During the current period of funding, we have shown that the framework of the equilibrium-point hypothesis can be used to address issues of synergy organization. A novel method for analysis of the structure of variability of multi-element systems has been developed and tested experimentally. The next challenges are to generalize the applicability of these tools and approaches to different effector systems and tasks and to link them to physiological processes within the human body. If this is accomplished successfully, our understanding of the human motor function will reach a level when direct application of the presently theoretical and metaphorical notions to practical issue of motor disorders and rehabilitation becomes possible. Hence, our next plans include: (1) Testing the new method of analysis of the structure of variability as a tool for discovering performance variables that are selectively stabilized during a variety of motor tasks; (2) Studying the process of synergy evolution with practice; and (3) Approaching the central mechanisms of synergy organization using the method of transcranial magnetic stimulation. We plan to address the following specific hypothesis: 1). Within a synergy, variability of individual elements is structured so as to selectively stabilize functionally important variables; 2). Learning a novel multi-element task leads to the creation of a synergy reflected in changes of the structure of variability within the state space of elements and responses of the elements to stimulation of the corticospinal tract; 3). Organization of elements into synergies with practice leads to plastic changes reflected in task-specific patterns of finger force responses to transcranial magnetic stimulation; and 4). Quick corrections to perturbations are organized in a synergy-specific way, so as to minimize deviations of functionally important variables. Their qualitative pattern (timing of muscle activation) may be largely independent of the local joint kinematics while quantitative features reflect joint kinematics in accordance with the EP-hypothesis. Seven experiments with oscillatory and discrete force production are suggested to test the hypotheses using tasks of multi-finger coordination within a hand and multi-finger coordination between the two hands. We also plan to monitor changes in indices of synergy organization with practice of an unusual multi-finger coordination task.
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