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 destabilize grasp control are adequately controlled by cerebellar patients. We examined patients with unilateral cerebellar lesions who had largely recovered 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-stopped drawer pull and (2) a loading impact when the drawer was pulled out to the mechanical stop. The results showed that when a self-stopped movement was perturbed during its trajectory, anticipatory grip force increase was smaller for the affected than for the unaffected hand, illustrating a disturbed gain control due to cerebellar dysfunction. When the mechanical stop arrested the movement, the amount of grip force did not differ significantly between the affected and unaffected side; however, both hands used different control strategies. Whereas the unaffected hand anticipated the load perturbation by a ramp-like increase of grip force toward the impending impact, the affected hand increased grip force at movement onset to a default level and maintained this value until the task was ended. In addition, the latency between impact and reactive peak in grip force was prolonged for the affected hand, suggesting a delayed cerebellar transmission of reactive responses. In conclusion, these findings demonstrate that the cerebellum is involved in anticipatory and reactive mechanisms dealing with load perturbations during goal-directed behavior.