Constructive episodic simulation in dreams

Abstract

Memories of the past help us adaptively respond to similar situations in the future. Originally described by Schacter & Addis in 2007, the "constructive episodic simulation" hypothesis proposes that waking thought combines fragments of various past episodes into imagined simulations of events that may occur in the future. This same framework may be useful for understanding the function of dreaming. N = 48 college students were asked to identify waking life sources for a total of N = 469 dreams. Participants frequently traced dreams to at least one past or future episodic source (53.5% and 25.7% of dreams, respectively). Individual dreams were very often traced to multiple waking sources (43.9% of all dreams with content), with fragments of past memory incorporated into scenarios that anticipated future events. Waking-life dream sources are described in terms of their phenomenology and distribution across time and sleep stage, providing new evidence that dreams not only reflect the past, but also utilize memory in simulating potential futures.

Fig 1. Co-occurrence of past and future dream sources.

Data are shown as the raw number of reports identified in each category, and as a % of all dreams with a waking source identification. The “general/semantic” category collapses across reports identified as related to general categories of past experience and future concerns.

Fig 2. Dream sources by sleep stage.

Proportion of content-filled dream reports from each sleep stage by type of waking source. REM = Rapid eye movement sleep. NREM = Non-rapid eye movement sleep. Error bars = 95% CI. Binomial confidence intervals calculated using the Clopper–Pearson “exact” method.

Fig 3. Temporal orientation of episodic sources varies by time of night.

Proportion of content-filled dream reports related to past and future episodes, by quartile of the night. Error bars = 95% CI. Binomial confidence intervals calculated using the Clopper–Pearson “exact” method.

Fig 4. Past and future temporal references by sleep stage.

Episodic sources by temporal origin and sleep stage. Percentages are relative to all content-filled reports with a valid source. NREM = Non-rapid eye movement sleep. REM = Rapid eye movement sleep.