Is prior knowledge essential? Additional training opportunities restore sleep-associated memory benefits under conditions of low prior knowledge.

Sleep-mediated memory benefits are modulated by several factors. Prior knowledge is assumed critical for consolidation during sleep, despite inconclusive empirical findings. Additionally, prior knowledge facilitates encoding, leading to differences in memory strength already before the retention filled with sleep. We tested whether increasing memory strength of unfamiliar learning material pre-sleep can restore sleep-mediated memory benefits in cases of low prior knowledge. One-hundred and fifty-four healthy young students learned translations of Dutch words. One group was German-speaking, the other French-speaking. As French is less similar to Dutch than German, we expected a lower prior knowledge in French participants. We manipulated memory strength during pre-sleep encoding by varying the number of learning possibilities (one and two rounds for German-speaking, two and three rounds for French-speaking participants). When using the same learning paradigm for both groups (two rounds), lower prior knowledge modulated sleep-mediated memory benefits: French-speaking participants showed no advantage in memory after nighttime sleep compared with daytime wakefulness. In contrast, German-speaking participants showed robust sleep-mediated memory benefits. However, increasing memory strength before sleep restored sleep-mediated memory benefits in French subjects to a level of German-speaking participants. Conversely, reducing the training in German-speaking participants reduced sleep-mediated memory benefits. Our results show that prior knowledge and memory strength strongly modulate sleep-associated memory benefits. However, in cases of low prior knowledge, sleep-mediated memory benefits can be successfully restored by additional training. While prior knowledge might modulate encoding and consolidation processes more generally, its effect on sleep-specific processes of memory retention might be less important than previously assumed.

The influence of experience and modality of presentation (online vs. offline) on hypnotizability.

Introduction: Hypnotizability is conceptualized as a stable personality trait describing the ability to respond to suggestions given under hypnosis. Hypnotizability is a key factor in explaining variance in the effects of hypnotic suggestions on behavior and neural correlates, revealing robust changes mostly in high hypnotizable participants. However, repeated experience and training have been discussed as possible ways to increase willingness, motivation, and ability to follow hypnotic suggestions, although their direct influence on hypnotizability are still unclear. Additionally, it is important whether hypnotizability can be assessed reliably online. Methods: We investigated the influence of the degree of experience with hypnosis and the presentation mode (online versus live) on the stability of hypnotizability in two groups of 77 and 102 young, healthy students, respectively. The first group was tested twice with the Harvard Group Scale of Hypnotic Susceptibility (HGSHS) after two weeks. During this period, participants either repeatedly listened to a hypnosis or trained on a progressive muscle relaxation or served as waitlist control group. In the secondgroup, participants performed both an online or offline version of the HGSHS, with varying time intervals (1-6 weeks). Results: Contrary to our expectations, hypnotizability declined from the first to second assessment in the first group. The reductionwas most prominent in initially highly hypnotizable subjects and independent of the experience intervention. We observed a similar reduction of hypnotizability in the second group, independent of presentation modality. The reduction was again driven by initially highly hypnotizable subjects, while the scores of low hypnotizable subjects remained stable. The presentation modality (online vs. offline) did not influence HGSHS scores, but the test-retest reliability was low to moderate (rtt = 0.44). Discussion: Our results favor the conclusion that generally, hypnotizability is a relatively stable personality trait which shows no major influence of preexperience or modality of assessment. However, particularly highly hypnotizable subjects are likely to experience a decline in hypnotizability in a retest. The role of the concrete assessment tool, psychological factors, and interval length are discussed. Future studies should replicate the experiments in a clinical sample which might have higher intrinsic motivation of increasing responsiveness toward hypnotic interventions or be more sensitive to presentation mode.

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.

Pre-sleep social media use does not strongly disturb sleep: a sleep laboratory study in healthy young participants.

