Article

Night Watch in One Brain Hemisphere during Sleep Associated with the First-Night Effect in Humans

April 2016
Current Biology 26(9)

DOI:10.1016/j.cub.2016.02.063

Authors:

Masako Tamaki

RIKEN

Ji Won Bang

Brown University

We often experience troubled sleep in a novel environment [1]. This is called the first-night effect (FNE) in human sleep research and has been regarded as a typical sleep disturbance [2-4]. Here, we show that the FNE is a manifestation of one hemisphere being more vigilant than the other as a night watch to monitor unfamiliar surroundings during sleep [5, 6]. Using advanced neuroimaging techniques [7, 8] as well as polysomnography, we found that the temporary sleep disturbance in the first sleep experimental session involves regional interhemispheric asymmetry of sleep depth [9]. The interhemispheric asymmetry of sleep depth associated with the FNE was found in the default-mode network (DMN) involved with spontaneous internal thoughts during wakeful rest [10, 11]. The degree of asymmetry was significantly correlated with the sleep-onset latency, which reflects the degree of difficulty of falling asleep and is a critical measure for the FNE. Furthermore, the hemisphere with reduced sleep depth showed enhanced evoked brain response to deviant external stimuli. Deviant external stimuli detected by the less-sleeping hemisphere caused more arousals and faster behavioral responses than those detected by the other hemisphere. None of these asymmetries were evident during subsequent sleep sessions. These lines of evidence are in accord with the hypothesis that troubled sleep in an unfamiliar environment is an act for survival over an unfamiliar and potentially dangerous environment by keeping one hemisphere partially more vigilant than the other hemisphere as a night watch, which wakes the sleeper up when unfamiliar external signals are detected.

The insensitivity of sleep to an unfamiliar sleeping environment in patients with insomnia disorder

Article

Full-text available

Sep 2023
SLEEP BREATH

Background Sleeping in an unfamiliar environment, such as a sleep laboratory, is thought to disturb sleep in healthy individuals and could express a hyperarousal state called the first night effect. Insomnia disorder (ID) is a highly prevalent health problem characterized by increased arousal during the night and daytime. Whether or not a similar phenomenon occurs in patients with ID is unclear. This study aimed to investigate the effect of an unfamiliar environment on the sleep of patients with ID. Methods In an unfamiliar sleep laboratory, polysomnographic recording testing was performed for two consecutive nights in patients with ID and age- and sex-matched healthy control subjects (HC). We collected sleep diaries and questionnaires regarding sleep, medical conditions, psychological status, and health history. Sleep continuity and architecture in both groups were compared and analyzed for two consecutive nights. Results Participants with ID (n = 39) and HC (n = 35) demonstrated differentially poor sleep on laboratory adaptation after exposure to the sleep laboratory. Patients with ID had longer rapid eye movement (REM) latency on the first night than on the second sleep night. HC showed increased duration and percentage of N1, decreased duration and percentage of N3, and decreased REM percentage during initial nights compared to subsequent nights. The other sleep variables showed no differences between the first and second sleep nights in patients with ID and HC. Conclusions An unfamiliar sleep environment does not aggravate the disruption of sleep continuity and sleep architecture but only affects the REM latency in patients with ID compared with HC.

Asymmetry of sleep electrophysiological markers in patients with focal epilepsy

Article

Full-text available

May 2023

Sleep can modulate epileptic activities, but our knowledge of sleep perturbation by epilepsy remains sparse. Interestingly, epilepsy and sleep both present with defining electrophysiological features in the form of specific graphoelements on EEG. This raises the possibility to identify, within ongoing EEG activity, how epilepsy impacts and disrupts sleep. Here, we asked whether the presence of a lateralized epileptic focus interferes with the expression of the dominant electrophysiological hallmarks of sleep: slow oscillations, slow waves and spindles. To this aim, we conducted a cross-sectional study and analysed sleep recordings with surface EEG from 69 patients with focal epilepsy (age range at EEG: 17-61 years, 29 females, 34 left focal epilepsy). Comparing patients with left and right focal epilepsy, we assessed inter-hemispheric asymmetry of sleep slow oscillations power (delta range, 0.5-4 Hz); sleep slow wave density; amplitude, duration and slope; and spindle density, amplitude, duration as well as locking to slow oscillations. We found significantly different asymmetries in slow oscillation power (P < 0.01); slow wave amplitude (P < 0.05) and slope (P < 0.01); and spindle density (P < 0.0001) and amplitude (P < 0.05). To confirm that these population-based differences reflect actual patient-by-patient differences, we then tested whether asymmetry of sleep features can classify laterality of the epileptic focus using a decision tree and a 5-fold cross-validation. We show that classification accuracy is above chance level (accuracy of 65%, standard deviation: 5%) and significantly outperforms a classification based on a randomization of epileptic lateralization (randomization data accuracy: 50%, standard deviation 7%, unpaired t-test, P < 0.0001). Importantly, we show that classification of epileptic lateralization by the canonical epileptic biomarker, i.e. interictal epileptiform discharges, improves slightly but significantly when combined with electrophysiological hallmarks of physiological sleep (from 75% to 77%, P < 0.0001, one-way ANOVA + Sidak's multiple comparisons test). Together, we establish that epilepsy is associated with inter-hemispheric perturbation of sleep-related activities and provide an in-depth multi-dimensional profile of the main sleep electrophysiological signatures in a large cohort of patients with focal epilepsy. We provide converging evidence that the underlying epileptic process interacts with the expression of sleep markers, in addition to triggering well-known pathological activities, such as interictal epileptiform discharges.

The First-Night Effect on the Instability of Stage N2: Evidence from the Activity of the Central and Autonomic Nervous Systems

Article

Full-text available

Apr 2023
BSRCCS

A series of studies have suggested that stage N2 is vulnerable and strongly affected by the first-night effect (FNE). However, the neurophysiological mechanism underlying the vulnerability of stage N2 of the FNE has not been well examined. A total of 17 healthy adults (11 women and 6 men, mean age: 21.59 ± 2.12) underwent two nights of polysomnogram recordings in the sleep laboratory. We analyzed sleep structure and central and autonomic nervous system activity dur-ing stage N2 and applied the electroencephalographic (EEG) activation index (beta/delta power ratio) and heart rate variability to reflect changes in central and autonomic nervous system activi-ty caused by the FNE. Correlation analyses were performed between EEG activation and heart rate variability. The results showed that EEG activation and high-frequency heart rate variability increased on the adaptation night (Night 1). Importantly, EEG activation was significantly associ-ated with the percentage of stage N1, and the correlation between EEG activation and high-frequency heart rate variability decreased due to the FNE. These findings indicate that the FNE affects the instability of stage N2 by increasing central nervous system activity and uncou-pling the activity between the central and autonomic nervous systems.

Relationship Between Sleep and Memory Consolidation

Article

Full-text available

Feb 2023

Beyza Aslı Bi̇lsel

Sleep and memory are complex phenomena that are not fully understood, and the underlying mechanisms are still not fully understood. Besides being an adaptive behavior, sleep can modulate plasticity in the brain at the level of synaptic connections between neurons and neuronal plasticity affects sleep. Understanding how sleep is modulated by internal and external stimuli and how sleep modulates memory and plasticity is a key question in neuroscience. Sleep is characterized as a brain state that optimizes the memory consolidation. Although the initial encoding of a memory is a fast process, its long-term maintenance requires processes that continue to replace relevant data for hours or even years. The general name of this process is memory consolidation and the replacement of existing memories is the reconsolidation process. Memory consolidation refers to a process in which unstable newly formed memory traces are progressively transformed into long-term memories and become more resistant to interaction, although they may remain susceptible to further updates and modifications. Consolidation results from the reactivation of recently encoded neuronal memory representations that occur during slow-wave activity and transform the relevant representations into long-term memory for integration. Continued rapid eye movement sleep can stabilize transformed memories. According to recent research, sleep-related consolidation processes can be placed in different sizes for different types of memory. Slow wave activity, which is restorative sleep, is hypothesized to play an important role in memory by processing and consolidating newly acquired information. In this review, general research was conducted on the relationship between sleep and memory.

A brief nap during an acute stressor improves negative affect

Article

Full-text available

Jul 2022

Overnight sleep can reduce perceived stress, and improve associated cognitive disruptions and negative affect after an acute stressor. Whether a brief nap can also bestow these benefits in a non‐sleep‐restricted population is currently unknown. In this study that used a between‐subjects design, stress was triggered by administering a modified Trier Social Stress Test to two groups of participants (nap [n = 29], wake [n = 41]). All participants were instructed they would give a speech during the study but the topic would be withheld until later, and then completed a math task. After a 40‐min break in which participants watched a neutral video or took a nap monitored with electroencephalography, stress was reinforced by presenting the speech topics and giving participants a 10‐min preparation period. Next, instead of giving a speech, the study ended and participants were debriefed. Negative affect, perceived stress and working memory were measured at multiple time points before and after the break. Both groups showed lower perceived stress and improved working memory after the break than before, but a nap did not confer additional benefits for perceived stress or working memory beyond taking a break. However, the nap group exhibited lower negative affect after the break than the wake group, and only the nap group showed a reduction in negative affect compared with initial negative affect levels. These results indicate a nap can improve negative emotions accompanying a stressor to a greater extent than taking a break, and suggest that brief naps may be a useful way to improve mood while experiencing an acute stressor.

Non-invasive sleep EEG measurement in hand raised wolves

Article

Full-text available

Jun 2022

Sleep research greatly benefits from comparative studies to understand the underlying physiological and environmental factors affecting the different features of sleep, also informing us about the possible evolutionary changes shaping them. Recently, the domestic dog became an exceedingly valuable model species in sleep studies, as the use of non-invasive polysomnography methodologies enables direct comparison with human sleep data. In this study, we applied the same polysomnography protocol to record the sleep of dog’s closest wild relative, the wolf. We measured the sleep of seven captive (six young and one senior), extensively socialized wolves using a fully non-invasive sleep EEG methodology, originally developed for family dogs. We provide the first descriptive analysis of the sleep macrostructure and NREM spectral power density of wolves using a completely non-invasive methodology. For (non-statistical) comparison, we included the same sleep data of similarly aged dogs. Although our sample size was inadequate to perform statistical analyses, we suggest that it may form the basis of an international, multi-site collection of similar samples using our methodology, allowing for generalizable, unbiased conclusions. As we managed to register both macrostructural and spectral sleep data, our procedure appears to be suitable for collecting valid data in other species too, increasing the comparability of non-invasive sleep studies.

Comparative biology of sleep in diverse animals

Article

Full-text available

Jul 2023
J EXP BIOL

Sleep is a familiar, periodic occurrence in our lives. Despite its place in everyday experience, the existence of this suspended state of consciousness has intrigued and puzzled philosophers and scientists for decades. For much of its history, sleep science has focused on humans and mammals. In contrast, in the last 20 years or so, it has become increasingly clear that sleep is essentially universal. Sleep states have been observed in animals from mammals to cnidaria. Here, we review recent progress in sleep science through the lens of comparative physiology. We highlight broad insights into sleep phenomenology, physiology and function that have come from this comparative approach. These include the plasticity of sleep in response to environmental challenges and ecological niches, the discovery of distinct sleep stages in diverse taxa and conserved functions of sleep. Indeed, we argue, a comparative approach is essential to any comprehensive account of sleep.

