English translation of the first study reporting cyclical periods of increased respiration and eye and body motility during sleep in infants in 1926, with commentary

This is the first English translation of the work Periodic phenomena in the sleep in children, published in 1926 in the Journal Novoe v refleksologii i fiziologii nervnoi sistemy (Vol. 2, pp. 338-345) by Maria Denisova and Nicholai Figurin; it is the first study to report data on what is currently termed rapid eye movement (REM) sleep. The authors acquired continuous quantitative respiration data, as well as, eye and body movements during sleep in children for up to 6 hours, and discovered several novel features of sleep cycles in healthy infants from birth to about 1 year of age. First, the study reports cyclical periods of increased respiration and eye and body movements, with rapid ocular movements visible under relaxed eyelids (separation: 0.5-1 mm). These observations suggest atonia of REM sleep. Second, the length of the complete cycle (alternating active and quiet sleep phases or states) is about 50 minutes, an estimate that is consistent with later work. Third, the study identifies infant-specific ordering of sleep states, with the active phase beginning after sleep onset, followed by the quiescence phase. Importantly, these published data on sleep cycles precede all published studies related to the state now termed REM sleep by about 30 years (i.e. publishing in Science and in the Journal of Applied Physiology in the 1950s by Eugene Aserinski and Nathaniel Kleitman). In the historical commentary accompanying this translation, the findings of those later works are carefully compared to the original data on respiration and ocular and body motility cycles during sleep in infants, first reported and published by Denisova and Figurin (1926).

Regional variability in intracerebral properties of NREM to REM sleep transitions in humans

Transitions between wake and sleep states show a progressive pattern underpinned by local sleep regulation. In contrast, little evidence is available on non-rapid eye movement (NREM) to rapid eye movement (REM) sleep boundaries, considered as mainly reflecting subcortical regulation. Using polysomnography (PSG) combined with stereoelectroencephalography (SEEG) in humans undergoing epilepsy presurgical evaluation, we explored the dynamics of NREM-to-REM transitions. PSG was used to visually score transitions and identify REM sleep features. SEEG-based local transitions were determined automatically with a machine learning algorithm using features validated for automatic intra-cranial sleep scoring (10.5281/zenodo.7410501). We analyzed 2988 channel-transitions from 29 patients. The average transition time from all intracerebral channels to the first visually marked REM sleep epoch was 8 s ± 1 min 58 s, with a great heterogeneity between brain areas. Transitions were observed first in the lateral occipital cortex, preceding scalp transition by 1 min 57 s ± 2 min 14 s (d = -0.83), and close to the first sawtooth wave marker. Regions with late transitions were the inferior frontal and orbital gyri (1 min 1 s ± 2 min 1 s, d = 0.43, and 1 min 1 s ± 2 min 5 s, d = 0.43, after scalp transition). Intracranial transitions were earlier than scalp transitions as the night advanced (last sleep cycle, d = -0.81). We show a reproducible gradual pattern of REM sleep initiation, suggesting the involvement of cortical mechanisms of regulation. This provides clues for understanding oneiric experiences occurring at the NREM/REM boundary.

Sleep, plasticity, and sensory neurodevelopment

A defining feature of early infancy is the immense neural plasticity that enables animals to develop a brain that is functionally integrated with a growing body. Early infancy is also defined as a period dominated by sleep. Here, we describe three conceptual frameworks that vary in terms of whether and how they incorporate sleep as a factor in the activity-dependent development of sensory and sensorimotor systems. The most widely accepted framework is exemplified by the visual system where retinal waves seemingly occur independent of sleep-wake states. An alternative framework is exemplified by the sensorimotor system where sensory feedback from sleep-specific movements activates the brain. We prefer a third framework that encompasses the first two but also captures the diverse ways in which sleep modulates activity-dependent development throughout the nervous system. Appreciation of the third framework will spur progress toward a more comprehensive and cohesive understanding of both typical and atypical neurodevelopment.

Twitches emerge postnatally during quiet sleep in human infants and are synchronized with sleep spindles

In humans and other mammals, the stillness of sleep is punctuated by bursts of rapid eye movements (REMs) and myoclonic twitches of the limbs.¹ Like the spontaneous activity that arises from the sensory periphery in other modalities (e.g., retinal waves),² sensory feedback arising from twitches is well suited to drive activity-dependent development of the sensorimotor system.³ It is partly because of the behavioral activation of REM sleep that this state is also called active sleep (AS), in contrast with the behavioral quiescence that gives quiet sleep (QS)-the second major stage of sleep-its name. In human infants, for which AS occupies 8 h of each day,⁴ twitching helps to identify the state;^5-8 nonetheless, we know little about the structure and functions of twitching across development. Recently, in sleeping infants,⁹ we documented a shift in the temporal expression of twitching beginning around 3 months of age that suggested a qualitative change in how twitches are produced. Here, we combine behavioral analysis with high-density electroencephalography (EEG) to demonstrate that this shift reflects the emergence of limb twitches during QS. Twitches during QS are not only unaccompanied by REMs, but they also occur synchronously with sleep spindles, a hallmark of QS. As QS-related twitching increases with age, sleep spindle rate also increases along the sensorimotor strip. The emerging synchrony between subcortically generated twitches and cortical oscillations suggests the development of functional connectivity among distant sensorimotor structures, with potential implications for detecting and explaining atypical developmental trajectories.

