Default network response to a working memory challenge after withdrawal of continuous positive airway pressure treatment for obstructive sleep apnea

Higher substance use is associated with low executive control neural activity and higher inflammation

Individuals with substance use problems show lower executive control and alterations in prefrontal brain systems supporting emotion regulation and impulse control. A separate literature suggests that heightened inflammation also increases risk for substance use, in part, through targeting brain systems involved in executive control. Research on neural and inflammatory signaling in substance use, however, has occurred in parallel. Drawing on recent neuroimmune network models, we used fMRI to examine the relationships between executive control-related brain activity (as elicited by an n-back working memory task), peripheral inflammation, as quantified by inflammatory cytokines and C-reactive protein (CRP), and substance use for the past month in 93 participants [mean age = 24.4 (SD = 0.6)]. We operationalized low executive control as a neural inefficiency during the n-back task to achieve normative performance, as reflected in higher working memory-related brain activity and lower activity in the default mode network (DMN). Consistent with prediction, individuals with low executive control and high inflammation reported more substance use over the past month, controlling for behavioral performance on the n-back, sex, time between assessments, body-mass-index (BMI), and personal socioeconomic status (SES) (interaction between inflammation and working memory-related brain activity, b = 0.210, p = 0.005; interaction between inflammation and DMN, b = -0.219, p < 0.001). Findings suggest that low executive control and high inflammation may be associated with higher substance use. This has implications for understanding psychological, neural, and immunological risk for substance use problems and the development of interventions to target each of these components.

Daytime Hypercapnia Impairs Working Memory in Young and Middle-Aged Patients with Obstructive Sleep Apnea Hypopnea Syndrome

Purpose

Obstructive sleep apnea hypopnea syndrome (OSAHS) can lead to cognitive impairment, though few studies have so far examined hypercapnia as its causal mechanism, due to the invasive nature of conventional arterial CO2 measurement. The study aims to investigate the effects of daytime hypercapnia on working memory in young and middle-aged patients with OSAHS.

Patients and Methods

This prospective study screened 218 patients and eventually recruited 131 patients (aged 25-60 years) with polysomnography (PSG)-diagnosed OSAHS. Using a cut-off of 45mmHg daytime transcutaneous partial pressure of carbon dioxide (PtcCO2), 86 patients were assigned into the normocapnic group and 45 patients into the hypercapnic group. Working memory was evaluated using the Digit Span Backward Test (DSB) and the Cambridge Neuropsychological Test Automated Battery.

Results

Compared with the normocapnic group, the hypercapnic group performed worse in verbal, visual, and spatial working memory tasks. PtcCO2≥45mmHg was an independent predictor for lower DSB scores (OR=4.057), lower accuracy in the immediate Pattern Recognition Memory (OR=2.600), delayed Pattern Recognition Memory (OR=2.766) and Spatial Recognition Memory (OR=2.722) tasks, lower Spatial Span scores (OR=4.795), and more between errors in the Spatial Working Memory task (OR=2.734 and 2.558, respectively). Notably, PSG indicators of hypoxia and sleep fragmentation did not predict task performance.

Conclusion

Hypercapnia may be plays an important role in working memory impairment in patients with OSAHS, perhaps more so than hypoxia and sleep fragmentation. Routine CO2 monitoring in these patients could prove of utility in clinical practices.

Autobiographical Memory From Different Life Stages in Individuals With Obstructive Sleep Apnea

OBJECTIVES

Autobiographical memory dysfunction is a marker of vulnerability to depression. Patients with obstructive sleep apnea (OSA) experience high rates of depression and memory impairment, and autobiographical memory impairments have been observed compared to healthy controls; however, these groups were not age-matched. This study aimed to determine whether individuals with untreated OSA have impaired autobiographical memory when compared to age-matched controls, and to assess the quality of autobiographical memories from three broad time points.