Lateralized tactile stimulation during NREM sleep globally increases both slow and fast frequency activities

Article

Full-text available

Sep 2022

Slow frequency activity during non-rapid eye movement (NREM) sleep emerges from synchronized activity of widely distributed thalamo-cortical and cortico-cortical networks, reflecting homeostatic and restorative properties of sleep. Slow frequency activity exhibits a reactive nature, and can be increased by acoustic stimulation. Although non-invasive brain stimulation is a promising technique in basic and clinical sleep research, sensory stimulation studies focusing on modalities other than the acoustic are scarce. We explored here the potential of lateralized vibro-tactile stimulation (VTS) of the finger to locally modify electroencephalographic activity during nocturnal NREM sleep. Eight seconds-long sequences of vibro-tactile pulses were delivered at a rate of 1 Hz either to the left or to the right index finger, in addition to a sham condition, in fourteen healthy participants. VTS markedly increased slow frequency activity that peaked between 1–4 Hz but extended to higher (~13 Hz) frequencies, with fronto-central dominance. Enhanced slow frequency activity was accompanied by increased (14–22 Hz) fast frequency power peaking over central and posterior locations. VTS increased the amplitude of slow waves, especially during the first 3–4 s of stimulation. Noticeably, we did not observe local-hemispheric effects, that is, VTS resulted in a global cortical response regardless of stimulation laterality. VTS moderately increased slow and fast frequency activities in resting wakefulness, to a much lower extent compared to NREM sleep. The concomitant increase in slow and fast frequency activities in response to VTS indicates an instant homeostatic response coupled with wake-like, high-frequency activity potentially reflecting transient periods of increased environmental processing. © 2022 The Authors. Psychophysiology published by Wiley Periodicals LLC on behalf of Society for Psychophysiological Research.

Insomnia subtypes characterised by objective sleep duration and NREM spectral power and the effect of acute sleep restriction: an exploratory analysis

Preprint

Full-text available

Aug 2021

Insomnia disorder (ID) is a heterogeneous disorder with proposed subtypes based on objective sleep duration. We speculated that insomnia subtyping with additional power spectral analysis and measurement of response to acute sleep restriction may be informative in overall assessment of ID. To explore alternative classifications of ID subtypes, insomnia patients (n = 99) underwent two consecutive overnight sleep studies: (i) habitual sleep opportunity (polysomnography, PSG) and, (ii) two hours less sleep opportunity (electroencephalography, EEG), with the first night compared to healthy controls (n = 25). ID subtypes were derived from data-driven classification of PSG, EEG spectral power and interhemispheric EEG asymmetry index. Three insomnia subtypes with different sleep duration and NREM spectral power were identified. One subtype (n = 26) had shorter sleep duration and lower NREM delta power than healthy controls (short-sleep delta-deficient; SSDD), the second subtype (n = 51) had normal sleep duration but lower NREM delta power than healthy controls (normal-sleep delta-deficient; NSDD) and a third subtype showed (n = 22) no difference in sleep duration or delta power from healthy controls (normal neurophysiological sleep; NNS). Acute sleep restriction improved multiple objective sleep measures across all insomnia subtypes including increased delta power in SSDD and NSDD, and improvements in subjective sleep quality for SSDD ( p = 0.03), with a trend observed for NSDD ( p = 0.057). These exploratory results suggest evidence of novel neurophysiological insomnia subtypes that may inform sleep state misperception in ID and with further research, may provide pathways for personalised care.

Neural Synchronization, Chimera States and Sleep Asymmetry

Article

Full-text available

Oct 2021

We model the dynamics of sleep states in two connected model brain hemispheres, using groups of coupled individual Hindmarsh-Rose neural oscillators. In a single isloated hemisphere, sleep-promoting neurons and wake-promoting neurons exhibit alternating levels of within-group mean field activity, as well as alternating levels of stochastic phase synchronization, as the system moves between simulated day and night. In a two-hemisphere model, we find differences in the behavior of the sleep-promototing or wake-promoting regions between hemispheres, indicative of chimera-like behavior. We observe phase-cluster states, in which different hemispheres exhibit different bursting dynamics, as well as differences in synchronization between hemispheres. This provides a basis for modeling unihemispheric sleep, which occurs naturally in cetaceans and some bird species, among others, as well as asymmetric sleep, which occurs in human subjects suffering from sleep apnea or experiencing the “first night effect” induced by sleeping in a novel environment.

Phase-amplitude coupling of NREM sleep oscillations is unaffected by pre-sleep learning but related to overnight memory gains depending on the declarative learning paradigm

Preprint

Full-text available

Nov 2023

There is growing evidence in humans linking the temporal coupling between spindles and slow oscillations during NREM sleep with the overnight stabilization of memories encoded from daytime experiences in humans. However, whether the type and strength of learning influence that relationship is still unknown. Here we tested whether the amount or type of verbal word-pair learning prior to sleep affects subsequent phase-amplitude coupling (PAC) between spindles and slow oscillations (SO). We measured the strength and preferred timing of such coupling in the EEG of 41 healthy human participants over a post-learning and control night, to compare intra-individual changes with inter-individual differences. We leveraged learning paradigms of varying word-pair (WP) load: 40 WP learned to a minimum criterion of 60% correct (n=11); 40 WP presented twice (n=15); 120 WP presented twice (n=15). There were no significant differences in the preferred phase or strength between the control and post-learning nights, in all learning conditions. We observed an overnight consolidation effect (improved performance at delayed recall) for the criterion learning condition only, and only in this condition was the overnight change in memory performance significantly positively correlated with the phase of SO-spindle coupling. These results suggest that the coupling of brain oscillations during human NREM sleep are stable traits that are not modulated by the amount of pre-sleep learning, yet are implicated in the sleep-dependent consolidation of memory.

The Negative Effects of Travel on Student Athletes Through Sleep and Circadian Disruption

Article

Nov 2023
J BIOL RHYTHM

Collegiate athletes must satisfy the academic obligations common to all undergraduates, but they have the additional structural and social stressors of extensive practice time, competition schedules, and frequent travel away from their home campus. Clearly such stressors can have negative impacts on both their academic and athletic performances as well as on their health. These concerns are made more acute by recent proposals and decisions to reorganize major collegiate athletic conferences. These rearrangements will require more multi-day travel that interferes with the academic work and personal schedules of athletes. Of particular concern is additional east-west travel that results in circadian rhythm disruptions commonly called jet lag that contribute to the loss of amount as well as quality of sleep. Circadian misalignment and sleep deprivation and/or sleep disturbances have profound effects on physical and mental health and performance. We, as concerned scientists and physicians with relevant expertise, developed this white paper to raise awareness of these challenges to the wellbeing of our student-athletes and their co-travelers. We also offer practical steps to mitigate the negative consequences of collegiate travel schedules. We discuss the importance of bedtime protocols, the availability of early afternoon naps, and adherence to scheduled lighting exposure protocols before, during, and after travel, with support from wearables and apps. We call upon departments of athletics to engage with sleep and circadian experts to advise and help design tailored implementation of these mitigating practices that could contribute to the current and long-term health and wellbeing of their students and their staff members.

Condensation of eigenmodes in functional brain network and its correlation to chimera state

Article

Full-text available

Oct 2023

Condensation has long been a closely studied problem in statistical physics but little attention has been paid to neural science. Here, we discuss this problem in brain networks and discover the condensation of a functional brain network whereby all its eigenmodes are condensed only into a few or even a single eigenmode of the structural brain network. We show that the condensation occurs due to the emergence of both chimera states and brain functions from the structure of the brain network. Furthermore, the condensation only appears in the regions of chimera and the condensed eigenmodes are only limited to the lower ones. Condensation is confirmed across different levels of brain subnetworks, including hemispheres, cognitive subnetworks, and isolated cognitive subnetworks, which are further supported by resting-state functional connectivity from empirical data. Our results indicate that condensation could be a potential mechanism for performing brain functions.

Hunter-Gatherer Sleep and Novel Human Sleep Adaptations

Chapter

Jan 2019

Frequency chimera state induced by time delays in neural networks

Preprint

Full-text available

Sep 2023

The delay of information transmission is an inherent factor of the nervous systems, which has great influences on their collective dynamic behaviors. In this paper, we constructed a ring neural network using FHN neuron model as the network node and memristive synapses as the connection mode. Our primary focus was on investigating the effects of time delay and coupling strength on the firing frequency of neurons. Simulation results revealed that the frequency chimera state could be induced in the neural network with appropriate time delay, which is a new type of chimera state characterized by firing frequency rather than membrane potential. By adjusting the time delay properly, the neural network can also display multi-cluster frequency chimera states that coexisted with various incoherent regions and coherent regions. Meanwhile, we exhibit that initial value and coupling strength could have great influences on the effects of time delay on inducing frequency chimera state of the nervous systems.

SPEED FACTOR IN RELATION TO THE UNCONSCIOUS IN ART PRACTICES

Thesis

Full-text available

Jun 2022

Burcu Nur Cengiz

Within the changing parameters of the 21st century, the concept of speed emerges as a priority in every field and makes the speed culture phenomenon real. The speed culture does not contain established patterns and ingrained habits, and prioritizes skills such as quickness in thinking and comprehension and adaption to the new. Our habits, which are difficult to break, are realized unconsciously as a product of automatisms and are under the umbrella of implicit memory. Automatism, which is the common point of habits and the skills acquired through the repetition art practices, is characterized by features such as speed, unconsciousness, uncontrollability and effortlessness. Artists and designers from different movements use speed and speed’s dynamics such as automatism, intuitiveness, randomness and uncertainty to trigger the unconscious realm, develop their creativity and form a unique artistic language (idiolect/idiostyle). Art practices that are developed to this end do not aim to further automate a skill that is already automatic, but to add something to it and liberate the creative process, include breaking habit cycles such as conditioned gaze. The gesture drawing practices used in visual arts education provide a fertile field to develop cognitive flexibility that enables breaking established habits, thinking creatively. By bringing an original and current interpretation to this field, experimental and gesture drawing sessions were carried out with art students from Anadolu University Fine Arts Faculty Painting, Sculpture, Graphic Arts, Cartoon and Animation Departments. It can be accepted the speed factor turns into a mechanism that helps reveal the instantaneous and random forms, unconscious content and associations, which are considered as positive predictors of creativity. Keywords: Speed, Habitude, Automatism, Creativity, Visual Arts.

Dissociation of Arousal Index Between REM and NREM Sleep in Elderly Adults with Cognitive Impairment, No Dementia: A Pilot Study

Article

Aug 2023
J ALZHEIMERS DIS

Background: Sleep disruption in elderly has been associated with an increased risk of cognitive impairment and its transition into Alzheimer's disease (AD). High arousal indices (AIs) during sleep may serve as an early-stage biomarker of cognitive impairment non-dementia (CIND). Objective: Using full-night polysomnography (PSG), we investigated whether CIND is related to different AIs between NREM and REM sleep stages. Methods: Fourteen older adults voluntarily participated in this population-based study that included Mini-Mental State Examination, Neuropsi battery, Katz Index of Independence in Activities of Daily Living, and single-night PSG. Subjects were divided into two groups (n = 7 each) according to their results in Neuropsi memory and attention subtests: cognitively unimpaired (CU), with normal results; and CIND, with -2.5 standard deviations in memory and/or attention subtests. AIs per hour of sleep during N1, N2, N3, and REM stages were obtained and correlated with Neuropsi total score (NTS). Results: AI (REM) was significantly higher in CU group than in CIND group. For the total sample, a positive correlation between AI (REM) and NTS was found (r = 0.68, p = 0.006), which remained significant when controlling for the effect of age and education. In CIND group, the AI (N2) was significantly higher than the AI (REM) . Conclusion: In CIND older adults, this attenuation of normal arousal mechanisms in REM sleep are dissociated from the relative excess of arousals observed in stage N2. We propose as probable etiology an early hypoactivity at the locus coeruleus noradrenergic system, associated to its early pathological damage, present in the AD continuum.

