The current study investigated the neural correlates of voluntary motor control in 24 adult Gilles de la Tourette (GTS) patients. We examined whether imagination and the execution of the same voluntary movement - finger oppositions with either hand - were associated with specific patterns of activation. We also explored whether these patterns correlated with the severity of the syndrome, as measured by the Yale Global Tic Severity Scale (YGTSS) for motor tics. The presence of brain morphometric abnormalities was also assessed using voxel-based morphometry. Crucial to our experiment was the manipulation of the presence of an explicit motor outflow in the tasks. We anticipated a reduction in the ticking manifestation during the explicit motor task and brain activation differences between GTS patients and 24 age/gender-matched normal controls. The anticipated differences were all evident in the form of hyperactivations in the GTS patients in the premotor and prefrontal areas for both motor tasks for both hands; however, the motor imagery hyperactivations also involved rostral pre-frontal and temporo-parietal regions of the right hemisphere. The blood oxygen level-dependent responses of the premotor cortices during the motor imagery task were significantly correlated with the YGTSS scores. In contrast, no significant brain morphometric differences were found. This study provides evidence of a different neurofunctional organisation of motor control between adult patients with GTS and healthy controls that is independent from the actual execution of motor acts. The presence of an explicit motor outflow in GTS mitigates the manifestation of tics and the need for compensatory brain activity in the brain regions showing task-dependent hyperactivations.
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