Nocturnal exposure to a preferred ambient scent does not affect dream emotionality or post-sleep core affect valence in young adults.

Emotions experienced within sleep mentation (dreaming) affect mental functioning in waking life. There have been attempts at enhancing dream emotions using olfactory stimulation. Odors readily acquire affective value, but to profoundly influence emotional processing, they should bear personal significance for the perceiver rather than be generally pleasant. The main objective of the present sleep laboratory study was to examine whether prolonged nocturnal exposure to self-selected, preferred ambient room odor while asleep influences emotional aspects of sleep mentation and valence of post-sleep core affect. We asked twenty healthy participants (12 males, mean age 25 ± 4 years) to pick a commercially available scented room diffuser cartridge that most readily evoked positively valenced mental associations. In weekly intervals, the participants attended three sessions. After the adaptation visit, they were administered the odor exposure and odorless control condition in a balanced order. Participants were awakened five minutes into the first rapid eye movement (REM) stage that took place after 2:30 a.m. and, if they had been dreaming, they were asked to rate their mental sleep experience for pleasantness, emotional charge, and magnitude of positive and negative emotions and also to evaluate their post-sleep core affect valence. With rs < 0.20, no practically or statistically significant differences existed between exposure and control in any outcome measures. We conclude that in young, healthy participants, the practical value of olfactory stimulation with self-selected preferred scents for enhancement of dream emotions and post-sleep core affect valence is very limited.

REM sleep: Out-dreaming fear.

The ability to forget fear-inducing situations is essential for adapting to our environment, but the neural mechanisms underlying 'fear forgetting' remain unclear. Novel findings reveal that the activity of the infralimbic cortex - specifically during REM sleep - contributes to the extinction of fear memory.

Consciousness and sleep.

Sleep is a universal, essential biological process. It is also an invaluable window on consciousness. It tells us that consciousness can be lost but also that it can be regained, in all its richness, when we are disconnected from the environment and unable to reflect. By considering the neurophysiological differences between dreaming and dreamless sleep, we can learn about the substrate of consciousness and understand why it vanishes. We also learn that the ongoing state of the substrate of consciousness determines the way each experience feels regardless of how it is triggered-endogenously or exogenously. Dreaming consciousness is also a window on sleep and its functions. Dreams tell us that the sleeping brain is remarkably lively, recombining intrinsic activation patterns from a vast repertoire, freed from the requirements of ongoing behavior and cognitive control.

Shared EEG correlates between non-REM parasomnia experiences and dreams.

Sleepwalking and related parasomnias result from incomplete awakenings out of non-rapid eye movement sleep. Behavioral episodes can occur without consciousness or recollection, or in relation to dream-like experiences. To understand what accounts for these differences in consciousness and recall, here we recorded parasomnia episodes with high-density electroencephalography (EEG) and interviewed participants immediately afterward about their experiences. Compared to reports of no experience (19%), reports of conscious experience (56%) were preceded by high-amplitude EEG slow waves in anterior cortical regions and activation of posterior cortical regions, similar to previously described EEG correlates of dreaming. Recall of the content of the experience (56%), compared to no recall (25%), was associated with higher EEG activation in the right medial temporal region before movement onset. Our work suggests that the EEG correlates of parasomnia experiences are similar to those reported for dreams and may thus reflect core physiological processes involved in sleep consciousness.

Social media-related nightmare - a potential explanation for poor sleep quality and low affective well-being in the social media era?

