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The study aims to develop a novel methodology to demonstrate the vestibulo-ocular reflex (VOR) and nystagmus by caloric stimulation in an undergraduate medical physiology laboratory. The experimental setup involved two sets of electrodes: one set positioned laterally to both eyes, and another set positioned vertically over either the right or left eye. The caloric method is used to stimulate ears, which involves irrigation of warm (44°C) and cold (30°C) water into the ears while maintaining a temperature difference of approximately ±7°C from the body temperature. The changes in chorioretinal potential were calibrated to angular displacement by a two-point calibration method, and angular velocity was derived after taking the first-time derivative. The results obtained from the digital data acquisition system were compared to the traditional instrument used in our Otorhinolaryngology Department [Interacoustics Videonystagmography (VNG) System for hospitals, medical grade] for the normal subject's data. No significant differences in angular velocity were noted (P > 0.05). The cold stimuli elicit a more pronounced VOR compared to the warm stimuli. It has been consistently observed that the onset of nystagmus occurs approximately 20 s after irrigation, reaching its peak intensity between 45 and 90 s, and gradually diminishing until it ceases after approximately 200 s. Our developed methodology enables the recording and quantification of nystagmus using easily accessible equipment. This study serves the goal of visualizing the physiological process of VOR and thereby fulfills the goal of an effective teaching tool for demonstrating to undergraduate medical students. NEW & NOTEWORTHY: We developed a novel methodology to demonstrate and visualize the most common and important physiological phenomenon like the vestibulo-ocular reflex as a teaching module for undergraduate students. [ABSTRACT FROM AUTHOR]

To evaluate pre- and post-operative semicircular canal function in patients with vestibular schwannoma (VS) by the video Head Impulse Test (vHIT). Nineteen patients with VS who underwent surgery were enrolled in this study. The gain in vestibulo-ocular reflex (VOR) and the degree of scatter in catch-up saccades were examined pre- and post-operatively for the semicircular canals in VS patients. Ten of 19 cases (52.6 %) with VS were defined as demonstrating both superior vestibular nerve (SVN) and inferior vestibular nerve (IVN) impairment from the results of pre-operative vHIT. Hearing level and subjective vestibular symptoms showed significant correlations with pre-operative semicircular canal function. Compared to pre-operative vHIT results, VOR gains within 1 month after surgery were significantly reduced in all three canals; however, significant differences had disappeared in the anterior and posterior semicircular canals at 6 months after surgery. Cases of unknown origin had a significantly greater reduction in posterior semicircular canal function after surgery compared with those with disease of IVN origin. As vHIT could evaluate pre-operative vestibular nerve impairment, post-operative VOR gain reduction and the degree of vestibular compensation, semicircular canal function evaluated by vHIT provides a good deal of useful information regarding VS patients undergoing surgery compared to caloric testing, and vHIT should be performed pre- and post-operatively for patients with VS. [ABSTRACT FROM AUTHOR]

Ocular torsion and vertical divergence reflect the brain's sensorimotor integration of motion through the vestibulo-ocular reflex (VOR) and the optokinetic reflex (OKR) to roll rotations. Torsion and vergence however express different response patterns depending on several motion variables, but research on their temporal dynamics remains limited. This study investigated the onset times of ocular torsion (OT) and vertical vergence (VV) during visual, vestibular, and visuovestibular motion, as well as their relative decay rates following prolonged optokinetic stimulations. Temporal characteristics were retrieved from three separate investigations where the level of visual clutter and acceleration were controlled. Video eye-tracking was used to retrieve the eye-movement parameters from a total of 41 healthy participants across all trials. Ocular torsion consistently initiated earlier than vertical vergence, particularly evident under intensified visual information density, and higher clutter levels were associated with more balanced decay rates. Additionally, stimulation modality and accelerations affected the onsets of both eye movements, with visuovestibular motion triggering earlier responses compared to vestibular motion, and increased accelerations leading to earlier onsets for both movements. The present study showed that joint visuovestibular responses produced more rapid onsets, indicating a synergetic sensorimotor process. It also showed that visual content acted as a fusional force during the decay period, and imposed greater influence over the torsional onset compared to vergence. Acceleration, by contrast, did not affect the temporal relationship between the two eye movements. Altogether, these findings provide insights into the sensorimotor integration of the vestibulo-ocular and optokinetic reflex arcs. [ABSTRACT FROM AUTHOR]

Monocular torsional eye oscillations are a rare form of disconjugate nystagmus and the underlying pathophysiology is not well understood. Here, we present and discuss a case with disabling torsional oscillopsia in one eye only. The patient exhibited (i) spontaneous pendular torsional nystagmus of the left eye and (ii) rhythmic involuntary movements of the soft palate and uvula, consistent with the syndrome of oculopalatal tremor with monocular nystagmus. Brain MRI revealed an infarct of the left dentate nucleus in the cerebellum and, more caudally, a secondary hypertrophic degeneration of the right inferior olivary nucleus. To account for the presence of torsional nystagmus on the eye contralateral to the side of inferior olivary hypertrophy and ipsilateral to the lesioned dentate nucleus, we discuss the hypothesis of a (inferior olivary nucleus-mediated) malfunctioning adaptation of the anterior canal vestibulo-ocular reflex. [ABSTRACT FROM AUTHOR]

Oculomotor deficits are common in hereditary ataxia, but disproportionally neglected in clinical ataxia scales and as outcome measures for interventional trials. Quantitative assessment of oculomotor function has become increasingly available and thus applicable in multicenter trials and offers the opportunity to capture severity and progression of oculomotor impairment in a sensitive and reliable manner. In this consensus paper of the Ataxia Global Initiative Working Group On Digital Oculomotor Biomarkers, based on a systematic literature review, we propose harmonized methodology and measurement parameters for the quantitative assessment of oculomotor function in natural-history studies and clinical trials in hereditary ataxia. MEDLINE was searched for articles reporting on oculomotor/vestibular properties in ataxia patients and a study-tailored quality-assessment was performed. One-hundred-and-seventeen articles reporting on subjects with genetically confirmed (n=1134) or suspected hereditary ataxia (n=198), and degenerative ataxias with sporadic presentation (n=480) were included and subject to data extraction. Based on robust discrimination from controls, correlation with disease-severity, sensitivity to change, and feasibility in international multicenter settings as prerequisite for clinical trials, we prioritize a core-set of five eye-movement types: (i) pursuit eye movements, (ii) saccadic eye movements, (iii) fixation, (iv) eccentric gaze holding, and (v) rotational vestibulo-ocular reflex. We provide detailed guidelines for their acquisition, and recommendations on the quantitative parameters to extract. Limitations include low study quality, heterogeneity in patient populations, and lack of longitudinal studies. Standardization of quantitative oculomotor assessments will facilitate their implementation, interpretation, and validation in clinical trials, and ultimately advance our understanding of the evolution of oculomotor network dysfunction in hereditary ataxias. [ABSTRACT FROM AUTHOR]

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

Background: Our primary objective was to monitor nonprogressive unilateral vestibular schwannomas (VSs) to assess the efficiency of rapid bedside examinations, such as the video head impulse test (vHIT) and skull vibration-induced nystagmus test (SVINT), in identifying vestibular damage. Methods: An observational study was conducted from March 2021 to March 2022 on all adult patients (>18 years old) with a confirmed nonprogressive VS (no active treatment). The SVINT (using a 100 Hz vibrator with two (SVINT2) or three (SVINT3) stimulation locations) and vHIT (for the six semicircular canals (SCCs)) were performed on all patients. The asymmetry of function between the vestibules was considered significant when the gain asymmetry was greater than 0.1. Rapid and repeatable assessment of VSs using two- and three-stimulation SVINT plus vHIT was performed to quantify intervestibular asymmetry. Results: SVINT3 and SVINT2 triggered VIN in 40% (24/60) and 65% (39/60) of patients, respectively. There was significant asymmetry in the vestibulo-ocular reflex (VOR), as shown by a VS-side gain < healthy-side gain in 58% (35/60) of the patients. Among the patients with significant gain asymmetry between the two vestibules according to the vHIT (VS-side gain < healthy-side gain), the proportion of patients expressing vestibular symptomatology was significantly greater than that of patients without any symptoms [67% (29/43) vs. 35% (6/17), respectively; p = 0.047]. Conclusions: The SVINT2 can be combined with the vHIT to form an interesting screening tool for revealing vestibular asymmetry. This work revealed the superiority of mastoid stimulation over vertex stimulation for SVINT in patients with unilateral vestibular loss. [ABSTRACT FROM AUTHOR]

