Cognitive and balance functions of astronauts after spaceflight are comparable to those of individuals with bilateral vestibulopathy.

Introduction: This study compares the balance control and cognitive responses of subjects with bilateral vestibulopathy (BVP) to those of astronauts immediately after they return from long-duration spaceflight on board the International Space Station. Methods: Twenty-eight astronauts and thirty subjects with BVP performed five tests using the same procedures: sit-to-stand, walk-and-turn, tandem walk, duration judgment, and reaction time. Results: Compared to the astronauts' preflight responses, the BVP subjects' responses were impaired in all five tests. However, the BVP subjects' performance during the walk-and-turn and the tandem walk tests were comparable to the astronauts' performance on the day they returned from space. Moreover, the BVP subjects' time perception and reaction time were comparable to those of the astronauts during spaceflight. The BVP subjects performed the sit-to-stand test at a level that fell between the astronauts' performance on the day of landing and 1 day later. Discussion: These results indicate that the alterations in dynamic balance control, time perception, and reaction time that astronauts experience after spaceflight are likely driven by central vestibular adaptations. Vestibular and somatosensory training in orbit and vestibular rehabilitation after spaceflight could be effective countermeasures for mitigating these post-flight performance decrements.

Diagnosis of dizziness in the emergency department: A 1-year prospective single-center study.

BACKGROUND: The management of dizziness and vertigo can be challenging in the emergency department (ED). It is important to rapidly diagnose vertebrobasilar stroke (VBS), as therapeutic options such as thrombolysis and anticoagulation require prompt decisions. OBJECTIVE: This study aims to assess the rate of misdiagnosis in patients with dizziness caused by VBS in the ED. METHODS AND RESULTS: The cohort was comprised of 66 patients with a mean age 56 years; 48% were women and 52% men. Among dizzy patients, 14% had VBS. We used Cohen's kappa test to quantify the agreement between two raters -namely, emergency physicians and neurologists -regarding the causes of dizziness in the ED. The Kappa value was 0.27 regarding the final diagnosis of central vertigo disorders and VBS, thus showing the low agreement. We used the χi2 test to show the association between the presence of two or more cardiovascular risk factors and admission to the stroke unit (p = 0.015). CONCLUSION: There is a substantial rate of misdiagnosis in patients with dizziness caused by VBS in the ED. To reduce the number of missing diagnoses of VBS in the future, there is a need to train emergency physicians in neurovestibular examinations, including the HINTS examination for acute vestibular syndrome (AVS) and the Dix-Hallpike (DH) maneuver for episodic vestibular syndrome. Using video head impulse test could help reduce the rate of misdiagnosis of VBS in the ED.

Navigation strategies in patients with vestibular loss tested in a virtual reality T-maze.

During navigation, humans mainly rely on egocentric and allocentric spatial strategies, two different frames of reference working together to build a coherent representation of the environment. Spatial memory deficits during navigation have been repeatedly reported in patients with vestibular disorders. However, little is known about how vestibular disorders can change the use of spatial navigation strategies. Here, we used a new reverse T-maze paradigm in virtual reality to explore whether vestibular loss specifically modifies the use of egocentric or allocentric spatial strategies in patients with unilateral (n = 23) and bilateral (n = 23) vestibular loss compared to healthy volunteers (n = 23) matched for age, sex and education level. Results showed that the odds of selecting and using a specific strategy in the T-maze were significantly reduced in both unilateral and bilateral vestibular loss. An exploratory analysis suggests that only right vestibular loss decreased the odds of adopting a spatial strategy, indicating an asymmetry of vestibular functions. When considering patients who used strategies to navigate, we observed that a bilateral vestibular loss reduced the odds to use an allocentric strategy, whereas a unilateral vestibular loss decreased the odds to use an egocentric strategy. Age was significantly associated with an overall lower chance to adopt a navigation strategy and, more specifically, with a decrease in the odds of using an allocentric strategy. We did not observe any sex difference in the ability to select and use a specific navigation strategy. Findings are discussed in light of previous studies on visuo-spatial abilities and studies of vestibulo-hippocampal interactions in peripheral vestibular disorders. We discuss the potential impact of the history of the disease (chronic stage in patients with a bilateral vestibulopathy vs. subacute stage in patients with a unilateral vestibular loss), of hearing impairment and non-specific attentional deficits in patients with vestibular disorders.

