The neural correlates of dreaming

Motor events during REM sleep are associated with occipital lobe activity in Parkinson's disease

STUDY OBJECTIVES

Abnormal motor events during REM sleep are common in Parkinson's disease (PD), but few studies have evaluated motor events comprehensively. This study aimed to categorize different types of motor events and explore their relationships with clinical symptoms, sleep structure and cortical electrophysiological characteristics.

METHODS

116 PD patients (49 women and 67 men) underwent a clinical assessment and video-polysomnography. REM sleep-related motor events were classified into elementary motor events and complex motor events. Patients were categorized into three groups: PD-non motor events (PD-nME), PD-elementary motor events (PD-eME), and PD-complex motor events (PD-cME). Receiver operating characteristic (ROC) curves were used to calculate the predictive value of PSG-EEG for motor events during REM sleep.

RESULTS

PD-cME group showed prolonged total sleep time, increased REM sleep percentage, and shortened REM latency compared to other groups. Both PD-eME and PD-cME groups exhibited higher theta relative power and lower beta relative power across extensive cortical regions compared to PD-nME group. Additionally, PD-cME group showed reduced alpha relative power in the left occipital lobe compared to other groups. The theta/beta ratio (TBR) in the right occipital lobe demonstrated significant predictive value for both elementary and complex motor events during REM sleep.

CONCLUSION

Both elementary and complex motor events during REM sleep in PD patients were associated with abnormal cortical activation. The occipital cortex may potentially constitute a component of the neural circuitry underlying REM sleep.

SleepEEGpy: a Python-based software integration package to organize preprocessing, analysis, and visualization of sleep EEG data

Sleep research uses electroencephalography (EEG) to infer brain activity in health and disease. Beyond standard sleep scoring, there is growing interest in advanced EEG analysis that requires extensive preprocessing to improve the signal-to-noise ratio and specialized analysis algorithms. While many EEG software packages exist, sleep research has unique needs (e.g., specific artifacts, event detection). Currently, sleep investigators use different libraries for specific tasks in a 'fragmented' configuration that is inefficient, prone to errors, and requires the learning of multiple software environments. This complexity creates a barrier for beginners. Here, we present SleepEEGpy, an open-source Python package that simplifies sleep EEG preprocessing and analysis. SleepEEGpy builds on MNE-Python, PyPREP, YASA, and SpecParam to offer an all-in-one, beginner-friendly package for comprehensive sleep EEG research, including (i) cleaning, (ii) independent component analysis, (iii) sleep event detection, (iv) spectral feature analysis, and visualization tools. A dedicated dashboard provides an overview to evaluate data and preprocessing, serving as an initial step prior to detailed analysis. We demonstrate SleepEEGpy's functionalities using overnight high-density EEG data from healthy participants, revealing characteristic activity signatures typical of each vigilance state: alpha oscillations in wakefulness, spindles and slow waves in NREM sleep, and theta activity in REM sleep. We hope that this software will be adopted and further developed by the sleep research community, and constitute a useful entry point tool for beginners in sleep EEG research.

Synchrony and subjective experience: the neural correlates of the stream of consciousness

Human subjectivity, our first-person conscious experience of the world, is among the deepest scientific mysteries. This opinion article lays out an approach to examining the neural correlates of subjectivity as it unfolds over time. Subjective experience is inherently idiosyncratic, arising from effortless interpretations that feel like perceived facts (p-interpretations), and integrative, with past and expected future moments influencing the current experience. Differential synchrony effects (i.e., neural synchrony that differs between groups) suggest that parts of gestalt cortex (inferior parietal lobule and posterior temporal cortex) and posterior medial cortex track p-interpretations. Differential synchrony may result from each person's preexisting idiosyncratic non-sensory representations (e.g., expectations, memories, motivations) being integrated with sensory inputs to yield unique meaning-infused immediate experiences across the stream of consciousness.

Conscious tactile perception entails distinct neural dynamics within somatosensory areas

Distilling the neural correlates of consciousness (NCCs) in humans is challenging due to limitations in the spatiotemporal resolution of recording techniques and confounds related to pre- and post-perceptual processes. In this study, we leveraged the detailed insights provided by human intracortical recordings to elucidate how somatosensory responses to simple tactile stimuli vary across different stimulus intensities and reporting conditions. Among the various spatiotemporal components of somatosensory processing, we observed tonic responses in posterior perisylvian regions that exhibited all the key characteristics of somatosensory NCCs. These responses remained invariant regardless of reporting, displayed an all-or-nothing pattern at the verge of the sensory threshold, and showed the most pronounced divergence between perceived and non-perceived stimuli. Overall, our findings indicate that conscious perception of simple tactile stimuli depends on higher-order somatosensory regions and that sustained neural dynamics in these areas may serve as an organizational principle of somatosensory awareness.

Dreams and Nightmares in Early Pregnancy: A Comparative Study with a Control Group

Purpose

This study investigated dream characteristics in women during the first trimester of pregnancy compared to a group of non-pregnant women, aiming to identify variables associated with the observed differences.

Participants and Method

A sample of 100 pregnant women in their first trimester was compared to a control group of 100 age-matched non-pregnant women. Participants completed online questionnaires to assess dream activity, sleep quality, depressive symptoms, and sociodemographic variables.

Results

Controlling for socio-demographic variables, statistical comparisons revealed that pregnant women reported fewer nightmares and showed less interest in their dream activity compared to non-pregnant women. Ordinal logistic regression revealed that being in the control group, greater attention to dreams, the presence of depressive symptoms, and a higher frequency of lucid dreaming were significant predictors of more frequent nightmares. Moderation analysis showed no significant interaction between pregnancy status and dream attitude.

Conclusion

Contrary to expectations, first-trimester pregnant women had fewer nightmares than non-pregnant women. However, the results are coherent with the finding that parasomnia-like events decrease during pregnancy. The rapid hormonal changes and specific sleep and emotional features of this stage of gestation may explain the lower presence of nightmares as compared to our control group. Moreover, we confirmed a crucial role of dream attitude in recalling nightmares, suggesting that some stable, trait-like features may contribute to nightmare experiences independently of pregnancy status. Our results also confirmed, according to the Continuity hypothesis, that depressive symptoms are associated with nightmares. Also, the presence of lucid dreaming in association with nightmares may be interpreted as an attempt to cope with unpleasant emotions. Longitudinal studies are needed to examine how dream activity evolves across pregnancy stages.

