Predictive coding, multisensory integration, and attentional control: A multicomponent framework for lucid dreaming.

Lucid dreaming (LD) is a mental state in which we realize not being awake but are dreaming while asleep. It often involves vivid, perceptually intense dream images as well as peculiar kinesthetic sensations, such as flying, levitating, or out-of-body experiences. LD is in the cross-spotlight of cognitive neuroscience and sleep research as a particular case to study consciousness, cognition, and the neural background of dream experiences. Here, we present a multicomponent framework for the study and understanding of neurocognitive mechanisms and phenomenological aspects of LD. We propose that LD is associated with prediction error signals arising during sleep and occurring at higher or lower levels of the processing hierarchy. Prediction errors are resolved by generating a superordinate self-model able to integrate ambiguous stimuli arriving from sensory periphery and higher-order cortical regions. While multisensory integration enables lucidity maintenance and contributes to peculiar kinesthetic experiences, attentional control facilitates multisensory integration by dynamically regulating the balance between the influence of top-down mental models and the precision weighting of bottom-up sensory inputs. Our novel framework aims to link neural correlates of LD with current concepts of sleep and arousal regulation and provide testable predictions on interindividual differences in LD as well as neurocognitive mechanisms inducing lucid dreams.

Treating narcolepsy-related nightmares with cognitive behavioural therapy and targeted lucidity reactivation: A pilot study.

Nightmares are a common symptom in narcolepsy that has not been targeted in prior clinical trials. This study investigated the efficacy of Cognitive Behavioural Therapy for Nightmares (CBT-N), adapted for narcolepsy, in a small group of adults. Given the high prevalence of lucid dreaming in narcolepsy, we added a promising adjuvant component, targeted lucidity reactivation (TLR), a procedure designed to enhance lucid dreaming and dream control. Using a multiple baseline single-case experimental design, adults with narcolepsy and frequent nightmares (≥3/week, N = 6) were randomised to a 2 or 4 week baseline and received seven treatment sessions (CBT-N or CBT-N + TLR). Across the groups, there was a large effect size (between-case standardised mean difference [BC-SMD] = -0.97, 95% CI -1.79 to -0.14, p < 0.05) for reduced nightmare frequency from baseline (M = 8.38/week, SD = 7.08) to posttreatment (M = 2.25/week, SD = 1.78). Nightmare severity improved significantly with large effect sizes on sleep diaries (BC-SMD = -1.14, 95% CI -2.03 to -0.25, p < 0.05) and the Disturbing Dream and Nightmare Severity Index (z = -2.20, p = 0.03, r = -0.64). Treatment was associated with a reduction for some participants in sleep paralysis, sleep-related hallucinations, and dream enactment. NREM parasomnia symptoms (z = -2.20, p = 0.03, r = -0.64) and self-efficacy for managing symptoms (z = -2.02, p = 0.04, r = -0.58) improved significantly with large effect sizes. Participants who underwent TLR (n = 3) all recalled dreams pertaining to their rescripted nightmare. In interviews, participants noted reduced shame and anxiety about sleep/nightmares. This study provides a proof of concept for the application of TLR as a therapeutic strategy with clinical populations, as well as preliminary evidence for the efficacy of CBT-N in treating narcolepsy-related nightmares.

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.

Sleep and lucid dreaming in adolescent athletes and non-athletes.

During lucid dreaming (LD), dreamers are aware of experiencing a dream and may consciously influence its content. This study used an online questionnaire to investigate the LD frequency and applications in 193 adolescent athletes and non-athletes (17.40 ± 2.09 years; 46% athletes, 54% controls). Given the critical role that sleep plays in adolescent health, development, and performance, associations of LD with various sleep parameters were also explored. LD is prominent in adolescents (67.4% experienced it at least once, 30.0% once a month or more, 12.9% at least once a week), but similar in terms of frequency and uses between athletes and non-athletes. A higher proportion of those who practiced sports/dance during LD reported improved waking self-efficacy (57.1%) over sport performance (42.9%). There was no indication that chronotype preference may influence LD nor that LD may be detrimental to adolescent sleep. Athletes and controls had similar sleep durations, daytime sleepiness, and sleep disturbances frequency, but athletes reported higher sleep quality. Despite, on average, meeting the minimum sleep recommendation guidelines for their age, a relatively large proportion of adolescents did not attain sufficient sleep, particularly on weeknights (47.4% 14-17 years; 20.0% 18-21 years), suggesting that restricted sleep remains prevalent in adolescent populations.

A systematic review of new empirical data on lucid dream induction techniques.

