Feedback reliance during an arm-tapping task with obstacle avoidance in adults with Down syndrome.

Optimal movement control reflects a combination of both feedback and feedforward processes. However, as motor control evolves, feedforward mechanisms become prevailing respect to feedback-based movements, and less reliance on sensory information leads to a decreased number of corrections in the trajectory. In subjects with Down syndrome (DS), the study of the wrist's trajectory during an arm-tapping task revealed feedback-based corrections designed to reduce the degree of discrepancy between the position of the limb and the target, leading to the assumption that performers with DS have problems with movement planning and feedforward control. The present study was aimed at expanding the evidence about motor control in DS by evaluating the influence of a perturbing factor (an obstacle) on motor control strategies during an arm-tapping task and to clarify if the presence of an obstacle elicited a higher reliance on feedback control in controls and in DS. Sixteen right-handed adults with DS and 21 right-handed, age-matched control subjects (N) were evaluated by means of quantitative motion analysis. The results suggest that the presence of an obstacle elicited changes in the motor strategies of both DS and N, with a destabilizing effect that led subjects to rely more on feedback control. DS showed some aspects of movement efficiency that were in accordance with N strategies, but the prevailing factor of optimization in these subjects remained safety. A focused rehabilitation could help DS subjects to develop more efficient motor strategies in the presence of motor uncertainty and perturbations.