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    [Show abstract] [Hide abstract] ABSTRACT: Trains that tilt on curves can go faster, but passengers complain of motion sickness. We studied the control signals and tilts to determine why this occurs and how to maintain speed while eliminating motion sickness. Accelerometers and gyros monitored train and passenger yaw and roll, and a survey evaluated motion sickness. The experimental train had 3 control configurations: an untilted mode, a reactive mode that detected curves from sensors on the front wheel set, and a predictive mode that determined curves from the train's position on the tracks. No motion sickness was induced in the untilted mode, but the train ran 21% slower than when it tilted 8° in either the reactive or predictive modes (113 vs. 137 km/h). Roll velocities rose and fell faster in the predictive than the reactive mode when entering and leaving turns (0.4 vs. 0.8 s for a 4°/s roll tilt, P<0.001). Concurrently, motion sickness was greater (P<0.001) in the reactive mode. We conclude that the slower rise in roll velocity during yaw rotations on entering and leaving curves had induced the motion sickness. Adequate synchronization of roll tilt with yaw velocity on curves will reduce motion sickness and improve passenger comfort on tilting trains.
    Full-text · Article · Jul 2011 · The FASEB Journal
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    [Show abstract] [Hide abstract] ABSTRACT: We investigated spatial responses of the aVOR to small and large accelerations in six canal-plugged and lateral canal nerve-sectioned monkeys. The aim was to determine whether there was spatial adaptation after partial and complete loss of all inputs in a canal plane. Impulses of torques generated head thrusts of ≈ 3,000°/s². Smaller accelerations of ≈ 300°/s² initiated the steps of velocity (60°/s). Animals were rotated about a spatial vertical axis while upright (0°) or statically tilted fore-aft up to ± 90°. Temporal aVOR yaw and roll gains were computed at every head orientation and were fit with a sinusoid to obtain the spatial gains and phases. Spatial gains peaked at ≈ 0° for yaw and ≈ 90° for roll in normal animals. After bilateral lateral canal nerve section, the spatial yaw and roll gains peaked when animals were tilted back ≈ 50°, to bring the intact vertical canals in the plane of rotation. Yaw and roll gains were identical in the lateral canal nerve-sectioned monkeys tested with both low- and high-acceleration stimuli. The responses were close to normal for high-acceleration thrusts in canal-plugged animals, but were significantly reduced when these animals were given step stimuli. Thus, high accelerations adequately activated the plugged canals, whereas yaw and roll spatial aVOR gains were produced only by the intact vertical canals after total loss of lateral canal input. We conclude that there is no spatial adaptation of the aVOR even after complete loss of specific semicircular canal input.
    Full-text · Article · Feb 2011 · Experimental Brain Research
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    Mingjia Dai · Ted Raphan · Bernard Cohen
    [Show abstract] [Hide abstract] ABSTRACT: The angular vestibulo-ocular reflex (aVOR) and optokinetic nystagmus (OKN) were elicited simultaneously at low frequencies to study effects of habituation of the velocity storage time constant in the vestibular system on motion sickness. Twenty-nine subjects, eleven of whom were susceptible to motion sickness from common transportation, were habituated by sinusoidal rotation at 0.017 Hz at peak velocities from 5 to 20°/s, while they watched a full-field OKN stimulus. The OKN stripes rotated in the same direction and at the same frequency as the subjects, but at a higher velocity. This produced an OKN opposite in direction to the aVOR response. Motion sickness sensitivity was evaluated with off-vertical axis rotation (OVAR) and by the response to transportation before and after 5 days of visual-vestibular habituation. Habituation did not induce motion sickness or change the aVOR gains, but it shortened the vestibular time constants in all subjects. This greatly reduced motion sickness produced by OVAR and sensitivity to common transport in the motion susceptible subjects, which persisted for up to 18 weeks. Two motion susceptible subjects who only had aVOR/OKN habituation without being tested with OVAR also became asymptomatic. Normal subjects who were not habituated had no reduction in either their aVOR time constants or motion sickness sensitivity. The opposing aVOR/OKN stimulation, which has not been studied before, was well tolerated, and for the first time was an effective technique for rapid and prolonged habituation of motion sickness without exposure to drugs or other nauseating habituation stimuli.
