Attempted induction of signalled lucid dreaming by transcranial alternating current stimulation

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.

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.

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.

Dream lucidity positively correlates with reality monitoring

Dream lucidity, the awareness of consciousness in dreams, is linked to functions that support reality monitoring in differentiating between internally and externally generated memories. However, lucid dreams have been argued to result from thin reality-fantasy boundaries that lead to reality monitoring errors. To examine the relationship between dream lucidity and reality monitoring, we recruited 31 college students to rate their dream lucidity for 7 days and then complete a reality monitoring test in Experiment 1, observing a positive correlation between dream lucidity and reality monitoring. In Experiment 2, 109 participants rated dream lucidity and the memory characteristics of perceived and imagined events. Dream lucidity was negatively correlated with differences in sensory details between the memories of perceived and imagined events. The findings indicate that individuals with high dream lucidity have a superior ability to discriminate between externally and internally generated events that are susceptible to reality monitoring errors.

Nothingness Is All There Is: An Exploration of Objectless Awareness During Sleep

Recent years have seen a heightened focus on the study of minimal forms of awareness during sleep to advance the study of consciousness and understand what makes a state conscious. This focus draws on an increased interest in anecdotical descriptions made by classic Indian philosophical traditions about unusual forms of awareness during sleep. For instance, in the so-called state of witnessing-sleep or luminosity sleep, one is said to reach a state that goes beyond ordinary dreaming and abide in a state of just awareness, a state in which one is not aware of anything else other than one’s own awareness. Moreover, for these traditions, this state is taken to be the essence or background of consciousness. Reports on such a state opens the door to exciting new lines of research in the study of consciousness, such as inquiry into the so-called objectless awareness during sleep—states of awareness that lack an ordinary object of awareness. In this two-staged research project, we attempted to find the phenomenological blueprints of such forms of awareness during sleep in 18 participants by conducting phenomenological interviews, informed by a novel tool in qualitative research, the micro-phenomenological interview (MPI) method. Following a phenomenological analysis, we isolated a similar phase across 12 reported experiences labeled as “nothingness phase” since it described what participants took to be an experience of “nothingness.” This common phase was characterized by minimal sense of self—a bodiless self, yet experienced as being “somewhere”—, the presence of non-modal sensations, relatively pleasant emotions, an absence of visual experience, wide and unfocused attention, and an awareness of the state as it unfolded.

Lucid dreaming occurs in activated rapid eye movement sleep, not a mixture of sleep and wakefulness

STUDY OBJECTIVES

(1) To critically test whether a previously reported increase in frontolateral 40 Hz power in lucid REM sleep, used to justify the claim that lucid dreaming is a "hybrid state" mixing sleep and wakefulness, is attributable to the saccadic spike potential (SP) artifact as a corollary of heightened REM density. (2) To replicate the finding that lucid dreams are associated with physiological activation, including heightened eye movement density, during REM sleep. (3) To conduct an exploratory analysis of changes in EEG features during lucid REM sleep.

METHODS

We analyzed 14 signal-verified lucid dreams (SVLDs) and baseline REM sleep segments from the same REM periods from six participants derived from the Stanford SVLD database. Participants marked lucidity onset with standard left-right-left-right-center (LR2c) eye-movement signals in polysomnography recordings.

RESULTS

Compared to baseline REM sleep, lucid REM sleep had higher REM density (β = 0.85, p = 0.002). Bayesian analysis supported the null hypothesis of no differences in frontolateral 40 Hz power after removal of the SP artifact (BH = 0.18) and ICA correction (BH = 0.01). Compared to the entire REM sleep period, lucid REM sleep showed small reductions in low-frequency and beta band spectral power as well as increased signal complexity (all p < 0.05), which were within the normal variance of baseline REM sleep.

CONCLUSIONS

Lucid dreams are associated with higher-than-average levels of physiological activation during REM sleep, including measures of both subcortical and cortical activation. Increases in 40 Hz power in periorbital channels reflect saccadic and microsaccadic SPs as a result of higher REM density accompanying heightened activation.

Dreaming of the sleep lab

The phenomenon of dreaming about the laboratory when participating in a sleep study is common. The content of such dreams draws upon episodic memory fragments of the participant's lab experience, generally, experimenters, electrodes, the lab setting, and experimental tasks. However, as common as such dreams are, they have rarely been given a thorough quantitative or qualitative treatment. Here we assessed 528 dreams (N = 343 participants) collected in a Montreal sleep lab to 1) evaluate state and trait factors related to such dreams, and 2) investigate the phenomenology of lab incorporations using a new scoring system. Lab incorporations occurred in over a third (35.8%) of all dreams and were especially likely to occur in REM sleep (44.2%) or from morning naps (48.4%). They tended to be related to higher depression scores, but not to sex, nightmare-proneness or anxiety. Common themes associated with lab incorporation were: Meta-dreaming, including lucid dreams and false awakenings (40.7%), Sensory incorporations (27%), Wayfinding to, from or within the lab (24.3%), Sleep as performance (19.6%), Friends/Family in the lab (15.9%) and Being an object of observation (12.2%). Finally, 31.7% of the lab incorporation dreams included relative projections into a near future (e.g., the experiment having been completed), but very few projections into the past (2.6%). Results clarify sleep stage and sleep timing factors associated with dreamed lab incorporations. Phenomenological findings further reveal both the typical and unique ways in which lab memory elements are incorporated de novo into dreaming. Identified themes point to frequent social and skillful dream scenarios that entail monitoring of one's current state (in the lab) and projection of the self into dream environments elaborated around local space and time. The findings have implications for understanding fundamental dream formation mechanisms but also for appreciating both the advantages and methodological pitfalls of conducting laboratory-based dream collection.

Investigation on Neurobiological Mechanisms of Dreaming in the New Decade

Dream research has advanced significantly over the last twenty years, thanks to the new applications of neuroimaging and electrophysiological techniques. Many findings pointed out that mental activity during sleep and wakefulness shared similar neural bases. On the other side, recent studies have highlighted that dream experience is promoted by significant brain activation, characterized by reduced low frequencies and increased rapid frequencies. Additionally, several studies confirmed that the posterior parietal area and prefrontal cortex are responsible for dream experience. Further, early results revealed that dreaming might be manipulated by sensory stimulations that would provoke the incorporation of specific cues into the dream scenario. Recently, transcranial stimulation techniques have been applied to modulate the level of consciousness during sleep, supporting previous findings and adding new information about neural correlates of dream recall. Overall, although multiple studies suggest that both the continuity and activation hypotheses provide a growing understanding of neural processes underlying dreaming, several issues are still unsolved. The impact of state-/trait-like variables, the influence of circadian and homeostatic factors, and the examination of parasomnia-like events to access dream contents are all opened issues deserving further deepening in future research.