Hippocampus volume and subjective sleepiness in older people with sleep-disordered breathing: a preliminary report

Is there an association between daytime napping, cognitive function, and brain volume? A Mendelian randomization study in the UK Biobank

OBJECTIVES

Daytime napping has been associated with cognitive function and brain health in observational studies. However, it remains elusive whether these associations are causal. Using Mendelian randomization, we studied the relationship between habitual daytime napping and cognition and brain structure.

METHODS

Data were from UK Biobank (maximum n = 378,932 and mean age = 57 years). Our exposure (daytime napping) was instrumented using 92 previously identified genome-wide, independent genetic variants (single-nucleotide polymorphisms, SNPs). Our outcomes were total brain volume, hippocampal volume, reaction time, and visual memory. Inverse-variance weighted was implemented, with sensitivity analyses (Mendelian randomization-Egger and Weighted Median Estimator) for horizontal pleiotropy. We tested different daytime napping instruments to ensure the robustness of our results.

RESULTS

Using Mendelian randomization, we found an association between habitual daytime napping and larger total brain volume (unstandardized ß = 15.80 cm3 and 95% CI = 0.25; 31.34) but not hippocampal volume (ß = -0.03 cm3 and 95% CI = -0.13;0.06), reaction time (expß = 1.01 and 95% CI = 1.00;1.03), or visual memory (expß = 0.99 and 95% CI = 0.94;1.05). Additional analyses with 47 SNPs (adjusted for excessive daytime sleepiness), 86 SNPs (excluding sleep apnea), and 17 SNPs (no sample overlap with UK Biobank) were largely consistent with our main findings. No evidence of horizontal pleiotropy was found.

CONCLUSIONS

Our findings suggest a modest causal association between habitual daytime napping and larger total brain volume. Future studies could focus on the associations between napping and other cognitive or brain outcomes and replication of these findings using other datasets and methods.

Cortical thinning in male obstructive sleep apnoea patients with excessive daytime sleepiness

Background and purpose

Obstructive sleep apnoea is associated with excessive daytime sleepiness due to sleep fragmentation and hypoxemia, both of which can lead to abnormal brain morphology. However, the pattern of brain structural changes associated with excessive daytime sleepiness is still unclear. This study aims to investigate the effects of excessive daytime sleepiness on cortical thickness in patients with obstructive sleep apnoea.

Materials and methods

61 male patients with newly diagnosed obstructive sleep apnoea were included in the present study. Polysomnography and structural MRI were performed for each participant. Subjective daytime sleepiness was assessed using the Epworth Sleepiness Scale score. Surface-based morphometric analysis was performed using Statistical Parametric Mapping 12 and Computational Anatomy 12 toolboxes to extract cortical thickness.

Results

Using the median Epworth Sleepiness Scale score, patients were divided into the non-sleepiness group and the sleepiness group. The cortical thickness was markedly thinner in the sleepiness group in the left temporal, frontal, and parietal lobe and bilateral pre- and postcentral gyri (pFWE < 0.05). There was a significant negative correlation between the cortical thickness and the Epworth Sleepiness Scale score. After adjusting for age, body mass index, and obstructive sleep apnoea severity, the Epworth Sleepiness Scale score remained an independent factor affecting the cortical thickness of the left middle temporal lobe, transverse temporal and temporal pole.

Conclusion

Subjective daytime sleepiness is associated with decreased cortical thickness, and the Epworth Sleepiness Scale score may be of utility as a clinical marker of brain injury in patients with obstructive sleep apnoea.

Self-reported sleepiness associates with greater brain and cortical volume and lower prevalence of ischemic covert brain infarcts in a community sample

STUDY OBJECTIVES

We evaluated if self-reported sleepiness was associated with neuroimaging markers of brain aging and ischemic damage in a large community-based sample.

METHODS

Participants from the Framingham Heart Study Offspring cohort (n = 468, 62.5 ± 8.7 years old, 49.6%M) free of dementia, stroke, and neurological diseases, completed sleep questionnaires and polysomnography followed by magnetic resonance imaging (MRI), 3 years later on average. We used linear and logistic regression models to evaluate the associations between Epworth Sleepiness Scale (ESS) scores and total brain, cortical and subcortical gray matter, and white matter hyperintensities volumes, and the presence of covert brain infarcts.

