Palsy of upward and downward saccadic, pursuit, and vestibular movements with a unilateral midbrain lesion: pathophysiologic correlations.

Upward and downward gaze palsy was measured by a magnetic search coil technique and correlated with neuropathologic findings in a patient with a unilateral midbrain infarct. Oculography demonstrated (1) saccadic palsy above primary position and slow, limited vertical saccades below; (2) low-gain, restricted vertical pursuit; and (3) low-gain, abnormal phase lead, and restricted range of the vertical vestibulo-ocular reflex (VOR). Bidirectional palsy of vertical saccades is attributed to unilateral loss of burst cells in the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) and interruption of burst cell fibers from the opposite riMLF. Pathways mediating vertical pursuit and integration of the vertical VOR also traversed the infarct, which included the interstitial nucleus of Cajal.