Daytime Activity Levels Research Articles

Distinguishing Subgroups Based on Psychomotor Functioning among Patients with Major Depressive Disorder

Background: Retardation and agitation are symptoms of major depressive disorder (MDD), and their presence could play a role in determining clinically meaningful depressive subtypes such as nonmelancholic depression (NMD) and melancholic depression (MD). In this project, we explored whether three depression subgroups (NMD, MD with psychotic symptoms, and MD without psychotic symptoms) could be distinguished based on objective measures of psychomotor functioning. Methods: Sixty-nine patients with MDD underwent extensive clinical and psychomotor testing prior to treatment with electroconvulsive therapy. Psychomotor functioning was assessed subjectively using the Core Assessment of Psychomotor Change (CORE) and objectively by means of both 24-h actigraphy and performance on a fine motor drawing task. Results: The daytime activity levels measured by actigraphy were significantly lower (F = 7.1, p = 0.0004) in MD patients both with and without psychotic symptoms than in those with NMD. No objective psychomotor variable was able to distinguish between melancholic patients with and those without psychotic symptoms. Conclusions: The depression subtypes NMD, MD with psychotic symptoms, and MD without psychotic symptoms are not marked by increasing psychomotor retardation, possibly because psychomotor disturbance in MD with psychotic symptoms often consists of agitation rather than retardation, or a mixture of the two. However, psychomotor functioning as measured by actigraphy can be used to distinguish between NMD patients and MD patients.

Gene expression profiling of the SCN in young and old rhesus macaques.

In mammals, the suprachiasmatic nucleus (SCN) is the location of a master circadian pacemaker. It receives photic signals from the environment via the retinal hypothalamic tract, which play a key role in synchronizing the body's endogenously generated circadian rhythms with the 24-h rhythm of the environment. Therefore, it is plausible that age-related changes within the SCN contribute to the etiology of perturbed activity-rest cycles that become prevalent in humans during aging. To test this hypothesis, we used gene arrays and quantitative RT-PCR to profile age-related gene expression changes within the SCN of male rhesus macaques - a pragmatic translational animal model of human aging, which similarly displays an age-related attenuation of daytime activity levels. As expected, the SCN showed high expression of arginine vasopressin, vasoactive intestinal polypeptide, calbindin and nuclear receptor subfamily 1, group D, member 1 (NR1D1) (also known as reverse strand of ERBA (REV-ERBα), both at the mRNA and protein level. However, no obvious difference was detected between the SCNs of young (7-12 years) and old animals (21-26 years), in terms of the expression of core clock genes or genes associated with SCN signaling and neurotransmission. These data demonstrate the resilience of the primate SCN to normal aging, at least at the transcriptional level and, at least in males, suggest that age-related disruption of activity-rest cycles in humans may instead stem from changes within other components of the circadian system, such as desynchronization of subordinate oscillators in other parts of the body.

Effect of androgen supplementation on 24-hour activity-rest patterns of aged male rhesus macaques

Like elderly men, old male rhesus macaques show attenuated circulating levels of testosterone and dehydroepiandrosterone sulfate, and many of them also show reduced levels of daytime activity. It is unclear, however, if this age-associated behavioral change is causally related to the underlying decrease in circulating androgen levels. To test this possibility, old male rhesus macaques were given daily supplements of testosterone and DHEA for 6 months, designed to mimic the mean 24-hour circulating hormone patterns of young adults. Compared with the young adults, the old controls showed attenuated daytime activity levels. However, there was no difference between the androgen-supplemented old animals and the aged-matched controls, even after 6 months of treatment. The data suggest that age-associated decreases in circulating androgen levels are unlikely to be a primary reason for altered activity-rest patterns in elderly men, and that androgen supplementation paradigms might not provide any obvious therapeutic benefit.

Quantifying the effect of body mass index, age, and depression severity on 24-h activity patterns in persons with a lifetime history of affective disorders.

