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See detailCircadian and homeostatic modulation of cerebral correlates of vigilance under high and low sleep pressure
Maire, Micheline; Reichert, Carolin; Phillips, Christophe ULg et al

Scientific conference (2015, September)

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See detailCircadian and homeostatic modulation of cognition-related cerebral activity in humans
Schmidt, Christina ULg; Maire, Micheline; Reichert, Carolin et al

Conference (2012)

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See detailCircadian and homeostatic modulation of cognition-related cerebral activity in humans
Schmidt, Christina ULg; Maire, Micheline; Reichert, Carolin et al

in Journal of Sleep Research (2012), 21(Suppl.1), 13

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See detailCircadian and homeostatic regulation of sleep
Schmidt, Christina ULg

Scientific conference (2014)

Detailed reference viewed: 13 (0 ULg)
See detailCircadian and homeostatic regulation of sleep
Schmidt, Christina ULg

Scientific conference (2013)

Detailed reference viewed: 12 (0 ULg)
See detailCircadian and homeostatic regulation of sleep
Schmidt, Christina ULg

Scientific conference (2012)

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See detailCircadian and homeostatic regulation of sleep
Schmidt, Christina ULg

Scientific conference (2011)

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See detailCircadian and homeostatic regulation of sleepiness and cognition and its neuronal underpinnings
Schmidt, Christina ULg; Chellappa, Sarah Laxhmi ULg; Chellappa, Sarah Laxhmi ULg

in Garbarino, Sergio (Ed.) Sleepiness and Human Impact Assessment (2014)

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See detailCircadian and sleep homeostatic regulation of cerebral correlates of working memory: time of day matters
Reichert, Carolin; Maire, Micheline; Gabel, Virginie et al

Conference (2015, June)

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See detailThe Circadian Clock and the homeostatic hourglass - two timepieces controlling Sleep and wakefulness
Chellappa, Sarah Laxhmi ULg; Cajochen, Christian

in Albercht, Urs (Ed.) The circadian clock (2010)

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See detailCircadian preference modulates the neural substrate of conflict processing across the day
Schmidt, Christina ULg; Peigneux, Philippe ULg; Leclercq, Yves ULg et al

in PLoS ONE (2012), 7(1), 29658

Human morning and evening chronotypes differ in their preferred timing for sleep and wakefulness, as well as in optimal daytime periods to cope with cognitive challenges. Recent evidence suggests that ... [more ▼]

Human morning and evening chronotypes differ in their preferred timing for sleep and wakefulness, as well as in optimal daytime periods to cope with cognitive challenges. Recent evidence suggests that these preferences are not a simple by-product of socio-professional timing constraints, but can be driven by inter-individual differences in the expression of circadian and homeostatic sleep-wake promoting signals. Chronotypes thus constitute a unique tool to access the interplay between those processes under normally entrained day-night conditions, and to investigate how they impinge onto higher cognitive control processes. Using functional magnetic resonance imaging (fMRI), we assessed the influence of chronotype and time-of-day on conflict processing-related cerebral activity throughout a normal waking day. Sixteen morning and 15 evening types were recorded at two individually adapted time points (1.5 versus 10.5 hours spent awake) while performing the Stroop paradigm. Results show that interference-related hemodynamic responses are maintained or even increased in evening types from the subjective morning to the subjective evening in a set of brain areas playing a pivotal role in successful inhibitory functioning, whereas they decreased in morning types under the same conditions. Furthermore, during the evening hours, activity in a posterior hypothalamic region putatively involved in sleep-wake regulation correlated in a chronotype-specific manner with slow wave activity at the beginning of the night, an index of accumulated homeostatic sleep pressure. These results shed light into the cerebral mechanisms underlying inter-individual differences of higher-order cognitive state maintenance under normally entrained day-night conditions. [less ▲]

