Postural motor learning in people with Parkinson's disease.

Protective postural responses to external perturbations are hypokinetic in people with Parkinson's disease (PD), and improving these responses may reduce falls. However, the ability of people with PD to improve postural responses with practice is poorly understood. Our objective was to determine whether people with PD can improve protective postural responses similarly to healthy adults through repeated perturbations, and whether improvements are retained or generalize to untrained perturbations. Twelve healthy adults and 15 people with PD underwent 25 forward and 25 backward translations of the support surface, eliciting backward, and forward protective steps, respectively. We assessed whether: (1) performance improved over one day of practice, (2) changes were retained 24 h later, and (3) improvements generalized to untrained (lateral) postural responses. People with PD and healthy adults improved postural response characteristics, including center of mass displacement after perturbations (p < 0.001), margin of stability at first footfall (p = 0.001), step latency (p = 0.044), and number of steps (p = 0.001). However, unlike controls, improvements in people with PD occurred primarily in the first block of trials. Improvements were more pronounced during backward protective stepping than forward, and with the exception of step latency, were retained 24 h later. Improvements in forward-backward stepping did not generalize to lateral protective stepping. People with PD can improve protective stepping over the course of 1 day of perturbation practice. Improvements were generally similar to healthy adults, and were retained in both groups. Perturbation practice may represent a promising approach to improving protective postural responses in people with PD; however, additional research is needed to understand how to enhance generalization.