12 | Reduced motion sickness with phase-dependent brain stimulation

Background: The development of a non-pharmacological approach (e.g., brain stimulation) that does not require redesigning VR content to mitigate VR motion sickness (VRMS) is a promising direction. This approach aims to enhance users’ resistance to VRMS rather than promote reliance on modified VR environments. VRMS is commonly attributed to abnormal multisensory integration in the temporoparietal junction (TPJ), a superficial cortical region.1–4 While frequency-dependent brain stimulation methods on TPJ-related regions have shown effectiveness in reducing visually induced VRMS,1,2 the potential of phase-dependent techniques remains largely unexplored. Materials and Methods: Transcranial alternating current stimulation (tACS) non-invasively modulates phase relationships across or within superficial cortical areas using weak electrical currents. Given the TPJ’s accessibility, it is a strong candidate for tACS targeting. We first identified two electroencephalography (EEG) beta-freqeuncy phase-locking patterns in TPJ-related regions during visually induced VRMS (N = 42), and then examined their causal relevance in visually induced VRMS (N = 18) and in a multisensory (visual + vestibular) VRMS context (N = 80), using counter-signals delivered via tACS. Results: The two EEG phase-locking patterns were: increased 18 Hz phase-locking value (PLV) at the left TPJ and decreased 20 Hz PLV at the right TPJ. To counteract these patterns, we found that random-phase tACS at 18 Hz targeting the left TPJ mitigated visually induced VRMS from 10 to 16 minutes post-stimulation, while in-phase 20 Hz tACS at the right TPJ reduced multisensory VRMS from 3 to 18 minutes. These findings indicate a causal role for beta-frequency phase-locking across different types of VRMS.