Seasonality in human sleep

The timing of sleep and sleep EEG parameters in 10 healthy male subjects were investigated in four seasons under controlled conditions. The phase of nocturnal sleep was delayed about one and a half hours in winter as compared to that in summer. The duration of stage 4 sleep decreased and REM sleep increased significantly in winter compared with summer. The seasonality in the timing of sleep can be explained by photoperiodic time cues, but the changes in sleep EEG parameters are diffucult to explain in terms of photoperiod.     

Seasonality in human sleep.

The timing of sleep and sleep EEG parameters in 10 healthy male subjects were investigated in four seasons under controlled conditions. The phase of nocturnal sleep was delayed about one and a half hours in winter as compared to that in summer. The duration of stage 4 sleep decreased and REM sleep increased significantly in winter compared with summer. The seasonality in the timing of sleep can be explained by photoperiodic time cues, but the changes in sleep EEG parameters are difficult to explain in terms of photoperiod.     

Sleep in the tortoiseKinosternon sp.

Summary Individuals ofKinosternon sp., previously confined to laboratory conditions, were chronically implanted with electrodes for electroencephalogram, electro-oculogram and electrocardiogram recording. Behavioral states of waking and sleep were clearly observed. Two sleep stages were present: quiet sleep and REM or active sleep. Electrical cerebral activity was polymorphic and irregular. EEG frequencies declined and amplitudes diminished with sleep. Arrhythmic spikes occurred during behavioral sleep and declined with waking. Heart rate decreased when passing from wakefulness to quiet sleep. It was slightly but consistently higher during active sleep compared with quiet sleep.     

Interhemispheric asynchrony of the sleep EEG in northern fur seals

In northern fur seals the two brain hemispheres can generate the EEG slow waves during sleep not only simultaneously, as in all the terrestrial mammals investigated, but also independently as in dolphins.     

Interhemispheric asynchrony of the sleep EEG in northern fur seals

Summary In northern fur seals the two brain hemispheres can generate the EEG slow waves during sleep not only simultaneously, as in all the terrestrial mammals investigated, but also independently as in dolphins.     

Electrophysiological semeiology of sleep

Summary The main characteristics of electroencephalograms, electro-oculograms and electromyograms in human sleep are described. This electrophysiological semeiology permits the identification of the different stages in normal sleep. In animals, sleep is generally less differentiated; the possibility of recording subcortical structures allows the observation of additional phenomena such as hippocampal theta, activity and PGO spikes. Evoked brain electrical activity is less well known than the spontaneous activity in sleep. Recent technological developments offer many interesting possibilities in the processing of the EEG and other physiological signals.     

Proposed effects of brain noradrenaline on neuronal activity and cerebral blood flow during REM sleep.

We propose that the observed increases of both neuronal activity and cerebral blood flow seen throughout the brain during REM sleep may be effects of decreased central noradrenaline release.     

Arousal deficit shown in aged rat's quantitative EEG and ameliorative action of pramiracetam compared to piracetam

Summary The basal EEG profile of the aged Fisher-344 rat was consistently different from that of the young rat, showing dominant high voltage slow-wave components. These slow waves were present in both the frontal cerebral cortex and dorsal hippocampus. Absent or greatly attenuated in the aged rat's hippocampal EEG was rhythmic theta activity, which was always dominant in the young awake rat's hippocampus. These EEG differences were clearly apparent only under basal test conditions, i.e, following habituation to the test situation. Pramiracetam sulfate acted strongly to normalize the aged rat's EEG, while the action of piracetam was weak and appeared to undergo tolerance development.     

Arousal deficit shown in aged rat's quantitative EEG and ameliorative action of pramiracetam compared to piracetam

The basal EEG profile of the aged Fisher-344 rat was consistently different from that of the young rat, showing dominant high voltage slow-wave components. These slow waves were present in both the frontal cerebral cortex and dorsal hippocampus. Absent or greatly attenuated in the aged rat's hippocampal EEG was rhythmic theta activity, which was always dominant in the young awake rat's hippocampus. These EEG differences were clearly apparent only under basal test conditions, i.e., following habituation to the test situation. Pramiracetam sulfate acted strongly to normalize the aged rat's EEG, while the action of piracetam was weak and appeared to undergo tolerance development.     

Proposed effects of brain noradrenaline on neuronal activity and cerebral blood flow during REM sleep

Summary We propose that the observed increases of both neuronal activity and cerebral blood flow seen throughout the brain during REM sleep may be effects of decreased central noradrenaline release.     

