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Dr Nayantara Santhi


Research Fellow at the Surrey Sleep Research Centre
PhD
+44 (0)1483 686749
17 MA 00

University roles and responsibilities

  • Research Fellow at the Surrey Sleep Research Centre
  • Member - Section of Sleep

My publications

Publications

Chang AM, Santhi N, St Hilaire M, Gronfier C, Bradstreet DS, Duffy JF, Lockley SW, Kronauer RE, Czeisler CA (2012) Human responses to bright light of different durations., J Physiol 590 (Pt 13) pp. 3103-3112
Light exposure in the early night induces phase delays of the circadian rhythm in melatonin in humans. Previous studies have investigated the effect of timing, intensity, wavelength, history and pattern of light stimuli on the human circadian timing system. We present results from a study of the duration?response relationship to phase-delaying bright light. Thirty-nine young healthy participants (16 female; 22.18±3.62 years) completed a 9-day inpatient study. Following three baseline days, participants underwent an initial circadian phase assessment procedure in dim light (
Cain SW, Dennison CF, Zeitzer JM, Guzik AM, Khalsa SB, Santhi N, Schoen MW, Czeisler CA, Duffy JF (2010) Sex differences in phase angle of entrainment and melatonin amplitude in humans., J Biol Rhythms 25 (4) pp. 288-296
Studies of sex differences in the timing of human circadian rhythms have reported conflicting results. This may be because the studies conducted to date have not controlled for the masking effects of the rest activity cycle on the circadian rhythms being assessed. In the present analysis of data collected under controlled conditions, we examined sex differences in the timing of circadian rhythms while minimizing masking from behavioral and environmental factors using a constant routine (CR) protocol. All participants (28 women and 28 men paired by habitual wake time; age range, 18 30 years) maintained a regular self selected sleep wake schedule at home prior to the study. After 3 baseline days in the laboratory, participants began a CR. Women were found to have a significantly higher melatonin amplitude and lower temperature amplitude than men. While sleep timing was the same between the 2 groups, the timing of the circadian rhythms of core body temperature and pineal melatonin secretion was earlier relative to sleep time in women as compared to men. Sleep therefore occurred at a later biological time for women than men, despite being at the same clock time. Given that sleep propensity and structure vary with circadian phase and are impacted by circulating melatonin, these findings may have important implications for understanding sex differences in sleep timing and duration, diurnal preference, and the prevalence of sleep disorders such as insomnia.
Santhi N, Lazar AS, Mccabe P, Archer SN, Groeger JA, Dijk D-J (2014) Circadian regulation in cognition and subjective assessment of waking function in humans, JOURNAL OF SLEEP RESEARCH 23 pp. 48-48 WILEY-BLACKWELL
Santhi N, Thorne HC, Van Der Veen DR, Johnsen S, Mills SL, Hommes V, Schlangen LJM, Archer SN, Dijk DJ (2012) The spectral composition of evening light and individual differences in the suppression of melatonin and delay of sleep in humans, Journal of Pineal Research 53 (1) pp. 47-59
The effect of light on circadian rhythms and sleep is mediated by a multi-component photoreceptive system of rods, cones and melanopsinexpressing intrinsically photosensitive retinal ganglion cells. The intensity and spectral sensitivity characteristics of this system are to be fully determined.Whether the intensity and spectral composition of light exposure at home in the evening is such that it delays circadian rhythms and sleep also remains to be established. We monitored light exposure at home during 6-8 wk and assessed light effects on sleep and circadian rhythms in the laboratory. Twenty-two women and men (23.1 ± 4.7 yr) participated in a six-way, cross-over design using polychromatic light conditions relevant to the light exposure at home, but with reduced, intermediate or enhanced efficacy with respect to the photopic and melanopsin systems. The evening rise of melatonin, sleepiness and EEG-assessed sleep onset varied significantly (P
Lázár AS, Slak A, Lo JC, Santhi N, von Schantz M, Archer SN, Groeger JA, Dijk DJ (2012) Sleep, diurnal preference, health, and psychological well-being: a prospective single-allelic-variation study., Chronobiol Int 29 (2) pp. 131-146
