Grip-load force coordination in cerebellar patients

The study examined the anticipatory grip force modulations to load force ch anges during a drawer-opening task. An impact force was induced by a mechan ical stop which abruptly arrested movement of the pulling hand. In performi ng this task, normal subjects generated a typical grip force profile charac terized by an initial force impulse related to drawer movement onset, follo wed by a ramp-like grip force increase prior to the impending load perturba tion. Finally, a reactive response was triggered by the impact. In patients with bilateral cerebellar dysfunction, the drawer-opening task was perform ed with an alternative control strategy. During pulling, grip force was inc reased to a high (overestimated) default level. The latter suggests that ce rebellar patients were unable to adjust and to scale precisely the grip for ce according to the load force. In addition, the latency between impact and reactive activity was prolonged in the patients, suggesting an impaired ce rebellar transmission of the long-latency responses. In conclusion, these d ata demonstrate the involvement of cerebellar circuits in both proactive an d reactive mechanisms in view of predictable load perturbations during mani pulative behavior.