Mitigating motion sickness with non-invasive cortical vestibular brain stimulation (vBS) is promising because it does not require redesigning VR content or altering the motion profile of a moving platform. Instead, it aims to enhance individuals' intrinsic resistance to motion sickness. However, the mechanism underlying its online efficacy remains unclear (Here, "online efficacy" means the observed motion sickness reduction during vBS not before or after vBS). Motivated by lower motion sickness susceptibility observed in congenital nystagmus patients, we hypothesized that reductions in motion sickness under vBS condition are associated with increased eye movement instability. Leveraging sham-controlled, sex-balanced eye-tracking data from an open-access database, this study presents the first evaluation of a 20 Hz-vBS approach targeting the vestibular cortices as a countermeasure to motion sickness, using spatiotemporal eye movement metrics derived from eye-tracking data collected in VR. Results show that reduced motion sickness under active vBS indeed increased eye movement instability temporarily and spatially, compared to sham vBS. We also found that the temporal metrics was more strongly associated with female participants, whereas the spatial metric was more strongly associated with male participants.

The increasing use of virtual reality (VR) in public transportation enables travelers to engage in immersive entertainment or productive tasks, thereby enhancing the overall travel experience. However, mismatched VR visual motion and physical car motion can cause motion sickness (MS), leading to nausea, postural instability and reduced time for enjoyment or productive tasks. Thus, the benefits of using VR in transportation systems are currently limited to individuals who do not experience MS. Thus, effective MS mitigation is essential for improving travel safety, maximizing travel time, and expanding VR accessibility. Neuromodulation targeting the vestibular apparatus, such as bone-conducted vibration (BCV), has shown promise in reducing MS. However, it remains unclear whether neuromodulation directly targeting vestibular cortical regions, such as transcranial alternating current stimulation (tACS), is superior. This paper focuses on the design and validation of a novel vestibular cortical neuromodulation approach using tACS in mitigating MS in a novel simulated in-car VR environment. Eighty participants were recruited to evaluate the tACS approach. The results demonstrate that the proposed tACS approach effectively reduces nausea, enhances postural stability, and extends survival time in MS. Compared to BCV, tACS demonstrates a faster onset of action and longer mitigation effects. However, from an applied perspective, the effects of our tACS approach were relatively short-lived and accompanied by side effects such as tingling and itching.