Iron-Deficiency Anemia is Associated with Altered Characteristics of Sleep Spindles in NREM Sleep in Infancy

Objective To determine the effects of iron-deficiency anemia on the development of non-rapid-eye-movement (NREM) sleep stages, as indexed by sleep spindles. Study design Patterns of sleep spindles during NREM sleep stages 2 and 3–4 (slow-wave-sleep, SWS) were compared in 26 otherwise healthy 6-month-old Chilean infants with iron-deficiency anemia and 18 non-anemic control infants. From polygraphic recordings, EEG activity was analyzed for sleep spindles to assess their number (density), duration, frequency, and inter-spindle interval. Results Iron-deficient anemic infants differed from the control group by having sleep spindles with reduced density, lower frequency, and longer inter-spindle intervals in NREM sleep stage 2 and SWS. Conclusions These results provide evidence of delayed sleep spindle patterns in iron-deficient anemic infants, suggesting that iron is an essential micronutrient for the normal progression of NREM sleep pattern development in the human. Special issue dedicated to Dr. Moussa Youdim.     

Topographical EEG Mapping in a Case of Recurrent Sleep Terrors

Sleep terrors are characterized by marked CNS arousal and typically occur during stage 3-4 sleep within the first NREM cycle. Studies of the EEG during sleep terrors suggest that delta power and synchrony in the EEG may be important physiological markers of sleep terror presence and intensity. An EEG mapping study was undertaken with a single participant who experienced three sleep terror episodes in the laboratory. A one-minute section of EEG was sampled immediately prior to the onset of each of the three sleep terrors. Similar EEG sections were taken from 10 healthy sex- and age-matched controls. The sleep tenors and control (normative) data were then compared topographically with z-scores (z-mapping). The z-maps indicated that all three sleep terrors contained more total and delta power in central and frontal areas than the control EEG sections. Moreover, relative delta power in these areas for the three sleep terrors was proportional to the subjective intensity of the episode. Although this pre-arousal EEG pattern may be related to ongoing slow-wave sleep mentation that may sometimes trigger sleep terror episodes, its functional significance remains an open question. The results demonstrate the utility of EEG mapping for the quantification of brain activation during sleep terror attacks and suggest that discrete activity profiles are identifiable for different types of dreaming-related arousal.     

A Laboratory Study of Sleep and Dreaming in a Case of Asperger's Syndrome

Asperger's Syndrome (AS) is a pervasive developmental disorder whose continuity with High-Functioning Autism is still a matter of debate. Clinical observations suggest that patients with AS may present the same sleep disorders as autistic patients, including difficulties in initiating and maintaining sleep as well as poor dream recall. We recorded the sleep of a 25-year-old male patient with AS for two nights using a full EEG montage and compared the second night to that of a group of normal participants. We found low levels of slow wave sleep (SWS: stages 3 + 4), high levels of stage 1, and a large number of awakenings. The organization of REM sleep was unremarkable, including normal REM density. Analyses of phasic EEG events revealed a very low incidence of sleep spindles and a normal number of K-complexes over bilateral frontal and central EEG leads. In order to collect dream reports, the patient was awakened three times over two nights following at least 15 minutes of REM sleep in each case. On each occasion the patient was not aware of any mental activity happening just prior to awakening. These observations are discussed with regards to the connections that may exist between EEG sleep spindle activity, selective attention, and the capacity to generate a dream report.     

Sleep EEG as a nonlinear dynamic process: a comparison of global correlation dimension of human EEG and measures of linear interdependence between channels

The goal of this work was to study (1) whether the estimation of correlation dimension (D2) using spatial embedding distinguishes between sleep stages and (2) whether information gained from the application of global D2 is redundant to measures of linear interdependence between channels. Twenty one-channel EEG segments of 12 healthy male subjects recorded during waking and sleep stages REM, I, II, and III-IV (according to the Rechtshaffen and Kales criteria) were analyzed with global (multichannel) D2, mean square correlation coefficients (MS) and proportion of variance accounted for by the first principal component (PC1). D2 was found to decrease progressively from stage I to stage III-IV with D2 values of waking and REM being close to those of stages I and II. MS and PC1 did not distinguish among sleep stages but yielded significant differences between waking and sleep. The results suggest that global D2 extracts information from human EEG. That sort of evidence cannot be obtained with measures of linear interdependence between channels.     

