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Background: Sopite syndrome is a poorly understood symptom complex characterized by drowsiness and lethargy relating to motion sickness. Though often occurring in conjunction with the classic symptomatology of motion sickness, the literature suggests that sopite syndrome is a separate entity that may occur independently of the feelings of nausea characteristic of traditional motion sickness. Additionally, the syndrome can last long after symptoms of nausea have subsided and can be debilitating to some patients. Due to the frequent concomitance of sopite syndrome and the classic symptoms of motion sickness, the syndrome may frequently go unidentified and there is a paucity of data recording its exact incidence in the available literature., Case Report: In this study, we report a case of sopite syndrome identified in a 23-yr-old student naval aviator who was ultimately unable to overcome his symptoms and adapt to the dynamic environment of flight., Discussion: This process is particularly relevant to student aviators and others involved in transportation settings where the existence of even mild performance challenges may create the potential for operational hazards. Because the training of aviators and flight officers is historically one of the most expensive investments undertaken by the Department of the Navy each year, documenting unique manifestations of this common problem and addressing them early in the training pipeline may help reduce the time and financial burden associated with student naval aviator attrition in the later stages of training.Gemender MS, Sholes PC, Haight SP. Sopite syndrome identified in a student naval aviator. Aerosp Med Hum Perform. 2018; 89(9):848-850.

In 1976, Graybiel and Knepton proposed the term "sopite syndrome" to describe a symptom complex centering on drowsiness and lethargy related to motion sickness. However, existing descriptions and definitions of sopite syndrome have limitations in fully conveying the appropriate information to the reader. Our objective is to propose a revised definition providing a more adequate conceptual framework for research. The proposed definition of sopite syndrome addresses the nonspecificity of soporific symptoms, the health state of the individuals, and the existence of a motion stimulus.

Introduction: Previous research has shown that retinal slip can be a significant factor in causing motion sickness. Stroboscopic illumination may prevent retinal slip by providing snapshots of the visual environment that are brief enough so each image is stationary on the retina., Methods: The purpose of this study was to determine the effectiveness of an 8-Hz stroboscopic environment as a motion sickness countermeasure for passengers during a nauseogenic flight in a helicopter. The study population was comprised of 18 motion sickness susceptible subjects. Subjects completed a motion sickness symptom questionnaire, a psychomotor vigilance test, weapons utilization tasks, a time estimation task, and a sustained attention task after nauseogenic flights with and without 8-Hz stroboscopic illumination in the cabin., Results: Baseline-corrected scores of self-reported nausea were significantly lower after the stroboscopic condition (M = 36.57 +/- 6.95) than the nonstroboscopic condition (M = 50.88 +/- 7.36). Furthermore, the stroboscopic condition resulted in significantly better performance on the vigilance task than the nonstroboscopic condition. However, baseline-corrected scores of oculomotor symptoms were greater after the stroboscopic condition (M = 33.27 +/- 5.52) than the nonstroboscopic condition (M = 24.85 +/- 4.10)., Discussion: These results support the use of stroboscopic illumination as a nonpharmacologic countermeasure for motion sickness related to retinal slip. However, due to the uncontrolled nature of the flights, the possibility that these results could have been influenced by differences in motion between flights cannot be excluded. This technology should be investigated in other forms of transportation (i.e., ground vehicles).

Background: Motion sickness is a common aeromedical problem that may occur in pilots exposed to increased gravitoinertial load in the head-to-foot direction (+Gz). Since motion sickness may affect autonomic nervous functions including cardiovascular control, it was hypothesized that it might interfere with cardiovascular responses to high +Gz, thereby decreasing G tolerance., Methods: G tolerance and cardiovascular responses to increased G load were studied in nine subjects in a centrifuge environment under two conditions. In the motion sickness condition, the subject was exposed to a motion sickness provocation (MSP) comprising repeated rapid changes in G load in combination with a regimen of head movements. In the control condition the subject was exposed to similar cumulative G-time stress, but without the MSP. Mean arterial pressure (MAP) was measured. An index of peripheral vascular resistance was achieved by measuring the difference in skin temperature between the forearm and fingertip (deltaT(forearm-fingertip))., Results: MSP decreased gradual-onset rate G tolerance from 5.1 +/- 1.0 G (mean +/- SD) to 4.6 +/- 0.9 G. There was no change in gradual-onset rate G tolerance in the control condition. Rapid-onset rate G tolerance was lower in the motion sickness (2.9 +/- 0.5 G) than in the control (3.4 +/- 0.3 G) condition. MSP reduced MAP by 11 mmHg and deltaT(forearm-fingertip) by 4.2 +/- 4.1 degrees C. In the control condition MAP and deltaT(forearm-fingertip) were unaffected., Conclusions: Motion sickness may reduce the arterial pressure response to the extent that the capacity of an individual to withstand increased G loads in the head-to-foot direction is significantly diminished.

