Experimental Night Research Articles

Rapid eye movement sleep mediates age-related decline in prospective memory consolidation.

Prospective memory, or remembering to execute future intentions, accounts for half of everyday forgetting in older adults. Sleep intervals benefit prospective memory consolidation in young adults, but it is unknown whether age-related changes in slow wave activity, sleep spindles, and/or rapid eye movement (REM) sleep mediate hypothesized effects of aging on prospective memory consolidation. After an adaptation night, 76 adults aged 18-84 completed two experimental nights of in-laboratory polysomnography recording. In the evening, participants encoded and practiced a prospective memory task and were tested the next morning. On a counterbalanced night, they encoded and practiced a control task, and were tested the following morning. Increasing age predicted worse prospective memory consolidation (r = -.34), even when controlling for encoding, speed, and control-task performance (all ps < .05). Frontal delta power, slow oscillations, and spindle density were not related to prospective memory consolidation. REM sleep duration, however, explained significant variance in prospective memory consolidation when controlling for age (∆R2 = .10). Bootstrapping mediation showed that less REM sleep significantly mediated the aging effect on prospective memory consolidation [b = -.0016, SE = 0.0009 (95% confidence interval [CI] = -0.0042 to -0.0004)]. REM sleep continued to mediate 24.29% of the total effect of age on prospective memory after controlling for numerous demographic, cognitive, mental health, and sleep variables. Age-related variance in REM sleep is informative to how prospective memory consolidation changes with increasing age. Future work should consider how both REM sleep and slow wave activity contribute, perhaps in a sequential or dynamic manner, to preserving cognitive functioning with increasing age.

Differential effects of bifrontal tDCS on arousal and sleep duration in insomnia patients and healthy controls

BackgroundArousal and sleep represent basic domains of behavior, and alterations are of high clinical importance. Objective/hypothesisThe aim of this study was to further elucidate the neurobiology of insomnia disorder (ID) and the potential for new treatment developments, based on the modulation of cortical activity through the non-invasive brain stimulation technique transcranial direct current stimulation (tDCS). Specifically, we tested the hypotheses that bi-frontal anodal tDCS shortens and cathodal tDCS prolongs total sleep time in patients with ID, compared to sham stimulation. Furthermore, we tested for differences in indices of arousal between ID patients and healthy controls and explored their potential impact on tDCS effects. MethodsNineteen ID patients underwent a within-subject repeated-measures sleep laboratory study with adaptation, baseline and three experimental nights. Bifrontal anodal, cathodal and sham tDCS was delivered in a counterbalanced order immediately prior to sleep. Wake EEG was recorded prior to and after tDCS as well as on the following morning. Subsequently, we compared patients with ID to a healthy control group from an earlier dataset. ResultsAgainst our hypothesis, we did not observe any tDCS effects on sleep continuity or sleep architecture in patients with ID. Further analyses of nights without stimulation demonstrated significantly increased levels of arousal in ID patients compared to healthy controls, as indexed by subjective reports, reduced total sleep time, increased wake after sleep onset and increased high frequency EEG power during wakefulness and NREM sleep. Of note, indices of increased arousal predicted the lack of effect of tDCS in ID patients. ConclusionsOur study characterizes for the first time differential effects of tDCS on sleep in patients with ID and healthy controls, presumably related to persistent hyperarousal in ID. These findings suggest that adapted tDCS protocols need to be developed to modulate arousal and sleep dependent on baseline arousal levels.

Age effect on the locomotor activity rhythm of Armadillidium granulatum (Crustacea, Isopoda)

ABSTRACTIn this present paper, we propose to characterize the locomotor behavior of the Oniscidea Armadillidium granulatum Brandt, 1833 and to highlight the effect of age on its locomotor patterns. Individuals of A. granulatum were collected from the supralittoral zone of Sebkha El Ouafi. Adult and young specimens were maintained in spring under two successive regimens: the light–dark (LD) cycle and the constant darkness (DD) at a constant temperature. Whatever the age, double-plotted actograms and waveforms showed that specimens of A. granulatum concentrated their activity during the experimental and subjective nights. In addition, the majority of locomotor activity patterns were unimodal; whereas, adults and juveniles intensified their activities respectively around the dusk and in the middle of the night. Through periodogram analysis, circadian and ultradian components were determined. The first one was significantly longer under DD than under natural LD cycle for adults as well as for juveniles. These last were characterized by the most stable and well-defined locomotor activity rhythm. Furthermore, Adult specimens were more active under entraining conditions contrary to juveniles that showed an important activity time under DD. With reference to environmental stability and variability, the differences of locomotor activity characteristics observed between juveniles and adults were explained as a need for plasticity to adapt to environmental changes.

