All-night Sleep Research Articles

Can the Brain's Thermostatic Mechanism Generate Sleep-Wake and NREM-REM Sleep Cycles? A Nested Doll Model of Sleep-Regulating Processes.

Evidence is gradually accumulating in support of the hypothesis that a process of thermostatic brain cooling and warming underlies sleep cycles, i.e., the alternations between non-rapid-eye-movement and rapid-eye-movement sleep throughout the sleep phase of the sleep-wake cycle. A mathematical thermostat model predicts an exponential shape of fluctuations in temperature above and below the desired temperature setpoint. If the thermostatic process underlies sleep cycles, can this model explain the mechanisms governing the sleep cyclicities in humans? The proposed nested doll model incorporates Process s generating sleep cycles into Process S generating sleep-wake cycles of the two-process model of sleep-wake regulation. Process s produces ultradian fluctuations around the setpoint, while Process S turns this setpoint up and down in accord with the durations of the preceding wake phase and the following sleep phase of the sleep-wake cycle, respectively. Predictions of the model were obtained in an in silico study and confirmed by simulations of oscillations of spectral electroencephalographic indexes of sleep regulation obtained from night sleep and multiple napping attempts. Only simple-inverse exponential and exponential-functions from the thermostatic model were used for predictions and simulations of rather complex and varying shapes of sleep cycles during an all-night sleep episode. To further test the proposed model, experiments on mammal species with monophasic sleep are required. If supported, this model can provide a valuable framework for understanding the involvement of sleep-wake regulatory processes in the mechanism of thermostatic brain cooling/warming.

Three Contactless Sleep Technologies Compared With Actigraphy and Polysomnography in a Heterogeneous Group of Older Men and Women in a Model of Mild Sleep Disturbance: Sleep Laboratory Study.

Contactless sleep technologies (CSTs) hold promise for longitudinal, unobtrusive sleep monitoring in the community and at scale. They may be particularly useful in older populations wherein sleep disturbance, which may be indicative of the deterioration of physical and mental health, is highly prevalent. However, few CSTs have been evaluated in older people. This study evaluated the performance of 3 CSTs compared to polysomnography (PSG) and actigraphy in an older population. Overall, 35 older men and women (age: mean 70.8, SD 4.9 y; women: n=14, 40%), several of whom had comorbidities, including sleep apnea, participated in the study. Sleep was recorded simultaneously using a bedside radar (Somnofy [Vital Things]: n=17), 2 undermattress devices (Withings sleep analyzer [WSA; Withings Inc]: n=35; Emfit-QS [Emfit; Emfit Ltd]: n=17), PSG (n=35), and actigraphy (Actiwatch Spectrum [Philips Respironics]: n=18) during the first night in a 10-hour time-in-bed protocol conducted in a sleep laboratory. The devices were evaluated through performance metrics for summary measures and epoch-by-epoch classification. PSG served as the gold standard. The protocol induced mild sleep disturbance with a mean sleep efficiency (SEFF) of 70.9% (SD 10.4%; range 52.27%-92.60%). All 3 CSTs overestimated the total sleep time (TST; bias: >90 min) and SEFF (bias: >13%) and underestimated wake after sleep onset (bias: >50 min). Sleep onset latency was accurately detected by the bedside radar (bias: <6 min) but overestimated by the undermattress devices (bias: >16 min). CSTs did not perform as well as actigraphy in estimating the all-night sleep summary measures. In an epoch-by-epoch concordance analysis, the bedside radar performed better in discriminating sleep versus wake (Matthew correlation coefficient [MCC]: mean 0.63, SD 0.12, 95% CI 0.57-0.69) than the undermattress devices (MCC of WSA: mean 0.41, SD 0.15, 95% CI 0.36-0.46; MCC of Emfit: mean 0.35, SD 0.16, 95% CI 0.26-0.43). The accuracy of identifying rapid eye movement and light sleep was poor across all CSTs, whereas deep sleep (ie, slow wave sleep) was predicted with moderate accuracy (MCC: >0.45) by both Somnofy and WSA. The deep sleep duration estimates of Somnofy correlated (r2=0.60; P<.01) with electroencephalography slow wave activity (0.75-4.5 Hz) derived from PSG, whereas for the undermattress devices, this correlation was not significant (WSA: r2=0.0096, P=.58; Emfit: r2=0.11, P=.21). These CSTs overestimated the TST, and sleep stage prediction was unsatisfactory in this group of older people in whom SEFF was relatively low. Although it was previously shown that CSTs provide useful information on bed occupancy, which may be useful for particular use cases, the performance of these CSTs with respect to the TST and sleep stage estimation requires improvement before they can serve as an alternative to PSG in estimating most sleep variables in older individuals.

