Otolith Research Articles

Perception of Verticality and Vestibular Disorders of Balance and Falls.

Objective: To review current knowledge of the perception of verticality, its normal function and disorders. This is based on an integrative graviceptive input from the vertical semicircular canals and the otolith organs.Methods: The special focus is on human psychophysics, neurophysiological and imaging data on the adjustments of subjective visual vertical (SVV) and the subjective postural vertical. Furthermore, examples of mathematical modeling of specific vestibular cell functions for orientation in space in rodents and in patients are briefly presented.Results: Pathological tilts of the SVV in the roll plane are most sensitive and frequent clinical vestibular signs of unilateral lesions extending from the labyrinths via the brainstem and thalamus to the parieto-insular vestibular cortex. Due to crossings of ascending graviceptive fibers, peripheral vestibular and pontomedullary lesions cause ipsilateral tilts of the SVV; ponto-mesencephalic lesions cause contralateral tilts. In contrast, SVV tilts, which are measured in unilateral vestibular lesions at thalamic and cortical levels, have two different characteristic features: (i) they may be ipsi- or contralateral, and (ii) they are smaller than those found in lower brainstem or peripheral lesions. Motor signs such as head tilt and body lateropulsion, components of ocular tilt reaction, are typical for vestibular lesions of the peripheral vestibular organ and the pontomedullary brainstem (vestibular nucleus). They are less frequent in midbrain lesions (interstitial nucleus of Cajal) and rare in cortical lesions. Isolated body lateropulsion is chiefly found in caudal lateral medullary brainstem lesions. Vestibular function in the roll plane and its disorders can be mathematically modeled by an attractor model of angular head velocity cell and head direction cell function. Disorders manifesting with misperception of the body vertical are the pusher syndrome, the progressive supranuclear palsy, or the normal pressure hydrocephalus; they may affect roll and/or pitch plane.Conclusion: Clinical determinations of the SVV are easy and reliable. They indicate acute unilateral vestibular dysfunctions, the causative lesion of which extends from labyrinth to cortex. They allow precise topographical diagnosis of side and level in unilateral brainstem or peripheral vestibular disorders. SVV tilts may coincide with or differ from the perception of body vertical, e.g., in isolated body lateropulsion.

Characterizing the Role of Kcnq5a in Zebrafish Inner Ear Hair Cells

Hair cells (HCs) are specialized mechanoreceptors in the vertebrate inner ear that function in hearing and balance. Non‐mammalian HCs have electrophysiological properties that resemble both that of mammalian vestibular or cochlear HCs, including mechanotransduction, as well as potassium ion (K+) and calcium ion (Ca2+) currents. While mammals rely upon mechanical mechanisms to generate tuned receptor potentials, non‐mammalian HCs exhibit electrical resonance, a unique feature for frequency tuning of HCs that is modulated by voltage‐dependent conductances. In non‐mammalian HCs, the channel kinetics and interplay of K+ and Ca2+ channels result in oscillation of the membrane potential, generating electrical resonance that enhances the frequency tuning of the HCs. However, the molecular identity of the channels involved in electrical resonance in non‐mammalian HCs remains largely unknown. This study focused on kcnq5a, a gene encoding the voltage‐dependent potassium channel KQT‐like subfamily member 5a (Kcnq5a). The channels of the KCNQ gene family are responsible for generating sub‐threshold M‐currents in neurons, stabilizing resting membrane potential and thereby influencing cell excitability. We hypothesized that Kcnq5a is responsible for generating electrical resonance and maintaining resting membrane potential of zebrafish inner ear HCs. Both RT‐qPCR and in situ hybridization studies confirmed that kcnq5a was expressed in HCs of the inner ear. To characterize the function of the Kcnq5a channel in inner ear HCs, morpholinos were injected into one‐cell stage embryos for targeted knockdown of kcnq5a mRNA. Morphology of HCs in both injected and wildtype zebrafish was examined with confocal microscopy. Auditory function was measured using microphonic responses of otolithic organs in larval zebrafish, while auditory sensitivity was measured using a behavioral prepulse inhibition assay. Following knockdown of kcnq5a, the larvae (5dpf) showed a decrease in microphonic amplitude and hearing threshold. This study represents a preliminary examination of the role of Kcnq5a in electrical resonance and frequency selectivity in zebrafish inner ear HCs.Support or Funding InformationThis work has been supported by the NIH grant R01 DC 016807‐01 to Dr. David HeThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Thermoregulation through the glutamatergic neurons in vestibular nucleus complex