Lucid dreams are defined as dreams in which the dreamers are aware of the fact that they are dreaming as dreams continue. It has been ~12 years since the last review of the efficiency of lucid dream induction techniques was conducted. Hence, the present study aimed to review the lucid dream induction techniques published in the past decade. The second aim was to propose a modified classification for the existing lucid dream induction techniques, including cognitive techniques, external stimulation, substance intervention, and cortical stimulation. The third aim was to assess the methodological quality of the studies included in the review. It was hypothesised that, comparing with the studies included in the last review, the studies included in the present review had better overall methodological quality. A total of 19 peer-reviewed studies were included and analysed in the present review, from which 14 lucid dream induction techniques were identified. The results indicated that the mnemonic induction of lucid dream technique was the most effective for inducing lucid dreams. Moreover, two new techniques, the senses-initiated lucid dream technique and galantamine intervention, might also be competitive candidates for lucid dream induction but further replications are needed. As hypothesised, the overall methodological quality of the studies included in the present review was higher than that of the studies included the previous review. In all, 17 studies had moderate methodological quality, whereas only three studies had poor methodological quality.

The effectiveness of lucid dreaming therapy in patients with nightmares: A systematic review.

OBJECTIVES: Nightmares can be defined as "an unpleasant dream with anxiety and oppression". They represent a symptom possibly leading to serious psychiatric and physical consequences. It occurs to 2% to 8% of the general population. Lucid dreaming therapy (LDT) is an interesting upcoming psychotherapy for the treatment of nightmares. The aim of this study was to evaluate the efficacy of LDT in the treatment of nightmares in adults and children. METHODS: We performed a systematic review of the literature, based on the Cochrane organisation's methodology. We explored the PubMed, Cochrane library, PsycINFO via Ovid and Embase databases and clinical trial registries (CTR), namely clinicaltrials.gov, EU clinical trials and the WHO clinical trials registry platform. RESULTS: Four randomized controlled trials (RCT), 2 case series and 5 case reports were included. Most of the included studies found LDT effective in reducing nightmare frequency among adults with chronic and recurring nightmares. We did not identify any reports in children. CONCLUSIONS: Despite a limited internal validity for the included studies, these first results are encouraging. Nonetheless, larger and more rigorous studies would allow to better assess the utility of LDT for nightmares.

Could sleep paralysis be pleasant?

Sleep paralysis is an inability to move at sleep onset or upon awakening. It is often a distressing experience that can be associated with significant clinical consequences. Few studies have focussed on pleasant sleep paralysis episodes. The present study aimed to determine the relative prevalence of pleasant episodes of sleep paralysis as well as variables that may make them more likely to occur. Participants (N = 172) with recurrent episodes of sleep paralysis completed a battery of questionnaires investigating sleep paralysis episodes, trauma symptoms, life satisfaction, and Big Five personality traits. Pleasant sleep paralysis was found to be a fairly common experience (i.e. 23%). Episodes were emotionally complex, with pleasant episodes often involving some admixture of fear. In terms of hallucinations, pleasant episodes were more likely to involve vestibular-motor sensations (i.e. illusory body movements) and some individuals reported an ability to induce these hallucinations. Contrary to expectation, neither lower trauma symptomatology nor higher levels of reported life satisfaction predicted pleasant sleep paralysis. However, the ability to lucid dream and higher levels of trait openness to new experiences appeared to make pleasant episodes more likely. Clinical implications are discussed.

Unexpected awakenings in severe dementia from case reports to laboratory.

OBJECTIVE: Case report notions of unexpected memory retrieval in patients with severe dementia near to death are starting to alter the central "irreversible" paradigm of dementia and locate dementia as a problem of memory retrieval, not consolidation. We suggest that the most likely central tenet of this paradoxical memory retrieval is the fluctuation of neuromodulators projecting from the brain stem to the medial prefrontal cortex and the hippocampus. The neuromodulation-centric explanation of this phenomenon aims to open the "irreversible" paradigm of dementia up for discussion and suggest a plausible treatment strategy by questioning how the devastating process of death fluctuates memory performance in severe dementia. BACKGROUND: Supporting demented patients, who are mostly unresponsive, without making demands or asking a question and regarding them as valuable human beings unexpectedly improve their memory performance around the time of death. NEW LUCIDITY HYPOTHESIS: Around the time of death, neurological signs (hyper-arousal and -attention) of demented people point out that neurotransmitter discharges are dramatically changed. Relatively resistant neuromodulator circuits to neurodegeneration can maintain optimal levels of arousal and attention for memory processing. In this way, unexpected episodes of lucidity can be triggered. Also, corticotropin-releasing peptides might increase mental clarity by increasing the excitability of the neuromodulator circuits. The science of memory retrieval is more complicated and nuanced than retrieval observations in case reports, but the rapid development of new techniques holds promise for future understanding of lucidity in severe dementia. MAJOR CHALLENGE FOR THE MODEL: There is no an animal or human model to test this hypothesis; however, the similarities between neurological signs (instantaneous cognitive fluctuations) of delirium and paradoxical lucidity could provide a unique window to understand neural events of terminal lucidity on a modified animal model of delirium. Likewise, similarities between unexpected consciousness signs of terminal lucidity and lucid dreaming suggest that lucid dreaming episodes might be considered a human model for terminal lucidity research.

