Functional role of median longitudinal fasciculus in evoked conjugate ocular deviations in cats

¹ Departments of Physiology, Anatomy and Physiological Chemistry, University of California Medical Center, Los Angeles, California

Functional deficits of evoked conjugate ocular movements were assessed following acute surgical interruption of the median longitudinal fasciculus (MLF) in cats prepared as encéphale isolés. a) In horizontal deviations, adduction evoked by stimulation of dorsal midbrain, zona incerta and medial reticular substance of medulla was abolished by bilateral section of the MLF at or anterior to the level of the 6th nucleus. Unilateral sections differentially abolished adduction from the three stimulated areas. Abduction from dorsal midbrain stimulation required a higher voltage following section of MLF between or just posterior to the sixth nuclei. b) Conjugate ocular torsion evoked by stimulation of zona incerta was significantly altered by sections of internuclear MLF as well as by coagulating lesions in the vestibular nuclear complex. Results indicate first that no single group of fibers in the MLF serves as ‘the common path’ for ocular adduction in all types of horizontal conjugate movements. Second, the degree of torsion induced by stimulation of the zona incerta is at least partially dependent on vestibulomesencephalic impulses ascending the MLF.