Individual differences in sleep and diurnal preference associate with physical and mental health characteristics, but few genetic determinants of these differences have been identified. A variable number tandem repeat (VNTR) polymorphism in the PERIOD3 (PER3) gene (rs57875989) has been reported to associate with diurnal preference, i.e., preferred timing of waking and sleep. Here, the authors investigate in a prospective single-candidate genetic variant study whether allelic variation for this polymorphism associates also with reported actual sleep timing and sleep duration, as well as psychological and health measures. Six hundred and seventy-five subjects, aged 20 to 35 yrs, completed questionnaires to assess sleep and psychological and health characteristics and were genotyped for the PER3 VNTR. Homozygosity for the longer allele (PER3(5/5)) of the VNTR was associated with increased morning preference, earlier wake time and bedtime, and reduced daytime sleepiness. Separate analyses of work and rest days demonstrated that the increase in time in bed during rest days was greatest in PER3(5/5) homozygotes. PER3 genotype modified the effects of sleep timing and duration on fluid intelligence and body mass index. Genotype was not associated with physical or psychological characteristics as assessed by the SF-36 Health Questionnaire, the General Health Questionnaire, the Big Five Inventory, the Behavioral Inhibition System-Behavioral Activation System scales, and the Positive and Negative Affect Scale, even though these measures varied significantly with diurnal preference as assessed by the Morningness-Eveningness Questionnaire. Whereas diurnal preference also predicts mental health and psychological characteristics, as well as sleep timing, the PER3 VNTR specifically affects measures of sleep timing and may also modify the effects of sleep on health outcome measures.
Hasan S, Santhi N, Lazar AS, Slak A, Lo J, von Schantz M, Archer SN, Johnston JD, Dijk DJ (2012) Assessment of circadian rhythms in humans: comparison of real-time fibroblast reporter imaging with plasma melatonin., FASEB J
We compared the period of the rhythm of plasma melatonin, driven by the hypothalamic circadian pacemaker, to in vitro periodicity in cultured peripheral fibroblasts to assess the effects on these rhythms of a polymorphism of PER3 (rs57875989), which is associated with sleep timing. In vitro circadian period was determined using luminometry of cultured fibroblasts, in which the expression of firefly luciferase was driven by the promoter of the circadian gene Arntl (Bmal1). The period of the melatonin rhythm was assessed in a 9-d forced desynchrony protocol, minimizing confounding effects of sleep-wake and light-dark cycles on circadian rhythmicity. In vitro periods (32 participants, 24.61±0.33 h, mean±sd) were longer than in vivo periods (31 participants, 24.16±0.17 h; P0.4). Analyses of replicate in vitro assessments demonstrated that circadian period was reproducible within individuals (intraclass correlation=0.62), but in vivo and in vitro period assessments did not correlate (P>0.9). In accordance with circadian entrainment theory, in vivo period correlated with the timing of melatonin (P
Santhi N, Duffy JF, Horowitz TS, Czeisler CA (2006) Moderate intensity light in combination with scheduled sleep facilitates adaptation to night work, SLEEP 29 pp. A52-A53 AMER ACADEMY SLEEP MEDICINE
Santhi N, Reeves A (2004) The roles of distractor noise and target certainty in search: A signal detection model, VISION RESEARCH 44 (12) pp. 1235-1256 PERGAMON-ELSEVIER SCIENCE LTD
Archer SN, Kitamura S, Santhi N, Dijk D-J (2014) Effects of circadian typology and partial and total sleep deprivation on the human transcriptome, JOURNAL OF SLEEP RESEARCH 23 pp. 55-55 WILEY-BLACKWELL
Lazar A, Santhi N, Lo J, Slak A, Hasan S, Von Schantz M, Archer S, Dijk D-J (2012) The circadian and homeostatic regulation of sleep spindle activity: effect of the PER3 VNTR polymorphism, JOURNAL OF SLEEP RESEARCH 21 pp. 82-82 WILEY-BLACKWELL
Santhi N, Duffy JF, Horowitz TS, Czeisler CA (2005) Scheduling of sleep/darkness affects the circadian phase of night shift workers (vol 384, pg 316, 2005), NEUROSCIENCE LETTERS 390 (3) pp. 187-187 ELSEVIER IRELAND LTD
Price LLA, Khazova M, Ohagan JB, Santhi N, Dijk D-J (2012) Developing an architectural dosimetry protocol for residential properties in circadian sleep research, JOURNAL OF SLEEP RESEARCH 21 pp. 199-199 WILEY-BLACKWELL
Lo JC, Groeger JA, Santhi N, Arbon EL, Lazar AS, Hasan S, von Schantz M, Archer SN, Dijk DJ (2012) Effects of partial and acute total sleep deprivation on performance across cognitive domains, individuals and circadian phase., PLoS One 7 (9)
Cognitive performance deteriorates during extended wakefulness and circadian phase misalignment, and some individuals are more affected than others. Whether performance is affected similarly across cognitive domains, or whether cognitive processes involving Executive Functions are more sensitive to sleep and circadian misalignment than Alertness and Sustained Attention, is a matter of debate.
