Structural brain changes following peripheral vestibulo-cochlear lesion may indicate multisensory compensation

Altered Functional Connectivity of the Multisensory Vestibular Cortex in Patients with Chronic Unilateral Vestibulopathy

Background: Chronic unilateral vestibulopathy (CUVP) is a common chronic vestibular syndrome; the mechanisms of central vestibular compensation in CUVP are rarely studied. Methods: This study analyzed the data of 18 patients with CUVP and 18 healthy controls (HCs) and used seed-based functional connectivity (FC) and voxel-mirrored homotopic connectivity (VMHC) analyses to explore the FC alterations. Results: Compared with HCs, patients with CUVP showed decreased FC between the left dorsolateral superior frontal gyrus and the right hippocampus; the left middle frontal gyrus and the right posterior cingulate gyrus, the right hippocampus, the right parahippocampal gyrus. There is also a reduction in FC between the left and right insula. There was enhanced FC between the left supplementary motor area (SMA) and the bilateral superior occipital gyrus, the left hippocampus and the left posterior cingulate gyrus, as well as a the left middle temporal gyrus (p = 0.03). Additionally,VMHC was decreased between the bilateral medial superior frontal gyrus, the bilateral precentral gyrus, and the bilateral postcentral gyrus (p = 0.001). The zVMHC values in the bilateral superior frontal gyrus and the precentral gyrus were both negatively corrected with the Dizziness Handicap Inventory (DHI) score.well as Conclusions: Altered FC in regions of bilateral multisensory vestibular cortex existed in patients with CUVP. Decreased FC and VMHC in the bilateral multisensory vestibular cortex may affect vestibular information integration, thus affecting self-motion perception, spatial orientation, and postural control.

Vestibular dysfunction and its association with cognitive impairment and dementia

The vestibular system plays an important role in maintaining balance and posture. It also contributes to vertical perception, body awareness and spatial navigation. In addition to its sensory function, the vestibular system has direct connections to key areas responsible for higher cognitive functions, such as the prefrontal cortex, insula and hippocampus. Several studies have reported that vestibular dysfunction, in particular bilateral vestibulopathy, is associated with an increased risk of cognitive impairment and the development of dementias such as Alzheimer's disease. However, it is still controversial whether there is a causal relationship between vestibular damage and cognitive dysfunction. In this mini-review, we will explore the relationship between the vestibular system, cognitive dysfunction and dementia, hypotheses about the hypothesis and causes that may explain this phenomenon and also some potential confounders that may also lead to cognitive impairment. We will also review multimodal neuroimaging approaches that have investigated structural and functional effects on the cortico-vestibular network and finally, describe some approaches to the management of patients with vestibular damage who have shown some cognitive impairment.

Altered parietal operculum cortex 2 functional connectivity in benign paroxysmal positional vertigo patients with residual dizziness: A resting-state fMRI study

AIMS

To investigate changes in functional connectivity (FC) focusing on parietal operculum cortex 2 (OP2) in benign paroxysmal positional vertigo (BPPV) patients with residual dizziness (RD) after successful canalith repositioning procedure (CRP).

METHODS

High-resolution three-dimensional T1 and resting-state functional magnetic resonance imaging (fMRI) were performed on 55 healthy controls (HCs), 55 BPPV patients with RD, and 55 patients without RD after successful CRP. Seed-based (bilateral OP2) FC was calculated to investigate the changes in FC among the three groups. Additionally, we further explored the associations between abnormal FC and clinical symptoms.

RESULTS

One-way analysis of covariance showed significant FC differences among the three groups. Post-hoc analysis showed that patients with RD exhibited decreased FC between left OP2 and regions of left angular gyrus (AG), thalamus, precuneus, middle frontal gyrus (MFG), and right cerebellum posterior lobe (CPL) in comparison with HCs. In addition, compared with patients without RD, patients with RD showed decreased FC between left OP2 and regions of left MFG, AG, middle temporal gyrus, and right CPL. Moreover, in patients with RD, the FC between left thalamus and OP2 was negatively correlated with duration of RD, and the FC between left AG and OP2 was negatively correlated with duration of BPPV.

CONCLUSION

BPPV patients with RD showed reduced FC between brain regions involved in vestibular processing and spatial cognition; These results suggested that BPPV patients with RD might have diminished central processing of vestibular information and impaired spatial cognition.

Assessment of functional and structural brain abnormalities with resting-state functional MRI in patients with vestibular neuronitis

BACKGROUND

Vestibular neuritis (VN) is a disorder manifesting as acute, isolated, spontaneous vertigo. There are few comprehensive studies on the changes in related functional and structural brain regions.

PURPOSE

To evaluate alterations in spontaneous neural activity, functional connectivity (FC), and gray matter volume (GMV) in patients with VN.

MATERIAL AND METHODS

A total of 24 patients with VN and 22 age- and sex-matched healthy controls underwent resting-state functional magnetic resonance imaging (rs-fMRI) and three-dimensional T1-weighted anatomical imaging. We calculated the amplitude of low frequency fluctuation (ALFF), regional homogeneity (ReHo), and degree centrality (DC) to discern local brain abnormalities. The most abnormal brain region was selected as the region of interest (ROI) for FC analysis based on ALFF and ReHo values after Bonferroni correction. Voxel-based morphometry (VBM) was used to assess differences in GMV.

RESULTS

Patients with VN, compared to healthy controls, showed increased ALFF (P < 0.001), ReHo values (P = 0.002, <0.001), and DC (P = 0.013) in the left lingual gyrus and right postcentral gyrus. FC analysis demonstrated enhanced connectivity between the left lingual gyrus and the left superior frontal gyrus, and decreased connectivity with the right insula gyrus, right and left supramarginal gyrus (P = 0.012, 0.004, <0.001, 0.014). In addition, GMV was reduced in the bilateral caudate (P = 0.022, 0.014).

CONCLUSIONS

Patients with VN exhibit abnormal spontaneous neural activity and changes in ALFF, ReHo, DC, GMV, and FC. Understanding these functional and structural brain abnormalities may elucidate the underlying mechanisms of VN.

