Acoustic Clicks Activate both the Canal and Otolith Vestibulo-Ocular Reflex Pathways in Behaving Monkeys

Acoustic activation of the vestibular system has been well documented in humans and animal models. In the past decade, sound-evoked myogenic potentials in the sternocleidomastoid muscle (cVEMP) and the extraocular muscles (oVEMP) have been extensively studied, and their potentials as new tests for vestibular function have been widely recognized. However, the extent to which sound activates the otolith and canal pathways remains controversial. In the present study, we examined this issue in a recently developed nonhuman primate model of acoustic activation of the vestibular system, i.e., sound-evoked vestibulo-ocular reflexes (VOR) in behaving monkeys. To determine whether the canal and otolith VOR pathways are activated by sound, we analyzed abducens neurons' responses to clicks that were delivered into either ear. The main finding was that clicks evoked short-latency excitatory responses in abducens neurons on both sides. The latencies of the two responses, however, were different. The mean latency of the contralateral and ipsilateral abducens neurons was 2.44 ± 0.4 and 1.65 ± 0.28 ms, respectively. A further analysis of the excitatory latencies, in combination with the known canal and otolith VOR pathways, suggests that the excitatory responses of the contralateral abducens neurons were mediated by the contralateral disynaptic VOR pathways that connect the lateral canal to the contralateral abducens neurons, and the excitatory responses of the ipsilateral abducens neurons were mediated by the ipsilateral monosynaptic VOR pathways that connect the utricle to the ipsilateral abducens neurons. These results provide new insights into the understanding of the neural basis for sound-evoked vestibular responses, which is essential for developing new tests for both canal and otolith functions in humans.     

Compound Action Potential and Cochlear Microphonic Extracted from Electrocochleographic Responses to Condensation or Rarefaction Clicks

In electrocochleography (ECochG) compound action potential (CAP) and summation potential (SP) are usually separated from the cochlear microphonic (CM) by the CM cancellation technique consisting in averaging the responses evoked by rarefaction and condensation clicks. With the aim of analysing the ECochG responses evoked by monophasic clicks, we developed a numerical method based on the theory of optimal filtering, which makes no assumptions about the unknown potentials. The application of the filtering technique to the ECochG recordings obtained from 6 normally hearing children and 10 children with cochlear hearing loss allowed us to perform CAP extraction in cases where CM was not cancelled by the conventional method. Differences in SP amplitude and polarity were found between rarefaction and condensation click-evoked responses in cochlear hearing losses.     

Asymmetry and Microstructure of Temporal-Suppression Patterns in Basilar-Membrane Responses to Clicks: Relation to Tonal Suppression and Traveling-Wave Dispersion

Journal of the Association for Research in Otolaryngology - The cochlea’s wave-based signal processing allows it to efficiently decompose a complex acoustic waveform into frequency...     

Glutamate is the Afferent Neurotransmitter in the Human Cochlea

Glutamate, the most important afferent neurotransmitter in the auditory system, is thought to be the afferent transmitter between the cochlear inner hair cells and afferent neurons, hitherto visualized only in the cochlea of animal species. It has been identified for the first time in sections from the human inner ear. L-glutamate, NMDAR2B and the enzyme glutamine synthetase were identified by using monoclonal antibodies. The distribution pattern of the transmitter L-glutamate in the human cochlea is similar to that observed in other mammals. L-glutamate was identified adjacent to outer and inner hair cells and in the spiral ganglion. Similar distributions were found for glutamine synthetase and the ionotropic NMDA receptor subunit NMDAR2. The identification of neurotransmitters and their receptors in the human cochlea has implications for the pharmacotherapy of inner ear diseases.     

