The influence of in-car air quality on drivers’ brain states with hybrid fNIRS and EEG

• Investigated the effects of CO 2 and body odor on driving brain states during driving. • Enrolled 25 participants in simulated highway driving under varying conditions. • Observed significant impact of CO 2 on very few EEG channels. • Altered EEG band power ratios found during cognition task due to body odor. • No significant impact of CO 2 or body odor on all fNIRS channels. This study investigates the effects of in-car carbon dioxide (CO 2 ) and body odor on cognitive performance during driving using advanced neuroimaging technologies. Prior literature on building environments suggested that CO 2 and body odor can negatively impact cognitive abilities, especially when building ventilation is limited. Various indoor environmental factors may hinder cognition and therefore driving performance, thereby raising concerns for transportation safety. In our study, we investigated the influence of elevated CO 2 and body odor on performance of driving and N-back tasks. We enrolled 25 participants in simulated highway driving scenarios for a two-factor experimental setup, varying the indoor CO 2 concentrations across three levels (800, 1800, and 3500 ppm) and two levels of body odor. CO 2 concentrations in the cabin were increased by introducing pure CO 2 and body odor was simulated by placing worn T-shirts in the cabin, while maintaining other environmental factors constant. Electroencephalography (EEG) and functional Near-Infrared Spectroscopy (fNIRS) were applied to monitor brain activities during driving. EEG data features included power spectral density (PSD) in delta, theta, alpha, and beta bands, and various band power ratios, while fNIRS data focused on the metrics of oxyhemoglobin (HbO) and deoxyhemoglobin (HbR). The findings indicated that body odor significantly impacts EEG band power ratios, especially during the secondary cognition task while driving. Specifically, the ratio index (α+θ)/β was lower in the condition with body odor from T-shirts, indicating increased alertness. Concurrently, with body odor, we found a lower θ/β ratio that was associated with an increase in stimulus-driven attention and an enhanced ability of the subjects to concentrate. In contrast, CO 2 levels exhibited a nuanced influence on cognitive functions, with insignificant impact on EEG band power or band power ratios observed. The results suggest a complex or trivial relationship between CO 2 exposure and cognitive responses that our neuroimaging modalities could not directly unravel. Moreover, fNIRS data did not indicate significant hemodynamic response changes attributable to CO 2 or body odor. The study contributes to the understanding of how CO 2 and body odor affect cognitive performance during driving, with implications for improving driving safety and designing better in-car environments.