Blood-Based Transcriptomic Biomarkers Are Predictive of Neurodegeneration Rather Than Alzheimer's Disease.

Alzheimer's disease (AD) is a growing global health crisis affecting millions and incurring substantial economic costs. However, clinical diagnosis remains challenging, with misdiagnoses and underdiagnoses being prevalent. There is an increased focus on putative, blood-based biomarkers that may be useful for the diagnosis as well as early detection of AD. In the present study, we used an unbiased combination of machine learning and functional network analyses to identify blood gene biomarker candidates in AD. Using supervised machine learning, we also determined whether these candidates were indeed unique to AD or whether they were indicative of other neurodegenerative diseases, such as Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS). Our analyses showed that genes involved in spliceosome assembly, RNA binding, transcription, protein synthesis, mitoribosomes, and NADH dehydrogenase were the best-performing genes for identifying AD patients relative to cognitively healthy controls. This transcriptomic signature, however, was not unique to AD, and subsequent machine learning showed that this signature could also predict PD and ALS relative to controls without neurodegenerative disease. Combined, our results suggest that mRNA from whole blood can indeed be used to screen for patients with neurodegeneration but may be less effective in diagnosing the specific neurodegenerative disease.

Region-specific changes in brain activity and memory after continuous positive airway pressure therapy in obstructive sleep apnea: a pilot high-density electroencephalography study.

STUDY OBJECTIVES: Limited channel electroencephalography (EEG) investigations in obstructive sleep apnea (OSA) have revealed deficits in slow wave activity (SWA) and spindles during sleep and increased EEG slowing during resting wakefulness. High-density EEG (Hd-EEG) has also detected local parietal deficits in SWA (delta power) during NREM. It is unclear whether effective continuous positive airway pressure (CPAP) treatment reverses regional SWA deficits, and other regional sleep and wake EEG abnormalities, and whether any recovery relates to improved overnight memory consolidation. METHODS: A clinical sample of men with moderate-severe OSA underwent sleep and resting wake recordings with 256-channel Hd-EEG before and after 3 months of CPAP. Declarative and procedural memory tasks were administered pre- and post-sleep. Topographical spectral power maps and differences between baseline and treatment were compared using t-tests and statistical nonparametric mapping (SnPM). RESULTS: In 11 compliant CPAP users (5.2 ±â€…1.1 hours/night), total sleep time did not differ after CPAP but N1 and N2 sleep were lower and N3 was higher. Centro-parietal gamma power during N3 increased and fronto-central slow spindle activity during N2 decreased (SnPM < 0.05). No other significant differences in EEG power were observed. When averaged specifically within the parietal region, N3 delta power increased after CPAP (p = 0.0029) and was correlated with the change in overnight procedural memory consolidation (rho = 0.79, p = 0.03). During resting wakefulness, there were trends for reduced delta and theta power. CONCLUSIONS: Effective CPAP treatment of OSA may correct regional EEG abnormalities, and regional recovery of SWA may relate to procedural memory improvements in the short term.

Hippocampal Neuronal Integrity and Functional Connectivity Within the Default Mode Network in Mild Cognitive Impairment: A Multimodal Investigation.

