HYPNOTIC SUGGESTIONS GIVEN BEFORE NIGHTTIME SLEEP EXTEND SLOW-WAVE SLEEP AS COMPARED TO A CONTROL TEXT IN HIGHLY HYPNOTIZABLE SUBJECTS

HGSHS-5:G-First results with the short version of the test for the Harvard Group Scale of Hypnotic Susceptibility and a comparison with the full version

Introduction

The HGSHS:A is one of the most commonly used measures of hypnotic suggestibility. However, this test suffers from low feasibility due to a time requirement exceeding 1 h, and from a questionable representation of the normal population. Recently, a short version of HGSHS-5:G was developed and published, and now the first results are available. The scope of this investigation was to verify the assumption of equally positioned and normally distributed scores, resulting in equally sized suggestibility groups in a number of different studies with full or short versions of HGSHS, and to compare the results of the 11-item score with the 5-item score, the latter being calculated from either the full version or the short version test.

Methods

Data from 21 studies with testing for HGSHS were analyzed, 15 using the HGSHS:A full version and six using the HGSHS-5:G short version, for a total of 2,529 data sets. Position and distribution of both the 11-item score and the 5-item score were tested. Linear regression analysis was used to compare the two scores, as well as cross-table and weighted Cohen's kappa to determine the match of grouping into low and high suggestibility. To evaluate contributing factors to the observed differences in the study results, a multifactorial analysis of variance was performed.

Results

In the different studies, position and distribution of scores, as well as group sizes for low and high suggestibles, varied. All score distributions were found to be non-normal and shifted to the right from the middle score; the shift was more extensive with the 11-item score. The correlation between both scores calculated from full version tests was moderate (R 2 = 0.69), as was the match of suggestibility grouping (κ = 0.58). Studies using the short version involving less student-dominated populations showed sufficient agreement with the full version, but lower scores were caused by an increase in the zero score.

Conclusion

A normal population is not represented in most applications of HGSHS, and grouping into low and high suggestibles varies, mainly due to different positions of score distributions. A direct comparison of full and short versions of HGSHS tested in the same subjects is still missing.

Extracting Stress-Related EEG Patterns From Pre-Sleep EEG for Forecasting Slow-Wave Sleep Deficiency

Sleep is vital to our daily activity. Lack of proper sleep can impair functionality and overall health. While stress is known for its detrimental impact on sleep quality, the precise effect of pre-sleep stress on subsequent sleep structure remains unknown. This study introduced a novel approach to study the pre-sleep stress effect on sleep structure, specifically slow-wave sleep (SWS) deficiency. To achieve this, we selected forehead resting EEG immediately before and upon sleep onset to extract stress-related neurological markers through power spectra and entropy analysis. These markers include beta/delta correlation, alpha asymmetry, fuzzy entropy (FuzzEn) and spectral entropy (SpEn). Fifteen subjects were included in this study. Our results showed that subjects lacking SWS often exhibited signs of stress in EEG, such as an increased beta/delta correlation, higher alpha asymmetry, and increased FuzzEn in frontal EEG. Conversely, individuals with ample SWS displayed a weak beta/delta correlation and reduced FuzzEn. Finally, we employed several supervised learning models and found that the selected neurological markers can predict subsequent SWS deficiency. Our investigation demonstrated that the classifiers could effectively predict varying levels of slow-wave sleep (SWS) from pre-sleep EEG segments, achieving a mean balanced accuracy surpassing 0.75. The SMOTE-Tomek resampling method could improve the performance to 0.77. This study suggests that stress-related neurological markers derived from pre-sleep EEG can effectively predict SWS deficiency. Such information can be integrated with existing sleep-improving techniques to provide a personalized sleep forecasting and improvement solution.

Behavioral and psychological treatments for NREM parasomnias: A systematic review

BACKGROUND

Non-rapid eye movement (NREM) parasomnias are often benign and transient, requiring no formal treatment. However, parasomnias can also be chronic, disrupt sleep quality, and pose a significant risk of harm to the patient or others. Numerous behavioral strategies have been described for the management of NREM parasomnias, but there have been no published comprehensive reviews. This systematic review was conducted to summarize the range of behavioral and psychological interventions and their efficacy.

