Horizontal Vestibulo-ocular Reflex Research Articles

Vestibular Loss in Older Adults Is Associated with Impaired Spatial Navigation: Data from the Triangle Completion Task.

Vestibular inputs have been shown to play a critical role in spatial navigation. In this study, we sought to evaluate whether vestibular loss due to aging contributes to impaired spatial navigation as measured by the triangle completion task (TCT). We recruited three types of participants: young controls <55 years of age, older controls ≥55 years of age, and older patients from a Neurotology Clinic with evidence of vestibular physiologic impairment but who did not have any known vestibular disorder. We performed the cervical vestibular-evoked myogenic potential to evaluate saccular function and video head impulse testing to quantify horizontal semicircular canal vestibulo-ocular reflex gain. To assess spatial navigation ability, we administered the TCT, in which participants were conveyed along two segments of a pre-drawn triangular path and instructed to complete the final segment independently. We measured the angle (degrees) and distance (centimeters) of deviation from the correct trajectory. We evaluated the influence of vestibular inputs on TCT performance. Forty-eight adults participated in the study (mean age: 62.0 years; 52.1% females), including 9 young controls, 15 older controls, and 24 clinic patients. Clinic patients had the greatest distance of deviation (67.7 cm), followed by older controls (45.4 cm), then young controls (27.8 cm; p < 0.01). Similarly, clinic patients had greater rotational angles (22.1°) compared to older (13.3°) and younger controls (12.4°; p < 0.01). Following multivariate linear regression adjusting for demographic variables, loss of otolith function was associated with an 18.2 cm increase in distance of deviation (95% CI: 15.2-47.4) and a 9.2° increase in rotational angle (95% CI: 3.0-15.5). Abnormal semicircular canal function was associated with a 26.0 cm increase in distance of deviation (95% CI: 0.2-51.8) and a 10.8° increase in rotational angle (95% CI: 3.0-15.5). Participants with both otolith and canal abnormalities had a larger distance error (β = 25.3, 95% CI: 6.2-44.4) and angle of deviation (β = 18.1, 95% CI: 10.1-26.2) than with either condition alone. Vestibular loss in older adults was associated with poorer performance on a dynamic spatial navigation task relative to old and young controls.

The Spectrum of Vestibular and Ocular Motor Abnormalities in Thiamine Deficiency

The first aim of this review is to summarize recent ocular motor signs in pre-encephalopathy patients with nutritional deficiency at risk of thiamine deficiency. Timely recognition of thiamine depletion in these patients, who may have a normal brain MRI, could lead to appropriate management and prevention of Wernicke's encephalopathy (WE) with full recovery. The second aim is to incorporate recent diagnostic testing on the revised WE diagnostic criteria and the identification of patients who may show slow, partial, or no response to treatment. Selective vulnerability of periventricular gray neurons in thiamine deficiency is well known. Involvement of the vestibular and abducens nuclei may precede encephalopathy. Studies have shown mild ophthalmoparesis and bilateral symmetric vestibular loss in thiamine deficiency. Moreover, quantitative data has shown decreased horizontal vestibulo-ocular reflex (VOR) gain and nystagmus, with a favorable response to timely treatment. Ophthalmoparesis, horizontal nystagmus, and decreased gain of the horizontal VOR, sparing the vertical VOR, may be present in the early pre-encephalopathy stage of thiamine deficiency. Rapid response to a loading dose of parenteral thiamine might be seen in some cases and normalization, albeit slower in others. In contrast, analogous to the Korsakoff's syndrome, ocular motor and vestibular abnormalities may show only partial improvement. Future studies in larger populations at risk are needed to confirm the results of these preliminary observations.

Functional Organization of Vestibulo-Ocular Responses in Abducens Motoneurons.

