The oculomotor system uses both vestibular and visual information to stabilize images on the retina. Together, they maintain the angle of gaze when either the individual or the visual surroundings are moving. By modelling consistent with experimental data, it has been suggested that several mathematical integrations are necessary to produce the adequate gaze signal in the CNS. The velocity storage integrator holds or stores activity related to slow phase eye velocity, which is utilized in generating OKN and OKAN, and it is also responsible for producing the dominant time constant of vestibular nystagmus. Recent studies have shown that the velocity storage system has a three-dimensional structure dependent on gravity (cross-coupling).
The neural circuits, however, underlying the velocity storage are still unknown. Recently, we recorded single units in the vestibular nuclei (VN) and the nucleus prepositus hypoglossi (PPH) and stimulated these sites electrically to determine the location of the neural structures associated with the various integrators. Our data suggest that there are two different integrators in the rostral medulla. One is the velocity storage integrator, which appears to lie in the VN. The other is the velocity-to-position integrator, probably closely associated with the PPH.