Introduction: Low-frequency lateral oscillation is a cause of motion sickness in some forms of transport. However, the relationship between occurrence of sickness and the frequency of lateral oscillation is not known. This paper presents a study of motion sickness with lateral oscillation at frequencies between 0.0315 Hz and 0.20 Hz., Method: There were 120 subjects, in 6 groups of 20, who were exposed for up to 30 min to sinusoidal lateral oscillation with a peak velocity of 1.0 ms(-1) at one of six frequencies (0.0315, 0.05, 0.08, 0.125, 0.16, 0.20 Hz). Subjects provided ratings of their motion sickness symptoms at 1-min intervals., Results: There was a highly significant effect of the frequency of lateral oscillation on the occurrence of mild nausea., Discussion: The present results have been combined with those from a previous experiment conducted with higher frequencies of oscillation to produce a frequency weighting for motion sickness caused by lateral oscillation over the range 0.0315 to 0.8 Hz., Conclusions: Mild nausea caused by lateral oscillation may be predicted by an acceleration frequency weighting that is independent of frequency from 0.0315 to 0.25 Hz and reduces at 12 dB per octave (i.e., proportional to displacement) from 0.25 to 0.8 Hz. This weighting differs from the frequency weighting currently used for predicting motion sickness caused by vertical oscillation. The frequency weighting for lateral oscillation may not be applicable in those environments in which there is roll motion during lateral oscillation.

Purpose: The purpose of the study was to examine the effectiveness of P6 acupressure on nausea associated with visually-induced motion sickness., Method: There were 64 subjects randomly divided into 4 groups: P6 acupressure, dummy-point acupressure, sham P6 acupressure, and control. Each subject sat in an optokinetic drum for a 12-min baseline and 12-min drum rotation period. Subjects' electrogastrograms (EGG's) and subjective symptoms of motion sickness were obtained., Results: The results indicated that the subjects in the P6 acupressure group reported significantly less nausea [F(3,60) = 8.16, p < 0.0001] during drum rotation period than those in the dummy-point acupressure, sham acupressure, and control groups. The scores for symptoms of motion sickness of the P6 acupressure group were significantly lower than those in the sham acupressure and control groups [F(3,60) = 3.49, p < 0.02]. Also, the subjects in the P6 acupressure group showed significantly less abnormal gastric myoelectric activity, tachyarrhythmia, than those in the sham acupressure and control groups [F(3,60) = 2.78, p < 0.04]. However, the subjects in the dummy-point acupressure group did not report significantly fewer symptoms and show less tachyarrhythmia than those in the sham acupressure and control groups., Conclusion: We conclude that P6 acupressure reduces the severity of symptoms of visually-induced motion sickness and gastric tachyarrhythmia.

Little is known about the factors that control individual differences in susceptible to motion sickness. A serendipitous observation in our laboratory that most Chinese subjects become motion sick prompted this study. We used a rotating optokinetic drum to provoke motion sickness and compared gastric responses and symptom reports of Chinese, European-American, and African-American subjects. There was no difference in the responses of European-American and African-American subjects; however, Chinese subjects showed significantly greater disturbances in gastric activity and reported significantly more severe symptoms. We suggest that this hyper-susceptibility presents a natural model for the study of physiological mechanisms of nausea and other symptoms of motion sickness.