We propose a new interface concept; Proprioceptive Menu with Tactons, an eyes- and ears-free menu in a proprioceptive space that uses a set of Tactons to describe its menu items. While previous proprioceptive menus utilized vibrotactile feedback only to express the boundary between menu items, we spot an unexplored possibility that distinct vibrotactile stimuli, Tactons, can be used to describe the status of each menu item. As an instance of this concept, we present WristMenu with Tactons, an eyes- and ears-free menu using a one-dimensional proprioceptive space of the axial wrist rotation. Users can grasp an overview of each menu item's status through Tactons delivered on their wrist skin and eventually decide to select the desired item. Our evaluation study showed that users could find a target item among five candidates and recognize its status in 5 seconds on average at the accuracies of 93% and 86% in seated and walking conditions, respectively. Through our evaluation, we could confirm the feasibility of the proposed concept. [ABSTRACT FROM AUTHOR]

Animal models are instrumental to understanding the mechanisms underlying autism spectrum disorder, yet translating human behavioral phenotypes remains challenging. Wang et al. leverage a conserved sensorimotor reflex to elucidate synaptic deficits in S cn2a haploinsufficiency and pilot novel rescue strategies. [ABSTRACT FROM AUTHOR]

PP2B-Dependent Cerebellar Plasticity Sets the Amplitude of the Vestibulo-ocular Reflex during Juvenile Development [ABSTRACT FROM AUTHOR]

Introduction: Acute unilateral vestibulopathy (AUVP) is defined as an acute peripheral vestibular syndrome without evidence of central neurological or audiological symptoms. Currently, there is no uniform instrumental testing protocol for the diagnosis and follow-up of patients with AUVP. Vestibular tests provide information in different frequency bands of the vestibuloocular reflex (VOR); therefore, the aim of our study is to evaluate the contribution of multifrequency VOR testing in the evaluation of patients with AUVP. Methods: 22 patients (9 females and 13 males) with a diagnosis of AUVP were prospectively examined. Multifrequency testing included spontaneous nystagmus with visual fixation cancellation (SPN), Head Shaking Test (HST), bithermal air caloric test, and video Head Impulse Test (vHIT). The first examination was performed within one week of AUVP; follow-up examinations were performed 3 and 6 months apart. On the third examination, the Dizziness handicap inventory (DHI) questionnaire was completed. Results: The rate of the slow component of spontaneous and induced nystagmus during HST and the values of unilateral weakness (UW) during caloric testing decreased during follow-up with a statistically significant difference (P <0.05) between both the first and second and between the second and third examinations. On vHIT, there was a statistically significant increase in the gains of individual channels during follow-up. Dissociation of vHIT and caloric test results was found in 22.73% of patients on the second and 18.18% of patients on the third examination. There was a statistically significant difference in the changes in test results of patients with different DHI. Conclusion: Multifrequency VOR testing provides a comprehensive overview of the status of vestibular function, recovery dynamics, and clinical impact of residual vestibular dysfunction after AUVP. [ABSTRACT FROM AUTHOR]

The aim was to evaluate the vestibular system of children who had undergone cochlear implant surgery and to compare them with the healthy population by vestibulo-ocular reflex (VOR) gains in unilateral and bilateral implant users, with the implants both on and off. Patients older than 5 years who had undergone cochlear implant surgery between 2012 and 2020 and who were cochlear implant users for at least one year were included. After consent was obtained, a video head impulse test (VHIT) was performed to evaluate the three semicircular canals, with devices on and off, and VOR gains were evaluated. VHIT was also used to assess VOR gains in the control group. The VOR gains of the study and control groups, VOR gains of unilateral and bilateral implant users, and VOR gains with implants on and off were compared. When the VOR gains of 24 unilateral and 13 bilateral cochlear implant users and the control group (n = 30) were compared, a significant difference was found only in the anterior semicircular canal, although the VOR gains were found to be low in all three semicircular canals in the implant users (p < 0.05). There was no significant difference between the VOR gains of unilateral and bilateral implant users. There was no significant difference between the VOR gains when either on or off. There was no correlation between cochlear implant usage time, implant insertion age, patient age and VOR gain. The effects of cochlear implant surgery on the vestibular system continue in the late period, but no correlation was observed between implant usage time and VOR gain after the first year. It was observed that having the cochlear implant on or off had no effect on VOR gain. Furthermore, bilateral implant surgery did not lead to additional vestibular dysfunction compared to unilateral implant surgery. [ABSTRACT FROM AUTHOR]

After unilateral peripheral vestibular lesions, the neural activity of neurons in the ipsi-lesional medial vestibular nucleus (ipsi-MVe) are markedly decreased, resulting in static and dynamic asymmetries of the vestibulo-ocular and vestibulo-spinal reflexes. Consequently, static vestibular symptoms such as spontaneous nystagmus and postural deviation and dynamic vestibular symptoms such as oscillopsia and swaying gait are induced. However, these behavioral asymmetries gradually recover after the lesion. Progressive balance restoration is termed vestibular compensation, which is divided into two phases: static and dynamic. Static vestibular compensation is further divided into initial and late processes. In the initial process of static vestibular compensation after unilateral labyrinthectomy (UL) in rats, plastic changes in the cerebello-vestibular and vestibular commissural inhibitory pathways suppress neurons in the contra-lesional MVe (contra-MVe), resulting in the restoration of symmetrical resting activity of MVe neurons on both sides at low levels. The declining frequency of spontaneous nystagmus after UL is an index of the initial process, and short-term administration of diazepam, a GABA A receptor agonist, has been shown to accelerate the initial process in rats. Accordingly, short-term administration of diazepam is recommended for the treatment of acute vertigo in patients with unilateral vestibular dysfunction. In the late process of static vestibular compensation after UL in rats, the resting activity of ipsi-MVe neurons gradually recovers due to changes in cell membrane properties, resulting in the reinforcement of balanced intervestibular nuclear activities to nearly normal levels without the suppression of contra-MVe neurons. The declining number of MK801-induced Fos-positive neurons in contra-MVe after UL is an index of the late process, and long-term administration of betahistine, a histamine H 3 receptor antagonist, has been shown to accelerate the late process in rats. Accordingly, long-term administration of betahistine is recommended for the treatment of subacute vertigo in patients who were not compensated for unilateral vestibular dysfunction. In the process of dynamic vestibular compensation after UL, the sensitivity of ipsi-MVe neurons to head velocity and acceleration is restored due to synaptic changes such as long-term potentiation and sprouting of commissures, resulting in the restoration of the dynamic vestibulo-ocular and vestibulo-spinal reflexes. To facilitate dynamic vestibular compensation, early ambulation and subsequent vestibular rehabilitation exercise are recommended for the treatment of chronic vertigo in patients with uncompensated unilateral vestibular dysfunction. Although vestibular compensation after bilateral vestibular loss is not expected, vestibular rehabilitation with a sensory-substitution strategy can improve imbalance in patients with bilateral vestibular lesions. [ABSTRACT FROM AUTHOR]