Heart Rate Variability and Firstbeat Method for Detecting Sleep Stages in Healthy Young Adults: Feasibility Study

Background

Polysomnography (PSG) is considered the only reliable way to distinguish between different sleep stages. Wearable devices provide objective markers of sleep; however, these devices often rely only on accelerometer data, which do not enable reliable sleep stage detection. The alteration between sleep stages correlates with changes in physiological measures such as heart rate variability (HRV). Utilizing HRV measures may thus increase accuracy in wearable algorithms.

Objective

We examined the validity of the Firstbeat sleep analysis method, which is based on HRV and accelerometer measurements. The Firstbeat method was compared against PSG in a sample of healthy adults. Our aim was to evaluate how well Firstbeat distinguishes sleep stages, and which stages are most accurately detected with this method.

Methods

Twenty healthy adults (mean age 24.5 years, SD 3.5, range 20-37 years; 50% women) wore a Firstbeat Bodyguard 2 measurement device and a Geneactiv actigraph, along with taking ambulatory SomnoMedics PSG measurements for two consecutive nights, resulting in 40 nights of sleep comparisons. We compared the measures of sleep onset, wake, combined stage 1 and stage 2 (light sleep), stage 3 (slow wave sleep), and rapid eye movement (REM) sleep between Firstbeat and PSG. We calculated the sensitivity, specificity, and accuracy from the 30-second epoch-by-epoch data.

Results

In detecting wake, Firstbeat yielded good specificity (0.77), and excellent sensitivity (0.95) and accuracy (0.93) against PSG. Light sleep was detected with 0.69 specificity, 0.67 sensitivity, and 0.69 accuracy. Slow wave sleep was detected with 0.91 specificity, 0.72 sensitivity, and 0.87 accuracy. REM sleep was detected with 0.92 specificity, 0.60 sensitivity, and 0.84 accuracy. There were two measures that differed significantly between Firstbeat and PSG: Firstbeat underestimated REM sleep (mean 18 minutes, P=.03) and overestimated wake time (mean 14 minutes, P<.001).

Conclusions

This study supports utilizing HRV alongside an accelerometer as a means for distinguishing sleep from wake and for identifying sleep stages. The Firstbeat method was able to detect light sleep and slow wave sleep with no statistically significant difference to PSG. Firstbeat underestimated REM sleep and overestimated wake time. This study suggests that Firstbeat is a feasible method with sufficient validity to measure nocturnal sleep stage variation.

A video polysomnographic study of spontaneous smiling during sleep in newborns

The objective of the present study was to confirm the link between spontaneous smiling and active sleep in newborns, and to identify the role of the cortex in the generation of spontaneous smiles. A total of 12 healthy newborns born at term and three infants with major congenital abnormalities (two with hydranencephaly and one with a left hemispherectomy) were evaluated by video and polysomnography during a 3-hr sleep period. Smiles were graded and their association with isolated rapid eye movements and grouped rapid eye movements was analysed. In all, 383 smiles were recorded of which 377 occurred during active sleep. Smiles were shown to be significantly associated with active sleep (p < .0001) and with grouped rapid eye movements (p < .0001). Bilateral smiles were more frequent than asymmetrical smiles. Among asymmetrical smiles, left-sided smiles were more frequent than right-sided smiles (p < .0001). Maternal stimulation during active sleep did not increase smiles. Smiling was absent during active sleep only in the infant with total hydranencephaly in whom nearly all cortical tissue was absent. In conclusion, smiling occurs in healthy newborns, almost exclusively in active sleep and is associated with grouped rapid eye movements. In infants with major congenital abnormalities, smiling is abolished only when nearly all of the cerebral cortex is absent. These results support the hypothesis of the role of active sleep in the stimulation of neuronal circuits responsible for spontaneous smiling and emphasise the importance of cortical areas in newborn smiling.