Santhi N, Aeschbach D, Horowitz TS, Czeisler CA (2008) The impact of sleep timing and bright light exposure on attentional impairment during night work, JOURNAL OF BIOLOGICAL RHYTHMS 23 (4) pp. 341-352 SAGE PUBLICATIONS INC
Santhi N, Reeves A (1999) Popout or random walk in efficient visual search, INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE 40 (4) pp. S51-S51 ASSOC RESEARCH VISION OPHTHALMOLOGY INC
Chang A, Santhi N, Bradstreet DS, Lockley SW, Duffy JF, Kronauer RE, Czeisler CA (2011) DURATION RESPONSE CURVE TO BRIGHT LIGHT IN HUMANS, SLEEP 34 pp. A162-A162
Reeves AJ, Santhi N (2002) A performance model for visual search, PERCEPTION 31 pp. 101-101 PION LTD
Lazar AS, Santhi N, Hasan S, Lo JCY, Johnston JD, Schantz MV, Archer SN, Dijk DJ (2013) Circadian period and the timing of melatonin onset in men and women: Predictors of sleep during the weekend and in the laboratory, Journal of Sleep Research 22 (2) pp. 155-159
Sleep complaints and irregular sleep patterns, such as curtailed sleep during workdays and longer and later sleep during weekends, are common. It is often implied that differences in circadian period and in entrained phase contribute to these patterns, but few data are available. We assessed parameters of the circadian rhythm of melatonin at baseline and in a forced desynchrony protocol in 35 participants (18 women) with no sleep disorders. Circadian period varied between 23 h 50 min and 24 h 31 min, and correlated positively (n = 31, rs = 0.43, P = 0.017) with the timing of the melatonin rhythm relative to habitual bedtime. The phase of the melatonin rhythm correlated with the Insomnia Severity Index (n = 35, rs = 0.47, P = 0.004). Self-reported time in bed during free days also correlated with the timing of the melatonin rhythm (n = 35, rs = 0.43, P = 0.01) as well as with the circadian period (n = 31, rs = 0.47, P = 0.007), such that individuals with a more delayed melatonin rhythm or a longer circadian period reported longer sleep during the weekend. The increase in time in bed during the free days correlated positively with circadian period (n = 31, rs = 0.54, P = 0.002). Polysomnographically assessed latency to persistent sleep (n = 34, rs = 0.48, P = 0.004) correlated with the timing of the melatonin rhythm when participants were sleeping at their habitual bedtimes in the laboratory. This correlation was significantly stronger in women than in men (Z = 2.38, P = 0.017). The findings show that individual differences in circadian period and phase of the melatonin rhythm associate with differences in sleep, and suggest that individuals with a long circadian period may be at risk of developing sleep problems.
