Arbitration Between Habitual and Goal-directed Behavior in Obsessive-compulsive Disorder: Circuit Dynamics and Effects of Noninvasive Neurostimulation

Investigators will recruit 30 male and female adults (age 18-65) with OCD and 30 age-, sex-, and education-matched healthy (medically, neurologically and psychiatrically) controls for this project. Each participant will come for three sessions. There will be 3-4 days interval between sessions:

Session 1 that includes initial clinical assessment and obtaining T1 structural image (needed for neuronavigation analysis and electric field modeling).

Session 2 and 3 that include performing two separate decision-making and symptom provocation-avoidance tasks by participants with OCD and healthy controls under two conditions: while scanned inside the MRI scanner (no tDCS) or while receiving neuronavigated tDCS neurostimulation outside the scanner (no fMRI imaging). As participates will perform each task twice, there might be an order effect on task performance. For minimizing the impact of such a potential order effect on imaging and tDCS results, participants will be randomly assigned to undergo scanning in the session 2 and then receive tDCS in the session 3 or in the opposite order (tDCS in session 2 and then imaging in session 3) but in each session only one of imaging or tDCS experiments (for both tasks) will be conducted for each participant. OCD-relevant and aversive picture rating (explained below) will be done always in the session 3 as the last experiment.

A) OCD participants inclusion criteria:

• DSM-5 diagnostic criteria for OCD as primary (most severe) diagnosis (based on the Mini International Neuropsychiatric Interview).
• Yale-Brown Obsessive-Compulsive Scale (YBOCS) total score is equal or greater than 16.
• unmediated or being on a stable dose of medication (only SSRIs and clomipramine) for at least 12 weeks prior to the study.
• fluent English speaker.
• signed informed consent.

B) OCD participants exclusion criteria:

• IQ greater than 80 on the Wechsler Abbreviated Scales of Intelligence.
• lifetime DSM-5 diagnosis of mania, psychotic disorder, or substance dependence (per MINI).
• current DSM-5 diagnosis of MDD if Montgomery-Asberg Depression Scale (MADRS) scores are equal or greater than 35 (severe), or ADHD.
• taking any psychotropic medication other than SSRIs or clomipramine.
• severe psychiatric symptom that requires immediate inpatient psychiatric intervention such as suicidality.
• presence of any serious psychiatric, psychosocial, or neurological condition requiring immediate treatment.

C) Healthy control inclusion criteria:

1-males and females age 18-65 years with signed informed consent and IQ greater than 80 on WASI.

D) Exclusion criteria for all participants:

• presence of any MR scan contraindications particularly body metal or positive pregnancy test.
• medical conditions in which cerebral metabolism might be compromised such as thyroid disorders, diabetes or current tobacco smoking (potential effect on imaging endpoints).
• any history of seizure disorders.