Sensitive dynamics of brain cognitive networks and its resource constraints

Article

Jun 2023

It is well known that brain functions are closely related to the synchronization of brain networks, but the underlying mechanisms are still not completely understood. To study this problem, we here focus on the synchronization of cognitive networks, in contrast to that of a global brain network, as individual brain functions are in fact performed by different cognitive networks but not the global network. In detail, we consider four different levels of brain networks and two approaches, i.e., either with or without resource constraints. For the case of without resource constraints, we find that global brain networks have fundamentally different behaviors from that of the cognitive networks; i.e., the former has a continuous synchronization transition, while the latter shows a novel transition of oscillatory synchronization. This feature of oscillation comes from the sparse links among the communities of cognitive networks, resulting in coupling sensitive dynamics of brain cognitive networks. While for the case of resource constraints, we find that at the global level, the synchronization transition becomes explosive, in contrast to the continuous synchronization for the case of without resource constraints. At the level of cognitive networks, the transition also becomes explosive and the coupling sensitivity is significantly reduced, thus guaranteeing the robustness and fast switch of brain functions. Moreover, a brief theoretical analysis is provided.

A non-oscillatory, millisecond-scale embedding of brain state provides insight into behavior

Preprint

Full-text available

Jun 2023

Sleep and wake are understood to be slow, long-lasting processes that span the entire brain. Brain states correlate with many neurophysiological changes, yet the most robust and reliable signature of state is enriched in rhythms between 0.1 and 20 Hz. The possibility that the fundamental unit of brain state could be a reliable structure at the scale of milliseconds and microns has not been addressable due to the physical limits associated with oscillation-based definitions. Here, by analyzing high resolution neural activity recorded in 10 anatomically and functionally diverse regions of the murine brain over 24 h, we reveal a mechanistically distinct embedding of state in the brain. Sleep and wake states can be accurately classified based in 10^0 to 10^1 ms of neuronal activity sampled from 100 μm of brain tissue. In contrast to canonical rhythms, this embedding persists above 1,000 Hz. This latent fast embedding is robust to substates and nested neurophysiological events. To ascertain whether such fast and local structure is meaningful, we leveraged our observation that individual circuits intermittently switch states independently of the rest of the brain. Brief state discontinuities in subsets of circuits correspond with brief behavioral discontinuities during both sleep and wake. Our results suggest that the fundamental unit of state in the brain is consistent with the spatial and temporal scale of neuronal computation, and that this resolution can contribute to an understanding of cognition and behavior.

Origin, synchronization, and propagation of sleep slow waves in children

Article

Full-text available

Apr 2023
NEUROIMAGE

Study objectives: Sleep slow wave activity, as measured using EEG delta power (<4 Hz), undergoes significant changes throughout development, mirroring changes in brain function and anatomy. Yet, age-dependent variations in the characteristics of individual slow waves have not been thoroughly investigated. Here we aimed at characterizing individual slow wave properties such as origin, synchronization, and cortical propagation at the transition between childhood and adulthood. Methods: We analyzed overnight high-density (256 electrodes) EEG recordings of healthy typically developing children (N=21, 10.3±1.5 years old) and young healthy adults (N=18, 31.1±4.4 years old). All recordings were preprocessed to reduce artifacts, and NREM slow waves were detected and characterized using validated algorithms. The threshold for statistical significance was set at p=0.05. Results: The slow waves of children were larger and steeper, but less widespread than those of adults. Moreover, they tended to mainly originate from and spread over more posterior brain areas. Relative to those of adults, the slow waves of children also displayed a tendency to more strongly involve and originate from the right than the left hemisphere. The separate analysis of slow waves characterized by high and low synchronization efficiency showed that these waves undergo partially distinct maturation patterns, consistent with their possible dependence on different generation and synchronization mechanisms. Conclusions: Changes in slow wave origin, synchronization, and propagation at the transition between childhood and adulthood are consistent with known modifications in cortico-cortical and subcortico-cortical brain connectivity. In this light, changes in slow-wave properties may provide a valuable yardstick to assess, track, and interpret physiological and pathological development.

Chimera state in a feed-forward neuronal network

Article

Full-text available

Jan 2023
COGN NEURODYNAMICS

Feed-forward effect gives rise to synchronization in neuron firing in deep layers of multiple neuronal network. But complete synchronization means the loss of encoding ability. In order to avoid the contradiction, we ask whether partial synchronization (coexistence of disordered and synchronized neuron firing emerges, also called chimera state) as a compromise strategy can achieve in the feed-forward multiple-layer network. The answer is YES. In order to manifest our argument, we design a multi-layer neuronal network in which neurons in every layer are arranged in a ring topology and neuron firing propagates within (intra-) and across (inter-) the multiply layers. Emergence of chimera state and other patterns highly depends on initial condition of neuronal network and strength of feed-forward effect. Chimera state, cluster and synchronization intra- and inter- layers are displayed by sequence through layers when initial values are elaborately chosen to guarantee emergence of chimera state in the first layer. All type of patterns except chimera state propagates down toward deeper layers in different speeds varying with strength of feed-forward effect. If chimera state already exists in every layer, feed-forward effect with strong and moderate strength spoils chimera states in deep layers and they can only survive in first few layers. When the effect is small enough, chimera states will propagate down toward deeper layers. Indeed, chimera states could exist and transit to deeper layers in a regular multiple network under very strict conditions. The results help understanding better the neuron firing propagating and encoding scheme in a feed-forward neuron network.

Chimeralike oscillation modes in excitable scale-free networks

Article

Full-text available

Jan 2023

A topological mechanism of the emergence of chimeralike oscillation modes (CLOMs) consisting of coherent synchronous firings and incoherent nonsynchronous oscillations is proposed in excitable scale-free networks (ESFNs). It is revealed that the topology heterogeneity of the network is responsible for forming and maintaining the CLOM in the ESFN, which is definitely different from the mechanism of the normal oscillation mode (NOM) possessing only a single dynamical mode in homogeneous excitable systems. An effective-driving approach is proposed, which provides a criterion for the formation of the CLOM in excitable complex networks. Our contributions may shed light on a perspective of CLOMs in complex systems, and can help us understand competitions and self-organizations of NOM and CLOM in excitable systems with topological homogeneity and heterogeneity.

Sensehacking the guest’s multisensory hotel experience

Article

Full-text available

Dec 2022

Charles Spence

This narrative review discusses the literature on contemporary sensory marketing as it applies to hotel design. The role of each of the guest’s senses in the different stages of the customer journey are highlighted, and the functional benefits (to the guest’s multisensory experience), and likely commercial gains, of engaging more effectively with the guest’s non-visual senses, both individually, and in combination, are reviewed. While the visual elements of hotel design are undoubtedly important, the hotelier neglects the non-visual senses at their peril, given the negative effect of poor design on the customers’ overall multisensory experience (and ratings). A number of the crossmodal effects and multisensory interactions that have been suggested to modulate the guest’s experience of hotels (and resorts) are discussed. Mention is also made of the nature effect/biophilic design and how it is increasingly being incorporated in total design to help deliver on guest/customer well-being; the latter is a theme that has grown rapidly in relevance for those working in the hospitality sector. Taken together, there are numerous opportunities for hotel managers to ‘sensehack’ their guests’ multisensory experiences through environmental psychology The originality of this review stems from the analysis of the hierarchy of the guest’s senses and an explanation of how multisensory interactions affect sensory marketing in the design of hotel experiences for guests.

Studying dream experience through dream reports: Points of contact between dream research and first-person methods in consciousness science

Preprint

Nov 2022

In this chapter, we present the problem of dream reports in philosophy and empirical research, examine how the variability of methods and measures influences research results, and suggest that research on the phenomenological features of dreaming could benefit from insights from first-person methods in consciousness research. We consider two interview-based methods developed for acquiring detailed phenomenological reports on waking subjective experience - descriptive experience sampling (Hurlburt, 1990, 2011) and micro-phenomenology (Petitmengin, 2006) - discuss their applicability in dream research, and outline some promising research directions. [Manuscript for a chapter in Dreaming and Memory: Philosophical Issues; prior to peer-review.]

Type 1 diabetes as a prototypical condition challenging what we know about sleep

Article

Sep 2022

Dear Editor, Type 1 diabetes (T1D) is a form of organ failure impacting pancreatic insulin production. Without insulin, blood glucose levels become perilously high and can damage multiple organs. Exogenous insulin is lifesaving, but levels need to be constantly tweaked, and misjudgment can cause hypoglycemia, which can constitute a medical emergency. There is both circadian and sleep regulation of glucose metabolism, and acute complications from T1D are perhaps greatest whilst asleep. In this letter, we argue that T1D can be considered a prototypical condition that threatens some of what we know about sleep; and acts as a reminder to take care when conceptualizing sleep and offering advice on this topic to those with conditions and comorbidities necessitating a degree of nighttime management. We also outline a research agenda. Sleep and T1D are jarring bedpartners [1]. This difficult relationship can appear even prediagnosis, with nocturnal enuresis constituting a presenting symptom of T1D. Unfortunately, T1D is a 24-h condition meaning that the urgency with which hypoglycemia and hyperglycemia must be treated does not diminish at night when vigilance decreases and sleep arrives. Furthermore, when critical treatment decisions are made at night, they may be suboptimal due to circadian factors, sleep inertia (a groggy state following waking) or sleep deprivation. The future of T1D management currently appears to be technological advances, exemplified by incredible developments in closed-loop systems. Such technologies impressively improve blood glucose levels, but also necessitate 24/7 access to electronic insulin pumps, continuous glucose monitors, and mobile phones [2]. Ironically, standard sleep hygiene advice involves removing technology from the bedroom.

Effects of One Night of Forced Wakefulness on Morning Resting Blood Pressure in Humans: The Role of Biological Sex and Weight Status

Article

Full-text available

Sep 2022

Permanent night shift work is associated with adverse health effects, including elevated blood pressure (BP) and hypertension. Here, we examined the BP response to one night of forced wakefulness in a sitting position in a cohort without night shift work experience. According to a counterbalanced crossover design, 47 young adults with either obesity (N = 22; 10 women) or normal weight (N = 25; 11 women) participated in one night of sleep and one night of forced wakefulness under in-laboratory conditions. Resting ankle and brachial arterial BP were assessed in the morning, i.e., the time of the day when adverse cardiovascular events peak. After forced wakefulness, diastolic and mean arterial BP were ~4 mmHg higher at the ankle site and ~3 mmHg higher at the brachial site than after regular sleep (p < 0.05). The increase in BP following overnight forced wakefulness was more pronounced among men vs. women and more significant for diastolic BP at both sites among participants with normal weight vs. those with obesity. If confirmed in larger cohorts, including 24 h BP monitoring, people with occupations involving night shifts might benefit from regular BP monitoring. Particular attention should be paid to possible sex- and weight-specific effects of night shift work on BP.

