The vestibular system: balancing more than just the body

Unreliable association between self-reported sense of direction and peripheral vestibular function

BACKGROUND

Uni- or bilateral peripheralvestibular impairment causes objective spatial orientation deficits, which can be measured using pen-and-paper-tests or sensorimotor tasks (navigation or pointing). For patients' subjective orientation abilities, questionnaires are commonly used (e.g., Santa Barbara sense of direction scale [SBSODS]). However, the relationship between subjective assessment of spatial skills and objective vestibular function has only been scarcely investigated.

METHODS

A total of 177 patients (mean age 57.86 ± 17.53 years, 90 females) who presented in our tertiary Center for Vertigo and Balance Disorders underwent neuro-otological examinations, including bithermal water calorics, video head impulse test (vHIT), and testing of the subjective visual vertical (SVV), and filled out the SBSODS (German version). Correlation analyses and linear multiple regression model analyses were performed between vestibular test results and self-assessment scores. Additionally, groupwise vestibular function for patients with low, average, and high self-report scores was analyzed.

RESULTS

Forty-two patients fulfilled the diagnostic criteria for bilateral vestibulopathy, 93 for chronic unilateral vestibulopathy (68 unilateral caloric hypofunction and 25 isolated horizontal vestibulo-ocular reflex deficits), and 42 patients had normal vestibular test results. SBSODS scores showed clear sex differences with higher subjective skill levels in males (mean score males: 4.94 ± 0.99, females 4.40 ± 0.94; Student's t-test: t-3.78, p < .001***). No stable correlation between objective vestibular function and subjective sense of spatial orientation was found. A multiple linear regression model could not reliably explain the self-reported variance. The three patient groups with low, average, and high self-assessment-scores showed no significant differences of vestibular function.

CONCLUSION

Self-reported assessment of spatial orientation does not robustly correlate with objective peripheral vestibular function. Therefore, other methods of measuring spatial skills in real-world and virtual environments are required to disclose orientation deficits due to vestibular hypofunction.

Human senses and sensors from Aristotle to the present

This historical review on the semantic evolution of human senses and sensors revealed that Aristotle's list of the five senses sight, hearing, touch, taste, and smell is still in use among non-scientific lay persons. It is no surprise that his classification in the work "De Anima" (On the Soul) from 350 BC confuses the sensor "touch" with the now more comprehensively defined somatosensory system and that senses are missing such as the later discovered vestibular system and the musculotendinous proprioception of the position of parts of the body in space. However, it is surprising that in the three most influential ancient cultures, Egypt, Greece, and China-which shaped the history of civilization-the concept prevailed that the heart rather than the brain processes perception, cognition, and emotions. This "cardiocentric view" can be traced back to the "Doctrine of Aristotle," the "Book of the Dead" in ancient Egypt, and the traditional Chinese medicine of correspondence documented in the book "Huang di Neijing." In Greek antiquity the philosophers Empedocles, Democritus and Aristotle were proponents of the allocation of the spirit and the soul to the heart connected to the body via the blood vessels. Opponents were the pre-Socratic mathematician Pythagoras, the philosopher Plato, and especially the Greek physician Hippocrates who regarded the brain as the most powerful organ in humans in his work "De Morbo Sacro." The Greek physician Galen of Pergamon further elaborated on the concept of the brain ("cephalocentric hypothesis") connected to the body by a network of nerves. The fundamental concepts for understanding functions and disorders of the vestibular system, the perception of self-motion, verticality and balance control were laid by a remarkable group of 19th century scientists including Purkynӗ, Mach, Breuer, Helmholtz, and Crum-Brown. It was also in the 19th century that Bell described a new sense of a reciprocal sensorimotor loop between the brain and the muscles which he called "muscular sense," later termed "kinaesthesia" by Bastian and defined in 1906 as "proprioception" by Sherrington as "the perception of joint and body movements as well as position of the body or body segments, in space." Both, the vestibular system and proprioception could be acknowledged as senses six or seven. However, we hesitate to recommend "pain"-which is variously assigned to the somatosensory system or extero-, intero-, visceroception-as a separate sensory system. Pain sensors are often not specific but have multisensory functions. Because of this inconsistent, partly contradictory classification even by experts in the current literature on senses and sensors we consider it justified to recommend a comprehensive reorganization of classification features according to the present state of knowledge with an expansion of the number of senses. Such a project has also to include the frequent task-dependent multisensory interactions for perceptual and sensorimotor achievements, and higher functions or disorders of the visual and vestibular systems as soon as cognition or emotions come into play. This requires a cooperation of sensory physiologists, neuroscientists and experienced physicians involved in the management of patients with sensory and multisensory disorders.

Post-stroke dizziness, depression and anxiety

OBJECTIVE

Vestibular and psychiatric disorders are very closely related. Previous research shows that the discomfort and dysfunction caused by dizziness in patients can affect psychological processes, leading to anxiety and depression, and the irritation of anxiety and depression can aggravate the discomfort of dizziness. But the causal relationship between dizziness in the recovery period of stroke and Post-stroke depression (PSD) / Post-stroke anxiety (PSA) is not clear. Identifying the causal relationship between them can enable us to conduct more targeted treatments.

METHODS

We review the epidemiology and relationship of dizziness, anxiety, and depression, along with the related neuroanatomical basis. We also review the pathophysiology of dizziness after stroke, vestibular function of patients experiencing dizziness, and the causes and mechanisms of PSD and PSA. We attempt to explore the possible relationship between post-stroke dizziness and PSD and PSA.

CONCLUSION

The treatment approach for post-stroke dizziness depends on its underlying cause. If the dizziness is a result of PSD and PSA, addressing these psychological factors may alleviate the dizziness. This can be achieved through targeted treatments for PSD and PSA, such as psychotherapy, antidepressants, or anxiolytics, which could indirectly improve dizziness symptoms. Conversely, if PSA and PSD are secondary to vestibular dysfunction caused by stroke, a thorough vestibular function assessment is crucial. Identifying the extent of vestibular impairment allows for tailored interventions. These could include vestibular rehabilitation therapy and medication aimed at vestibular restoration. By improving vestibular function, secondary symptoms like anxiety and depression may also be mitigated.

Electrical stimulation of the peripheral and central vestibular system

PURPOSE OF REVIEW

Electrical stimulation of the peripheral and central vestibular system using noninvasive (galvanic vestibular stimulation, GVS) or invasive (intracranial electrical brain stimulation, iEBS) approaches have a long history of use in studying self-motion perception and balance control. The aim of this review is to summarize recent electrophysiological studies of the effects of GVS, and functional mapping of the central vestibular system using iEBS in awake patients.

RECENT FINDINGS

The use of GVS has become increasingly common in the assessment and treatment of a wide range of clinical disorders including vestibulopathy and Parkinson's disease. The results of recent single unit recording studies have provided new insight into the neural mechanisms underlying GVS-evoked improvements in perceptual and motor responses. Furthermore, the application of iEBS in patients with epilepsy or during awake brain surgery has provided causal evidence of vestibular information processing in mostly the middle cingulate cortex, posterior insula, inferior parietal lobule, amygdala, precuneus, and superior temporal gyrus.

SUMMARY

Recent studies have established that GVS evokes robust and parallel activation of both canal and otolith afferents that is significantly different from that evoked by natural head motion stimulation. Furthermore, there is evidence that GVS can induce beneficial neural plasticity in the central pathways of patients with vestibular loss. In addition, iEBS studies highlighted an underestimated contribution of areas in the medial part of the cerebral hemispheres to the cortical vestibular network.

Histaminergic System and Vestibular Function in Normal and Pathological Conditions

Most neurotransmitter systems are represented in the central and peripheral vestibular system and are thereby involved both in normal vestibular signal processing and the pathophysiology of vestibular disorders. However, there is a special relationship between the vestibular system and the histaminergic system. The purpose of this review is to document how the histaminergic system interferes with normal and pathological vestibular function. In particular, we will discuss neurobiological mechanisms such as neuroinflammation that involve histamine to modulate and allow restoration of balance function in the situation of a vestibular insult. These adaptive mechanisms represent targets of histaminergic pharmacological compounds capable of restoring vestibular function in pathological situations. The clinical use of drugs targeting the histaminergic system in various vestibular disorders is critically discussed.