Inter-Hemispheric Oscillations in Human Sleep

Sleep is generally categorized into discrete stages based on characteristic electroencephalogram (EEG) patterns. This traditional approach represents sleep architecture in a static way, but it cannot reflect variations in sleep across time and across the cortex. To investigate these dynamic aspects of sleep, we analyzed sleep recordings in 14 healthy volunteers with a novel, frequency-based EEG analysis. This approach enabled comparison of sleep patterns with low inter-individual variability. We then implemented a new probability dependent, automatic classification of sleep states that agreed closely with conventional manual scoring during consolidated sleep. Furthermore, this analysis revealed a previously unrecognized, interhemispheric oscillation during rapid eye movement (REM) sleep. This quantitative approach provides a new way of examining the dynamic aspects of sleep, shedding new light on the physiology of human sleep.     

Modeling the effect of sleep regulation on a neural mass model

In mammals, sleep is categorized by two main sleep stages, rapid eye movement (REM) and non-REM (NREM) sleep that are known to fulfill different functional roles, the most notable being the consolidation of memory. While REM sleep is characterized by brain activity similar to wakefulness, the EEG activity changes drastically with the emergence of K-complexes, sleep spindles and slow oscillations during NREM sleep. These changes are regulated by circadian and ultradian rhythms, which emerge from an intricate interplay between multiple neuronal populations in the brainstem, forebrain and hypothalamus and the resulting varying levels of neuromodulators. Recently, there has been progress in the understanding of those rhythms both from a physiological as well as theoretical perspective. However, how these neuromodulators affect the generation of the different EEG patterns and their temporal dynamics is poorly understood. Here, we build upon previous work on a neural mass model of the sleeping cortex and investigate the effect of those neuromodulators on the dynamics of the cortex and the corresponding transition between wakefulness and the different sleep stages. We show that our simplified model is sufficient to generate the essential features of human EEG over a full day. This approach builds a bridge between sleep regulatory networks and EEG generating neural mass models and provides a valuable tool for model validation.     

Spindle activity during sleep in subjects with a deficit in pallesthetic sensibility

Sleep spindle activity was studied on four subjects affected by pallesthesic deficit due to injury the posterior funiculi of the cord. The spindle activity was studied as density (number of spindles min.), duration and percent of sleep time utilized in spindle activity. The polygraph sleep records included EOG, EMG and 6 monopolar EEG recordings, 3 for each side, on the frontal, parietal and occipital regions. The records showed a spindle activity which was similar in different subjects and that was significantly higher than the physiological values. In fact, the spindle density was about 250%, the duration was about 130% and the spindle percent was about 280%, with respect to the physiological values assumed to be 100%.     

Individual differences in the sleep/wake cycle of Arctic flexitime workers

Daytime workers tend to have shorter sleep duration and earlier sleep onset during work days than on days off. Large individual differences in sleep onset and sleep duration may be observed on work days, but work usually synchronizes sleep offset to a similar time. The present study describes individual differences in sleep behaviour of 48 daytime workers (25 men, aged 20–58 years) from an iron ore mine in Northern Sweden. The aim of the study was to determine whether differences in sleep patterns during work days were associated with the outcomes of sleepiness and sleep complaints. Cluster analysis was used to group workers into two categories of sleep onset and sleep duration. The “Late Sleep Onset” cluster comprised workers who slept 1.30 h later than the “Early Sleep Onset” cluster (p < 0.0001 for all weekdays). The “Long Sleep Duration” cluster slept 1.10 h longer than the “Short Sleep Duration” cluster (p < 0.0002 for work nights). The “Late Sleep Onset” cluster reported less refreshing sleep (p < 0.01) and had lower sufficient sleep scores (p < 0.01) than the “Early Sleep Onset” cluster. The “Short Sleep Duration” cluster also reported lower scores for sufficient sleep (p < 0.04) than the “Long Sleep Duration” cluster. For combined characteristics (phase and duration), workers with a late phase and short sleep duration reported greater sleep debt and sleepiness than workers with an early phase and short sleep duration (p < 0.02). Work schedule and commuting time modulate both sleep phase and sleep duration independently. Workers, classified as having an intermediate sleep phase preference, can organize their sleep time in order to minimize sleep debt and sleepiness symptoms. Individual differences in sleep phase and duration should be considered when promoting well-being at work even among groups with similar sleep needs. In order to minimize sleep debt and sleepiness symptoms, successful sleep behaviour could be promoted involving extend use of flexitime arrangement (i.e. later starting times) and reduce use of alarm clocks.     

