bluuebunny/crossref_metadata_2025 huggingface dataset:
Comorbidities in vestibular migraine
Authors: Eggers Scott D.Z. , Neff Brian A. , Shepard Neil T. , Staab Jeffrey P.
Published: December 2019

A growing body of clinical and epidemiological evidence supports a specific relationship between vestibular symptoms and migraine. Without a biomarker or complete understanding of pathophysiology, diagnosis of vestibular migraine (VM) currently depends upon symptoms in two dimensions: episodic vestibular symptoms temporally related to migraine symptoms. The Bárány Society and the International Headache Society have recently developed consensus diagnostic criteria. However, many issues remain unsettled, including the type, duration, and timing of vestibular symptoms related to headache that should be required for diagnosing VM. This paper focuses on the challenging third dimension of comorbidity, a frequent cause of diagnostic uncertainty that may confound clinical application and research validation of VM criteria. Several other neurotologic conditions occur more frequently in migraineurs than controls, including benign paroxysmal positional vertigo, Ménière's disease, and motion sickness. Patients with VM also have high rates of chronic subjective dizziness, which may be associated with anxious, introverted temperaments that can affect clinical presentation and treatment response. Broadly inclusive studies of well-characterized patients with other neurotologic and psychiatric comorbidities are needed to fully understand how vestibular symptoms and migraine interact in order to truly validate vestibular migraine, distill its essential features, define its boundaries, and characterize overlapping comorbidities.
Impaired vestibulo-ocular reflex (VOR) in spinocerebellar ataxia type 3 (SCA3): Bedside and search coil evaluation
Authors: Gordon Carlos R. , Zivotofsky Ari Z. , Caspi Avi
Published: December 2019

Vestibulo-Ocular Reflex (VOR) abnormalities in cerebellar ataxias are a matter of renewed interest. We have previously reported vestibular areflexia in a group of Yemenite-Jews with Spinocerebellar Ataxia Type 3 (SCA3) who had clear bilateral pathological horizontal Head Impulse Test (HIT). The objective of this study was to evaluate the VOR of ten SCA3 patients who have variable bedside HIT responses by recording their eye movements using magnetic search coils and to correlate these results with their clinical and genetic data. Eight out of the ten patients have abnormal horizontal HIT detected by both clinical bedside examination and laboratory tests. Results of bedside HIT testing were significantly correlated with the VOR gain recorded using magnetic search coils. No significant correlations were found between VOR gain and other clinical or genetic data. Our study confirms the presence of defective VOR in SCA3 patients and corroborates the useful of the HIT as a reliable bedside test for diagnosis of VOR deficits.
Fear of heights freezes gaze to the horizon
Authors: Kugler Günter , Huppert Doreen , Schneider Erich , Brandt Thomas
Published: December 2019

Fear of heights is elicited by a glance into an abyss. However, the visual exploration behavior of fearful subjects at height has not been analyzed yet. We investigated eye- and head movements, i.e. visual exploration behavior, of subjects susceptible to fear of heights during exposure to a visual cliff. The movements of eyes and head were recorded in 19 subjects susceptible to fear of heights and 18 controls while standing still on an emergency balcony 20 meters above ground level for periods of 30 seconds. Participants wore mobile, infrared eye-tracking goggles with inertial sensors for recording head movements. Susceptibles exhibited fewer and smaller-amplitude eye-in-head saccades with fixations of longer duration. Spontaneous head movements were reduced by 49% in susceptibles with a significantly lower mean absolute angular velocity (5.3°/s vs. 10.4°/s), and all three dimensions (yaw, pitch and roll) were equally affected. Gaze-in-space – which indicates exploration by coordinated eye-head movements – covered a smaller total area of the visual scene (explored horizontal angle: 19° vs. 32°, vertical: 9° vs. 17°). We hypothesize that the susceptibles suppress eye and head movements to alleviate fear of heights. However, this behavior has the potential disadvantage of impairing the visual stabilization of postural balance.
Reading while moving: The functional assessment of VOR
Authors: Versino Maurizio , Colagiorgio Paolo , Sacco Simone , Colnaghi Silvia , Quaglieri Silvia , Manfrin Marco , Benazzo Marco , Moglia Arrigo , Ramat Stefano
Published: December 2019

The head impulse test (HIT) is nowadays recognized as the gold standard for clinical testing of the angular vestibulo-ocular reflex (VOR). By imposing unpredictable, abrupt head rotations in canal pairs' planes it aims at unveiling the dysfunction of the semicircular canal towards which the head is rotated based on Ewald's II law. Functional testing of the VOR aims at assessing the ability of the reflex to stabilize gaze in space and thus allow clear vision during head movements. The HIT device (HITD) approach exploits impulsive head rotations spawning a range of angular accelerations while requiring subjects to identify optotypes briefly displayed on a screen. Here we also recorded eye movements, so that the evaluation of the individual subject is based both on the VOR gain and on the percentage of correct answers with respect to a population of controls. Here we used the HITD to study 14 patients suffering from vestibular neuritis and 7 of those were re-tested after three months. We found that the HITD was able to unveil the ipsilesional deficit and the contralesional impairment, together with the improvement in the follow-up test.
CANVAS an update: Clinical presentation, investigation and management
Authors: Szmulewicz David J. , McLean Catriona A. , MacDougall Hamish G. , Roberts Leslie , Storey Elsdon , Halmagyi G. Michael
Published: December 2019