The third-person perspective full-body illusion induced by visual-tactile stimulation in virtual reality for stroke patients

This paper attempts to induce the third-person perspective full body illusion (3PP-FBI) with virtual reality (VR) in stroke patients. Nineteen individuals with stroke were recruited. The 3PP-FBI induction method, which was well-established in healthy individuals, using synchronous visual-tactile stimulation on one body part was used. Questionnaire scores and proprioceptive drift values were collected under different conditions for characterizing the induced 3PP-FBI. Results showed that synchronous visual-tactile stimulation of a single body part (back or upper limb) was sufficient to elicit 3PP-FBI in stroke patients, forming a sense of ownership (SOO) over the entire virtual body. Moreover, the intensity of 3PP-FBI was stronger when the back was stimulated, compared to stimulating the impaired upper limb. This study demonstrated the viability of visual-guided rehabilitation training while having a SOO to a virtual body from the third-person perspective, in anticipation of achieving better rehabilitation outcome for movements beyond the first-person perspective.

Cellular and Molecular Mechanisms of Vestibular Ageing

While age-related auditory deficits and cochlear alterations are well described, those affecting the vestibular sensory organs and more broadly the central vestibular pathways are much less documented. Although there is inter-individual heterogeneity in the phenomenon of vestibular ageing, common tissue alterations, such as losses of sensory hair cells or primary and secondary neurons during the ageing process, can be noted. In this review, we document the cellular and molecular processes that occur during ageing in the peripheral and central vestibular system and relate them to the impact of age-related vestibular deficits based on current knowledge.

Vestibular rehabilitation therapy on balance and gait in patients after stroke: a systematic review and meta-analysis

BACKGROUND

There is limited evidence to support the use of vestibular rehabilitation therapy (VRT) on improving balance and gait in patients after stroke. This systematic review aimed to evaluate the effects of VRT in addition to usual rehabilitation compared with usual rehabilitation on improving balance and gait for patients after stroke.

METHODS

This review followed the Preferred Reporting Items for Systematic reviews and Meta-Analysis statement guidelines. Ten electronic databases were searched up to 1 June 2023 without restrictions in language and publication status. The PEDro scale and the Grading of Recommendations Assessment Development, and Evaluation were used to evaluate the risk of bias and the certainty of evidence. The meta-analysis was conducted with Review Manager 5.3.

RESULTS

Fifteen randomised controlled trials with 769 participants were included. PEDro scale was used to assess the risk of bias with a mean score of 5.9 (0.7). VRT was effective in improving balance for patients after stroke (SMD = 0.59, 95% CI (0.40, 0.78), p < 0.00001), particularly for patients after stroke that occurred within 6 months (SMD = 0.56, 95% CI (0.33, 0.79), p < 0.00001) with moderate certainty of evidence. Subgroup analysis showed that VRT provided as gaze stability exercises combined with swivel chair training (SMD = 0.85, 95% CI (0.48, 1.22), p < 0.00001) and head movements (SMD = 0.75, 95% CI (0.43, 1.07), p < 0.00001) could significantly improve balance. Four-week VRT had better effect on balance improvement (SMD = 0.64, 95% CI (0.40, 0.89), p < 0.00001) than the less than 4-week VRT. The pooled mean difference of values of Timed Up-and-Go test showed that VRT could significantly improve gait function for patients after stroke (MD =  -4.32, 95% CI (-6.65, -1.99), p = 0.0003), particularly for patients after stroke that occurred within 6 months (MD =  -3.92, 95% CI (-6.83, -1.00), p = 0.008) with moderate certainty of evidence.

CONCLUSIONS

There is moderate certainty of evidence supporting the positive effect of VRT in improving balance and gait of patients after stroke.

TRIAL REGISTRATION

PROSPERO CRD42023434304.

Eagle-449: A volumetric, whole-brain compilation of brain atlases for vestibular functional MRI research

Human vestibular processing involves distributed networks of cortical and subcortical regions which perform sensory and multimodal integrative functions. These functional hubs are also interconnected with areas subserving cognitive, affective, and body-representative domains. Analysis of these diverse components of the vestibular and vestibular-associated networks, and synthesis of their holistic functioning, is therefore vital to our understanding of the genesis of vestibular dysfunctions and aid treatment development. Novel neuroimaging methodologies, including functional and structural connectivity analyses, have provided important contributions in this area, but often require the use of atlases which are comprised of well-defined a priori regions of interest. Investigating vestibular dysfunction requires a more detailed atlas that encompasses cortical, subcortical, cerebellar, and brainstem regions. The present paper represents an effort to establish a compilation of existing, peer-reviewed brain atlases which collectively afford comprehensive coverage of these regions while explicitly focusing on vestibular substrates. It is expected that this compilation will be iteratively improved with additional contributions from researchers in the field.

Effect of Interventional Therapy Unexplained Dizziness and Relationship Between Dizziness Handicap Inventory and Right-to-Left Shunt Grading

Objective

Unexplained dizziness remains a clinical challenge. Our previous studies have shown that unexplained dizziness may be related to patent foramen ovale (PFO). This study aims to explore whether the degree of shunt is correlated with the degree of unexplained dizziness and looking for the possible clinical intervention for patients with unexplained dizziness.

Methods

This study was a large single-center, prospective, controlled study. From March 2019 to March 2022, patients with unexplained dizziness and explained dizziness and healthy controls were recruited. Contrast-enhanced transcranial Doppler sonography (c-TCD) was performed to detect the existence of right-to-left shunt (RLS) and shunt grading. The dizziness handicap inventory (DHI) was completed to evaluate the dizziness. Unexplained dizziness patients with large amount of PFO were volunteered to receive medication treatment and transcatheter PFO closure and followed up six months.

Results

A total of 387 patients (132 unexplained, 123 explained and 132 controls) were enrolled. There was a statistical difference in the RLS grading with three groups (p < 0.001). The Spearman correlation coefficient of RLS grading and DHI scores in unexplained dizziness patients (r=0.122, p=0.163) and explained dizziness patients (r=0.067, p=0.460). In the unexplained group, there were 49 cases with massive grading RLS. Of which 25 patients received percutaneous PFO closure treatment and 24 cases received medication treatment. Followed up six months after treatment, the amount of DHI scores change in patients who received the percutaneous PFO closure was significantly higher than that in the medication treatment group (p < 0.001).

Conclusion

RLS may play an important role in unexplained dizziness. For unexplained dizziness patients, PFO closure may contribute to better outcomes. In the future, large-scale randomized controlled studies are still needed.

The brain-body disconnect: A somatic sensory basis for trauma-related disorders

Although the manifestation of trauma in the body is a phenomenon well-endorsed by clinicians and traumatized individuals, the neurobiological underpinnings of this manifestation remain unclear. The notion of somatic sensory processing, which encompasses vestibular and somatosensory processing and relates to the sensory systems concerned with how the physical body exists in and relates to physical space, is introduced as a major contributor to overall regulatory, social-emotional, and self-referential functioning. From a phylogenetically and ontogenetically informed perspective, trauma-related symptomology is conceptualized to be grounded in brainstem-level somatic sensory processing dysfunction and its cascading influences on physiological arousal modulation, affect regulation, and higher-order capacities. Lastly, we introduce a novel hierarchical model bridging somatic sensory processes with limbic and neocortical mechanisms regulating an individual's emotional experience and sense of a relational, agentive self. This model provides a working framework for the neurobiologically informed assessment and treatment of trauma-related conditions from a somatic sensory processing perspective.

Vestibular dysfunction is an important contributor to the aging of visuospatial ability in older adults–Data from a computerized test system

Background

A convergence of research supports a key role of the vestibular system in visuospatial ability. However, visuospatial ability may decline with age. This work aims to elucidate the important contribution of vestibular function to visuospatial ability in old adults through a computerized test system.

