Loss of Ipsidirectional Quick Phases of Torsional Nystagmus with a Unilateral Midbrain Lesion 1

We report a patient with a long-standing, unilateral lesion of the midbrain who showed ipsidirectional loss of torsional quick phases, impairment of all vertical eye movements and normal horizontal eye movements. The findings are consistent with recent reports of the effects of experimental lesions, in monkeys, of the,rostral interstitial nucleus of the medial longitudinal fasciculus and the interstitial nucleus of Cajal.