Altered cortical and subcortical local coherence in obstructive sleep apnea: a functional magnetic resonance imaging study

Multilayer network analysis of dynamic network reconfiguration in patients with moderate-to-severe obstructive sleep apnea and its association with neurocognitive function

BACKGROUND

Brain functional network disruption and neurocognitive dysfunction have been reported in obstructive sleep apnea (OSA) patients. Nevertheless, most research studies static networks, while brain evolution continues dynamically.

PURPOSE

To investigate the characteristics of dynamical networks in moderate-to-severe OSA patients using multilayer network analysis of dynamic networks and compare their association with neurocognitive function.

METHODS

Twenty-seven moderate-to-severe OSA patients and twenty-five matched healthy controls (HCs) who completed the examination of the Epworth sleepiness scale (ESS), neurocognitive function, polysomnography, and functional magnetic resonance imaging (fMRI) were prospectively included. The dynamic variations of resting-state functional networks in both groups were described via network switching rate. Switching rates and their correlation with clinical parameters were analyzed.

RESULTS

At the global level, network switching rates were notably lower in the OSA group than in the HCs group (p = 0.002). More specifically, the differences include the default mode network (DMN), auditory network, and ventral attention network at the subnetwork level, and the right rolandic operculum, left middle temporal gyrus, and right precentral gyrus at the nodal level. Furthermore, these altered switching rates have a close correlation with ESS, sleep parameters, and neurocognitive function.

CONCLUSION

Patients with moderate-to-severe OSA showed lower network switching rates, especially in the DMN, auditory network, and ventral attention network. The disruption of dynamic functional networks may be a potentially crucial mechanism of neurocognitive dysfunction in moderate-to-severe OSA patients.

Abnormal dynamic functional connectivity in the hippocampal subregions of patients with untreated moderate-to-severe obstructive sleep apnea

OBJECTIVE

To investigate the dynamic change characteristics of dynamic functional connectivity (dFC) between the hippocampal subregions (anterior and posterior) and other brain regions in obstructive sleep apnoea (OSA) and its relationship with cognitive function, and to explore whether these characteristics can be used to distinguish OSA from healthy controls (HCs).

METHODS

Eighty-five patients with newly diagnosed moderate-to-severe OSA and 85 HCs were enrolled. All participants underwent resting-state functional magnetic resonance imaging (fMRI). The difference between dFC values between the hippocampal subregions and other brain regions in OSA patients and HCs was compared using the two-sample t tests. Correlation analyses were used to assess the relationship between dFC, clinical data, and cognitive functions in OSA patients. dFC values from different brain regions were used as classification features to distinguish between the two groups using a support vector machine.

RESULTS

Compared with HCs, the dFC values between the left anterior hippocampus and right culmen of the cerebellum anterior lobe, right anterior hippocampus and left lingual gyrus, and left posterior hippocampus and left precentral gyrus were significantly lower, and the dFC values between the left posterior hippocampus and precuneus were significantly higher in OSA patients. The dFC values between the left posterior hippocampus and the precuneus of OSA patients were associated with sleep-related indicators and Montreal Cognitive Assessment scores. Support vector machine analysis results showed that dFC values in different brain regions could distinguish OSA patients from HCs.

CONCLUSION

dFC patterns between the hippocampal subregions and other brain regions were altered in patients with OSA, including the cerebellum, default mode networks, sensorimotor networks, and visual function networks, which is possibly associated with cognitive decline. In addition, the dFC values of different brain regions could effectively distinguish OSA patients from HCs. These findings provide new perspectives on neurocognition in these patients.

Changes in Functional Connectivity of Hippocampal Subregions in Patients with Obstructive Sleep Apnea after Six Months of Continuous Positive Airway Pressure Treatment

Previous studies have shown that the structural and functional impairments of hippocampal subregions in patients with obstructive sleep apnea (OSA) are related to cognitive impairment. Continuous positive airway pressure (CPAP) treatment can improve the clinical symptoms of OSA. Therefore, this study aimed to investigate functional connectivity (FC) changes in hippocampal subregions of patients with OSA after six months of CPAP treatment (post-CPAP) and its relationship with neurocognitive function. We collected and analyzed baseline (pre-CPAP) and post-CPAP data from 20 patients with OSA, including sleep monitoring, clinical evaluation, and resting-state functional magnetic resonance imaging. The results showed that compared with pre-CPAP OSA patients, the FC between the right anterior hippocampal gyrus and multiple brain regions, and between the left anterior hippocampal gyrus and posterior central gyrus were reduced in post-CPAP OSA patients. By contrast, the FC between the left middle hippocampus and the left precentral gyrus was increased. The changes in FC in these brain regions were closely related to cognitive dysfunction. Therefore, our findings suggest that CPAP treatment can effectively change the FC patterns of hippocampal subregions in patients with OSA, facilitating a better understanding of the neural mechanisms of cognitive function improvement, and emphasizing the importance of early diagnosis and timely treatment of OSA.

Functional Connectivity Changes in the Insular Subregions of Patients with Obstructive Sleep Apnea after 6 Months of Continuous Positive Airway Pressure Treatment

This study was aimed at investigating the functional connectivity (FC) changes between the insular subregions and whole brain in patients with obstructive sleep apnea (OSA) after 6 months of continuous positive airway pressure (CPAP) treatment and at exploring the relationship between resting-state FC changes and cognitive impairment in OSA patients. Data from 15 patients with OSA before and after 6 months of CPAP treatment were included in this study. The FC between the insular subregions and whole brain was compared between baseline and after 6 months of CPAP treatment in OSA. After 6 months of treatment, OSA patients had increased FC from the right ventral anterior insula to the bilateral superior frontal gyrus and bilateral middle frontal gyrus and increased FC from the left posterior insula to the left middle temporal gyrus and left inferior temporal gyrus. Hyperconnectivity was found from the right posterior insula to the right middle temporal gyrus, bilateral precuneus, and bilateral posterior cingulate cortex, which mainly involved the default mode network. There are changes in functional connectivity patterns between the insular subregions and whole brain in OSA patients after 6 months of CPAP treatment. These changes provide a better understanding of the neuroimaging mechanisms underlying the improvement in cognitive function and emotional impairment in OSA patients and can be used as potential biomarkers for clinical CPAP treatment.

Inherent regional brain activity changes in male obstructive sleep apnea with mild cognitive impairment: A resting-state magnetic resonance study

Obstructive sleep apnea (OSA) is the most common sleep disorder worldwide. Previous studies have shown that OSA patients are often accompanied by cognitive function loss, and the underlying neurophysiological mechanism is still unclear. This study aimed to determine whether there are differences in regional homogeneity (Reho) and functional connectivity (FC) across the brain between OSA patients with MCI (OSA-MCI) and those without MCI (OSA-nMCI) and whether such differences can be used to distinguish the two groups. Resting state magnetic resonance data were collected from 48 OSA-MCI patients and 47 OSA-nMCI patients. The brain regions with significant differences in Reho and FC between the two groups were identified, and the Reho and FC features were combined with machine learning methods for classification. Compared with OSA-nMCI patients, OSA-MCI patients showed significantly lower Reho in bilateral lingual gyrus and left superior temporal gyrus. OSA-MCI patients also showed significantly lower FC between the bilateral lingual gyrus and bilateral cuneus, left superior temporal gyrus and left middle temporal gyrus, middle frontal gyrus, and bilateral posterior cingulate/calcarine/cerebellar anterior lobe. Based on Reho and FC features, logistic regression classification accuracy was 0.87; sensitivity, 0.70; specificity, 0.89; and area under the curve, 0.85. Correlation analysis showed that MoCA scale score in OSA patients was significant positive correlation sleep efficiency and negatively correlation with neck circumference. In conclusion, our results showed that the OSA-MCI group showed decreased Reho and FC in specific brain regions compared with the OSA-nMCI group, which may help to understand the underlying neuroimaging mechanism of OSA leading to cognitive dysfunction and may serve as a potential biomarker to distinguish whether OSA is accompanied by cognitive impairment.

