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Purpose: The objective of this study was to determine the normative vestibulo-ocular reflex gain output values of the computerized rotational head impulse test (crHIT) with stationary visual targets (earth bound) in healthy participants in each decade age band of life: 10-19, 20-29, 30-39, 40-49, 50-59, 60-69, and 70+ years., Method: Seventy-seven community-dwelling participants (10-85 years of age) with normal lateral semicircular canal (SCC) functioning and no symptoms or history of vestibular dysfunction were recruited through convenience sampling and assessed with the crHIT using stationary targets. These participants were assessed using two standard protocols in a randomized order., Results: Results from 77 participants ( M age = 46 years; 43 women, 34 men) were analyzed. Pearson's correlation coefficient and simple linear regression indicated a statistically significant relationship between crHIT gain output and age ( p > .05) for right gain, 1030°/s 2 , and left gain, 1005°/s 2 . Although a statistically significant relationship was found, the slope was minor, demonstrating that the clinical effect of age on crHIT gain output was insignificant. Furthermore, no statistically significant relationship exists between crHIT gain output and gender ( p > .05). Age-dependent normative data were calculated using the 2.5th and 97.5th confidence interval (CI) percentile method. The responses of angular vestibulo-ocular reflex (aVOR) gain values for crHIT are expected to occur within the range for lower limit reference interval (RI) of 0.85-0.9 and upper limit RI of 1.11-1.18 for 1030°/s 2 and lower limit RI of 0.86-0.92 and upper limit RI of 1.13-1.16 for 1005°/s 2 . It can be expected that 90% CI of the population with normal lateral SCC functioning will have aVOR gain values that fall within this range., Conclusion: Despite a statistically significant relationship that exists with aVOR gain output and age, the changes are minor, declining by 0.0088 units per 10 years, justifying the same normative data for all decade age bands.

Objectives: Lateral semicircular canal BPPV (LSC-BPPV) is diagnosed with the Head Yaw Test (HYT) by observing nystagmus direction and comparing the nystagmus intensity on both sides according to Ewald's laws. Head Pitching Test (HPT) is a diagnostic maneuver performed in the upright position by bending the patient's head forward (bowing) and backward (leaning) and observing the evoked nystagmus. We aimed to assess the sensitivity of HPT in correctly diagnosing LSC-BPPV through the quantitative measurement of Bowing and Leaning nystagmus slow-phase velocity (SPV)., Methods: One hundred cases of LSC-BPPV were prospectively enrolled. HPT was performed, looking for pseudospontaneous, bowing, and leaning nystagmus. HYT was considered for the "final diagnosis." HPT was defined as "diagnostic" if the nystagmus was present in at least one position, "undiagnostic" if no nystagmus was detectable. The direction and the SPV of nystagmus in all positions were analyzed and compared to determine the degree of agreement between HPT and HYT., Outcomes: Sixty-four geotropic and 36 apogeotropic forms were diagnosed. HPT was diagnostic in 80 cases, with no difference between the two forms. According to Ewald's laws, the direction of stronger nystagmus evoked by HPT agreed with the HYT results in 39/52 (75%) cases in geotropic forms and 21/28 (75%) cases in apogeotropic forms. The agreement between HPT and HYT was "substantial" considering all the cases and "almost complete" considering only the patients with diagnostic HPT., Conclusion: Quantitative HPT is a valid test in diagnosing the affected side and form of LSC-BPPV, even if less reliable than HYT., Competing Interests: The authors declare no conflict of interest., (Copyright © 2024, Otology & Neurotology, Inc.)

Academia often uses the "circular geometry hypothesis" to explain the sensing principle of the human semicircular canal (SCC) system for angular acceleration, which is widely accepted as an important angular acceleration sensor in the human balance system. On the basis of this hypothesis and the anatomical structure of human SCCs, a series of physical SCC models with different geometries at 4× magnification were prepared via three-dimensional printing and modification of hydrogels. Theoretical models of the SCC perception mechanism were established. Then, impulse angular acceleration, sinusoidal rotation, and sinusoidal linear stimulation were applied to the models, and their responses were visually observed and analyzed in detail. As a result, the circular SCC model had a larger system gain and a smaller phase difference for angular acceleration stimulation but a smaller system gain and a larger phase difference for linear acceleration stimulation. These results verified that the circular semicircular canal was more sensitive to angular acceleration. Our bionic model is hoped to be used for demonstrating the human SCC working process, facilitating researchers in better understanding of the working mechanism of the human SCC, or as a manual model for medical staff to simulate the diagnosis and treatment of human SCC., (Copyright © 2025 by ASME.)

Objectives: Canalith repositioning procedures to treat benign paroxysmal positional vertigo are often applied following standardized criteria, without considering the possible anatomical singularities of the membranous labyrinth for each individual. As a result, certain patients may become refractory to the treatment due to significant deviations from the ideal membranous labyrinth, that was considered when the maneuvers were designed. This study aims to understand the dynamics of the endolymphatic fluid and otoconia, within the membranous labyrinth geometry, which may contribute to the ineffectiveness of the Epley maneuver. Simultaneously, the study seeks to explore methods to avoid or reduce treatment failure., Design: We conducted a study on the Epley maneuver using numerical simulations based on a three-dimensional medical image reconstruction of the human left membranous labyrinth. A high-quality micro-computed tomography of a human temporal bone specimen was utilized for the image reconstruction, and a mathematical model for the endolymphatic fluid was developed and coupled with a spherical particle model representing otoconia inside the fluid. This allowed us to measure the position and time of each particle throughout all the steps of the maneuver, using equations that describe the physics behind benign paroxysmal positional vertigo., Results: Numerical simulations of the standard Epley maneuver applied to this membranous labyrinth model yielded unsatisfactory results, as otoconia do not reach the frontside of the utricle, which in this study is used as the measure of success. The resting times between subsequent steps indicated that longer intervals are required for smaller otoconia. Using different angles of rotation can prevent otoconia from entering the superior semicircular canal or the posterior ampulla. Steps 3, 4, and 5 exhibited a heightened susceptibility to failure, as otoconia could be accidentally displaced into these regions., Conclusions: We demonstrate that modifying the Epley maneuver based on the numerical results obtained in the membranous labyrinth of the human specimen under study can have a significant effect on the success or failure of the treatment. The use of numerical simulations appears to be a useful tool for future canalith repositioning procedures that aim to personalize the treatment by modifying the rotation planes currently defined as the standard criteria., Competing Interests: The authors have no conflicts of interest to disclose., (Copyright © 2024 The Authors. Ear & Hearing is published on behalf of the American Auditory Society, by Wolters Kluwer Health, Inc.)