0267 Development and validation of low-level Transcranial Electrical Stimulation to enhance slow oscillations during human NREM sleep

Abstract Introduction Sleep disruption, and in particular decreased NREM stage N3 sleep, has been implicated in cognition and pathogenesis of Alzheimer's Disease (AD). Several recent findings suggest that enhancing N3 sleep may mitigate impairments due to chronic sleep disruption. However, approaches such as transcranial electrical stimulation (TES) have been limited by discomfort, awakenings, and lack of blinding. In response to the need to develop low-level TES, our team first identified the source of slow oscillations (SOs) of N3 sleep using high-density EEG array modeling (Sourcerer®), which localized within anterior limbic brain structures. Next, we showed that low-level TES targeted to this region induced and enhanced SOs during N3 sleep in the laboratory. More recently, we developed a portable TES device with the minimum deployable set of stimulation electrodes targeting the anterior limbic SO-generating regions: Wireless Interface Sensor Pod (WISP). Methods Thirteen healthy adults (m = 42 years) participated in three all-night sleep EEG recordings where they received low level (0.5 mA) TES designed to target anterior limbic SO-generating regions and a sham stimulation (placebo). TES was initiated after 4 minutes of naturally occurring NREM N2 sleep and included five TES blocks of five minutes each separated by one minute rest periods. Subjects were blinded to stimulation and sham conditions, and outcomes included feasibility, acceptability, and total time in each sleep stage. A convolutional neural network (CNN) was developed, trained, and tested on manually scored EEG sleep staging for automated sleep scoring. Results Subjects rated that the WISP device was highly feasible and acceptable. Subjects were adequately blinded to sham versus stimulation. When compared to the sham session, limbic-targeted TES significantly increased the duration of N3 sleep and spectral power in the 0.5-1 Hz frequency band. Finally, our CNN was able to detect sleep stages with good accuracy (84%, kappa 0.77). Conclusion These results suggest that low-level portable TES using a minimum deployable set of electrodes, when specifically targeting anterior limbic sites, is feasible, acceptable, maintains blinding, and increases deep (N3) sleep. The WISP device is a promising method to both assess and manipulate sleep in the home setting. Support (if any) DoD MOMRP MTEC-21-06-MPAI-129

Season is related to the slow wave and sigma activity of infants and toddlers

Objective/BackgroundSlow wave activity (SWA) and sigma frequency activity (SFA) are hallmarks of NREM sleep EEG and important indicators of neural plasticity, development of the central nervous system, and cognition. However, little is known about the factors that modulate these sleep EEG activities, especially in small children. Patients/methodsWe analyzed the power spectral densities of SWA (1–4 Hz) and SFA range (10–15 Hz) from six EEG derivations of 56 infants (8 months) and 60 toddlers (24 months) during their all-night sleep and during the first and the last half of night sleep. The spectral values were compared between the four seasons. ResultsIn the spring group of infants, compared with the darker seasons, SFA was lower in the centro-occipital EEG derivations during both halves of the night. The SWA findings of the infants were restricted to the last half of the night (SWA2) and frontally, where SWA2 was higher during winter than spring. The toddlers presented less frontal SWA2 during winter compared with autumn. Both age groups showed a reduction in both SWA and SFA towards the last half of the night. ConclusionsThe sleep EEG spectral power densities are more often associated with seasons in infants’ SFA range. The results might stem from seasonally changing light exposure, but the exact mechanism warrants further study. Moreover, contrary to the adult-like increment of SFA, the SFA at both ages was lower at the last part of the night sleep. This suggests different regulation of spindle activity in infants and toddlers.

Effect of selective sleep deprivation on heart rate variability in post-90s healthy volunteers.

