Project summary Treatment of severe obsessive-compulsive disorder (OCD) with deep brain stimulation (DBS) is evolving to provide precision modulation of pathological brain circuits. One promising DBS target for OCD is a large and complex white matter fiber bundle called the anterior limb of the internal capsule (ALIC). A clear challenge to effective dissemination of this treatment is the lack of specificity in targeting the necessary and sufficient ALIC pathways. To prepare DBS for broad dissemination, we must build the knowledge and tools to enhance the precision with which stimulation is applied to individual brains. The overarching hypothesis of the proposed research is that DBS-mediated responses (clinical, behavioral, and electrocortical) reflect activation of specific pathways traveling through the ALIC. In testing this hypothesis, our proposal will construct an atlas of circuit- response maps, which can be used to guide clinical programming decisions and enhance the precision of surgical targeting for ALIC DBS. Individuals receiving ALIC DBS to treat OCD (n=20) will undergo 7T magnetic resonance imaging and electroencephalography, as well as behavioral testing at multiple time points. Aim 1 will produce a connectome blueprint that characterizes white matter pathways implicated in effective treatment of OCD. Aim 2 provides a patient-level, electrophysiological read-out to indicate which pathways are stimulated at tractography-defined locations in the ALIC. Aim 3 constructs a behavioral-connectome blueprint by linking change in task performance to DBS at tractography-defined locations in the ALIC. Combined, this research constructs a connectomic atlas for OCD using the association of white matter structures, electrocortical response and behavioral outcomes to specify the ideal anatomical target for DBS.