The effect of dream report collection and dream incorporation on memory consolidation during sleep

We are the Sensors of Consciousness! A Review and Analysis on How Awakenings During Sleep Influence Dream Recall

Purpose

Since the 1930s, researchers have awakened people from different stages of sleep to record what they have experienced. While some aspects, including asking whether participants had dreams or thoughts before awakening, largely remain the same, others, such as the method of awakening, vary greatly. In addition, it is often assumed that the influence of participant characteristics, such as personality traits, motivation, memory, and attention, is reduced by collecting experiences immediately after they occur, rather than through delayed morning recall. However, the extent to which these variables influence dream recall upon awakening has not yet been thoroughly investigated.

Materials and Methods

To explore possible contextual and individual influences, this review analyzed 69 awakening studies conducted between 2000 and 2024 and utilized the DREAM database. Differences between sleep stages were quantified and experiences analyzed using the categories "with recall", "without recall", and "no report".

Results

Similar levels of null reports were found in NREM stage 2 and stage 3. Significant factors affecting dream recall included the method of awakening (lower recall with an alarm compared to calling the participant's name), the number of study days (reduced recall for multiple days) and the sleep environment (higher recall at home compared to the laboratory), along with participant characteristics beyond age, sex and study design. Recall rates from NREM sleep are particularly sensitive to the method of awakening and interindividual differences.

Conclusion

Both the awakening procedure and participant characteristics influence the amount of reported sleep experiences, which can impact study outcomes, such as the identification of neural correlates of consciousness. Therefore, greater emphasis needs to be placed on how experiences are collected and on participant characteristics, such as openness to experience or familiarity with different states of consciousness.

Enhancing and advancing the understanding and study of dreaming and memory consolidation: Reflections, challenges, theoretical clarity, and methodological considerations

Empirical investigations that search for a link between dreaming and sleep-dependent memory consolidation have focused on testing for an association between dreaming of what was learned, and improved memory performance for learned material. Empirical support for this is mixed, perhaps owing to the inherent challenges presented by the nature of dreams, and methodological inconsistencies. The purpose of this paper is to address critically prevalent assumptions and practices, with the aim of clarifying and enhancing research on this topic, chiefly by providing a theoretical synthesis of existing models and evidence. Also, it recommends the method of Targeted Memory Reactivation (TMR) as a means for investigating if dream content can be linked to specific cued activations. Other recommendations to enhance research practice and enquiry on this subject are also provided, focusing on the HOW and WHY we search for memory sources in dreams, and what purpose (if any) they might serve.

Dreaming for two: A systematic review of mental sleep activity during pregnancy

Changes in sleep and dreams are often observed during pregnancy. Dreaming may represent privileged access to the inner world of individuals, providing relevant information about their well-being. For this reason, a growing but heterogeneous literature has investigated dream experiences of pregnant women. The present paper aimed to systematically review the available evidence on the relationship between pregnancy and oneric activity, focusing on dream and nightmare frequency, dream contents, and emotional features. Moreover, dream changes between pre-partum and post-partum periods and the impact of previous pregnancy-related adverse events on dreaming have been summarized. Overall, 17 studies have been examined. The reviewed evidence suggests that women tend to have an abundant production of dreams and nightmares during pregnancy, and some results support the view that a high rate of dream recall is associated with poor sleep quality. Most studies have shown a high presence of pregnancy-related dream content, likely reflecting waking experiences and concerns. Additionally, dreaming may promote psychological preparation and activation of functional coping strategies to face life changes after childbirth.

A meta-analysis of the relation between dream content and memory consolidation

The frequent appearance of newly learned information in dreams suggests that dream content is influenced by memory consolidation. Many studies have tested this hypothesis by asking whether dreaming about a learning task is associated with improved memory, but results have been inconsistent. We conducted a meta-analysis to determine the strength of the association between learning-related dreams and post-sleep memory improvement. We searched the literature for studies that (1) trained participants on a pre-sleep learning task and then tested their memory after sleep, and (2) associated post-sleep memory improvement with the extent to which dreams incorporated learning task content. Sixteen studies qualified for inclusion, which together reported 45 effects. Integrating across effects, we report a strong and statistically significant association between task-related dreaming and memory performance (SMD = 0.51 [95% CI 0.28, 0.74], p < 0.001). Among studies using polysomnography, this relationship was statistically significant for dreams collected from non-rapid eye movement (NREM) sleep (n = 10) but not for dreams collected from rapid eye movement (REM) sleep (n = 12). There was a significant association between dreaming and memory for all types of learning tasks studied. This meta-analysis provides further evidence that dreaming about a learning task is associated with improved memory performance, suggesting that dream content may be an indication of memory consolidation. Furthermore, we report preliminary evidence that the relationship between dreaming and memory may be stronger in NREM sleep compared to REM.