Reeves AJ, Santhi N (2000) Super-pop-out with oddity: a signal-detection approach., INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE 41 (4) pp. S750-S750 ASSOC RESEARCH VISION OPHTHALMOLOGY INC
Klerman H, St Hilaire MA, Kronauer RE, Gooley JJ, Gronfier C, Hull JT, Lockley SW, Santhi N, Wang W, Klerman EB (2012) Analysis method and experimental conditions affect computed circadian phase from melatonin data., PLoS One 7 (4)
Accurate determination of circadian phase is necessary for research and clinical purposes because of the influence of the master circadian pacemaker on multiple physiologic functions. Melatonin is presently the most accurate marker of the activity of the human circadian pacemaker. Current methods of analyzing the plasma melatonin rhythm can be grouped into three categories: curve-fitting, threshold-based and physiologically-based linear differential equations. To determine which method provides the most accurate assessment of circadian phase, we compared the ability to fit the data and the variability of phase estimates for seventeen different markers of melatonin phase derived from these methodological categories. We used data from three experimental conditions under which circadian rhythms - and therefore calculated melatonin phase - were expected to remain constant or progress uniformly. Melatonin profiles from older subjects and subjects with lower melatonin amplitude were less likely to be fit by all analysis methods. When circadian drift over multiple study days was algebraically removed, there were no significant differences between analysis methods of melatonin onsets (P = 0.57), but there were significant differences between those of melatonin offsets (P
Blume C, Santhi N, Schabus M (2016) ?nparACT? package for R: A free software tool for the non-parametric analysis of actigraphy data, MethodsX 3 pp. 430-435 Elsevier
For many studies, participants? sleep-wake patterns are monitored and recorded prior to, during and following an experimental or clinical intervention using actigraphy, i.e. the recording of data generated by movements. Often, these data are merely inspected visually without computation of descriptive parameters, in part due to the lack of user-friendly software. To address this deficit, we developed a package for R Core Team [6], that allows computing several non-parametric measures from actigraphy data. Specifically, it computes the interdaily stability (IS), intradaily variability (IV) and relative amplitude (RA) of activity and gives the start times and average activity values of M10 (i.e. the ten hours with maximal activity) and L5 (i.e. the five hours with least activity). Two functions compute these ?classical? parameters and handle either single or multiple files. Two other functions additionally allow computing an L-value (i.e. the least activity value) for a user-defined time span termed ?Lflex? value. A plotting option is included in all functions. The package can be downloaded from the Comprehensive R Archives Network (CRAN).
Archer SN, Laing EE, Möller-Levet CS, van der Veen DR, Bucca G, Lazar AS, Santhi N, Slak A, Kabiljo R, von Schantz M, Smith CP, Dijk DJ (2014) Mistimed sleep disrupts circadian regulation of the human transcriptome., Proc Natl Acad Sci U S A 111 (6) pp. E682-E691
Circadian organization of the mammalian transcriptome is achieved by rhythmic recruitment of key modifiers of chromatin structure and transcriptional and translational processes. These rhythmic processes, together with posttranslational modification, constitute circadian oscillators in the brain and peripheral tissues, which drive rhythms in physiology and behavior, including the sleep-wake cycle. In humans, sleep is normally timed to occur during the biological night, when body temperature is low and melatonin is synthesized. Desynchrony of sleep-wake timing and other circadian rhythms, such as occurs in shift work and jet lag, is associated with disruption of rhythmicity in physiology and endocrinology. However, to what extent mistimed sleep affects the molecular regulators of circadian rhythmicity remains to be established. Here, we show that mistimed sleep leads to a reduction of rhythmic transcripts in the human blood transcriptome from 6.4% at baseline to 1.0% during forced desynchrony of sleep and centrally driven circadian rhythms. Transcripts affected are key regulators of gene expression, including those associated with chromatin modification (methylases and acetylases), transcription (RNA polymerase II), translation (ribosomal proteins, initiation, and elongation factors), temperature-regulated transcription (cold inducible RNA-binding proteins), and core clock genes including CLOCK and ARNTL (BMAL1). We also estimated the separate contribution of sleep and circadian rhythmicity and found that the sleep-wake cycle coordinates the timing of transcription and translation in particular. The data show that mistimed sleep affects molecular processes at the core of circadian rhythm generation and imply that appropriate timing of sleep contributes significantly to the overall temporal organization of the human transcriptome.
