New advances regarding adaptation of the vestibulo-ocular reflex

Virtual Reality-Induced Modification of Vestibulo-Ocular Reflex Gain in Posturography Tests

Background: The aim of the study was to demonstrate the influence of virtual reality (VR) exposure on postural stability and determine the mechanism of this influence. Methods: Twenty-six male participants aged 21-23 years were included, who underwent postural stability assessment twice before and after a few minute of single VR exposure. The VR projection was a computer-generated simulation of the surrounding scenery. Postural stability was assessed using the Sensory Organization Test (SOT), using Computerized Dynamic Posturography (CDP). Results: The findings indicated that VR exposure affects the visual and vestibular systems. Significant differences (p < 0.05) in results before and after VR exposure were observed in tests on an unstable surface. It was confirmed that VR exposure has a positive influence on postural stability, attributed to an increase in the sensory weight of the vestibular system. Partial evidence suggested that the reduction in vestibulo-ocular reflex (VOR) reinforcement may result in an adaptive shift to the optokinetic reflex (OKR). Conclusions: By modifying the process of environmental perception through artificial sensory simulation, the influence of VR on postural stability has been demonstrated. The validity of this type of research is determined by the effectiveness of VR techniques in the field of vestibular rehabilitation.

Long-term dance training modifies eye-head coordination in response to passive head impulse

Long-term dance training is known to improve postural control, especially in challenging postural tasks. However, the effect of dance training on the vestibulo-ocular reflex (VOR) has yet to be properly assessed. This study directly investigated whether VOR parameters are influenced by long-term dance training by testing dancers and controls using the video head impulse test. VOR gains using two of the most common methods (area ratio and instantaneous gains), latency and amplitude of the first saccade, if applicable, were computed. Results revealed a larger VOR gain as measured by area gain and instantaneous gain at 40 ms specifically for left-head impulses, but not right-head impulses. No significant differences in saccade frequency, amplitude, or latency were observed between groups. These differences appear to stem from a modified eye-to-head relationship during high-velocity head impulses in dancers. More specifically, the dancers' eyes lead head movement during passively applied head impulses, which result in higher VOR gain.NEW & NOTEWORTHY This study demonstrates, for the first time, that long-term dance training results in a nonlinear relationship between eye and head velocity within the first milliseconds following passive head impulse. The data also suggest a larger VOR gain in dancers. This finding suggests that dance training may modify eye-head relationship in passive high-frequency head movements. This is of particular interest for vestibular rehabilitation.

Influence of Visual Feedback on Roll Tilt Perceptual Training

HYPOTHESIS

We hypothesized that the addition of visual feedback during roll tilt perceptual training would yield a significant reduction in vestibular perceptual thresholds relative to a control group.

BACKGROUND

We previously showed that roll tilt vestibular thresholds could be improved through a perceptual training protocol that used a simple auditory cue. Variability in training outcomes within the treatment group suggested that an auditory cue alone may be suboptimal for improving self-motion perception.

METHODS

In 10 healthy adults, roll tilt vestibular thresholds, quantifying the smallest motion that can be reliably perceived, were measured before ("pretraining") and after ("posttraining") a training protocol designed to improve roll tilt perception. The protocol included 1,300 trials of 0.5 Hz whole-body roll tilt over 5 days, with participants being given both an auditory cue ("correct' vs. "incorrect') and visual feedback (viewing a stationary visual scene) after indicating their perceived direction of tilt. A control group (N = 10) underwent only the "pretraining" and "posttraining" assessments.

RESULTS

The training group showed an average decrease in roll tilt vestibular thresholds of 1.7% ± 56%, with training outcomes varying widely. Three individuals showed an average increase in roll tilt thresholds of 69.7%, whereas the remaining seven adults showed an average decrease in thresholds of 32.3%.

CONCLUSION

These data show that visual feedback during roll tilt perceptual training leads to heterogenous outcomes, but in a subset of individuals, it may lead to improvements in perceptual precision. Additional work is needed to define the optimal training parameters, including feedback schema, before investigating potential clinical applications.