The 5-minute frequency domain method was used to examine the effects of polysomnography (PSG)-guided acute selective sleep deprivation (REM/SWS) on the cardiovascular autonomic nervous system, heart rate, and rhythm in healthy volunteers to understand the relationship between cardiac neuro regulatory homeostasis and cardiovascular system diseases in healthy subjects. The study included 30 healthy volunteers selected through the randomized-controlled method, randomly divided into REM sleep deprivation and SWS sleep deprivation groups. PSG analyses and dynamic electrocardiogram monitoring were done at night, during slow wave sleep or REM sleep. An all-night sleep paradigm, without any interruptions, was tested 3 times for comparison. The frequency domain parameter method was further used to monitor the volunteers 5 min before and after a period of sleep deprivation. According to the characteristics of the all-night sleep scatter plot, healthy volunteers were divided into abnormal and normal scatter plot groups. When compared with the period before sleep deprivation, high frequency (HF) and normalized high-frequency component (HFnu) were found to be decreased. Normalized low-frequency component (LFnu) increased in the abnormal scatter plot group after sleep deprivation, and this difference was statistically significant (P < 0.05). The scatter plot also showed that very low frequency (VLF) increased only in the normal group after deprivation and this difference, as well, was statistically significant (P < 0.05). The increase in diastolic blood pressure in the abnormal group was statistically significant (P < 0.05), but the change in blood pressure in the normal group was not statistically significant (P > 0.05). There are 62.5% of the patients and 20% of the employees that were observed to have abnormal whole-night sleep patterns during the uninterrupted whole-night sleep regime. Patients with atrial or ventricular premature beats (more than 0.1%), and those with ST-t changes during sleep, were all ascertained as abnormal. We concluded that some healthy people could face unstable autonomic nervous functioning related to their long-term tension, anxiety, time urgency, hostility, and other chronic stress states. In the face of acute sleep deprivation selectivity, mild stress based excitability of the vagus nerve is reduced, which diminishes the protective function, making them susceptible to conditions such as premature ventricular arrhythmia.

Intracortical Functional Connectivity Predicts Arousal to Noxious Stimuli during Sleep in Humans.

Nociceptive stimuli disrupt sleep, but may, or may not, entail an arousal. While arousal reactions go along with the activation of a widespread cortical network, the factors enabling such activation remain unknown. Here we used intracranial EEG in humans to test the relation between the cortical activity immediately preceding a noxious stimulus and the capacity of such a stimulus to trigger arousal. Intracranial EEG signals were analyzed during all-night sleep in 14 epileptic patients (4 women), who received laser stimuli slightly above their individual pain threshold. During 5 s preceding each stimulus, the functional correlation (spectral phase-coherence) between the main spinothalamic sensory area (posterior insula) and 12 other brain regions, grouped in four networks, as well as their spectral contents, were contrasted according to the presence of a stimulus-induced arousal, and then fed into a logistic regression model to assess their predictive value. Enhanced prestimulus phase-coherence between the sensory posterior insula and neocortical and limbic areas increased significantly the probability of arousal to nociceptive stimuli, in both slow-wave (N2) and rapid eye movements/paradoxical sleep. Furthermore, during N2 sleep, arousal was facilitated by stimulus delivery in periods of attenuated slow-wave activity. Together, these data indicate that sleep micro-states with enhanced interareal communication facilitate information transfer from sensory to higher-order cortical areas, and hence physiological arousal.SIGNIFICANCE STATEMENT Sleep is commonly subdivided into stages based on specific electrophysiological characteristics; however, within each single sleep stage, the functional state of the brain is continuously changing. Here we show that the probability for a phasic noxious stimulus to entail an arousal is modulated by the prestimulus interareal phase-coherence between sensory and higher-level cortical areas. Fluctuations in interareal communication immediately before the noxious stimulus may determine the responsiveness to incoming input by facilitating or preventing the transfer of noxious information from sensory to multiple higher-level cortical networks.

