Advanced Circadian Timing and Sleep Fragmentation Differentially Impact on Memory Complaint Subtype in Subjective Cognitive Decline

Shedding light on neurofilament involvement in cognitive decline in obstructive sleep apnea and its possible role as a biomarker

Obstructive sleep apnea is one of the most common sleep disorders with a high estimated global prevalence and a large number of associated comorbidities in general as well as specific neuropsychiatric complications such as cognitive impairment. The complex pathogenesis and effects of the disorder including chronic intermittent hypoxia and sleep fragmentation may lead to enhanced neuronal damage, thereby contributing to neuropsychiatric pathologies. Obstructive sleep apnea has been described as an independent risk factor for several neurodegenerative diseases, including Alzheimer's disease and all-cause dementia. The influence of obstructive sleep apnea on cognitive deficits is still a topic of recent debate, and several mechanisms, including neurodegeneration and depression-related cognitive dysfunction, underlying this correlation are taken into consideration. The differentiation between both pathomechanisms of cognitive impairment in obstructive sleep apnea is a complex clinical issue, requiring the use of multiple and costly diagnostic methods. The studies conducted on neuroprotection biomarkers, such as brain-derived neurotrophic factors and neurofilaments, are recently gaining ground in the topic of cognition assessment in obstructive sleep apnea patients. Neurofilaments as neuron-specific cytoskeletal proteins could be useful non-invasive indicators of brain conditions and neurodegeneration, which already are observed in many neurological diseases leading to cognitive deficits. Additionally, neurofilaments play an important role as a biomarker in other sleep disorders such as insomnia. Thus, this review summarizes the current knowledge on the involvement of neurofilaments in cognitive decline and neurodegeneration in obstructive sleep apnea patients as well as discusses its possible role as a biomarker of these changes.

Cognitive complaints in older adults in primary care and associated factors

Cognitive complaints are common in older people. They can progress into a more severe cognitive decline and then deterioration of quality of life. They are associated with several factors.

Objective

This study aimed to determine the factors associated with cognitive complaints in older adults in the city of Marrakech, Morocco.

Methods

This study was conducted between March and June 2022 among 281 people aged 50 years and older who attended primary health care centers in the city of Marrakech. Cognitive complaints were measured using the McNair-Kahn scale. Data on sociodemographic and clinical characteristics were collected through interviews with the participants and consultation of their medical records. Analysis was done using Statistical Package for Social Sciences (SPSS) version 25, Ink software.

Results

Of the total participants, 51.6% had cognitive complaints. Multivariate analysis showed that people aged 75 years and over had a sevenfold higher risk of cognitive complaints than people aged 50-64 years (p=0.033; OR=7.64; 95%CI 1.17-49.72), and that illiteracy (p=0.004; OR=3.39; 95%CI 1.48-7.76), cardiovascular disease (p=0.018; OR=4.30; 95%CI 1.29-14.32), diabetes (p=0.001; OR=3.14; 95%CI 1.64-6.04), visual impairment (p=0.017; OR=2.22; 95%CI 1.15-4.19), depression (p= 0.027; OR=2.36; 95%CI 1.10-5.05) and sleepiness (p=0.034; OR=1.96; 95%CI 1.05-3.66) are associated variables.

Conclusions

Cognitive complaints are frequent in older adults and are associated with several sociodemographic and health factors. Some measures could help maintain stable memory performance in old age and prevent severe cognitive declines, such as regular follow-up of at-risk individuals, and cognitive, physical and leisure activities.

Associations between objectively measured sleep parameters and cognition in healthy older adults: A meta-analysis

Multiple studies have examined associations between sleep and cognition in older adults, but a majority of these depend on self-reports on sleep and utilize cognitive tests that assess overall cognitive function. The current meta-analysis involved 72 independent studies and sought to quantify associations between objectively measured sleep parameters and cognitive performance in healthy older adults. Both sleep macrostructure (e.g., sleep duration, continuity, and stages) and microstructure (e.g., slow wave activity and spindle activity) were evaluated. For macrostructure, lower restlessness at night was associated with better memory performance (r = 0.43, p = 0.02), while lower sleep onset latency was associated with better executive functioning (r = 0.28, p = 0.03). Greater relative amount of N2 and REM sleep, but not N3, positively correlated with cognitive performance. The association between microstructure and cognition in older adults was marginally significant. This relationship was moderated by age (z = 0.07, p < 0.01), education (z = 0.26, p = 0.03), and percentage of female participants (z = 0.01, p < 0.01). The current meta-analysis emphasizes the importance of considering objective sleep measures to understand the relationship between sleep and cognition in healthy older adults. These results also form a base from which researchers using wearable sleep technology and measuring behavior through computerized testing tools can evaluate their findings.

