Abstract
Substantial advances in understanding of oculomotor function have come from basing models of the oculomotor system on the control system theory. In this model, vestibular nystagmus, OKN and OKAN are produced by combined activation of two important pathways. One process, called the direct-pathway, produced rapid changes in eye velocity. A second process (indirect pathway) causes only slow changes in eye velocity and contains a non-ideal integrator. This integrator, labeled a “velocity-storage integrator”, appears to hold or store activity related to slow phase eye velocity. Activities in the direct and indirect pathways combine to form the velocity signal (This signal drives the “velocity-to-position integrator”, which drives the oculomotor plant). The velocity storage mechanism serves as a focus for superimposing a variety of sensory inputs that signal motion and provide the central nervous system with a coordinate basis for interpreting continuous movement of the head relative to the environment. However, neural circuits underlying these mechanism are still unknown. The recent studies suggest that the velocity-storage integrator appears to lie in the vestibular nuclei (mainly medial vestibular nucleus, MVN), while the velocity-to-position-integrator is probably closely associated with the prepositus hypoglossi nuclei. The recent extracellular recording study shows that activities of “vestibular only” and “vestibular, plus saccade” units in the rostral MVN are likely to carry an eye velocity signal related to velocity storage.