Background: In older people with mild cognitive impairment (MCI), the relationship between early changes in functional connectivity and in vivo changes in key neurometabolites is not known. Two established correlates of MCI diagnosis are decreased N-acetylaspartate (NAA) in the hippocampus, indicative of decreased neuronal integrity, and changes in the default mode network (DMN) functional network. If and how these measures interrelate is yet to be established, and such understanding may provide insight into the processes underpinning observed cognitive decline. Objectives: To determine the relationship between NAA levels in the left hippocampus and functional connectivity within the DMN in an aging cohort. Methods: In a sample of 51 participants with MCI and 30 controls, hippocampal NAA was determined using magnetic resonance spectroscopy, and DMN connectivity was quantified using resting-state functional MRI. The association between hippocampal NAA and the DMN functional connectivity was tested within the MCI group and separately within the control group. Results: In the DMN, we showed a significant inverse association between functional connectivity and hippocampal NAA in 20 specific brain connections for patients with MCI. This was despite no evidence of any associations in the healthy control group or group differences in either of these measures alone. Conclusions: This study suggests that decreased neuronal integrity in the hippocampus is associated with functional change within the DMN for those with MCI, in contrast to healthy older adults. These results highlight the potential of multimodal investigations to better understand the processes associated with cognitive decline. Impact statement This study measured activity within the default mode network (DMN) and quantified N-acetylaspartate (NAA), a measure of neuronal integrity, within the hippocampus in participants with mild cognitive impairment (MCI) and healthy controls. In participants with MCI, NAA levels were inversely associated with connectivity between specific regions of the DMN, a relationship not evident in healthy controls. This association was present even in the absence of group differences in DMN connectivity or NAA levels. This research illustrates the possibility of using multiple magnetic resonance modalities for more sensitive measures of early cognitive decline to identify and intervene earlier.

A Systematic Review of Quality Dementia Clinical Guidelines for the Development of WHO's Package of Interventions for Rehabilitation.

BACKGROUND AND OBJECTIVES: As part of the WHO Rehabilitation 2030 call for action, the WHO Rehabilitation Programme is developing its Package of Interventions for Rehabilitation (PIR) to support ministries of health around the globe in integrating rehabilitation services into health systems. As a vital step for this PIR development, we conducted a systematic review of clinical practice guidelines (CPGs) for dementia to identify interventions for rehabilitation and related evidence. RESEARCH DESIGN AND METHODS: Following WHO Rehabilitation Programme and Cochrane Rehabilitation's methodology, quality CPGs published in English between January 2010 and March 2020 were identified using PubMed, Embase, CINAHL, PEDro, Google Scholar, guideline databases, and professional society websites. Guideline quality was assessed using the Appraisal of Guidelines for Research and Evaluation (II). RESULTS: Of the 22 CPGs that met the selection criteria, 6 satisfied the quality evaluation. Three hundred and thirty rehabilitation-related recommendations were identified, mostly concentrated in the areas of cognition, emotion, and carer support. There were many strong interventions, with moderate- to high-quality evidence that could be easily introduced in routine practice. However, major limitations were found both in the quality of evidence and scope, especially in areas such as education and vocation, community and social life, and lifestyle modifications. DISCUSSION AND IMPLICATIONS: Further rigorous research is needed to build quality evidence in dementia rehabilitation in general, and especially in neglected areas for rehabilitation. Future work should also focus on the development of CPGs for dementia rehabilitation. A multipronged approach is needed to achieve Universal Health Coverage for dementia rehabilitation.

Engagement in cognitively stimulating activities in individuals with Mild Cognitive Impairment: relationships with neuropsychological domains and hippocampal volume.

Late-life participation in cognitively stimulating activities is thought to contribute to an individual's cognitive reserve and thus protect against cognitive decline, yet its association with clinical markers of neurodegeneration is not well established. To investigate, we developed a 13-item self-report "cognitively stimulating activities" questionnaire (CSA-Q), which was completed by a community sample of 269 older adults (>50 years) at risk of dementia. Participants met criteria for Mild Cognitive Impairment (MCI) and were classified as amnestic (aMCI; n = 93) or non-amnestic (naMCI; n = 176). Weighted CSA-Q dimensions were calculated for activity intensity, mental engagement and social engagement via a panel of 23 inter-raters. The CSA-Q mean and its dimensions were examined in relation to: (a) demographics (age, sex), (b) cognitive reserve proxies (years of education, premorbid IQ), (c) neuropsychological markers across cognitive domains of executive function, processing speed, learning, and memory storage, and (d) neuroimaging markers (left and right hippocampal volume). Analyses were conducted for all MCI, as well as for aMCI and naMCI sub-types. The CSA-Q was found to have concurrent validity with cognitive reserve proxies. Among all MCI, the CSA-Q dimensions of intensity and mental engagement had moderate associations with left hippocampal volume, but not with neuropsychological performance. For naMCI, the CSA-Q had moderate associations with left hippocampal volume, and small associations with aspects of executive functioning and processing speed. No equivalent associations emerged for the aMCI subtype. Our findings show that the CSA-Q may be particularly useful for older adults with non-amnestic cognitive deficits.

