Sleep in a 1-year diary from the mid-18th century.

A 1-year systematic diary was kept by an anonymous diarist in Hamburg in the year 1755-1756. Sleep, activities, food intake, urine volume, and meteorological data were documented daily. The systematic recording of sleep and naps, with an accuracy of a quarter of an hour allowed analysis of the placement, duration, and consistency of sleep. The mean (range) night sleep duration was 6 (3-9) h. The distribution of sleep interruptions showed two peaks, short (≤30 min) and long (≥45 min) interruptions. The latter indicted nights with segmented sleep. Time in bed was subject to strong seasonal variations. Bedtime and rise time were earlier in summer than in winter and sleep latency was shorter in summer than in winter. However, sleep duration displayed a large spread in all seasons and did not differ substantially between summer and winter. Seasonal variations of sleep timing were related to the varying daylight hours during the year. Finally, the results of this individual case may prompt a more detailed investigation of the variability of sleep behaviour in the pre-industrial period.

The history of sleep research and sleep medicine in Europe.

Sleep became a subject of scientific research in the second half of the 19th century. Since sleep, unlike other physiological functions, cannot be attributed to a specific organ, there was no distinct method available to study sleep until then. With the development of physiology and psychology, and a rapidly increasing knowledge of the structure and functioning of the nervous system, certain aspects of sleep became accessible to objective study. A first step was to measure responsiveness to external stimuli systematically, during sleep, allowing a first representation of the course of sleep (Schlaftiefe = sleep depth). A second method was to register continuously the motor activity across the sleep-wake cycle, which allowed the documentation in detail of rest-activity patterns of monophasic and polyphasic sleep-wake rhythms, or between day or night active animals. The central measurement for sleep research, however, became the electroencephalogram in the 1930s, which allowed observation of the sleeping brain with high temporal resolution. Beside the development of instruments to measure sleep, prolonged sleep deprivation was applied to study physiological and psychological effects of sleep loss. Another input came from clinical and neuropathological observations of patients with pronounced disorders of the sleep-wake cycle, which for the first time allowed localisation of brain areas that are essentially involved in the regulation of sleep and wakefulness. Experimental brain stimulation and lesion studies were carried out with the same aim at this time. Many of these activities came to a halt on the eve of World War II. It was only in the early 1950s, when periods with rapid eye movements during sleep were recognised, that sleep became a research topic of itself. Jouvet and his team explored the brain mechanisms and transmitters of paradoxical sleep, and experimental sleep research became established in all European countries. Sleep medicine evolving simultaneously in different countries, with early centres in Italy and France. In the late 1960s sleep research and chronobiology began to merge. In recent decades, sleep research, dream research, and sleep medicine have benefited greatly from new methods in genetic research and brain imaging techniques. Genes were identified that are involved in the regulation of sleep, circadian rhythms, or sleep disorders. Functional imaging enabled a high spatial resolution of the activity of the sleeping brain, complementing the high temporal resolution of the electroencephalogram.

Asynchronous Antarctic and Greenland ice-volume contributions to the last interglacial sea-level highstand.

The last interglacial (LIG; ~130 to ~118 thousand years ago, ka) was the last time global sea level rose well above the present level. Greenland Ice Sheet (GrIS) contributions were insufficient to explain the highstand, so that substantial Antarctic Ice Sheet (AIS) reduction is implied. However, the nature and drivers of GrIS and AIS reductions remain enigmatic, even though they may be critical for understanding future sea-level rise. Here we complement existing records with new data, and reveal that the LIG contained an AIS-derived highstand from ~129.5 to ~125 ka, a lowstand centred on 125-124 ka, and joint AIS + GrIS contributions from ~123.5 to ~118 ka. Moreover, a dual substructure within the first highstand suggests temporal variability in the AIS contributions. Implied rates of sea-level rise are high (up to several meters per century; m c-1), and lend credibility to high rates inferred by ice modelling under certain ice-shelf instability parameterisations.

Black Sea outflow response to Holocene meltwater events.