METHODS

We conducted a systematic search of the literature to identify all reports of behavioral and psychological treatments for NREM parasomnias (confusional arousals, sexsomnia, sleepwalking, sleep terrors, sleep-related eating disorder, parasomnia overlap disorder). This review was conducted in line with PRISMA guidelines. The protocol was registered with PROSPERO (CRD42021230360). The search was conducted in the following databases (initially on March 10, 2021 and updated February 24, 2023): Ovid (MEDLINE), Cochrane Library databases (Wiley), CINAHL (EBSCO), PsycINFO (EBSCO), and Web of Science (Clarivate). Given a lack of standardized quantitative outcome measures, a narrative synthesis approach was used. Risk of bias assessment used tools from Joanna Briggs Institute.

RESULTS

A total of 72 publications in four languages were included, most of which were case reports (68%) or case series (21%). Children were included in 32 publications and adults in 44. The most common treatment was hypnosis (33 publications) followed by various types of psychotherapy (31), sleep hygiene (19), education/reassurance (15), relaxation (10), scheduled awakenings (9), sleep extension/scheduled naps (9), and mindfulness (5). Study designs and inconsistent outcome measures limited the evidence for specific treatments, but some evidence supports multicomponent CBT, sleep hygiene, scheduled awakenings, and hypnosis.

CONCLUSIONS

This review highlights the wide breadth of behavioral and psychological interventions for managing NREM parasomnias. Evidence for the efficacy of these treatments is limited by the retrospective and uncontrolled nature of most research as well as the infrequent use of validated quantitative outcome measures. Behavioral and psychological treatments have been studied alone and in various combinations, and recent publications suggest a trend toward preference for multicomponent cognitive behavioral therapies designed to specifically target priming and precipitating factors of NREM parasomnias.

Feasibility of a Self-Administered Hypnosis Intervention for Improving Sleep in College Students

Approximately two out of three college students report experiencing suboptimal sleep quality. The aim of this study was to examine the feasibility of a self-administered hypnosis intervention to improve sleep in college students. Twenty-two college students who self-reported poor sleep quality were enrolled in a 4-week study comprising 1 baseline week and a 3-week self-administered hypnosis intervention. Sleep onset latency and sleep efficiency as measured by wrist actigraphy were significantly improved. The mean average nightly sleep duration during the baseline week was 398.88 minutes (SD = 56.44), which increased to a mean of 413.88 minutes (SD = 57.80) during the 3rd week of intervention. However, the results show that there was no statistically significant difference between weeks on objective nightly sleep duration, 95% CI [-11.13, 41.13], t(15) = 1.224, p = .240. Also, results showed that there was no significant difference between weeks on self-reported nightly sleep duration, F(3, 57) = 2.155, p = .103. Twenty participants (91%) completed the study intervention and adherence to daily self-hypnosis practice with an audio recording was high. Zero study-related adverse events were reported, and participants perceived the intervention as easy to use and helpful for improving sleep. These results provide evidence for the feasibility and safety of a self-administered hypnosis intervention to improve sleep in college students. A larger randomized clinical trial is warranted to determine efficacy.

To sleep or not to sleep, that is the question: A systematic review and meta-analysis on the effect of post-trauma sleep on intrusive memories of analog trauma

Distressing intrusive memories of a traumatic event are one of the hallmark symptoms of posttraumatic stress disorder. Thus, it is crucial to identify early interventions that prevent the occurrence of intrusive memories. Both, sleep and sleep deprivation have been discussed as such interventions, yet previous studies yielded contradicting effects. Our systematic review aims at evaluating existing evidence by means of traditional and individual participant data (IPD) meta-analyses to overcome power issues of sleep research. Until May 16th, 2022, six databases were searched for experimental analog studies examining the effect of post-trauma sleep versus wakefulness on intrusive memories. Nine studies were included in our traditional meta-analysis (8 in the IPD meta-analysis). Our analysis provided evidence for a small effect favoring sleep over wakefulness, log-ROM = 0.25, p < .001, suggesting that sleep is associated with a lower number of intrusions but unrelated to the occurrence of any versus no intrusions. We found no evidence for an effect of sleep on intrusion distress. Heterogeneity was low and certainty of evidence for our primary analysis was moderate. Our findings suggest that post-trauma sleep has the potential to be protective by reducing intrusion frequency. More research is needed to determine the impact following real-world trauma and the potential clinical significance.