Distinct functional brain abnormalities in insomnia disorder and obstructive sleep apnea

Insomnia disorder (ID) and obstructive sleep apnea (OSA) are the two most prevalent sleep disorders worldwide, but the pathological mechanism has not been fully understood. Functional neuroimaging findings indicated regional abnormal neural activities existed in both diseases, but the results were inconsistent. This meta-analysis aimed to explore concordant regional functional brain changes in ID and OSA, respectively. We conducted a coordinate-based meta-analysis (CBMA) of resting-state functional magnetic resonance imaging (rs-fMRI) studies using the anisotropic effect-size seed-based d mapping (AES-SDM) approach. Studies that applied regional homogeneity (ReHo), amplitude of low-frequency fluctuations (ALFF) or fractional ALFF (fALFF) to analyze regional spontaneous brain activities in ID or OSA were included. Meta-regressions were then applied to investigate potential associations between demographic variables and regional neural activity alterations. Significantly increased brain activities in the left superior temporal gyrus (STG.L) and right superior longitudinal fasciculus (SLF.R), as well as decreased brain activities in several right cerebral hemisphere areas were identified in ID patients. As for OSA patients, more distinct and complicated functional activation alterations were identified. Several neuroimaging alterations were functionally correlated with mean age, duration or illness severity in two patients groups revealed by meta-regressions. These functionally altered areas could be served as potential targets for non-invasive brain stimulation methods. This present meta-analysis distinguished distinct brain function changes in ID and OSA, improving our knowledge of the neuropathological mechanism of these two most common sleep disturbances, and also provided potential orientations for future clinical applications.Registration number: CRD42022301938.

Dynamic regional homogeneity alterations and cognitive impairment in patients with moderate and severe obstructive sleep apnea

Background and purpose

Previous studies have found that abnormal local spontaneous brain activity in patients with obstructive sleep apnea (OSA) was associated with cognitive impairment, and dynamic functional connections can capture the time changes of functional connections during magnetic resonance imaging acquisition. The purpose of this study was to investigate the dynamic characteristics of regional brain connectivity and its relationship with cognitive function in patients with OSA and to explore whether the dynamic changes can be used to distinguish them from healthy controls (HCs).

Methods

Seventy-nine moderate and severe male OSA patients without any treatment and 84 HCs with similar age and education were recruited, and clinical data and resting functional magnetic resonance imaging data were collected. The dynamic regional homogeneity (dReHo) was calculated using a sliding window technique, and a double-sample t-test was used to test the difference in the dReHo map between OSA patients and HCs. We explored the relationship between dReHo and clinical and cognitive function in OSA patients using Pearson correlation analysis. A support vector machine was used to classify the OSA patients and HCs based on abnormal dReHo.

Result

Compared with HCs, OSA patients exhibited higher dReHo values in the right medial frontal gyrus and significantly lower dReHo values in the right putamen, right superior temporal gyrus, right cingulate gyrus, left insula and left precuneus. The correlation analysis showed that the abnormal dReHo values in multiple brain regions in patients with OSA were significantly correlated with nadir oxygen saturation, the oxygen depletion index, sleep period time, and Montreal cognitive assessment score. The support vector machine classification accuracy based on the dReHo difference in brain regions was 81.60%, precision was 81.01%, sensitivity was 81.01%, specificity was 82.14%, and area under the curve was 0.89.

Conclusion

The results of this study suggested that there was abnormal dynamic regional spontaneous brain activity in patients with OSA, which was related to clinical and cognitive evaluation and can be used to distinguish OSA patients from HCs. The dReHo is a potential objective neuroimaging marker for patients with OSA that can further the understanding of the neuropathological mechanism of patients with OSA.

Brain regional homogeneity changes after short-term positive airway pressure treatment in patients with obstructive sleep apnea

Patients with obstructive sleep apnea (OSA) reveal functional changes in brain sites involved in autonomic, cognitive, and mood regulations. However, it is unclear whether these brain changes reverse with short-term positive airway pressure (PAP) treatment. Our aim was to examine brain functional changes in response to 3-months of PAP treatment using regional homogeneity (ReHo) measures, where increased and decreased ReHo value indicates hyper- and hypo-local neural activities, respectively, and considered as functional deficits. We collected brain magnetic resonance imaging data as well as mood, cognitive, and sleep variables from 17 treatment-naïve OSA at baseline and after 3-months of PAP treatment and 25 age- and gender-matched healthy controls. Whole-brain ReHo maps were calculated and compared between OSA and controls and OSA subjects before and after PAP treatment. At baseline, treatment-naïve OSA subjects showed higher ReHo in the bilateral thalamus, putamen, postcentral gyrus, paracentral lobule, supplementary motor area, and right insula, and lower ReHo in the frontal and parietal cortices, compared to controls. After 3-months of PAP treatment, abnormal sleep and mood scores decreased significantly to normal levels. ReHo decreased in the autonomic and somatosensory control areas, including the thalamus, putamen, postcentral gyrus, and insula, and increased in the cognitive and affective regulatory parietal regions. The normalized ReHo was correlated with improved sleep quality and reduced anxiety symptoms. These findings suggest that 3-months of PAP use can improve sleep, mood issues, and partly recover brain activities, however, longer PAP treatment may be required to fully and permanently reverse brain functional deficits.

Mindfulness-based stress reduction training modulates striatal and cerebellar connectivity

Mindfulness is a meditation practice frequently associated with changes in subjective evaluation of cognitive and sensorial experience, as well as with modifications of brain activity and morphometry. Aside from the anatomical localization of functional changes induced by mindfulness practice, little is known about changes in functional and effective functional magnetic resonance imaging (fMRI) connectivity. Here we performed a connectivity fMRI analysis in a group of healthy individuals participating in an 8-week mindfulness-based stress reduction (MBSR) training program. Data from both a "mind-wandering" and a "meditation" state were acquired before and after the MBSR course. Results highlighted decreased local connectivity after training in the right anterior putamen and insula during spontaneous mind-wandering and the right cerebellum during the meditative state. A further effective connectivity analysis revealed (a) decreased modulation by the anterior cingulate cortex over the anterior portion of the putamen, and (b) a change in left and right posterior putamen excitatory input and inhibitory output with the cerebellum, respectively. Results suggest a rearrangement of dorsal striatum functional and effective connectivity in response to mindfulness practice, with changes in cortico-subcortical-cerebellar modulatory dynamics. Findings might be relevant for the understanding of widely documented mindfulness behavioral effects, especially those related to pain perception.

Aberrant Hippocampal Network Connectivity Is Associated With Neurocognitive Dysfunction in Patients With Moderate and Severe Obstructive Sleep Apnea

Objectives: This work aims to explore the changes of functional connectivity (FC) within the hippocampus network in patients with moderate and severe obstructive sleep apnea (OSA) and its correlation with neurocognitive dysfunction to explore the potential neurophysiological mechanism. Methods: A total of 32 treatment-naïve patients with moderate or severe OSA and 26 healthy controls (HCs), matched in age, gender, and education, underwent the evaluations of Epworth Sleep Scale, neurocognitive function, full-night polysomnography, and resting-state functional magnetic resonance imaging. The FC map of the hippocampus to other brain areas was compared among 15 OSA patients and 15 HCs with little head motion. Finally, the correlation between hippocampus FC strength and respiratory sleep parameters and neurocognitive assessments was analyzed. Results: Compared with HCs, the right hippocampus showed a significantly decreased FC with the bilateral insular lobe, right thalamus, and right anterior cingulate gyrus (ACG) and an increased FC with the right superior and middle temporal gyrus, left posterior cingulate gyrus, and left angular gyrus in the patients with OSA. The left hippocampus presented a significantly decreased FC with the left anterior cerebellum in patients with OSA. In addition, the aberrant right hippocampal FC with the right ACG was significantly correlated with disease severity and disrupted sleep architecture in the OSA group. Furthermore, after adjusting the related confounding factors, the FC strength between the right hippocampus, right insular lobe, and right thalamus was positively associated with the scores of Stroop Color-Word Test (SCWT) or Hopkins Verbal Learning Test-Revised (HVLT-R), while the FC between the right hippocampus and the right middle temporal gyrus was negatively correlated with the scores of HVLT-R. The right hippocampus FC with right superior temporal gyrus, left angular gyrus, and ACG were all negatively related to the scores of the symbol coding test (r = -0.642, p = 0.045; r = -0.638, p = 0.047; r = -0.753, p = 0.012), respectively. The FC between the left hippocampal and the left anterior cerebellar lobe showed a positive relationship with the scores of HVLT-R (r = 0.757, p = 0.011) and CPT-3D (r = -0.801, p = 0.005). Conclusion: The hippocampus presented abnormal FC with the cerebral and cerebellar regions extensively in OSA, and the correlation between abnormal hippocampal network FC and neurocognitive dysfunction in OSA suggests a promising insight to explore the potential biomarker and pathophysiologic mechanism of neurocognitive dysfunction of OSA.

