Sleep: A Novel Mechanistic Pathway, Biomarker, and Treatment Target in the Pathology of Alzheimer's Disease?

Sleep health inequities in vulnerable populations: Beyond sleep deserts

Despite the importance of sleep to overall health and well-being, there is a high prevalence of undiagnosed sleep disorders and adverse sleep health, particularly among vulnerable populations. Such vulnerable populations include people experiencing homelessness (PEH), refugees, and incarcerated individuals. In this narrative review, we provide an overview of the literature on sleep health and disorders among key and vulnerable populations (e.g., PEH, refugees, and incarcerated individuals). The limited research among these populations indicated a high prevalence of sleep disorders, mainly insomnia, short sleep duration, and fatigue. Substance abuse and PTSD were commonly found among PEH and refugee populations, respectively, which were was related to poor sleep. Similar across the included vulnerable populations, the individuals reside in environments/facilities with inopportune light exposure, noise disruption, inadequate bedding, and forced sleep schedules. Studies also found a high prevalence of psychosocial stress and reports of threats to safety, which were associated with poor sleep health outcomes. Additionally, several studies reported environmental barriers to adherence to sleep disorder treatment. This paper highlighted the conditions in which these vulnerable populations reside, which may inform interventions within these various facilities (homeless shelters, refugee camps, prisons/jails). The improvement of these facilities with a sleep equity focus may in turn improve quality of life and daily functioning.

Risk factors associated with the Motoric Cognitive Risk syndrome: A meta-analysis of data from a cross-national study

BACKGROUND

Identifying risk factors associated with the Motoric Cognitive Risk (MCR) syndrome (a pre-dementia syndrome) can assist in developing risk reduction strategies and interventions to delay progression to dementia. Tailored interventions require comparisons of high- and middle-income countries to determine if the same or different risk factors should be targeted. We examined risk factors associated with MCR in seven Health and Retirement Studies with harmonized measures.

METHODS

Data from adults aged ≥65 years (n = 20,036, mean age 71.2(SD 6.2)-80.1(SD 4.1)) from the U.S. Health and Retirement Study, English Longitudinal Study of Aging, Survey of Health, Aging and Retirement in Europe, China Health and Retirement Longitudinal Study, Harmonized Diagnostic Assessment of Dementia for Longitudinal Aging Study in India, Mexican Health and Aging Study, and Brazilian Longitudinal Study of Aging was included. MCR was defined as the presence of cognitive complaints and slow gait (no mobility disability and dementia). Associations of demographic [education], medical [hypertension, diabetes, heart disease, obesity, stroke, Parkinson's, falls], psychological [depressive symptoms, psychiatric problems], sensorimotor [grip strength, hearing], and behavioral factors [smoking, sedentariness, sleep], with prevalent MCR were examined using age- and sex-adjusted logistic regression models. A meta-analysis was performed to compare risk factors for MCR in high- versus middle-income countries.

RESULTS

Except for depressive symptoms and weak grip strength, different risk factor clusters were associated with individual studies. Poor sleep, hearing, weak grip, and multiple falls emerged as novel associations with MCR. When grouped by income, some risk factors (i.e., education) were associated with MCR in high- and middle-income countries. Others (i.e., obesity) were specific to high-income countries.

CONCLUSIONS

This cross-sectional, cross-national study identified new, shared, and specific risk factors associated with MCR in high- and middle-income countries, providing insights to develop public health approaches and interventions to forestall the onset of dementia in those with MCR.

Sleep Health Analysis Through Sleep Symptoms in 35,808 Individuals Across Age and Sex Differences: Comparative Symptom Network Study

BACKGROUND

Sleep health is a multidimensional construct that includes objective and subjective parameters and is influenced by individual sleep-related behaviors and sleep disorders. Symptom network analysis allows modeling of the interactions between variables, enabling both the visualization of relationships between different factors and the identification of the strength of those relationships. Given the known influence of sex and age on sleep health, network analysis can help explore sets of mutually interacting symptoms relative to these demographic variables.

OBJECTIVE

This study aimed to study the centrality of symptoms and compare age and sex differences regarding sleep health using a symptom network approach in a large French population that feels concerned about their sleep.

METHODS

Data were extracted from a questionnaire provided by the Réseau Morphée health network. A network analysis was conducted on 39 clinical variables related to sleep disorders and sleep health. After network estimation, statistical analyses consisted of calculating inferences of centrality, robustness (ie, testifying to a sufficient effect size), predictability, and network comparison. Sleep clinical variable centralities within the networks were analyzed by both sex and age using 4 age groups (18-30, 31-45, 46-55, and >55 years), and local symptom-by-symptom correlations determined.

RESULTS

Data of 35,808 participants were obtained. The mean age was 42.7 (SD 15.7) years, and 24,964 (69.7%) were women. Overall, there were no significant differences in the structure of the symptom networks between sexes or age groups. The most central symptoms across all groups were nonrestorative sleep and excessive daytime sleepiness. In the youngest group, additional central symptoms were chronic circadian misalignment and chronic sleep deprivation (related to sleep behaviors), particularly among women. In the oldest group, leg sensory discomfort and breath abnormality complaint were among the top 4 central symptoms. Symptoms of sleep disorders thus became more central with age than sleep behaviors. The high predictability of central nodes in one of the networks underlined its importance in influencing other nodes.

CONCLUSIONS

The absence of structural difference between networks is an important finding, given the known differences in sleep between sexes and across age groups. These similarities suggest comparable interactions between clinical sleep variables across sexes and age groups and highlight the implication of common sleep and wake neural circuits and circadian rhythms in understanding sleep health. More precisely, nonrestorative sleep and excessive daytime sleepiness are central symptoms in all groups. The behavioral component is particularly central in young people and women. Sleep-related respiratory and motor symptoms are prominent in older people. These results underscore the importance of comprehensive sleep promotion and screening strategies tailored to sex and age to impact sleep health.

Causal relationship between sleep disorders and the risk of Alzheimer's disease: A Mendelian randomization study

BACKGROUND AND OBJECTIVE

Epidemiological studies have shown that sleep disorders are risk factors for Alzheimer's disease (AD), but the causal relationship between sleep disorders and AD risk is unknown. We aim to assess the potential genetic causal association between sleep characteristics and AD, which may contribute to early identification and prediction of risk factors for AD.

METHODS

Seven sleep-related traits and the outcome phenotype AD were selected from published genome-wide association studies (GWASs). These sleep-related characteristics and instrumental variables (IVs) for AD were extracted. Two-sample and multivariate Mendelian randomization (MR) analyses were performed to assess the causal relationships between sleep characteristics and AD. The inverse variance weighted (IVW), weighted median (WME), weighted mode (WM), MR-Egger regression (MR-Egger) and simple mode (SM) models were used to evaluate causality. The existence of pleiotropy was detected and corrected by MR-Egger regression, MR pleiotropy residuals and outliers.

RESULTS

A two-sample MR study revealed a positive causal association between sleep duration and the onset of AD (OR = 1.002, 95 % CI: 1.000-1.004), and the risk of AD increased with increasing sleep duration. The MR-Egger regression method and MR-PRESSO were used to identify and correct pleiotropy, indicating that there was no horizontal pleiotropy. Heterogeneity was evaluated by Cochran's Q, which indicated no heterogeneity. In a multivariate MR study with seven sleep characteristics corrected for each other, we found that sleep duration remained causally associated with AD (OR = 1.004, 95 % CI: 1.000-1.007). Moreover, we found that after mutual correction, daytime napping had a causal relationship with the onset of AD, and daytime napping may reduce the risk of AD (OR = 0.995, 95 % CI: 0.991-1.000).

CONCLUSION

This study is helpful for the early identification and prediction of risk factors for AD, long sleep durations are a risk factor for AD, and daytime napping can reduce the risk of AD.

Long Objective Sleep Duration is a Marker of Cognitive Impairment in Older Adults: Findings from the Cretan Aging Cohort

 We examined associations between objective sleep duration and cognitive status in older adults initially categorized as cognitively non-impaired (CNI, n = 57) or diagnosed with mild cognitive impairment (MCI, n = 53). On follow-up, 8 years later, all participants underwent neuropsychiatric/neuropsychological evaluation and 7-day 24-h actigraphy. On re-assessment 62.7% of participants were cognitively declined. Patients who developed dementia had significantly longer night total sleep time (TST) than persons with MCI who, in turn, had longer night TST than CNI participants. Objective long sleep duration is a marker of worse cognitive status in elderly with MCI/dementia and this association is very strong in older adults.

