A robot‑aided visuomotor wrist training induces motor and proprioceptive learning that transfers to the untrained ipsilateral elbow

Abstract

Background Learning of a visuomotor task not only leads to changes in motor performance but also improves proprioceptive function of the trained joint/limb system. Such sensorimotor learning may show intra-joint transfer that is observable at a previously untrained degrees of freedom of the trained joint. In addition, it may transfer to the homologous joint of contralateral side. Objective Here, we examined if and to what extent such learning transfers to neighboring joints of the same limb and whether such transfer is observable in the motor as well as in the proprioceptive domain. Documenting such intra-limb transfer of sensorimotor learning holds promise for the neurorehabilitation of an impaired joint by training the neighboring joints. Methods Using a robotic exoskeleton, 15 healthy young adults (18–35 years) underwent a visuomotor training that required them to make continuous, increasingly precise, small amplitude wrist movements. Wrist and elbow position sense just-noticeable‐difference (JND) thresholds and spatial movement accuracy error (MAE) at wrist and elbow in an untrained pointing task were assessed before and immediately after, as well as 24 hours after training. Results First, all participants showed evidence of proprioceptive and motor learning in both trained and untrained joints. The mean JND threshold decreased significantly by 30% in trained wrist (M: 1.26° to 0.88°) and by 35% in untrained elbow (M: 1.96° to 1.28°). Second, mean MAE in untrained pointing task reduced by 20% in trained wrist and the untrained elbow. Third, after 24 hours the gains in proprioceptive learning persisted at both joint, while motor learning gains had decayed to such extent that they were no longer significant at the group level. Conclusion Our findings document that a one-time sensorimotor training induces rapid learning gains in proprioceptive acuity and untrained motor performance at the practiced joint. Importantly, these gains transfer almost fully to the neighboring, proximal joint/limb system.