Prefrontal Neuromodulation Restores Model-Based Control in Obsessive-Compulsive Disorder

Poster Session F - Tuesday, March 10, 2026, 8:00 – 10:00 am PDT, Fairview/Kitsilano Ballrooms

Hongyao Gao¹ (hongyao-gao@uiowa.edu), Reza Tadayon-Nejad^2,3, Jeffrey Cockburn^1,3; ¹University of Iowa, ²UCLA Semel Institute for Neuroscience and Human Behavior, ³California Institute of Technology

Reinforcement learning (RL) is often described in terms of model-free (MF) strategies that incrementally update action values based on reward history, and model-based (MB) strategies that rely on an internal model of the environment to plan future actions. Obsessive-compulsive disorder (OCD) has been associated with altered RL, particularly reduced expression of MB control. However, it remains unclear whether this reflects impairment of MB mechanisms or dysfunction in the arbitration between these systems. Here, we address this question using a modified version of the two-step decision task combined with transcranial direct current stimulation (tDCS) targeting the inferior lateral prefrontal cortex (ilPFC), a region implicated in the arbitration between MF and MB control. Individuals with OCD (N=32) and healthy controls (N=30) performed the task under baseline, sham, inhibitory, and excitatory stimulation conditions. Consistent with prior work, OCD participants showed reduced MB behavior relative to controls during baseline and sham sessions. Critically, excitatory stimulation of the ilPFC selectively enhanced MB control in the OCD group, while inhibitory stimulation produced no significant change in either group. No effect of excitatory stimulation was observed in healthy controls. Computational modeling within an RL framework further supported these findings. Moreover, excitatory stimulation improved behavioral flexibility following reward revaluation in the OCD group, whereas inhibition induced perseveration. Healthy controls showed the opposite pattern. Together, these results suggest that enhancing activity in the ilPFC promotes model-based behavior and improves adaptive flexibility in OCD. Consequently, individuals with OCD may exhibit dysfunction in the arbitration between MF and MB decision systems.

Topic Area: THINKING: Decision making