Motion sickness is a common physical ailment that can cause discomfort in the epigastric region, nausea, and vomiting in severe cases. Despite advances in technology, motion sickness remains an unpleasant experience during transportation. The emergence of autonomous and semi-autonomous vehicles may increase the incidence and risk of motion sickness. Additionally, digital devices and displays are also becoming a concern for those susceptible to motion sickness. Studies have found that 3D displays can cause more symptoms of motion sickness compared to 2D displays.
A new study, published in the journal Scientific Reports, investigated the effects of transauricular electrical stimulation (tES) on autonomic function during visually induced motion sickness. The aim was to determine the efficacy of tES by comparing sham and tES conditions in a randomised, within-subjects, cross-over design in 14 healthy participants.
The study found that tES reduced motion sickness symptoms by increasing normalised high-frequency (HF) power and decreasing normalised low-frequency (LF) power and the power ratio of LF and HF components (LF/HF ratio). The behavioural data recorded using the motion sickness assessment questionnaire (MSAQ) also showed significant differences in decreased symptoms during tES compared to the sham condition for the total MSAQ scores, and central and sopite categories of the MSAQ.
These findings suggest that administering tES may increase parasympathetic modulation and restore autonomic imbalance induced by motion sickness. This study provides preliminary evidence that tES may have the potential as a non-pharmacological neuromodulation tool to alleviate motion sickness symptoms, potentially protecting people from becoming motion sick and accelerating recovery from the malady.
The exact cause of motion sickness is not yet fully understood, and various theories have been proposed to explain its underlying mechanisms. One influential theory, known as the sensory conflict theory, suggests that the conflicting information from the eyes and vestibular system contributes to the onset of motion sickness.
Reason later expanded on this theory to develop the neural mismatch theory. Neuroimaging studies have revealed that this sensory ambiguity, particularly with regard to visual stimuli, activates certain regions of the brain, such as the limbic system and insula, both of which are involved in regulating autonomic function. In addition, research has shown that motion video can lead to changes in the autonomic nervous system, such as increased sympathetic activity and decreased parasympathetic activity. Symptoms of motion sickness include a wide range of features, including sweating, dizziness, drowsiness, headache, eyestrain, nausea, and vomiting, many of which are related to autonomic functioning.
The study has some limitations, including a small sample size which reduced the statistical power of the analysis. Additionally, the sham sessions lacked active stimulation, leading some participants to differentiate between tES and sham conditions. This awareness of the verum and sham stimulation may have influenced the motion sickness-related changes observed in the study. Future research should consider using different sham conditions to minimize the potential confounding effects of expectations. However, participants in the study were naive to tES and sham stimulation electrode placement. Another limitation was the insufficient number of male participants in the study.
The study did not report any unexpected adverse effects from the stimulation parameters used, and the nauseogenic stimuli were well-tolerated by all participants. Although some participants prematurely stopped the presentation of nauseogenic stimulus due to a high feeling of nausea, no one vomited at the end of the stimulus presentation.
The researchers suggest that future research should examine the physiological correlates of motion sickness, such as neuroendocrine hormones like arginine vasopressin and norepinephrine. The key questions for future research include identifying optimal stimulation parameters to improve the efficacy of tES for motion sickness reduction, and whether increased stimulation duration could improve the effects of tES on ameliorating motion sickness. The researchers plan to address these questions in their future research and also administer an individually adjusted electrical current intensity.