Vestibulo-ocular reflexes (VORs) are the dominating contributors to gaze stabilization in all vertebrates. During horizontal head movements, abducens motoneurons form the final element of the reflex arc that integrates visuovestibular inputs into temporally precise motor commands for the lateral rectus eye muscle. Here, we studied a possible differentiation of abducens motoneurons into subtypes by evaluating their morphology, discharge properties, and synaptic pharmacology in semi-intact in vitro preparations of larval Xenopus laevis Extracellular nerve recordings during sinusoidal head motion revealed a continuum of resting rates and activation thresholds during vestibular stimulation. Differences in the sensitivity to changing stimulus frequencies and velocities allowed subdividing abducens motoneurons into two subgroups, one encoding the frequency and velocity of head motion (Group I), and the other precisely encoding angular velocity independent of stimulus frequency (Group II). Computational modeling indicated that Group II motoneurons are the major contributor to actual eye movements over the tested stimulus range. The segregation into two functional subgroups coincides with a differential activation of glutamate receptor subtypes. Vestibular excitatory inputs in Group I motoneurons are mediated predominantly by NMDA receptors and to a lesser extent by AMPA receptors, whereas an AMPA receptor-mediated excitation prevails in Group II motoneurons. Furthermore, glycinergic ipsilateral vestibular inhibitory inputs are activated during the horizontal VOR, whereas the tonic GABAergic inhibition is presumably of extravestibular origin. These findings support the presence of physiologically and pharmacologically distinct functional subgroups of extraocular motoneurons that act in concert to mediate the large dynamic range of extraocular motor commands during gaze stabilization.SIGNIFICANCE STATEMENT Outward-directed gaze-stabilizing eye movements are commanded by abducens motoneurons that combine different sensory inputs including signals from the vestibular system about ongoing head movements (vestibulo-ocular reflex). Using an amphibian model, this study investigates whether different types of abducens motoneurons exist that become active during different types of eye movements. The outcome of this study demonstrates the presence of specific motoneuronal populations with pharmacological profiles that match their response dynamics. The evolutionary conservation of the vestibulo-ocular circuitry makes it likely that a similar motoneuronal organization is also implemented in other vertebrates. Accordingly, the physiological and pharmacological understanding of specific motoneuronal contributions to eye movements might help in designing drug therapies for human eye movement dysfunctions such as abducens nerve palsy.

Compensatory Saccades Are Associated With Physical Performance in Older Adults: Data From the Baltimore Longitudinal Study of Aging.

To determine whether compensatory saccade metrics observed in the video head impulse test, specifically saccade amplitude and latency, predict physical performance. Cross-sectional analysis of the Baltimore Longitudinal Study of Aging, a prospective cohort study. National Institute on Aging Intramural Research Program Clinical Research Unit in Baltimore, Maryland. Community-dwelling older adults. Video head impulse testing was performed, and compensatory saccades and horizontal vestibulo-ocular reflex (VOR) gain were measured. Physical performance was assessed using the Short Physical Performance Battery (SPPB), which included the feet side-by-side, semitandem, tandem, and single-leg stance; repeated chair stands; and usual gait speed measurements. Compensatory saccade amplitude and latency, VOR gain, and SPPB performance. In 183 participants who underwent vestibular and SPPB testing (mean age 71.8 yr; 53% females), both higher mean saccade amplitude (odds ratio [OR] =1.62, p = 0.010) and shorter mean saccade latency (OR = 0.88, p = 0.004) were associated with a higher odds of failing the tandem stand task. In contrast, VOR gain was not associated with any physical performance measure. We observed in a cohort of healthy older adults that compensatory saccade amplitude and latency were associated with tandem stance performance. Compensatory saccade metrics may provide insights into capturing the impact of vestibular loss on physical function in older adults.

The usefulness of the video head impulse test in children and adults post-concussion.

Dizziness after concussion have been reported in both youths and adults. It is not clear if the dizziness experienced post-concussion is from peripheral or central etiology. New technology has been developed to quickly and easily quantify the magnitude of peripheral vestibular disorders that is non-invasive and acceptable to youths and adults. The purpose of this study was to determine if youths and adults' post-concussion have evidence of decreased horizontal semicircular canal vestibulo-ocular reflex (VOR) gains as measured with the video head impulse test (vHIT), which would indicate a peripheral vestibular disorder. An additional purpose was to determine if VOR gain scores correlate with functional performance measures. Descriptive cross sectional. Large medical center out-patient concussion program. Fifty-six subjects with concussion. Subjects completed the vHIT testing, the Dizziness Handicap Inventory (DHI), the Vestibular Activities and Participation (VAP) scale, the Pediatric Vestibular Symptom Questionnaire, gait speed assessment, the Dynamic Gait Index (DGI) and a verbal analog scale of symptom provocation before and after the vHIT testing. There were no abnormal vHIT findings in any subject. Headaches, dizziness and nausea were significantly worse post vHIT testing (p < 0.05). Youths had better DGI and DHI scores than subjects older than 20 (p < 0.05). The vHIT did not detect horizontal semicircular canal weakness in any of the subjects tested. In addition, older adults reported more activity and participation limitations than the younger subjects with concussion.

