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

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

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See detailTwo time pieces for sleep regulation: the circadian clock and the homeostatic hourglass
Cajochen, Christian; Schmidt, Christina; Chellappa, Sarah Laxhmi ULg

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

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See detailNeurophysiological basis of sleep and wakefulness
Chellappa, Sarah Laxhmi ULg; Schmidt, Christina; Cajochen, Christian

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

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See detailUltradian and circadian modulation of dream recall: EEG correlates and age effects
Chellappa, Sarah Laxhmi ULg; Cajochen, Christian

in International Journal of Psychophysiology (2013)

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See detailAcute exposure to blue-enriched light impacts on melatonin and sleep in humans
Chellappa, Sarah Laxhmi ULg; Steiner, Roland; Oelhafen, Peter et al

in Journal of Sleep Research (2012)

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See detailAdaptating test timing to the sleep-wake schedule: effects on diurnal neurobehavioral performance changes in young evening and older morning chronotypes
Schmidt, Christina ULg; Peigneux, Philippe ULg; Cajochen, Christian et al

in Chronobiology International (2012), 29(4), 482-490

The synchrony effect refers to the beneficial impact of temporal matching between the timing of cognitive task administration and preferred time of day for diurnal activity. Aging is often associated with ... [more ▼]

The synchrony effect refers to the beneficial impact of temporal matching between the timing of cognitive task administration and preferred time of day for diurnal activity. Aging is often associated with an advance in sleep-wake timing and concomitant optimal performance levels in the morning. In contrast, young adults often perform better in the evening hours. So far, the synchrony effect has been tested at fixed clock times, neglecting the individual’s sleep-wake schedule and thus introducing confounds such as differences in accumulated sleep pressure or circadian phase that may exacerbate synchrony effects. To probe this hypothesis, we tested older morning and young evening chronotypes with a psychomotor vigilance and a Stroop paradigm once at fixed morning and evening hours and once adapting testing time to their preferred sleep-wake schedule in a within-subject design. We observe a persistence of synchrony effects for overall median reaction times during a psychomotor vigilance task even when testing time is adapted to the specific individual’s sleep-wake schedule. However, data analysis also indicates that time-of-day modulations are weakened under those conditions for incongruent trials on Stroop performance and the slowest reaction times on the psychomotor vigilance task. The latter result suggests that the classically observed synchrony effect may be partially mediated by a series of parameters, such as differences in socio-professional timing constraints, the amount of accumulated sleep need or circadian phase, all leading to differential arousal levels at testing. [less ▲]

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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 detailDepression and sleepiness: A chronobiological approach
Chellappa, Sarah Laxhmi ULg; Cajochen, Christian

in Thorpy, Michael; Billiard, Michael (Eds.) Sleepiness Causes, Consequences and Treatment (2011)

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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 detailHomeostatic sleep pressure and responses to sustained attention in the suprachiasmatic area.
Schmidt, Christina ULg; Collette, Fabienne ULg; Leclercq, Yves ULg et al

in Science (2009), 324(5926), 516-9

Throughout the day, cognitive performance is under the combined influence of circadian processes and homeostatic sleep pressure. Some people perform best in the morning, whereas others are more alert in ... [more ▼]

Throughout the day, cognitive performance is under the combined influence of circadian processes and homeostatic sleep pressure. Some people perform best in the morning, whereas others are more alert in the evening. These chronotypes provide a unique way to study the effects of sleep-wake regulation on the cerebral mechanisms supporting cognition. Using functional magnetic resonance imaging in extreme chronotypes, we found that maintaining attention in the evening was associated with higher activity in evening than morning chronotypes in a region of the locus coeruleus and in a suprachiasmatic area (SCA) including the circadian master clock. Activity in the SCA decreased with increasing homeostatic sleep pressure. This result shows the direct influence of the homeostatic and circadian interaction on the neural activity underpinning human behavior. [less ▲]

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See detailChronotype-dependent performance modulation according to time of day : a functional neuroimaging approach
Schmidt, Christina; Collette, Fabienne ULg; Sterpenich, Virginie et al

in NeuroImage (2008), 41(Suppl. 1),

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See detailOwl or lark? Stroop-related cerebral activity is modulated by time of day and chronotype
Schmidt, Christina; Collette, Fabienne ULg; Sterpenich, Virginie et al

in Journal of Sleep Research (2008), 17(Suppl. 1),

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See detailA Time to Think: Circadian Rhythms in Human Cognition
Schmidt, Christina ULg; Collette, Fabienne ULg; Cajochen, Christian et al

in Cognitive Neuropsychology (2007), 24(7), 755-89

Although peaks and troughs in cognitive performance characterize our daily functioning, time-of-day fluctuations remain marginally considered in the domain of cognitive psychology and neuropsychology ... [more ▼]

Although peaks and troughs in cognitive performance characterize our daily functioning, time-of-day fluctuations remain marginally considered in the domain of cognitive psychology and neuropsychology. Here, we attempt to summarize studies looking at the effects of sleep pressure, circadian variations, and chronotype on cognitive functioning in healthy subjects. The picture that emerges from this assessment is that beyond physiological variables, time-of-day modulations affect performance on a wide range of cognitive tasks measuring attentional capacities, executive functioning, and memory. These performance fluctuations are also contingent upon the chronotype, which reflects interindividual differences in circadian preference, and particularly upon the synchronicity between the individuals' peak periods of circadian arousal and the time of the day at which testing occurs. In themselves, these conclusions should direct both the clinician's and the researcher's attention towards the utmost importance to account for time-of-day parameters when assessing cognitive performance in patients and healthy volunteers. [less ▲]

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See detailEncoding Difficulty Promotes Postlearning Changes in Sleep
Schmidt, Christina ULg; Peigneux, Philippe ULg; Muto, Vincenzo ULg et al

in Journal of Neuroscience (2006), 26(35), 8976-8982

Learning-dependent increases in sleep spindle density have been reported during nocturnal sleep immediately after the learning session. Here, we investigated experience-dependent changes in daytime sleep ... [more ▼]

Learning-dependent increases in sleep spindle density have been reported during nocturnal sleep immediately after the learning session. Here, we investigated experience-dependent changes in daytime sleep EEG activity after declarative learning of unrelated word pairs. At weekly intervals, 13 young male volunteers spent three 24 h sessions in the laboratory under carefully controlled homeostatic and circadian conditions. At approximately midday, subjects performed either one of two word-pair learning tasks or a matched nonlearning control task, in a counterbalanced order. The two learning lists differed in the level of concreteness of the words used, resulting in an easier and a more difficult associative encoding condition, as confirmed by performance at immediate cued recall. Subjects were then allowed to sleep for 4 h; afterward, delayed cued recall was tested. Compared with the control condition, sleep EEG spectral activity in the low spindle frequency range and the density of low-frequency sleep spindles (11.25–13.75 Hz) were both significantly increased in the left frontal cortex after the difficult but not after the easy encoding condition. Furthermore, we found positive correlations between theseEEG changes during sleep and changes in memory performance between pre nap and post-nap recall sessions. These results indicate that, like during nocturnal sleep, daytime sleep EEG oscillations including spindle activity are modified after declarative learning of word pairs. Furthermore, we demonstrate here that the nature of the learning material is a determinant factor for sleep-related alterations after declarative learning. [less ▲]

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