Sleepers Selectively Suppress Informative Inputs during Rapid Eye Movements

Sleep leads to a disconnection from the external world. Even when sleepers regain consciousness during rapid eye movement (REM) sleep, little, if any, external information is incorporated into dream content [1-3]. While gating mechanisms might be at play to avoid interference on dreaming activity [4], a total disconnection from an ever-changing environment may prevent the sleeper from promptly responding to informative events (e.g., threat signals). In fact, a whole range of neural responses to external events turns out to be preserved during REM sleep [5-9]. Thus, it remains unclear whether external inputs are either processed or, conversely, gated during REM sleep. One way to resolve this issue is to consider the specific impact of eye movements (EMs) characterizing REM sleep. EMs are a reliable predictor of reporting a dream upon awakening [10, 11], and their absence is associated with a lower arousal threshold to external stimuli [12]. We thus hypothesized that the presence of EMs would selectively prevent the processing of informative stimuli, whereas periods of REM sleep devoid of EMs would be associated with the monitoring of external signals. By reconstructing speech in a multi-talker environment from electrophysiological responses, we show that informative speech is amplified over meaningless speech during REM sleep. Yet, at the precise timing of EMs, informative speech is, on the contrary, selectively suppressed. These results demonstrate the flexible amplification and suppression of sensory information during REM sleep and reveal the impact of EMs on the selective gating of informative stimuli during sleep.

Spatiotemporal organization of myoclonic twitching in sleeping human infants

During the perinatal period in mammals when active sleep predominates, skeletal muscles twitch throughout the body. We have hypothesized that myoclonic twitches provide unique insight into the functional status of the human infant's nervous system. However, assessments of the rate and patterning of twitching have largely been restricted to infant rodents. Thus, here we analyze twitching in human infants over the first seven postnatal months. Using videography and behavioral measures of twitching during bouts of daytime sleep, we find at all ages that twitching across the body occurs predominantly in bursts at intervals of 10 s or less. We also find that twitching is expressed differentially across the body and with age. For example, twitching of the face and head is most prevalent shortly after birth and decreases over the first several months. In addition, twitching of the hands and feet occurs at a consistently higher rate than does twitching elsewhere in the body. Finally, the patterning of twitching becomes more structured with age, with twitches of the left and right hands and feet exhibiting the strongest coupling. Altogether, these findings support the notion that twitches can provide a unique source of information about typical and atypical sensorimotor development.

Effects of late-night short-sleep on in-home polysomnography: relation to adult age and sex

Bedtime is frequently delayed by many factors in life, and a homeostatic response to the delay may compensate partly for increased time awake and shortened sleep. Because sleep becomes shorter with age and women complain of disturbed sleep more often than men, age and sex differences in the homeostatic response to a delayed bedtime may modify the homeostatic response. The purpose of the present study was to investigate the effect of late-night short-sleep (3 h with awakening at about 07:00 hours) on in-home recorded sleep in men and women in two age groups (20-30 and 65-75 years). Results (N = 59) showed that late-night short-sleep was associated with an increase in percentage of N3 sleep and a decrease in percentage of rapid eye movement sleep, as well as decreases in several measures of sleep discontinuity and rapid eye movement density. Men showed a smaller decrease in percentage of rapid eye movement sleep than women in response to late-night short-sleep, as did older individuals of both sexes compared with younger. Older men showed a weaker percentage of N3 sleep in response to late-night short-sleep than younger men. In general, men showed a greater percentage of rapid eye movement sleep and a lower percentage of N3 sleep than women, and older individuals showed a lower percentage of N3 sleep than younger. In particular, older men showed very low levels of percentage of N3 sleep. We conclude that older males show less of a homeostatic response to late-night short-sleep. This may be an indication of impaired capacity for recovery in older men. Future studies should investigate if this pattern can be linked to gender-associated differences in morbidity and mortality.

Towards a Functional Understanding of PGO Waves

Ponto-Geniculo-Occipital (PGO) waves are biphasic field potentials identified in a range of mammalian species that are ubiquitous with sleep, but can also be identified in waking perception and eye movement. Their role in REM sleep and visual perception more broadly may constitute a promising avenue for further research, however what was once an active field of study has recently fallen into stasis. With the reality that invasive recordings performed on animals cannot be replicated in humans; while animals themselves cannot convey experience to the extent required to elucidate how PGO waves factor into awareness and behavior, innovative solutions are required if significant research outcomes are to ever be realized. Advances in non-invasive imaging technologies and sophistication in imaging methods now offer substantial scope to renew the study of the electrophysiological substrates of waking and dreaming perception. Among these, Magnetoencephalogram (MEG) stands out through its capacity to measure deep brain activations with high temporal resolution. With the current trend in sleep and dream research to produce translational findings of psychopathological and medical significance, in addition to the clear links that PGO wave generation sites share, pharmacologically, with receptors involved in expression of mental illness; there is a strong case to support scientific research into PGO waves and develop a functional understanding of their broader role in human perception.