    Preview · Article · Feb 2011 · Experimental Brain Research
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    [Show abstract] [Hide abstract] ABSTRACT: We tested the hypothesis that motion sickness is produced by an integration of the disparity between eye velocity and the yaw-axis orientation vector of velocity storage. Disparity was defined as the magnitude of the cross product between these two vectors. OVAR, which is known to produce motion sickness, generates horizontal eye velocity with a bias level related to velocity storage, as well as cyclic modulations due to re-orientation of the head re gravity. On average, the orientation vector is close to the spatial vertical. Thus, disparity can be related to the bias and tilt angle. Motion sickness sensitivity was defined as a ratio of maximum motion sickness score to the number of revolutions, allowing disparity and motion sickness sensitivity to be correlated. Nine subjects were rotated around axes tilted 10 degrees-30 degrees from the spatial vertical at 30 degrees/s-120 degrees/s. Motion sickness sensitivity increased monotonically with increases in the disparity due to changes in rotational velocity and tilt angle. Maximal motion sickness sensitivity and bias (6.8 degrees/s) occurred when rotating at 60 degrees/s about an axis tilted 30 degrees. Modulations in eye velocity during OVAR were unrelated to motion sickness sensitivity. The data were predicted by a model incorporating an estimate of head velocity from otolith activation, which activated velocity storage, followed by an orientation disparity comparator that activated a motion sickness integrator. These results suggest that the sensory-motor conflict that produces motion sickness involves coding of the spatial vertical by the otolith organs and body tilt receptors and processing of eye velocity through velocity storage.
    Preview · Article · Jul 2010 · Experimental Brain Research
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    Mingjia Dai · Theodore Raphan · Bernard Cohen
    [Show abstract] [Hide abstract] ABSTRACT: Head movements in a rotating frame of reference are commonly encountered, but their long term effects on the angular vestibulo-ocular reflex (aVOR) are not well understood. To study this, monkeys were oscillated about a naso-occipital (roll) axis for several hours while rotating about a spatial vertical axis (roll-while-rotating, RWR). This induced oscillations in roll and pitch eye velocity and continuous horizontal (yaw) nystagmus. For several hours thereafter, simple roll in darkness induced horizontal nystagmus and pitch and roll oscillations. The rising and falling time constants of the horizontal velocity indicated that the nystagmus arose in velocity storage. The continuous nystagmus was correlated with a phase shift of vertical eye velocity from 90 degrees to 0 degrees re head position. As the phases reverted toward pre-adaptive values, the horizontal velocity declined. Similar yaw nystagmus and pitch and roll velocities were produced by oscillation in roll after adaptation with roll and horizontal optokinetic nystagmus (OKN), but not after adaptation with pitch-while-rotating (PWR). Findings were explained by a model that shifted the roll orientation vector of velocity storage toward the pitch axis during adaptation with RWR and Roll & OKN. This shift produced modulation in vertical eye velocity in the post adaptive state, which was approximately in phase with roll head position, generating horizontal nystagmus. Similar orientation changes to prolonged exposure to complex motion environments may be responsible for producing post-stimulus motion sickness and/or mal de debarquement.
    Preview · Article · Jun 2009 · Experimental Brain Research
  • [Show abstract] [Hide abstract] ABSTRACT: Reduction of the dominant time constant (T(VOR)) of the angular vestibulo-ocular reflex (aVOR) by habituation is associated with a decrease in motion sickness susceptibility. Baclofen, a GABA(b) agonist, reduces the time constant of the velocity storage integrator in the aVOR in a dose-dependent manner. The high frequency aVOR gain is unaltered by baclofen. Here we demonstrate that the reduction in T(VOR) produced by oral administration of 20 mg of baclofen causes a significant reduction in motion sickness susceptibility, tested with roll while rotating (RWR). These data show that motion sickness susceptibility can be pharmacologically manipulated with a GABA(b) agonist and support our conclusion that motion sickness is generated through velocity storage. We also show how baclofen acts on velocity storage at the neural level. A vestibular-plus-saccade (VPS) neuron was recorded in the rostral medial vestibular nucleus (rMVN) of a cynomolgus monkey, an area where we postulate that velocity storage is generated. The cell had a time constant during steps of velocity that was close to that of the T(VOR). After parenteral administration of baclofen, there was a similar decrease in the time constants of the VPS neuron and the T(VOR). This is the first demonstration of the concurrence of unit and aVOR time constants before and after baclofen. The data support the hypothesis that the velocity storage integrator is generated through activity of vestibular-only (VO) and VPS neurons in rMVN and suggest that GABA(b) synapses on VO and VPS neurons are likely to be involved in the baclofen-induced reduction in motion sickness susceptibility.