Santhi N, Horowitz TS, Czeisler CA (2005) Night shift work impairs decision-making in visual search, SLEEP 28 pp. A64-A64 AMER ACADEMY SLEEP MEDICINE
Dunne SP, Santhi N, Scheuermaier K, Munch MY, Duffy JF (2010) COMPARISON OF RESPONSES ON TWO SUBJECTIVE SLEEPINESS SCALES IN YOUNG AND OLDER ADULTS, SLEEP 33 pp. A363-A363
Santhi N, Duffy JF, Czeisler CA (2009) ATTENTIONAL FAILURES ARE MORE PRONOUNCED IN THE LATTER HALF OF A WAKE EPISODE FOLLOWING AN INVERSION OF THE SLEEP-WAKE SCHEDULE, SLEEP 32 pp. A53-A53 AMER ACAD SLEEP MEDICINE
Reeves A, Santhi N, Decaro S (2005) A random-ray model for speed and accuracy in perceptual experiments, SPATIAL VISION 18 (1) pp. 73-83 VSP BV
Santhi N, Horowitz TS, Duffy JF, Czeisler CA (2007) Acute Sleep Deprivation and Circadian Misalignment Associated with Transition onto the First Night of Work Impairs Visual Selective Attention, PLOS ONE 2 (11) ARTN e1233 PUBLIC LIBRARY SCIENCE
Reeves A, Santhi N (2002) Speed, accuracy and performance in visual search, PERCEPTION 31 (3) pp. 381-381 PION LTD
Groeger JA, Lo JC, Santhi N, Arbon EL, Lazar A, Hasan S, Von Schantz M, Archer SN, Dijk DJ (2012) 'Trait-like' susceptibility to sleep loss varies with circadian phase and the task used to index vulnerable-resilient sleep-deprived performance, JOURNAL OF SLEEP RESEARCH 21 pp. 36-37 WILEY-BLACKWELL
Santhi N, Lazar AS, McCabe PJ, Lo JC, Groeger JA, Dijk DJ (2016) Sex differences in the circadian regulation of sleep and waking cognition in humans, Proceedings of the National Academy of Sciences of USA 113 (19) pp. E2730-E2739 National Academy of Sciences
The sleep?wake cycle and circadian rhythmicity both contribute to brain function, but whether this contribution differs between men and women and how it varies across cognitive domains and subjective dimensions has not been established. We examined the circadian and sleep?wake-dependent regulation of cognition in 16 men and 18 women in a forced desynchrony protocol and quantified the separate contributions of circadian phase, prior sleep, and elapsed time awake on cognition and sleep. The largest circadian effects were observed for reported sleepiness, mood, and reported effort; the effects on working memory and temporal processing were smaller. Although these effects were seen in both men and women, there were quantitative differences. The amplitude of the circadian modulation was larger in women in 11 of 39 performance measures so that their performance was more impaired in the early morning hours. Principal components analysis of the performance measures yielded three factors, accuracy, effort, and speed, which reflect core performance characteristics in a range of cognitive tasks and therefore are likely to be important for everyday performance. The largest circadian modulation was observed for effort, whereas accuracy exhibited the largest sex difference in circadian modulation. The sex differences in the circadian modulation of cognition could not be explained by sex differences in the circadian amplitude of plasma melatonin and electroencephalographic slow-wave activity. These data establish the impact of circadian rhythmicity and sex on waking cognition and have implications for understanding the regulation of brain function, cognition, and affect in shift-work, jetlag, and aging.
Aeschbach D, Strong BL, Cutler AJ, Ronda JM, Baddam SK, Santhi N (2008) Dependence of planning efficiency on EEG slow-wave activity during sleep, JOURNAL OF SLEEP RESEARCH 17 pp. 271-271 WILEY-BLACKWELL PUBLISHING, INC
Santhi N, Horowitz T, Wolfe J, Czeisler C (2007) Sleep deprivation impairs search for rare targets, SLEEP 30 pp. A22-A22 AMER ACADEMY SLEEP MEDICINE
Lazar AS, Santhi N, Hasan S, Lo JC, Johnston JD, Von Schantz M, Archer SN, Dijk DJ (2012) Circadian period and the timing of melatonin onset in men and women: predictors of sleep during the weekend and in the laboratory., J Sleep Res
Sleep complaints and irregular sleep patterns, such as curtailed sleep during workdays and longer and later sleep during weekends, are common. It is often implied that differences in circadian period and in entrained phase contribute to these patterns, but few data are available. We assessed parameters of the circadian rhythm of melatonin at baseline and in a forced desynchrony protocol in 35 participants (18 women) with no sleep disorders. Circadian period varied between 23 h 50 min and 24 h 31 min, and correlated positively (n = 31, r(s)  = 0.43, P = 0.017) with the timing of the melatonin rhythm relative to habitual bedtime. The phase of the melatonin rhythm correlated with the Insomnia Severity Index (n = 35, r(s)  = 0.47, P = 0.004). Self-reported time in bed during free days also correlated with the timing of the melatonin rhythm (n = 35, r(s)  = 0.43, P = 0.01) as well as with the circadian period (n = 31, r(s)  = 0.47, P = 0.007), such that individuals with a more delayed melatonin rhythm or a longer circadian period reported longer sleep during the weekend. The increase in time in bed during the free days correlated positively with circadian period (n = 31, r(s)  = 0.54, P = 0.002). Polysomnographically assessed latency to persistent sleep (n = 34, r(s)  = 0.48, P = 0.004) correlated with the timing of the melatonin rhythm when participants were sleeping at their habitual bedtimes in the laboratory. This correlation was significantly stronger in women than in men (Z = 2.38, P = 0.017). The findings show that individual differences in circadian period and phase of the melatonin rhythm associate with differences in sleep, and suggest that individuals with a long circadian period may be at risk of developing sleep problems.
