The act of drawing is a cognitive process. The object to be drawn must be realized and the perception of this object transformed into the drawing action itself. The goal of this project is to better understand the neural substrate for this transformation and the general principles used by the central nervous system to carry out this transformation. Using a set of behavioral tasks designed to create illusions, the perception of movement will be separated from the actual movement. Rhesus monkeys will be trained to draw a variety of objects in 3D space. By selecting the correct orientations of the object and providing partial visual feedback to the animals, they will believe that they are drawing one object when in fact they are drawing another. Neurons in the primate motor cortex have been shown to encode the arm's trajectory during drawing movements and are implicated in the transformation between the intention to move and the implementation of the movement. To understand the role of the motor cortex in these tasks, it will determined whether the kinematic representation in this region of the brain is better related to the perceived movement or the actual movement. To further understand how the motor cortex contributes to the implementation of volitional movements, the temporal pattern of force produced in many of the arm muscles during these movements will be determined and compared to the activity of single cortical units. It is expected that the two signals will be best related over specific intervals of the drawing movement. The determination of the force produced by individual muscles during movement is a basic problem because of the large number of redundant arm muscles and the complex geometry of the arm. Three types of modeling techniques will be used to derive these forces from kinematic, electromyographic and anatomical data. Since the cells of the motor cortex encode movement direction rather simplistically, a fundamental relation between the activity of motor cortical cells and muscles may be based on their common directional action.
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