Walsh & Hoyt: Vestibulo-Ocular Reflex

Summary. The vestibulo-ocular reflex (VOR) prevents slippage of retinal images by moving the eyes at the same speed as the head as it accelerates in the opposite direction. The angular VOR is activated by the semicircular canals as the head rotates. The translational VOR operates when the head moves in the horizontal plane or frontal plane or up and down; it is activated by otolith receptors, which also generate the tilt VOR when the head rotates relative to gravity. Head acceleration signals are integrated by mechanical properties of the semicircular canals so that the vestibular nerve transmits head velocity signals to the vestibular nucleus. Second order neurons in the vestibular nuclei take several routes. For the horizontal VOR, axons of second-order neurons in the medial vestibular nucleus transmit velocity commands to the abducens nucleus where they synapse on lateral rectus motoneurons, and abducens internuclear neurons that project through the MLF to the medial rectus subdivisions of the oculomotor nucleus. The horizontal VOR is also served by another direct excitatory projection from the horizontal semicircular canal to second-order neurons in the medial vestibular nucleus. Their axons pass through the ipsilateral abducens nucleus without synapse and ascend to the ipsilateral medial rectus subnucleus through the ascending tract of Deiters, which lies just lateral to the MLF. Second-order vestibular neurons in the medial and superior vestibular nuclei transmit vertical and torsional smooth eye movement signals through the MLF and the brachium conjunctivum to the oculomotor and trochlear nuclei.