AUTHOR=Hayashi Takuji , Nozaki Daichi 

TITLE=Improving a Bimanual Motor Skill Through Unimanual Training

JOURNAL=Frontiers in Integrative Neuroscience

VOLUME=Volume 10 - 2016

YEAR=2016

URL=https://www.frontiersin.org/journals/integrative-neuroscience/articles/10.3389/fnint.2016.00025

DOI=10.3389/fnint.2016.00025

ISSN=1662-5145

ABSTRACT=When we learn a bimanual motor skill (e.g., rowing a boat), we often break it down into unimanual practices (e.g., a rowing drill with the left or right arm). Such unimanual practice is thought to be useful for learning bimanual motor skills efficiently because the learner can concentrate on learning to perform a simpler component. However, it is not so straightforward to assume that unimanual training improves bimanual performance. We have previously demonstrated that motor memories for reaching movements consist of 3 different parts: unimanual-specific, bimanual-specific, and overlapping parts. According to this scheme, unimanual training appears to be less effective, as its training effect is only partially transferred to the same limb for bimanual movement. In the present study, counter-intuitively, we demonstrate that, even after the bimanual skill is almost fully learned by means of bimanual training, additional unimanual training could further improve bimanual skill. We hypothesized that this effect occurs because unimanual training increases the memory content in the overlapping part, which might contribute to an increase in the memory for bimanual movement. To test this hypothesis, we examined whether the unimanual training performed after sufficient bimanual training could improve the bimanual performance. Participants practiced performing bimanual reaching movements in the presence of a novel force-field imposed only on their left arm. As an index for the motor performance, we used the error-clamp method (i.e., after-effect of the left arm) to evaluate the force output to compensate for the force-field during the reaching movement. After sufficient bimanual training, the training effect reached a plateau. However, unimanual training performed subsequently improved the bimanual performance significantly. In contrast, when the same amount of bimanual training was continued, the bimanual performance remained unchanged, highlighting the beneficial effect of unimanual training on bimanual performance. Considering memory structure, we also expected that bimanual training could improve unimanual performance, which was confirmed by another experiment. These results provide a new interpretation of why unimanual training was useful for improving a bimanual skill, and propose a practical strategy for enhancing performance by performing training in various contexts.