Sleep-dependent memory processing

Enhancing and advancing the understanding and study of dreaming and memory consolidation: Reflections, challenges, theoretical clarity, and methodological considerations

Empirical investigations that search for a link between dreaming and sleep-dependent memory consolidation have focused on testing for an association between dreaming of what was learned, and improved memory performance for learned material. Empirical support for this is mixed, perhaps owing to the inherent challenges presented by the nature of dreams, and methodological inconsistencies. The purpose of this paper is to address critically prevalent assumptions and practices, with the aim of clarifying and enhancing research on this topic, chiefly by providing a theoretical synthesis of existing models and evidence. Also, it recommends the method of Targeted Memory Reactivation (TMR) as a means for investigating if dream content can be linked to specific cued activations. Other recommendations to enhance research practice and enquiry on this subject are also provided, focusing on the HOW and WHY we search for memory sources in dreams, and what purpose (if any) they might serve.

The Relation Between the Power of Prefrontal Gamma in Rest-state EEG Under Normal Sleep and Reactive Aggression Behaviour After Sleep Deprivation

Whether sleep deprivation affects aggressive behaviour is still under debate. The present study examined the influence of individual differences in reactive aggressive behaviour after sleep deprivation and preliminarily explored an electrophysiological marker to identify individuals with more aggressive behaviour after sleep deprivation. Thirty participants performed the Taylor Aggression Paradigm task under two sleep conditions: normal sleep (NS, one night of regular sleep) and total sleep deprivation (SD, 30 h of wakefulness), and 5-minute resting-state electroencephalogram (EEG) acquisition was completed under the NS condition. The results found that although sleep deprivation did not have significant effects on aggressive behaviour in the overall analysis, the participants can be classified as an increased group (n = 16) and a no-increased group (n = 14) by different changes in the two sleep conditions (SD-NS). In addition, prefrontal gamma (γ) power was significantly lower in the increased group than in the no-increased group, which may reflect the difference in ability on inhibition. Furthermore, more critical is that γ power was significantly negatively correlated with change in the reactive aggressive behaviour. These results indicate that the effect of SD on reactive aggression varies between individuals, and prefrontal γ power may be an effective electrophysiological marker for identifying people at risk of aggressive behaviour after SD.

Activation of dopamine D2 receptors attenuates neuroinflammation and ameliorates the memory impairment induced by rapid eye movement sleep deprivation in a murine model

The proinflammatory state, which may be induced by sleep deprivation, seems to be a determining factor in the development of neurodegenerative processes. Investigations of mechanisms that help to mitigate the inflammatory effects of sleep disorders are important. A new proposal involves the neurotransmitter dopamine, which may modulate the progression of the immune response by activating receptors expressed on immune cells. This study aimed to determine whether dopamine D2 receptor (D2DR) activation attenuates the proinflammatory response derived from rapid eye movement (REM) sleep deprivation in mice. REM sleep deprivation (RSD) was induced in 2-month-old male CD1 mice using the multiple platform model for three consecutive days; during this period, the D2DR receptor agonist quinpirole (QUIN) was administered (2 mg/kg/day i.p.). Proinflammatory cytokine levels were assessed in serum and homogenates of the brain cortex, hippocampus, and striatum using ELISAs. Long-term memory deficits were identified using the Morris water maze (MWM) and novel object recognition (NOR) tests. Animals were trained until learning criteria were achieved; then, they were subjected to RSD and treated with QUIN for 3 days. Memory evocation was determined afterward. Moreover, we found RSD induced anhedonia, as measured by the sucrose consumption test, which is commonly related to the dopaminergic system. Our data revealed increased levels of proinflammatory cytokines (TNFα and IL-1β) in both the hippocampus and serum from RSD mice. However, QUIN attenuated the increased levels of these cytokines. Furthermore, RSD caused a long-term memory evocation deficit in both the MWM and NOR tests. In contrast, QUIN coadministration during the RSD period significantly improved the performance of the animals. On the other hand, QUIN prevented the anhedonic condition induced by RSD. Based on our results, D2DR receptor activation protects against memory impairment induced by disturbed REM sleep by inhibiting neuroinflammation.

Investigating the effects of sleep and sleep loss on the different stages of episodic emotional memory: A narrative review and guide to the future

For two decades, sleep has been touted as one of the primary drivers for the encoding, consolidation, retention, and retrieval of episodic emotional memory. Recently, however, sleep's role in emotional memory processing has received renewed scrutiny as meta-analyses and reviews have indicated that sleep may only contribute a small effect that hinges on the content or context of the learning and retrieval episodes. On the one hand, the strong perception of sleep's importance in maintaining memory for emotional events may have been exacerbated by publication bias phenomena, such as the "winner's curse" and "file drawer problem." On the other hand, it is plausible that there are sets of circumstances that lead to consistent and reliable effects of sleep on emotional memory; these circumstances may depend on factors such as the placement and quality of sleep relative to the emotional experience, the content and context of the emotional experience, and the probes and strategies used to assess memory at retrieval. Here, we review the literature on how sleep (and sleep loss) influences each stage of emotional episodic memory. Specifically, we have separated previous work based on the placement of sleep and sleep loss in relation to the different stages of emotional memory processing: (1) prior to encoding, (2) immediately following encoding during early consolidation, (3) during extended consolidation, separated from initial learning, (4) just prior to retrieval, and (5) post-retrieval as memories may be restructured and reconsolidated. The goals of this review are three-fold: (1) examine phases of emotional memory that sleep may influence to a greater or lesser degree, (2) explicitly identify problematic overlaps in traditional sleep-wake study designs that are preventing the ability to better disentangle the potential role of sleep in the different stages of emotional memory processing, and (3) highlight areas for future research by identifying the stages of emotional memory processing in which the effect of sleep and sleep loss remains under-investigated. Here, we begin the task of better understanding the contexts and factors that influence the relationship between sleep and emotional memory processing and aim to be a valuable resource to facilitate hypothesis generation and promote important future research.