Locomotor behaviour of three sympatric species Ligia italica, Armadillo officinalis and Chaetophiloscia elongata (Crustacea, Oniscidea) from Ghar El Melh lagoon (Northeast Tunisia)

ABSTRACTThe locomotor behaviour of three terrestrial isopod species, Ligia italica, Chaetophiloscia elongata and Armadillo officinalis, were investigated in populations collected from the supralittoral zone of Ghar El Melh lagoon. Locomotor rhythms were recorded in individual animals in spring under two successive experimental regimens during 15 days. In the first 5 days, individuals were kept under light-dark cycle in phase with the natural diel cycle. During the rest of experience, animals were maintained under constant darkness (DD). Using actograms and waveforms curves, results revealed that C. elongata and A. officinalis concentrated their activity during the experimental and subjective nights showing thus a nocturnal behaviour. In these species, whatever the regimen, the most important activity peak was situated respectively in the middle of the night and around the dusk. However, L. italica was characterized by a diurnal behaviour by maintaining its activity during the experimental and subjective days. The three species exhibited a circadian rhythmicity of the locomotor activity. Under light-dark cycle, mean periods determined by periodogram analysis were appreciably similar and were close to 24 h. Under constant darkness, these periods showed a slight extension. Furthermore, individuals of A. officinalis were significantly less active under nLD cycle (4h21 ± 1h53) as well as under DD (3h48 ± 1h58). The differences in the activity patterns between species highlighted in the present study will be discussed as an adaptive strategy to respond to interspecific competitive interactions.

Eave ribbons treated with the spatial repellent, transfluthrin, can effectively protect against indoor-biting and outdoor-biting malaria mosquitoes

BackgroundLong-lasting insecticide-treated nets and indoor residual spraying protect against indoor-biting and indoor-resting mosquitoes but are largely ineffective for early-biting and outdoor-biting malaria vectors. Complementary tools are, therefore, needed to accelerate control efforts. This paper describes simple hessian ribbons treated with spatial repellents and wrapped around eaves of houses to prevent outdoor-biting and indoor-biting mosquitoes over long periods of time.MethodsThe eave ribbons are 15 cm-wide triple-layered hessian fabrics, in lengths starting 1 m. They can be fitted onto houses using nails, adhesives or Velcro, without completely closing eave-spaces. In 75 experimental nights, untreated ribbons and ribbons treated with 0.02%, 0.2%, 1.5% or 5% transfluthrin emulsion (spatial repellent) were evaluated against blank controls using two experimental huts inside a 202 m2 semi-field chamber where 500 laboratory-reared Anopheles arabiensis were released nightly. Two volunteers sat outdoors (one/hut) and collected mosquitoes attempting to bite them from 6 p.m. to 10 p.m. (outdoor-biting), then went indoors and slept under bed nets, beside which CDC-light traps collected mosquitoes from 10 p.m. to 6.30 a.m. (indoor-biting). To assess survival, 200 caged mosquitoes were suspended near the huts nightly and monitored for 24 h thereafter. Additionally, field tests were done in experimental huts in a rural Tanzanian village to evaluate treated ribbons (1.5% transfluthrin). Here, indoor-biting was assessed using window traps and Prokopack® aspirators, and outdoor-biting assessed using volunteer-occupied double-net traps.ResultsIndoor-biting and outdoor-biting decreased > 99% in huts fitted with eave ribbons having ≥ 0.2% transfluthrin. Even 0.02% transfluthrin-treated ribbons provided 79% protection indoors and 60% outdoors. Untreated ribbons however reduced indoor-biting by only 27% and increased outdoor-biting by 18%, though these were non-significant (P > 0.05). Of all caged mosquitoes exposed near treated huts, 99.5% died within 24 h. In field tests, the ribbons provided 96% protection indoors and 84% outdoors against An. arabiensis, plus 42% protection indoors and 40% outdoors against Anopheles funestus. Current prototypes cost ~ 7USD/hut, are made of widely-available hessian and require no specialized expertise.ConclusionTransfluthrin-treated eave ribbons significantly prevented outdoor-biting and indoor-biting malaria vectors and could potentially complement current tools. The technique is simple, low-cost, highly-scalable and easy-to-use; making it suitable even for poorly-constructed houses and low-income groups.

