Attempts to understand the control of multijoint movements raise issues that have no counterpart in single-degree-of-freedom control. These arise from redundant degrees of freedom, complex intersegmental dynamics, and the role of multiarticular muscles. Each of these issues, considered in isolation, requires for its resolution the accurate knowledge of a large number of parameters and extensive computations by the CNS. The present proposal seeks to develop and test an alternative scheme for the control of multijoint movement, which is not computation intensive. Namely, given the initial configuration of the segments, and given the task (e.g., final configuration), the CNS chooses as a first approximation a pattern of muscle activity which represents a combination of patterns from its repertoire, and launches the movement. The patten, however, may need considerable sculpting via motion-dependent feedback in order to achieve the task. Previous results from this laboratory, concerning initial muscle activity for two-joint, horizontal-plane arm movements, support this scheme. The scheme is proposed to be tested further in the context of vertical-plane movements that include gravitational effects, and also by allowing trunk movements as an additional degree of freedom. Another aim of the studies is to investigate the role of proprioceptive reflexes, including interjoint effects, in sculpting the activity patterns during movement. The studies will elucidate the strengths and weaknesses of the proposed scheme, shed light on the participation of paraspinal and abdominal musculature in everyday arm movements (heretofore neglected), and provide a new perspective for understanding the role of reflexes in multijoint movements. This knowledge can be of practical use in designing the strategies for artificial control of muscles. It would also provide the framework for quantifying pathological deficits, especially in view of the fact that the most apparent consequences of pathology in the neural motor-control system are manifested in multijoint rather than single-joint movements.
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