Posterior semicircular canal dehiscence (PSCD) has been demonstrated to result in a third mobile window mechanism (TMWM) in the inner ear similar to superior semicircular canal dehiscence (SSCD). Typical clinical and instrumental features of TMWM, including low-frequency conductive hearing loss (CHL), autophony, pulsatile tinnitus, sound/pressure-induced vertigo and enhanced vestibular-evoked myogenic potentials, have been widely described in cases with PSCD. Nevertheless, video-head impulse test (vHIT) results have been poorly investigated. Here, we present six patients with PSCD presenting with a clinical scenario consistent with a TMWM and an impaired vestibulo-ocular reflex (VOR) for the affected canal on vHIT. In two cases, an additional dehiscence between the facial nerve and the horizontal semicircular canal (HSC) was detected, leading to a concurrent VOR impairment for the HSC. While in SSCD, a VOR gain reduction could be ascribed to a spontaneous "auto-plugging" process due to a dural prolapse into the canal, the same pathomechanism is difficult to conceive in PSCD due to a different anatomical position, making a dural herniation less likely. Alternative putative pathomechanisms are discussed, including an endolymphatic flow dissipation during head impulses as already hypothesized in SSCD. The association of symptoms/signs consistent with TMWM and a reduced VOR gain for the posterior canal might address the diagnosis toward PSCD. [ABSTRACT FROM AUTHOR]

Background: The vestibular phenotypes of patients with genetic hearing loss are poorly understood. Methods: we performed genetic testing including exome sequencing and vestibular function tests to investigate vestibular phenotypes and functions in patients with genetic hearing loss. Results: Among 627 patients, 143 (22.8%) had vestibular symptoms. Genetic variations were confirmed in 45 (31.5%) of the 143 patients. Nineteen deafness genes were linked with vestibular symptoms; the most frequent genes in autosomal dominant and recessive individuals were COCH and SLC26A4, respectively. Vestibular symptoms were mostly of the vertigo type, recurrent, and persisted for hours in the genetically confirmed and unconfirmed groups. Decreased vestibular function in the caloric test, video head impulse test, cervical vestibular-evoked myogenic potential, and ocular vestibular-evoked myogenic potential was observed in 42.0%, 16.3%, 57.8%, and 85.0% of the patients, respectively. The caloric test revealed a significantly higher incidence of abnormal results in autosomal recessive individuals than in autosomal dominant individuals (p = 0.011). The genes, including SLC26A4, COCH, KCNQ4, MYH9, NLRP3, EYA4, MYO7A, MYO15A, and MYH9, were heterogeneously associated with abnormalities in the vestibular function test. Conclusions: In conclusion, diverse vestibular symptoms are commonly concomitant with genetic hearing loss and are easily overlooked. [ABSTRACT FROM AUTHOR]

Purpose: When a dizzy patient with episodic vertigo has an abnormal caloric and a normal video head impulse test (vHIT), this caloric–vHIT dissociation provides vital information for a diagnosis of Ménière's disease (MD). Endolymphatic hydrops (EH), a histological marker of MD, is hypothesized to be involved in the caloric–vHIT dissociation in MD through hydropic duct distension of the horizontal semicircular canal (SC). This study was designed to determine the impact of EH on the function of horizontal SC during caloric stimulation. Methods: Caloric test and vHIT were used to evaluate the function of horizontal SC every six months, annual magnetic resonance imaging (MRI) was used to evaluate the degree of EH size in the vestibule, and monthly vertigo and hearing evaluation was done for 12 months. EH shrinkage was defined as the size change of vestibular EH from significant to none. Results: Among 133 MD patients evaluated for eligibility, 67 patients with caloric–vHIT dissociation entered the study. Fifteen participants had EH shrinkage (G-I), while 52 participants had no remarkable EH change (G-II). Average values (IQR) of the maximum slow phase velocity in G-I and G-II were 29.6 (13.0–34.0) and 25.9 (17.3–31.3), respectively, at baseline, 26.1 (9.0–38.0) and 23.6 (18.0–28.3) at 12 months. Two-factor repeated-measures ANOVA showed no significant differences between the groups (P = 0.486). The values of vestibulo-ocular reflex gain of the horizontal SC in G-I and G-II remained above 0.8 during the study period. Conclusions: EH detected by MRI shows limited correlation with caloric stimulation results. [ABSTRACT FROM AUTHOR]

Determining the sites and directions of plasticity underlying changes in neural activity and behavior is critical for understanding mechanisms of learning. Identifying such plasticity from neural recording data can be challenging due to feedback pathways that impede reasoning about cause and effect. We studied interactions between feedback, neural activity, and plasticity in the context of a closed-loop motor learning task for which there is disagreement about the loci and directions of plasticity: vestibulo-ocular reflex learning. We constructed a set of circuit models that differed in the strength of their recurrent feedback, from no feedback to very strong feedback. Despite these differences, each model successfully fit a large set of neural and behavioral data. However, the patterns of plasticity predicted by the models fundamentally differed, with the direction of plasticity at a key site changing from depression to potentiation as feedback strength increased. Guided by our analysis, we suggest how such models can be experimentally disambiguated. Our results address a long-standing debate regarding cerebellum-dependent motor learning, suggesting a reconciliation in which learning-related changes in the strength of synaptic inputs to Purkinje cells are compatible with seemingly oppositely directed changes in Purkinje cell spiking activity. More broadly, these results demonstrate how changes in neural activity over learning can appear to contradict the sign of the underlying plasticity when either internal feedback or feedback through the environment is present. [ABSTRACT FROM AUTHOR]

BACKGROUND: Machado Joseph Disease (MJD) is an autosomal dominant neurodegenerative disease. In previous studies, we described significant bilateral horizontal Vestibulo-Ocular Reflex (VOR) deficit within this population without any reference to the presence of vestibular symptomatology. OBJECTIVE: To evaluate whether, beyond cerebellar ataxia complaints, MJD patients have typical vestibular symptomatology corresponding to the accepted diagnostic criteria of Bilateral Vestibulopathy (BVP) according to the definition of the International Barany Society of Neuro-Otology. METHODS: Twenty-one MJD, 12 clinically stable chronic Unilateral Vestibulopathy (UVP), 15 clinically stable chronic BVP, and 22 healthy Controls underwent the video Head Impulse Test (vHIT) evaluating VOR gain and filled out the following questionnaires related to vestibular symptomatology: The Dizziness Handicap Inventory (DHI), the Activities-specific Balance Confidence Scale (ABC), the Vertigo Visual Scale (VVS) and the Beck Anxiety Inventory (BAI). RESULTS: The MJD group demonstrated significant bilateral vestibular impairment with horizontal gain less than 0.6 in 71% of patients (0.54±0.17). Similar to UVP and BVP, MJD patients reported a significantly higher level of symptoms than Controls in the DHI, ABC, VVS, and BAI questionnaires. CONCLUSIONS: MJD demonstrated significant VOR impairment and clinical symptoms typical of BVP. We suggest that in a future version of the International Classification of Vestibular Disorders (ICVD), MJD should be categorized under a separate section of central vestibulopathy with the heading of bilateral vestibulopathy. The present findings are of importance regarding the clinical diagnosis process and possible treatment based on vestibular rehabilitation. [ABSTRACT FROM AUTHOR]