The vestibular system is one of the sensory systems which contributes to the sense of balance and spatial orientation. This also participates in the autonomic nervous response, which stimulation of the peripheral vestibular organs induces sympathoexcitation. This response is observed in both rodents and human beings, and we have reported that vestibular system contributes to the arterial pressure response during postural change as one of the feedforward control system (Morita, Abe et al., Sci Rep, 2016). In the other autonomic nervous responses, stimulation of the otolith organs in the inner ear induces hypothermia; exposure to the hypergravity environment decreases body temperature by 8 degree Celsius in mice. This response was attenuated by vestibular lesion or genetic deletion of otolith. In order to elucidate the central mechanism of hypergravity‐induced hypothermia, we examined the role of Vglut2, Vgat and ChAT neurons in vestibular nucleus complex (VNC) on thermoregulation in mice. We used Vglut2‐cre, Vgat‐cre, and ChAT‐cre mice to manipulate each neuron in VNC. Based on the previous work (Abe et al., Nat Neurosci, 2017), AAV‐DIO type viral vector was injected in VNC to express photo sensors (channelrhodopsin or archaerhodopsin) for optogenetics or hM3D(Gq) for chemogenetics. Unilateral photostimulation of the Vglut2 neurons in VNC induced body tilt to the ipsilateral side, while photoinhibition induced body tilt to the contralateral side. In Vgat‐cre mice, opposite response was observed compared with Vglut2‐cre mouse. Photostimulation of ChAT neurons did not show any responses. Chemogenetics stimulation of Vglut2 neurons showed hypothermia with increasing in activity, while Vgat stimulation increased body temperature with decreasing in activity. Deletion of Vglut2 neurons in VNC using AAV2–DIO–taCasp3–TEVp attenuated hypothermia induced by hypergravity exposure. On the other hand, hypothermia was still observed by deletion of Vgat neurons in VNC. Interestingly, chemogenetics stimulation of Vglut2 neurons in VNC 2 days before hypergravity exposure, the hypothermia was attenuated. Taken together, hypothermia induced by hypergravity exposure is due to activation of Vglut2 neurons in VNC.Support or Funding InformationGrant‐in‐Aid for Scientific Research on Innovative Areas 15H05940 (HM) and 18H04974 (CA), Grant‐in‐Aid for Scientific Research (C) 18K06850 (HM), The Takeda Science Foundation (CA), The Uehara Memorial Foundation (CA), Kato Memorial Bioscience Foundation (CA), The Nakatomi Foundation (CA)This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The neural basis of motion sickness.

Although motion of the head and body has been suspected or known as the provocative cause for the production of motion sickness for centuries, it is only within the last 20 yr that the source of the signal generating motion sickness and its neural basis has been firmly established. Here, we briefly review the source of the conflicts that cause the body to generate the autonomic signs and symptoms that constitute motion sickness and provide a summary of the experimental data that have led to an understanding of how motion sickness is generated and can be controlled. Activity and structures that produce motion sickness include vestibular input through the semicircular canals, the otolith organs, and the velocity storage integrator in the vestibular nuclei. Velocity storage is produced through activity of vestibular-only (VO) neurons under control of neural structures in the nodulus of the vestibulo-cerebellum. Separate groups of nodular neurons sense orientation to gravity, roll/tilt, and translation, which provide strong inhibitory control of the VO neurons. Additionally, there are acetylcholinergic projections from the nodulus to the stomach, which along with other serotonergic inputs from the vestibular nuclei, could induce nausea and vomiting. Major inhibition is produced by the GABAB receptors, which modulate and suppress activity in the velocity storage integrator. Ingestion of the GABAB agonist baclofen causes suppression of motion sickness. Hopefully, a better understanding of the source of sensory conflict will lead to better ways to avoid and treat the autonomic signs and symptoms that constitute the syndrome.