Systematic Review of Hypnotherapy for Sleep and Sleep Disturbance

Sleep disturbance can negatively affect physical and psychological health. Hypnotherapy may be effective for improving sleep with fewer side effects than other treatments. The purpose of this systematic review is to comprehensively identify studies and evidence regarding hypnotherapy for sleep disturbances. Four databases were searched to identify studies examining the use of hypnotherapy for sleep in adult populations. The search yielded 416 articles, of which 44 were included. Qualitative data analysis revealed that 47.7% of the studies showed positive results regarding the impact of hypnotherapy for sleep, 22.7% showed mixed results, and 29.5% showed no impact. A subset of 11 studies that set sleep disturbance as an inclusion criterion and included suggestions for sleep were examined separately and had more favorable results, such that 54.5% showed positive results, 36.4% showed mixed results, and 9.1% showed no impact results. Hypnotherapy appears to be a promising treatment for sleep disturbance. Future studies should report effect sizes, adverse events, and hypnotizability and include sleep-specific suggestions, standardized measures, and descriptions of hypnotherapy intervention procedures.

Sleep-Directed Hypnosis Improves Subjective Sleep Quality but not Extinction Memory After Exposure to Analog Trauma

Background

Evidence-based treatments of posttraumatic stress disorder (PTSD) aim to promote fear extinction learning. Post-learning sleep, particularly slow wave sleep (SWS), promotes memory consolidation and recall. Thus, boosting SWS might strengthen extinction recall. The current study investigated whether sleep-directed hypnosis designed to increase SWS and sleep quality improves extinction recall and reduces analog PTSD symptoms.

Method

In two subsamples (remote/laboratory), 211 healthy individuals underwent fear conditioning with a traumatic film clip. On the next evening, they underwent extinction training. Thereafter, the experimental group received sleep-directed hypnosis, whereas the control group listened to a control text. Extinction recall and generalization and film-related intrusions and rumination were assessed on the following morning.

Results

Subjective sleep quality declined following exposure to an aversive film. No group differences were found in SWS though exploratory analyses indicated less rapid eye movement sleep after hypnosis. After hypnosis, the experimental group reported improved sleep quality, whereas the control group showed a further deterioration. Hypnosis had no effects on extinction retention and generalization nor on analog intrusions and rumination.

Conclusion

The current results indicate that sleep-directed hypnosis may be beneficial for improving subjective sleep quality after trauma but not for enhancing extinction memory and reducing analog PTSD symptoms.

Pre-sleep arousal induced by suspenseful series and cliffhangers have only minor effects on sleep: A sleep laboratory study

