Role of the accessory optic system in the optokinetic nystagmus of the frog.

Abstract

The localization of structures essential foroptokinetic nystagmus (OKN) was investigated in the frog. Isolated lesions were placed in the optic tectum, the pretectal area, the lateral geniculate body, the nucleus of Bellonci and the telencephalon. After simultaneous destruction of these structures in different combinations, the optokinetic response persisted. Transient irregularities in the amplitude and frequency of the OKN were observed after tectal ablation, and the fast phase was often absent when the pretectal region was destroyed.Sectioning of the basal optic root or destruction of its nucleus abolished the OKN.It is suggested that the accessory optic system, together with the surrounding mesencephalic tegmentum, is indispensable for optokinetic responses.