REVERSIBLE INACTIVATION OF MONKEY SUPERIOR COLLICULUS: II. MAPS OF SACCADIC
DEFICITS.
Christian Quaia, Hiroshi Aizawa, Lance M. Optican, Robert H. Wurtz.
Laboratory of Sensorimotor Research, National Eye Institute, Bethesda, MD
20892-4435, USA.
APStracts 4:348N, 1997.
ABSTRACT
Neurons in the superior colliculus (SC) are organized as maps of visual and
motor space. The companion paper (Aizawa and Wurtz, 1998) showed that muscimol
injections into intermediate layers of the SC alter the trajectory of the
movement and confirmed previously reported effects on latency, amplitude, and
speed of saccades. In this paper we analyze the pattern of these deficits
across the visual field by systematically comparing the magnitude of each
deficit throughout a grid of targets covering a large fraction of the visual
field. We also translate these deficits onto the SC map of the visual/movement
fields to obtain a qualitative estimate of the extent of the deficit in the
SC. We found a consistent pattern of substantially increased saccadic latency
to targets in the contralateral visual hemifield, accompanied by slight and
inconsistent increases and decreases for saccades to the ipsilateral
hemifield. The initial and peak speed of saccades was reduced after the
injection. The post-injection amplitude of the saccades were either hypometric
or normometric, but rarely hypermetric. Although errors in the initial
direction of the post-injection saccades were small, they consistently formed
a simple pattern: an initial direction with minimal errors (a null direction)
separating regions with clockwise and counter-clockwise rotations of the
initial direction. However, the null direction did not go through the center
of the inactivated zone, as would be expected if the SC alone were determining
saccade direction, e.g., with a population code. One hypothesis that can
explain the misalignment of the null direction with the lesion site is that
another system, acting in parallel with the SC, contributes to the
determination of saccadic trajectory.
Received 20 June 1997; accepted in final form 2 December 1997.
APS Manuscript Number J517-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 12 December 1997