Hippocampal volume in patients with bilateral and unilateral peripheral vestibular dysfunction

Previous studies have found that peripheral vestibular dysfunction is associated with altered volumes in different brain structures, especially in the hippocampus. However, published evidence is conflicting. Based on previous findings, we compared hippocampal volume, as well as supramarginal, superior temporal, and postcentral gyrus in a sample of 55 patients with different conditions of peripheral vestibular dysfunction (bilateral, chronic unilateral, acute unilateral) to 39 age- and sex-matched healthy controls. In addition, we explored deviations in gray-matter volumes in hippocampal subfields. We also analysed correlations between morphometric data and visuo-spatial performance. Patients with vestibular dysfunction did not differ in total hippocampal volume from healthy controls. However, a reduced volume in the right presubiculum of the hippocampus and the left supramarginal gyrus was observed in patients with chronic and acute unilateral vestibular dysfunction, but not in patients with bilateral vestibular dysfunction. No association of altered volumes with visuo-spatial performance was found. An asymmetric vestibular input due to unilateral vestibular dysfunction might lead to reduced central brain volumes that are involved in vestibular processing.

White Matter Hyperintensities (WMH) and clinical outcome after vestibular neuritis

OBJECTIVES

Identification of patients at high risk for chronic dizziness after Vestibular Neuritis (VN) would allow these patients to be the target of focused therapies. However, there is a discrepancy between studies with regard to which factors best predict symptom recovery. The present study provides a comprehensive evaluation of Vestibular Neuritis and the major predictors for the development of chronic vestibular insufficiency.

METHODS

All subjects (n = 54) with acute vestibular neuritis admitted to the Department of Neurology of Beijing Luhe Hospital affiliated to Capital Medical University from 2018 to 2020 were retrospectively identified . Forty-three subjects who received a 4-test battery as well as 3.0T brain MRI, were included in the study. Patients were divided into two groups: Group 1 with complete recovery and Group 2 without recovery, as determined by symptoms 3 months after the VN episode. In addition, we recruited 21 healthy subjects to characterize the profiles of acute VN .

RESULTS

The total WMH score negatively correlated with a clinical recovery (Phi coefficient = -0.808, p value = 0.000). Statistical regression for predicting the outcome of clinical recovery using cerebral white matter changes as an independent variable was significant (p = 0.004). However, clinical recovery was not associated with the nerve divisions (Phi coefficient = 0.108, p = 0.492), age (p = 0.247) and the grade of nystagmus (p = 0.797)   .

CONCLUSIONS

A 4-test battery provides essential information to identify vestibular nerve dysfunction. Cerebral white matter change on MRI was predictive of chronic vestibular insufficiency after vestibular neuritis.

Chronic, Mild Vestibulopathy Leads to Deficits in Spatial Tasks that Rely on Vestibular Input While Leaving Other Cognitive Functions and Brain Volumes Intact

Objectives: In this study, based on the known vestibulo-hippocampal connections, we asked whether mild chronic vestibulopathy leads only to vestibular-related deficits or whether there are effects on hippocampal function, structure, and cognition in general. In more detail, we assessed whether chronic vestibulopathy leads to (a) deficits in vestibular tasks without cognitive demand (balancing), (b) deficits in spatial cognitive tasks that require vestibular input (path integration, rotational memory), (c) deficits in spatial cognitive tasks that do not rely on vestibular input, (d) deficits in general cognitive function, and (e) atrophy in the brain. Methods: A total of 15 patients with chronic uni- or bilateral vestibulopathy (56.8 ± 10.1 years; 4 females) were included in this study and were age- and gender-matched by the control participants (57.6 ± 10.5) in a pairwise manner. Given their clinical symptoms and their deficits of the vestibulo-ocular reflex (VOR) the patients could be classified as being mildly affected. All participants of the underwent the following tests: clinical balance (CBT), triangle completion (TCT) for path integration, rotational memory (RM), the visuo-spatial subset of the Berlin intelligence structure test (BIS-4) and d2-R for attention and concentration, and a structural MRI for gray matter analysis using voxel-based morphometry (VBM). Results: Compared to the healthy controls, the vestibulopathy patients performed significantly worse in terms of CBT, TCT, and RM but showed no differences in terms of the BIS-4 and d2-R. There were also no significant volumetric gray matter differences between the two groups. Conclusions: This study provides evidence that both non-cognitive and cognitive functions that rely on vestibular input (balancing, path integration, rotational memory) are impaired, even in mild chronic vestibulopathy, while other cognitive functions, which rely on visual input (visuo-spatial memory, attention), are unimpaired in this condition, together with an overall intact brain structure. These findings may reflect a segregation between vestibular- and visual-dependent processes in the medial temporal lobe on the one hand and a structure–function dissociation on the other.

The Cognitive-Vestibular Compensation Hypothesis: How Cognitive Impairments Might Be the Cost of Coping With Compensation

Previous research in vestibular cognition has clearly demonstrated a link between the vestibular system and several cognitive and emotional functions. However, the most coherent results supporting this link come from rodent models and healthy human participants artificial stimulation models. Human research with vestibular-damaged patients shows much more variability in the observed results, mostly because of the heterogeneity of vestibular loss (VL), and the interindividual differences in the natural vestibular compensation process. The link between the physiological consequences of VL (such as postural difficulties), and specific cognitive or emotional dysfunction is not clear yet. We suggest that a neuropsychological model, based on Kahneman's Capacity Model of Attention, could contribute to the understanding of the vestibular compensation process, and partially explain the variability of results observed in vestibular-damaged patients. Several findings in the literature support the idea of a limited quantity of cognitive resources that can be allocated to cognitive tasks during the compensation stages. This basic mechanism of attentional limitations may lead to different compensation profiles in patients, with or without cognitive dysfunction, depending on the compensation stage. We suggest several objective and subjective measures to evaluate this cognitive-vestibular compensation hypothesis.

