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 detailLight modulation of human sleep depends on a polymorphism in the clock gene PER3
Chellappa, Sarah Laxhmi ULg; Viola, Antoine; Schmidt, Christina ULg et al

in Behavioural Brain Research (2014), 271

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See detailLight modulation of human sleep depends on a polymorphism in the clock gene Period3.
Chellappa, Sarah Laxhmi ULg; Viola, Antoine U.; Schmidt, Christina ULg et al

in Behavioural brain research (2014), 271

Non-image-forming (NIF) responses to light powerfully modulate human physiology. However, it remains scarcely understood how NIF responses to light modulate human sleep and its EEG hallmarks, and if there ... [more ▼]

Non-image-forming (NIF) responses to light powerfully modulate human physiology. However, it remains scarcely understood how NIF responses to light modulate human sleep and its EEG hallmarks, and if there are differences across individuals. Here we investigated NIF responses to light on sleep in individuals genotyped for the PERIOD3 (PER3) variable-number tandem-repeat (VNTR) polymorphism. Eighteen healthy young men (20-28 years; mean+/-SEM: 25.9+/-1.2) homozygous for the PER3 polymorphism were matched by age, body-mass index, and ethnicity. The study protocol comprised a balanced cross-over design during the winter, during which participants were exposed to either light of 40lx at 6500K (blue-enriched) or light at 2500K (non-blue enriched), during 2h in the evening. Compared to light at 2500K, light at 6500K induced a significant increase in all-night NREM sleep slow-wave activity (SWA: 1.0-4.5Hz) in the occipital cortex for PER3(5/5) individuals, but not for PER3(4/4) volunteers. Dynamics of SWA across sleep cycles revealed increased occipital NREM sleep SWA for virtuallyall sleep episode only for PER3(5/5) individuals. Furthermore, they experienced light at 6500K as significantly brighter. Intriguingly, this subjective perception of brightness significantly predicted their increased occipital SWA throughout the sleep episode. Our data indicate that humans homozygous for the PER3(5/5) allele are more sensitive to NIF light effects, as indexed by specific changes in sleep EEG activity. Ultimately, individual differences in NIF light responses on sleep may depend on a clock gene polymorphism involved in sleep-wake regulation. [less ▲]

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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 detailEffects of Artificial Dawn and Morning Blue Light on Daytime Cognitive Performance, Well-being, Cortisol and Melatonin Levels.
Gabel, Virginie; Maire, Micheline; Reichert, Carolin F. et al

in Chronobiology International (2013), 30(8), 988-97

Light exposure elicits numerous effects on human physiology and behavior, such as better cognitive performance and mood. Here we investigated the role of morning light exposure as a countermeasure for ... [more ▼]

Light exposure elicits numerous effects on human physiology and behavior, such as better cognitive performance and mood. Here we investigated the role of morning light exposure as a countermeasure for impaired cognitive performance and mood under sleep restriction (SR). Seventeen participants took part of a 48h laboratory protocol, during which three different light settings (separated by 2 wks) were administered each morning after two 6-h sleep restriction nights: a blue monochromatic LED (light-emitting diode) light condition (BL; 100 lux at 470 nm for 20 min) starting 2 h after scheduled wake-up time, a dawn-simulating light (DsL) starting 30 min before and ending 20 min after scheduled wake-up time (polychromatic light gradually increasing from 0 to 250 lux), and a dim light (DL) condition for 2 h beginning upon scheduled wake time (<8 lux). Cognitive tasks were performed every 2 h during scheduled wakefulness, and questionnaires were administered hourly to assess subjective sleepiness, mood, and well-being. Salivary melatonin and cortisol were collected throughout scheduled wakefulness in regular intervals, and the effects on melatonin were measured after only one light pulse. Following the first SR, analysis of the time course of cognitive performance during scheduled wakefulness indicated a decrease following DL, whereas it remained stable following BL and significantly improved after DsL. Cognitive performance levels during the second day after SR were not significantly affected by the different light conditions. However, after both SR nights, mood and well-being were significantly enhanced after exposure to morning DsL compared with DL and BL. Melatonin onset occurred earlier after morning BL exposure, than after morning DsL and DL, whereas salivary cortisol levels were higher at wake-up time after DsL compared with BL and DL. Our data indicate that exposure to an artificial morning dawn simulation light improves subjective well-being, mood, and cognitive performance, as compared with DL and BL, with minimal impact on circadian phase. Thus, DsL may provide an effective strategy for enhancing cognitive performance, well-being, and mood under mild sleep restriction. [less ▲]