Type, dose, and outcomes of physical therapy interventions for unilateral peripheral vestibular hypofunction: protocol for a systematic review

BACKGROUND

Unilateral peripheral vestibular hypofunction can result in symptoms of dizziness, gaze and gait instability, and impaired navigation and spatial orientation. These impairments and activity limitations may negatively impact an individual's quality of life, ability to perform activities of daily living, drive, and work. There is strong evidence supporting vestibular physical therapy for reducing symptoms, improving gaze and postural stability, and improving function in individuals with vestibular hypofunction. However, there is great variability in clinical practice with regard to the type of interventions and only weak evidence to guide optimal exercise dosage. It is important to identify the most appropriate interventions and exercise dosage to optimize and accelerate recovery of function and to decrease distress. The objective of this systematic review is to determine which interventions and which doses are most effective in decreasing dizziness or vertigo, improving postural control, and improving quality of life in adults with unilateral peripheral vestibular hypofunction.

METHODS

The literature will be systematically searched using the following online databases: PubMed/MEDLINE, EMBASE, Web of Science (Science and Social Science Citation Index), Cumulative Index for Nursing and Allied Health Literature (CINAHL), and The Cochrane Library (Cochrane Database of Systematic Reviews, Cochrane Central Register of Controlled Trials [CENTRAL], Cochrane Methodology Register). The review will include randomized controlled trials (RCTs), including cluster RCTs, to assess the beneficial effects of the interventions. Assessment of methodological quality and risk of bias will be performed by two independent, blinded reviewers using the PEDro scale and Cochrane Risk of Bias version 2, respectively. The primary outcome measure will be change in self-perceived handicap related to dizziness from baseline to the end of the study, measured using the Dizziness Handicap Inventory. Other relevant outcome measures will include self-reported change in symptoms (to include severity, frequency, and duration) such as verbal or visual analog scales for dizziness. Tertiary outcome measures will include questionnaires related to disability and/or quality of life.

DISCUSSION

This systematic review will identify, evaluate, and integrate the evidence on the effectiveness of physical therapy interventions for unilateral peripheral vestibular hypofunction in an adult population. We anticipate our findings may inform individualized treatment and future research. Clinical recommendations generated from this systematic review may inform vestibular physical therapy treatment of individuals with unilateral peripheral vestibular hypofunction.

TRIAL REGISTRATION

In accordance with the guidelines, our systematic review protocol was registered with the International Prospective Register of Systematic Reviews (PROSPERO) on 06 August 2021 (registration number CRD42021266163 ). In the event of protocol amendments, the date of each amendment will be accompanied by a description of the change and the rationale.

The contribution of image minification to discomfort experienced in wearable optics

Wearable optics have a broad range of uses, for example, in refractive spectacles and augmented/virtual reality devices. Despite the long-standing and widespread use of wearable optics in vision care and technology, user discomfort remains an enduring mystery. Some of this discomfort is thought to derive from optical image minification and magnification. However, there is limited scientific data characterizing the full range of physical and perceptual symptoms caused by minification or magnification during daily life. In this study, we aimed to evaluate sensitivity to changes in retinal image size introduced by wearable optics. Forty participants wore 0%, 2%, and 4% radially symmetric optical minifying lenses binocularly (over both eyes) and monocularly (over just one eye). Physical and perceptual symptoms were measured during tasks that required head movement, visual search, and judgment of world motion. All lens pairs except the controls (0% binocular) were consistently associated with increased discomfort along some dimension. Greater minification tended to be associated with greater discomfort, and monocular minification was often-but not always-associated with greater symptoms than binocular minification. Furthermore, our results suggest that dizziness and visual motion were the most reported physical and perceptual symptoms during naturalistic tasks. This work establishes preliminary guidelines for tolerances to binocular and monocular image size distortion in wearable optics.

The vergence-mediated gain increase: Physiology and clinical relevance

BACKGROUND

During near-viewing, the vestibulo-ocular reflex (VOR) response/gain increases to compensate for the relatively larger translation of the eyes with respect to the target.

OBJECTIVE

To review vergence-mediated gain increase (VMGI) testing methods stimuli and responses (latency and amplitude), peripheral/central pathways and clinical relevance.