BackgroundPatients with affective disorders of different ages have been found to present weight changes and different circadian activity patterns. This study assessed the effects of age, Body Mass Index (BMI) and depression severity on the activity-rest cycle in persons with affective disorders using a novel multifactorial 24-h analysis method.MethodsTwo hundred and thirty-six participants aged between 14 and 85 years underwent 5 to 22 days of actigraphy monitoring (mean duration = 14 days). BMI was also recorded and symptom severity was assessed with the Hamilton Depression Rating Scale (HDRS). Participants were divided into two groups: healthy controls (n = 68) and participants with a lifetime diagnosis of affective disorders (n = 168). First, the multiple regression method was employed to formulate the circadian activity pattern in term of the factors age, BMI and HDRS. For each group, the functional linear analysis method was applied to assess the relative effects of the factors. Finally, Wald-tests were used to assess the contribution of each factor on the circadian activity pattern.ResultsIn the affective disorders group, higher BMI was associated with higher activity levels from 3 am until 5.30 am and with lower activity levels from 10 am until 10.30 pm. Older age was associated with less activity across the day, evening, and night - from 11 am until 5.30 am. Higher HDRS scores were associated with higher activity around 1:30 am. In healthy controls, the effects of BMI and age on activity patterns were less pronounced and affected a narrower portion of the 24-h period.ConclusionThese findings suggest that older age and higher BMI are linked to lower daytime activity levels. Higher BMI and worse symptom severity were also associated with nocturnal activity patterns suggestive of sleep disturbances. The influence of age and BMI on 24-h activity profiles appear to be especially pronounced in people with affective disorders.

Effect of experimental change in children's sleep duration on television viewing and physical activity

Paediatric observational studies demonstrate associations between sleep, television viewing and potential changes in daytime activity levels. To determine whether experimental changes in sleep lead to changes in children's sedentary and physical activities. Using a within-subject counterbalanced design, 37 children 8-11 years old completed a 3-week study. Children slept their typical amount during a baseline week and were then randomized to increase or decrease mean time in bed by 1.5 h/night for 1 week; the alternate schedule was completed the final week. Children wore actigraphs on their non-dominant wrist and completed 3-d physical activity recalls each week. Children reported watching more television (p < 0.001) and demonstrated lower daytime actigraph-measured activity counts per epoch (p = 0.03) when sleep was decreased (compared with increased). However, total actigraph-measured activity counts accrued throughout the entire waking period were higher when sleep was decreased (and children were awake for longer) than when it was increased (p < 0.001). Short sleep during childhood may lead to increased television viewing and decreased mean activity levels. Although additional time awake may help to counteract negative effects of short sleep, increases in reported sedentary activities could contribute to weight gain over time.

Functional Somatic Syndromes: Skin Temperatures and Activity Measurements Under Ambulatory Conditions

Functional somatic syndromes are mostly associated with pain and emotional distress. As one marker for the autonomic stress response, the distal skin temperature decreases during psychological stress. In patients with functional somatic syndromes, the distal skin temperature under baseline conditions (without stress induction) is usually lower than in healthy subjects, which could be due to the sustained presence of pain-related stress in such patients. The aim of our study was to investigate whether patients with functional somatic syndromes show altered skin temperatures also under everyday life conditions.14 patients with functional somatic syndromes and 14 matched healthy control subjects were investigated under ambulatory conditions over six consecutive days. During this time, distal and proximal skin temperatures were continuously recorded and sleep-wake cycles were monitored by actimetry and sleep-wake diaries. Unexpectedly, the patients showed higher distal skin temperatures than control subjects in the afternoon. The objective temperature data did not match the patients' subjective experience: ratings of thermal comfort did not vary between the two groups. Moreover, similar levels of daytime activity were recorded in the two samples, even though patients reported more tiredness and more body tension than controls. We interpret the observed dissociation between objective skin temperature measurements and subjective ratings of the bodily thermal comfort as support for the notion of an alexisomia account (reduced bodily awareness) for functional somatic syndromes. Moreover, findings indicate that subjective complaints of tiredness and tension do not necessarily result in physical avoidance behaviour.