OBJECTIVE: Sleep is critical for our mental health and optimal cognitive functioning. Social media use is increasingly common and suspected to disturb sleep due to increasing bedtime arousal. However, most studies rely on self-reported sleep. METHODS: We tested the effects of 30 min social media use on arousal and subsequent sleep in the sleep laboratory in 32 healthy young volunteers. Effects of blue-light were excluded in this study. We compared it to 30 min progressive muscle relaxation (PMR) and neutral sleep in a within-subject design. RESULTS: Thirty minutes of social media use immediately before sleep did not significantly increase arousal and did neither disturb objective nor subjective sleep. After social media use, participants only spent less time in sleep stage N2. In contrast, PMR had the expected positive effects on pre-sleep arousal level indicated by reduced heart rate. In addition, PMR improved sleep efficiency, reduced sleep onset latency, and shortened the time to reach slow-wave sleep compared to a neutral night. Oscillatory power in the slow-wave activity and spindle bands remained unaffected. CONCLUSION: Social media use before sleep (controlling for effects of blue-light) had little effect on bedtime arousal and sleep quality than what was previously expected. The most notable effect appears to be the additional time spent engaging in social media use at bedtime, potentially keeping people from going to sleep. As wake up-time is mostly determined externally, due to school or working hours, limiting personal media use at bedtime-and especially in bed-is recommended to get sufficient hours of 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.

No evidence for intra-individual correlations between sleep-mediated declarative memory consolidation and slow-wave sleep.

STUDY OBJECTIVES: Memory consolidation benefits from a retention period filled with sleep. Several theoretical accounts assume that slow-wave sleep (SWS) contributes functionally to processes underlying the stabilization of declarative memories during sleep. However, reports on correlations between memory retention and the amount of SWS are mixed and typically rely on between-subject correlations and small sample sizes. Here we tested for the first time whether the amount of SWS during sleep predicts the effect of sleep on memory consolidation on an intra-individual level in a large sample. METHODS: One hundred and fifty-nine healthy participants came to the lab twice and took a 90 min nap in both sessions. Sleep-mediated memory benefits were tested using the paired associates word-learning task in both sessions. RESULTS: In contrast to the theoretical prediction, intra-individual differences in sleep-mediated memory benefits did not significantly correlate with differences in SWS or SWA between the two naps. Also between subjects, the amount of SWS did not correlate with memory retention across the nap. However, subjective ratings of sleep quality were significantly associated with the amount of SWS. CONCLUSION: Our results question the notion that the amount of SWS per se is functionally related to processes of memory consolidation during sleep. While our results do not exclude an important role of SWS for memory, they suggest that "more SWS" does not necessarily imply better memory consolidation.

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.

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.

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

While slow-wave sleep (SWS) is fundamental for maintaining health and well-being, it is typically reduced with stress or age. The authors have previously reported that hypnotic suggestions before sleep increased SWS duration and slow-wave activity (SWA) during a midday nap in hypnotizable younger and older women. To test generalizability, they investigated this effect across 8 hours nighttime sleep in 43 healthy young French-speaking subjects (19 males) of high and low hypnotizability. In accordance with their previous results, listening to hypnotic suggestions before sleep was followed by higher amounts of SWS in highly hypnotizable subjects and higher SWA power compared to a control condition. The effects were most pronounced at the beginning of the night. Further studies are needed to examine whether hypnotic suggestions can deepen sleep also above non-intervention nights. The findings provide a basis for the examination and potential application of hypnosis to improve sleep in clinical populations.

Effects of Relaxing Music on Healthy Sleep.

Sleep is vital for human health and wellbeing, and sleep disturbances are comorbid to many mental and physiological disorders. Music consistently improves subjective sleep quality, whereas results for objective sleep parameters diverge. These inconsistencies might be due to inter-individual differences. Here, 27 female subjects listened to either music or a control text before a 90 minutes nap in a within-subjects design. We show that music improved subjective sleep quality as compared to the text condition. In all participants, music resulted in a reduced amount of sleep stage N1 during the nap. In addition, music significantly increased the amount of slow-wave sleep (SWS) and increased the low/high frequency power ratio. However, these effects occurred only in participants with a low suggestibility index. We conclude that listening to music before a nap can improve subjective and objective sleep parameters in some participants.

[Sleep Disturbances in General Practitioners' Offices: From Screening to Initial Therapy - Update 2019]. / Schlafprobleme in der Allgemeinpraxis: Vom Screening zur initialen Therapie ­ Update 2019.

Sleep Disturbances in General Practitioners' Offices: From Screening to Initial Therapy - Update 2019 Abstract. The field of sleep medicine has established internationally as an interdisciplinary specialization. Due to prevailing evidence, sleep disturbances are listed in a separate chapter in the new ICD 11 classification system. With the International Classification of Sleep Disorders (ICSD-3rd version) a standalone classification system exists. In Switzerland, one third of the population suffers from sleep disturbances. Even differential diagnosis is hard to establish. The current article aims at practitioners, who are frequently confronted with sleep complaints and must categorize, triage and initially treat their patients with simple screening methods.