METHODS

The authors discuss publications listed in PUBMED since 1980 in the light of their own studies.

RESULTS

The VMGI can be measured during rotational, linear and combined head accelerations. It has short-latency, non-compensatory amplitude, and relies on irregularly discharging peripheral afferents and their pathways. It is driven by a combination of perception, visual-context and internal modelling.

CONCLUSIONS

Currently, there are technical barriers that hinder VMGI measurement in the clinic. However, the VMGI may have diagnostic value, especially with regards to measuring otolith function. The VMGI also may have potential value in rehabilitation by providing insight about a patient's lesion and how to best tailor a rehabilitation program for them, that potentially includes VOR adaptation training during near-viewing.

Unidirectional Vertical Vestibuloocular Reflex Adaptation in Humans Using 1D and 2D Scenes

HYPOTHESIS

The vertical vestibuloocular reflex (VOR) in response to pitch head impulses can be optimally trained to increase in one direction using a two-dimensional (2D) visual training target with minimal effect on the horizontal VOR.

BACKGROUND

We modified the incremental VOR adaptation (IVA) technique, shown to increase the horizontal VOR in patients with vestibular hypofunction, to drive vertical VOR adaptation in healthy control subjects.

METHODS

We measured the horizontal and vertical active (self-generated) and passive (imposed) head impulse VOR gains (eye velocity/head velocity) before and after 15 minutes of unidirectional downward IVA training. IVA training consisted of two sessions, one using a single-dot one-dimensional (1D) target, the other a grid-of-dots 2D target.

RESULTS

The downward head impulse VOR gain significantly increased because of training by 13.3%, whereas the upward VOR gain did not change. The addition of extraretinal (2D) feedback did not result in greater adaptation, i.e., 1D and 2D gain increases were 15.5% and 10.6%, respectively. The vertical VOR gain increase resulted in a 3.2% decrease in horizontal VOR gain.

CONCLUSION

This preliminary study is the first to show that physiologically relevant (high frequency) unidirectional increases in vertical VOR gain are possible with just 15 minutes of training. This study sets the basis for future clinical trials examining vertical IVA training in patients, which may provide the first practical rehabilitation treatment to functionally improve the vertical VOR.

Multiple field tests on landing day: Early mobility may improve postural recovery following spaceflight

Adaptation to microgravity causes astronauts to experience sensorimotor disturbances during return to Earth leading to functional difficulties. Recently, the Field Test (FT) study involving an incrementally demanding sensorimotor functional test battery has allowed for an unprecedented view into early decrements and recovery from multiple tests conducted on the landing day following 6-months International Space Station missions. Although the protocol was challenging and temporarily increased motion sickness symptoms, there were anecdotal reports that performing these tasks within the first few hours of landing accelerated their recovery. Therefore, results from computerized dynamic posturography (CDP) following return to Houston were used to compare recovery between crewmembers that participated in FT (n = 18) with those that did not (controls, n = 11). While there were significant decrements in postural performance for both groups, some FT participants tended to perform closer to their preflight baseline in the most challenging condition of the CDP sensitive to vestibular function—eyes closed, unstable support and head movements. However, the distribution of difference scores appeared bimodal with other FT participants in the lower range of performance. We attribute these observations to the manner in which the field tests were implemented—some benefitted by encouraging early movement to drive adaptation when performed in a constrained incremental fashion; however, movements above aversive thresholds may have impaired adaptation in others. Challenging the sensorimotor system with increasingly provocative movements performed as close to landing as possible, as long as within individual thresholds, could be a useful intervention to accelerate astronaut’s sensorimotor readaptation that deserves further study.