Brain Photobiomodulation Improves Sleep Quality in Subjective Cognitive Decline: A Randomized, Sham-Controlled Study

Background: Sleep appears to be a sensitive biomarker that facilitates early detection and effective intervention for Alzheimer’s disease, while subjective cognitive decline (SCD) is a risk factor for Alzheimer’s disease. Prefrontal cortex atrophy is associated with both sleep disruption and cognitive decline. Transcranial brain photobiomodulation (PBM) therapy can enhance frontal cortex oxygen consumption, increasing frontal cortex mediated memory function. Objective: This study aimed to test whether PBM therapy targeting the frontal cortex could improve sleep and cognitive function in SCD. Methods: Fifty-eight SCDs were divided into the PBM group (N = 32) in which real light therapy was administered and a sham light therapy group (N = 26). All the participants received either real light or sham light therapy for 6 days consecutively, while the sleep data were recorded. The n-back task was employed to measure each participant’s working memory. Results: We found no differences in sleep efficiency change (F = 211, p = 0.279), REM stage percent change (F = 420, p = 0.91), and wake-up time (F = 212, p = 0.277) between the two groups. The sleep efficiency and REM were improved within the true light group on the fifth day. The true light group perform better than the control group in the n-back test, the accuracy was higher in the 2-back test (88.6% versus 79.6%, p = 0.001), and the reaction time in 1-back was shorter (544.80±202.00 versus 592.87±222.05, p = 0.003). Conclusion: After five days of PBM therapy targeting the prefrontal cortex, sleep efficiency and N-back cognitive performance were improved on the fifth day.

Involvement of the adenosine A1 receptor in the hypnotic effect of rosmarinic acid

Insomnia, the most common sleep disorder, is characterized by a longer sleep latency, greater sleep fragmentation, and consequent excessive daytime fatigue. Due to the various side effects of prescribed hypnotics, demand for new drugs is still high. Recent studies have suggested the adenosine receptor (AR) as a potential therapeutic target for insomnia, however, clinically useful hypnotics targeting AR are not yet available. In the present study, we evaluated the hypnotic effect of rosmarinic acid, a phenolic compound widely found in medicinal plants, through pentobarbital-induced sleep test, electroencephalography/electromyography (EEG/EMG), and immunohistochemistry in mice. The underlying mechanisms were assessed by pharmacological approach using 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) and SCH5826, antagonists for A1R and A2AR, respectively. Receptor-binding assay and functional agonism were also performed. Our study provides a new evidence that rosmarinic acid has a direct binding activity (Ki = 14.21 ± 0.3 μM) and agonistic activity for A1R. We also found that rosmarinic acid significantly decreased sleep fragmentation and onset latency to NREM sleep, and these effects were abolished by DPCPX. The results from c-Fos immunostaining showed that rosmarinic acid decreased the neuronal activity in wake-promoting brain regions, such as the basal forebrain and the lateral hypothalamus, while increasing the neuronal activity in the ventrolateral preoptic nucleus, a sleep-promoting region; all these effects were significantly inhibited by DPCPX. Taken together, this study suggests that rosmarinic acid possesses novel activity as an A1R agonist and thereby exerts a hypnotic effect, and thus it may serve as a potential therapeutic agent for insomnia through targeting A1R.

Subjective Cognitive Decline: Level of Risk for Future Dementia and Mild Cognitive Impairment, a Meta-Analysis of Longitudinal Studies

