Vestibulo-ocular reflex pathway

Each of the semicircular canals has its own projection pattern; here, we focus on the horizontal canal’s excitation of the ocular nuclei because it is the most clinically helpful pathway to learn. We show the left vestibular nuclear complex, which spans much of the height of the pons and the medulla. The vestibular nuclear complex excites the contralateral CN 6, which stimulates the final common pathway. As well, the vestibular nuclear complex sends direct projections to the ipsilateral oculomotor nucleus via the ascending tract of Deiters and simultaneously inhibits the ipsilateral abducens nucleus and contralateral oculomotor nucleus. Of the four vestibular nuclei, the medial and lateral nuclei have the most robust ocular projections. For a simple way to remember this circuitry at the bedside, hold your fists in front of you and show that the left vestibular nuclear complex drives the eyes to the right and the right vestibular nuclear complex drive the eyes to the left. Next, drop one fist to demonstrate that when one vestibular nuclear complex is damaged, the eyes deviate toward the damaged side, away from the intact side.