Sacculo-ocular reflex connectivity in cats

Convergent innervations of mesencephalic trigeminal and vestibular nuclei neurons onto oculomotor and pre-oculomotor neurons-Tract tracing and triple labeling in rats

In studies of vestibulo-ocular reflex (VOR), the horizontal VOR circuit is much clearer than vertical-torsional VOR. The circuit and mechanism of gravity-related vertical-torsional VOR is probably weak. "Somatosensory vestibular interaction" is a known extra source to facilitate VOR, and cervico-ocular reflex is a representative for torsional VOR compensation. Whereas, how the cervical afferents finally reach the oculomotor system is less documented. Actually, when the head tilts, which generates cervico-ocular reflex, not only the neck muscle is activated, but also the jaw muscle is stretched by gravity dragged mandible and/or tissue-muscle connection between the mandible and clavicle. We have previously identified a projection from the jaw muscle afferent mesencephalic trigeminal nucleus (Vme) neurons to oculomotor nuclei (III/IV) and their premotor neurons in interstitial nucleus of Cajal (INC)-a well-known pre-oculomotor center manipulating vertical-torsional eye movements. We hypothesized that these projections may interact with vestibulo-ocular signals during vertical-torsional VOR, because effects of gravity on jaw muscles and bones has been reported. Thus, we injected different anterograde tracers into the Vme and medial vestibular nucleus (MVN)-the subnuclear area particularly harboring excitatory vestibulo-ocular neurons, and immunostained III/IV motoneurons. Retrograde tracer was injected into the III in the same animals after dual anterograde tracers' injections. Under confocal microscope, we observed the Vme and MVN neuronal endings simultaneously terminated onto the same III/IV motoneurons and the same INC pre-oculomotor neurons. We consider that jaw muscle proprioceptive Vme neurons projecting to the III/IV and INC would sense spindle activity if the jaw muscle is stretched by gravity dragged mandible or connection between mandible and clavicle during head rolling. Therefore, the convergent innervation of the Vme and MVN neurons onto the oculomotor and pre-oculomotor nuclei would be a neuroanatomic substrate for interaction of masticatory proprioception with the vestibulo-ocular signals upon the oculomotor system during vertical-torsional VOR.

Skull Vibration Induced Nystagmus Test: Correlations with Semicircular Canal and Otolith Asymmetries

Background: To establish in patients with peripheral vestibular disorders relations between skull vibration-induced nystagmus (SVIN) different components (horizontal, vertical, torsional) and the results of different structurally related vestibular tests. Methods: SVIN test, canal vestibular test (CVT: caloric test + video head impulse test: VHIT), otolithic vestibular test (OVT: ocular vestibular evoked myogenic potential oVEMP + cervical vestibular evoked myogenic potential cVEMP) performed on the same day in 52 patients with peripheral vestibular diseases (age < 65 years), and 11 control patients were analyzed. Mixed effects logistic regression analysis was performed to assert whether the presence of nystagmus in SVIN (3D analysis) have an association with the presence of peripheral vestibular dysfunction measured by vestibular explorations (CVT or OVT). Results: We obtained different groups: Group-Co (control group), Group-VNT (dizzy patients with no vestibular tests alterations), Group-O (OVT alterations only), Group-C (CVT alterations only), Group-M (mixed alterations). SVIN-SPV horizontal component was significantly higher in Group-M than in the other groups (p = 0.005) and correlated with alterations of lateral-VHIT (p < 0.001), caloric test (p = 0.002) and oVEMP (p = 0.006). SVIN-SPV vertical component was correlated with the anterior-VHIT and oVEMP alterations (p = 0.007; p = 0.017, respectively). SVIN-SPV torsional component was correlated with the anterior-VHIT positivity (p = 0.017). SVIN was the only positive test for 10% of patients (83% of Group-VNT). Conclusion: SVIN-SPV analysis in dizzy patients shows significant correlation to both CVT and OVT. SVIN horizontal component is mainly relevant to both vestibular tests exploring lateral canal and utricle responses. SVIN-SPV is significantly higher in patients with combined canal and otolith lesions. In some patients with dizziness, SVIN may be the only positive test.

Selective Asymmetry of Ocular Vestibular-Evoked Myogenic Potential in Patients with Acute Utricular Macula Loss

OBJECTIVES

We retrospectively evaluated a chart review of 3,525 patients evaluated for any acute disturbance. A total of 1,504 patients with acute vestibular syndrome (AVS) received an instrumental vestibular assessment within 72 h from the onset of the symptoms evaluated using simultaneously a combination of ocular vestibular-evoked myogenic potential (oVEMPs), cervical vestibular-evoked myogenic potential (cVEMPs), video head-impulse test (vHIT), and subjective visual vertical (SVV) were included in this study.

MATERIALS AND METHODS

A total of 41 patients with AVS that showed a normal horizontal canal function tested with vHIT, a normal cVEMP function, unilaterally reduced or absent oVEMP n10, and an altered SVV were enrolled.

RESULTS

We found that although these patients referred acute vertigo and presented spontaneous nystagmus, they showed physiological values of vHIT and a normal saccular function, as shown by symmetrical cVEMPs.

CONCLUSION

Our findings support the hypothesis that a percentage of patients evaluated during an AVS using an instrumental vestibular assessment could present selective utricular macula dysfunction.

Association between vestibular dysfunction and findings of horizontal head-shaking and vibration-induced nystagmus

BACKGROUND

The association between vestibular function and findings of horizontal head-shaking nystagmus (HHSN) and vibration-induced nystagmus (VIN) tests is not well understood.

OBJECTIVE

To investigate the association between function in the five distinct vestibular end organs and findings of these nystagmus tests.

METHODS

We retrospectively reviewed the medical records of 50 patients with vestibular diseases who underwent HHSN testing, VIN testing, video head impulse testing (vHIT), cervical vestibular evoked myogenic potential testing to air-conducted sound (ACS cVEMP) and ocular VEMP testing to ACS (ACS oVEMP). We performed mixed-effects logistic regression analyses to see whether age, sex or the presence of nystagmus in HHSN or VIN have an association with the presence of peripheral vestibular dysfunction on the opposite side to the direction of nystagmus.

RESULTS

The presence of HHSN had a significant association with abnormal vHIT in the lateral semicircular canal (LSCC) on the opposite side to the direction of nystagmus. The presence of VIN had a significant association with abnormal vHIT in all the SCCs and abnormal ACS oVEMP on the opposite side to the direction of nystagmus.

