Effect of cognitive reserve on the association between slow wave sleep and cognition in community-dwelling older adults

Circadian rhythm disturbances in Alzheimer's disease: insights from plaque-free and plaque-burdened stages in APPSWE/PS1dE9 mice

BACKGROUND

Disruptions in circadian rhythms are commonly observed in patients with Alzheimer's disease (AD) and could potentially accelerate the progression of the condition. However, the relationship between circadian rhythm disruptions and AD development, as well as the mechanisms involved, remain poorly understood.

METHODS

This study investigated the circadian behavior, rhythmic gene expression in multiple brain regions, and its correlation with sleep architecture of AD mice at two disease stages: plaque-free stage (2-month-old) and plaque-burdened stage (10-month-old) as compared to age-matched wild-type (WT) mice.

RESULTS

Two-month-old AD mice already displayed alteration in the activity patterns compared to WT mice, showing increased activity during the light phase and decreased activity during the dark phase, and the change in the activity pattern of 10-month-old AD mice was more significant. Further, electroencephalogram (EEG) examination showed increased wakefulness and reduced non-rapid eye movement (NREM) sleep in 2- and 10-month-old AD mice. In addition, we documented a significant change in circadian core clock genes in the suprachiasmatic nucleus (SCN), hippocampus, and cortex of 2- and 10-month-old AD mice. Correlation analyses demonstrated the close relationship between circadian clock gene expression level and specific sleep-wake parameters, especially within the SCN and hippocampus.

CONCLUSIONS

These findings revealed that circadian rhythm disturbances in AD mice preceded Aβ deposition. The circadian rhythm disturbances observed in the early AD might be attributed to the abnormal expression of core clock genes in the brain regions involved in circadian rhythm regulation.

Sleep architecture in Alzheimer's disease continuum: The deep sleep question

As sleep appears to be closely related to cognitive status, we aimed to explore the association between the percentage of deep sleep, cognitive state, and the cerebrospinal fluid (CSF) biomarker amyloid-beta 42 in non-demented individuals. In this cross-sectional study, 90 non-demented participants from the Aiginition Longitudinal Biomarker Investigation of Neurodegeneration cohort underwent a one-night WatchPAT sleep evaluation. Participants were categorized by cognitive status (patients with mild cognitive impairment [MCI] or cognitively normal [CN] individuals) and CSF Aβ42 status (Aβ42 ≤ 1,030 pg/mL [A+] or Ab42 > 1,030 pg/mL [A-]). After controlling for age, sex, and years of education, a significant inverse association was found between the percentage of deep sleep and the odds of being classified as MCI compared to CN (OR = 0.86, 95% CI [0.76-0.97], p = 0.012). However, a non-significant trend for an inverse association between the percentage of deep sleep and the odds of being classified as A+ was observed (OR = 0.92, 95% CI [0.84-1.01], p = 0.092). This study demonstrates a significant link between deep sleep and MCI. Although more longitudinal studies are needed, deep sleep could potentially serve as a novel biomarker of cognitive decline and an intervention target for dementia prevention.

The impact of cognitive reserve relative to risk of Alzheimer's disease and rate of progression: an up-to-date review of the literature

INTRODUCTION

Cognitive reserve (CR) is a crucial factor in explaining individual differences in the risk of Alzheimer's disease (AD) and cognitive decline. CR refers to the brain's ability to cope with pathology through compensatory mechanisms. This review examines the various methods used to measure, predict, and influence CR.

AREAS COVERED

Based on a search of PubMed, PubMed Central, EMBASE, Scopus, and the Cochrane Library (up to 1 June 2024), this review addresses key CR proxies, highlighting their strengths and limitations. The review also explores established and emerging interventions. We critically evaluate the statistical methods used to measure CR and assess its practical application.