Video head impulse test for evaluation of vestibular function in patients with vestibular neuritis and benign paroxysmal positional vertigo

Objective: To assess the clinical application of video head impulse test (vHIT) for vestibular function in vestibular neuritis (VN) and benign paroxysmal positional vertigo (BPPV) patients. Methods: Thirty-three patients with VN and 43 patients with BPPV were enrolled from Sir Run Run Shaw Hospital and Ningbo Second Hospital from March 15 to September 10, 2015; and 50 healthy controls were also enrolled in the study. vHIT was used to quantitatively test the vestibulo-ocular reflex (VOR) gains of a pair of horizontal semicircular canals. VOR gains two pairs of vertical semicircular canals, and the corresponding asymmetrical value of three VOR gains. The saccades information was also recorded. Results: Compared with the healthy control group and BPPV patients, the affected horizontal and vertical VOR gains were declined and the corresponding asymmetries were increased in VN patients (all P<0.01). BPPV group also showed higher vertical VOR gain asymmetries compared with the healthy control group (all P<0.01), but no significant difference was observed in VOR gains and horizontal VOR gain asymmetry (all P>0.05). The sensibility of vHIT in diagnosis of VN was 87.9%. Among 33 VN patients, 22 were diagnosed with superior vestibular nerve dysfunction, 7 were found with inferior vestibular nerve dysfunction and 3 were with both dysfunction; and 1 case was not distinguished. Conclusion: Video head impulse test can quantitatively evaluate the vestibular dysfunction of VN and can help early diagnosis of VN, which may be widely used in clinic.

Saccadic Velocity in the New Suppression Head Impulse Test: A New Indicator of Horizontal Vestibular Canal Paresis and of Vestibular Compensation.

To determine whether saccadic velocity in the suppression head impulse paradigm (SHIMP) test is a reliable indicator of vestibular loss at the acute and at the chronic stage in patients suffering from different vestibular pathologies. Thirty-five normal subjects and 57 patients suffering from different vestibular pathologies associated with unilateral vestibular loss (UVL) or bilateral vestibular loss (BVL) were tested in the SHIMPs paradigm. SHIMPs were performed by turning the head 10 times at high velocities to the left or right side, respectively. The patients were instructed to fixate on a red spot generated by a head-fixed laser projected on the wall. In this SHIMPs paradigm, healthy subjects made a large anti-compensatory saccade at the end of the head turn (a SHIMP saccade). The peak saccadic velocity, the percentage of the trials completed with saccades in 10 trials, and the latency of the saccades were quantified in each group. A video-head impulse test (v-HIT) was systematically performed in all of our subjects as well as a caloric test. The dizziness handicap inventory questionnaire was also given to chronic UVL and BVL patients. At the acute stage after a complete UVL, patients had zero or a few anti-compensatory saccades for low velocity head turns toward the lesioned side. These saccades had lower velocity than the anti-compensatory saccades recorded during head rotation toward the intact side and/or compared with the saccades measured in control subjects. At the chronic stage, some of the patients recovered the ability to perform SHIMP saccades at each head turn toward the lesioned side, but very often these saccades were of significantly lower velocity. In BVL patients, no anti-compensatory saccades, or only significantly smaller ones, could be detected for head turns to both sides. SHIMP is a specific and sensitive test to detect a complete horizontal canal loss at the acute stage. In addition, it reflects the ability of patients with moderate horizontal vestibulo-ocular reflex gain decrease to generate anti-compensatory saccades in the chronic stage. In association with v-HIT, it allows determination of the residual vestibular function and to detect anti-compensatory saccades.

