Introduction
Dreaming does not have a unanimous definition among psychologists and sleep researchers. Some argue that dreams are mental experiences during sleep that include our thoughts and feelings (Tsunematsu, Reference Tsunematsu2023), while others proport them as a mix of visual, motor, verbal, emotional and cognitive processes that occur during sleep (Scarpelli et al., Reference Scarpelli, Alfonsi, Gorgoni and De Gennaro2022). Dreaming has also been termed as sleep mentation (Scarpelli et al., Reference Scarpelli, Alfonsi, Gorgoni, Giannini and De Gennaro2021) or oneiric production (Scarpelli et al., Reference Scarpelli, Alfonsi, Gorgoni and De Gennaro2022), which occurs during rapid eye movement (REM) sleep or non-REM (NREM) sleep (Tsunematsu, Reference Tsunematsu2023). While the definition of dreaming is debatable, perhaps more contentious among scholars are the sources of dream production and how we come to experience them in our sleep. A central focus of this debate is the role of neurocognitive mechanisms in dreaming. Some theories propose that dreams are created by manifestations of our unconscious desires, random neural activity, an attempt to process daily experiences and emotions or memory consolidation (Nir and Tononi, Reference Nir and Tononi2010). While other theories suggests dreams prepare humans for real life dangers or represent a form of imagination (Nir and Tononi, Reference Nir and Tononi2010). Although there are many theories of dream production, here we focus on the theory of memory consolidation. In this theory, it is proposed that dreams may reflect the processing of information from our waking experiences (Graveline and Wamsley, Reference Graveline and Wamsley2015). Thus, our waking experience creates the foundation for the imagery, perceptions and other sensations emoted during dreams (Graveline and Wamsley, Reference Graveline and Wamsley2015; Wamsley, Reference Wamsley2014). However, it is still unclear whether dream production that relies on waking cognitive function, such as learning and memory, utilizes the same neurobiological pathways that are required for these functions while awake (Tononi et al., Reference Tononi, Boly and Cirelli2024). If these pathways turn out to be the same, a better understanding of the neurobiological mechanisms behind the creation of dreams will provide insight into areas of the brain that are involved in memory encoding (Tononi et al., Reference Tononi, Boly and Cirelli2024).
When dreaming processes are imbued with negative content, we experience a phenomenon known as nightmares. Like dreams, nightmares do not have a unified definition that spans research and clinical settings. For example, in one study, researchers defined the occurrence of a nightmare as when the participant wakes up due to the unpleasantness of what they saw or felt while asleep (Blagrove et al., Reference Blagrove, Farmer and Williams2004). Elsewhere, nightmares are described as intense negative dreams with a clear recall afterward, regardless of whether the participant had awakened at that time (Lancee and Schrijnemaekers, Reference Lancee and Schrijnemaekers2013). Clinically, the Diagnostic and Statistical Manual of Mental Disorders defines nightmares as dreams that induce dysphoric emotions and are remembered upon awakening (American Psychiatric Association, 2022). Albeit subjective, the ability to recall nightmares is key to defining them and allows for empirical inquiry of dream content and categorization. Differences in when or if a nightmare induces arousal make it difficult to approximate their prevalence, but it is estimated that 4–10% of the population experiences nightmares (Levin and Nielsen, Reference Levin and Nielsen2007). While this number may not be large, nightmares can have a profound impact on mental health, particularly depression and suicidal ideation (Lancee and Schrijnemaekers, Reference Lancee and Schrijnemaekers2013; Youngren et al., Reference Youngren, Bishop, Carr, Mattera and Pigeon2024; Bernert et al., Reference Bernert, Joiner, Cukrowicz, Schmidt and Krakow2005; Hedström et al., Reference Hedström, Bellocco, Hössjer, Ye, Trolle Lagerros and Åkerstedt2021; Harris et al., Reference Harris, Huang, Linthicum, Bryen and Ribeiro2020). Therefore, studies of nightmares are of great importance to better understand the mechanisms behind the phenomenon, as well as to examine strategies to prevent their negative effects.