Vestibular Evoked Myogenic Potentials After Epleys Manoeuvre Among Individuals with Benign Paroxysmal Positional Vertigo.

VEMP abnormalities in individuals with BPPV are often reported to be associated with utricle and saccule degeneration. The aim of the present study is to assess the frequency of VEMP abnormalities using vestibular evoked myogenic potentials in individuals with Posterior canal Benign Paroxysmal Positional Vertigo (BPPV) after Epley's manoeuvre. 36 individuals (36 ears) with definite posterior canal BPPV and 36 healthy controls were considered for the present study. All the them underwent otoscopic examination, Dix-Hallpike manoeuvre to diagnose posterior canal BPPV. Further Audiological Evaluation including pure tone audiometry was carried out to rule out vestibular disorders associated with hearing loss. Epley's manoeuvre was performed on all individuals with BPPV by an experienced otorhinolaryngologist. Cervical and Ocular Vestibular Evoked Myogenic Potentials (VEMP) were used to investigate the saccule and utricle functions following Epley's manoeuvre. Cervical VEMP and ocular VEMP abnormalities were observed in 8/36 (22.22%) and 18/36 (50%) affected ears with BPPV respectively. Cervical VEMP responses were reduced in amplitude among 1/36 (2.77%) and absent in 7/36 (19.44%) of affected ears with BPPV. Ocular VEMP responses were reduced in amplitude on 11/36 (30.55%), followed by absent responses in 5/36 (13.88%) ears with BPPV. Two patients with posterior canal BPPV i.e., 4/64 (5.55%) ears had bilateral absence of ocular VEMP responses. Two ears with BPPV 2/36 (5.55%) had absence of both cervical and ocular VEMP responses in BPPV affected ear. T test showed significant difference (p < 0.01) in the amplitude of ocular VEMP among posterior canal BPPV individuals when compared to cervical VEMP. The present study highlights individuals with Posterior canal BPPV may have otoconia dislodgement or macular degeneration of utricle, saccule, both utricle and saccule unilaterally, or bilaterally. VEMP may be useful in evaluating degeneration of both otolith organs associated with BPPV.

Rocking Promotes Sleep in Mice through Rhythmic Stimulation of the Vestibular System

Rocking has long been known to promote sleep in infants and, more recently, also in adults, increasing NREM sleep stage N2 and enhancing EEG slow waves and spindles. Nevertheless, whether rocking also promotes sleep in other species, and what the underlying mechanisms are, has yet to be explored. In the current study, C57BL/6J mice equipped with EEG and EMG electrodes were rocked laterally during their main sleep period, i.e., the 12-h light phase. We observed that rocking affected sleep in mice with a faster optimal rate than in humans (1.0 versus 0.25Hz). Specifically, rocking mice at 1.0Hz increased time spent in NREM sleep through the shortening of wake episodes and accelerated sleep onset. Although rocking did notincrease EEG activity in the slow-wave and spindle-frequency ranges in mice, EEG theta activity (6-10Hz) during active wakefulness shifted toward slower frequencies. To test the hypothesis that the rocking effects are mediated through the vestibular system, we used the otoconia-deficient tilted (tlt) mouse, which cannot encode linear acceleration. Mice homozygous for the tlt mutation were insensitive to rocking at 1.0Hz, while the sleep and EEG response of their heterozygous and wild-type littermates resembled those of C57BL/6J mice. Our findings demonstrate that rocking also promotes sleep in the mouse and that this effect requires input from functional otolithic organs of the vestibule. Our observations also demonstrate that the maximum linear acceleration applied, and not the rocking rate per se, is key in mediating the effects of rocking on sleep.