Pre-sleep arousal impairs sleep. Therefore, watching suspenseful TV series before sleep is not recommended as they increase arousal. In particular, the consumption of multiple episodes of the same suspenseful TV series in one sitting - termed binge-watching - could lead to large increases in physiological arousal delaying sleep onset. Furthermore, abrupt endings during critical scenes - termed cliffhangers - result in unfinished story lines, which further increase cognitive arousal and could negatively impact sleep architecture and the number of awakenings. However, the effects of binge-watching and cliffhangers on objective sleep parameters are still unknown. Here we tested in a controlled sleep-laboratory setting whether pre-sleep arousal induced by watching 3-4 episodes of a suspenseful TV series has negative effects on sleep in 50 healthy young participants (39 females, mean age = 22.62 ± 2.60 (SD)). Watching a neutral TV series served as a control condition, according to a within-subject design. In one group of participants, the suspenseful TV series ended with a cliffhanger. In the other group, the same TV series ended where no ongoing action was interrupted. Pre-sleep arousal was measured both subjectively with the self-reported level of stress and objectively with the mean heart rate and cortisol level. As expected, suspenseful TV series induced higher cognitive and physiological pre-sleep arousal than neutral control TV series, with highest values for TV series with cliffhangers. In spite of the high pre-sleep arousal, participants fell asleep faster after watching the suspenseful compared with the neutral TV series (F_(1,48) = 4.89, p = 0.032, η² = 0.09). Sleep architecture and the number of awakenings remained unaffected. However, in the first two sleep cycles, heart rate was still higher after watching suspenseful TV series (F_(1,48) = 6.76, p = 0.012, η² = 0.12). And only after cliffhangers, objective sleep quality - measured as the ratio between slow-wave and beta activity during sleep - was lower than in the other conditions (interaction effect, F_(1,48) = 5.05, p = 0.029, η² = 0.10). Our results speak against large impairments of pre-sleep watching of multiple episodes of suspenseful TV series and cliffhangers on sleep quality and architecture. However, unfinished narratives might induce more subtle changes in oscillatory power during sleep, possibly reflecting ongoing cognitive processing during sleep.

Hypnotizability May Relate to Interoceptive Ability to Accurately Perceive Sleep Depth: An Exploratory Study

When individuals score high on hypnotizability, they usually report experiencing an altered state of consciousness, physiological changes, and attentional shifts during hypnotic induction procedures as well. We hypothesize that a better interoception of such internal changes is also relevant for accurate sleep perception. We compared subjects scoring high versus low on hypnotizability to the accuracy of their estimations of Sleep Onset Latency (SOL) time awake, and sleep depth and explored their objective sleep. We sampled seven studies performed in our sleep labs across a midday nap or a night resulting in n = 231 subjects (aged 30.11 (SD = 17.02) years, range 18-82 with 15.2% males). Hypnotizability did not influence the accuracy of the perception of time needed to fall asleep or time spent awake. However, the reported sleep depth correlated significantly with the measured amount of slow-wave sleep in high hypnotizables. This pattern appeared across a nap as well as a whole night's sleep studies. We did not find any significant differences in objective sleep patterns depending on hypnotizability. Probably, high hypnotizables benefit from a better interoceptive ability for their perception of their sleep depth.

Hypnotic enhancement of slow-wave sleep increases sleep-associated hormone secretion and reduces sympathetic predominance in healthy humans

Sleep is important for normal brain and body functioning, and for this, slow-wave sleep (SWS), the deepest stage of sleep, is assumed to be especially relevant. Previous studies employing methods to enhance SWS have focused on central nervous components of this sleep stage. However, SWS is also characterized by specific changes in the body periphery, which are essential mediators of the health-benefitting effects of sleep. Here we show that enhancing SWS in healthy humans using hypnotic suggestions profoundly affects the two major systems linking the brain with peripheral body functions, i.e., the endocrine and the autonomic nervous systems (ANS). Specifically, hypnotic suggestions presented at the beginning of a 90-min afternoon nap to promote subsequent SWS strongly increased the release of growth hormone (GH) and, to a lesser extent, of prolactin and aldosterone, and shifted the sympathovagal balance towards reduced sympathetic predominance. Thus, the hypnotic suggestions induced a whole-body pattern characteristic of natural SWS. Given that the affected parameters regulate fundamental physiological functions like metabolism, cardiovascular activity, and immunity, our findings open up a wide range of potential applications of hypnotic SWS enhancement, in addition to advancing our knowledge on the physiology of human SWS.

The hypnotic enhancement of slow wave sleep, the deepest stage of sleep, goes beyond the central nervous system, causing changes at the level of the endocrine and the autonomic nervous systems.