One technique that may be a solution for circumventing the effects of nightmares is known as lucid dreaming (de Macêdo et al., Reference de Macêdo, Ferreira, de Almondes, Kirov and Mota-Rolim2019). Lucid dreaming is when an individual becomes consciously aware throughout a dreaming episode (Tononi et al., Reference Tononi, Boly and Cirelli2024). This conscious awareness allows the person to interact with their dreams as if they were awake and even allows them to control the dreaming narrative (Tononi et al., Reference Tononi, Boly and Cirelli2024). A meta-analysis reported that 55% of 24,282 individuals had experienced lucid dreaming at least once in their lifetime (Saunders et al., Reference Saunders, Roe, Smith and Clegg2016). Interestingly, it is possible to learn how to induce lucid dreams through different training methods (Tan and Fan, Reference Tan and Fan2023). The successful control of dream content raises the possibility that tapping underlying neurobiological and psychological resources could be used as a therapy for nightmare relief (de Macêdo et al., Reference de Macêdo, Ferreira, de Almondes, Kirov and Mota-Rolim2019). Beyond the treatment of nightmares, lucid dreaming could also be a potential means to enhance our learning (Bonamino et al., Reference Bonamino, Watling and Polman2023). In support of this notion, a meta-analysis that reviewed lucid dreaming germane to motor tasks concluded that motor tasks practiced during lucid dreaming showed significant performance improvements during waking (Bonamino et al., Reference Bonamino, Watling and Polman2023). Thus, lucid dreaming represents not only a promising avenue for combating distressing dream content, it may also provide a key to strengthening neuroplasticity (de Macêdo et al., Reference de Macêdo, Ferreira, de Almondes, Kirov and Mota-Rolim2019; Bonamino et al., Reference Bonamino, Watling and Polman2023).
Herein we present findings pertaining to queries that were posed by Palagini et al. including the “relationship between dreaming and memory, pathological dreaming (e.g., nightmares) their neurobiological processes and how they affect mental health and psychological functioning, and the mechanisms of lucid dreaming and the role of lucid dreaming in psychological functioning.” We do not cover the emotional processing and conscious aspects of memory as it relates to dreaming, nor do we cover other mental health impacts of nightmares aside from depression and suicide. We also do not cover other therapeutic interventions for nightmares aside from lucid dreaming. Addressing these questions is important because doing so clarifies how dreaming contributes to memory consolidation through stage-specific neural activity, elucidates the neurological mechanisms underlying pathological dreaming, including dysfunction in limbic and prefrontal circuits, and identifies clinically relevant interventions such as lucid dreaming that may mitigate nightmare-related distress and enhance psychological functioning.