BACKGROUND: Hyperventilation-induced nystagmus test (HINT) is capable of generating a response in 77.2% of cases of acute unilateral vestibulopathy (AUVP); both nystagmus toward the affected side (excitatory pattern) and toward the healthy side (inhibitory pattern) have been described. The aim of the study is to investigate the clinical and prognostic role of the test by evaluating its correlation with vestibulo-ocular reflex (VOR) gain. METHODS: We evaluated 33 AUVP patients by performing the HINT and video head impulse test (V-HIT) during the acute phase and then at 15 and 90 days after the onset of the symptoms. The correlation between the VOR gain of the affected side and test responses was evaluated first, phase by phase, and then considering the pattern shown during the first assessments. RESULTS: Patients with a negative HINT had a higher mean VOR gain than patients with a positive test at both 15 and 90 days. Patients who showed an inhibitory pattern at the first assessment had a continuous improvement in V-HIT performance, while patients with an initial excitatory response had a transient decrease in gain at the subsequent evaluation (P=.001). No difference between these 2 groups emerged at 90 days (P=.09). CONCLUSION: The finding of a negative HINT during the follow-up correlates with good V-HIT performance and could be an indicator of good recovery. The inhibitory pattern is associated with a subsequent improvement; and it would be indicative of compensation. but, despite this, the prognostic value of the test is limited [ABSTRACT FROM AUTHOR]

This article provides an overview of vestibular disease in horses, explaining the anatomy of the vestibular system and discussing the clinical signs and common causes of the disease. It emphasizes the importance of diagnostic tests in reaching a diagnosis. The article titled "Ethics Statement" by Sarah F. Colmer and Amy L. Johnson discusses the absence of an ethics statement in a clinical commentary and explains the purpose and importance of an ethics statement in research articles. [Extracted from the article]

Background: The current pandemic of COVID-19, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has resulted in significant morbidity and mortality primarily associated with respiratory failure. However, it has also been reported that COVID-19 can evolve into a nervous system infection. The direct and indirect mechanisms of damage associated with SARS-CoV-2 neuropathogenesis could affect our sensory functionality, including hearing and balance. Summary: In order to investigate a possible association between SARS-CoV-2 viral infection and possible damage to the vestibular system, this review describes the main findings related to diagnosing and evaluating otoneurological pathologies. Key Messages: The clinical evidence shows that SARS-CoV-2 causes acute damage to the vestibular system that would not leave significant sequelae. Recovery is similar to vestibular pathologies such as vestibular neuronitis and benign paroxysmal positional vertigo. Further basic science, clinical, and translational research is needed to verify and understand the short- and long-term effects of COVID-19 on vestibular function. [ABSTRACT FROM AUTHOR]

Usher Syndrome classification takes into account the absence of vestibular function but its correlation with genotype is not well characterized. We intend to investigate whether video Head Impulse Test (vHIT) is useful in screening and to differentiate Usher Syndrome types. 29 Usher patients (USH) with a genetically confirmed diagnosis and 30 healthy controls were studied with vHIT and dizziness handicap inventory questionnaire (DHI). Statistical significant differences between USH1, USH2 and controls were found in the vestibulo-ocular-reflex (VOR) gain of all SCCs, with USH1 patients consistently presenting smaller gains. VOR gain of the right lateral SCC could discriminate controls from USH1, and USH2 from USH1 with an overall diagnostic accuracy of 90%. USH1 DHI correlated with VOR (ρ = − 0,971, p = 0.001). Occurrence rate of covert and overt lateral semicircular canals refixation saccades (RS) was significantly different between groups, being higher in USH1 patients (p < 0.001). USH1 peak velocity of covert and overt saccades was higher for lateral semicircular canals (p < 0.05 and p = 0.001) compared with USH2 and controls. Covert saccades occurrence rate for horizontal SCCs could discriminate USH1 from USH2 patients and controls with a diagnostic accuracy of 85%. vHIT is a fast and non-invasive instrument which allowed us to screen and distinguish Usher patients from controls with a high precision. Importantly, its use allowed further discrimination between USH1 from USH2 groups. Moreover, VOR gain seems to correlate with vertigo-related quality of life in more severe phenotypes. [ABSTRACT FROM AUTHOR]

Purpose: To assess the differences in the miRNA expression profile between small (stage I Koos classification) and large solid vestibular schwannoma (VS) tumors, using the RNA-seq technique. Methods: Twenty tumor samples (10 small and 10 large tumors) were collected from patients operated for VS in a Tertiary Academic Center. Tumor miRNA expression was analyzed using high-throughput RNA sequencing (RNA-seq) technique, with NovaSeq 6000 Illumina system. Bioinformatics analysis was done using statistical software R. Gene enrichment and functional analysis was performed using miRTargetLink 2.0 and DIANA miRpath 3.0 online tools. Results: We identified 9 differentially expressed miRNAs in large VS samples: miR-7, miR-142 (-3p and -5p), miR-155, miR-342, miR-1269, miR-4664, and miR-6503 were upregulated, whereas miR-204 was significantly down-regulated in comparison to small VS samples. Gene enrichment analysis showed that the most enriched target genes were SCD, TMEM43, LMNB2, JARID2, and CCND1. The most enriched functional pathways were associated with lipid metabolism, along with signaling pathways such as Hippo and FOXO signaling pathway. Conclusion: We identified a set of 9 miRNAs that are significantly deregulated in large VS in comparison to small, intracanalicular tumors. The functional enrichment analysis of these miRNAs suggests novel mechanisms, such as that lipid metabolism, as well as Hippo and FOxO signaling pathways that may play an important role in VS growth regulation. [ABSTRACT FROM AUTHOR]

The results of video head impulse tests (video-HITs) may be confounded by data artifacts of various origins, including pupil size and eyelid obstruction of the pupil. This study aimed to determine the effect of these factors on the results of video-HITs. We simulated ptosis by adopting pharmacological dilatation of the pupil in 21 healthy participants (11 women; age 24–58 years). Each participant underwent video-HITs before and after pupillary dilatation using 0.5% tropicamide. We assessed the changes in the vestibulo-ocular reflex (VOR) gain, corrective saccade amplitude, and frequency of eyelid flicks. After pupillary dilatation, the VOR gain decreased for both right (RAC; 1.12 ± 0.12 vs. 1.01 ± 0.16, p = 0.011) and left anterior canals (LACs; 1.15 ± 0.13 vs. 0.96 ± 0.14, p < 0.001), and right posterior canal (RPC, 1.10 ± 0.13 vs. 0.98 ± 0.09, p = 0.001). The corrective saccade amplitudes also decreased significantly for all four vertical canals. The frequency of eyelid flicks, however, did not change. The changes of VOR gain were positively correlated with the lid excursion in RPC (r = 0.629, p = 0.002) and LPC (r = 0.549, p = 0.010). Our study indicates that eyelid position and pupil size should be considered when interpreting the results of video-HITs, especially for the vertical canals. Pupils should be shrunk in a very well-lit room, and artifacts should be prevented by taping or lifting the eyelids as required during video-HITs. [ABSTRACT FROM AUTHOR]

Long-term deficits of the vestibulo-ocular reflex (VOR) elicited by head rotation can be partially compensated by catch-up saccades (CuS). These saccades are initially visually guided, but their latency can greatly decrease resulting in short latency CuS (SL-CuS). It is still unclear what triggers these CuS and what are the underlying neural circuits. In this study, we aimed at evaluating the impact of cerebellar pathology on CuS by comparing their characteristics between two groups of patients with bilateral vestibular hypofunction, with or without additional cerebellar dysfunction. We recruited 12 patients with both bilateral vestibular hypofunction and cerebellar dysfunction (BVH-CD group) and 12 patients with isolated bilateral vestibular hypofunction (BVH group). Both groups were matched for age and residual VOR gain. Subjects underwent video head impulse test recording of the horizontal semicircular canals responses as well as recording of visually guided saccades in the step, gap, and overlap paradigms. Latency and gain of the different saccades were calculated. The mean age for BVH-CD and BVH was, respectively, 67.8 and 67.2 years, and the mean residual VOR gain was, respectively, 0.24 and 0.26. The mean latency of the first catch-up saccade was significantly longer for the BVH-CD group than that for the BVH group (204 ms vs 145 ms, p < 0.05). There was no significant difference in the latency of visually guided saccades between the two groups, for none of the three paradigms. The gain of covert saccades tended to be lower in the BVH-CD group than in BVH group (t test; p = 0.06). The mean gain of the 12° or 20° visually guided saccades were not different in both groups. Our results suggest that the cerebellum plays a role in the generation of compensatory SL-CuS observed in BVH patients. [ABSTRACT FROM AUTHOR]