Subjective Cognitive Decline (SCD) in older adults has been identified as a risk factor for dementia, although the literature is inconsistent, and it is unclear which factors moderate progression from SCD to dementia. Through separate meta-analyses, we aimed to determine if SCD increased the risk of developing dementia or mild cognitive impairment (MCI). Furthermore, we examined several possible moderators. Longitudinal studies of participants with SCD at baseline, with data regarding incident dementia or MCI, were extracted from MEDLINE and PsycINFO. Articles were excluded if SCD occurred solely in the context of dementia, MCI, or as part of a specific disease. Pooled estimates were calculated using a random-effects model, with moderator analyses examining whether risk varied according to SCD definition, demographics, genetics, recruitment source, and follow-up duration. Risk of study bias was assessed using the Quality Assessment of Diagnostic Accuracy Studies (QUADAS)-2 tool. 46 studies with more than 74,000 unique participants were included. SCD was associated with increased risk of developing dementia (HR = 1.90, 95% CI 1.52-2.36; OR = 2.48, 95% CI 1.97-3.14) and MCI (HR = 1.73, 95% CI 1.18-2.52; OR = 1.83, 95% CI 1.56-2.16). None of the potential moderating factors examined influenced the HR or OR of developing dementia. In contrast, including worry in the definition of SCD, younger age, and recruitment source impacted the OR of developing MCI, with clinic samples demonstrating highest risk. SCD thus represents an at-risk phase, ideal for early intervention, with further research required to identify effective interventions for risk reduction, and cognitive-behavioural interventions for cognitive management. PROSPERO, protocol number: CRD42016037993.

Sleep in Normal Aging, Homeostatic and Circadian Regulation and Vulnerability to Sleep Deprivation

In the context of geriatric research, a growing body of evidence links normal age-related changes in sleep with many adverse health outcomes, especially a decline in cognition in older adults. The most important sleep alterations that continue to worsen after 60 years involve sleep timing, (especially early wake time, phase advance), sleep maintenance (continuity of sleep interrupted by numerous awakenings) and reduced amount of sigma activity (during non-rapid eye movement (NREM) sleep) associated with modifications of sleep spindle characteristics (density, amplitude, frequency) and spindle-Slow Wave coupling. After 60 years, there is a very clear gender-dependent deterioration in sleep. Even if there are degradations of sleep after 60 years, daytime wake level and especially daytime sleepiness is not modified with age. On the other hand, under sleep deprivation condition, older adults show smaller cognitive impairments than younger adults, suggesting an age-related lower vulnerability to extended wakefulness. These sleep and cognitive age-related modifications would be due to a reduced homeostatic drive and consequently a reduced sleep need, an attenuation of circadian drive (reduction of sleep forbidden zone in late afternoon and wake forbidden zone in early morning), a modification of the interaction of the circadian and homeostatic processes and/or an alteration of subcortical structures involved in generation of circadian and homeostatic drive, or connections to the cerebral cortex with age. The modifications and interactions of these two processes with age are still uncertain, and still require further investigation. The understanding of the respective contribution of circadian and homeostatic processes in the regulation of neurobehavioral function with aging present a challenge for improving health, management of cognitive decline and potential early chronobiological or sleep-wake interventions.

Older Adults' Subjective Cognitive Decline Correlated with Subjective but Not Objective Sleep: A Mediator Role of Depression

This study examined the relationship between older adults' subjective versus objective sleep and subjective cognitive decline (SCD), and explored the role of depression on this association. One hundred and four community-dwelling older adults underwent a week of actigraphic sleep monitoring, and completed a series of neuropsychological screeners. Older adults'SCD score was positively correlated with subjective insomnia, but not with objective sleep parameters. Further mediation modeling revealed that older adults'depression mediated the association between subjective insomnia and SCD. Subjective sleep, rather than objective sleep, may be a more sensitive indicator for older adults' SCD, with depression symptoms appearing to account for most of the variance. These findings extend our perspective on the relationship between sleep disruption and cognitive decline, and highlight the necessity of early targeted interventions on sleep to reduce the risk of cognitive impairment in the elderly with SCD.

Sleep disorders in Alzheimer's disease: the predictive roles and potential mechanisms

Sleep disorders are common in patients with Alzheimer's disease, and can even occur in patients with amnestic mild cognitive impairment, which appears before Alzheimer's disease. Sleep disorders further impair cognitive function and accelerate the accumulation of amyloid-β and tau in patients with Alzheimer's disease. At present, sleep disorders are considered as a risk factor for, and may be a predictor of, Alzheimer's disease development. Given that sleep disorders are encountered in other types of dementia and psychiatric conditions, sleep-related biomarkers to predict Alzheimer's disease need to have high specificity and sensitivity. Here, we summarize the major Alzheimer's disease-specific sleep changes, including abnormal non-rapid eye movement sleep, sleep fragmentation, and sleep-disordered breathing, and describe their ability to predict the onset of Alzheimer's disease at its earliest stages. Understanding the mechanisms underlying these sleep changes is also crucial if we are to clarify the role of sleep in Alzheimer's disease. This paper therefore explores some potential mechanisms that may contribute to sleep disorders, including dysregulation of the orexinergic, glutamatergic, and γ-aminobutyric acid systems and the circadian rhythm, together with amyloid-β accumulation. This review could provide a theoretical basis for the development of drugs to treat Alzheimer's disease based on sleep disorders in future work.

