bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of vestibular ocular reflex (VOR) time constants with a caloric step stimulus*
Authors: Formby C. , Robinson D.A.
Published: September 2021

A protocol is described for measuring responses to a broadband (1–2 Hz) caloric step stimulus from which the vestibular ocular reflex (VOR) and adaptation time constants can be estimated. This novel stimulation is the caloric equivalent to a rotatory step of head acceleration. In this protocol, the ear is irrigated continuously for 5 min with water at a constant temperature. During the initial 2-min period of irrigation the subject is seated and leaning forward in a nonstimulable position (horizontal canals in a horizontal plane). This irrigation phase establishes a steady-state thermal gradient across the horizontal canal, effectively eliminating thermal dynamic properties of the caloric transmission as a confounding factor. At the end of this phase, the subject is rapidly reclined to a stimulable position (horizontal canals in vertical plane) that elicits the VOR nystagmus response to an on-step of force on the cupula. Consistent with adaptation processes, the VOR response first increases and then declines gradually over the 2-min period that the step of force is maintained. Four minutes after the onset of irrigation, the subject is rapidly returned to the nonstimulable position (off-step), which is then maintained for a final 1 min. The response after the off-step, which releases the force on the cupula, reveals reversed after-nystagmus due to adaptation. Five subjects provided caloric step responses for 26 caloric temperature conditions spanning the range from 28.4 to 43.0 ∘ C. The resulting responses were fitted with an adaptation model similar to models applied to rotatory acceleration step responses. Estimates of the model parameters for robust caloric stimulation, including time constants for the VOR (18.3 sec) and for vestibular adaptation (153.2 sec), are considered in relation to corresponding values reported in the literature for rotatory and caloric vestibular stimulation. The results suggest that caloric step stimulation can be used successfully to probe VOR dynamics.
Characteristics of secondary phase post-rotatory nystagmus following off-vertical axis rotation in humans
Authors: Furman Joseph M. , Koizuka Izumi , Schor Robert H.
Published: September 2021

The nystagmus following yaw earth-vertical axis rotation often reverses direction, a phenomenon known as the “secondary phase”. The purpose of this study was to examine the existence and the spatial and temporal properties of the secondary phase of post-rotatory nystagmus following off-vertical axis rotation (OVAR). Eleven normal human subjects were rotated at 120 or 180 ∘ /s about an off-vertical axis and stopped in the left ear down or right ear down lateral position. Horizontal and vertical eye positions were recorded with a scleral search coil, and horizontal and vertical slow component eye velocities were computed. Our results indicate that (a) there is a robust secondary phase nystagmus following OVAR, and (b) the direction of the secondary phase nystagmus tends to align with earth-horizontal. These results can be explained by a minor modification of an existing VOR model that has been shown to produce secondary phase responses.
The influence of an immersive virtual environment on the segmental organization of postural stabilizing responses
Authors: Keshner E.A. , Kenyon R.V.
Published: September 2021

We examined the effect of a 3-dimensional stereoscopic scene on segmental stabilization. Eight subjects participated in static sway and locomotion experiments with a visual scene that moved sinusoidally or at constant velocity about the pitch or roll axes. Segmental displacements, Fast Fourier Transforms, and Root Mean Square values were calculated. In both pitch and roll, subjects exhibited greater magnitudes of motion in head and trunk than ankle. Smaller amplitudes and frequent phase reversals suggested control of the ankle by segmental proprioceptive inputs and ground reaction forces rather than by the visual-vestibular signals. Postural controllers may set limits of motion at each body segment rather than be governed solely by a perception of the visual vertical. Two locomotor strategies were also exhibited, implying that some subjects could override the effect of the roll axis optic flow field. Our results demonstrate task dependent differences that argue against using static postural responses to moving visual fields when assessing more dynamic tasks.
Effects of gymnastics expertise on the perception of body orientation in the pitch dimension
Authors: Bringoux Lionel , Marin Ludovic , Nougier Vincent , Barraud Pierre-Alain , Raphel Christian
Published: September 2021

The purpose of this study was to investigate how experts in motor skills requiring a fine postural control perceive their body orientation with few gravity based sensory cues. In Experiment 1, expert gymnasts and controls had to detect their body tilt when pitching at a velocity of 0.05 deg . s − 1 , in two conditions of body restriction (strapped and body cast altering the somatosensory cues). Contrary to the experts, the controls exhibited a larger body tilt when totally restrained in the body cast. In Experiment 2, subjects had to estimate their Subjective Postural Vertical (SPV) starting from different angles of pitch tilt. The controls exhibited significant errors of SPV judgement whereas the experts were very precise. These results suggest that 1) somatosensory cues are more informative than otolithic cues for the perception of body orientation, and 2) the efficiency of otolithic and/or interoceptive inputs can be improved through a specific training to compensate for the lack of somatosensory cues.
Asymmetry of ocular motor and perceptual vestibular processing in humans with unilateral vestibular deafferentation
Authors: Crane Benjamin T. , Tian Junru , Demer Joseph L.
Published: September 2021

