Abstract
We have shown previously that saccadic adaptation occurs faster when repeated after a short interval, a phenomenon we call facilitated adaptation. In the present study, we attempted to delimit where in the oculomotor system the saccadic motor learning might be facilitated. To this end, we investigated how adaptation of horizontal or vertical saccades affected subsequent adaptation of oblique saccades in rhesus monkeys. Saccadic adaptation was induced by intrasaccadic step (ISS) of the target. After the gain of horizontal or vertical saccades was substantially reduced by backward ISS (control adaptation), we used forward ISS to increase the gain back to ~1.0. Then we changed the target step direction by 45 deg and subjected oblique saccades to a similar backward ISS (test adaptation). The rate of gain change was estimated as a slope of a regression line fitted to the initial 100-200 saccades. Analyses of gain change rates indicated that preceding adaptation of horizontal or vertical saccades facilitated adaptation of oblique saccades. Further analysis revealed that the horizontal and vertical components of oblique saccades exhibited different gain change rates. When preceded by adaptation of horizontal saccades, horizontal component adapted faster than vertical component. Similarly, preceding vertical saccade adaptation exerted a larger facilitatory effect on vertical component. The facilitation thus appears to be dominant in the learned component. These results imply that saccadic adaptation facilitation may occur at a structure that controls the component gain of saccades. [Jpn J Physiol 54 Suppl:S180 (2004)]