METHODS

A total of 44 participants with OSA (M age=49.4±13.0) and 44 age-matched controls (M age=50.0±13.1) completed the Autobiographical Memory Interview (AMI) to assess semantic and episodic memories from three different life stages, and 44 OSA participants and 37 controls completed the Autobiographical Memory Test (AMT) to assess overgeneral memory recall (an inability to retrieve specific memories).

RESULTS

OSA participants had significantly poorer semantic recall of early adult life on the AMI (p&lt;.001), and more overgeneral autobiographical memories recalled on the AMT (=.001), than controls. Poor semantic recall from early adult life was significantly correlated with more depressive symptoms (p=0.006) and lower education (p&lt;0.02), while higher overgeneral memory recall was significantly associated with older age (p=.001).

CONCLUSIONS

A specific deficit in semantic autobiographical recall was observed in individuals with OSA. OSA patients recalled more overgeneral memories, suggesting that aspects of the sleep disorder affect their ability to recollect specific details of events from their life. These cognitive features of OSA may contribute to the high incidence of depression in this population. (JINS 2019, 25, 266-274).

Tailored approach to sleep health education (TASHE): study protocol for a web-based randomized controlled trial

BACKGROUND

Obstructive sleep apnea (OSA) is a sleep disorder that disproportionately affects African Americans (hereafter referred to as blacks). Moreover, blacks may underutilize sleep services including overnight polysomnography. Thus, OSA among blacks may go undiagnosed and untreated, which has significant health consequences, including hypertension, diabetes, cognitive impairment, and daytime sleepiness.

DESIGN AND METHODS

This two-arm randomized controlled trial will assign 200 participants to a culturally and linguistically tailored web-based sleep educational platform. The website will be developed to ensure that the content is user friendly and that it is readable and acceptable by the target community. Participants will receive login information to a password-protected website and will have access to the website for 2 months. Study assessments will be collected at baseline, 2 months (post-enrollment) and at 6 months (follow-up). We will use qualitative and quantitative methods to develop tailored materials and to ascertain whether tailored materials will increase OSA knowledge and OSA health literacy by comparing blacks exposed to tailored materials versus those exposed to standard sleep health literature. We hypothesize that exposure to tailored OSA information will improve OSA health literacy.

DISCUSSION

Few studies have investigated the racial/ethnic disparities in relation to OSA screening and treatment comparing blacks and whites. Moreover, we know of no interventions designed to increase OSA knowledge and health literacy among blacks. Use of the Internet to disseminate health information is growing in this population. Thus, the Internet may be an effective means to increase OSA health literacy, thereby potentially increasing utilization of sleep-related services in this population.

TRIAL REGISTRATION

The study is registered at clinicaltrials.gov, reference number NCT02507089 . Registered on 21 July 2015.

Abnormal resting-state functional connectivity within the default mode network subregions in male patients with obstructive sleep apnea

BACKGROUND AND OBJECTIVE

Abnormal resting-state functional connectivity (rs-FC) between the central executive network and the default mode network (DMN) in patients with obstructive sleep apnea (OSA) has been reported. However, the effect of OSA on rs-FC within the DMN subregions remains uncertain. This study was designed to investigate whether the rs-FC within the DMN subregions was disrupted and determine its relationship with clinical symptoms in patients with OSA.

METHODS

Forty male patients newly diagnosed with severe OSA and 40 male education- and age-matched good sleepers (GSs) underwent functional magnetic resonance imaging (fMRI) examinations and clinical and neuropsychologic assessments. Seed-based region of interest rs-FC method was used to analyze the connectivity between each pair of subregions within the DMN, including the medial prefrontal cortex (MPFC), posterior cingulate cortex (PCC), hippocampus formation (HF), inferior parietal cortices (IPC), and medial temporal lobe (MTL). The abnormal rs-FC strength within the DMN subregions was correlated with clinical and neuropsychologic assessments using Pearson correlation analysis in patients with OSA.