    No preview · Article · Feb 2008 · Progress in brain research
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    Mingjia Dai · Theodore Raphan · Bernard Cohen
    [Show abstract] [Hide abstract] ABSTRACT: The angular vestibulo-ocular reflex (aVOR) has a fast pathway, which mediates compensatory eye movements, and a slow (velocity storage) pathway, which determines its low frequency characteristics and orients eye velocity toward gravity. We have proposed that motion sickness is generated through velocity storage, when its orientation vector, which lies close to the gravitational vertical, is misaligned with eye velocity during head motion. The duration of the misalignment, determined by the dominant time constant of velocity storage, causes the buildup of motion sickness. To test this hypothesis, we studied bilateral labyrinthine-defective subjects with short vestibular time constants but normal aVOR gains for their motion sickness susceptibility. Time constants and gains were taken from rotational responses. Motion sickness was generated by rolling the head while rotating, and susceptibility was assessed by the number of head movements made before reaching intolerable levels of nausea. More head movements signified lower motion sickness susceptibility. Labyrinthine-defective subjects made more head movements on their first exposure to roll while rotating than normals (39.8 +/- 7.2 vs 13.7 +/- 5.5; P < 0.0001). Normals were tested eight times, which habituated their time constants and reduced their motion sickness susceptibility. Combining data from all subjects, there was a strong inverse relationship between time constants and number of head movements (r = 0.94), but none between motion sickness susceptibility and aVOR gains. This provides further evidence that motion sickness is generated through velocity storage, not the direct pathway, and suggests that motion sickness susceptibility can be reduced by reducing the aVOR time constant.
    Preview · Article · May 2007 · Experimental Brain Research
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    Mingjia Dai · Theodore Raphan · Bernard Cohen
    [Show abstract] [Hide abstract] ABSTRACT: The purpose of this study was to determine the effect of baclofen, a GABA(B) agonist on the angular vestibulo-ocular reflex (aVOR). Model studies have shown that the aVOR comprises a "direct" pathway, which determines its high frequency gain g (1), and an indirect "velocity storage" pathway, which determines its low frequency characteristics. Velocity storage can be characterized by an integrator with a dominant time constant, T (VOR), and a gain g (0) that couples afferent information from the semicircular canals to the integrator. Baclofen preferentially shortens the velocity storage time constant in monkeys, but its effect on T (VOR), g (0), and g (1) in humans is unknown. Six subjects were tested after administration of a placebo or of 10, 20, or 30 mg of baclofen in a double-blind design. The aVOR was elicited in darkness with steps of rotation at 138 degrees /s, and g (1), g (0), and T (VOR) were determined from model fits of the slow phase velocity of the per- and post-rotatory nystagmus. Baclofen significantly reduced both T (VOR) and g (0) at dosages of 20 and 30 mg, but had no effect on g (1). Small reductions in g (0) were associated with large reductions in vestibular output. Thus, baclofen does not affect the direct aVOR pathway in humans, but controls the low frequency aVOR in two ways: it limits the input to velocity storage and modulates its time constant. We speculate that pre-synaptic GABA(B) terminals in the vestibular nuclei are responsible for the control of the afferent input to velocity storage through g (0), while the post-synaptic GABA(B) terminals are responsible for altering the duration of activity that reflects the time constant. The lack of effect of baclofen on the aVOR gain suggests that only GABA(A) receptors are utilized in the direct aVOR pathway.
    Preview · Article · Jun 2006 · Experimental Brain Research
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    [Show abstract] [Hide abstract] ABSTRACT: It is clear that cellular and subcellular constituents of the vestibular pathways are modified in response to altered gravitational stimuli. In the vestibular periphery, opposite structural effects appear to result from hypo- and hyper-gravity stimulation. In the central vestibular system, neural circuits may well exhibit apparently identical structural changes in response to diverse hypo- and hyper-gravity stimuli, reflecting the more dynamic, highly regulated interactions of the central pathways. More research will be needed to resolve the inconsistencies in the current published literature.
