Sustained bias of spatial attention in a 3 T MRI scanner.

When lying inside a MRI scanner and even in the absence of any motion, the static magnetic field of MRI scanners induces a magneto-hydrodynamic stimulation of subjects' vestibular organ (MVS). MVS thereby not only causes a horizontal vestibular nystagmus but also induces a horizontal bias in spatial attention. In this study, we aimed to determine the time course of MVS-induced biases in both VOR and spatial attention inside a 3 T MRI-scanner as well as their respective aftereffects after participants left the scanner. Eye movements and overt spatial attention in a visual search task were assessed in healthy volunteers before, during, and after a one-hour MVS period. All participants exhibited a VOR inside the scanner, which declined over time but never vanished completely. Importantly, there was also an MVS-induced horizontal bias in spatial attention and exploration, which persisted throughout the entire hour within the scanner. Upon exiting the scanner, we observed aftereffects in the opposite direction manifested in both the VOR and in spatial attention, which were statistically no longer detectable after 7 min. Sustained MVS effects on spatial attention have important implications for the design and interpretation of fMRI-studies and for the development of therapeutic interventions counteracting spatial neglect.

Classification of short and long term mild traumatic brain injury using computerized eye tracking.

Accurate, and objective diagnosis of brain injury remains challenging. This study evaluated useability and reliability of computerized eye-tracker assessments (CEAs) designed to assess oculomotor function, visual attention/processing, and selective attention in recent mild traumatic brain injury (mTBI), persistent post-concussion syndrome (PPCS), and controls. Tests included egocentric localisation, fixation-stability, smooth-pursuit, saccades, Stroop, and the vestibulo-ocular reflex (VOR). Thirty-five healthy adults performed the CEA battery twice to assess useability and test-retest reliability. In separate experiments, CEA data from 55 healthy, 20 mTBI, and 40 PPCS adults were used to train a machine learning model to categorize participants into control, mTBI, or PPCS classes. Intraclass correlation coefficients demonstrated moderate (ICC > .50) to excellent (ICC > .98) reliability (p < .05) and satisfactory CEA compliance. Machine learning modelling categorizing participants into groups of control, mTBI, and PPCS performed reasonably (balanced accuracy control: 0.83, mTBI: 0.66, and PPCS: 0.76, AUC-ROC: 0.82). Key outcomes were the VOR (gaze stability), fixation (vertical error), and pursuit (total error, vertical gain, and number of saccades). The CEA battery was reliable and able to differentiate healthy, mTBI, and PPCS patients reasonably well. While promising, the diagnostic model accuracy should be improved with a larger training dataset before use in clinical environments.

Temporal dynamics of ocular torsion and vertical vergence during visual, vestibular, and visuovestibular rotations.

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.

Differentiation of peripheral and non-peripheral etiologies in children with vertigo/dizziness: The video-head impulse test and suppression head impulse paradigm.

OBJECTIVES: To identify the etiology of vertigo/dizziness and determine the effectiveness of the video-head impulse test (vHIT) and the suppression head impulse paradigm (SHIMP) tests in distinguishing between peripheral and non-peripheral etiologies in children who presented to the otolaryngology department with complaints of vertigo/dizziness. METHODS: The vHIT and SHIMP tests were applied to the children. The vestibulo-ocular reflex (VOR) gain and saccade parameters were compared. RESULTS: In 27 children presenting with vertigo/dizziness, the most common etiological factor was inner ear malformation (IEM) (n = 6/27, 22.2%), followed by cochlear implant surgery (11.1%) and migraine (11.1%). Vestibular hypofunction was indicated by the vHIT results at a rate of 60% (9/15 children) and SHIMP results at 73.3% (11/15 children) among the children with a peripheral etiology, while these rates were 8.3% (1/12 children) and 25% (3/12 children), respectively, in the non-peripheral etiology group. SHIMP-VOR and vHIT-VOR gain values had a moderate positive correlation (p = 0.01, r = 0.349). While there were overt/covert saccades in the vHIT, anti-compensatory saccade (ACSs) were not observed in the SHIMP test (p = 0.041). The rates of abnormal vHIT-VOR gain (p = 0.001), over/covert saccades (p = 0.019), abnormal vHIT response (p = 0.014), ACSs (p = 0.001), and abnormal SHIMP response (p = 0.035) were significantly higher in the peripheral etiology group. CONCLUSIONS: IEM was the most common etiological cause, and the rate of vestibular hypofunction was higher in these children with peripheral vertigo. vHIT and SHIMP are effective and useful vestibular tests for distinguishing peripheral etiology from non-peripheral etiology in the pediatric population with vertigo/dizziness. These tests can be used together or alone, but the first choice should be the SHIMP test, considering its short application time (approximately 4-5 min) and simplicity.