Adolescent sleep health and school start times: Setting the research agenda for California and beyond: A research summit summary: A research summit summary

In fall 2019, California passed and signed into law SB328, the first US statewide legislation explicitly designed to protect adolescent sleep health by requiring most California public school districts to start no earlier than 8:00 AM for middle schools and 8:30 AM for high schools. Recognizing the unique opportunity presented by the bill's 3-year implementation period, a group of experts in adolescent sleep and school start times held a virtual summit on January 22-23, 2021 to (1) summarize the research on adolescent sleep and school start time change; (2) develop recommendations for relevant, refined, and innovative research areas and research questions; (3) provide input regarding research design, methodology, and implementation; and (4) offer a forum for networking, exchanging ideas, and establishing interdisciplinary research collaborations. Participants represented a multidisciplinary range of academic backgrounds including sleep and circadian biology, neuroscience, education, medicine, public health, mental health, safety, public policy, economics, implementation science, criminology, diversity studies, and science communication. This paper summarizes summit presentations regarding current knowledge on adolescent sleep health and school start times and key research recommendations from small group workshops on topics including research design and tools, methodological issues, sleep health disparities, logistical challenges in conducting school-based research, public-health impact, and novel and expanded approaches to research.

Moderating effects of sleep difficulties on relations between posttraumatic stress disorder symptoms and positive memory count

OBJECTIVES

Posttraumatic stress disorder (PTSD) severity relates to positive memory retrieval difficulties. One variable potentially influencing this relation is sleep difficulties. We examined moderating effects of sleep difficulties (duration and quality) on relations between PTSD severity and count of specific positive memories covarying for age, gender, and depression.

METHODS

Participants were an Amazon Mechanical Turk-recruited trauma-exposed community sample of 205 respondents (M age  = 35.44; 61.40% women).

RESULTS

Moderated regression analyses indicated significant interaction effects between sleep quality (b = 0.03; p = 0.036) and PTSD severity on specific positive memory count. Among individuals reporting better sleep quality, there were negative associations between PTSD severity and specific positive memory count (b = -0.04, SE = 0.02, p = 0.010). Similar results were obtained for PTSD's intrusion and arousal clusters.

CONCLUSION

Results support targeting sleep quality and PTSD severity to improve positive memory retrieval in PTSD and memory interventions, and the importance of considering sleep when examining links between PTSD and positive memory retrieval.

Artificial grammar learning is facilitated by distributed practice: Evidence from a letter reordering task

Previous studies have shown that distributed practice-a training strategy that is known to facilitate memory-is likely to result in greater learning than massed practice. This effect has been demonstrated largely in explicit tasks. The purpose of this study was to test whether statistical learning of artificial grammar is affected by the lag between learning sessions overall, and by high and low complexity stimuli (as measure by chunk strength). Two groups (spaced-short and spaced-long) learned strings of letters created according to a set of rules and were required to produce new strings using given letter sets. For the spaced-short group, the two learning sessions, each including training and a test phase, took place sequentially with a 10-min break, whereas for the spaced-long group, learning sessions were distributed across two days (1-day lag). Overall results showed improved performance following spaced-long practice compared to spaced-short practice. The results also indicated that in the low chunk strength strings (indicating high complexity), both groups demonstrated similar improvement from first to second testing, while in the high chunk strength strings (indicating low complexity), improvement in letter reordering performance was significantly higher when the learning sessions were distributed across two days. This pattern of findings suggests that stimuli complexity affects the extent to which distributed practice enhance artificial grammar learning.

Relationship Between Major Depression Symptom Severity and Sleep Collected Using a Wristband Wearable Device: Multicenter Longitudinal Observational Study

BACKGROUND

Sleep problems tend to vary according to the course of the disorder in individuals with mental health problems. Research in mental health has associated sleep pathologies with depression. However, the gold standard for sleep assessment, polysomnography (PSG), is not suitable for long-term, continuous monitoring of daily sleep, and methods such as sleep diaries rely on subjective recall, which is qualitative and inaccurate. Wearable devices, on the other hand, provide a low-cost and convenient means to monitor sleep in home settings.

OBJECTIVE

The main aim of this study was to devise and extract sleep features from data collected using a wearable device and analyze their associations with depressive symptom severity and sleep quality as measured by the self-assessed Patient Health Questionnaire 8-item (PHQ-8).

METHODS

Daily sleep data were collected passively by Fitbit wristband devices, and depressive symptom severity was self-reported every 2 weeks by the PHQ-8. The data used in this paper included 2812 PHQ-8 records from 368 participants recruited from 3 study sites in the Netherlands, Spain, and the United Kingdom. We extracted 18 sleep features from Fitbit data that describe participant sleep in the following 5 aspects: sleep architecture, sleep stability, sleep quality, insomnia, and hypersomnia. Linear mixed regression models were used to explore associations between sleep features and depressive symptom severity. The z score was used to evaluate the significance of the coefficient of each feature.