Transcranial Electrical Stimulation targeting limbic cortex increases the duration of human deep sleep

BackgroundResearchers have proposed that impaired sleep may be a causal link in the progression from Mild Cognitive Impairment (MCI) to Alzheimer's Disease (AD). Several recent findings suggest that enhancing deep sleep (N3) may improve neurological health in persons with MCI, and buffer the risk for AD. Specifically, Transcranial Electrical Stimulation (TES) of frontal brain areas, the inferred source of the Slow Oscillations (SOs) of N3 sleep, can extend N3 sleep duration and improve declarative memory for recently learned information. Recent work in our laboratory using dense array Electroencephalography (dEEG) localized the sources of SOs to anterior limbic sites – suggesting that targeting these sites with TES may be more effective for enhancing N3. MethodsFor the present study, we recruited 13 healthy adults (M = 42 years) to participate in three all-night sleep EEG recordings where they received low level (0.5 mA) TES designed to target anterior limbic areas and a sham stimulation (placebo). We used a convolutional neural network, trained and tested on professionally scored EEG sleep staging, to predict sleep stages for each recording. ResultsWhen compared to the sham session, limbic-targeted TES significantly increased the duration of N3 sleep. TES also significantly increased spectral power in the 0.5–1 Hz frequency band (relative to pre-TES epochs) in left temporoparietal and left occipital scalp regions compared to sham. ConclusionThese results suggest that even low-level TES, when specifically targeting anterior limbic sites, can increase deep (N3) sleep and thereby contribute to healthy sleep quality.

Analysis of influencing factors of excessive daytime sleepiness in adults with different degrees of sleep-disordered breathing

Objective:To explore the main influencing factors of excessive daytime sleepiness（EDS） in adults with different degrees of sleep-disordered breathing（SDB）, which will provide the scientific evidences for the individualized diagnosis and treatment. Method:Retrospective analysis was performed on the clinical data of 361 young and middle-aged snoring patients monitored by polysomnography. According to the presence or absence of obstructive sleep apnea（OSA） and apnea hypopnea index（AHI） levels, they were divided into primary snoring（AHI<5）, mild OSA（AHI 5-<15）, moderate OSA（AHI 15-<30） and severe OSA（AHI≥30）. From sleep efficiency（ES）, different sleep stages（REM, NREM1, NREM2, NREM3） ratio of total sleep, oxygen reduction index（ODI）, blood oxygen saturation<90% of total sleep time（TS90%）, the average saturation of blood oxygen（MSaO₂） and the lowest blood oxygen saturation（LSaO₂） of all-night sleep, and AHI in different sleep stages（REM-AHI, NREM-AHI）, MSaO₂ in different sleep stages（REM-MSaO₂, NREM-MSaO₂） and LSaO₂ in different sleep stages（REM-LSaO₂, NREM-LSaO₂）, the main influencing factors of EDS were discussed. Result:Among the 361 patients, 23 patients suffered from the primary snoring, 47 patients with mild OSA, 56 patients with moderate OSA, and 235 patients with severe OSA. REM-AHI, ODI and TS90% in EDS group were 10.9, 9.6 and 0.2 respectively in patients with primary snoring, which were significantly higher than those without EDS（P<0.01）. The main influencing factors of EDS were REM-AHI, ODI, and TS90%. However, among patients with mild OSA, REM-AHI was the main influencing factor of EDS, REM-AHI of the EDS group was 29.6, which was significantly higher than that of the non-EDS（P<0.05）. In patients with moderate OSA, LSaO₂ of the EDS group was 76.2, significantly lower than the group without EDS（P<0.05）, the main influencing factor of EDS is LSaO₂. In patients with severe OSA, BMI, ODI and TS90% in EDS group were significantly higher than those without EDS（P<0.05 or P<0.01）, while NREM-MSaO₂, MSaO₂ and LSaO₂ were significantly lower than those without EDS（P<0.05 or P<0.01）. The main influencing factors of EDS were BMI, NREM-MSaO₂, MSaO₂, LSaO₂, ODI and TS90%. Conclusion:Frequent apnea during REM stage may be one of the important factors causing EDS in patients with primary snoring and mild OSA. For patients with moderate and severe OSA, intermittent hypoxia at night may be the main factor leading to EDS, and obesity may promote the development of the disease and the occurrence of sleepiness.

