Motion sickness: more than nausea and vomiting

Abstract

Motion sickness is a complex syndrome that includes many features besides nausea and vomiting. This review describes some of these factors and points out that under normal circumstances, many cases of motion sickness go unrecognized. Motion sickness can occur during exposure to physical motion, visual motion, and virtual motion, and only those without a functioning vestibular system are fully immune. The range of vulnerability in the normal population varies about 10,000 to 1. Sleep deprivation can also enhance susceptibility. Systematic studies conducted in parabolic flight have identified velocity storage of semicircular canal signals-velocity integration-as being a key factor in both space motion sickness and terrestrial motion sickness. Adaptation procedures that have been developed to increase resistance to motion sickness reduce this time constant. A fully adequate theory of motion sickness is not presently available. Limitations of two popular theories, the evolutionary and the ecological, are described. A sensory conflict theory can explain many but not all aspects of motion sickness elicitation. However, extending the theory to include conflicts related to visceral afferent feedback elicited by voluntary and passive body motion greatly expands its explanatory range. Future goals should include determining why some conflicts are provocative and others are not but instead lead to perceptual reinterpretations of ongoing body motion. The contribution of visceral afferents in relation to vestibular and cerebellar signals in evoking sickness also deserves further exploration. Substantial progress is being made in identifying the physiological mechanisms underlying the evocation of nausea, vomiting, and anxiety, and a comprehensive understanding of motion sickness may soon be attainable. Adequate anti-motion sickness drugs without adverse side effects are not yet available.

Fig. 1

Cardinal signs and symptoms of motion sickness and criteria for grading motion sickness severity (Graybiel et al. 1968b)

Fig. 2

Illustration of Coriolis cross-coupling stimulation

Fig. 3

Results of the Skylab M-131 experiment for the three Skylab 4 astronauts. The columns represent the severity of motion sickness on the Graybiel scale (see Fig. 1). The rows of numbers at the bottom of the figure represent the angular velocity of body rotation in rpm, number of head movements made, rotation direction, and flight day

Fig. 4

Schematic flight profile of aircraft performing parabolic maneuvers to generate alternating period of free fall and increased gravito-inertial force

Fig. 5

Angular displacement perception as a function of gravito-inertial force level for recumbent yaw rotation. LED left ear down, RED right ear down