RESULTS

We tested our models on the entire dataset and separately on the data of 3 different study sites. We identified 14 sleep features that were significantly (P<.05) associated with the PHQ-8 score on the entire dataset, among them awake time percentage (z=5.45, P<.001), awakening times (z=5.53, P<.001), insomnia (z=4.55, P<.001), mean sleep offset time (z=6.19, P<.001), and hypersomnia (z=5.30, P<.001) were the top 5 features ranked by z score statistics. Associations between sleep features and PHQ-8 scores varied across different sites, possibly due to differences in the populations. We observed that many of our findings were consistent with previous studies, which used other measurements to assess sleep, such as PSG and sleep questionnaires.

CONCLUSIONS

We demonstrated that several derived sleep features extracted from consumer wearable devices show potential for the remote measurement of sleep as biomarkers of depression in real-world settings. These findings may provide the basis for the development of clinical tools to passively monitor disease state and trajectory, with minimal burden on the participant.

Sleep, Cognition and Cortisol in Addison's Disease: A Mechanistic Relationship

Sleep is a critical biological process, essential for cognitive well-being. Neuroscientific literature suggests there are mechanistic relations between sleep disruption and memory deficits, and that varying concentrations of cortisol may play an important role in mediating those relations. Patients with Addison's disease (AD) experience consistent and predictable periods of sub- and supra-physiological cortisol concentrations due to lifelong glucocorticoid replacement therapy, and they frequently report disrupted sleep and impaired memory. These disruptions and impairments may be related to the failure of replacement regimens to restore a normal circadian rhythm of cortisol secretion. Available data provides support for existing theoretical frameworks which postulate that in AD and other neuroendocrine, neurological, or psychiatric disorders, disrupted sleep is an important biological mechanism that underlies, at least partially, the memory impairments that patients frequently report experiencing. Given the literature linking sleep disruption and cognitive impairment in AD, future initiatives should aim to improve patients' cognitive performance (and, indeed, their overall quality of life) by prioritizing and optimizing sleep. This review summarizes the literature on sleep and cognition in AD, and the role that cortisol concentrations play in the relationship between the two.

The Impact of Sleep and Circadian Disorders on Physician Burnout

Nearly 50% of physicians report symptoms of clinical burnout. Occupational factors and personal health play substantial roles in physician burnout. The role of sleep in physician burnout is not well understood. Burnout is at epidemic levels in health care, with research suggesting nearly one in two physicians experience clinical burnout as defined according to the Maslach Burnout Index. Sleep deprivation, burnout, and clinician health are intricately intertwined. The relation between sleep deprivation and burnout is not only suggested in hypothetical models but also confirmed in observational studies of workers of all types. Models describing the relation between burnout and sleep suggest as potential causative mechanisms of sleep disturbances the following: (1) a chronic depletion of energy stores; or (2) activation of the hypothalamic-pituitary-adrenal axis and increasing levels of bodily stress. Sleep deprivation and burnout are widespread in health-care workers, affecting not only nurses but also medical students, physicians-in-training, and practicing physicians. Although sleep deprivation is associated with clinical burnout, direct studies showing that sleep extension can improve burnout recovery are lacking. Early detection and early intervention to improve both sleep deprivation and burnout are warranted in health-care professionals. Interventions should be directed not only at individuals but also at the entire health system. This review highlights the latest developments and emerging concepts concerning the role of sleep and circadian disorders in physician burnout.

Uninterrupted Infant Sleep, Development, and Maternal Mood

OBJECTIVES

Contrary to the importance of total sleep duration, the association between sleeping through the night and development in early infancy remains unclear. Our aims were to investigate the proportion of infants who sleep through the night (6- or 8-hour sleep blocks) at ages 6 and 12 months in a longitudinal cohort and to explore associations between sleeping through the night, mental and psychomotor development, maternal mood, and breastfeeding.

METHODS

At 6 and 12 months of age, maternal reports were used to assess the longest period of uninterrupted infant sleep and feeding method (n = 388). Two different criteria were used to determine if infants slept through the night: 6 and 8 hours of uninterrupted sleep. Mental and psychomotor developmental indices (Bayley Scales of Infant Development II) and maternal mood (Center for Epidemiologic Studies Depression Scale) were measured at 6, 12, and 36 months of age.

RESULTS

Using a definition of either 6 or 8 hours of uninterrupted sleep, we found that 27.9% to 57.0% of 6- and 12-month-old infants did not sleep through the night. Linear regressions revealed no significant associations between sleeping through the night and concurrent or later mental development, psychomotor development, or maternal mood (P > .05). However, sleeping through the night was associated with a much lower rate of breastfeeding (P < .0001).

CONCLUSIONS

Considering that high proportions of infants did not sleep through the night and that no associations were found between uninterrupted sleep, mental or psychomotor development, and maternal mood, expectations for early sleep consolidation could be moderated.

Is poor sleep associated with obesity in older adults? A narrative review of the literature

INTRODUCTION

To address the worldwide epidemic of obesity, a sizable literature implicates sleep problems in the onset of obesity in younger populations. However, less is known about how this process may operate among older adults, which is of concern, given demographic shifts that have resulted in a much higher proportion of developed nations around the world reaching late life.

