Late evening electric light exposure is associated with low sleep regularity in adolescents living in rural areas.

In this study, we tested the prediction that sleep regularity would be lower in adolescents exposed to late evening electric light (LEEL) than in those without exposure to it. The Sleep Regularity Index was calculated based on actigraph recordings from adolescents living in rural communities in Argentina and Brazil that were either exposed to LEEL or not. The effect of the LEEL on sleep variables was tested using linear models considering sex and age, as well as accounting for the differences between countries. Sleep onset was delayed, sleep duration shortened, and Sleep Regularity Index was 4 [1-8] points lower in the group exposed to LEEL (p = .0176, eta2 =0.13). Our results show that beyond sleep phase and duration, which are known to be affected by LEEL in this age group, sleep irregularity should also be considered as an important outcome variable when assessing the adverse effects of evening light on adolescents.

Daily light exposure, sleep-wake cycle and attention in adolescents from different urban contexts.

OBJECTIVE: to compare daily light exposure, activity-rest rhythm, sleep-wake cycle (SWC) and attention in Brazilian students living in different levels of urbanization. METHODS: 115 adolescents (74 girls), aged 14-18 years (mean 15.5 ± 0.7 years), from the first years of high school have participated. The SWC was evaluated by actimetry and a Sleep Diary for 10 days. Besides, the "Health and Sleep" Questionnaire, the Morningness and Eveningness Scale for adolescents, the Pittsburgh Sleep Quality Index, and the Pediatric Daytime Sleepiness Scale were answered. Attention was assessed by a Continuous Performance Task. RESULTS: In the less urbanized region, there were a greater exposure to light during the day accompanied by a higher proportion of morning-types and less occurrence of excessive daytime sleepiness. Otherwise, in the more urbanized region, adolescents showed a trend to sleep less in weekdays and presented more irregularity in sleep duration between weekdays and weekend, with 83 ± 15% of sleep efficiency, 01:04 ± 1:30 h of WASO and 7 ± 6.7 awakenings per night on the weekdays, suggestive of poor sleep quality. Despite of this, they showed better attentional performance: more correct responses (tonic and phasic alertness, and sustained attention) and less omissions (for all components). Regardless of the degree of urbanization, there was partial sleep deprivation, irregular sleep schedules and poor sleep quality in adolescents. CONCLUSIONS: The daily light exposure and activity-rest profiles, SWC and attention in adolescents varied according to the degree of urbanization. Besides, the negative impacts of early school starting times leading to sleep deprivation, irregular sleep times and poor sleep quality were observed irrespective of the degree of urbanization, reinforcing that the early school starting time at morning is a strong temporal challenge for teenagers, having negative impacts on cognition and academic performance.

Aging-related changes on social synchronization of circadian activity rhythm in a diurnal primate (Callithrix jacchus).

The input of environmental time cues and expression of circadian activity rhythms may change with aging. Among nonphotic zeitgebers, social cues from conspecific vocalizations may contribute to the stability and survival of individuals of social species, such as nonhuman primates. We evaluated aging-related changes on social synchronization of the circadian activity rhythm (CAR) in a social diurnal primate, the common marmoset. The activity of 18 male marmosets was recorded by actiwatches in two conditions. (1) Experimental - 4 young adult (5 ± 2 yrs of age) and 4 older (10 ± 2 yrs of age) animals maintained under LD 12/12 h and LL in a room with full insulation for light but only partial insulation for sound from vocalizations of conspecifics maintained outdoors in the colony; and (2) Control - 10 young adult animals maintained outdoors in the colony (5 animals as a control per age group). In LL, the CAR of young adults showed more stable synchronization with controls. Among the aged marmosets, two free-ran with τ > 24 h, whereas the other two showed relative coordination during the first 30 days in LL, but free-ran thereafter. These differences were reflected in the "social" phase angles (ψon and ψoff ) between rhythms of experimental and control animal groups. Moreover, the activity patterns of aged animals showed lower social synchrony with controls compared to young adults, with the time lags of the time series between each experimental group and control group being negative in aged and positive in young adult animals (t-test, p < 0.05). The index of stability of the CAR showed no differences according to age, while the intradaily variability of the CAR was higher in the aged animals during LD-resynchronization, who took additional days to resynchronize. Thus, the social modulation on CAR may vary with age in marmosets. In the aged group, there was a lower effect of social synchronization, which may be associated with aging-related changes in the synchronization and generation of the CAR as well as in system outputs.

