Consolidation of use-dependent motor memories induced by passive movement training.

Motor adaptation, a type of motor learning, is often thought to involve two distinct processes: error-based and use-dependent learning. Passive movement training, which is associated with use-dependent learning, can facilitate motor adaptation, although it is unknown how long its facilitative effect can last. The objective of this study was to examine the lasting effect of passive training on visuomotor adaptation for the duration of up to 24 h. Neurotypical, right-handed subjects experienced four experimental sessions: baseline, training, time delay and testing. In the training session, all subjects received passive training of their dominant arm that was moved by an exoskeletal robot in a "desired" target direction repeatedly. Following that, the subjects experienced a time delay of 5 min, 1 h or 24 h. In the testing session, the subjects performed reaching movements under a novel visuomotor condition, in which the visual display was rotated 30 degrees counterclockwise about the start circle. Control subjects experienced the baseline and testing sessions with a time delay of 5 min between the two sessions. Results indicate that the 1-h and 24-h groups, but not the 5-min group, adapted to the rotation significantly better than the controls. This finding has an implication for neurorehabilitation suggesting, for example, that passive proprioceptive training may indeed be a viable option for improving arm motor function in stroke survivors with severe hemiparesis, for whom efficient intervention techniques are very limited.