To investigate the effect of asymmetrical vestibular input on the perceived straight-ahead direction, we compared 7 subjects (age 59 ± 8 yrs, mean ± SD) who had chronic ( > 10 mos) unilateral vestibular deafferentation with 10 age matched controls (age 61 ± 6 younger controls (age 28 ± 7 yrs). Despite the age difference, the two control groups performed similarly and were therefore pooled. Eye and head movements were recorded using search coils as subjects underwent 30 s trials of sinusoidal, whole body oscillation (0.4–2 Hz, peak velocities 0 – 120 ∘ /s) in darkness while attempting to maintain gaze on a remembered target 5 m distant. As a control, most stimulus oscillations were randomly superimposed on an imperceptible, constant velocity of ± 0 . 5 ∘ /s that produced a whole-body offest of 15 ∘ by the end of the trial. Following oscillation, subjects remained motionless in darkness and were asked to orient both gaze and a manipulandum to the remembered target location. In control subjects, mean final gaze and manipulandum positions were within 15 ∘ of the target for all testing conditions. There was no dependence of final gaze and manipulandum positions on the frequency or velocity of the preceding whole-body oscillations ( p > 0.05). In four of seven unilaterally deafferented subjects there was an ipsilesional bias of final eye position of ⩾ 10 ∘ . These subjects moved both eye and manipulandum to the ipsilesional side, with the error increasing at higher stimulus velocities. For the 120 ∘ /s peak head velocity, mean ipsilesional gaze bias ranged from 10 – 37 ∘ and mean manipulandum bias ranged from 26 – 108 ∘ . Although the errors depended on velocity p < 0.01), errors were independent of frequency ( p > 0.1). In the remaining three subjects with vestibular deafferentation, final gaze and manipulandum positions were not statistically different from controls. Early gain (eye velocity / head velocity) of the VOR averaged 0.82 ± 0.01 for the first 10 s of all trials and was similar in all groups ( p > 0.1). Gain during the final 10 s gain averaged 0.78 ± 0.01 for control subjects, but was significantly lower at 0.70 ± 0.01 for unilaterally deafferented subjects, whose eye positions reached the limit of the ocular motor range. We conclude that many humans with chronic unilateral vestibular deafferentation have a large ipsilesional dynamic bias of eye position and the perceived straight ahead direction reflecting persistent asymmetry of vestibular processing.
The vertical vestibulo-ocular reflex, and its interaction with vision during active head motion: Effects of aging
Authors: Kim Ji Soo , Sharpe James A.
Published: September 2021

The effects of aging on the vertical vestibulo-ocular reflex (VOR), and its interactions with vision during active head motion had not been investigated. We measured smooth pursuit, combined eye-head tracking, the VOR, and its visual enhancement and cancellation during active head motion in pitch using a magnetic search coil technique in 21 younger (age < 65) and 10 elderly (age ⩾ 65) subjects. With the head immobile, subjects pursued a target moving sinusoidally with a frequency range of 0.125 to 2.0 Hz, and with peak target accelerations (PTAs) ranging from 12 to 789Âř/s 2 . Combined eye-head tracking, the VOR in darkness, and its visual enhancement during fixation of an earth-fixed target (VVOR) were measured during active sinusoidal head motion with a peak-to-peak amplitude of 20Âř at frequencies of 0.25, 0.5, 1.0 and 2.0 Hz. The efficacy of VOR cancellation was determined from VOR gains during combined eye-head tracking. VOR and VVOR gains were symmetrical in both directions and did not change with aging, except for reduced gains of the downward VOR and VVOR at low frequency (0.25 Hz). However, in the elderly, smooth pursuit, and combined eye-head tracking gains and the efficacy of cancellation of the VOR were significantly lower than in younger subjects. In both the young and elderly groups, VOR gain in darkness did not vary with the frequency of active head motion while the gains of smooth pursuit, combined eye-head tracking, and VVOR declined with increasing target frequency. VOR and VVOR performance in the elderly implicates relative preservation of neural structures subserving vertical vestibular smooth eye motion in senescence.
The human oculomotor response to simultaneous visual and physical movements at two different frequencies
Authors: Wall C. , Assad A. , Aharon G. , Dimitri P.S. , Harris L.R.
Published: September 2021

In order to investigate interactions in the visual and vestibular systems' oculomotor response to linear movement, we developed a two-frequency stimulation technique. Thirteen subjects lay on their backs and were oscillated sinusoidally along their z-axes at between 0.31 and 0.81 Hz. During the oscillation subjects viewed a large, high-contrast, visual pattern oscillating in the same direction as the physical motion but at a different, non-harmonically related frequency. The evoked eye movements were measured by video-oculography and spectrally analysed. We found significant signal level at the sum and difference frequencies as well as at other frequencies not present in either stimulus. The emergence of new frequencies indicates non-linear processing consistent with an agreement-detector system that have previously proposed.
Plasticity of γ-aminobutyrate receptors in the medial vestibular nucleus of rat after inferior cerebellar peduncle transection
Authors: Sun Yizhe , Godfrey Donald A. , Rubin Allan M.
Published: September 2021