Dreaming and cognition: memory sources of dreaming
Although dreaming is often associated with REM sleep, it is also present during NREM sleep and dream content may be influenced by both stages (Tsunematsu, Reference Tsunematsu2023). Typically, dreams that occur during REM sleep are more vivid, emotionally intense and bizarre, whereas dreams that take place during NREM sleep are more likely to reflect recent episodic memories (Wamsley, Reference Wamsley2014; Malinowski and Horton, Reference Malinowski and Horton2021; Hudachek and Wamsley, Reference Hudachek and Wamsley2023). Episodic and semantic memories are both classified under declarative memory, a type of memory involved in accessing past information (Dickerson and Eichenbaum, Reference Dickerson and Eichenbaum2010). When such memories are recalled years later, they are referred to as remote memories (Dickerson and Eichenbaum, Reference Dickerson and Eichenbaum2010; Kreutzer et al., Reference Rich, Kreutzer, DeLuca and Caplan2011). Episodic memory refers to the capability of storing, processing and retrieving lived personal experiences (Dickerson and Eichenbaum, Reference Dickerson and Eichenbaum2010). This type of memory is what is involved in remembering attending sports events or participating in childhood activities. In contrast, semantic memory refers to the ability to recall specific learned facts, such as the color of bees or the shape of a stop sign (Dickerson and Eichenbaum, Reference Dickerson and Eichenbaum2010). Several studies have explored the idea of episodic memory as a foundation for dreams (Graveline and Wamsley, Reference Graveline and Wamsley2015). In one study, participants watched a film in a laboratory and, upon dreaming were more likely to incorporate elements of the laboratory such as wearing electrodes, than elements of the film into their dreams (Graveline and Wamsley, Reference Graveline and Wamsley2015). This suggests that recent lived experiences contribute more to dream production than the passive intake of information (Graveline and Wamsley, Reference Graveline and Wamsley2015). Such contextual integration likely stems from NREM sleep-associated consolidation of episodic memories (Malinowski and Horton, Reference Malinowski and Horton2021). Notably, the episodic memories that surface in dreams are not usually exact replays of remembered events (Wamsley, Reference Wamsley2014). Furthermore, not all dreams are constructed from episodic memories; most dreams rely on prior experiences and can therefore also include other remote and semantic memories (Wamsley, Reference Wamsley2014). For example, when dreaming of unfamiliar people, their faces are structurally represented with prior knowledge of facial features (Wamsley, Reference Wamsley2014).
The incorporation of episodic memory fragments into our dreams can help us process emotions and strengthen learning (Malinowski and Horton, Reference Malinowski and Horton2021; Picard-Deland et al., Reference Picard-Deland, Aumont, Samson-Richer, Paquette and Nielsen2021). One hypothesis posits that memory reactivation during sleep recapitulates these elements into our dreams (Wamsley, Reference Wamsley2014). In support of this hypothesis, a noninvasive technique known as targeted memory reactivation (TMR) has been shown to aid in reactivating certain memories during sleep via sensory cues (Carbone and Diekelmann, Reference Carbone and Diekelmann2024). For example, an odor can be presented during a learning task to associate the odor with that specific cue. When that same odor is presented during sleep, it can aid the sleeper in recalling the learned cue while dreaming (Carbone and Diekelmann, Reference Carbone and Diekelmann2024). TMR has also been suggested to be beneficial for declarative and procedural memories, with an undetermined impact on the processing of emotional memories (Carbone and Diekelmann, Reference Carbone and Diekelmann2024). Therefore, TMR may be a promising avenue for the integration of episodic memories into dreams (Carbone and Diekelmann, Reference Carbone and Diekelmann2024).
To further explore the impact of sensory cues on dreams, a systematic review of 51 studies explored the influence of various external sensory stimuli on dream content (Salvesen et al., Reference Salvesen, Capriglia, Dresler and Bernardi2024). The authors concluded that somatosensory stimuli, that is, stimuli responsible for perceiving “touch, pressure, temperature, pain and proprioception,” were more likely to influence dream content than auditory stimuli (Salvesen et al., Reference Salvesen, Capriglia, Dresler and Bernardi2024). They also noted that olfactory stimuli influenced the emotional content of dream production, whereas visual stimuli had little impact on dream content (Salvesen et al., Reference Salvesen, Capriglia, Dresler and Bernardi2024). In addition, it seemed to matter whether the stimulus could be rationally incorporated into the dream, with the authors suggesting that if a dreamer was unable to seamlessly incorporate the stimulus, it could act as a cue for them to become aware that they are dreaming and inadvertently induce lucid dreaming (Salvesen et al., Reference Salvesen, Capriglia, Dresler