Are life episodes replayed during dreaming?

doi:10.1016/S1364-6613(03)00162-1

Trends in Cognitive Sciences

Volume 7, Issue 8, August 2003, Pages 325-327

https://doi.org/10.1016/S1364-6613(03)00162-1 Get rights and content

Abstract

New phenomenological data demonstrate that integrated life episodes are incorporated in no more than 1–2% of dream reports. This appears to be at odds with the replay of temporally sequenced memory at the level of neuronal ensembles observed in some animals during sleep. This result will constrain emerging ideas on memory reactivation during sleep and the role of sleep in memory consolidation.

Section snippets

The memory-replay hypothesis

To understand the implications of this paper, it is useful to place it in the context of other related studies. Several studies have examined the beneficial effects of sleep (or the detrimental effects of sleep deprivation) on subsequent behavioral performance on trained tasks 5, 6, 7, 8 and on learning-related neural changes [9]. In addition, several studies have investigated memory reprocessing during sleep 10, 11, 12, 13. Converging evidence has accumulated to suggest that some waking

Functional dissociations in the sleeping brain

Fosse et al. found that all the 297 confidently identified memory entries came from a subset of 170 dreams. This means that 65% of the dreams contained on average two specific features from the waking life of the subjects. Incorporation of such specific experiential elements from waking life in dreams is a well documented fact 18, 19, 20. In light of the new findings of an absence of replay of whole integrated episodic events, we still have to understand why isolated episodic elements do appear

Dreams are like thoughts: towards a new heuristic

Importantly, the stepwise coding procedure used by Fosse et al. revealed that a significant proportion of memories in dreams referred to waking thoughts rather than to actual perceptions, representing one-third of the final episodic candidates scored by the subjects. These were not included, however, as episodic memory candidates (Step 7 in Fig. 1). This is because our incessant thoughts, explicit expectancies, and other mental representations do not fit the conventional definition of life

Acknowledgements

S.S. is supported by the Swiss National Science Foundation (grant 8210–061240). The author thanks Pierre Maquet and Patrik Vuilleumier for helpful discussions.

References (25)

C. Smith
Sleep states and memory processes
Behav. Brain Res.
(1995)
K. Louie et al.
Temporally structured replay of awake hippocampal ensemble activity during rapid eye movement sleep
Neuron
(2001)
S. Schwartz et al.
Sleep imaging and the neuro-psychological assessment of dreams
Trends Cogn. Sci.
(2002)
A.W. Epstein
The waking event-dream interval
Am. J. Psychiatry
(1985)
C.J.G. Marquardt
An empirical investigation into the day-residue and dream-lag effects
Dreaming
(1996)
C. Cavallero
Memory sources of REM and NREM dreams
Sleep
(1990)
M.J. Fosse
Dreaming and episodic memory: a functional dissociation?
J. Cogn. Neurosci.
(2003)
S. Gais
Early sleep triggers memory for early visual discrimination skills
Nat. Neurosci.
(2000)
R. Stickgold
Visual discrimination learning requires sleep after training
Nat. Neurosci.
(2000)
W. Plihal et al.
Effects of early and late nocturnal sleep on declarative and nondeclarative memory
J. Cogn. Neurosci.
(1997)

P. Maquet

Sleep-related consolidation of a visuomotor skill: brain mechanisms as assessed by functional magnetic resonance imaging

J. Neurosci.

(2003)

M.A. Wilson et al.

Reactivation of hippocampal ensemble memories during sleep

Science

(1994)

Cited by (58)