Cannabinoid and Orexigenic Systems Interplay as a New Focus of Research in Alzheimer's Disease

Alzheimer's disease (AD) remains a significant health challenge, with an increasing prevalence globally. Recent research has aimed to deepen the understanding of the disease pathophysiology and to find potential therapeutic interventions. In this regard, G protein-coupled receptors (GPCRs) have emerged as novel potential therapeutic targets to palliate the progression of neurodegenerative diseases such as AD. Orexin and cannabinoid receptors are GPCRs capable of forming heteromeric complexes with a relevant role in the development of this disease. On the one hand, the hyperactivation of the orexins system has been associated with sleep-wake cycle disruption and Aβ peptide accumulation. On the other hand, cannabinoid receptor overexpression takes place in a neuroinflammatory environment, favoring neuroprotective effects. Considering the high number of interactions between cannabinoid and orexin systems that have been described, regulation of this interplay emerges as a new focus of research. In fact, in microglial primary cultures of APPSw/Ind mice model of AD there is an important increase in CB2R-OX1R complex expression, while OX1R antagonism potentiates the neuroprotective effects of CB2R. Specifically, pretreatment with the OX1R antagonist has been shown to strongly potentiate CB2R signaling in the cAMP pathway. Furthermore, the blockade of OX1R can also abolish the detrimental effects of OX1R overactivation in AD. In this sense, CB2R-OX1R becomes a new potential therapeutic target to combat AD.

Multi-night acoustic stimulation is associated with better sleep, amyloid dynamics, and memory in older adults with cognitive impairment

Sleep is a potential early, modifiable risk factor for cognitive decline and dementia. Impaired slow wave sleep (SWS) is pronounced in individuals with cognitive impairment (CI). Cognitive decline and impairments of SWS are bi-directionally linked in a vicious cycle. SWS can be enhanced non-invasively using phase-locked acoustic stimulation (PLAS), potentially breaking this vicious cycle. Eighteen healthy older adults (HC, agemean±sd, 68.3 ± 5.1) and 16 older adults (agemean±sd, 71.9 ± 3.9) with CI (Montreal Cognitive Assessment ≤ 25) underwent one baseline (sham-PLAS) night and three consecutive stimulation nights (real-PLAS). EEG responses and blood-plasma amyloid beta Aβ42/Aβ40 ratio were measured pre- and post-intervention, as was episodic memory. The latter was again evaluated 1 week and 3 months after the intervention. In both groups, PLAS induced a significant electrophysiological response in both voltage- and time-frequency analyses, and memory performance improved in association with the magnitude of this response. In the CI group, both electrophysiological and associated memory effects were delayed compared to the healthy group. After 3 intervention nights, electrophysiological response to PLAS was no longer different between CI and HC groups. Only in the CI sample, stronger electrophysiological responses were significantly associated with improving post-intervention Aβ42/Aβ40 ratios. PLAS seems to improve SWS electrophysiology, memory, and amyloid dynamics in older adults with CI. However, effects on memory require more time to unfold compared to healthy older adults. This indicates that PLAS may become a potential tool to ameliorate cognitive decline, but longer interventions are necessary to compensate for declining brain integrity. This study was pre-registered (clinicaltrials.gov: NCT04277104).

Sleep duration, sleep efficiency, and amyloid β among cognitively healthy later-life adults: a systematic review and meta-analysis

BACKGROUND

Abnormal amyloid β (Aβ) deposits in the brain are a hallmark of Alzheimer's disease (AD). Insufficient sleep duration and poor sleep quality are risk factors for developing AD. Sleep may play a role in Aβ regulation, but the magnitude of the relationship between sleep and Aβ deposition remains unclear. This systematic review examines the relationship between sleep (i.e., duration and efficiency) with Aβ deposition in later-life adults.

METHODS

A search of PubMed, CINAHL, Embase, and PsycINFO generated 5,005 published articles. Fifteen studies met the inclusion criteria for qualitative syntheses; thirteen studies for quantitative syntheses related to sleep duration and Aβ; and nine studies for quantitative syntheses related to sleep efficiency and Aβ.

RESULTS

Mean ages of the samples ranged from 63 to 76 years. Studies measured Aβ using cerebrospinal fluid, serum, and positron emission tomography scans with two tracers: Carbone 11-labeled Pittsburgh compound B or fluorine 18-labeled. Sleep duration was measured subjectively using interviews or questionnaires, or objectively using polysomnography or actigraphy. Study analyses accounted for demographic and lifestyle factors. Based on 13 eligible articles, our synthesis demonstrated that the average association between sleep duration and Aβ was not statistically significant (Fisher's Z = -0.055, 95% CI = -0.117 ~ 0.008). We found that longer self-report sleep duration is associated with lower Aβ (Fisher's Z = -0.062, 95% CI = -0.119 ~ -0.005), whereas the objectively measured sleep duration was not associated with Aβ (Fisher's Z = 0.002, 95% CI = -0.108 ~ 0.113). Based on 9 eligible articles for sleep efficiency, our synthesis also demonstrated that the average association between sleep efficiency and Aβ was not statistically significant (Fisher's Z = 0.048, 95% CI = -0.066 ~ 0.161).

CONCLUSION

The findings from this review suggest that shorter self-reported sleep duration is associated with higher Aβ levels. Given the heterogeneous nature of the sleep measures and outcomes, it is still difficult to determine the exact relationship between sleep and Aβ. Future studies with larger sample sizes should focus on comprehensive sleep characteristics and use longitudinal designs to better understand the relationship between sleep and AD.

The effectiveness of exercise interventions targeting sleep in older adults with cognitive impairment or Alzheimer's disease and related dementias (AD/ADRD): A systematic review and meta-analysis

Sleep loss is associated with reduced health and quality of life, and increased risk of Alzheimer's disease and related dementias. Up to 66% of persons with Alzheimer's disease and related dementias experience poor sleep, which can predict or accelerate the progression of cognitive decline. Exercise is a widely accessible intervention for poor sleep that can protect against functional and cognitive decline. No previous systematic reviews have investigated the effectiveness of exercise for sleep in older adults with mild cognitive impairment or Alzheimer's disease and related dementias. We systematically reviewed controlled interventional studies of exercise targeting subjectively or objectively (polysomnography/actigraphy) assessed sleep in persons with mild cognitive impairment or Alzheimer's disease and related dementias. We conducted searches in PubMed, Embase, Scopus and Cochrane-Library (n = 6745). Nineteen randomised and one non-randomised controlled interventional trials were included, representing the experiences of 3278 persons with mild cognitive impairment or Alzheimer's disease and related dementias. Ten had low-risk, nine moderate-risk, and one high-risk of bias. Six studies with subjective and eight with objective sleep outcomes were meta-analysed (random-effects model). We found moderate- to high-quality evidence for the beneficial effects of exercise on self-reported and objectively-measured sleep outcomes in persons with mild cognitive impairment or Alzheimer's disease and related dementias. However, no studies examined key potential moderators of these effects, such as sex, napping or medication use. Our results have important implications for clinical practice. Sleep may be one of the most important modifiable risk factors for a range of health conditions, including cognitive decline and the progression of Alzheimer's disease and related dementias. Given our findings, clinicians may consider adding exercise as an effective intervention or adjuvant strategy for improving sleep in older persons with mild cognitive impairment or Alzheimer's disease and related dementias.

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.

Developmental alcohol exposure is exhausting: Sleep and the enduring consequences of alcohol exposure during development

Prenatal alcohol exposure is the leading nongenetic cause of human intellectual impairment. The long-term impacts of prenatal alcohol exposure on health and well-being are diverse, including neuropathology leading to behavioral, cognitive, and emotional impairments. Additionally negative effects also occur on the physiological level, such as the endocrine, cardiovascular, and immune systems. Among these diverse impacts is sleep disruption. In this review, we describe how prenatal alcohol exposure affects sleep, and potential mechanisms of those effects. Furthermore, we outline the evidence that sleep disruption across the lifespan may be a mediator of some cognitive and behavioral impacts of developmental alcohol exposure, and thus may represent a promising target for treatment.

Glymphatic system dysfunction in middle-aged and elderly chronic insomnia patients with cognitive impairment evidenced by diffusion tensor imaging along the perivascular space (DTI-ALPS)

BACKGROUND

Chronic insomnia impairs the glymphatic system and may lead to cognitive impairment and dementia in elderly population. The diffusion tensor image analysis along the perivascular space (DTI-ALPS) has been proposed as a non-invasive method to measure the activity of human brain glymphatic. We aim to explore whether glymphatic function is impaired in middle-aged and elderly chronic insomnia individuals and to identify the relationships between glymphatic dysfunction and cognitive impairment.

METHODS

A total of 33 chronic insomnia patients (57.36 ± 5.44 years, 30 females) and 20 age- and sex-matched healthy controls (57.95 ± 5.78 years, 16 females) were prospectively enrolled between May 2022 and January 2023. All participants completed MRI screening, cognition and sleep assessments, and DTI-ALPS index analysis.

RESULTS

Our findings revealed that the DTI-ALPS index was significantly difference among the chronic insomnia patients with impaired cognition group (1.32 ± 0.14), with normal cognition group (1.46 ± 0.09), and healthy controls (1.61 ± 0.16) (p = 0.0012, p < 0.0001, p = 0.0008, respectively). Mini-Mental State Examination (MMSE) scores of chronic insomnia patients with cognitive impairment were positively correlated with the DTI-ALPS index (Partial correlation analyses after correction for age, sex, education level and duration of chronic insomnia: r = 0.78, p = 0.002). DTI-ALPS had moderate accuracy in distinguishing chronic insomnia patients with cognitive impairment from those with normal cognition.