Lo JC, Groeger JA, Santhi N, Arbon EL, Lazar AS, Hasan S, Von Schantz M, Archer SN, Dijk DJ (2012) Effects of circadian phase and prior partial sleep deprivation on executive functions during total sleep deprivation are modulated by PER3 polymorphism, JOURNAL OF SLEEP RESEARCH 21 pp. 41-41 WILEY-BLACKWELL
Archer SN, Laing EE, Moller-Levet CS, van der Veen DR, Bucca G, Lazar AS, Lo JCY, Santhi N, Slak A, Kabiljo R, von Schantz M, Smith CP, Dijk DJ (2014) Mistimed sleep disrupts the circadian regulation of the human transcriptome, JOURNAL OF SLEEP RESEARCH 23 pp. 15-15 WILEY-BLACKWELL
Santhi N (2012) Individual differences in sensitivity to light, JOURNAL OF SLEEP RESEARCH 21 pp. 60-61 WILEY-BLACKWELL
Santhi N, Duffy JF, Gronfier C, Lockley SW, Czeisler CA (2006) Moderate intensity room light can entrain the circadian pacemaker to a non-24-h day, JOURNAL OF SLEEP RESEARCH 15 pp. 54-54 BLACKWELL PUBLISHING
Santhi N, Duffy JF, Horowitz TS, Czeisler CA (2005) Scheduling of sleep/darkness affects the circadian phase of night shift workers, NEUROSCIENCE LETTERS 384 (3) pp. 316-320 ELSEVIER IRELAND LTD
Santhi N, Horowitz TS, Czeisler CA (2008) Reducing nighttime attentional failures with bright light exposure: timing it right, JOURNAL OF SLEEP RESEARCH 17 pp. 23-23 WILEY-BLACKWELL PUBLISHING, INC
Möller-Levet CS, Archer SN, Bucca G, Laing EE, Slak A, Kabiljo R, Lo JC, Santhi N, von Schantz M, Smith CP, Dijk DJ (2013) Effects of insufficient sleep on circadian rhythmicity and expression amplitude of the human blood transcriptome., Proc Natl Acad Sci U S A 110 (12) pp. E1132-E1141
Insufficient sleep and circadian rhythm disruption are associated with negative health outcomes, including obesity, cardiovascular disease, and cognitive impairment, but the mechanisms involved remain largely unexplored. Twenty-six participants were exposed to 1 wk of insufficient sleep (sleep-restriction condition 5.70 h, SEM = 0.03 sleep per 24 h) and 1 wk of sufficient sleep (control condition 8.50 h sleep, SEM = 0.11). Immediately following each condition, 10 whole-blood RNA samples were collected from each participant, while controlling for the effects of light, activity, and food, during a period of total sleep deprivation. Transcriptome analysis revealed that 711 genes were up- or down-regulated by insufficient sleep. Insufficient sleep also reduced the number of genes with a circadian expression profile from 1,855 to 1,481, reduced the circadian amplitude of these genes, and led to an increase in the number of genes that responded to subsequent total sleep deprivation from 122 to 856. Genes affected by insufficient sleep were associated with circadian rhythms (PER1, PER2, PER3, CRY2, CLOCK, NR1D1, NR1D2, RORA, DEC1, CSNK1E), sleep homeostasis (IL6, STAT3, KCNV2, CAMK2D), oxidative stress (PRDX2, PRDX5), and metabolism (SLC2A3, SLC2A5, GHRL, ABCA1). Biological processes affected included chromatin modification, gene-expression regulation, macromolecular metabolism, and inflammatory, immune and stress responses. Thus, insufficient sleep affects the human blood transcriptome, disrupts its circadian regulation, and intensifies the effects of acute total sleep deprivation. The identified biological processes may be involved with the negative effects of sleep loss on health, and highlight the interrelatedness of sleep homeostasis, circadian rhythmicity, and metabolism.
