Excessive action monitoring in Tourette syndrome.

Tourette Syndrome (TS) has been related to hyperactive basal-ganglia thalamocortical pathways. This suggests that action monitoring might also be hyperactive. The present study used the event-related brain potential (ERP) technique to investigate this hypothesis. A simple "oddball" reaction time experiment was administered to a group of TS patients and a matched control group. In order to investigate variations in attentional allocation separate experimental runs were undertaken with target frequencies of 50% and 80%. The P3b component to targets was taken as an indicator of the target evaluation process and the response locked error-related negativity (ERN) served as an indicator of action monitoring. We hypothesized that the amplitudes of ERN and P3b would vary with respect to target frequency. The TS group would show an overall enhanced ERN but an unchanged P3b.ERN and P3b amplitudes were lower in the 80% target condition than in the 50% condition. In comparison with control subjects TS patients displayed an ERN of overall higher amplitude but with similar variations between target conditions. P3b amplitudes did not differ between groups. The data are interpreted to support the assumption of an abnormal action monitoring system in TS. A number of similarities to Obsessive-Compulsive Disorder are outlined and it is argued that the findings could be related to a hyperactive frontal-striatal-thalamic-frontal circuit.