Guiding multiple muscles and joints without redundancy problems: the principle of minimal interaction

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The aim of this research program is to diminish the gap in the understanding of the basic principles underlying the ability of the nervous system to control multiple muscles and degrees of freedom of the body in a coherent and task-specific way. Based on the previous research funded by NSERC, we successfully verified and further developed the threshold control theory of motor control. Applied to actions involving the whole body, this theory suggests that the electromyographic (EMG) activity of multiple skeletal muscles emerges from the comparison of the actual configuration (Q) of the body with its internal geometric image or referent (R) configuration modified by the brain according to task demands. The difference between these configurations can be considered as a global factor influencing the EMG activity of all skeletal muscles of the body. Local biomechanical and neurophysiological factors (e.g., autogenic and heterogenic reflexes) combined with the global factor diversify muscular EMG patterns. It was also assumed that, to produce a motor action, the nervous system shifts the threshold (virtual) position of an appropriate effector (e.g. the hand). In response, the emerging neural and muscular activity tends to minimize the difference between the actual and the virtual position of the effector, in the limits defined by internal and external constrains. Each element of the neuromuscular system may or may not be involved in the action depending on its ability to diminish the difference between the virtual and the actual position of the effector(s). These ideas offer a solution to the ill-posed redundancy problem in the control of multiple muscles and body segments. The present research proposal is designed to test the applicability of these new ideas to the production, first, of different hand-wrist gestures and, second, to a sequence of actions associated with the transition from sitting to standing and walking. Testing will involve both experimental analysis and mathematical modeling of these actions. The project may help not only in the understanding of the basic principles of motor control but also in designing muti-joint artificial limbs in prosthetics and robotics.