Lane JM, Chang A-M, Bjonnes AC, Aeschbach D, Anderson C, Cade BE, Cain SW, Czeisler CA, Gharib SA, Gooley JJ, Gottlieb DJ, Grant SFA, Klerman EB, Lauderdale DS, Lockley SW, Munch M, Patel S, Punjabi NM, Rajaratnam SMW, Rueger M, Hilaire MAS, Santhi N, Scheuermaier K, Van Reen E, Zee PC, Shea SA, Duffy JF, Buxton OM, Redline S, Scheer FAJL, Saxena R (2016) Impact of Common Diabetes Risk Variant in MTNR1B on Sleep, Circadian, and Melatonin Physiology, DIABETES 65 (6) pp. 1741-1751 AMER DIABETES ASSOC
Santhi N, Groeger JA, Archer SN, Gimenez M, Schlangen LJ, Dijk DJ (2013) Morning sleep inertia in alertness and performance: effect of cognitive domain and white light conditions., PLoS One 8 (11)
The transition from sleep to wakefulness entails a temporary period of reduced alertness and impaired performance known as sleep inertia. The extent to which its severity varies with task and cognitive processes remains unclear. We examined sleep inertia in alertness, attention, working memory and cognitive throughput with the Karolinska Sleepiness Scale (KSS), the Psychomotor Vigilance Task (PVT), n-back and add tasks, respectively. The tasks were administered 2 hours before bedtime and at regular intervals for four hours, starting immediately after awakening in the morning, in eleven participants, in a four-way cross-over laboratory design. We also investigated whether exposure to Blue-Enhanced or Bright Blue-Enhanced white light would reduce sleep inertia. Alertness and all cognitive processes were impaired immediately upon awakening (p
Santhi N, Horowitz TS, Hilton MF, Shea SA (2005) Efficiency of temporal selective attention is modulated by circadian phase and duration of wakefulness, SLEEP 28 pp. A351-A351 AMER ACADEMY SLEEP MEDICINE
Blume C, Lechinger J, Santhi N, del Giudice R, Gnjezda M, Pichler G, Scarpatetti M, Donis J, Michitsch G, Schabus M (2017) Significance of circadian rhythms in severely brain-injured patients. A clue to consciousness?, Neurology 88 (20) pp. 1933-1941 American Academy of Neurology
Objective: To investigate the relationship between the presence of a circadian body temperature rhythm and behaviourally assessed consciousness levels in patients with disorders of consciousness (DOC, i.e. vegetative state/unresponsive wakefulness syndrome [VS/UWS] or minimally conscious state [MCS]). Methods: In a cross-sectional study, we investigated the presence of circadian temperature rhythms across six to seven days using external skin temperature sensors in 18 patients suffering from DOC. Beyond this; we examined the relationship between behaviourally assessed consciousness levels and circadian rhythmicity. Results: Interestingly, analyses with Lomb-Scargle periodograms revealed significant circadian rhythmicity in all patients (range 23.5-26.3h). We found that especially scores on the arousal subscale of the Coma Recovery Scale-Revised (CRS-R) were closely linked to the integrity of circadian variations in body temperature. Finally, we piloted whether bright light stimulation could boost circadian rhythmicity and found positive evidence in two out of eight patients. Conclusion: In conclusion, the study provides first evidence for an association between circadian body temperature rhythms and arousal as a necessary precondition for consciousness. Thereby, our findings also make a case for circadian rhythms as a target for treatment as well as the application of diagnostic and therapeutic means at times when cognitive performance is expected to peak.
Laing E, Moller-Levet C, Poh N, Santhi N, Archer S, Dijk D (2017) Blood transcriptome based biomarkers for human circadian phase, eLife pp. 1-26 eLife Sciences Publications Ltd
Diagnosis and treatment of circadian rhythm sleep-wake disorders requires assessment of circadian phase of the brain?s circadian pacemaker. The gold-standard univariate method is based on collection of a 24 h time series of plasma melatonin, a suprachiasmatic nucleus driven pineal hormone. We developed and validated a multivariate whole-blood mRNA based predictor of melatonin phase which requires few samples. Transcriptome data were collected under normal, sleep-deprivation and abnormal sleep-timing conditions to assess robustness of the predictor. Partial least square regression (PLSR), applied to the transcriptome, identified a set of 100 biomarkers primarily related to glucocorticoid signaling and immune function. Validation showed that PLSR-based predictors outperform published blood-derived circadian phase predictors. When given one sample as input, the R2 of predicted vs observed phase was 0.74, whereas for two samples taken 12 h apart, R2 was 0.90. This blood transcriptome based model enables assessment of circadian phase from a few samples.