Thalamic abnormalities in older adults with remitted early-onset depression using structural magnetic resonance imaging.

BACKGROUND: The thalamus is a key diencephalic structure involved in major depressive disorder (MDD). Studies have consistently revealed abnormalities in thalamic volumes in older adults with late-onset depression (LOD), however abnormalities in older adults with early-onset depression (EOD) have not yet been well-studied. METHODS: Fifty-nine euthymic participants with a history of EOD and fifty-nine matched comparison participants without a lifetime history of depression underwent neuroimaging, medical and neuropsychological assessments. Thalamic volumes were compared between groups. To investigate the previously-proposed right hemispheric (RH) dominance theory of MDD, we explored the bilateral, right and left hemispheric (LH) thalamic volumes. Multiple regression analyses were used to evaluate between-group and within-group effects. Correlational analyses examined associations between group and cognitive performance. RESULTS: Relative to the comparison group, those with EOD had significantly larger bilateral, LH and RH thalamic volumes. Those with EOD, those who were younger, and those who had fewer years of education demonstrated larger bilateral and LH thalamic volumes. For RH thalamic volumes, those with EOD and those who were younger demonstrated larger RH thalamic volumes. EOD within-group models were also run to assess associations between relevant depression variables. The results showed that only age was significant for bilateral and RH thalamic volumes. For the LH thalamic volumes, the model was not significant. No significant correlations were found between cognitive performance and EOD groups. CONCLUSION: Older adults with a history of EOD showed significantly larger bilateral, RH and LH thalamic volumes. Further research is needed to delineate potential underlying mechanisms of this change.

Safety of higher doses of melatonin in adults: A systematic review and meta-analysis.

Melatonin is commonly used for sleep and jetlag at low doses. However, there is less documentation on the safety of higher doses, which are being increasingly used for a wide variety of conditions, including more recently COVID-19 prevention and treatment. The aim of this review was to investigate the safety of higher doses of melatonin in adults. Medline, Scopus, Embase and PsycINFO databases from inception until December 2019 with convenience searches until October 2020. Randomised controlled trials investigating high-dose melatonin (≥10 mg) in human adults over 30 years of age were included. Two investigators independently abstracted articles using PRISMA guidelines. Risk of bias was assessed by a committee of three investigators. 79 studies were identified with a total of 3861 participants. Studies included a large range of medical conditions. The meta-analysis was pooled data using a random effects model. The outcomes examined were the number of adverse events (AEs), serious adverse events (SAEs) and withdrawals due to AEs. A total of 29 studies (37%) made no mention of the presence or absence of AEs. Overall, only four studies met the pre-specified low risk of bias criteria for meta-analysis. In that small subset, melatonin did not cause a detectable increase in SAEs (Rate Ratio = 0.88 [0.52, 1.50], p = .64) or withdrawals due to AEs (0.93 [0.24, 3.56], p = .92), but did appear to increase the risk of AEs such as drowsiness, headache and dizziness (1.40 [1.15, 1.69], p < .001). Overall, there has been limited AE reporting from high-dose melatonin studies. Based on this limited evidence, melatonin appears to have a good safety profile. Better safety reporting in future long-term trials is needed to confirm this as our confidence limits were very wide due to the paucity of suitable data.

Brain oxidative stress and cognitive function in older adults with diabetes and pre-diabetes who are at risk for dementia.