During the Holocene, North American ice sheet collapse and rapid sea-level rise reconnected the Black Sea with the global ocean. Rapid meltwater releases into the North Atlantic and associated climate change arguably slowed the pace of Neolithisation across southeastern Europe, originally hypothesized as a catastrophic flooding that fueled culturally-widespread deluge myths. However, we currently lack an independent record linking the timing of meltwater events, sea-level rise and environmental change with the timing of Neolithisation in southeastern Europe. Here, we present a sea surface salinity record from the Northern Aegean Sea indicative of two meltwater events at ~8.4 and ~7.6 kiloyears that can be directly linked to rapid declines in the establishment of Neolithic sites in southeast Europe. The meltwater events point to an increased outflow of low salinity water from the Black Sea driven by rapid sea level rise >1.4 m following freshwater outbursts from Lake Agassiz and the final decay of the Laurentide ice sheet. Our results shed new light on the link between catastrophic sea-level rise and the Neolithisation of southeastern Europe, and present a historical example of how coastal populations could have been impacted by future rapid sea-level rise.

End-member modelling as a tool for climate reconstruction-An Eastern Mediterranean case study.

The Eastern Mediterranean Sea is a sink for terrigenous sediments from North Africa, Europe and Asia Minor. Its sediments therefore provide valuable information on the climate dynamics in the source areas and the associated transport processes. We present a high-resolution dataset of sediment core M40/4_SL71, which was collected SW of Crete and spans the last ca. 180 kyr. We analysed the clay mineral composition, the grain size distribution within the silt fraction, and the abundance of major and trace elements. We tested the potential of end-member modelling on these sedimentological datasets as a tool for reconstructing the climate variability in the source regions and the associated detrital input. For each dataset, we modelled three end members. All end members were assigned to a specific provenance and sedimentary process. In total, three end members were related to the Saharan dust input, and five were related to the fluvial sediment input. One end member was strongly associated with the sapropel layers. The Saharan dust end members of the grain size and clay mineral datasets generally suggest enhanced dust export into the Eastern Mediterranean Sea during the dry phases with short-term increases during Heinrich events. During the African Humid Periods, dust export was reduced but may not have completely ceased. The loading patterns of two fluvial end members show a strong relationship with the Northern Hemisphere insolation, and all fluvial end members document enhanced input during the African Humid Periods. The sapropel end member most likely reflects the fixation of redox-sensitive elements within the anoxic sapropel layers. Our results exemplify that end-member modelling is a valuable tool for interpreting extensive and multidisciplinary datasets.

The Development of Sleep Medicine: A Historical Sketch.

ABSTRACT: For centuries the scope of sleep disorders in medical writings was limited to those disturbances which were either perceived by the sleeper him- or herself as troublesome, such as insomnia, or which were recognized by an observer as strange behavioral acts during sleep, such as sleepwalking or sleep terrors. Awareness of other sleep disorders, which are caused by malfunction of a physiological system during sleep, such as sleep-related respiratory disorders, were widely unknown or ignored before sleep monitoring techniques became available, mainly in the second half of the 20(th) century. Finally, circadian sleep-wake disorders were recognized as a group of disturbances by its own only when chronobiology and sleep research began to interact extensively in the last two decades of the 20(th) century. Sleep medicine as a medical specialty with its own diagnostic procedures and therapeutic strategies could be established only when key findings in neurophysiology and basic sleep research allowed a breakthrough in the understanding of the sleeping brain, mainly since the second half of the last century.

Guidelines for the recording and evaluation of pharmaco-sleep studies in man: the International Pharmaco-EEG Society (IPEG).

The International Pharmaco-EEG Society (IPEG) presents guidelines summarising the requirements for the recording and computerised evaluation of pharmaco-sleep data in man. Over the past years, technical and data-processing methods have advanced steadily, thus enhancing data quality and expanding the palette of sleep assessment tools that can be used to investigate the activity of drugs on the central nervous system (CNS), determine the time course of effects and pharmacodynamic properties of novel therapeutics, hence enabling the study of the pharmacokinetic/pharmacodynamic relationship, and evaluate the CNS penetration or toxicity of compounds. However, despite the presence of robust guidelines on the scoring of polysomnography -recordings, a review of the literature reveals inconsistent -aspects in the operating procedures from one study to another. While this fact does not invalidate results, the lack of standardisation constitutes a regrettable shortcoming, especially in the context of drug development programmes. The present guidelines are intended to assist investigators, who are using pharmaco-sleep measures in clinical research, in an effort to provide clear and concise recommendations and thereby to standardise methodology and facilitate comparability of data across laboratories.

