Cybersickness-related changes in brain hemodynamics: A pilot study comparing transcranial Doppler and near-infrared...

Our aim was to assess cerebral blood flow changes during cybersickness. Transcranial Doppler (TCD) ultrasound and near infrared spectroscopy (NIRS) were used separately in two independent experiments. In both studies, a 15-min virtual roller coaster ride was used as a provocative visual stimulus. Subjective nausea ratings were obtained at 1 min intervals. The TCD study was performed in 14 healthy subjects (8 males and 6 females); in this study we also measured heart rate and arterial pressure. In a separate study a 52-channel NIRS device (Hitachi ETG-4000) was used to monitor activated brain regions by measuring oxy-hemoglobin (HbO₂₎ concentration in 9 healthy subjects (4 male, 5 females). The TCD study results showed a significant increase in systolic (+3.8 ± 1.8 mm Hg) and diastolic (+6.7 ± 1.3 mm Hg) pressure at the end of the virtual ride (maximum nausea) compared to baseline (no nausea). We also found that middle cerebral artery (MCA) and posterior cerebral artery (PCA) systolic flow velocity decreased significantly at the end of the ride when compared to baseline values. Likewise, the relative systolic and diastolic conductance in the MCA decreased significantly (-0.03 ± 0.02 cm × s^-1 × mm Hg^-1, t, p = 0.0058 and -0.03 ± 0.01 cm × s^-1 × mm Hg^-1, p = 0.05, respectively) at maximum nausea when compared to no nausea. Additionally, there was a significant decrease (-0.02 ± 0.01 cm × s^-1 × mm Hg^-1, p = 0.03) in the relative systolic conductance in the PCA at the end of the ride. Analysis of the NIRS results showed a significant increase in HbO₂ concentration in 15/52 channels in parieto-temporal regions of both hemispheres in participants who experienced motion sickness symptoms during the experiment. This increase in HbO₂ concentration correlated with increasing nausea and motion sickness symptoms. We conclude that cybersickness causes complex changes in cerebral blood flow, with an increase in perfusion in some cortical regions, but with a decrease of global cerebral perfusion.