Transcranial Magnetic Stimulation (TMS) and Obsessive Compulsive Disorder (OCD)

This study will evaluate the clinical efficacy of functional Magnetic Resonance Imaging (fMRI) guided 1 Hz repetitive Transcranial Magnetic Stimulation (rTMS) applied to the Supplementary Motor Area (SMA) in OCD patients who have not fully responded to conventional therapies. The investigators will collect TMS measures of motor cortex excitability to test whether rTMS restores normal levels of intracortical inhibition found to be deficient in OCD. The investigators hypothesize that: 1. Compared to sham (placebo), active rTMS will improve symptoms of OCD as assessed with the Yale Brown Obsessive Compulsive Scale (Y-BOCS) and Clinical Global Impression (CGI). 2. Active (but not sham) rTMS will normalize levels of motor cortex excitability, as reflected by increased intracortical inhibition, motor threshold, and cortical silent period, and by decreased intracortical facilitation, relative to pre-treatment baseline.