Sensorimotor control: computing the immediate future from the delayed present

BackgroundThe predictive nature of the primate sensorimotor systems, for example the smooth pursuit system and their ability to compensate for long delays have been proven by many physiological experiments. However, few theoretical models have tried to explain these facts comprehensively. Here, we propose a sensorimotor learning and control model that can be used to (1) predict the dynamics of variable time delays and current and future sensory states from delayed sensory information; (2) learn new sensorimotor realities; and (3) control a motor system in real time.ResultsThis paper proposed a new time-delay estimation method and developed a computational model for a predictive control solution of a sensorimotor control system under time delay. Simulation experiments are used to demonstrate how the proposed model can explain a sensorimotor system’s ability to compensate for delays during online learning and control. To further illustrate the benefits of the proposed time-delay estimation method and predictive control in sensorimotor systems a simulation of the horizontal Vestibulo-Ocular Reflex (hVOR) system is presented.Without the proposed time-delay estimation and prediction, the hVOR can be unstable and could be affected by high frequency oscillations. These oscillations are reminiscent of a fast correction mechanism, e.g., a saccade to compensate for the hVOR delays. Comparing results of the proposed model with those in literature, it is clear that the hVOR system with impaired time-delay estimation or impaired sensory state predictor can mimic certain outcomes of sensorimotor diseases. Even more, if the control of hVOR is augmented with the proposed time-delay estimator and the predictor for eye position relative to the head, then hVOR control system can be stabilized.ConclusionsThree claims with varying degrees of experimental support are proposed in this paper. Firstly, the brain or any sensorimotor system has time-delay estimation circuits for the various sensorimotor control systems. Secondly, the brain continuously estimates current/future sensory states from the previously sensed states. Thirdly, the brain uses predicted sensory states to perform optimal motor control.

VOR Gain Is Related to Compensatory Saccades in Healthy Older Adults.

Objective: Vestibulo-ocular reflex (VOR) gain is well-suited for identifying rotational vestibular dysfunction, but may miss partial progressive decline in age-related vestibular function. Since compensatory saccades might provide an alternative method for identifying subtle vestibular decline, we describe the relationship between VOR gain and compensatory saccades in healthy older adults.Methods: Horizontal VOR gain was measured in 243 subjects age 60 and older from the Baltimore Longitudinal Study of Aging using video head impulse testing (HIT). Saccades in each HIT were identified as either “compensatory” or “compensatory back-up,” i.e., same or opposite direction as the VOR response respectively. Saccades were also classified as “covert” (occurring during head movement) and “overt” (occurring after head movement). The relationship between VOR gain and percentage of HITs with saccades, as well as the relationship between VOR gain and saccade latency and amplitude, were evaluated using regression analyses adjusting for age, gender, and race.Results: In adjusted analyses, the percentage of HITs with compensatory saccades increased 4.5% for every 0.1 decrease in VOR gain (p < 0.0001). Overt compensatory saccade amplitude decreased 0.6° (p < 0.005) and latency increased 90 ms (p < 0.001) for every 0.1 increase in VOR gain. Covert back-up compensatory saccade amplitude increased 0.4° for every 0.1 increase in VOR gain.Conclusion: We observed significant relationships between VOR gain and compensatory saccades in healthy older adults. Lower VOR gain was associated with larger amplitude, shorter latency compensatory saccades. Compensatory saccades reflect underlying rotational vestibular hypofunction, and may be particularly useful at identifying partial vestibular deficits as occur in aging adults.

Effects of high intensity noise on the vestibular system in rats

Some individuals with noise-induced hearing loss (NIHL) also report balance problems. These accompanying vestibular complaints are not well understood. The present study used a rat model to examine the effects of noise exposure on the vestibular system. Rats were exposed to continuous broadband white noise (0–24 kHz) at an intensity of 116 dB sound pressure level (SPL) via insert ear phones in one ear for three hours under isoflurane anesthesia. Seven days after the exposure, a significant increase in ABR threshold (43.3 ± 1.9 dB) was observed in the noise-exposed ears, indicating hearing loss. Effects of noise exposure on vestibular function were assessed by three approaches. First, fluorescein-conjugated phalloidin staining was used to assess vestibular stereocilia following noise exposure. This analysis revealed substantial sensory stereocilia bundle loss in the saccular and utricular maculae as well as in the anterior and horizontal semicircular canal cristae, but not in the posterior semicircular canal cristae. Second, single unit recording of vestibular afferent activity was performed under pentobarbital anesthesia. A total of 548 afferents were recorded from 10 noise-treated rats and 12 control rats. Noise exposure produced a moderate reduction in baseline firing rates of regular otolith afferents and anterior semicircular canal afferents. Also a moderate change was noted in the gain and phase of the horizontal and anterior semicircular canal afferent's response to sinusoidal head rotation (1 and 2 Hz, 45°/s peak velocity). Third, noise exposure did not result in significant changes in gain or phase of the horizontal rotational and translational vestibulo-ocular reflex (VOR). These results suggest that noise exposure not only causes hearing loss, but also causes substantial damage in the peripheral vestibular system in the absence of immediate clinically measurable vestibular signs. These peripheral deficits, however, may lead to vestibular disorders over time.

