Symmetric projection attractor reconstruction: Transcutaneous auricular vagus nerve stimulation for visually induced motion sickness

Motion sickness is an enigma that has plagued humans for millennia - and could be exacerbated by automated vehicles and virtual reality. Here, we examined the neuromodulatory effects of transcutaneous auricular vagus nerve stimulation (taVNS) - a non-invasive brain stimulation tool - on autonomic function in response to motion sickness-induced nausea. We conducted a crossover randomized controlled study of healthy participants (n = 29) administered with active taVNS and sham, concurrent with visually-induced motion sickness during electrocardiogram (ECG) acquisition. Using symmetric projection attractor reconstruction (SPAR), a recent mathematical tool that computes images ("attractors") of morphology and variability of any approximately periodic signals, we show that taVNS induces a significant reduction in measures derived from these attractor image data, compared to sham. Notably, we found that a taVNS-evoked decrease in peak theta density showed a marked correlation with improvements in motion-induced nausea symptom severity. Furthermore, the use of machine learning revealed differential discriminatory power of taVNS response with an area under the receiver operating characteristic curve (AUC) of 0.81. Taken together, these findings provide novel insights into taVNS for motion-induced nausea; and additionally suggest that ECG SPAR-based features may be important for evaluating taVNS therapy response - with implications for adaptive taVNS.