Claim

Short, repeated overnight CO2 excursions above ~1500 ppm reduce next-day executive performance (set-shifting / inhibition), even when sleep duration and bedtime are stable.

Why this is plausible

• Controlled studies show higher indoor CO2 is associated with worse decision-making and cognitive scores in office-like settings (Allen et al., 2016; Satish et al., 2012).
• Sleep studies often focus on apnea/oxygen drops, but typical homes can reach high CO2 without obvious awakenings, creating a potentially under-measured pathway for daytime mental performance.

Testable experiment

A 4-week randomized crossover N-of-1 (or small cohort):

1. Ventilated nights: keep bedroom CO2 <900 ppm (window/ERV/fan strategy).
2. Usual nights: no intervention (natural occupancy/ventilation).
3. Hold bedtime, wake time, caffeine timing, and sleep duration constant as much as possible.
4. Record overnight CO2 (1-min sensor logging), temperature, RH.
5. Measure next-day cognition at fixed times using brief tasks (Stroop, task-switching, PVT, n-back) + subjective focus.

Predicted result

Nights with higher cumulative CO2 burden (AUC above 1200–1500 ppm) will predict worse next-day task-switching accuracy/reaction time, independent of total sleep time.

Falsification criteria

• No within-subject association between CO2 burden and next-day cognition after controlling for sleep duration/temperature.
• Effect disappears when randomization/blinding proxies are strengthened.

Practical value

If true, low-cost ventilation changes could improve daily cognition similarly to other lifestyle interventions, especially in tightly sealed bedrooms.

Starting references

• Allen JG, et al. Associations of cognitive function scores with carbon dioxide, ventilation, and volatile organic compound exposures in office workers: a controlled exposure study. Environ Health Perspect. 2016;124(6):805-812. doi:10.1289/ehp.1510037
• Satish U, et al. Is CO2 an indoor pollutant? Direct effects of low-to-moderate CO2 concentrations on human decision-making performance. Environ Health Perspect. 2012;120(12):1671-1677. doi:10.1289/ehp.1104789