CONCLUSIONS

HHSN had an association with LSCC dysfunction alone. VIN had an association with dysfunction in all the SCCs and the utricle.

Evidence-based diagnostic use of VEMPs : From neurophysiological principles to clinical application

BACKGROUND

Vestibular evoked myogenic potentials (VEMPs) are increasingly being used for testing otolith organ function.

OBJECTIVE

This article provides an overview of the anatomical, biomechanical and neurophysiological principles underlying the evidence-based clinical application of ocular and cervical VEMPs (oVEMPs and cVEMPs).

MATERIAL AND METHODS

Systematic literature search in PubMed until April 2019.

RESULTS

Sound and vibration at a frequency of 500 Hz represent selective vestibular stimuli for the otolith organs. The predominant specificity of oVEMPs for contralateral utricular function and of cVEMPs for ipsilateral saccular function is defined by the different central projections of utricular and saccular afferents. VEMPs are particularly useful in the diagnosis of superior canal dehiscence and otolith organ specific vestibular dysfunction and as an alternative diagnostic approach in situations when video oculography is not possible or useful.

CONCLUSION

The use of VEMPs is a simple, safe, reliable and selective test of dynamic function of otolith organs.

Investigating short latency subcortical vestibular projections in humans: what have we learned?

Vestibular evoked myogenic potentials (VEMPs) are now widely used for the noninvasive assessment of vestibular function and diagnosis in humans. This review focuses on the origin, properties, and mechanisms of cervical VEMPs and ocular VEMPs; how these reflexes relate to reports of vestibular projections to brain stem and cervical targets; and the physiological role of (otolithic) cervical and ocular reflexes. The evidence suggests that both VEMPs are likely to represent the effects of excitation of irregularly firing otolith afferents. While the air-conducted cervical VEMP appears to mainly arise from excitation of saccular receptors, the ocular VEMP evoked by bone-conducted stimulation, including impulsive bone-conducted stimuli, mainly arises from utricular afferents. The surface responses are generated by brief changes in motor unit firing. The effects that have been demonstrated are likely to represent otolith-dependent vestibulocollic and vestibulo-ocular reflexes, both linear and torsional. These observations add to previous reports of short latency otolith projections to the target muscles in the neck (sternocleidomastoid and splenius) and extraocular muscles (the inferior oblique). New insights have been provided by the investigation and application of these techniques.

[Evidence-based diagnostic use of VEMPs : From neurophysiological principles to clinical application. German version]

BACKGROUND

Vestibular evoked myogenic potentials (VEMPs) are increasingly being used for testing otolith organ function.

OBJECTIVE

This article provides an overview of the anatomical, biomechanical and neurophysiological principles of an evidence-based clinical application of ocular and cervical VEMPs (oVEMPs and cVEMPs).

MATERIAL AND METHODS

Systematic literature search in PubMed until April 2019.

RESULTS

Sound and vibration at a frequency of 500 Hz represent selective vestibular stimuli for the otolith organs. The predominant specificity of oVEMPs for contralateral utricular function and of cVEMPs for ipsilateral saccular function is defined by the different neuronal projections of the utricle and the saccule. VEMPs are particularly useful in the diagnosis of superior canal dehiscence and otolith organ-specific vestibular dysfunction and as an alternative diagnostic approach in situations when video oculography is not possible or useful.

CONCLUSION

The use of VEMPs is a simple, safe, reliable and selective test of dynamic function of otolith organs.

Vestibular evoked myogenic potentials in practice: Methods, pitfalls and clinical applications

•

Vestibular evoked myogenic potentials (VEMPs) are used to test the otolith organs in patients with vertigo and imbalance.

•

This review discusses the optimal procedures for recording VEMPs and the pitfalls commonly encountered by clinicians.

•

Better understanding of VEMP methodology should lead to improved quality of recordings.

Vestibular evoked myogenic potentials (VEMPs) are a useful and increasingly popular component of the neuro-otology test battery. These otolith-dependent reflexes are produced by stimulating the ears with air-conducted sound or skull vibration and recorded from surface electrodes placed over the neck (cervical VEMPs) and eye muscles (ocular VEMPs). VEMP abnormalities have been reported in various diseases of the ear and vestibular system, and VEMPs have a clear role in the diagnosis of superior semicircular canal dehiscence. However there is significant variability in the methods used to stimulate the otoliths and record the reflexes. This review discusses VEMP methodology and provides a detailed theoretical background for the techniques that are typically used. The review also outlines the common pitfalls in VEMP recording and the clinical applications of VEMPs.

Assessment of Subjective Visual Vertical (SVV) Using the "Bucket Test" and the Virtual SVV System

OBJECTIVE

The purpose of this study was to describe the variability and test-retest reliability of a commercially available subjective visual vertical (SVV) system known as Virtual SVV (Interacoustics). In addition, the study aimed to compare the reliability of the Virtual system with a previously established bucket test of SVV.

STUDY DESIGN

Fifteen participants with normal hearing, normal middle ear function, and normal utricular function were included in the study. Each participant underwent static SVV testing using both the Virtual system and the bucket test. Subjects completed 2 testing sessions to determine test-retest reliability. For each test, data were collected with the head at 0°, tilted 45° to the right, and tilted 45° to the left.

SETTING

This study was conducted in a balance function laboratory embedded in a large, tertiary care otology clinic.

RESULTS

The mean SVV values obtained with the Virtual system were within 1°-2° from 0 with the head positioned at 0°, which is in agreement with many other studies of SVV with the head at 0° (Akin & Murnane, 2009; Halmagyi & Curthoys, 1999; Zwergal, Rettinger, Frenzel, Dieterich, & Strupp, 2009). Using the intraclass correlation coefficient, test-retest reliability of the Virtual system was excellent in the 45° left position and fair to good in the 45° right and 0° position. Test-retest reliability of the bucket test was poor in all head positions.

CONCLUSIONS

The Virtual system is a more reliable measure of static SVV than the bucket test. Therefore, the Virtual system could be utilized as a screening device for utricular dysfunction in busy clinical settings.

