Cathodal tDCS over right orbitofrontal cortex enhances the ability in subclinical obsessive-compulsive disorder to shift to model-based control.

While transcranial direct current stimulation (tDCS) targeting the orbitofrontal cortex (OFC) demonstrates therapeutic potential for obsessive-compulsive disorder (OCD), its neurocognitive mechanisms leading to reduced compulsive behaviors remain poorly understood. This study investigates the effects of stimulating the OFC on impaired arbitration between model-based (MB) and model-free (MF) reinforcement learning systems in subclinical OCD. In a randomized, sham-controlled trial, participants with elevated Obsessive-Compulsive Inventory-Revised (OCI-R) scores received six sessions of anodal (excitatory; n = 30), cathodal (inhibitory; n = 31), and sham (n = 32) tDCS over the right OFC, respectively. Arbitration control was quantified pre-/post-stimulation using a two-step decision-making task with computational modeling of MB-MF dynamics. Cathodal tDCS significantly enhanced inhibition of MB-to-MF transitions during MB-optimal complex task condition, promoting stable MB control (p < 0.001). Anodal stimulation showed no significant effects relative to sham. Right OFC cathodal tDCS improves arbitration control in subclinical OCD by facilitating context-appropriate MB strategy implementation, revealing a novel therapeutic mechanism for compulsivity remediation.