BACKGROUND: Up to now, sleep stages have traditionally been determined by the visual inspection of individual EEG waves. However, the exact physiological meaning of the sleep waves is not known. The purpose of this study was to try and find out the physiological parameters of the EEG of the sleep and wakefulness states by calculating one of the non-linear chaos parameter, the largest Lyapunov exponent (LLE), of EEG time series. METHODS: The digital EEG of the wakefulness with eye opening (WEO), wakefulness with eye closure (WEC), stage1 (S1), stage2 (S2), stage3 or 4 (S34) were recorded at centroparietal region (C4-P4 bipolar derivation) in 10 normal subjects. Lyapunov exponents of 50 EEG time series in different states were compared. RESULTS: LLE's of WEO, WEC, S1, S2, S34 showed an increas-ing tendency as states switched from wakefulness to sleep. LLE of sleep was larger than that of awake state. CONCLUSIONS: The EEG of the sleep state appeared to be more chaotic than that of the awake state. This nonlinear chaos parameter can be used as a physiological parameter of normal sleep and awake states.
Electroencephalography* ; Sleep Stages ; Wakefulness*

In accordance with the development of EEG and polysomnography in the field of sleep research, the sleep onset period (SOP) between wakefulness and sleep has been considered an important part for understanding the physiology of sleep. SOP in the transition from wakefulness to sleep is a gradual process integrating various viewpoints such as behavior, EEG, physiology and subjective report. Particularly, based on understanding of EEG changes during sleep, SOP has been regarded as a pattern of topographical change in specific frequency and specific state in EEG. Studies on quantitative EEG (qEEG) and event-related potential (ERP) have suggested that SOP shows the changes of functional coordination at the specific cortical areas in qEEG and the changes of regular patterns in response to environmental stimulation in ERP. The development of sleep EEG and topographic mapping of EEG is expected to integrate various viewpoints of SOP and clarify the neurophysiologic mechanism of SOP further.
Electroencephalography ; Evoked Potentials ; Polysomnography ; Wakefulness

OBJECTIVES: Much is still unknown about the neurophysiological mechanisms or dynamics of the sleep onset process. Detrended fluctuation analysis (DFA) is a new tool for the analysis of electroencephalography (EEG) that may give us additional information about electrophysiological changes. The purpose of this study is to analyze long-range correlations of electroencephalographic signals by DFA and their changes in the sleep onset process. METHODS: Thirty channel EEG was recorded in 61 healthy subjects (male : female = 34 : 27, age = 27.2 +/- 3.0 years). The scaling exponents, alpha, were calculated by DFA and compared between four kinds of 30s sleep-wakefulness states such as wakefulness, transition period, early sleep, and late sleep (stage 1). These four states were selected by the distribution of alpha and theta waves in O1 and O2 electrodes. RESULTS: The scaling exponents, alpha, were significantly different in the four states during sleep onset periods, and also varied with the thirty leads. The interaction between the sleep states and the leads was significant. The means (+/- standard deviation) of alphas for the states were 0.94 (+/- 0.12), 0.98 (+/- 0.12), 1.10 (+/- 0.10), 1.07 (+/- 0.07) in the wakefulness, transitional period, early sleep and late sleep state respectively. The mean alpha of anterior fifteen leads was greater than that of posterior fifteen leads, and the two regions showed the different pattern of changes of the alpha during the sleep onset periods. CONCLUSIONS: The characteristic findings in the sleep onset period were the increasing pattern of scaling exponent of DFA, and the pattern was slightly but significantly different between fronto-temporal and parieto-occipital regions. It suggests that the long-range correlations of EEG have a tendency of increasing from wakefulness to early sleep, but anterior and posterior brain regions have different dynamical process. DFA, one of the nonlinear analytical methods for time series, may be a useful tool for the investigation of the sleep onset period.
Brain ; Electroencephalography ; Female ; Humans ; Wakefulness