Extracellular single unit recordings were made from regularly discharging medial vestibular nucleus neurons in brain slices from control rats and from rats surviving 7 days after bilateral transection of the inferior cerebellar peduncle. Decreases in firing rate during perfusion with the Îş-aminobutyric acid (GABA) agonists, muscimol (GABA A ) and baclofen (GABA B ), were greater in lesioned rats than in control rats. For the grouped data, the half-maximally-effective concentrations of muscimol and baclofen were 3.2 µM, as compared with 19.6 µM for control, and 0.8 µM, as compared with 2.7 µM for control, respectively. The antagonists bicuculline (GABA A ) and 2-OH-saclofen (GABA B ) only minimally affected the spontaneous firing rates of neurons in lesioned rats, significantly less than in control rats. The data suggest that the decreases of endogenous GABA levels in the medial vestibular nucleus after inferior cerebellar peduncle transection are accompanied by up-regulation of GABA A and, to a lesser extent, GABA B receptors.
Improvements in path integration after vestibular rehabilitation
Authors: Cohen Helen S. , Kimball Kay T.
Published: September 2021

Fifty-three subjects with peripheral, chronic vestibulopathies, who were referred for vestibular rehabilitation, were tested on a path integration task before and after doing four weeks of five times daily habituation exercises for vertigo reduction. The task involved walking over a 7.62 m path with eyes closed. Dependent measures were velocity and angle of veering from the straight ahead. At the post-test and at succeeding follow-up tests for up to six months, subjects had significant increases in velocity and significant declines in angle of veering. Length of time subjects had vertigo prior to starting rehabilitation, and speed of head movement exercises were not associated with improvements. These data support the previous finding that patients with vestibular impairments have decreased performance on this task. The data also suggest that vestibular rehabilitation, given as a simple home program, is associated with improvements in this skill.
Ocular counterrolling in response to static and dynamic tilting: Implications for human otolith function
Authors: Markham Charles H. , Diamond Shirley G.
Published: September 2021

Nineteen subjects underwent rotation about the naso-occipital axis to examine ocular counterrolling (OCR) responses in both dynamic and static conditions. Dynamic rotation consisted of tilt to 90Âř right and left at constant velocity of 3Âř/s, with acceleration at 0.2Âř/s 2 . Static rotation (stepwise tilting) consisted of one minute at steps 30Âř, 60Âř, 90Âř, 60Âř, 30Âř to each side. OCR amplitudes at each of the above head tilts in dynamic vs. static tilt showed highly significant differences, with dynamic tilt exceeding that of static. Although OCR disconjugacy was greater in static than dynamic in most subjects, that difference was not statistically significant. Possible explanations for the disparity in the responses to dynamic and static tilt in humans lie in vestibular experiments leading to the conclusion that the otolith membrane in cats moves not as a unit, but rather in patches [28]. This is supported by work showing the otolith membrane in bullfrogs does not move en bloc [1]. In addition, hair cell responses are found to be amplified during motion as compared to the responses during static positioning [20]. Functionally, it is suggested that the otolith system may perform better in moving than in static conditions.
Convection, buoyancy or endolymph expansion: what is the actual mechanism responsible for the caloric response of semicircular canals?
Authors: Valli Paolo , Buizza Angelo , Botta Laura , Zucca Giampiero , Ghezzi Luciano , Valli Stefano
Published: September 2021

The mechanisms underlying caloric nystagmus are still matter of debate. The original theory proposed by Barany [2] and more recently by Pau and Limberg [14] suggested that convective endolymphatic currents were involved. In contrast Gentine et al. [5,6,7,8,9] suggested that the main mechanism responsible for caloric nystagmus is buoyancy due to calorization of the endolymph, without the need of continuous convective currents. Finally, other authors (Scherer and Clarke [16], Arai et al. [1]) proposed that thermal expansion or contraction of the endolymph were involved. In the present study experimental conditions have been considered able to discriminate between these different models. The experiments, were carried out on isolated labyrinth preparations of the frog. Only the predictions of the model based on buoyancy were fully consistent with the experimental results whereas those provided by the other models were not.
Lack of gender difference in motion sickness induced by vestibular Coriolis cross-coupling
Authors: Cheung Bob , Hofer Kevin
Published: September 2021

It has been reported that females are more susceptible to motion sickness than males. Supporting evidence is primarily based on retrospective survey questionnaires and self-reporting. We investigated if there is a gender difference in motion sickness susceptibility using objective and subjective measurements under controlled laboratory conditions. Thirty healthy subjects (14 males and 16 females) between the ages of 18-46 years were exposed to Coriolis cross-coupling stimulation, induced by 120°/s yaw rotation and a simultaneous 45° pitch forward head movement in the sagittal plane every 12 seconds. Cutaneous forearm and calf blood flow, blood pressure, and heart rate were monitored. Graybiel's diagnostic criteria were used to assess sickness susceptibility before and after motion exposure. Golding and Kerguelen's scale was used to assess the severity of symptoms during motion exposure. A significant (p < 0.01) increase of forearm and calf blood flow during cross-coupling stimulation was observed in both sexes. However, the subjective symptoms rating and blood flow measurements indicate that there was no significant difference between male and female subjects. Our data also suggests that females may be more inclined to admit discomfort as indicated by their responses to a survey of motion sickness history prior to the experiment.
Identifying head-trunk and lower limb contributions to gaze stabilization during locomotion
Authors: Mulavara Ajitkumar P. , Bloomberg Jacob J.
Published: September 2021