Interoception and embodiment in patients with bilateral vestibulopathy.

There are tight functional and anatomical links between the vestibular and interoceptive systems, and both systems have shown to fundamentally underlie emotional processes and our sense of a bodily self. Yet, nothing is known about how long-term bilateral vestibulopathy (BVP) influences interoception and its relation to embodiment and the sense of self. We thus compared cardiac interoceptive accuracy, confidence in the performance, and general body awareness in 25 BVP patients and healthy controls using a heartbeat tracking task, self-reports about interoceptive awareness, as well as measures of self-localization and of self-body closeness. Results showed no difference between patients and controls regarding interoceptive accuracy, confidence and body awareness, suggesting that long-term BVP does not influence cardiac interoception. Patients and controls did not differ either regarding self-location and self-body closeness. However, in our overall sample of patients and controls, we found that interoceptive accuracy increased with perceived self-body closeness, suggesting that anchoring the self to the body is generally linked with better cardiac interoception. This result is in line with previous suggestions of an important contribution of interoception to the sense of embodiment.

Electrophysiological and inner ear MRI findings in patients with bilateral vestibulopathy.

PURPOSE: Bilateral vestibulopathy (BV) is an uncommon disorder and the etiology remained idiopathic in most cases. Delayed 3D-FLAIR sequences have provided new insights into various inner ear diseases, allowing the evaluation of the endolymphatic space and the permeability of the blood-labyrinthine barrier (BLB). The aim of this study was to assess both the morphology of the endolymphatic space and the permeability of the BLB in patients with BV as evaluated by delayed 3D-FLAIR sequences. METHODS: In this retrospective study, we performed 3D-FLAIR sequences 4 h after administering contrast media to 42 patients with BV. Two radiologists independently evaluated the morphology of the endolymphatic space (either vestibular atelectasis or endolymphatic hydrops) and the permeability of the BLB. RESULTS: Morphologic anomalies of the endolymphatic space and vestibular blood-labyrinthine barrier impairment were observed in 59.6% of patients with BV. Bilateral vestibular atelectasis (VA) was found in 21 patients (50%), involving only the utricle and all three ampullas while the saccule was always observed with no sign of collapse: idiopathic BV (n = 19), aminoglycoside administration (n = 1) and few days following abdominal surgery (n = 1). One patient had bilateral vestibular malformation. BLB impairment was observed in five patients (11.9%): paraneoplastic (n = 1), lymphoma (n = 1), autoimmune (n = 1), and vestibular "neuritis" (n = 2). Seventeen patients (40.4%) had normal MRI with no endolymphatic space anomaly or BLB impairment. CONCLUSION: Patients with BV presented with morphologic anomalies of the endolymphatic space or BLB impairment in 59.6% of patients.

Influence of Visual and Vestibular Hypersensitivity on Derealization and Depersonalization in Chronic Dizziness.

Objective: The aim of this study was to investigate the relation between visual and vestibular hypersensitivity, and Depersonalization/Derealization symptoms in patients with chronic dizziness. Materials and Methods: 319 adult patients with chronic dizziness for more than 3 months (214 females and 105 males, mean age: 58 years, range: 13-90) were included in this prospective cross-sectional study. Patients underwent a complete audio-vestibular workup and 3 auto questionnaires: Hospital Anxiety and Depression (HAD), Depersonalization/Derealization Inventory (DDI), and an in-house questionnaire (Dizziness in Daily Activity, DDA) assessing 9 activities with a score ranging from 0 (no difficulty) to 10 (maximal discomfort) and 11 (avoidance) to detect patients with visual and vestibular hypersensitivity (VVH, a score > 41 corresponding to mean + 1 standard deviation). Results: DDI scores were higher in case of VVH (6.9 ± 6.79, n = 55 vs. 4.2 ± 4.81, n = 256 without VVH, p < 0.001, unpaired t-test), migraine (6.1 ± 6.40, n = 110 vs. 4.0 ± 4.42, n = 208no migraine, p < 0.001, unpaired t-test), and motion sickness (6.8 ± 5.93, n = 41 vs. 4.4 ± 5.11, n = 277 no motion sickness, p < 0.01, unpaired t-test). Women scored DDI higher than men (5.1 ± 5.42, n = 213 vs. 3.9 ± 4.91, n = 105, respectively, p < 0.05, unpaired t-test). DDI scores were also related to depression and anxiety. DDI score was also higher during spells than during the basal state. Conclusion: During chronic dizziness, Depersonalization/Derealization symptoms seem to be related to anxiety and depression. Moreover, they were prominent in women, in those with visual and vestibular hypersensitivity, migraine, and motion sickness.

