Electrophysiological manifestations of stimulus evaluation, response inhibition and motor processing in Tourette syndrome patients

Gilles de la Tourette syndrome (GTS) is a neuropsychiatric disorder with childhood onset presenting with multiple fluctuating motor tics and one or more phonic tics. A significant proportion of people suffering from GTS are still symptomatic in adulthood and present other emotional and cognitive difficulties, along with motor problems that often accompany these comorbid conditions. The nature of these difficulties is still poorly understood and multiple comorbidities are often inadequately controlled. The current study investigates both stimulus evaluation and motor processing in GTS while controlling for comorbidity. Fifteen adults with GTS and 20 control participants were matched on gender, laterality and intelligence. The P300 component, the no-go anteriorization (NGA) as well as the stimulus and response-locked lateralized-readiness potentials (S-LRP, R-LRP) were elicited during a stimulus-response compatibility (SRC) paradigm. The standard version of the Stroop Color-Word Test (SCWT) was also administered. Reaction times showed that participants with GTS processed both the SRC and the SCWT more rapidly than the control group, while producing a delayed P300 peak latency. The GTS group also showed faster S-LRP onset in response to the incompatible and faster processing of interference in the SCWT. There was also a tendency toward a greater frontal shift of the NGA in the GTS group. The P300 latency showed that with GTS patients, stimulus evaluation occurs later whereas the overlapping pre-motor response selection processes occur faster. Our findings are congruent with a probable cortical motor over-activation hypothesis of GTS involving faster motor program selection in processing conflicting SR configuration.