The goal of the present study was to determine how the multiple, interdependent full-body sensorimotor subsystems respond to a change in gaze stabilization task constraints during locomotion. Nine subjects performed two gaze stabilization tasks while walking at 6.4 km/hr on a motorized treadmill: 1) focusing on a central point target; 2) reading numeral characters; both presented at 2 m in front at the level of their eyes. While subjects performed the tasks we measured: temporal parameters of gait, full body sagittal plane segmental kinematics of the head, trunk, thigh, tibia and foot, accelerations along the vertical axis at the head and the tibia, and the vertical forces acting on the support surface. We tested the hypothesis that with the increased demands placed on visual acuity during the number recognition task, subjects would modify full-body segmental kinematics in order to reduce perturbations to the head in order to successfully perform the task. We found that while reading numeral characters as compared to the central point target: 1) compensatory head pitch movement was on average 22% greater despite the fact that the trunk pitch and trunk vertical translation movement control were not significantly changed; 2) coordination patterns between head and trunk as reflected by the peak cross correlation between the head pitch and trunk pitch motion as well as the peak cross correlation between the head pitch and vertical trunk translation motion were not significantly changed; 3) knee joint total movement was on average 11% greater during the period from the heel strike event to the peak knee flexion event in stance phase of the gait cycle; 4) peak acceleration measured at the head was significantly reduced by an average of 13% in four of the six subjects. This was so even when the peak acceleration at the tibia and the transmission of the shock wave at heel strike (measured by the peak acceleration ratio of the head/tibia and the time lag between the tibial and head peak accelerations) remained unchanged. Taken together these results provide further evidence that the full body contributes to gaze stabilization during locomotion, and that its different functional elements can be modified online to contribute to gaze stabilization for different visual task constraints.
Sensorimotor aspects of high-speed artificial gravity: I. Sensory conflict in vestibular adaptation
Authors: Brown Erika L. , Hecht Heiko , Young Laurence R.
Published: September 2021

Short-radius centrifugation offers a promising and affordable countermeasure to the adverse effects of prolonged weightlessness. However, head movements made in a fast rotating environment elicit Coriolis effects, which seriously compromise sensory and motor processes. We found that participants can adapt to these Coriolis effects when exposed intermittently to high rotation rates and, at the same time, can maintain their perceptual-motor coordination in stationary environments. In this paper, we explore the role of inter-sensory conflict in this adaptation process. Different measures (vertical nystagmus, illusory body tilt, motion sickness) react differently to visual-vestibular conflict and adapt differently. In particular, proprioceptive-vestibular conflict sufficed to adapt subjective parameters and the time constant of nystagmus decay, while retinal slip was required for VOR gain adaptation. A simple correlation between the strength of intersensory conflict and the efficacy of adaptation fails to explain the data. Implications of these findings, which differ from existing data for low rotation rates, are discussed.
Sensorimotor aspects of high-speed artificial gravity: III. Sensorimotor adaptation
Authors: DiZio Paul , Lackner James R.
Published: September 2021

As a countermeasure to the debilitating physiological effects of weightlessness, astronauts could live continuously in an artificial gravity environment created by slow rotation of an entire spacecraft or be exposed to brief daily "doses" in a short radius centrifuge housed within a non-rotating spacecraft. A potential drawback to both approaches is that head movements made during rotation may be disorienting and nauseogenic. These side effects are more severe at higher rotation rates, especially upon first exposure. Head movements during rotation generate aberrant vestibular stimulation and Coriolis force perturbations of the head-neck motor system. This article reviews our progress toward distinguishing vestibular and motor factors in side effects of rotation, and presents new data concerning the rates of rotation up to which adaptation is possible. We have studied subjects pointing to targets during constant velocity rotation, because these movements generate Coriolis motor perturbations of the arm but do not involve unusual vestibular stimulation. Initially, reaching paths and endpoints are deviated in the direction of the transient lateral Coriolis forces generated. With practice, subjects soon move in straighter paths and land on target once more. If sight of the arm is permitted, adaptation is more rapid than in darkness. Initial arm movement trajectory and endpoint deviations are proportional to Coriolis force magnitude over a range of rotation speeds from 5 to 20 rpm, and there is rapid, complete motor adaptation at all speeds. These new results indicate that motor adaptation to high rotation rates is possible. Coriolis force perturbations of head movements also occur in a rotating environment but adaptation gradually develops over the course of many head movements.
Vestibulo-autonomic control in man: Short- and long-latency vestibular effects on cardiovascular function
Authors: Radtke Andrea , Popov Konstantin , Bronstein Adolfo M. , Gresty Michael A.
Published: September 2021

