Kinematic effects of deafferentation and cerebellar ablation.

Trajectories of hand movements directed visually toward a stationary target were compared by kinematic methods in control monkeys, those with bilateral upper limb deafferentation, those with cerebellar ablation and those with both these lesions. The purpose of the investigation was to determine whether: (1) deafferented animals display kinematic abnormalities similar to those of decerebellate animals, and (2) a combination of these two lesions results in cumulative motor disorders. The decerebellate preparation had significant increases of the ratio of path length to target distance, mean deviation from a straight line path, segment angle (average change in direction between successive segments of the trajectory), target angle (average angle between the path taken by the hand and a straight line path to the target), peak velocity, average acceleration and peak acceleration. The deafferented preparation had increases of these parameters significantly greater than the decerebellate preparation. Neither preparation showed abnormalities of average linear velocity. The deafferented preparation rendered decerebellate had significant additional increases in all parameters except average segment angle, an index of angular velocity. Scatter plots of acceleration versus velocity and of segment angle versus target angle revealed increasing dispersion in the sequence: control, decerebellate, deafferented, deafferented with subsequent cerebellar ablation. The quantitative demonstration of cumulative worsening of motor performance when the deafferented animal is rendered decerebellate indicates that there are mechanisms of cerebellar dysmetria independent of the fusimotor efferent-spindle afferent reflex arc.