Effects of dentate cooling on precentral unit activity following torque pulse injections into elbow movements.

(1) The effects were studied of brief, reversible cooling of the dentate nucleus of two Cebus monkeys on the activity of 69 precentral neurons that were related to self-paced elbow flexions or extensions. Sixty-two neurons were studied when movements were randomly perturbed by transient load changes. (2) During unperturbed movements dentate cooling altered precentral activity and movement parameters in the same direction. Extension movements and extension-related precentral neurons developed oscillations and rhythmical activity at about 4 Hz with increased peak values of acceleration and discharge intensity. Flexion peak accelerations and dynamic properties of flexion-related precentral neurons decreased. (3) Dentate cooling had no major effects on the "early" precentral responses to torque pulses and on the initial rapid movement adjustment. (4) Dentate cooling decreased intensity of "late" precentral responses and slowed their frequency together with associated movement oscillations from 5-6 Hz to 3-4 Hz. EMG bursts of biceps and triceps were prolonged accordingly. (5) It is concluded that the tightly coupled interaction between precentral motor cortex and the evolving movement was independent of dentate function in the early stage of the cortical load compensation. The dentate nucleus was involved, however, in adjusting intensity and frequency of subsequent late precentral responses and of movement oscillations.