Neurophysiological features of dream recall and the phenomenology of dreams: Auditory stimulation impacts dream experiences

Studies on the electrophysiological and phenomenological aspects of dream experiences provide insight on consciousness during sleep. Whole night polysomnography (PSG) studies were conducted among 29 healthy young participants with high dream recall abilities. Dreams reports were collected during the second night by multiple awakening protocol. On the third night, participants were presented with an audiovisual task and during subsequent sleep, dream reports were collected following an auditory stimuli presentation. REM sleep dreams favor high dream recall rates when compared to N2 dreams. Enhanced EEG beta activity, functional connectivity across the brain structures of the default mode network (DMN) and activation of medial frontal cortex were observed during dream recall irrespective of the sleep states. Auditory stimulations influenced emotional dream experiences highlighting the possibility of target memory reactivation. The study highlights the potential role of dream states and dream experiences in understanding consciousness during sleep.

The Awakening Brain is Characterized by a Widespread and Spatiotemporally Heterogeneous Increase in High Frequencies

Morning awakening is part of everyday life. Surprisingly, information remains scarce on its underlying neurophysiological correlates. Here simultaneous polysomnography and stereo-electroencephalography recordings from 18 patients are used to assess the spectral and connectivity content of the process of awakening at a local level 15 min before and after the awakening. Awakenings from non-rapid eye movement sleep are accompanied by a widespread increase in ripple (>80 Hz) power in the fronto-temporal and parieto-insular regions, with connectivity showing an almost exclusive increase in the ripple band in the somatomotor, default, dorsal attention, and frontoparietal networks. Awakenings from rapid eye movement sleep are characterized by a widespread and almost exclusive increase in the ripple band in all available brain lobes, and connectivity increases mainly in the low ripple band in the limbic system as well as the default, dorsal attention, somatomotor, and frontoparietal networks.

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.

The Phenomenology of Offline Perception: Multisensory Profiles of Voluntary Mental Imagery and Dream Imagery

Both voluntary mental imagery and dream imagery involve multisensory representations without externally present stimuli that can be categorized as offline perceptions. Due to common mechanisms, correlations between multisensory dream imagery profiles and multisensory voluntary mental imagery profiles were hypothesized. In a sample of 226 participants, correlations within the respective state of consciousness were significantly bigger than across, favouring two distinct networks. However, the association between the vividness of voluntary mental imagery and vividness of dream imagery was moderated by the frequency of dream recall and lucid dreaming, suggesting that both networks become increasingly similar when higher metacognition is involved. Additionally, the vividness of emotional and visual imagery was significantly higher for dream imagery than for voluntary mental imagery, reflecting the immersive nature of dreams and the continuity of visual dominance while being awake and asleep. In contrast, the vividness of auditory, olfactory, gustatory, and tactile imagery was higher for voluntary mental imagery, probably due to higher cognitive control while being awake. Most results were replicated four weeks later, weakening the notion of state influences. Overall, our results indicate similarities between dream imagery and voluntary mental imagery that justify a common classification as offline perception, but also highlight important differences.

Connectome harmonic decomposition tracks the presence of disconnected consciousness during ketamine-induced unresponsiveness

BACKGROUND

Ketamine, in doses suitable to induce anaesthesia in humans, gives rise to a unique state of unresponsiveness accompanied by vivid experiences and sensations, making it possible to disentangle the correlated but distinct concepts of conscious awareness and behavioural responsiveness. This distinction is often overlooked in the study of consciousness.

METHODS

The mathematical framework of connectome harmonic decomposition (CHD) was used to view functional magnetic resonance imaging (fMRI) signals during ketamine-induced unresponsiveness as distributed patterns across spatial scales. The connectome harmonic signature of this particular state was mapped onto signatures of other states of consciousness for comparison.

RESULTS

An increased prevalence of fine-grained connectome harmonics was found in fMRI signals obtained during ketamine-induced unresponsiveness, indicating higher granularity. After statistical assessment, the ketamine sedation harmonic signature showed alignment with signatures of LSD-induced (fixed effect =0.0113 [0.0099, 0.0127], P<0.001) or ketamine-induced (fixed effect =0.0087 [0.0071, 0.0103], P<0.001) psychedelic states, and misalignment with signatures seen in unconscious individuals owing to propofol sedation (fixed effect =-0.0213 [-0.0245, -0.0181], P<0.001) or brain injury (fixed effect =-0.0205 [-0.0234, -0.0178], P<0.001).

CONCLUSIONS

The CHD framework, which only requires resting-state fMRI data and can be applied retrospectively, has the ability to track alterations in conscious awareness in the absence of behavioural responsiveness on a group level. This is possible because of ketamine's unique property of decoupling these two facets, and is important for consciousness and anaesthesia research.

Neural mechanisms of psychedelic visual imagery

Visual alterations under classic psychedelics can include rich phenomenological accounts of eyes-closed imagery. Preclinical evidence suggests agonism of the 5-HT2A receptor may reduce synaptic gain to produce psychedelic-induced imagery. However, this has not been investigated in humans. To infer the directed connectivity changes to visual connectivity underlying psychedelic visual imagery in healthy adults, a double-blind, randomised, placebo-controlled, cross-over study was performed, and dynamic causal modelling was applied to the resting state eyes-closed functional MRI scans of 24 subjects after administration of 0.2 mg/kg of the serotonergic psychedelic drug, psilocybin (magic mushrooms), or placebo. The effective connectivity model included the early visual area, fusiform gyrus, intraparietal sulcus, and inferior frontal gyrus. We observed a pattern of increased self-inhibition of both early visual and higher visual-association regions under psilocybin that was consistent with preclinical findings. We also observed a pattern of reduced inhibition from visual-association regions to earlier visual areas that indicated top-down connectivity is enhanced during visual imagery. The results were analysed with behavioural measures taken immediately after the scans, suggesting psilocybin-induced decreased sensitivity to neural inputs is associated with the perception of eyes-closed visual imagery. The findings inform our basic and clinical understanding of visual perception. They reveal neural mechanisms that, by affecting balance, may increase the impact of top-down feedback connectivity on perception, which could contribute to the visual imagery seen with eyes-closed during psychedelic experiences.

Dreaming conundrum

Dreaming, a common yet mysterious cognitive phenomenon, is an involuntary process experienced by individuals during sleep. Although the fascination with dreams dates back to ancient times and gained therapeutic significance through psychoanalysis in the early twentieth century, its scientific investigation only gained momentum with the discovery of rapid eye movement (REM) sleep in the 1950s. This review synthesises current research on the neurobiological and psychological aspects of dreaming, including factors influencing dream recall and content, neurophysiological correlates, and experimental models, and discusses the implications for clinical practice.

The futuristic manifolds of REM sleep

Since one of its first descriptions 70 years ago, rapid eye movement sleep has continually inspired and excited new generations of sleep researchers. Despite significant advancements in understanding its neurocircuitry, underlying mechanisms and microstates, many questions regarding its function, especially beyond the early neurodevelopment, remain unanswered. This opinion review delves into some of the unresolved issues in rapid eye movement sleep research, highlighting the ongoing need for comprehensive exploration in this fascinating field.

