The brain stem pathway for vertical saccades involves the PPRF, rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF), nucleus of Cajal, and the nuclei of cranial nerves III and IV. For upgaze, projections from the riMLF traverse through the posterior commissure, whereas there are direct downgaze projections from the riMLF to cranial nerve nuclei III and IV. These differences explain why lesions causing upgaze paralysis are less specific to a particular region than those causing downgaze paralysis.
Robert B. Daroff, MD, Professor of Neurology, School of Medicine, CASE Western Reserve University, University Hospitals - Case Medical Center
Spencer S. Eccles Health Sciences Library, University of Utah