Lucid Dreams in Veterans With Posttraumatic Stress Disorder Include Nightmares.

A previous study in military veterans with posttraumatic stress disorder (PTSD) and recurrent nightmares found a high prevalence of lucid dreaming (LD), the awareness while a dream continues that one is dreaming, and an "LD profile" characterized by frequent dream awareness and rare dream content control. Given the importance of the nightmare disturbance in PTSD, this study assessed with questionnaires the prevalence and characteristics of lucid nightmares, specifically, in a sample of 54 veterans with PTSD. Over half the sample endorsed experiencing LD, with nearly all of these individuals explicitly reporting lucidity in nightmares. The lucid nightmare profile was characterized by high awareness and low content control. Veterans reported feeling stuck and anxious, trying unsuccessfully to awaken from lucid nightmares. We conclude that lucid nightmares may occur commonly in veterans with PTSD, with a profile resembling that previously reported for LD experiences generally in this group.

Increased creative thinking in narcolepsy.

Some studies suggest a link between creativity and rapid eye movement sleep. Narcolepsy is characterized by falling asleep directly into rapid eye movement sleep, states of dissociated wakefulness and rapid eye movement sleep (cataplexy, hypnagogic hallucinations, sleep paralysis, rapid eye movement sleep behaviour disorder and lucid dreaming) and a high dream recall frequency. Lucid dreaming (the awareness of dreaming while dreaming) has been correlated with creativity. Given their life-long privileged access to rapid eye movement sleep and dreams, we hypothesized that subjects with narcolepsy may have developed high creative abilities. To test this assumption, 185 subjects with narcolepsy and 126 healthy controls were evaluated for their level of creativity with two questionnaires, the Test of Creative Profile and the Creativity Achievement Questionnaire. Creativity was also objectively tested in 30 controls and 30 subjects with narcolepsy using the Evaluation of Potential Creativity test battery, which measures divergent and convergent modes of creative thinking in the graphic and verbal domains, using concrete and abstract problems. Subjects with narcolepsy obtained higher scores than controls on the Test of Creative Profile (mean ± standard deviation: 58.9 ± 9.6 versus 55.1 ± 10, P = 0.001), in the three creative profiles (Innovative, Imaginative and Researcher) and on the Creative Achievement Questionnaire (10.4 ± 25.7 versus 6.4 ± 7.6, P = 0.047). They also performed better than controls on the objective test of creative performance (4.3 ± 1.5 versus 3.7 ± 1.4; P = 0.009). Most symptoms of narcolepsy (including sleepiness, hypnagogic hallucinations, sleep paralysis, lucid dreaming, and rapid eye movement sleep behaviour disorder, but not cataplexy) were associated with higher scores on the Test of Creative Profile. These results highlight a higher creative potential in subjects with narcolepsy and further support a role of rapid eye movement sleep in creativity.

Dream lucidity is associated with positive waking mood.

Lucid dreaming is a unique phenomenon with potential applications for therapeutic interventions. Few studies have investigated the effects of lucidity on an individual's waking mood, which could have valuable implications for improving psychological wellbeing. The current experiment aims to investigate whether the experience of lucidity enhances positive waking mood, and whether lucidity is associated with dream emotional content and subjective sleep quality. 20 participants were asked to complete lucid dream induction techniques along with an online dream diary for one week, which featured a 19-item lucidity questionnaire, and subjective ratings of sleep quality, dream emotional content, and waking mood. Results indicated that higher lucidity was associated with more positive dream content and elevated positive waking mood the next day, although there was no relationship with sleep quality. The results of the research and suggestions for future investigations, such as the need for longitudinal studies of lucidity and mood, are discussed.

Sleep fragmentation and lucid dreaming.