RESULTS

Compared with GSs, patients with OSA had significantly decreased rs-FC between the right HF and the PCC, MPFC, and left MTL. However, patients with OSA had significantly increased rs-FC between the MPFC and left and right IPC, and between the left IPC and right IPC. The rs-FC between the right HF and left MTL was positively correlated with rapid eye movement (r=0.335, P=0.035). The rs-FC between the PCC and right HF was negatively correlated with delayed memory (r=-0.338, P=0.033).

CONCLUSION

OSA selectively impairs the rs-FC between right HF and PCC, MPFC, and left MTL within the DMN subregions, and provides an imaging indicator for assessment of cognitive dysfunction in OSA patients.

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.

Regional Cerebral Blood Flow during Wakeful Rest in Older Subjects with Mild to Severe Obstructive Sleep Apnea

OBJECTIVES

To evaluate changes in regional cerebral blood flow (rCBF) during wakeful rest in older subjects with mild to severe obstructive sleep apnea (OSA) and healthy controls, and to identify markers of OSA severity that predict altered rCBF.

DESIGN

High-resolution (99m)Tc-HMPAO SPECT imaging during wakeful rest.

SETTING

Research sleep laboratory affiliated with a University hospital.

PARTICIPANTS

Fifty untreated OSA patients aged between 55 and 85 years, divided into mild, moderate, and severe OSA, and 20 age-matched healthy controls.

INTERVENTIONS

N/A.

MEASUREMENTS

Using statistical parametric mapping, rCBF was compared between groups and correlated with clinical, respiratory, and sleep variables.

RESULTS

Whereas no rCBF change was observed in mild and moderate groups, participants with severe OSA had reduced rCBF compared to controls in the left parietal lobules, left precentral gyrus, bilateral postcentral gyri, and right precuneus. Reduced rCBF in these regions and in areas of the bilateral frontal and left temporal cortex was associated with more hypopneas, snoring, hypoxemia, and sleepiness. Higher apnea, microarousal, and body mass indexes were correlated to increased rCBF in the basal ganglia, insula, and limbic system.

CONCLUSIONS

While older individuals with severe obstructive sleep apnea (OSA) had hypoperfusion in the sensorimotor and parietal areas, respiratory variables and subjective sleepiness were correlated with extended regions of hypoperfusion in the lateral cortex. Interestingly, OSA severity, sleep fragmentation, and obesity correlated with increased perfusion in subcortical and medial cortical regions. Anomalies with such a distribution could result in cognitive deficits and reflect impaired vascular regulation, altered neuronal integrity, and/or undergoing neurodegenerative processes.

Increased functional connectivity within memory networks following memory rehabilitation in multiple sclerosis

Identifying effective behavioral treatments to improve memory in persons with learning and memory impairment is a primary goal for neurorehabilitation researchers. Memory deficits are the most common cognitive symptom in multiple sclerosis (MS), and hold negative professional and personal consequences for people who are often in the prime of their lives when diagnosed. A 10-session behavioral treatment, the modified Story Memory Technique (mSMT), was studied in a randomized, placebo-controlled clinical trial. Behavioral improvements and increased fMRI activation were shown after treatment. Here, connectivity within the neural networks underlying memory function was examined with resting-state functional connectivity (RSFC) in a subset of participants from the clinical trial. We hypothesized that the treatment would result in increased integrity of connections within two primary memory networks of the brain, the hippocampal memory network, and the default network (DN). Seeds were placed in left and right hippocampus, and the posterior cingulate cortex. Increased connectivity was found between left hippocampus and cortical regions specifically involved in memory for visual imagery, as well as among critical hubs of the DN. These results represent the first evidence for efficacy of a behavioral intervention to impact the integrity of neural networks subserving memory functions in persons with MS.