RESULTS

Higher sleepiness scores were associated with larger total brain volume, greater cortical gray matter volume, and a lower prevalence of covert brain infarcts, even when adjusting for a large array of potential confounders, including demographics, sleep profiles and disorders, organic health diseases, and proxies for daytime cognitive and physical activities. Interactions indicated that more sleepiness was associated with larger cortical gray matter volume in men only and in APOE ε4 noncarriers, whereas a trend for smaller cortical gray matter volume was observed in carriers. In longitudinal analyses, those with stable excessive daytime sleepiness over time had greater total brain and cortical gray matter volumes, whereas baseline sleepiness scores were not associated with subsequent atrophy or cognitive decline.

CONCLUSION

Our findings suggest that sleepiness is not necessarily a marker of poor brain health when not explained by diseases or sleep debt and sleep disorders. Rather, sleepiness could be a marker of preserved sleep-regulatory processes and brain health in some cases.

Gender-specific association between obstructive sleep apnea and cognitive impairment among adults

OBJECTIVES

This study aims to explore the gender-specific association between obstructive sleep apnea (OSA) and cognitive impairment.

METHODS

Participants from UK biobank who have completed at least one of the five baseline cognitive tests (visuospatial memory, prospective memory, fluid intelligence, short numeric memory and reaction time) were included, which were initially divided into two groups based on gender and were further categorized into three subgroups: (1) OSA, (2) self-reported snoring but without OSA, and (3) healthy controls (without OSA or snoring). Multivariable regression analysis was performed to examine the associations among snoring, OSA and performance of each of the five cognitive domains.

RESULTS

A total of 267,889 participants (47% male, mean age: 57 years old) were included in our study. In the multivariable regression analysis, female participants in the OSA group had a higher risk of having poor prospective memory (OR: 1.24, 95% CI: 1.02～1.50, p = 0.03). Meanwhile, among female participants, OSA were inversely associated with the performances of fluid intelligence (β: 0.29, 95% CI: 0.46～-0.13, p &lt; 0.001) and short-numeric memory (β: 0.14, 95% CI: 0.35～0.08, p = 0.02). Besides, age-related subgroup analyses showed that these associations were largely reserved in younger (＜65 years old) female participants rather than older (≥65 years old) female participants. In contrast, among male participants, no significant association was observed between OSA and impairment of the five cognitive domains.

CONCLUSIONS

OSA was significantly associated with cognitive impairment at certain dimensions in female participants rather than in male participants, indicating that more special attention and timely interventions should be given to younger female OSA patients to prevent further cognitive impairment.

Self-reported sleep relates to hippocampal atrophy across the adult lifespan: results from the Lifebrain consortium

Objectives

Poor sleep is associated with multiple age-related neurodegenerative and neuropsychiatric conditions. The hippocampus plays a special role in sleep and sleep-dependent cognition, and accelerated hippocampal atrophy is typically seen with higher age. Hence, it is critical to establish how the relationship between sleep and hippocampal volume loss unfolds across the adult lifespan.

Methods

Self-reported sleep measures and MRI-derived hippocampal volumes were obtained from 3105 cognitively normal participants (18–90 years) from major European brain studies in the Lifebrain consortium. Hippocampal volume change was estimated from 5116 MRIs from 1299 participants for whom longitudinal MRIs were available, followed up to 11 years with a mean interval of 3.3 years. Cross-sectional analyses were repeated in a sample of 21,390 participants from the UK Biobank.

Results

No cross-sectional sleep—hippocampal volume relationships were found. However, worse sleep quality, efficiency, problems, and daytime tiredness were related to greater hippocampal volume loss over time, with high scorers showing 0.22% greater annual loss than low scorers. The relationship between sleep and hippocampal atrophy did not vary across age. Simulations showed that the observed longitudinal effects were too small to be detected as age-interactions in the cross-sectional analyses.

Conclusions

Worse self-reported sleep is associated with higher rates of hippocampal volume decline across the adult lifespan. This suggests that sleep is relevant to understand individual differences in hippocampal atrophy, but limited effect sizes call for cautious interpretation.