Objective: To investigate the altered function of the semicircular canal and otolith graviceptive pathway in patients diagnosed with motion sickness disorder (MSD) based on the diagnostic criteria of the Bárány society, and explore its relevance to the pathogenesis of MSD. Methods: This is a case-control study. Twenty patients with MSD and age-and sex-matched healthy controls without a history of MSD from the Department of Neurology of Aerospace Center Hospital between March and August 2022 were recruited. All subjects completed the motion sickness susceptibility questionnaire-short version (MSSQ-short) and the motion sickness assessment questionnaire (MSAQ). Canal function was evaluated using caloric stimulation test and video head impulse test (vHIT), and subjective visual vertical/horizontal (SVV/SVH) and vestibular evoked myogenic potential (VEMP) were employed to assess otolith graviceptive function. Differences in vestibular function and correlations between the two groups were analyzed. Results: Each group consisted of 20 cases (9 males and 11 females). The mean age of the MSD and control groups was (26.9±3.9) years and (27.0±3.4) years, respectively. The scores of MSSQ-short [27.0 (22.5, 38.8) vs 1.2 (0, 3.2), P <0.001] and MSAQ [70.1 (54.5, 78.1) vs 11.8 (11.1, 13.9), P <0.001] were significantly higher in the MSD group compared with those of the control group. Evaluation of canal function revealed a significantly higher incidence of caloric stimulation intolerance in MSD patients (60.0%, 12/20) compared with that of the control group (20.0%, 4/20) ( P =0.010). Evaluation of otolith graviceptive pathway indicated no significant difference in SVV, SVH and cervical VEMP (cVEMP) abnormality rates between the two groups (all P >0.05). The ocular VEMP (oVEMP) abnormality rate was significantly higher in the MSD group (55.0%, 11/20) than that of the control group (10.0%, 2/20) ( P =0.002), with a delayed P1-wave latency compared with the control group [(18.4±1.2) ms vs (17.6±0.8) ms, P =0.018]. Further correlation analysis revealed that P1-wave latency in oVEMP was positively correlated with MSSQ-short ( r =0.486, P =0.002) and MSAQ ( r =0.391, P =0.015) scores, and duration of caloric intolerance symptoms ( r =0.377, P =0.004). Conclusion: The presence of hypersensitivity to caloric stimulation and delayed latency of otolith function in patients with MSD suggests a "separation" between semicircular canal and otolithic function, which may be related to sensory conflict.

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., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Background: Vestibular stimulation causes postural unsteadiness accompanied by a sensation of tilt., Aims/objectives: 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., Material and Methods: 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., Results: 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., Conclusion and Significance: 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.

Noninvasive electrical stimulation of the vestibular system in humans has become an increasingly popular tool with a broad range of research and clinical applications. However, common assumptions regarding the neural mechanisms that underlie the activation of central vestibular pathways through such stimulation, known as galvanic vestibular stimulation (GVS), have not been directly tested. Here, we show that GVS is encoded by VIIIth nerve vestibular afferents with nonlinear dynamics that differ markedly from those predicted by current models. GVS produced asymmetric activation of both semicircular canal and otolith afferents to the onset versus offset and cathode versus anode of applied current, that in turn produced asymmetric eye movement responses in three awake-behaving male monkeys. Additionally, using computational methods, we demonstrate that the experimentally observed nonlinear neural response dynamics lead to an unexpected directional bias in the net population response when the information from both vestibular nerves is centrally integrated. Together our findings reveal the neural basis by which GVS activates the vestibular system, establish that neural response dynamics differ markedly from current predictions, and advance our mechanistic understanding of how asymmetric activation of the peripheral vestibular system alters vestibular function. We suggest that such nonlinear encoding is a general feature of neural processing that will be common across different noninvasive electrical stimulation approaches. SIGNIFICANCE STATEMENT Here, we show that the application of noninvasive electrical currents to the vestibular system (GVS) induces more complex responses than commonly assumed. We recorded vestibular afferent activity in macaque monkeys exposed to GVS using a setup analogous to human studies. GVS evoked notable asymmetries in irregular afferent responses to cathodal versus anodal currents. We developed a nonlinear model explaining these GVS-evoked afferent responses. Our model predicts that GVS induces directional biases in centrally integrated head motion signals and establishes electrical stimuli that recreate physiologically plausible sensations of motion. Altogether, our findings provide new insights into how GVS activates the vestibular system, which will be vital to advancing new clinical and biomedical applications., (Copyright © 2023 the authors.)

Strong magnetic fields induce dizziness, vertigo, and nystagmus due to Lorentz forces acting on the cupula in the semi-circular canals, an effect called magnetic vestibular stimulation (MVS). In this article, we present an experimental setup in a 7T MRT scanner (MRI scanner) that allows the investigation of the influence of strong magnetic fields on nystagmus as well as perceptual and cognitive responses. The strength of MVS is manipulated by altering the head positions of the participants. The orientation of the participants' semicircular canals with respect to the static magnetic field is assessed by combining a 3D magnetometer and 3D constructive interference in steady-state (3D-CISS) images. This approach allows to account for intra- and inter-individual differences in participants' responses to MVS. In the future, MVS can be useful for clinical research, for example, in the investigation of compensatory processes in vestibular disorders. Furthermore, it could foster insights into the interplay between vestibular information and cognitive processes in terms of spatial cognition and the emergence of self-motion percepts under conflicting sensory information. In fMRI studies, MVS can elicit a possible confounding effect, especially in tasks influenced by vestibular information or in studies comparing vestibular patients with healthy controls.

Objectives: Although vestibular deficits can have severe repercussions on the early motor development in children, vestibular assessment in young children has not yet been routinely integrated in clinical practice and clear diagnostic criteria to detect early vestibular deficits are lacking. In young children, specific adjustments of the test protocol are needed, and normative data are age-dependent as the vestibular pathways mature through childhood. Therefore, this study aims to demonstrate the feasibility of an extensive age-dependent vestibular test battery, to provide pediatric normative data with the concurrent age trends, and to offer a clinical framework for pediatric vestibular testing., Design: This normative study included 133 healthy children below the age of 4 years (mean: 22 mo, standard deviation: 12.3 mo, range: 5-47 mo) without history of hearing loss or vestibular symptoms. Children were divided into four age categories: 38 children younger than 1 year old, 37 one-year olds, 33 two-year olds, and 25 three-year olds. Children younger than 3 years of age were examined with the video Head Impulse Test (vHIT) of the horizontal semicircular canals, cervical vestibular evoked myogenic potentials (cVEMP) with bone conduction stimuli, and the rotatory test at 0.16, 0.04, and 0.01 Hz. In 3-year old children, the vHIT of the vertical semicircular canals and ocular vestibular evoked myogenic potentials (oVEMP) using a minishaker were added to the protocol., Results: The horizontal vHIT appeared to be the most feasible test across age categories, except for children younger than 1-year old in which the success rate was the highest for the cVEMP. Success rates of the rotatory test varied the most across age categories. Age trends were found for the vHIT as the mean vestibulo-ocular reflex (VOR) gain increased significantly with age (r = 0.446, p < 0.001). Concerning the cVEMP, a significant increase with age was found for latency P1 (r = 0.420, p < 0.001), rectified interpeak amplitude P1-N1 (r = 0.574, p < 0.001), and averaged electromyographic (EMG) activity (r = 0.430, p < 0.001), whereas age trends for the latency N1 were less pronounced (r = 0.264, p = 0.004). Overall, the response parameters of the rotatory test did not show significant age effects ( p > 0.01), except for the phase at 0.01 Hz (r = 0.578, p < 0.001). Based on the reported success rates and age-dependent normative vestibular data, straightforward cutoff criteria were proposed (vHIT VOR gain < 0.7, cVEMP rectified interpeak amplitude < 1.3, oVEMP interpeak amplitude < 10 µV) with accompanying clinical recommendations to diagnose early vestibular impairment., Conclusions: In this large cohort of typically developing children below the age of 4 years, the vHIT and cVEMP were the most feasible vestibular tests. Moreover, the age-dependent normative vestibular data could specify age trends in this group of young children. Finally, based on the current results and clinical experience of more than ten years at the Ghent University Hospital (Belgium), a clinical framework to diagnose early vestibular deficits in young patients is proposed., Competing Interests: None of the authors have financial or non-financial conflicts of interest to disclose relevant to this paper., (Copyright © 2022 Wolters Kluwer Health, Inc. All rights reserved.)