Video head impulse test in peripheral vestibular diseases

The function of the semicircular canal receptors and the pathway of the vestibulo-ocular reflex (VOR) can be diagnosed with the clinical head impulse test. The aim of the study was to investigate the horizontal VOR by means of video head impulse test in peripheral vestibular disorders. Using the vHIT, we examined horizontal semicircular canal VOR in a group of 55 patients and a control group of 20 healthy subjects. The group of patients included 10 cases of vestibular neuritis (VN), 6 cases of vestibular schwannoma (VS), 12 cases of Meniere's disease (MD), and 15 cases of bilateral vestibulopathy (BV), as well as 13 cases of idiopathic sudden hearing loss with vertigo (ISHL). Instantaneous gains of 40 ms, 60 ms and 80 ms of horizontal VOR were 0.88 ± 0.17, 0.94 ± 0.13 and 0.96 ± 0.13, respectively. Regression gain at 60 ms was 0.99 ± 0.11, and asymmetry was 5.6 ± 3.5. Normal range of 60 ms instantaneous gain was > 0.73, normal range of regression gain was > 0.80. Abnormal vHIT was found in VS (100%), VN (90.9%), BV (86.7%), MD (40.0%) and ISHL (38.5%). Three conditions of refixation saccades occurred in cases with abnormal VOR: isolated covert saccades (12.5%), isolated overt saccades (45.0%) and the combination of overt and covert saccades (42.5%). The vHIT detects abnormal VOR changes in the combination of gain assessment and refixation saccades. Since isolated covert saccades in VOR changes can only be seen with vHIT, peripheral vestibular disorders are likely to be misdiagnosed with the HIT.

Crouzon Syndrome: Relationship of Eye Movements to Pattern Strabismus.

To characterize conjugate eye movements in Crouzon syndrome (CS) patients with and without strabismus. Smooth pursuit, saccades, horizontal optokinetic nystagmus (OKN), and horizontal vestibulo-ocular reflex (VOR) were recorded using binocular video-oculography (VOG) in 10 children with CS (5 orthotropic, 5 strabismic) and 12 age-matched controls. Hess-Lancaster plots were generated from Orbit 1.8 using rectus muscle pulley locations from computed tomography imaging. Two-dimensional eye scan paths from VOG recordings were compared with the Hess-Lancaster plots. Targeted saccades were normometric on average but variable, and followed the main sequence in both CS groups. Smooth pursuit gains were normal for both CS groups; however, SP gains of the fixating eye in subjects with strabismus were significantly lower. Optokinetic nystagmus gains were reduced in both CS groups (P < 0.02) but were lower in subjects with strabismus. Shifting misalignments of binocular eye position in primary and eccentric gazes were associated with reduction in OKN gain in both CS groups. Vestibulo-ocular reflex gains for both CS groups were largely normal despite the presence of an off-axis vertical component. Normal gains for saccades and smooth pursuit in CS patients with strabismus are consistent with accurate execution of both movements despite extorsion of the globe. Vestibulo-ocular reflex in CS patients with strabismus had an off-axis vertical component consistent with extorted muscle pulleys. Optokinetic nystagmus is reduced in CS without strabismus owing to binocular position disparities and in CS with strabismus is likely due to cortical suppression associated with cross-axis orientation and exotropia.

The map of dizziness in vestibular schwannoma.

Dizziness is a frequent complaint in patients with vestibular schwannoma (VS). An abnormal vestibulo-ocular reflex (VOR) can explain this dizziness in patients with VS. The video Head impulse test (vHIT) offers a chance to describe specifically the VOR findings in such patients. Retrospective cases series study in a tertiary referral hospital. Fifty consecutive patients with VS were classified in accordance with the morphology of the VOR; gain, covert saccade, and overt saccade were analyzed both in the affected side and in the healthy side. For all patients, caloric tests were performed. All patients were tested before surgery. Caloric response was normal in 31 of 50 patients. The video Head impulse test was abnormal in 45 of 50 patients. For the affected side, low horizontal VOR gain was found in 27 of 50 patients, covert saccade was observed in 37 of 50, and overt saccade was observed in 26 of 50. In the healthy side, vHIT was abnormal in 29 of 50 patients, with a low gain in four of 50, covert saccade in seven of 50, and overt saccade in 23 of 50. In VS, gain for the affected side is not associated with caloric response, but gain for the affected side is associated with gain in the healthy side. Covert and overt saccade for the affected side is associated with gain for the affected side. In the healthy side, overt saccade is associated with low gain for the affected side. Video head impulse test improves the vestibular testing before surgery in patients with VS and should be included in the usual clinical tests for these patients. 4.

