Role of the cerebellum in tuning anticipatory and reactive grip force responses

The aim of our study was to determine if load perturbations that could dest abilize grasp control are adequately controlled by cerebellar patients. We examined patients with unilateral cerebellar lesions who had largely recove red from their initial symptoms and compared grip force regulation for the affected and unaffected hand during a drawer-opening task. Two experimental paradigms were included: (1) a brief load perturbation during a self-stopp ed drawer pull and (2) a loading impact when the drawer was pulled out to t he mechanical stop. The results showed that when a self-stopped movement wa s perturbed during its trajectory, anticipatory grip force increase was sma ller for the affected than for the unaffected hand, illustrating a disturbe d gain control due to cerebellar dysfunction. When the mechanical stop arre sted the movement, the amount of grip force did not differ significantly be tween the affected and unaffected side; however, both hands used different control strategies. Whereas the unaffected hand anticipated the load pertur bation by a ramp-like increase of grip force toward the impending impact, t he affected hand increased grip force at movement onset to a default level and maintained this value until the task was ended. In addition, the latenc y between impact and reactive peak in grip farce was prolonged for the affe cted hand, suggesting a delayed cerebellar transmission of reactive respons es. In conclusion these Endings demonstrate that the cerebellum is involved in anticipatory and reactive mechanisms dealing with load perturbations du ring goal-directed behavior.