![]() ![]() Previous studies have suggested muscle synergies as potential physiological blocks of computationally-derived primitive-based models 12, but only in recent years muscle synergies analysis has been used to describe adaptive behaviors, including visuomotor adaptations during isometric reaching movements 35– 37. In humans, on top of the fertile literature describing muscle synergies during natural behaviors 27– 32, studies on impaired individuals have demonstrated the solidity of this hypothesis in describing neurological conditions such as stroke 33, 34.Īs motor adaptations have been mainly studied, in humans, using computational models derived from metrics of biomechanical error, there is small evidence connecting the re-organization of the internal models that happens during adaptation with the supposed functional constituents of movement. Studies employing stimulation 21– 24 and optogenetics 25, 26 techniques have individuated the presence of such modules in the spinal cord of rodents, frogs and primates. Muscle synergies are thought to be the functional building blocks of force production during natural movements. ![]() These motor primitives are thought to explain the mapping between state variables such as limb position and movement velocities, into motor commands 12.Ī conceptually correlated theory of motor primitives and movement modularity has been proposed and widely demonstrated in both animal models and humans, that is, the muscle synergies hypothesis 17– 20. ![]() Several seminal studies have suggested that internal models are constituted by combinations of motor primitives 8– 12, an observation that is corroborated by the fact that adaptation to specific perturbations can be generalized to untrained compatible contexts 9– 11, 13– 16. Internal models can be adapted as a response to changes in the mapping between movement and its associated feedback or in response to perturbations modifying the dynamic characteristics of the movement in a relevant way 7. This is achieved through the recalibration of the neural representation of the body and the environmental interaction dynamics that are thought to be stored in internal models that characterize both the forward and inverse dynamics of movement 1– 6. Our results confirm synergies as invariant motor primitives whose recruitment is dynamically tuned during motor adaptations.Ĭomplex movements can be easily adapted in response to discrepancies between the expected and actual sensorimotor outputs. We also show that the characteristics of the different tunings correlate with the presence and extent of generalization of adaptation to untrained portions of the workspace. Nevertheless, these tunings resulted in the same net biomechanical adaptation patterns. We found that exposing healthy individuals to two visuomotor rotation perturbations covering different parts of the same workspace in a different order resulted in different tunings of the activation of the same set of synergies. Here we tested if: 1) different synergistic tunings can be achieved in response to the same perturbations applied with different orders of exposure 2) different synergistic tunings can explain different patterns of generalization of adaptation. Previous studies have shown that motor adaptations are achieved by tuning the recruitment of robust synergy modules. A theory of motor primitives has shown that natural movements can be described as combinations of muscle synergies. This is achieved by tuning different motor primitives, generating adaptations that can be generalized also to relevant untrained scenarios. Humans can adapt their motor commands in response to alterations in the movement environment. ![]()
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