Research has posited that social media use during the day may be reflected in nighttime dreams. Nevertheless, no prior studies have explored frightening, unpleasant dreams arising from social media use. This study introduces the construct of the social media-related nightmare by (a) developing and validating a scale capturing negative-valenced dreams with themes of helplessness, loss of control, inhibition, victimization, and making mistakes in social media, and (b) examining relationships between social media use, social media-related nightmares, sleep quality, and affective well-being. A convenience sample of 595 Iranian adult social media users (Mage = 27.45, SDage = 11.42) reported on social media-related nightmare, social media use integration, anxiety, peace of mind, sleep quality, and nightmare distress. The Social Media-Related Nightmare Scale (SMNS) demonstrated a unidimensional structure with sound psychometric properties. The most common nightmares involved the inability to log in to social media and the disruption of relationships with other users. Social media use intensity predicted frequency of social media-related nightmares. These nightmares were correlated with increased anxiety, lower peace of mind, poor sleep quality, and nightmare distress. Importantly, social media-related nightmares mediated the relationship between social media use intensity and low affective well-being (i.e., anxiety and peace of mind), poor sleeping, and nightmare distress. The findings suggest that social media-related nightmares could be a potential pathway through which social media engagement may lead to affective distress and sleep difficulties.

Aphantasia and hyperphantasia: exploring imagery vividness extremes.

The vividness of imagery varies between individuals. However, the existence of people in whom conscious, wakeful imagery is markedly reduced, or absent entirely, was neglected by psychology until the recent coinage of 'aphantasia' to describe this phenomenon. 'Hyperphantasia' denotes the converse - imagery whose vividness rivals perceptual experience. Around 1% and 3% of the population experience extreme aphantasia and hyperphantasia, respectively. Aphantasia runs in families, often affects imagery across several sense modalities, and is variably associated with reduced autobiographical memory, face recognition difficulty, and autism. Visual dreaming is often preserved. Subtypes of extreme imagery appear to be likely but are not yet well defined. Initial results suggest that alterations in connectivity between the frontoparietal and visual networks may provide the neural substrate for visual imagery extremes.

Influencing dreams through sensory stimulation: A systematic review.

Sleep is typically considered a state of disconnection from the environment, yet instances of external sensory stimuli influencing dreams have been reported for centuries. Explaining this phenomenon could provide valuable insight into dreams' generative and functional mechanisms, the factors that promote sleep continuity, and the processes that underlie conscious awareness. Moreover, harnessing sensory stimuli for dream engineering could benefit individuals suffering from dream-related alterations. This PRISMA-compliant systematic review assessed the current evidence concerning the influence of sensory stimulation on sleep mentation. We included 51 publications, of which 21 focused on auditory stimulation, ten on somatosensory stimulation, eight on olfactory stimulation, four on visual stimulation, two on vestibular stimulation, and one on multimodal stimulation. Furthermore, nine references explored conditioned associative stimulation: six focused on targeted memory reactivation protocols and three on targeted lucid reactivation protocols. The reported frequency of stimulus-dependent dream changes across studies ranged from 0 to ∼80%, likely reflecting a considerable heterogeneity of definitions and methodological approaches. Our findings highlight a lack of comprehensive understanding of the mechanisms, functions, and neurophysiological correlates of stimulus-dependent dream changes. We suggest that a paradigm shift is required for meaningful progress in this field.

Altered parasympathetic activity during sleep and emotionally arousing wakefulness in frequent nightmare recallers.

Nightmare disorder is characterized by dysfunctional emotion regulation and poor subjective sleep quality reflected in pathophysiological features such as abnormal arousal processes and sympathetic influences. Dysfunctional parasympathetic regulation, especially before and during rapid eye movement (REM) phases, is assumed to alter heart rate (HR) and its variability (HRV) of frequent nightmare recallers (NM). We hypothesized that cardiac variability is attenuated in NMs as opposed to healthy controls (CTL) during sleep, pre-sleep wakefulness and under an emotion-evoking picture-rating task. Based on the polysomnographic recordings of 24 NM and 30 CTL participants, we examined HRV during pre-REM, REM, post-REM and slow wave sleep, separately. Additionally, electrocardiographic recordings of resting state before sleep onset and under an emotionally challenging picture-rating task were also analyzed. Applying repeated measures analysis of variance (rmANOVA), a significant difference was found in the HR of NMs and CTLs during nocturnal segments but not during resting wakefulness, suggesting autonomic dysregulation, specifically during sleep in NMs. As opposed to the HR, the HRV values were not significantly different in the rmANOVA in the two groups, implying that the extent of parasympathetic dysregulation on a trait level might depend on the severeness of dysphoric dreaming. Nonetheless, in the group comparisons, the NM group showed increased HR and reduced HRV during the emotion-evoking picture-rating task, which aimed to model the nightmare experience in the daytime, indicating disrupted emotion regulation in NMs under acute distress. In conclusion, trait-like autonomic changes during sleep and state-like autonomic responses to emotion-evoking pictures indicate parasympathetic dysregulation in NMs.