AIMS: Diabetes is an established risk factor for dementia. This study aimed to examine the relationship between various cognitive domains, brain oxidative stress and markers of diabetes in older adults at risk for dementia. METHODS: Older adults at risk for dementia underwent comprehensive neuropsychological and medical assessment. At risk was defined as those with subjective and/or objective cognitive impairment. Pre-diabetes and type 2 diabetes were defined using American Diabetes Association definitions for fasting blood glucose and HbA1c. Brain oxidative stress as indicated by glutathione (GSH) was assessed via magnetic resonance spectroscopy in the anterior cingulate cortex. RESULTS: One-hundred and forty-seven older adults completed a neuropsychological assessment and fasting blood sample with 63 also undergoing magnetic resonance spectroscopy. Those with pre-diabetes/diabetes according to FBG had impaired memory retention, set-shifting and response inhibition, compared to those with normal blood glucose. In contrast, there were no significant differences in any cognitive outcome using the HbA1c definition. Increasing glucose and HbA1c levels were associated with reduced GSH concentration in the anterior cingulate. CONCLUSIONS: This study demonstrates that in older adults at risk for dementia, having pre-diabetes or diabetes is associated with impaired memory and executive dysfunction. It also highlights the potential role of oxidative stress as a pathophysiological mechanism that may underpin the link between diabetes and cognitive dysfunction.

Poorer Theory of Mind in Amnestic Mild Cognitive Impairment Is Associated with Decreased Functional Connectivity in the Default Mode Network.

BACKGROUND: Older adults living with amnestic mild cognitive impairment (aMCI) not only demonstrate impairments in Theory of Mind (ToM), relative to adults with non-amnestic MCI (naMCI), but are also at a higher risk of developing dementia. OBJECTIVE: Our primary objective was to ascertain whether default mode network (DMN) functional connectivity was differentially associated with ToM abilities between MCI subgroups. METHODS: Using functional magnetic resonance imaging, we investigated alterations in resting-state functional connectivity within the brain's DMN in a sample of 43 older adults with aMCI (n = 19) and naMCI (n = 24), previously reported to demonstrate poorer ToM abilities. RESULTS: Compared to naMCI, the aMCI subgroup revealed a significant association between poorer ToM performance and reduced functional connectivity between the bilateral temporal pole (TempP) and the left lateral temporal cortex (LTC) (LTC_L-TempP_L: b = -0.06, t(33) = -3.53, p = 0.02; LTC_L-TempP_R: b = -0.07,t(33) = -3.20, p = 0.03); between the right TempP and the dorsal medial prefrontal cortex (dMPFC) (b = -0.04, t(33) = -3.02, p = 0.03) and between the left and right TempP (b = -0.05, t(33) = -3.26, p = 0.03). In the naMCI subgroup, the opposite relationship was present between the bilateral TempP and the left LTC (Combined correlation: r = -0.47, p = 0.02), however, not between the right TempP and the dMPFC (r = -0.14, p = 0.51) or the left and right TempP (r = -0.31, p = 0.14). CONCLUSION: Our findings suggest that alterations in functional connectivity within the DMN involving temporal and frontal lobe regions are associated with ToM deficits in aMCI.

Association between lifetime depression history, hippocampal volume and memory in non-amnestic mild cognitive impairment.

Hippocampal subfield volume loss in older adults with amnestic mild cognitive impairment (aMCI) and depression history are associated with amyloid beta and tau pathology, thereby increasing the risk for Alzheimer's disease (AD). However, no studies have exclusively examined distinct alterations in hippocampal subfields in non-amnestic MCI (naMCI) in relation to depression history. Here, we used both longitudinal and transverse hippocampal segmentation methods using the automated FreeSurfer software to examine whether a lifetime depression history is associated with differences in hippocampal head/body/tail (H/B/T) and key subfield volumes (CA1, subiculum, dentate gyrus) in older adults with naMCI. Further, we explored whether differences in hippocampal H/B/T and subfield volumes were associated with structured and unstructured verbal encoding and retention, comparing those with and without a depression history. The naMCI with a depression history group demonstrated larger or relatively preserved right CA1 volumes, which were associated with better unstructured verbal encoding and as well as structured verbal memory retention. This association between memory encoding and hippocampal CA1 and total head volume was significantly different to those with no depression history. The relationship between right CA1 volume and memory retention was also moderated by depression history status F (5,143) = 7.84, p < 0.001, R2  = 0.22. Those participants taking antidepressants had significantly larger hippocampal subiculum (p = 0.008), and right hippocampal body (p = 0.004) and better performance on structured encoding (p = 0.011) and unstructured memory retention (p = 0.009). These findings highlight the importance of lifetime depression history and antidepressant use on the hippocampus and encoding and memory retention in naMCI.

