THE FRONTAL LOBE AND THE CEREBRAL CONTROL OF ADAPTIVE SPATIAL-MOTOR BEHAVIOR

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I have initiated a study of the behavioral neurophysiology of four major divisions of the frontal lobe of primates: the primary motor cortex (MI), the dorsal premotor cortex (PMd), the ventral premotor cortex (PMv), and, the supplementary motor area (SMA). A new laboratory for studying the activity of single cortical neurons and highly skilled reaching movements of the arm was set up in order to investigate the relationship between neuronal activity in frontal cortical motor areas and the processing of visual-spatial information presented to the monkey in instructed delay tasks. Monkeys will perform two variations of tasks involving the serial presentation of spatial information required in the preparation of multi-directional reaching movements. In one, either a previously learned or a novel movement sequence is prepared and executed by the monkey. This task will help identify which spatial aspects of reaching are preprocessed and encoded in neuronal activity at the cortical level in signals either retrieved from memory or generated de novo. In the other, servo motors at the shoulder and elbow joints are used to simulate collisions between the arm and "virtual" objects at specific locations along the movement trajectory. This task will help identify whether the spatial tuning of cortical neurons is part of a representational map of visual space, per se, or of the path of the intended movement through space. Furthermore, since the location, size, and shape of obstacles can be presented visually to the monkey, or, as perceived by the monkey using only somatosensory information from the moving arm, it will be possible to evaluate the contribution of frontal cortical neurons to the monkey's adaptive behavior as successive reaching movements are adjusted to avoid obstacles, and also, the source of afferent information, visual or somatosensory, used in this form of motor learning.