A Novel Insight of Effects of a 3-Hz Binaural Beat on Sleep Stages During Sleep.

The dichotic presentation of two almost equivalent pure tones with slightly different frequencies leads to virtual beat perception by the brain. In this phenomenon, the so-called binaural beat has a frequency equaling the difference of the frequencies of the two pure tones. The binaural beat can entrain neural activities to synchronize with the beat frequency and induce behavioral states related to the neural activities. This study aimed to investigate the effect of a 3-Hz binaural beat on sleep stages, which is considered a behavioral state. Twenty-four participants were allocated to experimental and control groups. The experimental period was three consecutive nights consisting of an adaptation night, a baseline night, and an experimental night. Participants in both groups underwent the same procedures, but only the experimental group was exposed to the 3-Hz binaural beat on the experimental night. The stimulus was initiated when the first epoch of the N2 sleep stage was detected and stopped when the first epoch of the N3 sleep stage detected. For the control group, a silent sham stimulus was used. However, the participants were blinded to their stimulus group. The results showed that the N3 duration of the experimental group was longer than that of the control group, and the N2 duration of the experimental group was shorter than that of the control group. Moreover, the N3 latency of the experimental group was shorter.

Developmental changes of sleep spindles and their impact on sleep-dependent memory consolidation and general cognitive abilities: A longitudinal approach.

Sleep spindles are related to sleep‐dependent memory consolidation and general cognitive abilities. However, they undergo drastic maturational changes during adolescence. Here we used a longitudinal approach (across 7 years) to explore whether developmental changes in sleep spindle density can explain individual differences in sleep‐dependent memory consolidation and general cognitive abilities. Ambulatory polysomnography was recorded during four nights in 34 healthy subjects (24 female) with two nights (baseline and experimental) at initial recording (age range 8–11 years) and two nights at follow‐up recording (age range 14–18 years). For declarative learning, participants encoded word pairs with a subsequent recall before and after sleep. General cognitive abilities were measured by the Wechsler Intelligence Scale. Higher slow (11–13 Hz) than fast (13–15 Hz) spindle density at frontal, central, and parietal sites during initial recordings, followed by a shift to higher fast than slow spindle density at central and parietal sites during follow‐up recordings, suggest that mature spindle topography develops throughout adolescence. Fast spindle density increases from baseline to experimental night were positively related to sleep‐dependent memory consolidation. In addition, we found that the development of fast spindles predicted the improvement in memory consolidation across the two longitudinal measurements, a finding that underlines a crucial role for mature fast spindles for sleep‐dependent memory consolidation. Furthermore, slow spindle changes across adolescence were related to general cognitive abilities, a relationship that could indicate the maturation of frontal networks relevant for efficient cognitive processing. A video abstract of this article can be viewed at: https://www.youtube.com/watch?v=7NXJzm8HbIw and https://www.youtube.com/watch?v=iuMQY1OIJ0s

Executive functioning is preserved in healthy young adults under acute sleep restriction.

Objectives:This study aimed to evaluate if a partial morning or evening sleep restriction protocol could affect executive functioning in healthy young adults.Methods:Participants were assigned to one of three groups: control (n=18), in which participants maintained their habitual sleep/wake cycle; morning restriction (n=17), in which volunteers terminated sleep approximately three hours earlier than the usual on the experimental night, and evening restriction (n=13), in which volunteers initiated sleep approximately three hours later than the usual on the experimental night. On the day of the experiment, they performed the Stroop Test, the Go-NoGo Test and the Iowa Gambling Task (IGT).Results:When compared to the control group, neither morning nor evening sleep-restricted individuals displayed any significant deficits in: a) selective attention as assessed by the interference index (H=3.38; p=0.18) and time to performed the interference card (H=2.61; p=0.27) on the Stroop test; b) motor response inhibition as assessed by number of false alarms (H=0.8; p=0.67) on the Go-NoGo Test; and c) in decision-making as assessed by total won (H=2.64; p=0.26) and number of selected advantageous cards (H=4.43; p=0.11) on the IGT.Conclusion:These findings suggest that the ability to pay attention, inhibit a motor response and make decisions is preserved following approximately 3 hours of sleep restriction, regardless of its timing (in the morning or in the evening).

