Impaired predictive and reactive control of precision grip in chronic stroke patients

Skilled hand movements require a precise coordination between the grip force and the load force. To coordinate those forces, we rely on both a predictive and a reactive control. On the basis of specific impairments observed previously in children with hemiplegic cerebral palsy, we aimed to assess the predictive or reactive nature of hand deficits in stroke patients. This case-control study was carried out with eight stroke patients and eight control participants. The load of a handheld object was rapidly increased by dropping a mass attached to the object. We tested predictive and reactive aspects of the movement in the same task as the drop was triggered either unexpectedly by the examiner (reactive condition) or by the patient himself (predictive condition). Deficits observed in the paretic hand were similar to those highlighted previously in children with hemiplegic cerebral palsy. Under predictive conditions, temporal deficits were observed after impact. Under reactive conditions, the reflex latency was slightly increased in the paretic hand. The nonparetic hand showed similar results to controls. The predictive mechanism is present but altered in the paretic hand. These alterations suggest an inability to anticipate the consequences of dynamic perturbations in the paretic hand only.