Hypoxia-inducible factors and obstructive sleep apnea

Intermittent hypoxia (IH) is a hallmark manifestation of obstructive sleep apnea (OSA), a widespread disorder of breathing. This Review focuses on the role of hypoxia-inducible factors (HIFs) in hypertension, type 2 diabetes (T2D), and cognitive decline in experimental models of IH patterned after O2 profiles seen in OSA. IH increases HIF-1α and decreases HIF-2α protein levels. Dysregulated HIFs increase reactive oxygen species (ROS) through HIF-1-dependent activation of pro-oxidant enzyme genes in addition to reduced transcription of antioxidant genes by HIF-2. ROS in turn activate chemoreflex and suppress baroreflex, thereby stimulating the sympathetic nervous system and causing hypertension. We also discuss how increased ROS generation by HIF-1 contributes to IH-induced insulin resistance and T2D as well as disrupted NMDA receptor signaling in the hippocampus, resulting in cognitive decline.

Obstructive Sleep Apnea and the Brain: a Focus on Gray and White Matter Structure

PURPOSE OF REVIEW

Obstructive sleep apnea is extremely prevalent in the elderly and may precipitate dementia. We review recent advances on gray and white matter structure in obstructive sleep apnea, the impact of treatment, and potential pathological and neurodegenerative processes underlying brain structural changes.

RECENT FINDINGS

Two opposite patterns are observed in neuroimaging studies of obstructive sleep apnea. One may indicate cellular damage (gray matter atrophy, higher white matter hyperintensity burden, lower white matter fractional anisotropy, higher water diffusivities), while the other (gray matter hypertrophy, restricted white matter diffusivities) may reflect transitory responses, such as intracellular edema, reactive gliosis or compensatory structural changes. Treating obstructive sleep apnea could partly reverse these structural changes. Structural alterations related to obstructive sleep apnea may follow a multi-determined biphasic pattern depending on numerous factors (e.g. severity, symptomatology, age) that could tip the scale toward neurodegeneration and need to be investigated by longitudinal studies.

Neurocognitive and Synaptic Potentiation Deficits Are Mitigated by Inhibition of HIF1a Signaling following Intermittent Hypoxia in Rodents

Highlighted Research Paper:A HIF1a-Dependent Pro-Oxidant State Disrupts Synaptic Plasticity and Impairs Spatial Memory in Response to Intermittent Hypoxia. Alejandra Arias-Cavieres, Maggie A. Khuu, Chinwendu U. Nwakudu, Jasmine E. Barnard, Gokhan Dalgin and Alfredo J. Garcia III

Case report: narcolepsy type 2 due to temporal lobe glioma

RATIONALE

The orexin projection system includes the lateral hypothalamus, reticular activating structure, and ventrolateral preoptic nucleus, and this system is related to the pathogenesis of narcolepsy. Here, we report a case of narcolepsy type 2 caused by hippocampal glioma of the right temporal lobe.

PATIENT CONCERNS

A 44-year-old male farmer complained of excessive daytime sleepiness (EDS) over the past 3 months and more.

INTERVENTIONS

The lesion of the right anteromedial temporal lobe was removed and its pathological examination was carried out.

OUTCOMES

General examination showed no abnormalities of his heart, lungs, or abdomen. Neurological examination showed no positive sign. The blood routine and biochemical examination were normal. He scored 7 on the Pittsburg sleep quality index, 16 on the Epworth sleepiness scale, 52 on the self-rating anxiety scale, and 48 on the self-rating depression scale. The multiple sleep latency test data showed 2 periods of sleep-onset rapid eyes movement period across 4 successive tests; the average sleep latency was under 8 minutes, and the rapid eyes movement latency was under 7 minutes. Lesion of glioma in hippocampus area of the right anteromedial temporal lobe was confirmed through magnetic resonance imaging, magnetic resonance spectroscopy, and histological examination. After surgical removal of the glioma from the hippocampus area of the right anteromedial temporal lobe, the patient's EDS symptoms disappeared immediately. He scored 3 on the Epworth sleepiness scale. During our follow-up three months later, he remained well with no complications.

DIAGNOSIS

We diagnosed the patient with narcolepsy type 2 according to the 3rd Edition of International Classification of Sleep Disorders (ICSD-3).

CONCLUSION

The patient suffered from EDS and was diagnosed with narcolepsy type 2. The narcolepsy type 2 was linked to glioma of the hippocampus area. The hippocampus might be another part of regulating the sleep-arousal pathway, and the glioma secretion might interact with the orexin projection system.