Cortical and subcortical gray matter changes in patients with chronic tinnitus sustaining after vestibular schwannoma surgery

Tinnitus is attributed to partial sensory deafferentation resulting in a central maladaptive neuroplasticity. Unfortunately, the agent of deafferentation is usually unknown or irreversible. In patients with unilateral vestibular schwannoma (VS), however, the auditory nerve is affected by a benign tumor. Hence, removal of the tumor can cease the tinnitus. In turn, sustaining complaints after surgery indicate cortical neuroplasticity. The present study is a cross sectional study which aims to track cortical structural changes by surface-based morphometry in 46 VS patients with sustained (i.e. centralized) or ceased (i.e. peripheral) tinnitus after surgery. A volumetric analysis of cortical and subcortical gray matter (GM) anatomy was performed on preoperative high-resolution MRI and related to the presence of hearing impairment, pre- and/or postoperative tinnitus. Patients with sustained (i.e. chronic) tinnitus showed an increased GM volume of the bilateral caudate nucleus, the contralateral superior colliculus, the middle frontal and middle temporal gyrus, the fusiform gyrus as well as the ipsilateral pars orbitalis when compared to those patients in whom tinnitus ceased postoperatively. Chronic tinnitus in VS patients is associated with characteristic structural changes in frontal, temporal and subcortical areas. Notably, a significant GM change of the caudate nucleus was detected providing further support for the striatal gaiting model of tinnitus.

Altered spontaneous functional activity of the right precuneus and cuneus in patients with persistent postural-perceptual dizziness

Persistent postural-perceptual dizziness (PPPD) is a functional vestibular disorder, and is the most common cause of chronic vestibular syndrome. However, the pathogenesis of PPPD is currently unclear. This study aimed to analyze the changes of brain spontaneous functional activities in PPPD patients during the resting state, and to explore the underlying pathogenesis of PPPD, particularly the abnormal integration of visual and vestibular information. Ten PPPD patients and 10 healthy controls were enrolled from January to June 2018, and baseline data were collected from all subjects. Videonystagmography (VNG), the vestibular caloric test, the video head impulse test (vHIT) and vestibular evoked myogenic potentials (VEMPs) were measured to exclude peripheral vestibular lesions. Functional MRI (fMRI) was conducted in PPPD patients and healthy controls. The amplitude of low frequency fluctuation (ALFF) and regional homogeneity (ReHo), and functional connectivity were calculated to explore changes in brain spontaneous functional activity during the resting state. Compared with healthy controls, ALFF and ReHo values in the right precuneus and cuneus were significantly lower in PPPD patients (both P < 0.05). Further seed-based functional connectivity analysis showed decreased functional connectivity between precuneus, cuneus and left precentral gyrus (P < 0.05). Our findings suggest that the spontaneous functional activity of cuneus and precuneus in PPPD patients were altered, potentially leading to abnormal integration of visual and vestibular information. Weakened functional connectivity between the precuneus and the precentral gyrus may be associated with aggravated symptoms during upright posture, active or passive movements.

Neuroimaging Markers of Mal de Débarquement Syndrome

Mal de débarquement syndrome (MdDS) is a motion-induced disorder of oscillating vertigo that persists after the motion has ceased. The neuroimaging characteristics of the MdDS brain state have been investigated with studies on brain metabolism, structure, functional connectivity, and measurements of synchronicity. Baseline metabolism and resting-state functional connectivity studies indicate that a limbic focus in the left entorhinal cortex and amygdala may be important in the pathology of MdDS, as these structures are hypermetabolic in MdDS and exhibit increased functional connectivity to posterior sensory processing areas and reduced connectivity to the frontal and temporal cortices. Both structures are tunable with periodic stimulation, with neurons in the entorhinal cortex required for spatial navigation, acting as a critical efferent pathway to the hippocampus, and sending and receiving projections from much of the neocortex. Voxel-based morphometry measurements have revealed volume differences between MdDS and healthy controls in hubs of multiple resting-state networks including the default mode, salience, and executive control networks. In particular, volume in the bilateral anterior cingulate cortices decreases and volume in the bilateral inferior frontal gyri/anterior insulas increases with longer duration of illness. Paired with noninvasive neuromodulation interventions, functional neuroimaging with functional magnetic resonance imaging (fMRI), electroencephalography (EEG), and simultaneous fMRI-EEG have shown changes in resting-state functional connectivity that correlate with symptom modulation, particularly in the posterior default mode network. Reduced parieto-occipital connectivity with the entorhinal cortex and reduced long-range fronto-parieto-occipital connectivity correlate with symptom improvement. Though there is a general theme of desynchronization correlating with reduced MdDS symptoms, the prediction of optimal stimulation parameters for noninvasive brain stimulation in individuals with MdDS remains a challenge due to the large parameter space. However, the pairing of functional neuroimaging and noninvasive brain stimulation can serve as a probe into the biological underpinnings of MdDS and iteratively lead to optimal parameter space identification.

Dynamic whole-brain metabolic connectivity during vestibular compensation in the rat

Unilateral damage to the inner ear results in an acute vestibular syndrome, which is compensated within days to weeks due to adaptive cerebral plasticity. This process, called central vestibular compensation (VC), involves a wide range of functional and structural mechanisms at the cellular and network level. The short-term dynamics of whole-brain functional network recruitment and recalibration during VC has not been depicted in vivo. The purpose of this study was to investigate the interplay of separate and distinct brain regions and in vivo networks in the course of VC by sequential [¹⁸F]-FDG-PET-based statistical and graph theoretical analysis with the aim of revealing the metabolic connectome before and 1, 3, 7, and 15 days post unilateral labyrinthectomy (UL) in the rat. Temporal changes in metabolic brain connectivity were determined by Pearson's correlation (|r| > 0.5, p < 0.001) of regional cerebral glucose metabolism (rCGM) in 57 segmented brain regions. Metabolic connectivity analysis was compared to univariate voxel-wise statistical analysis of rCGM over time and to behavioral scores of static and dynamic sensorimotor recovery. Univariate statistical analysis revealed an ipsilesional relative rCGM decrease (compared to baseline) and a contralesional rCGM increase in vestibular and limbic networks and an increase in bilateral cerebellar and sensorimotor networks. Quantitative analysis of the metabolic connections showed a maximal increase from baseline to day 3 post UL (interhemispheric: 2-fold, ipsilesional: 3-fold, contralesional: 12-fold) and a gradual decline until day 15 post UL, which paralleled the dynamics of vestibular symptoms. In graph theoretical analysis, an increase in connectivity occurred especially within brain regions associated with brainstem-cerebellar and thalamocortical vestibular networks and cortical sensorimotor networks. At the symptom peak (day 3 post UL), brain networks were found to be organized in large ensembles of distinct and highly connected hubs of brain regions, which separated again with progressing VC. Thus, we found rapid changes in network organization at the subcortical and cortical level and in both hemispheres, which may indicate an initial functional substitution of vestibular loss and subsequent recalibration and reorganization of sensorimotor networks during VC.

