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INTRODUCTION Sleep and rest–activity rhythm alterations are common in neurodegenerative diseases. However, their characterization in patients with behavioral variant frontotemporal dementia (bvFTD) has proven elusive. We investigated rest–activity rhythm alterations, sleep disturbances, and their neural correlates in bvFTD. METHODS Twenty‐seven bvFTD patients and 25 healthy controls completed sleep questionnaires and underwent 7 days of actigraphy while concurrently maintaining a sleep diary. Cortical complexity and thickness were calculated from T1‐weighted magnetic resonance (MR) images. RESULTS Compared to controls, bvFTD patients showed longer time in bed (95% confidence interval [CI]: 79.31, 321.83) and total sleep time (95% CI: 24.38, 321.88), lower sleep efficiency (95% CI: −12.58, −95.54), and rest–activity rhythm alterations in the morning and early afternoon. Increased sleep duration was associated with reduced cortical thickness in frontal regions. DISCUSSION Patients with bvFTD showed longer sleep duration, lower sleep quality, and rest–activity rhythm alterations. Actigraphy could serve as a cost‐effective and accessible tool for ecologically monitoring changes in sleep duration in bvFTD patients. Highlights We assessed sleep and circadian rhythms in behavioral variant frontotemporal dementia (bvFTD) using actigraphy. Patients with bvFTD show increased sleep duration and reduced sleep quality. Patients with bvFTD show rest–activity alterations in the morning and early afternoon. Sleep duration is associated with reduced cortical thickness in frontal regions. These alterations may represent an early sign of neurodegeneration.

Objective Rest‐activity rhythms (RARs) are perturbed in many forms of neuropsychiatric illness. In this study, we applied wrist actigraphy to describe RAR perturbations in intellectually disabled adults with epilepsy (“E + ID”), using a cross‐sectional case–control design. We examined whether RAR phenotypes correlated with epilepsy severity, deficits in adaptive function, and/or comorbid psychopathology. Methods Caregivers of E + ID subjects provided informed consent during routine ambulatory clinic visits and were asked to complete standardized surveys of overall epilepsy severity (GASE, Global Assessment of Severity of Epilepsy), adaptive function (ABAS‐3, Adaptive Behavior Assessment System‐3) and psychopathology (ABCL, Adult Behavior Checklist). Caregivers were also asked to ensure that subjects wore an Actiwatch‐2 device continuously for at least ten days. From actograms, we calculated RAR amplitude, acrophase, robustness, intradaily variability (IV), interdaily stability (IS), and estimates of sleep quantity and timing. We compared these RAR metrics against those from (i) a previously published cohort of adults with epilepsy without ID (E–ID), and (ii) a historical control cohort of age‐ and sex‐matched intellectually able subjects from the Study of Latinos (SOL). Results 46 E + ID subjects (median age 26, 47% female) provided a median recording duration of 11 days. Surveys reflected low to extremely low levels of adaptive function and low/subclinical levels of psychopathology. Compared with E‐ID and SOL cohorts, E + ID subjects displayed significantly lower measures of RAR amplitude, robustness, and IS, with significantly higher IV and total daily sleep. K‐means clustering of E + ID subjects recognized a cluster with pronounced hypoactivity, hypersomnia, and elevated rhythm fragmentation (cluster A), an intermediate group with metrics similar to E‐ID, and cluster “C” subjects that featured hyper‐robust and high amplitude RARs. All three clusters were similar in age, body mass index, antiseizure medication (ASM) polytherapy, ABAS3, and ABCL scores. Significance Adults with epilepsy and intellectual disability display a wide spectrum of RAR phenotypes that do not neatly correlate with measures of adaptive function or epilepsy severity. Prospective studies are necessary to determine whether continuous actigraphic monitoring can sensitively capture changes in chronobiological health that may arise with disease progression, ASM side effects, or other acute health deteriorations. Plain Language Summary Rest‐activity rhythms (RARs) can be measured using continuously worn wrist activity monitors. We show that compared to controls, adults with epilepsy and intellectual disability (E + ID) display RARs that are more fragmented, weaker in amplitude, and unstable across days. Within our E + ID cohort, we observed a wide spectrum of RAR phenotypes that we clustered into three subtypes, which were similar in overall average measures of adaptive functioning and psychiatric symptoms.

