Showing papers in "Journal of Vestibular Research-equilibrium & Orientation in 2012"

Vestibular migraine: diagnostic criteria

Abstract: This paper presents diagnostic criteria for vestibular migraine, jointly formulated by the Committee for Classification of Vestibular Disorders of the Barany Society and the Migraine Classification Subcommittee of the International Headache Society (IHS) The classification includes vestibular migraine and probable vestibular migraine Vestibular migraine will appear in an appendix of the third edition of the International Classification of Headache Disorders (ICHD) as a first step for new entities, in accordance with the usual IHS procedures Probable vestibular migraine may be included in a later version of the ICHD, when further evidence has been accumulated The diagnosis of vestibular migraine is based on recurrent vestibular symptoms, a history of migraine, a temporal association between vestibular symptoms and migraine symptoms and exclusion of other causes of vestibular symptoms Symptoms that qualify for a diagnosis of vestibular migraine include various types of vertigo as well as head motion-induced dizziness with nausea Symptoms must be of moderate or severe intensity Duration of acute episodes is limited to a window of between 5 minutes and 72 hours

The effect of vestibular rehabilitation on adults with bilateral vestibular hypofunction: a systematic review

Abstract: Purpose :A dults with bilateral vestibular hypofunction (BVH) experience signi ficant disability. A systematic review assessed evidence for vestibular rehabilitation (VR). Number of studies :1 4 studies. Materials/methods :S earch identi fication of studies based on inclusion criteria: (a) population: adults with BVH of peripheral origin; (b) interventions: vestibular exercises, balance training, education, or sensory prosthetics; (c) comparison: single interventions or compared to another psychophysical intervention, placebo, or healthy population; (d) outcomes: based on International Classification of Functioning, Disability and Health (ICF) Body Functions and Structure, Activity, and Participation; (e) study designs: prospective and interventional, Levels of Evidence I to III per Centre of Evidence-based Medicine grading. Coding and appraisal based on ICF framework and strength of evidence synthesis. Results :F ive Level II studies and nine Level III studies: All had outcomes on gaze and postural stability,five with outcomes on gait speed and perceptions of oscillopsia and disequilibrium. Conclusions :( a) Moderate evidence strength on improved gaze and postural stability (ICF-Body Functions) following exercise- based VR; (b) Inadequate number of studies supporting benefi to f VR on ICF-Participation outcomes; (c) Sensory prosthetics in early phase of development. Clinical relevance :M oderate evidence strength in support of VR from an impairment level; clinical practice and research needed to explore interventions extending to ICF-Activity and Participation.

The effect of virtual reality on visual vertigo symptoms in patients with peripheral vestibular dysfunction: a pilot study

Abstract: Individuals with vestibular dysfunction may experience visual vertigo (VV), in which symptoms are provoked or exacerbated by excessive or disorientating visual stimuli (e.g. supermarkets). VV can significantly improve when customized vestibular rehabilitation exercises are combined with exposure to optokinetic stimuli. Virtual reality (VR), which immerses patients in realistic, visually challenging environments, has also been suggested as an adjunct to VR to improve VV symptoms. This pilot study compared the responses of sixteen patients with unilateral peripheral vestibular disorder randomly allocated to a VR regime incorporating exposure to a static (Group S) or dynamic (Group D) VR environment. Participants practiced vestibular exercises, twice weekly for four weeks, inside a static (Group S) or dynamic (Group D) virtual crowded square environment, presented in an immersive projection theatre (IPT), and received a vestibular exercise program to practice on days not attending clinic. A third Group D1 completed both the static and dynamic VR training. Treatment response was assessed with the Dynamic Gait Index and questionnaires concerning symptom triggers and psychological state. At final assessment, significant between- group differences were noted between Groups D (p = 0.001) and D1 (p = 0.03) compared to Group S for VV symptoms with the former two showing a significant 59.2% and 25.8% improvement respectively compared to 1.6% for the latter. Depression scores improved only for Group S (p = 0.01) while a trend towards significance was noted for Group D regarding anxiety scores (p = 0.07). Conclusion: Exposure to dynamic VR environments should be considered as a useful adjunct to vestibular rehabilitation programs for patients with peripheral vestibular disorders and VV symptoms.

Vestibular-somatosensory convergence in head movement control during locomotion after long-duration space flight.

