Modulation of central nystagmus by vision, proprioception, and efference copy signals: a systematic evaluation

Central vestibular dysfunction: don't forget vestibular rehabilitation

INTRODUCTION

Vestibular rehabilitation (VR) is now a subject of active studies and has been shown to be effective for multiple vestibular disorders, peripheral or central. VR is a physical therapy that helps train the central nervous system to compensate for vestibular dysfunction. There is moderate to strong evidence that VR is safe and effective for the management of peripheral vestibular dysfunction. Nonetheless, the studies on how VR works on central vestibular dysfunction remains scanty.

AREAS COVERED

This article addressed the rehabilitation strategies and possible mechanisms, including how central vestibular function might improve upon rehabilitation. In addition, it provides some examples concerning the effect of VR on central vestibular dysfunction.

EXPERT OPINION

VR works on the vestibular system through repetition of specific physical exercises that activate central neuroplastic mechanisms to achieve adaptive compensation of the impaired functions. VR has become a mainstay in the management of patients with dizziness and balance dysfunction. Individualized VR programs are a safe and effective treatment option for a large percentage of patients with central vestibular disease reporting imbalance and dizziness. Exploration of various treatment strategies and possible mechanisms will help develop the best and personalized VR treatment for patients with central vestibular dysfunction.

Vascular vertigo and dizziness: Diagnostic criteria

This paper presents diagnostic criteria for vascular vertigo and dizziness as formulated by the Committee for the Classification of Vestibular Disorders of the Bárány Society. The classification includes vertigo/dizziness due to stroke or transient ischemic attack as well as isolated labyrinthine infarction/hemorrhage, and vertebral artery compression syndrome. Vertigo and dizziness are among the most common symptoms of posterior circulation strokes. Vascular vertigo/dizziness may be acute and prolonged (≥24 hours) or transient (minutes to  < 24 hours). Vascular vertigo/dizziness should be considered in patients who present with acute vestibular symptoms and additional central neurological symptoms and signs, including central HINTS signs (normal head-impulse test, direction-changing gaze-evoked nystagmus, or pronounced skew deviation), particularly in the presence of vascular risk factors. Isolated labyrinthine infarction does not have a confirmatory test, but should be considered in individuals at increased risk of stroke and can be presumed in cases of acute unilateral vestibular loss if accompanied or followed within 30 days by an ischemic stroke in the anterior inferior cerebellar artery territory. For diagnosis of vertebral artery compression syndrome, typical symptoms and signs in combination with imaging or sonographic documentation of vascular compromise are required.

Vestibular Perception in Time and Space During Whole-Body Rotation in Humans

We investigated the vestibular perception of position, velocity, and time (duration) in humans with rotational stimuli including low velocities and small amplitudes. The participants were categorized into young, middle, and old age groups, and each consisted of 10 subjects. Position perception was assessed after yaw rotations ranged from 30 to 180° in both clockwise and counterclockwise directions. For each position, the rotation was delivered at two or more different velocities ranging from 15 to 120°/s. Position perception tended to underestimate the actual position and was similar during the slow and fast rotations. However, the trends of underestimation disappeared in the old age group. Velocity perception was evaluated by forcing the selection of the faster direction in each pair of rotations toward two positions (30° and 60°) with velocity differences from 0 to 20°/s. Velocity discrimination was similar between the rotation amplitudes or among the age groups. For duration perception, participants chose the rotation of longer duration for three test paradigms with different amplitudes (small vs. large) and durations (short vs. long) of rotation. The accuracy of discriminating duration was similar across the test paradigms or age groups, but the precision was lower in the older group and altered significantly according to the test paradigm. In conclusion, vestibular perception can be assessed using rotations of low velocities and small amplitudes. The perception of position and duration is affected by aging. The precision of duration perception can be influenced by the interactions between the amplitude and duration of motion.

Ocular Reflex Phase during Off-Vertical Axis Rotation in Humans is Modified by Head-Turn-On-Trunk Position

Constant velocity Off-Vertical Axis Rotation (OVAR) imposes a continuously varying orientation of the head and body relative to gravity, which generates a modulation of horizontal (conjugate and vergence), vertical, and torsional eye movements. We introduced the head-turn-on-trunk paradigm during OVAR to examine the extent to whether the modulation of these ocular reflexes is mediated by graviceptors in the head, i.e., otoliths, versus other body graviceptors. Ten human subjects were rotated in darkness about their longitudinal axis 20° off-vertical at a constant velocity of 45 and 180°/s, corresponding to 0.125 and 0.5 Hz. Binocular responses were obtained with the head and trunk aligned, and then with the head turned relative to the trunk 40° to the right or left of center. The modulation of vertical and torsional eye position was greater at 0.125 Hz while the modulation of horizontal and vergence slow phase velocity was greater at 0.5 Hz. The amplitude modulation was not significantly altered by head-on-trunk position, but the phases shifted towards alignment with the head. These results are consistent with the modulation of ocular reflexes during OVAR being primarily mediated by the otoliths in response to the sinusoidally varying linear acceleration along the interaural and naso-occipital head axis.