The fact that amphetamine, a noradrenaline releaser, prevents motion sickness leads the hypothesis of Wood and Graybiel that the noradrenergic neuron system in the brain stem acts against the development of motion sickness. To evaluate the hypothesis, the effects of rotational stress on the turnovers of noradrenaline and dopamine in the rat brain stem were examined. Rats were rotated about two axes simultaneously (double rotational) or about one axis (single rotation) for 60 min. Measurement of kaolin intake (pica) induced by rotation, as an index of motion sickness, showed that double rotation produced motion sickness, whereas single rotation did not. Both single and double rotation significantly increased the turnovers of noradrenaline and dopamine in the brain stem. However, there were no significant differences between the increases in catecholamine turnover induced by double and single rotations. Moreover, pretreatment of rats with methamphetamine (5 mg/kg) just before double rotation, which prevented the induction of motion sickness by double rotation, did not affect increases of the catecholamine turnover in the brain stem by double rotation. These findings do not support the hypothesis of Wood and Graybiel, suggesting that the catecholaminergic neuron systems in the brain stem are not involved in motion sickness and that the therapeutic effect of methamphetamine is not due to its direct effect on the brain stem.

The susceptibility of rhesus monkeys to motion sickness was investigated using test conditions that are provocative for eliciting motion sickness in squirrel monkeys. Ten male rhesus monkeys and ten male Bolivian squirrel monkeys were rotated in the vertical axis at 150 degrees/s for a maximum duration of 45 min. Each animal was tested in two conditions, continuous rotation and intermittent rotation. None of the rhesus monkeys vomited during the motion tests but all of the squirrel monkeys did. Differences were observed between the species in the amount of activity that occurred during motion tests, with the squirrel monkeys being significantly more active than the rhesus monkeys. These results, while substantiating anecdotal reports of the resistance of rhesus monkeys to motion sickness, should be interpreted with caution because of the documented differences that exist between various species with regard to stimuli that are provocative for eliciting motion sickness.

Approximately 60% of healthy human subjects experience motion sickness when exposed to a rotating optokinetic drum. The purpose of the present study was to determine the effects of certain visual factors on susceptibility to motion sickness. Vection data (illusory self-motion), horizontal eye movement recordings, subjective motion sickness report, and a measure of gastric myoelectric activity (electrogastrogram, EGG) were obtained from 45 subjects, who were randomly divided into the following three groups: a control group that observed the entire visual field with no fixation, a group that fixated on a central target, and a third group that had a visual field restricted to 15 degrees. The experimental session was divided into the following three 12-min periods: baseline, drum rotation, and recovery. The results showed that fixation greatly reduced nystagmus and slightly reduced vection. The restricted visual field slightly reduced nystagmus and greatly reduced vection. Both of these manipulations significantly reduced symptoms of motion sickness and tachyarrhythmia, the abnormal gastric myoelectric activity that usually accompanies nausea.

Drowsiness is one of the cardinal symptoms of motion sickness; therefore, a symptom-complex centering around "drowsiness" has been identified which, for convenience, has been termed the sopite syndrome. Generally, the symptoms characterizing this syndrome are interwoven with other symptoms but under two circumstances the sopite syndrome comprises the main or sole overt manifestation of motion sickness. One circumstance is that in which the intensity of the eliciting stimuli is closely matched to a person's susceptibility, and the sopite syndrome is evoked either before other symptoms of motion sickness appear or in their absence. The second circumstance occurs during prolonged exposure in a motion environment when adaptation results in the disappearance of motion sickness symptoms, except for responses characterizing the sopite syndrome. Typical symptoms of the syndrome are: 1) yawning, 2) drowsiness, 3) disinclination for work, either physical or mental, and 4) lack of participation in group activities. Phenomena derived from an analysis of the symptomatology of the sopite syndrome are qualitatively similar but may differ quantitatively from abstractions derived in other motion sickness responses. One example is the sometimes unique time course of the sopite syndrome. This implies that the immediate eliciting mechanisms not only differ from those involved in evoking other symptoms, but, also, that they must represent first order responses. Diagnosis is difficult unless the syndrome under discussion is kept in mind. Prevention poses a greater problem than treatment.

Three previously motion-emetic sensitive squirrel monkeys were rendered refractory to a standard motion-emetic regimen by a two-stage utriculosacculectomy procedure which preserved the cristae ampullares of semicircular canals. Three non-operated control squirrel monkeys tested on the same motion-emetic regimen time schedule as the operated animals remained motion-emetic sensitive with regard to incidence, frequency, and latency of motion-induced emetic responses. Following a sham surgical procedure (stapedectomy) performed on two of the latter animals and one additional new animal, the emetic incidence decreased from 100% to 89%, but the frequency and latency were not altered significantly.