Study of nystagmus suppression in the Rotatory Tests.

Thirty one healthy subjects ranging in age between 21 and 50, participated voluntarily in the following experiment: they underwent programmed sequential alternating rotations, while their nystagmus was recorded by way of electronystagmography. The direction of rotation was changed every minute, and the total rotation time was 36 minutes. The subjects were rotated under external conditions which were altered every six minutes; these conditions included the following: 1. Rotation in the light with visual fixation and convergence. 2. Rotation in the light with visual fixation without convergence (one eye closed, the other looking at the target). 3. Rotation in the light without visual fixation (both eyes covered by a shade or by Frenzel's glasses). 4. Rotation in the dark without convergence (looking straight ahead). 5. Rotation in the dark with convergence (looking at the thumb, closely placed in front of the nose). The purpose of the experiment was to study the phenomenon of nystagmus suppression observed with visual fixation and often attributed to cortical activity. The conclusion of the study is that nystagmus may be suppressed by light alone as well as by visual stimuli, convergence and proprioceptive stimuli. The inference is that the mechanism involves brain stem reflexes and not necessarily visual cortex activity.