PubMed · 14180361
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D J HICKS, S SCALISI, F WOODY, B SKINNER. 1964. INCREASING UPPER EXTREMITY FUNCTION.. https://pubmed.ncbi.nlm.nih.gov/14180361/
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Previous studies of multijoint arm movements have shown that the CNS holds arm kinematics constant in different situations by predictively compensating for the effects of interaction torques. We determined whether this was also the case for wrist joint flexion in natural overarm throws performed by skilled subjects in 3D, a situation where large passive torques can occur at the wrist. Specifically, we investigated whether wrist flexion amplitudes are held constant in throws of different speeds. Joint rotations were recorded at 1,000 Hz with the search-coil technique. Contrary to a previous study on constrained 2D throwing, indirect evidence was found that in fast throws passive torques associated with forearm deceleration were exploited to increase wrist flexion velocity. This increase in wrist flexion velocity was associated with constant wrist flexion amplitudes at ball release (mean 27 degrees) for throws of different speeds. Furthermore, final wrist flexion positions after ball release were similar for a particular subject irrespective of the speed of the throw. This was associated in faster throws with increased magnitudes of wrist flexor and wrist extensor EMG activity which damped passive torques associated with forearm angular deceleration. It is concluded that wrist flexion in overarm throws of different speeds is produced by central signals which precisely control net joint torque by both exploiting and damping passive torques during different parts of the throw to keep wrist joint angular position parameters constant. As such the results show that control strategies for natural 3D throwing are different from those for constrained 2D throwing.
This paper presents an approach to robot-arm control that exploits the natural dynamics of the arm. This is in contrast to traditional approaches, which either ignore or cancel out arm dynamics. While the traditional approaches are more general, they often result in systems and robot designs that are not robust. The alternative approach gives systems that are computationally simple, robust to variation in system parameters, robust to changes in the dynamics themselves, and versatile. The approach is examined using the example of a compliant robot arm, controlled by independent neural oscillators, in a crank-turning task. A model is constructed, and the robot behaviour compared with the model. These data show that the arm-oscillator system is exploiting the natural dynamics by finding and exciting the resonant mode of the underlying mechanical system. Since this is a natural behaviour of the system, the robot behaviour is robust. The paper concludes by discussing the opportunities and limitations of this approach.
Event-related functional magnetic resonance imaging was used to examine activation in the posterior parietal cortex when subjects made pointing movements or saccades to the same spatial location. One region, well positioned to be homologous to the monkey parietal reach region (PRR), responded preferentially during memory-delay trials in which the subject planned to point to a specific location as compared to trials in which the subject planned to make a saccade to that same location. We therefore conclude that activation in this region is related to specific motor intent; i.e. it encodes information related to the subject's intention to make a specific movement to a particular spatial location.