Memory corticalization triggered by REM sleep: mechanisms of cellular and systems consolidation

Once viewed as a passive physiological state, sleep is a heterogeneous and complex sequence of brain states with essential effects on synaptic plasticity and neuronal functioning. Rapid-eye-movement (REM) sleep has been shown to promote calcium-dependent plasticity in principal neurons of the cerebral cortex, both during memory consolidation in adults and during post-natal development. This article reviews the plasticity mechanisms triggered by REM sleep, with a focus on the emerging role of kinases and immediate-early genes for the progressive corticalization of hippocampus-dependent memories. The body of evidence suggests that memory corticalization triggered by REM sleep is a systemic phenomenon with cellular and molecular causes.     

Sleep disturbance due to transportation noise: ear plugs vs oral drugs

Conclusion Sleep is not only the output of an EEG machine but a global phenomenon with unique physiological, environmental and psychological features occurring in a given individual. There is no question that statistical evaluation of noise-induced sleep disturbances in non homogeneous groups of subjects has resulted in the construction of a magnificent neurophysiological edifice by assembling a few individual bricks. In this respect, whether subjectively disturbed or not, we now know that when we sleep in noisy areas our delta sleep is reduced, our heart rate fails to habituate to individual noises, and we are more likely to develop psychic disturbances than residents in quiet areas. Data from these studies are however interspersed with results from a number of experiments during which the subject has been looked upon as nothing but a sleeper, i.e., experiments in which day-time stresses and noises were considered as irrelevant for the night-time study. It seems important therefore that future studies should gather more longitudinal data based on a limited number of subjects selected according to their day-time habits and psychological (e.g., extroverts/introverts) and physiological (e.g., short or long sleepers) characteristics. The knowledge about these situational factors and personality traits might provide new insights into individual biological strategies developed to cope with noise stress. The difficulties in assessing the effect of noise on sleep are particularly obvious if we consider another finding: deaf subjects spend significantly less time in delta sleep than do control subjects⁴⁷ and they present sleep pattern alterations remarkably similar to those which are most consistently described in noisy conditions.Research by the authors has been supported by grants from the Ministère de la Qualité de la Vie et de l'Environnement (France) and Commission of European Communities.     

Internal interactions within the human circadian system: the masking effect

In the realm of human circadian rhythms, the masking effect is defined as the change in the course of deep body temperature induced by changes in the degree of physical activity, or by the alteration between sleep and wake. This effect is particularly obvious during internal desynchronization where the rhythms of deep body temperature, and the sleep-wake sleep cycle - i.e. one of the masking factors - run with different periods. Every sleep onset is accompanied by a rapid drop, and wake onset by a rapid rise in deep body temperature, each one with an overshoot of about 50% of the steady state variations. When rhythms are calculated, with the dominant temperature period as the screening period, exclusively from data obtained during sleep episodes, on the one hand, and from those obtained exclusively during wake, on the other, two average cycles emerge: the 'sleep temperature curve' and the 'wake temperature curve'. Both run in parallel but are separated by the 'masking effect'. As derived from many experiments, the mean masking effect amounts to 0.28 +/- 0.06 degree C. The masking effect also depends to some extent on the phase of the temperature rhythm; it is larger than average around the temperature maximum and during the descending phase of the temperature cycle, where the alertness commonly is highest and the probability to sleep, in general, and the REM sleep propensity, in particular, are smaller than average. This also can be interpreted to indicate that the sleep temperature curve is phase advanced relative to the wake temperature curve; this, on the average, by 0.9 +/- 0.3 h. If the individually determined amount of masking is added to the temperature data obtained during sleep, or subtracted from the temperature data obtained during wake, a temperature curve emerges that can be thought of as being 'purified' of the masking effect. Analyses of this artificial curve allow estimation of that part of the internal interactions uninfluenced by the masking effect. On the average, about half of the amount of interaction between the rhythm of sleep-wake and that of deep body temperature is explained by the masking effect, whereas the other half is 'oscillatory interaction'. Both types of interaction are inherent and inseparable parts of the circadian clock mechanism, as can be deduced from model considerations.     

Behavioral phenomenology of sleep (somatic and vegetative)

Conclusions The foregoing analysis of behavioral sleep phenomenology shows that the most significant factual and theoretical aspects of sleep can be logically organized only according to several criteria, it being impossible to choose a singli one as truly paradigmatic. For this reason an ordinal classification of sleep phases was preferred. This fact does not detract from the usefulness of classifications based consistently on 1 criterion at a time (e.g.: synchronized-desynchronized; quiet-active; orthodoxical-paradoxical; NREM-REM; homeostatic-poikilostatic; spindle wave-slow wave-fast wave; external appetitive-internal appetitive-internal consummatory; and so on). In this respect, the bioelectrical classification is surely the best as it allows an analytical subdivision of the evolution of sleep with high resolving power^137–139. In particular, the electroencephalographic activity of late phase II (stage 4 in man¹³⁹ and slow wave¹¹ or deep slow wave¹⁴⁰ sleep in the cat) appears to be related to the triggering mechanisms and to the quantitative regulation of the circadian amount of phase III^3,5,11,140. However, in extending the field of functional implications of sleep phenomenology other criteria may be more significant. In fact, the somatic and vegetative events of sleep also lend themselves to an analysis according to the behavioral model of ethology^6,141–144 and the theory of homeostasis^{3–5, 145}, respectively. As an example, a number of classifying criteria are indicated in the table, where others, particularly neurochemical ones^146,147, could be added. At any rate, the difficulty of organizing sleep events into a satisfactory operational scheme is due to the fact that sleep is still an open problem as far as its mechanisms and functional significance are concerned.     

