Vol. 7 1, No. 3, March 1994. Printed in U.S.A.
Inertial Representation of Angular
Rhesus Monkeys. I. Vestibuloocu
1Motion in the Vestibular System of
DORA E. ANGELAKI AND BERNHARD J. M. HESS
Department of Neurology, University of Ziirich, CH-8091 Ziirich, Switzerland
SUMMARY AND CONCLUSIONS away from the pitch head axis until residual postrotatory velocity
1. The spatial organization of the vestibuloocular reflex
decayed along a line approximately parallel to gravity.
(VOR) was studied in six rhesus monkeys by applying fast, short-
7. The time constant of the vertical postrotatory slow phase
lasting, passive head and body tilts immediately after constant-ve- velocity in ear-down positions was 18.0 t 6.3 s (upward slow
locity rotation (&90" /s) about an earth-vertical axis. Two alterna- phase velocity) and 12.8 t 4.6 s (downward slow phase velocity).
tive hypotheses were investigated regarding the reference frame Time constants decreased as the animals were tilted toward
used for coding angular motion. 1) If the vestibular system is orga- upright position and were minimal after tilts to the upright posi-
nized in head-centered coordinates, postrotatory eye velocity tion (upward slow phase velocity 3.0 t 0.8 s; downward slow
would decay invariably along the direction of applied head angu- phase velocity 3.5 * 1.4 s). When monkeys were tilted toward
lar acceleration. 2) Alternatively, if the vestibular system codes upside-down position, time constants increased continuously up