Improving self-motion perception and balance through roll tilt perceptual training

The present study aimed to determine if a vestibular perceptual learning intervention could improve roll tilt self-motion perception and balance performance. Two intervention groups (n = 10 each) performed 1,300 trials of roll tilt at either 0.5 Hz (2 s/motion) or 0.2 Hz (5 s/motion) distributed over 5 days; each intervention group was provided feedback (correct/incorrect) after each trial. Roll tilt perceptual thresholds, measured using 0.2-, 0.5-, and 1-Hz stimuli, as well as quiet stance postural sway, were measured on day 1 and day 6 of the study. The control group (n = 10) who performed no perceptual training, showed stable 0.2-Hz (+1.48%, P > 0.99), 0.5-Hz (-4.0%, P > 0.99), and 1-Hz (-17.48%, P = 0.20) roll tilt thresholds. The 0.2-Hz training group demonstrated significant improvements in both 0.2-Hz (-23.77%, P = 0.003) and 0.5-Hz (-22.2%, P = 0.03) thresholds. The 0.5-Hz training group showed a significant improvement in 0.2-Hz thresholds (-19.13%, P = 0.029), but not 0.5-Hz thresholds (-17.68%, P = 0.052). Neither training group improved significantly at the untrained 1-Hz frequency (P > 0.05). In addition to improvements in perceptual precision, the 0.5-Hz training group showed a decrease in sway when measured during "eyes open, on foam" (dz = 0.57, P = 0.032) and "eyes closed, on foam" (dz = 2.05, P < 0.001) quiet stance balance tasks. These initial data suggest that roll tilt perception can be improved with less than 5 h of training and that vestibular perceptual training may contribute to a reduction in subclinical postural instability.NEW & NOTEWORTHY Roll tilt vestibular perceptual thresholds, an assay of vestibular noise, were recently found to correlate with postural sway. We therefore hypothesized that roll tilt perceptual training would yield improvements in both perceptual precision and balance. Our data show that roll tilt perceptual thresholds and quiet stance postural sway can be significantly improved after less than 5 h of roll tilt perceptual training, supporting the hypothesis that vestibular noise contributes to increased postural sway.

Vestibular Autorotation Test: The Differences in Peripheral and Central Acute Vestibular Syndrome

Objective

To evaluate the difference between the vestibular autorotation test (VAT) in the peripheral and central acute vestibular syndrome (AVS). Methodology. Patients with AVS diagnosed by clinical manifestation admitted to the third affiliated hospital of Qiqihar Medical College from January 2019 to January 2021 were enrolled and divided into peripheral AVS (peripheral group) and central AVS (central group) according to the results of the MRI examination.

Results

A total of 332 patients with AVS were recruited, including 282 patients in the peripheral group and 50 patients in the central group. The horizontal gain of both groups showed a downward trend at 2–6 Hz. There was no significant change in the horizontal phase between the two groups at 2–6 Hz. The horizontal gain of the two groups was stable at 2–6 Hz with no significant changes in the horizontal phase between 2–6 Hz in both groups. The central group showed a significantly lower proportion of gain increase coupled with loss and a strikingly higher proportion of gain increase without a loss than in the peripheral group (all P < 0.001).

Conclusion

The increased horizontal and vertical gain of VAT in patients with AVS is of high value in the diagnosis of ACS. Significant differences in the results of VAT in patients with central and peripheral AVS could provide a reference for diagnosis.

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.

Cervicovestibular Rehabilitation in Adults with Mild Traumatic Brain Injury: A Randomised Clinical Trial

The objective of this study was to compare the effects of a cervicovestibular rehabilitation program combined with symptom-limited aerobic exercise (SLAE) program to a SLAE program alone in adults with persistent symptoms following mild traumatic brain injury (mTBI) on severity of symptoms and other indicators of clinical recovery. In this single-blind, parallel-group randomised clinical trial, 60 adults with persistent symptoms following mTBI were randomly assigned to: 1) a 6-week SLAE program or 2) a 6-week cervicovestibular rehabilitation program combined with SLAE program. All participants took part in 4 evaluation sessions (baseline, week 6, 12 and 26) performed by a blinded evaluator. The primary outcome was the Post-Concussion Symptoms Scale (PCSS). The secondary outcomes were Numerical Pain Rating Scale (NPRS), Neck Disability Index (NDI), Headache Disability Inventory (HDI), Dizziness Handicap Inventory (DHI), time to return to function, and physical cervical and vestibular measures. Nonparametric analysis for longitudinal data was used to evaluate the effect of interventions on outcomes. For PCSS, NPRS, NDI, HDI, DHI and return to function, there were no group-by-time interactions at any time-points follow-up (p>0.05); clinically significant time effects were however observed (p0.05). There were group-by-time interactions at weeks 6 and 12 for vestibulo-ocular reflex (p0.003) and the cranio-vertebral mobility (p0.001) measures in favor of the cervicovestibular rehabilitation group. The study indicates that a cervicovestibular rehabilitation program combined with SLAE was not superior to a SLAE program alone in term of symptoms and functional level improvement but resulted in improved physical cervical and vestibular function. Keywords: mild traumatic brain injury, rehabilitation, neck pain, dizziness, headache.