Background: Cerebellar Ataxia with Neuropathy and bilateral Vestibular Areflexia Syndrome (CANVAS) is a multi-system ataxia which results in cerebellar ataxia, a bilateral vestibulopathy and a somatosensory deficit. This sensory deficit has recently been shown to be a neuronopathy, with marked dorsal root ganglia neuronal loss. The characteristic oculomotor clinical sign is an abnormal visually enhanced vestibulo-ocular reflex. Objective: To outline the expanding understanding of the pathology in this condition, as well as diagnostic and management issues encountered in clinical practice. Methods: Retrospective data on 80 CANVAS patients is reviewed. Results: In addition to the triad of cerebellar impairment, bilateral vestibulopathy and a somatosensory deficit, CANVAS patients may also present with orthostatic hypotension, a chronic cough and neuropathic pain. Management of falls risk and dysphagia is a major clinical priority. Conclusions: CANVAS is an increasingly recognised cause of late-onset ataxia and disequilibrium, and is likely to be a recessive disorder.
Influences of monocular and binocular vision on postural stability
Authors: Wu Kuo-Tung , Lee Guo-She
Published: December 2019

To compare the influences of monocular vision versus binocular vision on postural control, twenty-seven otherwise healthy adults, aged from 19 to 38 years, with corrected visual acuity of better than or equal to 20/20, were recruited. Body sway for standing 30 seconds on a force platform in 3 conditions was recorded for each participant: one with both eyes open (BEO), one with left eye open (LEO) and the other with both eyes closed (BEC). Postural stability was subsequently evaluated by measuring the total track length (TL) and surface area (SA) of center of pressure of body sway. The results show that the values of TL and SA of BEC were significantly greater than those of LEO and BEO. Moreover, the values of TL and SA of BEO were significantly smaller than those of LEO (p < 0.05, one-way repeated measures ANOVA and post hoc of Fisher's LSD procedure). The Romberg coefficient of LEO was also significantly greater than that of BEO (p < 0.05, paired sample t-test). We concluded that optimal binocular vision provides more information for keeping balance than monocular vision according to the results revealed in our study. Assessment of visual acuity is recommended before doing a posturographic test in the clinical setting. However, the long-term impact of blindness on controlling posture is uncertain and needs further investigation.
Appraisal of the signal-to-noise-ratio of uni- and bipolar recordings of ocular vestibular evoked myogenic potentials
Authors: Ertl M. , Kirsch V. , Gerb J. , Boegle R. , Krafczyk S. , Dieterich M.
Published: December 2019

Ocular vestibular evoked myogenic potentials (oVEMPs) are a non-invasive method to investigate otolith function mediated via the superior vestibular nerve. However, the herein used recordings and protocols may alter within different studies. In particular the diverging use of electrode configuration regarding polarity or even electrode position varies across studies. Therefore, a systematic analysis and appraisal of the different electrode configuration seems mandatory. In this study we compared the quality of uni- and bipolar recordings based on the signal to noise ratio (SNR). We recoded oVEMPs using a uni- and bipolar electrode configuration simultaneously and compared the recorded amplitudes and latencies and calculated the SNR. The amplitudes recorded by the unipolar configurations were significantly (p < 0.01) increased compared to the bipolar configuration. However, the SNR of the bipolar setup was significantly better (p < 0.05) when compared to the unipolar setup. Additionally, we estimated a transfer function that enabled a comparison of uni- and bipolar recordings. To conclude, the variety of setups used for oVEMP recording hinder a comparison of results and unipolar electrode configurations have clear disadvantages.
Modeling Slow Correcting Gaze Movements
Authors: Lefèvre P. , Missal M. , Galiana H.L.
Published: December 2019

Recent experimental results show evidence for the corrective role of postsaccadic drifts. This paper addresses the modeling of these slow correcting gaze movements (SCMs). Classical arguments to explain drifts are presented, both in the head fixed condition (pulse-step mismatch) and in the head free condition (vestibulo-ocular reflex (VOR)). The most significant behavioral and electrophysiological experimental data related to SCMs are then briefly reported, with the conclusion that SCMs have a clear corrective role, incompatible with classical explanations of drifts. Based on these experimental data, existing models of the saccadic system are then compared. A theoretical comparison of the classical Robinson model with an alternative model is proposed. Two possible (slow and fast) pathways involved in the control of SCMs are examined, and simulation results are presented. Finally, the discussion addresses the observed species differences in SCMs. The link between natural SCMs and electrical SC stimulations, and the interactions between saccades, VOR, and SCMs are also discussed.
Eye Position Signals in the Abducens and Oculomotor Nuclei of Monkeys During Ocular Convergence
Authors: King W. Michael , Zhou Wu , Tomlinson R. David , McConville Kathleen M.V. , Page William K. , Paige Gary D. , Maxwell James S.
Published: December 2019