Clinical experience with video Head Impulse Test in children

BackgroundA standardized diagnostic protocol for children's vestibular assessment is still missing in daily clinical life. As rotatory chair testing and caloric test are usually not tolerated well by children, the aim of our study was not only to evaluate the importance and practicability of the video head impulse test performed in children with and without balance problems, but also to outline a diagnostic algorithm for children with balance problems. MethodsFifty-five children aged 3–16 years have been included in this prospective monocentric study. Balance was assessed using results from health screening examinations of the participants and results from a specific dizziness questionnaire for children. The children were then divided in two groups: group I without any sign of vestibular development disorder and group II with possible signs for a pathological equilibrium development. Horizontal vestibulo-ocular reflex (HVOR) was assessed using a video-oculography system device (EyeSeeCam©). Gain at 40, 60, and 80ms and gain variance has been measured. Furthermore, it was evaluated how calibration of the system was tolerated by the participants, how the test itself was accomplishable in children, and which difficulties arose during testing. ResultsReproducible test results were accomplished in 42 children (75%). Children with no balance problems in history showed a median gain of 1.02 (±0.28). A significant gain reduction between 40 and 80ms was found (P<0.05). Catch-up saccades were found in none of the children. Children with balance problems had a significantly reduced gain. (0.47±0.3; P<0.05) In this group, catch-up saccades could be detected in 4 out of 6 patients. For both groups, performing the test approximately took 20min, which is significantly longer than in adults (P<0.05). Calibration of the system with laser dots was easily doable in children aged 6 and older, whereas children between 3 and 5 years had better calibration results using colorful little icons. ConclusionsVideo head impulse test is a sensitive and efficient vestibular test in children, which is tolerated well by children aged 3–16 years. Therefore, video head impulse test can be easily used as a screening tool to detect vestibular dysfunction in the pediatric population.

Preserved otolith organ function in caspase-3-deficient mice with impaired horizontal semicircular canal function.

Genetically engineered mice are valuable models for elucidation of auditory and vestibular pathology. Our goal was to establish a comprehensive vestibular function testing system in mice using: (1) horizontal angular vestibulo-ocular reflex (hVOR) to evaluate semicircular canal function and (2) otolith-ocular reflex (OOR) to evaluate otolith organ function and to validate the system by characterizing mice with vestibular dysfunction. We used pseudo off-vertical axis rotation to induce an otolith-only stimulus using a custom-made centrifuge. For the OOR, horizontal slow-phase eye velocity and vertical eye position were evaluated as a function of acceleration. Using this system, we characterized hVOR and OOR in the caspase-3 (Casp3) mutant mice. Casp3 (-/-) mice had severely impaired hVOR gain, while Casp3 (+/-) mice had an intermediate response compared to WT mice. Evaluation of OOR revealed that at low-to-mid frequencies and stimulus intensity, Casp3 mutants and WT mice had similar responses. At higher frequencies and stimulus intensity, the Casp3 mutants displayed mildly reduced otolith organ-related responses. These findings suggest that the Casp3 gene is important for the proper function of the semicircular canals but less important for the otolith organ function.

Hybrid model of the context dependent vestibulo-ocular reflex: implications for vergence-version interactions.

The vestibulo-ocular reflex (VOR) is an involuntary eye movement evoked by head movements. It is also influenced by viewing distance. This paper presents a hybrid nonlinear bilateral model for the horizontal angular vestibulo-ocular reflex (AVOR) in the dark. The model is based on known interconnections between saccadic burst circuits in the brainstem and ocular premotor areas in the vestibular nuclei during fast and slow phase intervals of nystagmus. We implemented a viable switching strategy for the timing of nystagmus events to allow emulation of real nystagmus data. The performance of the hybrid model is evaluated with simulations, and results are consistent with experimental observations. The hybrid model replicates realistic AVOR nystagmus patterns during sinusoidal or step head rotations in the dark and during interactions with vergence, e.g., fixation distance. By simply assigning proper nonlinear neural computations at the premotor level, the model replicates all reported experimental observations. This work sheds light on potential underlying neural mechanisms driving the context dependent AVOR and explains contradictory results in the literature. Moreover, context-dependent behaviors in more complex motor systems could also rely on local nonlinear neural computations.