Plasticity and repair of the vestibulo-ocular reflex

It is self-evident, once one thinks about it, that the vestibulo-ocular reflex must have caretaker systems that keep it operating correctly over the span of a lifetime. When a movement is not correct (e.g., in position, speed, direction) it is said to be dysmetric. For the vestibulo-ocular reflex (VOR), if eye velocity is not equal and opposite to head velocity within reasonable limits, one has vestibulo-ocular dysmetria. Consequently, the function of the caretaker systems is to eliminate vestibulo-ocular dysmetria. These systems are first required to act just after birth when the gain of the reflex is usually not normal, and must be initially calibrated; and then maintained as the animal grows older; and then in adult life an important function of the caretaker systems is the compensation required after damage. The mechanisms of this caretaker system and ensuring motor learning is the focus of this chapter.

Comparison of Incremental Vestibulo-ocular Reflex Adaptation Training Versus x1 Training in Patients With Chronic Peripheral Vestibular Hypofunction: A Two-Year Randomized Controlled Trial

BACKGROUND AND PURPOSE

A crossover, double-blinded randomized controlled trial to investigate once-daily incremental vestibulo-ocular reflex (VOR) adaptation (IVA) training over 2 years in people with stable and chronic peripheral vestibular hypofunction.

METHODS

Twenty-one patients with peripheral vestibular hypofunction were randomly assigned to intervention-then-control (n = 12) or control-then-intervention (n = 9) groups. The task consisted of either x1 (control) or IVA training, once daily every day for 15 minutes over 6-months, followed by a 6-month washout, then repeated for arm 2 of the crossover. Primary outcome: vestibulo-ocular reflex gain. Secondary outcomes: compensatory saccades, dynamic visual acuity, static balance, gait, and subjective symptoms. Multiple imputation was used for missing data. Between-group differences were analyzed using a linear mixed model with repeated measures.

RESULTS

On average patients trained once daily 4 days per week. IVA training resulted in significantly larger VOR gain increase (active: 20.6% ± 12.08%, P = 0.006; passive: 30.6% ± 25.45%, P = 0.016) compared with x1 training (active: -2.4% ± 12.88%, P = 0.99; passive: -0.6% ± 15.31%, P = 0.68) (P < 0.001). The increased IVA gain did not significantly reduce with approximately 27% persisting over the washout period. x1 training resulted in greater reduction of compensatory saccade latency (P = 0.04) and increase in amplitude (P = 0.02) compared with IVA training. There was no difference between groups in gait and balance measures; however, only the IVA group had improved total Dizziness Handicap Inventory (P = 0.006).

DISCUSSION AND CONCLUSIONS

Our results suggest IVA improves VOR gain and reduces perception of disability more than conventional x1 training. We suggest at least 4 weeks of once-daily 4 days-per-week IVA training should be part of a comprehensive vestibular rehabilitation program.Video Abstract available for more insights from the authors (see the Video, Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A356).

Absence of a vergence-mediated vestibulo-ocular reflex gain increase does not preclude adaptation

BACKGROUND

The gain (eye-velocity/head-velocity) of the angular vestibuloocular reflex (aVOR) during head impulses can be increased while viewing near-targets and when exposed to unilateral, incremental retinal image velocity error signals. It is not clear however, whether the tonic or phasic vestibular pathways mediate these gain increases.

