About sleep's role in memory

Age-associated sleep spindle characteristics in Duchenne muscular dystrophy

Brain oscillations of non-rapid eye movement sleep, including slow oscillations (SO, 0.5-1.5 Hz) and spindles (10-16 Hz), mirror underlying brain maturation across development and are associated with cognition. Hence, age-associated emergence and changes in the electrophysiological properties of these rhythms can lend insight into cortical development, specifically in comparisons between pediatric populations and typically developing peers. We previously evaluated age-associated changes in SOs in male patients with Duchenne muscular dystrophy (DMD), finding a significant age-related decline between 4 and 18 years. While primarily a muscle disorder, male patients with DMD can also have sleep, cognitive, and cortical abnormalities, thought to be driven by altered dystrophin expression in the brain. In this follow-up study, we characterized the age-associated changes in sleep spindles. We found that age-dependent spindle characteristics in patients with DMD, including density, frequency, amplitude, and duration, were consistent with age-associated trends reported in the literature for typically developing controls. Combined with our prior finding of age-associated decline in SOs, our results suggest that SOs, but not spindles, are a candidate intervention target to enhance sleep in patients with DMD.

Memory reactivation in slow wave sleep enhances relational learning in humans

Sleep boosts the integration of memories, and can thus facilitate relational learning. This benefit may be due to memory reactivation during non-REM sleep. We set out to test this by explicitly cueing reactivation using a technique called targeted memory reactivation (TMR), in which sounds are paired with learned material in wake and then softly played during subsequent sleep, triggering reactivation of the associated memories. We specifically tested whether TMR in slow wave sleep leads to enhancements in inferential thinking in a transitive inference task. Because the Up-phase of the slow oscillation is more responsive to cues than the Down-phase, we also asked whether Up-phase stimulation is more beneficial for such integration. Our data show that TMR during the Up-Phase boosts the ability to make inferences, but only for the most distant inferential leaps. Up-phase stimulation was also associated with detectable memory reinstatement, whereas Down-phase stimulation led to below-chance performance the next morning. Detection of memory reinstatement after Up-state stimulation was negatively correlated with performance on the most difficult inferences the next morning. These findings demonstrate that cueing memory reactivation at specific time points in sleep can benefit difficult relational learning problems.

Individual sleep need is flexible and dynamically related to cognitive function

Given that sleep deprivation studies consistently show that short sleep causes neurocognitive deficits, the effects of insufficient sleep on brain health and cognition are of great interest and concern. Here we argue that experimentally restricted sleep is not a good model for understanding the normal functions of sleep in naturalistic settings. Cross-disciplinary research suggests that human sleep is remarkably dependent on environmental conditions and social norms, thus escaping universally applicable rules. Sleep need varies over time and differs between individuals, showing a complex relationship with neurocognitive function. This aspect of sleep is rarely addressed in experimental work and is not reflected in expert recommendations about sleep duration. We recommend focusing on the role of individual and environmental factors to improve our understanding of the relationship between human sleep and cognition.

The effect of 8-week mindfulness counseling on sexual self-efficacy of women suffering from human immunodeficiency syndrome: A randomized controlled trial in Iran

Background and Aims

Sexual self-efficacy refers to a woman's belief that she can be sexually active and attractive for her sexual partner and has acceptable sexual function. One of the issues that may negatively affect sexual self-efficacy is HIV infection. The present study aimed to evaluate the effect of 8 weeks of counseling based on mindfulness on sexual self-efficacy of women affected with HIV.

Methods

This was a randomized controlled trial involving 62 HIV-positive women in their reproductive age. Women in the intervention group were further divided into four groups. Each group received eight sessions of counseling based on mindfulness, while the control group received no intervention. A demographic questionnaire and sexual self-efficacy questionnaire were used to collect the data. The independent t test, χ 2, and repeated measure tests were used to analyze the data.

Results

The mean change of total score of sexual self-efficacy in Week 8 compared with before intervention was 37.04 (95% CI: 31.38-42.70, p < 0001) and in Week 12 compared with before intervention was 36.97 (95% CI: 31.59-42.34, p < 0.0001), while in the control group, it almost remained unchanged. The score of readiness for sexual relationship, sexual self-stimulation, intimacy without sexual intercourse, and orgasm improved significantly 8 and 12 weeks after intervention (p < 0.0001), whereas no significant differences were observed in these dimensions in the control group.

Conclusion

The results of this study showed that 8 weeks of counseling based on mindfulness could significantly improve all dimensions of sexual self-efficacy and its total score in women affected with HIV. Thus, this method of counseling is recommended for HIV-positive women.

Impact of single-trial avoidance learning on subsequent sleep

Both non-rapid eye movement (NonREM) sleep and rapid eye movement (REM) sleep, as well as sleep spindle and ripple oscillations, are important for memory formation. Through cortical EEG recordings of prefrontal cortex and hippocampus during and after an inhibitory avoidance task, we analysed the dynamic changes in the amounts of sleep, spindle and ripple oscillations related to memory formation. The total amount of NonREM sleep was reduced during the first hour after learning. Moreover, significant decrease of the total spindle and ripple counts was observed at the first hour after learning as well. In addition, foot shock alone, with no associated learning, produced little effect on the dynamics of sleep oscillations, indicating that the learning experience is necessary for these changes to occur.

Associative Visuomotor Learning Using Transcranial Magnetic Stimulation Induces Stimulus-Response Interference

Classical conditioning states that the systematic co-occurrence of a neutral stimulus with an unconditioned stimulus can cause the neutral stimulus to, over time, evoke the same response as the unconditioned stimulus. On a neural level, Hebbian learning suggests that this type of learning occurs through changes in synaptic plasticity when two neurons are simultaneously active, resulting in increased connectivity between them. Inspired by associative learning theories, we here investigated whether the mere co-activation of visual stimuli and stimulation of the primary motor cortex using TMS would result in stimulus-response associations that can impact future behavior. During a learning phase, we repeatedly paired the presentation of a specific color (but not other colors) with a TMS pulse over the motor cortex. Next, participants performed a two-alternative forced-choice task where they had to categorize simple shapes and we studied whether the shapes' task-irrelevant color (and its potentially associated involuntary motor activity) affected the required motor response. Participants showed more errors on incongruent trials for stimuli that were previously paired with high intensity TMS pulses, but only when tested on the same day. Using a drift diffusion model for conflict tasks, we further demonstrate that this interference occurred early, and gradually increased as a function of associated TMS intensity. Taken together, our findings show that the human brain can learn stimulus-response associations using externally induced motor cortex stimulation. Although we were inspired by the Hebbian learning literature, future studies should investigate whether Hebbian or other learning processes were also what brought about this effect.

Sleep shapes the associative structure underlying pattern completion in multielement event memory

Sleep supports the consolidation of episodic memory. It is, however, a matter of ongoing debate how this effect is established, because, so far, it has been demonstrated almost exclusively for simple associations, which lack the complex associative structure of real-life events, typically comprising multiple elements with different association strengths. Because of this associative structure interlinking the individual elements, a partial cue (e.g., a single element) can recover an entire multielement event. This process, referred to as pattern completion, is a fundamental property of episodic memory. Yet, it is currently unknown how sleep affects the associative structure within multielement events and subsequent processes of pattern completion. Here, we investigated the effects of post-encoding sleep, compared with a period of nocturnal wakefulness (followed by a recovery night), on multielement associative structures in healthy humans using a verbal associative learning task including strongly, weakly, and not directly encoded associations. We demonstrate that sleep selectively benefits memory for weakly associated elements as well as for associations that were not directly encoded but not for strongly associated elements within a multielement event structure. Crucially, these effects were accompanied by a beneficial effect of sleep on the ability to recall multiple elements of an event based on a single common cue. In addition, retrieval performance was predicted by sleep spindle activity during post-encoding sleep. Together, these results indicate that sleep plays a fundamental role in shaping associative structures, thereby supporting pattern completion in complex multielement events.

