Vertical eye deviation and nystagmus inhibition during mental tasking

Twenty subjects with no vestibular complaints and normal otoscopic exams were stimulated with 44 degrees C water for 5 minutes in one ear and their nystagmus was recorded by vertical and horizontal electro-oculography. Changes in vertical eye position and nystagmus inhibition were correlated during periods of mental tasking, relaxation, and voluntary eye elevation. The results showed an average of 42 degree eye depression with mental tasking during irrigation. In addition, mental arithmetic had a "releasing" effect on horizontal nystagmus. Elevation of the eyes on command, however, produced marked irregularity in the horizontal tracings, simulating inhibition. Almost every subject had an apparent vertical deflection on ENG with eye closure. These findings suggest a mechanical component to the phenomenon of inhibition as well as an active central mechanism.