Abstract

A number of authors have argued that obsessive-compulsive disorder (OCD) is associated with a significant disturbance of executive functions (e.g., response inhibition, mental flexibility). The present investigation employed both neuropsychological tests and event-related potentials (ERPs) to evaluate this hypothesis. In experiment one 23 outpatients with OCD and 23 normal control participants (matched for age, gender, education and handedness) completed a battery of neuropsychological tests assessing the domains of executive functions, verbal memory, nonverbal memory, language abilities, visuospatial and motor functioning. Data were evaluated for group differences on raw test scores, composite scores formed by averaging standardized tests scores grouped according to sensitivity to areas of neuropsychological functioning, and effect size. Results have revealed poorer language ability in the context of overall adequate functioning in the OCD group. This finding may have been due in part to subtle disturbances in other cognitive functions as statistical evidence of differential deficit was not observed. Results could not be accounted for by demographic or clinical characteristics of the participants. In experiment two 16 outpatients with OCD and 18 normal control participants completed a visual go/nogo task while ERPs were recorded. Results failed to support previous observation of nogo P300 topographic differences implicating impaired response inhibition in OCD. In contrast, controls demonstrated shorter posterior N100 latency, suggesting that OCD may be characterized by less efficient recruitment of posterior cortical pathways involved in the encoding of visual stimuli. In addition, the OCD group demonstrated shorter N200 and P300 latencies related to task parameters, consistent with previous investigations. The functional significance of the N200 and P300 findings is unclear but may reflect disturbances in the monitoring of self-generated actions and dysregulation of stimulus evaluation processes, respectively. Finally, unmedicated OCD patients demonstrated larger P300 amplitude to go than nogo stimuli suggesting that this group may have been composed largely of individuals who would show a positive response to treatment with selective serotonin reuptake inhibitors. Again, results could not be fully accounted for by demographic or clinical characteristics of the participants. The pattern of findings suggest that OCD may be related to a subtle disturbance of response monitoring. Further investigations addressing the potential influence of symptom subtypes, level of insight and comorbid diagnoses on executive functions in OCD are likely to prove fruitful.