How Eye Movements Stabilize Posture in Patients With Bilateral Vestibular Hypofunction.

Chronic patients with bilateral vestibular hypofunction (BVH) complain of oscillopsia and great instability particularly when vision is excluded and on irregular surfaces. The real nature of the visual input substituting to the missing vestibular afferents and improving posture control remains however under debate. Is retinal slip involved? Do eye movements play a substantial role? The present study tends to answer this question in BVH patients by investigating their posture stability during quiet standing in four different visual conditions: total darkness, fixation of a stable space-fixed target, and pursuit of a visual target under goggles delivering visual input rate at flicker frequency inducing either slow eye movements (4.5 Hz) or saccades (1.2 Hz). Twenty one chronic BVH patients attested by both the caloric and head impulse test were examined by means of static posturography, and compared to a control group made of 21 sex-and age-matched healthy participants. The posturography data were analyzed using non-linear computation of the center of foot pressure (CoP) by means of the wavelet transform (Power Spectral Density in the visual frequency part, Postural Instability Index) and the fractional Brownian-motion analysis (stabilogram-diffusion analysis, Hausdorff fractal dimension). Results showed that posture stability was significantly deteriorated in darkness in the BVH patients compared to the healthy controls. Strong improvement of BVH patients' posture stability was observed during fixation of a visual target, pursuit with slow eye movements, and saccades, whereas the postural performance of the control group was less affected by the different visual conditions. It is concluded that BVH patients improve their posture stability by (1) using extraocular signals from eye movements (efference copy, muscle re-afferences) much more than the healthy participants, and (2) shifting more systematically than the controls to a more automatic mode of posture control when they are in dual-task conditions associating the postural task and a concomitant visuo- motor task.

Defining Clinical-Posturographic and Intra-Posturographic Discordances: What Do These Two Concepts Mean?

The European Society for Clinical Evaluation of Balance Disorders - ESCEBD - Executive Committee meets yearly to identify and address clinical equilibrium problems that are not yet well understood. This particular discussion addressed "discordances" (defined as "lack of agreement") in clinical assessment. Sometimes there is disagreement between a clinical assessment and measured abnormality (ies); sometimes the results within the assessment do not agree. This is sometimes thought of as "malingering" or an attempt to exaggerate what is wrong, but this is not always the case. The Committee discussed the clinical significance of unexpected findings in a patient's assessment. For example intraposturographic discordances sometimes exhibit findings (eg performance on more difficult trials may sometimes be better than on simpler trials). This can be suggestive of malingering, but in some situations can be a legitimate finding. The extreme malingerer and the genuine patient are at opposite ends of a spectrum but there are many variations along this spectrum and clinicians need to be cautious, as a posturography assessment may or may not be diagnostically helpful. Sometimes there is poor correlation between symptom severity and test results. Interpretation of posturography performance can at times be difficult and a patient's results must be correlated with clinical findings without stereotyping the patient. It is only in this situation that assessment in a diagnostic setting can be carried out in an accurate and unbiased manner.

Visual Input Is the Main Trigger and Parametric Determinant for Catch-Up Saccades During Video Head Impulse Test in Bilateral Vestibular Loss.