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See detailAcute exposure to evening blue-enriched light impacts on human sleep
Chellappa, Sarah Laxhmi ULg; Steiner, Roland; Oelhafen, Peter et al

in Journal of Sleep Research (2013)

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See detailAge effects on spectral electroencephalogram activity prior to dream recall.
Chellappa, Sarah Laxhmi ULg; Munch, Mirjam; Knoblauch, Vera et al

in Journal of Sleep Research (2012), 21(3), 247-56

Ageing is associated with marked changes in sleep timing, structure and electroencephalographic (EEG) activity. Older people exhibit less slow-wave and spindle activity during non-rapid eye movement (NREM ... [more ▼]

Ageing is associated with marked changes in sleep timing, structure and electroencephalographic (EEG) activity. Older people exhibit less slow-wave and spindle activity during non-rapid eye movement (NREM) sleep, together with attenuated levels of rapid eye movement (REM) sleep as compared to young individuals. However, the extent to which these age-related changes in sleep impact on dream processing remains largely unknown. Here we investigated NREM and REM sleep EEG activity prior to dream recall and no recall in 17 young (20-31 years) and 15 older volunteers (57-74 years) during a 40 h multiple nap protocol. Dream recall was assessed immediately after each nap. During NREM sleep prior to dream recall, older participants displayed higher frontal EEG delta activity (1-3 Hz) and higher centro-parietal sigma activity (12-15 Hz) than the young volunteers. Conversely, before no recall, older participants had less frontal-central delta activity and less sigma activity in frontal, central and parietal derivations than the young participants. REM sleep was associated to age-related changes, such that older participants had less frontal-central alpha (10-12 Hz) and beta (16-19 Hz) activity, irrespective of dream recall and no recall. Our data indicate that age-related differences in dream recall seem to be directly coupled to specific frequency and topography EEG patterns, particularly during NREM sleep. Thus, the spectral correlates of dreaming can help to understand the cortical pathways of dreaming. [less ▲]

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See detailInterindividual differences in circadian rhythmicity and sleep homeostasis in older people: effect of a PER3 polymorphism.
Viola, Antoine U.; Chellappa, Sarah Laxhmi ULg; Archer, Simon N. et al

in Neurobiology of Aging (2012), 33(5), 101017-27

Aging is associated with marked changes in the timing, consolidation and structure of sleep. Older people wake up frequently, get up earlier and have less slow wave sleep than young people, although the ... [more ▼]

Aging is associated with marked changes in the timing, consolidation and structure of sleep. Older people wake up frequently, get up earlier and have less slow wave sleep than young people, although the extent of these age-related changes differs considerably between individuals. Interindividual differences in homeostatic sleep regulation in young volunteers are associated with the variable-number, tandem-repeat (VNTR) polymorphism (rs57875989) in the coding region of the circadian clock gene PERIOD3 (PER3). However, predictors of these interindividual differences have yet to be identified in older people. Sleep electroencephalographic (EEG) characteristics and circadian rhythms were assessed in 26 healthy older volunteers (55-75 years) selected on the basis of homozygosity for either the long or short allele of the PER3 polymorphism. Homozygosity for the longer allele (PER3(5/5)) associated with a phase-advance in the circadian melatonin profile and an earlier occurrence of the melatonin peak within the sleep episode. Furthermore, older PER3(5/5) participants accumulated more nocturnal wakefulness, had increased EEG frontal delta activity (0.75-1.50 Hz), and decreased EEG frontal sigma activity (11-13 Hz) during non-rapid eye movement (REM) sleep compared with PER3(4/4) participants. Our results indicate that the polymorphism in the clock gene PER3 may contribute to interindividual differences in sleep and circadian physiology in older people. [less ▲]

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See detailHuman melatonin and alerting response to blue-enriched light depend on a polymorphism in the clock gene PER3.
Chellappa, Sarah Laxhmi ULg; Viola, Antoine U.; Schmidt, Christina et al

in Journal of Clinical Endocrinology and Metabolism (2012), 97(3), 433-7

CONTEXT: Light exposure, particularly at the short-wavelength range, triggers several nonvisual responses in humans. However, the extent to which the melatonin-suppressing and alerting effect of light ... [more ▼]