The Contributions of Vestibular Evoked Myogenic Potentials and Acoustic Vestibular Stimulation to Our Understanding of the Vestibular System

Vestibular-evoked myogenic potentials (VEMPs) are short-latency muscle reflexes typically recorded from the neck or eye muscles with surface electrodes. They are used clinically to assess otolith function, but are also interesting as they can provide information about the vestibular system and its activation by sound and vibration. Since the introduction of VEMPs more than 25 years ago, VEMPs have inspired animal and human research on the effects of acoustic vestibular stimulation on the vestibular organs, their projections and the postural muscles involved in vestibular reflexes. Using a combination of recording techniques, including single motor unit recordings, VEMP studies have enhanced our understanding of the excitability changes underlying the sound-evoked vestibulo-collic and vestibulo-ocular reflexes. Studies in patients with diseases of the vestibular system, such as superior canal dehiscence and Meniere's disease, have shown how acoustic vestibular stimulation is affected by physical changes in the vestibule, and how sound-evoked reflexes can detect these changes and their resolution in clinical contexts. This review outlines the advances in our understanding of the vestibular system that have occurred following the renewed interest in sound and vibration as a result of the VEMP.

Animal Models of Vestibular Evoked Myogenic Potentials: The Past, Present, and Future

Vestibular-evoked myogenic potentials (VEMPs) provide a simple and cost-effective means to assess the patency of vestibular reflexes. VEMP testing constitutes a core screening method in a clinical battery that probes vestibular function. The confidence one has in interpreting the results arising from VEMP testing is linked to a fundamental understanding of the underlying functional anatomy and physiology. In this review, we will summarize the key role that studies across a range of animal models have fulfilled in contributing to this understanding, covering key findings regarding the mechanisms of excitation in the sensory periphery, the processing of sensory information in central networks, and the distribution of reflexive output to the motor periphery. Although VEMPs are often touted for their simplicity, work in animals models have emphasized how vestibular reflexes operate within a broader behavioral and functional context, and as such vestibular reflexes are influenced by multisensory integration, governed by task demands, and follow principles of muscle recruitment. We will conclude with considerations of future questions, and the ways in which studies in current and emerging animal models can contribute to further use and refinement of this test for both basic and clinical research purposes.

Effects of midline sagittal location on bone-conducted cervical and ocular vestibular evoked myogenic potentials

We have investigated the effectiveness of two bone-conducted (BC) stimuli in producing vestibular evoked myogenic potentials (VEMPs) following stimulation along midsagittal skull sites. Twenty subjects (mean age 24 yr, range: 18-34 yr; 6 men; 14 women) were studied using a smoothed impulse and a 500-Hz tone burst applied to Nz, Fpz, AFz, Fz, FCz, and Cz with both compressive and rarefactive onset phases. Cervical (cVEMPs) and ocular VEMPs (oVEMPs) were recorded as well as linear acceleration in three axes. cVEMPs evoked by 500 Hz showed no change in response polarity to either stimulus location or phase. cVEMPs evoked by the impulsive stimulus showed larger initial peak amplitudes at AFz and Fz using compressive stimuli and differences in initial peak latency between the two phases. In contrast, amplitude, latency, and response polarity for oVEMPs were markedly affected by stimulus location and phase, which were similar for both BC stimuli, with little correlation with induced acceleration of the head. Latencies were earliest at AFz and Fz where compressive onset stimuli evoked an initial negativity (average latency 8.6-11.0 ms). At other sites compressive onset stimuli usually evoked oVEMPs with an initial positivity. We conclude that both 500 Hz and impulsive stimuli are effective means of evoking cVEMPs and oVEMPs from mid sagittal skull sites. The effects depend upon both location and phase and differ for oVEMPs and cVEMPs. Initial negativities for oVEMPs following compressive stimuli were most consistently obtained using the AFz and Fz sites.NEW & NOTEWORTHY We investigated the effect of stimulus location and phase (compressive and rarefactive) in the midsagittal plane for the cVEMP and oVEMP evoked by bone-conducted (BC) 500 Hz and BC impulsive stimuli. For cVEMPs, location effects were limited but were observed for BC impulses. For oVEMPs, both stimuli affected amplitude, latency, and polarity, depending on stimulus location and phase. Compressive stimuli at Fz and AFz evoked early negative oVEMPs most reliably.

'Standard' versus 'nose reference' electrode placement for measuring oVEMPs with air-conducted sound: Test-retest reliability and preliminary patient results

OBJECTIVES

This study compared two electrode placements ('standard' versus 'nose reference' placement) for measuring oVEMPs, elicited by air-conducted 500Hz tone bursts. The test-retest reliability of both positions was evaluated and additionally both electrode placements were applied on a group of vestibular patients.

METHODS

Eighteen healthy volunteers (range of 20-25years) participated in the first part and were retested after one week for evaluation of the test-retest reliability. Eleven patients (range of 41-74years) with a variety of vestibular pathologies were tested once.

RESULTS

In the normal group, the nose reference electrode placement resulted in significantly larger peak-to-peak amplitudes (p<0.001), shorter n10 (p=0.001) and p15 (p<0.001) latencies and smaller 95% prediction intervals for the Inter-Ocular Ratio (IOR) ([-68, 68] for the standard position versus [-32, 32] for the nose reference position). Furthermore, an excellent amplitude and IOR test-retest reliability was observed with the nose reference configuration, as shown by the intraclass correlation coefficient (ICC), the coefficient of variation of the method error (CV_ME) and the minimal detectable differences (MDD). In the patient group, the same significant amplitude difference was found. Moreover, three patients presented with absent oVEMPs when recorded with the standard placement, whereas the nose reference placement could evoke a detectable oVEMP response.

CONCLUSIONS

This study demonstrated that a nose reference electrode position results in larger oVEMP amplitudes and achieves a better reliability for the most important clinical parameters (amplitude and IOR). Our patient data substantiate the possible clinical benefit of this position, but further systematic patient verification is required.

SIGNIFICANCE

The nose reference electrode position facilitates the detection of generally very small oVEMP responses and shows a high test-retest reliability, showing promising potential for future use in the vestibular clinic.