Sleep-Stage Correlates of Hippocampal Electroencephalogram in Primates

It has been demonstrated in the rodent hippocampus that rhythmic slow activity (theta) predominantly occurs during rapid eye movement (REM) sleep, while sharp waves and associated ripples occur mainly during non-REM sleep. However, evidence is lacking for correlates of sleep stages with electroencephalogram (EEG) in the hippocampus of monkeys. In the present study, we recorded hippocampal EEG from the dentate gyrus in monkeys overnight under conditions of polysomnographical monitoring. As result, the hippocampal EEG changed in a manner similar to that of the surface EEG: during wakefulness, the hippocampal EEG showed fast, desynchronized waves, which were partly replaced with slower waves of intermediate amplitudes during the shallow stages of non-REM sleep. During the deep stages of non-REM sleep, continuous, slower oscillations (0.5–8 Hz) with high amplitudes were predominant. During REM sleep, the hippocampal EEG again showed fast, desynchronized waves similar to those found during wakefulness. These results indicate that in the monkey, hippocampal rhythmic slow activity rarely occurs during REM sleep, which is in clear contrast to that of rodents. In addition, the increase in the slower oscillations of hippocampal EEG during non-REM sleep, which resembled that of the surface EEG, may at least partly reflect cortical inputs to the dentate gyrus during this behavioral state.     

The link between cardiac autonomic activity and sleep delta power is altered in men with sleep apnea-hypopnea syndrome

We hypothesize that sleep apnea-hypopnea alters interaction between cardiac vagal modulation and sleep delta EEG. Sleep apnea-hypopnea syndrome (SAHS) is related to cardiovascular complications in men. SAHS patients show higher sympathetic activity than normal subjects. In healthy men, non-rapid eye movement (NREM) sleep is associated with cardiac vagal influence, whereas rapid eye movement (REM) sleep is linked to cardiac sympathetic activity. Interaction between cardiac autonomic modulation and delta sleep EEG is not altered across a life span nor is the delay between appearances of modifications in both signals. Healthy controls, moderate SAHS, and severe SAHS patients were compared across the first three NREM-REM cycles. Spectral analysis was applied to ECG and EEG signals. High frequency (HF) and low frequency (LF) of heart rate variability (HRV), ratio of LF/HF, and normalized (nu) delta power were obtained. A coherency analysis between HF(nu) and delta was performed, as well as a correlation analysis between obstructive apnea index (AI) or hypopnea index (HI) and gain, coherence, or phase shift. HRV components were similar between groups. In each group, HF(nu) was larger during NREM, while LF(nu) predominated across REM and wake stages. Coherence and gain between HF(nu) and delta decreased from controls to severe SAHS patients. In SAHS patients, the delay between modifications in HF(nu) and delta did not differ from zero. AI and HI correlated negatively with coherence, while HI correlated negatively with gain only. Apneas-hypopneas affect the link between cardiac sympathetic and vagal modulation and delta EEG demonstrated by the loss of cardiac autonomic activity fluctuations across shifts in sleep stages. Obstructive apneas and hypopneas alter the interaction between both signals differently.     

