AN INTERIM ANALYSIS OF A DOUBLE-BLIND SHAM-CONTROLLED STUDY ON THE ACUTE EFFECTS OF TRANSCRANIAL DIRECT CURRENT STIMULATION IN OBSESSIVE-COMPULSIVE DISORDER

Abstract We describe the interim analysis of a double-blind sham controlled quasi-randomized study on the acute effects of transcranial direct current stimulation (tDCS) for individuals with obsessive-compulsive disorder (OCD). Twenty OCD patients were assigned to receive a single session of sham (n=10) or active (2mA) tDCS (n=10) for 30 minutes, with the cathode placed over the central supplementary motor area (SMA) and the anode on the supraorbital region. Assessments of outcome were made at baseline and one hour following tDCS using: a dot-probe task comprising images illustrating different OCD-related scenarios, the Positive and Negative Affect Schedule (PANAS), and the Yale-Brown Obsessive-Compulsive Challenge Scale (YBOCCS; a measure of symptoms in the preceding hour). Active and sham tDCS groups did not differ in terms of age, gender, medication use and baseline severity of OCD, depression and anxiety symptoms. Though a significant time-effect (before vs. after tDCS) was observed on YBOCCS, PANAS and dot-probe scores, there was no interaction between groups. However, exploratory analyses revealed that sham tDCS led to a significant decrease in OCD symptoms in the past hour, while active tDCS failed to do so. Although we did not observe acute effects of tDCS on OCD symptoms, this interim analysis suggests that inhibition of the SMA may interfere with sham response in OCD, probably through increasing vigilance towards OCD-related environmental stimuli.