The Success of Oral Appliance Therapy Based on Symptom-Driven Titration

STUDY OBJECTIVE

Obstructive sleep apnea (OSA) is a chronic condition that could lead to debilitating and sometimes life-threatening consequences. Oral appliance therapy (OAT) is effective in providing a conservative, nonsurgical treatment option for patients diagnosed with mild-to-moderate OSA. The primary goal of this study is to describe a symptom-based titration protocol and determine if the patients can be effectively managed with oral appliances (OAs).

METHOD

A retrospective chart review of patients who were treated with OAs was analyzed for the management of OSA. Patients were self-titrated for symptomatic improvement before posttreatment titration sleep studies were conducted.

RESULTS

Our study has found that 87.5% of the test population was successfully managed with OAs after overnight titration. Seventy-five percentage of the patients were titrated to Apnea-Hypopnea Index (AHI) < 5 with an average of 79.6% reduction from the baseline. Statistical studies showed that patients' body mass index and age at baseline polysomnogram studies significantly influenced the reduction in AHI achieved, whereas the baseline AHI did not show any significant correlation.

CONCLUSION

Oral appliance therapy (OAT) can be a reliable treatment modality to treat OSA, and performing a separate overnight posttreatment titration study further ensures its effectiveness. Furthermore, OAT can be an effective treatment modality even for moderate-to-severe OSA with posttreatment titration.

Multivariate classification of multichannel long-term electrophysiology data identifies different sleep stages in fruit flies

Identifying different sleep stages in humans and other mammals has traditionally relied on electroencephalograms. Such an approach is not feasible in certain animals such as invertebrates, although these animals could also be sleeping in stages. Here, we perform long-term multichannel local field potential recordings in the brains of behaving flies undergoing spontaneous sleep bouts. We acquired consistent spatial recordings of local field potentials across multiple flies, allowing us to compare brain activity across awake and sleep periods. Using machine learning, we uncover distinct temporal stages of sleep and explore the associated spatial and spectral features across the fly brain. Further, we analyze the electrophysiological correlates of microbehaviors associated with certain sleep stages. We confirm the existence of a distinct sleep stage associated with rhythmic proboscis extensions and show that spectral features of this sleep-related behavior differ significantly from those associated with the same behavior during wakefulness, indicating a dissociation between behavior and the brain states wherein these behaviors reside.

A daytime nap with REM sleep is linked to enhanced generalization of emotional stimuli

How memory representations are shaped during and after their encoding is a central question in the study of human memory. Recognition responses to stimuli that are similar to those observed previously can hint at the fidelity of the memories or point to processes of generalization at the expense of precise memory representations. Experimental studies utilizing this approach showed that emotions and sleep both influence these responses. Sleep, and more specifically rapid eye movement sleep, is assumed to facilitate the generalization of emotional memories. We studied mnemonic discrimination by the emotional variant of the Mnemonic Separation Task in participants (N = 113) who spent a daytime nap between learning and testing compared with another group that spent an equivalent time awake between the two sessions. Our findings indicate that the discrimination of similar but previously not seen items from previously seen ones is enhanced in case of negative compared with neutral and positive stimuli. Moreover, whereas the sleep and the wake groups did not differ in memory performance, participants entering rapid eye movement sleep exhibited increased generalization of emotional memories. Our findings indicate that entering into rapid eye movement sleep during a daytime nap shapes emotional memories in a way that enhances recognition at the expense of detailed memory representations.

Analysis of sleep for the American population: Result from NHANES database

OBJECTIVES

To assess the contemporary prevalence and decade-long trends of sleep duration, sleep disorders and trouble sleeping among adults in the United States, as well as their risk factors, from 2005 to 2018.

MATERIALS AND METHODS

We used National Health and Nutrition Examination Survey data to calculate the sleep duration and weighted prevalence of sleep disorders and trouble sleeping in adults aged 20 years or older. Sleep duration, sleep disorders and trouble sleeping were assessed by questionnaire.

RESULTS

A total of 27,399 people were included in the survey on sleep duration, with a weighted percentage of normal sleep (7-8 h/night) of 56.33 % (95 % CI, 53.06-59.60 %) and a weighted percentage of short sleep (5-6 h/night) of 31.73 %. In stratified descriptions, participants aged 40-49 years were more likely to sleep less than five hours, while women aged 80 years and older were more likely to sleep longer and blacks were more likely to sleep shorter. A total of 27,406 participants were included in the survey for sleep disorders. The weighted proportion of the population with sleep disorders was 8.44 % (95 % CI, 7.79-9.8 %). Independent risk factors for sleep disorders were being 40-69 years old, being white, having a high education level, smoking, having hypertension, diabetes, heart disease, and BMI ≥ 25. From 2005 to 2014, the prevalence of sleep disorders increased year by year, from 7.44 % in 2005-2006 to 10.40 % in 2013-2014 (P for Trend<0.001). A total of 38,165 participants were included in the survey on trouble sleeping. The weighted proportion of the population with troubled sleeping was 27.30 % (25.70-28.90 %). Independent risk factors for troubled sleeping were being 30-79 years old, being white, having a high education level, smoking, drinking, having hypertension, diabetes, heart disease and BMI ≥ 25. From 2005 to 2018, the prevalence of trouble sleeping increased annually, from 24.44 % in 2005-2006 to 30.58 % in 2017-2018 (P for trend<0.001).

CONCLUSION

Adults in the United States are likely to have abnormal sleep durations, and the prevalence of sleep disorders and troubled sleeping is on the rise.

Sleep and motor learning in stroke (SMiLES): a longitudinal study investigating sleep-dependent consolidation of motor sequence learning in the context of recovery after stroke

INTRODUCTION

There is growing evidence that sleep is disrupted after stroke, with worse sleep relating to poorer motor outcomes. It is also widely acknowledged that consolidation of motor learning, a critical component of poststroke recovery, is sleep-dependent. However, whether the relationship between disrupted sleep and poor outcomes after stroke is related to direct interference of sleep-dependent motor consolidation processes, is currently unknown. Therefore, the aim of the present study is to understand whether measures of motor consolidation mediate the relationship between sleep and clinical motor outcomes post stroke.

METHODS AND ANALYSIS

We will conduct a longitudinal observational study of up to 150 participants diagnosed with stroke affecting the upper limb. Participants will be recruited and assessed within 7 days of their stroke and followed up at approximately 1 and 6 months. The primary objective of the study is to determine whether sleep in the subacute phase of recovery explains the variability in upper limb motor outcomes after stroke (over and above predicted recovery potential from the Predict Recovery Potential algorithm) and whether this relationship is dependent on consolidation of motor learning. We will also test whether motor consolidation mediates the relationship between sleep and whole-body clinical motor outcomes, whether motor consolidation is associated with specific electrophysiological sleep signals and sleep alterations during subacute recovery.

ETHICS AND DISSEMINATION

This trial has received both Health Research Authority, Health and Care Research Wales and National Research Ethics Service approval (IRAS: 304135; REC: 22/LO/0353). The results of this trial will help to enhance our understanding of the role of sleep in recovery of motor function after stroke and will be disseminated via presentations at scientific conferences, peer-reviewed publication, public engagement events, stakeholder organisations and other forms of media where appropriate.

TRIAL REGISTRATION NUMBER

ClinicalTrials.gov: NCT05746260, registered on 27 February 2023.

