Title : Cognitive and Behavioral Mechanisms of Transcranial Direct Current Stimulation in Obsessive-Compulsive Disorder
Abstract:
Background. Obsessive-compulsive disorder (OCD) is a common and severe psychiatric disorder. Cognitive behavior therapy (CBT) with exposure and response prevention (ERP) is the gold standard intervention for OCD, but more than 40% of patients with this disorder remain impaired even after treatment. Transcranial direct current modulation (tDCS) is a safe and minimally invasive procedure that modulates cortical function by delivering a weak electrical current over the scalp. Although a growing body of literature suggests that tDCS may potentially improve CBT outcomes in OCD, a knowledge gap remains concerning the specific cognitive and behavioural mechanisms by which tDCS may augment the outcomes of CBT for OCD.
Purpose. The purpose of this study, which is in progress, is to investigate the cognitive and behavioural mechanisms of action of tDCS in the context of CBT with ERP for OCD. Specifically, it examines whether a single active session of bilateral tDCS is associated with 1) improved decision-making in uncertain conditions and 2) increased willingness to engage in ERP.
Methods. The target sample size is 50 adult patients diagnosed with OCD (N = 25 Active, 25 Sham), who undergo a course of group CBT for OCD at the Anxiety Treatment and Research Clinic (ATRC) in Ontario, Canada. Participants complete baseline measures prior to administration of the 20-minute tDCS. OCD symptom severity is assessed by the Yale-Brown Obsessive Compulsive Scale (Y-BOCS) and willingness to engage in ERP is measured by an Exposure Feedback Form (EFF). The study follows a double-blind placebo (sham) controlled design. Cathodal and anodal electrode placement is over areas F3 (left dorsolateral prefrontal cortex [DLPFC]) and F4 (right DLPFC), respectively. In both active and sham conditions, the current increases from 0 to 2mA over a period of 30s. To measure immediate cognitive effects, the Iowa Gambling Task (IGT)—a measure of decision-making under uncertainty and the cognitive outcome variable in the study—commences 10 minutes into the tDCS session. Upon completion of the tDCS and IGT, participants once again complete the behavioral outcome measure of their willingness to engage in ERP (i.e., the EFF). The EFF is repeated two days after the tDCS.
Data Analyses/Results. The cognitive hypothesis (IGT) will be tested using a one-way, two-group ANCOVA with Group (Active vs. Sham) as the between-subjects factor and covariates being any group baseline difference. The behavioural hypothesis (engagement in ERP) will be analyzed using a 2x2 repeated measures ANCOVA with time as the within-subjects factor, group as the between-subjects factor, and the same covariates.
Progress: Twenty-three participants have been tested to date. tDCS was well tolerated by all participants, and no adverse events were reported or observed. The acceptability of the procedure was high, as all participants completed the tDCS and all study assessments with no missing data.
Potential Implications. Evidence of tDCS effects on cognitive and behavioural aspects of ERP can provide a compelling rationale for the subsequent development and administration of a clinical trial of tDCS efficacy in OCD.
What will audience learn from the presentation?
- Overall, the audience will learn that tDCS is not only a putative candidate for adjuvant therapy for OCD and a range of neuropsychiatric conditions, but also that it is a valuable tool in neuroscience research, as its focality can be used to explore several brain aspects.
- It has been established that successful ERP is associated with functional changes in OCD-related brain circuits. Findings from this ongoing study present a promising avenue of investigation, namely the link between brain circuits implicated in OCD, their associated neurocognitive domains, and how the deficits in these domains affect treatment response.
- One of the most consistently identified areas of cognitive dysfunction in OCD is decision-making, particularly under uncertain conditions. Given that ERP involves situations that patients invariably perceive as uncertain, tDCS may improve decision-making processes in the context of such conditions. In turn, having improved decision-making in uncertain situations may also act to improve engagement in ERP, with regards to challenging exposure practices. The more an individual engages in exposure practices, the greater the treatment effects.
- This research could serve as preliminary groundwork for future researchers who may wish to examine changes in a much broader range of cognitive functions associated with tDCS administration in the context of CBT/ERP for OCD patients. In this respect, tDCS can be employed to modulate specific regions of the orbitofronto-striato-pallida-thalamic network, cortico-striatal-thalamo-cortical (CSTC) pathway, fronto-parietal network, and/or other extended regions to detect cognitive effects on attention, executive function, language, learning and memory, perceptual-motor function, and social cognition.
- In sum, researchers, health practitioners, and laypeople will learn that tDCS has unique characteristics such as ability to induce antagonistic effects in cortical excitability according to the parameters of stimulation; concomitant use with neuropsychological tests; non-invasiveness and thus absence of pharmacokinetics interactions—a putative substitutive/augmentative agent in neuropsychiatry; and low-cost and portability, making it suitable for increasing access to novel therapies for patients with OCD and other neuropsychiatric disorders.