Many neurons in oculomotor pathways encode signals related to eye position. For example, motoneurons in the third, fourth, and sixth cranial nuclei discharge at highly regular rates during fixation intervals. During fixations of far targets, their tonic discharge is linearly related to conjugate eye position. Previous studies provided evidence that premotor cells in brain stem pathways also encoded conjugate eye position. McConville et al. (this volume), however, measured eye movements during binocular fixations when the eyes were converged and concluded that the position signal encoded by premotor position-vestibular-pause (PVP) cells in the vestibular nuclei is related to monocular (right or left) eye position rather than to conjugate eye position. This surprising relationship would not have been noticed in earlier studies that measured the movements of only one eye (using a single eye coil) or that measured only the conjugate movements of the two eyes (using bitemporal EOG electrodes). How general a feature of oculomotor signal processing is this finding? In this paper, we re-examine the eye position signal in abducens and oculomotor neurons when the movements of the two eyes are conjugate and when they are disjunctive and therefore disassociated. The data suggest that abducens neurons (AMNs and AINs) and oculomotor neurons (putative medial rectus motoneurons), unlike PVP cells, are not monocular but encode mixtures of right and left eye position signals.
Changes in the Gastrointestinal Electric Pattern to Motion Sickness in Susceptibles and Insusceptibles During Fasting
Authors: Kolev Ognyan I. , Altaparmakov Ivan A.
Published: December 2019

The cardinal symptoms of motion sickness occur in the gastrointestinal system. This study sought to investigate the influence of sickness-provoking motion stimuli on the interdigestive migrating electric complex (IDMEC) of the gastrointestinal system. Thirteen susceptibles and 14 insusceptibles to motion sickness were subjected to intralumenal recording before and after caloric vestibular stimulations. Motion sickness developed in all subjects. The results indicate that there are no significant differences in the IDMECs of susceptibles and insusceptibles in a state of rest; vestibular stimulation changes the duration of IDMEC phases (P < 0.05 and P < 0.01); IDMEC changes differ slightly between susceptibles and insusceptibles; motion stimuli induce simultaneous nonpropulsive spike activity, which is more frequent in susceptibles (P < 0.01); vestibular stimulation applied during phase III of IDMEC does not provoke vomiting in susceptibles.
Influence of Arousal and Attention on the Control of Postural Sway1
Authors: Maki B.E. , McIlroy W.E.
Published: December 2019

Healthy young adults (n = 39) were asked to perform four different secondary cognitive tasks during quiet unperturbed stance, in order to investigate the influence of physiological arousal and attention distraction on the control of spontaneous postural sway. During each task, postural activity was quantified in terms of center-of-pressure displacement, leg-muscle activation, and ankle and hip rotation. Arousal was monitored via skin conductance, and questionnaires were used to assess state anxiety. Respiratory trunk movements were also recorded, to assess potential arousal-related destabilizing effects, but failed to show a strong association with the postural measures. The nature of the secondary task affected the postural responses in that subjects tended to lean slightly forward, and exhibited higher levels of activation in tibialis anterior, when performing a mental-arithmetic task. Although this task affected both attention and arousal, the leaning effect was limited to subjects who reported higher levels of anxiety-related autonomic or somatic symptoms during testing, and the degree of leaning was correlated with the level of physiological arousal. A secondary task that diverted attention but did not affect physiological arousal (listening to a spoken-word recording) failed to elicit changes in postural response. These findings suggest that the changes in leaning were associated with task-related changes in physiological arousal, and highlight the need to account for the potentially confounding influence of arousal when studying attentional effects. Given the potential influence on stability, the results also suggest that leaning should be monitored or controlled during balance assessment, particularly when dealing with individuals who may be anxious or afraid of falling.
Bilateral Vestibular Loss in Vertebrobasilar Dolichoectasia
Authors: Nuti O. , Passero S. , Di Girolamo S.
Published: December 2019

Bilateral vestibular loss (BVL) is a relatively uncommon syndrome that may produce problems of balance; unsteady gait, especially in the dark; and visual disorders and/or oscillopsia associated with walking and head movements. Sometimes patients with BVL remain asymptomatic. Ototoxic drugs are the most frequently identified cause of BVL, but there are many other possible causes. The aetiology remains unknown in a large percentage of patients. In some, vascular aetiology may be suspected. Here we report 4 cases of vertebrobasilar dolichoectasia (VBD) and symptomatic BVL. In 3 subjects, hearing was preserved, but in the 4th, there was retrolabyrinthine hearing loss. In our opinion, VBD may be the cause of BVL associated or not associated with hearing loss, the reason being that since the anterior vestibular artery is small and has no anastomoses, the horizontal semicircular canal is selectively susceptible to ischemia.
Visual-Vestibular Interaction During Off-Vertical Axis Rotation1
Authors: Furman Joseph M. , Mendoza Juan Carlos
Published: December 2019

