Chapter Two Altered Gray Matter Structural Covariance Networks In Postpartum Depression:A Graph Theoretical Analysis

Objective This study investigated the cortical structural alterations of postpartum depression(PPD)patients through multidimensional structural patterns and their potential correlations with clinical severity.Methods High-resolution 3D-T1 WI structural images were acquired from 21 drugnaive patients with PPD and 18 healthy postpartum women matched for age,educational level,and body mass index.The severity of PPD was assessed by using the Hamilton Depression Scale(HAMD)and Edinburgh Postnatal Depression Scale(EPDS)scores.Cortical morphological parameters including cortical thickness,surface area,and mean curvature were calculated using the surface-based morphometric method.General linear model(GLM)analyses were performed to evaluate the relationship of cortical morphological parameters with clinical scales.Results In the present study,PPD patients showed a thinner cortical thickness in the right inferior parietal lobule compared with the healthy controls.Increased surface area was observed in the left superior frontal gyrus,caudal middle frontal gyrus,middle temporal gyrus,insula,and right supramarginal cortex in PPD patients.Likewise,PPD patients exhibited a higher mean curvature in the left superior and right inferior parietal lobule.Furthermore,increased cortical surface area in the left insula had a positive correlation with EPDS scores,and higher mean curvature in the left superior parietal lobule was negatively correlated with EPDS scores.Conclusions The complex cortical structural alterations of patients with PPD mainly involved the prefrontal and parietal regions.The morphometric alterations in these specific regions may provide promising markers for assessing the severity of PPD.Objective This study investigates the brain structural covariance networks of patients with PPD by using graph theoretical analysis.Methods High-resolution 3D-T1 WI structural images were acquired from 21 drugnaive patients with PPD and 18 healthy postpartum women.Cortical thickness was extracted from 64 brain regions to construct the whole-brain structural covariance networks by calculating the Pearson correlation coefficients,and their topological properties(e.g.,small-worldness,efficiency,and nodal centrality)were analyzed by using graph theory.Nonparametric permutation tests were further used for group comparisons of topological metrics.A node was set as a hub if its betweenness centrality(BC)was at least two standard deviations higher than the mean nodal centrality.Network-based statistic(NBS)was used to determine the connected subnetwork.Results The PPD and control groups showed small-worldness of group networks,but the small-world network was more evidently in the PPD group.Moreover,the PPD group showed increased network local efficiency and almost similar network global efficiency.However,the difference of the network metrics was not significant across the range of network densities.The hub nodes of the patients with PPD were right inferior parietal lobule(BC = 13.69)and right supramarginal gyrus(BC = 13.15),whereas those for the HCs were left cuneus(BC = 14.96),right caudal anterior-cingulate cortex(BC =15.51),and right precuneus gyrus(BC = 15.74).NBS demonstrated two disrupted subnetworks that are present in PPD: the first subnetwork with decreased internodal connections is mainly involved in the cognitive-control network and visual network,and the second subnetwork with increased internodal connections is mainly involved in the default mode network,cognitive-control network and visual network.Conclusions This study demonstrates the alteration of topographical organization in the brain structural covariance network of patients with PPD,providing in sight on the notion that PPD could be characterized as a systems-level disorder.