Trans-radial upper extremity amputees are capable of adapting to a novel dynamic environment

Abstract

This study investigated differences in adaptation to a novel dynamic environment between eight trans-radial upper extremity (UE) prosthetic users and eight naive, neurologically intact subjects. Participants held onto the handle of a robotic manipulandum and executed reaching movements within a horizontal plane following a pseudo-random sequence of targets. Curl field perturbations were imposed by the robot motors, and we compared the rate and quality of adaptation between the prosthetic and control subjects. Adaptation was quantitatively assessed by peak error, defined as the maximum orthogonal distance between an observed trajectory and an ideal straight trajectory. Initial exposure to the curl field resulted in large errors, and as the subjects adapted to the novel environment, the errors decreased. During the early phase of adaptation, group differences in the rate of motor adaptation were not significant. However, during late learning, both error magnitude and variability were larger in the prosthetic group. The quality of adaptation, as indicated by the magnitude of the aftereffects, was similar between groups. We conclude that in persons with trans-radial arm amputation, motor adaptation to curl fields during reaching is similar to unimpaired individuals. These findings are discussed in relation to mechanisms of motor adaptation, neural plasticity following an upper extremity amputation (UEA), and potential motor recovery therapies for prosthetic users.