Since conjugate deviation of the eyes in a horizontal plane involves simultaneous contraction of the medial rectus muscle of one eye and the lateral rectus muscle of the other eye, some neural pathway between the nuclei of the extraocular muscles must provide for this synergistic action. While it has been suggested by many authors that fibers from the abducens or parabducens nucleus64 may ascend in the medial longitudinal fasciculus to the trochlear and oculomotor nuclei, these fibers have not been demonstrated. The principal ascending fibers in the medial longitudinal fasciculus rostral to the abducens nuclei originate from the vestibular nuclei. It is commonly acknowledged that the vestibular nuclei project fibers and/or collaterals to all of the nuclei of the extraocular muscles.8,14 The hypothesis that the secondary vestibular projection may play an essential rôle in all conjugate eye movements is strengthened by the experimental studies of Fluur,31
CARPENTER MB, McMASTERS RE. Disturbances of Conjugate Horizontal Eye Movements in the MonkeyII. Physiological Effects and Anatomical Degeneration Resulting from Lesions in the Medial Longitudinal Fasciculus. Arch Neurol. 1963;8(4):347–368. doi:10.1001/archneur.1963.00460040017001
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