Hyperconnectivity and High Temporal Variability of the Primary Somatosensory Cortex in Low-Back-Related Leg Pain: An fMRI Study of Static and Dynamic Functional Connectivity

Objective

To investigate the functional connectivity (FC) and its variability in the primary somatosensory cortex (S1) of patients with low-back-related leg pain (LBLP) in the context of the persistent stimuli of pain and numbness.

Patients and Methods

We performed functional magnetic resonance imaging on LBLP patients (n = 26) and healthy controls (HCs; n = 34) at rest. We quantified and compared static FC (sFC) using a seed-based analysis strategy, with 6 predefined bilateral paired spherical regions of interest (ROIs) in the S1 cortex. Then, we captured the dynamic FC using sliding window correlation of ROIs in both the LBLP patients and HCs. Furthermore, we performed a correlational analysis between altered static and dynamic FC and clinical measures in LBLP patients.

Results

Compared with controls, the LBLP patients had 1) significantly increased static FC between the left S1_back (the representation of the back in the S1) and right superior and middle frontal gyrus (SFG/MFG), between the left S1_chest and right SFG/MFG, between right S1_chest and right SFG/MFG, between the left S1_face and right MFG, and between the right S1_face and right inferior parietal lobule (P < 0.001, Gaussian random field theory correction); 2) increased dynamic FC only between the right S1_finger and the left precentral and postcentral gyrus and between the right S1_hand and the right precentral and postcentral gyrus (P < 0.01, Gaussian random field theory correction); and 3) a negative correlation between the Barthel index and the increased static FC between the left S1_face and right inferior parietal lobule (P = 0.048).

Conclusion

The present study demonstrated the hyperconnectivity of the S1 cortex to the default mode and executive control network in a spatial pattern and an increase in the tendency for signal variability in the internal network connections of the S1 cortex in patients with LBLP.

Pathophysiological dissociation of the interaction between time pressure and trait anxiety during spatial orientation judgments

Spatial orientation is achieved by integrating visual, vestibular and proprioceptive cues. Individuals that rely strongly upon visual cues to facilitate spatial orientation are termed visually dependent. Heightened visual reliance commonly occurs in patients following vestibular dysfunction and can influence clinical outcome. Additionally, psychological factors, including anxiety, are associated with poorer clinical outcome following vestibular dysfunction. Given that visual dependency measures are affected by psychological and contextual influences, such as time pressure, we investigated the interaction between time pressure and anxiety upon visual dependency in healthy controls and vestibular migraine patients. Visual dependency was assessed using a "Rod and Disk" task at baseline and under time pressure (3 s to complete the task). Non-situational (trait) and situational (state) anxiety levels were quantified using the Spielberg State-Trait Anxiety Inventory. We calculated the change in visual dependency (VD) [∆VD = VD_{time pressure}  - VD_baseline ] and correlated it with participants' trait anxiety scores. We observed a significant negative correlation between trait anxiety and the change in VD (R²  = .393, p < .001) in healthy controls and a positive correlation in dizzy patients (R²  = .317, p < .001). That is, healthy individuals that were more anxious became less visually dependent under time pressure (i.e., more accurate), whereas less anxious individuals became more visually dependent. The reverse was observed in vestibular migraine patients. Our results illustrate that anxiety can differentially modulate task performance during spatial orientation judgements under time pressure in healthy individuals and dizzy patients. These findings have potential implications for individualised patient rehabilitation therapies.

Stress and the vestibular system

In this chapter we review the existing literature regarding the interactions between stress and the mechanisms that maintain balance. Evidence suggests that the interplay between neuro-endocrine and psychological factors may have a significant role in balance function. For example, in healthy individuals vestibular stimulation has been shown to trigger the stress response as indicated by increased blood cortisol levels, whereas in patients with vestibular pathology factors such as resilience and anxiety may be the key focus of interactions with stress. Critically, factors such as anxiety are known to influence clinical outcomes, despite our mechanistic understanding of these processes remaining in their infancy.

Predictors of central vestibular compensation after surgery for vestibular schwannomas

Surgical removal of vestibular schwannoma causes acute vestibular symptoms, including postoperative vertigo which is the most negative factor affecting quality of life in patients after vestibular schwannoma surgery. The main aim of this study is to determine whether the results from routine electronystagmography with pathological visually-provoked responses can predict poor postoperative compensation. We also investigate whether postoperative central compensation is related to objective parameters such age, tumour size, length of surgery and persistent nystagmus. According to the results from preoperative electronystagmography, patients were divided into three groups: peripheral, central and combined vestibular syndrome. Signs of central compensation were evaluated by the presence of postoperative nystagmus, vertigo, deviation of subjective visual vertical and head impulse test. There were no statistically significant differences between groups in observed signs of compensation. These results suggest that pathological central oculomotor parameters are not a negative predictive factor for central vestibular compensation.

Increased brain responsivity to galvanic vestibular stimulation in bilateral vestibular failure

In this event-related functional magnetic resonance imaging (fMRI) study we investigated how the brain of patients with bilateral vestibular failure (BVF) responds to vestibular stimuli. We used imperceptible noisy galvanic vestibular stimulation (GVS) and perceptible bi-mastoidal GVS intensities and related the corresponding brain activity to the evoked motion perception. In contrast to caloric irrigation, GVS stimulates the vestibular organ at its potentially intact afferent nerve site.

Motion perception thresholds and cortical responses were compared between 26 BVF patients to 27 age-matched healthy control participants. To identify the specificity of vestibular cortical responses we used a parametric design with different stimulus intensities (noisy imperceptible, low perceptible, high perceptible) allowing region-specific stimulus response functions. In a 2 × 3 flexible factorial design all GVS-related brain activities were contrasted with a sham condition that did not evoke perceived motion.