Scalp and hippocampal sleep correlates of memory function in drug-resistant temporal lobe epilepsy

Seminal animal studies demonstrated the role of sleep oscillations such as cortical slow waves, thalamocortical spindles, and hippocampal ripples in memory consolidation. In humans, whether ripples are involved in sleep-related memory processes is less clear. Here, we explored the interactions between sleep oscillations (measured as traits) and general episodic memory abilities in 26 adults with drug-resistant temporal lobe epilepsy who performed scalp-intracranial electroencephalographic recordings and neuropsychological testing, including two analogous hippocampal-dependent verbal and nonverbal memory tasks. We explored the relationships between hemispheric scalp (spindles, slow waves) and hippocampal physiological and pathological oscillations (spindles, slow waves, ripples, and epileptic spikes) and material-specific memory function. To differentiate physiological from pathological ripples, we used multiple unbiased data-driven clustering approaches. At the individual level, we found material-specific cerebral lateralization effects (left-verbal memory, right-nonverbal memory) for all scalp spindles (rs > 0.51, ps < 0.01) and fast spindles (rs > 0.61, ps < 0.002). Hippocampal epileptic spikes and short pathological ripples, but not physiological oscillations, were negatively (rs > -0.59, ps < 0.01) associated with verbal learning and retention scores, with left lateralizing and antero-posterior effects. However, data-driven clustering failed to separate the ripple events into defined clusters. Correlation analyses with the resulting clusters revealed no meaningful or significant associations with the memory scores. Our results corroborate the role of scalp spindles in memory processes in patients with drug-resistant temporal lobe epilepsy. Yet, physiological and pathological ripples were not separable when using data-driven clustering, and thus our findings do not provide support for a role of sleep ripples as trait-like characteristics of general memory abilities in epilepsy.

Improving the detection of sleep slow oscillations in electroencephalographic data

Study objectives

We aimed to build a tool which facilitates manual labeling of sleep slow oscillations (SOs) and evaluate the performance of traditional sleep SO detection algorithms on such a manually labeled data set. We sought to develop improved methods for SO detection.

Method

SOs in polysomnographic recordings acquired during nap time from ten older adults were manually labeled using a custom built graphical user interface tool. Three automatic SO detection algorithms previously used in the literature were evaluated on this data set. Additional machine learning and deep learning algorithms were trained on the manually labeled data set.

Results

Our custom built tool significantly decreased the time needed for manual labeling, allowing us to manually inspect 96,277 potential SO events. The three automatic SO detection algorithms showed relatively low accuracy (max. 61.08%), but results were qualitatively similar, with SO density and amplitude increasing with sleep depth. The machine learning and deep learning algorithms showed higher accuracy (best: 99.20%) while maintaining a low prediction time.

Conclusions

Accurate detection of SO events is important for investigating their role in memory consolidation. In this context, our tool and proposed methods can provide significant help in identifying these events.

Does the absence or presence of sleep spindles on EEG have prognostic value for cognitive outcome in children with infantile epileptic spasms syndrome? A systematic literature review

Infantile Epileptic Spasms Syndrome (IESS) is an epileptic encephalopathy in childhood that affects infants under the age of two years. When spasm series occur, prognosis for cognitive outcome is poor in the majority of cases. The encephalopathy in IESS includes delayed maturation of normal sleep phenomena in the EEG, such as sleep spindles. Children with intellectual disabilities often have abnormal sleep, and children with sleep problems have difficulties learning at school. We examined whether there is evidence of prognostic value of detection of sleep spindles in the EEG of children with IESS on their future cognitive development. A systematic literature search yielded five studies touching this question. They were evaluated by two scorers independently. The lack of normal sleep patterns including lack of sleep spindles was used as a biomarker of poor cognitive outcome. Positive (PPV) and Negative (NPV) prognostic values were calculated. A summary of all five studies indicates a PPV of 82% and an NPV of 45%. Given the small amount of data, the retrospective quality of most studies, and the differences in the outcome parameters reported, it is prudent to say that currently available data do not allow us to conclude whether spindles have a specific and independent role in the cognitive prognosis of affected children. Since sleep spindles are needed for memory consolidation and demonstrate the active role of sleep for learning and memory, the hypothesis remains that their absence in the EEG may indicate an increased risk of cognitive delay, but more supporting data are needed to reach such a firm conclusion.

Exploring the impact of pediatric short bowel syndrome on parent well-being using a disease-specific pilot survey

BACKGROUND

Children with short bowel syndrome (SBS) have complex care needs, most of which are met in the home by family caregivers who may experience a range of stressors unique to this experience. Prior research suggests that parents of children with SBS have poorer health-related quality of life than peers parenting children without health needs, but the mechanisms shaping parent outcomes are understudied.

METHODS

A pilot survey was developed using a community-driven research design to measure the impact of disease-specific items on parent-perceived well-being. The cross-sectional survey, which included both closed-ended and open-ended items, was distributed to a convenience sample of parents of children with SBS. Quantitative and qualitative data were integrated for a mixed-methods analysis of how individual items impacted parent well-being.

RESULTS

Twenty parents completed the survey. Sleep interruptions, lack of support and resources, and psychological stressors and their mental health implications were more frequently reported as stressors than logistics related to caregiving (e.g., managing therapies and preparing specialized meals).

CONCLUSION

The impact of a child's SBS on parent well-being may stem mainly from three interconnected domains: poor sleep and its consequences, lack of access to support and resources, and a range of psychological stressors that affect parent mental health. Understanding the mechanisms through which SBS shapes parent well-being is a necessary first step for developing targeted interventions to support parents and provide family-centered care.

Sleep spindle architecture associated with distinct clinical phenotypes in older adults at risk for dementia

Sleep spindles are a hallmark of non-REM sleep and play a fundamental role in memory consolidation. Alterations in these spindles are emerging as sensitive biomarkers for neurodegenerative diseases of ageing. Understanding the clinical presentations associated with spindle alterations may help to elucidate the functional role of these distinct electroencephalographic oscillations and the pathophysiology of sleep and neurodegenerative disorders. Here, we use a data-driven approach to examine the sleep, memory and default mode network connectivity phenotypes associated with sleep spindle architecture in older adults (mean age = 66 years). Participants were recruited from a specialist clinic for early diagnosis and intervention for cognitive decline, with a proportion showing mild cognitive deficits on neuropsychological testing. In a sample of 88 people who underwent memory assessment, overnight polysomnography and resting-state fMRI, a k-means cluster analysis was applied to spindle measures of interest: fast spindle density, spindle duration and spindle amplitude. This resulted in three clusters, characterised by preserved spindle architecture with higher fast spindle density and longer spindle duration (Cluster 1), and alterations in spindle architecture (Clusters 2 and 3). These clusters were further characterised by reduced memory (Clusters 2 and 3) and nocturnal hypoxemia, associated with sleep apnea (Cluster 3). Resting-state fMRI analysis confirmed that default mode connectivity was related to spindle architecture, although directionality of this relationship differed across the cluster groups. Together, these results confirm a diversity in spindle architecture in older adults, associated with clinically meaningful phenotypes, including memory function and sleep apnea. They suggest that resting-state default mode connectivity during the awake state can be associated with sleep spindle architecture; however, this is highly dependent on clinical phenotype. Establishing relationships between clinical and neuroimaging features and sleep spindle alterations will advance our understanding of the bidirectional relationships between sleep changes and neurodegenerative diseases of ageing.

Slow oscillation-spindle cross-frequency coupling predicts overnight declarative memory consolidation in older adults

Cross-frequency coupling (CFC) between brain oscillations during non-rapid-eye-movement (NREM) sleep (e.g. slow oscillations [SO] and spindles) may be a neural mechanism of overnight memory consolidation. Declines in CFC across the lifespan might accompany coinciding memory problems with ageing. However, there are few reports of CFC changes during sleep after learning in older adults, controlling for baseline effects. Our objective was to examine NREM CFC in healthy older adults, with an emphasis on spindle activity and SOs from frontal electroencephalogram (EEG), during a learning night after a declarative learning task, as compared to a baseline night without learning. Twenty-five older adults (M [SD] age = 69.12 [5.53] years; 64% female) completed a two-night study, with a pre- and post-sleep word-pair associates task completed on the second night. SO-spindle coupling strength and a measure of coupling phase distance from the SO up-state were both examined for between-night differences and associations with memory consolidation. Coupling strength and phase distance from the up-state peak were both stable between nights. Change in coupling strength between nights was not associated with memory consolidation, but a shift in coupling phase towards (vs. away from) the up-state peak after learning predicted better memory consolidation. Also, an exploratory interaction model suggested that associations between coupling phase closer to the up-state peak and memory consolidation may be moderated by higher (vs. lower) coupling strength. This study supports a role for NREM CFC in sleep-related memory consolidation in older adults.