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.

Resting-state functional magnetic resonance imaging of high altitude patients with obstructive sleep apnoea hypopnoea syndrome

The objective of the study was to observe brain function changes in Obstructive Sleep Apnoea Hypopnoea Syndrome (OSAHS) patients at high altitude. Resting-state functional magnetic resonance imaging (rs-fMRI) in patients with OSAHS was assessed using regional homogeneity (ReHo), amplitude of low frequency fluctuation (ALFF) and functional connectivity (FC). In this study, 36 male patients with OSAHS and 38 healthy male subjects were recruited from high-altitude areas, specifically, altitudes of 2,000–3,000 m. OSAHS was diagnosed by polysomnography (PSG). The blood oxygen level-dependent (BOLD) signals of OSAHS patients and healthy controls in the resting state were obtained and compared using ReHo, ALFF and FC methods. The posterior cingulate cortex (PCC) was selected as the seed region in the comparison of FC between the two groups. Compared with the healthy control group, multiple brain functions in the OSAHS patient group were different. There were correlations between the brain function values of some brain regions and demographic data. We also found that in contrast to earlier findings with individuals in plains areas, the brain function at the frontal lobe and the precuneus were higher in OSAHS patients, and the PCC showed higher FC with the left caudate, which may be due to the high-altitude hypoxic environment.

Reduced regional homogeneity and neurocognitive impairment in patients with moderate-to-severe obstructive sleep apnea

BACKGROUND

Neurocognitive dysfunction and abnormal regional homogeneity (ReHo) have been reported in patients with obstructive sleep apnea (OSA). However, little is known about whether brain functional alteration could be used to differentiate from healthy controls (HCs) and its correlation with neurocognitive impairment.

METHODS

Thirty-three treatment-naive patients with moderate-to-severe OSA and 22 HCs with matched age, sex and education underwent the evaluation of Epworth sleepiness scale, neurocognitive function, full night polysomnography and resting-state functional magnetic resonance imaging scan. ReHo, support vector machine, and correlation with neurocognitive function were administrated to analyze the data.

RESULTS

Compared with HCs, patients with OSA showed decreased ReHo in the bilateral superior frontal gyrus (FG), bilateral superior medial prefrontal cortex (PFC)/right supplementary motor area (SMA), left middle FG, and right precentral/postcentral gyrus. Negative correlations were observed between the ReHo values in the left superior FG/middle FG and apnea hypopnea index, oxygen desaturation index in the OSA group. The scores of Stroop word test, Stroop color-word test, symbol coding test were all negatively correlated with the ReHo values in the right precentral gyrus/postcentral gyrus in patients. Scores of the animal naming fluency test were positively correlated with the ReHo values in the left superior FG/middle FG in patients. Moreover, support vector machine analysis showed the ReHo values in the left superior FG/middle FG or bilateral superior medial PFC/right SMA both could discriminate patients from HCs with good accuracies, sensitivities, and specificities (85.45%, 87.88%, 81.82% and 81.82%, 84.85%, 77.27%, respectively).

CONCLUSION

Dysfunction in the frontal lobe is a potentially pivotal neuro-pathophysiological mechanism of neurocognitive impairment in patients with moderate-to-severe OSA. And significantly lower ReHo values in the left superior FG/middle FG and/or superior medial PFC/SMA are promising imaging biomarkers to discriminate moderate-to-severe patients with OSA from HCs.

Alterations in sympathetic and parasympathetic brain networks in obstructive sleep apnea

OBJECTIVE/BACKGROUND

Obstructive sleep apnea (OSA) patients experience hypoxia and, potentially, autonomic impairments stemming from neural damage. In this study, the executive control networks (ECNs), salience networks (SNs), and default mode networks (DMNs) of adult OSA patients, as well as their relationships with autonomic impairment, were investigated through independent component analysis (ICA).

PATIENTS/METHODS

A total of 41 OSA patients and 19 healthy controls volunteers were recruited and subjected to polysomnography to ascertain their degree, if any, of sleep apnea. Each participant also underwent a cardiovascular autonomic survey, with the participant's baroreflex sensitivity (BRS) being determined based on heart rate and blood pressure alterations. The resting fMRI data of the participants was separated using probabilistic ICA, and six autonomic resting-state networks were established for group comparisons. The differences in autonomic parameters, autonomic functional connectivity (FC), and clinical severity were then correlated.

RESULTS

The OSA group had significantly worse BRS values than the controls, as well as lower FC in the posterior and anterior SNs, bilateral ECNs, and the ventral DMN, and higher FC in the left ECN. These intrinsic connectivity networks showed dissociable correlations with greater baroreflex impairment and clinical disease severity. The higher FC in the left ECN was associated with the lower FC in the ventral DMN.

CONCLUSIONS

Our findings suggest that autonomic dysfunction in OSA might be accompanied by central autonomic network alterations. The stronger sympathetic-associated regions in ECNs and the weaker parasympathetic-associated regions in DMNs may represent intrinsic neural architecture fluctuations underlining their consequent processes in OSA.

Aberrant Awake Spontaneous Brain Activity in Obstructive Sleep Apnea: A Review Focused on Resting-State EEG and Resting-State fMRI

As one of the most common sleep-related respiratory disorders, obstructive sleep apnea (OSA) is characterized by excessive snoring, repetitive apnea, arousal, sleep fragmentation, and intermittent nocturnal hypoxemia. Focused on the resting-state brain imaging techniques, we reviewed the OSA-related resting-state electroencephalogram and resting-state functional magnetic resonance imaging (rsfMRI) studies. Compared with the healthy control group, patients with OSA presented increased frontal and central δ/θ powers during resting-state wakefulness, and their slow-wave activity showed a positive correlation with apnea–hypopnea index. For rsfMRI, the prefrontal cortex and insula may be the vital regions for OSA and are strongly related to the severity of the disease. Meanwhile, some large-scale brain networks, such as the default-mode network, salience network, and central executive network, play pivotal roles in the pathology of OSA. We then discussed the contribution of resting-state brain imaging as an evaluation approach for disease interventions. Finally, we briefly introduced the effects of OSA-related physiological and mental diseases and discussed some future research directions from the perspective of resting-state brain imaging.

Cognitive impairment in obstructive sleep apnea syndrome: a descriptive review

PURPOSE

Obstructive sleep apnea syndrome is a clinical sleep disorder defined by total or partial airflow restraint during sleep that results in fragmented sleep and hypoxemia, impacting negatively with cognitive functioning. This review was conducted on studies investigating structural brain alteration and cognitive impairment in obstructive sleep apnea syndrome.

METHOD

We searched on PubMed databases and screening references of included studies and review articles for additional citations. From initial 190 publications, only 17 met search criteria and described the cognitive impairment in obstructive sleep apnea syndrome.

RESULTS

Findings showed that patients with this syndrome had worse performance than healthy controls in attention, memory, and executive functions, showing specific neuroanathomical features. Cognitive impairment is also related to the severity of pathology. Treatment could improve certain cognitive aspects.

CONCLUSIONS

Cognitive deficits seem to be mainly attributable to decreased daytime vigilance and nocturnal hypoxemia.

Interhemispheric sleep depth coherence predicts driving safety in sleep apnea

Obstructive sleep apnea is associated with increased risk of car crashes; however, conventional measures of sleep apnea severity do not clearly identify those individuals who are at greatest risk. Here we tested whether, among individuals with sleep apnea, those with reduced interhemispheric sleep depth coherence, measured by correlation between right and left hemisphere odds ratio product, are at greater risk. The sample was derived from the Sleep Heart Health Study, a prospective observational cohort study, and included 1,378 adults with sleep apnea. The occurrence of a car crash was ascertained by a questionnaire administered 2 years after the sleep study, which asked about the occurrence of crashes during the year prior to questionnaire administration. We computed the sleep depth coherence from electroencephalograms recorded during baseline sleep studies and after 5 years. The weighted kappa coefficient and Bangdiwala's B were 0.34 and 0.59, respectively, indicating a fair to moderate stability over a 5-year interval. Multivariate logistic regression, adjusted for age, sex, race, body mass index and miles driven per year, was used to assess the risk of a car crash. Compared to the lowest quartile of sleep depth coherence (<0.86), individuals in the highest quartile (>0.93) had a 62% (95% confidence interval, 22%-81%) lower risk of an accident. Further adjustments for usual sleep duration and sleepiness did not meaningfully alter these findings. Higher interhemispheric sleep depth coherence is associated with significantly lower risk of motor vehicle crashes in individuals with sleep apnea. This suggests that high interhemispheric sleep depth coherence may be a marker of resistance to sleep apnea-related adverse neurocognitive outcomes.