Diurnal activity patterns as a sensitive behavioural outcome in fish: effect of short‐term exposure to treated sewage and a sub‐lethal PPCP mixture

AbstractSub‐lethal toxicological responses are common occurrences in aquatic animals exposed to sewage wastewater and organic wastewater contaminants. Behavioural alterations are particularly sensitive indicators of sub‐lethal toxicological stress in animals exposed to various pollutants, and often correlate with higher‐level outcomes. Diurnal activity patterns in many fish species are sensitive to changes in natural biotic factors, but few studies have explored how environmental pollutants influence such rhythms. We investigated diurnal activity patterns in the mosquitofish (Gambusia holbrooki), after exposure to UV‐treated sewage and a mixture of key contaminants identified through chemical analysis and subsequent risk‐based prioritization of the wastewater. Exposure to 50% and 100% wastewater abolished daytime activity levels in male, but not female fish. Chemical analysis identified fluoxetine, diazinon and triclosan above their reported predicted‐no‐effect‐concentrations (PNECs), and fish were thus exposed to a mixture of these compounds at 1, 10 and 100 μg l–1. Behavioural responses were highly consistent between fish exposed to wastewater and the contaminant mixture, indicating that these prioritized contaminants are indeed likely contributing to the observed effects. Effective concentrations of the mixture were considerably lower than those reported as eliciting behavioural effects in previous studies exploring each of these compounds alone. Results warn of the potential for negative higher‐level consequences associated with exposures of fish to common organic wastewater contaminants, as altered diurnal activity patterns could conceivably scale‐up to influence performance including foraging success and predator avoidance. Further research is necessary to increase our understanding of linkages between alterations to diurnal activities and effects at the population level. Copyright © 2016 John Wiley &amp; Sons, Ltd.

A pathway underlying the impact of CPAP adherence on intimate relationship with bed partner in men with obstructive sleep apnea.

Our aim was to determine the pathway underlying the effects of continuous positive airway pressure (CPAP) adherence on intimate relationship with bed partner in men with obstructive sleep apnea (OSA). We hypothesized that CPAP with good adherence affected the intimate relationship with bed partner directly and indirectly, and it was mediated through daytime sleepiness and activity level in men with OSA. Data were obtained from an education program for enhancing CPAP adherence. Men who were newly diagnosed of OSA and CPAP therapy naïve were recruited in a tertiary teaching hospital. Self-reported quality of life [Functional Outcomes of Sleep Questionnaire], daytime sleepiness [Epworth Sleepiness Scale (ESS)], and negative emotion symptoms [depression, anxiety, stress scale] were assessed before and after CPAP treatment at 1-year assessment. Seventy-three men were included in the data analysis, with a mean ± SD age of 52 ± 10years, body mass index of 29.0 ± 5.2kg/m(2), ESS of 9.5 ± 5.6, and median [interquartile range(IR)] apnea and hypopnea index of 31 (21, 56) events/h. The median (IR) CPAP daily usage was 4.3(0, 6.1) h/day. From the path analysis, CPAP therapy was shown to improve intimate relationship directly (ß = 0.185) and indirectly (ß = 0.050) by reducing daytime sleepiness and increasing activity level. However, negative emotion symptoms were not the mediators between CPAP adherence and the intimate relationship. CPAP therapy with good adherence is related directly and indirectly to a better intimate relationship with bed partner in men with OSA. It was possibly attributed to reduced daytime sleepiness and increased activity level.

Activity Suppression Behavior Phenotype in SULT4A1 Frameshift Mutant Zebrafish.

