Rotation testing was performed to evaluate the functions of the vestibular system by applying a rotational stimulation to a subject and observing the eye movements caused by the vestibulo-ocular reflexes (VORs). VORs comprise the semicircular-ocular reflex (ScOR) and the otolith-ocular reflex (OOR). When the subject's lateral semicircular canal is positioned horizontal to the ground and earth vertical axis rotation (EVAR) is applied, the lateral semicircular canal is stimulated by rotational acceleration, resulting in eye movements caused by the ScOR. In contrast, with off-vertical axis rotation (OVAR), the direction of gravitational acceleration changes continuously during rotation, which simultaneously stimulates the otolith organ. The resultant eye movements are caused by both the ScOR and the OOR. In previous studies, the application of conflicting visual vestibular stimulation using a flat screen under EVAR conditions did not show a significant change in the VOR gain after stimulation. In the present study, we applied conflicting visual vestibular stimulation (-1 stimulation, ×2 stimulation) using a flat screen under OVAR conditions and compared the VOR gain before and after stimulation. No significant change in the VOR gain was observed before and after ×2 stimulation; however, a significant decrease in the VOR gain was observed after -1 stimulation. These results were obtained due to the effects of tilt suppression and because the conflicting visual vestibular stimulation we used was an appropriate form of stimulation to elicit the OOR.
While various methods of vestibular rehabilitation have been reported for equilibrium disturbances, the effects of tilt suppression and whether the stimulation used for vestibular rehabilitation is an appropriate form of stimulation need to be considered.