Feasibility of 3-month melatonin supplementation for brain oxidative stress and sleep in mild cognitive impairment: protocol for a randomised, placebo-controlled study.

INTRODUCTION: Melatonin has multiple proposed therapeutic benefits including antioxidant properties, synchronisation of the circadian system and lowering of blood pressure. In this protocol, we outline a randomised controlled trial to assess the feasibility, acceptability and tolerability of higher dose (25 mg) melatonin to target brain oxidative stress and sleep disturbance in older adults with mild cognitive impairment (MCI). METHODS AND ANALYSIS: The study design is a randomised double-blind, placebo-controlled, parallel group trial. Forty individuals with MCI will be recruited from the Healthy Brain Ageing Clinic, University of Sydney and from the community, and randomised to receive either 25 mg oral melatonin or placebo nightly for 12 weeks. The primary outcomes are feasibility of recruitment, acceptability of intervention and adherence to trial medication at 12 weeks. Secondary outcomes will include the effect of melatonin on brain oxidative stress as measured by magnetic resonance spectroscopy, blood pressure, blood biomarkers, mood, cognition and sleep. Outcomes will be collected at 6 and 12 weeks. The results of this feasibility trial will inform a future conclusive randomised controlled trial to specifically test the efficacy of melatonin on modifiable risk factors of dementia, as well as cognition and brain function. This will be the first trial to investigate the effect of melatonin in the population with MCI in this way, with the future aim of using this approach to reduce progression to dementia. ETHICS AND DISSEMINATION: This protocol has been approved by the Sydney Local Health District Ethics Committee (X18-0077). This randomised controlled trial will be conducted in compliance with the protocol published in the registry, the International Conference for Harmonisation on Good Clinical Practice and all other applicable regulatory requirements. The findings of the trial will be disseminated via conferences, publications and media, as applicable. Participants will be informed of results of the study at the conclusion of the trial. Eligible authors will include investigators who are involved in the conception and design of the study, the conduct of the trial, the analysis of the results, and reporting and presentation of study findings. TRIAL REGISTRATION NUMBER: Australian and New Zealand Clinical Trials Registry (ANZCTRN 12619000876190). PROTOCOL VERSION: V.8 15 October 2020.

Sleep-Dependent Memory in Older People With and Without MCI: The Relevance of Sleep Microarchitecture, OSA, Hippocampal Subfields, and Episodic Memory.

This study aimed to determine if, relative to cognitively healthy controls, sleep-dependent memory consolidation (SDMC) is diminished in mild cognitive impairment (MCI), a group at high risk of conversion to dementia. We also sought to determine whether SDMC is associated with sleep characteristics, daytime episodic memory, and hippocampal integrity. Participants with MCI (n = 43) and controls (n = 20) underwent clinical and neuropsychological profiling. From polysomnography, apnea hypopnea index (AHI) and non-REM sleep spindle characteristics were derived. From magnetic resonance imaging, hippocampal subfield volumes were computed. Participants learned a novel 32-item word-pair prior to sleep; morning retention of the word-pairs was used to determine SDMC. Results showed that SDMC did not differ between MCI and controls, but there was a large effect size decrement in SDMC in those with multiple domain MCI (Hedge's g = 0.85). In MCI, poorer SDMC was correlated with CA1 and CA3 hippocampal atrophy, shorter spindle duration, and worse daytime episodic memory. In controls, poorer SDMC was associated with higher AHI. Impaired daytime memory consolidation, reduced hippocampal volumes, shorter sleep spindles, and greater sleep apnea severity are indicators of diminished SDMC in older adults and should be explored in future studies.