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See detailThe circadian regulation of sleep: impact of a functional ADA-polymorphism and its association to working memory improvements.
Reichert, Carolin F.; Maire, Micheline; Gabel, Virginie et al

in PloS one (2014), 9(12), 113734

Sleep is regulated in a time-of-day dependent manner and profits working memory. However, the impact of the circadian timing system as well as contributions of specific sleep properties to this beneficial ... [more ▼]

Sleep is regulated in a time-of-day dependent manner and profits working memory. However, the impact of the circadian timing system as well as contributions of specific sleep properties to this beneficial effect remains largely unexplored. Moreover, it is unclear to which extent inter-individual differences in sleep-wake regulation depend on circadian phase and modulate the association between sleep and working memory. Here, sleep electroencephalography (EEG) was recorded during a 40-h multiple nap protocol, and working memory performance was assessed by the n-back task 10 times before and after each scheduled nap sleep episode. Twenty-four participants were genotyped regarding a functional polymorphism in adenosine deaminase (rs73598374, 12 G/A-, 12 G/G-allele carriers), previously associated with differences in sleep-wake regulation. Our results indicate that genotype-driven differences in sleep depend on circadian phase: heterozygous participants were awake longer and slept less at the end of the biological day, while they exhibited longer non rapid eye movement (NREM) sleep and slow wave sleep concomitant with reduced power between 8-16 Hz at the end of the biological night. Slow wave sleep and NREM sleep delta EEG activity covaried positively with overall working memory performance, independent of circadian phase and genotype. Moreover, REM sleep duration benefitted working memory particularly when occurring in the early morning hours and specifically in heterozygous individuals. Even though based on a small sample size and thus requiring replication, our results suggest genotype-dependent differences in circadian sleep regulation. They further indicate that REM sleep, being under strong circadian control, boosts working memory performance according to genotype in a time-of-day dependent manner. Finally, our data provide first evidence that slow wave sleep and NREM sleep delta activity, majorly regulated by sleep homeostatic mechanisms, is linked to working memory independent of the timing of the sleep episode within the 24-h cycle. [less ▲]

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See detailCircadian Rhythm of Heart Rate and Heart Rate Variability
Massin, M. M.; Maeyns, K.; Withofs, Nadia ULg et al

in Archives of Disease in Childhood (2000), 83(2), 179-82

BACKGROUND: Measurements of heart rate variability (HRV) are increasingly used as markers of cardiac autonomic activity. AIM: To examine circadian variation in heart rate and HRV in children. SUBJECTS: A ... [more ▼]

BACKGROUND: Measurements of heart rate variability (HRV) are increasingly used as markers of cardiac autonomic activity. AIM: To examine circadian variation in heart rate and HRV in children. SUBJECTS: A total of 57 healthy infants and children, aged 2 months to 15 years, underwent ambulatory 24 hour Holter recording. Monitoring was also performed on five teenagers with diabetes mellitus and subclinical vagal neuropathy in order to identify the origin of the circadian variation in HRV. METHODS: The following variables were determined hourly: mean RR interval, four time domain (SDNN, SDNNi, rMSSD, and pNN50) and four frequency domain indices (very low, low and high frequency indices, low to high frequency ratio). A chronobiological analysis was made by cosinor method for each variable. RESULTS: A significant circadian variation in heart rate and HRV was present from late infancy or early childhood, characterised by a rise during sleep, except for the low to high frequency ratio that increased during daytime. The appearance of these circadian rhythms was associated with sleep maturation. Time of peak variability did not depend on age. Circadian variation was normal in patients with diabetes mellitus. CONCLUSION: We have identified a circadian rhythm of heart rate and HRV in infants and children. Our data confirm a progressive maturation of the autonomic nervous system and support the hypothesis that the organisation of sleep, associated with sympathetic withdrawal, is responsible for these rhythms. [less ▲]

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See detailCircadian Rhythm Sleep Disorder: Genetic and Environmental Factors
Chellappa, Sarah Laxhmi ULg; Viola, Antoine; Mongrain, Valerie

in Kushida, Clete (Ed.) Encyclopaedia of Sleep (in press)