We examined the hypothesis that vestibular signals may exert a rapid control on the heart adjusting cardiovascular function to maintain homoestasis during changes in body posture. Short- and long-latency effects of vestibular stimulation on heart rate (HR), systolic blood pressure (SP), diastolic pressure (DP) and digital blood flow (BF) were studied in fourteen normal controls (NC) and nine labyrinthine-defective subjects (LDS) exposed to abrupt head accelerations. Subjects lay supine with their head suspended in a sling whose 'release' was triggered at delays of 170 ms and 570 ms after an R-spike of the ECG. Release caused the head to fall with an acceleration ∼0.8 g for approximately 140 ms. Three additional NC underwent head drops at 170 ms, 370 ms, 470 ms and 570 ms to determine response latencies with precision. In NC, the short-latency response to head drops timed 170 to 470 ms after an R-spike was to shorten the time to the next R-spike in comparison to pre-drop heartbeat cycles. Drops at 570 ms delay shortened only the succeeding post-stimulus RR-interval. In LDS, head drops timed 170 ms after a heartbeat failed to shorten the ongoing cardiac cycle. For both delays only the succeeding cardiac cycle was significantly shortened. In all subjects, SP rose slightly by approximately 1–3% and BF decreased by 7–24% after 3–4 heartbeats post-drop. The results are evidence for an excitatory vestibulo-cardiac reflex in man which accelerates heart rate at a latency circa 500–600 ms. SP and BF are affected at longer latencies of several heart beats. A delayed increase of heart rate in response to postural challenge may contribute to the autonomic distress experienced by patients with vestibular loss.
Respiratory control during postural changes in anesthetized cats
Authors: Miyashita Misao , Suzuki-Inatomi Takami , Hirai Naoki
Published: September 2021

The effect of postural changes on respiration was investigated in ten anesthetized cats by applying body tilting during the inspiration phase while recording respiratory patterns, as given by the diaphragmatic EMG, together with either the lung volume or the air flow temperature. The results show that the head-up tilting during inspiration reduced the period of the inspiratory phase and increased the end-inspiratory lung volume. On the other hand, the head-down tilting during inspiration had opposite effects. These effects disappeared after transection of the vagus nerve. However, labyrinthectomy did not diminish the effects, probably because of functional suppression of the vestibular system due to the anesthetic. When correlating the activity of 15 vagal afferents presumably originating from the slowly adapting lung stretch receptors with lung volume changes during tilting, their maximum firing rate (87 ± 15.7 Hz) was increased with an increase in the lung inflation volume and was attained earlier on head-up tilting and it was reduced with a decrease of the lung volume on head-down tilting (63 ± 16.6 Hz) as compared with the value in the horizontal position (74 ± 14.2 Hz). These results suggest that respiratory modulation during head-up or head-down tilting is consistent with the Hering-Breuer reflexes and minimizes the externally induced lung volume changes during postural changes.
Evaluation of betahistine for the prevention of seasickness: Effect on vestibular function, psychomotor performance and efficacy at sea
Authors: Gordon Carlos R. , Doweck Ilana , Nachum Zohar , Gonen Adi , Spitzer Orna , Shupak Avi
Published: September 2021

Betahistine was evaluated for the prevention of seasickness in a laboratory and sea study. The effect of 48 mg betahistine on the vestibulo-ocular reflex (VOR) and on psychomotor performance was evaluated in twelve young healthy subjects in a double-blind, placebo controlled, randomized, crossover design. The vestibulo-ocular reflex was evaluated by the Sinusoidal Harmonic Acceleration (SHA) test at frequencies of 0.01, 0.02, 0.04, 0.08 and 0.16 Hz. Psychomotor performance was assessed by both computerized and paper and pencil test batteries. No significant differences in VOR gain or phase were found between betahistine and placebo treatment for any of the frequencies tested. No significant differences were found between treatments for any of the psychomotor performance tests or other possible side effects. The effect of 48 mg betahistine on seasickness severity was evaluated in 83 subjects during a voyage in rough seas. Betahistine had a borderline non-statistically significant effect on the prevention of seasickness in comparison with placebo (p = 0.053), with no notable side effects. Although our results are insufficient to recommend betahistine as an anti-seasickness drug, further studies are required to determine its possible effectiveness in less provocative motion sickness situations.
Vestibular evoked myogenic potentials in response to skull taps for patients with vestibular neuritis
Authors: Brantberg Krister , Tribukait Arne , Fransson Per-Anders
Published: September 2021

In recent years it has been demonstrated that loud clicks generate short latency vestibular evoked myogenic potentials (VEMP). It has also been demonstrated that skull tap stimulation evokes similar VEMP. In the present study, the differences between the click-induced and the skull-tap induced VEMP were studied in 18 patients at onset of vestibular neuritis. Gentle skull taps were delivered manually above each ear on the side of the skull and on the forehead midline. The muscular responses were recorded over both sternocleidomastoid muscles using skin electrodes. Abnormal skull tap VEMP were found in the majority of the patients (10/18, 56%). However, only 4/18 (22%) showed asymmetry in the click-induced VEMP. The high percentage of abnormal skull tap VEMP might suggest that this response is not only dependent on the inferior division of the vestibular nerve, because the inferior division of this nerve is usually spared in vestibular neuritis. Moreover, the patients with abnormals kull tap VEMP differed from those with normal VEMP in their settings of the subjective visual horizontal with static head tilt in the roll plane. This might suggest that skull tap VEMP are (also) related to utricular function.
Sensorimotor coordination and the structure of space
Authors: McCollum Gin
Published: September 2021

