On the potential of transauricular electrical stimulation to reduce visually induced motion sickness

Abstract

Perturbations in the autonomic nervous system occur in individuals experiencing increasing levels of motion sickness. Here, we investigated the effects of transauricular electrical stimulation (tES) on autonomic function during visually induced motion sickness, through the analysis of spectral and time-frequency heart rate variability. To determine the efficacy of tES, we compared sham and tES conditions in a randomized, within-subjects, cross-over design in 14 healthy participants. We found that tES reduced motion sickness symptoms by significantly increasing normalized high-frequency (HF) power and decreasing both normalized low-frequency (LF) power and the power ratio of LF and HF components (LF/HF ratio). Furthermore, behavioral data recorded using the motion sickness assessment questionnaire (MSAQ) showed significant differences in decreased symptoms during tES compared to sham condition for the total MSAQ scores and, central and sopite categories of the MSAQ. Our preliminary findings suggest that by administering tES, parasympathetic modulation is increased, and autonomic imbalance induced by motion sickness is restored. This study provides first evidence that tES may have potential as a non-pharmacological neuromodulation tool to keep motion sickness at bay. Thus, these findings may have implications towards protecting people from becoming motion sick and possible accelerated recovery from the malady.

Figure 1

Spectral heart rate variability (HRV) measurements between participants at baseline and “Nausea” section, and between sham and transauricular electrical stimulation (tES) condition. (a) Average spectral power of low frequency (LF) and high frequency (HF), and LF/HF power ratio in response to nauseogenic stimuli. (b) Average change in LF, HF and LF/HF ratio in participants during sham and tES condition. Error bars represent standard error of the mean (SEM). The box plot central marks, box edges and whiskers represent medians, 25th to 75th percentiles and data range, respectively. The box plot also shows an outlier (red plus) in the sham condition for LF/HF ratio.

Figure 2

Time-varying power representations of heart rate variability (HRV) using the smoothed pseudo Wigner–Ville distribution (SPWVD) for an example participant. (a) Time-frequency power during sham (baseline subtracted) condition (b) and tES (baseline subtracted) condition. (c) Shows the time-frequency power difference between (Sham vs Baseline) and (tES vs Baseline). A statistical pixel-based permutation test using a pixel-level significance threshold of p $<0.05$ revealed 1 cluster around 270–290 s (two-tailed non-parametric permutation tests). The significant cluster (region) is outlined by a black contour in (c).

Figure 3

Time-varying power representations of heart rate variability (HRV) using the smoothed pseudo Wigner–Ville distribution (SPWVD) at the sample level. (a) Time-frequency power representation showing the power differences in tES and sham condition (after baseline subtraction within each condition). (b) Statistical z-map of the time-frequency power representation at the sample level, based on a cluster-level significance threshold p $<0.05$ (two-tailed non-parametric permutation tests). Significant clusters (regions) are indicated by black contours on the statistical z-map.

Figure 4

Summary of motion sickness assessment questionnaire (MSAQ) total and subscale scores across participants. (a) Average change in MSAQ total scores between sham and tES condition. (b) Average change in MSAQ scores within each category (gastrointestinal, central, peripheral, sopite) between sham and tES condition. Data are shown as mean ± SEM.

Figure 5

Scatterplots of linear regression, Spearman, and Pearson correlation analysis. (a) A linear regression between MSAQ during sham and the difference between tES and sham condition. (b) A Spearman correlation between HF power during tES condition and the latency to maximum nausea rating. (c) A Pearson correlation between the MSAQ total scores and log-transformed LF/HF ratio at Baseline and during tES as well as the difference between during and before tES intervention. (d) And MSAQ total scores and normalized HF at Baseline and during tES as well as the difference between during and before tES intervention. r, Spearman’s or Pearson’s correlation coefficient (p-values based on two-tailed statistical test).

Figure 6

Experimental overview illustrations. (a) The electrode was clipped at the tragus site of the left ear during tES condition. (b) And clipped to the earlobe of the left ear during sham condition. (c) Participants underwent a baseline, nauseogenic visual stimulation and recovery section, respectively in both week 1 (first visit) and week 2 (follow-up visit), separated by 1 week. Electrocardiogram (ECG) signals were recorded continuously from beginning of baseline to end of recovery. Participants were randomly assigned to receive tES or sham in week 1 (first visit) and to receive opposite treatment on follow-up.