Since its identification in 2000, sulfotransferase (SULT) 4A1 has presented an enigma to the field of cytosolic SULT biology. SULT4A1 is exclusively expressed in neural tissue, is highly conserved, and has been identified in every vertebrate studied to date. Despite this singular level of conservation, no substrate or function for SULT4A1 has been identified. Previous studies demonstrated that SULT4A1 does not bind the obligate sulfate donor, 3'-phosphoadenosine-5'-phosphosulfate, yet SULT4A1 is classified as a SULT superfamily member based on sequence and structural similarities to the other SULTs. In this study, transcription activator-like effector nucleases were used to generate heritable mutations in the SULT4A1 gene of zebrafish. The mutation (SULT4A1(Δ8)) consists of an 8-nucleotide deletion within the second exon of the gene, resulting in a frameshift mutation and premature stop codon after 132 AA. During early adulthood, casual observations were made that mutant zebrafish were exhibiting excessively sedentary behavior during the day. These observations were inconsistent with published reports on activity in zebrafish that are largely diurnal organisms and are highly active during the day. Thus, a decrease in activity during the day represents an abnormal behavior and warranted further systematic analysis. EthoVision video tracking software was used to monitor activity levels in wild-type (WT) and SULT4A1(Δ8/Δ8) fish over 48 hours of a normal light/dark cycle. SULT4A1(Δ8/Δ8) fish were shown to exhibit increased inactivity bout length and frequency as well as a general decrease in daytime activity levels when compared with their WT counterparts.

A novel pathway for sensory-mediated arousal involves splicing of an intron in the period clock gene.

D. melanogaster is an excellent animal model to study how the circadian (≅24-h) timing system and sleep regulate daily wake-sleep cycles. Splicing of a temperature-sensitive 3'-terminal intron (termed dmpi8) from the circadian clock gene period (per) regulates the distribution of daily activity in Drosophila. The role of dmpi8 splicing on daily behavior was further evaluated by analyzing sleep. Transgenic flies of the same genetic background but expressing either a wild-type recombinant per gene or one where the efficiency of dmpi8 splicing was increased were exposed to different temperatures in daily light-dark cycles and sleep parameters measured. In addition, transgenic flies were briefly exposed to a variety of sensory-mediated stimuli to measure arousal responses. Surprisingly, we show that the effect of dmpi8 splicing on daytime activity levels does not involve a circadian role for per but is linked to adjustments in sensory-dependent arousal and sleep behavior. Genetically altered flies with high dmpi8 splicing efficiency remain aroused longer following short treatments with light and non-photic cues such as mechanical stimulation. We propose that the thermal regulation of dmpi8 splicing acts as a temperature-calibrated rheostat in a novel arousal mechanism, so that on warm days the inefficient splicing of the dmpi8 intron triggers an increase in quiescence by decreasing sensory-mediated arousal, thus ensuring flies minimize being active during the hot midday sun despite the presence of light in the environment, which is usually a strong arousal cue for diurnal animals.

The Stability of Sleep Patterns in Children 3 to 7 Years of Age

To determine the reliability and stability of sleep (duration and quality) over time in young children using repeated accelerometer estimates of sleep. One hundred ninety-four children wore Actical accelerometers for 5-day periods (24-hour monitoring) at 3, 4, 5, 5.5, 6.5, and 7 years of age. Sleep variables of interest (duration, onset, offset, latency, efficiency, and wake after sleep onset) were estimated using the Sadeh algorithm within a commercial data reduction program (ActiLife). Children were divided into various groups according to sleep stability, and demographic and behavioral differences were compared across groups by ANOVA. All measures of sleep quantity and quality required 4-7 days of accelerometry to obtain acceptable reliability estimates, except morning wake time (2-4 days), and sleep latency (11-21 days). Average year-to-year correlations were only moderate for most measures (r = 0.41-0.51), but considerably higher than those observed for sleep latency, efficiency, and wake after onset (r = 0.15-0.24). Only 29 children were classified as sleep-stable over the 4 years. These children were less likely to be from ethnic minority groups (P = .017) and had higher levels of day-time physical activity (P = .032). Sleep patterns in children are not particularly stable, showing considerable variation both within a week and across the years. Few children exhibit stable sleep patterns over time, yet characterization of these children might provide further information regarding how sleep benefits health.