A HIF1a-Dependent Pro-Oxidant State Disrupts Synaptic Plasticity and Impairs Spatial Memory in Response to Intermittent Hypoxia

Sleep apnea causes cognitive deficits and is associated with several neurologic diseases. Intermittent hypoxia (IH) is recognized as a principal mediator of pathophysiology associated with sleep apnea, yet the basis by which IH contributes to impaired cognition remains poorly defined. Using a mouse model exposed to IH, this study examines how the transcription factor, hypoxia inducible factor 1a (HIF1a), contributes to disrupted synaptic physiology and spatial memory. In wild-type mice, impaired performance in the Barnes maze caused by IH coincided with a loss of NMDA receptor (NMDAr)-dependent long-term potentiation (LTP) in area CA1 and increased nuclear HIF1a within the hippocampus. IH-dependent HIF1a signaling caused a two-fold increase in expression of the reactive oxygen species (ROS) generating enzyme NADPH oxidase 4 (NOX4). These changes promoted a pro-oxidant state and the downregulation of GluN1 within the hippocampus. The IH-dependent effects were not present in either mice heterozygous for Hif1a (HIF1a^+/-) or wild-type mice treated with the antioxidant manganese (III) tetrakis(1-methyl-4-pyridyl) porphyrin (MnTMPyP). Our findings indicate that HIF1a-dependent changes in redox state are central to the mechanism by which IH disrupts hippocampal synaptic plasticity and impairs spatial memory. This mechanism may enhance the vulnerability for cognitive deficit and lower the threshold for neurologic diseases associated untreated sleep apnea.

Mean Oxygen Saturation during Sleep Is Related to Specific Brain Atrophy Pattern

OBJECTIVE

There is much controversy about the neurobiological mechanisms underlying the effects of sleep-disordered breathing on the brain. The aim of this study was to investigate the association between markers of sleep-related hypoxemia and brain anatomy.

METHODS

We used data from a large-scale cohort from the general population (n = 775, 50.6% males, age range = 45-86 years, mean age = 60.3 ± 9.9) that underwent full polysomnography and brain magnetic resonance imaging to correlate respiratory variables with regional brain volume estimates.

RESULTS

After adjusting for age, gender, and cardiovascular risk factors, only mean oxygen saturation during sleep was associated with bilateral volume of hippocampus (right: p = 0.001; left: p < 0.001), thalamus (right: p < 0.001; left: p < 0.001), putamen (right: p = 0.001; left: p = 0.001), and angular gyrus (right: p = 0.011; left: p = 0.001). We observed the same relationship in left hemispheric amygdala (p = 0.010), caudate (p = 0.008), inferior frontal gyrus (p = 0.004), and supramarginal gyrus (p = 0.003). The other respiratory variables-lowest oxygen saturation, percentage of sleep time with oxygen saturation < 90%, apnea-hypopnea index, and oxygen desaturation index-did not show any significant association with brain volumes.

INTERPRETATION

Lower mean oxygen saturation during sleep was associated with atrophy of cortical and subcortical brain areas known for high sensitivity to oxygen supply. Their vulnerability to hypoxemia may contribute to behavioral phenotype and cognitive decline in patients with sleep-disordered breathing. ANN NEUROL 2020;87:921-930.

Gray Matter Volume Correlates of Sleepiness: A Voxel-Based Morphometry Study in Younger and Older Adults

BACKGROUND

Subjectively experienced sleepiness is a problem in society, possibly linked with gray matter (GM) volume. Given a different sleep pattern, aging may affect such associations, possibly due to shrinking brain volume.

PURPOSE

The purpose of the present study was to investigate the association between subjectively rated sleepiness and GM volume in thalamus, insula, hippocampus, and orbitofrontal cortex of young and older adults, after a normal night's sleep.

METHODS

Eighty-four healthy individuals participated (46 aged 20-30 years, and 38 aged 65-75 years). Morphological brain data were collected in a 3T magnetic resonance imaging (MRI) scanner. Sleepiness was rated multiple times during the imaging sessions.

RESULTS

In older, relative to younger, adults, clusters within bilateral mid-anterior insular cortex and right thalamus were negatively associated with sleepiness. Adjustment for the immediately preceding total sleep time eliminated the significant associations.

CONCLUSION

Self-rated momentary sleepiness in a monotonous situation appears to be negatively associated with GM volume in clusters within both thalamus and insula in older individuals, and total sleep time seems to play a role in this association. Possibly, this suggests that larger GM volume in these clusters may be protective against sleepiness in older individuals. This notion needs confirmation in further studies.