Neurophysiological tests probing the vestibulo-ocular, colic and spinal pathways are the gold standard to evaluate the vestibular system in clinics. In contrast, vestibular perception is rarely tested despite its potential usefulness in professional training and for the longitudinal follow-up of professionals dealing with complex man-machine interfaces, such as aircraft pilots. This is explored here using a helicopter flight simulator to probe the vestibular perception of pilots. The vestibular perception of nine professional helicopter pilots was tested using a full flight helicopter simulator. The cabin was tilted six times in roll and six times in pitch (-15°, -10°, -5°, 5°, 10° and 15°) while the pilots had no visual cue. The velocities of the outbound displacement of the cabin were kept below the threshold of the semicircular canal perception. After the completion of each movement, the pilots were asked to put the cabin back in the horizontal plane (still without visual cues). The order of the 12 trials was randomized with two additional control trials where the cabin stayed in the horizontal plane but rotated in yaw (-10° and +10°). Pilots were significantly more precise in roll (average error in roll: 1.15 ± 0.67°) than in pitch (average error in pitch: 2.89 ± 1.06°) (Wilcoxon signed-rank test: p < 0.01). However, we did not find a significant difference either between left and right roll tilts (p = 0.51) or between forward and backward pitch tilts (p = 0.59). Furthermore, we found that the accuracies were significantly biased with respect to the initial tilt. The greater the initial tilt was, the less precise the pilots were, although maintaining the direction of the tilt, meaning that the error can be expressed as a vestibular error gain in the ability to perceive the modification in the orientation. This significant result was found in both roll (Friedman test: p < 0.01) and pitch (p < 0.001). However, the pitch trend error was more prominent (gain = 0.77 vs gain = 0.93) than roll. This study is a first step in the determination of the perceptive-motor profile of pilots, which could be of major use for their training and their longitudinal follow-up. A similar protocol may also be useful in clinics to monitor the aging process of the otolith system with a simplified testing device., (© 2023 The Authors. Physiological Reports published by Wiley Periodicals LLC on behalf of The Physiological Society and the American Physiological Society.)

With increasing life expectancy, there is an increase in the number of patients with symptoms caused by aging of the vestibular system - presbyvestibulopathy. Presbyvestibulopathy is based on degenerative processes in various parts of the vestibular analyzer - from the semicircular canals and otolithic receptors to the conduction tracts and vestibular nuclei. When examining such patients, it is necessary to take into account the multiplicity of damage to sensory systems in the elderly (impaired balance, vision, cognitive functions). Recognizing presbyvestibulopathy as part of the multifaceted aging process will help to develop comprehensive approaches to the treatment of patients who are always at risk for deterioration of the condition. In this review, we discuss the association of presbyvestibulopathy with neurodegenerative diseases, as well as the correlation between presbyvestibulopathy and balance, visual, cognitive, and psychological disorders.

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.

Background: During a simulated coordinated turn in a gondola centrifuge, experienced pilots show a substantial inter-individual variability in visual measures of perceived roll tilt. Because of the centrifuge's small radius, the pattern of stimuli to the semicircular canals during acceleration of the centrifuge differs in certain respects from that of an aircraft entering a turn., Objective: To explore whether these differences may be of significance for the pilot's roll- plane orientation and whether individual characteristics revealed in the centrifuge correspond to those during real flight., Method: 8 fixed-wing air-force pilots were tested in a centrifuge and a high-performance aircraft. The centrifuge was accelerated to 2 G (gondola inclination 60°) within 10 s. The duration at 2 G was 6 minutes. Similar profiles were created in the aircraft. The subjective visual horizontal (SVH) was measured using an adjustable luminous line in darkness. Each pilot was tested on three occasions: centrifuge (2 runs), aircraft (2 turns), centrifuge (2 runs). For each 2-G exposure, initial and final SVH values were established via curve fitting., Result: Despite a large inter-individual variability (±SD), group means were similar in the aircraft (initial: 43.0±20.6°; final: 22.5±14.8°) and centrifuge (initial: 40.6±17.0°; final: 20.5±16.0°). Further, individual peculiarities in response patterns were similar in the two conditions. For both the initial and final SVH tilt there was a high correlation between centrifuge and aircraft., Conclusion: The correspondence between conditions suggests that the centrifuge is an adequate means for demonstrating the fundamental motion pattern of coordinated flight and also for establishing the individual pilot's ability to perceive an aircraft's roll attitude.Findings are discussed in connection with vestibular learning and the possibility of underlying differences between pilots in the keenness for semicircular canal and somatosensory cues.

The vertebrate vestibular system is crucial for balance and navigation, and the evolution of its form and function in relation to species' lifestyle and mode of locomotion has been the focus of considerable recent study. Most research, however, has concentrated on aboveground mammals, with much less published on subterranean fauna. Here, we explored variation in anatomy and sensitivity of the semicircular canals among 91 mammal species, including both subterranean and non-subterranean representatives. Quantitative phylogenetically informed analyses showed significant widening of the canals relative to radius of curvature in subterranean species. A relative canal width above 0.166 indicates with 95% certainty that a species is subterranean. Fluid-structure interaction modelling predicted that canal widening leads to a substantial increase in canal sensitivity; a reasonably good estimation of the absolute sensitivity is possible based on the absolute internal canal width alone. In addition, phylogenetic comparative modelling and functional landscape exploration revealed repeated independent evolution of increased relative canal width and anterior canal sensitivity associated with the transition to a subterranean lifestyle, providing evidence of parallel adaptation. Our results suggest that living in dark, subterranean tunnels requires good balance and/or navigation skills which may be facilitated by more sensitive semicircular canals., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Background: Certain cases of superior semicircular canal dehiscence or benign paroxysmal positional vertigo can be treated by plugging of the affected semicircular canal. However, the extent of the impact on vestibular function and hearing during postoperative follow-up is not known., Objective: To evaluate the evolution of vestibular function and hearing after plugging of a semicircular canal., Methods: Six patients underwent testing before and 1 week, 2 months, and 6 months after plugging of the superior or posterior semicircular canal. Testing included caloric irrigation test, video Head Impulse Test (vHIT), cervical and ocular Vestibular Evoked Myogenic Potentials (VEMPs) and audiometry., Results: Initially, ipsilateral caloric response decreased in all patients and vHIT vestibulo-ocular reflex (VOR) gain of each ipsilateral semicircular canal decreased in 4/6 patients. In 4/6 patients, postoperative caloric response recovered to > 60% of the preoperative value. In 5/6 patients, vHIT VOR gain was restored to > 85% of the preoperative value for both ipsilateral non-plugged semicircular canals. In the plugged semicircular canal, this gain decreased in 4/5 patients and recovered to > 50% of the preoperative value. Four patients preserved cervical and ocular VEMP responses. Bone conduction hearing deteriorated in 3/6 patients, but recovered within 6 months postoperatively, although one patient had a persistent loss of 15 dB at 8 kHz., Conclusion: Plugging of a semicircular canal can affect both vestibular function and hearing. After initial deterioration, most patients show recovery during follow-up. However, a vestibular function loss or high-frequency hearing loss can persist. This stresses the importance of adequate counseling of patients considering plugging of a semicircular canal., (© 2021. The Author(s).)

This study aimed to test the role of the otolithic system in self-motion perception by examining adaptive responses to asymmetric off-axis vertical rotation. Self-movement perception was examined after a conditioning procedure consisting of prolonged asymmetric sinusoidal yaw rotation of the head on a stationary body with hemicycle faster than the other hemicycle. This asymmetric velocity rotation results in a cumulative error in spatial self-motion perception in the upright position that persists over time. Head yaw rotation conditioning was performed in different head positions: in the upright position to activate semicircular canals and in the supine and prone positions to activate both semicircular canals and otoliths with the phase of otolithic stimulation reversed with respect to activation of the semicircular canals. The asymmetric conditioning influenced the cumulative error induced by four asymmetric cycles of whole-body vertical axis yaw rotation. The magnitude of this error depended on the orientation of the head during the conditioning. The error increased by 50% after upright position conditioning, by 100% in the supine position, and decreased by 30% in the prone position. The enhancement and reduction of the perceptual error are attributed to otolithic modulation because of gravity influence of the otoliths during the conditioning procedure in supine and prone positions. These findings indicate that asymmetric velocity otolithic activation induces adaptive perceptual errors such as those induced by semicircular canals alone, and this adaptation may be useful in testing dynamic otolithic perceptual responses under different conditions of vestibular dysfunction., (© 2022. The Author(s).)