Developing neuroimaging phenotypes of the default mode network in PTSD: integrating the resting state, working memory, and structural connectivity

Complementary structural and functional neuroimaging techniques used to examine the Default Mode Network (DMN) could potentially improve assessments of psychiatric illness severity and provide added validity to the clinical diagnostic process. Recent neuroimaging research suggests that DMN processes may be disrupted in a number of stress-related psychiatric illnesses, such as posttraumatic stress disorder (PTSD). Although specific DMN functions remain under investigation, it is generally thought to be involved in introspection and self-processing. In healthy individuals it exhibits greatest activity during periods of rest, with less activity, observed as deactivation, during cognitive tasks, e.g., working memory. This network consists of the medial prefrontal cortex, posterior cingulate cortex/precuneus, lateral parietal cortices and medial temporal regions. Multiple functional and structural imaging approaches have been developed to study the DMN. These have unprecedented potential to further the understanding of the function and dysfunction of this network. Functional approaches, such as the evaluation of resting state connectivity and task-induced deactivation, have excellent potential to identify targeted neurocognitive and neuroaffective (functional) diagnostic markers and may indicate illness severity and prognosis with increased accuracy or specificity. Structural approaches, such as evaluation of morphometry and connectivity, may provide unique markers of etiology and long-term outcomes. Combined, functional and structural methods provide strong multimodal, complementary and synergistic approaches to develop valid DMN-based imaging phenotypes in stress-related psychiatric conditions. This protocol aims to integrate these methods to investigate DMN structure and function in PTSD, relating findings to illness severity and relevant clinical factors.

Mapping gray matter reductions in obstructive sleep apnea: an activation likelihood estimation meta-analysis

STUDY OBJECTIVES

The authors reviewed the literature on the use of voxel-based morphometry (VBM) in obstructive sleep apnea (OSA) magnetic resonance imaging (MRI) studies via the use of a meta-analysis of neuroimaging to identify consistent and specific structural deficits in patients with sleep apnea compared with healthy subjects.

DESIGN

Neuroimaging meta-analysis.

DATA SOURCES

We used PubMed to retrieve articles published between January 2000 and February 2012.

STUDY SELECTION

The authors included all VBM research on patients with OSA and healthy controls. They compared the findings of the studies by using gray matter volume (GMV) or gray matter concentration (GMC) to index differences in gray matter.

DATA EXTRACTION

Stereotactic data were extracted from eight VBM studies of 213 patients with OSA and 195 control subjects.

RESULTS

Regional gray matter reduction in the bilateral parahippocampus and less-convincing right superior frontal and left middle temporal gyri was demonstrated in patients with sleep apnea using an activation likelihood estimation (ALE) procedure to analyze significant differences.

CONCLUSIONS

Significant reductions in gray matter in patients with sleep apnea occurred in the bilateral parahippocampus and less-convincing frontotemporal regions, which may be related to the neurocognitive processing abnormalities that are common among populations of patients with sleep apnea.

Pathological consequences of intermittent hypoxia in the central nervous system

Intermittent hypoxia (IH) is a frequent occurrence in clinical settings. In the last decades, evidence has emerged implicating the gas exchange alterations and sleep disruption associated with those disorders in the high prevalence of cognitive and behavioral deficits afflicting these patients. In an effort to better characterize the role of IH, and to identify potential mechanisms of IH-induced central nervous system (CNS) dysfunction, a large number of rodent models have been recently developed. The cumulative evidence confirms that IH indeed induces a heterotopic pattern of injury in the brain, particularly affecting cortical, subcortical, and hippocampal regions, ultimately leading to neuronal apoptosis and activation of microglia. These IH-induced deleterious processes exhibit substantial variability across the lifespan, are under substantial modulatory influences of diet, physical or intellectual activity, and genetic factors, and preferentially recruit oxidative stress and inflammatory pathways.

