Sleep state switching

Sleep Alterations and Cognitive Decline

Sleep disturbances and cognitive decline are intricately connected, and both are prevalent in aging populations and individuals with neurodegenerative disorders such as Alzheimer's disease (AD) and other dementias. Sleep is vital for cognitive functions including memory consolidation, executive function, and attention. Disruption in these processes is associated with cognitive decline, although causal evidence is mixed. This review delves into the bidirectional relationship between alterations in sleep and cognitive impairment, exploring key mechanisms such as amyloid-β accumulation, tau pathology, synaptic homeostasis, neurotransmitter dysregulation, oxidative stress, and vascular contributions. Evidence from both experimental research and population-based studies underscores the necessity of early interventions targeting sleep to mitigate risks of neurodegenerative diseases. A deeper understanding of the interplay between sleep and cognitive health may pave the way for innovative strategies to prevent or reduce cognitive decline through improved sleep management.

A light in the darkness: Early phases of development and the emergence of cognition

During the prenatal period, the major brain development milestones are posed and calibrated through different mechanisms, among which endogenous activity, that prepares the "system" to face the external environment. However, the specific nature of the human nervous system, intended for brain plasticity that is varied by brain area and prolonged over time, requires much time for environmental experiences to shape the cerebral circuitries. Therefore, the neonate completely depends on the caregiver, and during the first months of postnatal life, it exhibits a transitory and limited repertoire of behaviors and skills that favors the mother in her new role. This transitory condition will gradually give way to more mature competencies, the milestones of which are posed within 2 years of age. This review takes a new perspective on early development and attempts to trace the remarkable changes from in-utero period to the second year of postnatal life, posing a bridge between the neurobiological substrate and behavioral development. We based our work on the "normal" development, pointing out the risks inherent in any development process.

Profiling the sleep architecture of ageing adults using a seven-state continuous-time Markov model

Sleep is a complex biological process regulated by networks of neurons and environmental factors. As one falls asleep, neurotransmitters from sleep-wake regulating neurones work in synergy to control the switching of different sleep states throughout the night. As sleep disorders or underlying neuropathology can manifest as irregular switching, analysing these patterns is crucial in sleep medicine and neuroscience. While hypnograms represent the switching of sleep states well, current analyses of hypnograms often rely on oversimplified temporal descriptive statistics (TDS, e.g., total time spent in a sleep state), which miss the opportunity to study the sleep state switching by overlooking the complex structures of hypnograms. In this paper, we propose analysing sleep hypnograms using a seven-state continuous-time Markov model (CTMM). This proposed model leverages the CTMM to depict the time-varying sleep-state transitions, and probes three types of insomnia by distinguishing three types of wake states. Fitting the proposed model to data from 2056 ageing adults in the Multi-Ethnic Study of Atherosclerosis (MESA) Sleep study, we profiled sleep architectures in this population and identified the various associations between the sleep state transitions and demographic factors and subjective sleep questions. Ageing, sex, and race all show distinctive patterns of sleep state transitions. Furthermore, we also found that the perception of insomnia and restless sleep are significantly associated with critical transitions in the sleep architecture. By incorporating three wake states in a continuous-time Markov model, our proposed method reveals interesting insights into the relationships between objective hypnogram data and subjective sleep quality assessments.

Deficient synaptic neurotransmission results in a persistent sleep-like cortical activity across vigilance states in mice

Growing evidence suggests that brain activity during sleep, as well as sleep regulation, are tightly linked with synaptic function and network excitability at the local and global levels. We previously reported that a mutation in synaptobrevin 2 (Vamp2) in restless (rlss) mice results in a marked increase of wakefulness and suppression of sleep, in particular REM sleep (REMS), as well as increased consolidation of sleep and wakefulness. In this study, using finer-scale in vivo electrophysiology recordings, we report that spontaneous cortical activity in rlss mice during NREM sleep (NREMS) is characterized by an occurrence of abnormally prolonged periods of complete neuronal silence (OFF-periods), often lasting several seconds, similar to the burst suppression pattern typically seen under deep anesthesia. Increased incidence of prolonged network OFF-periods was not specific to NREMS but also present in REMS and wake in rlss mice. Slow-wave activity (SWA) was generally increased in rlss mice relative to controls, while higher frequencies, including theta-frequency activity, were decreased, further resulting in diminished differences between vigilance states. The relative increase in SWA after sleep deprivation was attenuated in rlss mice, suggesting either that rlss mice experience persistently elevated sleep pressure or, alternatively, that the intrusion of sleep-like patterns of activity into the wake state attenuates the accumulation of sleep drive. We propose that a deficit in global synaptic neurotransmitter release leads to "state inertia," reflected in an abnormal propensity of brain networks to enter and remain in a persistent "default state" resembling coma or deep anesthesia.

The mechanism of different orexin/hypocretin neuronal projections in wakefulness and sleep

Since the discovery of orexin/hypocretin, numerous studies have accumulated evidence demonstrating its key role in various aspects of neuromodulation, including addiction, motivation, and arousal. This paper focuses on the projection of orexin neurons to specific target brain regions through distinct neural pathways to regulate sleep and arousal. We provide a detailed discussion of the projection mechanisms of orexin neurons to downstream neurons, particularly emphasizing their activation of monoaminergic and cholinergic neurons associated with arousal. Additionally, we briefly explore the immune response and inflammatory factors linked to the loss of orexin neurons. Our findings underscore the significance of understanding specific neural projections in the generation and maintenance of arousal, which could guide advancements in neuroscience and lead to new therapeutic opportunities for treating insomnia or narcolepsy.

The interaction between orexin, sleep deprivation and Alzheimer's disease: Unveiling an Emerging Connection

Alzheimer's disease (AD) is a devastating neurodegenerative disorder characterized by progressive cognitive decline and memory loss. Sleep-wake disorders are an extremely predominant and often disabling aspect of AD. Ox is vital in maintaining the sleep-wake cycle and promoting wakefulness. Dysfunction of Ox signaling has been associated with sleep disorders such as narcolepsy. In AD patients, the increase in cerebrospinal fluid Ox levels is related to parallel sleep deterioration. The relationship between AD and sleep disturbances has gained increasing attention due to their potential bidirectional influence. Disruptions in sleep patterns are commonly observed in AD patients, leading researchers to investigate the possible involvement of Ox in sleep disturbances characteristic of the disease. This review article explores the role of the Ox system in AD, and the intricate relationship between AD and sleep, highlighting the potential mechanisms, impact on disease pathology, and therapeutic interventions to improve sleep quality in affected individuals.

Emerging Technologies to Track and Improve Sleep Health

This review explores cutting-edge advancements, including wearable sleep trackers, brain age assessments, transcranial electrical stimulation (TES), acoustic stimulation, and glymphatic system modulation. Sleep trackers provide continuous monitoring of sleep patterns, while brain age estimation offers insights into brain health and early detection of accelerated aging. TES shows promise in improving mood, memory, and sleep. Acoustic stimulation during slow-wave sleep has been demonstrated to enhance memory consolidation. Additionally, optimizing the glymphatic system may facilitate brain waste clearance, crucial in preventing neurodegenerative diseases like Alzheimer's. However, significant challenges remain, including the need for rigorous longitudinal studies to validate these technologies' efficacy and safety.

Brain Health in Sleep Disorders

Sleep is a critical determinant of brain health, influencing cognitive, emotional, and physiologic functions. The complex bidirectional relationship between sleep and brain health underscores the importance of sleep in maintaining cognitive function, regulating brain homeostasis, and facilitating the clearance of metabolic waste through the glymphatic system. Chronic sleep deprivation and sleep disorders such as insomnia and obstructive sleep apnea have been shown to negatively impact brain structures and functions. This review discusses the impact of sleep disorders on brain health. It also explores the implications of impaired sleep on cardiovascular health, immune function, and neuroplasticity.