The aim of this study was to further define the eye movement response to combined visual and vestibular stimulation, especially during linear acceleration. Subjects included 15 asymptomatic healthy individuals (8 females and 7 males) between the ages of 20 and 31 years. Vestibular stimulation consisted of earth-vertical axis rotation and off-vertical axis rotation (OVAR). Visual stimuli consisted of projected vertical stripes that were rotated for optokinetic trials and stationary for visual augmentation trials. A small laser target (0.5 mW, 0.50° arc) that rotated with the subject was used for fixation trials. Eye movements were measured with electro-oculography. Results showed that visual-vestibular interaction during sinusoidal rotation was not affected by a 15° off-vertical tilt. Constant velocity OVAR induced a continuous nystagmus whose slow component velocity contained a nonzero baseline, that is, a bias, and a periodic fluctuation at the rotation frequency, that is, a modulation component. The modulation component during visual fixation was reduced as compared with that seen during rotation in the dark, but was not absent. Constant velocity OVAR in the presence of earth-fixed stripes induced a consistent sinusoidal modulation. Our results suggest that visual-vestibular interaction for otolith stimulation differs from visual-vestibular interaction for semicircular canal stimulation. The modulation component of the response to OVAR appears to be modified by visual stimulation to a lesser extent than other vestibular-induced eye movements and thus may reflect a more “direct” vestibulo-ocular response. The bias component of the response to OVAR can be substantially influenced by vision and thus may depend upon more “indirect” pathways.
Behavior of Cells Without Eye Movement Sensitivity in the Vestibular Nuclei During Combined Rotational and Translational Stimuli
Authors: Tomlinson R.D. , McConville K.M.V. , Na E.-Q.
Published: December 2019

A total of 74 neurons that lacked eye movement sensitivity were recorded within the confines of the rostral medial and medial lateral vestibular nuclei. Of these, 36 had response characteristics that were consistent with combined canal and otolith inputs (CAOT neurons), 18 received canal inputs only (CA neurons), and 20 had otolith inputs only (OT neurons). Responses were measured during both rotational and combined rotational and translational stimuli at 0.5 and 3.0 Hz. The otolith signal was found to lag acceleration markedly at both frequencies. Indeed, one subset of CAOT neurons had otolith responses that led translational velocity by only 12° at 0.5 Hz. All translation-responsive neurons decreased their phase lag with respect to acceleration when the stimulus frequency was increased and exhibited a large increase in sensitivity. As these cells have response dynamics that lie between those seen in otolith afferents and those required to drive the motoneurons during the translational VOR, they may represent an intermediate stage in the signal processing.
A Model That Relates Canal-Ocular to Otolith-Ocular Responses
Authors: Wall III C. , Arakawa G.K.
Published: December 2019

Rotation about the vertical stimulates primarily the horizontal semicircular canals and produces compensatory horizontal nystagmus whose slow component velocity response during constant velocity can be approximated as having a simple exponential decay time constant, TVOR, Constant velocity yaw rotation about a horizontal axis stimulates both the horizontal canals and the otolith organs, producing two additional nystagmus components thought to be of otolithic origin: a steady component called bias and a periodic component known as modulation. We tested a group of 7 human subjects using rotation about each of these axes. We found a strong, negative correlation (r=0.956) between these individuals' dominant time constants, TVOR, and the magnitude of their modulation components. Canal and otolith signals originate from different parts of the same endorgan and travel separately to the vestibular nucleus. The reflexive eye movements in response to these inputs are thought to be the result of additional processing by the central vestibular and ocular motor systems. Thus, the source of these strongly correlated otolith-ocular and canal-ocular reflex components could logically be due to common factors affecting peripheral transduction or to a subsequent common central processing step. Using anatomical measurements of human vestibular end organs, biophysical endorgan models, and models of central vestibular processes, we examined the alternatives to determine which was the most likely. Correlations were not found between TVOR and the anatomical data or between the TVOR and the biophysical model elements. However, modifications of the velocity storage integrator of Raphan to incorporate either a high pass filter (HPF) or a lowpass filter input for otolith modulation signals allowed for the desired strong negative correlation between TVOR and modulation. We argue in favor of the HPF configuration because it better explains the tendency for the modulation component to increase in amplitude as the modulation frequency is increased. In the above mentioned representation of the central processing of vestibular afferent inputs, we conclude that the modulation component input to the vestibuloocular reflex is within the indirect pathway, but it is “down stream” from the velocity storage integrator.
The Recovery of Static Vestibular Function Following Peripheral Vestibular Lesions in Mammals: The Intrinsic Mechanism Hypothesis1
Authors: Darlington Cynthia L. , Smith Paul F.
Published: December 2019