Abstract: Space flight causes astronauts to be exposed to adaptation in both the vestibular and body load-sensing somatosensory systems. The goal of these studies was to examine the contributions of vestibular and body load-sensing somatosensory influences on vestibular mediated head movement control during locomotion after long-duration space flight. Subjects walked on a motor driven treadmill while performing a gaze stabilization task. Data were collected from three independent subject groups that included bilateral labyrinthine deficient (LD) patients, normal subjects before and after 30 minutes of 40% bodyweight unloaded treadmill walking, and astronauts before and after long-duration space flight. Motion data from the head and trunk segments were used to calculate the amplitude of angular head pitch and trunk vertical translation movement while subjects performed a gaze stabilization task, to estimate the contributions of vestibular reflexive mechanisms in head pitch movements. Exposure to unloaded locomotion caused a significant increase in head pitch movements in normal subjects, whereas the head pitch movements of LD patients were significantly decreased. This is the first evidence of adaptation of vestibular mediated head movement responses to unloaded treadmill walking. Astronaut subjects showed a heterogeneous response of both increases and decreases in the amplitude of head pitch movement. We infer that body load-sensing somatosensory input centrally modulates vestibular input and can adaptively modify vestibularly mediated head-movement control during locomotion. Thus, space flight may cause central adaptation of the converging vestibular and body load-sensing somatosensory systems leading to alterations in head movement control.

Are evolutionary hypotheses for motion sickness "just-so" stories?

Abstract: Vertebrates have evolved rapidly conditionable nausea and vomiting reflexes mediated by gut and brainstem receptors, clearly as a defense against neurotoxin ingestion. In 1977 Treisman proposed that sensory orientation linkages to emetic centers evolved for the same reason, and that motion sickness was an accidental byproduct. It was an "adaptationist" explanation for motion sickness, since it assumed that evolution has shaped all phenotypic traits for survival advantage. Treisman's "poison" theory is plausible, and frequently cited as the accepted scientific explanation for motion sickness. However, alternative explanations have been proposed. The creation of hypotheses is an essential part of science - provided they are testable. This paper reviews the evidence for the Poison theory and several other adaptationist explanations. These hypotheses are certainly not "just-so stories", but supporting evidence is equivocal, and contradictory evidence exists Parsimony suggests an alternative "pluralistic" view: The vertebrate reticular formation maintains oxygenated blood flow to the brain, discriminates unexpected sensory stimuli- including postural disturbances, and detects and expels ingested neurotoxins. The three systems share neuroarchitectural elements but normally function independently. Brainstem sensory conflict neurons normally discriminate brief postural disturbances, but can be abnormally stimulated during prolonged passive transport (e.g. by boat, beginning about 150-200 generations ago). Sensory conflict signals cross couple into the neurotoxin expulsion and avoidance system, producing an arguably maladaptive emetic phenotype.

International Classification of Functioning, Disability and Health (ICF) Core Set for patients with vertigo, dizziness and balance disorders

Abstract: Vertigo, dizziness and balance disorders have major impact on independence, employability, activities and participation. There are many measures for the assessment of the impact of vertigo, but no consensus exists on which aspects should be measured. The objective of this study was to develop international standards (ICF Core Sets) for patients with vertigo and dizziness to describe functioning. The development of the ICF Core Sets involved a formal decision-making and consensus process, integrating evidence from preparatory studies including qualitative interviews with patients, a systematic review of the literature, a survey with health professionals, and empirical data collection from patients. Twenty-seven experts selected 100 second level categories for the comprehensive Core Set and 29 second level categories for the Brief Core Set. The largest number of categories was selected from the ICF component Activities and Participation (40). Twenty-five categories were selected from the component Body Functions, six from Body Structures, and 29 from Environmental Factors. The ICF Core Set for vertigo is designed for physicians, nurses, therapists and other health professionals working in inpatient or ambulatory settings. ICF Core Sets create patient-relevant outcomes that can be used as evidence for the success of treatments.

Posturography and locomotor tests of dynamic balance after long-duration spaceflight

Abstract: The currently approved objective clinical measure of standing balance in astronauts after space flight is the Sensory Organization Test battery of computerized dynamic posturography. No tests of walking balance are currently approved for standard clinical testing of astronauts. This study determined the sensitivity and specificity of standing and walking balance tests for astronauts before and after long-duration space flight. Astronauts were tested on an obstacle avoidance test known as the Functional Mobility Test (FMT) and on the Sensory Organization Test using sway-referenced support surface motion with eyes closed (SOT 5) before and six months after (n=15) space flight on the International Space Station. They were tested two to seven days after landing. Scores on SOT tests decreased and scores on FMT increased significantly from pre- to post-flight. In other words, post-flight scores were worse than pre-flight scores. SOT and FMT scores were not significantly related. ROC analyses indicated supra-clinical cut-points for SOT 5 and for FMT. The standard clinical cut-point for SOT 5 had low sensitivity to post-flight astronauts. Higher cut-points increased sensitivity to post-flight astronauts but decreased specificity to pre-flight astronauts. Using an FMT cut-point that was moderately highly sensitive and highly specific plus SOT 5 at the standard clinical cut-point was no more sensitive than SOT 5, alone. FMT plus SOT 5 at higher cut-points was more specific and more sensitive. The total correctly classified was highest for FMT, alone, and for FMT plus SOT 5 at the highest cut-point. These findings indicate that standard clinical comparisons are not useful for identifying problems. Testing both standing and walking balance will be more likely to identify balance deficits.

