A microstructural study of sleep instability in drug-naive patients with schizophrenia and healthy controls: sleep spindles, rapid eye movements, and muscle atonia

Sleep disturbances in early clinical stages of psychotic and bipolar disorders: A meta-analysis

OBJECTIVE

To provide a qualitative view and quantitative measure of sleep disturbances across and between early stages - clinical ultra high-risk and first episode - of psychotic and bipolar disorders.

METHODS

Electronic databases (PubMed, Cochrane, Embase, PsychINFO) were searched up to March 2021 for studies comparing sleep measures between individuals with an early stage and controls. Standard mean deviations (Cohen's d effect sizes) were calculated for all comparisons and pooled with random-effects models. Chi-square tests were used for direct between-subgroups (ultra high-risk vs first episode) comparisons of standard mean deviations. The effects of age, sex ratio, symptoms and treatment were examined in meta-regression analyses.

RESULTS

A database search identified 13 studies that contrasted sleep measures between individuals with an early stage (N = 537) and controls (N = 360). We observed poorer subjective sleep quality (standard mean deviation = 1.32; 95% confidence interval, [1.01, 1.62]), shorter total sleep time (standard mean deviation =-0.44; 95% confidence interval, [-0.67, -0.21]), lower sleep efficiency (standard mean deviation = -0.72; 95% confidence interval, [-1.08, -0.36]), longer sleep onset latency (standard mean deviation = 0.75; 95% confidence interval, [0.45, 1.06]) and longer duration of wake after sleep onset (standard mean deviation = 0.49; 95% confidence interval, [0.21, 0.77]) were observed in early stages compared to controls. No significant differences were observed for any of the reported electroencephalographic parameters of sleep architecture. No significant between-subgroups differences were observed. Meta-regressions revealed a significant effect of the age and the antipsychotic status on subjective measures of sleep.

CONCLUSION

The early stage population presents with significant impairments of subjective sleep quality continuity, duration and initiation. Systematic assessments of sleep in early intervention settings may allow early identification and treatment of sleep disturbances in this population.

Investigating sleep spindle density and schizophrenia: A meta-analysis

Sleep abnormalities are an early feature of schizophrenia (SZ) characterized by reductions in sleep spindles that are associated with deficits in brain connectivity and cognitive function. This study investigated sleep spindle density (SSD) differences between SZ, first episode psychosis (FEP), and family high-risk (FHR) populations and matched healthy controls (HC) by investigating recent studies via a meta-analysis. We collected experimental, demographic, and methodological metrics from eligible studies across multiple online databases. 14 total studies survived the inclusion and exclusion criteria for a total of 337 patients and relatives and 339 HC. R-Studio was used to run the meta-analysis via the meta and metaphor packages. A heterogeneity score of I² = 80% was calculated and thus a random effects model was chosen. We report a large effect size for SSD in patients compared to controls. Furthermore, illness duration was significantly associated with SSD. Our next step to understanding sleep spindles would be to investigate SSD's use as a predictor for SZ or attempt to normalize SSD deficits as a therapeutic option.

Association of neurocognitive functioning with sleep stage dissociation and REM sleep instability in medicated patients with schizophrenia

Many patients with schizophrenia present with impaired cognitive functioning and sleep disturbances. Dissociated stages of sleep represent instability within distinct sleep regulatory cerebral networks. Previous studies found increased rates of rapid eye movement (REM) sleep abnormalities in patients with schizophrenia and a positive association with psychopathology. In this study, we examined if sleep stage dissociation and REM sleep instability was associated with neurocognitive functioning in a sample of medicated patients with schizophrenia. The analyses were performed on 31 baseline polysomnographic recordings as well as baseline data on neurocognitive performance. Regression models were built with the cognitive composite score as primary dependent variable and measures of sleep stage dissociation, including REM sleep without atonia (RSWA), REM sleep without eye movements, non-REM sleep with eye movements, REM sleep percentage in REM periods and REM sleep stability as independent variables. Analyses were adjusted for age, gender, total antipsychotic dose, total benzodiazepine dose, and symptom severity. After correction for multiple testing, we found that the neurocognitive composite score was inversely associated with the degree of RSWA. Exploratory analyses with the cognitive sub scores as dependent variables showed that RSWA was associated with cognitive performance across several sub domains. Dissociated sleep stages, specifically the RSWA feature, might represent a new treatment target for improving cognitive impairment in patients with schizophrenia.