Frequency and phase effects on cervical vestibular evoked myogenic potentials (cVEMPs) to air-conducted sound

Few previous studies of tuning using air-conducted (AC) stimuli and the cervical vestibular evoked myogenic potential (cVEMP) have compensated for the effects of middle ear (ME) attenuation. Zhang et al. (Exp Brain Res 213:111-116, 2011a) who did allow for ME effects were able to show a secondary peak around 100 Hz for the ocular VEMP (oVEMP). Recently, it has become clear that the otolith afferents responsible for the cVEMP and oVEMP differ and thus the nature of tuning may be more related to the reflex studied determining which otolith receptors are activated rather than the properties of the stimulus. We wished to reinvestigate the tuning for the cVEMP using AC stimuli, to establish whether the low-frequency peak is specific for the oVEMP or a consequence of the stimulus modality itself. In response to recent evidence using a 500 Hz AC stimulus that there was no effect of stimulus phase, we also investigated whether phase (condensation or rarefaction) had an effect at any frequency. We measured corrected cVEMP amplitudes and latencies in response to stimuli between 50 and 1200 Hz in 10 normal volunteers using an AC stimulus adjusted for ME attenuation. We confirmed earlier reports of the similarity of the tuning for both the cVEMP and oVEMP reflexes but found no separate 100 Hz peak for the cVEMP. AC stimulus phase did not affect either amplitude or latency. Both the tuning pattern and the phase effects contrast with those previously reported for bone-conducted (BC) stimuli. Unlike BC stimulation, which shows tuning consistent with an action on the otolith membrane, AC stimuli are likely to act through a different mechanism, most likely directly at the hair cell level.

Vestibular-evoked myogenic potentials

The vestibular-evoked myogenic potential (VEMP) is a short-latency potential evoked through activation of vestibular receptors using sound or vibration. It is generated by modulated electromyographic signals either from the sternocleidomastoid muscle for the cervical VEMP (cVEMP) or the inferior oblique muscle for the ocular VEMP (oVEMP). These reflexes appear to originate from the otolith organs and thus complement existing methods of vestibular assessment, which are mainly based upon canal function. This review considers the basis, methodology, and current applications of the cVEMP and oVEMP in the assessment and diagnosis of vestibular disorders, both peripheral and central.

Ocular vestibular-evoked myogenic potentials using air-conducted sound: test parameters and normative data in healthy children; effect of body position on threshold

In the present prospective study, we both investigated positioning techniques for the enhancement of oVEMP procedures and the viability of oVEMP testing in a healthy children population. A total of 41 healthy children were enrolled in this study. 21 were boys and 20 were girls, with their ages ranging from 4 to 16 years. All children underwent audiometry and tympanometry prior to oVEMP test in upright and supine position. All subjects had normal hearing. The procedure was well tolerated by all children. Typical biphasic oVEMPs presented in 97.56 % in upright position and 90.25 % in the supine position. No statistically significant difference could be found concerning which position elicits the best or worst responses. However, a trend towards the supine position was noticed. It may be concluded that oVEMP test proved to be a well-tolerated examination of the vestibular system in children aged above 4 years old. Our results did not show a statistical difference on the oVEMP thresholds between the two body positions. However, further larger studies are needed to confirm these findings.

The Effect of Repetition Rate on Air-Conducted Ocular Vestibular Evoked Myogenic Potentials (oVEMPs)

PURPOSE

Ocular vestibular evoked myogenic potentials (oVEMPs) are used to describe utricular/superior vestibular nerve function; however, optimal recording parameters have not been fully established. This study investigated the effect of repetition rate on air-conducted oVEMPs.

METHOD

Ten healthy adults were evaluated using 500-Hz tone bursts (4-ms duration, Blackman gating, 122 dB pSPL). Four repetition rates were used (1.6, 4.8, 8.3, and 26.6 Hz) and resulting oVEMP response presence, amplitude, amplitude asymmetry, and n1/p1 latency were assessed.

RESULTS

Response presence was significantly reduced for 26.6 Hz using monaural stimulation and for 8.3 Hz and 26.6 Hz for binaural stimulation. For monaural stimulation using 1.6, 4.8, and 8.3 Hz, no significant differences were noted for amplitude or latency. Responses obtained using binaural stimulation demonstrated a significant effect of rate on amplitude, with 8.3 Hz producing significantly reduced amplitude. Binaural amplitudes were significantly larger than monaural contralateral responses but with reduced response presence. No significant differences were noted for latency or amplitude asymmetry.

CONCLUSION

Using repetition rates of approximately 5 Hz or less may produce more consistent oVEMP response presence with minimal effects on amplitude for monaural or binaural recordings.

Ageing Effect on Air-Conducted Ocular Vestibular Evoked Myogenic Potential

One of the recent diagnostic tests to assess the function of otolithic organs is through vestibular evoked myogenic potential (VEMP) testing. There are equivocal findings on effect of aging on ocular VEMP (oVEMP) parameters with reference to latencies. Hence this study was taken up to investigate the age related changes in oVEMP parameters. This present study considered 30 participants in each age group i.e., young adults, middle-aged adults and older adults. oVEMP were recorded using insert earphone at 100dBnHL at 500hZ short duration tone burst. The results showed in older adult significant difference in response rate, latencies and amplitude as compared to young and middle adult. Hence age should be taken into consideration when interpreting oVEMP results.

Binocular misalignments elicited by altered gravity provide evidence for nonlinear central compensation

Increased ocular positioning misalignments upon exposure to altered gravity levels (g-levels) have been strongly correlated with space motion sickness (SMS) severity, possibly due to underlying otolith asymmetries uncompensated in novel gravitational environments. We investigated vertical and torsional ocular positioning misalignments elicited by the 0 and 1.8 g g-levels of parabolic flight and used these data to develop a computational model to describe how such misalignments might arise. Ocular misalignments were inferred through two perceptual nulling tasks: Vertical Alignment Nulling (VAN) and Torsional Alignment Nulling (TAN). All test subjects exhibited significant differences in ocular misalignments in the novel g-levels, which we postulate to be the result of healthy individuals with 1 g-tuned central compensatory mechanisms unadapted to the parabolic flight environment. Furthermore, the magnitude and direction of ocular misalignments in hypo-g and hyper-g, in comparison to 1 g, were nonlinear and nonmonotonic. Previous linear models of central compensation do not predict this. Here we show that a single model of the form a + bg (ε), where a, b, and ε are the model parameters and g is the current g-level, accounts for both the vertical and torsional ocular misalignment data observed inflight. Furthering our understanding of oculomotor control is critical for the development of interventions that promote adaptation in spaceflight (e.g., countermeasures for novel g-level exposure) and terrestrial (e.g., rehabilitation protocols for vestibular pathology) environments.