Acute sleep loss increases CNS health biomarkers and compromises the ability to stay awake in a sex-and weight-specific manner

Article

Full-text available

Sep 2022

Night shift work impairs vigilance performance, reduces the ability to stay awake, and compromises brain health. To investigate if the magnitude of these adverse night shift work effects differs between sexes and weight groups, 47 men and women with either normal weight or obesity participated in one night of sleep and one night of total sleep loss. During the night of sleep loss, participants’ subjective sleepiness, vigilance performance, and ability to stay awake during 2-min quiet wake with eyes closed were repeatedly assessed. In addition, blood was collected in the morning after sleep loss and sleep to measure central nervous system (CNS) health biomarkers. Our analysis showed that women were sleepier during the night of sleep loss (P < 0.05) and spent more time in microsleep during quiet wake testing (P < 0.05). Finally, higher blood levels of neurofilament light chain, a biomarker of axonal damage, were found among women in the morning after sleep loss (P < 0.002). Compared with normal-weight subjects, those with obesity were more prone to fall asleep during quiet wake (P < 0.05) and exhibited higher blood levels of the CNS health biomarker pTau181 following sleep loss (P = 0.001). Finally, no differences in vigilance performance were noted between the sex and weight groups. Our findings suggest that the ability to stay awake during and the CNS health biomarker response to night shift work may differ between sexes and weight groups. Follow-up studies must confirm our findings under more long-term night shift work conditions.

Basins of attraction of chimera states on networks

Article

Full-text available

Sep 2022

Networks of identical coupled oscillators display a remarkable spatiotemporal pattern, the chimera state, where coherent oscillations coexist with incoherent ones. In this paper we show quantitatively in terms of basin stability that stable and breathing chimera states in the original two coupled networks typically have very small basins of attraction. In fact, the original system is dominated by periodic and quasi-periodic chimera states, in strong contrast to the model after reduction, which can not be uncovered by the Ott-Antonsen ansatz. Moreover, we demonstrate that the curve of the basin stability behaves bimodally after the system being subjected to even large perturbations. Finally, we investigate the emergence of chimera states in brain network, through inducing perturbations by stimulating brain regions. The emerged chimera states are quantified by Kuramoto order parameter and chimera index, and results show a weak and negative correlation between these two metrics.

Adaptive Solutions to the Problem of Vulnerability During Sleep

Article

Full-text available

Aug 2022

Lawrence J. Wichlinski

Sleep is a behavioral state whose quantity and quality represent a trade-off between the costs and benefits this state provides versus the costs and benefits of wakefulness. Like many species, we humans are particularly vulnerable during sleep because of our reduced ability to monitor the external environment for nighttime predators and other environmental dangers. A number of variations in sleep characteristics may have evolved over the course of human history to reduce this vulnerability, at both the individual and group level. The goals of this interdisciplinary review paper are (1) to explore a number of biological/instinctual features of sleep that may have adaptive utility in terms of enhancing the detection of external threats, and (2) to consider relatively recent cultural developments that improve vigilance and reduce vulnerability during sleep and the nighttime. This paper will also discuss possible benefits of the proposed adaptations beyond vigilance, as well as the potential costs associated with each of these proposed adaptations. Finally, testable hypotheses will be presented to evaluate the validity of these proposed adaptations.

Modelling the perception of music in brain network dynamics

Article

Full-text available

Aug 2022

We analyze the influence of music in a network of FitzHugh-Nagumo oscillators with empirical structural connectivity measured in healthy human subjects. We report an increase of coherence between the global dynamics in our network and the input signal induced by a specific music song. We show that the level of coherence depends crucially on the frequency band. We compare our results with experimental data, which also describe global neural synchronization between different brain regions in the gamma-band range in a time-dependent manner correlated with musical large-scale form, showing increased synchronization just before transitions between different parts in a musical piece (musical high-level events). The results also suggest a separation in musical form-related brain synchronization between high brain frequencies, associated with neocortical activity, and low frequencies in the range of dance movements, associated with interactivity between cortical and subcortical regions.

Why is human a night-oriented romancer?

Article

Full-text available

Jul 2022

Why do we schedule romantic meetings and trysts for dinner and not for breakfast? How many people do you know who prefer a romantic walk in the morning instead of in the evening? Why are the moon, sunset, night, and candle-light universally a part of the romantic lexicon? Population based data revealed that people usually make love when they go to bed at night and most sexual activities occur between 10 pm and 2 am. Given these universal patterns of behavior, what answers does neuroscience give to these questions? It appears that brain lateralization and its specific network processes offer a useful framework. In this hypothesis article we offer a view of night-oriented romantic processing based on findings concerning circadian rhythm, brain lateralization, and sleep evolution. Previous studies revealed a smooth change in brain lateralization from the left in the morning to the right hemisphere in the evening among right-handed people. Based on the hemispheric lateralization for emotional processing and evidence from evolutionary studies, we will try to draw a framework for analyzing night-oriented romantic behavior in humans. To this end, we review findings on brain lateralization and it s specific network processes with respect to emotion processing, sleep, waking and vigilance.

Frontal grey matter microstructure is associated with sleep slow waves characteristics in late midlife

Article

Full-text available

Jul 2022

Study objectives The ability to generate slow waves (SW) during non-rapid eye movement (NREM) sleep decreases as early as the 5 th decade of life, predominantly over frontal regions. This decrease may concern prominently SW characterised by a fast switch from hyperpolarised to depolarised, or down-to-up, state. Yet, the relationship between these fast and slow switcher SW and cerebral microstructure in ageing is not established. Methods We recorded habitual sleep under EEG in 99 healthy late-midlife individuals (mean age =59.3±5.3y; 68 women) and extracted SW parameters (density, amplitude, frequency) for all SW as well as according to their switcher type (slow vs. fast). We further used neurite orientation dispersion and density imaging (NODDI) to assess microstructural integrity over a frontal grey matter region of interest (ROI). Results In statistical models adjusted for age, sex, and sleep duration, we found that a lower SW density, particularly for fast switcher SW, was associated with a reduced orientation dispersion of neurites in the frontal ROI (p = 0.018, R²β* =0.06). In addition, overall SW frequency was positively associated with neurite density (p = 0.03, R²β* =0.05). By contrast, we found no significant relationships between SW amplitude and NODDI metrics. Conclusions Our findings suggest that the complexity of neurite organisation contributes specifically to the rate of fast switcher SW occurrence in healthy middle-aged individuals, corroborating slow and fast switcher SW as distinct types of SW. They further suggest that the density of frontal neurites plays a key role for neural synchronisation during sleep.

Pre-gelled Electrode Grid for Self-Applied EEG Sleep Monitoring at Home

Article

Full-text available

Jun 2022

The need for diagnostic capabilities for sleep disorders such as sleep apnea and insomnia far exceeds the capacity of inpatient sleep laboratories. Some home monitoring systems omit electroencephalography (EEG) because trained personnel may be needed to apply EEG sensors. Since EEG is essential for the detailed evaluation of sleep, better systems supporting the convenient and robust recording of sleep EEG at home are desirable. Recent advances in EEG acquisition with flex-printed sensors promise easier application of EEG sensor arrays for chronic recordings, yet these sensor arrays were not designed for sleep EEG. Here we explored the self-applicability of a new sleep EEG sensor array (trEEGrid) without prior training. We developed a prototype with pre-gelled neonatal ECG electrodes placed on a self-adhesive grid shape that guided the fast and correct positioning of a total of nine electrodes on the face and around the ear. Positioning of the sensors was based on the results of a previous ear-EEG sleep study (da Silva Souto et al., 2021), and included electrodes around the ear, one eye, and the chin. For comparison, EEG and electrooculogram channels placed according to the American Academy of Sleep Medicine criteria, as well as respiratory inductance plethysmography on thorax and abdomen, oxygen saturation, pulse and body position were included with a mobile polysomnography (PSG) system. Two studies with 32 individuals were conducted to compare the signal quality of the proposed flex-printed grid with PSG signals and to explore self-application of the new grid at home. Results indicate that the new array is self-applicable by healthy participants without on-site hands-on support. A comparison of the hypnogram annotations obtained from the data of both systems revealed an overall substantial agreement on a group level (Cohen’s κ = 0.70 ± 0.01). These results suggest that flex-printed pre-gelled sensor arrays designed for sleep EEG acquisition can facilitate self-recording at home.

Beyond traditional sleep scoring: Massive feature extraction and data-driven clustering of sleep time series

Article

Jun 2022
SLEEP MED

The widely used guidelines for sleep staging were developed for the visual inspection of electrophysiological recordings by the human eye. As such, these rules reflect a limited range of features in these data and are therefore restricted in accurately capturing the physiological changes associated with sleep. Here we present a novel analysis framework that extensively characterizes sleep dynamics using over 7700 time-series features from the hctsa software. We used clustering to categorize sleep epochs based on the similarity of their time-series features, without relying on established scoring conventions. The resulting sleep structure overlapped substantially with that defined by visual scoring. However, we also observed discrepancies between our approach and traditional scoring. This divergence principally stemmed from the extensive characterization by hctsa features, which captured distinctive time-series properties within the traditionally defined sleep stages that are overlooked with visual scoring. Lastly, we report time-series features that are highly discriminative of stages. Our framework lays the groundwork for a data-driven exploration of sleep sub-stages and has significant potential to identify new signatures of sleep disorders and conscious sleep states.

Bidirectional associations between nightly sleep and daily happiness and negative mood in adolescents

Article

Full-text available

May 2022

This study examined bidirectional associations between daily happiness and negative mood and subjective and objective sleep measures. Participants were 311 adolescents (Mage = 17.37 years; 51.8% female; 59.2% White/European American, 38.6% Black/African American, 1% Hispanic/Latinx American, 1.4% multi‐racial; 19.3% below poverty line) observed over a 7‐day period (2017–2018) using sleep diaries and actigraphy. Daily negative mood was related to greater subjective sleep/wake problems, and happiness was related to lower subjective sleep/wake problems. Conversely, shorter self‐reported sleep duration was related to higher negative mood the next day. For actigraphy measures, daily negative mood was related to greater sleep duration and efficiency, whereas happiness was related to lower sleep efficiency. Differences in associations based on subjective versus objective sleep measures are discussed.

What is sleep exactly? Global and local modulations of sleep oscillations all around the clock

Article

Nov 2023
NEUROSCI BIOBEHAV R

Unidirectional links prefer local firing propagation in the neural network of C. elegans

Article

Sep 2023

How we sleep: From brain states to processes

Article

Aug 2023
REV NEUROL-FRANCE

Thomas Andrillon

All our lives, we alternate between wakefulness and sleep with direct consequences on our ability to interact with our environment, the dynamics and contents of our subjective experience, and our brain activity. Consequently, sleep has been extensively characterised in terms of behavioural, phenomenological, and physiological changes, the latter constituting the gold standard of sleep research. The common view is thus that sleep represents a collection of discrete states with distinct neurophysiological signatures. However, recent findings challenge such a monolithic view of sleep. Indeed, there can be sharp discrepancies in time and space in the activity displayed by different brain regions or networks, making it difficult to assign a global vigilance state to such a mosaic of contrasted dynamics. Viewing sleep as a multidimensional continuum rather than a succession of non-overlapping and mutually exclusive states could account for these local aspects of sleep. Moving away from the focus on sleep states, sleep can also be investigated through the brain processes that are present in sleep, if not necessarily specific to sleep. This focus on processes rather than states allows to see sleep for what it does rather than what it is, avoiding some of the limitations of the state perspective and providing a powerful heuristic to understand sleep. Indeed, what is sleep if not a process itself that makes up wake up every morning with a brain cleaner, leaner and less cluttered.

