Chronobiology studies physiological variations due to the time of day, an unexplored factor in design research. This paper explores the effect of time of day on designers' physiological responses in idea generation. Convergent (CT) and divergent (DT) thinking, as building blocks of designing, are explored using pupil dilation as a proxy for cognitive load. Time of day and educational background are explored for engineering and industrial designers. Results show a larger pupil diameter in the afternoon than in the morning, especially for DT, with higher values for industrial designers.

Sensors are increasingly being used to monitor animal behaviour. Data handling methods have, however, lagged behind the continuous data stream to some extent, often being limited to summarizing data into daily averages at group level. This research reflection presents our opinion of the neglected application of 24-h pattern analysis. Recent studies of dairy cow behaviour have demonstrated that additional ways of analysing data improve our understanding of animal behaviour and add value to data that were already retrieved. The terminology for the described 24-h patterns differs between these studies, making them difficult to compare. Thus, diurnal, circadian, daily, periodicity and 24-h pattern are all terms used to describe dairy cow activities over a 24-h period. Several studies have shown that the 24-h behavioural pattern at herd level is relatively consistent over time, and that with well-established management routines, a specific herd signature will be evident. However, within a herd, individual cows may have individual 24-h patterns with more or less variability. Recent studies suggest that deviations from herd and/or individual 24-h patterns can be used to describe cow robustness, as well as to predict disease. We strongly believe that individual and herd 24-h patterns provide a great deal of information about behaviour and that these patterns offer opportunity for more precise and timely health management and welfare monitoring.

Chronobiology is the science that studies the role of time in biology. The study of time in human bodies revealed the presence of internal rhythms related to the time of day. Considering divergent thinking as one of the essential cognitive activities of conceptual design, this paper presents the results of investigating the effect of time of day on designers’ brain activity while performing divergent thinking tasks. An experiment was run with a revised Alternative Uses Task, measuring brain activity with an electroencephalogram (EEG) device. Students with different educational backgrounds were recruited for this experiment, including engineering and industrial design students, to determine if the time of day affected them differently. The brain waves and related power results show significant differences with respect to the time of day and educational background. The differences are particularly evident considering the interaction of these factors. Further studies are required to understand the relationship between the differences detected and the designers’ behavioural performance and to identify which time of day is most effective for idea-generation activities for designers.

The aim of this study was to explore the relationship between circadian preference and sensation seeking. To this aim 1041 university students (408 males and 633 females), ranging in age between 18 and 30 years, filled the reduced version of the Morningness-Eveningness Questionnaire (MEQr) and the Sensation Seeking Scale-Form V (SSS-V). Males scored higher than females in SSS-V total score and all subscales, except experience seeking (ES). As regards circadian preference, evening types scored higher than morning types in SSS-V total score and all subscales, except boredom susceptibility (BS) where they significantly differed only from intermediate types. On the whole our results highlight a significant relationship between circadian preference and sensation seeking.

The objective of this study was to provide a reliable instrument to measure morningness for upcoming studies in French samples, using the Composite Scale of Morningness (CSM), which has been translated into French. Nursing students (n = 356) completed the questionnaire between February and March 1997. The total score obtained was independent of age and gender, and normally distributed. The reliability was high (Cronbach's α = 0.85), and factorial analysis confirmed the unidimensionality of the scale. Evening-type subjects are thought to score under 31, and morning-type subjects are thought to score above 44. As an external validation, morningness was associated, on weekdays and weekends, with early rising times and bedtimes and early peak times of physical and mental performance. In conclusion, we found that the English and the French versions of the Composite Scale of Morningness gave identical results. The scale is reliable and can be used for French-speaking adult samples. Nevertheless, normative data and other external validity criteria are needed.