Vestibular evoked myogenic potentials (VEMPs) evoked by air- and bone-conducted stimuli in vestibular neuritis

OBJECTIVE

To compare and characterise abnormalities for short latency vestibular evoked myogenic potentials (VEMPs) elicited by air- (AC) and two differing types of bone-conducted (BC) stimuli during vestibular neuritis (VN).

METHODS

AC (500Hz short tone bursts) and two BC stimuli (500Hz at the forehead and impulses at the mastoids) were used to evoke cervical and ocular potentials (cVEMPs and oVEMPs) in VN patients (n=22) and healthy subjects.

RESULTS

More abnormalities were observed for the oVEMP than the cVEMP when using either AC 500Hz or BC 500Hz. The AC stimulus showed slightly more abnormalities than the BC 500Hz stimulus. In contrast, BC impulses produced frequent abnormalities for both oVEMPs and cVEMPs. The findings were modelled, based upon presumed selective lesions of the superior nerve.

CONCLUSIONS

AC 500Hz stimulation was slightly better than BC 500Hz in demonstrating abnormalities in patients with VN. BC impulses behave as expected for a predominantly utricular stimulus. The relative contributions of saccular and utricular fibres differ for stimulus type and target reflex.

SIGNIFICANCE

AC 500Hz is as effective as BC 500Hz for investigating VN. BC impulses act most strongly on utricular afferents.

Clinical Characteristics of Patients With Abnormal Ocular/Cervical Vestibular Evoked Myogenic Potentials in the Presence of Normal Caloric Responses

Objective:

To investigate the clinical features and vestibular symptoms of patients with abnormal ocular vestibular evoked myogenic potentials (oVEMPs) and/or cervical VEMPs (cVEMPs) in the presence of normal caloric responses.

Study Design:

Retrospective chart review.

Setting:

Tertiary referral center.

Methods:

One thousand five hundred twenty-one consecutive patients with balance problems who underwent the caloric, cVEMP, and oVEMP tests were included, and patients who showed abnormal oVEMPs and/or cVEMPs in the presence of normal caloric responses were selected. Clinical characteristics, diagnoses, and vestibular symptoms of the patients were analyzed.

Results:

Of the 1521 patients, 227 (15%) were found to have abnormal oVEMPs and/or cVEMP responses with normal caloric responses. Benign paroxysmal positional vertigo (BBPV), Meniere’s disease, and vestibular migraine were the common diagnoses of these patients. Eighty-one patients (36%) could not be diagnosed with a recognizable disease. Multiple episodes of spinning vertigo with a duration of seconds to hours were their most common vestibular symptoms.

Conclusion:

BPPV, Meniere’s disease, and vestibular migraine are the most frequent diagnoses showing abnormal oVEMP and/or cVEMPs without canal paresis. Apart from these clinical entities, a portion of undiagnosed patients with multiple episodes of vertigo might have a disease that involves the otolith organs only.

Semicircular canal-dependent developmental tuning of translational vestibulo-ocular reflexes in Xenopus laevis

Gaze stabilization during head/body movements is achieved to a large extent by vestibular-evoked compensatory eye movements. These reflexes derive from semicircular canal and otolith organs and depend on the transformation of the respective sensory signals into extraocular motor commands. To elicit directionally and dynamically appropriate compensatory eye movements, extraocular motoneurons require spatiotemporally specific inputs from semicircular canals and regions of the utricular epithelium with matching directional sensitivity. The ontogenetic establishment and maturation of the directional tuning of otolith inputs in extraocular motoneurons was studied in Xenopus laevis tadpoles. In young larvae at stage 46-48, superior oblique (SO) extraocular motoneurons receive omnidirectional utricular signals during horizontal translational motion, indicating an absence of spatial tuning. In contrast, in older larvae beyond stage 49 these motoneurons were activated by directionally more restricted otolith inputs with an increasingly enhanced spatial tuning until stage 53. This developmental process limited the origin of otolith signals to a utricular epithelial sector with a hair cell sensitivity that is coaligned with the pulling direction of the SO eye muscle. The maturation of the otolith response vector was abolished by enzymatic prevention of semicircular canal formation in postembryonic tadpoles at stage 44, suggesting that functionally intact semicircular canals are causally responsible for the observed directional tuning of utricular responses. A likely mechanism by which semicircular canals might influence the tuning of the otolith responses includes stabilization of coactivated and centrally converging sensory signals from semicircular canal and spatially aligned epithelial utricular regions during natural head/body motion.

Differing response properties of cervical and ocular vestibular evoked myogenic potentials evoked by air-conducted stimulation

•

cVEMPs and oVEMPS were recorded simultaneously from 15 healthy volunteers and 1 patient with superior canal dehiscence (SCD) using air conducted (AC) sound over a 30 dB range.

•

The SCD patient had larger amplitude responses at all intensities except for the cVEMP at the loudest intensity.

•

Whilst the cVEMP p13/n23 response was well fitted by a power law relationship the oVEMP n10/p16 response showed a change in gradient for the louder intensities and this may relate to differences in the pathways responsible.

Objective

To determine the amplitude changes of vestibular evoked myogenic potentials (VEMPs) recorded simultaneously from the neck (cVEMPs) and eyes (oVEMPs) in response to 500 Hz, 2 ms air-conducted sound pips over a 30 dB range.

Methods

Fifteen healthy volunteers (mean age 29, range 18–57 years old) and one patient with unilateral superior canal dehiscence (SCD) were studied. The stimulus was reduced in increments to 105 dB pSPL for the normals (81 dB pSPL for the SCD patient). A statistical criterion was used to detect responses.

Results

Ipsilateral (i-p13/n23) and contralateral (c-n12/p24/n30) peaks for the cVEMP montage and contralateral (c-n10/p16/n21) and ipsilateral (i-n13) peaks for the oVEMP montage were present for the baseline intensity. For the lowest intensity, 6/15 subjects had responses for the i-p13 cVEMP potential and 4/15 had c-n10 oVEMP responses. The SCD patient showed larger responses for nearly all intensities. The cVEMP potentials were generally well fitted by a power law relationship, but the oVEMP c-n10, p16 and n21 potentials showed a significant increase in gradient for the higher intensities.

Conclusion

Most oVEMP and cVEMP responses follow a power law relationship but crossed oVEMP responses showed a change in gradient above a threshold.

Significance

The pattern of response to AC stimulation may be a property of the pathways underlying the potentials.