Lucid dreaming-the phenomenon of experiencing waking levels of self-reflection within one's dreams-is associated with more wake-like levels of neural activation in prefrontal brain regions. In addition, alternating periods of wakefulness and sleep might increase the likelihood of experiencing a lucid dream. Here we investigate the association between sleep fragmentation and lucid dreaming, with a multi-centre study encompassing four different investigations into subjective and objective measures of sleep fragmentation, nocturnal awakenings, sleep quality and polyphasic sleep schedules. Results across these four studies provide a more nuanced picture into the purported connection between sleep fragmentation and lucid dreaming: While self-assessed numbers of awakenings, polyphasic sleep and physiologically validated wake-REM sleep transitions were associated with lucid dreaming, neither self-assessed sleep quality, nor physiologically validated numbers of awakenings were. We discuss these results, and their underlying neural mechanisms, within the general question of whether sleep fragmentation and lucid dreaming share a causal link.

Attempted induction of signalled lucid dreaming by transcranial alternating current stimulation.

Neurophysiological correlates of self-awareness during sleep ('lucid dreaming') remain unclear despite their importance for clarifying the neural underpinnings of consciousness. Transcranial direct (tDC) and alternating (tAC) current stimulation during sleep have been shown to increase dream self-awareness, but these studies' methodological weaknesses prompted us to undertake additional study. tAC stimulation was associated with signal-verified and self-rated lucid dreams-but so was the sham procedure. Situational factors may be crucial to inducing self-awareness during sleep.

Flying dreams stimulated by an immersive virtual reality task.

Despite a high prevalence and broad interest in flying dreams, these exceptional experiences remain infrequent. Our study aimed to (1) induce flying dreams using a custom-built virtual reality (VR) flying task, (2) examine their phenomenological correlates and (3) investigate their relations to participant state and trait factors. 137 participants underwent VR-flying followed by a morning nap. They also completed home dream journals for 5 days before and 10 days after the VR exposure. VR-flying successfully increased the reporting of flying dreams during the laboratory nap and on the following morning compared to both baseline frequencies and a control cohort. Flying dreams were also changed qualitatively, exhibiting higher levels of Lucid-control and emotional intensity, after VR exposure. Factors such as prior dream-flying experiences and level of VR sensory immersion modulated flying dream induction. Findings are consistent with a new vection-based explanation of dream-flying and may facilitate development of dream flight-induction technologies.

Inducing lucid dreams by olfactory-cued reactivation of reality testing during early-morning sleep: A proof of concept.

The reliable induction of lucid dreams is a challenge in lucid dream research. In a previous study by our research group we were able to induce in about 50% of the participants a lucid dream in a single sleep laboratory night by combining a wake-up-back-to-bed sleep protocol and a mnemonic technique. In the present study, we extended our previous procedure by additional presentation of an odor during sleep to reactivate memory traces about reality testing. In total 16 male participants spent a single night in the sleep lab whereas the procedure induced in two participants a lucid dream (12.5%). The induction rate stays below the success rate of our previous study and therefore odor-cueing seems not a promising technique for inducing lucid dreams. Beside the odor presentation, several other methodological changes have been made, which will be discussed and hopefully help further dream engineering to improve induction techniques.

Metacognitive mechanisms underlying lucid dreaming.

Lucid dreaming is a state of awareness that one is dreaming, without leaving the sleep state. Dream reports show that self-reflection and volitional control are more pronounced in lucid compared with nonlucid dreams. Mostly on these grounds, lucid dreaming has been associated with metacognition. However, the link to lucid dreaming at the neural level has not yet been explored. We sought for relationships between the neural correlates of lucid dreaming and thought monitoring. Human participants completed a questionnaire assessing lucid dreaming ability, and underwent structural and functional MRI. We split participants based on their reported dream lucidity. Participants in the high-lucidity group showed greater gray matter volume in the frontopolar cortex (BA9/10) compared with those in the low-lucidity group. Further, differences in brain structure were mirrored by differences in brain function. The BA9/10 regions identified through structural analyses showed increases in blood oxygen level-dependent signal during thought monitoring in both groups, and more strongly in the high-lucidity group. Our results reveal shared neural systems between lucid dreaming and metacognitive function, in particular in the domain of thought monitoring. This finding contributes to our understanding of the mechanisms enabling higher-order consciousness in dreams.

Lucid dreaming incidence: A quality effects meta-analysis of 50years of research.

