People utilize two behavioral strategies, goal-directed and habitual, when engaging in value-based decision-making that involves rewarding or punishing outcomes. Accumulating evidence suggests an imbalance between habitual and goal-directed behavior in favor of habitual control in parallel with exaggerated tendency toward compulsive/harm avoidance behavior in OCD. In healthy subjects, an arbitration mechanism has been proposed recently that controls the balance between those two strategies of action selection. Arbitration regions regulate the goal-directed/habitual decision-making balance by selectively downregulating the activity of the habitual regions. This project aims to explore the neurobehavioral characteristics of arbitration mechanism and its relationship with behaviors and clinical phenotypes in OCD by applying computational cognitive neuroscience, clinical task-based functional magnetic resonance imaging (fMRI) and transcranial direct current stimulation (tDCS) method.
Investigators will recruit 30 male and female adults (age 18-65) with OCD and 30 age-, sex-, and education-matched healthy (medically, neurologically and psychiatrically) controls for this project. Each participant will come for three sessions. There will be 3-4 days interval between sessions: Session 1 that includes initial clinical assessment and obtaining T1 structural image (needed for neuronavigation analysis and electric field modeling). Session 2 and 3 that include performing two separate decision-making and symptom provocation-avoidance tasks by participants with OCD and healthy controls under two conditions: while scanned inside the MRI scanner (no tDCS) or while receiving neuronavigated tDCS neurostimulation outside the scanner (no fMRI imaging). As participates will perform each task twice, there might be an order effect on task performance. For minimizing the impact of such a potential order effect on imaging and tDCS results, participants will be randomly assigned to undergo scanning in the session 2 and then receive tDCS in the session 3 or in the opposite order (tDCS in session 2 and then imaging in session 3) but in each session only one of imaging or tDCS experiments (for both tasks) will be conducted for each participant. OCD-relevant and aversive picture rating (explained below) will be done always in the session 3 as the last experiment.