Sleep disorders among educationally active elderly people in Bialystok, Poland: a cross-sectional study

BACKGROUND

Sleep disorders in an ageing society constitute a significant public health problem. It is estimated that approximately 50% of people aged 55 years and older have trouble sleeping, including initiating and maintaining sleep. The aim of this study was to determine the prevalence of sleep disorders in a group of educationally active elderly people living in Bialystok, Poland.

METHODS

The study included a total of 182 people - residents of Bialystok - aged 60 or older; 146 women (80.22%) and 36 men (19.78%). The study used three standardized psychometric scales: The Athens Insomnia Scale (AIS), The Epworth Sleepiness Scale (ESS) and The Insomnia Severity Index (ISI).

RESULTS

More than half of the respondents scored 6 or more points on the AIS, which is considered a value that indicates a high probability of insomnia symptom occurrence. A similar percentage of respondents obtained a point value on the ISI indicating the presence of insomnia. The vast majority of respondents scored below 11 points on the ESS, which means no symptoms of excessive sleepiness. There was a significant correlation between the results of the above scales in the examined group in total and also by sex.

CONCLUSIONS

Sleep disorders, particularly insomnia, constitute a significant social and health problem in the group of educationally active elderly people living in Bialystok. In light of the obtained study results, it is recommended to conduct and improve existing health education programs aimed at the elderly regarding sleep disorders to improve the quality of their sleep, and thus quality of life, and raise the awareness of the elderly about the importance of sleep in everyday life. There is a need for further research in the field of sleep disorders in the elderly to determine the prevalence of these disorders on a national scale.

Effect of sleep quality on amnestic mild cognitive impairment vulnerable brain regions in cognitively normal elderly individuals

STUDY OBJECTIVES

This study aims to evaluate the extent to which sleep quality impacts amnestic mild cognitive impairment (aMCI)-related brain regions in a cognitively normal cohort of individuals.

METHODS

Seventy-four participants were rigorously evaluated using a battery of cognitive tests and a detailed clinical assessment to verify normal cognitive status. We then screened for sleep quality using the Pittsburgh Sleep Quality Index (PSQI) and depressive symptoms using the Geriatric Depression Scale (GDS). Five subjects were excluded due to mild depression. Overall 38 individuals with mean age 70.7 ± 7 were classified as poor sleepers and 31 with mean age of 69.6 ± 6 years as normal sleepers. Structural MRI and Freesurfer brain parcellation were used to measure aMCI-related brain regions.

RESULTS

Relative to normal sleepers, poor sleepers exhibited significant reductions in cortical and subcortical volumes bilaterally in the hippocampi, as well as in the superior parietal lobules and left amygdala. The effects were strongest in the left superior parietal lobule (p < .015), followed by the hippocampi. Diffuse patterns of cortical thinning were observed in the frontal lobes, but significant effects were concentrated in the right mesial frontal cortex. Lower sleep duration was most correlated with cortical volume and thickness reductions among all subjects.

CONCLUSIONS

Atrophy related to poor sleep quality impacted a number of regions implicated in aMCI and Alzheimer's disease (AD). As such, interventions targeted towards improving sleep quality amongst the elderly may prove an effective tool for modulating the course of aMCI and AD.

Sleep, hippocampal volume, and cognition in adults over 90 years old

BACKGROUND

Several lines of research support associations between sleep and cognition in older adults. However, there is a paucity of data regarding sleep and cognition in nonagenarians and centenarians.

AIMS

The current study examined self-reported sleep quantity and sleep quality in relation to hippocampal volume and cognition in adults aged 90 and older.

METHODS

A total of 144 participants of The 90+ Study completed The Medical Outcomes Study sleep questionnaire. Participants reported subjective sleep duration in hours and three sleep quality factors: sleep problems, adequacy, and somnolence. Neuropsychological assessments of memory, global cognition, language, and executive function were completed, on average, 61 days from the questionnaire. Hippocampal volume on 3 T MRI, adjusted for intracranial volume, was obtained in 82 participants. We performed multiple linear regressions, controlling for age, sex, education, sleep medication, and depression, to examine sleep characteristics in relation to hippocampal volume and cognitive performance in all the subjects and then stratified by cognition.

