Cathodal tDCS in obsessive-compulsive disorder: cognitive and neurophysiological outcomes in a double-blind sham-controlled trial.

OBJECTIVE: This preliminary study examined the efficacy of cathodal transcranial direct current stimulation (tDCS) targeting the medial prefrontal cortex (mPFC) in reducing symptom severity, enhancing cognitive flexibility, and modulating brain-derived neurotrophic factor (BDNF) levels in individuals with obsessive-compulsive disorder (OCD). METHODS: A double-blind, randomized, sham-controlled trial was conducted with 20 patients meeting DSM-V criteria for OCD, of whom 15 completed the intervention and were included in the final analysis. Participants received cathodal mPFC-tDCS (2 mA, 20 min, 10 sessions) or sham stimulation. Symptom severity (Y-BOCS), cognitive flexibility (task-switching), salivary BDNF, and frontal alpha activity (qEEG at Fz) were measured at baseline, post-treatment, and follow-up. RESULTS: The tDCS group exhibited greater reductions in Y-BOCS scores over time (F(2, 26) = 12.562, p < 0.001, partial η2 = 0.425). Task-switching performance improved in the experimental group compared with controls (F(2, 26) = 20.351, p < 0.001, partial η2 = 0.531). Salivary BDNF levels increased significantly in the tDCS group at follow-up (F(2, 16) = 6.086, p = 0.01, partial η2 = 0.432). Trends toward normalization of frontal alpha activity were observed, but did not reach statistical significance. CONCLUSIONS: Cathodal mPFC-tDCS was associated with reduced OCD symptom severity, improved cognitive flexibility, and increased salivary BDNF. These preliminary findings warrant replication in larger controlled samples. SIGNIFICANCE: This study extends previous tDCS research in OCD by integrating clinical outcomes with cognitive performance and a peripheral marker of neuroplasticity. It provides preliminary support for mPFC-targeted tDCS as a potential intervention for OCD.