Assessing the Dream-Lag Effect for REM and NREM Stage 2 Dreams

Abstract

This study investigates evidence, from dream reports, for memory consolidation during sleep. It is well-known that events and memories from waking life can be incorporated into dreams. These incorporations can be a literal replication of what occurred in waking life, or, more often, they can be partial or indirect. Two types of temporal relationship have been found to characterize the time of occurrence of a daytime event and the reappearance or incorporation of its features in a dream. These temporal relationships are referred to as the day-residue or immediate incorporation effect, where there is the reappearance of features from events occurring on the immediately preceding day, and the dream-lag effect, where there is the reappearance of features from events occurring 5–7 days prior to the dream. Previous work on the dream-lag effect has used spontaneous home recalled dream reports, which can be from Rapid Eye Movement Sleep (REM) and from non-Rapid Eye Movement Sleep (NREM). This study addresses whether the dream-lag effect occurs only for REM sleep dreams, or for both REM and NREM stage 2 (N2) dreams. 20 participants kept a daily diary for over a week before sleeping in the sleep laboratory for 2 nights. REM and N2 dreams collected in the laboratory were transcribed and each participant rated the level of correspondence between every dream report and every diary record. The dream-lag effect was found for REM but not N2 dreams. Further analysis indicated that this result was not due to N2 dream reports being shorter, in terms of number of words, than the REM dream reports. These results provide evidence for a 7-day sleep-dependent non-linear memory consolidation process that is specific to REM sleep, and accord with proposals for the importance of REM sleep to emotional memory consolidation.

Dreaming and personality: Wake-dream continuity, thought suppression, and the Big Five Inventory

“…This is in keeping with both the day residue (Freud, 1900;Nielsen & Powell, 1992;Powell, Nielsen, Cheung, & Cervenka, 1995), and dream lag (Blagrove et al, 2011a(Blagrove et al, , 2011bNielsen, Kuiken, Alain, Stenstrom, & Powell, 2004) effects. Analyses in the present study illustrated the predominance of waking-life interpersonal relationships being represented in dreams, and to a lesser extent but still common waking-life concerns about work or studying, but financial worries in dreams were relatively rare.…”

The effect of time of night on wake–dream continuity.

“…Similarly, Blagrove et al (2011) demonstrated that the dream-lag effect was evident in REM but not NREM dreams, potentially demonstrating time of night effects also. In the present study, power analyses suggest that the small sample sizes may account for the null finding; however, Hall (1966, cited in Domhoff, 2003 did not replicate Verdone's findings, and significant results were found for other analyses with small samples in the present study, so this matter is still unresolved and is certainly worthy of further investigation.…”

The nature of delayed dream incorporation (‘dream‐lag effect’): Personally significant events persist, but not major daily activities or concerns

“…() have shown that the dream‐lag effect is not a result of confounding of the incorporation of weekly recurring events, where day‐residue incorporations of these might spuriously appear to refer to events from the previous week. The dream‐lag effect has been found using naturalistic events that occur in the participants' daily lives (Blagrove, Fouquet et al., ; Blagrove, Henley‐Einion et al., ; Nielsen et al., ; Nielsen & Powell, , experiment 1; van Rijn et al., , experiment 1, home dreams condition) and using standardized stimulus designs with stimuli such as a night sleeping in the sleep laboratory (Nielsen & Powell, , experiment 2; van Rijn et al., , experiment 2) or the watching of an emotionally arousing videotape of an animal sacrifice (Powell, Nielsen, Cheung, & Cervenka, ).…”