Electro-Encephalography and Electro-Oculography in Aeronautics: A Review Over the Last Decade (2010-2020)

Electro-encephalography (EEG) and electro-oculography (EOG) are methods of electrophysiological monitoring that have potentially fruitful applications in neuroscience, clinical exploration, the aeronautical industry, and other sectors. These methods are often the most straightforward way of evaluating brain oscillations and eye movements, as they use standard laboratory or mobile techniques. This review describes the potential of EEG and EOG systems and the application of these methods in aeronautics. For example, EEG and EOG signals can be used to design brain-computer interfaces (BCI) and to interpret brain activity, such as monitoring the mental state of a pilot in determining their workload. The main objectives of this review are to, (i) offer an in-depth review of literature on the basics of EEG and EOG and their application in aeronautics; (ii) to explore the methodology and trends of research in combined EEG-EOG studies over the last decade; and (iii) to provide methodological guidelines for beginners and experts when applying these methods in environments outside the laboratory, with a particular focus on human factors and aeronautics. The study used databases from scientific, clinical, and neural engineering fields. The review first introduces the characteristics and the application of both EEG and EOG in aeronautics, undertaking a large review of relevant literature, from early to more recent studies. We then built a novel taxonomy model that includes 150 combined EEG-EOG papers published in peer-reviewed scientific journals and conferences from January 2010 to March 2020. Several data elements were reviewed for each study (e.g., pre-processing, extracted features and performance metrics), which were then examined to uncover trends in aeronautics and summarize interesting methods from this important body of literature. Finally, the review considers the advantages and limitations of these methods as well as future challenges.

Sleep endophenotypes of schizophrenia: slow waves and sleep spindles in unaffected first-degree relatives

Sleep spindles and slow waves are the main brain oscillations occurring in non-REM sleep. Several lines of evidence suggest that spindles are initiated within the thalamus, whereas slow waves are generated and modulated in the cortex. A decrease in sleep spindle activity has been described in Schizophrenia (SCZ), including chronic, early course, and early onset patients. In contrast, slow waves have been inconsistently found to be reduced in SCZ, possibly due to confounds like duration of illness and antipsychotic medication exposure. Nontheless, the implication of sleep spindles and slow waves in the neurobiology of SCZ and related disorders, including their heritability, remains largely unknown. Unaffected first-degree relatives (FDRs) share a similar genetic background and several neurophysiological and cognitive deficits with SCZ patients, and allow testing whether some of these measures are candidate endophenotypes. In this study, we performed sleep high-density EEG recordings to characterise the spatiotemporal features of sleep spindles and slow waves in FDRs of SCZ probands and healthy subjects (HS) with no family history of SCZ. We found a significant reduction of integrated spindle activity (ISAs) in FDRs relative to HS, whereas spindle density and spindle duration were not different between groups. FDRs also had decreased slow wave amplitude and slopes. Altogether, our results suggest that ISAs deficits might represent a candidate endophenotype for SCZ. Furthermore, given the slow wave deficits observed in FDRs, we propose that disrupted cortical synchronisation increases the risk for SCZ, but thalamic dysfunction is necessary for the disorder to fully develop.

Sleep spindles and slow waves in schizophrenia and related disorders: main findings, challenges and future perspectives

Sleep abnormalities have recently gained renewed attention in patients diagnosed with schizophrenia. Disrupted thalamocortical brain oscillations hold promise as putative biomarkers or endophenotypes of the disorder. Despite an increase in studies related to sleep spindle and slow-wave activity, findings remain in part contradictory. Although sleep spindle deficits have been confirmed in several groups of patients with chronic, medicated schizophrenia, data on the early stages of the disorder and in unmedicated subjects are still insufficient. Findings on slow-wave abnormalities are largely inconclusive, possibly due to the different criteria employed to define the phenomenon and to the influence of atypical antipsychotics. In this review, we aim to address the methodological and practical issues that may have limited the consistency of findings across research groups and different patient populations. Given the neurobiological relevance of these oscillations, which reflect the integrity of thalamocortical and cortico-cortical function, research in this domain should be encouraged. To promote widespread consensus over the scientific and clinical implications of these sleep-related phenomena, we advocate uniform and sound methodological approaches. These should encompass electroencephalographic recording and analysis techniques but also selection criteria and characterization of clinical populations.

Childhood trauma, depression, and sleep quality and their association with psychotic symptoms and suicidality in schizophrenia

This study involved the examination of the relationship between childhood trauma and both psychotic symptoms and suicidality in patients with schizophrenia after controlling for the possible confounding factors, such as clinical features, depression, and sleep quality. The Childhood Trauma Questionnaire-Short Form, Positive and Negative Syndrome Scale (PANSS), Calgary Depression Scale for Schizophrenia (CDSS), Pittsburgh Sleep Quality Index (PSQI), and the suicidality subscale of Mini-International Neuropsychiatric Interview (MINI) were administered to 199 patients with schizophrenia. We used sequential multiple stepwise regression analyses in which positive symptoms, negative symptoms, overall psychopathology, total symptoms of schizophrenia, and suicidality were dependent variables. Depressive symptomatology and childhood physical abuse significantly contributed to positive, negative, general psychopathology, and global schizophrenia symptomatology. Interestingly, general psychopathology scores were negatively associated with childhood physical neglect. Also, subjective sleep quality significantly contributed to positive schizophrenia symptoms. Although prior suicide attempts and depression were significant antecedents of suicidal ideation, no association between suicidality and both childhood trauma and sleep was found. Childhood physical abuse could have an impact on psychopathology in schizophrenia. In addition to childhood trauma, depression, sleep disturbances, and clinical features should be considered and inquired about in the course of clinical care of schizophrenia patients.