DATA CONCLUSION

The glymphatic system dysfunction is involved in chronic insomnia among middle-aged and elderly individuals, and it has been found to be correlated with cognitive decline.

Clinical usefulness of dual orexin receptor antagonism beyond insomnia: Neurological and psychiatric comorbidities

Orexin is a neurotransmitter produced by a small group of hypothalamic neurons. Besides its well-known role in the regulation of the sleep-wake cycle, the orexin system was shown to be relevant in several physiological functions including cognition, mood and emotion modulation, and energy homeostasis. Indeed, the implication of orexin neurotransmission in neurological and psychiatric diseases has been hypothesized via a direct effect exerted by the projections of orexin neurons to several brain areas, and via an indirect effect through orexin-mediated modulation of sleep and wake. Along with the growing evidence concerning the use of dual orexin receptor antagonists (DORAs) in the treatment of insomnia, studies assessing their efficacy in insomnia comorbid with psychiatric and neurological diseases have been set in order to investigate the potential impact of DORAs on both sleep-related symptoms and disease-specific manifestations. This narrative review aimed at summarizing the current evidence on the use of DORAs in neurological and psychiatric conditions comorbid with insomnia, also discussing the possible implication of modulating the orexin system for improving the burden of symptoms and the pathological mechanisms of these disorders. Target searches were performed on PubMed/MEDLINE and Scopus databases and ongoing studies registered on Clinicaltrials.gov were reviewed. Despite some contradictory findings, preclinical studies seemingly support the possible beneficial role of orexin antagonism in the management of the most common neurological and psychiatric diseases with sleep-related comorbidities. However, clinical research is still limited and further studies are needed for corroborating these promising preliminary results.

Linking brain structure, cognition, and sleep: insights from clinical data

STUDY OBJECTIVES

To use relatively noisy routinely collected clinical data (brain magnetic resonance imaging (MRI) data, clinical polysomnography (PSG) recordings, and neuropsychological testing), to investigate hypothesis-driven and data-driven relationships between brain physiology, structure, and cognition.

METHODS

We analyzed data from patients with clinical PSG, brain MRI, and neuropsychological evaluations. SynthSeg, a neural network-based tool, provided high-quality segmentations despite noise. A priori hypotheses explored associations between brain function (measured by PSG) and brain structure (measured by MRI). Associations with cognitive scores and dementia status were studied. An exploratory data-driven approach investigated age-structure-physiology-cognition links.

RESULTS

Six hundred and twenty-three patients with sleep PSG and brain MRI data were included in this study; 160 with cognitive evaluations. Three hundred and forty-two participants (55%) were female, and age interquartile range was 52 to 69 years. Thirty-six individuals were diagnosed with dementia, 71 with mild cognitive impairment, and 326 with major depression. One hundred and fifteen individuals were evaluated for insomnia and 138 participants had an apnea-hypopnea index equal to or greater than 15. Total PSG delta power correlated positively with frontal lobe/thalamic volumes, and sleep spindle density with thalamic volume. rapid eye movement (REM) duration and amygdala volume were positively associated with cognition. Patients with dementia showed significant differences in five brain structure volumes. REM duration, spindle, and slow-oscillation features had strong associations with cognition and brain structure volumes. PSG and MRI features in combination predicted chronological age (R2 = 0.67) and cognition (R2 = 0.40).

CONCLUSIONS

Routine clinical data holds extended value in understanding and even clinically using brain-sleep-cognition relationships.

Clinical and cost-effectiveness of DREAMS START (Dementia RElAted Manual for Sleep; STrAtegies for RelaTives) for people living with dementia and their carers: a study protocol for a parallel multicentre randomised controlled trial

INTRODUCTION

Many people living with dementia experience sleep disturbance and there are no known effective treatments. Non-pharmacological treatment options should be the first-line sleep management. For family carers, relatives' sleep disturbance leads to interruption of their sleep, low mood and breakdown of care. Our team developed and delivered DREAMS START (Dementia RElAted Manual for Sleep; STrAtegies for RelaTives), a multimodal non-pharmacological intervention, showing it to be feasible and acceptable. The aim of this randomised controlled trial is to establish whether DREAMS START is clinically cost-effective in reducing sleep disturbances in people living with dementia living at home compared with usual care.

METHODS AND ANALYSIS

We will recruit 370 participant dyads (people living with dementia and family carers) from memory services, community mental health teams and the Join Dementia Research Website in England. Those meeting inclusion criteria will be randomised (1:1) either to DREAMS START or to usual treatment. DREAMS START is a six-session (1 hour/session), manualised intervention delivered every 1-2 weeks by supervised, non-clinically trained graduates. Outcomes will be collected at baseline, 4 months and 8 months with the primary outcome being the Sleep Disorders Inventory score at 8 months. Secondary outcomes for the person with dementia (all proxy) include quality of life, daytime sleepiness, neuropsychiatric symptoms and cost-effectiveness. Secondary outcomes for the family carer include quality of life, sleep disturbance, mood, burden and service use and caring/work activity. Analyses will be intention-to-treat and we will conduct a process evaluation.

ETHICS AND DISSEMINATION

London-Camden & Kings Cross Ethics Committee (20/LO/0894) approved the study. We will disseminate our findings in high-impact peer-reviewed journals and at national and international conferences. This research has the potential to improve sleep and quality of life for people living with dementia and their carers, in a feasible and scalable intervention.

TRIAL REGISTRATION NUMBER

ISRCTN13072268.

Sleep in Healthy and Pathological Aging

Human sleep physiology is strongly affected by age [...].

Altered sleep behavior strengthens face validity in the ArcAβ mouse model for Alzheimer's disease

Demographic changes will expand the number of senior citizens suffering from Alzheimer's disease (AD). Key aspects of AD pathology are sleep impairments, associated with onset and progression of AD. AD mouse models may provide insights into mechanisms of AD-related sleep impairments. Such models may also help to establish new biomarkers predicting AD onset and monitoring AD progression. The present study aimed to establish sleep-related face validity of a widely used mouse model of AD (ArcAβ model) by comprehensively characterizing its baseline sleep/wake behavior. Chronic EEG recordings were performed continuously on four consecutive days in freely behaving mice. Spectral and temporal sleep/wake parameters were assessed and analyzed. EEG recordings showed decreased non-rapid eye movement sleep (NREMS) and increased wakefulness in transgenic mice (TG). Vigilance state transitions were different in TG mice when compared to wildtype littermates (WT). During NREMS, TG mice had lower power between 1 and 5 Hz and increased power between 5 and 30 Hz. Sleep spindle amplitudes in TG mice were lower. Our study strongly provides sleep-linked face validity for the ArcAβ model. These findings extend the potential of the mouse model to investigate mechanisms of AD-related sleep impairments and the impact of sleep impairments on the development of AD.

Knowledge Structure and Emerging Trends of Mild Cognitive Impairment with Dyssomnias in Recent 20 Years: A Bibliometric Analysis via CiteSpace and VOSviewer

Background

Mild cognitive impairment (MCI), an intermediate stage between normal aging and dementia, has emerged as a prominent research area in geriatric care due to its heightened propensity for progressing toward dementia. Sleep plays a pivotal role in cognitive function, with dyssomnias not only exacerbating cognitive and affective symptoms associated with neurodegenerative diseases but also contributing to disease progression.

Aim

This bibliometric analysis investigates the global research on MCI with dyssomnias over the past two decades, aiming to discern key findings, research domains, and emerging trends in this field.

Methods

In this study, a bibliometric analysis was conducted using the search terms "MCI" and "sleep". Data were extracted from the Web of Science Core Collection database, and visualization and collaborative analysis were performed using CiteSpace and VOSviewer.

Results

This study encompassed 546 publications from 2003 to 2023. The publication volume and citation rate consistently increased over time. Neurosciences, Clinical Neurology, and Geriatrics Gerontology emerged as the top three research fields. The Journal of Alzheimer's Disease had the highest publication count, while Sleep Medicine received the most citations. USA, China, and Italy led in publication output. Collaborative clusters among authors and institutions were identified, but cooperation between clusters was limited. Active cocited reference clusters included "obstructive sleep apnea", "possible mediating pathways", and "isolated rapid eye movement sleep behaviour disorder". The top frequently mentioned keywords, besides "MCI", were "Alzheimer's disease", "dementia", "risk factor", and "Parkinson's Disease". Notable keyword clusters spanned circadian rhythm, Parkinson's disease, MCI, dementia with Lewy body, subjective cognitive impairment, Lewy body disease, Alzheimer's disease, and dietary patterns.

