Incorporation of fragmented visuo-olfactory episodic memory into dreams and its association with memory performance

Whether dream content reflects memory consolidation is an open question. After reviewing the literature, an experiment tested if incorporating recently learned material into dreams relates to better memory after sleep. Thirty-two high dream recallers freely explored new visuo-olfactory episodes for 3 consecutive days. During subsequent nights, they woke at 5am and their usual waking time to record dreams; 120 dreams were reported. Elements from the encoding phase appeared in 37 dreams, mostly visual rather than olfactory. On day 4, participants with learning-related dreams showed similar odor recognition and odor-evoked episodic memory as others, but significantly better visuo-spatial memory of the episodes. Results suggest the learning phase is loosely incorporated into dreams and this incorporation is associated with sleep-related memory consolidation.

Study at a glance

Abstract

Abstract The question of a possible link between dream content and memory consolidation remains open. After a comprehensive review of the literature, we present novel findings from an experiment testing whether the incorporation of recently learned stimuli into dream reports is associated with improved post-sleep memory performance. Thirty-two high dream recallers freely explored new visuo-olfactory episodes for 3 consecutive days. During the nights following each non-explicit encoding, participants wore a wrist actimeter, and woke up at 5am and their usual waking time to record their dreams (intensity of all oneiric sensory perception was assessed using scales). A total of 120 dreams were reported and elements related to the encoding phase were identified in 37 of them, either learning-related (mainly visual- and rarely olfactory-related elements), or experiment-related (lab- or experimenters-related elements). On the 4 th day, we found that participants with learning-related (n = 16) and participants with learning-related and/or experiment-related dreams (n = 21) had similar odor recognition and odor-evoked episodic memory with the other participants. However, they had significantly better visuo-spatial memory of the episodes in comparison to the other participants. Our results support the hypothesis that the learning phase is loosely incorporated into dreams and that this incorporation is associated with sleep related memory consolidation.