Disgust-Reduction Evaluative Conditioning (DREC) and tDCS in Contamination-Based OCD: A Randomized Controlled Trial

This randomized controlled trial investigated the efficacy of disgust-reduction evaluative conditioning (DREC) and transcranial direct current stimulation (tDCS) over the orbitofrontal cortex (OFC) in 48 patients with contamination-based OCD (C-OCD). Participants received either active/sham DREC (pairing contamination-related stimuli with pleasant images) and active/sham tDCS (cathodal stimulation targeting OFC) over 10 sessions. Results demonstrated significant reductions in disgust intensity (p≤0.01p≤0.01) and OCD symptoms (Y-BOCS, p<0.001p<0.001; C-PI-WSUR, p≤0.01p≤0.01) across active intervention groups (DREC, tDCS, or combined). The combined DREC+tDCS group showed the largest improvements, with sustained effects at two-month follow-up. Neurophysiological changes included decreased theta power (linked to symptom reduction) and reduced high-beta activity (indicating long-term neuromodulation), while cognitive improvements were limited to inhibitory control tasks (e.g., reduced commission errors in disgust trials, p=0.01p=0.01). Attentional bias remained unchanged, suggesting dissociation between clinical and cognitive outcomes.
The study highlights two mechanisms: (1) DREC’s reliance on associative learning to weaken disgust valuation via repeated CS-US pairings, which generalized to real-world triggers, and (2) tDCS-induced OFC modulation, transiently reducing cortical hyperexcitability associated with disgust appraisal. The synergy of DREC (behavioral) and tDCS (neural) interventions suggests enhanced plasticity in CSTC circuits, thogh tDCS alone lacked durability. Clinically, DREC offers a novel adjunct to exposure therapies by targeting disgust resistance to extinction, while OFC-focused tDCS may refine neuromodulation protocols for OCD subtypes. Limitations include a small, gender-imbalanced sample (85% female), concurrent pharmacotherapy/psychotherapy, and ethnic homogeneity. Future research should explore scalable DREC formats (e.g., mobile apps), larger unmedicated cohorts, and combination therapies (e.g., tDCS + rTMS) to optimize disgust-focused treatments across diverse populations.