The goal of this clinical trial is to learn if deep brain stimulation (DBS) works to treat refractory obsessive-compulsive disorder (OCD). The main questions it aims to answer are:

• Assess the effects of the anteromedial sub-thalamic nucleus (amSTN)stimulation on obsessive/compulsive symptoms.
• Map the amSTN using neuronal responses [single unit and local field potentials (LFP) recordings] at rest and under high frequency stimulation during surgery.
• Record chronic brain activity with the implanted pulse generator and look for neuronal signatures correlated with symptom severity.

Researchers will compare active deep brain stimulation to a placebo (sham stimulation) to see if DBS works to treat refractory OCD.

Participants will:

• Undergo surgery for the implantation of a deep brain stimulation device
• Follow-up visits every three weeks with study staff
• 6 month follow-up for the next 2-3 years after first year of study participation is complete

The primary goal of this research study is to conduct a small scale randomized, double-blind clinical cross-over trial of deep brain stimulation for obsessive-compulsive disorder targeting the anteromedial subthalamic nucleus (amSTN), with which study team will not only produce high quality data of the clinical efficacy of DBS for OCD, but also attain critical insights into the neurophysiological underpinnings of disease and symptoms in OCD. This work will support future innovative therapy development, including refinement of surgical targeting and optimization of therapeutic stimulation.

This will be a 3-year study with the aim of implanting 10 patients with bilateral amSTN DBS leads. Intra-operatively, precise single neuron recordings will be obtained at the therapeutic target while the patient participates symptom provocation. Participants will be implanted with a sensing pulse generator (Medtronic Percept) which enables chronic recordings from the amSTN target in addition to providing therapeutic stimulation. Each participant will be randomized to start with either a sham control stimulation phase or therapeutic stimulation, and cross-over at 4 months. If symptoms recur upon cross-over from therapeutic to sham stimulation, participants will exit the sham stimulation phase and rescue therapy/stimulation will be delivered. All participants will transition to an open label stimulation phase for chronic therapy. Multiple assessments of the participants will follow, including OCD severity, cognition, behavior, and side effects.

Formal psychiatric assessments will take place at two weeks, at one month, and then once every three weeks during the randomization blinded period and then every 6 weeks during the open label period. During psychiatric assessments, the PERCEPT device will be used to obtain neural recordings of the STN activity.

Additionally, for the secondary outcome measure for the association between amSTN activity and cognitive/emotional measure there are two components of this measure that are of a qualitative nature. Burstiness and coherence are unitless measures and thus will not be included in the outcome measure reporting section. They will instead be discussed in the limitation section at annual reporting.

Inclusion Criteria:

• Patients with a diagnosis of obsessive-compulsive disorder according to Diagnostic and Statistical Manual of Mental Disorders (DSM) 5 criteria
• Severe OCD assessed by the Yale-Brown Obsessive-Compulsive Scale (YBOCS) with a score of more than 27
• Refractory OCD; severe symptoms and impairment for more than 5 years despite pharmacological and psychological treatment.
• Have failed to improve following treatment with at least two serotonin transport inhibitors and one augmenting agent taken for an adequate time period.
• Having failed to improve despite adequate cognitive behavioral therapy, as evaluated by the study psychiatrist
• Patients between 22 and 75.
• Ability to understand and sign written informed consent by the patient.

Exclusion Criteria:

• Diagnosis of severe major depression disorder (MDD) with psychotic features.
• Significant suicidal risk [Hamilton Depression scale item 3 (suicide)>2].
• Comorbidity with any primary Psychotic Disorder, Post-Traumatic Stress Disorder (PTSD), or Eating Disorder.
• History of substance or alcohol dependence or abuse in the preceding 12 months.
• Significant cognitive decline, measured by Mini-Mental State Examination (MMSE <26) and Montreal Cognitive Assessment (MoCA; <24).
• Any other current clinical significant neurological disorder or medical illness affecting brain function, other than a tic disorder.
• Any clinically significant abnormality on preoperative MRI that would affect the safety of the surgical procedure in the opinion of the study neurosurgeon.
• Any DBS contraindication, infection, coagulopathy, significant cardiac risk factors, or other medical risk factors for surgery.
• Pregnancy.

Investigators with established research programs will be eligible for data sharing. Interested investigators will be required to submit a summary of proposed work and requested data elements. If approved by the Principal Investigator of the study, data will be shared. This data will be de-identified and coded. There is no plan to share identifiers outside the study team.

Neither the participant of investigator will know which treatment group an individual is assigned to. After the completion of the blinded portion of the trial, all participants will be transitioned to open-label stimulation/treatment.