Where is my mind? A neurocognitive investigation of mind blanking

During wakefulness, our thoughts transition between different contents. However, there are moments that are seemingly devoid of reportable content, referred to as mind blanking (MB). It remains unclear what these blanks represent, highlighting the definitional and phenomenological ambiguities surrounding MB. We map out MB in terms of its reportable expressions, neurophysiology, and relationship to adjacent phenomenology, including meditative practices and sleep. We propose a mechanistic account linking MB to changes at the physiological, neural, and cognitive levels. We suggest that ongoing experiences are characterized by degrees of richness, and that contentless events represent distinct mental states with their own diversity. We encourage future research to acknowledge MB as a reportable mental category, leading to a comprehensive understanding of ongoing experience.

A continuous approach to explain insomnia and subjective-objective sleep discrepancy

Understanding insomnia is crucial for improving its diagnosis and treatment. However, many subjective complaints about insomnia do not align with objective measures of sleep quality, as is the case in subjective-objective sleep discrepancy (SOSD). We address this discrepancy by measuring sleep intrusions and instability in polysomnographic recordings from a large clinical database. Using machine learning, we develop personalized models to infer hypnodensities-a continuous and probabilistic measure of sleep dynamics-, and analyze them via information theory to measure intrusions and instability in a principled way. We find that insomnia with SOSD involves sleep intrusions during intra-sleep wakefulness, while insomnia without SOSD shows wake intrusions during sleep, indicating distinct etiologies. By mapping these metrics to standard sleep features, we provide a continuous and interpretable framework for measuring sleep quality. This approach integrates and values subjective insomnia complaints with physiological data for a more accurate view of sleep quality and its disorders.

Clinical and intracranial electrophysiological signatures of post-operative and post-ictal delirium

OBJECTIVES

(1) Gain insight into the mechanisms of postoperative delirium (POD). (2) Determine mechanistic overlap with post-ictal delirium (PID). Epilepsy patients undergoing intracranial electrophysiological monitoring can experience both POD and PID, and thus are suitable subjects for these investigations.

METHODS

POD was assessed daily after surgery. PID was assessed following seizures. Resting state data were collected following delirium assessments, during a control period, and during sleep. Slow-wave activity (SWA: 1-4 Hz) and resting state functional connectivity were compared between different time points and according to delirium status.

RESULTS

POD was present in 6 of 20 participants. Post-operatively, SWA was globally elevated in all participants but highest in POD+ participants. POD+ participants exhibited altered functional connectivity compared to POD-. These differences persisted even after resolution of delirium. PID was present in 7 of 15 participants and was predicted by seizures involving prefrontal cortex. PID+ participants exhibited higher post-ictal SWA versus PID-; no differences in functional connectivity were observed. Post-operative and post-ictal SWA was comparable to sleep in some participants.

CONCLUSIONS

Elevated SWA may predispose patients to both post-operative and post-ictal delirium and may indicate overlapping mechanisms.

SIGNIFICANCE

Delirium treatments focused on SWA may be most effective for ameliorating cognitive symptoms.

Preliminaries to artificial consciousness: A multidimensional heuristic approach

The pursuit of artificial consciousness requires conceptual clarity to navigate its theoretical and empirical challenges. This paper introduces a composite, multilevel, and multidimensional model of consciousness as a heuristic framework to guide research in this field. Consciousness is treated as a complex phenomenon, with distinct constituents and dimensions that can be operationalized for study and for evaluating their replication. We argue that this model provides a balanced approach to artificial consciousness research by avoiding binary thinking (e.g., conscious vs. non-conscious) and offering a structured basis for testable hypotheses. To illustrate its utility, we focus on "awareness" as a case study, demonstrating how specific dimensions of consciousness can be pragmatically analyzed and targeted for potential artificial instantiation. By breaking down the conceptual intricacies of consciousness and aligning them with practical research goals, this paper lays the groundwork for a robust strategy to advance the scientific and technical understanding of artificial consciousness.

Systematic review: REM sleep, dysphoric dreams and nightmares as transdiagnostic features of psychiatric disorders with emotion dysregulation - Clinical implications

BACKGROUND

Fragmented rapid eye movement (REM) sleep disrupts the overnight resolution of emotional distress, a process crucial for emotion regulation. Emotion dysregulation, which is common across psychiatric disorders, is often associated with sleep disturbances. This systematic review explores how REM sleep and nightmares affect emotion processing and regulation in individuals with psychiatric disorders where emotion dysregulation is a key concern, suggesting novel sleep-related treatment pathways.

METHODS

We performed a PRISMA-compliant systematic search of the PUBMED, Web of Science, and EBSCO databases from January 1994-February 2023. This systematic review targeted studies on REM sleep, nightmares, and emotion regulation in a postpubescent clinical population with affective dysregulation. The quality of the studies was assessed via the Newcastle‒Ottawa Scale (NOS), adapted for cross-sectional studies.

RESULTS

From the 714 screened records, 28 articles met the inclusion criteria and focused on REM sleep, dreams, or nightmares in individuals with mood disorders (k = 8), anxiety disorders (k = 1), posttraumatic stress disorder (PTSD) (k = 16), non-suicidal self-injury (NSSI), personality disorders (k = 2), and autism (k = 1). Fifteen studies used objective sleep measures, seventeen used self-reported assessments, six included treatment components, eight investigated nightmares, and three examined dreams. NOS scores ranged from moderate to high.

CONCLUSIONS

REM sleep disturbances represent a transdiagnostic feature across psychiatric disorders and are crucial for emotion regulation. Nightmares are associated with suicidal behaviour and emotion dysregulation. Targeted sleep interventions may improve emotion regulation and mental health outcomes. Future research should explore the role of REM sleep in disorder prognosis to develop tailored interventions.

Arousal threshold reveals novel neural markers of sleep depth independently from the conventional sleep stages

Reports of sleep-specific brain activity patterns have been constrained by assessing brain function as it related to the conventional polysomnographic sleep stages. This limits the variety of sleep states and underlying activity patterns that one can discover. The current study used all-night functional MRI sleep data and defined sleep behaviorally with auditory arousal threshold (AAT) to characterize sleep depth better by searching for novel neural markers of sleep depth that are neuroanatomically localized and temporally unrelated to the conventional stages. Functional correlation values calculated in a four-min time window immediately before the determination of AAT were entered into a linear mixed effects model, allowing multiple arousals across the night per subject into the analysis, and compared to models with sleep stage to determine the unique relationships with AAT. These unique relationships were for thalamocerebellar correlations, the relationship between the right language network and the right "default-mode network dorsal medial prefrontal cortex subsystem," and the relationship between thalamus and ventral attention network. These novel neural markers of sleep depth would have remained undiscovered if the data were merely analyzed with the conventional sleep stages.

