Transcranial Direct Current Stimulation Potentiation of Fear Extinction in OCD

The investigators want to learn more about how human beings learn not to fear and the impact of changing the fear network in the brain using transcranial Direct Current Stimulation (tDCS) in individuals with obsessive compulsive disorder (OCD). The investigators hope this study will help us understand how future treatments can help patients with OCD better control unwanted fear.

Inclusion Criteria: * Fluent in English, willing to provide informed consent, and willing to comply with the study protocol * Primary OCD that causes at least moderate distress and/or impairment (Y-BOCS total score ≥ 16) * Comfortable and capable of using a computer and completing computerized tasks Exclusion Criteria: * History of head injury resulting in prolonged (i.e., \>1h) loss of consciousness and/or neurological sequelae; history of stroke; signs of increased intracranial pressure; prior neurosurgical procedure (e.g., DBS, aneurysm clips) * Contraindications to participate in tDCS including: metallic implants in head or neck; ventriculoperitoneal (VP) shunts; pacemakers; pregnancy; epilepsy. * Current or history of neurologic or psychiatric disease (e.g., mental retardation, dementia, brain damage, or other cognitive impairment) that would interfere with ability to participate in the study * Impaired (or uncorrected) vision that would interfere with participation. * Current clinically significant suicidality that requires psychiatric hospitalization, as indicated by clinical judgment. * Current substance use disorder (within the past 12 months) * Lifetime manic episode or psychosis * Documented resistance to 4 or more valid pharmacological trials and previous treatment with ≥12 sessions of cognitive behavioral therapy for OCD with no response (or worsening symptoms) * Use of most psychotropic medications (e.g., SSRIs and atypical antipsychotics) will be allowed. However, use of benzodiazepines within 2 weeks prior to the study is exclusionary (and participants will be asked to refrain from use of such medications during the study as they may interfere with the fear extinction paradigm). * Unable to obtain low enough impedance values to ensure safe and effective application of tDCS/EEG.