Sanat ve Sinizm (Yabancılaşma) İlişkisi: George Grosz ve Andy Warhol

Article

Full-text available

Jun 2023

Sanatçı ait olduğu toplumun diğer bireyleri gibi iletişim kurabilme ve çevresine karşılık verebilme yetisine bağlı olarak kendisini, benliğini ve sanatsal dilini inşa eder. Bu inşa sürecine kişisel deneyimleri, toplumsal değerleri ve savunma mekanizmaları da ortak olur. Araştırmada savaş, kapitalizm veya sermaye sömürüsü gibi nedenlerle bireyde gelişen sinizm ve yabancılaşma durumları, savunma mekanizmaları sanatçı-toplum dinamiğinde ele alınmakta, George Grosz ve Andy Warhol örnekleri üzerinden incelenmektedir. Grosz’un hicivci üslubu, mizah savunma mekanizmasıyla, Warhol’un kitle imgeleri ve medya ikonografisi, inkar ve özdeşleşme savunma mekanizmalarıyla ilişkilendirilmektedir. Araştırma literatür tarama yöntemi ile gerçekleştirilmiş olup, konuya ilişkin daha önceden gerçekleştirilen araştırmalar incelenmiştir. Ayrıca bu çalışma, George Grosz’un eski avangard, Andy Warhol’un yeni avangard olarak ortak ve farklı yönlerinin karşılaştırmalı değerlendirilmesiyle de önem kazanmaktadır. Araştırmanın ülke vatandaşı ve toplum gözlemcisi olarak sanatçının sahip olduğu ideolojik yaklaşım ve üretimlerinin sosyo-psikolojik bağlantılarının anlaşılabilir olması açısından yardımcı bir kaynak olabileceği düşünülmektedir.

Correlation of the Karolinska sleepiness scale with performance variables of the monotonous bimanual psychomotor test

Article

Jan 2023
ZH NEVROL PSIKHIATR

Objective: To assess the objectivity of measuring the level of sleepiness in the subjects using a monotonous psychomotor bimanual tapping test developed by us, performed on mobile devices running Android OS. Material and methods: Four hundred and ninety-four hour-long experiments with the performance of a psychomotor test were conducted on 102 students. Using the method of mixed linear models, correlations between the levels of sleepiness according to the Karolinska Sleepiness Scale (KSS) and the Epworth Sleepiness Scale (ESS) and the behavioral indicators of the test were evaluated. Results: Statistically significant correlations between the increase in KSS scores and such indicators as a decrease in the total number of button taps and an increase in the frequency of «microsleep» episodes are shown. Statistically significant correlations of ESS score characteristics with the behavioral indicators of the test were not found. Conclusion: A large statistical material shows a reliable correlation of the parameters of the psychomotor test with the level of sleepiness on the Karolinska scale, which allows using the mobile application developed by us to determine the current level of sleepiness /alertness in the field.

First-night effect in insomnia disorder: a systematic review and meta-analysis of polysomnographic findings

Article

May 2023
J SLEEP RES

Polysomnographic studies have been performed to investigate the first-night effect in insomnia disorder. However, these studies have revealed discrepant findings. This meta-analysis aimed to summarise and quantify the characteristics of the first-night effect in insomnia disorder. We performed a systematic search of the PubMed, Medline, EMBASE, Web of Science and PsycINFO databases to identify studies published through October 2019. A total of 11,862 articles were identified, and seven studies with eight independent populations were included in the meta-analysis. A total of 639 patients with insomnia disorder and 171 healthy controls underwent more than 2 consecutive nights of in-laboratory polysomnography. Pooled results demonstrated that both variables of sleep continuity and sleep architecture, other than slow-wave sleep were significantly altered in the first-night effect in insomnia disorder. Furthermore, the results indicated that patients with insomnia disorder had a disruption of sleep continuity in the first-night effect, including increased sleep onset latency and reduced total sleep time, compared to healthy controls. Overall, the findings show that patients with insomnia disorder experience the first-night effect, rather than reverse first-night effect, and the profiles of the first-night effect in patients with insomnia are different from healthy controls. These indicate that an adaptation night is necessary when sleep continuity and sleep architecture is to be studied in patients with insomnia disorder. More well-designed studies with large samples are needed to confirm the results.

Sleep and vigilance states: Embracing spatiotemporal dynamics

Article

May 2023

The classic view of sleep and vigilance states is a global stationary perspective driven by the interaction between neuromodulators and thalamocortical systems. However, recent data are challenging this view by demonstrating that vigilance states are highly dynamic and regionally complex. Spatially, sleep- and wake-like states often co-occur across distinct brain regions, as in unihemispheric sleep, local sleep in wakefulness, and during development. Temporally, dynamic switching prevails around state transitions, during extended wakefulness, and in fragmented sleep. This knowledge, together with methods monitoring brain activity across multiple regions simultaneously at millisecond resolution with cell-type specificity, is rapidly shifting how we consider vigilance states. A new perspective incorporating multiple spatial and temporal scales may have important implications for considering the governing neuromodulatory mechanisms, the functional roles of vigilance states, and their behavioral manifestations. A modular and dynamic view highlights novel avenues for finer spatiotemporal interventions to improve sleep function.

Pattern Selection in Multilayer Network with Adaptive Coupling

Article

Apr 2023
INT J BIFURCAT CHAOS

Feed-forward effect strongly modulates collective behavior of a multiple-layer neuron network and usually facilitates synchronization as signals are propagated to deep layers. However, a full synchronization of neuron system corresponds to functional disorder. In this work, we focus on a network containing two layers as the simplest model for multiple layers to investigate pattern selection during interaction between two layers. We first confirm that the chimera state emerges in layer 1 and it also induces chimera in layer 2 when the feed-forward effect is strong enough. A cluster is discovered as a transient state which separates full synchronization and chimera state and occupy a narrow region. Second, both feed-forward and back-forward effects are considered and we discover chimera states in both layers 1 and 2 under the same parameter for a large range of parameters selection. Finally, we introduce adaptive dynamics into inter-layer rather than intra-layer couplings. Under this circumstance, chimera state can still be induced and coupling matrix will be self-organized under suitable phase parameter to guarantee chimera formation. Indeed, chimera, cluster and synchronization can propagate from one layer to another in a regular multiple network for a corresponding parameter selection. More importantly, adaptive coupling is proved to control pattern selection of neuron firing in a network and this plays a key role in encoding scheme.

Two-attractor chimera and solitary states in a network of nonlocally coupled birhythmic van der Pol oscillators

Article

Apr 2023

In this paper, a network of van der Pol oscillators with extended nonlinearity is considered in the context of studies on symmetry-breaking phenomena. The van der Pol oscillator with extended nonlinearity has been widely considered as a model for coherent oscillations in enzyme–substrate systems. The particularity of this model is its multistability known as birhythmicity. Due to this feature of the local dynamics, the coupled dynamics shows a rich variety of symmetry-breaking phenomena, among which peculiar chimera and solitary states involving two types of attractors, namely a large limit cycle and a smaller attractor with quasiperiodic-like oscillations. The units of the main incoherent regions of a pattern of this two-attractor chimera evolve only on the large limit cycle whereas those of the main coherent regions evolve only on the smaller attractor. Also, as a consequence of birhythmicity, the mean phase velocity profile of this chimera pattern shows two levels of frequency, each level corresponding to each attractor. On the other hand, the frequencies of oscillations of the solitary units of the solitary states found there are different from the common frequency of oscillations in the coherent cluster, contrary to the classical solitary states for which all the network units are frequency locked. Interestingly, a phenomenon of coupling-induced birhythmicity is found here: two-attractor patterns emerge in the considered network with monorhythmic local dynamics. This study deepens our understanding of patterns formation in coupled multistable systems.

From Two-Cluster State to Chimera

Chapter

Feb 2023

Sindre Haugland

This chapter begins with the question “What is a chimera state?”, in light of which the last two decades of research on these states of coexistence of synchrony and incoherence are treated. Particular emphasis is placed on chimeras in coupled multi-component oscillators. Our original research focuses on how chimeras states evolve from two-cluster solutions in Stuart-Landau oscillators with nonlinear global coupling. For the minimal case N=4, two distinct types of chimera – with or without symmetry on average in the unsynchronized part of the ensemble – are found to emerge by means of separate bifurcation sequences. The symmetric-on-average type of chimera is found to consistently evolve for large ensemble sizes as well. However, beyond a certain ensemble size in the order of N≈15, we are unable to produce long-term chimera states with as many unsynchronized as synchronized oscillators. For long simulation times, the intact cluster is consistently found to absorb single oscillators, thereby also becoming more susceptible to perturbations. We conclude the chapter with a brief study of the spatially extended analogue of our model, resulting in a bifurcation sequence similar to that found for purely global coupling.

SENSORY GATING: BALANCE BETWEEN SLEEP AND LIFE

Article

Full-text available

Dec 2022

Anton Coenen

Sleep is a state of the brain characterized by a low level of vigilance and diminished consciousness. The reaction to external stimuli and the processing of stimuli are attenuated in sleep. During sleep, the reticular thalamic nucleus inhibits at the thalamus the flow of sensory activity from the senses to the cerebral cortex. After arrival at the afferent layer of the primary cortex, the reduced sensory flow is analyzed and personalized by layers of the cortical area and transferred by the corticofugal system back to appropriate subdivisions of the thalamus. Thalamic subdivisions target the information of the senses to related areas of the cerebral cortex, where the messages can be (sub)consciously perceived. When necessary, the sleeper can be awakened by a wake-up call, either by stimuli indicating danger or by personally meaningful stimuli. Evidently, sensory gating in sleep has two main features. First, it is favorable for sleep, by reducing the cerebral brain activity through the reticular thalamic nucleus, and second, it is necessary for the sleepers' safety and well-being, by analyzing the preserved activity on essential or dangerous external elements by the corticofugal system. These two features are analyzed in detail in non-REM sleep as well as in REM sleep. In the latter type of sleep, the process of sensory gating is almost similar to non-REM sleep, despite the enigmatic reconstruction of external stimuli into the dream. With the extended corticofugal system, sleep phenomena as the first-night effect, the occurrence of local sleep and wake states, as well as the unihemispheric sleep are comprehensible.

Spiral wave chimeras in populations of oscillators coupled to a slowly varying diffusive environment

Article

Feb 2023

Chimera states are firstly discovered in nonlocally coupled oscillator systems. Such a nonlocal coupling arises typically as oscillators are coupled via an external environment whose characteristic time scale τ is so small (i.e., τ → o) that it could be eliminated adiabatically. Nevertheless, whether the chimera states still exist in the opposite situation (i.e., τ ≫ 1) is unknown. Here, by coupling large populations of Stuart—Landau oscillators to a diffusive environment, we demonstrate that spiral wave chimeras do exist in this oscillator-environment coupling system even when τ is very large. Various transitions such as from spiral wave chimeras to spiral waves or unstable spiral wave chimeras as functions of the system parameters are explored. A physical picture for explaining the formation of spiral wave chimeras is also provided. The existence of spiral wave chimeras is further confirmed in ensembles of FitzHugh—Nagumo oscillators with the similar oscillator-environment coupling mechanism. Our results provide an affirmative answer to the observation of spiral wave chimeras in populations of oscillators mediated via a slowly changing environment and give important hints to generate chimera patterns in both laboratory and realistic chemical or biological systems.