Patients had a higher motion perception threshold and rated the vestibular stimuli higher than the healthy participants. There was a stimulus intensity related and region-specific increase of activity with steep stimulus response functions in parietal operculum (e.g. OP2), insula, superior temporal gyrus, early visual cortices (V3) and cerebellum while activity in the hippocampus and intraparietal sulcus did not correlate with vestibular stimulus intensity. Using whole brain analysis, group comparisons revealed increased brain activity in early visual cortices (V3) and superior temporal gyrus of patients but there was no significant interaction, i.e. stimulus-response function in these regions were still similar in both groups. Brain activity in these regions during (high)GVS increased with higher dizziness-related handicap scores but was not related to the degree of vestibular impairment or disease duration. nGVS did not evoke cortical responses in any group.

Our data indicate that perceptible GVS-related cortical responsivity is not diminished but increased in multisensory (visual-vestibular) cortical regions despite bilateral failure of the peripheral vestibular organ. The increased activity in early visual cortices (V3) and superior temporal gyrus of BVF patients has several potential implications: (i) their cortical reciprocal inhibitory visuo-vestibular interaction is dysfunctional, (ii) it may contribute to the visual dependency of BVF patients, and (iii) it needs to be considered when BVF patients receive peripheral vestibular stimulation devices, e.g. vestibular implants or portable GVS devices. Imperceptible nGVS did not elicit cortical brain responses making it unlikely that the reported balance improvement of BVF by nGVS is mediated by cortical mechanisms.

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Responsivity to galvanic vestibular stimuli is increased in the visual and superior temporal Cortex of patients with bilateral vestibulopathy.

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Group differences correlated with clinical scores of disability.

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Dysfunctional visual-vestibular interaction is proposed.

Functional Plasticity after Unilateral Vestibular Midbrain Infarction in Human Positron Emission Tomography

The aim of the study was to uncover mechanisms of central compensation of vestibular function at brainstem, cerebellar, and cortical levels in patients with acute unilateral midbrain infarctions presenting with an acute vestibular tone imbalance. Eight out of 17 patients with unilateral midbrain infarctions were selected on the basis of signs of a vestibular tone imbalance, e.g., graviceptive (tilts of perceived verticality) and oculomotor dysfunction (skew deviation, ocular torsion) in F18-fluordeoxyglucose (FDG)-PET at two time points: A) in the acute stage, and B) after recovery 6 months later. Lesion-behavior mapping analyses with MRI verified the exact structural lesion sites. Group subtraction analyses and comparisons with healthy controls were performed with Statistic Parametric Mapping for the PET data. A comparison of PET A of acute-stage patients with that of healthy controls showed increases in glucose metabolism in the cerebellum, motion-sensitive visual cortex areas, and inferior temporal lobe, but none in vestibular cortex areas. At the supratentorial level bilateral signal decreases dominated in the thalamus, frontal eye fields, and anterior cingulum. These decreases persisted after clinical recovery in contrast to the increases. The transient activations can be attributed to ocular motor and postural recovery (cerebellum) and sensory substitution of vestibular function for motion perception (visual cortex). The persisting deactivation in the thalamic nuclei and frontal eye fields allows alternative functional interpretations of the thalamic nuclei: either a disconnection of ascending sensory input occurs or there is a functional mismatch between expected and actual vestibular activity. Our data support the view that both thalami operate separately for each hemisphere but receive vestibular input from ipsilateral and contralateral midbrain integration centers. Normally they have gatekeeper functions for multisensory input to the cortex and automatic motor output to subserve balance and locomotion, as well as sensorimotor integration.

Probabilistic Fiber-Tracking Reveals Degeneration of the Contralateral Auditory Pathway in Patients with Vestibular Schwannoma

BACKGROUND AND PURPOSE

Vestibular schwannomas cause progressive hearing loss by direct damage to the vestibulocochlear nerve. The cerebral mechanisms of degeneration or plasticity are not well-understood. Therefore, the goal of our study was to show the feasibility of probabilistic fiber-tracking of the auditory pathway in patients with vestibular schwannomas and to compare the ipsi- and contralateral volume and integrity, to test differences between the hemispheres.

MATERIALS AND METHODS

Fifteen patients with vestibular schwannomas were investigated before surgery. Diffusion-weighted imaging (25 directions) was performed on a 3T MR imaging system. Probabilistic tractography was performed for 3 partial sections of the auditory pathway. Volume and fractional anisotropy were determined and compared ipsilaterally and contralaterally. The laterality ratio was correlated with the level of hearing loss.

RESULTS

Anatomically reasonable tracts were depicted in all patients for the acoustic radiation. Volume was significantly decreased on the hemisphere contralateral to the tumor side for the acoustic radiation and diencephalic section, while fractional anisotropy did not differ significantly. Tracking did not yield meaningful tracts in 3 patients for the thalamocortical section and in 5 patients for the diencephalic section. No statistically significant correlations between the laterality quotient and classification of hearing loss were found.

CONCLUSIONS

For the first time, this study showed that different sections of the auditory pathway between the inferior colliculus and the auditory cortex can be visualized by using probabilistic tractography. A significant volume decrease of the auditory pathway on the contralateral hemisphere was observed and may be explained by transsynaptic degeneration of the crossing auditory pathway.

Aspects of cerebral plasticity related to clinical features in acute vestibular neuritis: a "starting point" review from neuroimaging studies

Vestibular neuritis (VN) is one of the most common causes of vertigo and is characterised by a sudden unilateral vestibular failure (UVF). Many neuroimaging studies in the last 10 years have focused on brain changes related to sudden vestibular deafferentation as in VN. However, most of these studies, also due to different possibilities across diverse centres, were based on different times of first acquisition from the onset of VN symptoms, neuroimaging techniques, statistical analysis and correlation with otoneurological and psychological findings. In the present review, the authors aim to merge together the similarities and discrepancies across various investigations that have employed neuroimaging techniques and group analysis with the purpose of better understanding about how the brain changes and what characteristic clinical features may relate to each other in the acute phase of VN. Six studies that strictly met inclusion criteria were analysed to assess cortical-subcortical correlates of acute clinical features related to VN. The present review clearly reveals that sudden UVF may induce a wide variety of cortical and subcortical responses - with changes in different sensory modules - as a result of acute plasticity in the central nervous system.