Effects of Reflex Middle-Ear Muscle Contractions on Cochlear Responses to Bone-Conducted Sound

The effects of contralaterally elicited middle-ear muscle (MEM) reflexes on cochlear microphonic responses to air- and bone-conducted tones were examined in decerebrate cats. Stapedius effects on bone conduction were almost identical in configuration and amplitude to those on air conduction at all frequencies. However, tensor tympani effects were more complex, the configuration of the bone-conduction effects varying with the location of the transducer on the skull and with frequency. The relative contributions of the two muscles to the effects of joint contractions varied markedly between animals. It is suggested that non-reflex MEM contractions associated with activity of the facial musculature might provide protection against masking of environmental sounds by the low-frequency bone-conducted sound generated by such activity     

Disruption of Lateral Efferent Pathways: Functional Changes in Auditory Evoked Responses

The functional consequences of selectively lesioning the lateral olivocochlear efferent system in guinea pigs were studied. The lateral superior olive (LSO) contains the cell bodies of lateral olivocochlear neurons. Melittin, a cytotoxic chemical, was injected into the brain stem using stereotaxic coordinates and near-field evoked potentials to target the LSO. Brain stem histology revealed discrete damage to the LSO following the injections. Functional consequences of this damage were reflected in depressed amplitude of the compound action potential of the eighth nerve (CAP) following the lesion. Threshold sensitivity and N1 latencies were relatively unchanged. Onset adaptation of the cubic distortion product otoacoustic emission (DPOAE) was evident, suggesting a reasonably intact medial efferent system. The present results provide the first report of functional changes induced by isolated manipulation of the lateral efferent pathway. They also confirm the suggestion that changes in single-unit auditory nerve activity after cutting the olivocochlear bundle are probably a consequence of disrupting the more lateral of the two olivocochlear efferent pathways.     

Distribution of Brain Stem Responses to Acoustic Stimuli over the Human Scalp

Responses to acoustic stimuli are generated in neurons of nuclei on both sides of the brain stem. In order to determine whether there are electrode positions which can be used to record activity predominantly generated in the neurons of nuclei of one side, the distribution of brain stem responses to acoustic stimuli over the human scalp was investigated. The response is found to be maximum at the vertex, and diminishes gradually toward the nasion, inion and the mastoid process. There are no significant differences between responses to ipsi- and contralateral stimulation. It follows that there are no electrode positions, which can be used to record the activity generated in the neurons of nuclei of one side. There are, however, indications that monolateral pathology of brain stem nuclei may be detectable by comparing responses to stimuli presented on the right, the left and bilaterally.     

Preliminary Characterization of Voltage-Activated Whole-Cell Currents in Developing Human Vestibular Hair Cells and Calyx Afferent Terminals

We present preliminary functional data from human vestibular hair cells and primary afferent calyx terminals during fetal development. Whole-cell recordings were obtained from hair cells or calyx terminals in semi-intact cristae prepared from human fetuses aged between 11 and 18 weeks gestation (WG). During early fetal development (11–14 WG), hair cells expressed whole-cell conductances that were qualitatively similar but quantitatively smaller than those observed previously in mature rodent type II hair cells. As development progressed (15–18 WG), peak outward conductances increased in putative type II hair cells but did not reach amplitudes observed in adult human hair cells. Type I hair cells express a specific low-voltage activating conductance, G _K,L. A similar current was first observed at 15 WG but remained relatively small, even at 18 WG. The presence of a “collapsing” tail current indicates a maturing type I hair cell phenotype and suggests the presence of a surrounding calyx afferent terminal. We were also able to record from calyx afferent terminals in 15–18 WG cristae. In voltage clamp, these terminals exhibited fast inactivating inward as well as slower outward conductances, and in current clamp, discharged a single action potential during depolarizing steps. Together, these data suggest the major functional characteristics of type I and type II hair cells and calyx terminals are present by 18 WG. Our study also describes a new preparation for the functional investigation of key events that occur during maturation of human vestibular organs.     