A pilot study of actigraphy as an objective measure of SSRI activation symptoms: Results from a randomized placebo controlled psychopharmacological treatment study

Selective serotonin reuptake inhibitors (SSRIs) are an efficacious and effective treatment for pediatric obsessive-compulsive disorder (OCD) but have received scrutiny due to a potential side effect constellation called activation syndrome. While recent research introduced a subjective measure of activation syndrome, objective measures have not been tested. This pilot study, using data from a larger randomized-controlled trial, investigated the potential of actigraphy to provide an objective measure of activation symptoms in 44 youths with OCD beginning an SSRI medication regimen. Data were collected over the first four weeks of a multi-site, parallel, double-blind, randomized, placebo controlled psychopharmacological treatment study and statistical modeling was utilized to test how activation syndrome severity predicts daily and nightly activity levels. Results indicated that youths with higher activation symptoms had lower daytime activity levels when treatment averages were analyzed; in contrast youths who experienced onset of activation symptoms one week were more likely to have higher day-time and night-time activity ratings that week. Results support actigraphy as a potential objective measure of activation symptoms. Subsequent studies are needed to confirm these findings and test clinical applications for use by clinicians to monitor activation syndrome during SSRI treatment. National Institutes of Health (5UO1 MH078594-01); NCT00382291.

The Bidirectional Relationship Between Exercise and Sleep

Exercise has long been associated with better sleep, and evidence is accumulating on the efficacy of exercise as a nonpharmacologic treatment option for disturbed sleep. Recent research, however, has noted that poor sleep may contribute to low physical activity levels, emphasizing a robust bidirectional relationship between exercise and sleep. This article will briefly review the evidence supporting the use of exercise as a nonpharmacologic treatment for sleep disturbance, outline future research that is needed to establish the viability of exercise as a behavioral sleep treatment, describe recent research that has emphasized the potential influence of poor sleep on daytime activity levels, and discuss whether improving sleep may facilitate adoption and/or better adherence to a physically active lifestyle. With poor sleep and physical inactivity each recognized as key public health priorities, additional research into the bidirectional relationship between exercise and sleep has significant implications for facilitating greater exercise adherence and improving sleep in society.

Association Between Physical Activity and Sleep in Adults With Chronic Pain: A Momentary, Within-Person Perspective

Individuals with chronic pain consider improved sleep to be one of the most important outcomes of treatment. Physical activity has been shown to have beneficial effects on sleep in the general population. Despite these findings, the physical activity-sleep relationship has not been directly examined in a sample of people with chronic pain. This study aimed to examine the association between objective daytime physical activity and subsequent objective sleep for individuals with chronic pain while controlling for pain and psychosocial variables. An observational, prospective, within-person study design was used. A clinical sample of 50 adults with chronic pain was recruited. Participation involved completing a demographic questionnaire followed by 5 days of data collection. Over this period, participants wore a triaxial accelerometer to monitor their daytime activity and sleep. Participants also carried a handheld computer that administered a questionnaire measuring pain, mood, catastrophizing, and stress 6 times throughout the day. The results demonstrated that higher fluctuations in daytime activity significantly predicted shorter sleep duration. Furthermore, higher mean daytime activity levels and a greater number of pain sites contributed significantly to the prediction of longer periods of wakefulness at night. The small sample size used in this study limits the generalizability of the findings. Missing data may have led to overestimations or underestimations of effect sizes, and additional factors that may be associated with sleep (eg, medication usage, environmental factors) were not measured. The results of this study suggest that engagement in high-intensity activity and high fluctuations in activity are associated with poorer sleep at night; hence, activity modulation may be a key treatment strategy to address sleep complaints in individuals with chronic pain.