The memory sources of dreams: serial awakenings across sleep stages and time of night

Memories of waking-life events are incorporated into dreams, but their incorporation is not uniform across a night of sleep. This study aimed to elucidate ways in which such memory sources vary by sleep stage and time of night. Twenty healthy participants (11 F; 24.1 ± 5.7 years) spent a night in the laboratory and were awakened for dream collection approximately 12 times spread across early, middle, and late periods of sleep, while covering all stages of sleep (N1, N2, N3, REM). In the morning, participants identified and dated associated memories of waking-life events for each dream report, when possible. The incorporation of recent memory sources in dreams was more frequent in N1 and REM than in other sleep stages. The incorporation of distant memories from over a week ago, semantic memories not traceable to a single event, and anticipated future events remained stable throughout sleep. In contrast, the relative proportions of recent versus distant memory sources changed across the night, independently of sleep stage, with late-night dreams in all stages having relatively less recent and more remote memory sources than dreams earlier in the night. Qualitatively, dreams tended to repeat similar themes across the night and in different sleep stages. The present findings clarify the temporal course of memory incorporations in dreams, highlighting a specific connection between time of night and the temporal remoteness of memories. We discuss how dream content may, at least in part, reflect the mechanisms of sleep-dependent memory consolidation.

Sleep and dreaming in the light of reactive and predictive homeostasis

Dreams are often viewed as fascinating but irrelevant mental epihenomena of the sleeping mind with questionable functional relevance. Despite long hours of oneiric activity, and high individual differences in dream recall, dreams are lost into oblivion. Here, we conceptualize dreaming and dream amnesia as inherent aspects of the reactive and predictive homeostatic functions of sleep. Mental activity during sleep conforms to the interplay of restorative processes and future anticipation, and particularly during the second half of the night, it unfolds as a special form of non-constrained, self-referent, and future-oriented cognitive process. Awakening facilitates constrained, goal-directed prospection that competes for shared neural resources with dream production and dream recall, and contributes to dream amnesia. We present the neurophysiological aspects of reactive and predictive homeostasis during sleep, highlighting the putative role of cortisol in predictive homeostasis and forgetting dreams. The theoretical and methodological aspects of our proposal are discussed in relation to the study of dreaming, dream recall, and sleep-related cognitive processes.

Memory reactivations during sleep: a neural basis of dream experiences?

Newly encoded memory traces are spontaneously reactivated during sleep. Since their discovery in the 1990s, these memory reactivations have been discussed as a potential neural basis for dream experiences. New results from animal and human research, as well as from the rapidly growing field of sleep and dream engineering, provide essential insights into this question, and reveal both strong parallels and disparities between the two phenomena. We suggest that, although memory reactivations may contribute to subjective experiences across different states of consciousness, they are not likely to be the primary neural basis of dreaming. We identify important limitations in current research paradigms and suggest novel strategies to address this question empirically.

Investigating the effects of sleep and sleep loss on the different stages of episodic emotional memory: A narrative review and guide to the future

For two decades, sleep has been touted as one of the primary drivers for the encoding, consolidation, retention, and retrieval of episodic emotional memory. Recently, however, sleep's role in emotional memory processing has received renewed scrutiny as meta-analyses and reviews have indicated that sleep may only contribute a small effect that hinges on the content or context of the learning and retrieval episodes. On the one hand, the strong perception of sleep's importance in maintaining memory for emotional events may have been exacerbated by publication bias phenomena, such as the "winner's curse" and "file drawer problem." On the other hand, it is plausible that there are sets of circumstances that lead to consistent and reliable effects of sleep on emotional memory; these circumstances may depend on factors such as the placement and quality of sleep relative to the emotional experience, the content and context of the emotional experience, and the probes and strategies used to assess memory at retrieval. Here, we review the literature on how sleep (and sleep loss) influences each stage of emotional episodic memory. Specifically, we have separated previous work based on the placement of sleep and sleep loss in relation to the different stages of emotional memory processing: (1) prior to encoding, (2) immediately following encoding during early consolidation, (3) during extended consolidation, separated from initial learning, (4) just prior to retrieval, and (5) post-retrieval as memories may be restructured and reconsolidated. The goals of this review are three-fold: (1) examine phases of emotional memory that sleep may influence to a greater or lesser degree, (2) explicitly identify problematic overlaps in traditional sleep-wake study designs that are preventing the ability to better disentangle the potential role of sleep in the different stages of emotional memory processing, and (3) highlight areas for future research by identifying the stages of emotional memory processing in which the effect of sleep and sleep loss remains under-investigated. Here, we begin the task of better understanding the contexts and factors that influence the relationship between sleep and emotional memory processing and aim to be a valuable resource to facilitate hypothesis generation and promote important future research.

Constructive episodic simulation in dreams

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.

Whole-body procedural learning benefits from targeted memory reactivation in REM sleep and task-related dreaming

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.