Forerunners of REM sleep.

The development of sleep research can be divided into two main periods. The first one was initiated in 1863 by the first systematic measurement of the depth of sleep, the second in 1953 by the discovery of recurrent episodes of rapid eye movements in sleep. The main methodological procedure in the first of these two periods was the measurement of a single physiological variable, while beginning with long-term measurements of the electroencephalogram (EEG) in sleep, multi-channel, polygraphic recording became the method of choice for sleep studies. Although rhythmic changes in the ultradian frequency range of one to 2 h were observed early in many variables during sleep (movements, autonomic functions, penile erections), the recognition of the existence of two different states of sleep (rapid eye movement (REM) and non-rapid eye movement (NREM sleep)) was contingent upon a 'synthetic' view, which focus on the coalescence of multiple variables. The dual concept of sleep organization evolved stepwise in parallel to the rapid growth of neurophysiological knowledge and techniques in the first half of the 20th century, culminating in the discovery of REM sleep.

How treatment affects cognitive deficits in patients with sleep disorders: methodological issues and results.

Sleep disorders are frequently associated with impaired performance although the type and extent of cognitive deficits varies widely between different types of sleep disorders. Treatment is expected to ameliorate these deficits. However, cognitive functioning and its change with treatment depend on numerous factors. In this chapter we discuss methodological issues, including test selection, and person-specific, task-specific and environmental factors that influence cognitive functioning. In addition, features of study design and sampling strategies are discussed. The chapter ends with a short overview of routes by which treatment may affect cognition in sleep-disordered patients.

Modeling napping, post-lunch dip, and other variations in human sleep propensity.

STUDY OBJECTIVES: To model sleep propensity (SP) as a continuous variable across 24 hours and to model the post-noon nap zone, or post-lunch dip in performance, and the early evening trough in SP. METHODS: The present model is a variant of the 2-process model with 2 major modifications. (1) The circadian threshold process was replaced by sleep drive R, derived from REM sleep propensity, which shows a strong circadian modulation. (2) The model is based on a multiplicative interaction between the 2 input variables S and R. The model parameters S and R were estimated from experimental data. Thus, SP is modeled by multiplicative interaction of 2 sleep drives, S and R, the former of homeostatic, the latter of circadian nature. In short: SP = S x R. RESULTS: Under the condition of normal phase and duration of nighttime sleep, SP across 24 hours displays 4 characteristics, (a) a major peak at nighttime, (b) a secondary increase, which peaks post-noon, (c) a first local minimum at sleep offset in the morning, and (d) a second local minimum in the early evening hours. Model simulations with either delayed or advanced sleep times suggest that the magnitude of the post-noon nap zone depends on the phase of the major sleep period within 24 hours. While the nap zone is attenuated or disappears when night sleep is delayed, SP increases during daytime when night sleep is advanced. In all conditions, the evening local minimum of SP remained stable. CONCLUSIONS: SP can be modeled as a continuous variable, based on the multiplicative interaction of 2 basic sleep drives. The model predictions are in agreement with known variations of SP across 24 hours.

Rethinking sleep analysis.

Visual sleep scoring is the obligatory reference for sleep analysis. An essential step in sleep scoring is sleep staging. This technique was first described in 1937 and later adapted 3 times: first, in 1957, after the detection of rapid eye movement (REM) sleep, when electrooculography (EOG) was added; second, in 1968, when sleep staging was standardized and electromyography (EMG) was added; and third, in 2007, to integrate accumulated knowledge from sleep science, adding arousals and respiratory, cardiac, and movement events. In spite of the dramatic changes that have taken place in recording and storing techniques, sleep staging has undergone surprisingly few changes. The argument of the present comment is that sleep staging was appropriate as long as sleep biosignals were recorded in the analog mode as curves on paper, whereas this staging may be insufficient for digitally recorded and stored sleep data. Limitations of sleep staging are critically discussed and alternative strategies of sleep analysis are emphasized.