OBJECTIVE

Determine whether a shared pathway is responsible for gain enhancement between vergence and adaptation of aVOR gain in patients with unilateral vestibular hypofunction (UVH).

MATERIAL AND METHODS

20 patients with UVH were examined for change in aVOR gain during a vergence task and after 15-minutes of ipsilesional incremental VOR adaptation (uIVA) using StableEyes (a device that controls a laser target as a function of head velocity) during horizontal passive head impulses. A 5 % aVOR gain increase was defined as the threshold for significant change.

RESULTS

11/20 patients had >5% vergence-mediated gain increase during ipsi-lesional impulses. For uIVA, 10/20 patients had >5% ipsi-lesional gain increase. There was no correlation between the vergence-mediated gain increase and gain increase after uIVA training.

CONCLUSION

Vergence-enhanced and uIVA training gain increases are mediated by separate mechanisms and/or vestibular pathways (tonic/phasic). The ability to increase the aVOR gain during vergence is not prognostic for successful adaptation training.

Repeated video head impulse testing in patients is a stable measure of the passive vestibulo-ocular reflex

Objectives

The video head impulse test (vHIT) is used as a measure of compensation yet it's stability in patients with vestibular pathology is unknown.

Methods

144 patients (n = 72 female, mean 54.46 ± 15.8 years) were grouped into one of three primary diagnoses (Peripheral, Central, or Mixed). Subjects were further categorized based on sex (male versus female), ear (left versus right; ipsilesional versus contralesional), age (six groups ranging from 19 to 84 years), and duration between visits (five groups, mean 191.46 ± SE 29.42 days, median 55.5 days). The gain of the VOR during passive head rotation was measured for each semicircular canal (horizontal, anterior, posterior).

Results

There was no difference in the VOR gain within any semicircular canal between the two visits (horizontal: p = 0.179; anterior: p = 0.628; posterior: p = 0.613). However, the VOR gain from the horizontal canals was higher than the vertical canals for each visit (p < 0.001). Patients diagnosed with peripheral vestibular pathology had significantly lower (p ≤ 0.001) horizontal semicircular canal gains at each visit. There was no difference in VOR gain between sex (p = 0.215) or age groupings (p = 0.331). Test-retest reliability of vHIT in patient subjects is good (ICC = 0.801) and the VOR gain values across two separate visits were significant and positively correlated (r = 0.67) regardless of sex, ear, age, or duration between visits.

Conclusion

The vHIT is a stable measure of VOR gain over two different times across a variety of vestibular patients with no influence of age or sex.

Aging, Vestibular Function, and Balance: Proceedings of a National Institute on Aging/National Institute on Deafness and Other Communication Disorders Workshop

Balance impairment and falls are among the most prevalent and morbid conditions affecting older adults. A critical contributor to balance and gait function is the vestibular system; however, there remain substantial knowledge gaps regarding age-related vestibular loss and its contribution to balance impairment and falls in older adults. Given these knowledge gaps, the National Institute on Aging and the National Institute on Deafness and Other Communication Disorders convened a multidisciplinary workshop in April 2019 that brought together experts from a wide array of disciplines, such as vestibular physiology, neuroscience, movement science, rehabilitation, and geriatrics. The goal of the workshop was to identify key knowledge gaps on vestibular function and balance control in older adults and develop a research agenda to make substantial advancements in the field. This article provides a report of the proceedings of this workshop. Three key questions emerged from the workshop, specifically: (i) How does aging impact vestibular function?; (ii) How do we know what is the contribution of age-related vestibular impairment to an older adult's balance problem?; and more broadly, (iii) Can we develop a nosology of balance impairments in older adults that can guide clinical practice? For each of these key questions, the current knowledge is reviewed, and the critical knowledge gaps and research strategies to address them are discussed. This document outlines an ambitious 5- to 10-year research agenda for increasing knowledge related to vestibular impairment and balance control in older adults, with the ultimate goal of linking this knowledge to more effective treatment.