The individual determinants of morning dream recall

Evidence suggests that (almost) everyone dreams during their sleep and may actually do so for a large part of the night. Yet, dream recall shows large interindividual variability. Understanding the factors that influence dream recall is crucial for advancing our knowledge regarding dreams' origin, significance, and functions. Here, we tackled this issue by prospectively collecting dream reports along with demographic information and psychometric, cognitive, actigraphic, and electroencephalographic measures in 217 healthy adults (18-70 y, 116 female participants, 101 male participants). We found that attitude towards dreaming, proneness to mind wandering, and sleep patterns are associated with the probability of reporting a dream upon morning awakening. The likelihood of recalling dream content was predicted by age and vulnerability to interference. Moreover, dream recall appeared to be influenced by night-by-night changes in sleep patterns and showed seasonal fluctuations. Our results provide an account for previous observations regarding inter- and intra-individual variability in morning dream recall.

Unlocking Dreams and Dreamless Sleep: Machine Learning Classification With Optimal EEG Channels

Research suggests that dreams play a role in the regulation of emotional processing and memory consolidation; electroencephalography (EEG) is useful for studying them, but manual annotation is time-consuming and prone to bias. This study was aimed at developing an EEG-based machine learning (ML) model to automatically identify dream and dreamless states in sleep. We extracted features from EEG data using common spatial patterns (CSPs) and the discrete wavelet transform (DWT) and used them to classify EEG signals into dream and dreamless states using ML models. To determine the most informative channels for classification, we used the permutation-based channel selection method and the nondominated sorting genetic algorithm II (NSGA-II). We evaluated our proposal using a public dataset that is part of the DREAM project, which was collected from 58 EEG channels during rapid eye movement (REM) and non-REM sleep, while 28 subjects reported dream or dreamless experiences. We achieved accuracies greater than 0.85 to distinguish dream and dreamless states using CSP-based feature extraction combined with k-nearest neighbors (KNN), as well as through multiple combinations of EEG channels identified by channel selection methods. Our findings suggest that as few as 8-10 EEG channels may be sufficient for dream recognition. Excluding one subject at a time during model training revealed challenges in generalizing the models to unseen subjects. Channel selection methods have proven to be effective in selecting relevant subsets of EEG channels to classify dreams and dreamless experiences. Our results demonstrate the feasibility of automatic dream detection and highlight the need to improve ML generalization.

Talking to sleepwalkers? Response to communication efforts in disorders of arousals

STUDY OBJECTIVES

Disorders of arousal (DoA) are diagnosed on the basis of clinical criteria, including inappropriate or absent responsiveness to communication attempts. Surprisingly, the ability of patients to interact with others during DoA episodes has not been systematically investigated. To address this gap, we conducted three studies.

METHODS

First, we used a retrospective questionnaire to assess verbal responsiveness during episodes in 61 adult patients with DoA (Study 1). Second, we used auditory stimulation during polysomnographically verified N3 sleep to trigger DoA episodes in 14 patients. We then asked questions to test the possibility of verbal interactions during the episodes (Study 2). Third, we assessed the presence and quality of conversations with a bed partner in 364 home video-recorded episodes from 19 patients (Study 3).

RESULTS

In Study 1, most patients (81%) reported occasional conversations during parasomnia episodes. Patients' ongoing mental content influenced both their responses to questions during episodes and their perception of the outside world (including their surroundings and the identity of their interlocutor ). In Study 2, auditory stimulation had a limited effect in inducing episodes (7/157 trials). One patient indirectly responded to our verbal prompts in a DoA episode. In Study 3, we found 37 video instances of discussion between patients and their partner.

CONCLUSIONS

Overall, our findings suggest that DoA episodes are not a uniform state but may instead encompass varying states of consciousness, characterized by different levels of responsiveness and a complex interplay between internal and external information processing. These results highlight the limitations of current diagnostic criteria for DoA.

Behind closed eyes: Understanding nightmares in children and adolescents with autism spectrum disorder - A systematic review

INTRODUCTION

Brain and sleep development in childhood shapes emotional and cognitive growth, including the ability to recall dreams. In line with the continuity hypothesis of dreaming, several findings suggest a link between clinical symptoms and nightmare frequency. Sleep disorders and anxiety are among the most frequently co-occurring conditions in children and adolescents with autism spectrum disorder (ASD). However, their impact on nightmares has not yet been systematically explored. This review aims to address this research gap by investigating nightmares in autism and their influence on clinical symptoms and cognitive functioning.

METHODS

The literature was searched utilizing the databases PubMed, PsycINFO, Web of Science, and Scopus, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The included studies were assessed for methodological quality.

RESULTS

Twenty-nine papers were reviewed. The prevalence of nightmares occurring very frequently was below 5 %, with no significant difference in nightmare prevalence between children with ASD and their healthy peers. Furthermore, several findings reported a relationship between nightmares and other sleep disturbances among individuals with ASD.

DISCUSSION

The study of dreaming in ASD may provide valuable insights into the disorder. Although comorbid sleep disorders can influence nightmare frequency, the results of this review suggest that nightmares may not represent a distinctive feature of ASD. However, poor communication and introspection skills may explain the difficulties in reporting dream experiences. Given the preliminary nature of current research on nightmares in ASD, further studies are essential to overcome existing limitations and deepen our understanding.

The clinical neuroscience of lucid dreaming

During most dreams, the dreamer does not realize that they are in a dream. In contrast, lucid dreaming allows to become aware of the current state of mind, often accompanied by considerable control over the ongoing dream episode. Lucid dreams can happen spontaneously or be induced through diverse behavioural, cognitive or technological strategies. Such induction techniques have spurred research into the potential therapeutic aspects of lucid dreams. In this review, we gather evidence on the link between lucid dreams and conditions like nightmare disorder, depression, anxiety, psychosis, and dissociative states, and highlight the possible neurobiological basis of these associations. Furthermore, we explore contemplative sleep practices that train lucid states during sleep, such as Dream/Sleep Yoga and Yoga Nidrâ. The potential drawbacks of lucid dreaming interventions are outlined, accompanied by an examination of the impacts of lucid dreams on individuals without clinical conditions. By shedding light on these intricate relationships, the review contributes to a deeper understanding of the therapeutic possibilities and implications of lucid dreaming.

