Figure 1.
(A) Schematic summary of main premotor inputs to motoneurons innervating vertically acting extraocular muscles. riMLF, rostral interstitial nucleus of the medial longitudinal fasciculus; INC, interstitial nucleus of Cajal. See text for commentary. (B) Sagittal section of the monkey brain stem showing the locations of premotor burst neurons: excitatory burst neurons (EBN) for horizontal saccades lie in the paramedian pontine reticular formation (PPRF); inhibitory burst neurons (IBN) for horizontal saccades lie in the medullary reticular formation (Med RF); EBN for vertical and torsional saccades lie in the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF). Some vertical IBN may reside in or close to the interstitial nucleus of Cajal (INC). EBN and IBN project to ocular motoneurons lying in the abducens nucleus (VI), the trochlear nucleus (IV) and the oculomotor nucleus (III). Omnipause neurons (indicated by an asterisk) lie in the midline raphe of the pons between the rootlets of the abducens nerve (CN VI) and gate the activity of EBN and IBN. The mesencephalic reticular formation (MRF) may also contribute to vertical saccades. CG, central gray; MB, mammillary body; CN III, rootlets of the oculomotor nerve; CN IV, trochlear nerve; ND, nucleus of Darkschewitsch; NRTP, nucleus reticularis tegmenti pontis; PC, posterior commissure; NPH, nucleus prepositus hypoglossi; sc, superior colliculus; TR, tractus retroflexus. The arrow refers to the Horsley–Clarke plane of section. Figure courtesy of Dr. Jean Büttner-Ennever. (C) Probable location of cortical areas important for eye movements in human brain. MST, medial superior temporal visual area; MT, middle temporal visual area. Adapted from Leigh and Zee (2006) with permission. (D) Figures adapted with permission from Steele et al. (1964) that summarize the brainstem regions affected in PSP; the intensity of shading corresponds to the severity of the involvement.