Vestibular compensation: the neuro-otologist's best friend

Why vestibular compensation (VC) after an acute unilateral vestibular loss is the neuro-otologist’s best friend is the question at the heart of this paper. The different plasticity mechanisms underlying VC are first reviewed, and the authors present thereafter the dual concept of vestibulo-centric versus distributed learning processes to explain the compensation of deficits resulting from the static versus dynamic vestibular imbalance. The main challenges for the plastic events occurring in the vestibular nuclei (VN) during a post-lesion critical period are neural protection, structural reorganization and rebalance of VN activity on both sides. Data from animal models show that modulation of the ipsilesional VN activity by the contralateral drive substitutes for the normal push–pull mechanism. On the other hand, sensory and behavioural substitutions are the main mechanisms implicated in the recovery of the dynamic functions. These newly elaborated sensorimotor reorganizations are vicarious idiosyncratic strategies implicating the VN and multisensory brain regions. Imaging studies in unilateral vestibular loss patients show the implication of a large neuronal network (VN, commissural pathways, vestibulo-cerebellum, thalamus, temporoparietal cortex, hippocampus, somatosensory and visual cortical areas). Changes in gray matter volume in these multisensory brain regions are structural changes supporting the sensory substitution mechanisms of VC. Finally, the authors summarize the two ways to improve VC in humans (neuropharmacology and vestibular rehabilitation therapy), and they conclude that VC would follow a “top-down” strategy in patients with acute vestibular lesions. Future challenges to understand VC are proposed.

Hippocampal gray matter volume in bilateral vestibular failure

Bilateral vestibular failure (BVF) is a severe chronic disorder of the labyrinth or the eighth cranial nerve characterized by unsteadiness of gait and disabling oscillopsia during head movements. According to animal data, vestibular input to the hippocampus is proposed to contribute to spatial memory and spatial navigation. Except for one seminal study showing the association of impaired spatial navigation and hippocampal atrophy, patient data in BVF are lacking. Therefore, we performed a voxel-wise comparison of the hippocampal gray matter volume (GMV) in a clinically representative sample of 27 patients with incomplete BVF and 29 age- and gender-matched healthy controls to test the hypothesis of hippocampal atrophy in BVF. Although the two groups did not generally differ in their hippocampal GMV, a reduction of GMV in the bilateral hippocampal CA3 region was significantly correlated with increased vestibulopathy-related clinical impairment. We propose that GMV reduction in the hippocampus of BVF patients is related to the severity of vestibular-induced disability which is in line with combined hippocampal atrophy and disorders of spatial navigation in complete vestibular deafferentation due to bilateral nerve section. Clinically, however, the most frequent etiologies of BVF cause incomplete lesions. Accordingly, hippocampus atrophy and deficits in spatial navigation occur possibly less frequently than previously suspected. Hum Brain Mapp 37:1998-2006, 2016. © 2016 Wiley Periodicals, Inc.

Voxel Based Morphometry Alterations in Mal de Debarquement Syndrome

Background

Mal de debarquement syndrome (MdDS) is a disorder of chronic self-motion perception that occurs though entrainment to rhythmic background motion, such as from sea voyage, and involves the perception of low-frequency rocking that can last for months or years. The neural basis of this persistent sensory perception abnormality is not well understood.

Methods

We investigated grey matter volume differences underlying persistent MdDS by performing voxel-based morphometry on whole brain and pre-specified ROIs in 28 individuals with MdDS and comparing them to 18 age, sex, and handedness matched controls.

Results

MdDS participants exhibited greater grey matter volume in the left inferior parietal lobule, right inferior occipital gyrus (area V3v), right temporal pole, bilateral cerebellar hemispheric lobules VIII/IX and left lobule VIIa/VIIb. Grey matter volumes were lower in bilateral inferior frontal, orbitofrontal, pregenual anterior cingulate cortex (pgACC) and left superior medial gyri (t = 3.0, p<0.005_uncorr). In ROI analyses, there were no volume differences in the middle occipital gyrus (region of V5/MT) or parietal operculum 2 (region of the parietoinsular vestibular cortex). Illness duration was positively related to grey matter volume in bilateral inferior frontal gyrus/anterior insula (IFG/AI), right posterior insula, superior parietal lobule, left middle occipital gyrus (V5/MT), bilateral postcentral gyrus, anterior cerebellum, and left cerebellar hemisphere and vermian lobule IX. In contrast, illness duration was negatively related to volume in pgACC, posterior middle cingulate gyrus (MCC), left middle frontal gyrus (dorsolateral prefrontal cortex-DLPFC), and right cerebellar hemispheric lobule VIIIb (t = 3.0, p<0.005_uncorr). The most significant differences were decreased volume in the pgACC and increased volume in the left IFG/AI with longer illness duration (qFDR_corr <0.05). Concurrent medication use did not correlate with these findings or have a relationship with duration of illness. MdDS participants showed positive correlations between grey matter volume in pgACC and bilateral cerebellar lobules VIII/IX, which was not seen in controls.

Conclusions

Individuals with MdDS show brain volume differences from healthy controls as well as duration of illness dependent volume changes in (a) visual-vestibular processing areas (IPL, SPL, V3, V5/MT), (b) default mode network structures (cerebellar IX, IPL, ACC), (c) salience network structures (ACC and IFG/AI) (d) somatosensory network structures (postcentral gyrus, MCC, anterior cerebellum, cerebellar lobule VIII), and (e) a structure within the central executive network (DLPFC). The identification of these associations may enhance future investigations into how exposure to oscillating environments can modulate brain function and affect motion perception as well cognitive and affective control.

Magnetic resonance spectroscopy features of Heschl's gyri in patients with unilateral acoustic neuroma: preliminary study

RATIONALE AND OBJECTIVES

To evaluate neurochemical alterations in Heschl's gyri and determine the most affected side in case of unilateral acoustic neuroma using magnetic resonance spectroscopy (MRS).

MATERIALS AND METHODS

Fifteen patients with unilateral acoustic neuroma were studied. Following routine cranial MRI sequences, MRS of Heschl's gyri on tumor and nontumor sides was obtained. MRS metabolite values of both Heschl's gyri were statistically compared.

RESULTS

The values of N-acetylaspartate (NAA) and Cr on nontumor side Heschl's gyrus (HG) were significantly lower than that on tumor side.

CONCLUSIONS

We found nontumor side HG more affected with lower NAA and Cr values, suggesting neuronal damage and decreased energy metabolism compared to the tumoral side.