Consciousness in non-REM-parasomnia episodes

Sleepwalking and related parasomnias are thought to result from incomplete awakenings out of non-rapid eye movement (non-REM) sleep. Non-REM parasomnia behaviours have been described as unconscious and automatic, or related to vivid, dream-like conscious experiences. Similarly, some observations have suggested that patients are unresponsive during episodes, while others that they can interact with their surroundings. To better grasp and characterise the full spectrum of consciousness and environmental (dis)connection associated with behavioural episodes, 35 adult patients with non-REM sleep parasomnias were interviewed in-depth about their experiences. The level of consciousness during parasomnia episodes was reported to be variable both within and between individuals, ranging from minimal or absent consciousness and largely automatic behaviours (frequently/always present in 36% of patients) to preserved conscious experiences characterised by delusional thinking of varying degrees of specificity (65%), often about impending danger, variably formed, uni- or multisensory hallucinations (53%), impaired insight (77%), negative emotions (75%), and variable, but often pronounced, amnesia (30%). Patients described their experiences as a dream scene during which they felt awake ("awake dreaming"). The surroundings were either realistically perceived, misinterpreted (in the form of perceptual illusions or misidentifications of people), or entirely hallucinated as a function of the prevailing delusion. These observations suggest that the level of consciousness, amnesia and sensory disconnection during non-REM parasomnia episodes is variable and graded. In their full-fledged expression, non-REM parasomnia experiences feature several core features of dreams. They therefore represent a valuable model for the study of consciousness, sleep-related sensory disconnection and dreaming.

Dreaming in patients with epilepsy: a cross-sectional cohort study

Epilepsy impacts cognition during wakefulness. As epileptic activity is present and even augmented during sleep, epilepsy could also influence sleep-related cognitive processes. However, whether epilepsy modulates sleep-related experiences like dreaming remains poorly known. Here, we prospectively investigated the characteristics and determinants of dreaming in patients with epilepsy. Consecutive adult patients with epilepsy and no major cognitive deficit were recruited in an epilepsy outpatient clinic. They completed a questionnaire about their dreams, sleep and epilepsy over the past year. Medical data on epilepsy characteristics were gathered from the medical file. A generalised linear model was used to explore the determinants of dream recall frequency (DRF). We included 300 patients, with a mean (standard deviation [SD]) age of 40.4 (13.4) years and 51.3% female; 28.6% had more than one seizure/month, and 34.7% already had seizures during sleep. Patients recalled dreams on an average of 1.6 (1.5) days/week and 11% had one or more nightmare/week. Younger age, higher number of nocturnal awakenings, and lower seizures frequency predicted a higher DRF. In patients with focal epilepsy (65.3%), the localisation of the epileptic focus in the parieto-occipital area was negatively associated with DRF. Regarding dream content, 34.0% of patients reported having already dreamt about epilepsy. Dreams of seizures were associated with sleep-related seizures (p = 0.034) and dreams of epilepsy were associated with nightmare frequency (p = 0.004). Our results show that patients with epilepsy share several determinants of DRF (age, awakenings, role of the parieto-occipital area) with healthy subjects. In addition, epilepsy-related factors (seizure frequency, focus localisation) also impact DRF. Investigating dreams in patients with epilepsy can provide information on their epilepsy and their sleep.

Multi-region processing during sleep for memory and cognition

Over the past decades, the understanding of sleep has evolved to be a fundamental physiological mechanism integral to the processing of different types of memory rather than just being a passive brain state. The cyclic sleep substates, namely, rapid eye movement (REM) sleep and non-REM (NREM) sleep, exhibit distinct yet complementary oscillatory patterns that form inter-regional networks between different brain regions crucial to learning, memory consolidation, and memory retrieval. Technical advancements in imaging and manipulation approaches have provided deeper understanding of memory formation processes on multi-scales including brain-wide, synaptic, and molecular levels. The present review provides a short background and outlines the current state of research and future perspectives in understanding the role of sleep and its substates in memory processing from both humans and rodents, with a focus on cross-regional brain communication, oscillation coupling, offline reactivations, and engram studies. Moreover, we briefly discuss how sleep contributes to other higher-order cognitive functions.

Aperiodic neural activity distinguishes between phasic and tonic REM sleep

Traditionally categorized as a uniform sleep phase, rapid eye movement sleep exhibits substantial heterogeneity with its phasic and tonic constituents showing marked differences regarding many characteristics. Here, we investigate how tonic and phasic states differ with respect to aperiodic neural activity, a marker of arousal and sleep. Rapid eye movement sleep heterogeneity was assessed using either binary phasic-tonic (n = 97) or continuous (in 60/97 participants) approach. Slopes of the aperiodic power component were measured in the low (2-30 Hz, n = 97) and high (30-48 Hz, n = 60/97) frequency bands with the Irregularly Resampled Auto-Spectral Analysis applied on electroencephalography. Rapid eye movement amplitudes were quantified with the YASA applied on electrooculography (n = 60/97). The binary approach revealed that the phasic state is characterized by steeper low-band slopes with small effect sizes and some topographical heterogeneity over datasets. High-band aperiodic slopes were flatter in the phasic versus tonic state with medium-to-large effect sizes over all areas in both datasets. The continuous approach confirmed these findings. The temporal analysis within rapid eye movement episodes revealed that aperiodic activity preceding or following EM events did not cross-correlate with eye movement amplitudes. This study demonstrates that aperiodic slopes can serve as a reliable marker able to differentiate between phasic and tonic constituents of rapid eye movement sleep and reflect phasic rapid eye movement event intensity. However, rapid eye movement events could not be predicted by preceding aperiodic activity and vice versa, at least not with scalp electroencephalography.

Functional connectome gradient predicts clinical symptoms of chronic insomnia disorder

Insomnia is the second most prevalent psychiatric disorder worldwide, but the understanding of the pathophysiology of insomnia remains fragmented. In this study, we calculated the connectome gradient in 50 chronic insomnia disorder (CID) patients and 38 healthy controls (HC) to assess changes due to insomnia and utilized these gradients in a connectome-based predictive modeling (CPM) to predict clinical symptoms associated with insomnia. The results suggested that insomnia led to significant alterations in the functional gradients of some brain areas. Specifically, the gradient scores in the middle frontal gyrus, superior anterior cingulate gyrus, and right nucleus accumbens were significantly higher in the CID patients than in the HC group, whereas the scores in the middle occipital gyrus, right fusiform gyrus, and right postcentral gyrus were significantly lower than in the HC group. Further correlation analysis revealed that the right middle frontal gyrus is positively correlated with the self-rating anxiety scale (r=0.3702). Additionally, the prediction model built with functional gradients could well predict the sleep quality (r=0.5858), anxiety (r=0.6150), and depression (r=0.4022) levels of insomnia patients. This offers an objective depiction of the clinical diagnosis of insomnia, yielding a beneficial impact on the identification of effective biomarkers and the comprehension of insomnia.

Closed-loop auditory stimulation targeting alpha and theta oscillations during rapid eye movement sleep induces phase-dependent power and frequency changes

STUDY OBJECTIVES

Alpha and theta oscillations characterize the waking human electroencephalogram (EEG) and can be modulated by closed-loop auditory stimulation (CLAS). These oscillations also occur during rapid eye movement (REM) sleep, but their function here remains elusive. CLAS represents a promising tool to pinpoint how these brain oscillations contribute to brain function in humans. Here we investigate whether CLAS can modulate alpha and theta oscillations during REM sleep in a phase-dependent manner.

