The kinematic and electromyographic (EMG) characteristics of cerebellar tremor and dysmetria were investigated in six Cebus monkeys. Cerebellar dysfunction was produced by reversible cooling lesions of the dentate and interposed nuclei. The aims of the study were (1) to compare the characteristics of the cerebellar intention tremor that occurs after the end of a voluntary movement (static or terminal tremor) with the tremor that occurs after the limb has been perturbed, (2) to determine the role played by stretch-evoked activity in generating this tremor, (3) to investigate the nature of the tremor that occurs during a voluntary movement (kinetic tremor) and (4) to describe the characteristics of dysmetric movements.;It was found that the static intention tremor after an elbow movement had the same characteristics as the tremor that occurs after a perturbation of the same limb. The frequency of the tremor in both situations was affected in a similar way by different mechanical loads and neither was dependent on visual feedback of limb position. Stretch-evoked proprioceptive activity was essential to produce the classic 3-4Hz cerebellar intention tremor.;The kinetic tremor was associated with an early burst of EMG activity in the antagonist muscle. This burst was no longer accurately programmed and appeared to be produced from stretch of the antagonist muscle. This antagonist burst was followed by a second burst of activity in the agonist muscle. This burst had the properties of a motor-servo as it was independent of vision, of short latency (50-80 ms) from the time of the deflection in trajectory produced by the early antagonist and its size was directly proportional to the size of the deflection.;Dysmetric (hypermetric) movements made during cerebellar cooling were asymmetric; that is, they had accelerations of long duration and small magnitude and decelerations of short duration and large magnitude. Control movements of all amplitudes, on the other hand, are nearly symmetric. Thus dysmetric movements were not simply inappropriately triggered normal movements. Hypermetric movements were associated with prolonged and less phasic bursts of agonist activity and a delayed burst of antagonist activity.;It is concluded that cerebellar disorders result from inappropriate stretch-evoked activity and from disordered descending central commands
