Transfer of Gain Changes from Targeting to Other Types of Saccade in the Monkey: Constraints on Possible Sites of Saccadic Gain Adaptation. Fuchs, Albert F., David Reiner, and Milton Pong. Regional Primate Research Center and Department of Physiology and Biophysics, University of Washington, Seattle, Washington 98195.
APStracts 3:0100N, 1996.
1. Our goal was to use behavioral experiments to delimit where in the simian oculomotor system the gain of horizontal saccadic eye movements might be controlled. Our strategy was to change the gain of saccades to visual target steps (called targeting saccades) and to examine whether these changes transferred to other types of saccades. We reduced the gain of targeting saccades by jumping the target backward as a saccade was made so that the saccade appeared to overshoot. After 1000-1500 saccades to such back-stepping targets, the average overshoot, and therefore the saccadic gain, had decreased substantially. 2. After the gain of targeting saccades had been reduced by 15- 22%, several kinds of saccades were tested. Most were elicited by various visual targets. Some were made to jumping targets, which were timed to elicit saccades with longer (delayed saccades) or shorter (express saccades) latencies than normal or to targets that disappeared after a brief exposure (memory-guided saccades). Others were elicited to stationary targets (self- paced saccades) or in pursuit of a smoothly moving target (catch-up saccades). Finally, we tested the saccadic fast phases of vestibular and optokinetic nystagmus. 3. Gain reduction of targeting saccades transferred at least partially to all the other types of saccades made to target jumps. The percentage gain transfer was calculated as (gain reduction of test saccades)/(gain reduction of adapted targeting saccades). The average percent transfer to delayed, memory-guided and express saccades was 96%, 88% and 91%, respectively. 4. Monkeys also showed substantial gain transfer to self-paced saccades, which scanned stationary targets. The average percentage gain transfer was 69% in the 4 animals tested. When two humans performed the same task, there was no transfer at all. These data suggest that saccadic gain adjustment involves different processes in monkeys and humans. 5. The transfer of gain to the catch-up saccades of smooth pursuit varied from 41 to 100% across the 4 monkeys tested. Nevertheless, the average percentage gain transfer for all the animals was 75%. 6. As judged by the amplitude distribution of fast phases before and after adaptation, there was little, if any, saccadic gain transfer to the fast phases of vestibular or optokinetic nystagmus. In 12 of 13 experiments, there was no significant decrease in fast phase amplitude after a gain reduction of targeting saccades (P>0.1). 7. This study shows that the average percentage gain transfer from targeting to delayed, express, memory-guided, self-paced and catch-up saccades was never less than 69%. Although there was substantial transfer to saccades elicited by jumping, stationary, remembered, or slowly moving visual targets, there was relatively little to the saccade-like fast phases of nystagmus.

Received 10 October 1995; accepted in final form 17 May 1996.
APS Manuscript Number J669-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 June 96