Effect of partial-body heating on thermal comfort and sleep quality of young female adults in a cold indoor environment

This study evaluated the effectiveness of partial-body heating in improving the thermal comfort and sleep quality of young female adults sleeping in a cold indoor environment. A novel partial-body heating system (NPHS) was developed, consisting of three electrically heating pads in the feet, buttocks and shoulder regions with controllable surface temperatures, and the temperatures of the pads can be separately set on phone app. Eight female students were asked to sleep for 8 h in the CON (i.e., the NPHS with power off) and HEAT (i.e., the NPHS with power on) conditions randomly inside a climatic chamber. The chamber was controlled at 5 °C and 65% relative humidity. Physiological responses, including core and local skin temperatures, and heart rate, were recorded throughout all-night sleep. Participants' whole- and local-body thermal sensation, wetness and comfort sensations were evaluated. A subjective survey of sleep quality was also conducted after sleep. Results demonstrated that in comparison with CON, using HEAT showed significantly higher toe, calf and mean skin temperatures (p < 0.05), and remarkably improved whole- and local-body thermal and comfort sensations (p < 0.05), and provided a better sleep quality (p < 0.05). Besides, using NPHS did not induce body thermal stress evidenced by similar core temperatures and heart rate between HEAT and CON scenarios (p > 0.1). The present study shows that partial-body heating at the major body parts could effectively maintain thermoregulation, improve thermal comfort and provide a better sleep quality while sleeping in a cold environment.

Evaluation on the performance of quilts based on young people's sleep quality and thermal comfort in winter

This study evaluated the performance of three different quilts (white duck down quilt, white goose down quilt and cotton quilt) based on sleep quality and thermal comfort of young people in non-heating bedroom in winter. Thermal comfort and sleep quality were subjectively evaluated before and after sleep. Electroencephalograms (EEG), skin temperatures and bed climate were measured throughout the all-night sleep. Both subjective and physiological results showed that quilt materials had a significant effect on sleep quality and thermal comfort. The goose down quilt was evaluated the most comfortable in overall sleep comfort and sleep thermal sensation. The duration of slow wave sleep as calculated by EEG signal was longer, the skin temperatures and bed climate were higher when the goose down quilt was used. The results also show that there are gender differences in skin temperatures. Compared with males, the mean skin temperature (MST) of females was higher, while their foot temperature was significantly lower, which suggest that for females more attention should be paid to maintain warmth of extremity during sleep in winter. Our results suggest that sleep quality and thermal comfort is the most desirable when using goose down quilt and undesirable when using cotton quilt. Duvet could guarantee a comfortable bed climate in non-heating bedroom in winter of East China. Results also showed that lighter quilts would have a higher degree of satisfactions, indicating that young people in East China may have a preference for light quilt.

Electrical activity of the human amygdala during all-night sleep and wakefulness

ObjectiveThe aim of the present work was to characterize the dynamics of the human amygdala across the different sleep stages and during wakefulness. MethodsSimultaneous intracranial electrical recordings of the amygdala, hippocampus, and scalp electroencephalography during spontaneous sleep polysomnography in four patients suffering from epilepsy were analyzed. ResultsPower spectrum of the amygdala revealed no differences between rapid eye movement (REM) and wakefulness for all frequencies except higher power at 9 Hz during wakefulness and some low Gamma frequencies. Conversely, higher power was observed in non-REM (NREM) sleep than wakefulness for Delta, Theta and Sigma. ConclusionsOur results showed similar activity in the amygdala between wakefulness and REM sleep suggesting that the amygdala is as active in REM as during wakefulness. The higher power in Sigma frequencies during NREM sleep suggests that amygdala slow activity may play a significant role during NREM in concurrence with hippocampal activity. SignificanceWhile studies have described the metabolic activity of the human amygdala during sleep, our results show the corresponding electrical pattern during the whole night, pointing out an increase of slow activity during NREM sleep that might be subjected to similar influences as other subcortical brain structures, such as the hippocampus.