The formation, consolidation and retrieval of spatial memory depend on sequential firing patterns of place cells assembling in the hippocampus. Theta sequences of place cells during behavior play a role in acquisition of spatial memory, trajectory prediction and decision making. In awake rest and slow wave sleep, place cell sequences occur during the sharp wave-ripples (SWRs), called "replay", which is crucial for memory consolidation and retrieval. In this review, we summarize the functional significances of theta sequences and SWRs replay sequences and the mechanism of these sequences. We also discuss the relationship between theta and replay sequences with the formation of spatial memory. We propose the research direction in this field in future and aim to provide new ideas for related researches.
Hippocampus ; Sleep ; Spatial Memory ; Wakefulness

Anesthesia ; Anesthesia, General ; Humans ; Intubation, Intratracheal ; Wakefulness

OBJECTIVES: To investigate brain oscillatory characteristics according to brightness and color temperature of light emitting diode (LED) light in young and elderly subjects. METHODS: We analyzed 22 young (age, 29.0±5.2 years) and 23 elderly (age, 64.8±4.5 years) healthy subjects. A LED light source was used with a combination of two color temperature (6,500 K vs. 3,000 K) and two brightness (700 lx vs. 300 lx) conditions. Participants were exposed to each light condition in relaxed wakefulness. Then, we analyzed power spectral density and functional connectivity from eye-open electroencephalography. RESULTS: A main effect of brightness on delta (p=0.044) and theta (p=0.038) power was significant in the elderly subjects. Bright light enhanced delta and theta power in the frontal region. By contrast, power spectral density of young subjects was affected by color temperature; high color temperature significantly increased beta-band power of the central region (p=0.034). Regarding functional connectivity, a significant effect of color temperature was observed in delta (p=0.006) and beta (p=0.046) frequencies. High color temperature light enhanced beta connectivity of young subjects (p=0.007), while not affecting that of elderly subjects (p=0.979). CONCLUSIONS: The present study demonstrated that spectral power and functional connectivity as well as subjective feelings are affected by the brightness and color temperature of LED light. These results might help us to understand the neurophysiological effects of light and identify the optimal indoor lighting conditions for an individual's environment.
Aged ; Brain ; Electroencephalography ; Healthy Volunteers ; Humans ; Wakefulness

The awake prone position plays an important role in the treatment of hypoxemia and the improvement of respiratory distress symptoms in non-intubated patients. It is widely used in clinical practice because of its simple operation, safety, and economy. To enable clinical medical staff to scientifically and normatively implement prone position for awake patients without intubation, the committees of consensus formulation, guided by evidence-based methodology and Delphi method, conducted literature search, literature quality evaluation and evidence synthesis around seven topics, including indications and contraindications, evaluation, implementation, monitoring and safety management, termination time, complication prevention and health education of awake prone position. After two rounds of expert letter consultation, Expert consensus on implementation strategy of awake prone positioning for non-intubated patients in China (2023) was formulated, and provide guidance for clinical medical staff.
Humans ; Consensus ; Prone Position ; Wakefulness ; China ; Dyspnea

BACKGROUND: To assess in a laboratory setting the ability to stay awake in a sample of workers of an Italian hospital and to investigate the association between that ability and the risk of occupational injury. METHODS: Nine workers at the University Hospital of Udine who reported an occupational injury in the study period (cases), and seven noninjured workers (controls) underwent a polysomnography and four 40-minute maintenance of wakefulness tests (MWT). Differences in sleep characteristics and in wakefulness maintenance were assessed using Wilcoxon's rank sums tests and Fisher's exact tests. RESULTS: Controls had greater sleep latency, lower total sleep time, fewer leg movements, and a higher percentage ratio of cycling alternating pattern, were more likely not to fall asleep during the MWT and were less likely to have two or more sleep onsets. Although not all the differences reached statistical significance, cases had lower sleep onset times in Trials 1-3. CONCLUSION: In the literature, the evidence of an association between MWT results and real life risk of accidents is weak. Our results suggest a relationship between the MWT results and the risk of injury among hospital workers.
Case-Control Studies ; Hospitals, Teaching* ; Leg ; Occupational Injuries* ; Polysomnography ; Wakefulness*