    Full-text · Article · Feb 2005 · Advances in Space Biology and Medicine
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    Bernard Cohen · Mingjia Dai · Theodore Raphan
    [Show abstract] [Hide abstract] ABSTRACT: We propose that motion sickness is mediated through the orientation properties of velocity storage in the vestibular system that tend to align eye velocity produced by the angular vestibulo-ocular reflex (aVOR) with gravito-inertial acceleration (GIA). (GIA is the sum of the linear accelerations acting on the head. In the absence of translational accelerations, gravity is the GIA.) We further postulate that motion sickness produced by cross-coupled vestibular stimulation can be characterized by a metric composed of the disparity between the axis of eye rotation and the GIA, the strength of the response to angular motion, and the response duration, as determined by the central vestibular time constant, that is, by the time constant of velocity storage. The nodulus and uvula of the vestibulocerebellum are likely to be the central sites where the disparity is sensed, where the vestibular time constants are habituated, and where links are made to the autonomic system to produce the symptoms and signs.
    Preview · Article · Nov 2003 · Annals of the New York Academy of Sciences
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    [Show abstract] [Hide abstract] ABSTRACT: Tilting the head in roll to or from the upright while rotating at a constant velocity (roll while rotating, RWR) alters the position of the semicircular canals relative to the axis of rotation. This produces vertical and horizontal nystagmus, disorientation, vertigo, and nausea. With recurrent exposure, subjects habituate and can make more head movements before experiencing overpowering motion sickness. We questioned whether promethazine lessened the vertigo or delayed the habituation, whether habituation of the vertigo was related to the central vestibular time constant, i.e., to the time constant of velocity storage, and whether the severity of the motion sickness was related to deviation of the axis of eye velocity from gravity. Sixteen subjects received promethazine and placebo in a double-blind, crossover study in two consecutive 4-day test series 1 month apart, termed series I and II. Horizontal and vertical eye movements were recorded with video-oculography while subjects performed roll head movements of approx. 45 degrees over 2 s to and from the upright position while being rotated at 138 degrees /s around a vertical axis. Motion sickness was scaled from 1 (no sickness) to an endpoint of 20, at which time the subject was too sick to continue or was about to vomit. Habituation was determined by the number of head movements that subjects made before reaching the maximum motion sickness score of 20. Head movements increased steadily in each session with repeated testing, and there was no difference between the number of head movements made by the promethazine and placebo groups. Horizontal and vertical angular vestibulo-ocular reflex (aVOR) time constants declined in each test, with the declines being closely correlated to the increase in the number of head movements. The strength of vertiginous sensation was associated with the amount of deviation of the axis of eye velocity from gravity; the larger the deviation of the eye velocity axis from gravity, the more severe the motion sickness. Thus, promethazine neither reduced the nausea associated with RWR, nor retarded or hastened habituation. The inverse relationship between the aVOR time constants and number of head movements to motion sickness, and the association of the severity of motion sickness with the extent, strength, and time of deviation of eye velocity from gravity supports the postulate that the spatiotemporal properties of velocity storage, which are processed between the nodulus and uvula of the vestibulocerebellum and the vestibular nuclei, are likely to represent the source of the conflict responsible for producing motion sickness.