Electrical stimulation of semicircular canal afferents affects the perception of head orientation

Patients with vestibular dysfunction have visual, perceptual, and postural deficits. While there is considerable evidence that a semicircular canal prosthesis that senses angular head velocity and stimulates canal ampullary nerves can improve vision by augmenting the vestibulo-ocular reflex, no information is available regarding the potential utility of a canal prosthesis to improve perceptual deficits. In this study, we investigated the possibility that electrical stimulation of canal afferents could be used to modify percepts of head orientation. Two rhesus monkeys were trained to align a light bar parallel to gravity, and were tested in the presence and absence of electrical stimulation provided by an electrode implanted in the right posterior canal. While the monkeys aligned the light bar close to the true earth-vertical without stimulation, when the right posterior canal was stimulated their responses deviated toward their left ear, consistent with a misperception of head tilt toward the right. The deviation of the light bar from the earth-vertical exceeded the torsional deviation of the eyes, indicating that the perceptual changes were not simply visual in origin. Eye movements recorded during electrical stimulation in the dark were consistent with isolated activation of right posterior canal afferents, with no evidence of otolith stimulation. These results demonstrate that electrical stimulation of canal afferents affects the perception of head orientation, and therefore suggest that motion-modulated stimulation of canal afferents by a vestibular prosthesis could potentially improve vestibular percepts in patients lacking normal vestibular function.

New perspectives on vestibular evoked myogenic potentials

PURPOSE OF REVIEW

Although the vestibular evoked myogenic potential (VEMP) measured from the cervical muscles (cVEMP, cervical VEMP) is well described and has documented clinical utility, its analogue recorded from the extraocular muscles (oVEMP, ocular VEMP) has been described only recently and is currently emerging as an additional test of otolith function. This review will, therefore, summarize recent developments in VEMP research with a focus on the oVEMP.

RECENT FINDINGS

Recent studies suggest that the oVEMP is produced by otolith afferents in the superior vestibular nerve division, whereas the cVEMP evoked by sound is thought to be an inferior vestibular nerve reflex. Correspondingly, the oVEMP correlates better with caloric and subjective visual vertical tests than sound-cVEMPs. cVEMPs are more complicated than often thought, as shown by the presence of crossed responses and conflicting results of recent vibration studies. Altered inner ear mechanics produced by the vestibular diseases superior semicircular canal dehiscence and Ménière's disease lead to changes in the preferred frequency of the oVEMP and cVEMP.

SUMMARY

The oVEMP provides complementary diagnostic information to the cVEMP and is likely to be a useful addition to the diagnostic test battery in neuro-otology.

Influence of facial paresis on ocular vestibular-evoked myogenic potentials

CONCLUSION

The ocular vestibular-evoked myogenic potential (oVEMP) test with eyes up condition may help differentiate facial paresis with and without vestibular nerve deficit, while the oVEMP test with the eyes closed condition is not reliable for testing patients with facial paresis.

OBJECTIVE

This study investigated the influence of facial paresis on oVEMPs via the eyes up versus eyes closed conditions.

METHODS

Twenty patients with unilateral facial paresis underwent a battery of audiovestibular function tests. The oVEMP test was performed via bone-conducted vibration stimuli with the eyes up and eyes closed conditions used in a randomized order.

RESULTS

Under the eyes up condition, the rate of abnormal oVEMP tests in the lesion ear was 30%, significantly higher than the 0% in the opposite healthy ear, indicating that the lesion ear not the recorded eye is responsible for abnormal oVEMPs. However, abnormal oVEMP test results of lesion ears under the eyes closed condition did not significantly differ from those of opposite healthy ears. Analysis of caloric and oVEMP test results indicated that both tests obtained normal responses from 10 ears, and abnormal responses from 5 ears. The caloric and oVEMP test results were significantly correlated.

Characteristics and clinical applications of ocular vestibular evoked myogenic potentials

Recently, ocular vestibular evoked myogenic potentials (oVEMPs) have been described and added to the neuro-otologic test battery as a new measure for the vestibulo-ocular reflex. oVEMPs represent extraocular muscle activity in response to otolith stimulation e.g. by air-conducted sound or bone-conducted vibration. In response to vestibular stimulation, electromyographic activity of the extraocular muscles can be recorded by means of surface electrodes placed beneath the contralateral eye. oVEMPs are likely to reflect predominantly utricular function, while the widely established cervical vestibular evoked myogenic potentials (cVEMPs) assess saccular function. Thus, measuring oVEMPs and cVEMPs in addition to caloric and head impulse testing provides further evaluation of the vestibular system and enables quick and cost-effective assessment of otolith function. This review summarizes the neurophysiological properties of oVEMPs, gives recommendations for recording conditions and discusses oVEMP alterations in various disorders of the vestibular system. With increasing insight into oVEMP characteristics in vestibular disorders, e.g. Menière's disease and superior semicircular canal dehiscence syndrome, oVEMPs are becoming a promising new diagnostic tool for evaluating utricular function.

Single motor unit activity in human extraocular muscles during the vestibulo-ocular reflex

Motor unit activity in human eye muscles during the vestibulo-ocular reflex (VOR) is not well understood, since the associated head and eye movements normally preclude single unit recordings. Therefore we recorded single motor unit activity following bursts of skull vibration and sound, two vestibular otolith stimuli that elicit only small head and eye movements. Inferior oblique (IO) and inferior rectus (IR) muscle activity was measured in healthy humans with concentric needle electrodes. Vibration elicited highly synchronous, short-latency bursts of motor unit activity in the IO (latency: 10.5 ms) and IR (14.5 ms) muscles. The activation patterns of the two muscles were similar, but reciprocal, with delayed activation of the IR muscle. Sound produced short-latency excitation of the IO muscle (13.3 ms) in the eye contralateral to the stimulus. Simultaneous needle and surface recordings identified the IO as the muscle of origin of the vestibular evoked myogenic potential (oVEMP) thus validating the physiological basis of this recently developed clinical test of otolith function. Single extraocular motor unit recordings provide a window into neural activity in humans that can normally only be examined using animal models and help identify the pathways of the translational VOR from otoliths to individual eye muscles.

Correlation between caloric and ocular vestibular evoked myogenic potential test results

CONCLUSION

The ocular vestibular evoked myogenic potential (o-VEMP) test results correlate significantly with caloric test results for patients with acoustic neuroma (AN), but not for patients with Meniere's disease (MD), indicating that the o-VEMP test may replace the caloric test for evaluating the vestibular nerve from which the AN arises. Conversely, the caloric, o-VEMP, and cervical VEMP (c-VEMP) tests should be performed to map lesion sites in the vestibular labyrinth.