Sudden sensorineural hearing loss with vertigo (SHLV) and vestibular neuritis (VN) can result in prolonged dizziness. This study aimed to compare the video head impulse test (vHIT) of patients with SHLV and VN. Fifteen patients with SHLV and 21 patients with VN who visited the Vertigo/Dizziness Center of our hospital between December 2016 and February 2023 were included. vHIT was performed at the time of admission, and the VOR gain and catch up saccade (CUS) in the three types of semicircular canals (SCCs) were analyzed. Pathologic vHIT results were observed most frequently in the posterior SCC (73%), followed by lateral (53%) and anterior (13%) SCCs in the SHLV group. In contrast, pathologic vHIT results were observed most frequently in the lateral SCC (100%), followed by the anterior (43%) and posterior SCC (24%) SCCs in the VN group. Pathological vHIT results in the lateral and posterior SCC showed significant differences between the two groups, but for anterior SCC, no significant differences were found. Comparison of the two vHIT results revealed differences in the SCC dysfunction patterns. This may be due to the different pathophysiological mechanisms of the two vestibular disorders, which may result in prolonged vertigo. [ABSTRACT FROM AUTHOR]

Purpose: In case of an acute unilateral vestibulopathy (UVP), compensatory strategies such as restoration and adaptation will lead to a decrease in intensity of the symptoms. Although measurements of compensatory strategies are available, currently, an overview taking the different strategies into account is lacking. The objectives of this study are to explore compensatory strategies and to investigate the association between compensatory strategies and patient characteristics. Methods: Restoration was objectified by the vestibulo-ocular reflex (VOR) gain on the video head impulse test, and adaptation—consisting of visual, multisensory, and behavioral substitution—was objectified by the Visual Vertigo Analog Scale (VVAS), Antwerp Vestibular Compensation Index (AVeCI), and Perez and Rey score (PR score), respectively. Adequate restoration and adaptation levels were interpreted as follows: VOR gain > 0.80, VVAS ≤ 40%, AVeCI > 0 and PR score ≤ 55. Results: Sixty-two UVP patients, 34 men and 28 women, were included with an average age of 52.1 ± 17.3 years. At 10.5 ± 1.4 weeks after onset, 41.9% of the UVP patients reached adequate restoration levels and 58.1–86.9% reached adequate adaptation levels. Furthermore, significant associations were found between (1) restoration status and UVP etiology [Odds Ratio (OR) with 95% CI: 4.167 {1.353;12.828}] and balance performance (OR: 4.400 {1.258;15.386}), (2) visual sensory substitution status and perceived handicap (OR: 8.144 {1.644;40.395}), anxiety (OR: 10.000 {1.579;63.316}) and depression (OR: 16.667 {2.726;101.896}), and (3) behavioral substitution status and balance performance (OR: 4.143 {1.341;12.798}). Conclusion: UVP patients with adequate compensatory strategies presented with better balance performance, lower perceived handicap, and lower anxiety and depression scores. [ABSTRACT FROM AUTHOR]

Background: The relationship between the hearing phenotype and the SLC26A4 mutation in enlarged vestibular aqueduct cases has not been fully elucidated. Objectives: To detect SLC26A4 mutation in a group of cases with enlarged vestibular aqueduct who received cochlear implantation and to analyze the correlation between the SLC26A4 genotype and the progression of deafness. Materials and methods: Twenty-nine enlarged vestibular aqueduct patients were selected. Using the Sanger sequence to analyze SLC26A4 gene mutations. The 29 cases were divided into group A (carrying the c.919-2A > G mutation) and group B (not carrying the c.919-2A > G mutation). The difference in the duration of deafness was analyzed between the two groups. Results: The detection rate of the c.1174A > T mutation in the postlingual deafness group was 37.5%, higher than that in the prelingual deafness group (0%). The difference in the duration of deafness between groups A and B was not statistically significant by the Mann–Whitney U test (p > 0.05). Conclusions: The correlation between the SLC26A4 genotype and the duration of deafness in cases with enlarged vestibular aqueduct is not yet clear. However, the c.1174A > T mutation may be linked to delayed hearing loss and the progression of deafness may be relatively slow in some cases of c.919-2A > G mutation. [ABSTRACT FROM AUTHOR]

This article discusses a case of a cerebellar flocculus pseudomass, a lesser-known lesion that can occur in the cerebellopontine angle (CPA). The patient, a 73-year-old female, presented with gradual onset of right-sided low frequency hearing loss and was initially diagnosed with a vestibular schwannoma. However, further imaging revealed characteristics inconsistent with a vestibular schwannoma, leading to the diagnosis of a cerebellar flocculus pseudomass. The article emphasizes the importance of comprehensive MRI studies for CPA lesions to avoid misdiagnosis and inappropriate treatment. The presentation of a cerebellar flocculus pseudomass with unilateral hearing loss is considered novel, and more information about this condition is needed in the literature. [Extracted from the article]

Medial rectus motoneurons mediate nasally directed horizontal eye movements. These motoneurons receive two major excitatory inputs, from the abducens internuclear neurons (ABD Ints) and neurons of the lateral vestibular nucleus whose axons course through the ascending tract of Deiters (ATD). In the present work, we have recorded in the alert chronic cat preparation the discharge activity of these two premotor neurons simultaneously with eye movements, to discern their relative contribution to the firing pattern of medial rectus motoneurons. ABD Int discharge was accurately correlated with eye movements, displaying high sensitivities to eye position and eye velocity. ATD neurons also discharged in relation to spontaneous and vestibular eye movements but showed significantly lower eye position and eye velocity sensitivities. Outstandingly, ATD neurons presented a significantly lower eye position threshold for recruitment compared to both ABD Ints and medial rectus motoneurons. Therefore, ATD neurons exhibited eye position and velocity signals during spontaneous and vestibular eye movements, which were of lower magnitude than those of ABD Ints, but due to their low recruitment threshold, they could play a significant role in facilitating ABD Int signal transmission onto medial rectus motoneurons. [ABSTRACT FROM AUTHOR]

Vestibular nuclei and cerebellar function comprise vestibular neural networks that control vestibular-related responses. However, the vestibular-related responses to simultaneous stimulation of these regions are unclear. This study aimed to examine whether the combination of noisy galvanic vestibular stimulation (nGVS) and cerebellar transcranial direct current stimulation (ctDCS) using a complex transcranial electrical stimulation device alters vestibular-dominant standing stability and vestibulo-ocular reflex (VOR) function. The center of foot pressure (COP) sway and VOR of participants (28 healthy, young adults) were assessed under four conditions of transcranial electrical stimulation using nGVS and ctDCS. The COP was calculated with the participant standing on a soft-foam surface with eyes closed using a force plate to evaluate body sway. VOR measurements were collected via passive head movements and fixation on a target projected onto the front wall using a video head impulse test (vHIT). VOR gain was calculated in six directions using a semicircular canal structure based on the ratio of eye movement to head movement. The nGVS + ctDCS and nGVS + sham ctDCS conditions decreased COP sway compared to the sham nGVS + ctDCS and sham nGVS + sham ctDCS conditions. No significant differences were observed in the main effect of stimulation or the interaction of stimulation and direction on the vHIT parameters. The results of this study suggest that postural stability may be independently affected by nGVS. Our findings contribute to the basic neurological foundation for the clinical application of neurorehabilitation using transcranial electrical stimulation of the vestibular system. [ABSTRACT FROM AUTHOR]

