In conclusion, the time course of practice that we observe with our single joint system model in humans is similar to that observed by several other investigators studying tasks that involve many more degrees of freedom at both the kinematic, kinetic and neuromuscular level. Collectively these studies show the following:(1)Extensive myoelectric and kinematic changes occur in simple movements or isometric contractions, and these changes generalize to simple variants of the task such as moving various distances or generating various levels of torque.(2)The time course of the performance changes progresses at variable rates for varied movement parameters, and this may relate to varying neural substrates controlling different parameters of the movement.(3)Performance can continue improvement and thus learning occurs when there are disruptions in the circuitry of the basal ganglia as in the case of PD, but the performance changes may not occur for the same length of time as in healthy individuals. Such studies suggest that different neural systems underlie early learning and late learning. Further studies, similar to the sophisticated studies that have been conducted in the primary motor cortex, are now required to show the extent to which short-term practice might increase activity in cerebellar cortex and how long-term practice might decrease activation in the cerebellum and/or basal ganglia.
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