Consecutive learning of opposing unimanual motor tasks using the right arm followed by the left arm causes intermanual interference

Abstract

Intermanual transfer (motor memory generalization across arms) and motor memory interference (impairment of retest performance in consecutive motor learning) are well-investigated motor learning phenomena. However, the interplay of these phenomena remains elusive, i.e., whether intermanual interference occurs when two unimanual tasks are consecutively learned using different arms. Here, we examine intermanual interference when subjects consecutively adapt their right and left arm movements to novel dynamics. We considered two force field tasks A and B which were of the same structure but mirrored orientation (B = -A). The first test group (ABA-group) consecutively learned task A using their right arm and task B using their left arm before being retested for task A with their right arm. Another test group (AAA-group) learned only task A in the same right-left-right arm schedule. Control subjects learned task A using their right arm without intermediate left arm learning. All groups were able to adapt their right arm movements to force field A and both test groups showed significant intermanual transfer of this initial learning to the contralateral left arm of 21.9% (ABA-group) and 27.6% (AAA-group). Consecutively, both test groups adapted their left arm movements to force field B (ABA-group) or force field A (AAA-group). For the ABA-group, left arm learning caused significant intermanual interference of the initially learned right arm task (68.3% performance decrease). The performance decrease of the AAA-group (10.2%) did not differ from controls (15.5%). These findings suggest that motor control and learning of right and left arm movements involve partly similar neural networks or underlie a vital interhemispheric connectivity. Moreover, our results suggest a preferred internal task representation in extrinsic Cartesian-based coordinates rather than in intrinsic joint-based coordinates because interference was absent when learning was performed in extrinsically equivalent fashion (AAA-group) but interference occurred when learning was performed in intrinsically equivalent fashion (ABA-group).

Variable training but not sleep improves consolidation of motor adaptation

“…This explains the initially poorer Transfer performance of all the groups compared to their initial Training and Posttest performance. This suggests the generalization did not take place in an extrinsic force-field transformation, but through intrinsic, mirror symmetric coordinates, which contradicts previous findings 36 . Paradoxically, we did not find an even greater decrease in initial Transfer performance in the Random groups, as would be expected for a more consolidated intrinsic representation in this group, which gives rise to predicting a force field in the opposite (wrong) direction during Transfer.…”

Interference between competing motor memories developed through learning with different limbs

“…Thus, there was no opportunity for complete adaptation with one limb before learning with the other limb ensued, which may be essential for interference to be seen. In line with this thought, Stockinger et al (2017) very recently demonstrated interference when the left arm was exposed to a force-field B following substantial adaptation of the right arm to an opposite force-field A. We also noted significant interference once subjects had undergone complete adaptation to the rotation, suggesting that substantial learning with the two arms may be essential to reveal interference.…”

“…While our results appear similar to those of Stockinger et al (2017), important differences between the findings exist. Most crucial among these is Stockinger and colleagues’ finding that the learning of B produced a deterioration of ~68% of the prior memory of A, while a control group that did not learn B showed a decrement of only about 15%.…”

“…In contrast, we observed complete interference; performance during the early trials of re-exposure to A (CW R,2 for Group 1 and CW L,2 for Group 3) was never biased towards prior A learning (CW R,1 for Group 1 or CW L,1 for Group 3), and was in fact biased away from the prior learning in Group 1. The reason for this difference between the studies could include previously described differences in force-field versus visuomotor adaptation (Krakauer et al 1999; Rabe et al 2009; Wang and Sainburg 2004b), differences in orientation of the visual display and availability of visual feedback of the limb, differences in when interference was assessed (24-hour gap in our study versus immediately after B learning in Stockinger et al (2017)), and/or substantial but still incomplete adaptation to both A and B in their work. Nonetheless, both sets of results support the idea that interference can indeed occur when one arm adapts to a perturbation after the other arm has undergone substantial adaptation to an opposing perturbation.…”

Variable training but not sleep improves consolidation of motor adaptation

“…This 481 suggest the generalization did not take place in extrinsic force field transformation but rather in intrinsic, 482 mirror symmetric coordinates, that is, perturbation was expected to come from right on the right hand and 483 from left on the left hand. This agrees with the literature (Shadmehr and Mussa-Ivaldi, 1994) but contradicts 484 the preference of extrinsic coordinates in other studies (Malfait and Ostry, 2004;Stockinger et al, 2017). 485…”