Methods

Patients with a clinical history of recurrent vertigo and at least failed one vestibular test were included in this cross-sectional study. Healthy controls of three age groups: older, middle-aged, and young adults were also involved. Visuospatial cognitive outcomes including spatial memory, spatial navigation, and mental rotation of all the groups were recorded. Comparing the performance of the visuospatial abilities between patients and age-matched controls as well as within the controls.

Results

A total of 158 individuals were enrolled. Results showed that patients performed worse than the age-matched controls, with the differences in the forward span (p &lt; 0.001), the time of the maze 8 × 8 (p = 0.009), and the time of the maze 12 × 12 (p = 0.032) being significant. For the differences in visuospatial cognitive outcomes within the controls, the younger group had a significantly better performance than the other groups. The older group and the middle-aged group had comparable performances during all the tests.

Conclusions

Older patients with vestibular dysfunction had more difficulties during visuospatial tasks than age-matched controls, especially in spatial memory and spatial navigation. Within the controls, younger adults did much better than other age groups, while older adults behaved similarly to middle-aged adults. It is a valuable attempt to computerize the administration of tests for visuospatial ability.

Comparison of static balance and gait between subjects with plantar fasciitis and age-matched controls

BACKGROUND

Plantar fasciitis (PF) is a common condition amongst athletes as well as in non-sporting population. It is characterised by a sharp pain under the calcaneus during walking. The impact of pain due to PF on gait and static balance is examined in this observational study.

OBJECTIVE

To compare gait and balance between individuals with PF and age-matched controls without PF.

METHOD

A cross-sectional observational study was executed in an Outpatient Rehabilitation Centre. Twenty-nine participants were included, 14 with PF, and 15 age-matched healthy asymptomatic individuals. Main outcome measures were foot pain, foot function index (FFI), static balance measured with modified Romberg test, static balance measured on the TYMO® system, and gait with the G-Walk System.

RESULTS

Foot pain and FFI were adversely related to balance and gait parameters in subjects with PF. Static balance with eyes open and eyes closed on firm and soft surface measured on the TYMO® balance platform as well as gait parameters measured with the G-Walk system, were significantly lower in subjects with PF compared to age-matched healthy controls.

CONCLUSION

PF negatively affects parameters of static balance measured with TYMO® system and gait parameters measured with the G-Walk System. However, the Romberg balance test did not detect differences between subjects with PF and age-matched healthy controls.

Galvanic vestibular stimulation and its applications: a systematic review

OBJECTIVE

Galvanic vestibular stimulation has been evaluated in the context of vestibular rehabilitation. The objective was to identify evidence in the scientific literature about the clinical applications of galvanic vestibular stimulation.

METHODS

In this systematic review, the articles describing the applications of galvanic vestibular stimulation were extracted from PubMed, Web of Science, MEDLINE, Scopus, LILACS and SciELO databases. The survey was limited to articles published in English, Portuguese and Spanish. All the articles about the clinical applications of galvanic vestibular stimulation were compiled. Repeated articles in the databases, literature review articles, case reports, letters and editorials were excluded. The descriptors included: galvanic vestibular stimulation, postural balance, central nervous system diseases, vestibular diseases, spinal cord diseases and cognition.

RESULTS

The search strategy resulted in the initial selection of 994 articles; the reading of titles and abstracts was accomplished in 470 articles and the complete reading in 23 articles. Clinical applications of galvanic vestibular stimulation included Ménière's disease, vestibular neuritis, bilateral vestibular disorders, vestibular schwannoma, Parkinson's disease, ischemic central lesions, motor myelopathies, anxiety disorders, cognition and memory.

CONCLUSION

Galvanic vestibular stimulation has been considered a potentially useful strategy for balance rehabilitation, since it has the effect of stimulating the central connections related to the postural balance, favoring new neuronal synapses that allow the partial or total recovery of postural imbalance.

The Effects of Vestibular Rehabilitation on Poststroke Fatigue: A Randomized Controlled Trial Study

Background

A major complication caused by stroke is poststroke fatigue (PSF), and by causing limitations in doing activities of daily living (ADL), it can lower the quality of life.

Objective

The present study is an attempt to examine the effects of vestibular rehabilitation on BADL (Basic Activities of Daily Living), fatigue, depression, and Lawton Instrumental Activities of Daily Living (IADL) in patients with stroke.

Method

Patients with a history of stroke took part voluntarily in a single-blind clinical trial. The participants were allocated to control and experimental groups randomly. The experimental group attended 24 sessions of vestibular rehabilitation protocol, while the control group received the standard rehabilitation (including three sessions per week each for around 60 min). To measure fatigue, the Fatigue Impact Scale (FIS) and the Fatigue Assessment Scale (FAS) were used. Depression, BADL, and IADL were measured using the Beck Depression Inventory-II (BDI-II), Barthel Index (BI), and Lawton Instrumental Activities of Daily Living, respectively. All changes were measured from the baseline after the intervention.

Results

Significant improvement was found in the experimental group compared to the control group (p < 0.05) in FIS (physical, cognition, and social subscales), FAS, BDI-II, BADL, and IADL. Moreover, the results showed small to medium and large effect sizes for the physical subscale of FIS and FAS scores based on Cohen's d, respectively; however, no significant difference was found in terms of cognition and social subscales of FIS, BDI-II, BADL, and IADL scores.

Conclusion

It is possible to improve fatigue, depression, and independence in BADL and IADL using vestibular rehabilitation. Thus, it is an effective intervention in case of stroke, which is also well tolerated.

Predictors of cochleovestibular dysfunction in children with congenital cytomegalovirus infection

The purpose of this study is to assess the predictive factors of both hearing and vestibular impairment in congenitally cytomegalovirus-infected children (cCMV) through a multivariate analysis of clinical and imaging characteristics collected during pregnancy and at birth. This retrospective study was conducted between March 2014 and March 2020, including confirmed congenitally CMV-infected children with a complete vestibular and hearing assessment. Data concerning pregnancy, date of infection, clinical characteristics, and symptomatology at birth were collected. In total, 130 children were included, with a median age of 21 months. Eighty-three children (64%) presented with an inner ear impairment (both cochlear and vestibular impairment). Sex, modality of maternal infection (seroconversion or reactivation), pregnancy term, weight and head circumference at birth, neonatal clinical signs of infection, and treatment were not significantly correlated with inner ear impairment. However, multivariate analysis confirmed that there are two independent predictive factors of inner ear impairment: antenatal imaging lesions (OR_a = 8.02 [1.74; 60.27], p-value = 0.01) and infection during the first trimester (OR_a = 4.47 [1.21; 19.22], p-value = 0.03). Conversely, infections occurring during the second trimester were rarely associated with inner ear impairment: 4/13 (31%) in our series, with vestibular impairment alone (4/4) and no hearing loss. None of the children infected during the third trimester developed inner ear dysfunction.

CONCLUSION

Besides the symptomatic status of the CMV infection at birth, we found that antenatal imaging brain damage and early infection (mainly during the first trimester) constitute the two best independent predictive factors of inner ear involvement in congenitally CMV-infected children.

WHAT IS KNOWN

• Congenital cytomegalovirus infection is the leading infectious cause of neurological disabilities and sensorineural hearing loss in children and responsible of vestibular disorders, which are probably underestimated. • No articles have yet defined the predictive factors of the entire inner ear impairment (vestibule and cochlea).

WHAT IS NEW

• The timing of the infection during pregnancy (first and second trimester, ORa=4.47) and antenatal imaging lesions (ORa=8.02) are independently predictive (in a multivariate analysis) of inner ear involvement. • The symptomatic status at birth is a poor predictor of inner ear impairment.

The Relationship Between Patent Foramen Ovale and Unexplained Dizziness: A Prospective Analysis in China

Introduction

Patent foramen ovale (PFO) is potentially associated with abnormal embolisms, and it results in mixing of arteriovenous blood when its right-to-left shunt (RLS) emerges. Present studies have found that PFO is a risk factor that can lead to many diseases. However, few studies have examined the relationship between PFO and dizziness.