METHODS

We recorded high-density EEG during an extended overnight sleep period in 18 healthy young adults. Auditory stimulation was delivered during both phasic and tonic REM sleep in alternating 6-second ON and 6-second OFF windows. During the ON windows, stimuli were phase-locked to four orthogonal phases of ongoing alpha or theta oscillations detected in a frontal electrode.

RESULTS

The phases of ongoing alpha and theta oscillations were targeted with high accuracy during REM sleep. Alpha and theta CLAS induced phase-dependent changes in power and frequency at the target location. Frequency-specific effects were observed for alpha trough (speeding up) and rising (slowing down) and theta trough (speeding up) conditions. CLAS-induced phase-dependent changes were observed during both REM sleep substages, even though auditory evoked potentials were very much reduced in phasic compared to tonic REM sleep.

CONCLUSIONS

This study provides evidence that faster REM sleep rhythms can be modulated by CLAS in a phase-dependent manner. This offers a new approach to investigating how modulation of REM sleep oscillations affects the contribution of this vigilance state to brain function.

The association between dream activity and alexithymia during pregnancy: A cross-sectional study in a sample of pregnant women

The gestational period is a sensitive time marked by significant changes that can affect women's sleep and dreaming processes, with an augmented frequency and recall of dreams suggesting that dreaming represents an adaptive mechanism of emotional regulation. This study investigates the relationship between pregnancy-related variables, alexithymia, and depressive symptoms in influencing dream characteristics in women during the first trimester of pregnancy. A total of 118 pregnant women were recruited at the Obstetric Outpatient Service of an Italian University Hospital and completed the Mannheim Dream Questionnaire, the Toronto Alexithymia Scale-20, and the Edinburgh Postnatal Depression Scale. Regression analysis, t-test, and moderation analysis were conducted through Jamovi. Dream recall frequency was predicted by age, parity, and depressive symptoms. Nightmare frequency and lucid dream frequency were significantly predicted by depressive symptoms, while nightmare distress was predicted by an unplanned pregnancy. Alexithymia was linked to higher nightmare frequency and nightmare distress. Moderation analysis revealed that the presence of depressive symptoms predicted increased nightmare frequency only in women with higher levels of alexithymia. These findings highlight the role of emotional regulation in dreaming during pregnancy, particularly among women exhibiting alexithymic traits and depressive symptoms. Nightmare frequency may serve as an indicator of impaired emotional regulation, emphasising the need for targeted interventions to enhance emotional coping strategies in this population. Future research should examine the content of nightmares to further understand their implications for maternal mental health.

Three mechanisms of language comprehension are revealed through cluster analysis of individuals with language deficits

Analysis of linguistic abilities that are concurrently impaired in individuals with language deficits allows identification of a shared underlying mechanism. If any two linguistic abilities are mediated by the same underlying mechanism, then both abilities will be absent if this mechanism is broken. Clustering techniques automatically arrange these abilities according to their co-occurrence and therefore group together abilities mediated by the same mechanism. This study builds upon the discovery of three distinct mechanisms of language comprehension in 31,845 autistic individuals1. The current clustering analysis of a more diverse group of individuals with language impairments resulted in the three mechanisms identical to those found previously: (1) the most-basic command-language-comprehension-mechanism; (2) the intermediate modifier-language-comprehension-mechanism mediating comprehension of color, size, and number modifiers; and (3) the most-advanced syntactic-language-comprehension-mechanism. This discovery calls for mapping of the three empirically-defined language-comprehension-mechanisms in the context of cognitive neuroscience, which is the main goal of this study.

New strategies for the cognitive science of dreaming

Dreams have long captivated human curiosity, but empirical research in this area has faced significant methodological challenges. Recent interdisciplinary advances have now opened up new opportunities for studying dreams. This review synthesizes these advances into three methodological frameworks and describes how they overcome historical barriers in dream research. First, with observable dreaming, neural decoding and real-time reporting offer more direct measures of dream content. Second, with dream engineering, targeted stimulation and lucidity provide routes to experimentally manipulate dream content. Third, with computational dream analysis, the generation and exploration of large dream-report databases offer powerful avenues to identify patterns in dream content. By enabling researchers to systematically observe, engineer, and analyze dreams, these innovations herald a new era in dream science.

Conscious experiences during non-rapid eye movement sleep parasomnias

Disorders of Arousal (DOA) are non-rapid eye movement (NREM) parasomnias traditionally regarded as unconscious states. However, recent research challenges this assumption. This narrative review aims to explore the presence and qualitative features of conscious experiences in patients with DOA during their episodes. The literature indicates a higher recall of conscious experiences during DOA episodes than previously believed, estimated at about 50-60 % in adults (immediately post-episode). Data on children are limited but suggest a lower recall rate (<30 % when interviewed retrospectively). Patient reports range from brief scenic fragments to elaborate scenarios with plot development, often fraught with negative emotions and misfortunes and with considerable correspondence between subjective experiences and observed behaviors. In many of the described cases, patients appear to enact their dreams, entering a hallucinatory state where internally generated images overlay external percepts. The potential implications for clinical management, research endeavors, and legal considerations regarding nocturnal violence, along with existing limitations and controversial points, are discussed.

The association between sleep disturbance and nightmares: Temporal dynamics of nightmare occurrence and sleep architecture in the home

We collected measures of sleep architecture and nightmares from participants (N = 61) wearing the DREEM 3 headband across 2 weeks of data collection to test the hypothesis that there are bidirectional links between insomnia (measured as sleep disturbance) and nightmare events. Nightmares were predicted by increased sleep disturbance the night before the nightmare, but not on the same night or 2 nights before. We also found that nightmare occurrences did not predict increased sleep disturbance on the same night or the following 2 nights, rather nightmares predicted increased sleep disturbance at the between-subjects level only. We suggest that nightmares are associated with an N3 sleep rebound on the night of the nightmare following a night of sleep disturbance.

Sensory representations in primary visual cortex are not sufficient for subjective imagery

The contemporary definition of mental imagery is characterized by two aspects: a sensory representation that resembles, but does not result from, perception, and an associated subjective experience. Neuroimaging demonstrated imagery-related sensory representations in primary visual cortex (V1) that show striking parallels to perception. However, it remains unclear whether these representations always reflect subjective experience or if they can be dissociated from it. We addressed this question by comparing sensory representations and subjective imagery among visualizers and aphantasics, the latter with an impaired ability to experience imagery. Importantly, to test for the presence of sensory representations independently of the ability to generate imagery on demand, we examined both spontaneous and voluntary imagery forms. Using multivariate fMRI, we tested for decodable sensory representations in V1 and subjective visual imagery reports that occurred either spontaneously (during passive listening of evocative sounds) or in response to the instruction to voluntarily generate imagery of the sound content (always while blindfolded inside the scanner). Among aphantasics, V1 decoding of sound content was at chance during voluntary imagery, and lower than in visualizers, but it succeeded during passive listening, despite them reporting no imagery. In contrast, in visualizers, decoding accuracy in V1 was greater in voluntary than spontaneous imagery (while being positively associated with the reported vividness of both imagery types). Finally, for both conditions, decoding in precuneus was successful in visualizers but at chance for aphantasics. Together, our findings show that V1 representations can be dissociated from subjective imagery, while implicating a key role of precuneus in the latter.

