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Differences between the so-called larks and owls representing the opposite poles of morningness-eveningness dimension are widely known. However, scientific consensus has not yet been reached on the methodology for ranking and typing people along other dimensions of individual variation in their sleep-wake pattern. This review focused on the history and state-of-the-art of the methodology for self-assessment of individual differences in more than one trait or adaptability of the human sleep-wake cycle. The differences between this and other methodologies for the self-assessment of trait- and state-like variation in the perceived characteristics of daily rhythms were discussed and the critical issues that remained to be addressed in future studies were highlighted. These issues include a) a failure to develop a unidimensional scale for scoring chronotypological differences, b) the inconclusive results of the long-lasting search for objective markers of chronotype, c) a disagreement on both number and content of scales required for multidimensional self-assessment of chronobiological differences, d) a lack of evidence for the reliability and/or external validity of most of the proposed scales and e) an insufficient development of conceptualizations, models and model-based quantitative simulations linking the differences between people in their sleep-wake pattern with the differences in the basic parameters of underlying chronoregulatory processes. It seems that, in the nearest future, the wide implementation of portable actigraphic and somnographic devices might lead to the development of objective methodologies for multidimensional assessment and classification of sleep-wake traits and adaptabilities. © 2017 Taylor & Francis Group, LLC.

Background and objective: The lack of practical tools for quick and objective testing of sleepiness has become one of the critical barriers to reducing the threats of sleep loss to public health, productivity, and safety. The present analysis aimed to examine whether sleepiness can be measured quickly, directly, objectively, and in absolute terms. Participants and methods: The resting electroencephalogram (EEG) was recorded every other hour during a 43–61-h period of wakefulness in 15 young people. Using the sets of single-Hz powers (1–16 Hz) obtained during the first minute of eyes-closed relaxation, spectral alert (SAC) and drowsy component (SDC) scores were computed. Weights for SAC scoring were derived from differences between spectra for extreme (alert and sleepy) sub-states or distant (first and forth) deprivation phases. Weights for SDC scoring were obtained by correlating the time courses of single-Hz powers with the time course of either subjective or objective sleepiness measures. Results: The scores allowed differentiation of alertness–sleepiness sub-states and occipital scores changed their sign at the boundary between alertness and sleepiness states. Conclusion: SAC and SDC scoring of the EEG signal recorded during the first minute of eyes-closed relaxation can be applied in simple, quick, direct, and objective sleepiness testing. © 2015, Springer-Verlag Berlin Heidelberg.

Putilov A.A.,Research Institute for Molecular Biology and Biophysics | Donskaya O.G.,Research Institute for Molecular Biology and Biophysics
Chronobiology International | Year: 2016

Age-associated changes in different bandwidths of the human electroencephalographic (EEG) spectrum are well documented, but their functional significance is poorly understood. This spectrum seems to represent summation of simultaneous influences of several sleep–wake regulatory processes. Scoring of its orthogonal (uncorrelated) principal components can help in separation of the brain signatures of these processes. In particular, the opposite age-associated changes were documented for scores on the two largest (1st and 2nd) principal components of the sleep EEG spectrum. A decrease of the first score and an increase of the second score can reflect, respectively, the weakening of the sleep drive and disinhibition of the opposing wake drive with age. In order to support the suggestion of age-associated disinhibition of the wake drive from the antagonistic influence of the sleep drive, we analyzed principal component scores of the resting EEG spectra obtained in sleep deprivation experiments with 81 healthy young adults aged between 19 and 26 and 40 healthy older adults aged between 45 and 66 years. At the second day of the sleep deprivation experiments, frontal scores on the 1st principal component of the EEG spectrum demonstrated an age-associated reduction of response to eyes closed relaxation. Scores on the 2nd principal component were either initially increased during wakefulness or less responsive to such sleep-provoking conditions (frontal and occipital scores, respectively). These results are in line with the suggestion of disinhibition of the wake drive with age. They provide an explanation of why older adults are less vulnerable to sleep deprivation than young adults. © 2016 Taylor & Francis

