Tourette Syndrome and Obsessive-Compulsive Disorder:: Event-related brain potentials show similar mechansims of frontal inhibition but dissimilar target evaluation processes

Objectives: Tourette Syndrome (TS) and Obsessive-Compulsive Disorders (OCD) share many clinical similarities and show a strong comorbidity. Current theories view a frontal-striatal dysfunction as the underlying cause of many clinical aspects of both disorders. This study sought to investigate mechanisms of conceptual integration and attention in both disorders. We hypothesized that the processing of stimuli with interfering aspects would be altered in a similar way while attentional mechanisms could differ. Methods: Event-related brain potentials (ERPs) were recorded in a modified STROOP-paradigm in groups of TS and OCD patients and in a control group. The paradigm involved the presentation of color words in a range of different colors. The subjects had to respond to words of matching word content and color and to ignore mismatching stimuli. Results: Incongruent stimuli elicited a frontal negative component ("N450") which was enhanced in amplitude and prolonged in latency in both patient groups. Matching stimuli evoked enhanced N2 and P3b components representing target evaluation mechanisms. The OCD group alone displayed a larger P3b amplitude in comparison to both other groups. Conclusions: The data are interpreted to indicate that frontal inhibitory mechanisms are altered alike in TS and OCD. In contrast. only the OCD group showed evidence for aberrant target evaluation.