前庭動眼反射の短期、長期運動学習における小脳片葉の異なる役割

抄録

The vestibuloocular reflex (VOR) stabilizes retinal image during head motion by counter rotating the eyes with nearly an equal speed. When the VOR is inadequate the image slip on the retina evokes a visually-driven response to reduce the slip. If this situation persists, the VOR recalibrates its characteristics so that it can produce adequate eye movements without the aid of the visual system. This phenomenon is called VOR motor learning. In the laboratory it is induced chronically by magnifying or minifying lenses installed on the animal for several days to months, or acutely by exposing it to the visual stimulus moving in- or out-of-phase with a vestibular stimulus for several hours. It has been known the cerebellar flocculus complex (FL) is necessary for this motor learning, but its functional role has been in debate due to the inconsistent results of flocculectomy on the learned animals. We have addressed this problem by performing single unit recording from FL Purkinje (P) cells before and after acute and chronic vertical VOR motor learning in squirrel monkeys. We showed that the information content encoded in P cell firing changes in parallel with the learning in different ways for acute and chronic cases. We also showed that acutely learned VOR gains decay significantly while chronically learned gains do not. These results with other lines of evidence suggest that the memory of the acute VOR motor learning is expressed mainly in FL while that of chronic involves other site as well. [Jpn J Physiol 54 Suppl:S34 (2004)]