Sleep as a window to target traumatic memories

Post-traumatic stress disorder (PTSD) is a severe psychiatric disorder in which traumatic memories result in flashbacks and nightmares. With one-third of patients not responding to standard exposure-based psychotherapy, new treatment strategies are needed. Sleep offers a unique time window to enhance therapeutic efficacy. Traumatic memories that are neutralized in therapy need to be stored back into memory (consolidated) during sleep to solidify the treatment effect. New basic research shows that memory consolidation can be enhanced by presenting sounds or scents that were linked to the memory at encoding, again during sleep. This procedure, termed targeted memory reactivation (TMR), has, despite its clinical potential, not been tested in (PTSD) patients. In this narrative review, we explore the potential of TMR as a new sleep-based treatment for PTSD. First we provide the necessary background on the memory and sleep principles underlying PTSD as well as the present applications and conditional factors of TMR. Then, we will discuss the outstanding questions and most promising experimental avenues when testing TMR to treat traumatic memories.

Exposure to relaxing words during sleep promotes slow-wave sleep and subjective sleep quality

Our thoughts alter our sleep, but the underlying mechanisms are still unknown. We propose that mental processes are active to a greater or lesser extent during sleep and that this degree of activation affects our sleep depth. We examined this notion by activating the concept of "relaxation" during sleep using relaxation-related words in 50 healthy participants. In support of our hypothesis, playing relaxing words during non-rapid eye movement sleep extended the time spent in slow-wave sleep, increased power in the slow-wave activity band after the word cue, and abolished an asymmetrical sleep depth during the word presentation period. In addition, participants reported a higher sleep quality and elevated subjective alertness. Our results support the notion that the activation of mental concepts during sleep can influence sleep depth. They provide a basis for interventions using targeted activations to promote sleep depth and sleep quality to foster well-being and health.

Hypnosis Intervention for Sleep Disturbance: Determination of Optimal Dose and Method of Delivery for Postmenopausal Women

Sleep disturbances are a pervasive problem among postmenopausal women, with an estimated 40 to 64% reporting poor sleep. Hypnosis is a promising intervention for sleep disturbances. This study examined optimal dose and delivery for a manualized hypnosis intervention to improve sleep. Ninety postmenopausal women with poor sleep were randomized to 1 of 4 interventions: 5 in-person, 3 in-person, 5 phone, or 3 phone contacts. All received hypnosis audio recordings, with instructions for daily practice for 5 weeks. Feasibility measures included treatment satisfaction ratings and practice adherence. Sleep outcomes were sleep quality, objective and subjective duration, and bothersomeness of poor sleep. Results showed high treatment satisfaction, adherence, and clinically meaningful (≥ 0.5 SD) sleep improvement for all groups. Sleep quality significantly improved, p < .05, η2 = .70, with no significant differences between groups, with similar results for the other sleep outcomes across all treatment arms. Comparable results between phone and in-person groups suggest that a unique "dose" and delivery strategy is highly feasible and can have clinically meaningful impact. This study provides pilot evidence that an innovative hypnosis intervention for sleep (5 phone contacts with home practice) reduces the burden on participants while achieving maximum treatment benefit.

Systematic decrease of slow-wave sleep after a guided imagery designed to deepen sleep in low hypnotizable subjects

Slow-wave sleep is one of the most important restorative components of sleep and central for our health and cognitive functioning. Although the amount of slow-wave sleep depends on sleep drive, age and other factors, also the pre-sleep mental state might influence sleep depth. We had shown that a pre-sleep hypnotic suggestion to sleep more deeply increased slow-wave sleep duration in hypnotizable subjects. In contrast, low-hypnotizable participants decreased sleep depth after this intervention. A possible reason might be an aversion to and active resistance against hypnosis. To overcome this potential opposition, we introduced the procedure as 'guided imagery'. We replaced the hypnotic induction by a breathing relaxation. Importantly, the suggestion 'to sleep more deeply' remained identical. We expected that these changes would make it easier for low-hypnotizable subjects to benefit from the suggestion. In contrast, young healthy low-hypnotizable participants did not show positive effects. Similar to our previous studies, they exhibited a reduced slow-wave sleep duration after the intervention. Additionally, the ratio between slow-wave activity and beta band power decreased. Subjective sleep quality remained unaffected. Our results indicate that suggestions to sleep more deeply result in decreased sleep depth in low-hypnotizable participants regardless of the mental technique (guided imagery versus hypnosis). Thus, the aversion against hypnosis per se cannot explain the detrimental effect of the intervention on slow-wave sleep in low-hypnotizable subjects. The results support the notion that our mental state before sleep can influence subsequent slow-wave sleep. However, the mechanisms of the contradictory decrease in low-hypnotizable subjects remain unknown.

