Anticipatory grip adjustments are observed in both goal-directed movements and movement tics in an individual with Tourette's syndrome.

We examined grip force adjustments during movements of a hand-held object in a young man (BF) with Tourette's syndrome. We directly compared BF's voluntary up and down movements with tics in the same directions. Movement tics were elicited by cueing BF to move either up or down on a GO signal which appeared after a variable delay. During the delay period, we observed frequent tics which were almost always in the cued movement direction. BF's voluntary movements were well coordinated and featured precise and appropriate anticipatory grip force adjustments such that grip force was modulated in phase with movement-induced fluctuations in load. Precise anticipatory grip force adjustments were also observed in all of BF's movement tics. These results support the hypothesis that tics in Tourette's syndrome are purposeful voluntary movements that are well organized and coordinated.