Neurobiology of dreams
2023, Encyclopedia of Sleep and Circadian Rhythms: Volume 1-6, Second Edition
Dreaming is a common, if not universal experience, which occurs during sleep. While in wakefulness, much of what we experience is strongly influenced by our surroundings, during sleep, we progressively cease to perceive the external world and to act upon it. This sensory and motor disconnection is a defining feature of sleep across species. Its reversible nature distinguishes it from coma, as sensory stimuli readily wake up the sleeper, provided they are strong, sudden, or salient enough. Despite this striking disconnection from the environment, the sleeping brain is able to generate a remarkable variety of conscious experiences by itself, ranging from abstract thoughts to “immersive spatiotemporal hallucinations” that characterize full-fledged dreams (Windt, 2015). How does the sleeping brain accomplish this task, and why? This book article will describe how dream experiences change across the night and in different sleep stages and will review recent studies that have outlined electrophysiological, anatomical and neurophysiological correlates of dreaming. It will explain how phenomenological dream features relate to patterns of brain activity and will provide a brief summary of theories on dream function.
Episodic thought distinguishes spontaneous cognition in waking from REM and NREM sleep
2022, Consciousness and Cognition
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.
Whole-body procedural learning benefits from targeted memory reactivation in REM sleep and task-related dreaming
2021, Neurobiology of Learning and Memory
Citation Excerpt :
Here we add to this literature in finding that the extent to which REM sleep dreams reactivate elements of the VR task is correlated with greater overall task improvement. These task-dream reactivations are far from complete episodic replicates of the VR task sequence, a finding that is typically true for dream reactivations of all kinds (Fosse, Fosse, Hobson, & Stickgold, 2003; Schwartz, 2003). Rather, dreams integrate some clearly recognized task elements in novel and creative ways.
Sleep facilitates memory consolidation through offline reactivations of memory traces. Dreaming may play a role in memory improvement and may reflect these memory reactivations. To experimentally address this question, we used targeted memory reactivation (TMR), i.e., application, during sleep, of a stimulus that was previously associated with learning, to assess whether it influences task-related dream imagery (or task-dream reactivations). Specifically, we asked if TMR or task-dream reactivations in either slow-wave (SWS) or rapid eye movement (REM) sleep benefit whole-body procedural learning. Healthy participants completed a virtual reality (VR) flying task prior to and following a morning nap or rest period during which task-associated tones were readministered in either SWS, REM sleep, wake or not at all. Findings indicate that learning benefits most from TMR when applied in REM sleep compared to a Control-sleep group. REM dreams that reactivated kinesthetic elements of the VR task (e.g., flying, accelerating) were also associated with higher improvement on the task than were dreams that reactivated visual elements (e.g., landscapes) or that had no reactivations. TMR did not itself influence dream content but its effects on performance were greater when coexisting with task-dream reactivations in REM sleep. Findings may help explain the mechanistic relationships between dream and memory reactivations and may contribute to the development of sleep-based methods to optimize complex skill learning.
Apical drive—A cellular mechanism of dreaming?
2020, Neuroscience and Biobehavioral Reviews
Dreams are internally generated experiences that occur independently of current sensory input. Here we argue, based on cortical anatomy and function, that dream experiences are tightly related to the workings of a specific part of cortical pyramidal neurons, the apical integration zone (AIZ). The AIZ receives and processes contextual information from diverse sources and could constitute a major switch point for transitioning from externally to internally generated experiences such as dreams. We propose that during dreams the output of certain pyramidal neurons is mainly driven by input into the AIZ. We call this mode of functioning “apical drive”. Our hypothesis is based on the evidence that the cholinergic and adrenergic arousal systems, which show different dynamics between waking, slow wave sleep, and rapid eye movement sleep, have specific effects on the AIZ. We suggest that apical drive may also contribute to waking experiences, such as mental imagery. Future studies, investigating the different modes of apical function and their regulation during sleep and wakefulness are likely to be richly rewarded.
Partial memory reinstatement while (lucid) dreaming to change the dream environment
2020, Consciousness and Cognition
Citation Excerpt :
Based on the lack of episodic dream content in their study, Fosse et al. (2003) concluded that memory processing during REM sleep is not related to episodic memory. However, a lack of complete episodic reinstatement does not prevent episodic memory benefits from occurring, as dream content might include pieces of an episodic memory (Plailly, Villalba, Vallat, Nicolas, & Ruby, 2019; Schwartz, 2003; Wamsley, 2014) or learning benefits of memory replay during sleep might be based on contextual memory replay (Boyce, Williams, & Adamantidis, 2017). While episodic memory includes specific details of a time and place (Tulving, 2002), contextual memory is more generic (Smith & Vela, 2001).
Lucid dreams often coincide with having control over dream events in real-time, although the limitations of dream control are not completely understood. The current study probed the ability of lucid dreamers to reinstate waking scene memories while dreaming. After brief exposure to an experimental scene, participants were asked to reinstate the scene while lucid dreaming (i.e., change dream scenery to match real-world scene). Qualitative analysis revealed that successful dream scene reinstatements were overwhelmingly inaccurate with respect to the original experimental scene. Importantly, reinstatement inaccuracies held even when the dreamer was aware of them during the dream, suggesting a dissociation between memory access while dreaming and dream imagery. The ability to change the environment of a dream speaks to the high amount of lucid dream control, yet the inaccuracies speak to a lack of detailed control. Reinstating context during lucid sleep offers an experimental method to investigate sleep, dreams, and memory.
Sleep talking: A viable access to mental processes during sleep
2019, Sleep Medicine Reviews
Citation Excerpt :
The activation-synthesis hypothesis represents the first acknowledgement of a possible role of dreaming in cognitive processes involving memory reactivation [135]. Within this theoretical frame, the reactivation of recent waking experiences through dreams or sleep mentation could represent a sort of ‘cognitive replay’ [136,137]. Furthermore, performance in cognitive or emotional learning tasks executed before sleeping has shown a significant improvement the following morning, positively correlated to the ‘incorporation’ of task-related content into mental activity during sleep [138,139].
Sleep talking is one of the most common altered nocturnal behaviours in the whole population. It does not represent a pathological condition and consists in the unaware production of vocalisations during sleep.
Although in the last few decades we have experienced a remarkable increase in knowledge about cognitive processes and behavioural manifestations during sleep, the literature regarding sleep talking remains dated and fragmentary. We first provide an overview of historical and recent findings regarding sleep talking, and we then discuss the phenomenon in the context of mental activity during sleep. It is shown that verbal utterances, reflecting the ongoing dream content, may represent the unique possibility to access the dreamlike mental experience directly. Furthermore, we discuss such phenomena within a cognitive theoretical framework, considering both the atypical activation of psycholinguistic circuits during sleep and the implications of verbal ‘replay’ of recent learning in memory consolidation.
Despite current knowledge on such a common experience being far from complete, an in-depth analysis of sleep talking episodes could offer interesting opportunities to address fundamental questions on dreaming or information processing during sleep. Further systematic polysomnographic and neuroimaging investigations are expected to shed new light on the manifestation of the phenomenon and related aspects.

View all citing articles on Scopus

View full text

Trends in Cognitive Sciences

Research FocusAre life episodes replayed during dreaming?

Abstract

Section snippets

The memory-replay hypothesis

Functional dissociations in the sleeping brain

Dreams are like thoughts: towards a new heuristic

Acknowledgements

Behav. Brain Res.

Neuron

Trends Cogn. Sci.

The waking event-dream interval

Am. J. Psychiatry

An empirical investigation into the day-residue and dream-lag effects

Dreaming

Memory sources of REM and NREM dreams

Sleep

Dreaming and episodic memory: a functional dissociation?

J. Cogn. Neurosci.

Early sleep triggers memory for early visual discrimination skills

Nat. Neurosci.

Visual discrimination learning requires sleep after training