2022 Volume 81 Issue 2 Pages 46-58
This article deals with the neural circuits involved in the generation of horizontal and vertical saccades. Following an explanation about the horizontal saccade system, the vertical saccade system, which has not been described in textbooks, is discussed in detail. Comparing the results with the well-known vestibuloocular pathways, we propose that the saccade system uses the same frame of reference as the vestibuloocular system. The last part of this article explains that the neural circuits for saccades and the quick phase of vestibular nystagmus share a common pathway.
It has generally been accepted that voluntary eye movements are organized in horizontal and vertical systems, based on the results of clinical studies in humans and lesion studies in animals. However, this issue is still under debate, because the neural circuits for vertical saccades are yet to be identified. The riMLF was identified as a premotor center for vertical gaze by Büttner-Ennever, although the exact pathways from the superior colliculus to the vertical ocular motoneurons are unknown. Using intracellular recording and staining techniques, we found that both systems use the same 3D cartesian coordinates as the semicircular canal coordinates. The oldest phylogenetic system, the vestibular system, is used as a common coordinate system by the newer system, the voluntary eye movement subsystem, which constantly captures visual information in relation to the gravitational axis, and the sensory and motor coordinate systems that form the basis of visual cognition in the brain are unified using the common vestibular coordinate system. Use Assumption of the common coordinate system conflicts with Listing's law, but the excitatory commissural connection between the superior colliculi that we discovered is considered to provide the neural substrate for Listing's law.