Rest-activity functioning is related to white matter microarchitecture and modifiable risk factors in older adults at-risk for dementia.

STUDY OBJECTIVES: Growing evidence demonstrates pronounced alterations in rest-activity functioning in older adults at-risk for dementia. White matter degeneration, poor cardiometabolic functioning, and depression have also been linked to a greater risk of decline; however, limited studies have examined the white matter in relation to rest-activity functioning in at-risk older adults. METHODS: We investigated associations between nonparametric actigraphy measures and white matter microarchitecture using whole-brain fixel-based analysis of diffusion-weighted imaging in older adults (aged 50 years or older) at-risk for cognitive decline and dementia. The fixel-based metrics assessed were fiber density, fiber cross-section, and combined fiber-density, and cross-section. Interactions between rest-activity functioning and known clinical risk factors, specifically body mass index (BMI), vascular risk factors, depressive symptoms and self-reported exercise, and their association with white matter properties were then investigated. RESULTS: Sixty-seven older adults were included (mean = 65.78 years, SD = 7.89). Lower relative amplitude, poorer 24-h synchronization and earlier onset of the least active 5-h period were associated with reductions in markers of white matter atrophy in widespread regions, including cortico-subcortical and cortical association pathways. Preliminary evidence was also found indicating more pronounced white matter alterations in those with lower amplitude and higher BMI (ß = 0.25, 95% CI [0.05, 0.46]), poorer 24-h synchronization and more vascular risk factors (ß = 0.17, 95% CI [-0.02, 0.36]) and earlier onset of inactivity and greater depressive symptoms (ß = 0.17, 95% CI [0.03, 0.30]). CONCLUSIONS: These findings highlight the complex interplay between rest-activity rhythms, white matter, and clinical risk factors in individuals at-risk for dementia that should be considered in future studies.

Obesity and Oxidative Stress in Older Adults At Risk for Dementia: A Magnetic Resonance Spectroscopy Study.

OBJECTIVE: This study aimed to investigate the relationship between obesity and oxidative stress in older adults at risk for dementia. It also aimed to explore the influence of physical activity on the relationship between obesity and oxidative stress in this at risk cohort. METHODS: Older adults at risk for dementia underwent comprehensive medical, neuropsychological, and psychiatric assessment. At risk was defined as participants with subjective or mild cognitive impairment. Glutathione was assessed by magnetic resonance spectroscopy in the left hippocampus and the anterior and posterior cingulate cortex. Body mass index (BMI) was calculated and classified as healthy (BMI <25 kg/m2) or overweight/obese (BMI ≥25 kg/m2). RESULTS: Sixty-five older adults (mean age=66.2 y) were included for analysis. The overweight/obese group had significantly greater glutathione in the hippocampus compared with the healthy weight group (t=-2.76, P=0.008). No significant difference in glutathione was observed between groups in the anterior or posterior cingulate. In the overweight/obese group, a higher BMI was associated with a diabetes diagnosis and lower total time engaging in physical activity (r=-0.36, P=0.025), however, glutathione did not correlate with activity levels across groups. CONCLUSION: This study demonstrates that changes in in vivo markers of oxidative stress are present in overweight/obese older adults at risk for dementia. Future research should explore the relationship with diabetes and the longitudinal relationship between BMI and oxidative stress, and response to therapeutic interventions.

Irregular sleep-wake patterns in older adults with current or remitted depression.

