Data was analyzed from a previously collected dataset so no new participants were enrolled.

The study aims to improve patient-specific anatomical targeting of the Deep Brain Stimulation for the treatment of intractable OCD.

Recently, deep brain stimulation (DBS) has emerged as a potentially circuit-specific treatment for intractable OCD. DBS is programmable, allowing the clinician to "reshape" the volume of tissue activated within the standard ventral capsule/ventral striatum (VC/VS) target.

However, VC/VS DBS' efficacy is limited by two major factors: imperfect targeting and a lack of decision rules for stimulation adjustment. The VC/VS target is not a single identifiable structure, but encompasses white matter of the internal capsule and gray matter of the nucleus accumbens (NAc). In current practice for DBS in OCD, all patients are implanted at standard x,y,z coordinates in the VC/VS region. Due to this inter-subject anatomical variability, different fiber tracts are stimulated by ostensibly the "same" parameters in each subject, leading to variable outcomes. This investigation will identify aspects of VC/VS circuitry that may determine clinical response. The hypothesis is that good clinical outcomes may correlate to electrical field capture of either striatal gray matter or of white matter fibers connecting OFC to thalamus.

The current study looks to extend the neuroimaging investigation using anatomic white matter targeting, functional gray matter targeting and changes in changes in regional glucose metabolism of Deep Brain Stimulation (DBS) in severe obsessive-compulsive disorder (OCD) with the long-term aim of identifying biomarkers that could improve outcomes of this expensive and invasive therapy. Improved imaging would allow surgeons to place the DBS lead closer to the biological targets, thus improving efficacy of the treatment.

The objectives of this study are threefold:

• Improve the anatomic white matter targeting of the Deep Brain Stimulator (DBS) implant by tracing and identifying fibers of passage within the Ventral Capsule (VC) white matter using advance tractography methods in preoperative diffusion MRI data.
• Improve functional gray matter targeting by studying the overlap of the volume of tissue activated (VTA) with the VC voxels of maximal preoperative connectivity to the orbitofrontal cortex (OFC)
• Determine the changes in regional glucose metabolism using preoperative and post-treatment FDG-PET (Positron Emission Tomography) following 3 months of DBS treatment

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.

Subjects will be 11 patients with DSM-5-defined OCD of disabling severity, refractory to prolonged treatment trials with conventional medication and behavioral therapy, who would therefore otherwise be candidates for psychiatric neurosurgery.