OBJECTIVE : Modafinil, methylphenidate, and caffeine are wakefulness-promoting substances. Previously, it was reported that caffeine-induced wakefulness differs from natural wakefulness in terms of the EEG spectral profiles. In order to evaluate whether wakefulness induced by other psychostimulants differs from both caffeine-induced and natural wakefulness, we examined the effects of the psychostimulants on sleep-wake architecture and EEG spectral profiles. METHODS : Eighteen Sprague-Dawley male rats underwent an EEG/EMG recording session from 10 : 30 to 17 : 30. They received caffeine (7.5, 15, 30 mg/kg i.p.), methylphenidate (1, 2, 5, 10 mg/kg i.p.) or modafinil (5, 10, 25, 50, 100 mg/kg i.p.) at 13 : 30. The number, total duration, and average duration of sleepwake states were obtained. EEG band powers were calculated by spectral analysis. Frequency bands were divided into the following ranges : D1, 1-2.5 Hz ; D2, 2.5-4.5 Hz ; T1, 4.5-7 Hz ; T2, 7-10 Hz ; SI, 10-14 Hz ; B1, 14-22 Hz ; B2, 22-34 Hz ; GA, 34-50 Hz. RESULTS : All three psychostimulants significantly and dose-dependently increased active wake duration and decreased slow-wave sleep. Equipotent doses of caffeine, methylphenidate, and modafinil for increasing active wake and decreasing slow-wave sleep were 7.5 mg/kg, 10 mg/kg, and 100 mg/kg, respectively. In equipotent doses, an increase of active wake duration by caffeine and methylphenidate was attributed to increases of both frequency and average duration of active wake state, whereas increase of active wake duration by modafinil was attributed to increase of average duration of active wake state only. In equipotent doses, caffeine and methylphenidate decreased the power of lower frequency bands (1-22 Hz), whereas modafinil did not. During slow-wave sleep, modafinil and methylphenidate increased the power of lower frequency bands, but caffeine did not. All the psychostimulants increased the power of the GA band, which was more prominent in the frontal cortex than the parietal cortex. CONCLUSION : These results suggest that moda-nil-induced wakefulness differs from caffeine- or methylphenidate-induced wakefulness in terms of EEG spectral profiles and sleep-wake architecture.
Animals ; Benzhydryl Compounds ; Caffeine ; Electroencephalography ; Humans ; Male ; Methylphenidate ; Rats ; Wakefulness

Glutamate as an excitatory neurotransmitter in the central nervous system, participate in initiation and maintaining of sleep and wakefulness. The paper presents an overview of the research progress of glutamate in the regulation of sleep and wakefulness, especially focuses on its role in the brainstem, lateral hypothalamus and basal forebrain. Glutamate in the brain stem regulates the brain activity and maintains muscle tone during the wakefulness, as well as adjusts the electroencephalograph (EEG) in rapid eye movement phase and leads to muscle weakness. Glutamate in the lateral hypothalamus participates in the lateral hypothalamic arousal system by activating orexins neurons. The basal forebrain glutamatergic neurons take part in EEG synchronization and cause the decrease of sleep. Finally,The glutamatergic neurons of the cerebral cortex is not just a target of the arousal system, but itself contribute to regulation of arousal. Meantime, the glutamatergic neurons can regulate sleep stages through interaction with other types of neurons, which forms a complex sleep-wake regulation network in the brain. These indicate that the switches between different phases of sleep and wakefulness have different neuronal circuits.So we also reviewed the neuronal circuits and mechanisms that glutamate may be involved in. This review will help us to get a better understanding of the roles of glutamate in sleep and wakefulness.
Glutamic Acid ; physiology ; Humans ; Sleep ; physiology ; Wakefulness ; physiology