Vestibulomotor coupling and gain associated with cybersickness in virtual reality.

Cybersickness is a major barrier to the adoption of virtual reality (VR), yet its underlying neurophysiological mechanisms remain poorly understood. This study investigated whether vestibulomotor responses, quantified using coherence and gain between electrical vestibular stimulation (EVS) and mediolateral center-of-pressure (ML-CoP) responses, are associated with susceptibility to cybersickness. Thirty-eight healthy young adults (21 females, 17 males) completed a standing VR rollercoaster task while receiving continuous stochastic EVS (0-25 Hz; ±4.5 mA), with ML-CoP responses measured using a force plate. Cybersickness was assessed using the Fast Motion Sickness Scale (FMS), and participants were classified as nonsick (FMS < 5), medium-sick (FMS ≥ 5), or high-sick (terminated the VR exposure early due to intolerance). Baseline EVS-ML-CoP coherence and gain were significantly greater in high-sick than in nonsick participants, with gain increasing by 61%, indicating stronger vestibulomotor responses before symptom onset. During VR exposure, coherence declined over time in symptomatic participants but remained stable in nonsick participants. Despite this reduction in vestibulomotor coupling, postural sway variation increased in the high-sick group relative to the medium- and nonsick groups (+29% vs. -7% and -30% ML-CoP RMS, respectively), whereas vestibular-evoked response amplitude decreased. These findings indicate that greater baseline vestibulomotor responses were associated with increased susceptibility to cybersickness, whereas reductions during VR exposure were insufficient to prevent increases in sway variation and symptom progression. Together, the results suggest that baseline vestibulomotor responses are more strongly associated with cybersickness susceptibility than changes occurring during VR exposure.NEW & NOTEWORTHY We provide the first evidence that baseline vestibulomotor responses predict susceptibility to cybersickness in virtual reality and are dynamically reduced during exposure. Using electrical vestibular stimulation, we show that individuals who develop cybersickness exhibit greater baseline vestibulomotor coupling and larger vestibular-evoked postural responses, followed by progressive reductions in vestibulomotor coupling during VR exposure.