    Preview · Article · Aug 2003 · Experimental Brain Research
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    [Show abstract] [Hide abstract] ABSTRACT: Activation of the gravity sensors in the inner ear-the otoliths-generates reflexes that act to maintain posture and gaze. Ocular counter-rolling (OCR) is an example of such a reflex. When the head is tilted to the side, the eyes rotate around the line of sight in the opposite direction (i.e., counter-rolling). While turning comers, undergoing centrifugation, or making side-to-side tilting head movements, the OCR reflex orients the eyes towards the sum of the accelerations from body movements and gravity. Deconditioning of otolith-mediated reflexes following adaptation to microgravity has been proposed as the basis of many of the postural, locomotor, and gaze control problems experienced by returning astronauts. Evidence suggests that OCR is reduced postflight in about 75% of astronauts tested; but the data are sparse, primarily due to difficulties in recording rotational eye movements. During the Neurolab mission, a short-arm human centrifuge was flown that generated sustained sideways accelerations of 0.5-G and one-G to the head and upper body. This produces OCR; and so for the first time, the responses to sustained centrifugation could be studied without the influence of Earth's gravity on the results. This allowed us to determine the relative importance of sideways and vertical acceleration in the generation of OCR. This also provided the first test of the effects of exposure to artificial gravity in space on postflight otolith-ocular reflexes. There was little difference between the responses to centrifugation in microgravity and on Earth. In both conditions, the induced OCR was roughly proportional to the applied acceleration, with the OCR magnitude during 0.5-G centrifugation approximately 60% of that generated during one-G centrifugation. The overall mean OCR from the four payload crewmembers in response to one-G of sideways acceleration was 5.7 plus or minus 1.1 degree (mean and SD) on Earth. Inflight one-G centrifugation generated 5.7 plus or minus 1.1 degree of OCR, which was a small but significant decrease in OCR magnitude. The postflight OCR was 5.9 plus or minus 1.4 degree, which was not significantly different from preflight values. During both 0.5-G and one-G centrifugation in microgravity, where the head vertical gravitational component was absent, the OCR magnitude was not significantly different from that produced by an equivalent acceleration during static tilt on Earth. This suggests that the larger OCR magnitude observed during centrifugation on Earth was due to the larger body vertical linear acceleration component, which may have activated either the otoliths or the body tilt receptors. In contrast to previous studies, there was no decrease in OCR gain postflight. Our findings raise the possibility that inflight exposure to artificial gravity, in the form of intermittent one-G and 0.5-G centripetal acceleration, may have been a countermeasure to deconditioning of otolith-based orientation reflexes.
    Full-text · Article · Feb 2003
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    [Show abstract] [Hide abstract] ABSTRACT: Nystagmus induced by off-vertical axis rotation (OVAR) about a head yaw axis is composed of a yaw bias velocity and modulations in eye position and velocity as the head changes orientation relative to gravity. The bias velocity is dependent on the tilt of the rotational axis relative to gravity and angular head velocity. For axis tilts <15 degrees, bias velocities increased monotonically with increases in the magnitude of the projected gravity vector onto the horizontal plane of the head. For tilts of 15-90 degrees, bias velocity was independent of tilt angle, increasing linearly as a function of head velocity with gains of 0.7-0.8, up to the saturation level of velocity storage. Asymmetries in OVAR bias velocity and asymmetries in the dominant time constant of the angular vestibuloocular reflex (aVOR) covaried and both were reduced by administration of baclofen, a GABA(B) agonist. Modulations in pitch and roll eye positions were in phase with nose-down and side-down head positions, respectively. Changes in roll eye position were produced mainly by slow movements, whereas vertical eye position changes were characterized by slow eye movements and saccades. Oscillations in vertical and roll eye velocities led their respective position changes by approximately 90 degrees, close to an ideal differentiation, suggesting that these modulations were due to activation of the orienting component of the linear vestibuloocular reflex (lVOR). The beating field of the horizontal nystagmus shifted the eyes 6.3 degrees /g toward gravity in side down position, similar to the deviations observed during static roll tilt (7.0 degrees /g). This demonstrates that the eyes also orient to gravity in yaw. Phases of horizontal eye velocity clustered ~180 degrees relative to the modulation in beating field and were not simply differentiations of changes in eye position. Contributions of orientating and compensatory components of the lVOR to the modulation of eye position and velocity were modeled using three components: a novel direct otolith-oculomotor orientation, orientation-based velocity modulation, and changes in velocity storage time constants with head position re gravity. Time constants were obtained from optokinetic after-nystagmus, a direct representation of velocity storage. When the orienting lVOR was combined with models of the compensatory lVOR and velocity estimator from sequential otolith activation to generate the bias component, the model accurately predicted eye position and velocity in three dimensions. These data support the postulates that OVAR generates compensatory eye velocity through activation of velocity storage and that oscillatory components arise predominantly through lVOR orientation mechanisms.
