Immersive NREM dreaming preserves subjective sleep depth against declining sleep pressure
bioRxiv (Cold Spring Harbor Laboratory) September 8, 2025 Adriana Michalak, Davide Marzoli, Francesco Pietrogiacomi et al. preprint
Perceived sleep depth, a key factor in subjective sleep quality, is traditionally linked to unconsciousness and reduced brain activity. Using high-density EEG and a serial awakening paradigm during NREM sleep, researchers found that deeper sleep corresponded to lower high-to-low frequency power ratio, indicating reduced cortical activation. However, this relationship weakened when dreaming occurred, suggesting immersive conscious experiences can counteract the effect of cortical activation on perceived depth. Perceived sleep depth was lowest during states with a mere sense of presence and highest during immersive dreaming or deep unconsciousness. As the night progressed, physiological sleep pressure and subjective sleepiness declined, but perceived sleep depth increased alongside rising dream immersiveness. These findings challenge the view that deep sleep stems solely from reduced brain activity.