Most effective behavioral treatments of disordered anxiety involve repeated exposure to feared stimuli, which often results in systematic reductions in fearful responding to said stimuli. It is believed that this process results from successful fear extinction, a well-characterized learning process that is mediated by fear extinction brain circuitry. Namely, fear extinction is an inhibitory learning process that requires activation and plasticity within a variety of brain regions, including the medial prefrontal cortex (mPFC), which can exert inhibitory control over fearful responding and parts of the brain that drive said responding. Behavioral treatments of disordered anxiety, while effective, have serious limitations; many patients fail to respond at all or only partially respond to exposure-based treatments. One candidate reason for this is deficits in fear extinction learning or memory processes. The proposed study aims to examine the effects of non-invasive neuromodulation - namely, multifocal transcranial direct current stimulation (tDCS) targeting the mPFC - on therapeutic learning and memory among adults diagnosed with obsessive-compulsive disorder (OCD).

This study will recruit 26 subjects with OCD to complete a two-day experimental protocol to examine the effects of tDCS on therapeutic learning and memory, which will be measured with an exposure and response prevention laboratory challenge. On Day 1, OCD subjects will be randomized (1:1, double-blind) to receive Active (n = 13) or Sham (n = 13) tDCS prior to completing five 10-minute in vivo exposure exercises to assess the effects of tDCS on the acquisition of therapeutic learning. Subjects and raters (including those directing exposure sessions) will be blind to allocation. On Day 2, OCD subjects will return to complete five additional exposure trials to examine the effects of tDCS on recall of therapeutic learning. Subjective ratings of emotional distress (0-100) will be collected at baseline, before and after tDCS, and during each minute of each exposure trial. It is hypothesized that tDCS will improve the acquisition and recall of therapeutic learning (Aim 4); that participants randomized to Active tDCS would show more rapid reductions in subjective distress and would recall therapeutic learning on Day 2 when compared to participants randomized that Sham tDCS.

tDCS will be delivered using an 8-channel Starstim transcranial electric stimulator from Neuroelectrics. To target the mPFC, the anodal electrode will be placed over the frontal pole (Fpz, 10-20 EEG landmarks) and will be surrounded by five return (cathodal) electrodes in a circumferential array (AF7, AF8, F3, Fz, and F4). Subjects in the Active tDCS condition will receive 20 minutes of direct current stimulation for 20 minutes; current will be ramped in and out for 30 seconds at the beginning and end of the 20-minute period. Subjects in the Sham tDCS condition will receive the same electrode placement and ramping procedures, but no current will be delivered between ramping.

Linear mixed modeling will be used to assess within and between-trial exposure-relevant learning. Power analyses suggest that a sample of 24 (12 per condition) would adequately power a priori analyses when using linear mixed modeling. Mixed ANOVA will be used to assess recall of exposure-relevant learning. The proposed study will provide important preliminary data to examine the potential for medial prefrontal tDCS to augment exposure-relevant therapeutic learning.