METHODS

We offer a current review of the literature studying older adults and examining associations between sleep quality and obesity in this population. We consider both subjective and objectively measured sleep as well as both cross-sectional and longitudinal studies offering stronger causal inference.

RESULTS

We discuss seemingly contradictory literature showing that shorter sleep duration as well as longer sleep duration are associated with obesity risk, then review studies that tested for non-linear relationships and reported a U-shape pattern, suggesting that too much or too little sleep is detrimental. Besides sleep duration, we discuss evidence showing that other forms of sleep dysfunction related to night-time awakenings, REM sleep, slow-wave sleep, and daytime sleepiness, which are indicators of sleep quality, are also linked to obesity. Specific psychological and physiological mediators and moderators, suggesting possible mechanisms whereby sleep problems may affect obesity in older adults, are described.

CONCLUSION

We conclude by discussing areas, where additional research could help clarify this association, considering such factors as medical comorbidities common in late life, and health-related behaviors that may stem from poor sleep (such as disordered eating behavior). Such insights will have great value for clinical practice.

LEVEL OF EVIDENCE

Level V, narrative review.

Critical role of CA1 muscarinic receptors on memory acquisition deficit induced by total (TSD) and REM sleep deprivation (RSD)

AIM

Despite different theories regarding sleep physiological function, an overall census indicates that sleep is useful for neural plasticity which eventually strengthens cognition and brain performance. Different studies show that sleep deprivation (SD) leads to impaired learning and hippocampus dependent memory. According to some studies, cholinergic system plays an important role in sleep (particularly REM sleep), learning, memory, and its retrieval. So this study has been designed to investigate the effect of CA1 Cholinergic Muscarinic Receptors on memory acquisition deficit induced by total sleep deprivation (TSD) and REM sleep deprivation (RSD).

METHOD

A modified water box (locomotor activity may be provide a limiting factor in this method of SD) or multiple platforms were used for induction of TSD or RSD, respectively. Inhibitory passive avoidance apparatus has been used to determine the effects of SD and its changes by physostigmine (as cholinesterase inhibitor) or scopolamine (muscarinic receptor antagonist) on memory formation. Because locomotor activity and pain perception induce critical roles in passive avoidance memory formation, we also measured these factors by open field and hot-plate instruments, respectively.

RESULTS

The results showed that TSD and RSD for 24 hours impaired memory formation but they did not alter locomotor activity. TSD also induced analgesia effect, but RSD did not alter it. Intra-CA1 injection of physostigmine (0.0001μg/rat) and scopolamine (0.01μg/rat) did not alter memory acquisition in the sham-TSD or sham-RSD, by themselves. Moreover, intra-CA1 injection of sub-threshold dose of physostigmine (0.0001μg/rat) and scopolamine (0.01μg/rat) could restore the memory acquisition deficit induced by RSD, while scopolamine could restore TSD-induced amnesia. Both drugs reversed analgesia induced by TSD. None of previous interventions altered locomotor activity.

CONCLUSION

According to this study, CA1 cholinergic muscarinic receptors play an important role in amnesia induced by both TSD and RSD. However further studies are needed for showing cellular and molecular mechanisms of surprising result of similar pharmacological effects using compounds with opposite profiles.

Consciousness across Sleep and Wake: Discontinuity and Continuity of Memory Experiences As a Reflection of Consolidation Processes

The continuity hypothesis (1) posits that there is continuity, of some form, between waking and dreaming mentation. A recent body of work has provided convincing evidence for different aspects of continuity, for instance that some salient experiences from waking life seem to feature in dreams over others, with a particular role for emotional arousal as accompanying these experiences, both during waking and while asleep. However, discontinuities have been somewhat dismissed as being either a product of activation-synthesis, an error within the consciousness binding process during sleep, a methodological anomaly, or simply as yet unexplained. This paper presents an overview of discontinuity within dreaming and waking cognition, arguing that disruptions of consciousness are as common a feature of waking cognition as of dreaming cognition, and that processes of sleep-dependent memory consolidation of autobiographical experiences can in part account for some of the discontinuities of sleeping cognition in a functional way. By drawing upon evidence of the incorporation, fragmentation, and reorganization of memories within dreams, this paper proposes a model of discontinuity whereby the fragmentation of autobiographical and episodic memories during sleep, as part of the consolidation process, render salient aspects of those memories subsequently available for retrieval in isolation from their contextual features. As such discontinuity of consciousness in sleep is functional and normal.

Psychological Effect of an Analogue Traumatic Event Reduced by Sleep Deprivation

STUDY OBJECTIVE

To examine the effect of sleep deprivation compared to sleep, immediately after experimental trauma stimuli on the development of intrusive memories to that trauma stimuli.

DESIGN

Participants were exposed to a film with traumatic content (trauma film). The immediate response to the trauma film was assessed, followed by either total sleep deprivation (sleep deprived group, N = 20) or sleep as usual (sleep group, N = 22). Twelve hours after the film viewing the initial psychological effect of the trauma film was measured and for the subsequent 6 days intrusive emotional memories related to the trauma film were recorded in daily life.

SETTING

Academic sleep laboratory and participants' home environment.

PARTICIPANTS

Healthy paid volunteers.

MEASUREMENTS AND RESULTS

On the first day after the trauma film, the psychological effect as assessed by the Impact of Event Scale - Revised was lower in the sleep deprived group compared to the sleep group. In addition, the sleep deprived group reported fewer intrusive emotional memories (mean 2.28, standard deviation [SD] 2.91) compared to the sleep group (mean 3.76, SD 3.35). Because habitual sleep/circadian patterns, psychological health, and immediate effect of the trauma film were similar at baseline for participants of both groups, the results cannot be accounted for by pre-existing inequalities between groups.