Circadian and homeostatic modulation of the attentional blink.

An important property of attention is the limitation to process new information after responding to a stimulus. This property of attention can be evaluated by the Attentional Blink (AB), a phenomenon that consists of a failure to detect the second of two targets when the interval between them is 200-500 ms. The aim of the present work is to determine the possible existence of time awake (homeostatic changes) and time of day (circadian rhythm) variations in the AB. Eighteen undergraduate students, 11 men and 7 women, age = 18.06 ± 1.16 years, participated voluntarily in this research. They were recorded in a constant routine protocol during 29 h, in which rectal temperature was recorded every minute, while subjective sleepiness and responses to a Rapid Serial Visual Presentation (RSVP) task, to measure the AB, were recorded every hour. Homeostatic and circadian variations in all parameters of the RSVP task were observed, including changes in the capacity to process a new stimulus (Target 1 accuracy), a second stimulus occurring in a short interval after the first (Target 2 accuracy at lag 2, 200 ms) and to process another successive independent stimulus (Target 2 accuracy at lag 8, 800 ms). The acrophase of these parameters occurred with a phase delay of 2 h compared to the circadian rhythm of rectal temperature. The AB magnitude, an index of the AB, showed a decline with time awake, but no variations with time of day. In conclusion, there are homeostatic and circadian variations in the capacity to process any incoming information, especially in tasks with brief duration stimuli presented at a high frequency.

Mechanisms of social synchrony between circadian activity rhythms in cohabiting marmosets.

In marmosets, social synchrony between circadian profiles of activity is stronger in animals that cohabit in a family. The activity of three breeding pairs was recorded by actiwatches to investigate the mechanisms involved in the synchrony between the circadian activity profiles during cohabitation in marmoset reproductive pairs. The dyads were submitted to LD 12:12 (21 days) and LL: 1) cohabitation (24 days), 2) removal of the cage mate (20 days), 3) reintroduction of the mate into the cage of the 1st situation (30 days) and 4) removal of the cage mate (7 days). Next, they were rejoined and maintained in LD 12:12 (11 days). In conditions involving cohabitation of pair, the general and maximum correlation indexes between circadian profiles were higher in cage mates compared to animals of the same or different sex with which they maintain only acoustic and olfactive contact. This strong synchrony between rhythms was accompanied by a stable phase relationship at the activity onset and offset, with identical circadian periods between mates. When the pairs were separated, there was a break in stability in the phase relationships between activity profiles with different circadian periods and a greater phase angle difference between rhythms of cage mates. During separation, two females and one male progressively anticipated the activity onset and offset in a phase similar to that in previous conditions, expressing entrainment to the mate. During the first reintroduction, two pairs exhibited signs of masking in rhythm. Although modulation in the rhythm of some animals has been observed through acoustic cues from animals outside the colony, we suggest that cohabitation favors strong synchrony between the circadian activity profiles of marmoset reproductive pairs involving synchronization by entrainment and masking. Further studies in the absence of external social cues are necessary to clarify the role of these mechanisms on social synchronization in marmosets.

Gender differences in sleep habits and quality and daytime sleepiness in elementary and high school teachers.