Conclusion

The field of MCI with dyssomnias is rapidly expanding, encompassing a wide range of neurodegenerative disorders and sleep disturbances. Current research endeavors are primarily focused on elucidating the underlying pathogenesis, predicting disease progression, and developing innovative treatment strategies for individuals affected by MCI with dyssomnias.

Sleep Biomarkers for Predicting Cognitive Decline and Alzheimer's Disease: A Systematic Review of Longitudinal Studies

BACKGROUND

Sleep disturbances are considered a hallmark of dementia, and strong evidence supports the association between alterations in sleep parameters and cognitive decline in patients with mild cognitive impairment and Alzheimer's disease (AD).

OBJECTIVE

This systematic review aims to summarize the existing evidence on the longitudinal association between sleep parameters and cognitive decline, with the goal of identifying potential sleep biomarkers of AD-related neurodegeneration.

METHODS

Literature search was conducted in PubMed, Web of Science, and Scopus databases from inception to 28 March 2023. Longitudinal studies investigating the association between baseline objectively-measured sleep parameters and cognitive decline were assessed for eligibility.

RESULTS

Seventeen studies were included in the qualitative synthesis. Sleep fragmentation, reduced sleep efficiency, reduced REM sleep, increased light sleep, and sleep-disordered breathing were identified as predictors of cognitive decline. Sleep duration exhibited a U-shaped relation with subsequent neurodegeneration. Additionally, several sleep microstructural parameters were associated with cognitive decline, although inconsistencies were observed across studies.

CONCLUSIONS

These findings suggest that sleep alterations hold promise as early biomarker of cognitive decline, but the current evidence is limited due to substantial methodological heterogeneity among studies. Further research is necessary to identify the most reliable sleep parameters for predicting cognitive impairment and AD, and to investigate interventions targeting sleep that can assist clinicians in the early recognition and treatment of cognitive decline. Standardized procedures for longitudinal studies evaluating sleep and cognition should be developed and the use of continuous sleep monitoring techniques, such as actigraphy or EEG headband, might be encouraged.

Interrelationship of Sleep Disturbances and Cognitive Status on Mortality

Sleep disturbances may promote the development and advancement of Alzheimer's disease. Our purpose was to determine if sleep disturbances were associated with earlier mortality while accounting for cognition. The National Alzheimer's Coordinating Center database was used to evaluate mortality risk conferred by sleep, and the Montreal Cognitive Assessment score determined cognitive status. Demographics, sleep disturbances, cognitive status, and comorbid/other neuropsychiatric conditions were examined as predictors of survival time via Cox regression. The sample (N = 31,110) had a median age [interquartile range] of 72 [66, 79] years, MoCA score of 23 [16, 26], and survival time of 106.0 months [104.0,108.0]; 10,278 (33%) died during follow-up; 21% (n = 6461) experienced sleep disturbances. Sleep disturbances impacted survival time depending on cognition, with the greatest effect in transition from normal to cognitive impairment (P < .001). Findings support that sleep disturbances negatively impact survival time, and the impact of sleep disturbances on survival time is interrelated with cognition.

Reduced overnight memory consolidation and associated alterations in sleep spindles and slow oscillations in early Alzheimer's disease

Spatial navigation critically underlies hippocampal-entorhinal circuit function that is early affected in Alzheimer's disease (AD). There is growing evidence that AD pathophysiology dynamically interacts with the sleep/wake cycle impairing hippocampal memory. To elucidate sleep-dependent consolidation in a cohort of symptomatic AD patients (n = 12, 71.25 ± 2.16 years), we tested hippocampal place learning by means of a virtual reality task and verbal memory by a word-pair association task before and after a night of sleep. Our results show an impaired overnight memory retention in AD compared with controls in the verbal task, together with a significant reduction of sleep spindle activity (i.e., lower amplitude of fast sleep spindles, p = 0.016) and increased duration of the slow oscillation (SO; p = 0.019). Higher spindle density, faster down-to-upstate transitions within SOs, and the time delay between SOs and nested spindles predicted better memory performance in healthy controls but not in AD patients. Our results show that mnemonic processing and memory consolidation in AD is slightly impaired as reflected by dysfunctional oscillatory dynamics and spindle-SO coupling during NonREM sleep. In this translational study based on experimental paradigms in animals and extending previous work in healthy aging and preclinical disease stages, our results in symptomatic AD further deepen the understanding of the memory decline within a bidirectional relationship of sleep and AD pathology.

Investigating the relationship between sleep disturbances and white matter hyperintensities in older adults on the Alzheimer's disease spectrum

INTRODUCTION

While studies report that sleep disturbance can have negative effects on brain vasculature, its impact on cerebrovascular diseases such as white matter hyperintensities (WMHs) in beta-amyloid-positive older adults remains unexplored.

METHODS

Sleep disturbance, WMH burden, and cognition in normal controls (NCs), and individuals with mild cognitive impairment (MCI) and Alzheimer's disease (AD), were examined at baseline and longitudinally. A total of 912 amyloid-positive participants were included (198 NC, 504 MCI, and 210 AD).

RESULTS

Individuals with AD reported more sleep disturbances than NC and MCI participants. Those with sleep disturbances had more WMHs than those without sleep disturbances in the AD group. Mediation analysis revealed an effect of regional WMH burden on the relationship between sleep disturbance and future cognition.

DISCUSSION

These results suggest that WMH burden and sleep disturbance increase from aging to AD. Sleep disturbance decreases cognition through increases in WMH burden. Improved sleep could mitigate the impact of WMH accumulation and cognitive decline.

Mapping sleep's oscillatory events as a biomarker of Alzheimer's disease

INTRODUCTION

Memory-associated neural circuits produce oscillatory events including theta bursts (TBs), sleep spindles (SPs), and slow waves (SWs) in sleep electroencephalography (EEG). Changes in the "coupling" of these events may indicate early Alzheimer's disease (AD) pathogenesis.

METHODS

We analyzed 205 aging adults using single-channel sleep EEG, cerebrospinal fluid (CSF) AD biomarkers, and Clinical Dementia Rating® (CDR®) scale. We mapped SW-TB and SW-SP neural circuit coupling precision to amyloid positivity, cognitive impairment, and CSF AD biomarkers.

RESULTS

Cognitive impairment correlated with lower TB spectral power in SW-TB coupling. Cognitively unimpaired, amyloid positive individuals demonstrated lower precision in SW-TB and SW-SP coupling compared to amyloid negative individuals. Significant biomarker correlations were found in oscillatory event coupling with CSF Aβ42 /Aβ40 , phosphorylated- tau181 , and total-tau.

DISCUSSION

Sleep-dependent memory processing integrity in neural circuits can be measured for both SW-TB and SW-SP coupling. This breakdown associates with amyloid positivity, increased AD pathology, and cognitive impairment.

HIGHLIGHTS

At-home sleep EEG is a potential biomarker of neural circuits linked to memory. Circuit precision is associated with amyloid positivity in asymptomatic aging adults. Levels of CSF amyloid and tau also correlate with circuit precision in sleep EEG. Theta burst EEG power is decreased in very early mild cognitive impairment. This technique may enable inexpensive wearable EEGs for monitoring brain health.

Acoustic stimulation as a promising technique to enhance slow-wave sleep in Alzheimer's disease: results of a pilot study

STUDY OBJECTIVES

Sleep disturbances are common in people with Alzheimer's disease (AD), and a reduction in slow-wave activity is the most striking underlying change. Acoustic stimulation has emerged as a promising approach to enhance slow-wave activity in healthy adults and people with amnestic mild cognitive impairment. In this phase 1 study we investigated, for the first time, the feasibility of acoustic stimulation in AD and piloted the effect on slow-wave sleep (SWS).

METHODS

Eleven adults with mild to moderate AD first wore the DREEM 2 headband for 2 nights to establish a baseline registration. Using machine learning, the DREEM 2 headband automatically scores sleep stages in real time. Subsequently, the participants wore the headband for 14 consecutive "stimulation nights" at home. During these nights, the device applied phase-locked acoustic stimulation of 40-dB pink noise delivered over 2 bone-conductance transducers targeted to the up-phase of the delta wave or SHAM, if it detected SWS in sufficiently high-quality data.

RESULTS

Results of the DREEM 2 headband algorithm show a significant average increase in SWS (minutes) [t(3.17) = 33.57, P = .019] between the beginning and end of the intervention, almost twice as much time was spent in SWS. Consensus scoring of electroencephalography data confirmed this trend of more time spent in SWS [t(2.4) = 26.07, P = .053].

CONCLUSIONS

Our phase 1 study provided the first evidence that targeted acoustic stimuli is feasible and could increase SWS in AD significantly. Future studies should further test and optimize the effect of stimulation on SWS in AD in a large randomized controlled trial.

CITATION

Van den Bulcke L, Peeters A-M, Heremans E, et al. Acoustic stimulation as a promising technique to enhance slow-wave sleep in Alzheimer's disease: results of a pilot study. J Clin Sleep Med. 2023;19(12):2107-2112.