and Bernardi2024). However, when they explored the impact of a stimulus during different stages of dreaming, either REM or NREM, they found inconclusive evidence as to which stage had a greater impact on dream production (Salvesen et al., Reference Salvesen, Capriglia, Dresler and Bernardi2024). In another study examining the influence of somatosensory stimuli on dream content, researchers trained participants on a virtual reality (VR) flight task prior to dreaming while playing a vibraphone melody for successful tasks completed (Picard-Deland et al., Reference Picard-Deland, Aumont, Samson-Richer, Paquette and Nielsen2021). The participants were then randomly assigned to one of five groups: TMR vibraphone stimulation during NREM, TMR vibraphone stimulation during REM, a nap with TMR vibraphone stimulation, staying awake with TMR vibraphone stimulation and staying awake without TMR vibraphone stimulation (Picard-Deland et al., Reference Picard-Deland, Aumont, Samson-Richer, Paquette and Nielsen2021). After this period of sleep/wake, the VR flight task was then performed again by all participants. The researchers found that those who had incorporated elements of the VR flight task into their dreams performed better when they were retested compared to those who did not (Picard-Deland et al., Reference Picard-Deland, Aumont, Samson-Richer, Paquette and Nielsen2021). Interestingly, the type of element that participants incorporated into their dreams also impacted how participants performed, with those who incorporated a kinesthetic element performing better than those who incorporated a visual element (Picard-Deland et al., Reference Picard-Deland, Aumont, Samson-Richer, Paquette and Nielsen2021). The study concluded that dreaming of tasks in REM sleep resulted in more improvement on the second VR flight NREM (Picard-Deland et al., Reference Picard-Deland, Aumont, Samson-Richer, Paquette and Nielsen2021). Overall, these studies confirmed the notion that somatosensory stimuli have a greater impact on dream content than other types of stimuli, and further highlight the idea that task integration into dreams aid in memory consolidation (Picard-Deland et al., Reference Picard-Deland, Aumont, Samson-Richer, Paquette and Nielsen2021; Salvesen et al., Reference Salvesen, Capriglia, Dresler and Bernardi2024).
In a recent meta-analysis on learning and post-dream awakening, the authors suggested that memory consolidation happens during dreaming when one integrates the content of the learned task into the dream, because improved memory performance was observed on tasks post-dreaming (Hudachek and Wamsley, Reference Hudachek and Wamsley2023). They also found that NREM sleep was more likely to have a stronger impact on memory post-dreaming (Hudachek and Wamsley, Reference Hudachek and Wamsley2023). Based on these findings, the authors believe that NREM dreams are more likely to be sourced from recent declarative memories, and REM dreams are associated with remote memories (Hudachek and Wamsley, Reference Hudachek and Wamsley2023). However, these assertions are not uncontested, as some reports suggest that dreams are due to heightened neural connections that create opportunities for the remodeling of waking memories and allow the memories to either be encoded or forgotten (Voss and Klimke, Reference Voss and Klimke2018). Yet the interpretability of such findings is complicated by methodological inconsistences that pervade the field of dream research (Hudachek and Wamsley, Reference Hudachek and Wamsley2023).
Due to lack of consistency in dream research, methods of dream collection do not follow a standard procedure (Hudachek and Wamsley, Reference Hudachek and Wamsley2023). For instance, the number and timing of dream report queries vary considerably across studies, ranging from single morning recalls to up to fourteen nighttime awakenings per participant (Hudachek and Wamsley, Reference Hudachek and Wamsley2023). Such inconsistency affects the likelihood of capturing task-related dream content, especially given the known decay of dream recall and its dependence on sleep stage (Hudachek and Wamsley, Reference Hudachek and Wamsley2023). Additionally, the approaches used to quantify task incorporation differ substantially, with some studies employing dichotomous classifications of dream content, while others use graded or continuous measures, as raters varied from independent coders to the participants themselves (Hudachek and Wamsley, Reference Hudachek and Wamsley2023). These discrepancies in both sampling and scoring introduce methodological inconsistencies that complicates cross-study comparisons. One meta-analysis noted that, due to the extent of this variability, not all methodological design elements could be systematically accounted for in their analysis (Hudachek and Wamsley, Reference Hudachek and Wamsley2023). This limits the precision of the observed effects and underscores the urgent need for greater standardization in dream research methodologies. While ultimately studies emphasize the cognitive benefits of dreaming, disruptions in the dreaming process can give rise to maladaptive outcomes, most notably in the form of nightmares.