The extensive workload of teachers inside and outside the classroom may contribute to sleep problems. Such problems may occur more frequently in women due to the combination of professional demands, domestic tasks, and their relatively greater sleep needs compared to men. The objective of this cross-sectional study was to evaluate the influence of gender on sleep habits and quality, and daytime sleepiness in a sample of 243 teachers (77 men and 166 women) using questionnaires. Linear regression models were used to examine the effect of gender on sleep measures; the unadjusted model considered only gender and the adjusted model considered chronotype and work characteristics as potential confounders. Bedtimes of women were significantly earlier than men during the week, but not on weekends, in the unadjusted and adjusted models. Time in bed was longer for women throughout the week and weekend in the unadjusted model. However, in the adjusted model, this statistical significance disappeared, and longer time in bed during the week was associated with teaching in one shift and for both levels of education. In addition, the female gender was associated with higher sleepiness scores compared to males in both models, and worse sleep quality in the adjusted model. Also, sleep quality was worse in subjects working in three shifts and in both types of schools (public and private). The tendency to eveningness was associated with later bedtimes and wake up times during both week days and weekends, higher irregularity of bedtimes and wake up times, and higher sleepiness scores in the adjusted model. Therefore, we suggest that female teachers do not fulfill their sleep needs and show higher levels of diurnal sleepiness and poor sleep quality that can be modulated by chronotype and some work characteristics. More studies are needed to evaluate the role of double workload on this pattern.

Forced desynchronization model for a diurnal primate.

The circadian system is organized in a hierarchy of multiple oscillators, with the suprachiasmatic nucleus (SCN) as the master oscillator in mammals. The SCN is formed by a group of coupled cell oscillators. Knowledge of this coupling mechanism is essential to understanding entrainment and the expression of circadian rhythms. Some authors suggest that light-dark (LD) cycles with periods near the limit of entrainment may be good models for promoting internal desynchronization, providing knowledge about the coupling mechanism. As such, we evaluated the circadian activity rhythm (CAR) pattern of marmosets in LD cycles at lower limits of entrainment in order to study induced internal dissociation. To that end, two experiments were conducted: (1) 6 adult females were under symmetrical LD cycles T21, T22 and T21.5 for 60, 35 and 48 days, respectively; and (2) 4 male and 4 female adults were under T21 for 24 days followed by 18 days of LL, back to T21 for 24 days, followed by 14 days of LL. The CAR of each animal was continuously recorded. In experiment 1, vocalizations were also recorded. Under Ts shorter than 24 days, a dissociation pattern was observed for CAR and vocalizations. Two simultaneous circadian components emerged, one with the same period as the LD cycle, called the light-entrained component, and the other in free-running, denominated the non-light-entrained component. Both components were displayed in the CAR for all the animals in T21, five animals (83.3%) in T21.5 and two animals (33.3%) in T22. Our results are in accordance with the multioscillatory nature of the circadian system. Dissociation is partial synchronization to the LD cycle, with at least one group of oscillators synchronized by relative coordination and masking, while another group of oscillators free runs, but is also masked by the LD cycle. Since only T21 promoted the emergence of both circadian components in the circadian rhythms of all marmosets, it was considered the promoter period of circadian rhythm dissociation in this species, and is proposed as a good animal model for forced desynchronization in non-human diurnal primates.

Circadian activity rhythm in pre-pubertal and pubertal marmosets (Callithrix jacchus) living in family groups.

In marmosets, a phase advance was observed in activity onset in pubertal animals living in captivity under semi-natural conditions which had stronger correlation with the times of sunrise over the course of the year than the age of the animal. In order to evaluate the effect of puberty on the circadian activity rhythm in male and female marmosets living in family groups in controlled lighting conditions, the activity of 5 dyads of twins (4 ♀/♂ and 1 ♂/♂) and their respective parents was continuously monitored by actiwatches between the 4th and 12th months of age. The families were kept under LD 12:12 h with constant humidity and temperature. The onset of puberty was identified by monitoring fecal steroids. Juveniles showed higher totals of daily activity and differences in the daily distribution of activity in relation to parents, in which the bimodal profile was characterized by higher levels in evening activity in relation to morning activity. Regarding the phase, the activity onset and offset, occurred later in relation to parents. After entering puberty, the activity onset and offset occurred later and there was an increase in total daily activity. On the other hand, when assessing the effect of sex, only females showed a delay in the activity offset and an increase in total daily activity. Therefore, the circadian activity rhythm in marmosets has peculiar characteristics in the juvenile stage in relation to the total of daily activity, the onset and offset of the active phase, and the distribution of activity during this phase. Besides, the entering puberty was associated with a phase delay and increase on total daily activity, with differences between sexes, possibly due to hormonal influences and/or social modulation on rhythm.

