Contrapulsion of saccades and ipsilateral ataxia: A unilateral disorder of the rostral cerebellum

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Abstract
Contralateral pulsion of saccades and ipsilateral limb ataxia were manifestations of unilateral damage to the rostral cerebellum studied in a patient with occlusion of one superior cerebellar artery. The saccadic disorder consisted of three elements: (1) horizontal saccades away from the lesion during attempted vertical saccades, resulting in oblique trajectories; (2) hypermetria of contralateral saccades; and (3) hypometria of ipsilateral saccades. Magnetic search coil oculography showed that durations of the horizontal components of oblique contrapulsive saccades were lengthened toward the durations of the vertical components. Lengthening of horizontal vectors indicated temporal coupling of the orthogonal components, as occurs in normal oblique saccades. The bias of saccades arose proximal to brainstem loci that decompose commands for oblique saccades into their horizontal and vertical vectors. Contrapulsion of saccades may be explained by imbalanced cerebellar outflow.