Methods

This study was a large single-center, prospective, controlled study. From March 2019 to March 2021, we recruited patients with dizziness were divided into two groups: "explained" and "unexplained". All patients were submitted to contrast-enhanced transcranial Doppler ultrasound and screened for PFO. Transesophageal heart ultrasound or right heart catheterization was used to confirm PFO. Additionally, multiple factors were collected and statistical analysis was performed between the two groups.

Results

Among the 244 patients included, 123 were in the "explained" group and 121 were in the "unexplained" group. The prevalence of PFO in the "explained" group was 34 (27.4%) compared to 79 (64.7%) in the "unexplained" group. In the "explained" group, 7 were RLS level IV, 6 were level III, 7 were level II, and 14 were level I. For the "unexplained" group, the numbers of patients with levels IV, III, II and I were 27, 26, 12 and 14, respectively. Univariate analysis revealed that PFO (χ2= 34.77, P < 0.001) and age (t = -3.49, P < 0.001) seemed to be potential risk factor candidates for "unexplained" dizziness. In multiple regression analysis, age (OR = 0.97; 95% CI 0.95-0.99) and the prevalence of PFO (OR = 4.37; 95% CI 2.50-7.63) were statistically significant. Massively shunted PFO showed more pronounced risk factors (OR = 8.76; 95% CI 4.04-19.03).

Conclusion

There was a high prevalence of PFO and a greater RLS level in unexplained dizziness. PFO and age were independent risk factors for unexplained dizziness. When treating with unexplained dizziness, especially among young people, we must pay attention to the presence of PFO.

Express: Cognition in Zero Gravity: Effects of Non-Terrestrial Gravity on Human Behaviour

As humanity prepares for deep space exploration, understanding the impact of spaceflight on bodily physiology is critical. While the effects of non-terrestrial gravity on the body are well established, little is known about its impact on human behaviour and cognition. Astronauts often describe dramatic alterations in sensorimotor functioning, including orientation, postural control and balance. Changes in cognitive functioning as well as in socio-affective processing have also been observed. Here we have reviewed the key literature and explored the impact of non-terrestrial gravity across three key functional domains: sensorimotor, cognition, and socio-affective processing. We have proposed a neuroanatomical model to account for the effects of non-terrestrial gravity in these domains. Understanding the impact of non-terrestrial gravity on human behaviour has never been more timely and it will help mitigate against risks in both commercial and non-commercial spaceflight.

Hormones and Vestibular Disorders: The Quest for Biomarkers

The vestibular system exerts control over various functions through neural pathways that are not yet fully mapped. Functional dysregulations or tissue lesions at different levels of the peripheral and the central vestibular networks can alter these different functions, causing a wide variety of symptoms, ranging from posturo-locomotor alterations to psychiatric syndromes such as PPPD, including the deregulation of the main biological functions. These different symptoms differ by their expression kinetics (they each appear and regress with their own kinetics) by the targets affected (muscles, organs, and brain areas) and by the sensitivity specific to each individual. Vestibular pathologies thus cover a mosaic of distinct effects, and they involve various effectors—which constitute the many markers of their different types and stages. It is therefore crucial, to predict the onset of a vertigo syndrome, to follow its temporal course, or to monitor the impact of therapeutic approaches, and to have specific and reliable biomarkers. Hormonal variations are among the possible sources of biomarkers for neurotology. We know that specific hormonal profiles can promote the appearance of vestibular disorders. We also know that the expression of vertigo syndrome is accompanied by measurable hormonal variations. The link between endocrine deregulation and vestibular alterations therefore no longer needs to be proven. However, there are still few data on their precise correlations with the vertigo syndrome. This study was undertaken with the aim to deliver an extensive review of the hormonal alterations linked to vestibular disorders. A review of the literature covering the last two decades was carried out using the MEDLINE and COCHRANE databases in order to identify studies associating the terms vestibular system or vestibular pathologies and hormones. Bibliographic data provides several outcomes in terms of therapeutic innovation in the diagnosis and therapeutic follow-up of vestibular pathologies.

Vestibular Deficits in Deafness: Clinical Presentation, Animal Modeling, and Treatment Solutions

The inner ear is responsible for both hearing and balance. These functions are dependent on the correct functioning of mechanosensitive hair cells, which convert sound- and motion-induced stimuli into electrical signals conveyed to the brain. During evolution of the inner ear, the major changes occurred in the hearing organ, whereas the structure of the vestibular organs remained constant in all vertebrates over the same period. Vestibular deficits are highly prevalent in humans, due to multiple intersecting causes: genetics, environmental factors, ototoxic drugs, infections and aging. Studies of deafness genes associated with balance deficits and their corresponding animal models have shed light on the development and function of these two sensory systems. Bilateral vestibular deficits often impair individual postural control, gaze stabilization, locomotion and spatial orientation. The resulting dizziness, vertigo, and/or falls (frequent in elderly populations) greatly affect patient quality of life. In the absence of treatment, prosthetic devices, such as vestibular implants, providing information about the direction, amplitude and velocity of body movements, are being developed and have given promising results in animal models and humans. Novel methods and techniques have led to major progress in gene therapies targeting the inner ear (gene supplementation and gene editing), 3D inner ear organoids and reprograming protocols for generating hair cell-like cells. These rapid advances in multiscale approaches covering basic research, clinical diagnostics and therapies are fostering interdisciplinary research to develop personalized treatments for vestibular disorders.

Contributions of Body-Orientation to Mental Ball Dropping Task During Out-of-Body Experiences

Out-of-body experiences (OBEs) provide fascinating insights into our understanding of bodily self-consciousness and the workings of the brain. Studies that examined individuals with brain lesions reported that OBEs are generally characterized by participants experiencing themselves outside their physical body (i.e., disembodied feeling) (Blanke and Arzy, 2005). Based on such a characterization, it has been shown that it is possible to create virtual OBEs in immersive virtual environments (Ehrsson, 2007; Ionta et al., 2011b; Bourdin et al., 2017). However, the extent to which body-orientation influences virtual OBEs is not well-understood. Thus, in the present study, 30 participants (within group design) experienced a full-body ownership illusion (synchronous visuo-tactile stimulation only) induced with a gender-matched full-body virtual avatar seen from the first-person perspective (1PP). At the beginning of the experiment, participants performed a mental ball dropping (MBD) task, seen from the location of their virtual avatar, to provide a baseline measurement. After this, a full-body ownership illusion (embodiment phase) was induced in all participants. This was followed by the virtual OBE illusion phase of the experiment (disembodiment phase) in which the first-person viewpoint was switched to a third-person perspective (3PP), and participants' disembodied viewpoint was gradually raised to 14 m above the virtual avatar, from which altitude they repeated the MBD task. During the experiment, this procedure was conducted twice, and the participants were allocated first to the supine or the standing body position at random. Results of the MBD task showed that the participants experienced increased MBD durations during the supine condition compared to the standing condition. Furthermore, although the findings from the subjective reports confirmed the previous findings of virtual OBEs, no significant difference between the two postures was found for body ownership. Taken together, the findings of the current study make further contributions to our understanding of both the vestibular system and time perception during OBEs.

The "vestibular neuromatrix": A proposed, expanded vestibular network from graph theory in post-concussive vestibular dysfunction

Convergent clinical and neuroimaging evidence suggests that higher vestibular function is subserved by a distributed network including visuospatial, cognitive-affective, proprioceptive, and integrative brain regions. Clinical vestibular syndromes may perturb this network, resulting in deficits across a variety of functional domains. Here, we leverage structural and functional neuroimaging to characterize this extended network in healthy control participants and patients with post-concussive vestibular dysfunction (PCVD). Then, 27 healthy control subjects (15 females) and 18 patients with subacute PCVD (12 female) were selected for participation. Eighty-two regions of interest (network nodes) were identified based on previous publications, group-wise differences in BOLD signal amplitude and connectivity, and multivariate pattern analysis on affective tests. Group-specific "core" networks, as well as a "consensus" network comprised of connections common to all participants, were then generated based on probabilistic tractography and functional connectivity between the 82 nodes and subjected to analyses of node centrality and community structure. Whereas the consensus network was comprised of affective, integrative, and vestibular nodes, PCVD participants exhibited diminished integration and centrality among vestibular and affective nodes and increased centrality of visual, supplementary motor, and frontal and cingulate eye field nodes. Clinical outcomes, derived from dynamic posturography, were associated with approximately 62% of all connections but best predicted by amygdalar, prefrontal, and cingulate connectivity. No group-wise differences in diffusion metrics or tractography were noted. These findings indicate that cognitive, affective, and proprioceptive substrates contribute to vestibular processing and performance and highlight the need to consider these domains during clinical diagnosis and treatment planning.

