Eye Movement Deficits Following Ibotenic Acid Lesions of the Nucleus
Prepositus Hypoglossi in Monkeys. I. Saccades and Fixation
Chris R. S. Kaneko
Department of Physiology and Biophysics and Regional Primate Research
Center, University of Washington, Seattle, Washington 98195
APStracts 4:114N, 1997.
ABSTRACT
It has been suggested that the function of the nucleus prepositus hypoglossi
(nph) is the mathematical integration of velocity-coded signals to produce
position-coded commands that drive abducens motoneurons and generate
horizontal eye movements. In early models of the saccadic system, a single
integrator provided not only the signal that maintained steady gaze following
a saccade but also an efference copy of eye position, which provided a
feedback signal to control the dynamics of the saccade. In this study,
permanent, serial ibotenic acid lesions were made in the nph of three rhesus
macaques and their effects were studied while the alert monkeys performed a
visual tracking task. Localized damage to the nph was confirmed in both Nissl
and immunohistochemically stained material. The lesions were clearly
correlated with long-lasting deficits in eye movement. The animalsO ability to
fixate in the dark was quickly and uniformly compromised so that saccades to
peripheral locations were followed by post-saccadic centripetal drift. The
time constant of the drift decreased to approximately one-tenth of its normal
values but remained ten times longer than that attributable to the mechanics
of the eye. In contrast, saccades were minimally affected. The results are
more consistent with models of the neural saccade generator that use separate
feedback and position integrators than with the classical models that use a
single multipurpose element. Likewise, the data contradict models that rely on
feedback from the nph. In addition, they show that the oculomotor neural
integrator is not a single neural entity but is most likely distributed
amongst a number of nuclei.
Received 15 November 1996; accepted in final form 24 June 1997.
APS Manuscript Number J902-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 15 July 1997