Psychophysiological markers and the brain processing of visual motion induced nausea in healthy humans.

Abstract

Background: Nausea is a common and complex multi-system sensation however objective psychophysiological markers of nausea that also predict nausea susceptibility in humans are lacking. In addition, the regions of the brain that process the sensation of nausea are unknown. Aim: To investigate the brain processing of nausea in healthy individuals. Methods: Study 1 validated the visual motion induced nausea paradigm with autonomic measures. Study 2 preselected nausea susceptible versus nausea resistant subjects using the stimulus with autonomic, electrogastrographic and cortisol monitoring. Study 3 investigated the brain processing of the nausea sensation and Study 4 identified which brain regions were specific to the generation of nausea. Results: Studies 1 and 2 – The stimulus was validated with stardardised questionnaires and identified nausea susceptible and resistant individuals with those susceptible demonstrating more anxiety; sympathetic arousal, parasympathetic withdrawal; shift from normogastria to dysrhythmia after motion video. Studies 3 and 4 – The inferior frontal gyrus was positively correlated with increasing nausea and the parahippocampus was inhibited. However, nausea resistant subjects demonstrated increased activity in the parahippocampus. The scopolamine study was overall inconclusive due to nausea being induced by the drug itself. Conclusion: NS subjects decreased parasympathetics, normogastria and increased sympathetics, anxiety and gastric dysrhythmias suggesting these parameters could be used as markers of nausea susceptibility. The inferior frontal gyrus and parahippocampus appears to play a role in nausea genesis and should be investigated further in patients or with other nauseogenic stimulus, newer functional brain imaging modalities, as well as different pharmacological modulations