This theoretical paper describes the “intrinsic mechanism hypothesis”, a new hypothesis of vestibular compensation, the behavioral recovery that follows unilateral deafferentation of the vestibular labyrinth (UVD). The most salient characteristic of vestibular compensation is the decrease in the severity of the static ocular motor and postural symptoms that follow UVD, associated with a recovery of resting activity in the ipsilateral vestibular nucleus complex (VNC). The speed of static compensation in some mammalian species (for example, cat) has suggested that reactive synaptogenesis is an unlikely explanation because it is too slow. Other, more rapid mechanisms, such as denervation supersensitivity, receptor-up-regulation, or increased neurotransmitter release, were reasonable possibilities. However, to date, each study that has addressed these possibilities has failed to find any change that could account for the recovery of VNC resting activity. The search for such “substitutive” mechanisms was based on the hypothesis that something other than the VNC neurons themselves would have to “replace” the missing resting activity that the ipsilateral vestibular nerve normally provides. However, brainstem slice studies demonstrate that, at least in vitro, VNC neurons do not need the vestibular nerve in order to generate resting activity. On the basis of these and other considerations, we suggest that following a brief calcium-induced diaschisis, VNC neurons ipsilateral to the UVD reactivate the intrinsic membrane properties that normally contribute to their resting activity in vivo, and that this recovery of resting activity accounts for static vestibular compensation.
Evidence for the Involvement of NMDA Receptors in Vestibular Compensation
Authors: Aoki Mitsuhiro , Miyata Hideo , Mizuta Keisuke , Ito Yatsuji
Published: December 2019

The involvement of NMDA (N-methyl-D-aspartic acid) receptors in the initial stage of the vestibular compensation was evaluated by examining the effect of MK-801 on this compensation in guinea pigs. MK-801, injected 30 min before induction of unilateral labyrinthectomy by an arsanilate, significantly (P < 0.05) reduced the maximum frequency of the spontaneous nystagmus (SN) towards both the arsanilate-applied and the intact sides. In addition, injection of arsanilate into the opposite middle ear, 60 days subsequent to induction of the unilaterial labyrinthectomy, suppressed the SN towards the second injected side, but had no effect on the SN towards the first injected side. These results suggest that NMDA receptors may be linked to the initiation of the vestibular compensation.
The Influence of Otoliths and Somatic Graviceptors on Angular Velocity Estimation
Authors: Mittelstaedt Marie-Luise , Mittelstaedt Horst
Published: December 2019

In three psychophysical experiments subjects (Ss), blindfolded and earphoned with white noise, estimated their angular speed A) after brief acceleration to constant centric or eccentric rotation, and B) after deceleration to a full stop. Ss either indicated whenever they were rotated through 180°, or manipulated the objective velocity such that the subjective one stayed constant. With Ss in an earth-vertical attitude, subjective speed declined exponentially with a time constant that depended on eccentricity in paradigm A, but not in B. The time constant depended linearly on the amount of the centrifugal force, but not on its direction. Thus, centrifugal force has an enhancing effect on perceived angular speed. The relevant sense organs were identified with Ss in a radial, earth-horizontal attitude. The enhancing effect was minimal when the axis of rotation was caudal of the otoliths, indicating an effect of graviceptors in the trunk. This effect, just as the effect of recently discovered truncal graviceptors on the perception of posture, turned out to depend on leg position: The minimum of the enhancing effect shifted from about 30 cm to about 60 cm caudal of the otoliths, when leg position changed from flexed to extended. It is concluded that the centrifugal force, measured by otoliths and truncal graviceptors, serves to provide information on angular velocity at eccentric rotation, at least as long as the output of the velocity storage is not yet zero.
“Torso Rotation” Experiments; 3: Effects of Acute Changes in Vestibular Function on the Control of Voluntary Head Movements
Authors: Bouyer L.J.G. , Watt D.G.D.
Published: December 2019

“Torso Rotation” (TR) produces an acute, reversible change in human vestibular function. Experiments were performed to determine if repeated exposure to this technique would result in long-term adaptive modifications. In one experiment, VOR gain was evaluated. Measurements were obtained before and 3 times after 30 minutes of TR, on 7 consecutive days. VOR gain dropped each day after TR, returning to normal within about 20 min. In a separate experiment with different subjects, eyes-open gaze stability was measured during voluntary head shaking between 3.0 and 0.3 Hz. The same test schedule was used. Analysis of gaze stability (limited to frequencies between 1.0 and 2.0 Hz) was complicated by an unexpected finding. Despite careful instructions, head displacement increased each day after TR, also returning to normal within about 20 min. Surprisingly, subjects were unaware of this change. Combining the 2 experiments, VOR gain and head amplitude were averaged across all 7 days, separately for the 4 daily tests. Head amplitude was plotted against VOR gain for these 4 averages. Amplitude was greater when VOR gain was reduced, with a remarkably high correlation (R2=0.996). These findings confirm that vestibular feedback plays an important role in the control of voluntary head movement. Furthermore, the data suggest that instability of the visual scene reported by subjects shaking their heads after TR resulted not only from a lower VOR gain, but also from the inadvertent use of higher head velocities.
Considerations on the Mechanisms of Alternating Skew Deviation in Patients with Cerebellar Lesions
Authors: Zee David S.
Published: December 2019

