Dear Drs. Adeel Razi and Peter Zeidman (and SPM/DCM experts), I am trying to perform large-scale DCM analysis for resting-state fMRI data. I have 9 regions of interest - defined based on MNI coordinates from literature. I am interested in comparing the connectivity between these 9 regions between two groups: B and G. So I ran following steps (just to test, I used two subjects per group) using PEB wiki guidelines: -------------------- Steps I ran:-------------------- % Two Groups: B and G % DCM_DMN_B1.mat: Full model for subject 1 for group B % DCM_DMN_B2.mat: Full model for subject 2 for group B % DCM_DMN_G1.mat: Full model for subject 1 for group G % DCM_DMN_G2.mat: Full model for subject 2 for group G GCM = {'DCM_DMN_B1.mat';'DCM_DMN_B2.mat';'DCM_DMN_G1.mat';'DCM_DMN _G2.mat'}; GCM(:,1) = spm_dcm_fit(GCM(:,1)); GCM = spm_dcm_peb_fit(GCM); save('GCM_example.mat','GCM'); % Specify PEB model settings N = 4; % number of subjects M = struct(); M.alpha = 1; M.beta = 16; M.hE = 0; M.hC = 1/16; M.Q = 'single'; % Specify design matrix for N subjects M.X = ones(N,1); % Choose field field = {'A'}; % Estimate model PEB = spm_dcm_peb(GCM,M,field); save('PEB_example.mat','PEB'); BMA = spm_dcm_peb_bmc(PEB(1)); spm_dcm_peb_review(BMA,GCM) ------------------------------------------------------------ ------------------ This runs successfully, *but my output is showing a blank connectivity matrix (no connectivity between any pair of nodes among 9), even at no threshold. For your convenience**, here I am attaching one *.mat file (DCM_DMN_B1.mat) (dropbox link: https://www.dropbox.com/s/u8b7009lz86l2aj/DCM_DMN_B1.mat?dl=0 <https://www.dropbox.com/s/u8b7009lz86l2aj/DCM_DMN_B1.mat?dl=0>) and final output screen shot*. Also, its showing that there is one covariate, I am not sure what is that, as I didn't define any covariate in above steps. Could you please confirm if the above steps are correct and help me in figuring out what I am doing wrong here while comparing two groups: B and G? Also, any documentation to interpret the final results will be really useful. Thank you so much ! Best, Sahil