These experiments will test the hypothesis that arm trajectories are represented in the neuronal activity of the cells located in the proximal are area of primary motor cortex and that this activity contributes to the formation of behavioral strategies used to perform the movement. The neurons in this region of cortex are directionally sensitive. Their responses have been combined to produce a 'population vector' which points from the origin of a straight movement to its endpoint. An analytical technique, which relies on a series of 'instantaneous population vectors' calculated eery 20 msec throughout the movement, will be used in an attempt to describe movements that are not straight. Monkeys will draw sinusoidal curves of different spatial frequencies on a touch screen computer monitor using their fingers. Simultaneously, motor cortical unitary activity will be recorded, along with the position of the finger, wrist and endpoints of the arm segments. A neural 'image' of this shape will be constructed from the time series of population vectors and compared to the trajectory of the finger and the wrist. Their spatial and temporal correspondence will be quantitated using Fourier analysis. In the second part of the proposal, the neural representation of this movement will be analyzed with respect to the control strategy used by the motor system to produce these movements. The relation between a strategy, characterized by the stereotypic way that the movement is performed, and the series of instantaneous population vectors will be examined by comparing the rate of change in direction of the vector to the rate of directional change (curvature) taking place in the movement. Specifically, this proposal will examine a strategy in which the hand slows as the curvature of the movement increases. This should be reflected in the rate at which the directional information changes in the neural activity of motor cortical cells.
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