The circadian system temporally coordinates daily rhythms in feeding behaviour and energy metabolism. The objective of the present paper is to review the mechanisms that underlie circadian regulation of lipid metabolic pathways. Circadian rhythms in behaviour and physiology are generated by master clock neurons in the suprachiasmatic nucleus (SCN). The SCN and its efferent targets in the hypothalamus integrate light and feeding signals to entrain behavioural rhythms as well as clock cells located in peripheral tissues, including the liver, adipose tissue and muscle. Circadian rhythms in gene expression are regulated at the cellular level by a molecular clock comprising a core set of clock genes/proteins. In peripheral tissues, hundreds of genes involved in lipid biosynthesis and fatty acid oxidation are rhythmically activated and repressed by clock proteins, hence providing a direct mechanism for circadian regulation of lipids. Disruption of clock gene function results in abnormal metabolic phenotypes and impaired lipid absorption, demonstrating that the circadian system is essential for normal energy metabolism. The composition and timing of meals influence diurnal regulation of metabolic pathways, with food intake during the usual rest phase associated with dysregulation of lipid metabolism. Recent studies using metabolomics and lipidomics platforms have shown that hundreds of lipid species are circadian-regulated in human plasma, including but not limited to fatty acids, TAG, glycerophospholipids, sterol lipids and sphingolipids. In future work, these lipid profiling approaches can be used to understand better the interaction between diet, mealtimes and circadian rhythms on lipid metabolism and risk for obesity and metabolic diseases.

Irregularity in eating patterns could be a potential cardiometabolic risk factor. We aimed to study the associations of irregular intake of energy at meals in relation to cardiometabolic risk factors 10 and 17 years later. Variability of energy intake data – derived from 5-d estimated diet diaries of cohort members of the National Survey for Health and Development collected at ages 36 (n 1416), 43 (n 1505) and 53 years (n 1381) – was used as a measure for irregularity. Associations between meal irregularity scores with cardiometabolic risk factors measured 10 and 17 years later were investigated using linear mixed models and logistic regression models. The results showed that irregularity scores changed significantly over the years (P<0·05). At age 36 years, subjects with a more irregular intake of energy at lunch (OR 1·42; 95 % CI 1·05, 1·91) and between meals (OR 1·35; 95 % CI 1·01, 1·82) had an increased risk for the metabolic syndrome 17 years later; at lunch was also associated with an increased waist circumference (OR 1·58; 95 % 1·27, 1·96) and TAG levels (OR 1·33; 95 % CI 1·02, 1·72). At age 43 years, subjects with a more irregular intake at breakfast had an increased risk of the metabolic syndrome 10 years later (OR 1·53; 95 % CI 1·15, 2·04), as well as an increased BMI (OR 1·66; 95 % CI 1·31, 2·10), waist circumference (OR 1·53; 95 % CI 1·23, 1·90) and diastolic blood pressure (OR 1·42; 95 % CI 1·13, 1·78). In conclusion, subjects with a more irregular intake of energy, mostly at breakfast and lunch, appeared to have an increased cardiometabolic risk 10 and 17 years later.

Unequivocal results demonstrating a causal relationship between a disturbance in circadian rhythms and depression have not yet been reported (reviews). However, acute mood changes, such as the antidepressive effect of sleep deprivation, diurnal variations of mood and their interrelationship, are commonly put forward as evidence of the importance of circadian dysregulations in affective disorders. The purpose of the present study is to obtain more insight in the mechanisms underlying these mood changes. The results will be discussed in the context of a recently postulated non-chronobiological explanation.

Earlier studies have suggested that the relationship between diurnal variation of mood and the response to total sleep deprivation (TSD) is clear and unambiguous: improvement of mood during the day prior to TSD (a positive diurnal variation) is followed by a positive response (mood improvement) to TSD, while no improvement or deterioration of mood during the day prior to TSD (a negative diurnal variation) may result in no, or even a negative, TSD response (for references see Van den Hoofdakker). However, these conclusions were based on the results from cross-sectional studies, comparing single TSD effects across individuals. Comparison of sleep deprivation effects within individuals, however, revealed that the course of mood during the day prior to TSD is irrelevant for the TSD response. Accordingly, a favourable response to TSD appeared to be related to the patient's propensity to show diurnal mood variations per se, irrespective of their direction.