The effect of varying sinusoidal linear acceleration on perception of human motion was examined using 4 motion paradigms: off-vertical axis rotation, variable radius centrifugation, linear lateral translation, and rotation about an earth-horizontal axis. The motion profiles for each paradigm included 6 frequencies (0.01-0.6 Hz) and 5 tilt amplitudes (5°-20°). Subjects verbally reported the perceived angle of their whole-body tilt and the peak-to-peak translation of their head in space and used a joystick capable of recording 2-axis motion in the sagittal and transversal planes to indicate the phase between the perceived and actual motions. The amplitudes of perceived tilt and translation were expressed in terms of gain, i.e., the ratio of perceived tilt to equivalent tilt angle, and the ratio of perceived translation to equivalent linear displacement. Tilt perception gain decreased, whereas translation perception gain increased, with increasing frequency. During off-vertical axis rotation, the phase of tilt perception and of translation perception did not vary across stimulus frequencies. These motion paradigms elicited similar responses in roll tilt and interaural perception of translation, with differences likely due to the influence of naso-occipital linear accelerations and input to the semicircular canals that varied across motion paradigms., (© 2022. The Author(s).)

The vestibular system detects head motion to coordinate vital reflexes and provide our sense of balance and spatial orientation. A long-standing hypothesis has been that projections from the central vestibular system back to the vestibular sensory organs (i.e., the efferent vestibular system) mediate adaptive sensory coding during voluntary locomotion. However, direct proof for this idea has been lacking. Here we recorded from individual semicircular canal and otolith afferents during walking and running in monkeys. Using a combination of mathematical modeling and nonlinear analysis, we show that afferent encoding is actually identical across passive and active conditions, irrespective of context. Thus, taken together our results are instead consistent with the view that the vestibular periphery relays robust information to the brain during primate locomotion, suggesting that context-dependent modulation instead occurs centrally to ensure that coding is consistent with behavioral goals during locomotion., (© 2022. The Author(s).)

Background: Parkinson's disease (PD) is a common multi-system neurodegenerative disorder with possible vestibular system dysfunction, but prior vestibular function test findings are equivocal., Objective: To report and compare vestibulo-ocular reflex (VOR) gain as measured by the video head impulse test (vHIT) in participants with PD, including tremor dominant and postural instability/gait dysfunction phenotypes, with healthy controls (HC)., Methods: Forty participants with PD and 40 age- and gender-matched HC had their vestibular function assessed. Lateral and vertical semicircular canal VOR gains were measured with vHIT. VOR canal gains between PD participants and HC were compared with independent samples t-tests. Two distinct PD phenotypes were compared to HC using Tukey's ANOVA. The relationship of VOR gain with PD duration, phenotype, severity and age were investigated using logistic regression., Results: There were no significant differences between groups in vHIT VOR gain for lateral or vertical canals. There was no evidence of an effect of PD severity, phenotype or age on VOR gains in the PD group., Conclusion: The impulsive angular VOR pathways are not significantly affected by the pathophysiological changes associated with mild to moderate PD.

Direct and indirect pathways mediating the vestibulo-ocular reflexes, considering contributions made by the vestibular commissure, cerebellum, and vestibular efferent neurons are reviewed. This background leads to a detailed treatment of three-dimensional aspects of the vestibulo-ocular reflex, comparing the planes of the labyrinthine semicircular canals with the pulling directions of the extraocular muscles. By applying matrix algebra and rotational vectors, Robinson provides insights into the comparative anatomy of the vestibular system in different species, how central circuits process raw vestibular signals in three dimensions, and how the directions of eye movement caused by brainstem and cerebellar lesions can be explained., (Copyright © 2022 Elsevier B.V. All rights reserved.)

The biophysical properties of the labyrinthine semicircular canals, and the electrophysiological properties of peripheral vestibular afferent neurons over a range of stimulus frequencies, are reviewed. Resting discharge activity and adaptive properties of vestibular neurons are discussed. Central processing of vestibular signals is then examined, including push-pull organization and the velocity storage mechanism. A detailed treatment of the final common neural integrator for oculomotor signals follows with consideration of its neural substrate and how distributed networks of neurons can overcome several problems posed by conventional control-systems models, such as why neural signals, but not background discharge, are integrated. Next, the behavior of the vestibulo-ocular reflex in darkness is compared with how it satisfies visual demands during natural activities. Finally, the reflex's performance at high frequencies of head rotation is discussed., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Background: Vestibulo-ocular reflex (VOR) function is expected to be normal in patients with presbycusis during sudden head rotations., Aim: This study aimed to determine whether presbycusis was accompanied by vestibular system pathologies. In addition, it was examined whether there was a difference existed between the patients with and without presbycusis in terms of normative data., Materials and Methods: A total of 40 individuals were included in the study: 20 in the presbycusis group and 20 in the control group. The vestibular systems of both groups were evaluated using the video head impulse test and videonystagmography., Results: The right and left lateral VOR gain values were decreased in the group with presbycusis compared to the control group. The difference between the two groups in the mean VOR gains in the right lateral canal and left lateral canal were statistically significant ( p  = .040 and p  = .050, respectively). The air caloric tests of all individuals were found to be normal., Conclusions: This result suggests that the loss of vestibular hair cells and vestibular nerve degeneration in the lateral semicircular canal may be more severe in presbycusis than in the same age group with normal hearing.

The vestibular receptor of cupula acts an important role in maintaining body balance. However, the cupula buried in the semicircular canals (SCCs) will be destroyed if it is detached from the relevant environment. The mechanical properties of human cupula still remain ambiguous. In this paper, we explored the cupula responses changing with temperature by experiments and numerical simulation of SCCs model. We obtained 3 volunteers' nystagmus induced by constant angular acceleration when the temperature of volunteers' SCCs was 36 °C and 37 °C respectively. The slow-phase velocity of 3 volunteers decreased by approximately 3°/s when the temperature of SCCs reduced by 1 °C, which corresponded to the reduction of cupula deformation by 0.3-0.8 μm in the numerical model. Furthermore, we investigated the effects of the variation of endolymphatic properties induced by temperature reduction on cupula deformation through numerical simulation. We found that the decrease of cupula deformation was not caused by the change of endolymphatic properties, but probably by the increase of cupula's elastic modulus. With the temperature reducing by 1 °C, the cupula's elastic modulus may increase by 6-20%, suggesting that the stiffness of cupula is enhanced. This exploration of temperature characteristic of human cupula promotes the research of alleviating vestibular diseases.

Background: Otosclerosis and stapedotomy have some effects on the vestibular system, but there are very limited data on their effects on semicircular canals (SCCs)., Objective: The aim of the study is to investigate if otosclerosis and stapedotomy have an effect on SCCs and video head impulse test (vHIT)., Material and Methods: This retrospective study included 11 otosclerosis patients who had undergone stapedotomy and 30 healthy participants. Twenty-two ears of 11 patients with otosclerosis were divided into two groups based on whether the ear had been operated (12 ears) or not (10 ears). All participants underwent vHIT. We compared gains of all SCCs, presence of saccades among the operated ears, unoperated ears and control ears., Results: Significant difference ( p <.05) was noted in comparisons of gain of lateral SCCs among all groups. Control group had the highest gain, followed by unoperated and operated groups, respectively. Comparison of incidence of covert saccade showed significant difference ( p <.05) for lateral and posterior SCCs., Conclusions and Significance: Otosclerosis and otosclerosis surgery may have some effects on SCC functions and thereby vHIT. Lateral SCC is the most affected SCC in terms of gain. These findings appear to add important contributions to our knowledge.