Dynamic visual acuity testing for screening patients with vestibular impairments

Abstract: Dynamic visual acuity (DVA) may be a useful indicator of the function of the vestibulo-ocular reflex (VOR) but most DVA tests involve active head motion in the yaw plane. During gait the passive, vertical VOR may be more relevant and passive testing would be less likely to elicit compensatory strategies. The goal of this study was to determine if testing dynamic visual acuity during passive vertical motion of the subject would differentiate normal subjects from patients with known vestibular disorders. Subjects, normals and patients who had been diagnosed with either unilateral vestibular weaknesses or were post-acoustic neuroma resections, sat in a chair that could oscillate vertically with the head either free or constrained with a cervical orthosis. They viewed a computer screen 2 m away that showed Landholt C optotypes in one of 8 spatial configurations and which ranged in size from 0.4 to 1.0 logMAR. They were tested while the chair was stationary and while it was moving. Scores were worse for both groups during the dynamic condition compared to the static condition. In the dynamic condition patients' scores were significantly worse than normals' scores. Younger and older age groups differed slightly but significantly; the sample size was too small to examine age differences by decade. The data suggest that many well-compensated patients have dynamic visual acuity that is as good as age-matched normals. Results of ROC analyses were only moderate, indicating that the differences between patients and normals were not strong enough, under the conditions tested, for this test to be useful for screening people to determine if they have vestibular disorders. Modifications of the test paradigm may make it more useful for screening potential patients.

Tests of walking balance for screening vestibular disorders.

Abstract: Few reliable tests are available for screening people rapidly for vestibular disorders although such tests would be useful for a variety of testing situations. Balance testing is widely performed but of unknown value for screening. The goal of this study was to determine the value of tests of walking balance for screening people with vestibular impairments. We tested three groups of patients with known vestibular impairments: benign paroxysmal positional vertigo, unilateral vestibular weakness, and post-acoustic neuroma resection. We compared them to normal subjects. All subjects were independently ambulatory without gait aids. Subjects were tested on tandem walking (TW) with eyes open and eyes closed for 10 steps, walking with no additional head motions and with augmented head rotations in yaw for 7 m (WwHT), and an obstacle avoidance task, the Functional Mobility Test (FMT). Subjects wore a 3-D motion sensor centered at mid-torso to capture kinematic measures. Patients and normals differed significantly on some behavioral measures, such as the number of steps to perform TW, and on some but not all kinematic measures. ROC analyses, however, were at best only moderate, and failed to find strong differences and cut-points that would differentiate the groups. These findings suggest that although patients and normals differ in performance of these tests in some interesting ways the groups are not sufficiently different on these tests for easy use as screening tests to differentiate the populations.

Postural performance of vestibular loss patients under increased postural threat.

Abstract: The effects of increasing postural task difficulty on balance control was investigated in 9 compensated vestibular loss patients whose results were compared to 11 healthy adults. Subjects were tested in static (stable support) and dynamic (sinusoidal translation of the support) conditions, both at floor level and at height (62 cm above the floor), and with and without vision, to create an additional postural threat. Wavelet analysis of the center of foot pressure displacement and motion analysis of the body segments were used to evaluate the postural performance. Evaluation questionnaires were used to examine the compensation level of the patients (DHI test), their general anxiety level (SAST), fear of height (subjective scale), and workload (NASA TLX test). (Vestibular loss patients rely more on vision and spend more energy maintaining balance than controls, but they use the same postural strategy as normals in both static and dynamic conditions.) Questionnaire data all showed differences in behavior and perceptions between the controls and the patients. However, at height and without vision, a whole body strategy leading to rigid posture replaces the head stabilization strategy found for standing at floor level. The effects of height on postural control can be attributable to an increase in postural threat and attention changes resulting from modifications in perception.

Benign paroxysmal positional vertigo and head position during sleep.