Vestibular migraine in children and adolescents: clinical findings and laboratory tests.

Introduction: Vestibular migraine (VM) is the most common cause of episodic vertigo in children. We summarize the clinical findings and laboratory test results in a cohort of children and adolescents with VM. We discuss the limitations of current classification criteria for dizzy children.Methods: A retrospective chart analysis was performed on 118 children with migraine related vertigo at a tertiary care center. Patients were grouped in the following categories: (1) definite vestibular migraine (dVM); (2) probable vestibular migraine (pVM); (3) suspected vestibular migraine (sVM); (4) benign paroxysmal vertigo (BPV); and (5) migraine with/without aura (oM) plus vertigo/dizziness according to the International Classification of Headache Disorders, 3rd edition (beta version).Results: The mean age of all patients was 12 ± 3 years (range 3–18 years, 70 females). 36 patients (30%) fulfilled criteria for dVM, 33 (28%) for pVM, 34 (29%) for sVM, 7 (6%) for BPV, and 8 (7%) for oM. Somatoform vertigo (SV) co-occurred in 27% of patients. Episodic syndromes were reported in 8%; the family history of migraine was positive in 65%. Mild central ocular motor signs were found in 24% (most frequently horizontal saccadic pursuit). Laboratory tests showed that about 20% had pathological function of the horizontal vestibulo-ocular reflex, and almost 50% had abnormal postural sway patterns.Conclusion: Patients with definite, probable, and suspected VM do not differ in the frequency of ocular motor, vestibular, or postural abnormalities. VM is the best explanation for their symptoms. It is essential to establish diagnostic criteria in clinical studies. In clinical practice, however, the most reasonable diagnosis should be made in order to begin treatment. Such a procedure also minimizes the fear of the parents and children, reduces the need to interrupt leisure time and school activities, and prevents the development of SV.

Vestibular examinations in apogeotropic positional nystagmus caused by cerebellar tumor

Horizontal, direction changing apogeotropic positional nystagmus (HAPN) is known to be associated with cerebellar lesions [1]. However, the pathophysiologic mechanism of cerebellar HAPN is unknown. We encountered a patient with a metastatic cerebellar tumor who presented with HAPN that disappeared after tumorectomy. Hyperactive vestibular reflexes, indicated by the results of electrophysiologic examinations, might have been the mechanism underlying the HAPN in this patient. A 70-year-old woman with a 2-month history of progressive dizziness and difficulty in walking was admitted to our hospital. She presented with truncal ataxia and HAPN but no other neurologic or neuroophthalmologic abnormalities. Contrast brain MRI revealed a well-enhanced cerebellar tumor. Because chest X-ray and CT showed a left lung tumor suggestive of lung cancer, a cerebellar metastasis was diagnosed. The cerebellar tumor was removed surgically 10 days after the patient’s admission. Pathologic examination of the surgical specimen revealed adenocarcinoma. After the tumorectomy, the HAPN was fully resolved, and the truncal ataxia was improved. The horizontal angular vestibulo-ocular reflex (A-VOR), cervical vestibular-evoked myogenic potential (C-VEMP), and ocular vestibular-evoked myogenic potential (O-VEMP) were evaluated before (when the HAPN was present) and 10 days after tumorectomy (when the HAPN had disappeared). A-VORs were recorded in darkness by means of a video-oculography-basedVORrecording and analysis system (IRN-2, Morita Mfg. Corp., Kyoto, Japan), with the patient seated on a rotating armchair with a headrest [2]. The chair was rotatedmanually in sinusoidal fashion for 20 s (frequency 0.5–0.75 Hz, amplitude 20 ) [2]. VOR gain, i.e., the eye velocity to head velocity ratio, was analyzed. C-VEMP was recorded from the tonically contracting ipsilateral sternocleidomastoid muscle during monaural stimulation with 105-dB clicks or short tone bursts (MEB 2312 testing system, Nihon Kohden, Tokyo, Japan; bandwidth 20–2,000 Hz, 200 averaged signals). Latencies of the first positive wave (p13) and second negative wave (n23) and peak-to-peak p13–n23 amplitude were measured. O-VEMP was recorded from the lower eyelids (inferior oblique muscles) during stimulation with 105 dB clicks or short tone bursts (MEB 2312, Nihon Kohden, Tokyo, Japan; bandwidth 20–2,000 Hz, 200 averaged signals). The patient was instructed to continue looking straight ahead and upward 30 . Because O-VEMP was not adequately elicited by monaural stimulation, binaural sound stimulation was applied. Latencies of the first negative wave (n1) and second positive wave (p1) and peak-to-peak n1–p1 amplitude were measured. Absolute A-VOR gains were reduced in both directions after the tumorectomy (Table 1). Cand O-VEMP amplitudes were also reduced on almost all recordings after tumorectomy (Table 1). Latencies of Cand O-VEMPs did not change. A-VOR is mediated by a semicircular-ocular pathway. C-VEMP reflects the vertical linear vestibulo-ocular reflex Electronic supplementary material The online version of this article (doi:10.1007/s10072-015-2086-4) contains supplementary material, which is available to authorized users.