Alternating skew deviation, in which the side of the higher eye changes depending upon whether gaze is directed to the left or to the right, is a frequent sign in patients with posterior fossa lesions, including those restricted to the cerebellum. Here we propose a mechanism for alternating skews related to the otolith-ocular responses to fore and aft pitch of the head in lateral-eyed animals. In lateral-eyed animals the expected response to a static head pitch is cyclorotation of the eyes. But if the eyes are rotated horizontally in the orbit, away from the primary position, a compensatory skew deviation should also appear. The direction of the skew would depend upon whether the eyes were directed to the right (left eye forward, right eye backward) or to the left (left eye backward, right eye forward). In contrast, for frontal-eyed animals, skew deviations are counterproductive because they create diplopia and interfere with binocular vision. We attribute the emergence of skew deviations in frontal-eyed animals in pathological conditions to 1) an imbalance in otolithocular pathways and 2) a loss of the component of ocular motor innervation that normally corrects for the differences in pulling directions and strengths of the various ocular muscles as the eyes change position in the orbit. Such a compensatory mechanism is necessary to ensure optimal binocular visual function during and after head motion. This compensatory mechanism may depend upon the cerebellum.
A Ground-Based Animal Model of Space Adaptation Syndrome
Authors: Takeda Noriaki , Horii Arata , Uno Atsuhiko , Morita Masahiro , Mochizuki Takatoshi , Yamatodani Atsushi , Kubo Takeshi
Published: December 2019

We examined the effect and aftereffect of acute or chronic load of hypergravity produced by an animal centrifuge, on pica (that is, kaolin intake) in the rat as an index of motion sickness. Although the degree of pica initially induced by acute or chronic hypergravity was not different, the rate of decline of increased kaolin intake over poststimulus days was different. Pica after a 1-h load of 2g decreased rapidly. On the other hand, pica lasted 3 days after a 48-h load of 2g. These findings suggest that the aftereffects of chronic hypergravity application on pica are due to motion sickness induced by readaptation to normal gravity, and they support our idea that after adaptation to a hypergravity environment, return and readaptation to the normal gravity can simulate exposure and adaptation to microgravity. We concluded that motion sickness in rats induced by the aftereffects of chronic hypergravity stimulation can be used as a ground-based animal model of space adaptation syndrome.
Changes in Gain and Spatiotemporal Properties of the Vestibulospinal Reflex after Injection of a GABA-A Agonist in the Cerebellar Anterior Vermis
Authors: Manzoni D. , Andre P. , Pompeiano O.
Published: December 2019

Experiments were performed to study the influence of the cerebellar anterior vermis on both amplitude and directional properties of the vestibulospinal (VS) reflexes. In decerebrate cats, the multiunit EMG activity of the medial head of the forelimb extensor triceps brachii was recorded during wobble of the whole animal at 0.15 Hz. With this procedure the animals were submitted to a tilt characterized by a fixed amplitude (10°) and by a direction moving at constant velocity over the horizontal plane, in both a clockwise (CW) and a counterclockwise (CCW) direction. These dynamic stimuli permitted characterization of the triceps muscle response to animal tilt as a single vector in the horizontal plane. The gain of this vector was taken as the mean value obtained for the CW and CCW responses, while its orientation corresponded to the direction of head displacement, lying midway between the maximal response directions to CW and CCW rotations. The temporal phase was evaluated as the half difference between the directions of the CW and CCW responses. In all the experiments the response vector of the triceps brachii was closely aligned with the transverse axis and pointed to the side-down direction. Unilateral inactivation of the cerebellar anterior vermis after microinjection, in one or two folia of lobule V, of the GABA-A agonist muscimol (0.5μL at 8μg/μL saline), consistently and reversibly reduced in 20 to 40 min the amplitude of the EMG modulation of the ipsilateral triceps brachii to 46% to 80% of the control value, while only a small shift (up to 30°) of the response vector occurred either nosewards or tailwards. Small shifts in temporal phase were also observed. These findings suggest that the Purkinje (P)-cells, which usually fire out of phase with respect to the VS neurons, contribute positively to the amplitude of the VS reflexes. It was previously shown that P-cells with response vectors covering all the directions of animal displacement are present in small regions of the cerebellar anterior vermis; it is likely that these neurons represent functional units facilitating the VS reflexes elicited by animal tilt in the direction of their response vectors. By suppressing the activity of these cells, muscimol injections would lead to a general depression of the triceps responses to animal displacement, not associated with prominent changes in directional specificity.
On the Optokinetic Response During Step-Wise Changes in Stimulus Velocity in Squirrel Monkeys
Authors: Kröller J. , Behrens F.
Published: December 2019

