On the Secondary Phase of Nystagmus

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Abstract
Under various conditions, the authors have sought the secondary phase of vestibular and optokinetic nystagmus evoked in normal human subjects and rabbits. Results obtained are as follows 1) the secondary phase of nystagmus can be elicited easily even with rather weak stimuli as used clinically regardless of whether caloric or optokinetic stimuli were employed. If it cannot be observed, it is because of extinction due to inhibitory factors such as visual inputs or unknown effects. 2) in the authors' opinion, the secondary phase of nystagmus is organized by primitive tracts in the brain stem and is constantly influenced and controlled by the higher vestibular and optokinetic nystagmus tracts such as the cerebrum or cerebellum. 3) in rabbits, the authors have experienced some cases in which optokinetic nystagmus is transformed into eye movements resembling so-called “Nystagmus Clonus” or “Firing” which become completely independent of the original stimuli in regard to the frequency of beats. the presence of this phenomenon supplies us counter-evidence opposing Bárány's theory concerning the genesis of optokinetic nystagmus.