Outliers detect methods for time series data

The outliers are unavoidable anomalous points. It will affect the accuracy of time series data. A method of outlier detection and correction for time series data based on statistics is designed in this paper, which can effectively detect the position of anomalous points and make correction. The numerical experimental resultson hotel room night data show that the accuracy of the compressed dataset is improved by 3.4% to 4.4% compared with the original dataset.

The effects of one night of partial sleep deprivation on executive functions in individuals reporting chronic insomnia and good sleepers

Background and objectivesThe aim of the present study was to investigate the effects of a partial sleep deprivation night on executive functions in participants reporting chronic insomnia and good sleepers using a Task Switching paradigm. MethodsSixteen participants reporting symptoms of chronic insomnia and sixteen good sleepers were tested after a night of habitual sleep and after a night of partial sleep deprivation (5 h of sleep allowed). The Switch Cost (SC) and the Backward Inhibition (BI) were computed as measures of switching attention and response inhibition, respectively. ResultsWe observed a marginally significant interaction Night × Group on SC (F(1,29) = 4.06, p = 0.053), η2 = 0.123. Fisher's least significant difference (LSD) post-hoc revealed a smaller SC after the sleep deprived night relative to the habitual night for the good sleepers (p = 0.027; M = 192.23 ± 201.81 vs M = 98.99 ± 141.16). Differently, participants with insomnia did not show any change after the two nights. LimitationsSeveral limitations must be acknowledged including the use of a convenient sample of university students and the use of a single task of cognitive performance. ConclusionsWe found that SC was smaller in the good sleepers after a night of partial sleep deprivation compared to a habitual night, indicating a better switching performance. The insomnia group showed no differences in performance after the two experimental nights. Several factors may account for these results, including increased levels of arousal and cognitive effort during task execution.

Towards a characterization of the locomotor activity rhythm of the desertic species Porcellio olivieri (Crustacea, Isopoda) from Gabes (South of Tunisia)

The locomotor activity rhythm of the isopod, Porcellio olivieri, was investigated in Gannouch site in the south of Tunisia. The rhythm was monitored under constant temperature in individual animals in winter under two simultaneous regimens: the light–dark (LD) cycle and the continuous darkness (DD). Results revealed that whatever regimens, actograms, and mean activity curves showed that specimens of P. olivieri concentrated their activity during the experimental and subjective night. The species exhibited a locomotor rhythm period significantly shorter under LD (T = 23h13 ± 0h44) than DD (τ = 24h28 ± 0h58). However, the locomotor activity rhythm was less stable and the individuals were significantly more active under entraining conditions than constant darkness. The activity pattern of this species will be discussed as an adaptative strategy to respond to environmental conditions.

Odor cueing during slow-wave sleep benefits memory independently of low cholinergic tone

RationaleSleep-dependent memory consolidation depends on the concerted reactivation of memories in the hippocampo-neocortical system. The communication of reactivated information from the hippocampus to the neocortex is assumed to be enabled by low levels of acetylcholine, particularly during slow-wave sleep (SWS). Recent studies suggest that the reactivation of memories does not only occur spontaneously but can also be externally triggered by re-presenting learning-associated cues during sleep.ObjectivesHere we investigated whether the beneficial effect of cued memory reactivation during sleep depends on similar mechanisms as spontaneous reactivation, and specifically on low cholinergic tone.MethodsIn two experimental nights, healthy volunteers learned a visuo-spatial memory task in the presence of an odor before going to sleep for 40 min. In one night, subjects were presented with the odor again during SWS, whereas in the other night they received an odorless vehicle. In half of the subjects, the availability of acetylcholine during sleep was increased by administering the acetylcholine-esterase inhibitor physostigmine.ResultsContrary to our hypothesis, increased cholinergic tone during sleep did not abolish the beneficial effect of odor cueing: memory performance was better after odor cueing compared to odorless vehicle, independent of physostigmine or placebo administration.ConclusionsThis finding challenges the assumption that odor-cued and spontaneous memory reactivation rely on the same neuropharmacological mechanisms.