Cortical hyperarousal in individuals with frequent nightmares.

Nightmares are common among the general population and psychiatric patients and have been associated with signs of nocturnal arousal such as increased heart rate or increased high-frequency electroencephalographic (EEG) activity. However, it is still unclear, whether these characteristics are more of a trait occurring in people with frequent nightmares or rather indicators of the nightmare state. We compared participants with frequent nightmares (NM group; n = 30) and healthy controls (controls; n = 27) who spent 4 nights in the sleep laboratory over the course of 8 weeks. The NM group received six sessions of imagery rehearsal therapy (IRT), the 'gold standard' of cognitive-behavioural therapy for nightmares, between the second and the third night. Sleep architecture and spectral power were compared between groups, and between nights of nightmare occurrence and nights without nightmare occurrence in the NM group. Additionally, changes before and after therapy were recorded. The NM group showed increased beta (16.25-31 Hz) and low gamma (31.25-35 Hz) power during the entire night compared to the controls, but not when comparing nights of nightmare occurrence to those without. Moreover, low gamma activity in rapid eye movement sleep was reduced after therapy in the NM group. Our findings indicate, cortical hyperarousal is more of a trait in people with frequent nightmares within a network of other symptoms, but also malleable by therapy. This is not only a new finding for IRT but could also lead to improved treatment options in the future that directly target high-frequency EEG activity.

Acetylcholine and metacognition during sleep.

Acetylcholine is a neurotransmitter and neuromodulator involved in a variety of cognitive functions. Additionally, acetylcholine is involved in the regulation of REM sleep: cholinergic neurons in the brainstem and basal forebrain project to and innervate wide areas of the cerebral cortex, and reciprocally interact with other neuromodulatory systems, to produce the sleep-wake cycle and different sleep stages. Consciousness and cognition vary considerably across and within sleep stages, with metacognitive capacity being strikingly reduced even during aesthetically and emotionally rich dream experiences. A notable exception is the phenomenon of lucid dreaming-a rare state whereby waking levels of metacognitive awareness are restored during sleep-resulting in individuals becoming aware of the fact that they are dreaming. The role of neurotransmitters in these fluctuations of consciousness and cognition during sleep is still poorly understood. While recent studies using acetylcholinesterase inhibitors suggest a potential role of acetylcholine in the occurrence of lucid dreaming, the underlying mechanisms by which this effect is produced remains un-modelled and unknown; with the causal link between cholinergic mechanisms and upstream psychological states being complex and elusive. Several theories and approaches targeting the association between acetylcholine and metacognition during wakefulness and sleep are highlighted in this review, moving through microscopic, mesoscopic and macroscopic levels of analysis to detail this phenomenon at several organisational scales. Several exploratory hypotheses will be developed to guide future research towards fully articulating how metacognition is affected by activity at the acetylcholine receptor.

Learning beyond sensations: How dreams organize neuronal representations.