Assessing the journey of calcium supplementation: A mendelian randomization study on the causal link between calcium levels and sleep disorders

BACKGROUND & AIM

Sleep disorder is a growing concern, and calcium supplementation is often recommended as a potential intervention for sleep disorders. However, the causal relationship between calcium levels and the incidence of sleep disorders remains unclear. Mendelian randomization techniques utilizing genetic variants that affect calcium levels, can provide valuable insights into causality. This study aims to examine the association between calcium levels and sleep disorders in a diverse population that includes both adolescents and adults, and investigate the effects of calcium levels on sleep disorders.

METHODS

Mendelian randomization analysis was conducted using data from UK Biobank and FinnGen datasets. The inverse-variance weighting (IVW) was selected as the primary method. In addition, traditional mediation analysis was performed on a subset of the NHANES data spanning from 2007 to 2018.

RESULTS

Our findings provide evidence supporting a causal relationship between calcium intake and reduced risk of sleep disorders (beta = -0.079, SE = 0.0395, P = 0.0457). While not reaching statistical significance, other MR methods such as weighted median and Mr-Egger exhibited similar directional trends. Analysis of the NHANES cohort revealed a negative association between calcium levels and the prevalence of sleep disorders in male, black, and physically active populations. However, this association was not observed in other demographic groups.

CONCLUSION

Our results suggested that there is no significant correlation between calcium levels and sleep disorder in non-exercise populations. This raises concerns about the long-term high-dose calcium supplementation in clinical practice, which requires further investigation.

Evaluating sleep-stage classification: how age and early-late sleep affects classification performance

Sleep stage classification is a common method used by experts to monitor the quantity and quality of sleep in humans, but it is a time-consuming and labour-intensive task with high inter- and intra-observer variability. Using wavelets for feature extraction and random forest for classification, an automatic sleep-stage classification method was sought and assessed. The age of the subjects, as well as the moment of sleep (early-night and late-night), were confronted to the performance of the classifier. From this study, we observed that these variables do affect the automatic model performance, improving the classification of some sleep stages and worsening others.

Single closed-loop acoustic stimulation targeting memory consolidation suppressed hippocampal ripple and thalamo-cortical spindle activity in mice

Brain rhythms of sleep reflect neuronal activity underlying sleep-associated memory consolidation. The modulation of brain rhythms, such as the sleep slow oscillation (SO), is used both to investigate neurophysiological mechanisms as well as to measure the impact of sleep on presumed functional correlates. Previously, closed-loop acoustic stimulation in humans targeted to the SO Up-state successfully enhanced the slow oscillation rhythm and phase-dependent spindle activity, although effects on memory retention have varied. Here, we aim to disclose relations between stimulation-induced hippocampo-thalamo-cortical activity and retention performance on a hippocampus-dependent object-place recognition task in mice by applying acoustic stimulation at four estimated SO phases compared to sham condition. Across the 3-h retention interval at the beginning of the light phase closed-loop stimulation failed to improve retention significantly over sham. However, retention during SO Up-state stimulation was significantly higher than for another SO phase. At all SO phases, acoustic stimulation was accompanied by a sharp increase in ripple activity followed by about a second-long suppression of hippocampal sharp wave ripple and longer maintained suppression of thalamo-cortical spindle activity. Importantly, dynamics of SO-coupled hippocampal ripple activity distinguished SOUp-state stimulation. Non-rapid eye movement (NREM) sleep was not impacted by stimulation, yet preREM sleep duration was effected. Results reveal the complex effect of stimulation on the brain dynamics and support the use of closed-loop acoustic stimulation in mice to investigate the inter-regional mechanisms underlying memory consolidation.

Lifestyle and behavioural changes in older adults during the Covid-19 pandemic are associated with subjective cognitive complaints

Subjective cognitive complaints (SCC) is a self-reported experience of persistently impaired cognitive functions which could be the earliest red flag of neurocognitive disorders. The COVID-19 pandemic and related restriction measures changed the lifestyle and behaviour of older adults. The aim of this study was to assess the relation of these changes and SCC status in Hungary. This cross-sectional study analysed the data of 359 elderly Hungarians who filled out the WW-FINGERS-SARS-CoV2 survey. A quarter of the respondents (n:88) reported SCC in connection with the pandemic. We compared sociodemographic features, health status, lifestyle, and social life parameters between subjects with reported SCC and without. To eliminate the potential interrelation across group differences, stepwise logistic regression was applied. Participants with SCC showed the following characteristics, compared to individuals without: (1) they were older; (2) they were more likely to be women; (3) they had a higher number of chronic disorders; (4) showed more prominent impairment in physical mobility; (5) had worse sleep quality; (6) spent less time with family; and (7) used internet more frequently during the pandemic (all p's < 0.001). Logistic regression highlighted that only two parameters were related to SCC status independently, the physical mobility (ability to walk 500 m without difficulties; OR = 1.186; p < 0.001; 95%CI = 1.101, 1.270) and changes in time spent with grandchildren (OR = 1.04; p = 0.015; 95%CI = 1.008, 1.073). Our study draws attention to the importance of physical mobility and quality time with family as key factors in the cognitive well-being of elderly people.

A visual paired associate learning (vPAL) paradigm to study memory consolidation during sleep

Sleep improves the consolidation and long-term stability of newly formed memories and associations. Most research on human declarative memory and its consolidation during sleep uses word-pair associations requiring exhaustive learning. In the present study, we present the visual paired association learning (vPAL) paradigm, in which participants learn new associations between images of celebrities and animals. The vPAL is based on a one-shot exposure that resembles learning in natural conditions. We tested if vPAL can reveal a role for sleep in memory consolidation by assessing the specificity of memory recognition, and the cued recall performance, before and after sleep. We found that a daytime nap improved the stability of recognition memory and discrimination abilities compared to identical intervals of wakefulness. By contrast, cued recall of associations did not exhibit significant sleep-dependent effects. High-density electroencephalography during naps further revealed an association between sleep spindle density and stability of recognition memory. Thus, the vPAL paradigm opens new avenues for future research on sleep and memory consolidation across ages and heterogeneous populations in health and disease.

Neuromodulation via muscarinic acetylcholine pathway can facilitate distinct, complementary, and sequential roles for NREM and REM states during sleep-dependent memory consolidation

Across vertebrate species, sleep consists of repeating cycles of NREM followed by REM. However, the respective functions of NREM, REM, and their stereotypic cycling pattern are not well understood. Using a simplified biophysical network model, we show that NREM and REM sleep can play differential and critical roles in memory consolidation primarily regulated, based on state-specific changes in cholinergic signaling. Within this network, decreasing and increasing muscarinic acetylcholine (ACh) signaling during bouts of NREM and REM, respectively, differentially alters neuronal excitability and excitatory/inhibitory balance. During NREM, deactivation of inhibitory neurons leads to network-wide disinhibition and bursts of synchronized activity led by firing in engram neurons. These features strengthen connections from the original engram neurons to less-active network neurons. In contrast, during REM, an increase in network inhibition suppresses firing in all but the most-active excitatory neurons, leading to competitive strengthening/pruning of the memory trace. We tested the predictions of the model against in vivo recordings from mouse hippocampus during active sleep-dependent memory storage. Consistent with modeling results, we find that functional connectivity between CA1 neurons changes differentially at transition from NREM to REM sleep during learning. Returning to the model, we find that an iterative sequence of state-specific activations during NREM/REM cycling is essential for memory storage in the network, serving a critical role during simultaneous consolidation of multiple memories. Together these results provide a testable mechanistic hypothesis for the respective roles of NREM and REM sleep, and their universal relative timing, in memory consolidation.

Significance statement

Using a simplified computational model and in vivo recordings from mouse hippocampus, we show that NREM and REM sleep can play differential roles in memory consolidation. The specific neurophysiological features of the two sleep states allow for expansion of memory traces (during NREM) and prevention of overlap between different memory traces (during REM). These features are likely essential in the context of storing more than one new memory simultaneously within a brain network.