Bistability-induced chimeras in one-dimensional paced excitable ring with nonlocal couplings

Article

Full-text available

Sep 2022

In this paper, we provide a bistability-mechanism in giving rise to a new kind of chimeras in the one-dimensional (1D) paced nonlocally coupled excitable rings without rotational coupling scheme. It is exposed that the elements in the system can perform distinct modes and gives rise to the chimera pattern. By analyzing the response dynamics in the corresponding local excitable model with the same pacing, the initial-excitation-dependent bistability feature is revealed as the mechanism responsible for this chimera state. Furthermore, this bistability-induced chimera state is found to be pacing dependent, and the chimera parameter regions on the phase plane of pacing amplitude and frequency are exposed explicitly. Importantly, this new kind of chimera pattern can also self-organize to emerge in other paradigmatic network models, implying the genericity of the bistability-mechanism in inducing chimeras in paced excitable complex networks. The present work is expected to shed light on new perspectives of the chimeras in excitable systems.

Night-to-night variability in respiratory sleep parameters to diagnose obstructive sleep apnea in children: A systematic review and meta-analysis

Article

Aug 2022
Int J Pediatr Otorhinolaryngol

Purpose This systematic review aims to assess the night-to-night variability (NtNV) in respiratory sleep parameters in children and the accuracy of diagnosing obstructive sleep apnea (OSA) in children based on a single-night sleep study. Methods The PubMed, EMBASE, and Cochrane Library databases were searched until March 8, 2021. This study was registered in the International Prospective Register of Systematic Reviews (PROSPERO) database (CRD42021239838). Results Our study included 395 patients from 5 articles. The mean (SD) age of all included patients was 11.78 (4.05) years. AHI was reported for 325 participants in 4 studies, and the mean change between two consecutive nights was −0.13 [95% CI: −0.40, 0.14] events per hour. The mean change in OAI was −0.07 [95% CI: −0.27, 0.12] events per hour in 187 participants across 3 studies. Based on the diagnostic criteria used, three studies reported that the diagnostic rates of OSA patients in a single-night sleep study were 83%, 84.6%, and 91%. The NtNV in AHI in children with severe and moderate OSA was greater than that in children with mild OSA (3.35 [95% CI: 0.07, 6.62] events per hour vs −0.15 [95% CI: −0.42, 0.12] events per hour), and these children with more severe OSA may have shown a higher AHI on the first night. Conclusions The NtNV in AHI was not statistically significant in the group sample of children. However, there were significant differences in NtNV in AHI between children with mild and moderate-to-severe OSA. Individual NtNV in respiratory sleep parameters may cause children to be misdiagnosed by single-night diagnostic sleep studies.

Parasomnias during trans‐meridian and long‐distance travel: Critical literature review and clinical practice recommendations

Article

Full-text available

Jun 2022

Parasomnias are undesirable events that occur during sleep. They can be classified into rapid eye movement parasomnias and non‐rapid eye movement parasomnias. Those who experience parasomnias may be anxious about travel for many reasons, including the occurrence of unwanted events during the trip, increased exposure to environmental trigger factors, and the propensity for harm to occur due to unfamiliar surroundings while travelling. There is a paucity of literature examining this area. This review summarizes the relevant literature and the clinical experience of the authors to compile clinical practice recommendations. The clinical features of parasomnias and how they relate to trans‐meridian and long‐distance travel are described. Triggers for non‐rapid eye movement parasomnias, particularly the use of sedative hypnotic drugs, alcohol, drug withdrawal, sleep deprivation, emotional stress and environmental stimulations, are described. Management of parasomnias whilst travelling is reviewed, with a particular focus on trigger minimalization. The role for clonazepam and melatonin is outlined. At the pre‐travel health consultation, the physician is strongly advised to screen the traveller for co‐morbid sleep conditions, which exacerbate parasomnias. Areas for further research are explored, including the extent to which these sleep disorders impact on the travel experience.

Hypotalamic regulation of sleep and circadian rhythms

Article

Full-text available

Nov 2005

A series of findings over the past decade has begun to identify the brain circuitry and neurotransmitters that regulate our daily cycles of sleep and wakefulness. The latter depends on a network of cell groups that activate the thalamus and the cerebral cortex. A key switch in the hypothalamus shuts off this arousal system during sleep. Other hypothalamic neurons stabilize the switch, and their absence results in inappropriate switching of behavioural states, such as occurs in narcolepsy. These findings explain how various drugs affect sleep and wakefulness, and provide the basis for a wide range of environmental influences to shape wake-sleep cycles into the optimal pattern for survival.

Asymmetric sleep in apneic human patients

Article

Full-text available

Nov 2012
AM J PHYSIOL-REG I

Unilateral sleep in marine mammals has been considered as a defence against airway obstruction, as a sentinel for pod maintenance, and as a thermoregulatory mechanism. Birds also show asymmetric sleep, probably to avoid predation. The variable function of asymmetric sleep suggests a general capability for independence between brain hemispheres. Patients with obstructive sleep apnea share similar problems with diving mammals, but their eventual sleep asymmetry received little attention. The present report shows that human sleep apnea patients also present temporary interhemispheric variations in dominance during sleep, with significant differences when comparing periods of open and closed airways. The Magnitude of Squared Coherence, an index of interhemispheric EEG interdependence in phase and amplitude rises in the delta EEG range during apneic episodes, while the Phase Lag Index, a measure of linear and non-linear interhemispheric phase synchrony, drops to zero. The L index, which measures generalized nonlinear EEG interhemispheric synchronization, increases during apneic events. Thus, the three indexes show significant and congruent changes in interhemispheric symmetry depending on the state of the airways. In conclusion, when confronted with a respiratory challenge, sleeping humans undergo small but significant breathing-related oscillations in interhemispheric dominance, similar to those observed in marine mammals. The evidence points to a relation between cetacean unihemispheric sleep and their respiratory challenges.

Development of a Large-Scale Functional Brain Network during Human Non-Rapid Eye Movement Sleep

Article

Full-text available

Aug 2010
J NEUROSCI

Graph theoretical analysis of functional magnetic resonance imaging (fMRI) time series has revealed a small-world organization of slow-frequency blood oxygen level-dependent (BOLD) signal fluctuations during wakeful resting. In this study, we used graph theoretical measures to explore how physiological changes during sleep are reflected in functional connectivity and small-world network properties of a large-scale, low-frequency functional brain network. Twenty-five young and healthy participants fell asleep during a 26.7 min fMRI scan with simultaneous polysomnography. A maximum overlap discrete wavelet transformation was applied to fMRI time series extracted from 90 cortical and subcortical regions in normalized space after residualization of the raw signal against unspecific sources of signal fluctuations; functional connectivity analysis focused on the slow-frequency BOLD signal fluctuations between 0.03 and 0.06 Hz. We observed that in the transition from wakefulness to light sleep, thalamocortical connectivity was sharply reduced, whereas corticocortical connectivity increased; corticocortical connectivity subsequently broke down in slow-wave sleep. Local clustering values were closest to random values in light sleep, whereas slow-wave sleep was characterized by the highest clustering ratio (gamma). Our findings support the hypothesis that changes in consciousness in the descent to sleep are subserved by reduced thalamocortical connectivity at sleep onset and a breakdown of general connectivity in slow-wave sleep, with both processes limiting the capacity of the brain to integrate information across functional modules.

Increased sleep pressure reduces resting state functional connectivity

Article

Full-text available

Dec 2010

In humans, even a single night of partial sleep deprivation (PSD) can have a negative impact on cognition and affective processing, suggesting that sleep pressure represents a basic physiological constraint of brain function. Among the spontaneously fluctuating resting state networks, the default mode network (DMN) and its anticorrelated network (ACN) hold key functions in segregating internally and externally directed awareness. Task fMRI after sleep deprivation has revealed altered activation patterns in both networks. We hypothesized that effects of PSD in these intrinsically coupled networks can be detected by resting state fMRI. We obtained 6-minute echoplanar imaging time series (1.5 Tesla) during eyes-closed, wakeful-resting experiments from 16 healthy volunteers after normal sleep and after PSD. We used independent component and cross-correlation analysis to study functional connectivity (fc), focusing on the DMN and ACN. After PSD, focal reductions of auto-correlation strength were detected in the posterior and anterior midline node of the DMN and in the lateral parietal and insular nodes of the ACN. Cross-correlation analysis confirmed reduced cortico-cortical connectivity within and between the DMN and ACN. Increased sleep pressure is reflected in reduced fc of main DMN and ACN nodes during rest. Results have implications for understanding perceptual and cognitive changes after sleep deprivation and are relevant to clinical studies on conditions in which increased sleep propensity is present.

Evidence from intrinsic activity that asymmetry of the human brain is controlled by multiple factors

Article

Full-text available

Nov 2009
P NATL ACAD SCI USA

Cerebral lateralization is a fundamental property of the human brain and a marker of successful development. Here we provide evidence that multiple mechanisms control asymmetry for distinct brain systems. Using intrinsic activity to measure asymmetry in 300 adults, we mapped the most strongly lateralized brain regions. Both men and women showed strong asymmetries with a significant, but small, group difference. Factor analysis on the asymmetric regions revealed 4 separate factors that each accounted for significant variation across subjects. The factors were associated with brain systems involved in vision, internal thought (the default network), attention, and language. An independent sample of right- and left-handed individuals showed that hand dominance affects brain asymmetry but differentially across the 4 factors supporting their independence. These findings show the feasibility of measuring brain asymmetry using intrinsic activity fluctuations and suggest that multiple genetic or environmental mechanisms control cerebral lateralization.

Half-awake to the risk of predation

Article

Full-text available

Feb 1999

Birds have overcome the problem of sleeping in risky situations by developing the ability to sleep with one eye open and one hemisphere of the brain awake. Such unihemispheric slow-wave sleep is in direct contrast to the typical situation in which sleep and wakefulness are mutually exclusive states of the whole brain. We have found that birds can detect approaching predators during unihemispheric slow-wave sleep, and that they can increase their use of unihemispheric sleep as the risk of predation increases. We believe this is the first evidence for an animal behaviourally controlling sleep and wakefulness simultaneously in different regions of the brain.

Decoupling of the brain's default mode network during deep sleep

Article

Full-text available

Jul 2009
P NATL ACAD SCI USA

The recent discovery of a circuit of brain regions that is highly active in the absence of overt behavior has led to a quest for revealing the possible function of this so-called default-mode network (DMN). A very recent study, finding similarities in awake humans and anesthetized primates, has suggested that DMN activity might not simply reflect ongoing conscious mentation but rather a more general form of network dynamics typical of complex systems. Here, by performing functional MRI in humans, it is shown that a natural, sleep-induced reduction of consciousness is reflected in altered correlation between DMN network components, most notably a reduced involvement of frontal cortex. This suggests that DMN may play an important role in the sustenance of conscious awareness.

