Transcranial Direct Current Stimulation Augmented Exposure and Response Prevention for Obsessive-Compulsive Disorder

Inclusion Criteria: * Current primary OCD diagnosis and current Yale-Brown Obsessive-Compulsive Scale (Y-BOCS) total score of ≥16 * 18-65 years of age * Ability to speak, read, write, and understand English sufficiently well to complete study procedures and provide informed consent * Right-handed * No use of psychiatric medications or stable psychiatric medication use for a minimum of 6 week prior to study entry. Psychiatric medications will be limited to the following: serotonin reuptake inhibitors (SRI; including clomipramine), combination antidepressants (including bupropion and serotonin-norepinephrine reuptake inhibitors), buspirone, benzodiazepines, and/or stimulants * Naive to tDCS Exclusion Criteria: * Active substance use disorder * Lifetime diagnosis of psychotic or bipolar mood disorder * Previous minimally adequate trial of ERP (e.g., at least 16 sessions including both therapist and self-directed exposure and response prevention) * Therapy outside the study protocol which has evidence for efficacy with OCD during the study intervention period * Active suicidal or homicidal ideation * Organic brain disease or injury * Any health problems that would interfere with study participation, including contraindications to tDCS (e.g., skin condition, mental implant in skull) * Women who are pregnant or breastfeeding. All women participants of child-bearing age are required to have a negative pregnancy test prior to treatment, and must use medically acceptable birth control during study participation. Medically acceptable birth control includes: established oral, injected, implanted, or vaginal ring hormonal contraception, an intrauterine device (IUD), two barrier contraception methods (condom or occlusive cap with spermicidal foam/gel/film/cream/suppository), or having a vasectomized partner * Use of anticonvulsant medications (including depakote, gabapentin, tegretol, dilantin, lamictal) and/or glutamate-acting agents (including n-acetylcysteine, riluzole, amantadine, memantine).