BACKGROUND: Disturbed sleep and irregular sleep-wake patterns have been associated with poor outcomes in older adults. Sleep regularity however has not been studied in a sample with current or remitted major depression. METHODS: 138 participants (63.8±8.6 years; n=27 current major depression, n=64 remitted, and n=47 healthy controls) were monitored using wrist-worn actigraphy. The Sleep Regularity Index (SRI), sleep-wake fragmentation and stability, sleep onset and offset timing, number of awakenings and measures from cosinor analysis were computed. RESULTS: Compared with controls, older adults with current depression had lower SRI (p < 0.01), lower relative amplitude (p < 0.05), and higher activity during sleeping and post-midnight hours (p < 0.05). Older adults with remitted depression displayed lower activity during the day (p < 0.05), showed reduced average activity and lower amplitude than controls. Total sleep time, sleep timing, and number of awakenings did not differ between groups. All groups differed significantly in self-reported sleep quality and depression severity. LIMITATIONS: Longitudinal studies which examine how sleep-wake patterns change based on depressive episode recency, severity and how medications may influence these patterns are needed. CONCLUSIONS: Older adults with current or remitted major depression do not differ from controls on traditional sleep metrics but do report poor quality sleep and show differences in sleep regularity and rest-activity patterns. Reducing the risk of poor outcomes in both groups may be aided by interventions that help promote sleep regularity and increased activity.

Actigraphy-recorded sleep efficiency and hippocampal volume are related to visual and verbal rate of forgetting in older adults.

This study aimed to determine if older adults "at-risk" for dementia (those with MCI or SMC) exhibit accelerated long-term forgetting (ALF) and whether rate of forgetting (RoF) is associated with sleep efficiency, hippocampal volume and demographic/clinical features. Forty-nine "at-risk" participants and eighteen controls underwent examination. Memory was assessed using the Scene Memory Task (SMT) and WMS-III Logical Memory (LM) subtest. Tests were administered at baseline, 24 hours and 2 weeks. While our study did not find ALF in those "at-risk" for dementia, on the SMT, RoF over 24 hours and 2 weeks was negatively correlated with sleep efficiency. For LM, RoF at 2 weeks was moderately associated with left hippocampal volume. Neither visual or verbal RoF was correlated with demographic or clinical variables (age, MMSE, IQ, GDS-15). While ALF was not observed in this sample, our results suggest that visual and verbal forgetting have differential predictors.

Altered heart rate variability during sleep in mild cognitive impairment.

STUDY OBJECTIVES: Cardiovascular autonomic dysfunction, as measured by short-term diurnal heart rate variability (HRV), has been reported in older adults with mild cognitive impairment (MCI). However, it is unclear whether this impairment also exists during sleep in this group. We, therefore, compared overnight HRV during sleep in older adults with MCI and those with subjective cognitive impairment (SCI). METHODS: Older adults (n = 210) underwent overnight polysomnography. Eligible participants were characterized as multi-domain MCI or SCI. The multi-domain MCI group was comprised of amnestic and non-amnestic subtypes. Power spectral analysis of HRV was conducted on the overnight electrocardiogram during non-rapid eye movement (NREM), rapid eye movement (REM), N1, N2, N3 sleep stages, and wake periods. High-frequency HRV (HF-HRV) was employed as the primary measure to estimate parasympathetic function. RESULTS: The MCI group showed reduced HF-HRV during NREM sleep (p = 0.018), but not during wake or REM sleep (p > 0.05) compared to the SCI group. Participants with aMCI compared to SCI had the most pronounced reduction in HF-HRV across all NREM sleep stages-N1, N2, and N3, but not during wake or REM sleep. The naMCI sub-group did not show any significant differences in HF-HRV during any sleep stage compared to SCI. CONCLUSIONS: Our study showed that amnestic MCI participants had greater reductions in HF-HRV during NREM sleep, relative to those with SCI, suggesting potential vulnerability to sleep-related parasympathetic dysfunction. HF-HRV, especially during NREM sleep, may be an early biomarker for dementia detection.

Objective measurement of sleep in mild cognitive impairment: A systematic review and meta-analysis.

