DIRECT CORTICAL REPRESENTATION OF DRAWING

How the intention to act results in movement is a fundamental question of brain organization. Recent work has shown that this operation invo lves the cooperative interaction of large neuronal populations. A popu lation vector method, by transforming neuronal activity to the spatial domain, was used to visualize the motor cortical representation of th e hand's trajectory made by rhesus monkeys as they drew spirals. Hand path was accurately reflected by a series of population vectors calcul ated throughout the task. A psychophysical rule relating speed to curv ature, the ''power law,'' was found in this cortical representation. T he relative timing between each population vector and the correspondin g portion of the movement was variable. The population vectors only pr eceded the movement in a predictive manner in portions of the spiral w here the radius of curvature was greater than 6 centimeters. These res ults show that the movement trajectory is an important determinant of motor cortical activity and that this aspect of motor cortical activit y may contribute only to discrete portions of the drawing movement.