Influence of different light intensities on the daily grooming distribution of common marmosets Callithrix jacchus.

The daily distribution of autogrooming was evaluated in adult marmosets submitted to different illumination intensities in the light phase of the light-dark cycle. Autogrooming and locomotor activity were monitored and the faecal cortisol level assessed as a stress indicator. The distribution of autogrooming showed two distinct tendencies: when the light intensity varied from 500 to 200 lux, a slight increase in frequency and duration was observed, while a significant decrease in both variables occurred at 10 lux. Varying light intensities did not inhibit rhythm synchronization. The daily profile of autogrooming was mainly unimodal with an acrophase in the first half of the light phase. Faecal cortisol levels tended to increase in animals submitted to 100 and 10 lux, but these results are not conclusive. We suggest keeping captive marmosets in light intensities of at least 200 lux in the light phase, allowing animals to maintain autogrooming levels in order to reduce the discomfort caused by captivity and isolation.

Influence of seasonality on circadian motor activity rhythm in common marmosets during puberty.

The effect of puberty on circadian rhythmicity in nonhuman primates has been little studied, even though it has been demonstrated that puberty-related changes in circadian activity rhythm occur in a number of species, including humans. To characterize the motor activity rhythm during puberty in common marmosets (Callithrix jacchus), six animals was continuously monitored by actimeters between their 5th and 12th months of age. The animals were housed with their families in outdoor cages under seminatural conditions. Onset of puberty was determined from fecal estrogen and progesterone levels in females and androgen levels in males. The spectral power of the circadian component stabilized later in the last two animals to enter puberty. The bimodal characteristic of the active phase in this species became progressively more apparent over the course of the months in which the mean temperature was highest, irrespective of the animal's age. Although the onset of activity advanced after entry into puberty, this parameter showed a strong correlation with sunrise, indicating that seasonality influences this variable. Neither age nor climatic factors included in the regression model influenced the differences in phase angles between sunrise and onset of activity, and between sunset and offset of activity. Total activity was the only parameter influenced by age in the regression model, showing an increase after entry into puberty. Despite the evidence of pubertal influence on both the circadian component and total activity, under seminatural conditions seasonal factors may have a more important effect on motor activity rhythm in common marmosets.

Effect of nest box availability on the circadian activity rhythm of common marmosets (Callithrix jacchus).

The effect of nest box availability on the circadian activity rhythm (CAR) was compared in a diurnal primate kept in two conditions: with and without nest box, in a light-dark (LD) cycle (12:12) and constant light (LL). Marmosets kept in LD without nest box showed a longer duration of the activity phase (alpha), smaller day-to-day variability in activity onset and offset and higher levels of activity, particularly towards the end of the activity time. In LL, all animals maintained with nest box expressed free-running CAR, but without nest box, 3 of the 4 individuals showed relative coordination with the outdoor LD cycle, possibly due to social synchronization with captive marmosets maintained outdoors. All animals showed longer alpha and higher levels of activity without nest box. Thus, the availability of a nest box is an important aspect in maintaining marmosets, influencing CAR expression in this diurnal primate in LD and LL conditions, possibly due to differences in light exposure that induces masking. Further studies are needed to evaluate the effects of the unavailability of a nest box on CAR in LL conditions.