Solving the mystery of human sleep schedules one mutation at a time

Abstract

Sleep behavior remains one of the most enigmatic areas of life. The unanswered questions range from “why do we sleep?” to “how we can improve sleep in today’s society?” Identification of mutations responsible for altered circadian regulation of human sleep lead to unique opportunities for probing these territories. In this review, we summarize causative circadian mutations found from familial genetic studies to date. We also describe how these mutations mechanistically affect circadian function and lead to altered sleep behaviors, including shifted or shortening of sleep patterns. In addition, we discuss how the investigation of mutations can not only expand our understanding of the molecular mechanisms regulating the circadian clock and sleep duration, but also bridge the pathways between clock/sleep and other human physiological conditions and ailments such as metabolic regulation and migraine headaches.     

An Examination of Adult Women’s Sleep Quality and Sleep Routines in Relation to Pet Ownership and Bedsharing

ABSTRACT

People in many parts of the world commonly share their beds not only with human partners but also with dogs and cats. Self-report and actigraphy data have shown that sleeping with an adult human partner has both positive and negative impacts on human sleep, but there has been little exploration of the impacts that pets have on human sleep quality. We collected survey data online from 962 adult women living in the United States to investigate relationships between pet ownership and human sleep. Fifty-five percent of participants shared their bed with at least one dog and 31% with at least one cat. In addition, 57% of participants shared their bed with a human partner. Our findings did not show a strong relationship between pet ownership status or bedsharing conditions and sleep quality as assessed by the Pittsburgh Sleep Quality Index (PSQI), although according to this measure, a high percentage of study participants did experience sleep quality deficits. It is possible that pet ownership contributed to the high global PSQI scores we observed, especially since all but 7% of participants resided with dogs and/or cats. Other measures included in this study indicate that dogs and cats, and where they sleep, may indeed affect sleep habits and perceptions of sleep quality. Dog owners had earlier bedtimes and wake times than individuals who had cats but no dogs. Compared with human bed partners, dogs who slept in the owner’s bed were perceived to disturb sleep less and were associated with stronger feelings of comfort and security. Conversely, cats who slept in their owner’s bed were reported to be equally as disruptive as human partners, and were associated with weaker feelings of comfort and security than both human and dog bed partners. Follow-up research is necessary to determine if pet owners’ perceptions of pets’ impacts on their sleep align with objective measures of sleep quality.     

Sleep and EEG spectra in the pigeon (Columba livia) under baseline conditions and after sleep deprivation

Summary Sleep in adult domestic pigeons was studied by continuous 24-h recording of the EEG, EMG and EOG. Vigilance states were scored on the basis of behavioral observations, visual scoring of the polygraph records, and EEG power spectra.The animals showed a clear nocturnal preference for sleep. Throughout the dark period, EEG slow-wave activity was at a uniform level, whereas REM sleep (REMS) showed an increasing trend.EEG power density values differed significantly between the vigilance states. In general the values were highest in nonREM sleep (NREMS), intermediate in waking (W) and lowest in REMS.Twenty-four hour sleep deprivation reduced W and increased REMS, effects that are well documented in mammals. Unlike in mammals, EEG slow-wave activity remained unchanged, whereas EOG activity in W and NREMS was enhanced.Abbreviations EEG electroencephalogram - EMG electromyogram - EOG electrooculogram - SD sleep deprivation - L light - D dark - LD light dark - NREMS non rapid eye movement sleep - REMS REM sleep     

Sleep in birds: lying on the continuum of activity and rest

Abstract

Sleep is highly organized activity which is associated with decreased muscular activity and reduced response to environmental stimuli. The sleep is regulated by both, circadian and homeostatic mechanisms. Sleep patterns can be studied by behavioral assays by observing different sleep behaviors or by neuronal activity such as EEG (electroencephalogram), EOG (electro-oculogram), and EMG (electromyogram). Sleep is organized into non-rapid eye movement (NREM) and rapid eye movement. The sleep pattern in birds are similar to that in mammals, however, few differences such as existence of unihemispheric sleep (UHS) in almost all birds compared to few marine mammals do exist. The UHS results in asymmetry of the brain function measured as slow wave activity (SWA). Several migrants exhibit sleeplessness and they compensate it by NREM. They employ UHS during their migratory flight to remain alert while sleeping and maintain the balance while flying which is advantageous for these birds. Thus, sleep is of fundamental significance for the animal as it lies on the continuum of activity and rest. The present review focuses on some of above mentioned facts about sleep in higher vertebrates particularly in birds.     