We report a quality effects meta-analysis on studies from the period 1966-2016 measuring either (a) lucid dreaming prevalence (one or more lucid dreams in a lifetime); (b) frequent lucid dreaming (one or more lucid dreams in a month) or both. A quality effects meta-analysis allows for the minimisation of the influence of study methodological quality on overall model estimates. Following sensitivity analysis, a heterogeneous lucid dreaming prevalence data set of 34 studies yielded a mean estimate of 55%, 95% C. I. [49%, 62%] for which moderator analysis showed no systematic bias for suspected sources of variability. A heterogeneous lucid dreaming frequency data set of 25 studies yielded a mean estimate of 23%, 95% C. I. [20%, 25%], moderator analysis revealed no suspected sources of variability. These findings are consistent with earlier estimates of lucid dreaming prevalence and frequent lucid dreaming in the population but are based on more robust evidence.

Studies with lucid dreaming as add-on therapy to Gestalt therapy.

OBJECTIVES: The aim of the present exploratory clinical study was to evaluate LD as an add-on therapy for treating nightmares. METHODS: Thirty-two subjects having nightmares (ICD-10: F51.5) at least twice a week participated. Subjects were randomly assigned to group: A) Gestalt therapy group (= GTG), or B) Gestalt and lucid dreaming group therapy (= LDG). Each group lasted ten weeks. Participants kept a sleep/dream diary over the treatment. Examinations with respect to nightmare frequency and sleep quality (Pittsburgh Sleep Quality Index) were carried out at the beginning, after five and ten weeks and at a follow-up three months later. RESULTS: Concerning nightmare frequency, a significant reduction was found in both groups after the ten-week-study and at the follow-up (Wilcoxon test: P ≤ 0.05). Significant reduction in dream recall frequency could only be observed in the GTG (Wilcoxon test: P ≤ 0.05). For subjects having succeeded in learning lucid dreaming, reduction was sooner and higher. Sleep quality improved for both groups at the follow-up (P ≤ 0.05, Wilcoxon test). Only the LDG showed significant improvement at the end of therapy (P ≤ 0.05). CONCLUSION: Lucid dreaming, in combination with Gestalt therapy, is a potent technique to reduce nightmare frequency and improve the subjective quality of sleep.

Frequent Lucid Dreaming Is Associated with Meditation Practice Styles, Meta-Awareness, and Trait Mindfulness.

Lucid dreaming involves becoming aware that one's current experience is a dream, which has similarities with the notion of mindfulness-becoming aware of moment-to-moment changes in experience. Additionally, meta-awareness, the ability to explicitly notice the current content of one's own mental state, has also been proposed to play an important role both in lucid dreaming and mindfulness meditation practices. However, research has shown conflicting strengths of associations between mindfulness, meditation, and lucid dreaming frequency, and the link between lucid dreaming and meta-awareness has not yet been empirically studied. This study evaluated the associations between lucid dreaming frequency and different meditation practice styles, mindfulness traits, and individual differences in meta-awareness through an online survey (n = 635). The results suggest that daily frequent meditators experience more lucid dreams than non-frequent meditators. However, weekly frequent meditators did not have a higher lucid dreaming frequency. A positive association was observed between open monitoring styles of meditation and lucid dreaming. The findings also indicate that meta-awareness is higher for meditators and weekly lucid dreamers. Furthermore, frequent lucid dreaming was commonly associated with a non-reactive stance and experiencing transcendence. Overall, the findings suggest a positive relationship between specific meditation practices and lucid dreaming as well as the importance of meta-awareness as a cognitive process linking meditation, mindfulness, and lucid dreaming.

Neuropsychopharmacological Induction of (Lucid) Dreams: A Narrative Review.

Lucid dreaming (LD) is a physiological state of consciousness that occurs when dreamers become aware that they are dreaming, and may also control the oneiric content. In the general population, LD is spontaneously rare; thus, there is great interest in its induction. Here, we aim to review the literature on neuropsychopharmacological induction of LD. First, we describe the circadian and homeostatic processes of sleep regulation and the mechanisms that control REM sleep with a focus on neurotransmission systems. We then discuss the neurophysiology and phenomenology of LD to understand the main cortical oscillations and brain areas involved in the emergence of lucidity during REM sleep. Finally, we review possible exogenous substances-including natural plants and artificial drugs-that increase metacognition, REM sleep, and/or dream recall, thus with the potential to induce LD. We found that the main candidates are substances that increase cholinergic and/or dopaminergic transmission, such as galantamine. However, the main limitation of this technique is the complexity of these neurotransmitter systems, which challenges interpreting results in a simple way. We conclude that, despite these promising substances, more research is necessary to find a reliable way to pharmacologically induce LD.