Observations on central mechanisms common to vestibular and optokinetic nystagmus

The significance of attention and duration of the stimulation in optokinetic nystagmus

Twenty normal human subjects were exposed to horizontal optokinetic stimulation of (OKN) of one minute's duration. They were instructed either to look attentively at every passing target or to stare unattentively at the moving field. After one week the tests were repeated. Another group received optokinetic training for 10 days. It is concluded that arousal is of decisive importance for the reproducibility of OKN. Diversion of the attention did not cause a change in the neural path from a cortical to a subcortical predominance. The estimate of the velocity of the slow phase (EV) must be based on a sufficiently long period of stimulation. The maximum EV of individual beats was not representative of inattentive OKN. The training effect of OKN was short-lasting and insignificant.

Modification of the macaque's vestibulo-ocular reflex after ablation of the cerebellar vermis

In macaque, the vestibulo-ocular reflex (VOR) as evaluated by the time constant of nystagmus in a modified Bárány spinning test, shows a regular pattern of change with time after ablation of the vermis cerebelli. One day ablation the time constant is in the low normal range; it then increases, and after one week assumes values in the high normal range. While the time constant is high, the VOR is resistant to modification by repeated testing, but may be modified by unidirectional optokinetic nystagmus and by experience with reversing spectacles. These results suggest that the vermis of the cerebellum plays no crucial role in modifications of the VOR by visual inputs, but is involved when the VOR is modified by repeated vestibular experience.

The influence of intravenous injection of lidocaine on optokinetic nystagmus in rabbits

The effects of lidocaine in doses of 2.0--6.0 mg/kg with intravenous injection on optokinetic nystagmus were observed in 21 rabbits. No effect of lidocaine was obtained on the frequency of OKN. On the other hand, the amplitude of OKN in lidocaine groups decreased after the injection. The mode and place of the action of lidocaine on OKN were discussed.

Selective habituation of vestibular nystagmus by visual stimulation in the monkey

Four monkeys were exposed to a series of unidirectional rotating visual fields, of the type known to produce circularvection in man. As in the human case, the vestibulo-ocular reflex for rotation in the direction of the optokinetic nystagmus and circularvection during the preceding visual stimulation--was markedly decreased following that visual stimulation, whereas that in the opposite direction was increased. This finding corresponds to the results of nystagmus and psychophysical circularvection experiments on man. It suggests a link between single unit studies performed under identical conditions in monkey and psychophysical investigations.