Older adults with mild cognitive impairment (MCI) are at-risk of developing dementia, particularly Alzheimer's disease. While some research suggests that alterations in sleep architecture may mediate cognitive decline, the nature and magnitude of changes to sleep macro- (sleep stages) and micro-architecture (electroencephalography (EEG) oscillations) in MCI is not yet clear. This study aimed to systematically review and meta-analyse case-control studies objectively measuring sleep in MCI. A systematic search was conducted using PubMed, Scopus, Web of Science, Embase and Psycinfo databases and after review, a total of 10 studies met inclusion criteria. Of these, all reported sleep macro-architecture and four reported micro-architecture outcomes. A combined total of 430 participants (209 with and 221 without MCI) underwent objective sleep assessments in the included full text articles. Findings show that compared to healthy controls, those with MCI have pronounced changes in sleep macro-architecture with greater wake after sleep onset, reduced total sleep time, lower sleep efficiency, longer sleep onset latency, longer rapid eye movement sleep (REM) latency, reduced REM sleep, greater N1 sleep, and worse severity of hypoxemia. Pooling of sleep micro-architecture EEG measures was not possible due to limited studies, however reduced spindles in non-REM sleep and greater EEG slowing in REM sleep were reported.

Arterial stiffness relates to executive dysfunction in later life.

Cardiovascular disease in older people is often linked with cognitive impairment, particularly in domains of executive function and processing speed. Our aims examined whether carotid-femoral pulse wave velocity (PWV) related to subtle changes of executive function and processing speed. Fifty-six individuals with subjective mood and/or cognitive concerns underwent PWV and neuropsychological assessments of processing speed (Trail Making Test Part A) and executive functioning (Delis Kaplan Executive Function System Stroop Task; Trail Making Test Part B, TMT-B). Individuals with high PWV (≥12.0m/s) had poorer performance on TMT-B, compared to low PWV (<12.0m/s), and a moderate negative correlation (r = -0.38, p = .004) between PWV and TMT-B performance. Our results confirm that in older adults at-risk for cognitive decline, early markers of CVD are associated with subtle decrements in rapid set-shifting (executive function), supporting efforts towards early detection of CVD as a secondary prevention strategy for older individuals with cognitive decline.

Nocturnal Hypoxemia Is Associated with Altered Parahippocampal Functional Brain Connectivity in Older Adults at Risk for Dementia.

BACKGROUND: Obstructive sleep apnea is associated with an increased risk of developing mild cognitive impairment and dementia. Intermittent nocturnal hypoxemia in obstructive sleep apnea is associated with brain changes in key regions that underpin memory. OBJECTIVE: To determine whether older adults with severe nocturnal hypoxemia would exhibit reduced functional connectivity within these regions, with associated deficits in memory. METHODS: Seventy-two participants 51 years and over underwent polysomnography with continuous blood oxygen saturation recorded via oximetry. The oxygen desaturation index (ODI, 3% dips in oxygen levels per hour) was the primary outcome measure. ODI was split into tertiles, with analyses comparing the lowest and highest tertiles (N = 48). Thirty-five of the 48 participants from these two tertiles had mild cognitive impairment. Participants also underwent resting-state fMRI and comprehensive neuropsychological, medical, and psychiatric assessment. RESULTS: The highest ODI tertile group demonstrated significantly reduced connectivity between the left and right parahippocampal cortex, relative to the lowest ODI tertile group (t(42) = -3.26, p = 0.041, beta = -1.99).The highest ODI tertile group also had poorer working memory performance. In the highest ODI tertile group only, higher left-right parahippocampal functional connectivity was associated with poorer visual memory recall (between-groups z = -2.93, p = 0.0034). CONCLUSIONS: Older adults with severe nocturnal hypoxemia demonstrate impaired functional connectivity in medial temporal structures, key regions involved in sleep memory processing and implicated in dementia pathophysiology. Oxygen desaturation and functional connectivity in these individuals each relate to cognitive performance. Research is now required to further elucidate these findings.