CONTEXT: Light exposure, particularly at the short-wavelength range, triggers several nonvisual responses in humans. However, the extent to which the melatonin-suppressing and alerting effect of light differs among individuals remains unknown. OBJECTIVE: Here we investigated whether blue-enriched polychromatic light impacts differentially on melatonin and subjective and objective alertness in healthy participants genotyped for the PERIOD3 (PER3) variable-number, tandem-repeat polymorphism. DESIGN, SETTING, AND PARTICIPANTS: Eighteen healthy young men homozygous for the PER3 polymorphism (PER3(5/5)and PER3(4/4)) underwent a balanced crossover design during the winter season, with light exposure to compact fluorescent lamps of 40 lux at 6500 K and at 2500 K during 2 h in the evening. RESULTS: In comparison to light at 2500 K, blue-enriched light at 6500 K induced a significant suppression of the evening rise in endogenous melatonin levels in PER3(5/5) individuals but not in PER3(4/4). Likewise, PER3(5/5) individuals exhibited a more pronounced alerting response to light at 6500 K than PER3(4/4) volunteers. Waking electroencephalographic activity in the theta range (5-7 Hz), a putative correlate of sleepiness, was drastically attenuated during light exposure at 6500 K in PER3(5/5) individuals as compared with PER3(4/4). CONCLUSIONS: We provide first evidence that humans homozygous for the PER3 5/5 allele are particularly sensitive to blue-enriched light, as indexed by the suppression of endogenous melatonin and waking theta activity. Light sensitivity in humans may be modulated by a clock gene polymorphism implicated in the sleep-wake regulation. [less ▲]

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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 detailHigher frontal EEG synchronization in young women with major depression: a marker for increased homeostatic sleep pressure?
Birchler-Pedross, Angelina; Frey, Sylvia; Chellappa, Sarah Laxhmi ULg et al

in Sleep (2011), 34(12), 1699-706

STUDY OBJECTIVES: Major depressive disorder (MDD) is often associated with disturbances in circadian and/or sleep-wake dependent processes, which both regulate daytime energy and sleepiness levels. DESIGN ... [more ▼]

STUDY OBJECTIVES: Major depressive disorder (MDD) is often associated with disturbances in circadian and/or sleep-wake dependent processes, which both regulate daytime energy and sleepiness levels. DESIGN: Analysis of continuous electroencephalographic (EEG) recordings during 40 h of extended wakefulness under constant routine conditions. Artifact-free EEG samples derived from 12 locations were subjected to spectral analysis. Additionally, half-hourly ratings of subjective tension and sleepiness levels and salivary melatonin measurements were collected. SETTING: Centre for Chronobiology, Psychiatric Hospitals of the University of Basel, Switzerland. PARTICIPANTS: Eight young healthy women and 8 young untreated women with MDD. INTERVENTIONS: N/A. MEASUREMENTS AND RESULTS: MDD women exhibited higher frontal low-frequency (FLA) EEG activity (0.5-5.0 Hz) during extended wakefulness than controls, particularly during the night. Enhanced FLA was paralleled by higher levels of subjective sleepiness and tension. In MDD women, overall FLA levels correlated positively with depression scores. The timing of melatonin onset did not significantly differ between the two groups, but the nocturnal secretion of salivary melatonin was significantly attenuated in MDD women. CONCLUSIONS: Our data imply that young women with MDD live on a higher homeostatic sleep pressure level, as indexed by enhanced FLA during wakefulness. Its positive correlation with depression scores indicates a possible functional relationship. High FLA could reflect a use-dependent phenomenon in depression (enhanced cognitive rumination or tension) and/or an attenuated circadian arousal signal. [less ▲]

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See detailCan light make us bright? Effects of light on cognition and sleep.
Chellappa, Sarah Laxhmi ULg; Gordijn, Marijke C. M.; Cajochen, Christian

in Progress in Brain Research (2011), 190

Light elicits robust nonvisual effects on numerous physiological and behavioral variables, such as the human sleep-wake cycle and cognitive performance. Light effects crucially rely on properties such as ... [more ▼]

Light elicits robust nonvisual effects on numerous physiological and behavioral variables, such as the human sleep-wake cycle and cognitive performance. Light effects crucially rely on properties such as dose, duration, timing, and wavelength. Recently, the use of methods such as fMRI to assess light effects on nonvisual brain responses has revealed how light can optimize brain function during specific cognitive tasks, especially in tasks of sustained attention. In this chapter, we address two main issues: how light impinges on cognition via consolidation of human sleep-wake cycles; and how light directly impacts on sleep and cognition, in particular in tasks of sustained attention. A thorough understanding of how light affects sleep and cognitive performance may help to improve light settings at home and at the workplace in order to improve well-being. [less ▲]

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See detailCortical activation patterns herald successful dream recall after NREM and REM sleep.
Chellappa, Sarah Laxhmi ULg; Frey, Sylvia; Knoblauch, Vera et al

in Biological Psychology (2011), 87(2), 251-6

Dreaming pertains to both REM and NREM sleep. However, frequency and regional specific differences in EEG activity remains controversial. We investigated NREM and REM sleep EEG power density associated ... [more ▼]