Psychosocial Stress Before a Nap Increases Sleep Latency and Decreases Early Slow-Wave Activity.

Sleep disturbances are an important risk factor for stress-related diseases such as burnout or depression. In particular, slow-wave activity (SWA) during sleep might be eminently relevant for optimal maintenance of mental health and cognitive functioning. In spite of the clinical importance and the pertinence of stress-related processes in everyday life, the physiological mechanisms of the association between stress, sleep, and cognition are not well-understood. In the present study, we carefully mapped the time course of the influence of a psychosocial stressor on sleep architecture and sleep-related oscillations during a midday nap. We induced stress using a psychosocial laboratory stressor, the Montreal Imaging Stress Task, vs. a neutral control task. Afterward, participants were allowed to take a 90-min nap (n = 20) or stayed awake (n = 19) and cortisol was measured via saliva samples. We hypothesized that stress would decrease sleep efficiency and SWA in a time-dependent manner, with impairing effects on cognitive functioning. Psychosocial stress resulted in increased cortisol levels, which were elevated throughout the study interval. In the nap group, psychosocial stress increased sleep latency, but had only minor effects on sleep architecture. Still, SWA in the first 30 min of sleep was significantly reduced, whereas alpha activity was enhanced. These effects vanished after approximately 30 min. No impairing effect on cognitive functioning occurred. Our results show that psychosocial stress before sleep has an impact on sleep latency and early SWA during sleep. In contrast to our hypothesis, the effects were rather small and short-lasting. Importantly, cognitive functioning was maintained. We conclude that the effects of psychosocial stress before a nap are possibly better compensated than previously believed.

The effect of dream report collection and dream incorporation on memory consolidation during sleep.

Collecting dream reports typically requires waking subjects up from their sleep-a method that has been used to study the relationship between dreams and memory consolidation. However, it is unclear whether these awakenings influence sleep-associated memory consolidation processes. Furthermore, it is unclear how the incorporation of the learning task into dreams is related to memory consolidation. In this study we compared memory performance in a word-picture association learning task after a night with and without awakenings in 22 young and healthy participants. We then examined if the stimuli from the learning task are successfully incorporated into dreams, and if this incorporation is related to the task performance the next morning. We show that while the awakenings impaired both subjective and objective sleep quality, they did not affect sleep-associated memory consolidation. When dreams were collected during the night by awakenings, memories of the learning task were successfully incorporated into dreams. When dreams were collected in the morning, no incorporations were detected. Task incorporation into non-rapid eye movement sleep dreams, but not rapid eye movement sleep dreams positively predicted memory performance the next morning. We conclude that the method of awakenings to collect dream reports is suitable and necessary for dream and memory studies. Furthermore, our study suggests that dreams in non-rapid eye movement rather than rapid eye movement sleep might be related to processes of memory consolidation during sleep.

No effect of vocabulary reactivation in older adults.

Quality of memory and sleep declines with age. However, the mechanistic interactions underlying the memory function of sleep in older adults are still unknown. It is widely assumed that the beneficial effect of sleep on memory relies on reactivation during Non-rapid eye movement (NREM) sleep. Targeting these reactivations by cue re-exposure reliably improves memory in younger participants. Here we tested whether the memory reactivation mechanism during sleep is still functional in old age. For this purpose we applied targeted memory reactivation (TMR) during NREM sleep in healthy adults over 60 years and directly compared the results to a group of younger participants. In contrast to young participants, older adults' memories did not generally benefit from TMR during NREM sleep. On the oscillatory level, successful reactivation of Dutch words during sleep did not reveal the characteristic increases in early theta activity and frontal spindle activity previously reported in young participants. Only in a later time window, theta oscillations were similarly increased during successful cueing for both young and older participants. Our results suggest that reactivating memories during sleep might be possible also in older adults. However at the same time this reactivation by TMR does not necessarily lead to a strengthening of memories across sleep as in younger participants. Further studies are needed to examine a potential loss of functionality of memory reactivation for consolidation during sleep in older adults.

Modulating influences of memory strength and sensitivity of the retrieval test on the detectability of the sleep consolidation effect.