Abstract: To determine whether any particular head positions during sleep are associated with BPPV, head position during sleep was monitored for 3 days in 50 BPPV patients after the disappearance of positional nystagmus and in 25 normal control subjects. A gravity sensor was attached to the center of the subject's forehead at home. The positional angle of the head was measured at 5-second intervals during sleep. In BPPV, the posterior semicircular canal was involved in 40 patients and the lateral semicircular canal in 10 patients. Recurrence was found in 22 of 50 BPPV patients. BPPV patients with recurrence were significantly more likely to sleep in the affected-ear-down 45-degree head position than were patients with no history of recurrence (P< 0.02). When the head is in the affected-ear-down 45-degree head position, the non-ampullated half of the posterior semicircular canal and the non-ampullated half of the lateral semicircular canal are nearly in the earth-vertical position, making it easier for detached otoconia to fall into the posterior or lateral semicircular canal and to agglomerate and attain a certain size in the lowest portion of each semicircular canal. Our findings showed that the affected-ear-down 45-degree head position during sleep could be an etiological factor of BPPV, more particularly in patients with recurrent BPPV.

Subjective visual vertical perception in patients with vestibular neuritis and sudden sensorineural hearing loss.

Abstract: OBJECTIVE To determine the subjective visual vertical (SVV) perception in patients with vestibular neuritis (VN) and sudden sensorineural hearing loss (SSHL) using the SVV test and other neuro-otological examinations, namely, the vestibular evoked myogenic potential (VEMP) and caloric tests, and to clarify which vestibular nerve function is associated with an SVV shift. PATIENTS AND METHODS We performed the SVV test in 36 VN patients and 80 SSHL patients. Thereafter, we investigated directional changes in the SVV in the VN and SSHL patients, and compared the results of the SVV test with those of the VEMP and caloric tests. RESULTS Abnormal SVV (> 2° was found at a rate of 69.4% in the VN patients and 26.3% in the SSHL patients. In all except 1 VN patient, the SVV tilted to the lesion side. The rate of abnormal SVV was significantly higher in patients with complete canal paresis (CP) than in patients with partial CP. There was no significant relationship between the rates of abnormal SVV and VEMP. In the SSHL patients, neither the SVV nor the VEMP affected the hearing outcome and patients with abnormal VEMP tended to show abnormal SVV. CONCLUSION VN patients showed a higher rate of abnormal SVV than SSHL patients. From the results, it is speculated that the superior vestibular nerve function mainly affects the SVV tilt, although the inferior vestibular nerve function may also have an effect.

Mapping the vestibular evoked myogenic potential (VEMP)

Abstract: Effects of different electrode placements and indifferent electrodes were investigated for the vestibular evoked myogenic potential (VEMP) recorded from the sternocleidomastoid muscle (SCM). In 5 normal volunteers, the motor point of the left SCM was identified and an electrode placed there. A grid of 7 additional electrodes was laid out, along and across the SCM, based upon the location of the motor point. One reference electrode was placed over the sternoclavicular joint and another over C7. There were clear morphological changes with differing recording sites and for the two reference electrodes, but the earliest and largest responses were recorded from the motor point. The C7 reference affected the level of rectified EMG and was associated with an initial negativity in some electrodes. The latencies of the p13 potentials increased with distance from the motor point but the n23 latencies did not. Thus the p13 potential behaved as a travelling wave whereas the n23 behaved as a standing wave. The C7 reference may be contaminated by other evoked myogenic activity. Ideally recordings should be made with an active electrode over the motor point.

Ethical, anatomical and physiological issues in developing vestibular implants for human use.

Abstract: Effort towards the development of a vestibular implant for human use are being made. This paper will summarize the first important steps conducted in Geneva towards this ambitious goal. Basically, we have faced three major issues. First, an ethical issue. While it was clear that such development would require the collaboration of human volunteers, it was also clear that stimulation of the vestibular system may produce periods of significant incomfort. We know today how to minimize (and potentially eliminate) this type of incomfort. The second issue was anatomical. The anatomical topology of the vestibular system is complex, and of potentially dangerous access (i.e. facial nerve damage). We choose not to place the electrodes inside the ampullae but close the vestibular nerve branches, to avoid any opening of the inner ear and limit the risk of hearing loss. Work on cadaver heads, confirmed by acute stimulations trials on patients undergoing ear surgery under local anesthesia, demonstrated that it is possible to stimulate selectively both the posterior and lateral ampullary nerves, and elicit the expected vertical and horizontal nystagmic responses. The third issue was physiological. One of the goal of a vestibular implant will be to produce smooth eye movements to stabilize gaze direction when the head is moving. Indeed, after restoring a baseline or "rest" activity in the vestibular pathways with steady-state electrical stimulation, we demonstrated that modulation of this stimulation is producing smooth eye movements. In conclusion, humans can adapt to electrical stimulation of the vestibular system without too much discomfort. Surgical access to the posterior and lateral ampullary nerves have been developed and, electrical stimulation of the vestibular system can be used to artificially elicit smooth eye movements of different speeds and directions, once the system is in adapted state. Therefore, the major prerequisites to develop a prototype vestibular implant for human use are fulfilled.

