Children with Dystonia Can Learn a Novel Motor Skill: Strategies that are Tolerant to High Variability.

Children with dystonia are characterized by highly variable and seemingly uncontrolled movements. An important question for any rehabilitative effort is whether these children can learn and improve their performance. This study compared children with dystonia due to cerebral palsy, typically developing children, and healthy adults in their ability to acquire a novel sensorimotor skill. Using a virtual setup, subjects threw a virtual ball tethered to a post to hit a virtual target. Multiple combinations of release angle and velocity of the arm at ball release could achieve a target hit-the task was redundant and afforded solutions with different sensitivity to variability. Subjects performed 200 trials for two target locations that presented different types of redundancy. We hypothesized that children with dystonia develop strategies that are tolerant to their high variability. Estimating this variability highlighted the insufficiency of traditional outcome measures. Therefore, additional analyses of data distributions and of ball release timing were applied. Results showed that: 1) children with dystonia reduced their performance error despite their high variability; 2) this improvement was brought about by finding error-tolerant solutions; and 3) they generated arm trajectories that created time windows for ball release that were tolerant to timing variability. While reduced in magnitude, the performance improvements in children with dystonia paralleled those in healthy children and adults. These findings demonstrate that children with dystonia are able to adapt their behavior to their high variability, an important basis for any rehabilitative intervention.