According to the two-process model of sleep–wake regulation, a homeostatic sleep pressure, i.e. a pressure to enter into deep non-rapid eyes movement (NREM) sleep, must exhibit a purely exponential buildup during prolonged wakefulness. However, this pressure is usually measured indirectly, i.e. during the following episode of actual deep NREM sleep. The purpose of this paper was to show that, despite a prominent circadian modulation of time course of any waking EEG index, the model-postulated purely exponential buildup of the homeostatic sleep pressure can be directly confirmed. During two days of sleep deprivation experiments, the EEG of healthy adults (N = 30) was recorded every other hour throughout 5-min eyes closed relaxation. Sixteen ln-transformed single-Hz power densities (from 1 to 16 Hz) were computed for each of 5 one-min intervals. Differences between these densities obtained for the first and the following intervals were calculated and averaged. The obtained 16 values were used as the frequency weighting curve for weighting densities of each set of 16 single-Hz power densities. Summing-up of these weighted densities provided a single measure that was found to co-vary with self-rated sleepiness throughout two-day interval of sleep deprivation, thus reflecting the joint influence of the circadian and homeostatic processes. However, two-day time course of responsiveness of this measure to closing the eyes for just a few minutes exhibited a purely exponential buildup. It was concluded that this result provided a direct experimental confirmation of the model-predicted exponential buildup of the homeostatic sleep pressure across prolonged episode of wakefulness. © 2016 Informa UK Limited, trading as Taylor & Francis Group

Putilov A.A.,Research Institute for Molecular Biology and Biophysics
Biological Rhythm Research | Year: 2015

The spherical cube model was earlier proposed for explaining interrelationships between scales of multidimensional questionnaires designed for assessing adaptability of the human sleep-wake cycle. The purpose of this report was to use the models predictions for identification of new items associated with yet unassessed sub-traits of the sleep-wake adaptability. The 72-item Sleep-Wake Pattern Assessment Questionnaire (SWPAQ) and an initial 320-item list created for a new inventory were administered to 139 respondents. Results of correlating the responses to these items with scores on six SWPAQ scales were used for classification of items in accord with the nomenclature proposed by the model and for selection of 120 items for the new inventory that allowed the assessment of the majority (more than 24) of the sleep-wake adaptability sub-traits predicted by the model. Some of these newly assessed sub-traits reflect individual variation in the success of biological adaptation to night and shift work. © 2015 Taylor and Francis.

Putilov A.A.,Research Institute for Molecular Biology and Biophysics | Munch M.Y.,University of Basel | Munch M.Y.,Ecole Polytechnique Federale de Lausanne | Cajochen C.,University of Basel
Current Aging Science | Year: 2013

Age-related disturbances of the sleep-wake cycle can reflect ontogenetic changes in regulatory mechanisms underlying normal and pathological aging, but the exact nature of these changes remains unclear. The present report is the first attempt to apply principal component analysis to the electroencephalographic (EEG) spectrum to examine of whether the observed age-related changes in the objective sleep measures can be linked to the opponent sleep-promoting and wake-promoting processes. The EEG indicators of these processes - scores on the 1st and 2nd principal components of the EEG spectrum, respectively - were compared in 15 older (57-74 years) and 16 younger (20-31 years) healthy volunteers. The scores were calculated for non-REM sleep episodes which occurred during ten 75-min naps scheduled every 150 min throughout a 40-h constant routine protocol. Both, a decrease of the 1st principal component score and an increase of the 2nd principal component score were found to contribute to such most obvious age-related modification of the sleep EEG spectrum as attenuation of EEG slow-wave activity in older people. Therefore, we concluded that the normal aging process can reflect both a weakening of the sleep-promoting process and a strengthening of the wake-promoting process, respectively. Such bidirectional changes in chronoregulatory processes may explain why sleep of older people is characterized by the few profitable and a number of detrimental features (i.e., a better ability to cope with daytime sleepiness and sleep loss vs. difficulty of falling asleep, decreased total nighttime sleep, "lightened" and fragmentized sleep, unwanted early morning awakenings, etc.). © 2013 Bentham Science Publishers.

Putilov A.A.,Research Institute for Molecular Biology and Biophysics
Geometry of Individual Variation in Personality and Sleep-Wake Adaptability | Year: 2010

Scientific investigation is often aimed on generation and description of a low dimensional simple form that is, however, an accurate representation of the structure of numerous empirically obtained variables. In despite of this aim, some scientific descriptions of real world structures are difficult to visualize due to their dimensional complexity. This new book considers two such structures, the structure of personality lexicon and the structure of adaptive ability of the sleep-wake cycle. © 2011 by Nova Science Publishers, Inc. All rights reserved.

