Neural Mechanisms of Planning and Control of Movement

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DESCRIPTION:(provided by applicant) The long term goal of this research is to elucidate how the brain specifies movement parameters before the initiation of a motor response, transforms these parameters when needed, and monitors them during the execution of a movement. These processes are incessantly used in the behavioral repertoire of many animal species, for example in activities as diverse as hunting preys or playing tennis. However, little attention has been given so far to the neurophysiological mechanisms associated with the amendment of movement parameters. The activity of neurons from cortical areas related to the preparation and execution of arm movements will be recorded in rhesus monkeys while they perform in specific tasks. These areas include the primary motor cortex, the dorsal premotor cortex and the posterior parietal cortex, which are considered essential nodes in the neural network engaged in planning and executing movements. A series of tasks was planned to investigate the neural processes associated with specifying movement parameters, and the transformation of this representation as needed in response to changes in the environment. A first group of tasks requires either discrete pointing arm movements toward a visual target that switches position, or continuous tracking of a moving target that moves first in one direction and then suddenly changes direction. In both cases the visually specified direction of movement is modified at some point either before or during the movement and requires a corresponding change in the specification of the motor response. The tasks are designed to characterize the patterns of neuronal activity engaged in defining and updating the visually specified goal of the motor output. In the first two tasks mentioned above, only one visual stimulus is present at any time before or during the motor response, and therefore the aim of the response is always unambiguously defined. However, it is also common that multiple alternatives for the upcoming motor response are considered before one is actually selected and executed. For example, while hunting it may be expected that the prey is more likely to escape in some directions than others, or while playing tennis that the opponent player responds by sending the ball at some angles rather than others. The neural process of preparatory activity will be investigated by using a precuing paradigm: two stimuli indicating two alternative possible responses are displayed, and after a delay one of them will become the actual target The analysis of the neural activity will address the questions of what are the characteristics of the preparatory activity, in particular in relation with the degree of disparity between the alternative responses; and how is this activity transformed when one of the alternative motor responses is selected. In all the experiments planned, the neuronal activity will be investigated both at the single-cell and population level. The analysis will serve to characterize the dynamics of the neural representation of movement parameters, in particular direction and amplitude, while it is formed before the initiation of the movement, and while it is transformed in response to the requirements of the task.