Acoustic stimulation during sleep predicts long-lasting increases in memory performance and beneficial amyloid response in older adults

BACKGROUND

Sleep and neurodegeneration are assumed to be locked in a bi-directional vicious cycle. Improving sleep could break this cycle and help to prevent neurodegeneration. We tested multi-night phase-locked acoustic stimulation (PLAS) during slow wave sleep (SWS) as a non-invasive method to improve SWS, memory performance and plasma amyloid levels.

METHODS

32 healthy older adults (agemean: 68.9) completed a between-subject sham-controlled three-night intervention, preceded by a sham-PLAS baseline night.

RESULTS

PLAS induced increases in sleep-associated spectral-power bands as well as a 24% increase in slow wave-coupled spindles, known to support memory consolidation. There was no significant group-difference in memory performance or amyloid-beta between the intervention and control group. However, the magnitude of PLAS-induced physiological responses were associated with memory performance up to 3 months post intervention and beneficial changes in plasma amyloid. Results were exclusive to the intervention group.

DISCUSSION

Multi-night PLAS is associated with long-lasting benefits in memory and metabolite clearance in older adults, rendering PLAS a promising tool to build upon and develop long-term protocols for the prevention of cognitive decline.

Characterizing Common Phenotypes Across the Childhood Dementia Disorders: A Cross-sectional Study From Two Australian Centers

BACKGROUND

Childhood dementias are a group of rare pediatric conditions characterized by progressive neurocognitive decline. Quantifying and characterising phenotypes to identify similarities between specific conditions is critical to inform opportunities to optimize care and advance research.

METHODS

This cross-sectional study recruited primary caregivers of children (<18 years) living with a dementia syndrome from neurology and metabolic clinics in Sydney and Adelaide, Australia. Sociodemographic and clinical data were collated. Behavior, eating, sleep, pain, and neurological disability were assessed using validated tools, including Strengths and Difficulties, Child Eating Behaviour, and Children's Sleep Habits questionnaires and visual analog of pain and modified Rankin scales. Data were analyzed with descriptive statistics.

RESULTS

Among 45 children with 23 different dementia syndromes, the modified Rankin Scale demonstrated at least moderate neurological disability and functional dependence in 82% (37/45). Families reported delays in receiving an accurate diagnosis following initial symptoms (mean: 1.6 ± 1.4 years, range: 0-5 years). The most prevalent phenotypes included communication, comprehension, or recall difficulties (87%, 39/45); disturbances in sleep (80%, 36/45); appetite changes (74%, 29/39); mobility issues (53%, 24/45); and hyperactive behavior (53%, 21/40). Behavioral problems had a "high" or "very high" impact on everyday family life in 73% (24/33).

CONCLUSIONS

Childhood dementia disorders share substantial behavioral, motor, sensory, and socioemotional symptoms, resulting in high care needs, despite their vast heterogeneity in age of onset and progression. Considering their unifying characteristics under one collective term is an opportunity to improve treatment, provide quality care, and accelerate research.

Artificial intelligence for biomarker discovery in Alzheimer's disease and dementia

With the increase in large multimodal cohorts and high-throughput technologies, the potential for discovering novel biomarkers is no longer limited by data set size. Artificial intelligence (AI) and machine learning approaches have been developed to detect novel biomarkers and interactions in complex data sets. We discuss exemplar uses and evaluate current applications and limitations of AI to discover novel biomarkers. Remaining challenges include a lack of diversity in the data sets available, the sheer complexity of investigating interactions, the invasiveness and cost of some biomarkers, and poor reporting in some studies. Overcoming these challenges will involve collecting data from underrepresented populations, developing more powerful AI approaches, validating the use of noninvasive biomarkers, and adhering to reporting guidelines. By harnessing rich multimodal data through AI approaches and international collaborative innovation, we are well positioned to identify clinically useful biomarkers that are accurate, generalizable, unbiased, and acceptable in clinical practice. HIGHLIGHTS: Artificial intelligence and machine learning approaches may accelerate dementia biomarker discovery. Remaining challenges include data set suitability due to size and bias in cohort selection. Multimodal data, diverse data sets, improved machine learning approaches, real-world validation, and interdisciplinary collaboration are required.

BMAL1 loss in oligodendroglia contributes to abnormal myelination and sleep

Myelination depends on the maintenance of oligodendrocytes that arise from oligodendrocyte precursor cells (OPCs). We show that OPC-specific proliferation, morphology, and BMAL1 are time-of-day dependent. Knockout of Bmal1 in mouse OPCs during development disrupts the expression of genes associated with circadian rhythms, proliferation, density, morphology, and migration, leading to changes in OPC dynamics in a spatiotemporal manner. Furthermore, these deficits translate into thinner myelin, dysregulated cognitive and motor functions, and sleep fragmentation. OPC-specific Bmal1 loss in adulthood does not alter OPC density at baseline but impairs the remyelination of a demyelinated lesion driven by changes in OPC morphology and migration. Lastly, we show that sleep fragmentation is associated with increased prevalence of the demyelinating disorder multiple sclerosis (MS), suggesting a link between MS and sleep that requires further investigation. These findings have broad mechanistic and therapeutic implications for brain disorders that include both myelin and sleep phenotypes.

Deep brain stimulation of thalamic nucleus reuniens promotes neuronal and cognitive resilience in an Alzheimer's disease mouse model

The mechanisms that confer cognitive resilience to Alzheimer's Disease (AD) are not fully understood. Here, we describe a neural circuit mechanism underlying this resilience in a familial AD mouse model. In the prodromal disease stage, interictal epileptiform spikes (IESs) emerge during anesthesia in the CA1 and mPFC regions, leading to working memory disruptions. These IESs are driven by inputs from the thalamic nucleus reuniens (nRE). Indeed, tonic deep brain stimulation of the nRE (tDBS-nRE) effectively suppresses IESs and restores firing rate homeostasis under anesthesia, preventing further impairments in nRE-CA1 synaptic facilitation and working memory. Notably, applying tDBS-nRE during the prodromal phase in young APP/PS1 mice mitigates age-dependent memory decline. The IES rate during anesthesia in young APP/PS1 mice correlates with later working memory impairments. These findings highlight the nRE as a central hub of functional resilience and underscore the clinical promise of DBS in conferring resilience to AD pathology by restoring circuit-level homeostasis.

No phenotypic or genotypic evidence for a link between sleep duration and brain atrophy

Short sleep is held to cause poorer brain health, but is short sleep associated with higher rates of brain structural decline? Analysing 8,153 longitudinal MRIs from 3,893 healthy adults, we found no evidence for an association between sleep duration and brain atrophy. In contrast, cross-sectional analyses (51,295 observations) showed inverse U-shaped relationships, where a duration of 6.5 (95% confidence interval, (5.7, 7.3)) hours was associated with the thickest cortex and largest volumes relative to intracranial volume. This fits converging evidence from research on mortality, health and cognition that points to roughly seven hours being associated with good health. Genome-wide association analyses suggested that genes associated with longer sleep for below-average sleepers were linked to shorter sleep for above-average sleepers. Mendelian randomization did not yield evidence for causal impacts of sleep on brain structure. The combined results challenge the notion that habitual short sleep causes brain atrophy, suggesting that normal brains promote adequate sleep duration-which is shorter than current recommendations.

Effects of sleep on brain perivascular space in a cognitively healthy population

The magnetic resonance imaging (MRI) visible perivascular space (PVS) reportedly clears amyloid-β and metabolic waste during sleep. Previous studies reported an association between sleep and the PVS in small vessel disease, traumatic brain injury, and Alzheimer's disease. However, this relationship in a healthy cohort is still unclear. Here, we used the Human Connectome Project Aging dataset to analyze the relationship between sleep and the PVS in cognitively healthy adults across the aging continuum. We measured sleep parameters using the self-reported Pittsburgh Sleep Quality Index questionnaire. We found that older adults who had better sleep quality and sleep efficiency presented with a larger PVS volume fraction in the basal ganglia (BG). However, sleep measures were not associated with PVS volume fraction in the centrum semiovale (CSO). In addition, we found that body mass index (BMI) influenced the BG-PVS across middle-aged and older participants. In the entire cognitively healthy cohort, the effect of sleep quality on PVS volume fraction was mediated by BMI. However, BMI did not influence this effect in the older cohort. Furthermore, there are significant differences in PVS volume fraction across racial/ethnic cohorts. In summary, the effect of sleep on the PVS volume alteration was different in the middle-aged adults and older adults.

Closed-loop auditory stimulation of sleep slow oscillations: Basic principles and best practices

Sleep is essential for our physical and mental well-being. During sleep, despite the paucity of overt behavior, our brain remains active and exhibits a wide range of coupled brain oscillations. In particular slow oscillations are characteristic for sleep, however whether they are directly involved in the functions of sleep, or are mere epiphenomena, is not yet fully understood. To disentangle the causality of these relationships, experiments utilizing techniques to detect and manipulate sleep oscillations in real-time are essential. In this review, we first overview the theoretical principles of closed-loop auditory stimulation (CLAS) as a method to study the role of slow oscillations in the functions of sleep. We then describe technical guidelines and best practices to perform CLAS and analyze results from such experiments. We further provide an overview of how CLAS has been used to investigate the causal role of slow oscillations in various sleep functions. We close by discussing important caveats, open questions, and potential topics for future research.