Phasic Dopamine Release in the Nucleus Accumbens Influences REM Sleep Timing

Based on the activity of dopamine (DA) neurons during behavioral states, the DA system has long been thought to be foundational in regulating sleep-wake behavior; over the past decade, advances in circuit manipulation and recording techniques have strengthened this perspective. Recently, several studies have demonstrated that DA release in regions of the limbic system is important in the promotion of REM sleep. Yet how DA dynamics change within bouts of sleep, how these changes are regulated, and whether they influence future state changes remains unclear. To address these questions, in mice of both sexes we used in vivo fiber photometry and inhibitory optogenetics to identify a specific role of DA transients in the nucleus accumbens (NAcc) in state transitions from NREM sleep. We found that DA transients increase their frequency and amplitude over the duration of NREM sleep and that this increase is more pronounced during NREM bouts that transition into REM sleep. Next, we found that DA transients in NREM sleep are influenced by changes in REM sleep pressure. Finally, we show that transient DA release in the NAcc plays a functional role in regulating the timing of REM sleep entrances, as inhibition of midbrain DA neuron terminals in the NAcc prolonged bouts of NREM sleep and decreased the frequency of bouts of REM sleep. These findings demonstrate that DA release in the NAcc is dynamically regulated by sleep pressure and has a functional role in transitions from NREM sleep, particularly those into REM sleep.

Suprachiasmatic Neuromedin-S Neurons Regulate Arousal

Mammalian circadian rhythms, which orchestrate the daily temporal structure of biological processes, including the sleep-wake cycle, are primarily regulated by the circadian clock in the hypothalamic suprachiasmatic nucleus (SCN). The SCN clock is also implicated in providing an arousal 'signal,' particularly during the wake-maintenance zone (WMZ) of our biological day, essential for sustaining normal levels of wakefulness in the presence of mounting sleep pressure. Here we identify a role for SCN Neuromedin-S (SCN NMS ) neurons in regulating the level of arousal, especially during the WMZ. We used chemogenetic and optogenetic methods to activate SCN NMS neurons in vivo, which potently drove wakefulness. Fiber photometry confirmed the wake-active profile of SCN NM neurons. Genetically ablating SCN NMS neurons disrupted the sleep-wake cycle, reducing wakefulness during the dark period and abolished the circadian rhythm of body temperature. SCN NMS neurons target the dorsomedial hypothalamic nucleus (DMH), and photostimulation of their terminals within the DMH rapidly produces arousal from sleep. Pre-synaptic inputs to SCN NMS neurons were also identified, including regions known to influence SCN clock regulation. Unexpectedly, we discovered strong input from the preoptic area (POA), which itself receives substantial inhibitory input from the DMH, forming a possible arousal-promoting circuit (SCN->DMH->POA->SCN). Finally, we analyzed the transcriptional profile of SCN NMS neurons via single-nuclei RNA-Seq, revealing three distinct subtypes. Our findings link molecularly-defined SCN neurons to sleep-wake patterns, body temperature rhythms, and arousal control.

Significance Statement

Our study's findings provide a cellular and neurobiological understanding of how Neuromedin-S (NMS)-containing SCN neurons contribute to regulating circadian rhythms, sleep-wake patterns, body temperature, and arousal control in mammals. This research illuminates the circuit, cellular, and synaptic mechanisms through which SCN neurons regulate daily cycles of wakefulness and sleep, with implications for understanding and potentially manipulating these processes in health and disease.

Anything but small: Microarousals stand at the crossroad between noradrenaline signaling and key sleep functions

Continuous sleep restores the brain and body, whereas fragmented sleep harms cognition and health. Microarousals (MAs), brief (3- to 15-s-long) wake intrusions into sleep, are clinical markers for various sleep disorders. Recent rodent studies show that MAs during healthy non-rapid eye movement (NREM) sleep are driven by infraslow fluctuations of noradrenaline (NA) in coordination with electrophysiological rhythms, vasomotor activity, cerebral blood volume, and glymphatic flow. MAs are hence part of healthy sleep dynamics, raising questions about their biological roles. We propose that MAs bolster NREM sleep's benefits associated with NA fluctuations, according to an inverted U-shaped curve. Weakened noradrenergic fluctuations, as may occur in neurodegenerative diseases or with sleep aids, reduce MAs, whereas exacerbated fluctuations caused by stress fragment NREM sleep and collapse NA signaling. We suggest that MAs are crucial for the restorative and plasticity-promoting functions of sleep and advance our insight into normal and pathological arousal dynamics from sleep.

The subcortical correlates of self-reported sleep quality

Study objectives

To assess the association between self-reported measures of sleep quality and cortical and subcortical local morphometry.

Methods

Sleep quality, operationalized with the Pittsburgh Sleep Quality Index (PSQI), and neuroanatomical data from the full release of the young adult Human Connectome Project dataset were analyzed (N=1,112; 46% female; mean age: 28.8 years old). Local cortical and subcortical morphometry was measured with subject-specific segmentations resulting in voxelwise gray matter difference (i.e., voxel based morephometry) measurements for cortex and local shape measurements for subcortical regions. Associations between the total score of PSQI, two statistical groupings of its subcomponents (obtained with a principal component analysis), and their interaction with demographic (i.e., sex, age, handedness, years of education) and biometric (i.e., BMI) variables were assessed using a general linear model and a nonparametric permutation approach.

Results

Sleep quality-related variance was significantly associated with subcortical morphometry, particularly in the bilateral caudate, putamen, and left pallidum, where smaller shape measures correlated with worse sleep quality. Notably, these associations were independent of demographic and biometric factors. In contrast, cortical morphometry, along with additional subcortical sites, showed no direct associations with sleep quality but demonstrated interactions with demographic and biometric variables.

Conclusions

This study reveals a specific link between self-reported sleep quality and subcortical morphometry, particularly within the striatum and pallidum, reinforcing the role of these regions in sleep regulation. These findings underscore the importance of considering subcortical morphology in sleep research and highlight potential neuromodulatory targets for sleep-related interventions.

Intermittent Vibration Induces Sleep via an Allatostatin A-GABA Signaling Pathway and Provides Broad Benefits in Alzheimer's Disease Models

While animals across species typically experience suppressed consciousness and an increased arousal threshold during sleep, the responsiveness to specific sensory inputs persists. Previous studies have demonstrated that rhythmic and continuous vibration can enhance sleep in both animals and humans. However, the neural circuits underlying vibration-induced sleep (VIS) and its potential therapeutic benefits on neuropathological processes in disease models remain unclear. Here, it is shown that intermittent vibration, such as cycles of 30 s on followed by 30 s off, is more effective in inducing sleep compared to continuous vibration. A clear evidence is further provided that allatostatin A (AstA)-GABA signaling mediates short-term intermittent vibration-induced sleep (iVIS) by inhibiting octopaminergic arousal neurons through activating GABAA receptors. The existence of iVIS in mice is corroborated, implicating the GABAergic system in this process. Finally, intermittent vibration not only enhances sleep but also reduces amyloid-β (Aβ) deposition and reverses memory defects in Alzheimer's disease models. In conclusion, the study defines a central neural circuit involved in mediating short-term iVIS and the potential implications of vibration in treating sleep-related brain disorders.

