システムニューロサイエンス教育講座　　１３．　視運動性眼振の皮質下経路について

DOI 被引用文献2件 参考文献47件
  • 加藤 功
    聖マリアンナ医科大学耳鼻咽喉科学教室

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  • The Subcortical OKN Tracts in Mammals.

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The neural substrates subserving optokinetic nystagmus (OKN) in mammalian brainstem are reviewed. The accessory optic system (AOS) consists of 3 terminal nuclei, lateral (LTN), medial (MTN) and dorsal terminal nucleus (DTN) which are distributed along the brachium of the superior colliculus. All the AOS nuclei receive direct retinal inputs from the contralateral eye and a weak input from the ipsilateral eye and connect strongly with the nucleus of the optic tract (NOT) which is thought to provide the afferent limb of the horizontal OKN. LTN is the only nucleus where electrophysiological experiments have been performed in mammals as follows : <BR>(1) LTN units are direction-selective, responding preferentially during upward vertical background movements, and show a parafoveal receptive field. Most LTN neurons can provide both direction and velocity information only at lower velocities, and differ significantly from NOT neurons, responding to over 200°/s OKN stimuli. Therefore, it remains unclear how the LTN might subserve for the generation of OKN, other oculomotor or visual roles.<BR>(2) Ablation study of the NOT revealed the NOT contributes to the slow buildup of OKN which is thought to underlie the brainstem of lower vertebrates.<BR>(3) Pretectofugal fibers investigated using either biocytine or WGA HRP demonstrated the following : <BR>1) Fibers traversing the posterior commissure terminate in the contralateral NOT.<BR>2) Fibers descend medially through the nucleus reticularis pontis oralis to reach the lateral part of the ipsilateral nucleus reticularis tegmenti pontis.<BR>3) Fibers project into the dorsal cap of the inferior olive. At the level of the abducens nucleus, some fibers ascend through the nucleus pontis caudalis and reach the nucleus prepositus hypoglossi and medical vestibular nucleus.<BR>Consistent with the physiological data, direct terminals of the NOT neurons in themedial vestibular nucleus could drive storage mechanisms and produce OKN in the monkey.

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