Visual dependency and dizziness after vestibular neuritis

Symptomatic recovery after acute vestibular neuritis (VN) is variable, with around 50% of patients reporting long term vestibular symptoms; hence, it is essential to identify factors related to poor clinical outcome. Here we investigated whether excessive reliance on visual input for spatial orientation (visual dependence) was associated with long term vestibular symptoms following acute VN. Twenty-eight patients with VN and 25 normal control subjects were included. Patients were enrolled at least 6 months after acute illness. Recovery status was not a criterion for study entry, allowing recruitment of patients with a full range of persistent symptoms. We measured visual dependence with a laptop-based Rod-and-Disk Test and severity of symptoms with the Dizziness Handicap Inventory (DHI). The third of patients showing the worst clinical outcomes (mean DHI score 36-80) had significantly greater visual dependence than normal subjects (6.35° error vs. 3.39° respectively, p = 0.03). Asymptomatic patients and those with minor residual symptoms did not differ from controls. Visual dependence was associated with high levels of persistent vestibular symptoms after acute VN. Over-reliance on visual information for spatial orientation is one characteristic of poorly recovered vestibular neuritis patients. The finding may be clinically useful given that visual dependence may be modified through rehabilitation desensitization techniques.

Central vestibular system modulation in vestibular migraine

Background

Vestibular migraine affects 1% of the general population, and 30%–50% of all migraine patients describe occasionally associated vertigo or dizziness. We aimed to identify brain regions altered in vestibular migraine in order to evaluate the connection between migraine and the vestibular system.

Methods

Seventeen patients with definite vestibular migraine were compared to 17 controls using magnetic resonance imaging-based voxel-based morphometry.

Results

We found grey matter (GM) volume reduction in the superior, inferior and middle (MT/V5) temporal gyrus as well as in the mid. cingulate, dorsolateral prefontal, insula, parietal and occipital cortex. A negative correlation of disease duration and GM volume was observed in areas associated with pain and vestibular processing. Moreover, there was a negative correlation between headache severity and prefrontal cortex volume.

Conclusion

Alterations identified in vestibular migraine resemble those previously described for migraine, but also extend to areas involved in multisensory vestibular control and central vestibular compensation possibly representing the pathoanatomic connection between migraine and the vestibular system.

Altered resting-state functional connectivity in patients with chronic bilateral vestibular failure

Patients with bilateral vestibular failure (BVF) suffer from gait unsteadiness, oscillopsia and impaired spatial orientation. Brain imaging studies applying caloric irrigation to patients with BVF have shown altered neural activity of cortical visual-vestibular interaction: decreased bilateral neural activity in the posterior insula and parietal operculum and decreased deactivations in the visual cortex. It is unknown how this affects functional connectivity in the resting brain and how changes in connectivity are related to vestibular impairment. We applied a novel data driven approach based on graph theory to investigate altered whole-brain resting-state functional connectivity in BVF patients (n= 22) compared to age- and gender-matched healthy controls (n= 25) using resting-state fMRI. Changes in functional connectivity were related to subjective (vestibular scores) and objective functional parameters of vestibular impairment, specifically, the adaptive changes during active (self-guided) and passive (investigator driven) head impulse test (HIT) which reflects the integrity of the vestibulo-ocular reflex (VOR). BVF patients showed lower bilateral connectivity in the posterior insula and parietal operculum but higher connectivity in the posterior cerebellum compared to controls. Seed-based analysis revealed stronger connectivity from the right posterior insula to the precuneus, anterior insula, anterior cingulate cortex and the middle frontal gyrus. Excitingly, functional connectivity in the supramarginal gyrus (SMG) of the inferior parietal lobe and posterior cerebellum correlated with the increase of VOR gain during active as compared to passive HIT, i.e., the larger the adaptive VOR changes the larger was the increase in regional functional connectivity. Using whole brain resting-state connectivity analysis in BVF patients we show that enduring bilateral deficient or missing vestibular input leads to changes in resting-state connectivity of the brain. These changes in the resting brain are robust and task-independent as they were found in the absence of sensory stimulation and without a region-related a priori hypothesis. Therefore they may indicate a fundamental disease-related change in the resting brain. They may account for the patients' persistent deficits in visuo-spatial attention, spatial orientation and unsteadiness. The relation of increasing connectivity in the inferior parietal lobe, specifically SMG, to improvement of VOR during active head movements reflects cortical plasticity in BVF and may play a clinical role in vestibular rehabilitation.

Visual and proprioceptive interaction in patients with bilateral vestibular loss

Following bilateral vestibular loss (BVL) patients gradually adapt to the loss of vestibular input and rely more on other sensory inputs. Here we examine changes in the way proprioceptive and visual inputs interact. We used functional magnetic resonance imaging (fMRI) to investigate visual responses in the context of varying levels of proprioceptive input in 12 BVL subjects and 15 normal controls. A novel metal-free vibrator was developed to allow vibrotactile neck proprioceptive input to be delivered in the MRI system. A high level (100 Hz) and low level (30 Hz) control stimulus was applied over the left splenius capitis; only the high frequency stimulus generates a significant proprioceptive stimulus. The neck stimulus was applied in combination with static and moving (optokinetic) visual stimuli, in a factorial fMRI experimental design. We found that high level neck proprioceptive input had more cortical effect on brain activity in the BVL patients. This included a reduction in visual motion responses during high levels of proprioceptive input and differential activation in the midline cerebellum. In early visual cortical areas, the effect of high proprioceptive input was present for both visual conditions but in lateral visual areas, including V5/MT, the effect was only seen in the context of visual motion stimulation. The finding of a cortical visuo-proprioceptive interaction in BVL patients is consistent with behavioural data indicating that, in BVL patients, neck afferents partly replace vestibular input during the CNS-mediated compensatory process. An fMRI cervico-visual interaction may thus substitute the known visuo-vestibular interaction reported in normal subject fMRI studies. The results provide evidence for a cortical mechanism of adaptation to vestibular failure, in the form of an enhanced proprioceptive influence on visual processing. The results may provide the basis for a cortical mechanism involved in proprioceptive substitution of vestibular function in BVL patients.

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A novel air turbine vibrotactile device for the MRI environment is developed.

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Neck proprioception and visual motion are applied in a factorial fMRI experiment.