The effects of overnight nutrient intake on hypothalamic inflammation in a free-choice diet-induced obesity rat model

Consumption of fat and sugar induces hyperphagia and increases the prevalence of obesity and diabetes type 2. Low-grade inflammation in the hypothalamus, a key brain area involved in the regulation of energy homeostasis is shown to blunt signals of satiety after long term high fat diet. The fact that this mechanism can be activated after a few days of hyperphagia before apparent obesity is present led to our hypothesis that hypothalamic inflammation is induced with fat and sugar consumption. Here, we used a free-choice high-fat high-sugar (fcHFHS) diet-induced obesity model and tested the effects of differential overnight nutrient intake during the final experimental night on markers of hypothalamic inflammation. Male Wistar rats were fed a control diet or fcHFHS diet for one week, and assigned to three different feeding conditions during the final experimental night: 1) fcHFHS-fed, 2) fed a controlled amount of chow diet, or 3) fasted. RT-qPCR and Western blot were utilized to measure hypothalamic gene and protein expression, of cytokines and intermediates of the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathway. Lastly, we investigated the effects of acute fat intake on markers of hypothalamic inflammation in fat-naïve rats. fcHFHS-fed rats consumed more calories, increased adipose tissue, and showed elevated expression of hypothalamic inflammation markers (increased phosphorylation of NF-κB protein, Nfkbia and Il6 gene expression) compared to chow-fed rats. These effects were evident in rats consuming relative high amounts of fat. Removal of the fat and sugar, or fasting, during the final experimental night ameliorated hypothalamic inflammation. Finally, a positive correlation was observed between overnight acute fat consumption and hypothalamic NF-κB phosphorylation in fat-naïve rats. Our data indicate that one week of fcHFHS diet, and especially the fat component, promotes hypothalamic inflammation, and removal of the fat and sugar component reverses these detrimental effects.

Sleep-dependent motor sequence memory consolidation in individuals with periodic limb movements

Periodic limb movements (PLMs) during sleep increase with age and are associated with striatal neurodegeneration and dopamine deficiency. Limb movements are often associated with disruptions to non-rapid eye movement (NREM) sleep. Motor skill memory consolidation recruits the striatum, and learning-dependent striatal activation is associated with NREM sleep. Therefore, we investigated whether de novo individuals who significantly experience elevated levels of PLMs but have not been formally diagnosed with periodic limb movement disorder had learning and sleep-related memory deficits and whether these deficits were related to sleep quality and symptom severity.In total, 14 adults with significantly elevated PLMs (PLM condition), 15 age-matched controls (CTRL), and 14 age-matched “disturbed” sleep (through induced leg movements) controls (CTRL-ES) participated. The participants were trained (PM) and retested (AM) on procedural motor sequence learning (MSL) and declarative paired associates memory tasks.Baseline sleep quality was significantly worse in PLM than in CTRL. Despite the continued presence of PLMs in the PLM condition on the experimental night, remarkably, sleep quality improved and arousals decreased, vs. baseline, and did not differ from CTRL. MSL was significantly slower in the PLM condition than in CTRL at training but surprisingly exhibited overnight performance gains, which correlated with reduced arousals. As predicted, CTRL but not CTRL-ES had overnight gains in MSL. Taken together, this suggests that in the PLM condition, sleep quality was normalized following MSL, where they derived the same benefit of sleep to procedural memory consolidation as in CTRL. Sleep did not benefit declarative memory.Although preliminary, these results suggest that MSL in individuals with PLMs may provide a benefit to sleep, which in turn may benefit memory consolidation.

Eave tubes for malaria control in Africa: prototyping and evaluation against Anopheles gambiae s.s. and Anopheles arabiensis under semi-field conditions in western Kenya

BackgroundWhilst significant progress has been made in the fight against malaria, vector control continues to rely on just two insecticidal methods, i.e., indoor residual spraying and insecticidal bed nets. House improvement shows great potential to complement these methods and may further reduce indoor mosquito biting and disease transmission. Open eaves serve as important mosquito house entry points and provide a suitable location for intercepting host-seeking anophelines. This study describes semi-field experiments in western Kenya with eave tubes, a household protection product that leverages the natural behaviour of host-seeking malaria mosquitoes.MethodsSemi-field experiments were conducted in two screen-houses. In both of these a typical western Kenyan house, with mud walls and corrugated iron sheet roofing, was built. Eave tubes with bendiocarb- or deltamethrin-treated eave tube inserts were installed in the houses, and the impact on house entry of local strains of Anopheles gambiae and Anopheles arabiensis was determined. Experiments with open eave tubes (no netting) were conducted as a control and to determine house entry through eave tubes. Insecticidal activity of the inserts treated with insecticide was examined using standard 3-min exposure bioassays.ResultsExperiments with open eave tubes showed that a high percentage of released mosquitoes entered the house through tubes during experimental nights. When tubes were fitted with bendiocarb- or deltamethrin-treated inserts, on average 21% [95% CI 18–25%] and 39% [CI 26–51%] of An. gambiae s.s. were recaptured the following morning, respectively. This contrasts with 71% [CI 60–81%] in the treatment with open eaves and 54% [CI 47–61%] in the treatment where inserts were treated with fluorescent dye powder. For An. arabiensis recapture was 21% [CI 14–27%] and 22% [CI 18–25%], respectively, compared to 46% [CI 40–52%] and 25% [CI 15–35%] in the treatments with open tubes and fluorescent dye.ConclusionsInsecticide-treated eave tubes resulted in significant reductions in recapture rates for both malaria vector species, representing the first and promising results with this novel control tool against Kenyan malaria vectors. Further field evaluation of eave tubes under more realistic field conditions, as well as their comparison with existing approaches in terms of cost-effectiveness and community acceptance, is called for.