Establishing the objective sleep phenotype in hypersomnolence disorder with and without comorbid major depression

STUDY OBJECTIVES

To clarify whether hypersomnolence disorder is associated with a specific sleep phenotype and altered neurophysiological function in persons with and without hypersomnolence disorder and major depressive disorder (MDD).

METHODS

Eighty-three unmedicated persons with and without hypersomnolence disorder and/or MDD underwent ad libitum high-density EEG polysomnography. Clinical and sleep architecture variables were compared between groups. Topographic patterns of slow-wave activity (SWA) relative to healthy controls were compared, with correlations between topographic SWA and daytime sleepiness assessed. Reductions in SWA in hypersomnolence disorder were mapped to specific cortical areas using source localization.

RESULTS

Regardless of the presence or absence of comorbid MDD, persons with hypersomnolence disorder had increased sleep duration relative to both controls and persons with MDD without hypersomnolence. Participants with hypersomnolence disorder also demonstrated reduced bilateral centroparietal low-frequency activity during nonrapid eye movement sleep relative to controls, a pattern not observed in persons with MDD but without hypersomnolence. SWA in these regions was negatively correlated with subjective measures of daytime sleepiness. Source localization demonstrated reductions in SWA in the supramarginal gyrus, somatosensory, and transverse temporal cortex in participants with hypersomnolence disorder.

CONCLUSIONS

Hypersomnolence disorder is characterized by increased sleep duration with normal sleep continuity, regardless of the presence or absence of comorbid depression. Reduced local SWA may be a specific neurophysiological finding in hypersomnolence disorder. Further research is warranted to elucidate the mechanisms through which these cortical changes are related to clinical complaints of daytime sleepiness.

Brain functional changes in tibetan with obstructive sleep apnea hypopnea syndrome: A resting state fMRI study

Tibetan is a major ethnic group living on the Qinghai-Tibet Plateau in China. Due to their high-altitude hypoxia environment, sleeping disorder and obstructive sleep apnea hypopnea syndrome (OSAHS) are more prone to occur. In this study, we investigated the brain structural and functional differences between Tibetans OSAHS patients and Tibetans healthy controls using high resolution three-dimensional T1 weighted magnetic resonance imaging (MRI) and resting state functional MRI. The analysis was based on voxel-based morphology, regional homogeneity (ReHo), amplitude of low-frequence fluctuation (ALFF) and functional connection (FC) methods. A total of 14 OSAHS patients and 16 healthy control, all Tibetan male, matched closely in terms of age, education and living altitude, were recruited. The relationship between the ReHo and ALFF values at different brain areas and clinical features, including the apnea hypopnea index (AHI) in the OSAHS group, was analyzed using Pearson correlation. Compared with healthy control, OSAHS patients showed no significant gray matter volume or FC change. OSAHS group showed significantly increased ReHo values in the superior frontal gyrus dorsolateral, the left middle frontal gyrus, and the superior frontal gyrus medial. In contrast, OSAHS group showed decreased ReHo value in the left fusiform gyrus and cerebellum lobule 6. OSAHS group showed significantly increased ALFF values in the right inferior frontal gyrus orbital part, the right median cingulate and paracingulate gyri, the right Inferior frontal gyrus triangular part, the right insula and the left superior frontal gyrus dorsolateral. In the OSAHS group, the AHI showed a positive correlation with the ReHo value at the left cerebellum lobule 6 (r = 0.562, P = .037). Tibetan OSAHS patients had no significant change in brain structure and FC, which may be due to their adaption to the hypoxia environment. ReHo values and ALFF values changes in multiple brain areas in Tibetan OSAHS patients indicated brain functional impairment in multiple brain regions. The left cerebellum lobule 6 gradually compensates brain function as OSAHS progresses.

Psychological and Brain Connectivity Changes Following Trauma-Focused CBT and EMDR Treatment in Single-Episode PTSD Patients

Among the different therapeutic alternatives for post-traumatic stress disorder (PTSD), Trauma-Focused Cognitive-Behavioral Therapy (TF-CBT) and Eye Movement Desensitization and Reprocessing (EMDR) Therapy have shown promising results in helping patients cope with PTSD symptoms. However, given the different theoretical and methodological substrate of TF-CBT and EMDR, a potentially different impact on the brain for the two interventions could be hypothesized, as well as an interaction between trauma-specific PTSD symptomatology and response to a given psychotherapy. In this study, we monitored psychological and spontaneous functional connectivity fMRI patterns in two groups of PTSD patients who suffered by the same traumatic event (i.e., natural disaster), before and after a cycle of psychotherapy sessions based on TF-CBT and EMDR. Thirty-seven (37) PTSD patients were enrolled from a larger sample of people exposed to a single, acute psychological stress (i.e., 2002 earthquake in San Giuliano di Puglia, Italy). Patients were randomly assigned to TF-CBT (n = 14) or EMDR (n = 17) psychotherapy. Clinical assessment was performed using the Clinician-Administered PTSD Scale (CAPS), the Davidson Trauma Scale (DTS) and the Work and Social Adjustment Scale (WSAS), both at baseline and after treatment. All patients underwent a fMRI data acquisition session before and after treatment, aimed at characterizing their functional connectivity (FC) profile at rest, as well as potential connectivity changes associated with the clinical impact of psychotherapy. Both EMDR and TF-CBT induced statistically significant changes in clinical scores, with no difference in the clinical impact of the two treatments. Specific changes in FC correlated with the improvement at the different clinical scores, and differently for EMDR and TF-CBT. However, a similarity in the connectivity changes associated with changes in CAPS in both groups was also observed. Specifically, changes at CAPS in the entire sample correlated with an (i) increase in connectivity between the bilateral superior medial frontal gyrus and right temporal pole, and a (ii) decrease in connectivity between left cuneus and left temporal pole. Results point to a similar, beneficial psychological impact of EMDR and TF-CBT for treatment of natural-disaster PTSD patients. Neuroimaging data suggest a similar neurophysiological substrate for clinical improvement following EMDR and TF-CBT, involving changes affecting bilateral temporal pole connectivity.

Sleep Biomarkers, Health Comorbidities, and Neurocognition in Obstructive Sleep Apnea

OBJECTIVES

Obstructive sleep apnea (OSA) is associated with cognitive impairment but the relationships between specific biomarkers and neurocognitive domains remain unclear. The present study examined the influence of common health comorbidities on these relationships. Adults with suspected OSA (N=60; 53% male; M age=52 years; SD=14) underwent neuropsychological evaluation before baseline polysomnography (PSG). Apneic syndrome severity, hypoxic strain, and sleep architecture disturbance were assessed through PSG.

METHODS

Depression (Center for Epidemiological Studies Depression Scale, CESD), pain, and medical comorbidity (Charlson Comorbidity Index) were measured via questionnaires. Processing speed, attention, vigilance, memory, executive functioning, and motor dexterity were evaluated with cognitive testing. A winnowing approach identified 9 potential moderation models comprised of a correlated PSG variable, comorbid health factor, and cognitive performance.

RESULTS

Regression analyses identified one significant moderation model: average blood oxygen saturation (AVO2) and depression predicting recall memory, accounting for 31% of the performance variance, p<.001. Depression was a significant predictor of recall memory, p<.001, but AVO2 was not a significant predictor. The interaction between depression and AVO2 was significant, accounting for an additional 10% of the variance, p<.001. The relationship between low AVO2 and low recall memory performance emerged when depression severity ratings approached a previously established clinical cutoff score (CESD=16).

CONCLUSIONS

This study examined sleep biomarkers with specific neurocognitive functions among individuals with suspected OSA. Findings revealed that depression burden uniquely influence this pathophysiological relationship, which may aid clinical management. (JINS, 2018, 28, 864-875).