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See detailCircadian rhythms and the induction of flowering in the long-day grass Lolium temulentum L.
Périlleux, Claire ULg; Bernier, Georges ULg; Kinet, Jean Marie

in Plant, Cell & Environment (1994), 17(6), 755-761

Plants of Lolium temulentum L. strain Ceres were grown in 8-h short day (SD) for 45 d before being exposed either to a single long day (LD) or to a single 8-h SD given during an extended dark period. For ... [more ▼]

Plants of Lolium temulentum L. strain Ceres were grown in 8-h short day (SD) for 45 d before being exposed either to a single long day (LD) or to a single 8-h SD given during an extended dark period. For LD induction, the critical photoperiod was between 12 and 14 h, and more than 16 h were needed for a maximal flowering response. During exposure to a single 24-h LD, the translocation of the floral stimulus began between the fourteenth and the sixteenth hours after the start of the light period, and was completed by the twenty-fourth hour. Full flowering was also induced by one 8-h SD beginning 4 or 28 h after the start of a 40-h dark period, i.e. by shifting 12 h forward or beyond the usual SD. The effectiveness of a so-called 'displaced short day' (DSD) was not affected by light quality and light intensity. With a mixture of incandescent and fluorescent lights at a total photosynthetic photon flux density of 400 µmol m-2 s-1, a 4-h light exposure beginning 4 h after the start of a 40-h dark period was sufficient to induce 100 flowering. The flower-inducing effect of a single 8-h DSD was also assessed during a 64-h dark period. Results revealed two maxima at a 20-h interval. This fluctuation in light sensitivity suggests that a circadian rhythm is involved in the control of flowering of L. temulentum. [less ▲]

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See detailCircadian rhythms and the induction of flowering in the long-day plant Lolium temulentum L.
Périlleux, Claire ULg; Bernier, Georges; Kinet, Jean-Marie

in Physiologia Plantarum (1991), 85

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See detailCircadian Synchronization of Liver Regeneration in Adult Rats: The Role Played by Adrenal Hormones
Barbason, Hervé ULg; Bouzahzah, B.; Herens, Christian ULg et al

in Cell and Tissue Kinetics (1989), 22(6), 451-460

The role played by the adrenal hormones in the regulation of liver proliferation in adult rats was investigated under various experimental conditions. In untreated control groups, cell growth was very low ... [more ▼]

The role played by the adrenal hormones in the regulation of liver proliferation in adult rats was investigated under various experimental conditions. In untreated control groups, cell growth was very low and endogenous corticosterone levels showed a clearly-defined circadian rhythm with a peak in the evening. Adrenalectomy depressed the level of endogenous corticosterone immediately and the growth rate of the liver increased significantly. We were able to prevent this effect by repeated injections of corticosterone at physiological doses. After a 1/3 hepatectomy and a sham-operation, the corticosterone blood level maintained its normal circadian pattern with the exception of a transient increase during the first two post-operative hours. After a hepatectomy of this kind, a negative correlation was found to exist between the adrenal hormone level and the waves of DNA synthesis; the subsequent mitoses appeared in two successive circadian waves of decreasing amplitude, a maximum value being reached in the morning. In rats submitted to a 1/3 hepatectomy and an adrenalectomy simultaneously, the endogenous corticosterone level fell significantly after a post-operative peak. The regenerating pattern was completely different from that induced by 1/3 hepatectomy alone. The rise in the labelling index began earlier and rose to significantly higher values; it was then followed by a single large mitotic wave without any circadian rhythm. These results favour the hypothesis that adrenal hormones have a significant effect on the negative control of liver regeneration. Circadian changes in the corticosterone level were responsible for the nycthemeral pattern observed in the regenerating liver after a partial hepatectomy. The results show a marked inhibition of the G1-S transition, particularly in the evening, when the endogenous corticosterone concentration was at its highest. Also discussed is the relationship between corticoids and 'chalones', which synergetically inhibit the passage from G0 into the cell cycle. [less ▲]

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