Watching the Effects of Gravity. Vestibular Cortex and the Neural Representation of "Visual" Gravity

Gravity is a physical constraint all terrestrial species have adapted to through evolution. Indeed, gravity effects are taken into account in many forms of interaction with the environment, from the seemingly simple task of maintaining balance to the complex motor skills performed by athletes and dancers. Graviceptors, primarily located in the vestibular otolith organs, feed the Central Nervous System with information related to the gravity acceleration vector. This information is integrated with signals from semicircular canals, vision, and proprioception in an ensemble of interconnected brain areas, including the vestibular nuclei, cerebellum, thalamus, insula, retroinsula, parietal operculum, and temporo-parietal junction, in the so-called vestibular network. Classical views consider this stage of multisensory integration as instrumental to sort out conflicting and/or ambiguous information from the incoming sensory signals. However, there is compelling evidence that it also contributes to an internal representation of gravity effects based on prior experience with the environment. This a priori knowledge could be engaged by various types of information, including sensory signals like the visual ones, which lack a direct correspondence with physical gravity. Indeed, the retinal accelerations elicited by gravitational motion in a visual scene are not invariant, but scale with viewing distance. Moreover, the "visual" gravity vector may not be aligned with physical gravity, as when we watch a scene on a tilted monitor or in weightlessness. This review will discuss experimental evidence from behavioral, neuroimaging (connectomics, fMRI, TMS), and patients' studies, supporting the idea that the internal model estimating the effects of gravity on visual objects is constructed by transforming the vestibular estimates of physical gravity, which are computed in the brainstem and cerebellum, into internalized estimates of virtual gravity, stored in the vestibular cortex. The integration of the internal model of gravity with visual and non-visual signals would take place at multiple levels in the cortex and might involve recurrent connections between early visual areas engaged in the analysis of spatio-temporal features of the visual stimuli and higher visual areas in temporo-parietal-insular regions.

[Vestibular compensation and aging: An example of cellular and behavioral resilience over time]

The vestibular system has a remarkable capacity of self-repair. Vestibular compensation, a model of post-lesional plasticity of the central nervous system, refers to a set of endogenous neuroplasticity mechanisms in the vestibular nuclei in response to damage to the peripheral vestibular system, and underlying functional recovery. During aging, this "homeostatic" plasticity, although still present, diminishes and is accompanied by sensorimotor and cognitive disturbances. Regardless of age, vestibular compensation can be improved by pharmacological therapy but also by rehabilitation based on strengthening other sensory modalities such as visual and proprioceptive modalities, but also cognitive and motor components. In this article, we will first discuss neurobiological mechanisms of vestibular compensation, then document the impact of aging on this adaptive plasticity.

Vestibular-Evoked Cerebral Potentials

The human vestibular cortex has mostly been approached using functional magnetic resonance imaging and positron emission tomography combined with artificial stimulation of the vestibular receptors or nerve. Few studies have used electroencephalography and benefited from its high temporal resolution to describe the spatiotemporal dynamics of vestibular information processing from the first milliseconds following vestibular stimulation. Evoked potentials (EPs) are largely used to describe neural processing of other sensory signals, but they remain poorly developed and standardized in vestibular neuroscience and neuro-otology. Yet, vestibular EPs of brainstem, cerebellar, and cortical origin have been reported as early as the 1960s. This review article summarizes and compares results from studies that have used a large range of vestibular stimulation, including natural vestibular stimulation on rotating chairs and motion platforms, as well as artificial vestibular stimulation (e.g., sounds, impulsive acceleration stimulation, galvanic stimulation). These studies identified vestibular EPs with short latency (<20 ms), middle latency (from 20 to 50 ms), and late latency (>50 ms). Analysis of the generators (source analysis) of these responses offers new insights into the neuroimaging of the vestibular system. Generators were consistently found in the parieto-insular and temporo-parietal junction-the core of the vestibular cortex-as well as in the prefrontal and frontal areas, superior parietal, and temporal areas. We discuss the relevance of vestibular EPs for basic research and clinical neuroscience and highlight their limitations.

Unilateral vestibular neurectomy induces a remodeling of somatosensory cortical maps

Unilateral Vestibular Neurectomy (UVN) induces a postural syndrome whose compensation over time is underpinned by multimodal sensory substitution processes. However, at a chronic stage of compensation, UVN rats exhibit an enduring postural asymmetry expressed by an increase in the body weight on the ipsilesional paws. Given the anatomo-functional links between the vestibular nuclei and the primary somatosensory cortex (S1), we explored the interplay of vestibular and somatosensory cortical inputs following acute and chronic UVN. We determined whether the enduring imbalance in tactilo-plantar inputs impacts response properties of S1 cortical neurons and organizational features of somatotopic maps. We performed electrophysiological mapping of the hindpaw cutaneous representations in S1, immediately and one month after UVN. In parallel, we assessed the posturo-locomotor imbalance during the compensation process. UVN immediately induces an expansion of the cortical neuron cutaneous receptive fields (RFs) leading to a partial dedifferentiation of somatotopic maps. This effect was demonstrated for the ventral skin surface representations and was greater on the contralesional hindpaw for which the neuronal threshold to skin pressure strongly decreased. The RF enlargement was amplified for the representation of the ipsilesional hindpaw in relation to persistent postural asymmetries, but was transitory for the contralesional one. Our study shows, for the first time, that vestibular inputs exert a modulatory influence on S1 neuron's cutaneous responses. The lesion-induced cortical malleability highlights the influence of vestibular inputs on tactile processing related to postural control.

Selective optogenetic stimulation of glutamatergic, but not GABAergic, vestibular nuclei neurons induces immediate and reversible postural imbalance in mice

Glutamatergic and GABAergic neurons represent the neural components of the medial vestibular nuclei. We assessed the functional role of glutamatergic and GABAergic neuronal pathways arising from the vestibular nuclei (VN) in the maintenance of gait and balance by optogenetically stimulating the VN in VGluT2-cre and GAD2-cre mice. We demonstrate that glutamatergic, but not GABAergic VN neuronal subpopulation is responsible for immediate and strong posturo-locomotor deficits, comparable to unilateral vestibular deafferentation models. During optogenetic stimulation, the support surface dramatically increased in VN^VGluT2+ mice, and rapidly fell back to baseline after stimulation, whilst it remained unchanged during similar stimulation of VN^GAD2+ mice. This effect persisted when vestibular tactilo kinesthesic plantar inputs were removed. Posturo-locomotor alterations evoked in VN^VGluT2+ animals were still present immediately after stimulation, while they disappeared 1 h later. Overall, these results indicate a fundamental role for VN^VGluT2+ neurons in balance and posturo-locomotor functions, but not for VN^GAD2+ neurons, in this specific context. This new optogenetic approach will be useful to characterize the role of the different VN neuronal populations involved in vestibular physiology and pathophysiology.