Neurobiology of nightmares and effect on mental health
There are many theories as to the cause of nightmares. For example, psychoanalytic models of nightmare creation, such as the one proposed by Freud, suggest that nightmares reflect the transformation of libidinal urges into anxiety containment to preserve sleep (Nielsen and Levin, Reference Nielsen and Levin2007). The Threat Simulation Theory states that nightmares maintain a “biologically adaptive function” by rehearsing responses to danger, thus ensuring survival in waking life (Nielsen and Levin, Reference Nielsen and Levin2007). Moreover, Kramer’s mood regulatory theory of dreaming advocates for nightmares arising when nonnightmare dreaming fails to effectively manage emotional surges (Nielsen and Levin, Reference Nielsen and Levin2007). Another theory that has been put forward is the Affect Network Dysfunction Model, which roots nightmares in dysfunctional neural networks responsible for emotional regulation and fear extinction (Nielsen and Levin, Reference Nielsen and Levin2007). Such dysfunction fails to prevent the reorganization of fear memories into nonthreatening dreams (Nielsen and Levin, Reference Nielsen and Levin2007). In summary, prevailing theories converge on the view that nightmares originate from aberrant activity within neural circuits governing affect regulation, fear extinction and the cognitive integration of emotionally salient experiences during dreaming.
Among the many theories that have been proposed, the main theory that we will focus on here is the neurocognitive model proposed by Levin and Nielsen (Reference Levin and Nielsen2007). This model was selected over other theoretical frameworks due to its empirical grounding in neuroimaging evidence and its mechanistic specificity in implicating well-characterized neural circuits. The basis of this theory is that, on a neural level, nightmares originate from the interplay between the amygdala, hippocampus, medial prefrontal cortex and anterior cingulate cortex (Levin and Nielsen, Reference Levin and Nielsen2007). In support of this model, functional magnetic resonance imaging (fMRI) of nightmare sufferers has demonstrated that anterior cingulate activation is involved in nightmare production (Shen et al., Reference Shen, Wang and Ma2016). Furthermore, another fMRI found that increased activity in the medial prefrontal cortex, anterior cingulate cortex and hippocampus is correlated with nightmares (Marquis et al., Reference Marquis, Julien and Daneault2021). When fear is experienced in dream content the insular and midcingulate cortices are activated (Sterpenich et al., Reference Sterpenich, Perogamvros, Tononi and Schwartz2020), and severe nightmares reduce blood flow in the medial prefrontal and anterior cingulate cortices (Marquis et al., Reference Marquis, Julien and Baril2019). Together these studies support the neurocognitive model and tout the limbic system as a key locus of nightmare-related brain activity. However, more research is necessary to further understand the interaction of these areas and the molecular mechanisms involved.
