Neurons in the posterior interposed nucleus of the cerebellum related to
vergence and accommodation. I. steady-state characteristics.
Hongyu Zhang and Paul D. R. Gamlin.
Vision Science Research Center, University of Alabama at Birmingham,
Birmingham, AL 35294.
APStracts 4:311N, 1997.
ABSTRACT
The present study used single-unit recording and electrical microstimulation
techniques in alert, trained rhesus monkeys to examine the involvement of the
posterior interposed nucleus (IP) of the cerebellum in vergence and
accommodative eye movements. Neurons related to vergence and ocular
accommodation were encountered within a circumscribed region of the IP and
their activity during changes in viewing distance was characterized. The
activity of these neurons increased with decreases in vergence angle and
accommodation (the far-response), but none showed changes in activity during
changes in conjugate eye position, and we therefore term them “far-response
neurons”. Far-response neurons were found within a restricted region of the IP
that extended approximately 1 mm rostrocaudally and mediolaterally, and 2 mm
dorsal to the fourth ventricle. Microstimulation of this far-response region
of the IP with low currents (<30 (A) often elicited divergence and
accommodation for far. The behavior of 37 IP far-response neurons was examined
during normal binocular viewing, during monocular viewing (blur cue alone),
and during binocular viewing with accommodation open-loop (disparity cue
alone). The activity of all cells was modulated under all three conditions.
However, the change in activity of some of these neurons was significantly
different under these three viewing conditions. The behavior of 70 IP far-
response neurons was compared during normal binocular viewing and during
viewing in which the accommodative response was significantly dissociated from
the vergence response. The data from these two conditions was pooled and
multiple regression analyses for each neuron generated two coefficients
expressing the activity of the neuron relative to the vergence and to
accommodative response respectively. Based on these coefficients, the overall
activity of the neurons were classified as follows: thirty-four positively
correlated with divergence, eleven positively correlated with far
accommodation, fourteen positively correlated with divergence and far
accommodation, nine positively correlated with divergence and accommodation,
and two positively correlated with convergence and far accommodation. The
results of this study demonstrate the involvement of a specific region of the
posterior interposed nucleus of the cerebellum in vergence and accommodation.
IP far-response neurons are active for vergence and accommodation irrespective
of whether these eye movements are elicited by blur or disparity cues. The
data in the present study strongly suggest that this cerebellar region is a
“far-response” region that is involved in vergence as well as accommodative
eye movements
Received 30 July 1996; accepted in final form 4 November 1997.
APS Manuscript Number J603-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 14 November 1997