Re-examining the role of the dorsal fan-shaped body in promoting sleep in Drosophila

The needs fulfilled by sleep are unknown, though the effects of insufficient sleep are manifold. To better understand how the need to sleep is sensed and discharged, much effort has gone into identifying the neural circuits involved in regulating arousal, especially those that promote sleep. In prevailing models, the dorsal fan-shaped body (dFB) plays a central role in this process in the fly brain. In the present study we manipulated various properties of the dFB including its electrical activity, synaptic output, and endogenous gene expression. In each of these experimental contexts we were unable to identify any effect on sleep that could be unambiguously mapped to the dFB. Furthermore, we found evidence that sleep phenotypes previously attributed to the dFB were caused by genetic manipulations that inadvertently targeted the ventral nerve cord. We also examined expression of two genes whose purported effects have been attributed to functions within a specific subpopulation of dFB neurons. In both cases we found little to no expression in the expected cells. Collectively, our results cast doubt on the prevailing hypothesis that the dFB plays a central role in promoting sleep.

The Hierarchy of Coupled Sleep Oscillations Reverses with Aging in Humans

A well orchestrated coupling hierarchy of slow waves and spindles during slow-wave sleep supports memory consolidation. In old age, the duration of slow-wave sleep and the number of coupling events decrease. The coupling hierarchy deteriorates, predicting memory loss and brain atrophy. Here, we investigate the dynamics of this physiological change in slow wave-spindle coupling in a frontocentral electroencephalography position in a large sample (N = 340; 237 females, 103 males) spanning most of the human life span (age range, 15-83 years). We find that, instead of changing abruptly, spindles gradually shift from being driven by slow waves to driving slow waves with age, reversing the coupling hierarchy typically seen in younger brains. Reversal was stronger the lower the slow-wave frequency, and starts around midlife (age range, ∼40-48 years), with an established reversed hierarchy between 56 and 83 years of age. Notably, coupling strength remains unaffected by age. In older adults, deteriorating slow wave-spindle coupling, measured using the phase slope index (PSI) and the number of coupling events, is associated with blood plasma glial fibrillary acidic protein levels, a marker for astrocyte activation. Data-driven models suggest that decreased sleep time and higher age lead to fewer coupling events, paralleled by increased astrocyte activation. Counterintuitively, astrocyte activation is associated with a backshift of the coupling hierarchy (PSI) toward a "younger" status along with increased coupling occurrence and strength, potentially suggesting compensatory processes. As the changes in coupling hierarchy occur gradually starting at midlife, we suggest there exists a sizable window of opportunity for early interventions to counteract undesirable trajectories associated with neurodegeneration.SIGNIFICANCE STATEMENT Evidence accumulates that sleep disturbances and cognitive decline are bidirectionally and causally linked, forming a vicious cycle. Improving sleep quality could break this cycle. One marker for sleep quality is a clear hierarchical structure of sleep oscillations. Previous studies showed that sleep oscillations decouple in old age. Here, we show that, rather, the hierarchical structure gradually shifts across the human life span and reverses in old age, while coupling strength remains unchanged. This shift is associated with markers for astrocyte activation in old age. The shifting hierarchy resembles brain maturation, plateau, and wear processes. This study furthers our comprehension of this important neurophysiological process and its dynamic evolution across the human life span.

[Application of Polysomnography in Common Neurodegenerative Diseases]

At present, the etiology and pathogenesis of most neurodegenerative diseases are still not fully understood, which poses challenges for the prevention, diagnosis, and treatment of these diseases. Sleep disorders are one of the common chief complaints of neurodegenerative diseases. When patients suffer from comorbid sleep disorder and neurodegenerative diseases, the severity of their condition increases, the quality of their life drops further, and the difficulty of treatment increases. A large number of studies have been conducted to monitor the sleep of patients with neurodegenerative diseases, and it has been found that there are significant changes in their polysomnography (PSG) results compared to those of healthy control populations. In addition, there are also significant differences between the PSG findings of patients with different neurodegenerative diseases and the differences are closely associated with the pathogenesis and development of the disease. Herein, we discussed the characteristics of the sleep structure of patients with Parkinson's disease, Alzheimer's disease, Huntington's disease, and dementia with Lewy bodies and provided a brief review of the sleep disorders and the PSG characteristics of these patients. The paper will help improve the understanding of the pathogenesis and pathological changes of neurodegenerative diseases, clarify the relationship between sleep disorders and these diseases, improve clinicians' further understanding of these diseases, and provide a basis for future research.

Sleep Dysregulation Is Associated with 18F-FDG PET and Cerebrospinal Fluid Biomarkers in Alzheimer's Disease

Background

Sleep impairment has been commonly reported in Alzheimer's disease (AD) patients. The association between sleep dysregulation and AD biomarkers has been separately explored in mild cognitive impairment (MCI) and AD patients.

Objective

The present study investigated cerebrospinal-fluid (CSF) and 18F-fluoro-deoxy-glucose positron emission tomography (18F-FDG-PET) biomarkers in MCI and AD patients in order to explore their association with sleep parameters measured with polysomnography (PSG).

Methods

MCI and AD patients underwent PSG, 18F-FDG-PET, and CSF analysis for detecting and correlating these biomarkers with sleep architecture.

Results

Thirty-five patients were included in the study (9 MCI and 26 AD patients). 18F-FDG uptake in left Brodmann area 31 (owing to the posterior cingulate cortex) correlated negatively with REM sleep latency (p = 0.013) and positively with REM sleep (p = 0.033). 18F-FDG uptake in the hippocampus was negatively associated with sleep onset latency (p = 0.041). Higher CSF orexin levels were associated with higher sleep onset latency (p = 0.042), Non-REM stage 1 of sleep (p = 0.031), wake after sleep onset (p = 0.028), and lower sleep efficiency (p = 0.045). CSF levels of Aβ42 correlated negatively with the wake bouts index (p = 0.002). CSF total-tau and phosphorylated tau levels correlated positively with total sleep time (p = 0.045) and time in bed (p = 0.031), respectively.

Conclusion

Sleep impairment, namely sleep fragmentation, REM sleep dysregulation, and difficulty in initiating sleep correlates with AD biomarkers, suggesting an effect of sleep on the pathological processes in different AD stages. Targeting sleep for counteracting the AD pathological processes represents a timely need for clinicians and researchers.

Using gamma-band transcranial alternating current stimulation (tACS) to improve sleep quality and cognition in patients with mild neurocognitive disorders due to Alzheimer's disease: A study protocol for a randomized controlled trial

BACKGROUND

Sleep disturbances are highly prevalent in patients with age-related neurodegenerative diseases, which severely affect cognition and even lead to accumulated β-amyloid. Encouraging results from recent studies on transcranial direct current stimulation (tDCS) showed moderate positive effects on sleep quality in preclinical Alzheimer's disease (AD). Compared to tDCS, transcranial alternating current stimulation (tACS) enables the entrainment of neuronal activity with optimized focality through injecting electric current with a specific frequency and has significant enhancement effects on slow wave activities.

METHODS AND DESIGN

This is a randomized, double-blind, sham-controlled clinical trial comparing 40 Hz tACS with tDCS in mild neurocognitive disorders due to AD with sleep disturbances. Magnetic resonance imaging (MRI) data is used to construct personalized realistic head model. Treatment outcomes, including sleep quality, cognitive performance and saliva Aβ levels will be conducted at baseline, 4th week, 8th week, 12th week and 24th week.

CONCLUSIONS

It is expected that the repeated gamma-band tACS will show significant improvements in sleep quality and cognitive functions compared to tDCS and sham tDCS. The findings will provide high-level evidence and guide further advanced studies in the field of neurodegenerative diseases and sleep medicine.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT05544201.

NREM sleep loss increases neurofilament light chain levels in APP/PS1 and C57BL/6 J mice

PURPOSE

Sleep disturbances exacerbate the progression of Alzheimer's disease (AD), but disturbances of non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep may have different effects. Neurofilament light chain (NfL), an axon-specific protein, is an indicator of the severity of neuronal apoptosis. To investigate whether or not NREM or REM sleep is crucial to neuronal survival, we examined the effects of induced NREM or REM sleep loss on NfL levels in APP/PS1 mice, a model of AD, and their wild-type (WT) C57BL/6 J littermates.

METHODS

At 6 months of age, WT mice and AD mice were equally divided into six groups, namely, the WT-normal sleep (S), WT-total sleep deprivation (TSD), WT-REM deprivation (RD), AD-S, AD-TSD and AD-RD groups, according to the type of sleep intervention applied. All mice underwent 6 days of sleep intervention. Cerebrospinal fluid (CSF) and plasma NfL levels were measured at baseline and on days 2, 4 and 6, and spatial memory was assessed in the Morris water maze (MWM) test.