EXPERT OPINION

CR plays a crucial role in delaying the onset and progression of AD. Lifestyle choices and experiences build CR and impact cognitive aging. However, practical challenges remain in applying CR in clinical settings, particularly in individuals with advanced cognitive decline. Education, while commonly used as a proxy for CR, may not fully capture its complexity. Alternatives like occupational complexity could offer more practical measures, but their application is still evolving. Addressing these limitations is key to advancing dementia prevention strategies.

Bilingualism, sleep, and cognition: An integrative view and open research questions

Sleep and language are fundamental to human existence and have both been shown to substantially affect cognitive functioning including memory, attentional performance, and cognitive control. Surprisingly, there is little-to-no research that examines the shared impact of bilingualism and sleep on cognitive functions. In this paper, we provide a general overview of existing research on the interplay between bilingualism and sleep with a specific focus on executive functioning. First, we highlight their interconnections and the resulting implications for cognitive performance. Second, we emphasize the need to explore how bilingualism and sleep intersect at cognitive and neural levels, offering insights into potential ways of studying the interplay between sleep, language learning, and bilingual language use. Finally, we suggest that understanding these relationships could enhance our knowledge of reserve and its role in mitigating age-related cognitive decline.

The Complex Relationship between Sleep and Cognitive Reserve: A Narrative Review Based on Human Studies

Sleep and brain/cognitive/neural reserve significantly impact well-being and cognition throughout life. This review aims to explore the intricate relationship between such factors, with reference to their effects on human cognitive functions. The specific goal is to understand the bidirectional influence that sleep and reserve exert on each other. Up to 6 February 2024, a methodical search of the literature was conducted using the PubMed database with terms related to brain, cognitive or neural reserve, and healthy or disturbed sleep. Based on the inclusion criteria, 11 articles were selected and analyzed for this review. The articles focus almost exclusively on cognitive reserve, with no explicit connection between sleep and brain or neural reserve. The results evidence sleep's role as a builder of cognitive reserve and cognitive reserve's role as a moderator in the effects of physiological and pathological sleep on cognitive functions. In conclusion, the findings of the present review support the notion that both sleep and cognitive reserve are critical factors in cognitive functioning. Deepening comprehension of the interactions between them is essential for devising strategies to enhance brain health and resilience against age- and pathology-related conditions.

Preoperative recovery sleep ameliorates postoperative cognitive dysfunction aggravated by sleep fragmentation in aged mice by enhancing EEG delta-wave activity and LFP theta oscillation in hippocampal CA1

Sleep fragmentation (SF) is a common sleep problem experienced during the perioperative period by older adults, and is associated with postoperative cognitive dysfunction (POCD). Increasing evidence indicates that delta-wave activity during non-rapid eye movement (NREM) sleep is involved in sleep-dependent memory consolidation and that hippocampal theta oscillations are related to spatial exploratory memory. Recovery sleep (RS), a self-regulated state of sleep homeostasis, enhances delta-wave power and memory performance in sleep-deprived older mice. However, it remains unclear whether RS therapy has a positive effect on cognitive changes following SF in older mouse models. Therefore, this study aimed to explore whether preoperative RS can alleviate cognitive deficits in aged mice with SF. A model of preoperative 24-h SF combined with exploratory laparotomy-induced POCD was established in 18-month-old mice. Aged mice were treated with preoperative 6-h RS following SF and postoperative 6-h RS following surgery, respectively. The changes in hippocampus-dependent cognitive function were investigated using behavioral tests, electroencephalography (EEG), local field potential (LFP), magnetic resonance imaging, and neuromorphology. Mice that underwent 24-h SF combined with surgery exhibited severe spatial memory impairment; impaired cognitive performance could be alleviated by preoperative RS treatment. In addition, preoperative RS increased NREM sleep; enhanced EEG delta-wave activity and LFP theta oscillation in the hippocampal CA1; and improved hippocampal perfusion, microstructural integrity, and neuronal damage. Taken together, these results provide evidence that preoperative RS may ameliorate the severity of POCD aggravated by SF by enhancing delta slow-wave activity and hippocampal theta oscillation, and by ameliorating the reduction in regional cerebral blood flow and white matter microstructure integrity in the hippocampus.