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Canal–Otolith Interactions After Off-Vertical Axis Rotations. II. Spatiotemporal Properties of Roll and Pitch Postrotatory Vestibuloocular Reflexes

Department of Neurology, University of Zurich, Zurich, Switzerland

Submitted 14 April 2004; accepted in final form 31 October 2004

We have examined the spatiotemporal characteristics of postrotatory eye velocity after roll and pitch off-vertical axis rotations (OVAR). Three rhesus monkeys were placed in one of 3 orientations on a 3-dimensional (3D) turntable: upright (90° roll or pitch OVAR), 45° nose-up (45° roll OVAR), and 45° left ear-down (45° pitch OVAR). Subjects were then rotated at ±60°/s around the naso-occipital or interaural axis and stopped after 10 turns, in one of 7 final head orientations, each separated by 30°. We found that postrotatory eye velocity showed horizontal–vertical components after roll OVAR and horizontal–torsional components after pitch OVAR that varied systematically as a function of final head orientation. The quantitative analysis suggests that, in contrast to the analogous yaw OVAR paradigm, a system of up to 3 real, gravity-dependent eigenvectors and eigenvalues determines the spatiotemporal characteristics of the residual eye velocities after roll and pitch OVAR. One of these eigenvectors closely aligned with gravity, whereas the other 2 determined the orientation of the earth horizontal plane. We propose that the spatial characteristics of eye velocity after roll and pitch OVAR follow the physical constraints of stationary orientation in a gravitational field and reflect the brain’s best estimate of head-in-space orientation within an internal representation of 3D space.