Relationships between observer and Kalman Filter models for human dynamic spatial orientation.

Abstract: How does the central nervous system (CNS) combine sensory information from semicircular canal, otolith, and visual systems into perceptions of rotation, translation and tilt? Over the past four decades, a variety of input-output ("black box") mathematical models have been proposed to predict human dynamic spatial orientation perception and eye movements. The models have proved useful in vestibular diagnosis, aircraft accident investigation, and flight simulator design. Experimental refinement continues. This paper briefly reviews the history of two widely known model families, the linear "Kalman Filter" and the nonlinear "Observer". Recent physiologic data supports the internal model assumptions common to both. We derive simple 1-D and 3-D examples of each model for vestibular inputs, and show why - despite apparently different structure and assumptions - the linearized model predictions are dynamically equivalent when the four free model parameters are adjusted to fit the same empirical data, and perceived head orientation remains near upright. We argue that the motion disturbance and sensor noise spectra employed in the Kalman Filter formulation may reflect normal movements in daily life and perceptual thresholds, and thus justify the interpretation that the CNS cue blending scheme may well minimize least squares angular velocity perceptual errors.

Temporal constancy of perceived direction of gravity assessed by visual line adjustments.

Abstract: Here we investigated how well internal estimates of direction of gravity are preserved over time and if the subjective visual vertical (SVV) and horizontal (SVH) can be used inter-changeably. Fourteen human subjects repetitively aligned a luminous line to SVV, SVH or subjective visual oblique (± 45°) over 5 min in otherwise complete darkness and also in dim light. Both accuracy (i.e., the degree of veracity as reflected by the median adjustment error) and precision (i.e., the degree of reproducability as reflected by the trial-to-trial variability) of adjustments along the principle axes were significantly higher than along the oblique axes. Orthogonality was only preserved in a minority of subjects. Adjustments were significantly different between SVV vs. SVH (7/14 subjects) and between ±45° vs. -45° (12/14) in darkness and in 6/14 and 14/14 subjects, respectively, in dim light. In darkness, significant drifts over 5min were observed in a majority of trials (33/56). Both accuracy and precision were higher if more time was taken to make the adjustment. These results introduce important caveats when interpreting studies related to graviception. The test re-test reliability of SVV and SVH can be influenced by drift of the internal estimate of gravity. Based on spectral density analysis we found a noise pattern consistent with 1/fβ noise, indicating that at least part of the trial-to-trial dynamics observed in our experiments is due to the dependence of the serial adjustments over time. Furthermore, using results from the SVV and SVH inter-changeably may be misleading as many subjects do not show orthogonality. The poor fidelity of perceived ± 45° indicates that the brain has limited ability to estimate oblique angles.

Visual-vestibular stimulation influences spatial and non-spatial cognitive processing

Abstract: This study investigated the impact of visual-vestibular stimulation on performance of an auditory information processing task in young and older adults. Performance on a spatial choice reaction time task was compared to performance on a nonspatial choice reaction time task. The tasks were performed during simultaneous rotational and moving visual stimulation. The non-spatial task was an auditory frequency discrimination task while the spatial task was a right-left lateralization task. Visual and vestibular conditions consisted of a non-movement baseline, sinusoidal earth-vertical axis rotation (EVAR) in darkness, off-vertical axis rotation (OVAR) in darkness at a constant velocity, OVAR in darkness with a sinusoidal profile, EVAR with a lighted visual surround, constant velocity optokinetic stimulation, and sinusoidal optokinetic stimulation. Baseline reaction times were subtracted from reaction times during each stimulus condition to yield “task cost”, which was analyzed statistically. Subjects were healthy young (n = 20; 24 ± 2.7 yrs; 10F) and older (n = 29; 73 ± 6.0 yrs; 18F) adults. Results indicated that task cost was affected by the visual-vestibular condition and a task × condition interaction. There was no main effect of task or age group and no significant interaction with age. Otolithic stimulation and visual stimulation were associated with greater task cost compared to semicircular canal stimulation. Combining semicircular canal with otolithic or visual stimulation had no additional effect beyond otolithic or visual stimulation alone. This pattern of task cost being larger for otolith or visual vs. semicircular canal stimulation was found for both the spatial and non-spatial tasks. The significant interaction between condition and task type revealed that the task cost for the spatial task was larger than the task cost for the non-spatial task during visual conditions but not during non-visual conditions although the visual and non-visual conditions were not entirely comparable. This study suggests that interference of vestibular stimulation with cognitive processing is especially prominent for otolithic and visual stimulation although the strength of the various visual-vestibular stimuli may not have been uniform. Also, spatial tasks are more affected than non-spatial tasks during visual stimulation and interference between vestibular stimulation and cognitive processing is not age dependent for these relatively easy tasks.