Retinal image slip during head rotation drives motor learning in the rotational vestibulo-ocular reflex (VOR) and forms the basis of gaze-stability exercises that treat vestibular dysfunction. Clinical exercises, however, are unengaging, cannot easily be titrated to the level of impairment, and provide neither direct feedback nor tracking of the patient's adherence, performance, and progress. To address this, we have developed a custom application for VOR training based on an interactive computer game. In this study, we tested the ability of this game to induce VOR learning in individuals with normal vestibular function, and we compared the efficacy of single-step and incremental learning protocols. Eighteen participants played the game twice on different days. All participants tolerated the game and were able to complete both sessions. The game scenario incorporated a series of brief head rotations, similar to active head impulses, that were paired with a dynamic acuity task and with a visual-vestibular mismatch (VVM) intended to increase VOR gain (single-step: 300 successful trials at x1.5 viewing; incremental: 100 trials each of -x1.13, x1.33, and x1.5 viewing). Overall, VOR gain increased by 15 ± 4.7% (mean ± 95% CI, P < 0.001). Gains increased similarly for active and passive head rotations, and, contrary to our hypothesis, there was little effect of the learning strategy. This study shows that an interactive computer game provides robust VOR training and has the potential to deliver effective, engaging, and trackable gaze-stability exercises to patients with a range of vestibular dysfunctions. [ABSTRACT FROM AUTHOR]

OBJECTIVE: A normal video Head Impulse Test is the gold standard in the emergency department to rule-in patients with an acute vestibular syndrome and a stroke. We aimed to compare the diagnostic accuracy of vHIT metrics regarding the vestibulo-ocular reflex gain and the corrective saccades in detecting vestibular strokes. METHODS: Prospective cross-sectional study (convenience sample) of patients presenting with acute vestibular syndrome in the emergency department of a tertiary referral centre between February 2015 and May 2020. We screened 1677 patients and enrolled 76 patients fulfilling the inclusion criteria of acute vestibular syndrome. All patients underwent video head impulse test with automated and manual data analysis. A delayed MRI served as a gold standard for vestibular stroke confirmation. RESULTS: Out of 76 patients, 52 were diagnosed with acute unilateral vestibulopathy and 24 with vestibular strokes. The overall accuracy of detecting stroke with an automated vestibulo-ocular reflex gain was 86.8%, compared to 77.6% for cumulative saccade amplitude and automatic saccade mean peak velocity measured by an expert and 71% for cumulative saccade amplitude and saccade mean peak velocity measured automatically. Gain misclassified 13.1% of the patients as false positive or false negative, manual cumulative saccade amplitude and saccade mean peak velocity 22.3%, and automated cumulative saccade amplitude and saccade mean peak velocity 28.9% respectively. CONCLUSIONS: We found a better accuracy of video head impulse test for the diagnosis of vestibular strokes when using the vestibulo-ocular reflex gain than using saccade metrics. Nevertheless, saccades provide an additional and important information for video head impulse test evaluation. The automated saccade detection algorithm is not yet perfect compared to expert analysis, but it may become a valuable tool for future non-expert video head impulse test evaluations. [ABSTRACT FROM AUTHOR]

OBJECTIVE: In our study, it was aimed to compare vestibulo-ocular reflex (VOR) gain and saccade parameters in HIMP and SHIMP tests between gender, right and left ears, and age groups in healthy adults and to examine the correlation between the tests regarding these parameters. METHODS: The study included a total of 100 healthy participants aged 18–65 and without complaints of hearing loss, dizziness, lightheadedness, and/or imbalance. Participants underwent HIMP and SHIMP tests, respectively. RESULTS: No significant difference was found in HIMP and SHIMP VOR gain values according to gender and age groups. SHIMP duration was significantly longer in women. VOR gain values were lower in the right ear. HIMP amplitude values were higher and SHIMP amplitude values were lower with increasing age. In older age groups, SHIMP peak velocity and duration values were significantly decreased, while HIMP duration value increased and latency value was longer. In the 1st saccade, a significant difference was obtained between HIMP and SHIMP tests for all saccade parameters. There was a statistically significant positive correlation between the VOR gain values of HIMP and SHIMP tests. CONCLUSIONS: The present study showed that VOR gain and saccade parameters obtained in different age groups will be important in determining clinical outcomes in vestibular pathologies. [ABSTRACT FROM AUTHOR]

This document, titled "Ocular Flutter Evoked by Vestibular Stimulation," discusses a case study of a 26-year-old woman who experienced ocular flutter, a condition characterized by spontaneous bursts of eye movements, exclusively during head motion and vestibular stimulation. The patient presented with oscillopsia (the perception of objects moving) and other symptoms such as clumsiness and headache. Various tests and examinations were conducted, including video-oculography, which revealed the presence of ocular flutter during specific stimuli. The authors propose several mechanisms that may explain the occurrence of ocular flutter in this case, involving the interaction between the vestibular and saccadic systems. The patient's symptoms improved after receiving treatment with intravenous immunoglobulin and methylprednisolone. The study suggests that vestibular stimulation may play a role in generating ocular flutter. [Extracted from the article]

The sense of orientation of an animal is derived from the head direction (HD) system found in several limbic structures and depends on an intact vestibular labyrinth. However, how the vestibular system influences the generation and updating of the HD signal remains poorly understood. Anatomical and lesion studies point toward three key brainstem nuclei as key components for generating the HD signal--nucleus prepositus hypoglossi, supragenual nucleus, and dorsal paragigantocellularis reticular nuclei. Collectively, these nuclei are situated between the vestibular nuclei and the dorsal tegmental and lateral mammillary nuclei, which are thought to serve as the origin of the HD signal. To determine the types of information these brain areas convey to the HD network, we recorded neurons from these regions while female rats actively foraged in a cylindrical enclosure or were restrained and rotated passively. During foraging, a large subset of cells in all three nuclei exhibited activity that correlated with the angular head velocity (AHV) of the rat. Two fundamental types of AHV cells were observed; (1) symmetrical AHV cells increased or decreased their firing with increases in AHV regardless of the direction of rotation, and (2) asymmetrical AHV cells responded differentially to clockwise and counterclockwise head rotations. When rats were passively rotated, some AHV cells remained sensitive to AHV, whereas firing was attenuated in other cells. In addition, a large number of AHV cells were modulated by linear head velocity. These results indicate the types of information conveyed from the vestibular nuclei that are responsible for generating the HD signal. [ABSTRACT FROM AUTHOR]

This study utilized cervical vestibular-evoked myogenic potentials tests (cVEMP) and ocular vestibular-evoked myogenic potentials tests (oVEMP) to investigate the vestibulocollic and vestibuloocular reflex arcs and to evaluate cerebellar and brainstem involvement) in essential tremor (ET). Eighteen cases with ET and 16 age- and gender-matched healthy control subjects (HCS) were included in the present study. Otoscopic and neurologic examinations were performed on all participants, and both cervical and ocular VEMP tests were performed. Pathological cVEMP results were increased in the ET group (64.7%) compared to the HCS (41,2%; p > 0.05). The latencies of P1 and N1 waves were shorter in the ET group than in HCS (p = 0.01 and p = 0.001). Pathological oVEMP responses were significantly higher in the ET group (72.2%) compared to the HCS (37.5%; p = 0.01). There was no statistically significant difference in oVEMP N1-P1 latencies between groups (p > 0.05). Because the ET group had high pathological responses to the oVEMP, but not the cVEMP, the upper brainstem pathways may be more affected by ET. [ABSTRACT FROM AUTHOR]

