Retention of habituation of vestibulo-ocular reflex and sensation of rotation in humans

Abstract

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.

Influence of stimulus interval on the habituation of vestibulo-ocular reflex and sensation of rotation in humans

“…The 40-60% decline in VOR peak SPV, time constant, and PSR when steps are delivered after nystagmus reversal is comparable to the decline observed in previous studies during bidirectional or unidirectional habituation protocols [4,6,9,11]. The 25-30% decline in VOR peak SPV and time constant when steps are delivered prior to nystagmus reversal is also comparable to the decline observed after unidirectional habituation for the direction that was not stimulated during the habituation protocol (see Fig.…”

“…The 25-30% decline in VOR peak SPV and time constant when steps are delivered prior to nystagmus reversal is also comparable to the decline observed after unidirectional habituation for the direction that was not stimulated during the habituation protocol (see Fig. 2AB in [6]). The 50-60% decline in the duration of the perception of self-rotation for both directions of stimulation is also in agreement with our measurements after unidirectional habituation in humans [6].…”

“…The exact moment when the slow component of the vestibular nystagmus reverses direction in humans is therefore quite difficult to detect in real time. By contrast, the end of the PSR is easy to detect and previous studies have shown that PSR has shorter duration than the primary phase nystagmus [2,6,17]. Therefore, in the present study we have used the end of the PSR as a precursor to the nystagmus reversal.…”

“…After this PSR had stopped, we waited for 60 s before the chair was rotated CW again. The 60-s duration was long enough for the CW steps to be delivered after nystagmus reversal, based on previous data [2,6] and a validity check performed in the present study (see Fig. 2D).…”

“…In humans, vestibular habituation by repeated rotational stimulation induces not only a decline in the VOR, but also in the perception of self-rotation (PSR) [9,14,15,30]. When humans are exposed to repeated velocity steps in the same direction, habituation of the VOR takes place mostly for that direction of stimulation, but the PSR habituates for both directions of stimulation [6].…”