Novel applications of sleep pharmacology as delirium therapeutics

Sleep-wake and circadian disruption (SCD) is a core feature of delirium. It has been hypothesized that SCD contributes to delirium pathogenesis; therefore, interventions that prevent or reverse SCD represent an array of promising opportunities in relation to delirium. This review explores the relationship between sleep-wake/circadian physiology and delirium pathophysiology with a focus on neurotransmitter systems. Across potential targets aimed at preventing or treating delirium, three broad approaches are considered: 1. Pharmacological mechanisms that contribute to physiological sleep may preserve or restore next-day cognition in patients with or at risk for delirium (e.g., alpha 2 agonists, dopamine 2 antagonists, serotonin 2 A antagonists, dual orexin receptor antagonists, or GHB agonists); 2. Pharmacological mechanisms that promote wakefulness during the day may combat hypoactive delirium (e.g., adenosine 2 A antagonists, dopamine transporter antagonists, orexin agonists, histamine 3 antagonists); and 3. Melatonergic and other circadian interventions could strengthen the phase or amplitude of circadian rhythms and ensure appropriately entrained timing in patients with or at risk for delirium (e.g., as informed by a person's preexisting circadian phase).

Prolactin in sleep and EEG regulation: New mechanisms and sleep-related brain targets complement classical data

The role of prolactin in sleep regulation has been the subject of extensive research over the past 50 years, resulting in the identification of multiple, disparate functions for the hormone. Prolactin demonstrated a characteristic circadian release pattern with elevation during dark and diminution during light. High prolactin levels were linked to non-rapid eye movement sleep and electroencephalogram delta activity in humans. Conversely, hyperprolactinemia showed strong correlation with REM sleep in rodent studies. Prolactin may be implicated in the alterations in female sleep patterns observed during the reproductive cycle, it may play a role in the REM sleep enhancement following stress and in sleep-related immunological processes. In conclusion, prolactin appears to have a sleep-promoting role, particularly during the dark phase. However, it does not appear to play a central and coherent role in sleep regulation, as observed in some neuropeptides such as orexin. Conversely, its principal function may be to facilitate situational, yet adaptive, changes in sleep patterns in response to challenging physiological phases, such as those associated with stress, immunological challenges, or the reproductive cycle. Neuronal substrates for prolactin-mediated sleep effects remain unknown; however, recent rodent sleep studies may provide insights into the potential sites of these effects.

Neuroanatomical and pharmaco-physiological effects of hypoxia and esketamine on breathing, the sympathetic nerve system, and cortical function

Acute hypoxic ventilatory response is an important reflex that helps maintain breathing during low oxygen levels, but it is attenuated by most general anaesthetics. Analgesic doses of ketamine and esketamine are known to have respiratory stimulant effects. In their recent study in the British Journal of Anaesthesia, Jansen and colleagues show that low-dose esketamine preserved the acute hypoxic ventilatory response, while increasing breathing rate, systolic blood pressure, and heart rate. Participants also exhibited higher levels of alertness and unpleasant psychotropic effects compared with the control condition. We review the pharmaco-physiological effects of acute hypoxia and its interactions with esketamine. We provide a summary of the effects of hypoxia and esketamine on the neurocircuitry that leads to arousal, activation of the sympathetic nerve system, and increased drive to upper airway dilator and respiratory pump muscles.

Multiscale neural dynamics in sleep transition volatility across age scales: a multimodal EEG-EMG-EOG analysis of temazepam effects

Recent advances in computational modeling techniques have facilitated a more nuanced understanding of sleep neural dynamics across the lifespan. In this study, we tensorize multiscale multimodal electroencephalogram (EEG), electromyogram (EMG), and electrooculogram (EOG) signals and apply Generalized Autoregressive Conditional Heteroskedasticity (GARCH) modeling to quantify interactions between age scales and the use of pharmacological sleep aids on sleep stage transitions. Our cohort consists of 22 subjects in a crossover design study, where each subject received both a sleep aid and a placebo in different sessions. To understand these effects across the lifespan, three evenly distributed age groups were formed: 18-29, 30-49, and 50-66 years. The methodological framework implemented here employs tensor-based machine learning techniques to compute continuous wavelet transform time-frequency features and utilizes a GARCH model to quantify sleep signal volatility across age scales. Support Vector Machines are used for feature ranking, and our analysis captures interactions between signal entropy, age, and sleep aid status across frequency bands, sleep transitions, and sleep stages. GARCH model results reveal statistically significant volatility clustering in EEG, EMG, and EOG signals, particularly during transitions between REM and non-REM sleep. Notably, volatility was higher in the 50-66 age group compared to the 18-29 age group, with marked fluctuations during transitions from deep sleep to REM sleep (standard deviation of 0.35 in the older group vs. 0.30 in the 18-29 age group, p < 0.05). Statistical comparisons of volatility across frequency bands, age scales, and sleep stages highlight significant differences attributable to sleep aid use. Mean conditional volatility parameterization of the GARCH model reveals directional influences, with a causality index of 0.75 from frontal to occipital regions during REM sleep transition periods. Our methodological framework identifies distinct neural behavior patterns across age groups associated with each sleep stage and transition, offering insights into the development of targeted interventions for sleep regularity across the lifespan.

Spontaneous oxycodone withdrawal disrupts sleep, diurnal, and electrophysiological dynamics in rats

Opioid dependence is defined by an aversive withdrawal syndrome upon drug cessation that can motivate continued drug-taking, development of opioid use disorder, and precipitate relapse. An understudied but common opioid withdrawal symptom is disrupted sleep, reported as both insomnia and daytime sleepiness. Despite the prevalence and severity of sleep disturbances during opioid withdrawal, there is a gap in our understanding of their interactions. The goal of this study was to establish an in-depth, temporal signature of spontaneous oxycodone withdrawal effects on the diurnal composition of discrete sleep stages and the dynamic spectral properties of the electroencephalogram (EEG) signal in male rats. We continuously recorded EEG and electromyography (EMG) signals for 8 d of spontaneous withdrawal after a 14-d escalating-dose oxycodone regimen (0.5-8.0 mg/kg, 2×d; SC). During withdrawal, there was a profound loss (peaking on days 2-3) and gradual return of diurnal structure in sleep, body temperature, and locomotor activity, as well as decreased sleep and wake bout durations dependent on lights on/off. Withdrawal was associated with significant alterations in the slope of the aperiodic 1/f component of the EEG power spectrum, an established biomarker of arousal level. Early in withdrawal, NREM exhibited an acute flattening and return to baseline of both low (1-4 Hz) and high (15-50 Hz) frequency components of the 1/f spectrum. These findings suggest temporally dependent withdrawal effects on sleep, reflecting the complex way in which the allostatic forces of opioid withdrawal impinge upon sleep and diurnal processes. These foundational data based on continuous tracking of vigilance state, sleep stage composition, and spectral EEG properties provide a detailed construct with which to form and test hypotheses on the mechanisms of opioid-sleep interactions.

Nocturnal sleep dynamics alterations in the early stages of behavioral variant frontotemporal dementia

STUDY OBJECTIVES

Sleep disorders have been recognized as an integral component of the clinical syndrome in several neurodegenerative diseases, including Alzheimer's disease (AD). However, limited data exist for rarer types of neurodegenerative diseases, such as behavioral variant frontotemporal dementia (bvFTD). This study aims to analyze EEG power spectra and sleep stage transitions in bvFTD patients, hypothesizing that bvFTD may show distinctive sleep stage transitions compared to patients with AD.

METHODS

Eighteen probable bvFTD patients and 18 age- and sex-matched probable patients with AD underwent overnight polysomnography (PSG) and completed sleep disorders questionnaires. Sleep questionnaires, full-night EEG spectra, and sleep stage transition indexes were compared between groups.

