Common Frame of Reference of the Saccade Eye Movement System and the Vestibuloocular System

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  • Takahashi Mayu
    Department of Systems Neurophysiology, Tokyo Medical and Dental University

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  • サッケード眼球運動系と前庭動眼反射系の共通座標系

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<p>　In general, it is believed that voluntary eye movement systems such as the saccade system use horizontal and vertical two dimensional Cartesian coordinates. However, the vestibuloocular reflex system（VOR）, which has horizontal, vertical and torsional components, uses three dimensional（3D）semicircular canal coordinates. Unlike the well-known VOR three-neuron arc, the output pathways from the superior colliculus to ocular motoneurons, especially in the vertical saccade system, have not been determined thus far. Therefore, we analyzed the neural circuits from the superior colliculus to the ocular motoneurons using an intracellular technique, and found the upward and downward torsional saccade systems were similar to the anterior and posterior semicircular canal systems, respectively. Furthermore, similar to the anterior and posterior semicircular canal systems, the upward and downward torsional saccade systems are mutually inhibitory. These similarities between the saccade and VOR systems imply that the saccade system uses the same 3D semicircular canal coordinate as the VOR system. The excitatory commissural connections between the bilateral superior colliculi are most likely involved in generating pure vertical saccades by simultaneously activating bilateral symmetrical vertical systems to maintain Listing’s law.</p>

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