Emotionality can increase recall probability of memories as emotional information is highly relevant for future adaptive behavior. It has been proposed that memory processes acting during sleep selectively promote the consolidation of emotional memories, so that neutral memories no longer profit from sleep consolidation after learning. This appears as a selective effect of sleep for emotional memories. However, other factors contribute to the appearance of a consolidation benefit and influence this interpretation. Here we show that the strength of the memory trace before sleep and the sensitivity of the retrieval test after sleep are critical factors contributing to the detection of the benefit of sleep on memory for emotional and neutral stimuli. 228 subjects learned emotional and neutral pictures and completed a free recall after a 12-h retention interval of either sleep or wakefulness. We manipulated memory strength by including an immediate retrieval test before the retention interval in half of the participants. In addition, we varied the sensitivity of the retrieval test by including an interference learning task before retrieval testing in half of the participants. We show that a "selective" benefit of sleep for emotional memories only occurs in the condition with high memory strength. Furthermore, this "selective" benefit disappeared when we controlled for the memory strength before the retention interval and used a highly sensitive retrieval test. Our results indicate that although sleep benefits are more robust for emotional memories, neutral memories similarly profit from sleep after learning when more sensitive indicators are used. We conclude that whether sleep benefits on memory appear depends on several factors, including emotion, memory strength and sensitivity of the retrieval test.

No Evidence for Memory Decontextualization across One Night of Sleep.

Sleep after learning strengthens memory consolidation. According to the active system consolidation hypothesis, sleep supports the integration of newly acquired memories into cortical knowledge networks, presumably accompanied by a process of decontextualization of the memory trace (i.e., a gradual loss of memory for the learning context). However, the availability of contextual information generally facilitates memory recall and studies on the interaction of sleep and context on memory retrieval have revealed inconsistent results. Here, we do not find any evidence for a role of sleep in the decontextualization of newly learned declarative memories. In two separate studies, 104 healthy young adults incidentally learned words associated with a context. After a 12 h retention interval filled with either sleep or wakefulness, recall (Experiment 1) or recognition (Experiment 2) was tested with the same or different context. Overall, memory retrieval was significantly improved when the learning context was reinstated, as compared to a different context. However, this context effect of memory was not modulated by sleep vs. wakefulness. These findings argue against a decontextualization of memories, at least across a single night of sleep.

Improving sleep and cognition by hypnotic suggestion in the elderly.

Sleep quality markedly declines across the human lifespan. Particularly the amount of slow-wave sleep (SWS) decreases with age and this decrease is paralleled by a loss of cognitive functioning in the elderly. Here we show in healthy elderly females that the amount of SWS can be extended by a hypnotic suggestion "to sleep deeper" before sleep. In a placebo-controlled cross-over design, participants listened to hypnotic suggestions or a control tape before a midday nap while high density electroencephalography was recorded. After the hypnotic suggestion, we observed a 57% increase in SWS in females suggestible to hypnosis as compared to the control condition. Furthermore, left frontal slow-wave activity (SWA), characteristic for SWS, was significantly increased, followed by a significant improvement in prefrontal cognitive functioning after sleep. Our results suggest that hypnotic suggestions might be a successful alternative for widely-used sleep-enhancing medication to extend SWS and improve cognition in the elderly.

No effect of odor-induced memory reactivation during REM sleep on declarative memory stability.

Memory reactivations in hippocampal brain areas are critically involved in memory consolidation processes during sleep. In particular, specific firing patterns of hippocampal place cells observed during learning are replayed during subsequent sleep and rest in rodents. In humans, experimentally inducing hippocampal memory reactivations during slow-wave sleep (but not during wakefulness) benefits consolidation and immediately stabilizes declarative memories against future interference. Importantly, spontaneous hippocampal replay activity can also be observed during rapid eye movement (REM) sleep and some authors have suggested that replay during REM sleep is related to processes of memory consolidation. However, the functional role of reactivations during REM sleep for memory stability is still unclear. Here, we reactivated memories during REM sleep and examined its consequences for the stability of declarative memories. After 3 h of early, slow-wave sleep (SWS) rich sleep, 16 healthy young adults learned a 2-D object location task in the presence of a contextual odor. During subsequent REM sleep, participants were either re-exposed to the odor or to an odorless vehicle, in a counterbalanced within subject design. Reactivation was followed by an interference learning task to probe memory stability after awakening. We show that odor-induced memory reactivation during REM sleep does not stabilize memories against future interference. We propose that the beneficial effect of reactivation during sleep on memory stability might be critically linked to processes characterizing SWS including, e.g., slow oscillatory activity, sleep spindles, or low cholinergic tone, which are required for a successful redistribution of memories from medial temporal lobe regions to neocortical long-term stores.