Electrical Stimulation of the Interior of the Cerebellum in the Monkey1

Investigations of the cerebellar nuclei and the white matter adjacent to them have been very few in number as compared with many studies of cerebellar function based upon gross extirpation of this organ or upon destruction or stimulation of its cortex. It is well known, however, that the nuclei constitute at least the major source of all efferent cerebellar connections, and the small amount of attention which they have received is by no means commensurate with their importance in cerebellar activity. The difficulty of approaching these nuclei, situated as they are within the interior of the cerebellum, has doubtless been the primary obstacle to their study, but this difficulty has been overcome by several investigators. With the immediate object of investigating the reactivity of the cerebellar nuclei to electrical stimulation, Horsley and Clarke (1) devised their stereotaxic instrument for accurately orienting an electrode within the interior of the brain. Unfortunately their study of the cerebellar nuclei was never completed, and we have only brief and incidental mention of their results (1, 2). At Horsley’s invitation this work was continued by Sachs and Fincher (3) but only a preliminary report was made, in which again but brief mention of the results appeared. Some observations of the effect of electrical stimulation of the medial cerebellar nuclei, with the aid of the Horsley-Clarke instrument, have been reported by Mussen (4). In the work of Miller and Laughton (5, 6) on the decerebrate animal, the cerebellar nuclei were electrically stimulated after their exposure by ablating the over-lying cerebellar parts. In the present investigation, the Horsley-Clarke stereotaxic instrument has been employed in the electrical stimulation of the cerebellar nuclei and the territory adjacent to them in the rhesus monkey (Macaca mulatta). METHOD. Stimulation of the cerebellum was performed under light nembutal anesthesia (10-19 mgm. per kgm. of body weight) plus supplemental ether added when necessary by means of a tracheal cannula and ether bottle. The animal was suspended untied in a hammock with the limbs hanging free and the head in the freely swinging stereotaxic instru-