Reduced REM and N2 sleep, and lower dream intensity predict increased mind-wandering

Mind-wandering is a mental state in which attention shifts from the present environment or current task to internally driven, self-referent mental content. Homeostatic sleep pressure seems to facilitate mind-wandering as indicated by studies observing links between increased mind-wandering and impaired sleep. Nevertheless, previous studies mostly relied on cross-sectional measurements and self-reports. We aimed to combine the accuracy of objective sleep measures with the use of self-reports in a naturalistic setting in order to examine if objective sleep parameters predict the tendency for increased mind-wandering on the following day. We used mobile sleep electroencephalographic (EEG) headbands and self-report scales over 7 consecutive nights in a group of 67 healthy participants yielding ~400 analyzable nights. Nights with more wakefulness and shorter REM and slow wave sleep were associated with poorer subjective sleep quality at the intraindividual level. Reduced REM and N2 sleep, as well as less intense dream experiences, predicted more mind-wandering the following day. Our micro-longitudinal study indicates that intraindividual fluctuations in the duration of specific sleep stages predict the perception of sleep quality as assessed in the morning, as well as the intensity of daytime mind-wandering the following hours. The combined application of sleep EEG assessments and self-reports over repeated assessments provides new insights into the subtle intraindividual, night-to-day associations between nighttime sleep and the next day's subjective experiences.

Empowerment-based cognitive behavioural therapy for insomnia in persons with mild cognitive impairment: A sequential explanatory mixed-method pilot study

Insomnia is an emerging risk factor for the onset of mild cognitive impairment (MCI) and its progression to dementia. Impaired cognition and neuropsychiatric symptoms create challenges for persons with MCI to participate actively in non-pharmacological interventions. This study examined the feasibility and preliminary effects of empowerment-based cognitive-behavioural therapy for insomnia (CBT-I) on sleep, cognitive function, and health-related quality of life (HRQoL) in persons with MCI and sleep problems. Sixty participants were randomly allocated to the intervention or control group to receive empowerment-based CBT-I or usual care, respectively. The 12 week intervention comprised all core CBT-I techniques delivered through a group and individualised face-to-face approach. An empowerment approach with interactive teaching methods, goal setting, and action planning was used to deliver the intervention. Outcome measures included subjective and objective sleep quality and pattern, and a battery of neuropsychological tests and the 12-item Short Form Survey were administered 3 months (T1) and 6 months post-randomisation (T2). This intervention is feasible and highly acceptable for persons with MCI. The intervention group showed significant improvements in subjective and objective sleep-related outcomes compared with the control group. Moreover, the intervention group showed greater improvements in global cognition, processing speed, attention, and mental flexibility than the control group at T1 and/or T2. No significant between-group differences were observed in memory or HRQoL scores. The qualitative data converged with the quantitative data. In conclusion, empowerment-based CBT-I was well received by persons with MCI and had potential positive effects on improving sleep and cognition in this cohort.

A Matter of Time: A Web-Based Investigation of Rest and Sleep Effects on Speech Motor Learning

PURPOSE

Here, we examine the possibility that memory consolidation during a period of postpractice rest or nocturnal sleep can bolster speech motor learning in the absence of additional practice or effort.

METHOD

Using web-administered experiments, 74 typical, American English talkers trained in a nonnative vowel contrast then had a 12-hr delay with (SLEEP) or without nocturnal sleep (REST) or proceeded immediately (IMMEDIATE) to a posttraining production assessment. For ecological validity, 51 native Danish talkers perceptually identified the American English talkers' productions.

RESULTS

We observed that practice resulted in productions that were more acoustically similar to the Danish target. In addition, we found that rest in the absence of further practice reduced the token-to-token variability of the productions. Last, for vowels produced immediately following training, listeners more accurately identified vowels in the trained context, whereas in the untrained context, listener accuracy improved only for vowels produced by talkers who slept.

CONCLUSIONS

A single session of speech motor training promotes observable change to speech production behavior. Specifically, practice facilitates acoustic similarity to the target. Moreover, although a 12-hr postpractice period of rest appears to promote productions that are less variable, only the productions of those who slept are perceived as more accurate by listeners. This may point to sleep's role in contextualizing the acoustic goal of the production to the learner's own vocal tract and its role as a protective mechanism during learning. These results are unaccounted for under existing models and offer potential for future educational and clinical applications to maximize speech motor learning.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.24707442.

Treatments and regulatory mechanisms of acoustic stimuli on mood disorders and neurological diseases

Acoustic stimuli such as music or ambient noise can significantly affect physiological and psychological health in humans. We here summarize positive effects of music therapy in premature infant distress regulation, performance enhancement, sleep quality control, and treatment of mental disorders. Specifically, music therapy exhibits promising effects on treatment of neurological disorders such as Alzheimer's disease (AD) and Parkinson's disease (PD). We also highlight regulatory mechanisms by which auditory intervention affects an organism, encompassing modulation of immune responses, gene expression, neurotransmitter regulation and neural circuitry. As a safe, cost-effective and non-invasive intervention, music therapy offers substantial potential in treating a variety of neurological conditions.

rTMS reduces spatial learning and memory deficits induced by sleep deprivation possibly via suppressing the expression of kynurenine 3-monooxygenase in rats

INTRODUCTION

Impairment of learning and memory caused by sleep deprivation is a common symptom that significantly affects quality of life. Repetitive transcranial magnetic stimulation (rTMS) is a promising approach to exert a positive effect on cognitive impairment. However, there is less known about the mechanism of rTMS for learning and memory induced by chronic REM sleep deprivation (CRSD). This study was to detect the effects of rTMS on spatial learning and memory deficits by CRSD and explore possible mechanism.

METHODS

Sixty male Sprague-Dawley rats were randomly divided into four groups: wide platform (Control), sleep deprivation (SD), sleep deprivation + rTMS (TMS), and sleep deprivation + sham rTMS (Sham-TMS). Morris water maze (MWM) and open field test (OFT) assessed spatial learning and memory and anxiety of rats with pre/post-intervention. Golgi staining and transmission electron microscope (TEM) were used to observe structural variations of synapses in the hippocampus. The alteration in gene expression of different groups was analyzed by RNA-sequencing (RNA-Seq), and the key gene was screened and identified by quantitative polymerase chain reaction (qPCR) and subsequently verified with western blotting and immunofluorescence.

RESULTS

The behavioral test showed spatial learning and memory decreased and anxiety increased in the SD group compared to the Control and TMS groups. Moreover, rTMS improved spine density, ultrastructural damage, and quantities of synapses. In accordance with RNA-Seq, 56 differentially expressed genes (DEGs) were identified by comparing alternations in four groups and concentrated on kynurenine 3-monooxygenase (KMO). The expression of KMO increased significantly in rats of the SD group compared to the Control and TMS groups identified by qPCR, western blotting, and immunofluorescence.

CONCLUSION

1 Hz rTMS alleviated spatial learning and memory deficits induced by CRSD probably via down-regulating the expression of KMO and improving the structure and quantity of synapses in the hippocampus of rats.

Maturation-dependent changes in cortical and thalamic activity during sleep slow waves: Insights from a combined EEG-fMRI study

INTRODUCTION

Studies using scalp EEG have shown that slow waves (0.5-4 Hz), the most prominent hallmark of NREM sleep, undergo relevant changes from childhood to adulthood, mirroring brain structural modifications and the acquisition of cognitive skills. Here we used simultaneous EEG-fMRI to investigate the cortical and subcortical correlates of slow waves in school-age children and determine their relative developmental changes.

METHODS

We analyzed data from 14 school-age children with self-limited focal epilepsy of childhood who fell asleep during EEG-fMRI recordings. Brain regions associated with slow-wave occurrence were identified using a voxel-wise regression that also modelled interictal epileptic discharges and sleep spindles. At the group level, a mixed-effects linear model was used. The results were qualitatively compared with those obtained from 2 adolescents with epilepsy and 17 healthy adults.

