Walsh & Hoyt: Location of Lesions and Their Manifestations

Experimental lesions of the dorsal vermis (lobules VI and VII) and of the underlying fastigial nuclei (called the fastigial oculomotor region) cause saccadic dysmetria, typically hypometria if the vermis alone is involved and hypermetria if the deep nuclei are affected. Pursuit, especially the initial acceleration of the eyes during tracking, is also affected by dorsal vermis lesions. Lesions of the deep nuclei can lead to macrosaccadic oscillations, an extreme degree of hypermetria. Lesions restricted to the dorsal vermis produce not only saccadic dysmetria but also impaired initiation of pursuit with a decrease in the acceleration of the eyes during tracking, and disturbances of eye alignment including the development of an esodeviation. The pattern of saccadic dysmetria that occurs in cerebellar disease, as well as whether corrective saccades occur, may also vary with the type of visual stimulus. Saccades to remembered targets are more dysmetric. In some cerebellar patients, only corrective saccades are dysmetric. Saccadic dysmetria may be present for externally triggered movements to a visual target but not for internally triggered saccades during scanning of a visual scene. Deficits of pursuit may also be produced by lesions of the dorsal vermis, as can defects in motion perception. Bilateral symmetric lesions of the deep nuclei do not lead to pursuit deficits during sustained tracking, although unilateral lesions lead to a contralateral deficit, probably because of an imbalance in eye acceleration signals.