演題番号 : P3-h08
羽田 佳人 / Yoshito Haneda:1 三浦 真理子 / Mariko Miura:1 吉田 薫 / Kaoru Yoshida:1 岩本 義輝 / Yoshiki Iwamoto:1
1:筑波大院・人間総合・神経生理 / Lab Neurophysiol, Univ of Tsukuba, Tsukuba, Japan
The accuracy of saccades is ensured by a learning mechanism called saccade adaptation. Our previous work has shown that, when saccade adaptation is induced twice in a single experiment, the second adaptation occurs at a higher rate. This facilitating effect lasts for at least 30 minutes (Kojima et. al 2004). Does this effect last longer, as for days? Does it result from plasticity in the saccade circuitry? The present study investigates the effect of preceding adaptation on the speed of subsequent adaptation over days and weeks. Eye movements of rhesus monkeys were recorded by the magnetic search coil method with the head immobilized. We decreased the gain of saccades to 10° target steps in one horizontal direction by stepping the target backward by 35% during saccades. In each experiment, which lasted for ~2 hours, we first measured pre-adaptation gain, decreased the gain over ~1500 trials and brought the gain back to ~1.0. Between the experiments, the monkey was exposed to normal visual environment. Adaptation experiments were repeated on 2-4 consecutive days, which formed one series of adaptation. After one series of adaptation, we conducted washout experiments for ~7 days, in which the animal was required to make normometric saccades to target steps that were not followed by backward steps. Washout experiments were expected to erase the memory of the preceding series of adaptation. We compared adaptation in the first day and that in the last day in each series. We found that the rate of adaptation in the last day was higher than that in the first day (p<0.01). Thus, the facilitating effect of preceding adaptation lasts for more than a day. The present result suggests that a memory of saccade adaptation is retained for days. We are currently examining whether the facilitating effect exhibits specificity to saccade direction or to error direction, which may give a clue to the site of plasticity for the memory of prior experience.