Frequency dependence of human thresholds: both perceptual and vestibuloocular reflex thresholds.

Although perceptual thresholds have been widely studied, vestibuloocular reflex (VOR) thresholds have received less attention, so the relationship between VOR and perceptual thresholds remains unclear. We compared the frequency dependence of human VOR thresholds to human perceptual thresholds for yaw head rotation in both upright ("yaw rotation") and supine ("yaw tilt") positions, using the same human subjects and motion device. VOR thresholds were generally a little smaller than perceptual thresholds. We also found that horizontal VOR thresholds for both yaw rotation about an Earth-vertical axis and yaw tilt (yaw rotation about an Earth-horizontal axis) were relatively constant across four frequencies (0.2, 0.5, 1, and 2 Hz), with little difference between yaw rotation and yaw tilt VOR thresholds. For yaw tilt stimuli, perceptual thresholds were slightly lower at the lowest frequency and nearly constant at all other (higher) frequencies. However, for yaw rotation, perceptual thresholds increased significantly at the lowest frequency (0.2 Hz). We conclude 1) that VOR thresholds were relatively constant across frequency for both yaw rotation and yaw tilt, 2) that the known contributions of velocity storage to the VOR likely yielded these VOR thresholds that were similar for yaw rotation and yaw tilt for all frequencies tested, and 3) that the integration of otolith and horizontal canal signals during yaw tilt when supine contributes to stable perceptual thresholds, especially relative to the low-frequency perceptual thresholds recorded during yaw rotation.NEW & NOTEWORTHY We describe for the first time that human VOR thresholds differ from human forced-choice perceptual thresholds, with the difference especially evident at frequencies below 0.5 Hz. We also report that VOR thresholds are relatively constant across frequency for both yaw rotation and yaw tilt. These findings are consistent with the idea that high-pass filtering in cortical pathways impacts cognitive decision-making.

The headshake enhances oculomotor response to galvanic vestibular stimulation in healthy subjects.

OBJECTIVE: To investigate whether a headshake applied during galvanic vestibular stimulation (GVS) can enhance GVS-induced nystagmus in healthy subjects. METHODS: In nineteen healthy participants, we evaluated an average slow-phase velocity (aSPV) of nystagmus in a head-still and after the headshake conditions, with/out the bitemporal 2 mA GVS. The GVS was applied also with polarity congruent (supporting) or incongruent (suppressing) to any preexisting spontaneous nystagmus. RESULTS: The orientation of GVS-induced nystagmus depended on GVS polarity. In the head-still condition, the GVS-induced nystagmus in 14 subjects (74%) for congruent and in 12 subjects (63%) for incongruent GVS. During headshake, we recorded nystagmus in 16 subjects (84%) for congruent and 15 subjects (79%) for incongruent GVS. The aSPV of congruent GVS-induced nystagmus was higher (p = 0.0003) by 1.33 (SE 0.26) deg/s for headshake compared to head-still condition. The aSPV of incongruent GVS also induced higher nystagmus (p = 0.0014) by 1.24 (SE 0.28) deg/s for the headshake condition. CONCLUSION: Our study adds a new principle to the knowledge of the central processing of a GVS response in healthy subjects. The GVS-safety profile of current up to 2 mA was sufficient to elicit a significant GVS nystagmus response in a head-still position in 63% and after a headshake in 79%. Compared to the GVS head-still condition, a headshake enhanced the GVS-induced nystagmus more than twice. SIGNIFICANCE: The headshake helps to identify GVS-induced nystagmus, which can be weak or absent during the head-still condition.

Interactions between circuit architecture and plasticity in a closed-loop cerebellar system.

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.

PP2B-Dependent Cerebellar Plasticity Sets the Amplitude of the Vestibulo-ocular Reflex during Juvenile Development.