Responses evoked by a vestibular implant providing chronic stimulation

Abstract: Patients with bilateral vestibular loss experience dehabilitating visual, perceptual, and postural difficulties, and an implantable vestibular prosthesis that could improve these symptoms would be of great benefit to these patients. In previous work, we have shown that a one-dimensional, unilateral canal prosthesis can improve the vestibulooccular reflex (VOR) in canal-plugged squirrel monkeys. In addition to the VOR, the potential effects of a vestibular prosthesis on more complex, highly integrative behaviors, such as the perception of head orientation and posture have remained unclear. We tested a one-dimensional, unilateral prosthesis in a rhesus monkey with bilateral vestibular loss and found that chronic electrical stimulation partially restored the compensatory VOR and also that percepts of head orientation relative to gravity were improved. However, the one-dimensional prosthetic stimulation had no clear effect on postural stability during quiet stance, but sway evoked by head-turns was modestly reduced. These results suggest that not only can the implementation of a vestibular prosthesis provide partial restitution of VOR but may also improve perception and posture in the presence of bilateral vestibular hypofunction (BVH). In this review, we provide an overview of our previous and current work directed towards the eventual clinical implementation of an implantable vestibular prosthesis.

Experimental measurement of utricle dynamic response.

Abstract: The utricle of the red-eared turtle was subjected to forced sinusoidal oscillations across various frequencies (10-125 Hz) and amplitudes (5-9 μm) to determine dynamic characteristics of the utricle under natural inertial stimulation. The utricle was maintained in physiologic solution during the entire experiment. Utricular specimens were prepared so that the Otoconial Layer (OL) crystals were exposed yet undisturbed, and the neuroepithelium was secured to a glass slide with dental floss strands. A piezoelectric-actuated platform, fitted to the stage of the microscope, created controlled sinusoidal displacement along the utricle's medial-lateral direction. The OL surface displacement was measured through the microscope with high-speed video at 1500 fps. A sub-pixel image registration algorithm was used to achieve displacement resolution ⩽ 15 nm. The Membranous Shelf (MS), that overlies the macula, was recorded with high-speed video under identical amplitude and frequency inputs and was used as a reference point. Maximum displacement amplitudes of the OL and MS were used to determine the Amplitude Ratio (AR) of the OL relative to the MS. ARs at various frequencies were fit to a single degree of freedom model of the utricle to determine the utricle's natural frequency of 363 Hz (95% confidence intervals: 328, 397) with a damping ratio of 0.96 (0.8, 1.12).

Influence of head orientation and viewpoint oscillation on linear vection

Abstract: Sensory conflict theories predict that adding simulated viewpoint oscillation to self-motion displays should generate significant and sustained visual-vestibular conflict and reduce the likelihood of illusory self-motion (vection). However, research shows thatviewpoint oscillationenhances vection inupright observers. Thisstudy examined whether theoscillation advantage for vection depends on head orientation with respect to gravity. Displays that simulated forward/backward self-motion with/without horizontal and vertical viewpoint oscillation were presented to observers in upright (seated and standing) and lying (supine, prone, and left side down) body postures. Viewpoint oscillation was found to enhance vection for all of the body postures tested. Vection also tended to be stronger in upright postures than in lying postures. Changing the orientation of the head with respect to gravity was expected to alter the degree/saliency of the sensory conflict, which may explain the overall posture-based differences in vection strength. However, this does not explain why the oscillation advantage for vection persisted for all postures. Thus, the current postural and oscillation based vection findings appear to be better explained by ecology: Upright postures and oscillating flow (that are the norm during self-motion) improved vection, whereas lying postures and smooth optic flows (which are less common) impaired vection.

Subjective posture in tridimensional space

Abstract: The internal representation of the body is intimately related to postural orientation. This assists us to correctly identify our position relative to the earth-vertical. The postural orientation about the pitch-Y axis is by default forward tilted while there is no such default about the roll-X axis. We hypothetized that the internal representation of body position would be different between the Y and X axes. We designed a study to assess the accuracy of self-driven whole-body orienting to the horizontal and the vertical about the X (roll) and Y (pitch) axes, with healthy seated subjects in complete darkness. Consistent with our hypothesis, the results showed that when trying to reach the horizontal with the X-axis, subjects remained on the same tilted direction as the initial posture. On the return way to the vertical, the subjects did not cross this (vertical) line. Whereas when reaching the horizontal with the Y-axis, there was an undershoot on the supine direction, and an overshoot on the prone direction: this discrepancy could be due to somatosensory cues to subjects in seated posture. The relevant mechanisms related to the internal representation of the body and graviceptive systems underlying the construction of an head-foot line are discussed.