Embodiment of sleep-related words: Evidence from event-related potentials

Our thoughts can influence sleep, but the underlying mechanisms are unknown. According to the theory of "embodied cognition," the semantic content of cognitive processes is represented by multimodal networks in the brain, which include body-related functions. Such multimodal representations could offer a mechanism, which explains mutual influences between cognition and sleep. Here we tested whether sleep-related words are represented in multimodal networks by examining the effect of congruent versus incongruent body positions on word processing during wakefulness. We experimentally manipulated the body position of 66 subjects (19-40 years old) between standing upright and lying down. Sleep- and activity-related words were presented around the individual speech recognition threshold. Our results show that word processing was facilitated in congruent body positions (sleep words: lying down and activity words: standing upright) compared with incongruent body positions, as indicated by a reduced N400 in the congruent condition with the lowest volume. In addition, early sensory components of the ERP (N180 and P280) were enhanced, suggesting that words were also acoustically better understood in a congruent body position. However, the difference in ERPs did not translate to differences on a behavioral level. Our results support the prediction of embodied processing of sleep- and activity-related words. Body position potentially induces a pre-activation of multimodal networks, thereby enhancing access to the semantic concepts of words related to current body position. The link between semantic meaning and body-related function could be a key element in explaining the influences of cognitive processing on sleep.

Hypnotic Suggestions Increase Slow-Wave Parameters but Decrease Slow-Wave Spindle Coupling

PURPOSE

Sleep, in particular slow-wave sleep, is beneficial for memory consolidation. In two recent studies, a hypnotic suggestion to sleep more deeply increased the amount of slow-wave sleep in both a nap and a night design. In spite of these increases in slow-wave sleep, no beneficial effect on declarative memory consolidation was found. As coupling of slow-waves and sleep spindles is assumed to be critical for declarative memory consolidation during sleep, we hypothesized that the missing memory benefit after increased SWS could be related to a decrease in slow-wave/spindle coupling.

PARTICIPANTS AND METHODS

Data from 33 highly hypnotizable subjects were retrieved from a nap (n = 14) and a night (n = 19) study with a similar design and procedure. After an adaptation session, subjects slept in the sleep laboratory for two experimental sessions with polysomnography. Prior to sleep, a paired-associate learning task was conducted. Next, subjects either listened to a hypnotic suggestion to sleep more deeply or to a control text in a randomized order according to a within-subject design. After sleep, subjects performed the recall of the memory task. Here, we conducted a fine-grained analysis of the sleep data on slow-waves, spindles and their coupling.

RESULTS

In line with our hypothesis, listening to a hypnosis tape decreased the percentage of spindles coupled to slow-waves. Slow-wave parameters were consistently increased, but sleep spindles remained unaffected by the hypnotic suggestion.

CONCLUSION

Our results suggest that selectively enhancing slow-waves without affecting sleep spindles might not be sufficient to improve memory consolidation during sleep.

Updated Review of the Acoustic Modulation of Sleep: Current Perspectives and Emerging Concepts

With growing interest in the use of acoustic stimuli in sleep research and acoustic interventions used therapeutically for sleep enhancement, there is a need for an overview of the current lines of research. This paper summarizes the various ways to use acoustic input before sleep or stimulation during sleep. It thereby focuses on the respective methodological requirements, advantages, disadvantages, potentials and difficulties of acoustic sleep modulation. It highlights differences in subjective and objective outcome measures, immediate and whole night effects and short versus long term effects. This recognizes the fact that not all outcome parameters are relevant in every research field. The same applies to conclusions drawn from other outcome dimensions, consideration of mediating factors, levels of stimulation processing and the impact of inter-individual differences. In addition to the deliberate influences of acoustic input on sleep, one paragraph describes adverse environmental acoustic influences. Finally, the possibilities for clinical and basic research-related applications are discussed, and emerging opportunities are presented. This overview is not a systematic review but aims to present the current perspective and hence summarizes the most up-to-date research results and reviews. This is the first review providing a summary of the broad spectrum of possibilities to acoustically influence sleep.