In two awake untrained squirrel monkeys the horizontal optokinetic nystagmus (OKN) was studied. The goal was to quantify the buildup of the slow-phase eye movement velocity during the first two seconds and the eye movements after OKN interruption by a stationary surround. We intended to uncover possible effects of a ‘charged’ velocity storage on eye movements at a stationary surround. Using an optokinetic drum, a paradigm was designed to create sudden changes of the pattern (within 5 ms) between appearing to be stationary or rotating. Velocity steps from zero to 14 to 73°/s and back to zero could be achieved. OKN onset: 201 velocity trajectories were analyzed. The mean latency between the onset of pattern movement and the onset of slow-phase eye movements was 82.8±16.5 ms. Over a limited period the initial increase in slow-phase velocity could be approximated by a straight line. The slope was on average 103±67°/s2 and did not show a significant dependency on pattern movement velocity. Eye movement velocity at the end of the linear part increased linearly with drum velocity; the slope was 0.59. After the linear range, the slow-phase velocity increased further but at slower accelerations and usually reached the final gain within the two seconds. The initial linear acceleration component is an open-loop reflex response and we conclude that closing the loop happens when about 60% of the stimulus velocity is reached. OKN-offset: The influence of a fully charged OKN velocity storage mechanism on eye movements after a sudden exposure of a stationary surround was studied in 23 trials. After OKN interruption the velocity decay commenced after an interval of 83.5±16.6 ms. On average the slope of the consecutive linear velocity decay was −195.4±83.6°/s2. During 5.8±0.98 s the OKN still had some impact on the fixating eye movements. We conclude that this time represents the time for velocity storage discharging. An active process seems to control the impact of velocity storage on eye movements.
Visual Object Localization through Vestibular and Neck Inputs. 2: Updating Off-Mid-Sagittal-Plane Target Positions
Authors: Blouin Jean , Gauthier Gabriel M. , Vercher Jean-Louis
Published: December 2019

The vestibular signal plays a significant role in sensing changes in head orientation during rotations and in determining the magnitude of the rotations, but has only minor contributions in updating the internal representation of object positions with respect to the body after body rotations. The small contribution of the vestibular signal in egocentric object localization was evidenced in experiments in which the subjects reported the remembered position of eccentric earth-fixed targets after passive body rotations. The experiment reported here tested whether motor systems, such as the oculomotor system, make use of vestibular signals to generate accurate goal-directed motor responses toward a target whose position needs to be updated with respect to the body during and after whole-body rotations. The results showed that although subjects can produce saccadic eye movements of about the same magnitude as passive whole-body rotations (as previously reported by a number of researchers), they failed to generate accurate saccades toward the position of an extinguished peripheral visual target after the rotation. Overall, these results combined with those found in the literature suggest different central processes for determining changes in body orientation in complete darkness and for updating a target position with respect to the body during and after body rotations.
Head-Trunk Coordination During Hops Using One or Two Feet in Children and Adults
Authors: Assaiante C. , McKinley P.A. , Amblard B.
Published: December 2019

The main purpose of this study was to investigate the development of head-trunk coordination during single hops using one foot or two feet in children of two ages (5.5 to 6 and 7 to 7.5) and adults (n = 6/group). The kinematics of the subjects' hops were analyzed by means of an automatic optical TV-image processor called the ELITE system. The absolute angular dispersion of the head, trunk, and leg about the pitch and the roll axis were measured. Head and trunk pitch and roll anchoring indexes were calculated in order to compare the stabilization of a given segment with respect both to external space and to the underlying anatomical segment. Results were analyzed separately for 3 phases: take-off, flight, and landing. Only the last two phases, flight and landing, are presented in this paper, and the following was found: 1) During flight, under both unipedal and bipedal conditions, head and trunk stabilization in space about the pitch axis occurred in children as well as in adults, suggesting an articulated operation of the head-trunk unit. In contrast, during landing, in children and adults, head stabilization in space tended to disappear while trunk stabilization in space was still present, suggesting an en bloc operation of the head-trunk unit. Similarly, pelvis stabilization in space about the roll axis occurred in all subjects during both flight and landing under unipedal conditions, where lateral balance control is of primary importance. Taken together, these results suggest that head stabilization in space is phase dependent, while trunk stabilization is phase independent. The trunk, including the pelvis, may thus constitute a stable reference frame from which anteroposterior and lateral balance control is organized during hops. 2) For head-trunk coordination, whatever the component of rotation, the two groups of children differed from adults, but did not differ from each other, suggesting that, while jumping, the transition between 6 and 7 years of age in the organization of balance control takes place in the coordination of the lower limbs during the preparatory phase of the take-off.
Locomotor Head-Trunk Coordination Strategies Following Space Flight
Authors: Bloomberg Jacob J. , Peters Brian T. , Smith Shannon L. , Huebner William P. , Reschke Millard F.
Published: December 2019