The objective of this study is to investigate the association between actigraphic estimates of the sleep–wake rhythm and a range of functional domains that contribute to well-being in demented elderly patients. Eighty-seven women aged 85.5 ± 5.9 years (mean ± standard deviation) wore an actigraph for two weeks. Activity profiles were analyzed using nonparametric variables, including dichotomy indices, interdaily stability (IS), intradaily variability (IV), and relative amplitude (RA). The associations between these variables and cognitive, functional, behavioral, and emotional states (obtained from standardized neuropsychologic assessments and questionnaires administered to caregivers) were investigated by partial correlations and stepwise regressions. Cognitive, functional, behavioral, and emotional states showed medium to strong correlations with multiple rhythm variables. Partial correlations indicated that this could not be attributed to a uniform worsening with advancing cognitive decline. Stepwise regressions indicated three most distinctive rhythm variables: 1) the interdaily stability of the 24-hour rhythm was most strongly, negatively, related to cognitive decline and depression; 2) the median level of daytime activity was most strongly, negatively, related to impairments of function, of activities of daily living, and of social interaction; and 3) nocturnal restlessness was secondarily, positively, related to impairments of function and social interaction. Especially the interdaily stability and median daytime activity level, and secondarily nocturnal restlessness, showed a strong relationship with the functional status and well-being of demented elderly. This raises the possibility that treatments that enhance daytime activity and the stability of the rest–activity rhythm may improve well-being.

Growing evidence highlights a tight interplay linking circadian and sleep–wake disturbances to the pathophysiology of neurodegenerative disorders. In α-synucleinopathies, three key points have emerged: (1) circadian and sleep–wake disruptions may increase the risk of neurodegeneration; (2) these alterations reflect widespread dysfunction in neural circuits regulating sleep, wakefulness, and biological rhythms; and (3) the prodromal condition of isolated rapid eye movement (REM) sleep behavior disorder (iRBD) offers a unique window into early pathological changes, as it is characterized by neurodegeneration in brainstem structures critical for sleep–wake regulation and REM sleep control. Hence, sleep- and circadian-related biomarkers may represent feasible tools for early diagnosis, prevention, and treatment across the spectrum of α-synucleinopathies. However, despite their potential, diagnostic or therapeutic pathways grounded in sleep and circadian biology have yet to be systematically explored or validated, and key questions remain, including the trajectories that characterize the clinical progression from iRBD to overt α-synucleinopathies. Key challenges include translational barriers, inter-individual variability in biomarker profiles, and the need for longitudinal studies to define clinically actionable thresholds. Against this backdrop, this mini-review synthesizes current evidence on sleep–wake rhythm alterations in iRBD as a prodromal stage of α-synucleinopathy-driven neurodegeneration. Candidate circadian biomarkers are discussed, including objective parameters from long-term actigraphic monitoring, encompassing rest–activity rhythms modeled with parametric and non-parametric approaches, as well as physiological indicators such as dim light melatonin onset and core body temperature.

Abstract Study Objectives Mobility restrictions imposed to suppress transmission of COVID-19 can alter physical activity (PA) and sleep patterns that are important for health and well-being. Characterization of response heterogeneity and their underlying associations may assist in stratifying the health impact of the pandemic. Methods We obtained wearable data covering baseline, incremental mobility restriction, and lockdown periods from 1,824 city-dwelling, working adults aged 21–40 years, incorporating 206,381 nights of sleep and 334,038 days of PA. Distinct rest-activity rhythm (RAR) profiles were identified using k-means clustering, indicating participants’ temporal distribution of step counts over the day. Hierarchical clustering of the proportion of days spent in each of these RAR profiles revealed four groups who expressed different mixtures of RAR profiles before and during the lockdown. Results Time in bed increased by 20 min during the lockdown without loss of sleep efficiency, while social jetlag measures decreased by 15 min. Resting heart rate declined by ~2 bpm. PA dropped an average of 42%. Four groups with different compositions of RAR profiles were found. Three were better able to maintain PA and weekday/weekend differentiation during lockdown. The least active group comprising ~51% of the sample, were younger and predominantly singles. Habitually less active already, this group showed the greatest reduction in PA during lockdown with little weekday/weekend differences. Conclusion In the early aftermath of COVID-19 mobility restriction, PA appears to be more severely affected than sleep. RAR evaluation uncovered heterogeneity of responses to lockdown that could associate with different outcomes should the resolution of COVID-19 be protracted.