Complete cessation of epileptiform events caused by benign epilepsy with centrotemporal spikes (BECTS) in 9-year-old male

Event Abstract Back to Event Complete cessation of epileptiform events caused by benign epilepsy with centrotemporal spikes (BECTS) in 9-year-old male Shannon Leon1 and Jason Langhough1* 1 Dr. Shannon Leon Functional Neurology, United States Presentation Two prior EEG reports confirm presence of benign rolandic epilepsy of childhood with higher amplitude in bilateral temporal regions, right more than left, and with no activation of epileptiform activity induced by hyperventilation. Pertinent highlights of neurological exam were hypermetric saccades rightward, dyspraxic alternating hand movements on the right, impaired neural integrators resulting in decrease time constant of eccentric gaze rightward and up-and-rightward, thenar myoclonus in the left hand, decreased posture stability on foam platform with eyes closed in bilateral otolithic organs and bilateral posterior semicircular canals. Videonystagmography confirmed a decrease in amplitude of the right vestibulo-ocular reflex, and a right eye accommodation spasm. Musculoskeletal exam showed decrease rib expansion in the right side and overall poor posture. Intervention The nidus of treatment consisted of vestibular recalibration maneuvers to elicit, via canals and otoliths, the neural activation of putamen streams for inhibition of globus pallidus interna and thalamus, among other nuclei; sinusoidal micropursuits directed up-and-right to down-and-left performed in the patient’s field of views in lower left and in the upper right in order to elicit parietal pathways and thereby bypass, to degrees, deep central nuclei activation; and joint articulation of the right rib cage was restored to mobility to prevent hypoxic circumstance of nervous tissue. Patient scheduled for a frequency of one visit per week. Outcome After one visit, patient remarks on feeling “happier,” “calmer,” and “clear-minded.” Objective measurements saw improvement of balance on foam platform with eyes closed in all balance organ orientations to within normal limits, and vestibulo-ocular reflexes restored to accurate amplitude and velocity. Since initial treatment over one year ago, patient reports zero epileptic events, and patient’s parents observe noticeable increases in sports performances as well as an overall calmer demeanor. Perspective The wellspring of energy in childhood is meant for play and learning. When neuronal activation exceeds physiologic capacity and manifests epileptiform activity, even if benign, then rectifying therapy should be sought. BECTS is considered one of the most common childhood epileptic syndromes, and as such, it highlights the widespread significance of our outcome using a non-invasive, drug-free, phenomenological approach. Keywords: BECTS, benign epilepsy with centrotemporal spikes, Epilepsy, seizure, carrick eye exercises, Vestibulal Evoked Myogenic Potentials, Vestibular rehabilitation therapy Conference: International Symposium on Clinical Neuroscience, Orlando, United States, 24 May - 26 May, 2019. Presentation Type: Poster Presentation Topic: Clinical Neuroscience Citation: Leon S and Langhough J (2019). Complete cessation of epileptiform events caused by benign epilepsy with centrotemporal spikes (BECTS) in 9-year-old male. Front. Neurol. Conference Abstract: International Symposium on Clinical Neuroscience. doi: 10.3389/conf.fneur.2019.62.00026 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 30 Mar 2019; Published Online: 27 Sep 2019. * Correspondence: Dr. Jason Langhough, Dr. Shannon Leon Functional Neurology, Woodbury, Minnesota, 11797, United States, j.langhough@gmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Shannon Leon Jason Langhough Google Shannon Leon Jason Langhough Google Scholar Shannon Leon Jason Langhough PubMed Shannon Leon Jason Langhough Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

No Evidence of a Contribution of the Vestibular System to Frequent Falls in Progressive Supranuclear Palsy.

Background and PurposeConflicting results about vestibular function in progressive supranuclear palsy (PSP) prompted a systematic examination of the semicircular canal function, otolith function, and postural stability.MethodsSixteen patients with probable PSP [9 females, age=72±6 years (mean±SD), mean disease duration=3.6 years, and mean PSP Rating Scale score=31] and 17 age-matched controls were examined using the video head impulse test, caloric testing, ocular and cervical vestibular evoked myogenic potentials (o- and cVEMPs), video-oculography, and posturography.ResultsThere was no evidence of impaired function of the angular vestibulo-ocular reflex (gain=1.0±0.1), and caloric testing also produced normal findings. In terms of otolith function, there was no significant difference between PSP patients and controls in the absolute peakto-peak amplitude of the oVEMP (13.5±7.2 µV and 12.5±5.6 µV, respectively; p=0.8) or the corrected peak-to-peak amplitude of the cVEMP (0.6±0.3 µV and 0.5±0.2 µV, p=0.3). The total root-mean-square body sway was significantly increased in patients with PSP compared to controls (eyes open/head straight/hard platform: 9.3±3.7 m/min and 6.9±2.1 m/min, respectively; p=0.032). As expected, the saccade velocities were significantly lower in PSP patients than in controls: horizontal, 234±92°/sec and 442±66°/sec, respectively; downward, 109±105°/sec and 344±72°/sec; and upward, 121±110°/sec and 348±78°/sec (all p<0.01).ConclusionsWe found no evidence of impairment of either high- or low-frequency semicircular function or otolith organ function in the examined PSP patients. It therefore appears that other causes such as degeneration of supratentorial pathways lead to postural imbalance and falls in patients with PSP.

