On the origin of interindividual susceptibility to motion sickness

Binocular misalignments elicited by altered gravity provide evidence for nonlinear central compensation

Increased ocular positioning misalignments upon exposure to altered gravity levels (g-levels) have been strongly correlated with space motion sickness (SMS) severity, possibly due to underlying otolith asymmetries uncompensated in novel gravitational environments. We investigated vertical and torsional ocular positioning misalignments elicited by the 0 and 1.8 g g-levels of parabolic flight and used these data to develop a computational model to describe how such misalignments might arise. Ocular misalignments were inferred through two perceptual nulling tasks: Vertical Alignment Nulling (VAN) and Torsional Alignment Nulling (TAN). All test subjects exhibited significant differences in ocular misalignments in the novel g-levels, which we postulate to be the result of healthy individuals with 1 g-tuned central compensatory mechanisms unadapted to the parabolic flight environment. Furthermore, the magnitude and direction of ocular misalignments in hypo-g and hyper-g, in comparison to 1 g, were nonlinear and nonmonotonic. Previous linear models of central compensation do not predict this. Here we show that a single model of the form a + bg (ε), where a, b, and ε are the model parameters and g is the current g-level, accounts for both the vertical and torsional ocular misalignment data observed inflight. Furthering our understanding of oculomotor control is critical for the development of interventions that promote adaptation in spaceflight (e.g., countermeasures for novel g-level exposure) and terrestrial (e.g., rehabilitation protocols for vestibular pathology) environments.

Neuronal mechanisms and the treatment of motion sickness

The aim of this review is to provide an overview of the physiological basis, clinical picture and treatment options for motion sickness. Motion sickness is a well-known nausea and vomiting syndrome in otherwise healthy people. The physical signs of motion sickness occur in both humans and animals during travel by sea, automobile or airplane and in space. Furthermore, some other special situations, such as simulators, the cinema and video games, have been described as causing pseudomotion sickness. Children between 2 and 12 years old are most susceptible to motion sickness, and women are more frequently affected than men. Predisposing factors include menstruation, pregnancy, migraines and possibly a side difference in the mass of otoconia in the vestibular organs. Therapy is directed towards decreasing conflicting sensory input, accelerating the process of adaptation and controlling nausea and vomiting. To control these vegetative symptoms, scopolamine and antihistamines are the most effective drugs.