    Full-text · Article · Dec 2002 · Journal of Neurophysiology
  • [Show abstract] [Hide abstract] ABSTRACT: The spatial orientation of the slow-phase eye velocity of caloric nystagmus was investigated in cynomolgus monkeys after all six semicircular canals had been plugged. Normal animals generate responses that have dominant convective components produced by movement of the endolymph in the lateral canal toward or away from gravity. As a result, the direction of horizontal slow-phase velocity induced by cold-water irrigation changes direction with changes in head position with regard to gravity. Plugging produced a dense overgrowth of bone that blocked the flow of endolymph, but the end organs were intact. Robust caloric nystagmus was elicited after recovery, but the horizontal (yaw) component was now always toward the stimulated (ipsilateral) side, regardless of head position re gravity. The induced caloric nystagmus had strong spatial orientation properties after canal plugging. With animals upright, the three-dimensional velocity vector of the caloric nystagmus was close to the yaw axis with small vertical and roll components. Roll components became stronger in supine and prone positions and vertical components were enhanced in the right- and left-side down positions. In each instance, the addition of the roll and vertical components moved the velocity vector of the nystagmus closer to the spatial vertical. Modeling supported the postulate that the caloric nystagmus after canal plugging is influenced by three factors: (1) a reduction in neural activity in the ampullary nerves on the stimulated side due to cooling of the nerves; (2) contraction of the endolymph in the closed space between the cupula and the plug due to cooling, which resulted in deflection of the cupula and hair cells toward the plug (ampullofugal deflection); and (3) alignment of eye velocity to gravity due to the orientation properties of velocity storage. Although convection is the most prominent factor in producing caloric responses in the normal state, our results suggest that alteration of nerve activity due to thermal effects, endolymph contraction or expansion, and velocity storage are also likely to contribute to the total response.
    No preview · Article · May 2002 · Annals of the New York Academy of Sciences
  • [Show abstract] [Hide abstract] ABSTRACT: Horizontal movements of both eyes were recorded simultaneously using scleral search coils in 2 rhesus monkeys before and after the COSMOS 2229 spaceflight of 1992–1993. Another 9 monkeys were tested at comparable time intervals and served as controls. Ocular vergence, defined as the difference in horizontal position between the left and right eyes, was measured during off-vertical yaw axis rotation (OVAR) in darkness. Vergence was modulated sinusoidally as a function of head position with regard to gravity during OVAR. The amplitude of peak-to-peak modulation increased with increments in tilt of the angle of the rotational axis (OVAR tilt angle) that ranged from 15 to 90. Of the 11 monkeys tested, 1 had no measurable modulation in vergence. In the other 10, the mean amplitude of the peak to peak modulation was 5.51.3 at 90 tilt. Each of these monkeys had maximal vergence when its nose was pointed close to upward (gravity back; mean phase: -0.926). After space flight, the modulation in vergence was reduced by over 50% for the two flight monkeys, but the phase of vergence modulation was not altered. The reduction in vergence modulation was sustained for the 11-day postflight testing period. We conclude that changes in vergence are induced in monkeys by the sinusoidal component of gravity acting along the naso-occipital axis during yaw axis OVAR, and that the modulation of the vergence reflex is significantly less sensitive to linear acceleration after space flight.
    No preview · Article · Jan 1996 · Experimental Brain Research
  • [Show abstract] [Hide abstract] ABSTRACT: We recorded the horizontal (yaw), vertical (pitch), and torsional (roll) eye movements of two rhesus monkeys with scierai search coils before and after the COSMOS Biosatellite 2229 Flight. The aim was to determine effects of adaptation to microgravity on the vestibulo-ocular reflex (VOR). The animals flew for 11 days. The first postflight tests were 22 h and 55 h after landing, and testing extended for 11 days after reentry. There were four significant effects of spaceflight on functions related to spatial orientation: (1) Compensatory ocular counterrolling (OCR) was reduced by about 70% for static and dynamic head tilts with regard to gravity. The reduction in OCR persisted in the two animals throughout postflight testing. (2) The gain of the torsional component of the angular VOR (roll VOR) was decreased by 15% and 50% in the two animals over the same period. (3) An up-down asymmetry of nystagmus, present in the two monkeys before flight was reduced after exposure to microgravity. (4) The spatial orientation of velocity storage was shifted in the one monkey that could be tested soon after flight. Before flight, the yaw axis eigenvector of optokinetic afternystagmus was close to gravity when the animal was upright or tilted. After flight, the yaw orientation vector was shifted toward the body yaw axis. By 7 days after recovery, it had reverted to a gravitational orientation. We postulate that spaceflight causes changes in the vestibular system which reflect adaptation of spatial orientation from a gravitational to a body frame of reference. These changes are likely to play a role in the postural, locomotor, and gaze instability demonstrated on reentry after spaceflight.
