Responses of the oculomotor units to deep cerebellar stimulation

Abstract

The influence of electrical stimulations of deep cerebellar formations (nuclei and adjacent white substance) on the unitary discharge of the oculomotor nuclei was investigated in curarized guinea pigs. Different patterns of activation as well as of inhibition of the oculomotor unitary discharge were observed. All the oculomotor units underwent modification following stimulation of the cerebellar nuclei. The most outstanding effects followed stimulation of the dentate nuclei, which usually induced contralateral activation and ipsilateral inhibition of the oculomotor units. Fastigial and interpositus nuclei stimulations provoked facilitation of the oculomotor units regardless of the stimulated site. Stimulation of the white substance surrounding the cerebellar nuclei and of deep cerebellar lamellae was effective only in 71.7% and in 86.6% of cases respectively, although no clear-cut rule could be found for these variations. All the recorded oculomotor units were strikingly modified also by labyrinthine stimulation. Thus a convergence of labyrinthine and cerebellar nuclei impulses on the oculomotor units was shown. In another group of experiments, evoked potentials were recorded from the oculomotor nuclei following single shock stimulation of the cerebellar nuclei. The shortest latencies of the responses were observed after stimulation of the contralateral dentate or interpositus nuclei. On the basis of the latencies of such responses, a direct asynaptic pathway connecting the dentate and interpositus nuclei with the oculomotor nuclei is postulated.