Multi-timescale neural adaptation underlying long-term musculoskeletal reorganization.

The central nervous system (CNS) can effectively control body movements despite environmental changes. While much is known about adaptation to external environmental changes, less is known about responses to internal bodily changes. This study investigates how the CNS adapts to long-term alterations in the musculoskeletal system using a tendon transfer model in non-human primates. We surgically relocated finger flexor and extensor muscles to examine how the CNS adapts its strategy for finger movement control by measuring muscle activities during grasping tasks. Two months post-surgery, the monkeys demonstrated significant recovery of grasping function despite the initial disruption. Our findings suggest a two-phase CNS adaptation process: an initial phase enabling function with the transferred muscles, followed by a later phase abandoning this enabled function and restoring a control strategy that, while potentially less conflicted than the maladaptive state, resembled the original pattern, possibly representing a good enough solution. These results highlight a multi-phase CNS adaptation process with distinct time constants in response to sudden bodily changes, offering potential insights into understanding and treating movement disorders. SIGNIFICANCE STATEMENTAfter major changes to the bodys mechanics, the nervous system adapts using strategies on multiple timescales. Our primate tendon transfer study shows that core muscle synergy groupings remain stable, reflecting a default to modular control. However, the activation of these synergies changes dramatically; an initial, rapid swap of their timing proves to be maladaptive, impairing motor function. This conflict is only resolved through the gradual development of slower, compensatory strategies over several weeks. This process highlights the fundamental tension the CNS faces when its reliance on stable motor modules conflicts with the need for flexible control, offering insights into neural plasticity and staged rehabilitation.