Rest-activity rhythms, daytime symptoms, and functional performance among people with heart failure

Sleep disturbance and decreased daytime activity are well-described among people with chronic heart failure (HF) who suffer from disabling daytime symptoms and poor function. Alterations in the circadian rhythmicity of rest-activity may also be associated with these outcomes. However, little is known about the associations between rest-activity rhythms (RARS), symptoms, and functional performance or the extent to which they are explained by sleep characteristics among people with HF. The purpose of this study is to evaluate parametric and non-parametric circadian characteristics of RARs and the associations between these variables, daytime symptoms, and functional performance among patients with stable heart failure (HF). We recruited adults with stable HF from HF disease management programs. Participants wore wrist actigraphs for 3 d, completed one night of unattended polysomnography and the Six Minute Walk Test, and reported daytime symptoms and physical function. We performed cosinor, non-parametric, and spectral analyses to evaluate the rest-activity rhythms and computed bivariate correlations between the rest-activity rhythm, demographics, daytime symptoms, and functional performance. We conducted multiple regression analysis to examine how RARs contribute to daytime symptoms and functional performance after controlling for insomnia and covariates. The sample included 135 participants [Mean age = 60.6 (16.1) y, n = 88 (65.2%) male]. Older age, greater comorbidity, and poorer New York Heart Association (NYHA) Class, and more EEG arousals were associated with greater intra-daily variability of the RAR. More robust rhythmicity represented by the circadian quotient was associated with better NYHA class and less sleep fragmentation. A higher circadian quotient was significantly associated with lower fatigue, depression, and sleepiness, and better functional performance after controlling for insomnia and clinical and demographic characteristics. Circadian parameters of rest-activity are associated with symptoms and functional performance among people with HF independent of insomnia or sleep disordered breathing. Interventions targeted at improving the stability and strength of rest-activity rhythms may improve symptom and functional outcomes for these patients.

24-h Activity Rhythms and Health in Older Adults

Purpose of Review

Circadian rhythms, including 24-h activity rhythms, change with age. Disturbances in these 24-h activity rhythms at older age have also been implied in various diseases. This review evaluates recent findings on 24-h activity rhythms and disease in older adults.

Recent Findings

Growing evidence supports that 24-h activity rhythm disturbances at older age are related to the presence and/or progression of disease. Longitudinal and genetic work even suggests a potential causal contribution of disturbed 24-h activity rhythms to disease development. Interventional studies targeting circadian and 24-h activity rhythms demonstrate that 24-h rhythmicity can be improved, but the effect of improving 24-h rhythmicity on disease risk or progression remains to be shown.

Summary

Increasing evidence suggests that 24-h activity rhythms are involved in age-related diseases. Further studies are needed to assess causality, underlying mechanisms, and the effects of treating disturbed 24-h activity rhythms on age-related disease.

Associations between sleep and verbal memory in subjective cognitive decline: A role for semantic clustering

Age-related reductions in slow wave activity (SWA) and increased fragmentation during sleep play a key role in memory impairment. As the prefrontal cortex is necessary for the control processes relevant to memory encoding, including utilisation of internal heuristics such as semantic clustering, and is preferentially vulnerable to sleep disturbance, our study examined how SWA and sleep fragmentation relates to memory performance in individuals with Subjective Cognitive Decline (SCD). Thirty older adults with SCD (Mean Age = 69.34, SD = 5.34) completed a neurocognitive test battery, including the California Verbal Learning Test, which was used to assess semantic clustering. One week later, participants were admitted to the laboratory for a two night visit. SWA and sleep fragmentation were captured using sleep polysomnography. Next-day memory performance was tested using the Rey Auditory Verbal Learning Test. Poorer sleep (reduced SWA; increased arousals) was associated with reduced semantic clustering, which mediated impairment on verbal memory and learning tests conducted both the day after sleep was recorded (for both SWA and arousals), and a week prior (for arousals only). We demonstrate semantic clustering mediated the well described associations between sleep and verbal memory. As these strategies are a component of cognitive training interventions, future research may examine the role of simultaneous sleep interventions for improving cognitive training outcomes.