0164 EFFECT OF A DAYLIGHT LED VERSUS A CONVENTIONAL LED SOLUTION ON VISUAL COMFORT, DAYTIME ALERTNESS AND SLEEP

Conventional LED light sources have a discontinuous light spectrum with a prominent “blue” peak between 450-480nm, which potentially impacts on human circadian physiology and sleep. Thus, we investigated the effects of an advanced LED source simulating the natural daylight spectrum on visual comfort, daytime alertness and sleep. Twelve male young good sleepers spent twice 2.5-days in the laboratory once under a conventional (convLED) and once under a daylight simulating LED (dayLED) condition (16 hours LED exposure during scheduled wakefulness) in a balanced cross over design flanked by a 8-h baseline and a post-light exposure night. The same light settings were used for convLED and dayLED (100 photopic lux at the eye level with a color temperature of 4000K). However, the light spectrum and the color rendering index differed considerably between convLED and dayLED. Subjective visual comfort and sleepiness were continuously rated on conventional scales, and the PSGs were quantified for sleep stages and EEG spectral power density during nonREM sleep. The volunteers rated the light quality of the dayLED as being more pleasant than the convLED (p=0.07). They also felt significantly more alert during the dayLED condition compared to convLED (p<0.01), particularly in the morning/midday hours between 9 and 13h. In comparison to the baseline night, convLED significantly decreased the proportion of NREMS (-4.4 %, p<0.03) at the cost of REM sleep (+5.2%, p<0.004) and reduced EEG power density in the lower spindle frequency range between 11.5- 13.5 Hz (p<0.04), while such changes in sleep were not presented for dayLED. We have preliminary evidence that a daylight LED lighting solution has beneficial effects on visual comfort and daytime alertness and does not affect all-night sleep EEG activity when compared to a conventional LED solution. This study was supported by Toshiba Materials.

Spontaneous Swallowing during All-Night Sleep in Patients with Parkinson Disease in Comparison with Healthy Control Subjects.

Spontaneous saliva swallows (SS) appear especially during sleep. The rate of SS was rarely investigated in all-night sleep in patients with Parkinson disease (PD). Dysphagia is a frequent symptom in PD, but the rate of SS was never studied with an all-night sleep electroencephalogram (EEG). A total of 21 patients with PD and 18 age-matched healthy controls were included in the study. Frequencies of SS and coughing were studied in all-night sleep recordings of patients with PD and controls. During all-night sleep, video-EEG 12-channel recording was used including the electromyography (EMG) of the swallowing muscles, nasal airflow, and recording of vertical laryngeal movement using a pair of EEG electrodes over the thyroid cartilage. The total number of SS was increased while the mean duration of sleep was decreased in PD when compared to controls. Sialorrhea and clinical dysphagia, assessed by proper questionnaires, had no effect in any patient group. The new finding was the so-called salvo type of consecutive SS in one set of swallowing. The amount of coughing was significantly increased just after the salvo SS. In PD, the rate of SS was not sufficient to demonstrate the swallowing disorder, such as oropharyngeal dysphagia, but the salvo type of SS was quite frequent. This is a novel finding and may contribute to the understanding of swallowing problems in patients with dysphagic or nondysphagic PD.

Impaired slow wave sleep downscaling in patients with infantile spasms

BackgroundWest syndrome is a severe epileptic encephalopathy of infancy, characterized by infantile spasms, global retardation, and a severely abnormal electroencephalogram (EEG) pattern known as hypsarrhythmia, which is most prominent during slow waves sleep. The restorative function of slow wave sleep has been linked to downscaling, a neuronal process ensuring a balance of global synaptic strength, which is important for normal cortical functioning and development. A key electrophysiological marker for this downscaling is the reduction of the slope of slow waves across the night. MethodsWe retrospectively compared the slope of slow waves between 14 untreated patients with infantile spasms and healthy age and gender matched controls. Patients were examined in one all-night sleep EEG before treatment, and in two follow-up nap recordings, under and after treatment with corticosteroids. ResultsIn patients with infantile spasms the overnight reduction in the slope of slow waves was significantly diminished compared to controls (p = 0.009). Moreover, untreated patients revealed overall steeper slopes. During corticosteroid treatment the slope was reduced compared to controls (p = 0.001). After successful treatment the slope was similar between patients and controls. ConclusionOur results provide evidence for reduced downscaling in patients with infantile spasms. Moreover, the marked reduction of the slope during corticosteroid treatment may reflect a loss of synaptic connections due to the effect of glucocorticoids. This altered sleep dependent regulation of synaptic strength in infantile spasms may contribute the underlying pathomechanism of the developmental regression. Furthermore the normalization of synaptic strength due to corticosteroids might provide a potential mechanistic explanation for this treatment strategy.