Electroencephalographic Microstates During Sleep and Wake in Schizophrenia

Background

Aberrant functional connectivity is a hallmark of schizophrenia. The precise nature and mechanism of dysconnectivity in schizophrenia remains unclear, but evidence suggests that dysconnectivity is different in wake versus sleep. Microstate analysis uses electroencephalography (EEG) to investigate large-scale patterns of coordinated brain activity by clustering EEG data into a small set of recurring spatial patterns, or microstates. We hypothesized that this technique would allow us to probe connectivity between brain networks at a fine temporal resolution and uncover previously unknown sleep-specific dysconnectivity.

Methods

We studied microstates during sleep in patients with schizophrenia by analyzing high-density EEG sleep data from 114 patients with schizophrenia and 79 control participants. We used a polarity-insensitive k-means analysis to extract a set of 6 microstate topographies.

Results

These 6 states included 4 widely reported canonical microstates. In patients and control participants, falling asleep was characterized by a shift from microstates A, B, and C to microstates D, E, and F. Microstate F was decreased in patients during wake, and microstate E was decreased in patients during sleep. The complexity of microstate transitions was greater in patients than control participants during wake, but this reversed during sleep.

Conclusions

Our findings reveal behavioral state-dependent patterns of cortical dysconnectivity in schizophrenia. Furthermore, these findings are largely unrelated to previous sleep-related EEG markers of schizophrenia such as decreased sleep spindles. Therefore, these findings are driven by previously undescribed sleep-related pathology in schizophrenia.

Dynamical structure-function correlations provide robust and generalizable signatures of consciousness in humans

Resting-state functional magnetic resonance imaging evolves through a repertoire of functional connectivity patterns which might reflect ongoing cognition, as well as the contents of conscious awareness. We investigated whether the dynamic exploration of these states can provide robust and generalizable markers for the state of consciousness in human participants, across loss of consciousness induced by general anaesthesia or slow wave sleep. By clustering transient states of functional connectivity, we demonstrated that brain activity during unconsciousness is dominated by a recurrent pattern primarily mediated by structural connectivity and with a reduced capacity to transition to other patterns. Our results provide evidence supporting the pronounced differences between conscious and unconscious brain states in terms of whole-brain dynamics; in particular, the maintenance of rich brain dynamics measured by entropy is a critical aspect of conscious awareness. Collectively, our results may have significant implications for our understanding of consciousness and the neural basis of human awareness, as well as for the discovery of robust signatures of consciousness that are generalizable among different brain conditions.

High frequency oscillations in human memory and cognition: a neurophysiological substrate of engrams?

Despite advances in understanding the cellular and molecular processes underlying memory and cognition, and recent successful modulation of cognitive performance in brain disorders, the neurophysiological mechanisms remain underexplored. High frequency oscillations beyond the classic electroencephalogram spectrum have emerged as a potential neural correlate of fundamental cognitive processes. High frequency oscillations are detected in the human mesial temporal lobe and neocortical intracranial recordings spanning gamma/epsilon (60-150 Hz), ripple (80-250 Hz) and higher frequency ranges. Separate from other non-oscillatory activities, these brief electrophysiological oscillations of distinct duration, frequency and amplitude are thought to be generated by coordinated spiking of neuronal ensembles within volumes as small as a single cortical column. Although the exact origins, mechanisms and physiological roles in health and disease remain elusive, they have been associated with human memory consolidation and cognitive processing. Recent studies suggest their involvement in encoding and recall of episodic memory with a possible role in the formation and reactivation of memory traces. High frequency oscillations are detected during encoding, throughout maintenance, and right before recall of remembered items, meeting a basic definition for an engram activity. The temporal coordination of high frequency oscillations reactivated across cortical and subcortical neural networks is ideally suited for integrating multimodal memory representations, which can be replayed and consolidated during states of wakefulness and sleep. High frequency oscillations have been shown to reflect coordinated bursts of neuronal assembly firing and offer a promising substrate for tracking and modulation of the hypothetical electrophysiological engram.

EEG signature of near-death-like experiences during syncope-induced periods of unresponsiveness

During fainting, disconnected consciousness may emerge in the form of dream-like experiences. Characterized by extra-ordinary and mystical features, these subjective experiences have been associated to near-death-like experiences (NDEs-like). We here aim to assess brain activity during syncope-induced disconnected consciousness by means of high-density EEG monitoring. Transient loss of consciousness and unresponsiveness were induced in 27 healthy volunteers through hyperventilation, orthostasis, and Valsalva maneuvers. Upon awakening, subjects were asked to report memories, if any. The Greyson NDE scale was used to evaluate the potential phenomenological content experienced during the syncope-induced periods of unresponsiveness. EEG source reconstruction assessed cortical activations during fainting, which were regressed out with subjective reports collected upon recovery of normal consciousness. We also conducted functional connectivity, graph-theoretic and complexity analyses. High quality high-density EEG data were obtained in 22 volunteers during syncope and unresponsiveness (lasting 22±8 s). NDE-like features (Greyson NDE scale total score ≥7/32) were apparent for eight volunteers and characterized by higher activity in delta, theta and beta2 bands in temporal and frontal regions. The richness of the NDE-like content was associated with delta, theta and beta2 bands cortical current densities, in temporal, parietal and frontal lobes, including insula, right temporoparietal junction, and cingulate cortex. Our analyses also revealed a higher complexity and that networks related to delta, theta, and beta2 bands were characterized by a higher overall connectivity paralleled by a higher segregation (i.e., local efficiency) and a higher integration (i.e., global efficiency) for the NDE-like group compared to the non-NDE-like group. Fainting-induced NDE-like episodes seem to be sustained by surges of neural activity representing promising markers of disconnected consciousness.

Decreased Delta/Beta ratio index as the sleep state-independent electrophysiological signature of sleep state misperception in Insomnia disorder: A focus on the sleep onset and the whole night

PURPOSE

Sleep State Misperception (SSM) is described as the tendency of Insomnia Disorder (ID) patients to overestimate Sleep Latency (SL) and underestimate Total Sleep Time (TST). Literature exploring topographical components in ID with SSM is scarce and does not allow us to fully understand the potential mechanisms underlying this phenomenon. This study aims to evaluate the existence of sleep EEG topography alterations in ID patients associated with SSM compared to Healthy Controls (HC), focusing on two distinct periods: the Sleep Onset (SO) and the whole night.