RESULTS

Sleep duration > 8 h was associated with lower scores in tests of global cognition, memory, and executive function compared to sleep duration of 7-8 h when collapsing across cognitive status, but only with memory in cognitively impaired subjects, and not in cognitively normal subjects.

CONCLUSIONS AND DISCUSSION

Long-sleep duration is associated with poorer global cognition, memory, and executive function in the oldest-old, and is only associated with memory in cognitively impaired oldest-old. Additional research is necessary to determine if sleep duration is a risk factor or a result of poor cognition in advanced age.

Multimodal brain imaging investigation of self-reported sleep quality and daytime sleepiness in older adults with heart failure

PURPOSE OF THE STUDY

Individuals with heart failure (HF) have a high frequency of sleep problems. Patients with HF present with structural brain changes different from normal aging including reductions in brain volume, increases in white matter hyperintensity (WMH) and reduced cerebral blood flow. These structural changes in the brain may explain the pathophysiology of sleep and daytime problems. The objective of this study was to determine whether multimodal imaging data are related to self-reported sleep problems and daytime sleepiness in older adults with HF.

METHODS

Participants in this study underwent magnetic resonance imaging scans on the General Electric 3.0 T Discovery MR750 to acquire WMH, cerebral blood flow and brain volume. Data on 37 stable HF patients (mean age = 68; SD = 5.75) were included.

RESULTS

In this sample, WMH was associated with daytime sleepiness (p = 0.025). However, gray and white matter volume and cerebral blood flow were not associated with daytime sleepiness, sleep quality or insomnia.

CONCLUSION

Although further studies are needed to determine the relationship between WMH and sleep and daytime problems, the findings preliminarily support that increases in WMH from ischemic changes could explain increases in daytime sleepiness among people with HF.

Sleep apnoea in the asymptomatic elderly: a real issue for the brain?

The link between sleep apnoea and brain structure is unclear; although dysfunction of the hippocampus, middle temporal gyrus and brainstem/cerebellum have been observed previously. However, this link has been little explored in elderly subjects. The aim of this study was to explore the link between sleep apnoea and the brain in an elderly population.226 asymptomatic elderly subjects (age mean±sd 75.3±0.9 years, range 72.3-77.8 years) from the PROOF (Evaluation of Ageing, Autonomic Nervous System Activity and Cardiovascular Events) cohort study were explored using linear voxel-based or cortical thickness with apnoea/hypopnoea index (AHI; mean±sd 15.9±11.5 events·h^-1, range 6-63.6 events·h^-1) as a covariate of main interest. The brain volumes of 20 control subjects, 18 apnoeic (AHI >29 events·h^-1) treated patients and 20 apnoeic untreated patients from this population were compared using voxel-based morphometry, cortical thickness or surface-based analyses.AHI was not associated with any change in local brain volume, cortical thickness or cortex surface. Control subjects, apnoeic treated and untreated patients were not different in terms of local brain volume, cortical thickness or surface.In a specific population of asymptomatic elderly healthy subjects, sleep apnoea does not seem to be associated with a change in local brain volume or in cortical thickness.

Static and dynamic functional connectivity in patients with chronic fatigue syndrome: use of arterial spin labelling fMRI

Studies using arterial spin labelling (ASL) have shown that individuals with chronic fatigue syndrome (CFS) have decreased regional cerebral blood flow, which may be associated with changes in functional neural networks. Indeed, recent studies indicate disruptions in functional connectivity (FC) at rest in chronically fatigued patients including perturbations in static FC (sFC), that is average FC at rest between several brain regions subserving neurocognitive, motor and affect-related networks. Whereas sFC often provides information of functional network reorganization in chronic illnesses, investigations of temporal changes in functional connectivity between multiple brain areas may shed light on the dynamic characteristics of brain network activation associated with such maladies. We used ASL fMRI in 19 patients with CFS and 15 healthy controls (HC) to examine both static and dynamic changes in FC among several a priori selected brain regions during a fatiguing cognitive task. HC showed greater increases than CFS in static FC (sFC) between insula and temporo-occipital structures and between precuneus and thalamus/striatum. Furthermore, inferior frontal gyrus connectivity to cerebellum, occipital and temporal structures declined in HC but increased in CFS. Patients also showed lower dynamic FC (dFC) between hippocampus and right superior parietal lobule. Both sFC and dFC correlated with task-related fatigue increases. These data provide the first evidence that perturbations in static and dynamic FC may underlie chronically fatigued patients' report of task-induced fatigue. Further research will determine whether such changes in sFC and dFC are also characteristic for other fatigued individuals, including patients with chronic pain, cancer and multiple sclerosis.