Event-related potential measures of gap detection threshold during natural sleep

ObjectiveThe minimum time interval between two stimuli that can be reliably detected is called the gap detection threshold. The present study examines whether an unconscious state, natural sleep affects the gap detection threshold. MethodsEvent-related potentials were recorded in 10 young adults while awake and during all-night sleep to provide an objective estimate of this threshold. These subjects were presented with 2, 4, 8 or 16ms gaps occurring in 1.5 duration white noise. ResultsDuring wakefulness, a significant N1 was elicited for the 8 and 16ms gaps. N1 was difficult to observe during stage N2 sleep, even for the longest gap. A large P2 was however elicited and was significant for the 8 and 16ms gaps. Also, a later, very large N350 was elicited by the 16ms gap. An N1 and P2 was significant only for the 16ms gap during REM sleep. SignificanceERPs to gaps occurring in noise segments can therefore be successfully elicited during natural sleep. The gap detection threshold is similar in the waking and sleeping states.

A simplified approach to model-based analysis of the ultradian sleep homeostasis through fitting time courses of its eeg indicators obtained across routine clinical sleep lab recordings of all-night sleep and multiple 20-min napping attempts

A mathematical formulation of an ultradian process proposed by the elaborated version of the two-process model of sleep-wake regulation appears to be relatively complex compared to a very simple formulation of a homeostatic process suggested by this, and all earlier versions of the model. The methodology of numerical simulation of these two processes is based on fitting time courses of electroencephalographic (EEG) slow- wave activity obtained during, at least, two sleep episodes, a baseline sleep episode and the following episode challenged by shortening or prolongation of wakefulness. The aim of the present paper was to test a suggestion that the simulating approach to investigation of the diurnal and ultradian alternations between sleep-wake states and sub-states can benefit from several conceptual, mathematical, and methodological simplifications. In order to derive the parameters of both processes, similar (very simple) formulae were used for fitting time courses obtained during only baseline sleep of 14 women of different ages. The correlation coefficient between the simulated and empirical time courses attained value above 0.98. The derived parameters were used to predict a time course obtained across 12 very short (20-min) napping attempts of 9 sleep deprived and 9 sleep restricted young men. A coefficient between the predicted and empirical time courses (0.89) was only slightly lower than a coefficient between the same empirical time course and its direct simulation with the two-process model (0.92). In theoretical terms, the suggested simplified approach to modeling and simulation of the ultradian sleep homeostasis provides a parsimonious explanation of the basic principles of sleep-wake regulation. In practical terms, it can be implemented into a model-based analysis of numerous polysomnographic recordings of normal and disturbed sleep that are routinely collected every night in many clinical sleep laboratories around the world. The experimental and theoretical studies were supported by the Russian Foundation for Basic Research, and the Russian Foundation for Humanities (grants 07–06-00263-à, 10–06-00114- à, 06–06-00375-a, and 12–06-18001-e). I have benefited greatly from help of Olga Donskaya, Dr. Vladislav Palchikov, Dr. Konstantin Danilenko, and Dmitriy Zolotarev (Heffele) in the EEG data collection and analyses, and from help of Dr. Evgeniy Verevkin in simulation of these data.

Experimental study on a bedside personalized ventilation system for improving sleep comfort and quality

A bedside personalized ventilation (PV) system was investigated by experiments on human subjects including children, adults and elderly. Short-term exposure experiment was first carried out to find out the subjects’ perception of air movement and temperature and the effect on falling asleep. Through the comparative analysis of subjective questionnaires returned from participants and objective physiological tests in all-night sleep experiments, the influence of this system on sleep comfort and quality was obtained as well as the optimal system operation parameters. For conditions with bedside PV system, the returned questionnaires from participants reflected the thermal comfort level and subjective sleep quality were relatively higher than condition without the PV system. Physiological tests results like heart rate and heart rate variability also indicated that a calmer and more comfortable sleep could be obtained with this system. Bedside, PV system could provide a more obvious positive impact on children than adults in sleep quality, and the impact on elderly subjects was not significant. Optimal conditions for improving sleep comfort and quality are to keep the room ambient temperature at 22℃, PV outlet air temperature at 21℃ and air velocity of breathing zone at 0.1 m/s. Through this study, potential applications of bedside PV system could benefit human sleep comfort and quality, particularly in summer which could also be of benefit to hospital care of patients.