Patients with vestibular deficit use slow eye movements or catch-up saccades (CUS) to compensate for impaired vestibulo-ocular reflex (VOR). The purpose of CUS is to bring the eyes back to the visual target. Covert CUS occur during high-velocity head rotation and overt CUS are generated after head rotation has stopped. Dynamic visual acuity is improved with an increased rate and gain of CUS. Nevertheless, the trigger and the parametric determinants of CUS are still under debate. To clarify the underlying mechanism, especially the visual contribution, we analyzed the number, amplitude and latencies of the CUS in relation with the extent of VOR deficiency. The head and eye movements were recorded in 17 patients with bilateral vestibular loss (BVL) and in 33 subjects with normal VOR gain using the Video Head Impulse Test (vHIT) in two conditions: with visible target and in darkness with an imaginary target. Our study shows that in darkness without visible target the number of CUS is significantly reduced and the relationship between the amplitude of CUS and gaze position error is lost. Results showed that there is a correlation between the number of CUS and the drop in VOR gain. CUS occurring during the head movement and when the head remained still were not always sufficiently accurate. Up to four consecutive CUS could be required to bring eyes back to the visible target. A positive correlation was found between the amplitude of overt saccades with visible target and the gaze position error, namely the remaining eye movement to reach the target. These results suggest that the visual inputs are the main trigger and parametric determinant of the CUS or at least the presence of a visual target is necessary in most cases for a CUS to occur.

Subjective Visual Vertical in Idiopathic Bilateral Vestibular Hypofunction: Enhanced Role of Vision, Neck, and Body Proprioception.

INTRODUCTION: We aimed to study the participation of proprioceptive and visual inputs in subjective visual vertical (SVV) in bilateral vestibular hypofunction and in normal subjects. STUDY DESIGN: Prospective case-control study. SETTING: Tertiary referral center. MATERIALS AND METHODS: SVV (six replicates) was measured on a tiltable rehabilitation seat in 26 adult patients with idiopathic bilateral vestibular hypofunction (IBVH) and 33 adult controls. Subjects were asked to place vertically a 45 degrees-tilted red line on a screen (three replicates to left and three to right alternatively) using a remote control in total darkness and in seven body positions: vertical, head, and body left- and right-tilts to 12 and 24 degrees, and then body left- and right-tilt to 24 degrees with the head upright. RESULTS: In the vertical position, SVV did not differ between IBVH and controls. Patients with IBVH were more sensitive to body tilt than controls (SVV: -8.1 ±â€Š4.66 degrees for IBVH versus -0.2 ±â€Š3.23 for control at 24 degrees body and head left-tilt, p < 0.0001, unpaired t test). The visual attraction effect defined by a deviation of the SVV to the side of the initial line presentation appeared to be higher in the IBVH than in controls suggesting higher visual dependence in IBVH. Placing the head upright while the body was still tilted significantly reduced this difference. Similar results were observed for the right-tilts. CONCLUSION: Not only otolithic function but also visual plus body and neck proprioceptive entries participate in SVV. The influence of vision and proprioception appears to be enhanced in case of IBVH.

Anchoring the Self to the Body in Bilateral Vestibular Failure.

Recent findings suggest that vestibular information plays a significant role in anchoring the self to the body. Out-of-body experiences of neurological origin are frequently associated with vestibular sensations, and galvanic vestibular stimulation in healthy participants anchors the self to the body. Here, we provide the first objective measures of anchoring the self to the body in chronic bilateral vestibular failure (BVF). We compared 23 patients with idiopathic BVF to 23 healthy participants in a series of experiments addressing several aspects of visuo-spatial perspective taking and embodiment. In Experiment 1, participants were involved in a virtual "dot-counting task" from their own perspective or the perspective of a distant avatar, to measure implicit and explicit perspective taking, respectively. In both groups, response times increased similarly when the avatar's and participant's viewpoint differed, for both implicit and explicit perspective taking. In Experiment 2, participants named ambiguous letters (such as "b" or "q") traced on their forehead that could be perceived from an internal or external perspective. The frequency of perceiving ambiguous letters from an internal perspective was similar in both groups. In Experiment 3, participants completed a questionnaire measuring the experienced self/body and self/environment "closeness". Both groups reported a similar embodied experience. Altogether, our data show that idiopathic BVF does not change implicit and explicit perspective taking nor subjective anchoring of the self to the body. Our negative findings offer insight into the multisensory mechanisms of embodiment. Only acute peripheral vestibular disorders and neurological disorders in vestibular brain areas (characterized by strong multisensory conflicts) may evoke disembodied experiences.