The vectorial capacity of Biomphalaria pfeifferi from Ndiangue, Senegal, was investigated with an allopatric isolate of Schistosoma mansoni from Nkolbisson, Cameroon. The snail infection rate after exposure to a single miracidium per snail (MD1) was 56·3%, and 91·6% for snails exposed to 5 miracidia per snail (MD5). The minimum pre-patent period was 21 days. The mean total cercarial production for the MD1 group was 18511 cercariae per snail, and 9757 cercariae for the MD5 group. The maximum production of cercariae for 1 day was 4892 observed in a snail from the MD1 group at day 43 post-infection. The mean longevity of snails was higher in group MD1 (88 days p.i.) than in group MD5 (65 days p.i.). The chronobiological emergence pattern revealed a circadian rhythm with one shedding peak at mid-day. Comparisons are made with the vectorial capacity of the sympatric combination of B. pfeifferi Senegal/S. mansoni Senegal.

The construction of the Diama dam on the Senegal River and the ensuing ecological changes have led to a massive outbreak of Schistosoma mansoni infection in Northern Senegal, associated with very high intensity of infections, due to extremely intense transmission. The vectorial capacity of Biomphalaria pfeifferi from Ndombo, near Richard-Toll was investigated in order to assess the role of the snail–parasite relationship in this particular epidemiological situation. The results revealed an unusually high compatibility between the Senegalese S. mansoni strain and its local snail intermediate host, B. pfeifferi. The snail infection rate after exposure to a single miracidium per snail was 87%. The cercarial production of infected snails was very high, with a mean total production of 50456 cercariae per snail. No significant difference was found in the total cercarial output between snails exposed to 1 miracidium and those exposed to 5 miracidia. The increase in the rate of cercarial output was significantly greater in snails exposed to 5 miracidia, but there was a higher mortality in this group. The chronobiological cercarial production pattern showed a peak around mid-day. The implications of these findings on the epidemiology of schistosomiasis in Northern Senegal are discussed.

L'influence de la période (jour, nuit) et de la fréquence d'alimentation (1 à 4 repas fractionnés ou alimentation continue) a été étudiée sur la croissance et l'efficacité alimentaire chez un silure africain (Heterobranchus longifilis). L'expérience, d'une durée de 56 jours, a été réalisée sur des poissons de 74 g de poids moyen initial. Avec un même taux de rationnement (3 % du poids vif/jour), les poissons nourris la nuit ont une croissance significativement plus élevée que ceux nourris le jour et un nourrissage sur l'ensemble du nycthémère n'apporte pas d'amélioration. Les performances de croissance tendent à augmenter avec l'accroissement de la fréquence d'alimentation quelle que soit la période de nourrissage, et les croissances sont significativement plus élevées avec une alimentation en continu, de 2,36 à 2,64 g.j-1. L'indice de consommation est significativement plus faible pour les poissons nourris en continu que pour ceux recevant une alimentation par repas. Le rapport hépatosomatique est significativement plus élevé chez les poissons nourris la nuit que pour ceux nourris le jour. Par contre, les dépôts de graisse dans la cavité abdominale sont plus importants chez les individus nourris de jour et augmentent avec la fréquence des repas. L'analyse des compositions corporelles globales confirme ces observations. En pratique, il est recommandé de nourrir ce poisson en continu durant la nuit, ce mode d'alimentation conduisant aux meilleures performances de croissance.

Revue à travers les données de la littérature, la dépression apparaît comme un sujet de recherche très important, qui a déjà suscité de nombreuses théories chronobiologiques, souvent fondées sur des ≪critères diagnostiques objectifs≫. En revanche, l’impact thérapeutique de ces approches reste souvent limité à de rares services ultraspécialisés où les patients déprimés sont adressés en dernier recours.

