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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).
Highlights
The human sensorimotor system is capable of learning a variety of motor tasks and generalizing previously learned motor tasks to different contexts
We Intermanual interference in motor learning examined whether motor memory interference occurs across arms when subjects consecutively adapt their right and left arm movements to novel dynamic conditions
Intermanual interference in motor learning trials prior to the retest blocks and on pseudorandomly interspersed force channel trials during the retest blocks. (C-D) The performance quantified by the kinematic error is illustrated as progression of set mean values respectively representing all movement directions
Summary
The human sensorimotor system is capable of learning a variety of motor tasks and generalizing previously learned motor tasks to different contexts. In contrast to early findings, which detected such transfer only from the dominant to the non-dominant arm [7], more recent studies reported such transfer to occur in both directions [10,11] These findings suggest a bidirectional interplay of the corresponding neural networks or the involvement of at least partly similar neural networks for motor control and learning of both arms. According to the bilateral access model, practice-dependent adaptations occur in neural regions which are accessible for both the trained and untrained arm. It is still under debate which neural networks are involved in the transfer of motor learning [1,2]. It is assumed that ambiguous dynamics are learned in a preferred coordinate frame (e.g., extrinsic or intrinsic) but that the motor system can sculpt the particular coordinate representation in which the task is learned through experience [16]
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