Throughout life, the cerebellum plays a central role in the coordination and optimization of movements, using cellular plasticity to adapt a range of behaviors. Whether these plasticity processes establish a fixed setpoint during development, or continuously adjust behaviors throughout life, is currently unclear. Here, by spatiotemporally manipulating the activity of protein phosphatase 2B (PP2B), an enzyme critical for cerebellar plasticity in male and female mice, we examined the consequences of disrupted plasticity on the performance and adaptation of the vestibulo-ocular reflex (VOR). We find that, in contrast to Purkinje cell (PC)-specific deletion starting early postnatally, acute pharmacological as well as adult-onset genetic deletion of PP2B affects all forms of VOR adaptation but not the level of VOR itself. Next, we show that PC-specific genetic deletion of PP2B in juvenile mice leads to a progressive loss of the protein PP2B and a concurrent change in the VOR, in addition to the loss of adaptive abilities. Finally, re-expressing PP2B in adult mice that lack PP2B expression from early development rescues VOR adaptation but does not affect the performance of the reflex. Together, our results indicate that chronic or acute, genetic, or pharmacological block of PP2B disrupts the adaptation of the VOR. In contrast, only the absence of plasticity during cerebellar development affects the setpoint of VOR, an effect that cannot be corrected after maturation of the cerebellum. These findings suggest that PP2B-dependent cerebellar plasticity is required during a specific period to achieve the correct setpoint of the VOR.

Pre- and post-operative semicircular canal function evaluated by video head impulse test in patients with vestibular schwannoma.

OBJECTIVES: To evaluate pre- and post-operative semicircular canal function in patients with vestibular schwannoma (VS) by the video Head Impulse Test (vHIT). METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

Audiological and Vestibular Measurements in Chronic Renal Failure Patients Receiving Hemodialysis Treatment.

BACKGROUND: The aim was to evaluate the changes in the audiovestibular system in adult patients with the diagnosis of chronic renal failure who were treated with hemodialysis. METHODS: Thirty-five patients diagnosed with chronic renal failure and receiving hemodialysis treatment 3 days a week and 35 healthy individuals were tested with pure tone audiometry, video head impulse test, and post-head shake nystagmus test. Dizziness Handicap Inventory was applied to all participants. RESULTS: The Dizziness Handicap Inventory scores of the patient groups are higher than the control groups (P=.001). In the video head impulse test, there is no statistically significant difference between the patient and control groups in terms of gain asymmetry. 17.1% of the patients had both left and right lateral saccades (P=.03). A statistically significant difference was also found after the post-head shake test (P=.025). In the patient group, an inverse relationship between the presence of left anterior right posterior saccades and blood urea nitrogen-creatinine ratio and a direct relationship between the presence of right anterior left posterior saccades and creatinine elevation were determined. The presence of saccades in the video head impulse test increased significantly as the disease duration of hemodialysis patients increased. CONCLUSION: It was determined that the overt and covert saccades in the video head impulse test increased significantly as the creatinine increased and the duration of the disease increased in the patients with chronic renal failure. The common clinical usage of video head impulse test in monitoring the vestibular side effects of creatinine elevation and disease duration in chronic renal failure patients may be possible with future studies.

Measuring Optokinetic Reflex and Vestibulo-Ocular Reflex in Unilateral Vestibular Organ Damage Model of Zebrafish.

One-sided vestibular disorders are common in clinical practice; however, their models have not been fully established. We investigated the effect of unilateral or bilateral deficits in the vestibular organs on the vestibulo-ocular reflex (VOR) and optokinetic reflex (OKR) of zebrafish using in-house equipment. For physical dislodgement of the otoliths in the utricles of zebrafish larvae, one or both utricles were separated from the surrounding tissue using glass capillaries. The video data from VOR and OKR tests with the larvae was collected and processed using digital signal processing techniques such as fast Fourier transform and low-pass filters. The results showed that unilateral and bilateral damage to the vestibular system significantly reduced VOR and OKR. In contrast, no significant difference was observed between unilateral and bilateral damage. This study confirmed that VOR and OKR were significantly reduced in zebrafish with unilateral and bilateral vestibular damage. Follow-up studies on unilateral vestibular disorders can be conducted using this tool.

Is activation of the vestibular system by electromagnetic induction a possibility in an MRI context?