Much attention has been devoted to explaining the spatial distribution of foraging animals, but rather little to their temporal distribution (i.e. whether they are diurnal, nocturnal or crepuscular). Many animals face predictable diel cycles of food availability or predation risk, and so the approach of measuring the relative ratio of mortality risk to food gained (the `minimize μ/f rule) can be applied equally as well to different time periods of the day as to alternative food patches or habitats. 2. This method is used here to investigate the diel activity patterns of juvenile Atlantic salmon, which have previously been shown to become increasingly biased towards nocturnal activity in winter, hiding for much of the day in streambed refuges. Calculations based on published data show that nocturnal foraging in winter is far safer per unit of food obtained than is diurnal, despite greatly reduced food capture efficiency at night-time light levels. 3. Using an automated activity monitoring system based on passive integrated transponder (PIT) tags, this study shows that winter diel activity patterns in salmon are dependent on food availability. A change in food density led to a parallel change in time spent in the refuge, but (as predicted by the μ/f rule) the effect was greatest at the time of day with the least favourable ratio of predation cost to feeding benefit. Thus an experimental increase in food availability led to a 16% reduction in time spent in nocturnal foraging but a 98% reduction in time spent foraging by day, with fish spending only 0.6% of the daylight hours out of the refuge at the highest food density. 4. However, brief daytime foraging bouts had a major impact on growth rates (presumably because feeding efficiency was much greater in daylight), especially when food was scarce. Daytime feeding was thus profitable in terms of rapid food acquisition but normally suboptimal in terms of risk of predation. 5. Daily activity patterns are therefore suggested to be the result of a complex trade-off between growth and survival, which takes account of diel fluctuations in food availability, food capture efficiency and predation risk; individual variation in the extent of diurnal feeding in salmon may result from state-dependent differences in the benefits of rapid feeding and growth.

Insects have evolved physiological adaptations and behavioral strategies that allow them to cope with a broad spectrum of environmental challenges and contribute to their evolutionary success. Visual performance plays a key role in this success. Correlates between life style and eye organization have been reported in various insect species. Yet, if and how visual ecology translates effectively into different visual discrimination and learning capabilities has been less explored. Here we report results from optical and behavioral analyses performed in two sympatric ant species, Formica cunicularia and Camponotus aethiops. We show that the former are diurnal while the latter are cathemeral. Accordingly, F. cunicularia workers present compound eyes with higher resolution, while C. aethiops workers exhibit eyes with lower resolution but higher sensitivity. The discrimination and learning of visual stimuli differs significantly between these species in controlled dual-choice experiments: discrimination learning of small-field visual stimuli is achieved by F. cunicularia but not by C. aethiops, while both species master the discrimination of large-field visual stimuli. Our work thus provides a paradigmatic example about how timing of foraging activities and visual environment match the organization of compound eyes and visually-driven behavior. This correspondence underlines the relevance of an ecological/evolutionary framework for analyses in behavioral neuroscience.

