Differential Effect of a Bilateral Deep Cerebellar Nuclei Lesion on Externally and Internally Triggered Saccades in Humans

Visually guided saccades were recorded which occurred either at the onset of a peripheral target (externally triggered) or when scanning a static display (internally triggered) in a patient with a bilateral lesion of the nucleus fastigii and nucleus interpositus caused by a hemangioblastoma. The externally triggered saccades were hypermetric before and after surgery. In contrast, the internally triggered saccades (scanning saccades) were normometric. This finding supports the view that the midline cerebellum is involved in the control of saccades in a way that depends on the mode of saccade elicitation.