The significance of motion sickness in the vestibular system.

Takahashi M, Ogata M, Miura M.

Department of Otolaryngology, Yamaguchi University School of Medicine, Japan.

In order to clarify the significance of motion sickness in the vestibular system, we compared the findings of experimental motion sickness between different kinds of subjects, some of which were already reported. Subjects were healthy adults, healthy children between the ages of 4 and 15 years, and patients with congenital and acquired labyrinthine loss. They were asked to walk while wearing horizontally and vertically reversing goggles. Equilibrium ataxia as well as motion sickness were evoked by horizontal reversal, but not by vertical reversal in healthy subjects. Kindergarten children exhibited severe ataxia, but little nausea. The frequency of severe ataxia decreased during growth, inversely as the frequency of nausea syndrome increased. Although a patient with acquired loss became severely ataxic, a patient with congenital loss did not show any ataxia at all. The present study suggests that vestibular cues are indispensable to the ego-spatial relationship in the brain, and once the ego-spatial relationship becomes inadequate, discomfort acts as a safety device to brake uncontrollable actions. Then, perception of the outer world may automatically adjust voluntary actions by affecting motor commands. The importance of visual cues for representing an alternative framework may differ between congenital and acquired labyrinthine loss.

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Unusual vestibular and visual input in human dynamic balance as a motion sickness susceptibility test.

Severac Cauquil A, Dupui P, Costes Salon MC, Bessou P, Guell A.

Centre de Recherche Cerveau et Cognition, UMR. CNRS 5549 Faculte de Medecine, Toulouse, France.

BACKGROUND: Motion sickness (MS) is commonly thought to arise from a sensory conflict. However, few quantitative methods based on this theory are available to detect MS susceptibility. HYPOTHESIS: It was asked whether the standardized unusual stimulation of a single sensory channel under quantified dynamic balance conditions in man could elicit a sensory conflict and therefore trigger motion sickness (MS) METHODS: Vestibular and visual channels were stimulated by galvanic current and rotating prismatic glasses, respectively. The moving platform used to create the requirements for dynamic balance conditions was chosen not only to worsen the malaise but also to obtain an objective measurement of the balance consequences of the stimulations. RESULTS: Both vestibular and visual stimulation, applied separately, elicited MS-like symptoms (in 56% and 73% of subjects, respectively) and stereotyped balance reactions. A relationship was found between subjective MS-like symptoms and objective measurements of dynamic balance performance. Subjects sensitive to unusual vestibular messages differed from the others by a greater increase in the parameters indicating a difficulty of balance whereas subjects sensitive to unusual visual messages were recognized by the strategy they used to balance themselves. CONCLUSIONS: These results demonstrated that a sensory conflict can trigger MS-like symptoms. We conclude that the measured parameters of a global somatomotor activity, such as the dynamic balance task proposed here, could be useful for objectively detecting subjects predisposed to MS, for training them and testing the efficiency of anti-MS drugs.

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Objective and subjective time courses of recovery from motion sickness assessed by repeated motion challenges.

Golding JF, Stott JR.

Division of Psychology, University of Westminster, London, U.K.

The aim of this study was to determine whether the time course of recovery of tolerance, as assessed objectively by rechallenge with motion, paralleled the subjective recovery from motion sickness. Subjects (n = 20) were exposed to 5 pairs of nauseogenic motion challenges in which the time interval between the end of the first and the start of the second of each pair ranged from 15 min to 2 h. The cross-coupled motion challenge had an incrementing profile of rotational velocity from 4 degrees to 92 degrees.s-1 in steps of 4 degrees.s-1 every 30 s, with 8 head movements per 30 s, of approximately 45 degrees, and was continued to the point of moderate nausea. Objective loss of tolerance decreased from 15 min to 60 min after the first challenge, but increased again at 2 h. By contrast, most individuals reported subjective recovery by 15 min to 30 min. It was concluded that there is an underlying effect of motion sickness that sensitizes the response to subsequent motion for a period of at least 2 h. This underlying objective effect can occur in the absence of subjective symptoms, has a slower time course than the subjective recovery from symptoms, and appears to be non-monotonic.

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Human heart rate variability relation is unchanged during motion sickness.

Mullen TJ, Berger RD, Oman CM, Cohen RJ.

Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge 02139, USA. tjm atrium.mit.edu

In a study of 18 human subjects, we applied a new technique, estimation of the transfer function between instantaneous lung volume (ILV) and instantaneous heart rate (HR), to assess autonomic activity during motion sickness. Two control recordings of ILV and electrocardiogram (ECG) were made prior to the development of motion sickness. During the first, subjects were seated motionless, and during the second they were seated rotating sinusoidally about an earth vertical axis. Subjects then wore prism goggles that reverse the left-right visual field and performed manual tasks until they developed moderate motion sickness. Finally, ILV and ECG were recorded while subjects maintained a relatively constant level of sickness by intermittent eye closure during rotation with the goggles. Based on analyses of ILV to HR transfer functions from the three conditions, we were unable to demonstrate a change in autonomic control of heart rate due to rotation alone or due to motion sickness. These findings do not support the notion that moderate motion sickness is manifested as a generalized autonomic response.

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Active posture control during experimental motion sickness in guinea-pigs.

Ikeda T, Takahashi M.