When sleep is perceived as wakefulness: an experimental study on state perception during physiological sleep.

While electrophysiologically measured sleep and perception of sleep generally concur, various studies have shown this is not always the case. The objective of the present study was to assess the perception of actual state during sleep by the technique of planned awakenings and interviewing subjects on the preawakening state. Sixty-eight (43 females, 25 males) young (mean age: 24.1, SD 5.1 years) normal sleeping subjects were deliberately awakened out of consolidated sleep, either stage 2 (S2), or REM sleep, during the first night in a non-clinical sleep laboratory. While the preawakening state was experienced as sleep in 48 cases (70.6%), it was experienced as wakefulness in 20 cases (29.4%). The percentage of awake judgements was somewhat, but not significantly, higher for awakenings out of S2 (38.2%), to REM sleep (20.6%). The proportion of mismatches between electrophysiologically defined sleep and state judgements was time-dependent with more awake judgements for REM sleep in the second half of the sleep period (41.7%) than in the first one (17.4%). Those subjects who made an awake judgement more frequently had a feeling of being aware of the situation and their surroundings than those who made a sleep judgement (80% versus 33%). Awareness during sleep may be a cognitive style, which favours mismatches between state perception and electrophysiologically defined sleep. Sleep periods with concordant or discordant state judgements did not differ in electrophysiologically defined sleep onset latency, sleep efficiency, or sleep state distribution.

A taxonomic analysis of sleep stages.

STUDY OBJECTIVES: To study the structure of human sleep at the level of sleep stages. We applied taxonomic statistics to detect significant configurations (types) of different physiologic variables and their relationship to sleep stages. DESIGN AND STATISTICS: Polygraphic sleep recordings from 32 subjects (normal sleepers as well as patients with insomnia, sleep apnea, or narcolepsy; n = 8 per group) were visually scored and submitted to a configural frequency analysis. The configural frequency analysis was computed with 3 continuous input variables: an electroencephalogram parameter, which represents the point of gravity of the EEG frequency distribution; the alpha slow-wave index, and the Rest Index, based on the presence or absence of phasic electromyographic activity. These variables were dichotomized for further analysis. The combination of 2 levels ( + or -) and 3 variables resulted in 2(3) patterns ( +++ to - - - ). The configural frequency analysis is a nonparametric X2-type multivariate statistic that identifies significant patterns or types. RESULTS: Each sleep stage contained 3 or 4 types. For non-rapid eye movement sleep stages 2, 3, and 4, types overlapped, whereas there was no overlap of types between stages 1 and 2. Types of rapid eye movement sleep did not overlap with those from stages 2, 3, and 4 but did overlap with wake and stage 1 types. The majority of observed types were significant in all 4 groups of subjects. CONCLUSIONS: Sleep stages appear to be less homogenous than rule-based sleep scoring would suggest. Types were either restricted to one stage or overlapped with neighboring stages.

Awakening from sleep.

Awakening is a crucial event for the organism. The transition from sleep to waking implies physiological processes which lead to a new behavioural state. Spontaneous awakenings have varying features which may change as a function of several factors. The latter include intrasleep architecture, circadian phase, time awake, age, or disordered sleep. Despite its clear theoretical and clinical importance, the topic of awakening (in humans) has received little attention so far. This contribution focuses on major issues which relate to awakening from both basic (experimental) and clinical research. Recent knowledge on neurophysiological mechanisms is reported. The experimental data which provide in the human suggestions on the regulation of awakening are discussed, mainly those concerning sleep architecture and homeostatic/circadian factors also in a life-span perspective, since age is a powerful factor which may influence awakening. Clinical contributions will examine two main sleep disorders: insomnia and hypersomnia. Daytime functioning is shown in insomniac patients and compared to other pathologies like sleep apnea. A final section evokes links between some types of night waking and psychological factors.