Bilateral vestibular deficiency (BVD) results in chronic dizziness, blurry vision when moving the head, and postural instability. Vestibular prostheses (VPs) show promise as a treatment, but the VP-restored vestibulo-ocular reflex (VOR) gain in human trials falls short of expectations. We hypothesize that the slope of the rising ramp in stimulation pulses plays an important role in the recruitment of vestibular afferent units. To test this hypothesis, we utilized customized programming to generate ramped pulses with different slopes, testing their efficacy in inducing electrically evoked compound action potentials (eCAPs) and current spread via bench tests and simulations in a virtual inner model created in this study. The results confirmed that the slope of the ramping pulses influenced the recruitment of vestibular afferent units. Subsequently, an optimized stimulation pulse train was identified using model simulations, exhibiting improved modulation of vestibular afferent activity. This optimized slope not only reduced the excitation spread within the semicircular canals (SCCs) but also expanded the neural dynamic range. While the model simulations exhibited promising results, in vitro and in vivo experiments are warranted to validate the findings of this study in future investigations. [ABSTRACT FROM AUTHOR]

Aim: To determine the test and retest reliability of the functional head impulse test (fHIT) in healthy young adults. Materials and methods: Thirty-three healthy participants (17 women, 16 men) aged 18–30 years were included in the study. Each participant underwent the fHIT twice, 1 week apart, by the same experienced clinician. Intraclass correlation coefficients (ICCs) were used to determine test–retest reliability. Results: There was no statistically significant difference between the results of total percentage of correct answer (CA%) of the fHIT obtained in session 1 and session 2 measurements in the lateral, anterior, and posterior semicircular canals (SCCs) (p > 0.05). ICC values for test–retest reliability were found to range from 0.619 to 0.665 for the three semicircular canals (SCCs). Conclusion: The test–retest reliability of the fHIT device was moderate. Attention, cognition, and fatigue may be the factors reducing reliability. In the diagnosis, follow-up, and rehabilitation processes of vestibular diseases in clinics, changes in the fHIT CA% can be used to assess vestibulo-ocular reflex (VOR) functionality. [ABSTRACT FROM AUTHOR]

Here we review the clinical value of a video‐oculography test for clinical evaluation of vestibular otolith function. This test is known as the video ocular counter roll (vOCR) and is based on measurement of torsional vestibulo‐ocular reflex with a lateral head tilt. The vOCR test consists of a simple maneuver during which the head and torso are tilted en bloc by the examiner. The pattern of vOCR deficit among patients highlights its clinical value in identifying the stage of vestibular loss and recovery. The quick application of vOCR allows examination of otolith‐ocular function and assessment of vestibular recovery at the bedside. [ABSTRACT FROM AUTHOR]

The functional complementarity of the vestibulo-ocular reflex (VOR) and optokinetic reflex (OKR) allows for optimal combined gaze stabilization responses (CGR) in light. While sensory substitution has been reported following complete vestibular loss, the capacity of the central vestibular system to compensate for partial peripheral vestibular loss remains to be determined. Here, we first demonstrate the efficacy of a 6-week subchronic ototoxic protocol in inducing transient and partial vestibular loss which equally affects the canal- and otolith-dependent VORs. Immunostaining of hair cells in the vestibular sensory epithelia revealed that organ-specific alteration of type I, but not type II, hair cells correlates with functional impairments. The decrease in VOR performance is paralleled with an increase in the gain of the OKR occurring in a specific range of frequencies where VOR normally dominates gaze stabilization, compatible with a sensory substitution process. Comparison of unimodal OKR or VOR versus bimodal CGR revealed that visuo-vestibular interactions remain reduced despite a significant recovery in the VOR. Modeling and sweep-based analysis revealed that the differential capacity to optimally combine OKR and VOR correlates with the reproducibility of the VOR responses. Overall, these results shed light on the multisensory reweighting occurring in pathologies with fluctuating peripheral vestibular malfunction. [ABSTRACT FROM AUTHOR]

• Comparison between looking behavior in laboratory and naturalistic conditions (77). • Neural circuits driving voluntary and reflexive gaze shifts and stabilization (77). • Superior colliculus that receives and integrates gaze driving signals to brainstem (82). • Listings Law implemented by commissural connections between the superior colliculi (82). • Saccade system and VOR system share common semicircular canal coordinate (72). Organisms control their visual worlds by moving their eyes, heads, and bodies. This control of "gaze" or "looking" is key to survival and intelligence, but our investigation of the underlying neural mechanisms in natural conditions is hindered by technical limitations. Recent advances have enabled measurement of both brain and behavior in freely moving animals in complex environments, expanding on historical head-fixed laboratory investigations. We juxtapose looking behavior as traditionally measured in the laboratory against looking behavior in naturalistic conditions, finding that behavior changes when animals are free to move or when stimuli have depth or sound. We specifically focus on the brainstem circuits driving gaze shifts and gaze stabilization. The overarching goal of this review is to reconcile historical understanding of the differential neural circuits for different "classes" of gaze shift with two inconvenient truths. (1) "classes" of gaze behavior are artificial. (2) The neural circuits historically identified to control each "class" of behavior do not operate in isolation during natural behavior. Instead, multiple pathways combine adaptively and non-linearly depending on individual experience. While the neural circuits for reflexive and voluntary gaze behaviors traverse somewhat independent brainstem and spinal cord circuits, both can be modulated by feedback, meaning that most gaze behaviors are learned rather than hardcoded. Despite this flexibility, there are broadly enumerable neural pathways commonly adopted among primate gaze systems. Parallel pathways which carry simultaneous evolutionary and homeostatic drives converge in superior colliculus, a layered midbrain structure which integrates and relays these volitional signals to brainstem gaze-control circuits. [ABSTRACT FROM AUTHOR]

BACKGROUND: The aim of this study is to compare the possible functional involvement of the vestibulo-ocular reflex in the follicular and luteal phases. METHODS: The research was carried out at a university located in eastern Turkey. The study included 37 healthy female volunteering students aged 18-25 years. The functional head impulse test was applied twice in the follicular phase and in the luteal phase, and the results in both phases were compared. RESULTS: In the functional head impulse test, statistically significant differences were obtained between the follicular phase and the luteal phase at the stimulus to the lateral semicircular canal direction total and 6000°/s² acceleration percentage of correct answers values, the posterior semicircular canal direction stimulations at 3000°/s² and 5000°/s² acceleration percentage of correct answers values, and the anterior semicircular canal direction stimulations at 5000°/s² acceleration percentage of correct answers values. CONCLUSION: In the luteal phase, which corresponds to the period before menstruation, the vestibulo-ocular reflex is functionally negatively affected. [ABSTRACT FROM AUTHOR]

Purpose: To assess vestibular‐ocular reflex (VOR) function in patients with Parkinson's disease (PD) using a new method called functional head impulse test (fHIT). Study Design: Case–control study. Setting: Tertiary medical center. Participants: Twenty individuals with PD were recruited for PD group, and twenty healthy individuals for the control group. Ages of both groups ranged from 47 to 76 years. Main Outcome Measures: According to the modified Hoehn‐Yahr score, PD group was classified as an early stage with a range of 1–2.5 and a mid‐late stage with a range of 3–5. Percentage of correct answers (%CA) was calculated using fHIT for lateral, anterior and posterior semicircular canal (SCC) planes. Results: PD group had statistically lower fHIT %CA in the right lateral, left lateral, and left posterior SCC planes compared to control group (p <.05). There was no statistical difference between two PD severity groups and functional VOR abnormality. Conclusion: It was concluded that the functional VOR in the right lateral and left lateral and left posterior SCC plane was affected in individuals with PD. Our results show that impaired VOR and reduced dynamic visual acuity should be considered in individuals with PD for vestibular rehabilitation exercises. [ABSTRACT FROM AUTHOR]