Discussion about Visual Dependence in Balance Control: European Society for Clinical Evaluation of Balance Disorders.

The executive committee of the European Society for the clinical evaluation of balance disorders meets annually to address equilibrium problems that are not well understood. This is a review paper on discussions in the latest meeting we held. MATERIALS AND METHODS: Seeing patients with vestibular disorders who end up depending on visual information as part of their compensation process is a common clinical occurrence. However, this "visual dependence" can generate symptoms, which include nausea, sensations of imbalance, and anxiety. It is unclear how this develops, as symptoms can be widely variable from patient to patient. There are several triggering factors to this symptom set, and quantifying it in a given patient is extremely difficult Results: The committee agreed that the presence of this symptom set can be suggestive of vestibular pathology, but the pathology does not have to be present. As a result, there is no correlation between symptom severity and test results. CONCLUSION: Visual dependence can often be present in a patient, although little, if any, measurable pathology is present. It is important to emphasize that although we cannot accurately measure this with either standardized testing or pertinent questionnaires, "hypersensitive" patients have a genuine disease and their symptoms are not of psychiatric origin.

Maturation of Subjective Visual Vertical in Children.

OBJECTIVE: The attraction of the subjective visual vertical (SVV) to the side of initial rod presentation has already been described in adults. The aim of this study was to evaluate this phenomenon in children and to analyze the effect of sex and maturation in this population. STUDY DESIGN: Retrospective cross-sectional study. SETTING: Tertiary referral center. PATIENTS: Six hundred and one individuals aged between 4 and 19 years. INTERVENTION: All subjects underwent a complete balance workup. SVV was measured by presenting a laser line 12 times in total darkness with a 45 degrees deviation from the vertical alternatively on the left and the right. The patient was seated and asked to replace the bar vertically with a remote control. RESULTS: On average, SVV was tilted to the side of the rod presentation at each iteration. The cumulative tilt to the side of presentation after 12 measures was higher in the 4 to 7 years age group and decreased progressively with age (25 ±â€Š2.2 degrees in 4-7 years, n = 109 versus 5 ±â€Š1.4 in 15-19 years, n = 204, p < 0.001, analysis of variance [ANOVA]). The cumulative tilt was higher in girls than in boys in the 15 to 19 years group (8 ±â€Š2.5 degrees, n = 104 versus 2 ±â€Š1.2, n = 100, respectively, p < 0.001, ANOVA). This phenomenon appeared independent from the type of vestibular disorder. CONCLUSION: Young children are highly attracted to the side of rod presentation during SVV measurements. This phenomenon gradually disappears with maturation, faster in boys than in girls.

Subjective Visual Vertical Tilt Attraction to the Side of Rod Presentation: Effects of Age, Sex, and Vestibular Disorders.

OBJECTIVE: The aim of this study was to evaluate the effect of initial rod position on the subjective visual vertical (SVV) tilt and to investigate the effect of sex and age on the SVV tilt induced by this initial position. STUDY DESIGN: Prospective cross-sectional study. SETTING: Tertiary referral center. PATIENTS: The study included 6598 consecutive patients with a large range of vestibular disorders and 333 control subjects. The mean age was 55 years (range, 3-97), and the sex ratio was 0.6. INTERVENTION: SVV was measured by presenting a phosphorescent rod 12 times in total darkness with a 45-degree deviation from the vertical alternatively on the right and left. The patient was asked to replace the bar vertically with a remote control. RESULTS: On average, SVV at each iteration was tilted to the side of the rod presentation. It was stronger in female subjects, in younger individuals (<20 years) and seniors (>50). It was also higher in patients with a left vestibular loss in comparison to those with a right involvement. CONCLUSIONS: These effects suggest that short-term visual memory and multisensory cortical processing interfere with SVV measurements.

