[Opto-vestibular interaction based on nystagmometric data]

Nystagmograms recorded in healthy people (270 ENG from 30 children, aged 3 to 7) were analyzed quantitatively. The velocity of the slow component of the vestibular nystagmus during caloric tests, optokinetic nystagmus in response to stimuli applied at 20 and 10 degrees/sec, as well as vestibulo-optokinetic nystagmus resulting due to the inhibitory or enhancing effect of caloric stimulation were measured. The modulation level, i.e. the change of the velocity of the slow component that accompanied the transition of the optokinetic nystagmus to the vestibulo-optokinetic nystagmus, was always less than that of the vestibular nystagmus. This disagrees with the concept about algebraic summation of intensities of the reactions. The modulation level showed a low correlation with the vestibular nystagmus slow component velocity and depended on the optokinetic nystagmus velocity: at 10 degrees/sec the inhibitory effect was smaller than the enhancing one and at 20 degrees/sec the situation was the opposite. At 20 degrees/sec the slow component velocity was twice higher than at 10 degrees/sec. It is therefore suggested that the parameter reflects the level of the residual activity of the optokinetic system which is independent of vestibular afferentation.