Putilov A.A.,Research Institute for Molecular Biology and Biophysics | Donskaya O.G.,Research Institute for Molecular Biology and Biophysics | Verevkin E.G.,Research Institute for Molecular Biology and Biophysics
Computational Vision and Medical Image Processing V - Proceedings of 5th Eccomas Thematic Conference on Computational Vision and Medical Image Processing, VipIMAGE 2015 | Year: 2016

In spite of the extraordinary progress that has been made by sleep and behavioral sciences in the last decades, the assessment of sleepiness is one of the remaining challenges. The lack of practical tools for objective sleepiness testing has become one of the critical barriers to reducing the threats of increased sleepiness to public health, productivity, and safety. The first aim of the present report was to examine whether objective sleepiness testing can be facilitated by the quantitative analysis of the resting Electroencephalographic (EEG) signal recorded at the first minute following eyes closing. The second aim was to examine applicability of a new spectral EEG index for differentiation of 4 alertness-sleepiness substates (alert, neither, dozy, and sleepy) in participants of two sleep deprivation experiments. In the first (exploration) study of applicability of the new index, sleepiness of 15 young adults was self-scored every second hour simultaneously with recording of the resting EEG in the course of 43–61-hour wakefulness. In another (confirmation) study, one-minute eyes closed EEG recordings were obtained with a 3-hour interval during 24-hour wakefulness of 130 adolescents and adults. The sleepiness testing was based on calculation of Spectral Drowsy Component Score (SDCS). To compute SDCS, 16 (1–16 Hz) single-Hz powers of the EEG spectra were obtained for the first one-minute interval of eyes closed EEG signal, logtransformed, ipsatized, weighted, and summed. The 16 weights were the correlation coefficients between the time course of self-scored sleepiness and the time courses of single-Hz powers. The results indicate that SDCS provided reliable criteria for distinguishing between four sub-states of alertness-sleepiness. These criteria performed even better than the traditional criteria based on latency to sleep onset. Moreover, the occipital SDCS changed their sign exactly at the boundary between neither and dozy sub-states thus providing yes-or-no criterion of onset of sleepiness state as opposed to the preceding alert state. We concluded that SDCS might be recommended for quick (app. one-minute), direct and objective testing of sleepiness in absolute terms. © 2016 Taylor & Francis Group, London.

Putilov A.A.,Research Institute for Molecular Biology and Biophysics
Chronobiology International | Year: 2016

Various characteristics of the sleep-wake cycle can determine the success or failure of individual adjustment to certain temporal conditions of the today’s society. However, it remains to be explored how many such characteristics can be self-assessed and how they are inter-related one to another. The aim of the present report was to apply a three-dimensional structural representation of the sleep-wake adaptability in the form of “rugby cake” (scalene or triaxial ellipsoid) to explain the results of analysis of the pattern of correlations of the responses to the initial 320-item list of a new inventory with scores on the six scales designed for multidimensional self-assessment of the sleep-wake adaptability (Morning and Evening Lateness, Anytime and Nighttime Sleepability, and Anytime and Daytime Wakeability). The results obtained for sample consisting of 149 respondents were confirmed by the results of similar analysis of earlier collected responses of 139 respondents to the same list of 320 items and responses of 1213 respondents to the 72 items of one of the earlier established questionnaire tools. Empirical evidence was provided in support of the model-driven prediction of the possibility to identify items linked to as many as 36 narrow (6 core and 30 mixed) adaptabilities of the sleep-wake cycle. The results enabled the selection of 168 items for self-assessment of all these adaptabilities predicted by the rugby cake model. © 2016 Taylor & Francis

PubMed | Research Institute for Molecular Biology and Biophysics
Type: | Journal: Clinical EEG and neuroscience | Year: 2016

One of the critical barriers to reducing the threats of sleep loss to public health, safety, and productivity is a lack of practical tools for quick identification of objective level of sleepiness. We examined a novel sleepiness measure named spectral drowsy component score to provide evidence for generalizability of a frequency weighting curve required for calculation of this measure. Each spectral drowsy component score is a sum of 16 weighted ln-transformed single-Hz power densities (1-16 Hz) obtained by the fast Fourier transformation of an electroencephalographic signal recorded during the first minute after closing the eyes. A set of 16 weights (frequency weighting curve) is derived empirically. One type of such curve is a correlation spectrum. It consists of 16 coefficients of correlation of a group-averaged experimental time course of sleepiness with16 time courses of single-Hz power densities. Sleepiness is determined either subjectively (by self-scoring on the Karolinska Sleepiness Scale) or objectively (as sleep latency). Another type is a differential spectrum reflecting difference between 2 sets of 16 power densities obtained for either distant phases of sleep deprivation experiment or distinct alertness-sleepiness substates. Analysis of 3 datasets collected in sleep deprivation experiments with, in total, 160 participants showed that, despite differences in the protocols of these experiments and ages of their participants, the forms of frequency weighting curves always resembled one another. Such resemblance led to practical identity of scoring results. We concluded that spectral drowsy component scoring might be implemented into quick, simple, direct, transparent, and objective test of sleepiness.

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