Embedded in neural and behavioral organization is a structure of sensorimotor space. Both this embedded spatial structure and the structure of physical space inform sensorimotor control. This paper reviews studies in which the gravitational vertical and horizontal are crucial. The mathematical expressions of spatial geometry in these studies indicate methods for investigating sensorimotor control in freefall. In freefall, the spatial structure introduced by gravitation – the distinction between vertical and horizontal – does not exist. However, an astronaut arriving in space carries the physiologically-embedded distinction between horizontal and vertical learned on earth. The physiological organization based on this distinction collapses when the strong otolith activity and other gravitational cues for sensorimotor behavior become unavailable. The mathematical methods in this review are applicable in understanding the changes in physiological organization as an astronaut adapts to sensorimotor control in freefall. Many mathematical languages are available for characterizing the logical structures in physiological organization. Here, group theory is used to characterize basic structure of physical and physiological spaces. Dynamics and topology allow the grouping of trajectory ranges according to the outcomes or attractors. The mathematics of ordered structures express complex orderings, such as in multiphase movements in which different parts of the body are moving in different phase sequences. Conditional dynamics, which combines dynamics with the mathematics of ordered structures, accommodates the parsing of movement sequences into trajectories and transitions. Studies reviewed include those of the sit-to-stand movement and early locomotion, because of the salience of gravitation in those behaviors. Sensorimotor transitions and the conditions leading to them are characterized in conditional dynamic control structures that do not require thinking of an organism as an input-output device. Conditions leading to sensorimotor transitions on earth assume the presence of a gravitational vertical which is lacking in space. Thus, conditions used on earth for sensorimotor transitions may become ambiguous in space. A platform study in which sensorimotor transition conditions are ambiguous and are related to motion sickness is reviewed.
A critical period for gravitational effects on otolith formation
Authors: Wiederhold Michael L. , Harrison Jeffrey L. , Gao Wenyuan
Published: September 2021

The otoliths of adult animals do not change significantly during space flight. However, during the period when otoliths are first developing, rearing in space produces significantly larger otoliths. Conversely, animals reared on a centrifuge have smaller than normal otoliths. To identify a critical period during development for gravitational effects on otolith growth, fertilized zebrafish (Danio rerio) eggs were reared on a centrifuge for 1 week. The fine structure of their inner ear during development was studied by both light- and transmission electron microscopy. By 16 hours after fertilization (1-g, at 28.5°C), precursors of the otoliths are seen but no sign of a sensory epithelium is present. Mature hair cells, appearing capable of mechanotransduction, are not seen until between 48 and 72 hours after fertilization. Zebrafish reared at 3-g from 1 to 7 days after fertilization exhibit significantly slower otolith growth than did 1-g controls. Fish exposed to 3-g only from 12–36 h after fertilization had slightly smaller otoliths than 1-g controls, but this difference was not significant. Animals exposed to 3-g from 36h to 7d after fertilization did have significantly smaller otoliths. If the fish use their hair cells to assess otolith weight in a regulatory role, the hair cells would have to be functional. Thus the earliest stage zebrafish, which were not significantly affected by centrifugation, probably did not have an adequate means of sensing otolith weight to "correct" for the excess weight. (Supported by NASA: NAG2-952 and NAG10-0180)
Utricular sensitivity and preponderance assessed by the unilateral centrifugation test
Authors: L. Wuyts Floris , Hoppenbrouwers Mieke , Pauwels Griet , Van de Heyning Paul H.
Published: September 2021

Utricular sensitivity and preponderance of the right or left utricle can be assessed by means of the unilateral centrifugation test. In this test, subjects are rotated about an earth vertical axis at a velocity of 400 degrees per second. During the ongoing rotation, the subject is gradually translated 4 cm first to the right, and then to the left, along an interaural axis, to a position at which one utricle becomes aligned with the axis of rotation, and at this point is subjected only to gravitational forces. At this eccentric position, the contralateral utricle is exposed to the combination of gravity and a centrifugal acceleration of 0.4g, corresponding to an apparent roll-tilt of 21.7 degrees. This stimulus induces ocular counterrolling (OCR), which is measured on-line using three-dimensional video-oculography (VOG). We observed that ocular counterrolling appears as a linear function of the gravito-inertial acceleration tilt of the head centre (GIA H C ) during the lateral translation. We present a theoretical model for this linear relationship that contains two parameters: 1) the slope of the linear regression is a measure for the utricular sensitivity and 2) the intercept of the linear regression is a measure of the preponderance of the right or left utricle. The strength of the model is supported by data obtained from 28 healthy subjects and 14 patients with unilateral vestibular deafferentiation (UVD) due to acoustic neuroma surgery.
Ocular and perceptual responses to linear acceleration in microgravity: Alterations in otolith function on the COSMOS and Neurolab flights
Authors: Moore Steven T. , Clément Gilles , Dai Mingjai , Raphan Theodore , Solomon David , Cohen Bernard
Published: September 2021

