Dysfunctional decision-making may be a prominent mechanism underlying maladaptive behavior in multiple psychiatric disorders, including obsessive-compulsive disorder (OCD). Debilitating compulsivity and avoidance in OCD is believed to be a direct result of flawed decision-processing. A better understanding of the brain mechanisms of abnormal decision-making in OCD is essential for the development of more effective treatment options. This mentored patient-oriented research career development project plans to address this underexplored area. People utilize two behavioral strategies, goal-directed (GD) and habitual (HB), when engaging in value-based decision-making that involves rewarding or punishing outcomes. Furthermore, an arbitration mechanism has been proposed recently that controls the balance between those two strategies in healthy subjects. Arbitration regions (the frontopolar and inferolateral prefrontal cortex (ilPFC)) regulate the goal-directed/habitual decision-making balance by selectively downregulating the activity of the habitual regions (putamen and supplementary motor area). In OCD, an imbalance exists between GD and HB action selection in favor of HB action selection. This project aims to explore the neurobehavioral characteristics of arbitration mechanism and its relationship with behaviors and clinical phenotypes in OCD by applying cognitive neuroscience, clinical task-based fMRI and transcranial direct current stimulation (tDCS) approaches. Adults with OCD and healthy control participants will perform two tasks while being scanned, and when they receive inhibitory, excitatory and sham tDCS over the left ilPFC outside scanner: I) a decision-making task in which GD and HB strategies compete to control action selection and II) a clinically relevant symptom provocation-avoidance task in which avoidance decisions will be simulated. The project's research aims are to 1) explore the GD, HB and arbitration regions' neural activity and arbitration-habitual circuit connectivity in OCD; 2) examine the association between measures of behavioral performance, arbitration's neural and connectivity, and OCD clinical symptoms; and 3) investigate the behavioral consequences of tDCS over an arbitration region, the left ilPFC, during tasks performance.