小脳半球による随意眼球運動の制御機構

Abstract

The cerebellar hemispheres, which constitute the major portion of the primate cerebellum, are considered to be involved in voluntary movement control and cognitive functions. Unlike those of the flocculus-paraflocculus complex and vermal lobule VI/VII, the oculomotor functions of the hemispheres are not yet well known. We recently found a new eye movement area in the hemispheric lobule VI/VII (H-VI/VII) in macaque monkeys. Unilateral lesions of H-VI/VII decreased the velocities of smooth pursuit, and delayed the onset of smooth pursuit and saccades. No hypo- or hypermetria was observed in the saccade amplitudes. A 50% impairment of the adaptations of smooth pursuit velocities, examined by brief acceleration of the target velocity during smooth pursuit, was observed. These lesion effects were prominent in the eye movements directed to the lesioned side. No spontaneous or gaze nystagmic eye movements were observed in association with the H-VI/VII lesions. Based on the results of comparison of the mossy and climbing fiber input organizations among the flocculus-paraflocculus, vermal lobule VI/VII and H-VI/VII, we suggest that the H-VI/VII is a new member of the oculomotor cerebellum that mediates a different function from that of the flocculus, paraflocculus and vermis.