Vestibular rehabilitation in Europe: a survey of clinical and research practice

Vestibular rehabilitation (VR) is practiced across Europe but little in this area has been quantified. The aim of this study was to investigate current VR assessment, treatment, education, and research practices. This was an online, cross-sectional survey with 39 VR specific questions and four sections: demographics, current practice, education, and research. The survey was disseminated through the Dizzynet network to individual therapists through country-specific VR special interest groups. Results were analysed descriptively. A thematic approach was taken to analyse open questions. A total of 471 individuals (median age 41, range 23 - 68 years, 73.4% women), predominately physiotherapists (89.4%) from 20 European countries responded to the survey. They had worked for a median of 4 years (range < 1 - 35) in VR. The majority (58.7%) worked in hospital in-patient or out-patient settings and 21.4% in dedicated VR services. Most respondents specialized in neurology, care of the elderly (geriatrics), or otorhinolaryngology. VR was reported as hard/very hard to access by 48%, with the main barriers to access identified as lack of knowledge of health care professionals (particularly family physicians), lack of trained therapists, and lack of local services. Most respondents reported to know and treat benign paroxysmal positional vertigo (BPPV 87.5%), unilateral vestibular hypofunction (75.6%), and cervicogenic dizziness (63%). The use of vestibular assessment equipment varied widely. Over 70% used high-density foam and objective gait speed testing. Over 50% used dynamic visual acuity equipment. Infrared systems, Frenzel lenses, and dynamic posturography were not commonly employed (< 20%). The most frequently used physical outcome measures were the Clinical Test of the Sensory Interaction of Balance, Functional Gait Assessment/Dynamic Gait Index, and Romberg/Tandem Romberg. The Dizziness Handicap Inventory, Visual Analogue Scale, Falls Efficacy Scale, and the Vertigo Symptom Scale were the most commonly used patient reported outcome measures. Adaptation, balance, and habituation exercises were most frequently used (> 80%), with virtual reality used by 15.6%. Over 70% reported knowledge/use of Semont, Epley and Barbeque-Roll manoeuvres for the treatment of BPPV. Most education regarding VR was obtained at post-registration level (89.5%) with only 19% reporting pre-registration education. There was strong (78%) agreement that therapists should have professionally accredited postgraduate certification in VR, with blended learning the most popular mode. Three major research questions were identified for priority: management of specific conditions, effectiveness of VR, and mechanisms/factors influencing vestibular compensation and VR. In summary, the survey quantified current clinical practice in VR across Europe. Knowledge and treatment of common vestibular diseases was high, but use of published subjective and objective outcome measures as well as vestibular assessment varied widely. The results stress the need of improving both training of therapists and standards of care. A European approach, taking advantage of best practices in some countries, seems a reasonable approach.

Improved feasibility of astronaut short-radius artificial gravity through a 50-day incremental, personalized, vestibular acclimation protocol

The "Coriolis" cross-coupled (CC) illusion has historically limited the tolerability of utilizing fast-spin rate, short-radius centrifugation for in-flight artificial gravity. Previous research confirms that humans acclimate to the CC illusion over 10 daily sessions, though the efficacy of additional training is unknown. We investigated human acclimation to the CC illusion over up to 50 daily sessions of personalized, incremental training. During each 25-min session, subjects spun in yaw and performed roll head tilts approximately every 30 s, reporting the presence or absence of the illusion while rating motion sickness every 5 min. Illusion intensity was modulated by altering spin rate based upon subject response, such that the administered stimulus remained near each individual's instantaneous illusion threshold. Every subject (n = 11) continued to acclimate linearly to the CC illusion during the investigation. Subjects acclimated at an average rate of 1.17 RPM per session (95% CI: 0.63-1.71 RPM per session), with the average tolerable spin rate increasing from 1.4 to 26.2 RPM, corresponding to a reduction in required centrifuge radius from 456.6 to 1.3 m (to produce loading of 1 g at the feet). Subjects reported no more than slight motion sickness throughout their training (mean: 0.92/20, 95% CI: 0.35-1.49/20). We applied survival analysis to determine the probability of individuals reaching various spin rates over a number of training days, providing a tolerability trade parameter for centrifuge design. Results indicate that acclimation to a given, operationally relevant spin rate may be feasible for all subjects if given a sufficient training duration.