Semantic representations in higher sensory cortices form the basis for robust, yet flexible behavior. These representations are acquired over the course of development in an unsupervised fashion and continuously maintained over an organism's lifespan. Predictive processing theories propose that these representations emerge from predicting or reconstructing sensory inputs. However, brains are known to generate virtual experiences, such as during imagination and dreaming, that go beyond previously experienced inputs. Here, we suggest that virtual experiences may be just as relevant as actual sensory inputs in shaping cortical representations. In particular, we discuss two complementary learning principles that organize representations through the generation of virtual experiences. First, "adversarial dreaming" proposes that creative dreams support a cortical implementation of adversarial learning in which feedback and feedforward pathways engage in a productive game of trying to fool each other. Second, "contrastive dreaming" proposes that the invariance of neuronal representations to irrelevant factors of variation is acquired by trying to map similar virtual experiences together via a contrastive learning process. These principles are compatible with known cortical structure and dynamics and the phenomenology of sleep thus providing promising directions to explain cortical learning beyond the classical predictive processing paradigm.

The neurocognition of dreaming: key questions and foci.

Until recently, understanding the neurobiology of dreaming has relied upon on correlating a subjective dream report with a measure of brain activity or function sampled from a different occasion. As such, most assumptions about dreaming come from the neuroscience of rapid eye-movement (REM) sleep from which many, but not all, dream reports are recalled. Core features of REM sleep (intense emotional activation, a reduction in activity in most frontal regions, particularly the dorsolateral prefrontal cortex, along with increased dopamine, acetylcholine, cholinergic activation) align with typical dream characteristics (characterised by fear, reduced reality monitoring, increased bizarreness and hyperassociativity, respectively). The default mode network offers a way of understanding the nature of dreaming more independently from a REM sleep context, and electroencephalography methods paired with serial awakenings to elicit dream reports demonstrate how high-frequency activity in posterior regions may be associated with dreaming. Nevertheless, all measures of dreaming rely fundamentally on recall processes, so our understanding of dreaming must embrace and address memory's crucial involvement in dream report production.

REM sleep function: Mythology vs. reality.

Since the discovery of REM (Rapid Eye Movement) sleep in 1953, misconceptions have arisen as to the evidence for its adaptive function and its relation to dreams. Eye movements recorded during REM sleep have not been consistently reported to mirror the eye movements predicted by dream reports. But evidence on eye movement and somatic motor expression from patients with REM sleep behavior disorder (RBD) is consistent with dream enacting behavior. The assumption that dreaming occurs only in REM sleep is incorrect, with numerous reports of nonREM dreaming. However, there may be qualitative differences between REM and nonREM dreams. Early studies that suggested a vital role for REM sleep in psychological well-being are refuted by studies of pharmacologically induced partial or complete REM sleep suppression. Studies of sleep across species show that the primitive monotreme mammals, platypus and echidna, have far more REM sleep than any other homeotherm group, whereas birds have far less REM sleep than any other homeotherm group. Human REM sleep amounts are not unusual, are correlated with nonREM sleep durations but are not correlated with intelligence. Across groups of homeotherms, REM sleep time is highly and inversely correlated (r=-0.975, P=0.02) with average core body temperature, suggesting that REM sleep cycles with nonREM sleep to regulate brain temperature during sleep. Cetacean mammals (dolphins and whales) do not have REM sleep despite their very large brain sizes and impressive cognitive abilities. Reports of "REM sleep-like states" in arachnids, cephalopods and in zebrafish larvae are lacking critical evidence that the observed behaviors are occurring during sleep and that the behaviors are homologous to mammalian REM sleep.

Visual perspective, distance, and felt presence of others in dreams.