CONCLUSIONS

Our findings suggest that sleep deprivation on one night, rather than sleeping, reduces emotional effect and intrusive memories following exposure to experimental trauma.

Caffeine/sleep-deprivation interaction in mice produces complex memory effects

BACKGROUND

Sleep deprivation negatively impacts memory, causing deficits in memory processes. Of interest is any agent that can offset such deficits. Mice were given varying doses of caffeine for 14 days and then deprived of sleep for 6 hours by the 'gentle handling' method. Memory was assessed using the Novel Object Recognition Test and Y maze alternation.

PURPOSE

The study was designed to ascertain the impact of varying doses of caffeine combined with total sleep-deprivation on spatial and non spatial memory in mice.

METHODS

Adult Swiss Webster mice of both sexes were assigned to six groups viz., vehicle (distilled water), or one of five selected doses of caffeine (10, 20, 40, 80 and 120 mg/kg) for 14 days via the oral route. Open field novel object recognition test and Y maze spatial working memory tests were carried out on day 14. Results were analysed using multi-factorial ANOVA followed by Tukey HSD test and expressed as mean ± S.E.M, with p values less than 0.05 were considered statistically significant.

RESULTS

Novel object recognition tests (NOR) revealed that pre-training and pre-test sleep deprivation and caffeine combination impaired non spatial and spatial memory in male and female mice.

CONCLUSION

The study shows the complex interactions with memory that may arise when total sleep deprivation is superimposed on caffeine administration.

Sleep-Dependent Memory Consolidation in Children

In the past 30 years, much research has been conducted elucidating the role of sleep in memory and learning; however, the interaction between sleep and cognitive functioning may be unknown in clinical realms. This article serves to provide a primer on sleep-dependent memory consolidation, a process in which memory is stabilized or even enhanced over a period of sleep. Given the increased amounts of sleep needed in infancy and childhood, the link between sleep and neuronal plasticity is highlighted in this article. Furthermore, sleep disruptions are common to children with neurodevelopmental disorders such as attention-deficit hyperactivity disorder; thus, recent studies showing direct relationships between sleep and memory functioning in such vulnerable groups are discussed.

Sleep deprivation and hippocampal vulnerability: changes in neuronal plasticity, neurogenesis and cognitive function

Despite the ongoing fundamental controversy about the physiological function of sleep, there is general consensus that sleep benefits neuronal plasticity, which ultimately supports brain function and cognition. In agreement with this are numerous studies showing that sleep deprivation (SD) results in learning and memory impairments. Interestingly, such impairments appear to occur particularly when these learning and memory processes require the hippocampus, suggesting that this brain region may be particularly sensitive to the consequences of sleep loss. Although the molecular mechanisms underlying sleep and memory formation remain to be investigated, available evidence suggests that SD may impair hippocampal neuronal plasticity and memory processes by attenuating intracellular cyclic adenosine monophosphate (cAMP)-protein kinase A (PKA) signaling which may lead to alterations in cAMP response element binding protein (CREB)-mediated gene transcription, neurotrophic signaling, and glutamate receptor expression. When restricted sleep becomes a chronic condition, it causes a reduction of hippocampal cell proliferation and neurogenesis, which may eventually lead to a reduction in hippocampal volume. Ultimately, by impairing hippocampal plasticity and function, chronically restricted and disrupted sleep contributes to cognitive disorders and psychiatric diseases.

Emotional and Cognitive Impact of Sleep Restriction in Children

Several observational, cross-sectional, and longitudinal studies as well as a few well-controlled experimental studies have examined the impact of sleep loss on children's daytime functioning. The emerging results indicate that sleep plays a critical role in various aspects of daytime functioning in children, including cognitive and emotional functioning. Furthermore, studies indicate that daytime functioning may be impaired by even small amounts of sleep restriction in children.

Dawn simulation light impacts on different cognitive domains under sleep restriction

Chronic sleep restriction (SR) has deleterious effects on cognitive performance that can be counteracted by light exposure. However, it is still unknown if naturalistic light settings (dawn simulating light) can enhance daytime cognitive performance in a sustainable matter. Seventeen participants were enrolled in a 24-h balanced cross-over study, subsequent to SR (6-h of sleep). Two different light settings were administered each morning: a) dawn simulating light (DsL; polychromatic light gradually increasing from 0 to 250 lx during 30 min before wake-up time, with light around 250 lx for 20 min after wake-up time) and b) control dim light (DL; <8 lx). Cognitive tests were performed every 2 h during scheduled wakefulness and questionnaires were completed hourly to assess subjective mood. The analyses yielded a main effect of "light condition" for the motor tracking task, sustained attention to response task and a working memory task (visual 1 and 3-back task), as well as for the Simple Reaction Time Task, such that participants showed better task performance throughout the day after morning DsL exposure compared to DL. Furthermore, low performers benefited more from the light effects compared to high performers. Conversely, no significant influences from the DsL were found for the Psychomotor Vigilance Task and a contrary effect was observed for the digit symbol substitution test. No light effects were observed for subjective perception of sleepiness, mental effort, concentration and motivation. Our data indicate that short exposure to artificial morning light may significantly enhance cognitive performance in a domain-specific manner under conditions of mild SR.

