Unilateral Adaptation of the Human Angular Vestibulo-Ocular Reflex

Abstract

A recent study showed that the angular vestibuloocular reflex (VOR) can be better adaptively increased using an incremental retinal image velocity error signal compared with a conventional constant large velocity-gain demand (×2). This finding has important implications for vestibular rehabilitation that seeks to improve the VOR response after injury. However, a large portion of vestibular patients have unilateral vestibular hypofunction, and training that raises their VOR response during rotations to both the ipsilesional and contralesional side is not usually ideal. We sought to determine if the vestibular response to one side could selectively be increased without affecting the contralateral response. We tested nine subjects with normal vestibular function. Using the scleral search coil and head impulse techniques, we measured the active and passive VOR gain (eye velocity / head velocity) before and after unilateral incremental VOR adaptation training, consisting of self-generated (active) head impulses, which lasted ∼15 min. The head impulses consisted of rapid, horizontal head rotations with peak-amplitude 15 o , peak-velocity 150 o /s and peak-acceleration 3,000 o /s 2 . The VOR gain towards the adapting side increased after training from 0.92±0.18 to 1.11±0.22 (+22.7± 20.2 %) during active head impulses and from 0.91± 0.15 to 1.01±0.17 (+11.3±7.5 %) during passive head impulses. During active impulses, the VOR gain towards the non-adapting side also increased by ∼8 %, though this increase was ∼70 % less than to the adapting side. A similar increase did not occur during passive impulses. This study shows that unilateral vestibular adaptation is possible in humans with a normal VOR; unilateral incremental VOR adaptation may have a role in vestibular rehabilitation. The increase in passive VOR gain after active head impulse adaptation suggests that the training effect is robust.

Pilot Study of a New Rehabilitation Tool

“…During active head impulses, the two patients who quickly learned the adaptation training had significant adaptation toward the ipsilesional adapting side (+43.2% and +39.2%) and minimal adaptation toward the nonadapting side (j14.3% and j5.6%). These increases were greater than those seen in previous studies on bilateral and unilateral incremental adaptation training in UVH subjects (9) and normal subjects (10), respectively. For the other two patients, there was evidence of unilateral short-term adaptation, particularly in patient B1, whose VOR gain increased from 0.08 to 0.38 during passive head impulses toward the adapting side.…”

“…We did not use the incremental (initial gain = 1.1 demand driven to a final target gain = 2) adaptation training technique, which for bilateral adaptation has been shown to more effectively increase the VOR gain compared with Â2 ''all-at-once'' adaptation training (9). Instead, in this study, we used a continual Â1.5 (''all-at-once'') training, which for unilateral adaptation seems to be just as effective as the incremental adaptation training (10). This preliminary result suggests that the 0.1 increment in target gain between training epochs during incremental adaptation training (9,10) may be conservative.…”

“…Increasing the normal side is undesirable because it results in overcompensatory eye movements. The authors have recently showed that, under laboratory conditions, unilateral VOR short-term adaptation is possible in humans (10). In that study, nine normal subjects underwent the same experimental protocol as that of Schubert et al (9) for rotations to one side (adapting side) but, for rotations toward the other (nonadapting) side, the visual stimulus was removed.…”

Age-related Refixating Saccades in the Three-Dimensional Video-Head-Impulse Test

“…Majorly, those subjects use an optical correction with only about 2% having insufficient correction (31). Optical corrections are known to magnify (plus lenses) or miniaturize (minus lenses) the visual surrounding and adapt the VOR gain direction and frequency specific (32)(33)(34)(35)(36). In case of higher age we have to consider adaptive effects of magnifying optical corrections, which increase the VOR gain.…”

Influence of Time and Direction Information on Video Head Impulse Gains

“…Migliaccio and Schubert [23] suggest that with as little as 15 minutes of tutoring, unilateral incremental VOR adaptation can be stimulated in normal subjects. Their experiments showed that during active head impulses, VOR gain in the adapting direction was increased by -22% and by -11% during passive ones.…”