Early-onset autosomal recessive cerebellar ataxia associated with retinal dystrophy: new human hotfoot phenotype caused by homozygous GRID2 deletion.

PURPOSE: The aim of this study was to identify the genetic cause of early-onset autosomal recessive cerebellar ataxia associated with retinal dystrophy in a consanguineous family. METHODS: An affected 6-month-old child underwent neurological and ophthalmological examinations. Genetic analyses included homozygosity mapping, copy number analysis, conventional polymerase chain reaction, Sanger sequencing, quantitative polymerase chain reaction, and whole-exome sequencing. Expression analysis of GRID2 was performed by quantitative polymerase chain reaction and immunohistochemistry. RESULTS: A homozygous deletion of exon 2 of GRID2 (p.Gly30_Glu81del) was identified in the proband. GRID2 encodes an ionotropic glutamate receptor known to be selectively expressed in cerebellar Purkinje cells. Here, we demonstrated GRID2 expression in human adult retina and retinal pigment epithelium. In addition, Grid2 expression was demonstrated in different stages of murine retinal development. GRID2 immunostaining was shown in murine and human retina. Whole-exome sequencing in the proband did not provide arguments for other disease-causing mutations, supporting the idea that the phenotype observed represents a single clinical entity. CONCLUSION: We identified GRID2 as an underlying disease gene of early-onset autosomal recessive cerebellar ataxia with retinal dystrophy, expanding the clinical spectrum of GRID2 deletion mutants. We demonstrated for the first time GRID2 expression and localization in human and murine retina, providing evidence for a novel functional role of GRID2 in the retina.

Influence of body laterality on recovery from subjective visual vertical tilt after vestibular neuritis.

The subjective visual vertical (SVV) is an indicator of vestibular otolithic function and mainly processed by the nondominant parietal cortex. We investigated the hypothesis that recovery from SVV tilt after vestibular neuritis can be influenced by the body's lateral preference. This prospective cohort follow-up study included 254 consecutive adult patients with vestibular neuritis. The recovery from SVV tilt was faster in patients with a left hand or eye dominance than in those with a right dominance. While in left-handers the side of the neuritis did not affect the speed of recovery, in right-handed subjects, the recovery from a right-sided neuritis was significantly slower than from a left-sided affection. These observations suggest that subjects with a left sensorimotor dominance have developed more significant midline-crossing projections to the parietal cortex, allowing them to cope faster with a unilateral vestibular deficit.

[The eyes of the labyrinth]. / Les yeux du labyrinth.

Reliable knowledge of one's space is a prerequisite for effective action, and only sensory experience, although not alone sufficient, can provide access to knowledge of reality. All the diferent sensory modalities help to make sense of this mental construct, but visual information, when available, is predominant. This requires stable images and constant updating of one's awareness of gaze direction and position in space at the moment of acquisition. The vestibular system is sensitive to angular and linear accelerations and thus acts as a reference for stability--an inertial base which stabilizes and characterizes the gaze direction and encodes the subject's movement tracking. In clinical practice, loss of these capacities induces eye drift, nystagmus, oscillopsia, vertical eye misalignment and a shift in the representation of mental space, leading to dizziness, translational illusions, integration path error, and "senseless" perceptions of the self in space. The reaction time of the eye and of mental image stabilization is of the order of afew tens of milliseconds. Recent tools for vestibular exploration allow us to measure this reactivity, which is a determining factor for quality of life. The video head impulse test, dynamic visual acuity, and cervical vestibular evoked myogenic potentials explore the structures involved in gaze and image stabilization, while subjective visual vertical and ocular vestibular evoked myogenic potentials provide an approach to the utricular contribution. This clinical and instrumental semiology sometimes proves more sensitive than the most advanced and accurate medical imaging methods, but rational listening and multidisciplinary skills on the part of the physician remain necessary to identify "self in space perceptual alterations.