RESULTS

bvFTD patients had higher Insomnia Severity Index (ISI) scores (95% confidence intervals [CI]: 0, 5) and reported poorer sleep quality than AD patients (p < .01). Compared to AD, bvFTD patients showed higher N1 percentage (95% CI: 0.1, 6), lower N3 percentage (95% CI: -13.6, -0.6), higher sleep-wake transitions (95% CI: 1.49, 8.86) and N1 sleep-wake transitions (95% CI: 0.32, 6.1). EEG spectral analysis revealed higher spectral power in bvFTD compared to patients with AD in faster rhythms, especially sigma rhythm, across all sleep stages. In bvFTD patients, sleep-wake transitions were positively associated with ISI.

CONCLUSIONS

Patients with bvFTD present higher rates of transitions between wake and sleep than patients with AD. The increased frequency of sleep transitions indicates a higher degree of sleep instability in bvFTD, which may reflect an imbalance in sleep-wake-promoting systems. Sleep stage transitions analysis may provide novel insights into the sleep alterations of patients with bvFTD.

Aberrant individual large-scale functional network connectivity and topology in chronic insomnia disorder with and without depression

Insomnia is increasingly prevalent with significant associations with depression. Delineating specific neural circuits for chronic insomnia disorder (CID) with and without depressive symptoms is fundamental to develop precision diagnosis and treatment. In this study, we examine static, dynamic and network topology changes of individual large-scale functional network for CID with (CID-D) and without depression to reveal their specific neural underpinnings. Seventeen individual-specific functional brain networks are obtained using a regularized nonnegative matrix factorization technique. Disorders-shared and -specific differences in static and dynamic large-scale functional network connectivities within or between the cognitive control network, dorsal attention network, visual network, limbic network, and default mode network are found for CID and CID-D. Additionally, CID and CID-D groups showed compromised network topological architecture including reduced small-world properties, clustering coefficients and modularity indicating decreased network efficiency and impaired functional segregation. Moreover, the altered neuroimaging indices show significant associations with clinical manifestations and could serve as effective neuromarkers to distinguish among healthy controls, CID and CID-D. Taken together, these findings provide novel insights into the neural basis of CID and CID-D, which may facilitate developing new diagnostic and therapeutic approaches.

Arousal-promoting effect of the parabrachial nucleus and the underlying mechanisms: Recent advances

The parabrachial nucleus (PBN) is responsible for integrating both internal and external sensory information and controlling/regulating a wide range of physiological processes, such as feeding, thermogenesis, nociceptive and pruritic sensations, and respiration. Recently, the PBN has been found to be involved in mediating wakefulness maintenance, sleep-wake transition, exogenous neuromodulation of awakening, and arousal-promoting process triggered by drastic changes in the internal environments, such as hypercapnia, hypoxia, and hypertension. Multiple neural pathways and subpopulations of neurons are responsible for arousal-promoting effects of the PBN. The medial PBN seems to be more important for the maintenance of physiological arousal, while the lateral PBN are more crucial in mediating interoception-driven arousal. Glutamatergic projection from the PBN to the basal forebrain (BF) and GABAergic projection from the BF to the cerebral cortex GABAergic neurons are the most pivotal neural pathways for awareness-promotion. Here, we review the relevant literature in this field in recent years and emphasize the potential prospects of PBN stimulation in translational medicine for the rehabilitation of disorders of consciousness.

Compound 38, a novel potent and selective antagonist of adenosine A2A receptor, enhances arousal in mice

Adenosine A2A receptor (A2AR) plays a pivotal role in the regulation of sleep-wake behaviors. We previously reported an A2AR selective antagonist compound 38 with an IC50 value of 29.0 nM. In this study, we investigated its effect on sleep-wake regulation in mice. Wild-type (WT) mice were administered compound 38 (3.3, 5.0, 7.5, 15, 30 mg/kg, i.p.) at 9:00, and electroencephalography and electromyography were simultaneously recorded. We showed that administration of compound 38 exhibited a dose-dependent effect on wakefulness promotion. To investigate the impact of compound 38 on sleep rebound, we conducted a 6 h (13:00-19:00) sleep deprivation experiment. We found that administration of compound 38 (30 mg/kg) produced a wakefulness-promoting effect lasting for 1 h. Subsequently, we explored the critical role of A2AR in the wakefulness-promoting effect of compound 38 using A2AR knockout (KO) mice and their WT littermates. We found that compound 38 enhanced wakefulness in WT mice, but did not have an arousal-promoting effect in A2AR KO mice, suggesting that the arousal-promoting effect of compound 38 was mediated by A2AR. We conducted immunohistochemistry and selectively ablated A2AR-positive neurons using cell type-specific caspase-3 expression, which revealed an essential role of A2AR-positive neurons in the nucleus accumbens shell for the arousal-promoting effect of compound 38. In conclusion, as a novel A2AR antagonist, compound 38 promotes wakefulness in mice via the A2AR and exhibits promising applications for further advancements in the field of sleep-wake disorders.

Bibliometric and visual study of narcolepsy from 2000 to 2023

BACKGROUND

More studies explored the prevalence, causes, associated conditions, and therapeutic strategies of narcolepsy. With an increasing focus on understanding narcolepsy's prevalence, associated conditions, and therapeutic strategies, there's a notable absence of bibliometric analyses summarizing trends in research and identifying emerging areas of focus within this field.

AIM

To conduct a bibliometric analysis to investigate the current status and frontiers of narcolepsy.

METHODS

The documents related to narcolepsy are obtained from the Web of Science Core Collection database (WoSCC) from January 1, 2000, to December 31, 2023, and VOS viewer 1.6.16, and the WoSCC's literature analysis wire were used to conduct the bibliometric analysis.

RESULTS

A total of 4672 publications related to narcolepsy were included, and 16182 authors across 4397 institutions and 96 countries/regions contributed to these documents in 1131 different journals. The most productive author, institution, country and journal were Yves Dauvilliers, Stanford University, United States, and Sleep Medicine, respectively. The first high-cited document was published in Nature in 2005 by Saper et al, and this research underscores the role of certain neurons in ensuring the stability of sleep-wake transitions, offering insights into narcolepsy's pathophysiology.

CONCLUSION

In conclusion, the main research hotspots and frontiers in the field of narcolepsy are the diagnosis of narcolepsy, pathological mechanism of narcolepsy and the treatment of narcolepsy. More studies are needed to explore effective strategies for the diagnosis and treatment of narcolepsy.

Exploring structural features of sleep-enhancing peptides derived from casein hydrolysates by chemometrics and random forest methodology

Milk casein is regarded as source to release potential sleep-enhancing peptides. Although various casein hydrolysates exhibited sleep-enhancing activity, the underlying reason remains unclear. This study firstly revealed the structural features of potential sleep-enhancing peptides from casein hydrolysates analyzed through peptidomics and multivariate analysis. Additionally, a random forest model and a potential Tyr-based peptide library were established, and then those peptides were quantified to facilitate rapidly-screening. Our findings indicated that YP-, YI/L, and YQ-type peptides with 4-10 amino acids contributed more to higher sleep-enhancing activity of casein hydrolysates, due to their crucial structural features and abundant numbers. Furthermore, three novel strong sleep-enhancing peptides, YQKFPQY, YPFPGPIPN, and YIPIQY were screened, and their activities were validated in vivo. Molecular docking results elucidated the importance of the YP/I/L/Q- structure at the N-terminus of casein peptides in forming crucial hydrogen bond and π-alkyl interactions with His-102 and Asn-60, respectively in the GABAA receptor for activation.