METHODS

Twenty ID patients (mean age: 43.5 ± 12.7; 7 M/13F) and 18 HCs (mean age: 41.6 ± 11.9; 8 M/10F) underwent a night of Polysomnography (PSG) and completed sleep diaries the following morning upon awakening. Two SSM indices, referring to the misperception of SL (SLm) and TST (TSTm), were calculated by comparing objective and subjective sleep indices extracted by PSG and sleep diary. According to these indices, the entire sample was split into 4 sub-groups: ID +SLm vs HC -SLm; ID +TSTm vs HC -TSTm.

RESULTS

Considering the SO, the two-way mixed-design ANOVA showed a significant main effect of Groups pointing to a decreased delta/beta ratio in the whole scalp topography. Moreover, we found a significant interaction effect for the sigma and beta bands. Post Hoc tests showed higher sigma and beta power in anterior and temporo-parietal sites during the SO period in IDs +SLm compared to HC -SLm. Considering the whole night, the unpaired t-test revealed in IDs +TSTm significantly lower delta power during NREM, and lower delta/beta ratio index during NREM and REM sleep compared to HCs -TSTm. Finally, we found diffuse significant negative correlations between SSM indices and the delta/beta ratio during SO, NREM, and REM sleep.

CONCLUSION

The main finding of the present study suggests that higher SL overestimation and TST underestimation are both phenomena related to diffuse cortical hyperarousal interpreted as a sleep state-independent electrophysiological correlate of the SSM, both during the SO and the whole night.

The brain simulates actions and their consequences during REM sleep

Vivid dreams mostly occur during a phase of sleep called REM 1-5 . During REM sleep, the brain's internal representation of direction keeps shifting like that of an awake animal moving through its environment 6-8 . What causes these shifts, given the immobility of the sleeping animal? Here we show that the superior colliculus of the mouse, a motor command center involved in orienting movements 9-15 , issues motor commands during REM sleep, e.g. turn left, that are similar to those issued in the awake behaving animal. Strikingly, these motor commands, despite not being executed, shift the internal representation of direction as if the animal had turned. Thus, during REM sleep, the brain simulates actions by issuing motor commands that, while not executed, have consequences as if they had been. This study suggests that the sleeping brain, while disengaged from the external world, uses its internal model of the world to simulate interactions with it.

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.

Conscious but not thinking-Mind-blanks during visuomotor tracking: An fMRI study of endogenous attention lapses

Attention lapses (ALs) are complete lapses of responsiveness in which performance is briefly but completely disrupted and during which, as opposed to microsleeps, the eyes remain open. Although the phenomenon of ALs has been investigated by behavioural and physiological means, the underlying cause of an AL has largely remained elusive. This study aimed to investigate the underlying physiological substrates of behaviourally identified endogenous ALs during a continuous visuomotor task, primarily to answer the question: Were the ALs during this task due to extreme mind-wandering or mind-blanks? The data from two studies were combined, resulting in data from 40 healthy non-sleep-deprived subjects (20M/20F; mean age 27.1 years, 20-45). Only 17 of the 40 subjects were used in the analysis due to a need for a minimum of two ALs per subject. Subjects performed a random 2-D continuous visuomotor tracking task for 50 and 20 min in Studies 1 and 2, respectively. Tracking performance, eye-video, and functional magnetic resonance imaging (fMRI) were recorded simultaneously. A human expert visually inspected the tracking performance and eye-video recordings to identify and categorise lapses of responsiveness as microsleeps or ALs. Changes in neural activity during 85 ALs (17 subjects) relative to responsive tracking were estimated by whole-brain voxel-wise fMRI and by haemodynamic response (HR) analysis in regions of interest (ROIs) from seven key networks to reveal the neural signature of ALs. Changes in functional connectivity (FC) within and between the key ROIs were also estimated. Networks explored were the default mode network, dorsal attention network, frontoparietal network, sensorimotor network, salience network, visual network, and working memory network. Voxel-wise analysis revealed a significant increase in blood-oxygen-level-dependent activity in the overlapping dorsal anterior cingulate cortex and supplementary motor area region but no significant decreases in activity; the increased activity is considered to represent a recovery-of-responsiveness process following an AL. This increased activity was also seen in the HR of the corresponding ROI. Importantly, HR analysis revealed no trend of increased activity in the posterior cingulate of the default mode network, which has been repeatedly demonstrated to be a strong biomarker of mind-wandering. FC analysis showed decoupling of external attention, which supports the involuntary nature of ALs, in addition to the neural recovery processes. Other findings were a decrease in HR in the frontoparietal network before the onset of ALs, and a decrease in FC between default mode network and working memory network. These findings converge to our conclusion that the ALs observed during our task were involuntary mind-blanks. This is further supported behaviourally by the short duration of the ALs (mean 1.7 s), which is considered too brief to be instances of extreme mind-wandering. This is the first study to demonstrate that at least the majority of complete losses of responsiveness on a continuous visuomotor task are, if not due to microsleeps, due to involuntary mind-blanks.

The new science of sleep: From cells to large-scale societies

In the past 20 years, more remarkable revelations about sleep and its varied functions have arguably been made than in the previous 200. Building on this swell of recent findings, this essay provides a broad sampling of selected research highlights across genetic, molecular, cellular, and physiological systems within the body, networks within the brain, and large-scale social dynamics. Based on this raft of exciting new discoveries, we have come to realize that sleep, in this moment of its evolution, is very much polyfunctional (rather than monofunctional), yet polyfunctional for reasons we had never previously considered. Moreover, these new polyfunctional insights powerfully reaffirm sleep as a critical biological, and thus health-sustaining, requisite. Indeed, perhaps the only thing more impressive than the unanticipated nature of these newly emerging sleep functions is their striking divergence, from operations of molecular mechanisms inside cells to entire group societal dynamics.

The effect of REM-sleep disruption on affective processing: A systematic review of human and animal experimental studies

Evidence on the importance of rapid-eye-movement sleep (REMS) in processing emotions is accumulating. The focus of this systematic review is the outcomes of experimental REMS deprivation (REMSD), which is the most common method in animal models and human studies on REMSD. This review revealed that variations in the applied REMSD methods were substantial. Animal models used longer deprivation protocols compared with studies in humans, which mostly reported acute deprivation effects after one night. Studies on animal models showed that REMSD causes aggressive behavior, increased pain sensitivity, reduced sexual behavior, and compromised consolidation of fear memories. Animal models also revealed that REMSD during critical developmental periods elicits lasting consequences on affective-related behavior. The few human studies revealed increases in pain sensitivity and suggest stronger consolidation of emotional memories after REMSD. As pharmacological interventions (such as selective serotonin reuptake inhibitors [SSRIs]) may suppress REMS for long periods, there is a clear gap in knowledge regarding the effects and mechanisms of chronic REMS suppression in humans.