Dreaming and Episodic Memory: A Functional Dissociation?

Abstract

The activity that takes place in memory systems during sleep is likely to be related to the role of sleep in memory consolidation and learning, as well as to the generation of dream hallucinations. This study addressed the often-stated hypothesis that replay of whole episodic memories contributes to the multimodal hallucinations of sleep. Over a period of 14 days, 29 subjects kept a log of daytime activities, events, and concerns, wrote down any recalled dreams, and scored the dreams for incorporation of any waking experiences. While 65% of a total of 299 sleep mentation reports were judged to reflect aspects of recent waking life experiences, the episodic replay of waking events was found in no more than 1-2% of the dream reports. This finding has implications for understanding the unique memory processing that takes place during the night and is consistent with evidence that sleep has no role in episodic memory consolidation.

Cognitive and emotional processes during dreaming: A neuroimaging view

“…the ability to recollect personally experienced events anchored within a particular spatio-temporal context) (Cabeza & Nyberg, 2000). In accordance with this hypothesis, only a very small percentage of dream reports that contain residues of previous waking activity have been found to represent an exact replay of full memory episodes (Fosse, Fosse, Hobson, & Stickgold, 2003;Schwartz, 2003). Isolated episodic elements are reactivated during sleep (most likely via the activation of the hippocampus, limbic structures, and posterior cortical areas), but these elements do not form replicates of real life episodes (because of the deactivation of the DLPFC among other possible causes; see Fig.…”

Sleep and Emotional Functions

“…Phasic VTA dopamine signals during REM sleep could indeed favor an off-line replay of recent emotional memory traces during this sleep stage (Walker and van der Helm 2009). These memories would then serve both as salient and novel stimuli for the penduculopontine tegmental nuclei and VTA, because recent relevant memories (e.g., emotional events, current concerns) are activated in the absence of cognitive control from dorsolateral PFC during REM sleep (Fosse et al 2003;Schwartz 2003) (Fig. 3).…”

Evidence for the preferential incorporation of emotional waking-life experiences into dreams.

“…Fosse et al (2003) investigated the presence of episodic memories in dreams, and found that very few dreams (<2%) contained intact episodic memories, but that 65% of the dreams contained episodic memory entries, suggesting that episodic memory elements may be fragmentarily incorporated during sleep. Schwartz (2003) postulated that the fragments may be preferentially incorporated due to their novelty or salience.…”