Virtual reality and consciousness inference in dreaming

This article explores the notion that the brain is genetically endowed with an innate virtual reality generator that - through experience-dependent plasticity - becomes a generative or predictive model of the world. This model, which is most clearly revealed in rapid eye movement (REM) sleep dreaming, may provide the theater for conscious experience. Functional neuroimaging evidence for brain activations that are time-locked to rapid eye movements (REMs) endorses the view that waking consciousness emerges from REM sleep - and dreaming lays the foundations for waking perception. In this view, the brain is equipped with a virtual model of the world that generates predictions of its sensations. This model is continually updated and entrained by sensory prediction errors in wakefulness to ensure veridical perception, but not in dreaming. In contrast, dreaming plays an essential role in maintaining and enhancing the capacity to model the world by minimizing model complexity and thereby maximizing both statistical and thermodynamic efficiency. This perspective suggests that consciousness corresponds to the embodied process of inference, realized through the generation of virtual realities (in both sleep and wakefulness). In short, our premise or hypothesis is that the waking brain engages with the world to predict the causes of sensations, while in sleep the brain's generative model is actively refined so that it generates more efficient predictions during waking. We review the evidence in support of this hypothesis - evidence that grounds consciousness in biophysical computations whose neuronal and neurochemical infrastructure has been disclosed by sleep research.

Undiagnosed and comorbid disorders in patients with presumed chronic fatigue syndrome

OBJECTIVE

To assess undiagnosed and comorbid disorders in patients referred to a tertiary care center with a presumed diagnosis of chronic fatigue syndrome (CFS).

METHODS

Patients referred for chronic unexplained fatigue entered an integrated diagnostic pathway, including internal medicine assessment, psychodiagnostic screening, physiotherapeutic assessment and polysomnography+multiple sleep latency testing. Final diagnosis resulted from a multidisciplinary team discussion. Fukuda criteria were used for the diagnosis of CFS, DSM-IV-TR criteria for psychiatric disorders, ICSD-2 criteria for sleep disorders.

RESULTS

Out of 377 patients referred, 279 (74.0%) were included in the study [84.9% female; mean age 38.8years (SD 10.3)]. A diagnosis of unequivocal CFS was made in 23.3%. In 21.1%, CFS was associated with a sleep disorder and/or psychiatric disorder, not invalidating the diagnosis of CFS. A predominant sleep disorder was found in 9.7%, 19.0% had a psychiatric disorder and 20.8% a combination of both. Only 2.2% was diagnosed with a classical internal disease. In the total sample, a sleep disorder was found in 49.8%, especially obstructive sleep apnea syndrome, followed by psychophysiologic insomnia and periodic limb movement disorder. A psychiatric disorder was diagnosed in 45.2%; mostly mood and anxiety disorder.

CONCLUSIONS

A multidisciplinary approach to presumed CFS yields unequivocal CFS in only a minority of patients, and reveals a broad spectrum of exclusionary or comorbid conditions within the domains of sleep medicine and psychiatry. These findings favor a systematic diagnostic approach to CFS, suitable to identify a wide range of diagnostic categories that may be subject to dedicated care.

Auditory inhibition of rapid eye movements and dream recall from REM sleep

STUDY OBJECTIVES

There is debate in dream research as to whether ponto-geniculo-occipital (PGO) waves or cortical arousal during sleep underlie the biological mechanisms of dreaming. This study comprised 2 experiments. As eye movements (EMs) are currently considered the best noninvasive indicator of PGO burst activity in humans, the aim of the first experiment was to investigate the effect of low-intensity repeated auditory stimulation on EMs (and inferred PGO burst activity) during REM sleep. It was predicted that such auditory stimuli during REM sleep would have a suppressive effect on EMs. The aim of the second experiment was to examine the effects of this auditory stimulation on subsequent dream reporting on awakening.

DESIGN

Repeated measures design with counterbalanced order of experimental and control conditions across participants.

SETTING

Sleep laboratory based polysomnography (PSG) PARTICIPANTS: Experiment 1 : 5 males and 10 females aged 18-35 years (M = 20.8, SD = 5.4). Experiment 2 : 7 males and 13 females aged 18-35 years (M = 23.3, SD = 5.5).

INTERVENTIONS

Below-waking threshold tone presentations during REM sleep compared to control REM sleep conditions without tone presentations.

MEASUREMENTS AND RESULTS

PSG records were manually scored for sleep stages, EEG arousals, and EMs. Auditory stimulation during REM sleep was related to: (a) an increase in EEG arousal, (b) a decrease in the amplitude and frequency of EMs, and (c) a decrease in the frequency of visual imagery reports on awakening.

CONCLUSIONS

The results of this study provide phenomenological support for PGO-based theories of dream reporting on awakening from sleep in humans.