Vestibular function assessment in cochlear implant patients

BackgroundAnatomical and embryological relations between cochlear and vestibular end organs predispose them to same noxious or developmental factors, thus these may affect either or both systems. Cochlear implantation being a widely used procedure for restoration of hearing in patients who are not candidates for regular amplification, may affect by different means the vestibular system. One of these factors include the surgical procedure. The aim of this study is to assess the vestibular function in cochlear implant candidates before surgery to exclude coexisting vestibular affection with the sensorineural hearing loss (SNHL). Reassessment after operation was done to determine the risk posed by surgery and for correlating the surgical approach to vestibular findings.Materials and methodsThe case series presented herein is of cochlear implant candidates who underwent full audiological and radiological assessment. Vestibular assessment was done before and after operation and included cervical vestibular evoked myogenic potential (cVEMP) and ocular vemp (oVEMP) for evaluation of otolith organs. Video head impulse test (VHIT) was used to evaluate semicircular canal.ResultsPreliminary results show that patients may exhibit vestibular loss concomitant to the SNHL even with the absence of vestibular complaints. Patients who had normal preoperative vestibular function showed affected vestibular tests after the surgery. There was a mismatch between these objective findings and the subjective complaint of imbalance or vertigo.ConclusionDespite the minor risk posed by cochlear implant (CI) surgery for the subjective vestibular affection, the side with worse vestibular function should be chosen for CI if other factors are equal to avoid postoperative vestibular loss.

Noisy Galvanic Vestibular Stimulation Primarily Affects Otolith-Mediated Motion Perception

Noisy galvanic vestibular stimulation (nGVS) has been shown to improve vestibular perception in healthy subjects. However, it is unclear whether both the semicircular canals (SCCs) and otolith organs contribute to this enhancement or is it confined to one of these structures. To elucidate this matter, nGVS amplitudes with optimal effect on postural control were determined in 12 healthy subjects during upright stance. These amplitudes were then applied during perceptual direction-recognition tasks in inter-aural translation (otolith-mediated perception) as well as yaw rotation with the head pitched forward 71 deg (SCC-mediated perception) and compared to sham stimulation. Nine out of 12 subjects showed significantly improved direction-recognition thresholds in the inter-aural translation task during nGVS compared to sham stimulation (p ≤ 0.03; mean threshold reduction: 38.8%). Only 6 of 12 subjects showed mild improvements in the yaw rotation task during nGVS (p > 0.05). In addition, elevated baseline thresholds during the inter-aural translation task significantly correlated with a larger magnitude of improvement (R = 0.72, p = 0.01). In conclusion, nGVS appears to primarily impact otolith-mediated perception while only mildly affecting the SCCs. Thus, this stimulation approach could be a complementary candidate to vestibular implants that are currently limited to SCC-mediated vestibular function.

Proposal on the Diagnostic Criteria of Definite Isolated Otolith Dysfunction.