The Improvement in Sleep Quality by Zizyphi Semen in Rodent Models Through GABAergic Transmission Regulation

Background: Sleep, a process physiologically vital for mental health, faces disruptions in various sleep disorders linked to metabolic and neurodegenerative risks. Zizyphus seed (Zizy) has long been recognized for its diverse pharmacological attributes, including analgesic, sedative, insomnia, and anxiety alleviation. Objectives: In this study, the sleep-prolonging effects of Zizy extract (100, 200 mg/kg), along with their characterizing compounds jujuboside A (JuA) (5, 10 mg/kg), were evaluated in a mouse model under a pentobarbital-induced sleep. Additionally, the efficacy of Zizy extract was examined on caffeine-induced insomnia in mice. Methods: To confirm the efficacy of Zizy extract on the structure and quality of sleep, an electroencephalogram (EEG) analysis of rats was performed using the MATLAB algorithm. Additionally, Western blot analysis and measurement of intracellular chloride influx were performed to confirm whether these effects acted through the gamma-aminobutyric acid (GABA)ergic system. Administration of Zizy extract showed no effect on the locomotor performance of mice, but the extract and their characteristic compounds significantly prolonged sleep duration in comparison to the pentobarbital alone group in the pentobarbital-induced sleep mouse model. Furthermore, this extract alleviated caffeine-induced insomnia in mice. Results: The administration of Zizy extract extended non-rapid eye movement sleep (NREMS) duration without inducing significant changes in the brain wave frequency. Zizy extract regulated the expression of GABAA receptor subunits and GAD65/67 in specific brain regions (frontal cortex, hippocampus, and hypothalamus). JuA increased intracellular chloride influx in human SH-SY5Y cells, and it was reduced by GABAA receptor antagonists. These results suggest that the sleep-maintaining effects of Zizy extract may entail GABAergic regulation. In summary, Zizy extract demonstrated sleep-prolonging properties, improved insomnia, and regulated sleep architecture through GABAergic system modulation. Conclusions: These findings suggest that Zizy extract has potential as a therapeutic agent for stress-related neuropsychiatric conditions such as insomnia.

Comprehensive Gene Expression Analysis Using Human Induced Pluripotent Stem Cells Derived from Patients with Sleep Bruxism: A Preliminary In Vitro Study

Sleep bruxism (SB) involves involuntary jaw movements during sleep and is potentially caused by motor neuronal hyperexcitability and GABAergic system dysfunction. However, the molecular basis remains unclear. In this study, we aimed to investigate changes in the expression of several genes associated with the pathophysiology of SB. Bulk RNA sequencing (bulk RNA-seq) and single-nucleus RNA sequencing (snRNA-seq) of neurons derived from patient and control human induced pluripotent stem cells (hiPSCs) were performed to comprehensively assess gene expression and cell type-specific alterations, respectively. Bulk RNA-seq revealed significant upregulation of calcium signaling-related genes in SB neurons, including those encoding G protein-coupled receptors and receptor-operated calcium channels. snRNA-seq confirmed the increased expression of GRIN2B (an N-methyl-D-aspartate receptor subunit) and CHRM3 (an M3 muscarinic acetylcholine receptor), particularly in glutamatergic and GABAergic neurons. These alterations were linked to hyperexcitability, with GRIN2B contributing to glutamatergic signaling and CHRM3 contributing to cholinergic signaling. These findings suggest that disrupted calcium signaling and overexpression of GRIN2B and CHRM3 drive neuronal hyperexcitability, providing insight into the pathophysiology of SB. Targeting these pathways may inform therapeutic strategies for SB treatment.

The claustrum and synchronized brain states

Cortical activity is constantly fluctuating between distinct spatiotemporal activity patterns denoted by changes in brain state. States of cortical desynchronization arise during motor generation, increased attention, and high cognitive load. Synchronized brain states comprise spatially widespread, coordinated low-frequency neural activity during rest and sleep when disengaged from the external environment or 'offline'. The claustrum is a small subcortical structure with dense reciprocal connections with the cortex suggesting modulation by, or participation in, brain state regulation. Here, we highlight recent work suggesting that neural activity in the claustrum supports cognitive processes associated with synchronized brain states characterized by increased low-frequency network activity. As an example, we outline how claustrum activity could support episodic memory consolidation during sleep.

Resting-state functional connectome predicts sleep quality two months after the first negative COVID-19 antigen test

BACKGROUND

The COVID-19 pandemic has led to long-term neurological and psychological effects, including sleep disturbances. While prior studies have identified altered brain function post-COVID-19, specific functional connectivity (FC) patterns predicting sleep quality after recovery remain unclear. This study aims to identify FC patterns associated with sleep quality two months after the first negative COVID-19 antigen test.

METHODS

Using a connectome-based predictive modeling (CPM) approach, we identified the functional connectome regulating sleep quality based on a 164-region parcellation. Significant connections were analyzed using mediation models to examine their role in the relationship between anxiety, depression, and sleep.

RESULTS

FC between the right cerebellar peduncle and the left VIII of the cerebellum, and between the left middle temporal pole (MTP) and left ventral tegmental area (VTA), significantly predicted Pittsburgh Sleep Quality Index (PSQI) scores for sleep disturbances two months post-recovery (q2 = 0.059, MSE = 0.154, p = 0.017, r = 0.350). Mediation analysis showed a significant indirect effect of FC between the left MTP and VTA on the relationship between generalized anxiety and sleep disturbances (indirect effect = 0.013, 95% CI = [0.002, 0.03], pfdr <0.05). FC between the right dorsal raphe nucleus and ipsilateral regions-including occipital, parietal, and temporal areas-predicted PSQI scores for daytime dysfunction (q2 = 0.092, MSE = 0.678, p = 0.025, r = 0.342).

CONCLUSION

Post-COVID-19 brain connectivity and anxiety predict sleep quality. These findings highlight the potential for targeted therapeutic strategies to improve sleep and identify patients at risk for prolonged disturbances through FC biomarkers.

Sleep Disturbances in Autoimmune Neurological Diseases: Mechanisms, Clinical Characteristics, Assessment, and Treatment Strategies

PURPOSE OF REVIEW

Sleep disturbances are a hallmark feature of various autoimmune neurological diseases (AINDs). However, limited awareness of these sleep manifestations exists among clinicians. We provide a comprehensive overview of assessment methods, characteristic sleep disturbances, the impact of specific antibodies on sleep patterns, and treatment strategies for sleep disturbances in AINDs.

RECENT FINDINGS

Research advancements in sleep disturbances in autoimmune neurological disease focus primarily on four areas: mechanisms, clinical characteristics, assessment, and treatment. Regarding mechanisms, animal models for AINDs, particularly those involving specific antibodies like anti-NMDAR, anti-LGI1, and anti-IgLON5, have become more comprehensive. Recent advancements in animal models have led to the establishment of numerous models for AINDs; these models include a wide range of antibodies, including anti-NMDAR, anti-LGI1, and anti-IgLON5. Several studies using these models have revealed common mechanisms underlying sleep disturbances in these diseases. In terms of clinical characteristics, the identification of antibodies associated with recently discovered AINDs has expanded the spectrum of sleep disturbance symptoms observed compared to prior findings. A comprehensive evaluation system for the assessment of sleep disturbances has been established, including questionnaires, polysomnography, functional magnetic resonance imaging, and 18F-FDG PET/CT. Additionally, cardiopulmonary coupling shows promise as a novel assessment tool. Currently, no universally effective treatment exists for sleep disturbances in autoimmune neurological diseases, either through symptomatic treatment or immunosuppressive therapy. Further studies are needed to confirm the efficacy of new therapies and validate the benefits of existing treatments. Sleep disturbances are a hallmark feature of AINDs. Recent advancements have significantly expanded our understanding of their assessment and treatment. However, further studies are needed to address the remaining uncertainties in sleep disturbance management.

