P107 Assessing effectiveness and specificity of DLPFC rTMS using an unbiased resting-state approach
Question While the precise mechanism of action is still unclear, rTMS is an effective FDA-approved treatment in depression and shows beneficial behavioral effects in a range of pathologies. A better understanding could improve treatment success and reduce the number of non-treatment responders. This study is the first to investigate effectiveness and specificity of rTMS over left DLPFC using a large-scale (n = 60) sham-controlled cross-over design and an unbiased resting-state (RS) approach. Methods 60 healthy subjects (age: 25.01 ± 4.6 years, f/m: 31/29) underwent rTMS DLPFC and sham stimulation (see Fig. 1) Download : Download high-res image (493KB) Download : Download full-size image . Resting state (rs) fMRI scans were acquired before and twice after stimulation. We investigated BOLD signal changes in functional connectivity (fc) following 10 Hz rTMS (24  × 5 s trains, ITI 20s, 1200 pulses @ 90%MT) during a classic resting state paradigm. We examined rsfc changes using an unbiased approach based on a set of 20 well-established resting state networks derived from multicenter-data independent component analysis by Biswal et al. (2010a, http://fcon_1000.projects.nitrc.org ). Results Comparisons between pre and post stimulation revealed that 19 out of a total of 20 IC networks remained unchanged, i.e. showed no statistically significant differences before and after rTMS irrespective of real/sham stimulation (Fig. 2 A, blue) Download : Download high-res image (1MB) Download : Download full-size image . Only one network (IC17, red dashed) which includes the ACC and PFC showed DLPFC rTMS-related connectivity changes (while staying stable throughout the whole procedure in sham session, Fig. 2 B): The ACC had increased connection strength in the post-rTMS scan within this network, particularly with the DLPFC (stimulation site), bilateral insula and striatum. Conclusion For the first time this study shows in a model-free approach that rTMS over left DLPFC modulates functional connectivity within a specific network while other networks stay stable. This network is typically associated with attention, mood, reward processing and psychiatric conditions that are linked to maladaptive changes in these domains. This could have further implications on treatment, screening and treatment response monitoring of psychiatric conditions.