Sleep spindles provide indirect support to the consolidation of emotional encoding contexts

Emotional memories tend to be strengthened ahead of neutral memories during sleep-dependent consolidation. In recent work, however, we found that this is not the case when emotion pertains to the contextual features of a memory instead of its central constructs, suggesting that emotional contexts are influenced by distinct properties of sleep. We therefore examined the sleep-specific mechanisms supporting representations of emotional context and asked whether these differ to those already implicated in central emotional memory processing, such as rapid eye movement sleep (REM). Participants encoded neutral foreground images that were each associated with an emotionally negative or neutral background (context) image. Immediate and delayed tests for the emotionality of the foreground/background image association were separated by a 4-h consolidation period, which consisted of either total wakefulness or included a 2-h polysomnographically monitored nap. Although memory for negative contexts was not associated with REM, or any other parameter of sleep, sleep spindles (12-15 Hz) predicted increased forgetting and slowed response times for neutral contexts. Together with prior work linking spindles to emotional memory processing, our data may suggest that spindles provide multi-layered support to emotionally salient memories in sleep, with the nature of such effects depending on whether the emotionality of these memories pertains to their central or contextual features. Therefore, whereas spindles may mediate a direct strengthening of central emotional information, as suggested in prior work, they may also provide concurrent indirect support to emotional contexts by working to suppress non-salient neutral contexts.

Memory for therapy in bipolar disorder and comorbid insomnia

OBJECTIVE

To examine the extent to which patients recall the contents of therapy from 1 session to the next and to determine whether recall is associated with treatment outcome.

METHOD

Thirty interepisode individuals with bipolar disorder and comorbid insomnia (ages 21-62 years, 56.7% women, 56.7% Caucasian) participated in a randomized controlled trial of psychotherapies. Patients received either cognitive behavior therapy for insomnia (CBTI-BP; n = 17) or psychoeducation (PE; n = 13). At the beginning of each weekly session, patients freely recalled as many therapy points (i.e., distinct ideas, principles, and experiences) as they could from their previous session. After each session, therapists recorded a list of all therapy points delivered. Treatment outcome was measured via the Insomnia Severity Index (ISI), Pittsburgh Sleep Quality Index, Patient-Reported Outcome Measurement Info System-Sleep, and Quality of Life-Sleep (QOL-Sleep), administered pre- and posttreatment, and treatment evaluation questions administered posttreatment.

RESULTS

Patients recalled 19.6% to 36.9% of therapy points listed by therapists. Raw numbers of therapy points recalled were positively correlated with reductions in ISI scores and gains in QOL-Sleep and with most treatment evaluation questions. Percentages of therapy points recalled were positively correlated with gains in QOL-Sleep but with no other sleep outcome measures or any of the treatment evaluation questions. Patients in CBTI-BP recalled more therapy points than did those in PE but did not differ in the percentages of points recalled.

CONCLUSIONS

Memory for therapy is poor. The amount of content recalled is positively associated with treatment outcome. Enhancing memory for therapy might play a key role in improving treatment outcome.

[Cognitive impairment in patients with COPD: a review]

COPD (Chronic Obstructive Pulmonary Disease) is a respiratory disease characterized by progressive and largely irreversible airway limitation and extrapulmonary problems. The prevalence of COPD increases with age. Mental health problems, including cognitive capacity limitations, occur frequently. Patients with COPD may have problems with cognitive functioning, either globally or in single cognitive domains, such as information processing, attention and concentration, memory, executive functioning and self-regulation. Possible causes are hypoxemia, hypercapnia, exacerbations and decreased physical activity. Cognitive problems in these patients may be related to structural brain abnormalities, such as gray matter pathologic changes and the loss of white matter integrity. Because of the negative impact on health and daily life, it is important to assess cognitive functioning in patients with COPD in order to optimize patient-oriented treatment and to reduce personal discomfort, hospital admissions and mortality.

One night of partial sleep deprivation affects habituation of hypothalamus and skin conductance responses

Sleep disturbances are prevalent in clinical anxiety, but it remains unclear whether they are cause and/or consequence of this condition. Fear conditioning constitutes a valid laboratory model for the acquisition of normal and pathological anxiety. To explore the relationship between disturbed sleep and anxiety in more detail, the present study evaluated the effect of partial sleep deprivation (SD) on fear conditioning in healthy individuals. The neural correlates of 1) nonassociative learning and physiological processing and 2) associative learning (differential fear conditioning) were addressed. Measurements entailed simultaneous functional MRI, EEG, skin conductance response (SCR), and pulse recordings. Regarding nonassociative learning, partial SD resulted in a generalized failure to habituate during fear conditioning, as evidenced by reduced habituation of SCR and hypothalamus responses to all stimuli. Furthermore, SCR and hypothalamus activity were correlated, supporting their functional relationship. Regarding associative learning, effects of partial SD on the acquisition of conditioned fear were weaker and did not reach statistical significance. The hypothalamus plays an integral role in the regulation of sleep and autonomic arousal. Thus sleep disturbances may play a causal role in the development of normal and possibly pathological fear by increasing the susceptibility of the sympathetic nervous system to stressful experiences.

Sleep enhances exposure therapy

BACKGROUND

Sleep benefits memory consolidation. Here, we tested the beneficial effect of sleep on memory consolidation following exposure psychotherapy of phobic anxiety.