Do Older Adults Need Sleep? A Review of Neuroimaging, Sleep, and Aging Studies

PURPOSE OF REVIEW

Sleep habits, sleep physiology, and sleep disorders change with increasing age. However, there is a longstanding debate regarding whether older adults need sleep to maintain health and daily functioning (reduced-sleep-need view). An alternative possibility is that all older adults need sleep, but that many older adults have lost the ability to obtain restorative sleep (reduced-sleep-ability view). Prior research using behavioral and polysomnography outcomes has not definitively disentangled the reduced-sleep-need and reduced-sleep-ability views. Therefore, this review examines the neuroimaging literature to determine whether age-related changes in sleep cause-or are caused by-age-related changes in brain structure, function, and pathology.

RECENT FINDINGS

In middle-aged and older adults, poorer sleep quality, greater nighttime hypoxia, and shorter sleep duration related to cortical thinning in frontal regions implicated in slow wave generation, in frontoparietal networks implicated in cognitive control, and in hippocampal regions implicated in memory consolidation. Furthermore, poor sleep quality was associated with higher amyloid burden and decreased connectivity in the default mode network, a network that is disrupted in the pathway to Alzheimer's disease.

SUMMARY

All adults need sleep, but cortical thinning and amyloidal deposition with advancing age may weaken the brain's ability to produce restorative sleep. Therefore, sleep in older adults may not always support identical functions for physical, mental, and cognitive health as in young adults.

Gray Matter Hypertrophy and Thickening with Obstructive Sleep Apnea in Middle-aged and Older Adults

RATIONALE

Obstructive sleep apnea causes intermittent hypoxemia, hemodynamic fluctuations, and sleep fragmentation, all of which could damage cerebral gray matter that can be indirectly assessed by neuroimaging.

OBJECTIVES

To investigate whether markers of obstructive sleep apnea severity are associated with gray matter changes among middle-aged and older individuals.

METHODS

Seventy-one subjects (ages, 55-76 yr; apnea-hypopnea index, 0.2-96.6 events/h) were evaluated by magnetic resonance imaging. Two techniques were used: (1) voxel-based morphometry, which measures gray matter volume and concentration; and (2) FreeSurfer (an open source software suite) automated segmentation, which estimates the volume of predefined cortical/subcortical regions and cortical thickness. Regression analyses were performed between gray matter characteristics and markers of obstructive sleep apnea severity (hypoxemia, respiratory disturbances, and sleep fragmentation).

MEASUREMENTS AND MAIN RESULTS

Subjects had few symptoms, that is, sleepiness, depression, anxiety, and cognitive deficits. Although no association was found with voxel-based morphometry, FreeSurfer revealed increased gray matter with obstructive sleep apnea. Higher levels of hypoxemia correlated with increased volume and thickness of the left lateral prefrontal cortex as well as increased thickness of the right frontal pole, the right lateral parietal lobules, and the left posterior cingulate cortex. Respiratory disturbances positively correlated with right amygdala volume, and more severe sleep fragmentation was associated with increased thickness of the right inferior frontal gyrus.

CONCLUSIONS

Gray matter hypertrophy and thickening were associated with hypoxemia, respiratory disturbances, and sleep fragmentation. These structural changes in a group of middle-aged and older individuals may represent adaptive/reactive brain mechanisms attributed to a presymptomatic stage of obstructive sleep apnea.

Sleep-Disordered Breathing and Excessive Daytime Sleepiness

Sleep-related breathing disorders include obstructive sleep apnea (OSA), central sleep apnea, sleep-related hypoventilation, and sleep-related hypoxemia. Excessive daytime sleepiness (EDS) is frequently reported by patients with OSA but is not invariably present. The efficacy of positive airway pressure therapy in improving EDS is well established for OSA, but effectiveness is limited by suboptimal adherence. Non-OSA causes of sleepiness should be identified and treated before initiating pharmacotherapy for persistent sleepiness despite adequately treated OSA. Further research on the identification of factors that promote EDS in the setting of OSA is needed to aid in the development of better treatment options.