骨导ABR测试信号经气放射对结果的影响

为了解骨导听性脑干反应(ABR)测试中骨导振荡器测试信号经气放射对结果的影响,本组用Dantec-Evolution诱发电位系统测试了正常听力年青人20名38耳和传导性聋13例21耳的骨导ABR.两组结果比较,在较高刺激强度正常组有较大的刺激伪迹,对Ⅰ波干扰较大.两组反应阈、Ⅰ、Ⅲ和Ⅴ波潜伏期、Ⅰ-Ⅲ和Ⅲ-Ⅴ波间期无显著差异,但Ⅰ-Ⅴ波间期的差异有统计学意义.这是由于正常组骨导振荡器经气放射的刺激伪迹对波Ⅰ的影响使Ⅰ-Ⅴ波间期缩短.本结果提示在用骨导ABR确定反应阈时可不考虑这个影响,但在用于蜗后病变定位诊断时要考虑经气放射的影响问题,     

Cochleovestibular findings linked to COVID-19: A scoping review for clinical care planning in South Africa

BackgroundOn 30 January 2020, the World Health Organization (WHO) officially declared an outbreak of the coronavirus disease 2019 (COVID-19) to be a global health emergency. Research has focused on the impact and response to life-threatening symptoms of COVID-19 across the lifespan; however, there is a need to investigate the effects of COVID-19 on the cochleovestibular system, as viral infections are known to impact this system. This is particularly important for contexts where resources are limited and prioritisation of resources requires strong risk versus benefit evaluations.ObjectiveTherefore, the purpose of this scoping review was to investigate published evidence on the impact of COVID-19 on the cochleovestibular system across the lifespan in order to allow for strategic clinical care planning in South Africa, where capacity versus demand challenges exist.MethodsElectronic bibliographic databases such as CINAHL, EBSCOHost, MEDLINE, ProQuest, PubMed, Scopus and ScienceDirect were searched for peer-reviewed publications between January 2020 and January 2022. These had to be published in English and related to the impact of COVID-19 on the cochleovestibular system, where the question was: ‘what evidence has been published on the impact of COVID-19 on the cochleovestibular system?’ Review selection and characterisation was performed by the researcher with an independent review by a colleague using pretested forms.ResultsOf a total of 24 studies that met the inclusion criteria, the current scoping review revealed limited conclusive published evidence linking COVID-19 to permanent hearing function symptoms. Current evidence supports the possibility of COVID-19, similar to other viral infections in adults, impacting the cochleovestibular system and causing tinnitus, vertigo and sudden sensorineural hearing loss (SSNHL), with the symptoms being generally temporary and resolving either partially or completely following therapy with steroids, with very inconclusive findings in the paediatric population.ConclusionThese findings raise global implications for properly designed studies, which include longitudinal follow-up of cases across the lifespan, examining this link with some focus on establishing the pathophysiologic mechanisms at play as well. In the meanwhile, current findings raise the value of polymerase chain reaction (PCR) testing for all patients presenting with unexplained cochleovestibular symptoms during the pandemic, as these may be the only presenting symptoms indicating COVID-19, thus requiring careful treatment and management.     

Immune Responses against Streptococcus pyogenes in Human Palatine Tonsils

We investigated cellular immunity against Streptococcus pyogenes in human tonsils by measuring antigen-specific immunoglobulin-secreting cells and the production of cytokines from CD4⁺ T cells in response to M proteins. The incidence of S pyogenes in tonsils was significantly higher in patients with recurrent tonsillitis (RT) than in patients with tonsillar hypertrophy (TH). M protein-specific immunoglobulin A (IgA) and immunoglobulin G spot-forming cells were increased in patients with RT compared with patients with TH. In RT the number of M protein-specific IgA spot-forming cells was significantly greater in the S pyogenes-negative subjects than in the S pyogenes-positive subjects. Proliferation of CD4⁺ T cells and production of interferon-gamma (IFN-γ) and interleukins^?2,^? 4, ^?5, and ^?6 (IL-2, IL-4, IL-5, and IL-6) from those T cells were observed in response to M protein. The concentrations of IFN-γ and IL-4 were higher in RT than in TH. These findings suggest thatS pyogenes is associated with the pathogenesis of RT and that immune responses against M protein may play an important role in preventing the colonization of this bacteria in tonsils.     

