Adaptation and adaptation transfer characteristics of five different saccade types in the monkey.

Shifts in the direction of gaze are accomplished by different kinds of saccades, which are elicited under different circumstances. Saccade types include targeting saccades to simple jumping targets, delayed saccades to visible targets after a waiting period, memory-guided (MG) saccades to remembered target locations, scanning saccades to stationary target arrays, and express saccades after very short latencies. Studies of human cases and neurophysiological experiments in monkeys suggest that separate pathways, which converge on a common locus that provides the motor command, generate these different types of saccade. When behavioral manipulations in humans cause targeting saccades to have persistent dysmetrias as might occur naturally from growth, aging, and injury, they gradually adapt to reduce the dysmetria. Although results differ slightly between laboratories, this adaptation generalizes or transfers to all the other saccade types mentioned above. Also, when one of the other types of saccade undergoes adaptation, it often transfers to another saccade type. Similar adaptation and transfer experiments, which allow inferences to be drawn about the site(s) of adaptation for different saccade types, have yet to be done in monkeys. Here we show that simian targeting and MG saccades adapt more than express, scanning, and delayed saccades. Adaptation of targeting saccades transfers to all the other saccade types. However, the adaptation of MG saccades transfers only to delayed saccades. These data suggest that adaptation of simian targeting saccades occurs on the pathway common to all saccade types. In contrast, only the delayed saccade command passes through the adaptation site of the MG saccade.