Illusory self-motion and motion sickness: a model for brain-gut interactions and nausea.

Motion sickness provides a unique setting for the study of nausea. Studies of illusory self-motion have linked nausea and objective measures of gastric dysrhythmias and the stress hormones vasopressin and epinephrine. Electrogastrographic methods utilize Ag-AgCl electrodes placed on the abdominal surface in the epigastric region to record electrogastrograms (EGGs), a noninvasive measure of gastric myoelectrical activity. The EGG frequencies of interest are the normal range (2.4-3.6 cpm), tachygastrias (3.6-9.9 cpm), and bradygastrias (1.0-2.4 cpm), and duodenal respiratory frequencies (10.0-15.0 cpm). Illusory self-motion or vection is produced with a rotating drum. Minutes before vection-induced nausea is reported, the baseline EGG signal shifts into tachygastrias or mixed tachygastrias and bradygastrias. Quantitative analyses show that the percentage of power in the tachygastria range correlates with the intensity of nausea. Plasma vasopressin levels correlate positively with intensity of nausea. Asian subjects have higher intensity nausea and higher vasopressin levels compared with Caucasian subjects, indicating a potential genetic susceptibility to vection-induced motion sickness and nausea. Vection-induced motion sickness represents an experimental model of acute-onset nausea with accompanying symptoms such as headache, drowsiness, cold sweating, and fatigue. Illusory self-motion is a purely central nervous system (visual-vestibular) stimulation that evokes dramatic shifts in gastric electrical activity and significant release of the posterior pituitary hormone vasopressin. Central nervous systems pathways that evoke gastric dysrhythmias and release vasopressin may also have a pathophysiologic role in the cyclic vomiting syndrome.