Benign paroxysmal positional vertigo (BPPV) is a clinical condition. The existing diagnostic methods cannot determine the specific location of otolith on the short or long brachial sides. Thus, visual and quantitative evaluation of the existing clinical standard diagnostic modality Dix-Hallpike test is needed to improve medical efficiency. Our goal was to develop a real-time virtual simulation system to assess a BPPV treatment manipulation. In this study, we used the proposed simulation system to observe otolith movement during a posterior semicircular canal BPPV diagnostic test, and to analyze the diagnostic mechanisms and strategies. Through visual cluster analysis of otolith position and analysis of otolith movement time in the standard Dix-Hallpike test, we can find that the positions of otoliths are relatively scattered, especially on the z -axis ( z 1  = 10.67 ± 3.98), and the fall time of otoliths at different positions has relatively large changes ( t 1  = 22.21 ± 1.40). But in the modified experiment z 2  = 4.93 ± 0.32 and t 2  = 26.21 ± 0.28. The experimental results show that the simulation system could track the state and the movement of otolith in real-time, which is of great significance for understanding the diagnostic mechanisms of BPPV evaluations and improving the diagnostic method., (© 2021 Walter de Gruyter GmbH, Berlin/Boston.)

Background: The vHIT device, which has a mechanism based on measuring the VOR gain, helps us to quickly evaluate six semicircular canals., Aims/objectives: The aim of this study was to establish normative values for semicircular canal function with the video head impulse test (vHIT) battery in normal adolescents., Material and Methods: 100 (50 females, 50 males) individuals aged 11-18 years, with a mean age of 14.99 years, were included in the study., Results: As a result of the vHIT evaluations performed with vHIT Otometrics ICS Impulse A/S Taastrup, Denmark, the mean lateral canal vestibulo-ocular reflex (VOR) gain value was 0.96, the mean anterior canal VOR gain value was 0.89, and the mean posterior canal VOR gain value was 0.87, all of which were within the normal value range., Conclusion and Significance: While the VOR gain values and asymmetry values are within the normal value range and are similar to the literature, no statistically significant correlation was observed between these values and age. As a result, the vHIT battery is an easy, fast, and practical test method that can be used in adolescents.

Electrical stimulation of the mammalian efferent vestibular system (EVS) predominantly excites primary vestibular afferents along two distinct time scales. Although roles for acetylcholine (ACh) have been demonstrated in other vertebrates, synaptic mechanisms underlying mammalian EVS actions are not well-characterized. To determine if activation of ACh receptors account for efferent-mediated afferent excitation in mammals, we recorded afferent activity from the superior vestibular nerve of anesthetized C57BL/6 mice while stimulating EVS neurons in the brainstem, before and after administration of cholinergic antagonists. Using a normalized coefficient of variation (CV*), we broadly classified vestibular afferents as regularly- (CV* < 0.1) or irregularly-discharging (CV* > 0.1) and characterized their responses to midline or ipsilateral EVS stimulation. Afferent responses to efferent stimulation were predominantly excitatory, grew in amplitude with increasing CV*, and consisted of fast and slow components that could be identified by differences in rise time and post-stimulus duration. Both efferent-mediated excitatory components were larger in irregular afferents with ipsilateral EVS stimulation. Our pharmacological data show, for the first time in mammals, that muscarinic AChR antagonists block efferent-mediated slow excitation whereas the nicotinic AChR antagonist DHβE selectively blocks efferent-mediated fast excitation, while leaving the efferent-mediated slow component intact. These data confirm that mammalian EVS actions are predominantly cholinergic.

Reconstructing locomotor behaviour for fossil animals is typically done with postcranial elements. However, for species only known from cranial material, locomotor behaviour is difficult to reconstruct. The semicircular canals (SCCs) in the inner ear provide insight into an animal's locomotor agility. A relationship exists between the size of the SCCs relative to body mass and the jerkiness of an animal's locomotion. Additionally, studies have also demonstrated a relationship between SCC orthogonality and angular head velocity. Here, we employ two metrics for reconstructing locomotor agility, radius of curvature dimensions and SCC orthogonality, in a sample of twelve fossil rodents from the families Ischyromyidae, Sciuridae and Aplodontidae. The method utilizing radius of curvature dimensions provided a reconstruction of fossil rodent locomotor behaviour that is more consistent with previous studies assessing fossil rodent locomotor behaviour compared to the method based on SCC orthogonality. Previous work on ischyromyids suggests that this group displayed a variety of locomotor modes. Members of Paramyinae and Ischyromyinae have relatively smaller SCCs and are reconstructed to be relatively slower compared to members of Reithroparamyinae. Early members of the Sciuroidea clade including the sciurid Cedromus wilsoni and the aplodontid Prosciurus relictus are reconstructed to be more agile than ischyromyids, in the range of extant arboreal squirrels. This reconstruction supports previous inferences that arboreality was likely an ancestral trait for this group. Derived members of Sciuridae and Aplodontidae vary in agility scores. The fossil squirrel Protosciurus cf. rachelae is inferred from postcranial material as arboreal, which is in agreement with its high agility, in the range of extant arboreal squirrels. In contrast, the fossil aplodontid Mesogaulus paniensis has a relatively low agility score, similar to the fossorial Aplodontia rufa, the only living aplodontid rodent. This result is in agreement with its postcranial reconstruction as fossorial and with previous indications that early aplodontids were more arboreal than their burrowing descendants., (© 2020 Anatomical Society.)

The malfunctioning of semicircular canals (SCCs) in the vestibular system results in diseases that disrupt the individual's daily life. Vestibular diseases can be treated more effectively if the functioning of the SCCs is better understood. However, the SCC is difficult to dissect, because it is a complex structure buried deep in the inner ear. To thoroughly understand the function of SCCs and provide better treatment plans for vestibular diseases, we constructed a numerical model of human SCCs and validated it experimentally. Based on the principle of the vestibulo-ocular reflex, the cupula deformation deflects embedded sensory hair cell bundles, transmitting signals to the brain and inducing a slow compensatory eye movement. The slow-phase velocity (SPV) is the characteristic of the slow compensatory eye movement. We investigated the cupula deformation in the numerical model and the SPV under different conditions. The relationship between the cupula deformation and the SPV was quantified for three volunteers. It was observed that the maximal cupula deformation is proportional to the angular acceleration, while the SPV is changing nonlinearly with the angular acceleration. For three volunteers, the relationship between the cupula deformation and the SPV can be expressed by same type function of which the parameters are dependent on individual differences. These results validate the reliability of the numerical model.

For over a century, researchers have assumed that the plane of the lateral semicircular canal of the inner ear lies parallel to the horizon when the head is at rest, and used this assumption to reconstruct head posture in extinct species. Although this hypothesis has been repeatedly questioned, it has never been tested on a large sample size and at a broad taxonomic scale in mammals. This study presents a comprehensive test of this hypothesis in over one hundred "ungulate" species. Using CT scanning and manual segmentation, the orientation of the skull was reconstructed as if the lateral semicircular canal of the bony labyrinth was aligned horizontally. This reconstructed cranial orientation was statistically compared to the actual head posture of the corresponding species using a dataset of 10,000 photographs and phylogenetic regression analysis. A statistically significant correlation between the reconstructed cranial orientation and head posture is found, although the plane of the lateral semicircular canal departs significantly from horizontal. We thus caution against the use of the lateral semicircular canal as a proxy to infer precisely the horizontal plane on dry skulls and in extinct species. Diet (browsing or grazing) and head-butting behaviour are significantly correlated to the orientation of the lateral semicircular canal, but not to the actual head posture. Head posture and the orientation of the lateral semicircular canal are both strongly correlated with phylogenetic history.

