Saccadic dysmetria is similar in patients with a lateral medullary lesion and in monkeys with a lesion of the deep cerebellar nucleus

Some of the clinical hallmarks of lateral medullary infarction — Wallenberg’s syndrome — are saccadic dysmetria, smooth pursuit deficit, and lateropulsion of the body. Similar movement disorders are seen in monkeys after local unilateral injection of GABAergic drugs in the caudal fastigial nucleus of monkeys. These include an ipsilateral saccadic hypermetria and a contralateral saccadic hypometria as well as cogwheel smooth pursuit eye movements toward the contralateral side and an ipsiversive lateropulsion of the body. It was previously suggested that the lateral medullary infarction causes a lesion of climbing fibers to the cerebellum. This lack of climbing fiber input increases the activity of ipsilateral Purkinje cells, which consequently provide too much inhibition of the deep cerebellar nuclei.