Cortical network functional connectivity in the descent to sleep

Article

Full-text available

Apr 2009
P NATL ACAD SCI USA

Descent into sleep is accompanied by disengagement of the conscious brain from the external world. It follows that this process should be associated with reduced neural activity in regions of the brain known to mediate interaction with the environment. We examined blood oxygen dependent (BOLD) signal functional connectivity using conventional seed-based analyses in 3 primary sensory and 3 association networks as normal young adults transitioned from wakefulness to light sleep while lying immobile in the bore of a magnetic resonance imaging scanner. Functional connectivity was maintained in each network throughout all examined states of arousal. Indeed, correlations within the dorsal attention network modestly but significantly increased during light sleep compared to wakefulness. Moreover, our data suggest that neuronally mediated BOLD signal variance generally increases in light sleep. These results do not support the view that ongoing BOLD fluctuations primarily reflect unconstrained cognition. Rather, accumulating evidence supports the hypothesis that spontaneous BOLD fluctuations reflect processes that maintain the integrity of functional systems in the brain.

Source modeling sleep slow waves

Article

Full-text available

Feb 2009
P NATL ACAD SCI USA

Slow waves are the most prominent electroencephalographic (EEG) feature of sleep. These waves arise from the synchronization of slow oscillations in the membrane potentials of millions of neurons. Scalp-level studies have indicated that slow waves are not instantaneous events, but rather they travel across the brain. Previous studies of EEG slow waves were limited by the poor spatial resolution of EEGs and by the difficulty of relating scalp potentials to the activity of the underlying cortex. Here we use high-density EEG (hd-EEG) source modeling to show that individual spontaneous slow waves have distinct cortical origins, propagate uniquely across the cortex, and involve unique subsets of cortical structures. However, when the waves are examined en masse, we find that there are diffuse hot spots of slow wave origins centered on the lateral sulci. Furthermore, slow wave propagation along the anterior-posterior axis of the brain is largely mediated by a cingulate highway. As a group, slow waves are associated with large currents in the medial frontal gyrus, the middle frontal gyrus, the inferior frontal gyrus, the anterior cingulate, the precuneus, and the posterior cingulate. These areas overlap with the major connectional backbone of the cortex and with many parts of the default network.

A default mode of brain function

Article

Full-text available

Feb 2001

A baseline or control state is fundamental to the understanding of most complex systems. Defining a baseline state in the human brain, arguably our most complex system, poses a particular challenge. Many suspect that left unconstrained, its activity will vary unpredictably. Despite this prediction we identify a baseline state of the normal adult human brain in terms of the brain oxygen extraction fraction or OEF. The OEF is defined as the ratio of oxygen used by the brain to oxygen delivered by flowing blood and is remarkably uniform in the awake but resting state (e.g., lying quietly with eyes closed). Local deviations in the OEF represent the physiological basis of signals of changes in neuronal activity obtained with functional MRI during a wide variety of human behaviors. We used quantitative metabolic and circulatory measurements from positron-emission tomography to obtain the OEF regionally throughout the brain. Areas of activation were conspicuous by their absence. All significant deviations from the mean hemisphere OEF were increases, signifying deactivations, and resided almost exclusively in the visual system. Defining the baseline state of an area in this manner attaches meaning to a group of areas that consistently exhibit decreases from this baseline, during a wide variety of goal-directed behaviors monitored with positron-emission tomography and functional MRI. These decreases suggest the existence of an organized, baseline default mode of brain function that is suspended during specific goal-directed behaviors.

Interhemispheric asymmetry of human sleep EEG in response to selective slow-wave sleep deprivation

Article

Full-text available

Jan 2003

Recent evidence suggests that the human sleep electroencephalogram (EEG) shows regional differences over both the sagittal and coronal planes. In the present study, in a group of 10 right-handers, the authors investigated the presence of hemispheric asymmetries in the homeostatic regulation of human sleep EEG power during and after selective slow-wave sleep (SWS) deprivation. The SWS deprivation was slightly more effective over the right hemisphere, but the left hemisphere showed a markedly larger increase of EEG power in the 1.00-24.75 Hz range during recovery-night non-REM sleep, and a larger increase of EEG power during both deprivation-night and recovery-night REM sleep. These results support the greater need for sleep recuperative processes of the left hemisphere, suggesting that local sleep regulation processes may also act during REM sleep.

Examination of the First-Night Effect during the Sleep-Onset Period

Article

Full-text available

Mar 2005

The present study examined the first-night effect during the sleep-onset period using the 9 electroencephalogram stage scoring system. After a week of monitoring sleep-wake habits with sleep diaries and wrist actigraphy, polysomnography recording was made for 3 consecutive nights. Participants slept in their own private, individual, temperature-controlled bedroom in a sleep laboratory at the university. Eleven healthy student volunteers (5 women and 6 men, 21 to 25 years old, mean 22.7 years) who had no experience sleeping in a laboratory participated in the study. N/A. The electroencephalogram during the sleep-onset period was scored manually for every 5-second epoch into 9 electroencephalogram stages. Latencies of the electroencephalogram stages were delayed on the first night, especially during the alpha-wave intermittent stages. The average time of the alpha-wave train, intermittent (> 50%) and the electroencephalogram flattening stage increased on Night 1. Stage changes among these stages also increased on Night 1. In contrast, stage changes between the alpha-wave intermittent stage (< 50%) and the theta-wave stage increased on Night 3. Alpha-wave activity increased on Night 1, demonstrating that the activity of the wake-promoting system during the sleep-onset period was enhanced on the first night. From the second to the third night, the alpha-wave intermittent stage jumped to the theta-wave stage, omitting electroencephalogram flattening, suggesting that the electroencephalogram flattening stage is unlikely to appear during stable sleep-onset period. This is the first study to demonstrate the detail of the first-night effect during the sleep-onset period.

Ramelteon (TAK-375), a selective MT1/MT2-receptor agonist, reduces latency to persistent sleep in a model of transient insomnia related to a novel sleep environment

Article

Full-text available

Apr 2005

Evaluate the efficacy of ramelteon, an MT/1MT2-receptor agonist, for the treatment of transient insomnia in healthy adults. Randomized, double-blind, placebo-controlled design using a model of transient insomnia related to sleeping in a novel environment. Fourteen sleep research centers. Healthy adults (N=375; 228 women), aged 35 to 60 years, who had never previously slept in a sleep laboratory and had a reported usual sleep duration of 6.5 to 8.5 hours and usual bedtime between 8:30 PM and midnight. Single administration of ramelteon (16 or 64 mg) or placebo 30 minutes before bedtime. Primary efficacy measure was latency to persistent sleep. Also evaluated were total sleep time, wake after sleep onset, percentage of each sleep stage, subjective estimates of sleep from postsleep questionnaire, number of awakenings, and subjective number of awakenings. Residual effects were assessed via Digit Symbol Substitution Test and postsleep questionnaire. Participants in ramelteon-treated groups had significantly shorter latency to persistent sleep relative to placebo. They also were associated with significantly longer total sleep time. Wake after sleep onset and time spent in each sleep stage were not significantly different from placebo. The use of ramelteon (16 mg) was associated with a shorter subjective sleep latency compared to placebo. Other subjective measures of sleep did not differ significantly from placebo. Digit Symbol Substitution Test scores did not differ significantly among the 3 groups, but the use of the 64-mg [corrected] dose was associated with subjective reports of impairment in the morning. Ramelteon significantly improved latency to persistent sleep and total sleep time in this model of transient insomnia in healthy adults. No dose-related differences in latency to persistent sleep were observed, and both doses were well tolerated.

Breakdown of Cortical Effective Connectivity During Sleep

Article

Full-text available

Oct 2005
SCIENCE

When we fall asleep, consciousness fades yet the brain remains active. Why is this so? To investigate whether changes in cortical information transmission play a role, we used transcranial magnetic stimulation together with high-density electroencephalography and asked how the activation of one cortical area (the premotor area) is transmitted to the rest of the brain. During quiet wakefulness, an initial response (approximately 15 milliseconds) at the stimulation site was followed by a sequence of waves that moved to connected cortical areas several centimeters away. During non-rapid eye movement sleep, the initial response was stronger but was rapidly extinguished and did not propagate beyond the stimulation site. Thus, the fading of consciousness during certain stages of sleep may be related to a breakdown in cortical effective connectivity.

Wandering Minds: The Default Network and Stimulus-Independent Thought

Article

Full-text available

Feb 2007
SCIENCE

Despite evidence pointing to a ubiquitous tendency of human minds to wander, little is known about the neural operations that support this core component of human cognition. Using both thought sampling and brain imaging, the current investigation demonstrated that mind-wandering is associated with activity in a default network of cortical regions that are active when the brain is “at rest.” In addition, individuals' reports of the tendency of their minds to wander were correlated with activity in this network.

The Brain's Default Network

Article

Full-text available

Apr 2008

Thirty years of brain imaging research has converged to define the brain's default network-a novel and only recently appreciated brain system that participates in internal modes of cognition. Here we synthesize past observations to provide strong evidence that the default network is a specific, anatomically defined brain system preferentially active when individuals are not focused on the external environment. Analysis of connectional anatomy in the monkey supports the presence of an interconnected brain system. Providing insight into function, the default network is active when individuals are engaged in internally focused tasks including autobiographical memory retrieval, envisioning the future, and conceiving the perspectives of others. Probing the functional anatomy of the network in detail reveals that it is best understood as multiple interacting subsystems. The medial temporal lobe subsystem provides information from prior experiences in the form of memories and associations that are the building blocks of mental simulation. The medial prefrontal subsystem facilitates the flexible use of this information during the construction of self-relevant mental simulations. These two subsystems converge on important nodes of integration including the posterior cingulate cortex. The implications of these functional and anatomical observations are discussed in relation to possible adaptive roles of the default network for using past experiences to plan for the future, navigate social interactions, and maximize the utility of moments when we are not otherwise engaged by the external world. We conclude by discussing the relevance of the default network for understanding mental disorders including autism, schizophrenia, and Alzheimer's disease.

Animals in aquatic environments: Adaptation of mammals to the ocean

Article

Jan 1964

J.C. Lilly

The brain's default network: Anatomy, function and relevance to disease

Article

Jan 2008

The AASM Manual for the Scoring of Sleep and Associated Events: Rules, Terminology and Technical Specifications

Article

Jan 2007

Sleep and Synaptic Homeostasis

Article

Feb 2005
BEHAV BRAIN SCI

This paper discusses the synaptic homeostasis hypothesis of sleep. The main claim of the hypothesis is that plastic processes occurring during wakefulness result in a net increase in synaptic strength in many brain circuits, and that role of sleep is to downscale synaptic strength to a baseline level that is energetically sustainable, makes efficient use of gray matter space, and is beneficial for learning and memory. Thus, sleep is the price we have to pay for plasticity, and its goal is the homeostatic regulation of the total synaptic weight impinging on neurons. In this chapter we review evidence pro and contra the hypothesis, discuss similarities and differences with other hypotheses that focus on the role of sleep in neural plasticity, and mention ongoing and future experiments to test it directly.

Functional Asymmetry of the Brain in Dichotic Listening

Article

Jun 1967
CORTEX

Doreen Kimura

This paper reviews the evidence relating lateral asymmetry in auditory perception to the asymmetrical functioning of the two hemispheres of the brain. Because each ear has greater neural representation in the opposite cerebral hemisphere, the predominance of the left hemispere for speech is reflected in superior recognition for words arriving at the right ear, while the predominance of the right hemisphere in melodic-pattern perception is reflected in superior identification of melodies arriving at the left ear. Some applications of the dichotic listening technique to questions concerned with the development of cerebral dominance, and with the further specification of function of the left and right hemispheres, are also described.