Sleep and Memory in Children

Purpose of Review

This short review article aims at emphasizing interesting and important new insights about investigating sleep and memory in children aged between 6 and 13 years (middle childhood).

Recent Findings

That sleep in comparison to wakefulness benefits the consolidation of memories is well established—especially for the adult population. However, the underlying theoretical frameworks trying to explain the benefits of sleep for memory still strive for more substantiate findings including biological and physiological correlates.

Summary

Based on the most recent literature about sleep-related memory consolidation and its physiological markers during middle childhood, this article provides a review and highlights recent updates in this field.

Memory and Sleep: How Sleep Cognition Can Change the Waking Mind for the Better

The memories that we retain can serve many functions. They guide our future actions, form a scaffold for constructing the self, and continue to shape both the self and the way we perceive the world. Although most memories we acquire each day are forgotten, those integrated within the structure of multiple prior memories tend to endure. A rapidly growing body of research is steadily elucidating how the consolidation of memories depends on their reactivation during sleep. Processing memories during sleep not only helps counteract their weakening but also supports problem solving, creativity, and emotional regulation. Yet, sleep-based processing might become maladaptive, such as when worries are excessively revisited. Advances in research on memory and sleep can thus shed light on how this processing influences our waking life, which can further inspire the development of novel strategies for decreasing detrimental rumination-like activity during sleep and for promoting beneficial sleep cognition.

How robust are sleep-mediated memory benefits?

Memories benefit from a retention interval filled with sleep. Current theories assume that this beneficial effect relies on consolidation processes occurring during slow-wave sleep (SWS). However, in the last years, several key findings supporting these theories could not be replicated or occurred only under certain conditions, suggesting that effects of sleep on memory are smaller, more task-dependent, less SWS-related, less robust and less long-lasting than previously assumed. In this review, we summarize recent replication failures, null-findings, meta-analyses and studies reporting important boundary conditions for the effect of sleep on declarative memory. We argue that more attempts to replicate and meta-analytic approaches together with higher standards for reproducible science are critical to advance the field of sleep and memory.

Healthy Sleepers Can Worsen Their Sleep by Wanting to Do so: The Effects of Intention on Objective and Subjective Sleep Parameters

PURPOSE

Sleep is regulated by homeostatic and circadian factors. In addition, psychological factors have a strong modulatory impact on our sleep, but the exact underlying mechanisms are still largely unknown. Here, we examined the role of intentions on subjective and objective sleep parameters. Young healthy sleepers were instructed to voluntarily either worsen or improve their sleep. We predicted that participants would be capable of worsening, but not improving, their sleep compared to a regular sleep condition. In addition, we predicted that the instruction to alter sleep would lead to a higher discrepancy between subjective and objective sleep variables.

PARTICIPANTS AND METHODS

Twenty-two healthy students participated in one adaptation and three experimental nights. Polysomnography and subjective sleep parameters were measured during all four nights. Participants were instructed to sleep regularly ("neutral"), better ("good") or worse ("bad") than normal, in a counterbalanced order.

RESULTS

The instruction to sleep "bad" increased objective sleep onset latency and the number of awakings during the night. The effects were stronger on subjective sleep variables, resulting in a higher sleep misperception in the "bad" condition as compared to the other two conditions. The instruction to sleep "good" did not improve sleep nor did it affect sleep misperception.

CONCLUSION

We conclude that intention is sufficient to impair (but not improve) subjective and objective sleep quality and to increase sleep misperception in healthy young sleepers. Our results have important implications for the understanding of the impact of psychological factors on our sleep.