Sleep Spindle Deficit in Schizophrenia: Contextualization of Recent Findings

Sleep spindles are wax and waning brain oscillations at a frequency range of 11-16 Hz, lasting 0.5-2 s, that define non-rapid eye movement sleep stage 2. Over the past few years, several independent studies pointed to a decrease of sleep spindles in schizophrenia. The aim of this review is to contextualize these findings within the growing literature on these oscillations across other neuro-psychiatric disorders. Indeed, spindles reflect the coordinated activity of thalamocortical networks, and their abnormality can be observed in a variety of conditions that disrupt local or global thalamocortical connectivity. Although the broad methodological variability across studies limits the possibility of drawing firm conclusions, impaired spindling activity has been observed in several neurodevelopmental and neurodegenerative disorders. Despite such lack of specificity, schizophrenia remains the only condition with a typical late adolescence to young adulthood onset in which impaired spindling has been consistently reported. Further research is necessary to clearly define the pathogenetic mechanisms that lead to this deficit and the validity of its widespread use as a clinical biomarker.

A systematic review of the nature and correlates of sleep disturbance in early psychosis

Sleep disturbances are common in people with a diagnosis of schizophrenia and have been associated with increased symptom severity, neurocognitive deficits and reduced quality of life. Despite a significant body of literature in this field, there has been limited investigation of sleep disturbance in the early course of the illness. This systematic review aims to synthesise and evaluate the available data exploring sleep in early psychosis, with two key research questions: 1) What is the nature of sleep disturbance in early psychosis? and 2) What are the correlates of sleep disturbance in early psychosis? From an initial search, 16,675 papers were identified, of which 21 met inclusion/exclusion criteria. The preliminary evidence suggests that self-reported sleep disturbances are prevalent in early psychosis and may be associated with symptom severity, as well as elevated rates of both help-seeking and suicidality. Abnormalities in sleep architecture and sleep spindles are also commonly observed and may correlate with symptom severity and neurocognitive deficits. However, due to significant methodological limitations and considerable heterogeneity across studies, evidence to support the reliability of these associations is limited. We outline a research agenda, emphasising the prospective use of gold-standard sleep measurement to investigate the prevalence and nature of sleep disturbances in early psychosis, as well as how these may be related to the onset and persistence of psychotic symptoms.

Electrophysiological endophenotypes in rodent models of schizophrenia and psychosis

Schizophrenia is caused by a diverse array of risk factors and results in a similarly diverse set of symptoms. Electrophysiological endophenotypes lie between risks and symptoms and have the potential to link the two. Electrophysiological studies in rodent models, described here, demonstrate that widely differing risk factors result in a similar set of core electrophysiological endophenotypes, suggesting the possibility of a shared neurobiological substrate.

Impairment of sleep-related memory consolidation in schizophrenia: relevance of sleep spindles?

OBJECTIVES

Deficits in declarative memory performance are among the most severe neuropsychological impairments in schizophrenia and contribute to poor clinical outcomes. The importance of sleep for brain plasticity and memory consolidation is widely accepted, and sleep spindles seem to play an important role in these processes. The aim of this study was to test the associations of sleep spindles and picture memory consolidation in patients with schizophrenia and healthy controls.

METHODS

We studied 16 patients with schizophrenia on stable antipsychotic medication (mean age ± standard deviation, 29.4 ± 6.4 years) and 16 healthy controls matched for age and educational level. Sleep was recorded and scored according to American Academy of Sleep Medicine (AASM) standard criteria. We performed a picture recognition paradigm and compared recognition performance for neutral and emotional pictures in sleep and wake conditions.

RESULTS

Recognition accuracy was better in healthy controls than in patients with schizophrenia in the sleep and wake conditions. However, the memory-promoting effect of sleep was significantly lower in schizophrenia patients than in controls. Sleep spindle activity was reduced in patients, and sleep spindle density was correlated with sleep-associated facilitation of recognition accuracy for neutral pictures.

CONCLUSION

Reduced sleep spindles seem to play an important role as a possible mechanism or biomarker for impaired sleep-related memory consolidation in patients with schizophrenia, and are a new target for treatment to improve memory functions and clinical outcomes in these patients.