RESULTS

Slow waves were associated with hemodynamic-signal decreases in bilateral somatomotor areas. Such changes extended more posteriorly relative to those in adults. Moreover, the involvement of areas belonging to the default mode network changes as a function of age. No significant hemodynamic responses were observed in subcortical structures. However, we identified a significant correlation between age and thalamic hemodynamic changes.

CONCLUSIONS

Present findings indicate that the somatomotor cortex may have a key role in slow-wave expression throughout the lifespan. At the same time, they are consistent with a posterior-to-anterior shift in slow-wave distribution mirroring brain maturational changes. Finally, our results suggest that slow-wave changes may not reflect only neocortical modifications but also the maturation of subcortical structures, including the thalamus.

Could Accelerated Long-Term Forgetting Be a Feature of the Higher Rate of Memory Complaints Associated with Subjective Cognitive Decline? An Exploratory Study

Background

Recently, subjective cognitive decline (SCD) was proposed as an early risk factor for future Alzheimer's disease (AD).

Objective

In this study, we investigated whether accelerated long-term forgetting (ALF), assessed with extended testing intervals than those adopted in clinical practice, might be a cognitive feature of SCD. Using an explorative MRI analysis of the SCD sample, we attempted to investigate the areas most likely involved in the ALF pattern.

Methods

We recruited 31 individuals with SCD from our memory clinic and subdivided them based on their rate of memory complaints into mild SCDs (n = 18) and severe SCDs (n = 13). A long-term forgetting procedure, involving the recall of verbal and visuo-spatial material at four testing delays (i.e., immediate, 30 min, 24 h, and 7 days post-encoding) was used to compare the two sub-groups of SCDs with a healthy control group (HC; n = 16).

Results

No significant between-group difference was found on the standard neuropsychological tests, nor in the immediate and 30 min recall of the experimental procedure. By contrast, on the verbal test severe SCDs forgot significantly more than HCs in the prolonged intervals (i.e., 24 h and 7 days), with the greatest decline between 30 min and 24 h. Finally, in the whole SCD sample, we found significant associations between functional connectivity values within some cortical networks involved in memory (default mode network, salience network, and fronto-parietal network) and verbal long-term measures.

Conclusions

Our preliminary findings suggest that long-term forgetting procedures could be a sensitive neuropsychological tool for detecting memory concerns in SCDs, contributing to early AD detection.

Anxiety's correlation with sleepiness and memory among security officers during the COVID-19 pandemic

BACKGROUND

In the working population especially among older adults, anxiety problems have grown dramatically. This element has a significant impact on employee absenteeism and problems with physical and mental health. It was widely known that security personnel had several physical and mental difficulties during their various work hours. It is important to investigate the effects of anxiety on them.

OBJECTIVE

The present study aims to provide insights into the prevalence of anxiety disorders and explore the correlations between anxiety symptoms, sleep, and memory during the COVID-19 pandemic.

METHODS

To conduct a cross-sectional study, 42 older adult participants between the ages of sixty to seventy years were chosen and the procedure was explained.Data were gathered by giving instructions on how to complete the self-reported Generalized Anxiety Disorder Assessment -7 (GAD-7), the Epworth Sleepiness Scale, and the revised Everyday Memory Questionnaire.

RESULTS

A total of 36 out of 42 participants (85.71%) experienced moderate to severe anxiety. Anxiety and sleep had a correlation of 0.8, while anxiety and memory had a correlation of 0.87 with a positive EMQ-R relationship. Moreover, there was a statistically significant association between sleep and memory, with a positive correlation of 0.73.

CONCLUSION

The study concludes that, there is a substantial prevalence of anxiety accompanied by notable insomnia and memory problems in elderly security officers. Our findings indicate a clear relationship between sleep disturbances, memory issues, and most prevalent anxiety symptoms. These results emphasize the importance of incorporating mental health assessments and addressing an effective treatment for anxiety.

Sleep spindles in adolescents with major depressive disorder

Sleep spindle differences in adolescents with major depressive disorder (MDD) compared to healthy adolescents is an ongoing debate. Results mostly indicate decreased sleep spindle activity in adolescents with MDD. Given that sleep spindles predominate NREM and that acutely delaying the sleep period via a "sleep delay challenge" (SDC) increases non-rapid eye movement (NREM) sleep duration, it may be possible to increase spindle density in adolescents with MDD, which may provide a therapeutic benefit to depression symptoms. Here, we examined the impact of a SDC on spindle density and depression symptomology in adolescents with MDD (n = 66) and healthy controls (n = 62) tested across three nights: adaptation, normal sleep, and a SDC night which delayed bedtime by three hours. The results showed that; (1) there was no difference in spindle density between groups on the normal sleep night, (2) following the SDC, both males and females with MDD had a decrease in the frequency of slow spindles, while only females with MDD had an increase in the frequency of fast spindles, (3) acute SDC reduced depression symptoms in both groups, and (4) light sleep on the normal sleep night and slow spindle frequency at SDC predicted an 8 % improvement in depression symptoms, regardless of sex or MDD diagnosis. Taken together, these results suggest that; (a) spindles may be a useful biological marker of depression symptomatology regardless of clinical MDD diagnosis, and (b) that acute SDC may help alleviate depression symptoms in adolescents with MDD.

Dynamic neuronal instability generates synaptic plasticity and behavior: Insights from Drosophila sleep

How do neurons encode the information that underlies cognition, internal states, and behavior? This review focuses on the neural circuit mechanisms underlying sleep in Drosophila and, to illustrate the power of addressing neural coding in this system, highlights a specific circuit mediating the circadian regulation of sleep quality. This circuit exhibits circadian cycling of sleep quality, which depends solely on the pattern (not the rate) of spiking. During the night, the stability of spike waveforms enhances the reliability of spike timing in these neurons to promote sleep quality. During the day, instability of the spike waveforms leads to uncertainty of spike timing, which remarkably produces synaptic plasticity to induce arousal. Investigation of the molecular and biophysical basis of these changes was greatly facilitated by its study in Drosophila, revealing direct connections between genes, molecules, spike biophysical properties, neural codes, synaptic plasticity, and behavior. Furthermore, because these patterns of neural activity change with aging, this model system holds promise for understanding the interplay between the circadian clock, aging, and sleep quality. It is proposed here that neurophysiological investigations of the Drosophila brain present an exceptional opportunity to tackle some of the most challenging questions related to neural coding.

Propagating population activity patterns during spontaneous slow waves in the thalamus of rodents

Slow waves (SWs) represent the most prominent electrophysiological events in the thalamocortical system under anesthesia and during deep sleep. Recent studies have revealed that SWs have complex spatiotemporal dynamics and propagate across neocortical regions. However, it is still unclear whether neuronal activity in the thalamus exhibits similar propagation properties during SWs. Here, we report propagating population activity in the thalamus of ketamine/xylazine-anesthetized rats and mice visualized by high-density silicon probe recordings. In both rodent species, propagation of spontaneous thalamic activity during up-states was most frequently observed in dorsal thalamic nuclei such as the higher order posterior (Po), lateral posterior (LP) or laterodorsal (LD) nuclei. The preferred direction of thalamic activity spreading was along the dorsoventral axis, with over half of the up-states exhibiting a gradual propagation in the ventral-to-dorsal direction. Furthermore, simultaneous neocortical and thalamic recordings collected under anesthesia demonstrated that there is a weak but noticeable interrelation between propagation patterns observed during cortical up-states and those displayed by thalamic population activity. In addition, using chronically implanted silicon probes, we detected propagating activity patterns in the thalamus of naturally sleeping rats during slow-wave sleep. However, in comparison to propagating up-states observed under anesthesia, these propagating patterns were characterized by a reduced rate of occurrence and a faster propagation speed. Our findings suggest that the propagation of spontaneous population activity is an intrinsic property of the thalamocortical network during synchronized brain states such as deep sleep or anesthesia. Additionally, our data implies that the neocortex may have partial control over the formation of propagation patterns within the dorsal thalamus under anesthesia.