Gamma band EEG activity is enhanced after the occurrence of rapid eye movement during human REM sleep

Sleep and Biological Rhythms - This study investigated changes in gamma band (35–44 Hz) EEG activity associated with rapid eye movement (REM) during human REM sleep. Polysomnograms of eight...     

Ambulatory sleep recording in a healthcare network: a feasibility study

Sleep disorders have a high prevalence: around 20% of insomniacs, 10% hypersomnolent including 2 to 4% of sleep disordered breathing in the general adult population. The low availability of sleep centres implies the research of alternative recording techniques in the natural setting of the patient. The objective was to evaluate an ambulatory recorder and its integration in a managed healthcare network. Fifteen patients had a full set-up at home and ten patients were hooked-up in the hospital but recorded at home. Technical failures occurred in 2/15 with full polysomnographic recordings. Integration within an experimental sleep network is in progress. This managed care network will include training of general practitioners, teletransmissions between GP and sleep specialists for a graded use of available resources including ambulatory monitoring.     

Automatic EEG arousal detection for sleep apnea syndrome

Electroencephalographic (EEG) arousals are seen in EEG recordings as an awakening response of the human brain. Sleep apnea is a serious sleep disorder. Severe sleep apnea brings about EEG arousals and sleep for patients with sleep apnea syndrome (SAS) is thus frequently interrupted. The number of respiratory-related arousals during the whole night on PSG recordings is directly related to the quality of sleep. Detecting EEG arousals in the PSG record is thus a significant task for clinical diagnosis in sleep medicine. In this paper, a method for automatic detection of EEG arousals in SAS patients was proposed. To effectively detect respiratory-related arousals, threshold values were determined according to pathological events as sleep apnea and electromyogram (EMG). If resumption of ventilation (end of the apnea interval) was detected, much lower thresholds were adopted for detecting EEG arousals, including relatively doubtful arousals. Conversely, threshold was maintained high when pathological events were undetected. The proposed method was applied to polysomnographic (PSG) records of eight patients with SAS and accuracy of EEG arousal detection was verified by comparative visual inspection. Effectiveness of the proposed method in clinical diagnosis was also investigated.     

The cognitive neuroscience of sleep: neuronal systems,consciousness and learning

Sleep can be addressed across the entire hierarchy of biological organization. We discuss neuronal-network and regional forebrain activity during sleep, and its consequences for consciousness and cognition. Complex interactions in thalamocortical circuits maintain the electroencephalographic oscillations of non-rapid eye movement (NREM) sleep. Functional neuroimaging affords views of the human brain in both NREM and REM sleep, and has informed new concepts of the neural basis of dreaming during REM sleep -- a state that is characterized by illogic, hallucinosis and emotionality compared with waking. Replay of waking neuronal activity during sleep in the rodent hippocampus and in functional images of human brains indicates possible roles for sleep in neuroplasticity. Different forms and stages of learning and memory might benefit from different stages of sleep and be subserved by different forebrain regions.     

EEG source identification: frequency analysis during sleep

This article deals with a new approach in sleep characterization that combines EEG source localisation methods with standard frequency analysis of multielectrode EEGs. First, we describe the theoretical methodology and the benefits that we get from a three-dimensional image (LORETA) of the cerebral activity related to a frequency band. Then, this new application is used as signal-processing technique on sleep EEG recordings obtained from young male adults using four frequency bands (delta 0.5-3.5 Hz, theta 4.0-7.5 Hz, alpha 8.0-12.5 Hz and beta 13.0-32.0 Hz) in different sleep stages. Finally, we show that the obtained results are highly consistent with other physiological assessments (standard EEG mapping, functional magnetic resonance imaging, etc.), but give us more realistic additional information on the generators of electromagnetic cerebral activity.