In this paper we review space flight experiments performed by our laboratory. Rhesus monkeys were tested before and after 12 days in orbit on COSMOS flights 2044 (1989) and 2229 (1992–1993). There was a long-lasting decrease in post-flight ocular counter-rolling (70%) and vergence (50%) during off-vertical axis rotation. In one animal, the orientation of optokinetic after-nystagmus shifted by 28° from the spatial vertical towards the body vertical early post-flight. Otolith-ocular and perceptual responses were also studied in four astronauts on the 17-day Neurolab shuttle mission (STS-90) in 1998. Ocular counter-rolling was unchanged in response to 1-g and 0.5-g Gy centrifugation during and after flight and to post-flight static roll tilts relative to pre-flight values. Orientation of the optokinetic nystagmus eye velocity axis to gravito-inertial acceleration (GIA) during centrifugation was also unaltered by exposure to microgravity. Perceptual orientation to the GIA was maintained in-flight, and subjects did not report sensation of translation during constant velocity centrifugation. These studies suggest that percepts and ocular responses to tilt are determined by sensing the body vertical relative to the GIA. The findings also raise the possibility that 'artificial gravity' during the Neurolab flight counteracted adaptation of these otolith-ocular responses.
Cortical vestibular representation in the superior temporal gyrus
Authors: Hegemann Stefan , Fitzek Sabine , Fitzek Clemens , Fetter Michael
Published: September 2021

We present the unique case of a patient with a circumscribed solitary cerebral metastasis of a malignant melanoma extending from the medial part of the superior temporal gyrus to the lower part of the 1st long insular gyrus causing gait and stance instability and an ipsiversive tilt of the subjective visual vertical. Oculomotor disorders could not be detected. We suggest that the superior temporal gyrus is likely to be involved in spatial orientation presumably using otolithic information.
Postural responses exhibit multisensory dependencies with discordant visual and support surface motion
Authors: Keshner Emily A. , Kenyon Robert V. , Langston Jessica
Published: September 2021

The purpose of this study was to identify how the postural system weights coincident yet discordant disturbances of the visual and proprioceptive/vestibular systems. Eleven healthy subjects (25–38 yrs) received either fore-aft translations of an immersive, wide field-of-view visual environment (0.1 Hz, ± 3.7 m/sec), or anterior-posterior translations of the support surface (0.25 Hz, ± 15 cm/sec), or both concurrently. Kinematics of the head, trunk, and shank were collected with an Optotrak system and angular motion of each segment plotted across time. With only support surface translation, segmental responses were small (1°–2°) and mostly opposed the direction of sled translation. When only the visual scene was moving, segmental responses increased as the trial progressed. When the inputs were presented coincidentally, response amplitudes were large even at the onset of the trial. Mean RMS values across subjects were significantly greater with combined stimuli than for either stimulus presented alone and areas under the power curve across subjects were significantly increased at the frequency of the visual input when both inputs were presented. Thus, intra-modality dependencies were observed, such that responses to the visual inputs significantly increased and responses to the somatosensory signals reflected the stimulus amplitude only when the two inputs were combined. We believe it unlikely that the role of any single pathway contributing to postural control can be accurately characterized in a static environment if the function of that pathway is context dependent.
Head positioning control in a gravito-inertial field and in normal gravity
Authors: Sarès Frédéric , Bourdin Christophe , Prieur Jean-Michel , Vercher Jean-Louis , Menu Jean-Pierre , Gauthier Gabriel M.
Published: September 2021

The way in which the head is controlled in roll was investigated by dissociating the body axis and the gravito-inertial force orientation. Seated subjects (N = 8) were requested to align their head with their trunk, 30° to the left, 30° to the right or with the gravito-inertial vector, before, during (Per Rotation), after off-center rotation and on a tilted chair without rotation (Tilted). The gravito-inertial vector angle during rotation and the chair tilt angle were identical (17°). The subjects were either in total darkness or facing a visual frame that was fixed to the trunk. Both final error and within-subject variability of head positioning increased when the body axis and the gravito-inertial vector were dissociated (Per Rotation and Tilted). However, the behavior was different depending on whether the subjects were in the Tilted or Per Rotation conditions. The presentation of the visual frame reduced the within-subject variability and modified the perception of the gravito-inertial vector's orientation on the tilted chair. As head positioning with respect to the body and sensing of the gravito-inertial vector are modified when body axis and gravito-inertial vector orientation are dissociated, the observed decrease in performance while executing motor tasks in a gravito-inertial field may be at least in part attributed to the inaccurate sensing of head position.
The effects of state of alertness on the vestibulo-ocular reflex in normal subjects using the vestibular rotational chair
Authors: Matta F.V. , Enticott J.C.
Published: September 2021