The EEG indicators of the dynamic properties of sleep–wake regulating processes: comparison of the changes occurring across wake–sleep transition with the effects of prolonged wakefulness

Everyday oscillations between wakefulness and sleep might be ultimately delineated as cyclic alternations between opposing neurobiological processes, i.e. those promoting arousal and inhibiting sleep and those promoting sleep and inhibiting arousal. The question arises of whether it is possible to delineate the signatures of such regulating mechanisms in the human electroencephalogram (EEG). The major aim of the present analysis was to reveal the EEG indicators of the processes underlying wake–sleep transitions. Data included power spectra calculated for 1-min segments of 699 EEG records (315 attempts of 15 subjects to stay permanently awake for 43–61 h, 356 successful attempts of 32 subjects to fall asleep during multiple naps, and 28 commencements and terminations of all-night sleep in 14 subjects). Principal component analysis was performed on the sets of 16 single-Hz log-transformed EEG powers (1–16 Hz). A close similarity was found between the patterns of changes in the EEG measures during prolonged wakefulness and across wake–sleep transitions. The observed time courses of scores on the first and second principal components were interpreted as the pure representatives of the wake and sleep drives, respectively, while the time courses of powers in separate frequency bands might reflect simultaneous influences of both drives.

A transition-constrained discrete hidden Markov model for automatic sleep staging.

BackgroundApproximately one-third of the human lifespan is spent sleeping. To diagnose sleep problems, all-night polysomnographic (PSG) recordings including electroencephalograms (EEGs), electrooculograms (EOGs) and electromyograms (EMGs), are usually acquired from the patient and scored by a well-trained expert according to Rechtschaffen & Kales (R&K) rules. Visual sleep scoring is a time-consuming and subjective process. Therefore, the development of an automatic sleep scoring method is desirable.MethodThe EEG, EOG and EMG signals from twenty subjects were measured. In addition to selecting sleep characteristics based on the 1968 R&K rules, features utilized in other research were collected. Thirteen features were utilized including temporal and spectrum analyses of the EEG, EOG and EMG signals, and a total of 158 hours of sleep data were recorded. Ten subjects were used to train the Discrete Hidden Markov Model (DHMM), and the remaining ten were tested by the trained DHMM for recognition. Furthermore, the 2-fold cross validation was performed during this experiment.ResultsOverall agreement between the expert and the results presented is 85.29%. With the exception of S1, the sensitivities of each stage were more than 81%. The most accurate stage was SWS (94.9%), and the least-accurately classified stage was S1 (<34%). In the majority of cases, S1 was classified as Wake (21%), S2 (33%) or REM sleep (12%), consistent with previous studies. However, the total time of S1 in the 20 all-night sleep recordings was less than 4%.ConclusionThe results of the experiments demonstrate that the proposed method significantly enhances the recognition rate when compared with prior studies.

Nonlinear dynamical systems effects of homeopathic remedies on multiscale entropy and correlation dimension of slow wave sleep EEG in young adults with histories of coffee-induced insomnia

Investigators of homeopathy have proposed that nonlinear dynamical systems (NDS) and complex systems science offer conceptual and analytic tools for evaluating homeopathic remedy effects. Previous animal studies demonstrate that homeopathic medicines alter delta electroencephalographic (EEG) slow wave sleep. The present study extended findings of remedy-related sleep stage alterations in human subjects by testing the feasibility of using two different NDS analytic approaches to assess remedy effects on human slow wave sleep EEG. Subjects (N=54) were young adult male and female college students with a history of coffee-related insomnia who participated in a larger 4-week study of the polysomnographic effects of homeopathic medicines on home-based all-night sleep recordings. Subjects took one bedtime dose of a homeopathic remedy (Coffea cruda or Nux vomica 30c). We computed multiscale entropy (MSE) and the correlation dimension (Mekler-D2) for stages 3 and 4 slow wave sleep EEG sampled in artifact-free 2-min segments during the first two rapid-eye-movement (REM) cycles for remedy and post-remedy nights, controlling for placebo and post-placebo night effects. MSE results indicate significant, remedy-specific directional effects, especially later in the night (REM cycle 2) (CC: remedy night increases and post-remedy night decreases in MSE at multiple sites for both stages 3 and 4 in both REM cycles; NV: remedy night decreases and post-remedy night increases, mainly in stage 3 REM cycle 2 MSE). D2 analyses yielded more sporadic and inconsistent findings. Homeopathic medicines Coffea cruda and Nux vomica in 30c potencies alter short-term nonlinear dynamic parameters of slow wave sleep EEG in healthy young adults.MSE may provide a more sensitive NDS analytic method than D2 for evaluating homeopathic remedy effects on human sleep EEG patterns.