Transcutaneous Auricular Vagus Nerve Stimulation for Visually Induced Motion Sickness

Transcutaneous auricular vagus nerve stimulation (taVNS), a non-invasive form of electrical brain stimulation, has shown potent therapeutic potential for a myriad of diseases and disorders. How taVNS influences the neural and physiological response of motion sickness - a complex syndrome marked by progressive, multidimensional symptoms - remains unknown. To examine this, I developed a nauseogenic visual stimulus for nausea induction coalesced with taVNS (200 µs, 20 Hz) administration during continuous electroencephalogram (EEG) and electrocardiogram (ECG) data acquisition from healthy human participants in crossover randomized sham-controlled studies. To assess taVNS-induced effects on brain dynamics in response to motion-induced nausea, cortical neuronal generators were estimated from the obtained EEG using exact low-resolution brain electromagnetic tomography (eLORETA). Because taVNS has been shown to modulate the autonomic nervous system (ANS) toward parasympathetic predominance, and that motion-induced nausea is known to perturb ANS function, I performed analysis of ECG-derived heart rate variability (HRV) to quantify autonomic effects of taVNS for motion-induced nausea. Moreover, I obtained the symmetric projection attractor reconstruction (SPAR) transforms of ECG signals to parse taVNS-mediated effects on ECG morphology and variability. Subsequently, I trained machine learning algorithms on ECG SPAR transforms to classify differential response to motion-induced nausea, in addition to taVNS response detection. taVNS increased activity in the insula and middle frontal gyrus compared to baseline. Following taVNS, brain regions including the supramarginal, parahippocampal, middle frontal, and precentral gyri demonstrated a differential increase in neuronal activity. My HRV analyses revealed that taVNS restored autonomic balance to healthy levels during concurrent exposure to nauseogenic stimulation. Morphological and variability measures obtained from ECG-derived attractors showed differential effects of taVNS compared to sham. I also show that machine learning models can determine taVNS response from ECG SPAR-based features. To summarise, these findings provide new insights into taVNS-induced neural and autonomic changes, in addition to suggesting that small doses of electricity delivered at the tragus of the left ear may play an important role in motion sickness management.