Sleep quality and the integrity of ascending reticular activating system - A multimodal MRI study

Sleep is crucial for maintaining brain homeostasis and individuals with insufficient sleep are prone to more pronounced brain atrophy as compared to sufficiently sleeping peers. Moreover, sleep quality deteriorates with ageing and ageing is also associated with cerebral structural and functional changes, pointing to their mutual bidirectional interrelationship. This study aimed at determining whether sleep quality and age, separately, affect brain integrity and subsequently, whether sleep significantly modulates the effect of age on brain structural and functional integrity. 113 healthy volunteers underwent a multi-modal MRI imaging to extract information about the microstructure and function of major nodes of the ascending reticular activating system. Sleep quality was assessed by self-administered Pittsburgh's sleep quality index (PSQI) questionnaire. Subject were divided into good (global PSQI score <5) and poor (global PSQI score ≥5) sleep quality group. Whereas only borderline correlations were found between sleep quality and MRI metrics, age exhibited widespread correlations with both functional and microstructural MRI metrics. The latter effect was significantly modulated by sleep quality in ascending reticular activating system, hypothalamus, thalamus and also hippocampus in MRI metrics associated with iron load, cellularity and connectivity, mainly in the subgroup with poor sleep quality. Ergo, our results indicate sleep quality as a substantial contributor to both microstructural and functional brain changes in ageing and call for further research in this emerging topic.

Metabolomic Analysis Reveals the Linkage between Sleep-Enhancing Effects and Metabolite Biomarkers and Pathways of Different Casein Hydrolysates in Chronic Unpredictable Mild Stressed Mice

Casein hydrolysates have been proven to exert varying sleep-enhancing and anxiolytic effects due to their distinct release of potential peptides. However, their underlying sleep-enhancing mechanisms at the metabolic level remain unclear. This study aims to investigate the potential sleep-enhancing mechanism of casein hydrolysates through an integrated approach of untargeted and targeted metabolomics in CUMS-induced anxiety mice for the first time. The results showed seven potential biomarkers were identified and screened using orthogonal partial least-squares discriminant analysis, random forest model, and pathway analysis, including ornithine, l-proline, l-prolinamide, inhibitory neurotransmitters gamma-aminobutyric acid, 5-HIAA, fumaric acid, and 4-oxoglutaramate. Moreover, casein hydrolysates exerted sleep-enhancing effects through multiple metabolic pathways, mainly including the GABAergic system, tryptophan metabolism, and cAMP response signaling pathway, which was validated by targeted metabolomics and vital protein expressions. It was interesting that casein hydrolysates with diverse representative peptide compositions exhibited varying activity, which could be attributed to distinct alterations in metabolites via different pathways.

Growth hormone-releasing hormone and its analogues in health and disease

Growth hormone-releasing hormone (GHRH) and its ability to stimulate the production and release of growth hormone from the pituitary were discovered more than four decades ago. Since then, this hormone has been studied extensively and research into its functions is still ongoing. GHRH has multifaceted roles beyond the originally identified functions that encompass a variety of direct extrapituitary effects. In this Review, we illustrate the different biological activities of GHRH, covering the effects of GHRH agonists and antagonists in physiological and pathological contexts, along with the underlying mechanisms. GHRH and GHRH analogues have been implicated in cell growth, wound healing, cell death, inflammation, immune functions, mood disorders, feeding behaviour, neuroprotection, diabetes mellitus and obesity, as well as cardiovascular, lung and neurodegenerative diseases and some cancers. The positive effects observed in preclinical models in vitro and in vivo strongly support the potential use of GHRH agonists and antagonists as clinical therapeutics.

Orexin Receptor Antagonists for the Prevention and Treatment of Alzheimer's Disease and Associated Sleep Disorders

Orexins/hypocretins are neuropeptides produced by the hypothalamic neurons, binding two G-protein coupled receptors (orexin 1 and orexin 2 receptors) and playing a critical role in regulating arousal, wakefulness, and various physiological functions. Given the high prevalence of sleep disturbances in Alzheimer's disease (AD) and their reported involvement in AD pathophysiology, the orexin system is hypothesized to contribute to the disease pathogenesis. Specifically, recent evidence suggests that orexin's influence may extend beyond sleep regulation, potentially affecting amyloid-β and tau pathologies. Dual orexin receptor antagonists (DORAs), namely suvorexant, lemborexant, and daridorexant, demonstrated efficacy in treating chronic insomnia disorder across diverse clinical populations. Considering their stabilizing effects on sleep parameters and emerging evidence of a possible neuroprotective role, these agents represent a promising strategy for AD management. This leading article reviews the potential use of orexin receptor antagonists in AD, particularly focusing on their effect in modulating disease-associated sleep disturbances and clinical outcomes. Overall, clinical studies support the use of DORAs to enhance sleep quality in patients with AD with comorbid sleep and circadian sleep-wake rhythm disorders. Preliminary results also suggest that these compounds might influence AD pathology, potentially affecting disease progression. Conversely, research on selective orexin receptor antagonists in AD is currently limited. Further investigation is needed to explore orexin antagonism not only as a symptomatic treatment for sleep disturbances, but also for its broader implications in modifying AD neurodegeneration, emphasizing mechanisms of action and long-term outcomes.

A pontine-medullary loop crucial for REM sleep and its deficit in Parkinson's disease

Identifying the properties of the rapid eye movement (REM) sleep circuitry and its relation to diseases has been challenging due to the neuronal heterogeneity of the brainstem. Here, we show in mice that neurons in the pontine sublaterodorsal tegmentum (SubLDT) that express corticotropin-releasing hormone-binding protein (Crhbp+ neurons) and project to the medulla promote REM sleep. Within the medullary area receiving projections from Crhbp+ neurons, neurons expressing nitric oxide synthase 1 (Nos1+ neurons) project to the SubLDT and promote REM sleep, suggesting a positively interacting loop between the pons and the medulla operating as a core REM sleep circuit. Nos1+ neurons also project to areas that control wide forebrain activity. Ablating Crhbp+ neurons reduces sleep and impairs REM sleep atonia. In Parkinson's disease patients with REM sleep behavior disorders, CRHBP-immunoreactive neurons are largely reduced and contain pathologic α-synuclein, providing insight into the mechanisms underlying the sleep deficits characterizing this disease.

The localization of coma

Coma and disorders of consciousness (DoC) are common manifestations of acute severe brain injuries. Research into their neuroanatomical basis can be traced from Hippocrates to the present day. Lesions causing DoC have traditionally been conceptualized as decreasing "alertness" from damage to the ascending arousal system, and/or, reducing level of "awareness" due to structural or functional impairment of large-scale brain networks. Within this framework, pharmacological and neuromodulatory interventions to promote recovery from DoC have hitherto met with limited success. This is partly due to inter-individual heterogeneity of brain injury patterns, and an incomplete understanding of brain network properties that characterize consciousness. Advances in multiscale computational modelling of brain dynamics have opened a unique opportunity to explore the causal mechanisms of brain activity at the biophysical level. These models can provide a novel approach for selection and optimization of potential interventions by simulation of brain network dynamics individualized for each patient.

Parametric resonance brain model

The paper introduces a parametric resonance model for characterizing some features of the brain's electrical activity. This activity is assumed to be a fundamental aspect of brain functionality underpinning functions from basic sensory processing to complex cognitive operations such as memory, reasoning, and emotion. A pivotal element of the proposed parametric model is neuron synchronization which is crucial for generating detectable brain waves. The analysis of the frequency content of brain waves, categorized as delta (0÷4 Hz), theta (4÷7 Hz), alpha (8÷12 Hz), beta (13÷30 Hz), and gamma (30÷100 Hz) reveals, notably, that the mean frequency of each of these brain wave classes is, in sequence, approximately the double of that of the previous one. Based on this observation, the proposed parametric resonance model suggests a cascade of amplification effects. Following the proposed model, in the transition from wakefulness to sleep, the brain wave bands are energized at double frequency by higher frequency neighboring bands; on the contrary, in the sleep to awake transition, brain waves are energized at a half frequency by their lower frequency neighbor waves. Finally, the trend of increasing amplitude values from higher to lower frequencies lends empirical support to the parametric resonant brain model validity.

