Saccades in Gilles de la Tourette's syndrome

Gilles de la Tourette's syndrome (GTS) is presumed to be an inherited disorder with an unclear pathophysiology. An involvement of the basal ganglia is suspected. Besides vocal tics, one of the main symptoms is the presence of motor tics. As eye movements are a specialized part of the motor system, we investigated whether they differed in some typical way in GTS patients. To study the control of saccades in GTS, different paradigms were used to elicit saccades, which were either externally triggered and visually guided or internally triggered and without visual target. GTS patients (n = 10) showed a significant increase of the latency of antisaccades, a highly impaired performance of sequences of memory-guided saccades, and an isolated reduction of the peak velocity in the antisaccades. Overall the results were similar to those found with similar paradigms in patients with Huntington's disease (HD). In analogy to the known pathology of HD, these findings can be attributed to ascending loops from the basal ganglia that inappropriately activate the frontal cortex, especially some of the eye movement-related areas there. This impairment seems to be a rather specific effect, since some oculomotor features that are preserved by structures of the frontal cortex, such as the effect of a fixation target on saccadic latency ("gap effect"), were normal.