REM and NREM power spectral analysis on two consecutive nights in psychophysiological and paradoxical insomnia sufferers

Article

Jun 2013

The first night effect: An EEG study

Article

Jan 2007
PSYCHOPHYSIOLOGY

The electroencephalographic records from 43 subjects who slept for four consecutive nights in a laboratory environment were studied in an effort to describe the First Night Effect. These records showed that the first night of laboratory sleep contains more awake periods and less Stage I-rapid eye movement sleep. There is a delay in the onset of Stages IV and I-REM and the sleep is more changeable. These effects rapidly adapt out by the second night of sleep.

The first‐night effect occurs at the sleep‐onset period regardless of the temporal anxiety level in healthy students

Article

May 2005
SLEEP BIOL RHYTHMS

The present study analyzed if the temporal change in anxiety level under the critical range of the State Trait Anxiety Inventory determines the occurrence of the first-night effect (FNE) during the sleep-onset period (SOP) in healthy adults. Polysomnogram recordings were made for three consecutive nights. Electroencephalograms (EEG) were scored for every 5 s into nine EEG stages. Regardless of the anxiety level, the smooth process of the SOP was inhibited on the first night, which was expressed as delayed attenuation of alpha waves. The FNE during the SOP occurs especially as enhanced alpha activity even when the level of anxiety is not heightened on the first-night sleep taken in unfamiliar situation.

Spectral analysis of the first‐night effect on the sleep‐onset period

Article

Sep 2005
SLEEP BIOL RHYTHMS

The first-night effect (FNE) refers to the disruption of the sleep structure, which is recognized particularly on the first night of sleep in the laboratory. Difficulty in falling asleep is the most frequently reported characteristic of the FNE. We examined the FNE on the sleep-onset period (SOP) quantitatively to investigate how the wake- and the sleep-promoting systems were related to the occurrence of the FNE. Eight healthy student volunteers participated in the study. Polysomnogram recording was made for three consecutive nights. Power spectra of electroencephalogram (EEG) activities were computed by using a Fast Fourier Transform during waking and the SOP. The data obtained was divided into seven bands and the mean amplitudes in each band were calculated. On the first night, EEG amplitudes in the alpha and gamma bands were higher during waking and the SOP compared with the second and the third nights. In contrast, theta and sigma amplitudes were lower on the first night. It was suggested that the wake-promoting system was excited and the smooth activation of the sleep-promoting system was inhibited during the SOP on the first night. This phenomenon might contribute to the cause of the sleep onset difficulty, which occurs as the FNE.

Interhemispheric Asynchrony Correlates With Severity of Respiratory Disturbance Index in Patients With Sleep Apnea

Article

Jan 2011

Obstructive sleep apnea (OSA) hypopnea syndrome is a disorder characterized by airway obstructions during sleep; full obstructions are known as apnea and partial obstructions are called hypopnea. Sleep in OSA patients is significantly disturbed with frequent apnea/hypopnea and arousal events. We illustrate that these events lead to functional asymmetry of the brain as manifested by the interhemispheric asynchrony (IHA) computed using EEG recorded on the scalp. In this paper, based on the higher order spectra of IHA time series, we propose a new index [interhemispheric synchrony index (IHSI)], for characterizing brain asynchrony in OSA. The IHSI computation does not depend on subjective criteria and can be completely automated. The proposed method was evaluated on overnight EEG data from a clinical database of 36 subjects referred to a hospital sleep laboratory. Our results indicated that the IHSI could classify the patients into OSA/non-OSA classes with an accuracy of 91% (ρ = 0.0001), at the respiratory disturbance index threshold of 10, suggesting that the brain asynchrony carries vital information on OSA.

Cetacean sleep: An unusual form of mammalian sleep

Article

Oct 2008
NEUROSCI BIOBEHAV R

Our knowledge of the form of lateralized sleep behavior, known as unihemispheric slow wave sleep (USWS), seen in all members of the order Cetacea examined to date, is described. We trace the discovery of this phenotypically unusual form of mammalian sleep and highlight specific aspects that are different from sleep in terrestrial mammals. We find that for cetaceans sleep is characterized by USWS, a negligible amount or complete absence of rapid eye movement (REM) sleep, and a varying degree of movement during sleep associated with body size, and an asymmetrical eye state. We then compare the anatomy of the mammalian somnogenic system with what is known in cetaceans, highlighting areas where additional knowledge is needed to understand cetacean sleep. Three suggested functions of USWS (facilitation of movement, more efficient sensory processing and control of breathing) are discussed. Lastly, the possible selection pressures leading to this form of sleep are examined, leading us to the suggestion that the selection pressure necessitating the evolution of cetacean sleep was most likely the need to offset heat loss to the water from birth and throughout life. Aspects such as sentinel functions and breathing are likely to be proximate evolutionary phenomenon of this form of sleep.

Differential auditory processing continues during sleep

Article

Nov 1991
Electroencephalogr Clin Neurophysiol

Auditory evoked potentials (AEPs) were used to examine selective stimulus processing in sleep. In waking, repetitive stimuli generate exogenous P1, N1 and P2 components of the auditory evoked potential (AEP). Deviant stimuli generate endogenous cognitive components including the mismatch negativity (MMN), N2 and P3 components. We examined long-latency auditory evoked potentials elicited by repetitive and deviant stimuli during waking and stage II–IV sleep to assess whether stimulus deviance is detected during sleep.The waking P1, N1b and P2 had maximal amplitudes at fronto-central scalp sites, with additional peaks (N1a, N1c) at temporal sites. Deviant tones generated a frontal maximal MMN, and complex novel tones generated an additional P3 component maximal at centro-parietal sites. During stages II–IV sleep N1a, b, c amplitudes were reduced. During stage II sleep all stimuli generated increased P2 amplitudes and a late negative component (N340). Deviant stimuli generated greater P2 and N340 amplitudes than frequent stimuli in stage II sleep, as well as an additional P420 component. In stage III–IV sleep the P420 was absent and the AEP was dominated by a negativity of long duration whose amplitude increased in response to deviant stimuli.These data indicate that auditory evoked activity changes from wakefulness to sleep. The differential response to deviant sounds observed during waking and all sleep stages supports the theory that selective processing of auditory stimuli persists during sleep.

Dissociated wake-like and sleep-like electro-cortical activity during sleep

Article

Jun 2011
NEUROIMAGE

Effect of unilateral somatosensory stimulation prior to sleep on the sleep EEG in humans

Article

Sep 1994
J SLEEP RES

The hypothesis that local activation of brain regions during wakefulness affects the EEG recorded from these regions during sleep was tested by applying vibratory stimuli to one hand prior to sleep. Eight subjects slept in the laboratory for five consecutive nights. During a 6-h period prior to night 3, either the left or the right hand was vibrated intermittently (20 min on-8 min off), while prior to night 5 the same treatment was applied to the contralateral hand. The sleep EEG was recorded from frontal, central, parietal and occipital derivations and subjected to spectral analysis. The interhemispheric asymmetry index (IAI) was calculated for spectral power in nonREM sleep in the frequency range 0.25-25.0 Hz for 0.5-Hz or 1-Hz bins. In the first hour of sleep following right-hand stimulation, the IAI of the central derivation was increased relative to baseline, which corresponds to a shift of power towards the left hemisphere. This effect was most prominent in the delta range, was limited to the first hour of sleep and was restricted to the central derivation situated over the somatosensory cortex. No significant changes were observed following left-hand stimulation. Although the effect was small, it is consistent with the hypothesis that the activation of specific neuronal populations during wakefulness may have repercussions on their electrical activity pattern during subsequent sleep.

Increased sleep pressure reduces resting state functional connectivity

Article

Jan 2010

OBJECT: In humans, even a single night of partial sleep deprivation (PSD) can have a negative impact on cognition and affective processing, suggesting that sleep pressure represents a basic physiological constraint of brain function. Among the spontaneously fluctuating resting state networks, the default mode network (DMN) and its anticorrelated network (ACN) hold key functions in segregating internally and externally directed awareness. Task fMRI after sleep deprivation has revealed altered activation patterns in both networks. We hypothesized that effects of PSD in these intrinsically coupled networks can be detected by resting state fMRI. METHODS: We obtained 6-minute echoplanar imaging time series (1.5 Tesla) during eyes-closed, wakeful-resting experiments from 16 healthy volunteers after normal sleep and after PSD. We used independent component and cross-correlation analysis to study functional connectivity (fc), focusing on the DMN and ACN. RESULTS: After PSD, focal reductions of auto-correlation strength were detected in the posterior and anterior midline node of the DMN and in the lateral parietal and insular nodes of the ACN. Cross-correlation analysis confirmed reduced cortico-cortical connectivity within and between the DMN and ACN. CONCLUSIONS: Increased sleep pressure is reflected in reduced fc of main DMN and ACN nodes during rest. Results have implications for understanding perceptual and cognitive changes after sleep deprivation and are relevant to clinical studies on conditions in which increased sleep propensity is present.

The first night effect: an EEG study of sleep

Article

Feb 1966

Auditory awakening thresholds in REM and NREM sleep stages

Article

Jul 1966

The auditory awakening thresholds of the major electroencephalographically defined sleep stages were compared. A modification of the method of constant stimuli was used in an apparently successful attempt to minimize the incorporation of the experimental stimuli into the mental activity of the sleeper. A total of 319 experimental trials were distributed among seven human Ss who served for about six experimental nights each. The sequence and timing of experimental trials were counterbalanced to control for nights, habituation, amount of accumulated sleep, and amount of sleep since last awakening. The results showed approximately equal awakening thresholds during REM periods (the rapid eye movement stage of sleep) and stage 2 (low voltage EEG and 12 to 14 cps “sleep spindles”). Both these stages had lower awakening thresholds than delta sleep (large slow EEG waves). Awakening thresholds became lower with accumulated sleep, independent of sleep stage. There were no significant stage independent relationships between awakening threshold and time since last awakening or time since last body movement, although the latter were varied over a relatively narrow range which limits the generality of these findings. There was no stage independent relationship between heart rate and awakening threshold. The possible physiological determinants of the awakening response were discussed.

A two process model of sleep regulation

Article

Feb 1982
Hum Neurobiol

A. A. A. Borbely

Two processes play a dominant role in sleep regulation: a sleep-dependent process (Process S) and a sleep-independent circadian process (Process C). The time course of Process S was derived from the spectral analysis of slow wave activity in the human EEG. Its level shows an exponential decline during sleep and an increase during waking. The level of Process S at sleep onset is therefore a function of prior waking time. Process C is reflected by the rhythmic variation of sleep propensity during prolonged sleep deprivation, and is assumed to be controlled by a circadian oscillator. In the model, sleep propensity and the duration of sleep are determined by the combined action of the two processes. The model is able to simulate the variations of sleep duration as a function of sleep onset time. Since the amount of REM sleep is little influenced by prior sleep or waking and shows a marked circadian rhythmicity, it is assumed to reflect largely the level of Process C. The cyclic alternation of nonREM and REM sleep is assumed to result from a reciprocal interaction between the two sleep states. In contrast to previous models, only a single circadian oscillator is required to account for the sleep-wake cycle and the sleep organization under entrained and non-entrained schedules. The model also encompasses sleep regulation in animals and may provide indications as to the phylogenetic origin of sleep.

Unihemispheric enhancement of delta power in human frontal sleep EEG by prolonged wakefulness

Night Watch in One Brain Hemisphere during Sleep Associated with the First-Night Effect in Humans

Abstract

No full-text available