Abstract
The authors declare no competing financial interests.Author contributions: D.C.B., T.C., P.L., and F.C. designed research; D.C.B., L.B., and R.T.M. performed research; D.C.B. and F.C. analyzed data; D.C.B., T.C., P.L., and F.C. wrote the paper.F.C. is supported by the Fonds de la Recherche Scientifique, Belgium Grant 1.C.033.18F. D.C.B. is supported by the Science Foundation Ireland, Ireland Grant 17/FTL/4832. P.L. is supported by a grant from the European Space Agency. T.C. and R.T.M. are supported by the Natural Sciences and Engineering Research Council of Canada, Canada Grant 2017-04829.Humans exhibit lateralization such that most individuals typically show a preference for using one arm over the other for a range of movement tasks. The computational aspects of movement control leading to these differences in skill are not yet understood. It has been hypothesized that the dominant and nondominant arms differ in terms of the use of predictive or impedance control mechanisms. However, previous studies present confounding factors that prevented clear conclusions: either the performances were compared across two different groups, or in a design in which asymmetrical transfer between limbs could take place. To address these concerns, we studied a reach adaptation task during which healthy volunteers performed movements with their right and left arms in random order. We performed two experiments. Experiment 1 (18 participants) focused on adaptation to the presence of a perturbing force field (FF) and experiment 2 (12 participants) focused on rapid adaptations in feedback responses. The randomization of the left and right arm led to simultaneous adaptation, allowing us to study lateralization in single individuals with symmetrical and minimal transfer between limbs. This design revealed that participants could adapt control of both arms, with both arms showing similar performance levels. The nondominant arm initially presented a slightly worst performance but reached similar levels of performance in late trials. We also observed that the nondominant arm showed a different control strategy compatible with robust control when adapting to the force field perturbation. EMG data showed that these differences in control were not caused by differences in co-contraction across the arms. Thus, instead of assuming differences in predictive or reactive control schemes, our data show that in the context of optimal control, both arms can adapt, and that the nondominant arm uses a more robust, model-free strategy likely to compensate for less accurate internal representations of movement dynamics.