Wrist actigraphy has been used to assess sleep in older adult populations for nearly half a century. Over the years, the continuous raw activity data derived from actigraphy has been used for the characterization of factors beyond sleep/wake such as physical activity patterns and circadian rhythms. Behavioral activity rhythms (BAR) are useful to describe individual daily behavioral patterns beyond sleep and wake, which represent important and meaningful clinical outcomes. This paper reviews common rhythmometric approaches and summarizes the available data from the use of these different approaches in older adult populations. We further consider a new approach developed in our laboratory designed to provide graphical characterization of BAR for the observed behavioral phenomenon of activity patterns across time. We illustrate the application of this new approach using actigraphy data collected from a well-characterized sample of older adults (age 60+) with osteoarthritis (OA) pain and insomnia. Generalized additive models (GAM) were implemented to fit smoothed nonlinear curves to log-transformed aggregated actigraphy-derived activity measurements. This approach demonstrated an overall strong model fit (R2 = 0.82, SD = 0.09) and was able to provide meaningful outcome measures allowing for graphical and parameterized characterization of the observed activity patterns within this sample.

A \"landscape of fear\" (LOF) is a map that describes continuous spatial variation in an animal's perception of predation risk. The relief on this map reflects, for example, places that an animal avoids to minimize risk. Although the LOF concept is a potentially unifying theme in ecology that is often invoked to explain the ecological and conservation significance of fear, little is known about the daily dynamics of an LOF. Despite theory and data to the contrary, investigators often assume, implicitly or explicitly, that an LOF is a static consequence of a predator's mere presence within an ecosystem. We tested the prediction that an LOF in a large-scale, free-living system is a highly dynamic map with \"peaks\" and \"valleys\" that alternate across the diel (24-h) cycle in response to daily lulls in predator activity. We did so with extensive data from the case study of Yellowstone elk (Cervus elaphus) and wolves (Canis lupus) that was the original basis for the LOF concept. We quantified the elk LOF, defined here as spatial allocation of time away from risky places and times, across nearly 1,000-km² of northern Yellowstone National Park and found that it fluctuated with the crepuscular activity pattern of wolves, enabling elk to use risky places during wolf downtimes. This may help explain evidence that wolf predation risk has no effect on elk stress levels, body condition, pregnancy, or herbivory. The ability of free-living animals to adaptively allocate habitat use across periods of high and low predator activity within the diel cycle is an underappreciated aspect of animal behavior that helps explain why strong antipredator responses may trigger weak ecological effects, and why an LOF may have less conceptual and practical importance than direct killing.

Detectability of morphs in different light environments is one of the mechanisms favoring the persistence of color polymorphism via disruptive selection. This mechanism predicts that different morphs should be more active and successful when light conditions make them more cryptic. In nocturnal birds, no study has analyzed yet whether morphs show a different degree of nocturnality, showing different circadian activity rhythms in relation to night and day light. We analyze activity patterns and hunting efficiency of color morphs in relation to day/night light in the nocturnal polymorphic scops owl (Otus scops). Forty-four percent of owl activity took place in the first hours after sunrise and before sunset. Also, we found that nocturnal activity decreased from grey to brown females and that grey males fed their chicks more than brown ones at night. Visual modeling revealed that grey individuals would be more conspicuous to their prey than brownish ones during the day. These findings suggest that part of the activity of nocturnal scops owls may occur during the day and that grey individuals would be better adapted to forage during night-light than brownish ones. However, brown morphs seemed not to be better adapted to forage at day, suggesting that other mechanisms than visual detection by predators or prey contribute to the persistence of color polymorphism in the species.Significance statementCircadian activity patterns can vary intraspecifically in response to changing environmental conditions. Color variants in polymorphic species could change their circadian activity rhythms differently in relation to diel luminal variation, switching from nocturnality to diurnality or vice versa, to achieve better background matching. We study for the first time whether different color variants of the nocturnal polymorphic scops owl (Otus scops) show different circadian activity rhythms with respect to night and day light conditions by relying on GPS-tracking data and nest video recordings. We also use perceptual visual modeling to study crypsis of morphs during the day. We found that nearly half of the activity of owls took place in the first hours after sunrise and before sunset. Also, we found that grey individuals would be better adapted to forage during night-light than more brownish ones probably due to their poor background matching during the day for the visual system of insects. These results support the idea that in scops owls, color morphs may show different degree of nocturnality to improve their crypsis.