Topological Reorganization of the Default Mode Network in Severe Male Obstructive Sleep Apnea

Impaired spontaneous regional activity and altered topology of the brain network have been observed in obstructive sleep apnea (OSA). However, the mechanisms of disrupted functional connectivity (FC) and topological reorganization of the default mode network (DMN) in patients with OSA remain largely unknown. We explored whether the FC is altered within the DMN and examined topological changes occur in the DMN in patients with OSA using a graph theory analysis of resting-state functional magnetic resonance imaging data and evaluated the relationship between neuroimaging measures and clinical variables. Resting-state data were obtained from 46 male patients with untreated severe OSA and 46 male good sleepers (GSs). We specifically selected 20 DMN subregions to construct the DMN architecture. The disrupted FC and topological properties of the DMN in patients with OSA were characterized using graph theory. The OSA group showed significantly decreased FC of the anterior-posterior DMN and within the posterior DMN, and also showed increased FC within the DMN. The DMN exhibited small-world topology in both OSA and GS groups. Compared to GSs, patients with OSA showed a decreased clustering coefficient (C_p) and local efficiency, and decreased nodal centralities in the left posterior cingulate cortex and dorsal medial prefrontal cortex, and increased nodal centralities in the ventral medial prefrontal cortex and the right parahippocampal cortex. Finally, the abnormal DMN FC was significantly related to C_p, path length, global efficiency, and Montreal cognitive assessment score. OSA showed disrupted FC within the DMN, which may have contributed to the observed topological reorganization. These findings may provide further evidence of cognitive deficits in patients with OSA.

Aberrant brain functional connectome in patients with obstructive sleep apnea

OBJECTIVE

Obstructive sleep apnea (OSA) is accompanied by widespread abnormal spontaneous regional activity related to cognitive deficits. However, little is known about the topological properties of the functional brain connectome of patients with OSA. This study aimed to use the graph theory approaches to investigate the topological properties and functional connectivity (FC) of the functional connectome in patients with OSA, based on resting-state functional magnetic resonance imaging (rs-fMRI).

METHODS

Forty-five male patients with newly diagnosed untreated severe OSA and 45 male good sleepers (GSs) underwent a polysomnography (PSG), clinical evaluations, and rs-fMRI scans. The automated anatomical labeling (AAL) atlas was used to construct the functional brain connectome. The topological organization and FC of brain functional networks in patients with OSA were characterized using graph theory methods and investigated the relationship between functional network topology and clinical variables.

RESULTS

Both the patients with OSA and the GSs exhibited high-efficiency "small-world" network attributes. However, the patients with OSA exhibited decreased σ, γ, Eglob; increased Lp, λ; and abnormal nodal centralities in several default-mode network (DMN), salience network (SN), and central executive network (CEN) regions. However, the patients with OSA exhibited abnormal functional connections between the DMN, SN, and CEN. The disrupted FC was significantly positive correlations with the global network metrics γ and σ. The global network metrics were significantly correlated with the Epworth Sleepiness Scale (ESS) score, Montreal Cognitive Assessment (MoCA) score, and oxygen desaturation index.

CONCLUSION

The findings suggest that the functional connectome of patients with OSA exhibited disrupted functional integration and segregation, and functional disconnections of the DMN, SN, and CEN. The aberrant topological attributes may be associated with disrupted FC and cognitive functions. These topological abnormalities and disconnections might be potential biomarkers of cognitive impairments in patients with OSA.

Age of Insomnia Onset Correlates with a Reversal of Default Mode Network and Supplementary Motor Cortex Connectivity

Insomnia might occur as result of increased cognitive and physiological arousal caused by acute or long acting stressors and associated cognitive rumination. This might lead to alterations in brain connectivity patterns as those captured by functional connectivity fMRI analysis, leading to potential insight about primary insomnia (PI) pathophysiology as well as the impact of long-term exposure to sleep deprivation. We investigated changes of voxel-wise connectivity patterns in a sample of 17 drug-naïve PI patients and 17 age-gender matched healthy controls, as well as the relationship between brain connectivity and age of onset, illness duration, and severity. Results showed a significant increase in resting-state functional connectivity of the bilateral visual cortex in PI patients, associated with decreased connectivity between the visual cortex and bilateral temporal pole. Regression with clinical scores originally unveiled a pattern of increased local connectivity as measured by intrinsic connectivity contrast (ICC), specifically resembling the default mode network (DMN). Additionally, age of onset was found to be correlated with the connectivity of supplementary motor area (SMA), and the strength of DMN←→SMA connectivity was significantly correlated with both age of onset (R² = 41%) and disease duration (R² = 21%). Chronic sleep deprivation, but most importantly early insomnia onset, seems to have a significant disruptive effect over the physiological negative correlation between DMN and SMA, a well-known fMRI marker of attention performance in humans. This suggests the need for more in-depth investigations on the prevention and treatment of connectivity changes and associated cognitive and psychological deficits in PI patients.

Obstructive sleep apnea and cortical thickness in females and males

Introduction

Obstructive sleep apnea (OSA) affects approximately 10% of adults, and alters brain gray and white matter. Psychological and physiological symptoms of the disorder are sex-specific, perhaps related to greater injury occurs in female than male patients in white matter. Our objective was to identify influences of OSA separated by sex on cortical gray matter.

Methods

We assessed cortical thickness in 48 mild-severe OSA patients (mean age±std[range] = 46.5±9.0[30.8–62.7] years; apnea-hypopnea index = 32.6±21.1[6–102] events/hour; 12 female, 36 male; OSA severity: 5 mild, 18 moderate, 25 severe) and 62 controls (mean age = 47.7±8.9[30.9–65.8] years; 22 female, 40 male). All OSA patients were recently-diagnosed via polysomnography, and control subjects screened and a subset assessed with sleep studies. We used high-resolution magnetic resonance imaging to identify OSA-related cortical thinning, based on a model with condition and sex as independent variables. OSA and OSA-by-sex interaction effects were assessed (P<0.05, corrected for multiple comparisons).

Results

Multiple regions of reduced cortical thickness appeared bilaterally in the superior frontal lobe in female OSA vs. all other groups. Significant thinning within the pre- and post-central gyri and the superior temporal gyrus, extending into the insula, appeared between the general OSA populations vs. control subjects. No areas showed increased thickness in OSA vs. controls or positive female OSA interaction effects.

Conclusions

Reduced cortical thickness likely represents tissue atrophy from long term injury, including death of neurons and supporting glia from repeated intermittent hypoxic exposure in OSA, although disease comordities may also contribute to thinning. Lack of polysomnography in all control subjects means results may be confounded by undiagnosed OSA. The greater cortical injury in cognitive areas of female OSA patients may underlie enhanced symptoms in that group. The thinning associated with OSA in male and females OSA patients may contribute to autonomic dysregulation and impaired upper airway sensori-motor function.

Altered Functional Connectivity in Idiopathic Rapid Eye Movement Sleep Behavior Disorder: A Resting-State EEG Study

Study Objectives

Idiopathic rapid eye movement sleep behavior disorder (iRBD) is considered as a prodromal stage of synucleinopathy. Although loss of functional connectivity is implicated in neurodegenerative diseases, network characteristics of electroencephalography (EEG) in iRBD are unknown. Therefore, we evaluated resting-state EEG functional connectivity to identify the brain network changes in patients with iRBD.

Methods

We prospectively enrolled 20 patients with polysomnography-confirmed iRBD and 16 controls. Four patients with mild cognitive impairment were excluded from the analysis after cognitive function tests. EEG was recorded during relaxed wakefulness. We computed the weighted phase lag index as a measure of functional connectivity from EEG recordings.

Results

All patients with iRBD (mean age 64.3 years; men, 68.8%) had no overt manifestations of neurodegenerative diseases such as Parkinsonism or dementia. The mean duration from symptom onset was 4.8 years. Overall connectivity strength did not differ between the two groups in all frequency bands. However, comparisons of each functional connection with the nonparametric permutation test demonstrated iRBD had decreased delta-band functional connectivity in the frontal regions. There were no significantly increased functional connections in all frequencies. The altered connections had a significant correlation with RBD questionnaire scores. Notably, delta-band weighted phase lag index between left frontal and central regions was correlated with verbal fluency performance (r = 0.486, p = .007).

Conclusions

Resting-state brain network of iRBD was characterized by a loss of delta-band functional connectivity. Therefore, functional networks in iRBD are altered at the early phase of disease.

