Effects of sleeping at increased CO₂ levels and reduced ventilation on EEG activity upon waking the following morning

Inadequate bedroom ventilation affects sleep quality, but the effects on next-day cognitive performance remain insufficiently investigated. Moreover, the role of elevated carbon dioxide (CO₂) during sleep in influencing sleep quality and next-day cognitive performance is unclear. To address these questions, 22 participants slept for four nights each in two capsules under three conditions: high ventilation with metabolically generated CO₂ at 800 ppm (B800), reduced ventilation with metabolically generated CO₂ of 3000 ppm (B3000), and high ventilation with pure CO₂ added to reach 3000 ppm (P3000); the first night always served as adaptation at B800. Cognitive performance showed no significant differences across conditions; Stroop with feedback performance improved marginally at B800 (0.05<p < 0.1), and accuracy decreased on the Tsai–Partington test at P3000 (p < 0.05) after sleep compared to before. Participants reported exerting more effort when performing the same tasks at B3000 (p < 0.01), while the willingness to exert effort increased at P3000 and B800 (p < 0.05) after sleep compared to before sleep. EEG power for Alpha, Beta and total power recorded during the cognitive tasks decreased after sleeping at B800 and B3000, while the EEG power only in the Alpha band decreased after sleeping at P3000; all effects were statistically significant (p < 0.05). EEG power reductions were mainly confined to the occipital region at B800. Broader EEG power attenuation was observed across the all brain regions at B3000, while only Alpha power outside the frontal region was reduced at P3000. These results may indirectly suggest that poor bedroom air quality during sleep is associated with adverse effects on next-day cognitive performance, but require further validation.