Effects of Galvanic Vestibular Stimulation on Vestibular Compensation in Unilaterally Labyrinthectomized Mice

Objectives: To investigate the ameliorating effects of sinusoidal galvanic vestibular stimulation (GVS) on vestibular compensation from unilateral vestibular deafferentation (UVD) using a mouse model of unilateral labyrinthectomy (UL).Methods: Sixteen male C57BL/6 mice were allocated into two groups that comprise UL groups with GVS (GVS group, n = 9) and without GVS intervention (non-GVS group, n = 7). In the experimental groups, we assessed vestibulo-ocular reflex (VOR) recovery before (baseline) and at 3, 7, and 14 days after surgical unilateral labyrinthectomy. In the GVS group, stimulation was applied for 30 min daily from postoperative days (PODs) 0–4 via electrodes inserted subcutaneously next to both bony labyrinths.Results: Locomotion and VOR were significantly impaired in the non-GVS group compared to baseline. The mean VOR gain of the non-GVS group was attenuated to 0.23 at POD 3 and recovered continuously to the value of 0.54 at POD 14, but did not reach the baseline values at any frequency. GVS intervention significantly accelerated recovery of locomotion, as assessed by the amount of circling and total path length in the open field tasks compared to the non-GVS groups on PODs 3 (p < 0.001 in both amount of circling and total path length) and 7 (p < 0.01 in amount of circling and p < 0.001 in total path length, Mann–Whitney U-test). GVS also significantly improved VOR gain compared to the non-GVS groups at PODs 3 (p < 0.001), 7 (p < 0.001), and 14 (p < 0.001, independent t-tests) during sinusoidal rotations. In addition, the recovery of the phase responses and asymmetry of the VOR was significantly better in the GVS group than in the non-GVS group until 2 weeks after UVD (phase, p = 0.001; symmetry, p < 0.001 at POD 14).Conclusion: Recoveries for UVD-induced locomotion and VOR deficits were accelerated by an early intervention with GVS, which implies that GVS has the potential to improve vestibular compensation in patients with acute unilateral vestibular failure.

Vestibular physical therapy improves turning not straight walking during the inertial sensor-instrumented Timed Up and Go test

Background: Deficits in vestibular function increase the risk for fall while turning. However, the clinical assessment of turning in patients with vestibular dysfunction is lacking, and evidence is limited that identifies how effective vestibular physical therapy (VPT) is for improving turning performance. Objective: To quantify and compare walking and turning performance during the instrumented timed up and go (TUG) test using inertial measurement units (IMUs) for clinical settings. We investigate novel instrumented TUG parameters for ability to distinguish patients with unilateral vestibular deafferentation (UVD) from control groups, and discriminate the differences in turning parameters of UVD patients following a VPT program. Methods: We recruited 38 patients following UVD surgery, 26 age-matched Veteran patient (VA) controls with reports of non-vestibular dizziness, and 12 age-matched healthy controls. Individuals were donned with body-worn IMUs and given verbal instructions to complete the TUG test as fast as safely possible. The IMU-instrumented and automated assessment of the TUG test provided component-based TUG parameters, including the novel walking:turning ratio. Among the UVD patients, 19 patients completed an additional instrumented TUG testing after VPT. Results: The walking:turning time ratio showed that turning performance in pre VPT UVD patients are significantly more impaired than VA patients and healthy controls (p < 0.001). Vestibular rehabilitation significantly improved turning performance and “normalized” their walking:turning time ratio compared to healthy controls (p < 0.001). However, the duration of the straight walking component in UVD patients before VPT was not significantly different as to that after VPT as well as healthy controls. Conclusions: Our data showed that the IMU-instrumented TUG test can distinguish patients with vestibular deafferentation and objectively quantify the change in their turning performance after surgery. The IMU-based instrumented TUG parameters have potential to quantify the efficacy of VPT and be adopted in the clinic.

Evidence a shared mechanism mediates ipsi- and contralesional compensatory saccades and gait after unilateral vestibular deafferentation

The study objective was to understand how the contralesional labyrinth contributes to gaze and gait stability after unilateral vestibular deafferentation (UVD). Head impulse testing (vHIT) was completed in 37 individuals [22 women (59%); age 52.13 ± 11.59 yr, mean ± SD] with UVD from vestibular schwannoma resection. Compensatory saccades (CS) and vestibulo-ocular reflex (VOR) gain were analyzed for both ipsilesional and contralesional impulses. Gait speed (10-m walk test) and endurance (2-min walk test) were collected for 35 individuals. CS were recruited during contralesional head rotation regardless of VOR gain on either the ipsilesional [ρ = 0.21 (−0.14, 0.57); Spearman rank (95% confidence interval)] or contralesional side [ρ = −0.04 (−0.42, 0.35)]. Additionally, the latency of these CS (151.19 ± 52.41 ms) was similar to that of CS generated during ipsilesional rotation (165.65 ± 21.62 ms; P = 0.159). CS recruited during ipsilesional vHIT were of a higher velocity ( P < 0.001) and greater frequency ( P < 0.001) compared with contralesional CS. VOR gain asymmetry was significantly correlated with gait speed [ρ = −0.37 (−0.73, −0.01)], yet individual VOR gain was not correlated [ipsilesional: ρ = 0.17 (−0.20, 0.55); contralesional: ρ = −0.18 (−0.52, 0.15)]. Our data reveal CS are recruited at similar latencies without correlation to VOR gain or direction of head rotation, and that the central integration of ipsilesional and contralesional vestibular afference correlates with gait. Together, our data suggest the brain considers vestibular afference from both sides when generating related behavioral output after UVD. NEW & NOTEWORTHY After unilateral vestibular deafferentation, compensatory saccades (CS) have similar latencies regardless of the direction of head rotation, and those CS generated during contralesional head rotation are unrelated to extent of vestibular loss. Additionally, the extent of asymmetry in residual vestibular function, not the extent of vestibular loss, correlates with gait speed. Our data suggest a common mechanism is responsible for the generation of CS and restoration of gait speed in vestibular compensation.