Dreaming pertains to both REM and NREM sleep. However, frequency and regional specific differences in EEG activity remains controversial. We investigated NREM and REM sleep EEG power density associated with and without dream recall in 17 young subjects during a 40-h multiple nap protocol under constant routine conditions. NREM sleep was associated with lower EEG power density for dream recall in the delta range, particularly in frontal derivations, and in the spindle range in centro-parietal derivations. REM sleep was associated with low frontal alpha activity and with high alpha and beta activity in occipital derivations. Our data indicate that specific EEG frequency- and topography changes underlie differences between dream recall and no recall after both NREM and REM sleep awakening. This dual NREM-REM sleep modulation holds strong implications for the mechanistic understanding of this complex ongoing cognitive process. [less ▲]

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See detailNon-visual effects of light on melatonin, alertness and cognitive performance: can blue-enriched light keep us alert?
Chellappa, Sarah Laxhmi ULg; Steiner, Roland; Blattner, Peter et al

in PLoS ONE (2011), 6(1), 16429

BACKGROUND: Light exposure can cascade numerous effects on the human circadian process via the non-imaging forming system, whose spectral relevance is highest in the short-wavelength range. Here we ... [more ▼]

BACKGROUND: Light exposure can cascade numerous effects on the human circadian process via the non-imaging forming system, whose spectral relevance is highest in the short-wavelength range. Here we investigated if commercially available compact fluorescent lamps with different colour temperatures can impact on alertness and cognitive performance. METHODS: Sixteen healthy young men were studied in a balanced cross-over design with light exposure of 3 different light settings (compact fluorescent lamps with light of 40 lux at 6500K and at 2500K and incandescent lamps of 40 lux at 3000K) during 2 h in the evening. RESULTS: Exposure to light at 6500K induced greater melatonin suppression, together with enhanced subjective alertness, well-being and visual comfort. With respect to cognitive performance, light at 6500K led to significantly faster reaction times in tasks associated with sustained attention (Psychomotor Vigilance and GO/NOGO Task), but not in tasks associated with executive function (Paced Visual Serial Addition Task). This cognitive improvement was strongly related with attenuated salivary melatonin levels, particularly for the light condition at 6500K. CONCLUSIONS: Our findings suggest that the sensitivity of the human alerting and cognitive response to polychromatic light at levels as low as 40 lux, is blue-shifted relative to the three-cone visual photopic system. Thus, the selection of commercially available compact fluorescent lights with different colour temperatures significantly impacts on circadian physiology and cognitive performance at home and in the workplace. [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 detailWhat keeps us awake? The role of clocks and hourglasses, light, and melatonin.
Cajochen, Christian; Chellappa, Sarah Laxhmi ULg; Schmidt, Christina

in International Review of Neurobiology (2010), 93

What is it that keeps us awake? Our assumption is that we consciously control our daily activities including sleep-wake behavior, as indicated by our need to make use of an alarm clock to wake up in the ... [more ▼]

What is it that keeps us awake? Our assumption is that we consciously control our daily activities including sleep-wake behavior, as indicated by our need to make use of an alarm clock to wake up in the morning in order to be at work on time. However, when we travel across multiple time zones or do shift work, we realize that our intentionally planned timings to rest and to remain active can interfere with an intrinsic regulation of sleep/wake cycles. This regulation is driven by a small region in the anterior hypothalamus of the brain, termed as the "circadian clock". This clock spontaneously synchronizes with the environmental light-dark cycle, thus enabling all organisms to adapt to and anticipate environmental changes. As a result, the circadian clock actively gates sleep and wakefulness to occur in synchrony with the light-dark cycles. Indeed, our internal clock is our best morning alarm clock, since it shuts off melatonin production and boosts cortisol secretion and heart rate 2-3h prior awakening from Morpheus arms. The main reason most of us still use artificial alarm clocks is that we habitually carry on a sleep depth and/or the sleep-wake timing is not ideally matched with our social/work schedule. This in turn can lead hourglass processes, as indexed by accumulated homeostatic sleep need over time, to strongly oppose the clock. To add to the complexity of our sleep and wakefulness behavior, light levels as well as exogenous melatonin can impinge on the clock, by means of their so-called zeitgeber (synchronizer) role or by acutely promoting sleep or wakefulness. Here we attempt to bring a holistic view on how light, melatonin, and the brain circuitry underlying circadian and homeostatic processes can modulate sleep and in particular alertness, by actively promoting awakening/arousal and sleep at certain times during the 24-h day. [less ▲]

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