[Cerebellar movement disorders in monkeys. Comparison of rapidly alternating and slower target movements during cooling of the dentate nucleus (author's transl)].

The effects of short reversible cooling of the dentate nucleus in two groups of 3 and 4 cebus monkeys, with two different types of ipsilateral elbow movements, have been studied. One group was trained to turn a moving handle back and forth rapidly between two mechanical stops, while the second group was trained to move the handle between two target zones. Brief blocking of the dentate nucleus caused a delayed termination of contraction of the agonistic muscles (hypermetria) near the mechanical stop for very rapid, ballistic, alternating arm movements and, consequently, delayed initiation of the antagonistic return movement. The resulting increase of the duration of a single movement was not caused by a reduction of the peak acceleration of the movement. For the slower target movements, dentate nucleus cooling caused shortening of agonistic muscular contraction (hypometria) with corresponding, saccadic movement corrections. The frequency of the "movement tremor" lay between 3 and 5 Hz. The average velocity maxima during dentate cooling did not change. The findings indicate that different types of movements exhibit different disturbances of the movement pattern during the period of functional elimination of the same anatomical structure. The results indicate that the dentate nucleus and cerebellar hemispheres take part in preprogramming movement duration (Kornhuber) for rapid ballistic movements. In slower target movements, the dentate nucleus may be involved in sectional preprogramming of step movements.