Response Inhibition in Obsessive Compulsive Disorder and Co-occuring Psychopathology

Obsessive compulsive disorder (OCD) is a debilitating, chronic condition that affects up to 3% of the population. A significant number of patients do not respond or still have residual symptoms even after completing empirically supported treatments. The study of neurocognitive functioning has been identified as one path toward developing a better understanding of underlying mechanisms and identifying new treatment targets. Response inhibition (RI), the ability to suppress inappropriate or irrelevant responses, is a neurocognitive process that may be particularly relevant to OCD. RI deficits have been found in adults with OCD, however questions remain regarding the nature and specificity of the relationship between individual RI domains and OCD. This dissertation addresses such questions across three chapters. Chapter 1 investigates whether OCD symptomatology is related to RI deficits in an analogue sample of 222 participants. OCD symptomatology was a significant and unique predictor of one RI domain, action cancellation, controlling for ADHD, impulsivity, anxiety, and depressive symptomatology, supporting the possibility that action cancellation is an endophenotype or trait-based marker of OCD. In 99 of these participants, Chapter 2 explores whether cognitive processing speed mediates the relationship between depressive symptomatology and individual RI domains, a relationship that has been shown in previous research with clinical samples and referred to as evidence against the specificity of an RI deficit in OCD. RI domains, as well as cognitive processing speed, were unrelated to depressive symptomatology suggesting that neither RI nor cognitive processing speed are trait-based deficits underlying depressive disorders. In Chapter 3, 28 treatment-seeking youth with OCD were compared to 27 treatment-seeking youth with anxiety disorders on the three RI domains. No significant differences emerged between groups across RI domains and RI was unrelated to OCD, anxiety, or depressive severity but was correlated with age. Results from this study indicate that youth with OCD may not possess RI deficits, differing from adults with OCD. Possible explanations for this inconsistency related to neurodevelopmental processes are discussed