OBJECTIVE

This study performed caloric, o-VEMP, and c-VEMP tests on patients with central and peripheral vestibular disorders to investigate their relationships.

METHODS

In all, 66 patients comprising 16 with unilateral AN and 50 with unilateral definite MD were enrolled. All patients underwent caloric, o-VEMP, and c-VEMP tests.

RESULTS

In the AN group, the caloric test identified canal paresis and caloric areflexia in 10 ears, while the o-VEMP and c-VEMP tests identified abnormal (absent or delayed) responses in 12 and 11 ears, respectively. A significant correlation existed between caloric and o-VEMP test results, but not between caloric and c-VEMP test results, or between o-VEMP and c-VEMP test results. For the MD group, abnormal caloric, o-VEMP, and c-VEMP test results were obtained for 24%, 44%, and 38% of hydropic ears, respectively. No correlation existed between any two test results.

Differences between otolith- and semicircular canal-activated neural circuitry in the vestibular system

In the last two decades, we have focused on establishing a reliable technique for focal stimulation of vestibular receptors to evaluate neural connectivity. Here, we summarize the vestibular-related neuronal circuits for the vestibulo-ocular reflex, vestibulocollic reflex, and vestibulospinal reflex arcs. The focal stimulating technique also uncovered some hidden neural mechanisms. In the otolith system, we identified two hidden neural mechanisms that enhance otolith receptor sensitivity. The first is commissural inhibition, which boosts sensitivity by incorporating inputs from bilateral otolith receptors, the existence of which was in contradiction to the classical understanding of the otolith system but was observed in the utricular system. The second mechanism, cross-striolar inhibition, intensifies the sensitivity of inputs from both sides of receptive cells across the striola in a single otolith sensor. This was an entirely novel finding and is typically observed in the saccular system. We discuss the possible functional meaning of commissural and cross-striolar inhibition. Finally, our focal stimulating technique was applied to elucidate the different constructions of axonal projections from each vestibular receptor to the spinal cord. We also discuss the possible function of the unique neural connectivity observed in each vestibular receptor system.

Association of air-conducted sound oVEMP findings with cVEMP and caloric test findings in patients with unilateral peripheral vestibular disorders

CONCLUSION

This study showed that the ocular vestibular evoked myogenic potential (oVEMP) in response to air-conducted sound (ACS) reflects functions of different parts of the vestibular labyrinth from cervical VEMP (cVEMP).

OBJECTIVE

To determine whether the origin of the vestibular end organs of the oVEMP in response to ACS (500 Hz tone bursts) is the same as that of cVEMP.

METHODS

Twenty patients definitively diagnosed with unilateral Meniere's disease (MD), 6 patients with unilateral vestibular neuritis (VN), and 7 healthy subjects were enrolled. In these subjects, the oVEMP and cVEMP to air-conducted 500 Hz tone bursts (125 dBSPL) were measured. The patients also underwent caloric tests.

RESULTS

The MD patients did not show a significant association between their ACS oVEMP findings and ACS cVEMP findings but there was an association of ACS oVEMP findings with caloric test findings. When the MD patients were classified into four stages based on their hearing levels, the patients showed abnormal findings at earlier stages on ACS cVEMP than on other tests. While all six VN patients showed abnormal findings on ACS oVEMP and caloric tests, only two patients showed abnormal ACS cVEMPs. These findings support the hypothesis that the oVEMP in response to ACS predominantly reflects utricular functions while ACS cVEMP reflects saccular functions.

Bone conducted vibration activates the vestibulo-ocular reflex in the guinea pig

The aim of the study was: (a) to test whether short duration (6 ms) 500 Hz bone-conducted vibration (BCV) of the skull in alert head free guinea pigs would elicit eye movements; (b) to test whether these eye movements were vestibular in origin; and (c) to determine whether they corresponded to human eye movements to such stimuli. In this way we sought to establish the guinea pig as an acceptable model for testing the mechanism of the effect BCV on the vestibulo-ocular reflex. Consistent short-latency stimulus-locked responses to BCV were observed. The magnitude of eye displacement was directly related to stimulus intensity as recorded by accelerometers cemented onto the animal's skull. The strongest and most consistent response component was intorsion of both eyes. In lateral-eyed animals intorsion is produced by the combined contraction of the inferior rectus and superior oblique muscles. In humans the same pair of muscles acts to cause depression of the eye. To test whether the movements were vestibular we selectively ablated the vestibular endorgans: 3 of the 8 animals underwent a bilateral intratympanic injection of gentamicin, an ototoxic aminoglycoside antibiotic, to ablate their vestibular receptors. After ablation there was an overall reduction in the magnitude of eye displacement, as well as a reduction in the effectiveness of the BCV stimulus to elicit eye movements. The animals' hearing, as measured by the threshold for auditory brainstem responses, remained unchanged after gentamicin, confirming that the cochlea was not affected. The reduced magnitude of responses after vestibular receptor ablation demonstrates that the eye-movement responses to BCV are probably caused by the stimulation of vestibular receptors, which in turn activate the vestibulo-ocular reflex.

Direction-dependent excitatory and inhibitory ocular vestibular-evoked myogenic potentials (oVEMP) produced by oppositely directed accelerations along the midsagittal axis of the head [corrected]

Oppositely directed displacements of the head need oppositely directed vestibulo-ocular reflexes (VOR), i.e. compensatory responses. Ocular vestibular-evoked myogenic potentials (oVEMPs) mainly reflect the synchronous extraocular muscle activity involved in the process of generating the VOR. The oVEMPs recorded beneath the eyes when looking up represent electro-myographic responses mainly of the inferior oblique muscle. We aimed: (1) to study the properties of these responses as they were produced by head acceleration impulses to the forehead and to the back of the head; (2) to investigate the relationships between these responses and the 3-D linear head accelerations that might reflect the true stimulus that acts on the vestibular hair cells. We produced backward- and forward-directed acceleration stimuli in four conditions (positive and negative head acceleration impulses to the hairline and to the inion) in 16 normal subjects. The oVEMPs produced by backward- and forward-directed accelerations of the head showed consistent differences. They were opposite in the phase. The responses produced by backward accelerations of the head began with an initial negativity, n11; conversely, those produced by accelerations directed forward showed initially a positive response, p11. There was a high inter-subject correlation of head accelerations along the head anteroposterior and transverse axes, but almost no correlation of accelerations along the vertical axis of the head. We concluded that backward-directed head accelerations produced an initial excitatory response, and forward-directed accelerations of the head were accompanied by an initial inhibitory response. These responses showed dependence on acceleration direction in the horizontal plane of the head. This could be consistent with activation of the utricle.

