The role of the fastigial nucleus in saccadic eye oscillations.

For the first time, we provide functional magnetic resonance imaging evidence for a recent hypothesis that saccadic oscillations in opsoclonus may result from a disinhibition of the cerebellar fastigial nuclei. Two patients with severe opsoclonus were examined during fixation in the light and during eye closure and in darkness where opsoclonus disappeared. Their activation during opsoclonus was compared with 10 healthy subjects performing visually guided and self-paced saccades in the light and darkness. In contrast to the control subjects, the patients showed a strong bilateral midline cerebellar activation that involved the deep cerebellar nuclei. This is probably not just a secondary finding in the fastigial nuclei due to the high frequent saccadic activity because there was, concomitantly, no oculomotor vermal activation, which is normally seen in healthy subjects. We propose that cerebellar activation of the fastigial nuclei may cause opsoclonus via their projections to the brainstem saccadic generator.