RESULTS

Among the 18 WT and 18 AD mice, CSF and plasma NfL levels were higher in AD-TSD mice than in AD-S or AD-RD mice, while no significant difference was observed between the latter two groups. In AD-TSD mice, CSF and plasma NfL levels increased with the duration of sleep deprivation. A similar pattern of results was observed for the WT groups.

CONCLUSIONS

NREM sleep loss may increase CSF and plasma NfL levels in both WT and AD mice.

International Consensus Statement on Obstructive Sleep Apnea

BACKGROUND

Evaluation and interpretation of the literature on obstructive sleep apnea (OSA) allows for consolidation and determination of the key factors important for clinical management of the adult OSA patient. Toward this goal, an international collaborative of multidisciplinary experts in sleep apnea evaluation and treatment have produced the International Consensus statement on Obstructive Sleep Apnea (ICS:OSA).

METHODS

Using previously defined methodology, focal topics in OSA were assigned as literature review (LR), evidence-based review (EBR), or evidence-based review with recommendations (EBR-R) formats. Each topic incorporated the available and relevant evidence which was summarized and graded on study quality. Each topic and section underwent iterative review and the ICS:OSA was created and reviewed by all authors for consensus.

RESULTS

The ICS:OSA addresses OSA syndrome definitions, pathophysiology, epidemiology, risk factors for disease, screening methods, diagnostic testing types, multiple treatment modalities, and effects of OSA treatment on multiple OSA-associated comorbidities. Specific focus on outcomes with positive airway pressure (PAP) and surgical treatments were evaluated.

CONCLUSION

This review of the literature consolidates the available knowledge and identifies the limitations of the current evidence on OSA. This effort aims to create a resource for OSA evidence-based practice and identify future research needs. Knowledge gaps and research opportunities include improving the metrics of OSA disease, determining the optimal OSA screening paradigms, developing strategies for PAP adherence and longitudinal care, enhancing selection of PAP alternatives and surgery, understanding health risk outcomes, and translating evidence into individualized approaches to therapy.

A State-of-Art Review of the Vicious Circle of Sleep Disorders, Diabetes and Neurodegeneration Involving Metabolism and Microbiota Alterations

In the context of neurodegenerative disorders, cognitive decline is frequently reported in older population. Recently, numerous metabolic pathways have been implicated in neurodegeneration, including signaling disruption of insulin and other glucose-regulating hormones. In fact, Alzheimer's disease has now been considered as "type-3 diabetes". In this review, we tried to clarify the role of sleep impairment as the third major player in the complex relationship between metabolic and neurodegenerative diseases. Altered sleep may trigger or perpetuate these vicious mechanisms, leading to the development of both dementia and type 2 diabetes mellitus. Finally, we analyzed these reciprocal interactions considering the emerging role of the gut microbiota in modulating the same processes. Conditions of dysbiosis have been linked to circadian rhythm disruption, metabolic alterations, and release of neurotoxic products, all contributing to neurodegeneration. In a future prospective, gut microbiota could provide a major contribution in explaining the tangled relationship between sleep disorders, dementia and diabetes.

Investigating the relationship between sleep disturbances and white matter hyperintensities in older adults on the Alzheimer's disease spectrum

Background

While studies report that sleep disturbance can have negative effects on brain vasculature, its impact on cerebrovascular disease such as white matter hyperintensities (WMHs) in beta-amyloid positive older adults remains unexplored.

Methods

Linear regressions, mixed effects models, and mediation analysis examined the crosssectional and longitudinal associations between sleep disturbance, cognition, and WMH burden, and cognition in normal controls (NCs), mild cognitive impairment (MCI), and Alzheimer's disease (AD) at baseline and longitudinally.

Results

People with AD reported more sleep disturbance than NC and MCI. AD with sleep disturbance had more WMHs than AD without sleep disturbances. Mediation analysis revealed an effect of regional WMH burden on the relationship between sleep disturbance and future cognition.

Conclusion

These results suggest that WMH burden and sleep disturbance increases from aging to AD. Sleep disturbance decreases cognition through increases in WMH burden. Improved sleep could mitigate the impact of WMH accumulation and cognitive decline.

Variability in objective sleep is associated with Alzheimer's pathology and cognition

Both sleep duration and sleep efficiency have been associated with risk of Alzheimer's disease, suggesting that interventions to promote optimal sleep may be a way to reduce Alzheimer's disease risk. However, studies often focus on average sleep measures, usually from self-report questionnaires, ignoring the role of intra-individual variability in sleep across nights quantified from objective sleep measures. The current cross-sectional study sought to investigate the role of intra-individual variability in accelerometer-based objective sleep duration and sleep efficiency in relation to in vivo Alzheimer's disease pathology (β-amyloid and tau) using positron emission tomography imaging and cognition (working memory, inhibitory control, verbal memory, visual memory and global cognition). To examine these relationships, we evaluated 52 older adults (age = 66.4 ± 6.89, 67% female, 27% apolipoprotein E4 carriers) with objective early mild cognitive impairment. Modifying effects of apolipoprotein E4 status were also explored. Less intra-individual variability in sleep duration was associated with lower β-amyloid burden, higher global cognition and better inhibitory control, with a trend for lower tau burden. Less intra-individual variability in sleep efficiency was associated with lower β-amyloid burden, higher global cognition and better inhibitory control, but not with tau burden. Longer sleep duration was associated with better visual memory and inhibitory control. Apolipoprotein E4 status significantly modified the association between intra-individual variability in sleep efficiency and β-amyloid burden, such that less sleep efficiency variability was associated with lower β-amyloid burden in apolipoprotein E4 carriers only. There was a significant interaction between sleep duration and apolipoprotein E4 status, suggesting that longer sleep duration is more strongly associated with lower β-amyloid burden in apolipoprotein E4 carriers relative to non-carriers. These results provide evidence that lower intra-individual variability in both sleep duration and sleep efficiency and longer mean sleep duration are associated with lower levels of β-amyloid pathology and better cognition. The relationships between sleep duration and intra-individual variability in sleep efficiency with β-amyloid burden differ by apolipoprotein E4 status, indicating that longer sleep duration and more consistent sleep efficiency may be protective against β-amyloid burden in apolipoprotein E4 carriers. Longitudinal and causal studies are needed to better understand these relationships. Future work should investigate factors contributing to intra-individual variability in sleep duration and sleep efficiency in order to inform intervention studies.

Mapping Sleep's Oscillatory Events as a Biomarker of Alzheimer's Disease

Objective

Memory-associated neural circuits produce oscillatory events within single-channel sleep electroencephalography (EEG), including theta bursts (TBs), sleep spindles (SPs) and multiple subtypes of slow waves (SWs). Changes in the temporal "coupling" of these events are proposed to serve as a biomarker for early stages of Alzheimer's disease (AD) pathogenesis.

Methods

We analyzed data from 205 aging adults, including single-channel sleep EEG, cerebrospinal fluid (CSF) AD-associated biomarkers, and Clinical Dementia Rating® (CDR®) scale. Individual SW events were sorted into high and low transition frequencies (TF) subtypes. We utilized time-frequency spectrogram locations within sleep EEG to "map" the precision of SW-TB and SW-SP neural circuit coupling in relation to amyloid positivity (by CSF Aβ 42 /Aβ 40 threshold), cognitive impairment (by CDR), and CSF levels of AD-associated biomarkers.

Results

Cognitive impairment was associated with lower TB spectral power in both high and low TF SW-TB coupling (p<0.001, p=0.001). Cognitively unimpaired, amyloid positive aging adults demonstrated lower precision of the neural circuits propagating high TF SW-TB (p<0.05) and low TF SW-SP (p<0.005) event coupling, compared to cognitively unimpaired amyloid negative individuals. Biomarker correlations were significant for high TF SW-TB coupling with CSF Aβ 42 /Aβ 40 (p=0.005), phosphorylated-tau 181 (p<0.005), and total-tau (p<0.05). Low TF SW-SP coupling was also correlated with CSF Aβ 42 /Aβ 40 (p<0.01).

Interpretation

Loss of integrity in neural circuits underlying sleep-dependent memory processing can be measured for both SW-TB and SW-SP coupling in spectral time-frequency space. Breakdown of sleep's memory circuit integrity is associated with amyloid positivity, higher levels of AD-associated pathology, and cognitive impairment.