The peripersonal space, that is, the limited space surrounding the body, involves multisensory coding and representation of the self in space. Previous studies have shown that peripersonal space representation and the visual perspective on the environment can be dramatically altered when neurotypical individuals self-identify with a distant avatar (i.e., in virtual reality) or during clinical conditions (i.e., out-of-body experience, heautoscopy, depersonalization). Despite its role in many cognitive/social functions, the perception of peripersonal space in dreams, and its relationship with the perception of other characters (interpersonal distance in dreams), remain largely uncharted. The present study aimed to explore the visuospatial properties of this space, which is likely to underlie self-location as well as self/other distinction in dreams. 530 healthy volunteers answered a web-based questionnaire to measure their dominant visuo-spatial perspective in dreams, the frequency of recall for felt distances between their dream self and other dream characters, and the dreamers' viewing angle of other dream characters. Most participants reported dream experiences from a first-person perspective (1PP) (82%) compared to a third-person perspective (3PP) (18%). Independent of their dream perspective, participants reported that they generally perceived other dream characters in their close space, that is, at distance of either between 0 and 90 cm, or 90-180 cm, than in further spaces (180-270 cm). Regardless of the perspective (1PP or 3PP), both groups also reported more frequently seeing other dream characters from eye level (0° angle of viewing) than from above (30° and 60°) or below eye level (-30° and -60°). Moreover, the intensity of sensory experiences in dreams, as measured by the Bodily Self-Consciousness in Dreams Questionnaire, was higher in individuals who habitually see other dream characters closer to their personal dream self (i.e., within 0-90 cm and 90-180 cm). These preliminary findings offer a new, phenomenological account of space representation in dreams with regards to the felt presence of others. They might provide insights not only to our understanding of how dreams are formed, but also to the type of neurocomputations involved in self/other distinction.

Subjectively intense odor does not affect dream emotions during rapid eye movement sleep.

Dreams experienced during rapid eye movement (REM) sleep have emotional features. Intervention methods for dream affectivity have recently garnered interest; we previously demonstrated that negative dreams were induced during REM sleep by exposure to favorable or familiar odors. However, the underlying mechanisms behind this phenomenon remain unclear. Thus, to address this gap, we investigated whether more intense odors could induce negative dreams, as odors tend to be perceived as more intense when they are preferred or familiar. Contrary to our hypothesis, the results of our study indicated that subjective intense odors did not induce negative dreams. We initially anticipated stronger odors to have a greater impact on dream emotionality, as they stimulate the brain more intensely. Notably, during arousal, weak odors tended to evoke a more potent olfactory response, while strong odors tended to produce a weaker response. To investigate whether this difference influenced the effects on dreams, we compared the respiratory activities of the strongly and weakly perceived odor groups; however, no significant differences were observed. Our findings suggest that subjectively perceived strong odors are unlikely to affect dream emotionality and may be processed differently than favorable or familiar odors.

Targeted dream incubation at sleep onset increases post-sleep creative performance.

The link between dreams and creativity has been a topic of intense speculation. Recent scientific findings suggest that sleep onset (known as N1) may be an ideal brain state for creative ideation. However, the specific link between N1 dream content and creativity has remained unclear. To investigate the contribution of N1 dream content to creative performance, we administered targeted dream incubation (a protocol that presents auditory cues at sleep onset to introduce specific themes into dreams) and collected dream reports to measure incorporation of the selected theme into dream content. We then assessed creative performance using a set of three theme-related creativity tasks. Our findings show enhanced creative performance and greater semantic distance in task responses following a period of N1 sleep as compared to wake, corroborating recent work identifying N1 as a creative sweet spot and offering novel evidence for N1 enabling a cognitive state with greater associative divergence. We further demonstrate that successful N1 dream incubation enhances creative performance more than N1 sleep alone. To our knowledge, this is the first controlled experiment investigating a direct role of incubating dream content in the enhancement of creative performance.

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.

An ecological approach to clinically assess nightmares in military service members with severe PTSD.