Department of Otolaryngology, Yamaguchi University School of Medicine, Japan.

This study evaluated active posture control in guinea-pigs under motion sickness stimulation. Twelve guinea-pigs, which received training to stay on a moving perch, were divided into two groups: a motion sickness stimulation group and a control group. The motion sickness group was given a combined stimulation of turntable rotation and optokinetic drum rotation, and the control group was given turntable stimulation alone. Motion sickness was evaluated by conditioned taste aversion to saccharin solution. Active posture control was evaluated by the angle of nose tip displacement and the staying duration (length of time that guinea-pigs stayed on the turntable). The consumption of saccharin solution increased in the control group but did not increase in the motion sickness group. The motion sickness group showed a significant increase in the mean angle of nose tip displacement and a significant decrease in the staying duration on the turntable. These results indicate that active posture control was disturbed by motion sickness stimulation.

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Prevalence and correlates of susceptibility to motion sickness.

Sharma K, Aparna.

Department of Anthropology, Panjab University, Chandigarh, India.

Data on susceptibility to motion sickness were collected on a sample of 535 individuals divided into eight groups. The prevalence of motion sickness among Tibetans and Northeast Indians (28%) was slightly higher than Northwest Indians (26%). Generally speaking, females (27.3%) were more susceptible than males (16.8%). Among different groups, the highest incidence of susceptibility to motion sickness (SMS) was recorded in schizophrenic patients (30%), while the lowest in rowers (zero percent). Ears and eyes are the most potent receptors of provocative motion that causes sickness. Individuals with greater spatial and motor control, reflected in sports like rowing, athletics and professions like armed and paramilitary forces, were less susceptible to motion sickness. The SMS was significantly higher in individuals who suffered from spatial disorientation (35.05%), migraine (26.31%), gastrointestinal disorders (26.82%) and those who were more sensitive to unpleasant odours (24.64%) and preferred sweet flavours (24.48%) than their counterparts. These correlates have been utilized to explain the genesis of sickness using threshold model. Genetic and environmental pathways are strongly advocated. Past episodes of motion sickness acted as a strong psychological attribute in determining further episodes. The roadway buses and trucks proved more effective passive transportation types that caused sickness. The voluntary stabilization of the head and neck movements and gaze control proved very effective natural measures adopted by 38% subjects to avoid or limit motion sickness. About 50% of susceptible individuals became less susceptible or fully acclimatized to motion sickness due to habituation. The mean age at acclimatization was 21.98 +/- 5.93 years.

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Altered sensory-motor control of the head as an etiological factor in space-motion sickness.

Lackner JR, DiZio P.

Ashton Graybiel Spatial Orientation Laboratory, Brandeis University, Waltham, MA 02254.

Mechanical unloading during head movements in weightlessness may be an etiological factor in space-motion sickness. We simulated altered head loading on Earth without affecting vestibular stimulation by having subjects wear a weighted helmet. Eight subjects were exposed to constant velocity rotation about a vertical axis with direction reversals every 60 sec. for eight reversals with the head loaded and eight with the head unloaded. The severity of motion sickness elicited was significantly higher when the head was loaded. This suggests that altered sensory-motor control of the head is also an etiological factor in space-motion sickness.

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Immersed false vertical room. A new motion sickness model.

Coats AC, Norfleet WT.

Baylor College of Medicine, Houston, Texas 77030, USA.

We evaluated a new model of motion sickness--an enclosure decorated with visual cues to upright which was immersed either inverted or "front"-wall down, in Johnson Space Center's Weightless Environment Training Facility (WETF) pool. This "WETF False Vertical Room" (WFVR) was tested with 19 male and 3 female SCUBA diver subjects, aged 23 to 57, who alternately set clocks mounted near the room's 8 corners and made exaggerated pitch head movements. We found that (1) the WFVR test runs produced motion sickness symptoms in 56% and 36% of subjects in the room-inverted and room-front-down positions, respectively. (2) Pitch head movements were the most provocative acts, followed closely by setting the clocks--particularly when a clock face filled the visual field. (3) When measured with a self-ranking questionnaire, terrestrial motion sickness susceptibility correlated strongly (P < 0.005) with WFVR sickness susceptibility. (4) Standing instability, measured with a modified Fregly-Graybiel floor battery, also correlated strongly (P < 0.005) with WFVR sickness susceptibility. This result may reflect a relationship between visual dominance and WFVR sickness. (5) A control study demonstrated that the inverted and front-down positions produced WFVR sickness, but the upright position did not, and that adaptation may have occurred in some subjects with repeated exposure. The WFVR could become a useful terrestrial model of space motion sickness (SMS) because it duplicates the nature of the gravity-dependent sensory conflicts created by microgravity (visual and otolith inputs conflict while somatosensory gravity cues are minimized), and it also duplicates the nature of the provocative stimulus (sensory environment "rule change" versus application of motion to passive subject) more closely than any other proposed terrestrial SMS model. Also, unlike any other proposed terrestrial SMS model, the WFVR incorporates whole-body movement in all three spatial dimensions. However, the WFVR's sensory environment differs from that created by spaceflight in several respects, including the presence of frictional drag on limb movement, magnification at the face-mask-water interface, greater otolith conflict, exhaled bubbles, and the presence of some gravity-dependent somatosensory inputs.

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