Evening light exposure to computer screens disrupts human sleep, biological rhythms, and attention abilities

ABSTRACTThe use of electronic devices with light-emitting screens has increased exponentially in the last decade. As a result, humans are almost continuously exposed to unintentional artificial light. We explored the independent and combined effects of two aspects of screen illumination, light wavelength, and intensity, on sleep, its biological regulation, and related functional outcomes. The 2 × 2 repeated-measure design included two independent variables: screen light intensity (low ([LI] versus high [HI]) and wavelength (short [SWL] versus long [LWL]). Nineteen participants (11F, 8M; mean age 24.3 [±2.8] years) underwent four light conditions, LI/SWL, HI/SWL, LI/LWL, and HI/LWL, in counterbalanced order. Each light exposure lasted for two hours (21:00–23:00), following which participants underwent an overnight polysomnography. On each experimental night, oral temperature and urine samples (for melatonin analysis) were collected at multiple time points. Each morning, participants filled out questionnaires and conducted a computerized attention task. Irrespective of light intensity, SWL illumination significantly disrupted sleep continuity and architecture and led to greater self-reported daytime sleepiness. SWL light also altered biological rhythms, subduing the normal nocturnal decline in body temperature and dampening nocturnal melatonin secretion. Light intensity seemed to independently affect sleep as well, but to a lesser degree. Both light intensity and wavelength negatively affected morning attention. In sum, light wavelength seems to have a greater influence than light intensity on sleep and a wide-range of biological and behavioral functions. Given the widespread use of electronic devices today, our findings suggest that screen light exposure at evening may have detrimental effects on human health and performance.

0074 INVESTIGATING THE EFFECT OF ACUTE SLEEP DEPRIVATION ON HYPOTHALAMIC-PITUITARY-ADRENAL-AXIS RESPONSE TO A PSYCHOSOCIAL STRESSOR

The hypothalamic-pituitary-adrenal (HPA) axis has been previously identified as one potential mechanism that may explain the link between sleep deprivation and negative health outcomes. However, few studies have examined the direct impact of sleep deprivation on HPA-axis functioning, particularly in the context of stress. Therefore, the aim of the current study was to investigate the relationship between acute sleep deprivation and HPA-axis reactivity to a psychosocial stressor. Participants included 40 healthy, young adults between the ages of 18 - 29. The current protocol included spending two nights in the laboratory. After an adaptation night, participants were randomized into either a sleep deprivation condition (n = 20; 29 consecutive hours awake) or a control condition (n = 20; 8-hour sleep opportunity). Following the experimental night, all participants completed the Trier Social Stress Test (TSST). Salivary cortisol was collected before, during, and after the TSST. We used random effects growth curve models to examine the impact of experimental condition on cortisol stress trajectories - i.e., the effect of condition on pre-stress, baseline cortisol (intercept) and cortisol reactivity (non-linear slope) from baseline. Compared to participants in the control condition, participants in the sleep deprivation condition had greater baseline (i.e., pre-stress) cortisol [b = .727, p = .03], yet a blunted cortisol response to the TSST [b = -.026, p < .01]. These effects remained significant while controlling for known covariates (e.g., gender, mood, caffeine use). Taken together, a combination of elevated baseline cortisol (and its subsequent impact on HPA-axis regulatory processes) and a relative ‘ceiling’ on the amount of cortisol a laboratory stressor can produce may explain why participants in the sleep deprivation condition demonstrated blunted cortisol responses. The current findings suggest that future research investigating the relationship between health outcomes and HPA-axis stress reactivity should account for variability in sleep during the night prior to exposing participants to stress. Funding for this research was provided by the University of Michigan Department of Psychology and Rackham Graduate School, Blue Cross Blue Shield of Michigan Foundation, and the American Psychological Association of Graduate Students.

