Brain stem and cerebellar deficits in eye movement control.

Recent experimental studies allow more precise functional-anatomical correlations in patients with ocular motor disorders. The abducens nucleus contains two groups of cells that together subserve ipsilateral horizontal conjugate gaze: Motoneurons with axons that innervate the lateral rectus and internuclear neurons with axons that cross the midline, ascend in the medial longitudinal fasciculus (MLF) and impinge upon medial rectus motoneurons. The pontine paramedian reticular formation (PPRF) contains burst neurons for horizontal saccades. The rostral interstitial nucleus of the MLF (riMLF) in the midbrain contains burst neurons for vertical saccades. The dorsal lateral pontine nuclei are important for relaying smooth pursuit commands from the cerebrum to the cerebellar flocculus. The medial vestibular nuclei contain neurons important for eccentric gaze-holding. The cerebellar flocculus is also important for gaze-holding as well as for smooth pursuit and the control of the amplitude and direction of vestibular responses. The cerebellar nodulus is important for controlling the duration of vestibular responses. The cerebellar dorsal vermis (and underlying deep nuclei) are important for controlling saccade accuracy.