Local sleep in songbirds: different simultaneous sleep states across the avian pallium

Wakefulness and sleep have often been treated as distinct and global brain states. However, an emerging body of evidence on the local regulation of sleep stages challenges this conventional view. Apart from unihemispheric sleep, the current data that support local variations of neural oscillations during sleep are focused on the homeostatic regulation of local sleep, i.e., the role preceding awake activity. Here, to examine local differences in brain activity during natural sleep, we recorded the electroencephalogram and the local field potential across multiple sites within the avian pallium of zebra finches without perturbing the previous awake state. We scored the sleep stages independently in each pallial site and found that the sleep stages are not pallium-wide phenomena but rather deviate widely across electrode sites. Importantly, deeper electrode sites had a dominant role in defining the temporal aspects of sleep state congruence. Altogether, these findings show that local regulation of sleep oscillations also occurs in the avian brain without prior awake recruitment of specific pallial circuits and in the absence of mammalian cortical neural architecture.

Emerging Functions of Neuromodulation during Sleep

Neuromodulators act on multiple timescales to affect neuronal activity and behavior. They function as synaptic fine-tuners and master coordinators of neuronal activity across distant brain regions and body organs. While much research on neuromodulation has focused on roles in promoting features of wakefulness and transitions between sleep and wake states, the precise dynamics and functions of neuromodulatory signaling during sleep have received less attention. This review discusses research presented at our minisymposium at the 2024 Society for Neuroscience meeting, highlighting how norepinephrine, dopamine, and acetylcholine orchestrate brain oscillatory activity, control sleep architecture and microarchitecture, regulate responsiveness to sensory stimuli, and facilitate memory consolidation. The potential of each neuromodulator to influence neuronal activity is shaped by the state of the synaptic milieu, which in turn is influenced by the organismal or systemic state. Investigating the effects of neuromodulator release across different sleep substates and synaptic environments offers unique opportunities to deepen our understanding of neuromodulation and explore the distinct computational opportunities that arise during sleep. Moreover, since alterations in neuromodulatory signaling and sleep are implicated in various neuropsychiatric disorders and because existing pharmacological treatments affect neuromodulatory signaling, gaining a deeper understanding of the less-studied aspects of neuromodulators during sleep is of high importance.

Understanding the neurobiology of social behavior through exploring brain-wide dynamics of neural activity

Social behavior is highly complex and adaptable. It can be divided into multiple temporal stages: detection, approach, and consummatory behavior. Each stage can be further divided into several cognitive and behavioral processes, such as perceiving social cues, evaluating the social and non-social contexts, and recognizing the internal/emotional state of others. Recent studies have identified numerous brain-wide circuits implicated in social behavior and suggested the existence of partially overlapping functional brain networks underlying various types of social and non-social behavior. However, understanding the brain-wide dynamics underlying social behavior remains challenging, and several brain-scale dynamics (macro-, meso-, and micro-scale levels) need to be integrated. Here, we suggest leveraging new tools and concepts to explore social brain networks and integrate those different levels. These include studying the expression of immediate-early genes throughout the entire brain to impartially define the structure of the neuronal networks involved in a given social behavior. Then, network dynamics could be investigated using electrode arrays or multi-channel fiber photometry. Finally, tools like high-density silicon probes and miniscopes can probe neural activity in specific areas and across neuronal populations at the single-cell level.

REM sleep remains paradoxical: sub-states determined by thalamo-cortical and cortico-cortical functional connectivity

During paradoxical sleep (PS, aka REM sleep) the cerebral cortex displays rapid electroencephalographic activity similar to that of wakefulness, whereas in the posterior associative thalamus, rapid activity is interrupted by frequent periods of slow-wave (delta) oscillations at 2-3 Hz, thereby dissociating the intrinsic frequency in thalamus and cortex. Here we studied the functional consequences of such a dissociation using intrathalamic and intracortical recordings in 21 epileptic patients, applying coherence analysis to examine changes in functional connectivity between the posterior thalamus (mainly medial pulvinar) and six cortical functional networks, and also between each cortical network with respect to the others. Periods of slow-wave thalamic activity ('delta PS') were more prevalent than phases of 'rapid PS,' and the delta/rapid thalamic alternance did not overlap with the classical tonic/phasic dichotomy based on rapid eye movements. Thalamo-cortical and cortico-cortical functional connectivity significantly decreased during delta PS, relative to both rapid PS periods and to wakefulness. The fact that delta thalamic activity and low thalamo-cortical binding coincided with a suppression of cortico-cortical connectivity supports a crucial role for the posterior associative thalamus, and particularly the medial pulvinar, in ensuring trans-thalamic communication between distant cortical areas. Disruption of such a trans-thalamic communication during delta PS compromises the functional binding between cortical areas, and consequently might contribute to the alteration of perceptual experiences commonly reported during dreams. KEY POINTS: During paradoxical, or REM, sleep (PS), rapid thalamic activity is interrupted by frequent periods of slow delta waves at 2-3 Hz. During these periods of thalamic delta activity there was a drastic drop of functional connectivity between associative thalamus and cortex, and also among different cortical networks. The delta/rapid alternance did not overlap with the classically defined 'tonic/phasic' periods and therefore suggests a distinct dichotomy of functional states in PS. Recurrent decrease in thalamo-cortical and cortico-cortical functional connectivity during PS may compromise the spatio-temporal binding between cortical areas, which in turn could hinder the formation of coherent mental content during dreams.

Melatonin, Melatonin Receptors and Sleep: Moving Beyond Traditional Views

Sleep, constituting approximately one-third of the human lifespan, is a crucial physiological process essential for physical and mental well-being. Normal sleep consists of an orderly progression through wakefulness, non-rapid eye movement (NREM) sleep, and rapid eye movement (REM) sleep, all of which are tightly regulated. Melatonin, often referred to as the "hormone of sleep," plays a pivotal role as a regulator of the sleep/wake cycle and exerts its effects through high-affinity G-protein coupled receptors known as MT1 and MT2. Selective modulation of these receptors presents a promising therapeutic avenue for sleep disorders. This review examines research on the multifaceted role of melatonin in sleep regulation, focusing on selective ligands targeting MT1 and MT2 receptors, as well as studies involving MT1 and MT2 knockout mice. Contrary to common beliefs, growing evidence suggests that melatonin, through MT1 and MT2 receptors, might not only influence circadian aspects of sleep but likely, also modulate the homeostatic process of sleep and sleep architecture, or could be the molecule linking the homeostatic and circadian regulation of sleep. Furthermore, the distinct brain localization of MT1 and MT2 receptors, with MT1 receptors primarily regulating REM sleep and MT2 receptors regulating NREM sleep, is discussed. Collectively, sleep regulation extends beyond the circulating levels and circadian peak of melatonin; it also critically involves the expression, molecular activation, and regulatory functions of MT1 and MT2 receptors across various brain regions and nuclei involved in the regulation of sleep. This research underscores the importance of ongoing investigation into the selective roles of MT1 and MT2 receptors in sleep. Such research efforts are expected to pave the way for the development of targeted MT1 or MT2 receptors ligands, thereby optimizing therapeutic interventions for sleep disorders.