Sport as a Factor in Improving Visual Spatial Cognitive Deficits in Patients with Hearing Loss and Chronic Vestibular Deficit

Hearing loss and chronic vestibular pathologies require brain adaptive mechanisms supported by a cross-modal cortical plasticity. They are often accompanied by cognitive deficits. Spatial memory is a cognitive process responsible for recording information about the spatial environment and spatial orientation. Visual-spatial working memory (VSWM) is a kind of short-term working memory that allows spatial information to be temporarily stored and manipulated. It can be conditioned by hearing loss and also well-compensated chronic vestibular deficit. Vestibular rehabilitation and hearing aid devices or training are able to improve the VSWM. We studied 119 subjects suffering from perinatal or congenital hearing loss, compared with 532 healthy subjects and 404 patients with well-compensated chronic vestibular deficit (CVF). VSWM was evaluated by the eCorsi test. The subjects suffering from chronic hearing loss and/or unilateral or bilateral vestibular deficit showed a VSWM less efficient than healthy people, but much better than those with CVF, suggesting a better multimodal adaptive strategy, probably favored by a cross-modal plasticity which also provides habitual use of lip reading. The sport activity cancels the difference with healthy subjects. It is therefore evident that patients with this type of deficit since childhood should be supported and advised on a sport activity or repeated vestibular stimulation.

Clinical predictors of cybersickness in virtual reality (VR) among highly stressed people

The use of virtual reality (VR) in the treatment of psychiatric disorders is increasing, and cybersickness has emerged as an important obstacle to overcome. However, the clinical factors affecting cybersickness are still not well understood. In this study, we investigated clinical predictors and adaptation effect of cybersickness during VR application in highly stressed people. Eighty-three healthy adult participants with high stress level were recruited. At baseline, we conducted psychiatric, ophthalmologic, and otologic evaluations and extracted physiological parameters. We divided the participants into two groups according to the order of exposure to VR videos with different degrees of shaking and repetitively administered the Simulator Sickness Questionnaire (SSQ) and the Fast Motion sickness Scale (FMS). There was no significant difference in changes in the SSQ or the FMS between groups. The 40–59 years age group showed a greater increase in FMS compared to the 19–39 years age group. Smoking was negatively associated with cybersickness, and a high Positive Affect and Negative Affect Schedule score was positively associated with cybersickness. In conclusion, changing the intensity of shaking in VR did not affect cybersickness. While smoking was a protective factor, more expression of affect was a risk factor for cybersickness.

Impaired Attentional Processing During Parabolic Flight

Previous studies suggest that altered gravity levels during parabolic flight maneuvers affect spatial updating. Little is known about the impact of the experimental setting and psychological stressors associated with parabolic flight experiments on attentional processes. To address this gap, we investigated the level of alertness, selective and sustained attention in 1 and 0 g using a Go/No-Go Continuous Performance Task. We also identified several parameters associated with the experimental set-up of a parabolic flight that could be expected to affect attentional processing. These included the use of scopolamine, sleep quality prior to the flight day, participant’s stress level as well as mood and anxiety state before and after the parabolic flight. We observed a deterioration in attentional processing prior to the first parabola that was further aggravated in weightlessness and returned to baseline after the last parabola. Reaction Time, Hit and False Alarm Rate were moderately correlated with self-reported anxiety state, but not cortisol levels or emotional states. The use of scopolamine had minor effects on Reaction Time. Our results confirm previous studies reporting impairments of cognitive performance in 0 g, and highlight important aspects that should be considered for the design of behavioral research experiments in future parabolic flight campaigns.

Assessing head acceleration to identify a motor threshold to galvanic vestibular stimulation

Galvanic vestibular stimulation (GVS) is used to assess vestibular system function, but vestibulospinal responses can exhibit variability depending on protocols or intensities used. Here, we measured head acceleration in healthy subjects to identify an objective motor threshold on which to base GVS intensity when assessing standing postural responses. Thirteen healthy right-handed subjects stood on a force platform, eyes closed, and head facing forward. An accelerometer was placed on the vertex to detect head acceleration, and electromyography activity of the right soleus was recorded. GVS (200 ms; current steps 0.5, from 1 mA to 4 mA) was applied in a binaural and bipolar configuration. 1) GVS induced a biphasic accelerometer response at a latency of 15 ms. Based on response amplitude, we constructed a recruitment curve for all participants and determined the motor threshold. In parallel, the method of limits was used to devise a more rapid approach to determine motor threshold. 2) We observed significant differences between motor threshold based on a recruitment curve and all perceptual thresholds reported either by the subject (sensation of movement) or a standing experimenter observing the participant (perception of movement). No significant difference was observed between the motor threshold based on the method of limits and perceptual thresholds of movement. 3) Using orthogonal polynomial contrasts, we observed a linear progression between multiples of the objective motor threshold (0.5, 0.75, 1, 1.5× motor threshold) and the 95% confidence ellipse area, the first peak of center of pressure displacement velocity, and the short and medium latency responses in the soleus. Hence, an objective motor threshold for GVS based on head acceleration was identified in standing participants and a recruitment curve could be constructed for all participants. These novel approaches could enable better understanding of changes in the vestibular system in different conditions or over time.NEW & NOTEWORTHY Galvanic vestibular stimulation (GVS) has been used to assess the vestibular system, but the significant interindividual variability in the responses makes it difficult to quantitatively compare them between individuals or conditions. Using an accelerometer to quantify head movement induced by GVS, we were able to determine an objective motor threshold and construct a recruitment curve for all participants. These methods could help assess changes in the vestibular system under different conditions.

A neuronal blueprint for directional mechanosensation in larval zebrafish

Animals have a remarkable ability to use local cues to orient in space in the absence of a panoramic fixed reference frame. Here we use the mechanosensory lateral line in larval zebrafish to understand rheotaxis, an innate oriented swimming evoked by water currents. We generated a comprehensive light-microscopy cell-resolution projectome of lateralis afferent neurons (LANs) and used clustering techniques for morphological classification. We find surprising structural constancy among LANs. Laser-mediated microlesions indicate that precise topographic mapping of lateral-line receptors is not essential for rheotaxis. Recording neuronal-activity during controlled mechanical stimulation of neuromasts reveals unequal representation of water-flow direction in the hindbrain. We explored potential circuit architectures constrained by anatomical and functional data to suggest a parsimonious model under which the integration of lateralized signals transmitted by direction-selective LANs underlies the encoding of water-flow direction in the brain. These data provide a new framework to understand how animals use local mechanical cues to orient in space.

No Impact of Stochastic Galvanic Vestibular Stimulation on Arterial Pressure and Heart Rate Variability in the Elderly Population

Objective

Noisy galvanic vestibular stimulation (nGVS) is often used to improve postural stability in disorders, such as neurorehabilitation montage. For the safe use of nGVS, we investigated whether arterial pressure (AP) and heart rate vary during static supine and slow whole-body tilt with random nGVS (0.4 mA, 0.1–640 Hz, gaussian distribution) in a healthy elderly population.

Methods

This study was conducted with a double-blind, sham-controlled, cross-over design. Seventeen healthy older adults were recruited. They were asked to maintain a static supine position on a bed for 10 min, and the bed was tilted up (TU) to 70 degrees within 30 s. After maintaining this position for 3 min, the bed was passively tilted down (TD) within 30 s. Real-nGVS or sham-nGVS was applied from 4 to 15 min. The time course of mean arterial pressure (MAP) and RR interval variability (RRIV) were analyzed to estimate the autonomic nervous activity.

Result

nGVS and/or time, including pre-/post-event (nGVS-start, TU, and TD), had no impact on MAP and RRIV-related parameters. Further, there was no evidence supporting the argument that nGVS induces pain, vertigo/dizziness, and uncomfortable feeling.

Conclusion

nGVS may not affect the AP and RRIV during static position and whole-body tilting or cause pain, vertigo/dizziness, and discomfort in the elderly.

The role of delta and theta oscillations during ego-motion in healthy adult volunteers

The successful cortical processing of multisensory input typically requires the integration of data represented in different reference systems to perform many fundamental tasks, such as bipedal locomotion. Animal studies have provided insights into the integration processes performed by the neocortex and have identified region specific tuning curves for different reference frames during ego-motion. Yet, there remains almost no data on this topic in humans.

In this study, an experiment originally performed in animal research with the aim to identify brain regions modulated by the position of the head and eyes relative to a translational ego-motion was adapted for humans. Subjects sitting on a motion platform were accelerated along a translational pathway with either eyes and head aligned or a 20° yaw-plane offset relative to the motion direction while EEG was recorded.