Nightmares and psychological functioning
Nightmares can cause a person distress and adversely affect their mental health. In support of this notion, one study found that participants were more likely to experience depression the day after experiencing a nightmare (Lancee and Schrijnemaekers, Reference Lancee and Schrijnemaekers2013). Furthermore, it has been shown that a person who experiences a nightmare, regardless of frequency, is more likely to score lower on self-reported well-being than a person who does not have a nightmare (Blagrove et al., Reference Blagrove, Farmer and Williams2004). Interestingly, nightmare content is associated with the mental health of the person experiencing the nightmare. The type of nightmare a person experiences is also correlated to suicide risk (Youngren et al., Reference Youngren, Bishop, Carr, Mattera and Pigeon2024), even after controlling for depression (Bernert et al., Reference Bernert, Joiner, Cukrowicz, Schmidt and Krakow2005). Nightmares that are associated with trauma, also known as post-traumatic nightmares (Youngren et al., Reference Youngren, Bishop, Carr, Mattera and Pigeon2024), are more likely to be correlated with an increased incidence of suicidal ideation compared to nightmares of an unknown origin, or idiopathic nightmares (Youngren et al., Reference Youngren, Bishop, Carr, Mattera and Pigeon2024). There are, however, conflicting data on the link between nightmares and the risk of suicide. Some reports refute the idea that nightmares and suicide are linked but rather find that nightmares are associated with an increased risk of depression (Hedström et al., Reference Hedström, Bellocco, Hössjer, Ye, Trolle Lagerros and Åkerstedt2021). Indeed, a recent meta-analysis showed that nightmares were only weakly linked to suicide (Harris et al., Reference Harris, Huang, Linthicum, Bryen and Ribeiro2020). Some subjective tools often used in psychological research to assess different aspects of nightmare experiences are the Nightmare Frequency Questionnaire (NFQ) and the Nightmare Distress Questionnaire (NDQ). The NFQ is used in both clinical and nonclinical populations to measure how often individuals experience nightmares over a given time. Participants rate the frequency of their nightmares using a scale (e.g., from “never” to “several times a week”) and the metric also examines the association of nightmares with trauma, sleep quality, or mental health symptoms. Alternatively, the NDQ developed by Belicki (Reference Belicki1992), assesses the emotional and functional impact of nightmares, rather than just their frequency (Belicki, Reference Belicki1992). Participants answer 13 Likert-scale items targeting: difficulty coping with nightmares, sleep disruption, daytime distress and beliefs about nightmare origin and meaning. Thus, while nightmare frequency is a good outcome measure in research, nightmare distress correlates with psychopathology and impaired functioning. This distinction is crucial in both diagnosis and treatment planning as the intervention efficacy of treatment outcomes for nightmare-related distress can be studied. Regardless of the strength of the link between nightmares and suicide, the overall relationship between nightmares and mental health is an important topic that warrants further study due to the potential for negative health effects, and to completely understand the implications of future health outcomes.
Nightmares and lucid dreaming
One major question that has emerged from studies of nightmares is how can we treat them to improve the quality of life of those who suffer from them? One potential treatment approach for nightmares is lucid dreaming (Bonamino et al., Reference Bonamino, Watling and Polman2023). When we become aware that we are dreaming, it is then possible to interact with and change the content of our dreams, in essence, control dream outcomes (Gieselmann et al., Reference Gieselmann, Ait Aoudia and Carr2019). There are many ways to induce lucid dreaming (Tan and Fan, Reference Tan and Fan2023). Some induction methods include mnemonic induction of lucid dreams (MILD), reality testing (RT) and the senses-initiated lucid dream (SSILD) technique (Tan and Fan, Reference Tan and Fan2023). MILD involves awakening in the middle of the night, remembering what was dreamt about and watching out for those recalled signs of dreaming when sleep is resumed (Tan and Fan, Reference Tan and Fan2023). In the RT induction method, one must question if they are dreaming in addition to being observant of the dream environment (Tan and Fan, Reference Tan and Fan2023). Similar to MILD, SSILD requires the dreamer to wake up after 5 hours of sleep and focus on visual, auditory and somatic perceptions before waiting a predetermined amount of time prior to going back to sleep (Tan and Fan, Reference Tan and Fan2023).
In general, dream research relies on subjective measures, but eye signals are one way to objectively detect whether someone is lucid dreaming (Tan and Fan, Reference Tan and Fan2023). To perform studies using eye signals, prior to falling asleep, lucid dreamers are asked to move their eyes in a predetermined pattern such as looking left and right two times quickly once they realize they are in a dream (Baird et al., Reference Baird, Mota-Rolim and Dresler2019). When the subjects are determined to be asleep by polysomnography, these eye signals can then be recorded on an electrooculogram to verify that they are lucid dreaming (Baird et al., Reference Baird, Mota-Rolim and Dresler2019). A systematic review showed that MILD was the most effective technique with an induction rate of greater than >40% (Tan and Fan, Reference Tan and Fan2023).
