional connections and brain networks in the hippocampus are involved in the pathophysiological mechanism of MDD.