Disrupted brain network topology in chronic insomnia disorder: A resting-state fMRI study

This study investigated the topological characteristics of brain functional networks in chronic insomnia disorder (CID) patients. The resting-state functional magnetic resonance imaging and graph theory analysis method were applied to investigate the brain functional connectome patterns among 45 CID patients and 32 healthy controls. The brain functional connectome was constructed by thresholding partial correlation matrices of 90 brain regions from an automated anatomical labeling atlas. The topologic properties of brain functional connectomes at both global and nodal levels were tested. The CID patients had decreased number of module (p = .014) and hierarchy (p = .038), and increased assortativity (p = .035). Furthermore, some brain regions located in the default mode network, dorsal attention network, and sensory-motor network in these patients showed altered nodal centralities. Within these areas, the node betweenness of right central paracentral lobule had positive correlation with the Pittsburgh Sleep Quality Index score (R = 0.319, p = .039). The results imply that functional disruptions of CID patients may be related to disruptions in global and regional topological organization of the brain functional connectome, and provide new and important insights to understand the pathophysiological mechanisms of CID.

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Chronic insomnia disorder (CID) patients had disrupted global topological properties.

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Many brain regions of CID patients showed altered nodal centralities involving three different resting networks.

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Functional disruption of right central paracentral lobule may be a target for therapeutic intervention in pediatric CID.

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The disruption of topological organization might be explain the mechanism/reason of functional disruptions of CID.

CPAP Adherence is Associated With Attentional Improvements in a Group of Primarily Male Patients With Moderate to Severe OSA

STUDY OBJECTIVES

Obstructive sleep apnea (OSA) is a widespread condition that adversely affects physical health and cognitive functioning. The prevailing treatment for OSA is continuous positive airway pressure (CPAP), but therapeutic benefits are dependent on consistent use. Our goal was to investigate the relationship between CPAP adherence and measures of sustained attention in patients with OSA. Our hypothesis was that the Psychomotor Vigilance Task (PVT) would be sensitive to attention-related improvements resulting from CPAP use.

METHODS

This study was a secondary analysis of a larger clinical trial. Treatment adherence was determined from CPAP use data. Validated sleep-related questionnaires and a sustained-attention and alertness test (PVT) were administered to participants at baseline and at the 6-month time point.

RESULTS

Over a 6-month time period, the average CPAP adherence was 3.32 h/night (standard deviation [SD] = 2.53), average improvement in PVT minor lapses was -4.77 (SD = 13.2), and average improvement in PVT reaction time was -73.1 milliseconds (standard deviation = 211). Multiple linear regression analysis showed that higher CPAP adherence was significantly associated with a greater reduction in minor lapses in attention after 6 months of continuous treatment with CPAP therapy (β = -0.72, standard error = 0.34, P = .037).

CONCLUSIONS

The results of this study showed that higher levels of CPAP adherence were associated with significant improvements in vigilance. Because the PVT is a performance-based measure that is not influenced by prior learning and is not subjective, it may be an important supplement to patient self-reported assessments.

CLINICAL TRIAL REGISTRATION

Name: Effect of Self-Management on Improving Sleep Apnea Outcomes, URL: https://clinicaltrials.gov/ct2/show/NCT00310310, Identifier: NCT00310310.

Diffusion Tensor Imaging Tractography Reveals Disrupted White Matter Structural Connectivity Network in Healthy Adults with Insomnia Symptoms

Neuroimaging studies have revealed that insomnia is characterized by aberrant neuronal connectivity in specific brain regions, but the topological disruptions in the white matter (WM) structural connectivity networks remain largely unknown in insomnia. The current study uses diffusion tensor imaging (DTI) tractography to construct the WM structural networks and graph theory analysis to detect alterations of the brain structural networks. The study participants comprised 30 healthy subjects with insomnia symptoms (IS) and 62 healthy subjects without IS. Both the two groups showed small-world properties regarding their WM structural connectivity networks. By contrast, increased local efficiency and decreased global efficiency were identified in the IS group, indicating an insomnia-related shift in topology away from regular networks. In addition, the IS group exhibited disrupted nodal topological characteristics in regions involving the fronto-limbic and the default-mode systems. To our knowledge, this is the first study to explore the topological organization of WM structural network connectivity in insomnia. More importantly, the dysfunctions of large-scale brain systems including the fronto-limbic pathways, salience network and default-mode network in insomnia were identified, which provides new insights into the insomnia connectome. Topology-based brain network analysis thus could be a potential biomarker for IS.

An Evolutionary Game Theory Model of Spontaneous Brain Functioning

Our brain is a complex system of interconnected regions spontaneously organized into distinct networks. The integration of information between and within these networks is a continuous process that can be observed even when the brain is at rest, i.e. not engaged in any particular task. Moreover, such spontaneous dynamics show predictive value over individual cognitive profile and constitute a potential marker in neurological and psychiatric conditions, making its understanding of fundamental importance in modern neuroscience. Here we present a theoretical and mathematical model based on an extension of evolutionary game theory on networks (EGN), able to capture brain's interregional dynamics by balancing emulative and non-emulative attitudes among brain regions. This results in the net behavior of nodes composing resting-state networks identified using functional magnetic resonance imaging (fMRI), determining their moment-to-moment level of activation and inhibition as expressed by positive and negative shifts in BOLD fMRI signal. By spontaneously generating low-frequency oscillatory behaviors, the EGN model is able to mimic functional connectivity dynamics, approximate fMRI time series on the basis of initial subset of available data, as well as simulate the impact of network lesions and provide evidence of compensation mechanisms across networks. Results suggest evolutionary game theory on networks as a new potential framework for the understanding of human brain network dynamics.

A Meta-analysis of Voxel-based Brain Morphometry Studies in Obstructive Sleep Apnea

Gray matter (GM) anomalies may represent a critical pathology underlying obstructive sleep apnea (OSA). However, the evidence regarding their clinical relevance is inconsistent. We conducted a meta-analysis of voxel-based morphometry (VBM) studies of patients with OSA to identify their brain abnormalities. A systematic search was conducted based on PRISMA guidelines, and a meta-analysis was performed using the anisotropic effect-size-based algorithms (ASE-SDM) to quantitatively estimate regional GM changes in patients with OSA. Fifteen studies with 16 datasets comprising 353 untreated patients with OSA and 444 healthy controls were included. Our results revealed GM reductions in the bilateral anterior cingulate/paracingulate gyri (ACG/ApCG), left cerebellum (lobules IV/V and VIII), bilateral superior frontal gyrus (SFG, medial rostral part), right middle temporal gyrus (MTG), and right premotor cortex. Moreover, GM reductions in the bilateral ACG/ApCG were positively associated with body mass index (BMI) and age among patients with OSA, and GM reductions in the SFG (medial rostral part) were negatively associated with Epworth sleepiness scale (ESS) scores and sex (male). These abnormalities may represent structural brain underpinnings of neurocognitive abnormalities and respiratory-related abnormalities in OSA. In particular, this study adds to Psychoradiology, which is a promising subspecialty of clinical radiology mainly for psychiatric disorders.

Functional reorganization in obstructive sleep apnoea and insomnia: A systematic review of the resting-state fMRI

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Resting state functional MRI studies is a promising non-invasive tool for better understanding of the pathophysiology of sleep disorders.

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The salience network is involved in hyperarousal and affective symptoms in insomnia.

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The posterior default mode network appears to underlie cognitive and depressive symptoms of obstructive sleep apnoea.

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Disruption of intrinsic networks have been demonstrated in major depression, which is a common co-morbidity of sleep disorders.

Functional neuroimaging techniques have accelerated progress in the study of sleep disorders. Considering the striking prevalence of these disorders in the general population, however, as well as their strong bidirectional relationship with major neuropsychiatric disorders, including major depressive disorder, their numbers are still surprisingly low. This review examines the contribution of resting state functional MRI to current understanding of two major sleep disorders, insomnia disorder and obstructive sleep apnoea. An attempt is made to learn from parallels of previous resting state functional neuroimaging findings in major depressive disorder. Moreover, shared connectivity biomarkers are suggested for each of the sleep disorders. Taken together, despite some inconsistencies, the synthesis of findings to date highlights the importance of the salience network in hyperarousal and affective symptoms in insomnia. Conversely, dysfunctional connectivity of the posterior default mode network appears to underlie cognitive and depressive symptoms of obstructive sleep apnoea.

