Body Position and the Intensity of Caloric Nystagmus

Abstract

Caloric responses were obtained from 12 normal subjects placed, by means of a rotating bed, in different positions in the sagittal plane. The entire 360° range of positions was tested in 30° steps. Nystagmus was recorded electrically and maximum speed-of-slow-component used as the “intensity” measure. When the experimental plot of nystagmus intensity versus body position was compared with a theoretical curve based on the endolymph-flow theory, it was found that in all positions the theoretical face-up responses were increased and the face-down responses decreased by a constant amount. Near the neutral position, on the average, a response beating in a direction opposite to the theoretical direction was elicited. The best (though as yet unproven) explanation of these results is that they are produced by a secondary “direct” caloric response which is unaffected by body position and is superimposed on the endolymph-flow response.