BACKGROUND: The video head impulse test (vHIT) is a common assessment of semicircular canal function during high-speed impulses. Reliability of the vHIT for assessing vertical semicircular canals is uncertain. Vertical head impulses require a complex head movement, making it difficult to isolate a single semicircular canal and interpret resulting eye rotations. OBJECTIVE: The purpose of this study was to provide descriptive head kinematics and vestibular stimuli during vertical plane impulses to ultimately improve impulse delivery and interpretation of vHIT results for vertical semicircular canals. METHODS: Six participants received right anterior (RA) and left posterior (LP) semicircular canal impulses. Linear displacements, rotational displacements, and rotational velocities of the head were measured. Peak velocities in semicircular canal planes and peak-to-peak gravitoinertial accelerations at the otolith organs were derived from head kinematics. RESULTS: The largest rotational velocities occurred in the target semicircular canal plane, with non-negligible velocities occurring in non-target planes. Larger vertical displacements and accelerations occurred on the right side of the head compared to the left for RA and LP impulses. CONCLUSIONS: These results provide a foundation for designing protocols to optimize stimulation applied to a singular vertical semicircular canal and for interpreting results from the vHIT for vertical semicircular canals. [ABSTRACT FROM AUTHOR]

Alterations in neck sensory input from recurrent neck pain (known as subclinical neck pain (SCNP)) result in disordered sensorimotor integration (SMI). The cervico-ocular (COR) and vestibulo-ocular (VOR) reflexes involve various neural substrates but are coordinated by the cerebellum and reliant upon proprioceptive feedback. Given that proprioception and cerebellar processing are impaired in SCNP, we sought to determine if COR or VOR gain is also altered. COR and VOR were assessed using an eye-tracking device in 20 SCNP (9 M and 11 F; 21.8 (SD = 2.35) years) and 17 control (7 M and 10 F; 22.40 (SD = 3.66) years) participants. COR gain (10 trials): A motorized chair rotated the trunk at a frequency of 0.04 Hz and an amplitude of 5° while participants gazed at a circular target that disappeared after three seconds. VOR gain (30 trials): Rapid bilateral head movements away from a disappearing circular target while eyes fixated on the last observed target. Independent t-tests on COR and VOR gain were performed. SCNP had a significantly larger COR gain (p = 0.006) and smaller VOR gain (p = 0.487) compared to healthy controls. The COR group differences suggest an association between proprioceptive feedback and SMI, indicating COR may be a sensitive marker of altered cerebellar processing. [ABSTRACT FROM AUTHOR]

The vestibular cerebellum integrates multimodal sensory and motor information with vestibular input to compute internal models of self-motion. Adaptive plasticity in the floccular lobe underlies the vital computation that maintains vestibulo-ocular reflex calibration to ensure gaze stability. The anterior vermis plays a key role in two essential computations: (i) it transforms head-centered vestibular signals into the body-centered reference frame required for postural control, and (ii) it constructs a prediction of the sensory consequences of active self-motion. The nodulus and ventral uvula of the posterior vermis compute an internal representation of our spatial orientation and self-motion relative to gravity. The internal models underlying each of these computations are continually updated to account for constraints imposed by changes in the environment and/or neural mechanical dynamics. The vestibular cerebellum plays an essential role in maintaining our balance and ensuring perceptual stability during activities of daily living. Here I examine three key regions of the vestibular cerebellum: the floccular lobe, anterior vermis (lobules I–V), and nodulus and ventral uvula (lobules X–IX of the posterior vermis). These cerebellar regions encode vestibular information and combine it with extravestibular signals to create internal models of eye, head, and body movements, as well as their spatial orientation with respect to gravity. To account for changes in the external environment and/or biomechanics during self-motion, the neural mechanisms underlying these computations are continually updated to ensure accurate motor behavior. To date, studies on the vestibular cerebellum have predominately focused on passive vestibular stimulation, whereas in actuality most stimulation is the result of voluntary movement. Accordingly, I also consider recent research exploring these computations during active self-motion and emerging evidence establishing the cerebellum's role in building predictive models of self-generated movement. [ABSTRACT FROM AUTHOR]

Surgical plugging of the superior semicircular canal (SSC) represents an effective procedure to treat disabling symptoms in superior canal dehiscence (SCD), despite resulting in an impaired vestibulo-ocular reflex (VOR) gain for the SSC. On the other hand, SSC hypofunction on video head impulse test (vHIT) represents a common finding in patients with SCD exhibiting sound/pressure-induced vertigo, a low-frequency air–bone gap (ABG), and enhanced vestibular-evoked myogenic potentials (VEMPs). "Spontaneous canal plugging" has been assumed as the underlying process. Nevertheless, missing/mitigated symptoms and/or near-normal instrumental findings would be expected. An endolymphatic flow dissipation has been recently proposed as an alternative pathomechanism for SSC VOR gain reduction in SCD. We aimed to shed light on this debate by comparing instrumental findings from 46 ears of 44 patients with SCD exhibiting SSC hypofunction with post-operative data from 10 ears of 10 patients with SCD who underwent surgical plugging. While no difference in SSC VOR gain values was found between the two groups (p = 0.199), operated ears developed a posterior canal hypofunction (p = 0.002). Moreover, both ABG values (p = 0.012) and cervical/ocular VEMP amplitudes (p < 0.001) were significantly higher and VEMP thresholds were significantly lower (p < 0.001) in ears with SCD compared to operated ears. According to our data, canal VOR gain reduction in SCD should be considered as an additional sign of a third window mechanism, likely due to an endolymphatic flow dissipation. [ABSTRACT FROM AUTHOR]

Vestibular stimulation causes postural unsteadiness accompanied by a sensation of tilt. The mechanism of the sensation of tilt needs to be assessed by accurate calculation of the rotational axis of torsional eye position under various vestibular stimulations. Twenty-two healthy subjects participated in the study. Thirteen subjects underwent bilateral vestibular stimulation by on-axis yaw rotation under various head positions, and eighteen subjects underwent unilateral vestibular stimulation by caloric irrigation under various head positions. Listing's Plane was plotted for the eye movement data obtained by three-dimensional video-oculography. The offset of Listing's Plane showed sustained deviation of torsional eye position that was more prominent in head positions that stimulated lateral semicircular canals more than vertical semicircular canals. There was a less prominent and directionally reversed offset in head positions that stimulated vertical canals more than lateral semicircular canals. The sustained torsional eye position was validated by accurate assessment using Listing's Plane. The mechanism behind the deviation may be due to a combination of multiple anatomical components within the vestibular apparatus, with potentially stronger influence from lateral semicircular canals. [ABSTRACT FROM AUTHOR]

The diagnosis of spinocerebellar ataxia (SCA) currently depends upon genetic testing. Although genetic testing for SCA is highly specific, clinical parameters for the differentiation of SCAs are still insufficient. We aimed to assess the vestibulo-ocular reflex (VOR) parameters of various SCA subtypes to determine whether they have substantial value in differential diagnosis. We consecutively enrolled 33 genetically confirmed SCA patients (SCA2 = 8, SCA3 = 6, SCA6 = 10, SCA7 = 9). Normative data were obtained from 36 age- and gender-matched healthy controls. Quantitative indicators of VOR were measured using video head impulse test (HIT) and combined ocular motor dysfunctions were investigated using video-oculography. Compared with the control group, the VOR gains in SCA2 were relatively spared, but were markedly decreased for all six canals in SCA3. The VOR gains for the posterior canals (PCs) were significantly decreased in SCA6, and for both vertical canals were decreased in SCA7. The VOR gains for the horizontal canals in SCA3 were negatively correlated with disease severity (R = -0.900, p = 0.037). Abnormal catch-up saccades were common in SCA3 and SCA6, rare in SCA7 and absent in SCA2. Spontaneous, headshaking-induced, and positional nystagmus were only documented in SCA6. SCA3 and SCA6 commonly showed horizontal gaze-evoked nystagmus, but SCA2 and SCA7 had characteristic saccadic slowing without gaze-evoked nystagmus. VOR impairments are common in SCAs, but their patterns vary depending on subtype. In addition to ocular motor characteristics, distinctive VOR performance for each subtype using video HIT may aid the differential diagnosis of the SCA genotypes. [ABSTRACT FROM AUTHOR]