Unexpected reductions in regional cerebral perfusion during prolonged hypoxia

KEY POINTS

Cognitive performance is impaired by hypoxia despite global cerebral oxygen delivery and metabolism being maintained. Using arterial spin labelled (ASL) magnetic resonance imaging, this is the first study to show regional reductions in cerebral blood flow (CBF) in response to decreased oxygen supply (hypoxia) at 2 h that increased in area and became more pronounced at 10 h. Reductions in CBF were seen in brain regions typically associated with the 'default mode' or 'task negative' network. Regional reductions in CBF, and associated vasoconstriction, within the default mode network in hypoxia is supported by increased vasodilatation in these regions to a subsequent hypercapnic (5% CO₂ ) challenge. These results suggest an anatomical mechanism through which hypoxia may cause previously reported deficits in cognitive performance.

ABSTRACT

Hypoxia causes an increase in global cerebral blood flow, which maintains global cerebral oxygen delivery and metabolism. However, neurological deficits are abundant under hypoxic conditions. We investigated regional cerebral microvascular responses to acute (2 h) and prolonged (10 h) poikilocapnic normobaric hypoxia. We found that 2 h of hypoxia caused an expected increase in frontal cortical grey matter perfusion but unexpected perfusion decreases in regions of the brain normally associated with the 'default mode' or 'task negative' network. After 10 h in hypoxia, decreased blood flow to the major nodes of the default mode network became more pronounced and widespread. The use of a hypercapnic challenge (5% CO₂ ) confirmed that these reductions in cerebral blood flow from hypoxia were related to vasoconstriction. Our findings demonstrate steady-state deactivation of the default network under acute hypoxia, which become more pronounced over time. Moreover, these data provide a unique insight into the nuanced localized cerebrovascular response to hypoxia that is not attainable through traditional methods. The observation of reduced perfusion in the posterior cingulate and cuneal cortex, which are regions assumed to play a role in declarative and procedural memory, provides an anatomical mechanism through which hypoxia may cause deficits in working memory.

Accelerated Echo Planer J-resolved Spectroscopic Imaging of Putamen and Thalamus in Obstructive Sleep Apnea

Obstructive sleep apnea syndrome (OSAS) leads to neurocognitive and autonomic deficits that are partially mediated by thalamic and putamen pathology. We examined the underlying neurochemistry of those structures using compressed sensing-based 4D echo-planar J-resolved spectroscopic imaging (JRESI), and quantified values with prior knowledge fitting. Bilaterally increased thalamic mI/Cr, putamen Glx/Cr, and Glu/Cr, and bilaterally decreased thalamic and putamen tCho/Cr and GABA/Cr occurred in OSAS vs healthy subjects (p < 0.05). Increased right thalamic Glx/Cr, Glu/Cr, Gln/Cr, Asc/Cr, and decreased GPC/Cr and decreased left thalamic tNAA/Cr, NAA/Cr were detected. The right putamen showed increased mI/Cr and decreased tCho/Cr, and the left, decreased PE/Cr ratio. ROC curve analyses demonstrated 60–100% sensitivity and specificity for the metabolite ratios in differentiating OSAS vs. controls. Positive correlations were found between: left thalamus mI/Cr and baseline oxygen saturation (SaO₂); right putamen tCho/Cr and apnea hypopnea index; right putamen GABA/Cr and baseline SaO₂; left putamen PE/Cr and baseline SaO₂; and left putamen NAA/Cr and SaO₂ nadir (all p < 0.05). Negative correlations were found between left putamen PE/Cr and SaO₂ nadir. These findings suggest underlying inflammation or glial activation, with greater alterations accompanying lower oxygen saturation. These metabolite levels may provide biomarkers for future neurochemical interventions by pharmacologic or other means.

Changes in cerebral metabolites in obstructive sleep apnea: a systemic review and meta-analysis

Cognitive impairment is associated with changes in cerebral metabolites in patients with obstructive sleep apnea (OSA). Several studies have used magnetic resonance spectroscopy (MRS) to detect variations in cerebral metabolites; however, the results have been inconsistent. This meta-analysis summarizes the differences in cerebral metabolites between patients with OSA and controls. Two electronic databases, PubMed and Embase, were searched for articles (published before March 31, 2016) describing studies that used MRS to evaluate the cerebral metabolite changes. The overall effects were measured using the weighted mean difference with a 95% confidence interval. Subgroup analysis and sensitivity analysis were used to explore the sources of between-study heterogeneity and the stability of the results. Publication bias was also evaluated. Thirteen studies were ultimately included. In the hippocampus, the N-acetylaspartate (NAA)/creatine ratio was lower in patients with OSA. In the frontal lobe, only the NAA/choline ratio was lower in patients with OSA. Cerebral metabolites are significantly altered in the hippocampus in patients with OSA. Further clinical studies are needed to explore the underlying mechanisms between OSA and the changes in cerebral metabolites in the brain.

Aberrant Insular Functional Network Integrity in Patients with Obstructive Sleep Apnea

STUDY OBJECTIVES

Obstructive sleep apnea (OSA) is accompanied by tissue injury to the insular cortices, areas that regulate autonomic pain, dyspnea, and mood, all of which are affected in the syndrome. Presumably, the dysregulation of insular-related functions are mediated by aberrant functional connections with other brain regions; however, the integrity of the functional connectivity (FC) to other sites is undescribed. Our aim was to examine resting-state FC of the insular cortices to other brain areas in OSA, relative to control subjects.

METHODS

We collected resting-state functional magnetic resonance imaging (MRI) data from 67 newly diagnosed, treatment-naïve OSA and 75 control subjects using a 3.0-Tesla MRI scanner. After standard processing, data were analyzed for the left and right insular FC.

RESULTS

OSA subjects showed complex aberrant insular FC to several brain regions, including frontal, parietal, cingulate, temporal, limbic, basal ganglia, thalamus, occipital, cerebellar, and brainstem regions. Areas of altered FC in OSA showed linear relationships with magnitudes of sleep related and neuropsychologic-related variables, whereas control subjects showed no such relationships with those measures.

CONCLUSIONS

Brain functional connections from insular sites to other brain regions in OSA subjects represent abnormal autonomic, affective, sensorimotor, and cognitive control networks that may affect both impaired parasympathetic and sympathetic interactions, as well as abnormal sensorimotor integration, affected in the condition. The functional changes likely result from the previously reported structural changes in OSA subjects, as demonstrated by diverse neuroimaging studies.

Obstructive sleep apnoea and dementia: is there a link?

OBJECTIVE

Obstructive sleep apnoea is a common sleep disturbance in people of all ages, while dementia is an increasing entity among the ageing population of the world. Recent studies have established a link between sleep apnoea and cognitive decline. This literature review explores this relationship and examines the mechanisms, neurobiology and treatment modalities.

DESIGN

The study was conducted with the use of narrative literature overview.

RESULTS AND CONCLUSIONS

While there are numerous studies that establish a clear relationship between obstructive sleep apnoea, cognitive decline and dementia, more work is needed in understanding the mechanism and processes involved. A detailed understanding of pathophysiology of sleep and the relationship with cognitive decline will be vital in addressing the possibility of averting a likely reversible cause of dementia or cognitive decline.

Structural and functional neural adaptations in obstructive sleep apnea: An activation likelihood estimation meta-analysis

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The right basolateral amygdala, the hippocampus and the right insular cortex are important nodes in obstructive sleep apnea (OSA).

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Functional characterization of these regions suggested associated dysfunction of emotional, sensory, and limbic processes in OSA.

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Connectivity analysis demonstrated that these regions are part of a joint network comprising the anterior insula, posterior-medial frontal cortex and thalamus.

Obstructive sleep apnea (OSA) is a common multisystem chronic disorder. Functional and structural neuroimaging has been widely applied in patients with OSA, but these studies have often yielded diverse results. The present quantitative meta-analysis aims to identify consistent patterns of abnormal activation and grey matter loss in OSA across studies. We used PubMed to retrieve task/resting-state functional magnetic resonance imaging and voxel-based morphometry studies. Stereotactic data were extracted from fifteen studies, and subsequently tested for convergence using activation likelihood estimation. We found convergent evidence for structural atrophy and functional disturbances in the right basolateral amygdala/hippocampus and the right central insula. Functional characterization of these regions using the BrainMap database suggested associated dysfunction of emotional, sensory, and limbic processes. Assessment of task-based co-activation patterns furthermore indicated that the two regions obtained from the meta-analysis are part of a joint network comprising the anterior insula, posterior-medial frontal cortex and thalamus. Taken together, our findings highlight the role of right amygdala, hippocampus and insula in the abnormal emotional and sensory processing in OSA.