Using a distributed source localization approach, it was found that activity in area PFm, a part of Brodmann area 40, was modulated by the congruency of translational motion direction, eye, and head position. In addition, an asymmetry between the hemispheres in the opercular-insular region was observed during the cortical processing of the vestibular input. A frequency specific analysis revealed that low-frequency oscillations in the delta- and theta-band are modulated by vestibular stimulation. Source-localization estimated that the observed low-frequency oscillations are generated by vestibular core-regions, such as the parieto-opercular region and frontal areas like the mid-orbital gyrus and the medial frontal gyrus.

Stratification of hippocampal electrophysiological activation evoked by selective electrical stimulation of different angular and linear acceleration sensors in the rat peripheral vestibular system

It has become well established that vestibular information is important for hippocampal function and spatial memory. However, as yet, relatively little is known about how different kinds of vestibular information are 'represented' in different parts of the hippocampus. This study used selective electrical stimulation of each of the 5 vestibular sensors (the horizontal (HC), anterior (AC) and posterior (PC) semi-circular canals, and the utricle and saccule) in the rat and recorded local field potentials (LFPs) across the hippocampus, using a 16 electrode microarray. We found that stimulation of any vestibular sensor in the left labyrinth evoked triphasic LFPs in both hippocampi, although it was clear that, in general, the amplitudes were greater for the right, contralateral side. This was particularly true for Phase 1 for the HC, AC, utricle and saccule, Phase 2 for the HC, PC, utricle and saccule, and Phase 3 for the AC, PC and saccule. Overall, our results suggest that vestibular input to the hippocampus is bilateral, preferentially contralateral, but highly stratified in that stimulation of the same vestibular sensor results in activation of different specific areas of the hippocampus, with different LFP amplitudes and latencies. This suggests the possibility that different regions of the hippocampus use different kinds of vestibular information for different purposes and that there may be a high degree of redundancy in the representation of vestibular input, perhaps ensuring that the hippocampus is more robust to the partial loss of vestibular information.

Efficacy of Vestibular Rehabilitation in Patients With Neurologic Disorders: A Systematic Review

OBJECTIVE

The aim of this systematic review is to critically assess the effectiveness of vestibular rehabilitation (VR) administered either alone or in combination with other neurorehabilitation strategies in patients with neurologic disorders.

DATA SOURCES

An electronic search was conducted by 2 independent reviewers in the following databases: MEDLINE (PubMed), the Physiotherapy Evidence Database, and the Cochrane Database of Systematic Reviews.

STUDY SELECTION

All clinical studies carried out on adult patients with a diagnosis of neurologic disorders who performed VR provided alone or in combination with other therapies were included.

DATA EXTRACTION

Screening of titles, abstracts, and full texts and data extraction were undertaken independently by pairs of reviewers. Included studies were quality appraised using a modified version of the Newcastle-Ottawa Scale.

DATA SYNTHESIS

The summary of results was reported following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses. Twelve studies were included in the review. All the included studies, with 1 exception, report that improvements provided by customized VR in subject affected by a central nervous system diseases are greater than traditional rehabilitation programs alone.

CONCLUSIONS

Because of the lack of high-quality studies and heterogeneity of treatments protocols, clinical practice recommendations on the efficacy of VR cannot be made. Results show that VR programs are safe and could easily be implemented with standard neurorehabilitation protocols in patients affected by neurologic disorders. Hence, more high-quality randomized controlled trials of VR in patients with neurologic disorders are needed.

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.

Bilateral vestibulopathy: beyond imbalance and oscillopsia

Objective

To optimize the current diagnostic and treatment procedures for patients with bilateral vestibulopathy (BV), this study aimed to determine the complete spectrum of symptoms associated with BV.

Method

A prospective mixed-method study design was used. Qualitative data were collected by performing semi-structured interviews about symptoms, context, and behavior. The interviews were recorded and transcribed until no new information was obtained. Transcriptions were analyzed in consensus by two independent researchers. In comparison to the qualitative results, quantitative data were collected using the Dizziness Handicap Inventory (DHI), Hospital Anxiety and Depression Scale (HADS) and a health-related quality of life questionnaire (EQ-5D-5L).

Results

Eighteen interviews were transcribed. Reported symptoms were divided into fourteen physical symptoms, four cognitive symptoms, and six emotions. Symptoms increased in many situations, such as darkness (100%), uneven ground (61%), cycling (94%) or driving a car (56%). These symptoms associated with BV often resulted in behavioral changes: activities were performed more slowly, with greater attention, or were avoided. The DHI showed a mean score of severe handicap (54.67). The HADS questionnaire showed on average normal results (anxiety = 7.67, depression = 6.22). The EQ-5D-5L demonstrated a mean index value of 0.680, which is lower compared to the Dutch age-adjusted reference 0.839 (60–70 years).

Conclusion

BV frequently leads to physical, cognitive, and emotional complaints, which often results in a diminished quality of life. Importantly, this wide range of symptoms is currently underrated in literature and should be taken into consideration during the development of candidacy criteria and/or outcome measures for therapeutic interventions such as the vestibular implant.

Electronic supplementary material

The online version of this article (10.1007/s00415-020-10243-5) contains supplementary material, which is available to authorized users.

The Role of Prediagnosis Audiovestibular Dysfunction Versus Distress, Illness-Related Cognitions, and Behaviors in Predicted Ongoing Dizziness Handicap

OBJECTIVE

People with chronic vestibular diseases experience variable degrees of self-perceived disability. However, longitudinal data examining the predictive validity of relevant clinical variables alongside psychological variables are limited. The present study examined whether these factors predict self-reported dizziness handicap 3 months after assessment and diagnosis.

METHODS

Patients were recruited from a waiting list of a tertiary neuro-otology clinic and completed standardized mood, cognitive, behavioral, and dizziness handicap questionnaires before and 3 months after their initial consultation and diagnosis. All patients were clinically assessed and underwent comprehensive audiovestibular investigations.

RESULTS

Seventy-three percent of participants responded at follow-up (n = 135, 73% female, mean [standard deviation] age = 54.23 [17.53] years), of whom 88% were diagnosed with a neurotological condition. There were significant improvements in handicap, depression, and anxiety at 3 months. Thirty (22%) of 135 showed clinically meaningful improvement in handicap. The percentage of case-level depression and anxiety remained the same. Negative illness perceptions and symptom responses reduced, although participants still tended to view their condition negatively. Vestibular tests and type of diagnosis were not associated with self-reported handicap. Most baseline psychological variables significantly correlated with handicap at 3 months. When adjusting for baseline handicap and demographics, the baseline psychological variables only explained a significant ~3% of the variance in dizziness handicap at follow-up, with baseline handicap explaining most of the variance. All-or-nothing behavior was the most significant predictor.

CONCLUSIONS

Tertiary patients with vertigo and dizziness report negative illness perceptions and cognitive and behavioral responses to symptoms that are associated with self-reported handicap over time. Future studies are needed to investigate whether targeting these factors alongside traditional treatment approaches improves handicap in patients with chronic dizziness.

[The adult brain produces new neurons to restore balance after vestibular loss]

Following partial or total loss of peripheral vestibular inputs, a phenomenon called central vestibular compensation takes place in the hours and days following the injury. This neuroplasticity process involves a mosaic of profound rearrangements within the brain stem vestibular nuclei. Among them, the setting of a new neuronal network is maybe the most original and unexpected, as it involves an adult reactive neurogenesis in a brain area not reported as neurogenic so far. Both the survival and functionality of this newly generated neuronal network will depend on its integration to pre-existing networks in the deafferented structure. Far from being aberrant, this new structural organization allows the use of inputs from other sensory modalities (vision and proprioception) to promote the restoration of the posture and equilibrium. We choose here to detail this model, which does not belong to the traditional niches of adult neurogenesis, but it is the best example so far of the reparative role of the adult neurogenesis. Not only it represents an original neuroplasticity mechanism, interesting for basic neuroscience, but it also opens new medical perspectives for the development of therapeutic approaches to alleviate vestibular disorders.