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A cervico-visual fMRI interaction is shown in bilateral vestibular loss patients (BVL).

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This cervico-visual interaction in BVL mimics the normal visuo-vestibular interaction.

Changes in resting-state fMRI in vestibular neuritis

Vestibular neuritis (VN) is a sudden peripheral unilateral vestibular failure with often persistent head movement-related dizziness and unsteadiness. Compensation of asymmetrical activity in the primary peripheral vestibular afferents is accomplished by restoration of impaired brainstem vestibulo-ocular and vestibulo-spinal reflexes, but presumably also by changing cortical vestibular tone imbalance subserving, e.g., spatial perception and orientation. The aim of this study was to elucidate (i) whether there are changes of cerebral resting-state networks with respect to functional interregional connectivity (resting-state activity) in VN patients and (ii) whether these are related to neurophysiological, perceptual and functional parameters of vestibular-induced disability. Using independent component analysis (ICA), we compared resting-state networks between 20 patients with unilateral VN and 20 age- and gender-matched healthy control subjects. Patients were examined in the acute VN stage and after 3 months. A neural network (component 50) comprising the parietal lobe, medial aspect of the superior parietal lobule, posterior cingulate cortex, middle frontal gyrus, middle temporal gyrus, parahippocampal gyrus, anterior cingulate cortex, insular cortex, caudate nucleus, thalamus and midbrain was modulated between acute VN patients and healthy controls and in patients over time. Within this network, acute VN patients showed decreased resting-state activity (ICA) in the contralateral intraparietal sulcus (IPS), in close vicinity to the supramarginal gyrus (SMG), which increased after 3 months. Resting-state activity in IPS tended to increase over 3 months in VN patients who improved with respect to functional parameters of vestibular-induced disability (VADL). Resting-state activity in the IPS was not related to perceptual (subjective visual vertical) or neurophysiological parameters of vestibular-induced disability (e.g., gain of vestibulo-ocular reflex, caloric responsiveness, postural sway). VN leads to a change in resting-state activity of the contralateral IPS adjacent to the SMG, which reverses during vestibular compensation over 3 months. The ventral intraparietal area in the IPS contains multimodal regions with directionally selective responses to vestibular stimuli making them suitable for participating in spatial orientation and multisensory integration. The clinical importance is indicated by the fact that the increase in resting-state activity tended to be larger in those patients with only little disability at the follow-up examination. This may indicate powerful restitution-related or compensatory cortical changes in resting-state activity.

Depersonalization experiences are strongly associated with dizziness and vertigo symptoms leading to increased health care consumption in the German general population

This study investigated the association of depersonalization (DP) experiences with dizziness and its impact on subjective impairment and health care use. Trained interviewers surveyed a representative sample of 1287 persons using standardized self-rating questionnaires on dizziness, DP, and mental distress. Symptoms of dizziness were reported by 15.8% (n = 201). Thereof, 62.7% endorsed at least one symptom of DP, 40% reported impairment by symptoms of DP, and 8.5% reported clinically significant DP. Regression analyses identified DP as a significant, independent predictor for dizziness symptom severity, health care use, and impairment by dizziness. With regard to the Vertigo Symptom Scale, DP explained 34.1% (p < 0.001) of the variance for severity of symptoms of dysfunction in the balance system. In conclusion, symptoms of DP, highly prevalent in patients complaining of dizziness and vertigo, were independently associated with increased impairment and health care use. The presence of DP symptoms should actively be explored in patients complaining of dizziness.

Pure-tone auditory thresholds are not chronically elevated in multiple sclerosis

Despite the fact that acute cases of multiple sclerosis (MS)-related pure-tone hearing loss have been reported in the literature, consensus is lacking as to the chronic influences of MS on pure-tone thresholds. Most studies examining such influences have been limited by small sample sizes, lack of statistical comparisons between patients and controls, and confounding of the hearing measure with influences from sex and age. To date, associations between pure-tone thresholds and central MS-related brain lesions have not been assessed. In this study, pure-tone thresholds ranging from 0.5 to 8 kHz were measured in 73 MS patients and 73 individually age- and gender-matched normal controls. In 63 MS patients, correlations were computed between the threshold values and MRI-determined lesion activity in 26 central brain regions. Although thresholds were strongly influenced by sex, age, and tonal frequency, no meaningful influences of MS were discerned. Moreover, no significant association between the threshold values and central MS-related lesion activity was evident in any brain region evaluated. This study, the largest on this topic to use carefully matched control subjects and the sole study to assess relationships between auditory thresholds and central MS-related lesions, strongly suggests that (a) MS is not chronically associated with pure-tone hearing loss and (b) pure-tone thresholds are unrelated to MS lesion activity in higher brain regions. These findings, along with general reports from the literature, support the concept that when MS-related hearing threshold deficits are found, they are episodic and primarily dependent on lesions within the eighth nerve or brainstem.

Mutational ataxia resulting from abnormal vestibular acquisition and processing is partially compensated for

Due to the multisensory input into the balance system, the loss of one input, such as an ear, can generally be compensated for. However, when a mismatch or incomplete loss of inputs occurs, the ability to compensate for the stimulus misrepresentation may be compromised. The inner ear and cerebellum are important input and processing centers for balance but no genetic models have been generated to assess balance or compensation in the abnormal development of both these organs/brain areas. Important to their formation is regulation of proliferation mediated by the proto-oncogene N-Myc. Conditional knockouts (CKOs) of N-Myc using Tg(Pax2-Cre) have a misshapen and smaller ear with a fused utricle, saccule, and cochlea and absent horizontal canal, aberrant cochlear and vestibular innervations, and a size reduction in the cerebellum. CKOs are viable with obvious behavioral deficits, including circling behavior and unstable gait. To test the degree of ataxia and possible compensation of vestibular defects in these mutant mice, we use the Noldus Catwalk System to assess the gait of Tg(Pax2-Cre) N-Myc CKOs over five months. N-Myc CKOs perform worse than control littermates, in particular, in step regularity. We show that disrupting one member of the Myc family during embryonic development coincides with a differential loss of function in the cochlea compared to the vestibular apparatus. In addition, we show that the distortion in the ear morphology combined with a reduction of the cerebellum, rather than a complete loss of the vestibular-cerebellar pathway, leads to partial behavioral compensation that remains unchanged over time.