METHOD

A total of 40 individuals afflicted with spider phobia according to DSM-IV underwent a one-session virtual reality exposure treatment and either slept for 90 min or stayed awake afterwards.

RESULTS

Sleep following exposure therapy compared with wakefulness led to better reductions in self-reported fear (p = 0.045, d = 0.47) and catastrophic spider-related cognitions (p = 0.026, d = 0.53) during approaching a live spider, both tested after 1 week. Both reductions were associated with greater percentages of stage 2 sleep.

CONCLUSIONS

Our results indicate that sleep following successful psychotherapy, such as exposure therapy, improves therapeutic effectiveness, possibly by strengthening new non-fearful memory traces established during therapy. These findings offer an important non-invasive alternative to recent attempts to facilitate therapeutic memory extinction and consolidation processes with pharmacological or behavioral interventions.

Targeted memory reactivation during slow wave sleep facilitates emotional memory consolidation

STUDY OBJECTIVES

To investigate the mechanisms by which auditory targeted memory reactivation (TMR) during slow wave sleep (SWS) influences the consolidation of emotionally negative and neutral memories.

DESIGN

Each of 72 (36 negative, 36 neutral) picture-location associations were encoded with a semantically related sound. During a subsequent nap, half of the sounds were replayed in SWS, before picture-location recall was examined in a final test.

SETTING

Manchester Sleep Laboratory, University of Manchester.

PARTICIPANTS

15 adults (3 male) mean age = 20.40 (standard deviation ± 3.07).

INTERVENTIONS

TMR with auditory cues during SWS.

MEASUREMENTS AND RESULTS

Performance was assessed by memory accuracy and recall response times (RTs). Data were analyzed with a 2 (sound: replayed/not replayed) × 2 (emotion: negative/neutral) repeated measures analysis of covariance with SWS duration, and then SWS spindles, as the mean-centered covariate. Both analyses revealed a significant three-way interaction for RTs but not memory accuracy. Critically, SWS duration and SWS spindles predicted faster memory judgments for negative, relative to neutral, picture locations that were cued with TMR.

CONCLUSIONS

TMR initiates an enhanced consolidation process during subsequent SWS, wherein sleep spindles mediate the selective enhancement of reactivated emotional memories.

Associations between sleep problems and attentional and behavioral functioning in children with anxiety disorders and ADHD

This study examined associations between sleep problems and attentional and behavioral functioning in 137 children aged 7 to 13 years with anxiety disorders (n = 39), attention deficit hyperactivity disorder (ADHD; n = 38), combined anxiety disorder and ADHD (n = 25), and 35 controls. Diagnoses were made using the semistructured diagnostic interview Schedule for Affective Disorders and Schizophrenia for School-age Children-Present and Lifetime Version. Sleep problems were assessed using the Children's Sleep Habits Questionnaire, attention was measured by the Attention Network Test, and behavioral problems were measured by teacher ratings on the Achenbach System of Empirically Based Assessment, Teacher Report Form. Sleep problems were associated with reduced efficiency of the alerting attention system for all children and with increased internalizing problems in children with anxiety disorders.

Sleep enhances learning of a functional motor task in young adults

BACKGROUND

Sleep has been demonstrated to enhance simple motor skill learning "offline" in young adults. "Offline learning" refers to either the stabilization or the enhancement of a memory through the passage of time without additional practice. It remains unclear whether a functional motor task will benefit from sleep to produce offline motor skill enhancement. Physical therapists often teach clients functional motor skills; therefore, it is important to understand how sleep affects learning of these skills.

OBJECTIVE

The purpose of this study was to determine whether sleep enhances the learning of a functional motor task.

DESIGN

A prospective, cross-sectional, repeated-measures design was used.

METHODS

Young participants who were healthy (N=24) were randomly assigned to either a sleep group or a no-sleep group. The sleep group practiced a novel walking task in the evening and underwent retention testing the following morning, and the no-sleep group practiced the task in the morning and underwent retention testing in the evening. Outcome measures included time around the walking path and spatiotemporal gait parameters.

RESULTS

Only participants who slept after practicing the novel walking task demonstrated a significant offline improvement in performance. Compared with the no-sleep group, participants in the sleep group demonstrated a significant decrease in the time around the walking path, an increase in tandem velocity, an increase in tandem step length, and a decline in tandem step time.

LIMITATIONS

Time-of-day effect and inability to ensure a certain amount of sleep quantity and quality of participants were limitations of the study.

CONCLUSIONS

This study is the first to provide evidence that sleep facilitates learning clinically relevant functional motor tasks. Sleep is an important factor that physical therapists should consider when teaching clients motor skills.

Persistence of sleep problems in children with anxiety and attention deficit hyperactivity disorders

This study examines the persistence of sleep problems over 18 months in 76 referred children with anxiety disorders and/or attention deficit hyperactivity disorders (ADHD) and 31 nonreferred controls, and explores predictors of sleep problems at follow-up (T2) in the referred children. Diagnoses were assessed at initial assessment (T1) using the semi-structured interview Kaufman Schedule for Affective Disorders and Schizophrenia. Sleep problems were assessed using the Children's Sleep Habit Questionnaire at T1 and at T2. Persistence rate of total sleep problems in the clinical range was 72.4 % in referred children, and did not differ significantly between children with a T1 diagnosis of anxiety disorder (76.0 %), ADHD (70.6 %), anxiety disorder and ADHD (68.8 %) or nonreferred controls (50.0 %) The total sleep problems score at T1 significantly predicted the total sleep problems score at T2, whereas age, sex, parent education level and total number of life events did not.

