Fig. 1.

a Summary of simple models for generating horizontal gaze shifts in INO. Premotor excitatory burst neurons (right-eye burster: REB; left-eye burster: LEB), lying in the paramedian pontine reticular formation, project a pulse of innervation to the abducens nucleus (CN VI). Abducens motoneurons project the pulse of innervation via the sixth nerve to the right lateral rectus, which contracts rapidly to generate an abducting saccade of the right eye. Abducens internuclear neurons project the pulse of innervation, via the medial longitudinal fasciculus (MLF, internuclear pathway) to medial rectus motoneurons that, in turn, innervate the left medial rectus via the third nerve, to generate a fast adducting saccade of the left eye. If the MLF is demyelinated (indicate by X), signals are low-pass filtered, thereby reducing the size of the pulse and causing the adducting saccade of the left eye to be slow. Vergence burst neurons (VBN) project a fast vergence command directly to medial rectus motoneurons and are unaffected by INO. Bottom Schematic of test paradigms. b saccades between equidistant targets at 1 m. c saccades between equidistant targets at 35 cm. d Müller paradigm, with far and near targets aligned on the visual axis of the right eye