BACKGROUND: Trauma-related nightmares (TRNs) are distressing events which contribute to insomnia severity, chronicity and treatment resistance of PTSD. Therefore, recording TRNs is a crucial technical challenge in order to understand their physiopathological patterns and their impact on sleep. However, TRNs are difficult to record during a single night in a sleep laboratory, which, moreover, is likely to be considered by patients as a protective sleep environment that is therefore not representative of home sleep conditions. METHOD: In the present study, we investigate if objective sleep measures acquired at-home using two ambulatory devices is of clinical value by correlating with PTSD patients' complaints about sleep and nightmares. A secondary objective is to relate awakenings associated with TRNs to sleep stages and to provide new insights into the use of electrodermal activity (EDA) as a potential physiological marker of TRNs. Sixty veterans and active-duty service members were assessed by questionnaires and recorded for 5 consecutive nights in their homes. RESULTS: Our approach firstly identified positive correlations between subjective and objective sleep parameters (total sleep time, sleep-onset latency and TRNs frequency). We also developed a method of synchronization between the two ambulatory devices that allowed us to match 200 TRNs (reported by event marker push button) with sleep stages corresponding to 91 nights and 37 patients. Most awakenings associated with TRNs occurred during NREM sleep (65.5% versus 34.5% during REM sleep). Our results also reveal significant differences in the frequency of EDA peaks 10 min before the reported events, with a lower frequency in REM (13.7 peaks) than in NREM (24.8 peaks) awakenings associated with TRNs. This EDA peaks frequency in REM sleep is not statistically different from that in REM sleep preceding awakenings that are not associated with TRNs. CONCLUSION: The development of wearable devices to collect physiological parameters is of interest in clinical practice to improve our knowledge of sleep and trauma-related nightmares in patients with PTSD.

The dynamics of emotional behaviors in rapid eye movement sleep.

Dream's emotions could exert a major role in desensitizing negative emotions. Studying emotional dynamics (how emotions fluctuate across time) during rapid eye movement (REM) sleep could provide some insight into this function. However, studies so far have been limited to dream reports. To bypass this limit, REM sleep behavior disorder (RBD), in which participants enact their dreams, enables direct access to overt emotional dream behaviors (such as facial expressions and speeches). In total, 17 participants with RBD, and 39.7 h of REM sleep video were analyzed. The frequency of emotional behaviors did not differ between REM sleep episodes of early and late night. Within individual REM sleep episodes, emotional behaviors exhibited a biphasic temporal course, including an increased frequency for the first 10 min, followed by a progressive decrease. The negative emotional behaviors occurred earlier (mean time: 11.3 ± 10 min) than positive (14.4 ± 10.7 min) and neutral behaviors (16.4 ± 11.8 min). Emotional behaviors of opposing (negative and positive) valences were observed in 31% (N = 14) of episodes containing at least one emotional behavior, and were separated by a median time of 4.2 [1.1-10.9] min. The biphasic temporal course of behaviors in REM sleep could include the generation reactivation of emotional content during the ascending phase, followed by processing and extinction during the descending phase. The earlier occurrence time of negative emotional behavior suggests that negative emotions may need to be processed first. The rapid succession of emotions of opposite valence could prevent prolonged periods of negative emotions and eventually nightmares.

What are the neural mechanisms and physiological functions of dreams?

Dreams are mental experiences, including perceptions, thoughts, and emotions, that occur during sleep. In dreams, hallucinatory perceptions, particularly visual and motoric, are often accompanied by negative emotions. When people dream, they perceive them as real even though they are bizarre and distorted in time and space. People often cannot recall their dreams, even though people dream every night. Dreaming is a strange physiological phenomenon. Research has demonstrated that dreaming is closely associated with rapid eye movement (REM) sleep. It is known that dreaming also occurs during non-REM (NREM) sleep, but the content appears to be different. Dreams during REM sleep tend to be longer, more vivid, more story-like, and more bizarre than those during NREM sleep. In this review, the neural circuits underlying dreaming and the physiological functions associated with it are summarized. Two major theories have been proposed regarding the neural circuits involved in dreaming. One is that dreams are generated by the activation of neural activity in the brainstem and its signal transmission to the cortex. The other is that dreams are caused by forebrain activation by dopamine. Whereas the physiological function of dreams remains unclear, several hypotheses have been proposed that are associated with memory and emotions.