Human slow wave sleep: a review and appraisal of recent findings, with implications for sleep functions, and psychiatric illness.

Recent findings concerning human slow wave sleep (hSWS-stages 3 + 4; delta EEG activity) are critically reviewed. Areas covered include the significance of the first hSWS cycle; hSWS in extended sleep; relationship between hSWS, prior wakefulness and sleep loss; hSWS influence on sleep length; problems with hSWS deprivation; influence of the circadian rhythm; individual differences in hSWS, especially, age, gender and constitutional variables such as physical fitness and body composition. Transient increases in hSWS can be produced by increasing both the quality and quantity of prior wakefulness, with an underlying mechanism perhaps relating to the waking level of brain metabolism. Whilst there may also be thermoregulatory influences on hSWS, hypotheses that energy conservation and brain cooling are major roles for hSWS are debatable. hSWS seems to offer some form of cerebral recovery, with the prefrontal cortex being particularly implicated. The hSWS characteristics of certain forms of major psychiatric disorders may well endorse this prefrontal link.     

Human slow wave sleep: A review and appraisal of recent findings,with implications for sleep functions,and psychiatric illness

Recent findings concerning human slow wave sleep (hSWS-stages 3+4; delta EEG activity) are critically reviewed. Areas covered include the significance of the first hSWS cycle; hSWS in extended sleep; relationship between hSWS, prior wakefulness and sleep loss; hSWS influence on sleep length; problems with hSWS deprivation; influence of the circadian rhythm; individual differences in hSWS, especially, age, gender and constitutional variables such as physical fitness and body composition. Transient increases in hSWS can be produced by increasing both the quality and quantity of prior wakefulness, with an underlying mechanism perhaps relating to the waking level of brain metabolism. Whilst there may also be thermoregulatory influences on hSWS, hypotheses that energy conservation and brain cooling are major roles for hSWS are debatable. hSWS seems to offer some form of cerebral recovery, with the prefrontal cortex being particularly implicated. The hSWS characteristics of certain forms of major psychiatric disorders may well endorse this prefrontal link.     

The delta sleep inducing peptide (DSIP). Comparative properties of the original and synthetic nonapeptide

Summary Both the original and the synthetic nonapeptide Trp-Ala-Gly-Gly-Asp-Ala-Ser-Gly-Glu enhance, in recipient rabbits, spindle and delta EEG activity as in orthodox slow wave sleep.Acknowledgment. This work was supported by grants from the Swiss National Foundation for Scientific Research (No. 3.871.72, 3.527.75,3.443.074, 3.780.076), Fonds für Lehre und Forschung der Universität Basel, Merck Sharp and Dohme (USA), Ciba-Stiftung Basel, Hoffmann La Roche Ltd Basel, Sandoz Ltd Basel. We received valuable help from Dr S. Roncari, Dr B. Wilson and Dr C. D. Bennett for chemical research, and from Prof. A. Cerletti, Dr H. J. Tobler and Mr J. J. Regez (Division of Application and Research Development, Sandoz Ltd) for data processing.     

Sleep in an Amazonian manatee, Trichechus inunguis.

For the first time, sleep was studied in a representative of the order of Sirenia. Slow wave sleep occupied 27%, and paradoxical sleep 1% of the total recording time in the Amazonian manatee. Trichechus inunguis. The circadian rhythmicity of sleep was pronounced. During the sleep period, the manatee woke up for a short time for each respiratory act. Interhemispheric asynchrony of the electrocortical slow wave activity was found.     

Dépouillement automatique des enregistrements polygraphiques de sommeil

Summary Polygraphic recordings of human sleep are automatically analyzed by an original device, consisting of an analog component and a digital component (small computer). The device gives a minute by minute diagnosis of sleep stage, along with comments (artefacts) and numerical results for rapid and slow eye movements, muscle tone, heart and respiratory rates.     

The orthodox-paradoxical sleep cycle in the rat.

Under the postulated existence of a mechanism regulating the NREM sleep- REM sleep sequence and a reset of this mechanism by long awakenings, the variability of sleep cycle in the rat was studied. Awakenings of various durations were included in the definition of sleep cycle boundaries. Results show that an intervening awakening of 1 min is close to the limit under which the same cycle seems to be resumed after the awakening and above which the previous cycle is abortive and a new cycle will start after the next sleep onset.