Evaluation of the postural stability of elderly persons using time domain signal analysis

Abstract: A force platform is widely used in the evaluation of postural stability in man. Although an abundance of parameters are typically retrieved from force platform data, no uniform analysis of the data has been carried out. In general, the signal analysis does not analyze the underlying postural event, i.e., whether the signal consists of several small corrections or large excursions. In the present work, we studied the postural stability of 4589 elderly persons from Iceland on a force platform under visual and non-visual conditions during stance on a solid surface. We analyzed the internal relationship between frequently used time domain variables. In addition, we conducted a factor analysis using a subset of selected variables. Factor analysis yielded three components that can be considered different strategies for maintaining posture. In one control strategy, long swaying amplitues were pronounced, allowing the person to react when postural confidence limits are reached. In a second strategy, a high oscillation rate about the stationary point was the dominant characteristic of maintaining postural control. The third strategy appears to involve a short critical time period during which an open loop control changes into a closed loop that very rapidly controls excessive postural oscillations. The findings suggest that conventional parameters such as swaying velocity and amplitude alone do not provide sufficient information regarding a person's ability to maintain an upright stance.

Effects of plateau time and ramp time on ocular vestibular evoked myogenic potentials.

Abstract: The responses of ocular vestibular evoked myogenic potential (oVEMP) vary significantly with the type and setting of the stimuli This work was to investigate the effects of different ramp time and plateau time on oVEMP latency and amplitude Twenty-two healthy volunteers aged from 20 years to 39 years were enrolled The oVEMPs were acquired with the eyes upwards-gaze 30 degree above the head, and the sound stimuli included 01-ms click, and 500-Hz short tone burst (STB) of rise-plateau-fall time of 05-2-05 ms, 05-4-05 ms, 2-2-2 ms, and 2-4-2 ms The response rate of click oVEMP (66%) was lower than STB oVEMP (100%) The click oVEMP amplitude was significantly smaller (p < 001, one-way ANOVA and post-hoc Scheffe procedure) The latency n1 increased by 14 ms as the rise/fall time shifted from 05 ms to 2 ms for STB stimuli However, the latency and amplitude did not show significant difference between the STB stimuli with different plateau times The lower amplitude and response rate for click oVEMP were associated with its lower mechanical energy of click, especially the energy from 500 to 1000 Hz

Hair cell specific NTPDase6 immunolocalisation in vestibular end organs: Potential role of purinergic signaling in vestibular sensory transduction

Abstract: A complex extracellular nucleotide signalling system acting on P2 receptors is involved in regulation of cochlear function in the mammalian inner ear. Ectonucleoside triphosphate diphosphohydrolases (E-NTPDases) are ectonucleotidases that regulate P2 receptor signalling pathways in mammalian tissues by hydrolysing extracellular nucleotides to the respective nucleosides. AllenzymesfromtheCD39/ENTPDfamily(NTPDase1-8)areexpressedintheadult ratcochlea, buttheirexpression and distribution in the vestibular end organ is unknown. This report demonstrates selective expression of NTPDase6 by rat vestibular hair cells. Hair cells transducing both angular acceleration (crista ampullaris) and static head position (maculae of the utricle and saccule) exhibited strong immunolabelling with a bias towards the sensory pole and in particular, the hair cell bundle. NTPDase6 is an intracellular enzyme that can be released in a soluble form from cell cultures and shows an enzymatic preference for nucleoside 5'-diphosphates, such as guanosine 5'-diphosphate (GDP) and uridine 5'-diphosphate (UDP). The main function of NTPDase6 may be the regulation of nucleotide levels in cellular organelles by regulating the conversion of nucleotides to nucleosides. NTPDase6 immunolocalisation in the vestibular end organ could be linked to the regulation of P2 receptor signalling and sensory transduction, including maintenance of vestibular hair bundles.

Pre-flight sensorimotor adaptation protocols for suborbital flight.

Abstract: Commercial suborbital flights, which include 3-5 minutes of 0 g between hyper-g launch and landing phases, will present suborbital passengers with a challenging sensorimotor experience. Based on the results of neurovestibular research in parabolic and orbital flight, and the anticipated wide range of fitness and experience levels of suborbital passengers, neurovestibular disturbances are likely to be problematic in this environment. Pre-flight adaptation protocols might alleviate some of these issues. Therefore, we describe a set of sensorimotor tests to evaluate passengers before suborbital flight, including assessment of the angular vestibulo-ocular reflex (VOR), ocular skew and disconjugate torsion, subjective visual vertical, and roll vection. Performance on these tests can be examined for correlations with in-flight experience, such as motion sickness, disorientation, and visual disturbances, based on questionnaires and cabin video recordings. Through an understanding of sensorimotor adaptation to parabolic and orbital flight, obtained from many previous studies, we can then suggest appropriate pre-flight adaptation procedures.