[Glymphatic dysfunction and sleep disorders: indirect effects on Alzheimer's disease]

Modern research raises the question of the potentially significant role of glymphatic dysfunction in the development of neurodegeneration and pathological aging. The exact molecular mechanisms are not yet fully understood, but there is ample evidence of a link between sleep deprivation and decreased clearance of β-amyloid and other neurotoxin proteins that are associated with the development of neurodegenerative diseases, particularly Alzheimer's disease. The review analyzes current scientific information in this area of research, describes the latest scientific discoveries of the features of the glymphatic system, and also illustrates studies of markers that presumably indicate a deterioration in the glymphatic system. The relationship between sleep deprivation and pathophysiological mechanisms associated with neurodegenerative diseases is considered, and potential targets that can be used to treat or delay the development of these disorders are noted.

Artificial sharp-wave-ripples to support memory and counter neurodegeneration

Information processed in our sensory neocortical areas is transported to the hippocampus during memory encoding, and between hippocampus and neocortex during memory consolidation, and retrieval. Short bursts of high-frequency oscillations, so called sharp-wave-ripples, have been proposed as a potential mechanism for this information transfer: They can synchronize neural activity to support the formation of local neural networks to store information, and between distant cortical sites to act as a bridge to transfer information between sensory cortical areas and hippocampus. In neurodegenerative diseases like Alzheimer's Disease, different neuropathological processes impair normal neural functioning and neural synchronization as well as sharp-wave-ripples, which impairs consolidation and retrieval of information, and compromises memory. Here, we formulate a new hypothesis, that artificially inducing sharp-wave-ripples with noninvasive high-frequency visual stimulation could potentially support memory functioning, as well as target the neuropathological processes underlying neurodegenerative diseases. We also outline key challenges for empirical tests of the hypothesis.

Imaging microglia surveillance during sleep-wake cycles in freely behaving mice

Microglia surveillance manifests itself as dynamic changes in cell morphology and functional remodeling. Whether and how microglia surveillance is coupled to brain state switches during natural sleep-wake cycles remains unclear. To address this question, we used miniature two-photon microscopy (mTPM) to acquire time-lapse high-resolution microglia images of the somatosensory cortex, along with EEG/EMG recordings and behavioral video, in freely-behaving mice. We uncovered fast and robust brain state-dependent changes in microglia surveillance, occurring in parallel with sleep dynamics and early-onset phagocytic microglial contraction during sleep deprivation stress. We also detected local norepinephrine fluctuation occurring in a sleep state-dependent manner. We showed that the locus coeruleus-norepinephrine system, which is crucial to sleep homeostasis, is required for both sleep state-dependent and stress-induced microglial responses and β2-adrenergic receptor signaling plays a significant role in this process. These results provide direct evidence that microglial surveillance is exquisitely tuned to signals and stressors that regulate sleep dynamics and homeostasis so as to adjust its varied roles to complement those of neurons in the brain. In vivo imaging with mTPM in freely behaving animals, as demonstrated here, opens a new avenue for future investigation of microglia dynamics and sleep biology in freely behaving animals.

Neural reactivation during human sleep

Sleep promotes memory consolidation: the process by which newly acquired memories are stabilised, strengthened, and integrated into long-term storage. Pioneering research in rodents has revealed that memory reactivation in sleep is a primary mechanism underpinning sleep's beneficial effect on memory. In this review, we consider evidence for memory reactivation processes occurring in human sleep. Converging lines of research support the view that memory reactivation occurs during human sleep, and is functionally relevant for consolidation. Electrophysiology studies have shown that memory reactivation is tightly coupled to the cardinal neural oscillations of non-rapid eye movement sleep, namely slow oscillation-spindle events. In addition, functional imaging studies have found that brain regions recruited during learning become reactivated during post-learning sleep. In sum, the current evidence paints a strong case for a mechanistic role of neural reactivation in promoting memory consolidation during human sleep.

How do the sleep features that characterise depression impact memory?

Depression is associated with general sleep disturbance and abnormalities in sleep physiology. For example, compared with control subjects, depressed patients exhibit lower sleep efficiency, longer rapid eye movement (REM) sleep duration, and diminished slow-wave activity during non-REM sleep. A separate literature indicates that depression is also associated with many distinguishing memory characteristics, including emotional memory bias, overgeneral autobiographical memory, and impaired memory suppression. The sleep and memory features that hallmark depression may both contribute to the onset and maintenance of the disorder. Despite our rapidly growing understanding of the intimate relationship between sleep and memory, our comprehension of how sleep and memory interact in the aetiology of depression remains poor. In this narrative review, we consider how the sleep signatures of depression could contribute to the accompanying memory characteristics.

REM Sleep Loss-Induced Elevated Noradrenaline Plays a Significant Role in Neurodegeneration: Synthesis of Findings to Propose a Possible Mechanism of Action from Molecule to Patho-Physiological Changes

Wear and tear are natural processes for all living and non-living bodies. All living cells and organisms are metabolically active to generate energy for their routine needs, including for survival. In the process, the cells are exposed to oxidative load, metabolic waste, and bye-products. In an organ, the living non-neuronal cells divide and replenish the lost or damaged cells; however, as neuronal cells normally do not divide, they need special feature(s) for their protection, survival, and sustenance for normal functioning of the brain. The neurons grow and branch as axons and dendrites, which contribute to the formation of synapses with near and far neurons, the basic scaffold for complex brain functions. It is necessary that one or more basic and instinct physiological process(es) (functions) is likely to contribute to the protection of the neurons and maintenance of the synapses. It is known that rapid eye movement sleep (REMS), an autonomic instinct behavior, maintains brain functioning including learning and memory and its loss causes dysfunctions. In this review we correlate the role of REMS and its loss in synaptogenesis, memory consolidation, and neuronal degeneration. Further, as a mechanism of action, we will show that REMS maintains noradrenaline (NA) at a low level, which protects neurons from oxidative damage and maintains neuronal growth and synaptogenesis. However, upon REMS loss, the level of NA increases, which withdraws protection and causes apoptosis and loss of synapses and neurons. We propose that the latter possibly causes REMS loss associated neurodegenerative diseases and associated symptoms.

Respiration modulates sleep oscillations and memory reactivation in humans

The beneficial effect of sleep on memory consolidation relies on the precise interplay of slow oscillations and spindles. However, whether these rhythms are orchestrated by an underlying pacemaker has remained elusive. Here, we tested the relationship between respiration, which has been shown to impact brain rhythms and cognition during wake, sleep-related oscillations and memory reactivation in humans. We re-analysed an existing dataset, where scalp electroencephalography and respiration were recorded throughout an experiment in which participants (N = 20) acquired associative memories before taking a nap. Our results reveal that respiration modulates the emergence of sleep oscillations. Specifically, slow oscillations, spindles as well as their interplay (i.e., slow-oscillation_spindle complexes) systematically increase towards inhalation peaks. Moreover, the strength of respiration - slow-oscillation_spindle coupling is linked to the extent of memory reactivation (i.e., classifier evidence in favour of the previously learned stimulus category) during slow-oscillation_spindles. Our results identify a clear association between respiration and memory consolidation in humans and highlight the role of brain-body interactions during sleep.

Microstructural dynamics of motor learning and sleep-dependent consolidation: A diffusion imaging study

Memory consolidation can benefit from post-learning sleep, eventually leading to long-term microstructural brain modifications to accommodate new memory representations. Non-invasive diffusion-weighted magnetic resonance imaging (DWI) allows the observation of (micro)structural brain remodeling after time-limited motor learning. Here, we combine conventional diffusion tensor imaging (DTI) and neurite orientation dispersion and density imaging (NODDI) that allows modeling dendritic and axonal complexity in gray matter to investigate with improved specificity the microstructural brain mechanisms underlying time- and sleep-dependent motor memory consolidation dynamics. Sixty-one young healthy adults underwent four DWI sessions, two sequential motor trainings, and a night of total sleep deprivation or regular sleep distributed over five days. We observed rapid-motor-learning-related remodeling in occipitoparietal, temporal, and motor-related subcortical regions, reflecting temporary dynamics in learning-related neuronal brain plasticity processes. Sleep-related consolidation seems not to exert a detectable impact on diffusion parameters, at least on the timescale of a few days.