A recent systematic review highlighted the promise of lucid dreaming. Although most studies had small sample sizes, low evidence levels and risk of bias, ten of the 11 studies (4 randomized controlled trials (RCTs), 2 case series, 5 case reports) showed positive effects of lucid dreaming in children and adults, including reduced nightmare frequency (up to 50%) even without full lucidity (Ouchene et al., Reference Ouchene, El Habchi, Demina, Petit and Trojak2023). Unfortunately, a meta-analysis was not possible due to heterogeneity in the included study designs and protocols. Regardless, the authors call for standardizing protocols for better research and clinical application, as it is paramount for utilizing lucid dreaming as a patient-centered, nonpharmacological approach to address internal conflicts through dream control.
In agreement with this review, another study found that lucid dreaming was an effective therapy to combat nightmares (de Macêdo et al., Reference de Macêdo, Ferreira, de Almondes, Kirov and Mota-Rolim2019). Lucid dreaming has also shown to decrease levels of depression in those with chronic nightmares (Holzinger et al., Reference Holzinger, Saletu and Klösch2020). These outcomes are likely due to the ability to control the nightmare content, thus making them less stressful (Tan and Fan, Reference Tan and Fan2023).
Conclusion
This perspectives piece synthesized current evidence on the role of dreaming in memory consolidation, the neurobiological mechanisms underlying nightmares and the therapeutic potential of lucid dreaming. Findings suggest that NREM and REM sleep contribute differently to memory incorporation into dreams, with somatosensory stimuli enhancing task-related content and post-sleep performance. The neurocognitive model of nightmares, implicating dysfunction in the amygdala, hippocampus, medial prefrontal cortex and anterior cingulate cortex, is supported by emerging neuroimaging data. Lucid dreaming, through targeted induction techniques, demonstrates promise as a nonpharmacological intervention for nightmares and may facilitate motor learning.
One major area for improvement in sleep research is creating a unified, universally agreed upon definition and term for dreaming and nightmares (Tsunematsu, Reference Tsunematsu2023; Scarpelli et al., Reference Scarpelli, Alfonsi, Gorgoni and De Gennaro2022; Scarpelli et al., Reference Scarpelli, Alfonsi, Gorgoni, Giannini and De Gennaro2021; Blagrove et al., Reference Blagrove, Farmer and Williams2004; Lancee and Schrijnemaekers, Reference Lancee and Schrijnemaekers2013; American Psychiatric Association, 2022). One proposal is that dreaming is defined as a subjective, immersive sensory, emotional and cognitive mental experience that occurs during both REM and NREM stages of sleep. Establishing universal definitions would enable consistent study designs and enhance the comparability of studies, thus strengthening the conclusions of meta-analyses and systematic reviews in the field. Additionally, this standardization would support the development of unbiased measurement tools for assessing dream and nightmare experiences. For example, shared criteria for rating nightmare severity (i.e. emotional intensity) and frequency (i.e. per week) would improve consistency and replicability of clinical and experimental sleep research. Together, these ideas can continue pushing forward sleep medicine.
Data availability statement
Data availability is not applicable to this article as no new data were created or analyzed in this study.
Acknowledgements
We would like to thank Suzanne Fricke for technical assistance and Amy Sullivan at Obrizus Communications for helpful suggestions with manuscript organization.
Author contributions
L. Perez: Conceptualization, Investigation, Writing – Original Draft/Review and Editing, C.J. Davis: Supervision, Writing – Review and Editing.
Financial support
This research received no specific grant from any funding agency, commercial or not-for-profit sectors.
Competing interests
The authors have no conflicts of interest to declare in the writing or content of this publication.
Ethical standards
This manuscript constitutes original writing that has not been published or submitted in part or in full elsewhere.
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