Phase Reversal in Brain Stem Responses: Its Use in the Detection of Asymmetry in the Auditory Pathways

Electrode placement is an important consideration in the recording of a large-amplitude stable response. In this study, brain stem auditory-evoked potentials (BAEP) were obtained from subjects and patients under two electrode configurations, namely ‘vertex-mastoid’ and ‘mastoid-mastoid’. The BAEP waveforms to ipsilateral, contralateral and binaural stimulation were examined for their phase relation with respect to stimulation. In the mastoid-mastoid recording mode, a complete polarity reversal was shown upon changing stimulation from the ipsilateral (with respect to the active input) to the contralateral ear. On simultaneous binaural stimulation, the response was shown to summate to zero. This observation has led to the objective assessment of asymmetry of hearing. Several patients exhibiting recruitment were tested under the mastoid-mastoid recording configuration with binaural stimulation. The results show that a summated ‘null’ response only occurs at an intensity level where loudness equality is attained at the two ears and recruitment is complete. Applied in this way the technique has promising application in the determination of the presence or absence of recruitment and hence in the differential diagnosis of cochlear and retrocochlear lesions.

La position de l'électrode est d'une grande importance pour l'enregistrement d'une réponse stable et de grande amplitude. Dans cette étude, les potentiels évoqués du tronc cérébral ont été obtenus chez des sujets normaux et des malades dans deux conditions: électrodes vertex-mastoïde et électrodes mastoïde-mastoïde. Notre attention s'est portée sur les rapports entre les phases des réponses et la stimulation: homolatérale, contralatérale, binaurale. Lorsque l'enregistrement est fait entre les deux mastoïdes nous observons: 1) un changement de polarité de 180° en appliquant séparément le stimulus à l'une ou l'autre oreille; 2) une annulation des réponses si le stimulus est présenté de façon binaurale.

Nous disposons de la sorte d'un moyen objectif pour évaluer la symétrie de l'audition. Plusieurs malades présentant un recrutement ont été examinés; les résultats indiquent que Ton ne trouve l'annulation binaurale qu'aux niveaux sonores où le recrutement est complet. Ces observations nous conduisent à proposer notre épreuve comme un test objectif de recrutement complet et par conséquent un test pour le diagnostic des lésions cochléaires et rétrocochléaires.     

Amplitude Change with Click Rate in Human Brainstem Auditory-Evoked Responses

The effect of click rate on wave amplitude of human brainstem auditory-evoked response (BAER) was examined at repetition rates of 10, 30, 50, 70 and 90 Hz in 80 healthy children aged 1 month to 6 years and in 21 adults. As repetition rate was increased from 10 to 90 Hz at 70 dB HL, the amplitudes in different age groups decreased by 33-45% (0.109-179 μV) for wave I and 25-41% (0.055-0.145 μV) for wave V. The older the children, the larger the absolute decrements of wave amplitudes with increasing repetition rate, but the relative decrements or reduction rates of wave amplitudes exhibited no systematically age-related differences. The V/I amplitude ratio tended to increase with increasing repetition rate in most age groups, suggesting that the amplitude of wave I is affected by the repetition rate slightly more than that of wave V. The patterns of the changes in wave amplitudes with repetition rate at lower intensity levels were essentially similar.     