The ocular vestibular-evoked myogenic potential to air-conducted sound; probable superior vestibular nerve origin

OBJECTIVE

Intense air-conducted sound (ACS) elicits an ocular vestibular-evoked myogenic potential (oVEMP), and it has been suggested that it does so by stimulating saccular receptors and afferents in the inferior vestibular nerve and so activating a crossed sacculo-ocular pathway. Bone conducted vibration (BCV) also elicits an oVEMP probably by activating utricular receptors and a crossed utriculo-ocular pathway. Are there two separate pathways mediating oVEMPs for ACS and BCV? If saccular receptors and afferents are primarily responsible for the oVEMP to ACS, then the oVEMP to ACS should be normal in patients with reduced or absent utricular function--unilateral superior vestibular neuritis (SVN). If utricular receptors and afferents are primarily responsible for oVEMP n10, then oVEMP to ACS should be reduced or absent in SVN patients, and in these patients there should be a close relationship between the size of the oVEMP n10 to BCV and to ACS.

METHODS

The n10 component of the oVEMP to 500 Hz BCV and to 500 Hz ACS was recorded in 10 patients with unilateral SVN but who had saccular and inferior vestibular nerve function preserved, as shown by their normal cVEMP responses to ACS.

RESULTS

In SVN patients with normal saccular and inferior vestibular nerve function, the oVEMP n10 in response to ACS was reduced or absent. Across SVN patients there was a very close correspondence between the size of oVEMP n10 for ACS and for BCV.

CONCLUSIONS

The n10 component of the oVEMP to ACS is probably mediated predominantly by the superior vestibular nerve and so most likely by utricular receptors and afferents.

SIGNIFICANCE

The n10 component of the oVEMP to either ACS or BCV probably indicates mainly superior vestibular nerve function.

Waiting for the evidence: VEMP testing and the ability to differentiate utricular versus saccular function

The advent of cervical vestibular evoked myogenic potentials (CVEMPs) marked a milestone in clinical vestibular testing because they provided a simple means of assessing human otolith function. The availability of air-conducted (AC) sound and bone-conducted vibration (BCV) to evoke CVEMPs and development of a new technique of recording ocular vestibular-evoked myogenic potentials (OVEMPs) have increased the complexity of this simple test, yet extended its diagnostic capabilities. Here we highlight the evidence-based assumptions that guide interpretation of AC sound- and BCV-evoked VEMPs and the gaps in VEMP research thus far.

Single trial detection of human vestibular evoked myogenic potentials is determined by signal-to-noise ratio

Vestibular reflexes in humans can be assessed by means of acoustically evoked responses of myogenic origin. For the vestibular-collic pathway this is termed the vestibular evoked myogenic potential (or VEMP) and for the vestibular-ocular pathway the ocular VEMP (or OVEMP). Usually VEMPs require an averaging process to obtain a clear response against the background myogenic activity, but depending on the combination of target reflex and stimulus mode, in some cases clear responses can be observed in single trials without averaging. We aimed to test whether this difference in detectability was simply related to signal-to-noise ratio (SNR), or a manifestation of some other difference in the reflex pathways. In four healthy subjects we recorded VEMPs and OVEMPs in response to 2-ms, 500-Hz sound pips and 10-ms, 100-Hz transmastoid vibrations at four intensity levels, and also determined thresholds. A plot of probability of detection P vs. SNR for all subjects and conditions fell onto a single sigmoid curve. When fitted by a logistic function after linearization a regression yielded an R(2) of 0.89 (n = 64, p < 0.001), with parameter estimates of mu = 2.9 and sigma = 2.0. Three patients with superior canal dehiscence, characterized by significantly lowered thresholds for sound-activated responses, exhibited a similar detection curve. We conclude that single trial detection of evoked myogenic potentials is a property mainly determined by SNR. Thus vestibular reflexes, differing in both their response magnitude and in their levels of myogenic activity by more than an order of magnitude, can be described by a single relationship when their magnitude is expressed relative to background activity, demonstrating the fundamental importance of the SNR.

Frequency-dependent spatiotemporal tuning properties of non-eye movement related vestibular neurons to three-dimensional translations in squirrel monkeys

Responses of vestibular-only translation sensitive (VOTS) neurons in vestibular nuclei of two squirrel monkeys were studied at multiple frequencies to three-dimensional translations and rotations. A novel frequency-dependent spatiotemporal analysis examined in each neuron whether complex models, with unrestricted response dynamics in three-dimensional (3D) space, provided significantly better fits than restricted models following simple, cosine rule. Subsequently, the statistically selected optimal model was used to predict the maximum translation direction, expressed as a unitary vector, Vt(max), and its associated sensitivity and phase across frequencies. Simple models were sufficient to quantify the 3D translational responses of 66% of neurons. Most VOTS neurons, complex or simple, exhibited flat-gain or low-pass response dynamics. The Vt(max) of simple neurons was fixed, whereas that of complex neurons changed with frequency. The spatial distribution of Vt(max) in simple neurons, which fell within 30 degrees of either the horizontal plane or/and the sagittal plane, was closely aligned with Vt(max) of vestibular afferents. In contrast, the frequency-dependent Vt(max) of most complex neurons migrated from the dorsoventral axis at higher frequency toward the horizontal plane, especially the interaural axis, at lower frequency. When the maximum rotation direction was estimated from responses of the same VOTS neurons to 1.2 Hz yaw, pitch, and roll rotations, complex neurons were more likely to respond to rotations activating vertical canals. Responses to 0.15-0.3 Hz linear accelerations produced by inertial or gravitational forces were indistinguishable in most complex neurons but significantly different in most simple neurons. These observations suggest that simple and complex VOTS neurons constitute distinctive vestibular pathways where complex neurons, exhibiting a novel spatiotemporal filtering mechanism in processing otolith-related signals, are well suited to drive tilt-related responses, whereas simple neurons probably mediate pure translation related responses.