Effects of CPAP treatment interruption due to disasters: patients with sleep-disordered breathing in the Great East Japan Earthquake and tsunami area

INTRODUCTION

The 2011 Great East Japan Earthquake caused major disruptions in the provision of health care, including that for patients with sleep-disordered breathing (SDB) using a nasal continuous positive airway pressure (nCPAP) device. This study investigated the ability of SDB patients to continue using the nCPAP device in the weeks immediately following the earthquake, whether inability to use the nCPAP device led to symptom relapse, and measures that should be taken to prevent disruptions in nCPAP therapy during future disasters. Hypothesis If nCPAP devices cannot be used during disasters, SDB patients' health will be affected negatively.

METHODS

Within 14 days of the disaster, 1,047 SDB patients completed a questionnaire that collected data regarding ability to use, duration of inability to use, and reasons for inability to use the nCPAP device; symptom relapse while unable to use the nCPAP device; ability to use the nCPAP device use at evacuation sites; and recommendations for improvement of the nCPAP device.

RESULTS

Of the 1,047 patients, 966 (92.3%) had been unable to use the nCPAP device in the days immediately following the earthquake. The most common reason for inability to use the nCPAP device was power failure, followed by anxiety about sleeping at night due to fear of aftershocks, involvement in disaster-relief activities, loss of the nasal CPAP device, and fear of being unable to wake up in case of an emergency. Among the 966 patients, 242 (25.1%) had experienced relapse of symptoms, the most common of which was excessive daytime sleepiness (EDS), followed by insomnia, headache, irritability, and chest pain.

CONCLUSION

Developing strategies for the continuation of nCPAP therapy during disasters is important for providing healthy sleeping environments for SDB patients in emergency situations.

Neural correlates of working memory performance in primary insomnia

STUDY OBJECTIVES

To examine neural correlates of working memory performance in patients with primary insomnia (PIs) compared with well-matched good sleepers (GSs).

DESIGN

Twenty-five PIs and 25 GSs underwent functional MRI while performing an N-back working memory task.

SETTING

VA hospital sleep laboratory and University-based functional imaging center.

PATIENTS OR PARTICIPANTS

25 PIs, 25 GSs.

INTERVENTIONS

N/A.

MEASUREMENTS AND RESULTS

Although PIs did not differ from GSs in cognitive performance, PIs showed the expected differences from GSs in both self-reported and objective sleep measures. PIs, relative to GSs, showed reduced activation of task-related working memory regions. This manifested both as an overall reduction in activation of task-related regions and specifically as reduced modulation of right dorsolateral prefrontal cortex with increasing task difficulty. Similarly, PIs showed reduced modulation (i.e., reduced deactivation) of default mode regions with increasing task difficulty, relative to GSs. However, PIs showed intact performance.

CONCLUSIONS

These data establish a profile of abnormal neural function in primary insomnia, reflected both in reduced engagement of task-appropriate brain regions and an inability to modulate task-irrelevant (i.e., default mode) brain areas during working memory performance. These data have implications for better understanding the neuropathophysiology of the well established, yet little understood, discrepancy between ubiquitous subjective cognitive complaints in primary insomnia and the rarely found objective deficits during testing.

Altered resting-state brain activity in obstructive sleep apnea

STUDY OBJECTIVES

Structural and functional brain changes may contribute to neural dysfunction in patients with obstructive sleep apnea (OSA). However, the effect of OSA on resting-state brain activity has not been established. The objective of this study was to investigate alterations in resting-state functional connectivity (rsFC) of the common brain networks in patients with OSA and their relationships with changes in gray matter volume (GMV) in the corresponding brain regions.

DESIGNS

Resting-state functional and structural MRI data were acquired from patients with OSA and healthy controls. Seven brain networks were identified by independent component analysis. The rsFC in each network was compared between groups and the GMV of brain regions with significant differences in rsFC was also compared.

SETTING

University hospital.

PATIENTS AND PARTICIPANTS

Twenty-four male patients with untreated OSA and 21 matched healthy controls.

INTERVENTIONS

N/A.