Aims: Although the vestibular system has been widely investigated over the past 50 years, there is still an unsolved mystery. Some special vestibular afferent (SVA) neurons responding to both rotation and linear force were found through neurophysiological techniques, however, the sensory overlap mechanism of SVA neurons is still unclear, which may be closely related to vestibular-related diseases., Materials and Methods: To address the above-mentioned problem, a cupula buoyancy theory was established in the present study, where SVA neurons were considered semicircular canal afferent (SCCA) neurons. Then labyrinth anatomy and neural response dynamics of vestibular afferent neurons in chinchilla were investigated through vestibular labyrinth reconstruction and single unit recording technique, respectively., Key Findings: We analyzed the deflections of cupulae under multiple conditions with the help of Amira Software and predicted the neural response law of SCCA neurons to linear force based on the cupula buoyancy theory. Data analysis confirmed that the basic response characteristic of SVA neurons had no significant difference to those of SCCA neurons, but were significantly different from those of otolith afferent neurons. Further, the actual responses of SVA neurons to linear force are completely consistent with our predictions. These results strongly suggest that SVA neurons actually are SCCA neurons, and the cupula buoyancy theory is the key to the sensory overlap mechanism of SCCA neurons., Significance: Our study revealed the real identity of SVA neurons and provided a reasonable mechanism for sensory overlap of rotation and linear force, which improved our understanding about the vestibular system., Competing Interests: Declaration of competing interest The authors declare that they have no competing interests, and all authors confirmed the accuracy of the data., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Previous studies have found GABA in vestibular end organs. However, existence of GABA receptors or possible GABAergic effects on vestibular nerve afferents has not been investigated. The current study was conducted to determine whether activation of GABA B receptors affects calyx afferent terminals in the central region of the cristae of semicircular canals. We used patch-clamp recording in postnatal day 13-18 (P13-P18) Sprague-Dawley rats of either sex. Application of GABA B receptor agonist baclofen inhibited voltage-sensitive potassium currents. This effect was blocked by selective GABA B receptor antagonist CGP 35348. Application of antagonists of small (SK)- and large-conductance potassium (BK) channels almost completely blocked the effects of baclofen. The remaining baclofen effect was blocked by cadmium chloride, suggesting that it could be due to inhibition of voltage-gated calcium channels. Furthermore, baclofen had no effect in the absence of calcium in the extracellular fluid. Inhibition of potassium currents by GABA B activation resulted in an excitatory effect on calyx terminal action potential firing. While in the control condition calyces could only fire a single action potential during step depolarizations, in the presence of baclofen they fired continuously during steps and a few even showed repetitive discharge. We also found a decrease in threshold for action potential generation and a decrease in first-spike latency during step depolarization. These results provide the first evidence for the presence of GABA B receptors on calyx terminals, showing that their activation results in an excitatory effect and that GABA inputs could be used to modulate calyx response properties. NEW & NOTEWORTHY Using in vitro whole cell patch-clamp recordings from calyx terminals in the vestibular end organs, we show that activation of GABA B receptors result in an excitatory effect, with decreased spike-frequency adaptation and shortened first-spike latencies. Our results suggest that these effects are mediated through inhibition of calcium-sensitive potassium channels.

Background: Generally, vertical component of the skull vibratory nystagmus (VCN) is ignored in the clinical practise. Thus, the relative contribution of the vestibular organs in the presence of VCN remains unknown. Objectives: To determine the association between vertical semicircular canal (vSCC) function and the presence of VCN. Material and methods: Comparisons were made between Video Head Impulse Test and SVINT (100 Hz) results at the time of the acute peripheral vestibular lesion (PVL) and at the post-acute phase in patients diagnosed PVL. Later on, a paired analysis was performed restricting the assessments to patients with vestibular explorations in both the acute and post-acute phases. Results: In an univariable analysis, larger mean total gain differences (TGD) between vSCC VOR gains, significantly related with the appearance of VCN in nystagmography in the acute phase ( p  = .001), unlike the post-acute phase ( p  = .46). After a multivariate analysis, mean TGD was the only predictive factor of the VCN ( p  = .013). In the paired analysis, we found an increase in the post-acute phase mean TGD, approaching zero value. Conclusions and significance: Global relation between all vertical canals has at least a contributory role in the presence of the vertical component of nystagmus in SVINT.

Objective: We tested more frequency (0.01-3.0 Hz) of the sinusoidal harmonic acceleration test(SHAT) by the NKI rotation chair, aimed to analyze the results of the normal youth. Methods: Fifty normal young people were tested with sinusoidal harmonic acceleration by NKI rotation chair. Including 24 men and 26 women, aged from 20 to 40 years old, with median age of 27 years, with no vestibular dysfunction participated in the present study. All the volunteers accepted the sinusoidal harmonic acceleration test by the NKI rotation chair, the frequency included 0.01 Hz, 0.02 Hz, 0.03 Hz, 0.05 Hz, 0.1 Hz, 0.2 Hz, 0.3 Hz, 0.6 Hz, 1.0 Hz, 1.5 Hz, 2.0 Hz, 3.0 Hz. Taken the gain, phase, and asymmetry as the parameters, the trait of each frequency was analysed. Results: From 0.01 Hz to 1.5 Hz, the gain increased close to 1 gradually, and with fluctuates slightly at the 2.0 Hz and 3.0 Hz frequencies. The phase decreased as frequencies increased close to 0 at 0.3 Hz. The frequency above 0.6 Hz presented negative. Asymmetric values were distributed on both positive and negative sides at each frequency and were different from each other, both values were less than 20%. Conclusion: Broadband SHAT can accurately assess the horizontal semicircular canal function at different frequencies in a wider frequency range, and objectively, reflect the physiological function of the horizontal semicircular canal, and expand the clinical value of traditional SHAT.

Our research described in this article was motivated by the puzzling finding of the Skylab M131 experiments: head movements made while rotating that are nauseogenic and disorienting on Earth are innocuous in a weightless, 0- g environment. We describe a series of parabolic flight experiments that directly addressed this puzzle and discovered the gravity-dependent responses to semicircular canal stimulation, consistent with the principles of velocity storage. We describe a line of research that started in a different direction, investigating dynamic balancing, but ended up pointing to the gravity dependence of angular velocity-to-position integration of semicircular canal signals. Together, these lines of research and the theoretical framework of velocity storage provide an answer to at least part of the M131 puzzle. We also describe recently discovered neural circuits by which active, dynamic vestibular, multisensory, and motor signals are interpreted as either appropriate for action and orientation or as conflicts evoking motion sickness and disorientation.

Over 30 years ago, the head impulse test (HIT) was measured with search coil recordings and it provided robust evidence for a new test of vestibular function that could detect impairment of a single semicircular canal, that is, the lateral canal. Over the next two decades, the diagnostic spectrum of HIT was expanded to the testing of vertical canals, differentiation of central from peripheral vestibulopathy, and incorporation of visual interaction-the suppressed head impulse. However, HIT measurement was limited to very few specialized laboratories that were able to maintain the time-consuming and expensive operation of the scleral search coil system, which is the gold standard in eye movement recording. The video HIT (vHIT) was validated for the first time over 10 years ago, against the search coils, and its introduction into dizzy clinics worldwide has revolutionized the practice of neuro-otology. Here we review the basic physiology, practical aspects, and clinical application of the vHIT., Competing Interests: Disclosure The authors report no conflicts of interest in this work., (Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.)

