Structural-functional multilayer brain network properties and outcome of combined repetitive transcranial magnetic stimulation and psychotherapy for obsessive–compulsive disorder

Background Repetitive transcranial magnetic stimulation (rTMS) is a promising treatment for obsessive–compulsive disorder (OCD), but response rates are variable. Pre-treatment characteristics of the stimulated region can influence rTMS outcome. Objective/hypothesis: We investigated the relationship between network features of the rTMS stimulation location and treatment outcome in a randomised trial of rTMS combined with exposure and response prevention psychotherapy (ERP) for OCD, using graph analysis of single-layer functional and structural brain networks, and of structural–functional multilayer networks. Methods We analysed data from 58 treatment-refractory adult OCD patients. Participants received either: high frequency (HF) rTMS to the left dorsolateral prefrontal cortex (DLPFC) (n = 19); HF rTMS to the left pre-supplementary motor area (preSMA) (n = 21); or control rTMS to the vertex (n = 18), all combined with ERP. We used pre-treatment resting state functional MRI (rs-fMRI) and diffusion MRI (dMRI) scans to construct single-layer and structural–functional multilayer networks for each participant. We computed various centrality measures of the stimulated location and subnetwork, and examined their relationship with treatment outcome. Results We found no associations between functional/structural single-layer network characteristics and treatment outcome. However, higher average multilayer betweenness centrality of the stimulated subnetwork in the DLPFC rTMS group (but not in the preSMA/vertex groups) was associated with symptom reduction (p = 0.013). Conclusions Participants with greater integration of the stimulated subnetwork with the rest of the structural–functional network showed greater improvement following DLPFC rTMS-ERP. Our exploratory results give a preliminary indication of the importance of the interplay between structural and functional networks for rTMS outcome.