Effects of vestibular disorders on vestibular reflex and imagery.

The aim of this study was to establish the effect of vestibular lesion on vestibular imagery. Subjects were required to estimate verbally their passively travelled rotation angles in complete darkness, i.e., to activate vestibular imagery. During motion, the vestibulo-ocular reflex (VOR) was measured. Thus, we examined the coherence between the vestibulo-ocular reflex and self-rotation imagery, with vestibular-lesioned patients and healthy participants. Unilateral acute and chronic patients, bilateral patients, and healthy subjects were compared. The stimulus was a sequence of eight successive passive rotations, with four amplitudes (from 90° to 360°) in two directions. The VOR gain was lower in patients with unilateral lesions, for ipsilateral rotations. The healthy subjects had the highest gain and the bilateral group the lowest, on both rotation sides. Thanks to vestibular compensation after acute unilateral neuritis, the VOR gain increased in lesion side and decreased in healthy side, resulting in a similar gain in both sides. A deficit of vestibular imagery was found exclusively in patients with bilateral hyporeflexia, on both sides. The performance in vestibular imagery was good in the control group and correct in the unilateral patients. Finally, we found a significant correlation between the efficiency of the VOR and that of vestibular imagery, exclusively in the bilateral patients. The present study shows the complex relationship between vestibular imagery and the VOR. This imagery test contributes to another assessment of the spatial handicap of vestibular patients. It seems particularly interesting for patients with bilateral canal paresis and could be used to confirm this diagnosis.