Affiliations: Departments of Neurology, Physiology, and Biophysics, Mount Sinai School of Medicine, New York, USA and Dept of Computer and Information Sciences, Brooklyn College, CUNY, New York, USA
Note: [*] Corresponding author: Bernard Cohen, MD, Department of Neurology, Box 1135, Mount Sinai School of Medicine, 1 East 100th Street, New York, NY 10029-6574. Tel.: +212 241 7068; Fax: +212 831 1610; E-mail: bcohen@smtplink.mssm.edu
Abstract: During vestibular nystagmus, optokinetic nystagmus (OKN), and optokinetic afternystagmus (OKAN), the axis of eye rotation tends to align with the vector sum of linear accelerations acting on the head. This includes gravitational acceleration and the linear accelerations generated by translation and centrifugation. We define the summed vector of gravitational and linear accelerations as gravito-inertial acceleration (GIA) and designate the phenomenon of alignment as spatial orientation of the angular vestibuloocular reflex (aVOR). On the basis of studies in the monkey, we postulated that the spatial orientation of the aVOR is dependent on the slow (velocity storage) component of the aVOR, not on the short latency, compensatory aVOR component, which is in head-fixed coordinates. Experiments in which velocity storage was abolished by midline medullary section support this postulate. The velocity storage component of the aVOR is likely to be generated in the vestibular nuclei, and its spatial orientation was shown to be controlled through the nodulus and uvula of the vestibulo-cerebellum. Separate regions of the nodulus/uvula appear to affect the horizontal and vertical/torsional components of the response differently. Velocity storage is weaker in humans than in monkeys, but responds in a similar fashion in both species. We postulate that spatial orientation of the aVOR plays an important role in aligning gaze with the GIA and in maintaining balance during angular locomotion.