    No preview · Article · Dec 1993 · Experimental Brain Research
  • [Show abstract] [Hide abstract] ABSTRACT: We studied the three-dimensional vestibulo-ocular reflex (VOR) of rhesus monkeys before and after the COSMOS Biosatellite 2229 Mission of 1992-1993. This included tests of ocular counter-rolling (OCR), the gain of the vestibulo-ocular reflex (VOR), and spatial orientation of velocity storage. A four-axis vestibular and oculomotor stimulator was transported to the Institute of Biomedical Problems in Moscow for the pre- and postflight ground-based testing. Twelve normal juvenile male rhesus monkey were implanted surgically with eye coils and tested 60-90 days before spaceflight. Two monkey (7906 and 6151), selected from the twelve as flight animals, flew from 12/29/92 to 1/10/93. Upon recovery, they were tested for 11 days postflight along with three control animals. Compensatory ocular torsion was produced in two ways: (1) Lateral head tilts evoked OCR through otolith-ocular reflexes. OCR was also measured dynamically during off-vertical axis rotation (OVAR). (2) Rotation about a naso-occipital axis that was either vertical of horizontal elicited torsional nystagmus through semicircular canal-ocular reflexes (roll VOR). OCR from the otoliths was substantially reduced (70 percent) for 11 days after reentry on both modes of testing. The gain of the roll VOR was also decreased, but less than OCR. These data demonstrate that there was a long-lasting depression of torsional or roll eye movements after adaptation to microgravity in these monkeys, especially those movements produced by the otolith organs.
    No preview · Article · Dec 1993
  • Theodore Raphan · Mingjia Dai · Bernard Cohen
    [Show abstract] [Hide abstract] ABSTRACT: 1. A simplified three-dimensional state space model of visual vestibular interaction was formulated. Matrix and dynamical system operators representing coupling from the semicircular canals and the visual system to the velocity storage integrator were incorporated into the model. 2. It was postulated that the system matrix for a tilted position was a composition of two linear transformations of the system matrix for the upright position. One transformation modifies the eigenvalues of the system matrix while another rotates the pitch and roll eigenvectors with the head, while maintaining the yaw axis eigenvector approximately spatially invariant. Using this representation, the response characteristics of the pitch, roll, and yaw eye velocity were obtained in terms of the eigenvalues and associated eigenvectors. 3. Using OKAN data obtained from monkeys and comparing to the model predictions, the eigenvalues and eigenvectors of the system matrix were identified as a function of tilt to the side or of tilt to the prone positions, using a modification of the Marquardt algorithm. The yaw eigenvector for right-side-down tilt and for downward pitch cross-coupling was approximately 30 degrees from the spatial vertical. For the prone position, the eigenvector was computed to be approximately 20 degrees relative to the spatial vertical. For both side-down and prone positions, oblique OKN induced along eigenvector directions generated OKAN which decayed to zero along a straight line with approximately a single time constant. This was verified by a spectral analysis of the residual sequence about the straight line fit to the decaying data. The residual sequence was associated with a narrow autocorrelation function and a wide power spectrum. 4. Parameters found using the Marquardt algorithm were incorporated into the model. Diagonal matrices in a head coordinate frame were introduced to represent the direct pathway and the coupling of the visual system to the integrator. Model simulations predicted the behavior of yaw and pitch OKN and OKAN when the animal was upright, as well as the cross-coupling in the tilted position. The trajectories in velocity space were also accurately simulated. 5. There were similarities between the monkey eigenvectors and human perception of the spatial vertical. For side-down tilts and downward eye velocity cross-coupling, there was only an Aubert (A) effect. For upward eye velocity cross-coupling there were both Müller (E) and Aubert (A) effects. The mean of the eigenvectors for upward and downward eye velocities overlay human 1 x g perceptual data.(ABSTRACT TRUNCATED AT 400 WORDS)
    No preview · Article · Jun 1992 · Annals of the New York Academy of Sciences
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