Psychophysical, anatomical, electrophysiological, and lesion studies support the hypothesis that the dorsal promotor cortex (PMd) plays an important role in the transformation of visual information into motor commands. A more specific formulation of this hypothesis is that the PMd is responsible for non-standard mapping of visual (or other sensory stimuli) information into motor commands, that is, when the stimulus guiding an action is not the target of the action. Using chronic single unit recording studies in behaving primates, four Specific Aims are proposed to test specific hypotheses on how the discharge of PMd neurons encodes and transforms visuospatial information into movements. The first Specific Aim tests the hypothesis that the trajectory of a cell's directional tuning represents an optimal stimulus for a PMd neuron during the cue period and that this trajectory is independent of complex visuospatial stimuli. The discharge of PMd neurons will be studied during a pursuit tracking task when the target movement during the cue period mimics a cell's preferred direction trajectory and when the direction and velocity of the information presented in the cue are dissociated from the direction and velocity of the upcoming movement. The second specific aim tests the hypothesis that the properties of the directional tuning in the cue period provide a mechanism to map a visual stimulus presented in one direction into a movement made in another direction. The directional tuning of PMd cells will be evaluated during a pursuit tracking task when the animal performs a visuomotor redirection task. The third specific aim tests the hypothesis that the directional and velocity coding in the discharge of PMd cells is modified when the animal learns a new visuomotor mapping. PMd discharge will be evaluated before and after visuomotor transformations that require the animal to map the direction and velocity of visuospatial stimuli into novel movement directions or movement velocities. The fourth specific aim tests the hypothesis that the temporal ordering and encoding of specific parameters in the discharge of PMd cells is dependent on the timing of the visuomotor information presented during arm movements. PMd neurons will be studied in paradigms that 1) manipulate the information about the direction and amplitude of the upcoming movement and 2) manipulate the information about the direction and velocity of the movement. Overall, these studies will provide insights into the neuronal mechanisms in the PMd underlying the mapping of visuospatial information into movements.
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