About sleep's role in memory

Over more than a century of research has established the fact that sleep benefits the retention of memory. In this review we aim to comprehensively cover the field of "sleep and memory" research by providing a historical perspective on concepts and a discussion of more recent key findings. Whereas initial theories posed a passive role for sleep enhancing memories by protecting them from interfering stimuli, current theories highlight an active role for sleep in which memories undergo a process of system consolidation during sleep. Whereas older research concentrated on the role of rapid-eye-movement (REM) sleep, recent work has revealed the importance of slow-wave sleep (SWS) for memory consolidation and also enlightened some of the underlying electrophysiological, neurochemical, and genetic mechanisms, as well as developmental aspects in these processes. Specifically, newer findings characterize sleep as a brain state optimizing memory consolidation, in opposition to the waking brain being optimized for encoding of memories. Consolidation originates from reactivation of recently encoded neuronal memory representations, which occur during SWS and transform respective representations for integration into long-term memory. Ensuing REM sleep may stabilize transformed memories. While elaborated with respect to hippocampus-dependent memories, the concept of an active redistribution of memory representations from networks serving as temporary store into long-term stores might hold also for non-hippocampus-dependent memory, and even for nonneuronal, i.e., immunological memories, giving rise to the idea that the offline consolidation of memory during sleep represents a principle of long-term memory formation established in quite different physiological systems.

Sleep restores daytime deficits in procedural memory in children with attention-deficit/hyperactivity disorder

Sleep supports the consolidation of declarative and procedural memory. While prefrontal cortex (PFC) activity supports the consolidation of declarative memory during sleep, opposite effects of PFC activity are reported with respect to the consolidation of procedural memory during sleep. Patients with attention-deficit/hyperactivity disorder (ADHD) are characterised by a prefrontal hypoactivity. Therefore, we hypothesised that children with ADHD benefit from sleep with respect to procedural memory more than healthy children. Sixteen children with ADHD and 16 healthy controls (aged 9-12) participated in this study. A modification of the serial-reaction-time task was conducted. In the sleep condition, learning took place in the evening and retrieval after a night of sleep, whereas in the wake condition learning took place in the morning and retrieval in the evening without sleep. Children with ADHD showed an improvement in motor skills after sleep compared to the wake condition. Sleep-associated gain in reaction times was positively correlated with the amount of sleep stage 4 and REM-density in ADHD. As expected, sleep did not benefit motor performance in the group of healthy children. These data suggest that sleep in ADHD normalizes deficits in procedural memory observed during daytime. It is discussed whether in patients with ADHD attenuated prefrontal control enables sleep-dependent gains in motor skills by reducing the competitive interference between explicit and implicit components within a motor task.

Low-frequency stimulation of the hippocampus following fear extinction impairs both restoration of rapid eye movement sleep and retrieval of extinction memory

Post-learning rapid eye movement (REM) sleep deprivation has often been shown to impair hippocampal functioning, which results in deficit in retrieval of some types of memory. However, it remains to be determined whether post-learning alteration of hippocampal functioning affects, in turn, REM sleep. Recent studies have shown that both post-extinction REM sleep deprivation and post-extinction application of hippocampal low-frequency stimulation (LFS) impair memory of fear extinction, indicating possible bidirectional interactions between hippocampal functioning and REM sleep. To analyze the potential effect of post-extinction alteration of hippocampal functioning on REM sleep, rats were implanted with stimulating electrodes in the dorsal hippocampus for post-extinction LFS. Sleep was recorded before (two sessions, 1 day apart) and after conditioning (five tone and eyelid-shock pairings), and following extinction training (25 tone-alone presentations) for 6 h per session. Fear conditioning reduced time spent in REM sleep, which was restored with fear extinction. Hippocampal LFS, applied immediately following extinction training, abolished the restorative effect of fear extinction on REM sleep and impaired extinction retrieval. These data extend previous findings and suggest bidirectional interactions between hippocampal functioning and REM sleep for successful extinction retrieval.

Sleep and rest facilitate implicit memory in a visual search task

Several forms of learning have been demonstrated to show improvements with sleep. Based on rodent models, it has been suggested that replay of waking events in the hippocampus during sleep may underlie memory consolidation in humans. However, behavioral data for the role of sleep in human hippocampal-related memory have been inconsistent. To further investigate the role of sleep in hippocampal-mediated learning, we tested subjects in two sessions of a contextual cueing paradigm, a form of hippocampus-dependent implicit learning, separated by intervals of sleep, active wake, or carefully controlled quiet rest. Participants completed a visual search task, and unbeknownst to them, some search displays were occasionally repeated in the experiment. Contextual cueing was revealed by faster search speed on repeated trials (Old) than unrepeated ones (New), even though subjects were unaware of the trial repetition. Notably, performance in a second testing session was equivalent for participants who underwent quiet resting, daytime sleep, or nocturnal sleep between the two sessions. These four groups showed equivalent transfer of learning from Session 1. Notably, learning of New configurations in Session 2 was absent in the active wake group, but was equally strong among the other three groups. These results indicate that this form of hippocampal learning is independent of sleep, and vulnerable to proactive interference during active wake. They prompt a reevaluation of the hippocampal replay hypothesis as a general model of sleep-dependent learning.