Background and ObjectivesDizzy patients with abnormal otolith function tests, despite a normal caloric response, are defined as having specific (isolated) otolith organ dysfunction. This study was performed to compare the differences in clinical presentation between isolated otolith dysfunction (iOD) patients with lab- and Sx-based iOD group and lab-based iOD symptoms.Subjects and MethodsThe medical records of 23 iOD patients with normal caloric response but abnormal cervical vestibular evoked myogenic potential (VEMP), ocular VEMP, or subjective visual vertical were reviewed. Non-spinning vertigo was considered as otolith-related symptoms. The patients’ age, onset of dizziness, Numeric Rating Scale on the severity of dizziness, and concomitant vestibular disorders were analyzed.ResultsPatients in the lab-based iOD group were significantly older than those in the lab- and Sx-based iOD group. Known vestibular disorders were significantly more common in the lab-based iOD group (83.3%) compared to the lab- and Sx-based iOD group (18.2%). Despite the normal caloric response, catch-up saccade was found in the video head impulse test in more than half (54.5%) of the lab-based iOD group patients. There was no catch-up saccade in the lab- and Sx-based iOD group. There were no significant differences in gender ratio, frequency of dizziness attacks, and duration of illness.ConclusionsWe propose new definitions of definite iOD (lab- and Sx-based iOD) and probable iOD (lab- or Sx-based iOD). These new definitions may help researchers to identify patients who are more likely to have true iOD, and facilitate comparisons of results between different studies.

Aging Is a Risk Factor for Utricular Dysfunction in Idiopathic Benign Paroxysmal Positional Vertigo.

Benign paroxysmal positional vertigo (BPPV) is the most common cause of balance disorders in the elderly. Dislodgement of the otoconia in BPPV might have an association with damage to the otolith organs. The aim of this study was to investigate whether aging is a risk factor for otolith organ dysfunction in idiopathic BPPV. We retrospectively reviewed the medical records of 112 consecutive idiopathic BPPV patients who underwent cervical VEMP testing to air-conducted sound (ACS cVEMP), ocular VEMP testing to bone-conducted vibration (BCV oVEMP), and caloric testing. We performed binomial logistic regression analyses to see whether age, the side affected by BPPV or the canal affected by BPPV have an association with the presence of peripheral vestibular dysfunction in idiopathic BPPV patients. The elderly group (aged ≥65 years) had a significantly positive association with abnormalities in BCV oVEMPs (p = 0.0109), while the side affected by BPPV (p = 0.598) and the canal affected by BPPV (p = 0.576) did not. The odds ratio of the abnormal BCV oVEMPs for the elderly group compared with the non-elderly group (aged < 65 years) was 2.676 (95% confidence interval, 1.254–5.079). The elderly group had no significant association with the abnormalities in ACS cVEMPs (p = 0.0955) or caloric testing (p = 0.488). Dysfunction of the utricle, where the dislodgement of the otoconia mainly occurs, is affected by aging in idiopathic BPPV.

Directional hearing and sound source localization by fishes.

Directional hearing may enable fishes to seek out prey, avoid predators, find mates, and detect important spatial cues. Early sound localization experiments gave negative results, and it was thought unlikely that fishes utilized the same direction-finding mechanisms as terrestrial vertebrates. However, fishes swim towards underwater sound sources, and some can discriminate between sounds from different directions and distances. The otolith organs of the inner ear detect the particle motion components of sound, acting as vector detectors through the presence of sensory hair cells with differing orientation. However, many questions remain on inner ear functioning. There are problems in understanding the actual mechanisms involved in determining sound direction and distance. Moreover, very little is still known about the ability of fishes to locate sound sources in three-dimensional space. Do fishes swim directly towards a source, or instead "sample" sound levels while moving towards the source? To what extent do fishes utilize other senses and especially vision in locating the source? Further behavioral studies of free-swimming fishes are required to provide better understanding of how fishes might actually locate sound sources. In addition, more experiments are required on the auditory mechanism that fishes may utilize.

The occlusion effect in bone conducted cVEMP.

Vestibular evoked myogenic potentials (VEMP) are transient alteration in tonic activity of muscles elicited by auditory stimulation of the otolithic organs of the ear. VEMP can be triggered by auditory stimulation via air or bone conduction. Occlusion of the external auditory meatus has long been known to decrease thresholds for sound perception medicated by the cochlea. Proof that the occlusion effect is present for bone conducted (BC) cervical VEMPs (cVEMP). Measurement of the thresholds and raw amplitudes of BC-VEMPs in twenty healthy adults with the external auditory canal open and occluded. Thresholds for BC-VEMPs were similar for the open vs. the occluded condition. However, amplitudes were statistically significantly higher in the occluded (average 76.34μV) vs. open group (average 69.9μV). The occlusion effect is present in cVEMPs. This finding, described herein for the first time, has a number of clinical implications such as the surgically altered ear and the use of occluding hearing aids.

