REVERSIBLE INACTIVATION OF MONKEY SUPERIOR COLLICULUS: I. CURVATURE OF
SACCADIC TRAJECTORY.
Hiroshi Aizawa, Robert H. Wurtz.
Laboratory of Sensorimotor Research, National Eye Institute, Bethesda, MD
20892-4435, USA
APStracts 4:350N, 1997.
ABSTRACT
The neurons in the intermediate layers of the monkey superior colliculus (SC)
that discharge before saccadic eye movements can be divided into at least two
types, burst and buildup neurons, and the differences in their characteristics
are consistent with different functional contributions of the two cell types.
It has been suggested that a spread of activity across the population of the
buildup neurons during saccade generation may contribute to the control of
saccadic eye movements. The influence of any such spread should be on both the
horizontal and vertical components of the saccade because the map of the
movement fields on the SC is a two dimensional one; it should affect the
trajectory of saccade. The present experiments used muscimol injections to
inactivate areas within the SC in order to determine the functional
contribution of such a spread of activity on the trajectory of the saccades.
The analysis concentrated on saccades made to areas of the visual field that
should be affected primarily by alteration of buildup neuron activity.
Muscimol injections produced saccades with altered trajectories; they became
consistently curved after the injection, and successive saccades to the same
targets had similar curvatures. The curved saccades showed changes in their
direction and speed at the very beginning of the saccade, and for those
saccades that reached the target, the direction of the saccade was altered
near the end to compensate for the initially incorrect direction. Post-
injection saccades had lower peak speeds, longer durations, and longer
latencies for initiation. The changes in saccadic trajectories resulting from
muscimol injections, along with the previous observations on changes in speed
of saccades with such injections, indicate that the SC is involved in
influencing the eye position during the saccade as well as at the end of the
saccade. The changes in trajectory when injections were made more rostral in
the SC than the most active burst neurons also are consistent with a
contribution of the buildup neurons to the control of the eye trajectory. The
results do not, however, support the hypothesis that the buildup neurons in
the SC act as a spatial integrator.
Received 17 December 1996; accepted in final form 2 December 1997.
APS Manuscript Number J987-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 12 December 1997