CEREBRAL CORTICAL CONTROL OF MOVEMENT

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The ultimate purpose of the proposed study is to increase our understanding of how the motor cortex controls movements and subsequently to contribute toward the better treatment of human motor dysfunctions. The specific aim during the coming years is to elucidate the neuronal mechanisms of how peripheral sensory input contribute to the smooth execution of voluntary movements. It has been shown that there are closed loop circuits between the motor cortex and the periphery and each loop is specific for a particular muscle. It has recently been shown that these circuits play an important role during voluntary movements. As for the neuronal mechanisms of these circuits, we have proposed that each loop circulates impulses before and during the movements to increase the excitability of neurons related to each loop, i.e., preferential bias theory. This hypothesis will be examined through chronic and acute experiments. Chronic experiments will be carried out using cynomolgus monkeys. They will be trained to pick up food pellet from rotating food board. Then a closed chamber will be installed over the motor cortex and activity of motor cortical neurons will be studied before and during the pick-up movements. Distribution of preferentially biased neurons in relation to location of regular movement related neurons will be examined. Effect of interruption of the loop circuits to these preferential bias will also be examined. Acute experiments will be carried out using cats. It has been shown that peripherally evoked activity of motor cortical neurons is modified by the input from the sensory cortex. The mode of modification will be studied by delivering conditioning and testing stimuli to the sensory cortex and the thalamus. The effect of conditioning stimuli will be examined using monosynaptic PSPs elicited by the test stimuli as indicators. Various combinations of conditioning and test stimuli will be used.