During locomotion, angular head movements act in a compensatory fashion to oppose the vertical trunk translation that occurs during each step in the gait cycle. This coordinated strategy between head and trunk motion serves to aid gaze stabilization and perhaps simplifies the sensory coordinate transformation between the head and trunk, allowing efficient descending motor control during locomotion. Following space flight, astronauts often experience oscillopsia during locomotion in addition to postural and gait instabilities, suggesting a possible breakdown in head-trunk coordination. The goal of the present investigation was to determine if exposure to the microgravity environment of space flight induces alteration in head-trunk coordination during locomotion. Astronaut subjects were asked to walk (6.4 km/h, 20 s trials) on a motorized treadmill while visually fixating on a centrally located earth-fixed target positioned either 2 m (FAR) or 30 cm (NEAR) from the eyes. In addition, some trials were also performed during periodic visual occlusion. Head and trunk kinematics during locomotion were determined with the aid of a video-based motion analyzing system. We report data collected preflight (10 days prior to launch) and postflight (2 to 4 hours after landing). The coherence between pitch head and vertical trunk movements during gaze fixation of both FAR and NEAR targets was significantly reduced following space flight indicating decreased coordination between the head and trunk during postflight locomotion. Astronauts flying on their first mission showed greater alterations in the frequency spectra of pitch head movements as compared to their more experienced counterparts. These modifications in the efficacy of head movement control may account for the reported disruption in gaze performance during locomotion and may contribute to postflight postural and gait dysfunction.
The Control of Head Movements during Human Balance Corrections
Authors: Allum J.H.J. , Gresty M. , Keshner E. , Shupert C.
Published: December 2019

The assumption that the CNS regulates head stability during human balance corrections is explored in this review (an outgrowth of discussions initiated during the Head/Neck meeting held in Vail, Colorado, USA, July 1995). Two major questions were considered. First, how do the vestibulocollic (VCR) and cervicocollic (CCR) reflexes interact with intrinsic mechanical properties of the head neck system to control head position during balance corrections? Second, how is this interaction affected by factors such as vestibular loss, aging, and changes in behavioral goals or central set? The authors conclude that head velocities observed during balance corrections depend to a large extent on the movements of the head–neck mass-viscoelastic system whose properties could be altered by cocontracting the neck muscles. For experiments involving stance perturbations, much of the corrective response in neck muscles appeared to be triggered by trunk and leg proprioceptive signals, and a major role for the VCR was not established. Evidence consistent with a role for the vestibular system was found in other experimental paradigms in which the head was perturbed directly. In these paradigms the VCR modulates the amplitude of functionally stabilizing responses and damps mechanically induced instability of the head and neck.
Physiological Evidence that the Vestibular System Participates in Autonomic and Respiratory Control
Authors: Yates B.J. , Miller A.D.
Published: December 2019

Electrical or natural stimulation of the vestibular system results in changes in blood pressure and respiratory motor output. An increase in excitatory drive on the sympathetic nervous system occurs during nose-up vestibular stimulation in cats; this response is appropriate to offset orthostatic hypotension that could result from nose-up body rotations during movements such as vertical climbing. In addition, transection of the vestibular nerves in anesthetized or awake cats compromises the ability to correct decreases in blood pressure that result from nose-up body tilt. The vestibular system also has influences on respiratory muscles; these effects are appropriate to participate in making adjustments in the activity of respiratory muscles that are necessary to offset mechanical constraints on these muscles that occur during changes in body position. These data thus suggest that the influences of the vestibular system on the autonomic and respiratory systems serve to maintain homeostasis during movement.
Clinical Evidence That the Vestibular System Participates in Autonomic Control
Authors: Furman Joseph M. , Jacob Rolf G. , Redfern Mark S.
Published: December 2019

The vestibular system, including both the peripheral vestibular system, that is, the labyrinth, and the central vestibular system, is known to influence autonomic function in several ways that have clinical implications. This paper discusses evidence for vestibular influences on autonomic control from normal human subjects, evidence for vestibular influences on autonomic control from patients, clinical implications of vestibulo-autonomic regulation, and speculations regarding possible clinical implications of vestibulo-autonomic control. Situations that provoke vestibular-induced autonomic responses in normal subjects include vestibular laboratory testing, vehicular motion, simulators, and, possibly, exposure to microgravity. Patients with peripheral and central vestibular abnormalities manifest both symptoms and signs of autonomic dysfunction presumably via vestibulo-autonomic connections. Vestibulo-autonomic regulation impacts vestibular diagnostic testing, clinical diagnosis of balance disorders, and treatment of balance disorders. In addition to well-recognized peripheral and central vestibular disorders, anxiety disorders have recently been linked to vestibular dysfunction in a subset of patients. In particular, vestibular dysfunction has been linked to panic disorder and agoraphobia. Vestibular-autonomic connections may form a basis for an association between vestibular dysfunction and panic attacks. The importance of vestibulo-autonomic regulation in the clinical arena is not fully known. Two speculative areas discussed in this paper include vestibular-induced orthostatic intolerance and the role of vestibular-respiratory pathways on sleep apnea.