Disrupted functional brain network organization in patients with obstructive sleep apnea

INTRODUCTION

Obstructive sleep apnea (OSA) subjects show impaired autonomic, affective, executive, sensorimotor, and cognitive functions. Brain injury in OSA subjects appears in multiple sites regulating these functions, but the integrity of functional networks within the regulatory sites remains unclear. Our aim was to examine the functional interactions and the complex network organization of these interactions across the whole brain in OSA, using regional functional connectivity (FC) and brain network topological properties.

METHODS

We collected resting-state functional magnetic resonance imaging (MRI) data, using a 3.0-Tesla MRI scanner, from 69 newly diagnosed, treatment-naïve, moderate-to-severe OSA (age, 48.3 ± 9.2 years; body mass index, 31 ± 6.2 kg/m(2); apnea-hypopnea index (AHI), 35.6 ± 23.3 events/h) and 82 control subjects (47.6 ± 9.1 years; body mass index, 25.1 ± 3.5 kg/m(2)). Data were analyzed to examine FC in OSA over controls as interregional correlations and brain network topological properties.

RESULTS

Obstructive sleep apnea subjects showed significantly altered FC in the cerebellar, frontal, parietal, temporal, occipital, limbic, and basal ganglia regions (FDR, P < 0.05). Entire functional brain networks in OSA subjects showed significantly less efficient integration, and their regional topological properties of functional integration and specialization characteristics also showed declined trends in areas showing altered FC, an outcome which would interfere with brain network organization (P < 0.05; 10,000 permutations). Brain sites with abnormal topological properties in OSA showed significant relationships with AHI scores.

CONCLUSIONS

Our findings suggest that the dysfunction extends to resting conditions, and the altered FC and impaired network organization may underlie the impaired responses in autonomic, cognitive, and sensorimotor functions. The outcomes likely result from the prominent structural changes in both axons and nuclear structures, which occur in the condition.

Increased Intraregional Synchronized Neural Activity in Adult Brain After Prolonged Adaptation to High-Altitude Hypoxia: A Resting-State fMRI Study

The human brain is intrinsically plastic such that its functional architecture can be reorganized in response to environmental pressures and physiological changes. However, it remains unclear whether a compensatory modification of spontaneous neural activity occurs in adult brain during prolonged high-altitude (HA) adaptation. In this study, we obtained resting-state functional magnetic resonance (MR) images in 16 adults who have immigrated to Qinghai-Tibet Plateau (2300-4400 m) for 2 years and in 16 age-matched sea level (SL) controls. A validated regional homogeneity (Reho) method was employed to investigate the local synchronization of resting-state functional magnetic resonance imaging (fMRI) signals. Seed connectivity analysis was carried out subsequently. Cognitive and physiological assessments were made and correlated with the image metrics. Compared with SL controls, global mean Reho was significantly increased in HA immigrants as well as a regional increase in the right inferolateral sensorimotor cortex. Furthermore, mean z-Reho value extracted within the inferolateral sensorimotor area showed trend-level significant inverse correlation with memory search reaction time in HA immigrants. These observations, for the first time, provide evidence of adult brain resilience of spontaneous neural activity after long-term HA exposure without inherited and developmental effects. Resting-state fMRI could yield valuable information for central mechanisms underlying respiratory and cognitive compensations in adults during prolonged environmentally hypoxic adaptation, paving the way for future HA-adaptive training.

Functional Imaging of Autonomic Regulation: Methods and Key Findings

Central nervous system processing of autonomic function involves a network of regions throughout the brain which can be visualized and measured with neuroimaging techniques, notably functional magnetic resonance imaging (fMRI). The development of fMRI procedures has both confirmed and extended earlier findings from animal models, and human stroke and lesion studies. Assessments with fMRI can elucidate interactions between different central sites in regulating normal autonomic patterning, and demonstrate how disturbed systems can interact to produce aberrant regulation during autonomic challenges. Understanding autonomic dysfunction in various illnesses reveals mechanisms that potentially lead to interventions in the impairments. The objectives here are to: (1) describe the fMRI neuroimaging methodology for assessment of autonomic neural control, (2) outline the widespread, lateralized distribution of function in autonomic sites in the normal brain which includes structures from the neocortex through the medulla and cerebellum, (3) illustrate the importance of the time course of neural changes when coordinating responses, and how those patterns are impacted in conditions of sleep-disordered breathing, and (4) highlight opportunities for future research studies with emerging methodologies. Methodological considerations specific to autonomic testing include timing of challenges relative to the underlying fMRI signal, spatial resolution sufficient to identify autonomic brainstem nuclei, blood pressure, and blood oxygenation influences on the fMRI signal, and the sustained timing, often measured in minutes of challenge periods and recovery. Key findings include the lateralized nature of autonomic organization, which is reminiscent of asymmetric motor, sensory, and language pathways. Testing brain function during autonomic challenges demonstrate closely-integrated timing of responses in connected brain areas during autonomic challenges, and the involvement with brain regions mediating postural and motoric actions, including respiration, and cardiac output. The study of pathological processes associated with autonomic disruption shows susceptibilities of different brain structures to altered timing of neural function, notably in sleep disordered breathing, such as obstructive sleep apnea and congenital central hypoventilation syndrome. The cerebellum, in particular, serves coordination roles for vestibular stimuli and blood pressure changes, and shows both injury and substantially altered timing of responses to pressor challenges in sleep-disordered breathing conditions. The insights into central autonomic processing provided by neuroimaging have assisted understanding of such regulation, and may lead to new treatment options for conditions with disrupted autonomic function.

Brain Structure Network Analysis in Patients with Obstructive Sleep Apnea

Childhood obstructive sleep apnea (OSA) is a sleeping disorder commonly affecting school-aged children and is characterized by repeated episodes of blockage of the upper airway during sleep. In this study, we performed a graph theoretical analysis on the brain morphometric correlation network in 25 OSA patients (OSA group; 5 female; mean age, 10.1 ± 1.8 years) and investigated the topological alterations in global and regional properties compared with 20 healthy control individuals (CON group; 6 females; mean age, 10.4 ± 1.8 years). A structural correlation network based on regional gray matter volume was constructed respectively for each group. Our results revealed a significantly decreased mean local efficiency in the OSA group over the density range of 0.32-0.44 (p < 0.05). Regionally, the OSAs showed a tendency of decreased betweenness centrality in the left angular gyrus, and a tendency of decreased degree in the right lingual and inferior frontal (orbital part) gyrus (p < 0.005, uncorrected). We also found that the network hubs in OSA and controls were distributed differently. To the best of our knowledge, this is the first study that characterizes the brain structure network in OSA patients and invests the alteration of topological properties of gray matter volume structural network. This study may help to provide new evidence for understanding the neuropathophysiology of OSA from a topological perspective.

Intelligence-related differences in the asymmetry of spontaneous cerebral activity

Recent evidence suggests the spontaneous BOLD signal synchronization of corresponding interhemispheric, homotopic regions as a stable trait of human brain physiology, with emerging differences in such organization being also related to some pathological conditions. To understand whether such brain functional symmetries play a role into higher-order cognitive functioning, here we correlated the functional homotopy profiles of 119 healthy subjects with their intelligence level. Counterintuitively, reduced homotopic connectivity in above average-IQ versus average-IQ subjects was observed, with significant reductions in visual and somatosensory cortices, supplementary motor area, rolandic operculum, and middle temporal gyrus, possibly suggesting that a downgrading of interhemispheric talk at rest could be associated with higher cognitive functioning. These regions also showed an increased spontaneous synchrony with medial structures located in ipsi- and contralateral hemispheres, with such pattern being mostly detectable for regions placed in the left hemisphere. The interactions with age and gender have been also tested, with different patterns for subjects above and below 25 years old and less homotopic connectivity in the prefrontal cortex and posterior midline regions in female participants with higher IQ scores. These findings support prior evidence suggesting a functional role for homotopic connectivity in human cognitive expression, promoting the reduction of synchrony between primary sensory regions as a predictor of higher intelligence levels.