Over the last decade, our group has been pursuing a line of research with the overarching goal of discovering strategies used by the central nervous system (CMS) in motor tasks that require the coordination of redundant sets of elements. In this proposal, we plan to focus on the issue of timing in motor synergies. We view this issue as central for progress in understanding both basic mechanisms of and impairments in motor coordination. The development of the uncontrolled manifold hypothesis has allowed us to quantify synergies and to monitor their changes both in the process of action and with practice. Based on recent experiments and pilot studies, a set of specific hypotheses have been formulated related to: (1) Ability of the central nervous system (CMS) to quickly create or modify a task-specific synergy in response to an imperative stimulus or to a mechanical perturbation of one of the elements; (2) Two stages in the effects of practice on muscle synergies participating in the stabilization of the vertical posture; (3) The role of timing errors in outputs of individual elements in the structure of motor variability of a multi-element system such as the human hand; and (4) Existence of timing synergies, i.e. task-specific co-variations in the timing of changes in elemental variables that keep the timing of an important performance variable constant. Seven experiments will be performed to address eight specific hypotheses. The experiments will involve multi-finger force and moment production during pressing and grasping, as well as postural tasks. Two models will be developed. One of these will generalize to multi-element systems an earlier model of single joint motor variability. The other model will explore a neurophysiologically plausible network functioning on a central back-coupling principle, which can replicate certain salient features of motor synergies. ? ?
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