Orchestration of dreams: a possible tool for enhancement of mental productivity and efficiency

Deciphering the significance of dreams, remains a dream till date. A little is known about its underlying mechanism, brain regions involved and implications with wake life. This review is aimed to investigate the latest developments to summarize the differences in nature of dreams in Rapid eye movement and Non rapid eye movement sleep, possible role of dreams in day to day life with larger focus on Lucid Dreaming- its significant role in elevating productivity and efficiency. To carry out this review, combination of keywords like Lucid Dreaming, Rapid eye movement, Non rapid eye movement, Sleep Cycle, Dream Patterns, molecular mechanism of dreaming etc. were entered in databases like National library of Medicine, Google Scholar etc. Nature and composition of dreams are distinct in different sleep phases and it tends to influence cognitive skills, memory consolidation, mood and personal temperaments. It was observed that dreams in distinct phases, can be directly/indirectly related to development of cognition, skill enhancements, learning, healing, and even stress management affecting overall performance and productivity of an individual. Understanding the nature of dream contents in different phases can possibly inculcate insights for not only recovery aid in several mental illnesses but for elevated efficiency and productivity in normal individuals as well. Realising dreams as an effective tool for its contribution in daily activities might help organising our mood and overall mental well-being, a foremost component to thrive in the contemporary world which is currently undergoing the chaos of Novel Coronavirus Disease 2019.

Does Sleep Selectively Strengthen Certain Memories Over Others Based on Emotion and Perceived Future Relevance?

Sleep has been found to have a beneficial effect on memory consolidation. It has furthermore frequently been suggested that sleep does not strengthen all memories equally. The first aim of this review paper was to examine whether sleep selectively strengthens emotional declarative memories more than neutral ones. We examined this first by reviewing the literature focusing on sleep/wake contrasts, and then the literature on whether any specific factors during sleep preferentially benefit emotional memories, with a special focus on the often-suggested claim that rapid eye movement sleep primarily consolidates emotional memories. A second aim was to examine if sleep preferentially benefits memories based on other cues of future relevance such as reward, test-expectancy or different instructions during encoding. Once again, we first focused on studies comparing sleep and wake groups, and then on studies examining the contributions of specific factors during sleep (for each future relevance paradigm, respectively). The review revealed that although some support exists that sleep is more beneficial for certain kinds of memories based on emotion or other cues of future relevance, the majority of studies does not support such an effect. Regarding specific factors during sleep, our review revealed that no sleep variable has reliably been found to be specifically associated with the consolidation of certain kinds of memories over others based on emotion or other cues of future relevance.

Dormio: A targeted dream incubation device

Information processing during sleep is active, ongoing and accessible to engineering. Protocols such as targeted memory reactivation use sensory stimuli during sleep to reactivate memories and demonstrate subsequent, specific enhancement of their consolidation. These protocols rely on physiological, as opposed to phenomenological, evidence of their reactivation. While dream content can predict post-sleep memory enhancement, dreaming itself remains a black box. Here, we present a novel protocol using a new wearable electronic device, Dormio, to automatically generate serial auditory dream incubations at sleep onset, wherein targeted information is repeatedly presented during the hypnagogic period, enabling direct incorporation of this information into dream content, a process we call targeted dream incubation (TDI). Along with validation data, we discuss how Dormio and TDI protocols can serve as tools for controlled experimentation on dream content, shedding light on the role of dreams in the overnight transformation of experiences into memories.

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

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.

Social Media, Dreaming, and Personality: An Online Study

Social media consumption plays an important role in everyday life and, thus, one would expect that this topic is reflected in dreams. This online survey included 1,349 participants (763 women, 586 men) completing questions about social media use in waking, percentage of social media dreams, and the Big Five personality dimensions. Social media dreams were quite rare (two percent of all remembered dreams), but their frequency correlated with neuroticism and extraversion-in addition to the amount of time using social media in waking-supporting the hypothesis that social media have a stronger effect on those person's inner life due to the higher importance attached to this channel of communication. For future research it would be of interest to elicit emotions related to social media in waking and the emotional tones of social media dreams to study whether positive and/or negative aspects of waking-life social media use are directly reflected in dreams.

The effect of dream report collection and dream incorporation on memory consolidation during sleep

Collecting dream reports typically requires waking subjects up from their sleep—a method that has been used to study the relationship between dreams and memory consolidation. However, it is unclear whether these awakenings influence sleep‐associated memory consolidation processes. Furthermore, it is unclear how the incorporation of the learning task into dreams is related to memory consolidation. In this study we compared memory performance in a word–picture association learning task after a night with and without awakenings in 22 young and healthy participants. We then examined if the stimuli from the learning task are successfully incorporated into dreams, and if this incorporation is related to the task performance the next morning. We show that while the awakenings impaired both subjective and objective sleep quality, they did not affect sleep‐associated memory consolidation. When dreams were collected during the night by awakenings, memories of the learning task were successfully incorporated into dreams. When dreams were collected in the morning, no incorporations were detected. Task incorporation into non‐rapid eye movement sleep dreams, but not rapid eye movement sleep dreams positively predicted memory performance the next morning. We conclude that the method of awakenings to collect dream reports is suitable and necessary for dream and memory studies. Furthermore, our study suggests that dreams in non‐rapid eye movement rather than rapid eye movement sleep might be related to processes of memory consolidation during sleep.