Recent research has shown promising results for the development of a clinically feasible vestibular implant in the near future. However, correct electrode placement remains a challenge. It was shown that fluoroscopy was able to visualize the semicircular canal ampullae and electrodes, and guide electrode insertion in real time. Ninety-four percent of the 18 electrodes were implanted correctly (<1.5 mm distance to target). The median distances were 0.60 mm, 0.85 mm, and 0.65 mm for the superior, lateral, and posterior semicircular canal, respectively. These findings suggest that fluoroscopy can significantly improve electrode placement during vestibular implantation., (Copyright © 2019 The Author(s). Published by Elsevier Inc. All rights reserved.)

The normal function of the vestibular system is crucial for the sense of balance. The techniques used to assess the vestibular function plays a vital role in the research of the vestibular system. In this article, we have systematically reviewed some popular methods employing vestibular reflexes and vestibular evoked potentials for assessing the vestibular function in rodent models. These vestibular reflexes and vestibular evoked potentials to effective stimuli have been used as nondestructive and objective functional measures. The main types of vestibular reflexes include the vestibulo-ocular reflex (VOR), vestibulocollic reflex (VCR), and vestibulo-sympathetic reflex (VSR). They are all capable of indicating the functions of the semicircular canals and otoliths. However, the VOR assessment is much more prevalently used because of the relatively stereotypical inputoutput relationship and simple motion pattern of the ocular response. In contrast, the complicated motion pattern and small gain of the VCR response, as well as the undesired component possibly contributed from the acceleration receptors outside the labyrinths in the VSR response, restrict the widespread applications of VCR and VSR in the assessment of the vestibular system. The vestibular evoked myogenic potentials (VEMPs) and vestibular sensory evoked potentials (VsEPs) are the two typical evoked potentials that have been also employed for evaluating the vestibular function. Through exploiting different types of the VEMPs, the saccular and utricular functions can be evaluated separately. The sound-induced VEMPs, moreover, are capable of noninvasively assessing the unilateral vestibular function. The VsEPs, via the morphology of their signal waveforms, enable the access to the location-specific information that indicates the functional statuses of different components within the vestibular neural pathway., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Background: It has not yet been tested whether averaged gain values and the presence of pathological saccades are significantly altered by manual data selection or if data selection only done by the incorporated software detection algorithms provides a reliable data set following v-HIT testing., Objective: The primary endpoint was to evaluate whether the averaged gain values of all six SCCs are significantly altered by manual data selection with two different v-HIT systems., Method: 120 subjects with previously neither vestibular nor neurological disorders underwent four separate tests of all six SCCs with either EyeSeeCam® or ICS Impulse®. All v-HIT test reports underwent manual data selection by an experienced ENT Specialist with deletion of any noise and/or artifacts. Generalized estimating equations were used to compare averaged gain values based on unsorted data with averaged gain values based on the sorted data., Results: EyeSeeCam®: Horizontal SCCs: The estimate and the p-value (shown in parenthesis) for the right lateral SCC and the left lateral SCC were 0.00004 (0.95) and 0.00087 (0.70) respectively. Vertical SCCs: The estimate varied from -0.00858 to 0.00634 with p-values ranging from 0.31 to 0.78. ICS Impulse®: Horizontal SCCs: The estimate and the p-value for the right lateral SCC and the left lateral SCC were 0.00159 (0.18) and 0.00071 (0.38) respectively. Vertical SCCs: The estimate varied from 0.00217 to 0.01357 with p-values ranging from 0.00 to 0.17. Based upon the averaged gain value from the individual SCC being tested, 148 tests before and 127 after manual data selection were considered pathological., Conclusion: None of the two v-HIT systems revealed any clinically important effects of manual data selection. However, 21 fewer tests were considered pathological after manual data selection.

Background: Exposure to brain injury via blast or blunt mechanisms disrupts multiple sensorimotor systems simultaneously. Large numbers of US Gulf War era and Operation Iraqi/Enduring Freedom veterans with traumatic brain injury (TBI) are suffering the symptom of dizziness - presumed due to "Multi-Sensory Impairment", a clinical pattern of damage to the auditory, visual and vestibular sensorimotor systems., Objective: To describe the oculomotor response to rapid head rotation in a population of veterans with dizziness. We also describe the reliability of using the video head impulse test (vHIT) in a veteran population., Methods: We used the vHIT to evaluate the vestibular-ocular reflex (VOR) gain and presence of compensatory saccades (CS) in each semicircular canal of 81 veterans (31% TBI) with dizziness. Data was collected using the ICS Otometric™ vHIT. Data was processed using both the Otometric™ software and custom software written in MATLAB™. This data was evaluated through Kruskal-Wallis rank-sum test and analysis of regression., Results: Veterans with dizziness recruit CS in all semicircular canal planes even though their VOR gain is normal. The vHIT is a reliable clinical test to quantify the metrics of the VOR and CS in veterans., Conclusion: Veterans with dizziness symptoms use compensatory saccades in all planes of semicircular canal rotation, despite having normal peripheral VOR gain during rapid head rotation. The video head impulse test is a stable measure of vestibular slow phase and metrics of compensatory saccades in veterans with dizziness.

From animal experiments by Cohen and Suzuki et al. in the 1960s to the first-in-human clinical trials now in progress, prosthetic electrical stimulation targeting semicircular canal branches of the vestibular nerve has proven effective at driving directionally appropriate vestibulo-ocular reflex eye movements, postural responses, and perception. That work was considerably facilitated by the fact that all hair cells and primary afferent neurons in each canal have the same directional sensitivity to head rotation, the three canals' ampullary nerves are geometrically distinct from one another, and electrically evoked three-dimensional (3D) canal-ocular reflex responses approximate a simple vector sum of linearly independent components representing relative excitation of each of the three canals. In contrast, selective prosthetic stimulation of the utricle and saccule has been difficult to achieve, because hair cells and afferents with many different directional sensitivities are densely packed in those endorgans and the relationship between 3D otolith-ocular reflex responses and the natural and/or prosthetic stimuli that elicit them is more complex. As a result, controversy exists regarding whether selective, controllable stimulation of electrically evoked otolith-ocular reflexes (eeOOR) is possible. Using micromachined, planar arrays of electrodes implanted in the labyrinth, we quantified 3D, binocular eeOOR responses to prosthetic electrical stimulation targeting the utricle, saccule, and semicircular canals of alert chinchillas. Stimuli delivered via near-bipolar electrode pairs near the maculae elicited sustained ocular countertilt responses that grew reliably with pulse rate and pulse amplitude, varied in direction according to which stimulating electrode was employed, and exhibited temporal dynamics consistent with responses expected for isolated macular stimulation. NEW & NOTEWORTHY As the second in a pair of papers on Binocular 3D Otolith-Ocular Reflexes, this paper describes new planar electrode arrays and vestibular prosthesis architecture designed to target the three semicircular canals and the utricle and saccule. With this technological advancement, electrically evoked otolith-ocular reflexes due to stimulation via utricle- and saccule-targeted electrodes were recorded in chinchillas. Results demonstrate advances toward achieving selective stimulation of the utricle and saccule.

Background: Only a few studies in the literature demonstrate the effect of vestibular rehabilitation (VR) on all vestibular receptor organs. Furthermore, very little evidence of the effect of VR on isolated otolith dysfunction (IOD) is available., Objective: The study aimed to investigate the effect of VR on all vestibular receptor organs in patients with different types of unilateral vestibular hypofunction (UVH)., Methods: We enrolled 80 patients with three different types of UVH; combined and isolated loss of semicircular canal and otolith organ function. All patients performed a 12-week customized program of VR and received a full battery of vestibular function tests, before and after the VR. The DHI and SF-36 were performed before, after 6 weeks, and 12 weeks of the VR., Results: Parameters of the caloric test, video head impulse test, ocular and cervical vestibular evoked myogenic potentials were significantly improved after VR. A total of 59 (74%) patients fully recovered, with no significant difference in recovery regarding the type (p = 0.13) and stage of UVH (p = 0.13). All patients reported significantly lower disability and a better quality of life after the VR based on the DHI and SF-36 score., Conclusions: Vestibular rehabilitation has a positive effect on the recovery of all vestibular receptor organs and it should be used in patients with IOD.

