Episodic thought distinguishes spontaneous cognition in waking from REM and NREM sleep

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.

Keywords: Autonoetic consciousness; Dreaming; Episodic future thought; Episodic memory; Mental time travel; Mind-wandering; Spontaneous thought.

Figure 1.

Proportion of episodic past and future thoughts across waking spontaneous thought, NREM and REM dreaming sleep states. Episodic thoughts are common during waking spontaneous thought and exhibit a strong prospective bias. In contrast, episodic thoughts of both the past and the future rarely occur in both N2 sleep and REM sleep.

Figure 2.

Percentage of past and future thoughts involving self, goal and both self and goal-related content of spontaneous thoughts during wakefulness. Both past and future thoughts frequently involve the self, but future thought also frequently involves goal-directed operations on self-relevant information. Examples from each category are shown below for thoughts of the past and future, respectively.