Experimental Observations in Postural Nystagmus I. Extensive Lesions in Posterior Vermis of the Cerebellum

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Abstract
Ablation of the posterior vermis of the cerebellum was performed in the cat. Histologic controls showed that the lesion included pyramis, uvula and nodulus but tÜber vermis and nuclei fastigii may be encroached upon. The result was a syndrome characterized by disequilibrium and postural nystagmus during the unstabilized period of cerebellar deficiency followed by compensation. The postural nystagmus was a typical “benign paroxysmal type” which appeared mainly in supine position and consistently was vertical toward the nose. It was fatigable after several repeated tests and disappeared in a few days or weeks, and it cannot be reproduced in bilateral labyrinthecto-mized animals. It was indicated that, i) the term “paroxysmal” identified the clinical syndrome but not the location of the cause which may be peripheral or central, ii) The term “benign” is confusing because it may imply that this type of postural nystagmus is limited to peripheral lesions with a mild course. iii) Disappearance of postural nystagmus after destruction of the vestibular organ by operation or disease does not necessarily mean that the positional nystagmus was caused by a lesion in that organ. The experiments supported the concept that the paleocerebellum plays an important role in the regulation of vestibular reflexes. Some lesions of this area seemed to release the vestibular centers from cerebellar inhibition. It was postulated that this together with the existence of incoming signals from the peripheral receptors, carrying the information of position change of the head are the primary conditions that elicited the postural nystagmus in our animals. The neural mechanism of the disturbance remains still an obscure subject.

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