Effects of experimental night lighting on the daily timing of winter foraging in common European songbirds

The ecological effects of light pollution are becoming better understood, especially in birds. Recent studies have shown that several bird species can use street lighting to extend activity into the night during the breeding season. However, most of these studies are correlational and little is known about the effects of artificial night lighting on the timing of activities outside the breeding season. During winter, low temperatures and short days may limit foraging opportunities and can negatively affect survival of resident birds. However, night lighting may allow them to expand the time niche available for foraging. Here, we report on a study where we repeatedly manipulated the amount of night lighting during early winter at automated feeding stations in a natural forest. We used video‐recordings at the feeders to determine the time of the first (at dawn) and last (at dusk) foraging visits for six songbird species. We predicted that all species, and in particular the naturally early‐foraging species, would advance their daily onset of foraging during the mornings with night lighting, but would show minimal or no delays in their daily cessation of foraging during the lighted evenings. We found that two early‐foraging species, the blue tit and the great tit, started foraging earlier during the experimentally lighted mornings. However, in great tits, this effect was weak and restricted to nights with inclement weather. The light treatment did not have any effect on the start of foraging in the willow/marsh tit, the nuthatch, the European jay, and the blackbird. Artificial night lighting did not cause later foraging at dusk in any of the six species. Overall, our results suggest that artificial light during winter has only small effects on timing of foraging. We discuss these findings and the importance of temperature and winter weather in shaping the observed foraging patterns.

Light pulse effect on the locomotor activity rhythm of Talitrus saltator (Montagu) (Crustacea, Amphipoda)

The locomotor activity rhythm of the sandhopper Talitrus saltator (Amphipoda Talitridae) was investigated in Madfoun beach. The rhythm was monitored in individual and group animals during 21 days at constant temperature. During the first two weeks, animals were kept under light–dark cycle (d1–d7) and constant darkness (d8–d14). Light pulses of 2 h were applied, at the end of the experimental night, during the first 3 days of the third week (d15–d18). Then, constant darkness was restored for the rest of the experiment (d19–d21). Results revealed that Talitrus saltator individuals as well as groups concentrated their activities in experimental night under light–dark cycle and in the presence of pulses; whereas, a clear drift of activity is observed under constant darkness. Periodogram analysis showed the presence of circadian component whatever the recording type. An ultradian period was revealed in individual recording whatever the regimen, while for groups, this component appeared only under nLD cycle. Furthermore, the locomotor rhythm is more defined under nLD cycle for individuals and in constant darkness for groups.

Bites before and after bedtime can carry a high risk of human malaria infection

BackgroundUnderstanding biting distribution of potentially infectious (parous) mosquitoes at various hours of the night would be useful in establishing the likely impact of bed nets on malaria transmission. Bed nets are highly effective at preventing biting by older malaria vectors, which occurs when most people are in bed. However, this behaviour is likely to vary across ecological settings and among mosquito populations.MethodsField experiments were conducted in Minepa village within Kilombero Valley. Two outdoor catching stations located approximately 50 m from each other were established for mosquito collection. On each experimental night, mosquitoes were collected using human landing catch (HLC) by a single adult male at each station from 18:00 to 07:00 h. To compare the distribution of mosquito biting and the composition of their age structure, mosquitoes were sorted and recorded according to the hour they were collected. A sub-sample of Anopheles arabiensis was dissected to determine their parity status. Insectary-reared An. arabiensis within the semi-field system (SFS) with known age were also released in the SFS (10 m × 20 m) and recaptured hourly using HLC to determine the effect of parity on biting distribution.ResultsOverall, there was no statistical association between the parity status and the biting time of An. arabiensis either in the field or in the SFS (P ≥ 0.05). The wild and insectary-reared An. arabiensis were observed to exhibit different hourly biting patterns.ConclusionThe study has shown that mosquito biting time phenotype is not influenced by their parity status. These findings imply that the risk of human exposure to potentially infectious bites is equally distributed throughout the night, thus supplementary measures to protect people against bites in evening and morning are desirable.