Shared subcortical arousal systems across sensory modalities during transient modulation of attention

Subcortical arousal systems are known to play a key role in controlling sustained changes in attention and conscious awareness. Recent studies indicate that these systems have a major influence on short-term dynamic modulation of visual attention, but their role across sensory modalities is not fully understood. In this study, we investigated shared subcortical arousal systems across sensory modalities during transient changes in attention using block and event-related fMRI paradigms. We analyzed massive publicly available fMRI datasets collected while 1,561 participants performed visual, auditory, tactile, and taste perception tasks. Our analyses revealed a shared circuit of subcortical arousal systems exhibiting early transient increases in activity in midbrain reticular formation and central thalamus across perceptual modalities, as well as less consistent increases in pons, hypothalamus, basal forebrain, and basal ganglia. Identifying these networks is critical for understanding mechanisms of normal attention and consciousness and may help facilitate subcortical targeting for therapeutic neuromodulation.

REM sleep in narcolepsy

Narcolepsy is mainly associated with excessive daytime sleepiness, but the characteristic feature is abnormal rapid eye movement (REM) sleep phenomena. REM sleep disturbances can manifest as cataplexy (in narcolepsy type 1), sleep paralysis, sleep-related hallucinations, REM sleep behavior disorder, abnormal dreams, polysomnographic evidence of REM sleep disruption with sleep-onset REM periods, and fragmented REM sleep. Characterization of REM sleep and related symptoms facilitates the differentiation of narcolepsy from other central hypersomnolence disorders and aids in distinguishing between narcolepsy types 1 and 2. A circuit comprising regions within the brainstem, forebrain, and hypothalamus is involved in generating and regulating REM sleep, which is influenced by changes in monoamines, acetylcholine, and neuropeptides. REM sleep is associated with brainstem functions, including autonomic control, and REM sleep disturbances may be associated with increased cardiovascular risk. Medications used to treat narcolepsy (and REM-related symptoms of narcolepsy) include stimulants/wake-promoting agents, pitolisant, oxybates, and antidepressants; hypocretin agonists are a potential new class of therapeutics. The role of REM sleep disturbances in narcolepsy remains an area of active research in pathophysiology, symptom management, and treatment. This review summarizes the current understanding of the role of REM sleep and its dysfunction in narcolepsy.

Mapping the physiological changes in sleep regulation across infancy and young childhood

Sleep patterns in infancy and early childhood vary greatly and change rapidly during development. In adults, sleep patterns are regulated by interactions between neuronal populations in the brainstem and hypothalamus, driven by the circadian and sleep homeostatic processes. However, the neurophysiological mechanisms underlying the sleep patterns and their variations across infancy and early childhood are poorly understood. We investigated whether a well-established mathematical model for sleep regulation in adults can model infant sleep characteristics and explain the physiological basis for developmental changes. By fitting longitudinal sleep data spanning 2 to 540 days after birth, we inferred parameter trajectories across age. We found that the developmental changes in sleep patterns are consistent with a faster accumulation and faster clearance of sleep homeostatic pressure in infancy and a weaker circadian rhythm in early infancy. We also find greater sensitivity to phase-delaying effects of light in infancy and early childhood. These findings reveal fundamental mechanisms that regulate sleep in infancy and early childhood. Given the critical role of sleep in healthy neurodevelopment, this framework could be used to pinpoint pathophysiological mechanisms and identify ways to improve sleep quality in early life.

Prefrontal synaptic regulation of homeostatic sleep pressure revealed through synaptic chemogenetics

Sleep is regulated by homeostatic processes, yet the biological basis of sleep pressure that accumulates during wakefulness, triggers sleep, and dissipates during sleep remains elusive. We explored a causal relationship between cellular synaptic strength and electroencephalography delta power indicating macro-level sleep pressure by developing a theoretical framework and a molecular tool to manipulate synaptic strength. The mathematical model predicted that increased synaptic strength promotes the neuronal "down state" and raises the delta power. Our molecular tool (synapse-targeted chemically induced translocation of Kalirin-7, SYNCit-K), which induces dendritic spine enlargement and synaptic potentiation through chemically induced translocation of protein Kalirin-7, demonstrated that synaptic potentiation of excitatory neurons in the prefrontal cortex (PFC) increases nonrapid eye movement sleep amounts and delta power. Thus, synaptic strength of PFC excitatory neurons dictates sleep pressure in mammals.

Preoptic area controls sleep-related seizure onset in a genetic epilepsy mouse model

In genetic and refractory epileptic patients, seizure activity exhibits sleep-related modulation/regulation and sleep and seizure are intermingled. In this study, by using one het Gabrg2 Q390X KI mice as a genetic epilepsy model and optogenetic method in vivo, we found that subcortical POA neurons were active within epileptic network from the het Gabrg2 Q390X KI mice and the POA activity preceded epileptic (poly)spike-wave discharges(SWD/PSDs) in the het Gabrg2 Q390X KI mice. Meanwhile, as expected, the manipulating of the POA activity relatively altered NREM sleep and wake periods in both wt and the het Gabrg2 Q390X KI mice. Most importantly, the short activation of epileptic cortical neurons alone did not effectively trigger seizure activity in the het Gabrg2 Q390X KI mice. In contrast, compared to the wt mice, combined the POA nucleus activation and short activation of the epileptic cortical neurons effectively triggered or suppressed epileptic activity in the het Gabrg2 Q390X KI mice, indicating that the POA activity can control the brain state to trigger seizure incidence in the het Gabrg2 Q390X KI mice in vivo. In addition, the suppression of POA nucleus activity decreased myoclonic jerks in the Gabrg2 Q390X KI mice. Overall, this study discloses an operational mechanism for sleep-dependent seizure incidence in the genetic epilepsy model with the implications for refractory epilepsy. This operational mechanism also underlies myoclonic jerk generation, further with translational implications in seizure treatment for genetic/refractory epileptic patients and with contribution to memory/cognitive deficits in epileptic patients.

Vasoactive intestinal peptide-expressing interneurons modulate the effect of behavioral state on cortical activity

Animals live in a complex and changing environment with various degrees of behavioral demands. Behavioral states affect the activity of cortical neurons and the dynamics of neuronal populations, however not much is known about the cortical circuitry behind the modulation of neuronal activity across behavioral states. Here we show that a class of GABAergic inhibitory interneurons that express vasoactive intestinal peptide-expressing interneurons (VIP), namely VIP interneurons, play a key role in the circuits involved in the modulation of cortical activity by behavioral state, as reflected in the mice facial motion. We show that inhibition of VIP interneurons reduces the correlated activity between the behavioral state of the animal and the spiking of individual neurons. We also show that VIP inhibition during the quiet state decreases the synchronous spiking of the neurons but increases delta power and phase locking of spiking to the delta-band activity. Taken together our data show that VIP interneurons modulate the behavioral state-dependency of cortical activity across different time scales.

Locus coeruleus microstructural integrity is associated with vigilance vulnerability to sleep deprivation

Insufficient sleep compromises cognitive performance, diminishes vigilance, and disrupts daily functioning in hundreds of millions of people worldwide. Despite extensive research revealing significant variability in vigilance vulnerability to sleep deprivation, the underlying mechanisms of these individual differences remain elusive. Locus coeruleus (LC) plays a crucial role in the regulation of sleep-wake cycles and has emerged as a potential marker for vigilance vulnerability to sleep deprivation. In this study, we investigate whether LC microstructural integrity, assessed by fractional anisotropy (FA) through diffusion tensor imaging (DTI) at baseline before sleep deprivation, can predict impaired psychomotor vigilance test (PVT) performance during sleep deprivation in a cohort of 60 healthy individuals subjected to a rigorously controlled in-laboratory sleep study. The findings indicate that individuals with high LC FA experience less vigilance impairment from sleep deprivation compared with those with low LC FA. LC FA accounts for 10.8% of the variance in sleep-deprived PVT lapses. Importantly, the relationship between LC FA and impaired PVT performance during sleep deprivation is anatomically specific, suggesting that LC microstructural integrity may serve as a biomarker for vigilance vulnerability to sleep loss.