Submovement changes characterize generalization of motor recovery after stroke.

Submovements are hypothesized to be discrete building blocks of human movement. Changes in their parameters appear to account for features observed in processes of motor learning and motor recovery from stroke. Our previous studies analyzed submovement changes in subjects recovering from stroke. Subjects were trained on point-to-point movements with the assistance of a rehabilitation robot as part of a stroke treatment protocol. Results suggested that recovery starts first by regaining the ability to generate submovements and then, over a longer time period, by reacquiring the means to combine submovements. Over recovery submovements became fewer, longer, and faster and such changes contributed to changes in movement smoothness. Taken together these results lent support to the theory that movement is produced via centrally generated submovements and that changes in submovements characterize recovery. More recently, we investigated generalization of training. We found that stroke subjects trained on point-to-point movements became progressively better able to draw circles, a task on which they had received no training. The goal of this paper was to further investigate the changes that occur in untrained movements during motor recovery from stroke. Specifically we wanted to test whether changes in smoothness and submovements also characterize untrained movements. We analyzed circle drawing movements performed by 47 chronic stroke subjects who underwent training on point-to-point movements over an 18-session robot-assisted therapy program. We found that during recovery the shapes drawn by subjects became not only closer to circles (a task not trained during therapy) but also smoother. Concurrently, submovements grew fewer, longer, and faster. These results are consistent with the theory that movement is produced via submovements and suggest that changes in smoothness and submovements might characterize and describe the process of motor recovery from stroke. Also, they are consistent with the idea that motor recovery after a stroke shares similar traits with motor learning.