In recent years, an increasing number of studies have discussed the mechanisms of vestibular activation in strong magnetic field settings such as occur in a magnetic resonance imaging scanner environment. Amid the different hypotheses, the Lorentz force explanation currently stands out as the most plausible mechanism, as evidenced by activation of the vestibulo-ocular reflex. Other hypotheses have largely been discarded. Nonetheless, both human data and computational modeling suggest that electromagnetic induction could be a valid mechanism which may coexist alongside the Lorentz force. To further investigate the induction hypothesis, we provide, herein, a first of its kind dosimetric analysis to estimate the induced electric fields at the vestibular system and compare them with what galvanic vestibular stimulation would generate. We found that electric fields strengths from induction match galvanic vestibular stimulation strengths generating vestibular responses. This review examines the evidence in support of electromagnetic induction of vestibular responses, and whether movement-induced time-varying magnetic fields should be further considered and investigated.

[Dynamic visual acuity screening test results analysis of 25 patients with peripheral vertigo].

Objective:To observe the results of dynamic visual acuity screening tests in patients with peripheral vertigo and explore its clinical significance. Methods:The number of 48 healthy volunteers were enrolled as control group and 25 peripheral vertigo patients as experimental group. In the experimental group, there are 12 patients with vestibular neuritis, 1 patient with Hunt syndrome, 5 patients with sudden deafness with vertigo and 7 patients with bilateral vestibular dysfunction. Horizontal and vertical dynamic visual acuity screening tests were performed on them. The number of lost rows of horizontal and vertical dynamic visual acuity was compared between the control group and the experimental group to figure out if there is a statistical difference. The number of lost rows of horizontal and vertical dynamic visual acuity was compared within the experimental group to figure out if there is a statistical difference. The two groups of 18 cases of unilateral vestibular function decline and 7 cases of bilateral vestibular function decline in the experimental group were compared with the control group, and figure out if there is a statistical difference. Results:The median number of lost rows of horizontal dynamic visual acuity in 48 healthy volunteers was 1.5 and median number of lost rows of vertical dynamic visual acuity was 1.0 in the control group. The median number of lost rows of horizontal dynamic visual acuity of 26 healthy volunteers was 6 and median number of lost rows of vertical dynamic visual acuity was 5 in the experimental group. Compared to the experimental group, the number of lost rows both have statistical significance in horizontal and vertical dynamic visual acuity（P<0.01）. The comparison of horizontal and vertical lost rows within the test group also have statistical significance（P<0.01）. Twenty five patients with exceptional vestibular disease in the experimental group were divided into unilateral vestibular function reduction group（n=18） and bilateral vestibular function reduction group（n=7）. Compared with the control group, there was significant differences in the number of horizontal and vertical lost rows（P<0.01） within the three groups. After pairwise comparison, the number of lost rows of horizontal and vertical in the control group was significantly lower than that in the unilateral vestibular function reduction group and the bilateral vestibular function reduction group（P<0.01）. There was a highly significant correlation between the number of horizontally lost rows of DVA and the mean vHIT values of bilateral horizontal semicircular canals in 25 patients（P<0.01）; and a highly significant correlation between the number of vertically lost rows of DVA and the mean vHIT values of vertical semicircular canals in 4 groups bilaterally（P<0.01）. Conclusion:The Dynamic Visual Acuity Screening Test is a useful addition to existing tests of peripheral vestibular function, particularly the vHIT test, and provides a rapid assessment of the extent of 2 Hz VOR impairment in patients with reduced vestibular function.

Assessing the synergistic effectiveness of intermittent theta burst stimulation and the vestibular ocular reflex rehabilitation protocol in the treatment of Mal de Debarquement Syndrome: a randomised controlled trial.

