Patient-specific, Effective, and Rational Functional Connectivity Targeting for DBS in OCD

Inclusion Criteria: 1. OCD, diagnosed by Structured Clinical Interview for DSM-5 (SCID-5), judged of disabling severity with a Yale-Brown Obsessive Compulsive Scale (YBOCS) score of at least 28. 2. Persistence of severe symptoms and impairment for five or more years despite: i. at least three adequate (≥3 months at the maximum tolerated dose) serotonin transporter inhibitor trials (may use any serotonin or serotonin-norepinephrine inhibitors, but must include a trial of clomipramine) alone or in combination with ii. adequate behavior therapy (≥20 sessions of expert exposure and response prevention; At least 20 sessions of behavioral therapy must be attempted), and iii. augmentation of one of the selective SRIs with a neuroleptic or clonazepam. 3. Age between 21 and 64 years. 4. Able to understand and comply with instructions. 5. Able to give fully informed, written consent. 6. Approved to be implanted with a DBS device for OCD. Exclusion Criteria: 1. Current or past psychotic disorder. 2. Full-scale IQ below 75 on the Wechsler Abbreviated Scale of Intelligence (WAIS) or cognitive impairment that would affect a participant's ability to give informed consent or provide interview or self-report data reliably, as determined by the consent monitor and the site psychiatrist. A questionnaire assessing consent comprehension will be used with all study subjects, to ensure that they understand the key procedures of the study, and its risks and benefits. 3. A clinical history of bipolar mood disorder; substance-induced mania is not an exclusion. 4. Any current clinically significant neurological disorder or medical illness affecting brain function, other than tic disorders or Tourette syndrome. 5. Any clinically significant abnormality on preoperative magnetic resonance imaging (MRI). 6. Any labeled DBS contraindication, and/or inability to undergo presurgical MRI (cardiac pacemaker, pregnancy, metal in body, severe claustrophobia), infection, coagulopathy, inability to undergo an awake operation, significant cardiac or other medical risk factors for surgery. 7. Current or unstably remitted substance abuse, dependence, or a positive urine toxicology screen. 8. Pregnancy and women of childbearing age not using effective contraception. 9. Unable to adhere to operational and administrative study requirements (in the investigators' judgment). 10. Clinical history of severe personality disorder. 11. Imminent risk of suicide or an inability to control suicide attempts (in the investigators' judgment). History of serious suicidal behavior or one or more interrupted suicide attempts with potential lethality judged to result in serious injury or death. 12. Diagnosis of body dysmorphic disorder. 13. Evidence of dementia or other significant cognitive impairment on neuropsychological evaluation 14. Past or present diagnosis of hoarding disorder.