Age dependent normal horizontal VOR gain of head impulse test as measured with video-oculography.

BackgroundThe head impulse test (HIT) is a recognised clinical sign of the high frequency vestibulo-ocular reflex (VOR), which can be quantified with video-oculography. This measures the VOR gain as the ratio of angular eye velocity to angular head velocity. Although normative data is available for VOR gain with video-oculography, most normal studies in general include small numbers of subjects and do not include analysis of variation of VOR gain with age. The purpose of our study was to establish normative data across 60 control subjects aged 20 to 80 years to represent a population distribution.MethodsSixty control subjects without any current or previous form of brain disorder or vertigo participated in this study and form the basis for future comparison to patients with vestibular lesions. The relationship between the horizontal vestibulo-ocular reflex (HVOR) velocity gain and age was analysed using a mixed regression model with a random effect for subjects. Differences in testing technique were assessed to ensure reliability in results.ResultsThe mean HVOR velocity gain of 60 normal subjects was 0.97 (SD = 0.09) at 80 ms and 0.94 (SD = 0.10) at 60 ms. The 2 SD lower limit of normal HVOR velocity gain was 0.79 at 80 ms and 0.75 at 60 ms. No HVOR velocity gain fell below 0.76 and 0.65 at 80 ms and 60 ms respectively. The HVOR velocity gain declined by 0.012 and 0.017 per decade as age increased at 80 ms and 60 ms respectively. A non-physiologically high horizontal HVOR velocity gain was found to occur in tests where passive HITs were predictable in direction and time and where target distance was below 0.70 m.ConclusionsNormative data with respect to HVOR velocity gain decreases slightly with age, but with careful attention to methodology the 2 SD lower limit of normal is relatively robust across a wide age range and into the eighth decade, without requirement for adjustment with age.

Caloric stimulation and video-head impulse testing in Ménière’s disease and vestibular migraine

Conclusion: Both the bithermal caloric test and the video-head impulse test (vHIT) were more often abnormal in Ménière’s disease (MD) than in vestibular migraine (VM). Horizontal vestibulo-ocular reflex (hVOR) evaluation with caloric test (low-frequency test) was significantly more often abnormal than vHIT (high-frequency test). Therefore, both tests can be used in a complementary way for frequency-selective testing of peripheral vestibular function. Objectives: To compare the results of caloric testing and vHIT in MD and VM and to determine which test is more sensitive to uncover peripheral vestibular hypofunction. Methods: Patients with MD (n=30) or VM (n=23) were examined with the caloric test and vHIT. The parameters analyzed were the canal paresis factor for the caloric test and the hVOR gain on both sides in vHIT. Results: The caloric test was abnormal in 67% of patients with MD and in 22% with VM (p=0.002), while the vHIT showed an hVOR deficit in 37% in MD and 9% in VM (p=0.025). In all, 28% of patients with an abnormal caloric test had a normal vHIT, whereas 6% of those with an abnormal vHIT had a normal caloric test. The sensitivity of vHIT compared with caloric testing was 55% for MD and 40% for VM. Neither the caloric test nor vHIT could detect significant differences between early (<5 years) or advanced stages (>5 years) of MD or VM.