INTRODUCTION: Mal de Debarquement Syndrome (MdDS) is a rare central vestibular disorder characterised by a constant sensation of motion (rocking, swaying, bobbing), which typically arises after motion experiences (e.g. sea, air, and road travel), though can be triggered by non-motion events. The current standard of care is non-specific medications and interventions that only result in mild-to-moderate improvements. The vestibular ocular reflex (VOR) rehabilitation protocol, a specialised form of rehabilitation, has shown promising results in reducing symptoms amongst people with MdDS. Accumulating evidence suggests that it may be possible to augment the effects of VOR rehabilitation via non-invasive brain stimulation protocols, such as theta burst stimulation (TBS). METHODS: The aim of this randomised controlled trial was to evaluate the effectiveness of intermittent TBS (iTBS) over the dorsolateral prefrontal cortex in enhancing the effectiveness of a subsequently delivered VOR rehabilitation protocol in people with MdDS. Participants were allocated randomly to receive either Sham (n = 10) or Active (n = 10) iTBS, followed by the VOR rehabilitation protocol. Subjective outcome measures (symptom ratings and mental health scores) were collected 1 week pre-treatment and for 16 weeks post-treatment. Posturography (objective outcome) was recorded each day of the treatment week. RESULTS: Significant improvements in subjective and objective outcomes were reported across both treatment groups over time, but no between-group differences were observed. DISCUSSION: These findings support the effectiveness of the VOR rehabilitation protocol in reducing MdDS symptoms. Further research into iTBS is required to elucidate whether the treatment has a role in the management of MdDS. TRN: ACTRN12619001519145 (Date registered: 04 November 2019).

Impaired cerebellar plasticity hypersensitizes sensory reflexes in SCN2A-associated ASD.

Children diagnosed with autism spectrum disorder (ASD) commonly present with sensory hypersensitivity or abnormally strong reactions to sensory stimuli. Such hypersensitivity can be overwhelming, causing high levels of distress that contribute markedly to the negative aspects of the disorder. Here, we identify a mechanism that underlies hypersensitivity in a sensorimotor reflex found to be altered in humans and in mice with loss of function in the ASD risk-factor gene SCN2A. The cerebellum-dependent vestibulo-ocular reflex (VOR), which helps maintain one's gaze during movement, was hypersensitized due to deficits in cerebellar synaptic plasticity. Heterozygous loss of SCN2A-encoded NaV1.2 sodium channels in granule cells impaired high-frequency transmission to Purkinje cells and long-term potentiation, a form of synaptic plasticity important for modulating VOR gain. VOR plasticity could be rescued in mice via a CRISPR-activator approach that increases Scn2a expression, demonstrating that evaluation of a simple reflex can be used to assess and quantify successful therapeutic intervention.

Vestibulo-ocular reflex dynamics with head-impulses discriminates Usher patients type 1 and 2.

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.

Effect of vestibular loss on head-on-trunk stability in individuals with vestibular schwannoma.

The vestibulo-collic reflex generates neck motor commands to produce head-on-trunk movements that are essential for stabilizing the head relative to space. Here we examined the effects of vestibular loss on head-on-trunk kinematics during voluntary behavior. Head and trunk movements were measured in individuals with vestibular schwannoma before and then 6 weeks after unilateral vestibular deafferentation via surgical resection of the tumor. Movements were recorded in 6 dimensions (i.e., 3 axes of rotation and 3 axes of translation) using small light-weight inertial measurement units while participants performed balance and gait tasks. Kinematic measures differed between individuals with vestibular schwannoma (at both time points) and healthy controls for the more challenging exercises, namely those performed in tandem position or on an unstable surface without visual input. Quantitative assessment of the vestibulo-ocular reflex (VOR) revealed a reduction in VOR gain for individuals with vestibular schwannoma compared to control subjects, that was further reduced following surgery. These findings indicated that the impairment caused by either the tumor or subsequent surgical tumor resection altered head-on-trunk kinematics in a manner that is not normalized by central compensation. In contrast, we further found that head-on-trunk kinematics in individuals with vestibular schwannoma were actually comparable before and after surgery. Thus, taken together, our results indicate that vestibular loss impacts head-on-trunk kinematics during voluntary balance and gait behaviors, and suggest that the neural mechanisms mediating adaptation alter the motion strategies even before surgery in a manner that may be maladaptive for long-term compensation.

The vertical computerized rotational head impulse test.

The computerized rotational head impulse test (crHIT) uses a computer-controlled rotational chair to deliver whole-body rotational impulses to assess the semicircular canals. The crHIT has only been described for horizontal head plane rotations. The purpose of this study was to describe the crHIT for vertical head plane rotations. In this preliminary study, we assessed four patients with surgically confirmed unilateral peripheral vestibular abnormalities and two control subjects. Results indicated that the crHIT was well-tolerated for both horizontal head plane and vertical head plane stimuli. The crHIT successfully assessed each of the six semicircular canals. This study suggests that the crHIT has the potential to become a new laboratory-based vestibular test for both the horizontal and vertical semicircular canals.