P219 The variability of targets for repetitive transcranial magnetic stimulation based on navigated TMS mapping and intrinsic connectivity measures

Introduction Despite the quasi high effectiveness of the repetitive transcranial magnetic stimulation (rTMS) of left dorsolateral prefrontal cortex (lDLPFC) in treatment of major depression, the high effect size variability is noticed (Herbsman et al., 2009). One of the reasons for this variability is the imperfect targeting of stimulation point. Resting state functional MRI (rsfMRI) has become a very popular tool to measure an intrinsic connectivity. Seed-based connectivity analysis is the method to evaluate functional connectivity between a chosen region and the whole brain. This analysis could be used for rTMS point targeting (Fox et al., 2012). Objectives Our aim was to evaluate the possibilities of seed-based connectivity analysis in TMS stimulation point targeting and to measure the variability of these points compared to navigated transcranial magnetic stimulation (nTMS)-guided targeting. Materials and Methods Five patients (all females, mean age = 36.6, SD = 8.7) suffering major depression were enrolled in this study. They were clinically evaluated with Beck Depression Inventory (mean value = 28.5, SD = 12). Resting-state fMRI data was acquired on 3T MR-scanner. nTMS with Abductor pollicis brevis muscle mapping was also performed with NBS eXimia Nexstim device. Maps of functional connectivity were built using CONNtoolbox for MATLAB. Subgenual cingulated cortex area (10 mm radius sphere at MNI coordinates (6,16,-10) was taken as a seed region. Then points in lDLPFC with maximum value of negative correlation were found individually in seed maps. The second pool of points was determined as5 cmanterior to individual APB muscle hotspot. The coordinates of two pools of points were compared inter- and intra-individually. Results Maximal distance between nTMS-guided points was 13.27 mmvs.53.62 mm between rsfMRI-guided points. Mean distance to the center of points in nTMS-guided group was 5.45 mmvs 38.83 mmin rsfMRI-guided group. Mean distance between intraindividual nTMS- and rsfMRI-guided points was 40.02 mm (Fig. 1) . Conclusion The interindividual variability of rsfMRI-based points’ coordinates was much higher than in nTMS-based points. High intraindividual variability was also shown. We are starting a clinical trial comparing the effects of rTMS targeting with these two methods in major depression.