Self-Care Strategies to Relieve Fatigue in Patients Receiving Radiation Therapy

Despite advances in symptom management, patients commonly experience fatigue during radiation therapy (RT). Minimal research has been conducted to determine how evidence-based recommendations are put into clinical practice and used by patients to manage fatigue. The aims of the current study were to identify the self-care strategies used by patients receiving RT, explore the effectiveness of those strategies, and identify how patients learned about fatigue management. Participants reported using multiple recommended interventions to relieve fatigue. The majority of participants reported they primarily rested or slept to improve fatigue. They also reported decreasing their activity level, exercising, using stimulants and complementary therapies, and eating and drinking nutritious items. More than half of the participants reported some relief of fatigue regardless of the intervention used. The majority of participants reported that they learned how to manage their fatigue mostly through experience and trial and error. Nurses need to explore the complex dynamics of each patient's fatigue and tailor multiple evidence-based interventions to maximize each patient's functional status and quality of life. When assessing and teaching about fatigue, nurses need to explore patients' daytime activity level and daytime sleep to be sure that excessive inactivity is not contributing to fatigue.

Daytime Physical Activity Levels in School-Age Children With and Without Asthma

Physical activity (PA) is a significant predictor of health outcomes in children with and without chronic conditions. Few researchers have used actigraphy as an objective measure of PA during the child's normal daily routines, and the findings have been inconsistent. It is unclear if asthma can contribute to low PA levels. The aim of this study was to compare daytime PA levels in children with and without asthma and examine the relationships among asthma, PA, body mass index (BMI), and child reports of symptoms. Physical activity as measured by actigraphy and self-report symptoms of coughing, wheezing, chest tightness, perceived tiredness, sleepiness, and alertness were obtained in 54 children aged 9-11 years with and without asthma for 7 consecutive days. Activity variables derived from actigraphy included (a) mean daytime activity level; (b) peak daytime activity level; and (c) time duration spent in sedentary, light, moderate, vigorous, and total moderate plus vigorous PA (MVPA). Children with and without asthma did not differ on BMI or activity levels. Children with asthma reported more activity limitations due to breathing problems than children without asthma (p < .01). In multivariate analyses, asthma predicted reduced mean, peak, and total time spent in MVPA level after controlling for gender, BMI, and self-report of symptoms. A significant interaction was found between asthma and BMI on mean, peak, and total time spent in MVPA. The association between asthma and PA is complex when the child's BMI is considered. Results suggest that reduced PAs with respect to respiratory symptom severity, childhood obesity, and functional impairment are important areas for future studies.

Effect of age and feeding schedule on diurnal rest/activity rhythms in dogs

Dogs exhibit biorhythms like diurnal sleep/wake and rest/activity behavior patterns with circadian rhythmicity and, similar to other mammalian species, show age-dependent changes in activity rhythms. This study sought to further characterize night/day locomotor activity patterns in adult dogs of various ages, and to examine the effect of feeding frequency (once vs. twice). Three groups (early adults [EA], 1.5-4.5 years; late adults [LA], 7-9 years; senior, 11-14 years) of beagles (N = 48) wore the Actiwatch activity monitoring system for 3 days while housed indoors with 12-hour light/dark schedule. Activity recording devices were used to collect actigraphy data when dogs were on a once- or twice-daily feeding regimen. All dogs demonstrated a circadian activity pattern with high levels of daytime activity and low levels of nighttime activity. The main effect of age differed for both daytime (P < 0.0001) and nighttime (P = 0.002) activity counts. Daytime activity in senior dogs was 17% and 42% lower compared with LA and EA dogs, respectively. With nighttime activity, both LA and seniors had significantly lower counts compared with the EA. Compared to once-daily feeding, twice-daily feeding significantly increased night activity, night/day activity ratio, and activity counts 60 minutes before the light phase across all 3 age-groups. This study provides a comprehensive characterization of age-related changes in locomotor behavior patterns in dogs and uniquely demonstrates that frequency of feeding can influence nighttime activity levels, which is partially associated with level of prelight onset of activity.

