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In humans, habituation of vestibulo-ocular reflex (VOR) by repeated caloric or rotational stimulation has been well documented. However, less attention has been directed to the effect of habituation on the sensation of self-rotation and little is known about the retention duration of vestibular habituation. To investigate these characteristics, subjects were exposed to ten sessions of angular velocity steps in yaw, with a chair rotating either alternatively in both CW and CCW directions (bidirectional protocol) or always in the same direction (unidirectional protocol), i.e., CW or CCW. The retention of habituation of VOR and sensation of rotation induced by both protocols was studied for a period up to 8 months following the end of the habituation protocols. There was a progressive decline in the VOR peak slow phase velocity and time constant throughout the sessions during both protocols. These parameters then followed an exponential recovery with a time constant of about 1 month. The duration of the sensation of rotation also habituated during repeated angular velocity steps, but it was shorter for both directions of stimulation, including after the unidirectional protocol. Sinusoidal VOR gain was not affected by vestibular habituation to velocity steps, but sinusoidal VOR phase showed an increase in phase lead at 0.02 and 0.04 Hz, which also returned to baseline values within about 1 month. We conclude that vestibular habituation is a long-lasting phenomenon. These results may be helpful for designing and scheduling the protocols for drug studies using crossover design, rehabilitation of balance disorder patients, and for the application of intermittent artificial gravity during space missions. [ABSTRACT FROM AUTHOR]

Changes in the horizontal vestibulo-ocular reflex (VOR) in darkness were investigated in naive cats during: (1) repeated sessions of angular velocity steps, (2) one continuous 1-h session of sinusoidal oscillations at 0.01, 0.02, 0.04, or 0.12 Hz, and (3) repeated sessions of 1-h sinusoidal oscillations at 0.02 and 0.04 Hz. Before and after each vestibular training, the VOR response parameters elicited by both velocity steps and sinusoidal oscillations were measured in order to evaluate the transfer of habituation from one stimulus to the other. After training with velocity steps, the amplitude and duration of the VOR to velocity steps decreased by about 67% and 52%, respectively. This vestibular habituation transferred to the VOR response generated by sinusoidal oscillations, since a decrease in VOR gain was observed at 0.02 and 0.04 Hz, and an increase in phase lead was observed at 0.02, 0.04, and 0.08 Hz. After 1 h exposure to sinusoidal oscillations, the VOR gain was only reduced by 21–28%, whereas VOR phase lead decreased. The same changes were observed during subsequent sessions, with no retention of the response decrements from one session to the next. At the end of sinusoidal training, the amplitude of the VOR generated by velocity steps was slightly altered. After sinusoidal training, the weak changes in the VOR gain accompanied by a decrease in the VOR phase lead, and the absence of retention of these effects from one session to the next, suggest these changes are not characteristics of a vestibular habituation. Previous reports of vestibular habituation induced by repeated sinusoidal oscillations may be confounded by the fact that the angular velocity steps used for quantifying the effects may have been responsible for this habituation. [ABSTRACT FROM AUTHOR]