Background: In benign paroxysmal positional vertigo (BPPV), the otolithic debris may alter the dynamics of the endolymph or cupula during head-shaking. This dynamic may generate head-shaking nystagmus (HSN) but exact pathomechanism of HSN in BPPV has not been elucidated. The association of positional nystagmus induced by head-bending or lying-down with HSN may help to understand the dynamics of HSN., Objective: To assess the presence, pattern, and relationship with head-bending nystagmus (HBN) and lying-down nystagmus (LDN) of HSN in horizontal canal (HC)-BPPV., Methods: We recruited 173 patients with HC-BPPV (76 geotropic and 97 apogeotropic). We analyzed the pattern of HSN, and correlation with HBN and LDN., Results: Half of patients (83/173, 48%) with HC-BPPV showed HSN. The directional preponderance of HSN was also not found in patients with geotropic or apogeotropic HC BPPV (p = 0.488). The presence of HSN was related with the occurrence of HBN in both geotropic (p = 0.005) and apogeotropic type (p = 0.001). The direction of HSN was same with HBN and was opposite to LDN in both geotropic and apogeotropic type., Conclusions: HSN was frequently found in patients with HC-BPPV and related with HBN and LDN. HSN in BPPV might be contributed by the otolith movements related with endolymph dynamics.

Objective: The aim of the present study was to investigate the factors influencing semicircular canal function as evaluated by video Head Impulse Test (vHIT) in patients with vestibular schwannoma., Methods: Twenty-four patients with untreated vestibular schwannoma underwent vHIT examination. The correlations between semicircular canal function and factors including age, tumor size, disease duration and hearing loss were evaluated., Results: The functions of all three semicircular canals on the affected side evaluated by vHIT were significantly lower than those on the unaffected side. Although there were no significant correlations between semicircular canal function and age, tumor size or disease duration, a negative significant correlation between vestibulo-ocular reflex (VOR) gain as evaluated by vHIT and hearing loss was observed., Conclusions: From the results of the relationship between hearing loss and VOR gain, the damage to the audio and vestibular systems in patients with VS may be correlated. As it has been suggested that tumor size was not a significant factor in the VOR gain evaluated by vHIT, multifactorial causes rather than the simple compression of the vestibular nerves alone may be related to the dysfunction of the semicircular canals in patients with vestibular schwannoma.

Background: This paper discusses some of the concepts and major physiological issues in developing a means of electrically stimulating the otolithic system, with the final goal being the electrical stimulation of the otoliths in human patients. It contrasts the challenges of electrical stimulation of the otolith organs as compared to stimulation of the semicircular canals. Electrical stimulation may consist of trains of short-duration pulses (e.g., 0.1 ms duration at 400 Hz) by selective electrodes on otolith maculae or otolithic afferents, or unselective maintained DC stimulation by large surface electrodes on the mastoids - surface galvanic stimulation., Summary: Recent anatomical and physiological results are summarized in order to introduce some of the unique issues in electrical stimulation of the otoliths. The first challenge is that each otolithic macula contains receptors with opposite polarization (opposing preferred directions of stimulation), unlike the uniform polarization of receptors in each semicircular canal crista. The puzzle is that in response to the one linear acceleration in the one macula, some otolithic afferents have an increased activation whereas others have decreased activation. Key Messages: At the vestibular nucleus this opposite receptor hair cell polarization and consequent opposite afferent input allow enhanced response to the one linear acceleration, via a "push-pull" neural mechanism in a manner analogous to the enhancement of semicircular canal responses to angular acceleration. Within each otolithic macula there is not just one uniform otolithic neural input to the brain - there are very distinctly different channels of otolithic neural inputs transferring the neural data to the brainstem. As a simplification these channels are characterized as the sustained and transient systems. Afferents in each system have different responses to stimulus onset and maintained stimulation and likely different projections, and most importantly different thresholds for activation by electrical stimulation and different adaptation rates to maintained stimulation. The implications of these differences are considered., (© 2019 S. Karger AG, Basel.)

Background: The peripheral vestibular end organ is considered to consist of semi-circular canals (SCC) for detection of angular accelerations and the otoliths for detection of linear accelerations. However, otoliths being phylogenetically the oldest part of the vestibular sensory organs are involved in detection of all motions., Summary: This study elaborates on this property of the otolith organ, as this concept can be of importance for the currently designed vestibular implant devices. Key Message: The analysis of the evolution of the inner ear and examination of clinical examples shows the robustness of the otolith system and inhibition capacity of the SCC. The otolith system must be considered superior to the SCC system as illustrated by evolution, clinical evidence, and physical principles., (© 2020 The Author(s) Published by S. Karger AG, Basel.)

Introduction: Ocular vestibular evoked myogenic potential (oVEMP) is a diagnostic test employed in the evaluation of superior semicircular canal dehiscence (SSCD) syndrome. Previous work showed that the presence of the n10 component of oVEMP at 4000 Hz was diagnostic of SSCD with perfect sensitivity and specificity of 1.0 in a series of 22 patients. This study sought to validate the diagnostic accuracy of high-frequency oVEMP with comparison to 500 Hz oVEMP and cervical vestibular evoked myogenic potential (cVEMP) in a larger series of patients., Methods: Retrospective chart review of 171 patients with clinical symptoms consistent with SSCD who underwent oVEMP and cVEMP testing. Dehiscence of the superior semicircular canal (SCC) on high-resolution computed tomography (CT) imaging of the temporal bone was used to identify cases of likely SSCD. The presence or absence of 4000 Hz oVEMP n10 responses, increased amplitude of 500 Hz oVEMP responses, and reduced threshold of 500 Hz cVEMP responses were identified for each patient., Results: SCC dehiscence was identified by CT imaging in 48 of 171 patients with symptoms consistent with SSCD. High-frequency oVEMP testing at 4000 Hz elicited a n10 response in 40 of 48 (83.3%) of patients and was present in 48 of 171 (28.1%) patients overall. The corresponding sensitivity was 0.83, specificity was 0.93, positive predictive value was 0.83, and negative predictive value was 0.93. oVEMP and cVEMP testing at 500 Hz was less accurate with sensitivity of 0.62 and 0.64, respectively, and specificity of 0.73 and 0.73, respectively., Conclusion: The presence of a 4000 Hz oVEMP n10 response was predictive of SSC dehiscence on CT imaging among patients with symptoms consistent with SSCD with sensitivity of 0.83, specificity of 0.93, positive predictive value of 0.83, and negative predictive value of 0.93. A negative finding strongly rules out SSCD. High-frequency oVEMP was more accurate than 500 Hz oVEMP or cVEMP.

Semicircular canal afferent neurons transmit information about head rotation to the brain. Mathematical models of how they do this have coevolved with concepts of how brains perceive the world. A 19th-century "camera" metaphor, in which sensory neurons project an image of the world captured by sense organs into the brain, gave way to a 20th-century view of sensory nerves as communication channels providing inputs to dynamical control systems. Now, in the 21st century, brains are being modeled as Bayesian observers who infer what is happening in the world given noisy, incomplete, and distorted sense data. The semicircular canals of the vestibular apparatus provide an experimentally accessible, low-dimensional system for developing and testing dynamical Bayesian generative models of sense data. In this review, we summarize advances in mathematical modeling of information transmission by semicircular canal afferent sensory neurons since the first such model was proposed nearly a century ago. Models of information transmission by vestibular afferent neurons may provide a foundation for developing realistic models of how brains perceive the world by inferring the causes of sense data.