Morphine administration and abrupt cessation alter the behavioral diurnal activity pattern

In mammals, there is an underlying mechanism that dictates the organism's biological functions and daily activity schedule, known as circadian rhythms, which play a major role in maintaining steady metabolism, homeostasis, and immunity. Limited research has been done investigating the effects of continuous opiate administration on the circadian rhythm activity pattern. A change in circadian activity pattern is suggested as an experimental model to demonstrate long-term effect of the drug. The objective of this study was to investigate the effects of morphine treatment on the long term activity (24h) of the animal as well as the activity after abrupt removal, since prescribed medication containing morphine is widely used and abused and its long term effects are not known. Male Sprague–Dawley rats were contained in stable conditions with a standard light/dark cycle recordings taken before, during and after morphine pellet implantation. Cosinor analysis was used to fit a 24-hour curve to the activity pattern. Results indicate that morphine pellet administration alters the mesor, amplitude, the day-time and night-time activity levels, and demonstrates a remarkable change in the maximal circadian rhythm timing during the withdrawal period. The question whether morphine changes the circadian rhythm or a change in circadian rhythm results in tolerance and withdrawal is discussed.

The effect of ecologically relevant variations in light level on the performance of Mongolian gerbils on two visual tasks

Tests of rodent visual capacities are typically performed under standard laboratory illumination. However, light level can have subtle and complex effects on behavior in rodents. We tested Mongolian gerbils (Meriones unguiculatus) - a species that shows individual differences in activity pattern - on visual tasks at three ecologically relevant levels of ambient illuminance: approximating moonlight (1 lx), dawn or dusk (10 lx), and low daylight (100 lx). A jumping task and a grating discrimination quantified depth perception and grating acuity, respectively. Illuminance variations had important effects on behavior. Gerbils jumped faster in lower light on the depth discrimination task, but were also less accurate than in bright light. Daytime activity levels (possibly reflecting variations in activity pattern) mediated these effects, with animals that were awake during a lower proportion of daytime hours exhibiting a trend toward jumping faster with lower light level as compared to more day-active gerbils. Moreover, while illuminance did not affect acuity overall, it interacted with activity levels in a complex way: in both the darkest and lowest light levels, animals that were awake during a greater proportion of daytime hours showed higher acuity levels than animals that were less active during the day. These results indicate that gerbils show behavioral profiles in vision tasks that represent an interaction between visual ability and illuminance-sensitive motivational or emotional actors, perhaps including chronotype. Thus, the most ecologically relevant assessments of the visual performance of rodents will likely be achieved by testing at species-specific preferred light levels.

Mother-Infant Activity Synchrony as a Correlate of the Emergence of Circadian Rhythm

Entrainment to the day-night cycle is critical for infant sleep and social development. Synchronization of infant circadian systems with the social 24-hr day may require maternal activity signals as an entraining cue. This descriptive and exploratory research examines the activity level and circadian pattern in mothers and infants. Twenty-two healthy mothers and their infants (postnatal age 49.8 ± 17.1 days) wore actigraph monitors for seven days. Daytime (06:00-21:59) and nighttime (22:00-05:59) activity levels and circadian parameters of rest-activity patterns (i.e., mesor, amplitude, acrophase, and 24-hr cosinor fit) were calculated. Mothers and infants were significantly more active during the day than at night. The goodness-of-fit index for the model (R2) indicates that circadian rhythm accounted for a mean of 29 ± 10% and 12 ± 8% of the variability in maternal and infant activity, respectively. Acrophase of activity occurred at 15:46 ± 1:07 for the mothers and 15:20 ± 1:21 for the infants. The mean within-dyad correlation of activity counts was r = .46 ± .11, and the within-dyad correlation was associated with the amplitude (r = .66, p < .01) and 24-hr cosinor fit of infant activity (r = .67, p < .01). Our findings suggest maternal rhythms as a possible exogenous influence on shaping an infant's emerging rhythms and synchronizing them with the external light-dark cycle. Strong pattern synchrony between maternal and infant activity may support infant circadian entrainment and enhance a regular 24-hr sleep-wake schedule during the early postnatal weeks.