小脳と眼球運動―視標追跡眼球運動をモデルとした基礎研究と臨床応用―

Abstract

Recent studies implicate the cerebellum in cognitive functions in addition to its well-established roles in motor control and learning. Using a memory-based smooth-pursuit task that separates visual working memory from motor preparation and execution, monkeys were trained to pursue (i.e., go) or not pursue (i.e., no-go), a cued direction, based on the working memory of visual motion-direction and a go/no-go instruction. Task-related neuronal activity was examined in cerebral and cerebellar major smooth-pursuit pathways. Different cerebral and cerebellar areas carried distinctly different signals during memory-based smooth-pursuit. In the cerebellum, prediction-related signals (visual working memory, pursuit selection and movement preparation) were represented in the vermal lobules VI-VII and caudal fastigial nucleus, whereas the floccular region (flocculus and ventral paraflocculus) contained predominantly execution-related signals. This task was applied to patients with cerebellar degeneration and idiopathic Parkinson's disease (PD). None of the PD patients tested exhibited impaired working memory of motion-direction and/or go/no-go selection, but they did show task-specific difficulty in generating an initial smooth-pursuit component, suggesting difficulty in smooth-pursuit preparation. In contrast, most cerebellar patients exhibited impaired visual working memory in addition to difficulty in preparing for and executing smooth-pursuit. These results suggest different roles for the basal ganglia and cerebellum in smooth-pursuit planning.