Lesion in unilateral lower area of dorsal pontine tegmentum, which affects internuclear fibers of ipsilateral medial longitudinal fasciculus, abducens nucleus, and paramedian pontine reticular formation. Condition manifests as palsy of lateral gaze in 1 direction with internuclear ophthalmoplegia in other direction; also associated with slurred speech, vertigo, gait problems, and diplopia.