The Neurophysiology and Treatment of Motion Sickness.

Seasickness and travel sickness are classic types of motion illness. Modern simulation systems and virtual reality representations can also induce comparable symptoms. Such manifestations can be alleviated or prevented by various measures. This review is based on pertinent publications retrieved by a PubMed search, with special attention to clinical trials and review articles. Individuals vary in their susceptibility to autonomic symptoms, ranging from fatigue to massive vomiting, induced by passive movement at relatively low frequencies (0.2 to 0.4 Hz) in situations without any visual reference to the horizontal plane. Younger persons and women are considered more susceptible, and twin studies have revealed a genetic component as well. The various types of motion sickness are adequately explained by the intersensory conflict model, incorporating the vestibular, visual, and proprioceptive systems and extended to include consideration of postural instability and asymmetry of the otolith organs. Scopolamine and H1-antihistamines, such as dimenhydrinate and cinnarizine, can be used as pharmacotherapy. The symptoms can also be alleviated by habituation through long exposure or by the diminution of vestibular stimuli. The various types of motion sickness can be treated with general measures to lessen the intersensory conflict, behavioral changes, and drugs.

Loss of α-Calcitonin Gene-Related Peptide (αCGRP) Reduces Otolith Activation Timing Dynamics and Impairs Balance.

Calcitonin gene-related peptide (CGRP) is a neuroactive peptide that is thought to play a role at efferent synapses in hair cell organs including the cochlea, lateral line, and semicircular canal. The deletion of CGRP in transgenic mice is associated with a significant reduction in suprathreshold cochlear nerve activity and vestibulo–ocular reflex (VOR) gain efficacy when compared to littermate controls. Here we asked whether the loss of CGRP also influences otolithic end organ function and contributes to balance impairments. Immunostaining for CGRP was absent in the otolithic end organs of αCGRP null (-/-) mice while choline acetyltransferase (ChAT) immunolabeling appeared unchanged suggesting the overall gross development of efferent innervation in otolithic organs was unaltered. Otolithic function was assessed by quantifying the thresholds, suprathreshold amplitudes, and latencies of vestibular sensory-evoked potentials (VsEPs) while general balance function was assessed using a modified rotarod assay. The loss of αCGRP in null (-/-) mice was associated with: (1) shorter VsEP latencies without a concomitant change in amplitude or thresholds, and (2) deficits in the rotarod balance assay. Our findings show that CGRP loss results in faster otolith afferent activation timing, suggesting that the CGRP component of the efferent vestibular system (EVS) also plays a role in otolithic organ dynamics, which when coupled with reduced VOR gain efficacy, impairs balance.

Neuronal network-based mathematical modeling of perceived verticality in acute unilateral vestibular lesions: from nerve to thalamus and cortex.

Acute unilateral lesions of vestibular graviceptive pathways from the otolith organs and semicircular canals via vestibular nuclei and the thalamus to the parieto-insular vestibular cortex regularly cause deviations of perceived verticality in the frontal roll plane. These tilts are ipsilateral in peripheral and in ponto-medullary lesions and contralateral in ponto-mesencephalic lesions. Unilateral lesions of the vestibular thalamus or cortex cause smaller tilts of the perceived vertical, which may be either ipsilateral or contralateral. Using a neural network model, we previously explained why unilateral vestibular midbrain lesions rarely manifest with rotational vertigo. We here extend this approach, focussing on the direction-specific deviations of perceived verticality in the roll plane caused by acute unilateral vestibular lesions from the labyrinth to the cortex. Traditionally, the effect of unilateral peripheral lesions on perceived verticality has been attributed to a lesion-based bias of the otolith system. We here suggest, on the basis of a comparison of model simulations with patient data, that perceived visual tilt after peripheral lesions is caused by the effect of a torsional semicircular canal bias on the central gravity estimator. We further argue that the change of gravity coding from a peripheral/brainstem vectorial representation in otolith coordinates to a distributed population coding at thalamic and cortical levels can explain why unilateral thalamic and cortical lesions have a variable effect on perceived verticality. Finally, we propose how the population-coding network for gravity direction might implement the elements required for the well-known perceptual underestimation of the subjective visual vertical in tilted body positions.