Childhood Dementia: A Collective Clinical Approach to Advance Therapeutic Development and Care

Childhood dementias are a group of over 100 rare and ultra-rare pediatric conditions that are clinically characterized by chronic global neurocognitive decline. This decline is associated with a progressive loss of skills and shortened life expectancy. With an estimated incidence of one in 2800 births and less than 5% of the conditions having disease-modifying therapies, the impact is profound for patients and their families. Traditional research, care, and advocacy efforts have focused on individual disorders, or groups classified by molecular pathogenesis, and this has established robust foundations for further progress and collaboration. This review describes the shared and disease-specific clinical changes contributing to childhood dementia and considers these as potential indicators of underlying pathophysiologic processes. Like adult neurodegenerative syndromes, the heterogeneous phenotypes extend beyond cognitive decline and may involve changes in eating, motor function, pain, sleep, and behavior, mediated by physiological changes in neural networks. Importantly, these physiological phenotypes are associated with significant carer stress, anxiety, and challenges in care. These phenotypes are also pertinent for the development of therapeutics and optimization of best practice management. A collective approach to childhood dementia is anticipated to identify relevant biomarkers of prognosis or therapeutic efficacy, streamline the path from preclinical studies to clinical trials, increase opportunities for the development of multiple therapeutics, and refine clinical care.

Exposure to Low Levels of Radiofrequency Electromagnetic Fields Emitted from Cell-phones as a Promising Treatment of Alzheimer's Disease: A Scoping Review Study

BACKGROUND

Alzheimer's disease (AD) is one of the most significant public health concerns and tremendous economic challenges. Studies conducted over the past decades show that exposure to radiofrequency electromagnetic fields (RF-EMFs) may relieve AD symptoms.

OBJECTIVE

To determine if exposure to RF-EMFs emitted by cellphones affect the risk of AD.

MATERIAL AND METHODS

In this review, all relevant published articles reporting an association of cell phone use with AD were studied. We systematically searched international datasets to identify relevant studies. Finally, 33 studies were included in the review. Our review discusses the effects of RF-EMFs on the amyloid β (Aβ), oxidative stress, apoptosis, reactive oxygen species (ROS), neuronal death, and astrocyte responses. Moreover, the role of exposure parameters, including the type of exposure, its duration, and specific absorption rate (SAR), are discussed.

RESULTS

Progressive factors of AD such as Aβ, myelin basic protein (MBP), nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, and neurofilament light polypeptide (NFL) were decreased. While tau protein showed no change, factors affecting brain activity such as glial fibrillary acidic protein (GFAP), mitogen-activated protein kinases (MAPKs), cerebral blood flow (CBF), brain temperature, and neuronal activity were increased.

CONCLUSION

Exposure to low levels of RF-EMFs can reduce the risk of AD by increasing MAPK and GFAP and decreasing MBP. Considering the role of apoptosis in AD and the effect of RF-EMF on the progression of the process, this review indicates the positive effect of these exposures.

Sleep benefits different stages of memory in Drosophila

Understanding the physiological mechanisms that modulate memory acquisition and consolidation remains among the most ambitious questions in neuroscience. Massive efforts have been dedicated to deciphering how experience affects behavior, and how different physiological and sensory phenomena modulate memory. Our ability to encode, consolidate and retrieve memories depends on internal drives, and sleep stands out among the physiological processes that affect memory: one of the most relatable benefits of sleep is the aiding of memory that occurs in order to both prepare the brain to learn new information, and after a learning task, to consolidate those new memories. Drosophila lends itself to the study of the interactions between memory and sleep. The fruit fly provides incomparable genetic resources, a mapped connectome, and an existing framework of knowledge on the molecular, cellular, and circuit mechanisms of memory and sleep, making the fruit fly a remarkable model to decipher the sophisticated regulation of learning and memory by the quantity and quality of sleep. Research in Drosophila has stablished not only that sleep facilitates learning in wild-type and memory-impaired animals, but that sleep deprivation interferes with the acquisition of new memories. In addition, it is well-accepted that sleep is paramount in memory consolidation processes. Finally, studies in Drosophila have shown that that learning itself can promote sleep drive. Nevertheless, the molecular and network mechanisms underlying this intertwined relationship are still evasive. Recent remarkable work has shed light on the neural substrates that mediate sleep-dependent memory consolidation. In a similar way, the mechanistic insights of the neural switch control between sleep-dependent and sleep-independent consolidation strategies were recently described. This review will discuss the regulation of memory by sleep in Drosophila, focusing on the most recent advances in the field and pointing out questions awaiting to be investigated.

The promise of portable remote auditory stimulation tools to enhance slow-wave sleep and prevent cognitive decline

Dementia is the seventh leading cause of mortality, and a major source of disability and dependency in older individuals globally. Cognitive decline (and, to a lesser extent, normal ageing) are associated with sleep fragmentation and loss of slow-wave sleep. Evidence suggests a bidirectional causal link between these losses. Phase-locked auditory stimulation has emerged as a promising non-invasive tool to enhance slow-wave sleep, potentially ameliorating cognitive decline. In laboratory settings, auditory stimulation is usually supervised by trained experts. Different algorithms (simple amplitude thresholds, topographic correlation, sine-wave fitting, phase-locked loop, and phase vocoder) are used to precisely target auditory stimulation to a desired phase of the slow wave. While all algorithms work well in younger adults, the altered sleep physiology of older adults and particularly those with neurodegenerative disorders requires a tailored approach that can adapt to older adults' fragmented sleep and reduced amplitudes of slow waves. Moreover, older adults might require a continuous intervention that is not feasible in laboratory settings. Recently, several auditory stimulation-capable portable devices ('Dreem®', 'SmartSleep®' and 'SleepLoop®') have been developed. We discuss these three devices regarding their potential as tools for science, and as clinical remote-intervention tools to combat cognitive decline. Currently, SleepLoop® shows the most promise for scientific research in older adults due to high transparency and customizability but is not commercially available. Studies evaluating down-stream effects on cognitive abilities, especially in patient populations, are required before a portable auditory stimulation device can be recommended as a clinical preventative remote-intervention tool.

Sleep slow waves' negative-to-positive-phase transition: a marker of cognitive and apneic status in aging

The sleep slow-wave (SW) transition between negative and positive phases is thought to mirror synaptic strength and likely depends on brain health. This transition shows significant age-related changes but has not been investigated in pathological aging. The present study aimed at comparing the transition speed and other characteristics of SW between older adults with amnestic mild cognitive impairment (aMCI) and cognitively normal (CN) controls with and without obstructive sleep apnea (OSA). We also examined the association of SW characteristics with the longitudinal changes of episodic memory and executive functions and the degree of subjective cognitive complaints. aMCI (no/mild OSA = 17; OSA = 15) and CN (no/mild OSA = 20; OSA = 17) participants underwent a night of polysomnography and a neuropsychological evaluation at baseline and 18 months later. Participants with aMCI had a significantly slower SW negative-to-positive-phase transition speed and a higher proportion of SW that are "slow-switchers" than CN participants. These SW measures in the frontal region were significantly correlated with memory decline and cognitive complaints in aMCI and cognitive improvements in CN participants. The transition speed of the SW that are "fast-switchers" was significantly slower in OSA compared to no or mild obstructive sleep apnea participants. The SW transition-related metrics showed opposite correlations with the longitudinal episodic memory changes depending on the participants' cognitive status. These relationships were particularly strong in participants with aMCI. As the changes of the SW transition-related metrics in pathological aging might reflect synaptic alterations, future studies should investigate whether these new metrics covary with biomarker levels of synaptic integrity in this population.

Comparison of polysomnography in people with Alzheimer's disease and insomnia versus non-demented elderly people with insomnia

BACKGROUND

We used baseline polysomnography (PSG) data obtained during the clinical program development for suvorexant to compare the PSG profiles of people with Alzheimer's disease and insomnia (ADI) versus age-matched elderly individuals with insomnia (EI).

METHODS

Sleep laboratory baseline PSG data from participants age 55-80 years from 2 trials in people with insomnia and a trial in people with ADI were included. ADI participants had dementia of mild-to-moderate severity. Diagnostic criteria for insomnia, exclusion for other sleep problems, PSG recording procedures, and endpoint derivations were similar across the trials. All participants underwent a night of in-laboratory PSG prior to the baseline night to allow for screening/adaptation. Participants in the EI and ADI groups were compared with regard to sleep architecture, sleep micro-structure, and quantitative EEG power spectral endpoints. The analysis was performed on a post hoc basis using propensity score matching to compare sleep parameters separately in women and men while accounting for age group and total sleep time.

RESULTS

A total of 837 EI and 239 ADI participants were included, with the majority in each population (∼65%) being women. Compared to EI, those with ADI had a lower percentage of time spent in slow wave sleep (and a corresponding higher percentage of time spent in the lighter N1 sleep), a lower number of spindles per minute of N2 sleep, and lower absolute EEG power during NREM sleep, particularly in the lower-frequency bands. Trends for lower REM sleep percentage in ADI did not reach statistical significance.

CONCLUSIONS

Our findings in this large data set, in which the influence of sleep problems was effectively subtracted out (since both groups had insomnia), provide strong confirmatory support of results from previous smaller studies in indicating that AD of mild-to-moderate severity is associated with less slow wave sleep, spindles, and lower-frequency EEG power.

TRIAL REGISTRATION

ClinicalTrials.gov, numbers NCT01097616, NCT01097629, NCT02750306.