Rahman S, St. Hilaire M, Chang A, Santhi N, Duffy J, Kronauer R, Czeisler C, Lockley S, Klerman E (2017) Circadian phase resetting by a single short-duration light exposure, JCI Insight 2 (7) e89494 American Society for Clinical Investigation
BACKGROUND. In humans, a single light exposure of 12 minutes and multiple-millisecond light
exposures can shift the phase of the circadian pacemaker. We investigated the response of the
human circadian pacemaker to a single 15-second or 2-minute light pulse administered during the
biological night.
METHODS. Twenty-six healthy individuals participated in a 9-day inpatient protocol that included
assessment of dim light melatonin onset time (DLMO time) before and after exposure to a single
15-second (n = 8) or 2-minute (n = 12) pulse of bright light (9,500 lux; 4,100 K fluorescent) or control
background dim light ( between the two phase estimates.
RESULTS. Both 15-second and 2-minute exposures induced phase delay shifts [median (± SD)]
of ?34.8 ± 47.2 minutes and ?45.4 ± 28.4 minutes, respectively, that were significantly (P = 0.04)
greater than the control condition (advance shift: +22.3 ± 51.3 minutes) but were not significantly
different from each other. Comparisons with historic data collected under the same conditions
confirmed a nonlinear relationship between exposure duration and the magnitude of phase shift.
CONCLUSIONS. Our results underscore the exquisite sensitivity of the human pacemaker to even
short-duration single exposures to light. These findings may have real-world implications for
circadian disruption induced by exposure to brief light stimuli at night.
Santhi N, Ramsey D, Phillipson G, Hull D, Revell V, Dijk D (2017) Efficacy of a Topical Aromatic Rub
(Vicks VapoRub®) on Effects on Self-Reported
and Actigraphically Assessed Aspects of
Sleep in Common Cold Patients,
Open Journal of Respiratory Diseases 7 (2) 76608 pp. 83-101 Scientific Research Publishing
Common cold sufferers frequently report sleep disruption during the symptomatic
period of infections. We examined the effects of treatment with a
topical aromatic pharmaceutical ointment (Vicks VapoRub®), on associated
sleep disturbances. The effects of Vicks VapoRub® versus placebo (petrolatum
ointment) on subjective and objective measured sleep parameters were assessed
in an exploratory study of 100 common cold patients, in a randomized,
single blind, controlled, two-arm, parallel design study. The primary efficacy
variable was subjective sleep quality measured with the SQSQ (Subjective
Quality of Sleep Questionnaire). Additional measures included, ease of falling
asleep and depth of sleep (measured with a post-sleep Visual Analog Scale),
total sleep time, sleep onset latency, activity score, percentage of sleep, sleep
efficiency (measured with actigraphy and SQSQ) and sleep quality index
measured with a modified Karolinska Sleep Diary (KSD). The primary endpoint,
?How was the quality of your sleep last night?? showed a statistically
significant difference in change from baseline in favour of VapoRub treatment
(p = 0.0392) versus placebo. Positive effects of VapoRub versus placebo were
also observed for ?How refreshed did you feel upon waking up?? (p = 0.0122)
(SQSQ), ?Did you get enough sleep?? (p = 0.0036) (KSD), ?How was it to get
up?? (p = 0.0120) (KSD) and ?Do you feel well-rested?? (p = 0.0125) (KSD).
No statistically significant changes from baseline versus placebo were detected
in the Actiwatch endpoints. Vicks VapoRub®when applied before retiring to bed can reduce subjective sleep disturbances during a common cold. The results
of this exploratory study support the belief among patients that the use
of VapoRub improves subjective sleep quality during common cold which was
associated with more refreshing sleep.
Rahman Shadab A., St Hilaire Melissa A., Gronfier Claude, Chang Anne-Marie, Santhi Nayantara, Czeisler Charles A., Klerman Elizabeth B., Lockley Steven W. (2018) Functional decoupling of melatonin suppression and circadian phase resetting in humans, The Journal of Physiology 596 (11) pp. 2147-2157 Wiley
Continuous experimental light exposures show that, in general, the conditions that produce greater melatonin suppression also produce greater phase shift, leading to the assumption that one can be used as a proxy for the other. We tested this association in 16 healthy individuals who participated in a 9?day inpatient protocol by assessing melatonin suppression and phase resetting in response to a nocturnal light exposure (LE) of different patterns: (i) dim?light control (