Participants
Participants were 61 SZ who met the Diagnostic and Statistical Manual of Mental Disorders-IV (DSM-IV) criteria, and 63 matched healthy controls(HC) recruited from the same geographical areas through advertisement. Patients were progressively recruited at the Shanghai Mental Health Center outpatient department between August 2019 and December 2022. For each patient with SZ, the severity of symptoms were assessed by two experienced psychiatrists using the Positive and Negative Syndrome Scale (PANSS) [32]. We also assessed the cognitive performances by the Repeatable Battery for RBANS [33], Temporal Experience of pleasure,TEPS) and Snaith‑Hamilton Pleasure Scale(SHAPS) were used for assessing pleasure of each participant[34, 35]. Individuals with other psychiatric disorders, a history of substance use, medical comorbidities including hypertension, hyperglycemia and hyperlipidemia, pregnancy, breastfeeding, electroconvulsive therapy within the last six months were excluded.
The study protocol was approved by the Institutional Ethics Review Board of Shanghai Mental Health Center, Shanghai Jiao Tong University School of Medicine. All investigations were performed in strict accordance with the Declaration of Helsinki. Before the recruitment, all participants provided written informed consent.
MRI acquisition
T1-weighted imaging and DWI data were acquired on a 3.0-Tesla and 64-channel head coil Siemens Magneton Prisma system (Siemens Healthcare, Erlangen, Germany). T1 images were acquired using a three-dimensional magnetization-prepared rapid acquisition gradient echo (MPRAGE) sequence [voxel size = 0.9 × 0.9 × 0.9 mm3, repetition time (TR) = 2000 ms, echo time (TE) = 2.32 ms, flip angle = 8°, and number of slices = 208, slice thickness = 0.9mm]. DTI data were acquired with a single-shot echo-planar imaging sequence (repetition time = 3500 ms, echo time = 86 ms, flip angle = 90°, number of slice = 92, slice thickness = 1.5 mm, voxel size = 1.5 × 1.5 × 1.5 mm3, b values = 0 and 1000 s/mm2).
Image preprocessing
Structural images were preprocessed to extract brain tissue from images of the whole head using the automated FreeSurfer pipeline (version 6.0.0).[36] The image was segmented into 82 distinct regions including 68 cortices and 14 subcortical regions based on Desikan-Killiany atlas. Individual structural images were then registered to the diffusion space using bbregister. T1-weighted diffusion data were pre-processed by open-source software library FMRIB's Software Library (FSL) (https://fsl.fmrib.ox.ac.uk/fsl/fslwiki/FDT/UserGuide). Briefly, brain masks were generated from b0 image to detect nonbrain tissue using the Brain Extraction Tool (BET). Eddy current distortions and subject motions were then corrected in the individual DWI data.
Structural connectomes construction
To create structural connectomes, a node was assigned to each of the 82 regions from the Desikan-Killiany anatomical parellation. Each brain region was selected as a seed region, and its connectivity probability to the other 81 regions was calculated. By selecting each brain region as a seed region, and its streamline number to the remaining 81 regions was calculated by FSL probabilistic tractography with default options (number of samples = 5000, number of steps per sample = 2000, step length = 0.5 mm, and curvature threshold = 0.2) of the probtrackx2 GPU. Thus, an 82 × 82 probability weighted matrix was created to represent the constructed network.
Data analysis
Network-based statistics
We conducted a network-based statistic (NBS) analysis between SZ and HC groups to examine subnetwork connectivity within the structural connectome. The analysis was completed within the framework of component p-value and edge p-value being below 0.001 and 0.05 respectively, age and gender being the covariates for two-sample t-tests. Subsequently, specific network edges that displayed significant differences between SZ and HC were identified. To examine the significance of each subnetwork, permutation tests were employed. We randomly assigned the subjects into the HC and SZ groups 5000 times, generating a null distribution of the network size based on these randomized groupings.
Graph Theory Analysis Graph theoretical metrics were assessed using GRETNA (version 2.0.0) to characterize the topological organization of structural networks. We computed the strength and efficiency profiles for each network including shortest path length (Lp), global efficiency (Eglob), local efficiency (Eloc), as well as nodal properties including node efficiency (Ne), nodal local efficiency (NLe), degree and betweenness centrality (Dc and Bc), nodal clust coefficiency (NCp) in the binary networks with a set of network sparsity from 0.05 to 0.50 with an interval of 0.05 and 100 random networks. False discovery rate (FDR) correction was used to determine the statistical significance of group differences.
Between-Group Statistical Comparison and Correlation Analysis
Statistical Analysis
All statistical tests were two-tailed. Statistical significance was set at P < 0.05. Demographic data between HC and SZ were computed using independent t-test or chi-square tests for categorical variables.
Strength is calculated as the total number of connections (streamlines) of each node. We compared the mean streamlines across edges in each subnetwork component by t-test. We averaged streamline connectivity strength between subcortical regions, such as the thalamus, hippocampus and amygdala, to the cortex. Additionally, considering the substantial projections from the insula to other cortical areas, we also calculated the average connection strength of insula projections. Then group differences were compared. Furthermore, we conducted exploratory analysis. After controlling for gender and age, Pearson correlation analysis was used to explore the correlation between clinical disease characteristics, cognitive function status, and significant network features in patients with SZ.