MEASUREMENTS AND RESULTS

OSA specifically affected the cognitive and sensorimotor-related brain networks but not the visual and auditory networks. The medial prefrontal cortex and left dorsolateral prefrontal cortex (DLPFC) showed decreased rsFC and GMV in patients with OSA, suggesting structural and functional deficits. The right DLPFC and left precentral gyrus showed decreased rsFC and unchanged GMV, suggesting a functional deficit. The right posterior cingulate cortex demonstrated increased rsFC and unchanged GMV, suggesting functional compensation. In patients with OSA, the rsFC of the right DLPFC was negatively correlated with the apnea-hypopnea index.

CONCLUSIONS

OSA specifically affects resting-state functional connectivity in cognitive and sensorimotor-related brain networks, which may be related to the impaired cognitive and motor functions in these patients.

Cognition in obstructive sleep apnea-hypopnea syndrome (OSAS): current clinical knowledge and the impact of treatment

Obstructive sleep apnea-hypopnea syndrome (OSAS) is characterized by the presence of disordered breathing events that occur during sleep, as well as symptoms such as sleepiness and snoring. OSAS is associated with a number of adverse health consequences, and a growing literature focuses on its cognitive correlates. Although research in this field is mixed, multiple studies indicate that OSAS patients show impairment in attention, memory, and executive function. Continuous positive airway pressure (CPAP) is the most effective and widely used treatment of OSAS, and supplemental medications may supplement CPAP treatment to ameliorate associated symptoms. Here, we review the literature on OSAS and cognition, including studies that have investigated the impact of CPAP and stimulant medication on cognitive performance in patients with OSAS. In general, no consistent effect of CPAP use on cognitive performance was evident. This may be due, in part, to variability in study design and sampling methodology across studies. Studies of stimulant medications generally reported positive effects on cognitive performance. We conclude with a discussion of the mechanisms that have been proposed to explain cognitive dysfunction in OSAS and directions for future research.

Cognitive recovery following positive airway pressure (PAP) in sleep apnea

Obstructive sleep apnea-hypopnea syndrome (OSAHS) is a common sleep disorder that is characterized by repeated episodes of complete or partial cessation of breathing while sleeping. These recurrent breathing events result in fragmented sleep and recurrent hypoxemia. Distressing daytime sequelae reported by OSAHS patients include excessive daytime sleepiness, self-reported changes in mood, and cognitive problems. It has been well established that OSAHS can negatively impact functioning in multiple cognitive domains, such as attention and memory. In this chapter, neurobehavioral deficits in OSAHS are discussed, and proposed models of cognitive dysfunction are summarized. Current studies examining cognitive recovery with positive airway pressure treatment are presented. It appears that the cognitive dysfunction of OSAHS is not likely to be due to a single mediating mechanism, nor is it pervasive across all patients. Future research should attempt to identify these moderators for cognitive dysfunction in OSAHS and to highlight the mechanisms of dysfunction by cognitive domain.

Effects of nicotine withdrawal on verbal working memory and associated brain response

Previous literature has reported effects of nicotine withdrawal on brain function during cognitive tasks such as verbal working memory (VWM). Mechanisms of these withdrawal effects have not been clearly identified. Functional neuroimaging offers an objective method to examine brain mechanisms associated with observable behavior and subjective reports. To investigate these mechanisms, 12 smokers were administered a 2-Back VWM challenge during two functional magnetic resonance imaging sessions. Participants abstained from smoking prior to both sessions; however, they applied a nicotine patch before one session and a placebo patch prior to the other. Among regions that exhibited a significant response to the 2-Back during either session, withdrawal was associated with significantly greater deactivation in left and right temporal poles and left medial frontal gyrus. The magnitude of task-related activation showed a significant inverse relationship to craving in the majority of regions during placebo administration. Also, individual brain responses varied more during placebo, suggesting inefficient neural processing. Results suggest that differences in brain response to a VWM challenge during abstinence may be attributed to increased craving. Further deactivation of regions associated with the default network (medial frontal and anterior temporal clusters) during the placebo condition suggests further suspension of default activity, possibly to compensate for inefficient neural processing.