Dans cet article, les auteurs passent en revue quelques-unes des principales données de la littérature, en particulier celles qui concernent les aspects chronobiologiques de la dépression. Les investigations sophistiquées réalisées dans les unités de recherche peuvent avoir certaines conséquences cliniques et pratiques qui sont également évoquées. En effet, une évaluation clinique soigneuse, orientée sur des bases chronobiologiques suffit bien souvent à proposer des traitements individuels assez simples. Parmi ceux-ci, la privation partielle de sommeil (PPS) représente un moyen utile, permettant une amélioration rapide, mais malheureusement souvent imprévisible et transitoire, des troubles de l’humeur. Il semble possible de rendre plus fiables les PPS grâce à des interventions sur la température, la prise de nourriture et l’exposition à la lumiére.

De plus, les auteurs décrivent un moyen possible de pérenniser les effets antidépresseurs de la PPS par des «microprivations de sommeil» réalisées pendant 15 min, à un moment spécifique de la nuit. Les résultats concernant 11 patients déprimés graves soumis à cette méthode sont exposés, 7 de ces sujets étant maintenus depuis 6 à 20 mois dans un état euthymique.

Un des aspects essentiels de la cognition chez l’homme est lié à la qualité de son sommeil qui semble conditionner la fonction de mémorisation aussi bien que d’attention. Il est d’ailleurs remarquable de constater que les molécules hypnotiques peuvent avoir des effets différents sur la cognition, de façon peut-être corrélée à leur action sur les differents stades de sommeil et sûrement liée à la persistance de leurs effets sur la vigilance pendant la journée.

Il est désormais classique de différencier l’anxiété généralisée (AG) de la dépression majeure (DM) par la mise en évidence des variations circadiennes marquées sur les plans clinique, polygraphique, hormonal et physiologique dans la dépression alors qu’une non-rythmicité de l’anxiété généralisée est habituellement revendiquée. Certains rythmes peuvent néanmoins être mis en évidence, bien que de façon moins marquée dans cette pathologie. Ainsi, des variations circadiennes sont souvent notées sur le plan clinique, un maximum d’anxiété et d’attaques de panique se produisant l’après-midi et en début de soirée au moment de l’acmé de la courbe de température centrale. De même, certaines particularités sont notables au niveau de l’analyse des enregistrements polygraphiques de sommeil et des niveaux plasmatiques hormonaux.

Un des faits les plus troublants est de constater une certaine symetrie dans l’expression clinique et polygraphique des troubles dans la dépression majeure et l’anxiété généralisee: la DM est classiquement associée à un réveil très douloureux en milieu de nuit et à une désorganisation de la structure polygraphique du sommeil dans la deuxième partie de la nuit, moments où la température centrale après avoir atteint son niveau minimal amorce une remontée. A l’inverse, l’AG est à son maximum en fin d’après-midi et comporte une insomnie de la première partie de la nuit objectivée par un aspect haché du sommeil observable entre le moment du coucher et le milieu de la nuit, période où la temperature centrale est dans une phase descendante.

Certaines anomalies peuvent être également retrouvées aux niveaux physiologique et biologique. Ces ditférentes observations devraient sans doute, dans l’avenir, susciter des recherches chronobiologiques plus nombreuses et influencer les habitudes de prescription.

The multitype continuous-time Markov branching process has many biological applications where the environmental factors vary in a periodic manner. Circadian or diurnal rhythms in cell kinetics are an important example. It is shown that in the supercritical positively regular case the proportions of individuals of various types converge in probability to a non-random periodic vector, independent of the initial conditions, while the absolute numbers of individuals of various types converge in probability to that vector multiplied by a random variable whose distribution depends on the initial conditions. It is noted that the proofs are straightforward extensions of the well-known results for a constant environment.