Episodic thought distinguishes spontaneous cognition in waking from REM and NREM sleep.
Benjamin Baird, Mariel Kalkach Aparicio, Tariq Alauddin, Brady Riedner, Melanie Boly, Giulio Tononi
Consciousness and cognition January 1, 2022 DOI: 10.1016/j.concog.2021.103247
Summary
Episodic thoughts, essential for mental time travel, show a striking difference between waking and sleep states. In a study involving 138 participants, spontaneous thought reports revealed that while 70% of waking thoughts included episodic memory and future planning, these thoughts were rarely present during NREM or REM sleep. This indicates that autonoetic consciousness and mind-wandering are significantly diminished in sleep. The findings highlight how our cognitive processes vary dramatically between wakefulness and dreaming, suggesting a unique experience of consciousness across the sleep-wake cycle.
Abstract
Evidence suggests continuity between cognition in waking and sleeping states. However, one type of cognition that may differ is episodic thoughts of the past and future. The current study investigated this across waking, NREM sleep and REM sleep. We analyzed thought reports obtained from a large sample of individuals (N = 138) who underwent experience-sampling during wakefulness as well as serial awakenings in sleep. Our data suggest that while episodic thoughts are common during waking spontaneous thought, episodic thoughts of both the past and the future rarely occur in either N2 or REM sleep. Moreover, replicating previous findings, episodic thoughts during wakefulness exhibit a strong prospective bias and frequently involve autobiographical planning. Together, these results suggest that the occurrence of spontaneous episodic thoughts differs substantially across waking and dreaming sleep states. We suggest that this points to a difference in the way that human consciousness is typically experienced across the sleep-wake cycle.