CA3 hippocampal synaptic plasticity supports ripple physiology during memory consolidation

The consolidation of recent memories depends on memory replays, also called ripples, generated within the hippocampus during slow-wave sleep, and whose inactivation leads to memory impairment. For now, the mobilisation, localisation and importance of synaptic plasticity events associated to ripples are largely unknown. To tackle this question, we used cell surface AMPAR immobilisation to block post-synaptic LTP within the hippocampal region of male mice during a spatial memory task, and show that: 1- hippocampal synaptic plasticity is engaged during consolidation, but is dispensable during encoding or retrieval. 2- Plasticity blockade during sleep results in apparent forgetting of the encoded rule. 3- In vivo ripple recordings show a strong effect of AMPAR immobilisation when a rule has been recently encoded. 4- In situ investigation suggests that plasticity at CA3-CA3 recurrent synapses supports ripple generation. We thus propose that post-synaptic AMPAR mobility at CA3 recurrent synapses is necessary for ripple-dependent rule consolidation.

Altered Sleep Microarchitecture and Cognitive Impairment in Patients With Temporal Lobe Epilepsy

BACKGROUND AND OBJECTIVES

To investigate the spatiotemporal characteristics of sleep waveforms in temporal lobe epilepsy (TLE) and examine their association with cognition.

METHODS

In this retrospective, cross-sectional study, we examined overnight EEG data from adult patients with TLE and nonepilepsy comparisons (NECs) admitted to the epilepsy monitoring unit at Mass General Brigham hospitals. Automated algorithms were used to characterize sleep macroarchitecture (sleep stages) and microarchitecture (spindles, slow oscillations [SOs]) on scalp EEG and to detect hippocampal interictal epileptiform discharges (hIEDs) from foramen ovale electrodes simultaneously recorded in a subset of patients with TLE. We examined the association of sleep features and hIEDs with memory and executive function from clinical neuropsychological evaluations.

RESULTS

A total of 81 adult patients with TLE and 28 NEC adult patients were included with similar mean ages. There were no significant differences in sleep macroarchitecture between groups, including relative time spent in each sleep stage, sleep efficiency, and sleep fragmentation. By contrast, the spatiotemporal characteristics of sleep microarchitecture were altered in TLE compared with NEC and were associated with cognitive impairments. Specifically, we observed a ∼30% reduction in spindle density in patients with TLE compared with NEC, which was significantly associated with worse memory performance. Spindle-SO coupling strength was also reduced in TLE and, in contrast to spindles, was associated with diminished executive function. We found no significant association between sleep macroarchitectural and microarchitectural parameters and hIEDs.

DISCUSSION

There is a fundamental alteration of sleep microarchitecture in TLE, characterized by a reduction in spindle density and spindle-SO coupling, and these changes may contribute to neurocognitive comorbidity in this disorder.

More frequent naps are associated with lower cognitive development in a cohort of 8-38-month-old children, during the Covid-19 pandemic

Background

How often a child naps, during infancy, is believed to reflect both intrinsic factors, that is, the need of an immature brain to consolidate information soon after it is acquired, and environmental factors. Difficulty accounting for important environmental factors that interfere with a child's sleep needs (e.g., attending daycare) has clouded our ability to understand the role of intrinsic drivers of napping frequency.

Methods

Here we investigate sleep patterns in association with two measures of cognitive ability, vocabulary size, measured with the Oxford-Communicative Development Inventory (N = 298) and cognitive executive functions (EF), measured with the Early EF Questionnaire (N = 463), in a cohort of 8-38-month-olds. Importantly, because of the social distancing measures imposed during the Covid-19 Spring 2020 lockdown, in the UK, measures of sleep were taken when children did not access daycare settings.

Results

We find that children with more frequent but shorter naps than expected for their age had lower concurrent receptive vocabularies, lower cognitive EF and a slower increase in expressive vocabulary from spring to winter 2020, when age, sex, and SES were accounted for. The negative association between vocabulary and frequency of naps became stronger with age.

Conclusions

These findings suggest that the structure of daytime sleep is an indicator of cognitive development and highlight the importance of considering environmental perturbations and age when investigating developmental correlates of sleep.

Continuity and change in neural plasticity through embryonic morphogenesis, fetal activity-dependent synaptogenesis, and infant memory consolidation

There is an apparent continuity in human neural development that can be traced to venerable themes of vertebrate morphogenesis that have shaped the evolution of the reptilian telencephalon (including both primitive three-layered cortex and basal ganglia) and then the subsequent evolution of the mammalian six-layered neocortex. In this theoretical analysis, we propose that an evolutionary-developmental analysis of these general morphogenetic themes can help to explain the embryonic development of the dual divisions of the limbic system that control the dorsal and ventral networks of the human neocortex. These include the archicortical (dorsal limbic) Papez circuits regulated by the hippocampus that organize spatial, contextual memory, as well as the paleocortical (ventral limbic) circuits that organize object memory. We review evidence that these dorsal and ventral limbic divisions are controlled by the differential actions of brainstem lemnothalamic and midbrain collothalamic arousal control systems, respectively, thereby traversing the vertebrate subcortical neuraxis. These dual control systems are first seen shaping the phyletic morphogenesis of the archicortical and paleocortical foundations of the forebrain in embryogenesis. They then provide dual modes of activity-dependent synaptic organization in the active (lemnothalamic) and quiet (collothalamic) stages of fetal sleep. Finally, these regulatory systems mature to form the major systems of memory consolidation of postnatal development, including the rapid eye movement (lemnothalamic) consolidation of implicit memory and social attachment in the first year, and then-in a subsequent stage-the non-REM (collothalamic) consolidation of explicit memory that is integral to the autonomy and individuation of the second year of life.

Illustrations of interactions needed when investigating sleep using a type of AM-PM PM-AM design

Sleep has long been thought of and promoted to be beneficial for memory. Some claims that sleep aids memory have been made in the absence of a critical interaction. This condition is necessary when using a commonly-used experimental design (a type of AM-PM PM-AM design). We propose that a sleep effect exists only if there is an interaction between groups (experimental and time-of-day controls) and the time of test or study (morning and evening). We show different patterns of results that would and would not support a sleep effect with empirical and model-generated data from recognition memory experiments and hypothetical data. While we use these data to make our point, our suggestions apply to any memory and non-memory-related investigation (e.g., emotional memory, false memory susceptibility, language learning, problem-solving). Testing for and finding the proper interaction will add to the evidence that sleep boosts performance.

The role of sleep for memory consolidation: does sleep protect memories from retroactive interference?

Numerous studies suggest that sleep benefits memory. A major theoretical question in this area is however if sleep does so by passively shielding memories from interference that arises during wakefulness or by actively stabilizing and strengthening memories. A key finding by Ellenbogen et al. Current Biology, 16, 1290-1294 (2006a) indicates that sleep can protect memories from retroactive interference, which suggests that sleep plays more than a passive role for memory consolidation. Sample size in this study was however small and subsequent reports in the literature provided mixed results. We therefore conducted an online study via Zoom to replicate Ellenbogen et al. Current Biology, 16, 1290-1294 (2006a). Subjects were asked to study paired associates. After a 12-h delay that included either nocturnal sleep or daytime wakefulness, half of all subjects were asked to study an additional list to elicit retroactive interference. All participants were then asked to complete a memory test for the studied list(s). The results were fully consistent with those reported by Ellenbogen et al. Current Biology, 16, 1290-1294 (2006a). We discuss this successful replication against the background of the mixed literature, with a focus on the possibly critical role of study-design features, like the use of high learning criteria that resulted in performance being at ceiling, or a confound between interference and the length of the retention interval. A collaborative replication effort may be needed to reach a straightfoward answer to the question if sleep protects memories from interference (and under what conditions).