Cochleovestibular manifestations in Fabry disease: Importance of screening and systematic ENT evaluation

ObjectivesFabry disease (FD) is an X-linked inherited lysosomal storage disease. It is a multisystem pathology that can include ENT disorders. The aim of the present study was to investigate the cochleovestibular manifestations of FD, in order to show the importance of screening and systematic ENT evaluation.Material and methodsA single-center retrospective study included 14 male and 23 female FD patients. Hearing impairment was defined as hearing loss greater than the 90^th percentile for at least one frequency. Vestibular impairment was defined by lateral semicircular canal dysfunction. Age, ongoing enzyme replacement therapy (ERT) and organic (renal, cardiac and cerebrovascular) complications were used as severity markers.ResultsHearing impairment was found in 62.6% of cases, mostly at high frequencies, and was associated with age, ERT, and cardiac and cerebrovascular disorder. It affected 46.7% of asymptomatic adult patients.Vestibular impairment was found in 56% of cases, associated with age; it affected two-thirds of ERT patients, more than 60% of patients with organic complications, and 50% of asymptomatic adult patients.ConclusionsMore than half of patients had ENT involvement. All FD patients should undergo early ENT screening for diagnostic, prognostic and therapeutic purposes. Systematic complete ENT follow-up with auditory and vestibular evaluation should be performed regularly, even for heterozygous women.     

Dynamic Asymmetry of the Vestibulo‐ocular Reflex in Unilateral Peripheral Vestibular and Cochleovestibular Loss

Objective: Rotatory tests in the horizontal plane have shown various degrees of vestibulo‐ocular reflex (VOR) asymmetry in patients after surgical deafferentation of one labyrinth. The purpose of this work was to characterize dynamic horizontal VOR responses among patients presenting with a unilateral peripheral labyrinthine deficit of nonsurgical origin and to compare results in isolated vestibular loss versus cochleovestibular loss. Study Design: This study included 40 patients who presented with an acute, spontaneous unilateral peripheral labyrinthine lesion. Twenty‐two patients had vestibular loss alone (without associated hearing impairment) and 18 presented with a cochleovestibular deficit (sudden hearing loss with vertigo). The majority of these patients were part of a long‐term protocol to evaluate vestibular compensation. Methods: All patients underwent both the clockwise test and the counterclockwise rotatory test in the horizontal plane, using brief impulses of moderate intensity. Results were analyzed by a simplified model of vestibular function, allowing a parametric estimation of the response. Results: A weak and transitory horizontal VOR asymmetry was observed in the 22 patients with vestibular loss. However, the 18 patients with cochleovestibular loss demonstrated a more severe and persistent asymmetry. Conclusions: This study revealed a difference in the dynamic characteristics of the horizontal VOR between patients with vestibular loss and those with cochleovestibular loss. Our results support the presence of an extensive labyrinthine lesion in cochleovestibular deficit that involves the otolith organs. The implications of this involvement on the central mech‐ anisms of otolith‐canal interaction are discussed.     

Middle-Latency Auditory Components in Response to Clicks and Low- and Middle-Frequency Tone Pips (0.5-1 kHz)

Middle-latency auditory components (MLC) in response to clicks and tone pips have been recordedin 20 normal subjects, aged between 26 and 32 years,in order to verify their reliability in response to frequency-specific stimuli (0.5 and IkHz). The results indicate a good reliability of MLC obtained when using tone pips. The responses show the conventionally labeled P, N, Nb, Pb waves. The latencies of these waves tend to be greater than those of the corresponding waves elicited by clicks and their amplitudes are smaller. This is probably due to an asynchrony of the responses. The Po and Pa waves are the most resistant to decreasing stimulus intensity, as both are clearly detectable down to 20 dB nHL, but Po is the best threshold index because at 20 dB it has a more clear-cut shape than P, According to the latency values obtained for MLC elicited by both clicks and tone pips, the Po wave is probably generated at the inferior colliculus level. The latency shift towards the click-elicited Jewett wave Vis mainly due to the different filter settings employed. The morphology of MLC elicited by tone pips is less affected by changes in stimulus frequency than that of corresponding auditory brainstem responses. Thus, MLC are a reliable indicator for defining low- and middle-frequency auditory thresholds.