To address this question behaviorally and biologically, the investigators will use a, 2-day fear extinction paradigm while measuring behavioral psychophysiology (skin conductance response [SCR]) and neurophysiology (electroencephalography [EEG]). On Day 1 participants will undergo 1) habituation, 2) fear conditioning, and 3) extinction learning. On Day 2 they will undergo 4) extinction recall, and 5) reinstatement. SCR and EEG will be measured in both sessions. The investigators propose to investigate whether inhibitory tDCS to the pre-SMA before, during, or after fear extinction significantly 1) enhances the recall of extinction learning and 2) reduces fronto-medial theta power during extinction recall. Participants will be randomized to one of the following four conditions: active tDCS before, during, or after extinction learning, or sham tDCS. The fear extinction paradigm serves as a proxy of exposure-based CBT for OCD. Defining the combination protocol that optimally and significantly increases extinction recall behaviorally (psychophysiology) in OCD, will have critical implications for the mechanistically informed development of tDCS-augmented CBT for OCD. EEG measures will provide a response biomarker to characterize target engagement neurophysiologically. This is particularly relevant given EEG's ease of use, relatively low cost, and potential for greater translation to the clinic. Also, the higher signal-to-noise ratio (SNR) of EEG compared to SCR is a strength. Taken together, these data should reveal treatment targets, define optimal therapeutic protocols, and provide the foundation for a future clinical trial to test the synergistic efficacy of combined tDCS-CBT for OCD.
The investigators want to learn more about how human beings learn not to fear and the impact of changing the fear network in the brain using transcranial Direct Current Stimulation (tDCS) in individuals with obsessive compulsive disorder (OCD). The investigators hope this study will help us understand how future treatments can help patients with OCD better control unwanted fear.