Identification of New Biomarkers of Posturo-Locomotor Instability in a Rodent Model of Vestibular Pathology

The vestibular system plays a crucial role in maintaining postural balance. Unilateral vestibular lesions result in a typical syndrome characterized by postural imbalance, altered locomotor patterns and gaze stabilization, as well as cognitive and neurovegetative disorders. One of the main difficulties encountered in the development of new anti-vertigo drugs is the lack of sensitivity in the evaluation of this syndrome. Qualitative assessments of the vestibular syndrome have been developed, but methods of conducting quantitative evaluations are critically lacking. Recently, assessments with a dynamic weight-bearing device (DWB®, Bioseb) revealed postural alterations in rats subjected to unilateral vestibular neurectomy (UVN). Our team is evaluating a new version of this device capable of quantifying additional parameters of postural and locomotor equilibrium. The objective of this study was to use this device to assess these new posturo-locomotor parameters in a rat model of a vestibular pathology. The biomarkers measured by this device are as follows: the barycenter, the support surface and the weight distribution of the rats when they were moving or stationary. Before UVN, the rats showed a symmetric distribution of their weight along the lateral axis. In the acute phase after UVN on the left side, the rats distributed more weight on the right side than on the left side and then distributed more weight on the left side. These results corroborate those presented in our previous study. The support surface of the rats increased between 1 day and 30 days after UVN, and the barycenter distribution reflected the weight distribution. In addition, our results show smaller changes in the weight distributions when the animals are moving compared with when they are stationary in the acute phase after UVN. This study provides new information on the static and dynamic postural balance patterns observed after unilateral vestibular loss in rats. These data are relevant because they objectively quantify the posturo-locomotor component of vestibular syndrome as well as the compensatory strategies used after vestibular loss. These results may guide the development of rehabilitation protocols for vestibular patients and the validation of pharmacological compounds favoring the restoration of equilibrium.

Modeling Vestibular Compensation: Neural Plasticity Upon Thalamic Lesion

The present study in rats was conducted to identify brain regions affected by the interruption of vestibular transmission and to explore selected aspects of their functional connections. We analyzed, by positron emission tomography (PET), the regional cerebral glucose metabolism (rCGM) of cortical, and subcortical cerebral regions processing vestibular signals after an experimental lesion of the left laterodorsal thalamic nucleus, a relay station for vestibular input en route to the cortical circuitry. PET scans upon galvanic vestibular stimulation (GVS) were conducted in each animal prior to lesion and at post-lesion days (PLD) 1, 3, 7, and 20, and voxel-wise statistical analysis of rCGM at each PLD compared to pre-lesion status were performed. After lesion, augmented metabolic activation by GVS was detected in cerebellum, mainly contralateral, and in contralateral subcortical structures such as superior colliculus, while diminished activation was observed in ipsilateral visual, entorhinal, and somatosensory cortices, indicating compensatory processes in the non-affected sensory systems of the unlesioned side. The changes in rCGM observed after lesion resembled alterations observed in patients suffering from unilateral thalamic infarction and may be interpreted as brain plasticity mechanisms associated with vestibular compensation and substitution. The second set of experiments aimed at the connections between cortical and subcortical vestibular regions and their neurotransmitter systems. Neuronal tracers were injected in regions processing vestibular and somatosensory information. Injections into the anterior cingulate cortex (ACC) or the primary somatosensory cortex (S1) retrogradely labeled neuronal somata in ventral posteromedial (VPM), posterolateral (VPL), ventrolateral (VL), posterior (Po), and laterodorsal nucleus, dorsomedial part (LDDM), locus coeruleus, and contralateral S1 area. Injections into the parafascicular nucleus (PaF), VPM/VPL, or LDDM anterogradely labeled terminal fields in S1, ACC, insular cortex, hippocampal CA1 region, and amygdala. Immunohistochemistry showed tracer-labeled terminal fields contacting cortical neurons expressing the μ-opioid receptor. Antibodies to tyrosine hydroxylase, serotonin, substance P, or neuronal nitric oxide-synthase did not label any of the traced structures. These findings provide evidence for opioidergic transmission in thalamo-cortical transduction.

Vestibular deficits and psychological factors correlating to dizziness handicap and symptom severity

OBJECTIVE

To determine the relative contribution of demographic variables, objective testing and psychological factors in explaining the variance in dizziness severity and handicap.

METHODS

One-hundred and eighty-five consecutive patients on the waiting list to attend a diagnostic appointment in a tertiary neuro-otology clinic with a primary complaint of vertigo or dizziness completed a cross-sectional survey. Primary outcomes were the Dizziness Handicap Inventory and the vertigo subscale of the Vertigo Symptom Scale-Short Form. Psychological questionnaires assessed anxiety and depressive symptoms, illness perceptions, cognitive and behavioural responses to symptoms, beliefs about emotions and psychological vulnerability. Patients also underwent standardised audio-vestibular investigations and tests to reach a diagnosis at appointment.

RESULTS

Objective disease characteristics were not associated with handicap and only the presence of vestibular dysfunction on one test (caloric) was associated with symptom severity. Almost all the psychological factors were correlated with dizziness outcomes. The total hierarchical regression model explained 63% of the variance in dizziness handicap, and 53% was explained by the psychological variables. The regression model for symptom severity explained 36% of the variance, and 30% was explained by the psychological factors. In adjusted models, factors associated with dizziness handicap included age, female gender, distress, symptom focusing, embarrassment, avoidance, and beliefs about negative consequences. Fear avoidance was the only independent correlate in the fully adjusted model of symptom severity.

CONCLUSION

Self-reported dizziness severity and handicap are not correlated with clinical tests of vestibular deficits but are associated with psychological factors including anxiety, depression, illness perceptions, cognitive and behavioural responses.

Sensory Neuromodulation

We describe a model of neurological disease based on dysfunctional brain oscillators. This is not a new model, but it is not one that is widely appreciated by clinicians. The value of this model lies in the predictions it makes and the utility it provides in translational applications, in particular for neuromodulation devices. Specifically, we provide a perspective on devices that provide input to sensory receptors and thus stimulate endogenous sensory networks. Current forms of clinically applied neuromodulation, including devices such as (implanted) deep brain stimulators (DBS) and various, noninvasive methods such as transcranial magnetic stimulation (TMS) and transcranial current methods (tACS, tDCS), have been studied extensively. The potential strength of neuromodulation of a sensory organ is access to the same pathways that natural environmental stimuli use and, importantly, the modulatory signal will be transformed as it travels through the brain, allowing the modulation input to be consistent with regional neuronal dynamics. We present specific examples of devices that rely on sensory neuromodulation and evaluate the translational potential of these approaches. We argue that sensory neuromodulation is well suited to, ideally, repair dysfunctional brain oscillators, thus providing a broad therapeutic approach for neurological diseases.

Galvanic vestibular stimulation: from basic concepts to clinical applications

Galvanic vestibular stimulation (GVS) plays an important role in the quest to understand sensory signal processing in the vestibular system under normal and pathological conditions. It has become a highly relevant tool to probe neuronal computations and to assist in the differentiation and treatment of vestibular syndromes. Following its accidental discovery, GVS became a diagnostic tool that generates eye movements in the absence of head/body motion. With the possibility to record extracellular and intracellular spikes, GVS became an indispensable method to activate or block the discharge in vestibular nerve fibers by cathodal and anodal currents, respectively. Bernie Cohen, in his attempt to decipher vestibular signal processing, has used this method in a number of hallmark studies that have added to our present knowledge, such as the link between selective electrical stimulation of semicircular canal nerves and the generation of directionally corresponding eye movements. His achievements paved the way for other major milestones including the differential recruitment order of vestibular fibers for cathodal and anodal currents, pronounced discharge adaptation of irregularly firing afferents, potential activation of hair cells, and fiber type-specific activation of central circuits. Previous disputes about the structural substrate for GVS are resolved by integrating knowledge of ion channel-related response dynamics of afferents, fiber type-specific innervation patterns, and central convergence and integration of semicircular canal and otolith signals. On the basis of solid knowledge of the methodology, specific waveforms of GVS are currently used in clinical diagnosis and patient treatment, such as vestibular implants and noisy galvanic stimulation.