Age effects on spectral electroencephalogram activity prior to dream recall.

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

Light modulation of human clocks, wake and sleep

Light, through its non-imaging forming effects, plays a dominant role on a myriad of physiological functions, including the human sleep–wake cycle. The non-image forming effects of light heavily rely on specific properties such as intensity, duration, timing, pattern, and wavelengths. Here, we address how specific properties of light influence sleep and wakefulness in humans through acute effects, e.g., on alertness, and/or effects on the circadian timing system. Of critical relevance, we discuss how different characteristics of light exposure across the 24-h day can lead to changes in sleep–wake timing, sleep propensity, sleep architecture, and sleep and wake electroencephalogram (EEG) power spectra. Ultimately, knowledge on how light affects sleep and wakefulness can improve light settings at home and at the workplace to improve health and well-being and optimize treatments of chronobiological disorders

Enhancing daily light exposure increases the antibody response to influenza vaccination in patients with dementia

Enhancing lighting conditions in institutions for individuals with dementia improves their sleep, circadian rhythms and well-being. Here, we tested whether a greater long-term daily light exposure supports the immune response to the annual influenza vaccination. Eighty older institutionalised patients suffering from dementia (54 women and 26 men) continuously wore an activity tracker for 8 weeks to assess individual light exposure and rest-activity cycles. The patients’ immune response was analysed from two blood samples taken before and 4 - 5 weeks after the annual influenza vaccination. Individual antibody concentrations to three influenza virus strains (H3N2, H1N1, IB) were quantified via hemagglutination inhibition assays. By quantifying individual light exposure profiles (including daylight), we classified the patients into a low and a high light exposure group based on a median illuminance of 392.6 lux. The two light exposure groups did not differ in cognitive impairment severity, age or gender distribution. However, patients in the high light exposure group showed a significantly greater circadian rest-activity amplitude (i.e. more daytime activity and less nighttime activity) along with a significantly greater antibody titer increase to the H3N2 vaccine than patients in the low light exposure group, despite similar pre-vaccination concentrations. Sufficient seroprotective responses to all three influenza virus strains were attained for > 75 % of participants. These data provide first evidence for an enhanced immune response in patients with dementia when they received more daily light. Increasing daily light exposure may have beneficial effects on the human immune system, either directly or via circadian rhythm stabilisation

Bone Turnover Markers After Sleep Restriction and Circadian Disruption: A Mechanism for Sleep-Related Bone Loss in Humans

Context: Sleep abnormalities are associated with low bone mineral density. Underlying mechanisms are unknown. Objective: Investigate the impact of sleep restriction with circadian disruption on bone biomarkers. Design: Intervention study. Participants and Methods: Four bone biomarkers [C-terminal cross-linked telopeptide of type I collagen (CTX) = bone resorption, N-terminal propeptide of type I procollagen (P1NP) = bone formation, sclerostin and fibroblast growth factor 23 = osteocyte function] were measured in bihourly serum samples over 24 hours at baseline and after ∼3 weeks of sleep restriction (5.6 hours sleep/24 hours) with concurrent circadian disruption (recurring 28-hour “day” in dim light) in 10 men (age groups: 20 to 27 years, n = 6; 55 to 65 years, n = 4). The effects of sleep/circadian disruption and age on bone biomarker levels were evaluated using maximum likelihood estimation in a mixed model for repeated measures. Results: P1NP levels were lower after intervention compared with baseline (P \u3c 0.001); the decrease in P1NP was greater for younger compared with older men (28.0% vs 18.2%, P \u3c 0.001). There was no change in CTX (Δ = 0.03 ± 0.02 ng/mL, P = 0.10). Sclerostin levels were higher postintervention in the younger men only (Δ = 22.9% or 5.64 ± 1.10 pmol/L, P \u3c 0.001). Conclusions: These data suggest that 3 weeks of circadian disruption with concurrent sleep restriction can lead to an uncoupling of bone turnover wherein bone formation is decreased but bone resorption is unchanged. Circadian disruption and sleep restriction may be most detrimental to bone in early adulthood

Chronotype Genetic Variant in PER2 is Associated with Intrinsic Circadian Period in Humans

Abstract The PERIOD2 (PER2) gene is a core molecular component of the circadian clock and plays an important role in the generation and maintenance of daily rhythms. Rs35333999, a missense variant of PER2 common in European populations, has been shown to associate with later chronotype. Chronotype relates to the timing of biological and behavioral activities, including when we sleep, eat, and exercise, and later chronotype is associated with longer intrinsic circadian period (cycle length), a fundamental property of the circadian system. Thus, we tested whether this PER2 variant was associated with circadian period and found significant associations with longer intrinsic circadian period as measured under forced desynchrony protocols, the ‘gold standard’ for intrinsic circadian period assessment. Minor allele (T) carriers exhibited significantly longer circadian periods when determinations were based on either core body temperature or plasma melatonin measurements, as compared to non-carriers (by 12 and 11 min, respectively; accounting for ~7% of inter-individual variance). These findings provide a possible underlying biological mechanism for inter-individual differences in chronotype, and support the central role of PER2 in the human circadian timing system