Morphology of the utricular otolith organ in the toadfish, Opsanus tau.

The utricle provides the vestibular reflex pathways with the sensory codes of inertial acceleration of self-motion and head orientation with respect to gravity to control balance and equilibrium. Here we present an anatomical description of this structure in the adult oyster toadfish and establish a morphological basis for interpretation of subsequent functional studies. Light, scanning, and transmission electron microscopy techniques were applied to visualize the sensory epithelium at varying levels of detail, its neural innervation and its synaptic organization. Scanning electron microscopy was used to visualize otolith mass and morphological polarization patterns of hair cells. Afferent nerve fibers were visualized following labeling with biocytin, and light microscope images were used to make three-dimensional (3-D) reconstructions of individual labeled afferents to identify dendritic morphology with respect to epithelial location. Transmission electron micrographs were compiled to create a serial 3-D reconstruction of a labeled afferent over a segment of its dendritic field and to examine the cell-afferent synaptic contacts. Major observations are: a well-defined striola, medial and lateral extra-striolar regions with a zonal organization of hair bundles; prominent lacinia projecting laterally; dependence of hair cell density on macular location; narrow afferent dendritic fields that follow the hair bundle polarization; synaptic specializations issued by afferents are typically directed towards a limited number of 7-13 hair cells, but larger dendritic fields in the medial extra-striola can be associated with > 20 hair cells also; and hair cell synaptic bodies can be confined to only an individual afferent or can synapse upon several afferents.

Characteristics and mechanism of apogeotropic central positional nystagmus.

Here we characterize persistent apogeotropic type of central positional nystagmus, and compare it with the apogeotropic nystagmus of benign paroxysmal positional vertigo involving the lateral canal. Nystagmus was recorded in 27 patients with apogeotropic type of central positional nystagmus (22 with unilateral and five with diffuse cerebellar lesions) and 20 patients with apogeotropic nystagmus of benign paroxysmal positional vertigo. They were tested while sitting, while supine with the head straight back, and in the right and left ear-down positions. The intensity of spontaneous nystagmus was similar while sitting and supine in apogeotropic type of central positional nystagmus, but greater when supine in apogeotropic nystagmus of benign paroxysmal positional vertigo. In central positional nystagmus, when due to a focal pathology, the lesions mostly overlapped in the vestibulocerebellum (nodulus, uvula, and tonsil). We suggest a mechanism for apogeotropic type of central positional nystagmus based on the location of lesions and a model that uses the velocity-storage mechanism. During both tilt and translation, the otolith organs can relay the same gravito-inertial acceleration signal. This inherent ambiguity can be resolved by a 'tilt-estimator circuit' in which information from the semicircular canals about head rotation is combined with otolith information about linear acceleration through the velocity-storage mechanism. An example of how this mechanism works in normal subjects is the sustained horizontal nystagmus that is produced when a normal subject is rotated at a constant speed around an axis that is tilted away from the true vertical (off-vertical axis rotation). We propose that when the tilt-estimator circuit malfunctions, for example, with lesions in the vestibulocerebellum, the estimate of the direction of gravity is erroneously biased away from true vertical. If the bias is toward the nose, when the head is turned to the side while supine, there will be sustained, unwanted, horizontal positional nystagmus (apogeotropic type of central positional nystagmus) because of an inappropriate feedback signal indicating that the head is rotating when it is not.

Percepción de la vertical visual subjetiva. Medición y utilidad diagnóstica

Introduction and objective: The subjective visual vertical (SVV) is the position in which a subject would place a line when it is indicated that the adjustment to the real physical vertical that coincides with the gravitational axis. It is a diagnostic test that evaluates mainly the otolithic organs. We review in this article the diagnostic utility of this test. Method: A bibliographical review of the most significant authors was carried out for this purpose. Conclusions: Its measurement is simple and does not require sophisticated equipment and although it has a high sensitivity in acute processes, in the chronic its usefulness is more debatable. Neither does it allow locating the region of the vestibular pathway affected by the pathological process.