Twenty-four subjects with normal vestibular function underwent horizontal sinusoidal harmonic acceleration (SHA) and step-velocity rotational chair assessment twice, first in a heightened state-of-alertness, and second, in a low state-of-alertness. The effects of alertness on vestibulo-ocular reflex gain and time-constant (Tc) were then examined. Although the negative effect on SHA gain had previously been widely reported, the effect on the Tc had not been studied. It was found that SHA gain and step-velocity Tc were significantly and artificially reduced with decreased alertness. On average, SHA gain was reduced by 0.1 at each test frequency and the Tc was reduced from 15.8 seconds to 10.5 seconds. Whilst on average, step-velocity initial gain was only a little affected reducing from 0.53 to 0.49. This very small difference of 0.04 was significant, however, it suggested that this measurement is less affected by patient alertness than SHA gain and Tc.
Nitric oxide synthase and arginase expression changes in the rat perirhinal and entorhinal cortices following unilateral vestibular damage: A link to deficits in object recognition?
Authors: Liu Ping , Gliddon Catherine M. , Lindsay Libby , Darlington Cynthia L. , Smith Paul F.
Published: September 2021

Previous studies have shown that peripheral vestibular damage causes long-term neurochemical changes in the hippocampus which may be related to spatial memory deficits. Since recent studies have also demonstrated deficits in non-spatial object recognition memory following vestibular lesions, the aim of the present study was to extend these investigations into the perirhinal cortex (PRC), which is known to be important for object recognition, and the related entorhinal cortex (EC). We examined the effects of unilateral vestibular deafferentation (UVD) on the expression of four enzymes associated with neuronal plasticity, neuronal nitric oxide synthase (nNOS), endothelial nitric oxide synthase (eNOS), arginase I and arginase II (AI and II), in the rat EC and PRC using Western blotting. Tissue was collected at 10 hs, 50 hs and 2 weeks post-UVD. In the EC and PRC, nNOS protein expression decreased on the contralateral side at 2 weeks post-UVD but not before. At the same time, eNOS protein expression increased in both regions on the contralateral side. In the EC, AII protein expression increased on the ipsilateral side at 2 weeks post-UVD. In the PRC, AI increased and decreased on the contralateral and ipsilateral sides (respectively) at 2 weeks post-UVD. AII showed a bilateral increase in the PRC at 2 weeks post-UVD. These results demonstrate changes in NOS and arginase protein expression in the PRC and EC following UVD, which are unlikely to be due to the initial severity of the vestibular syndrome because they develop well after vestibular compensation has taken place. Neurochemical changes in these regions of the medial temporal lobe may be implicated in the development of object recognition deficits that contribute to cognitive dysfunction following peripheral vestibular damage.
Biomechanics of horizontal canal benign paroxysmal positional vertigo
Authors: Rajguru Suhrud M. , Ifediba Marytheresa A. , Rabbitt Richard D.
Published: September 2021

Horizontal canal (HC) benign paroxysmal positional vertigo (HC-BPPV) is a vestibular disorder characterized by bouts of horizontal ocular nystagmus induced during reorientation of the head relative to gravity. The present report addresses the application of a morphologically descriptive 3-canal biomechanical model of the human membranous labyrinth to study gravity-dependent semicircular canal responses during this condition. The model estimates dynamic cupular and endolymph displacements elicited during HC-BPPV provocative diagnostic maneuvers and canalith repositioning procedures (CRPs). The activation latencies in response to an HC-BPPV provocative diagnostic test were predicted to vary depending upon the initial location of the canalith debris (e.g. within the HC lumen vs. in the ampulla). Results may explain why the onset latency of ocular nystagmus evoked by the Dix-Hallpike provocative maneuver for posterior canal BPPV are typically longer than the latencies evoked by analogous tests for HC-BPPV. The model was further applied to assess the efficacy of a 360°-rotation CRP for the treatment of canalithiasis HC-BPPV.
Effects of head orientation and lateral body tilt on egocentric coding: Cognitive and sensory-motor accuracy
Authors: Prieur J.-M. , Bourdin C. , Sarès F. , Vercher J.-L.
Published: September 2021

A major issue in motor control studies is to determine whether and how we use spatial frames of reference to organize our spatially oriented behaviors. In previous experiments [2,16] we showed that simulated body tilt during off-axis rotation affected the performance in verbal localization and manual pointing tasks. It was hypothesized that the observed alterations were at least partly due to a change in the orientation of the egocentric frame of reference, which was indeed centered on the body but aligned with the gravitational vector. The present experiments were designed to test this hypothesis in a situation where no inertial constraints (except the usual gravitational one) exist and where the orientation of the body longitudinal z-axis was not aligned with the direction of the gravity. Eleven subjects were exposed to real static body tilt and were required to verbally localize (experiment 1) and to point as accurately as possible towards (experiment 2) memorized visual targets, in two conditions, Head-Free and Head-Fixed conditions. Results show that the performance was only affected by real body tilt in the localization task performed when the subject's head was tilted relative to the body. Thus, dissociation between gravity and body longitudinal z-axis alone is not responsible for localization nor for pointing errors. Therefore, the egocentric frame of reference seems independent from the orientation of the gravity with regard to body z-axis as expected from our previous studies. Moreover, the use of spatial referentials appears to be less mandatory than expected for pointing movements (motor task) than for localization task (cognitive task).