To clarify the difference between the vestibulo-ocular system and the vestibulospinal system, we analyzed the relationship between nystagmus and body sway induced by caloric stimulation. The subjects were 8 healthy males who were asked to maintain an upright standing position with eyes closed on the platform. Caloric stimulation was applied to the right ear with cold water (20°C). Eye movement was recorded by electronystagmography. Body sway was analyzed from the output of the X and Y axis components from the platform.
1) Increase in the amplitude of body sway corresponded closely with nystagmus intensity during caloric stimulation.
2) The parameters of left-right body sway were significantly positively correlated with the parameters of nystagmus.
3) No difference was observed in the velocity of body sway in either axis.
4) The directionality of body sway still remained after the caloric nystagmus had disappeared.
These results indicate that unilateral caloric stimulation has two effects on body equilibrium. One is a direct stimulus of the labyrinth which induces postural deviation during caloric stimulation. The other is a disturbance of the postural control system which induces body oscillation. The latter effect persists even after caloric nystagmus has disappeared.