The effect of galvanic vestibular stimulation on distortion product otoacoustic emissions

Abstract: Galvanic stimulation has long been used as a nonmechanical means of activating the vestibular apparatus through direct action on the vestibular nerve endings. This stimulation has been reported to be safe, but no studies have examined the potential changes in the corresponding cochlear receptors. The aim of the present study was to evaluate the effect of galvanic vestibular stimulation (GVS) on distortion product otoacoustic emissions (DPOAEs). Fourteen subjects underwent DPOAEs during several conditions of GVS. The DPOAEs ranged from ∼ 1 kHz to ∼ 8 kHz at 65/55 dB for f1/f2 and with an f2/f1 ratio of 1.2. The subjects were evaluated at 10 stimulation conditions that ranged from -2.0 mA to +2.0 mA for each frequency. Statistical analysis showed no significant differences in DPOAE amplitudes for all conditions with and without GVS. Results also showed no significant differences between DPOAE amplitudes before and after GVS. Multivariate analysis found subject variability in DPOAE amplitude, which was not thought to be GVS related. Results indicated that GVS produced neither temporary nor permanent changes in DPOAEs.

Sensory conflict compared in microgravity, artificial gravity, motion sickness, and vestibular disorders.

Abstract: Perceptual disturbances and motionsickness areoftenattributedtosensory conflict. Weinvestigatedseveral conditions: head movements in microgravity, periodic motions in 1-g, and locomotion with vestibular disorders. In every case, linear vectors such as linear and gravitational acceleration are crucial factors, as previously found for head movements in artificial gravity, and thus the importance of measuring linear vectors emerges as a common theme. By modeling the sensory conflict between the vestibular and somatosensory systems, we computed a measure of linear conflict known as the "Stretch Factor." We hypothesized that the motions with the greatest Stretch Factor would be the most provocative motions. Results: For head movements in microgravity, the Stretch Factor can explain why fast movements are more provocative than slow movements, and why pitch movements are more provocative than yaw movements. For off-vertical-axis rotation (OVAR) in 1-g, the Stretch Factor predicts that the most provocative frequency is higher than that for vertical linear oscillation (VLO). For example, the same sensor dynamics can predict a most provocative frequency around 0.2 Hz for VLO but 0.3 Hz for OVAR, solving a mystery of this experimentally observed discrepancy. Finally, we determined that certain sensory conflict perceptions reported by vestibular patients could be explained via mathematical simulation.

The ataxic mouse as a model for studying downbeat nystagmus.

Abstract: Downbeat nystagmus (DBN) is a common eye movement complication of cerebellar disease. Use of mice to study pathophysiology of vestibulocerebellar disease is increasing, but it is unclear if mice can be used to study DBN; it has not been reported in this species. We determined whether DBN occurs in the ataxic mutant tottering, which carries a mutation in the Cacna1a gene for P/Q calcium channels. Spontaneous DBN occurred only rarely, and its magnitude did not exhibit the relationship to head tilt seen in human patients. DBN during yaw rotation was more common and shares some properties with the tilt-independent, gaze-independent component of human DBN, but differs in its dependence on vision. Hyperactivity of otolith circuits responding to pitch tilts is hypothesized to contribute to the gaze-independent component of human DBN. Mutants exhibited hyperactivity of the tilt maculo-ocular reflex (tiltMOR) in pitch. The hyperactivity may serve as a surrogate for DBN in mouse studies. TiltMOR hyperactivity correlates with hyperdeviation of the eyes and upward deviation of the head during ambulation; these may be alternative surrogates. Muscimol inactivation of the cerebellar flocculus suggests a floccular role in the tiltMOR hyperactivity and provides insight into the rarity of frank DBN in ataxic mice.

Measuring dynamics of the subjective vertical and tilt using a joystick.

Abstract: Humans are able to estimate the vertical direction of an Earth fixed reference frame, which estimate is known as the subjective vertical (SV). To identify the SV, a distinction must be made between accelerations due to self-motion and gravity. Previous studies on this topic measured the SV using a variety of methods possibly affecting the outcome differently. In this study subjects were sinusoidally moved around their naso-occipital axis and their SV was dynamically measured using a joystick. In half the experimental conditions, the joystick was moved with the motion and was kept vertical on other experimental conditions, thus moving against self-motion. Although physically indicating the same angle, the average perceived angle was larger when moving the joystick with the motion than against. The difference can be explained by assuming an idiotropic vector being at issue when measuring the subjective vertical, and not when measuring subjective tilt.