Sleep, circadian rhythms, and interval timing: evolutionary strategies to time information

Cognitive load, fatigue and aversive simulator symptoms but not manipulated zeitgebers affect duration perception in virtual reality

The perceived duration of an interval depends on numerous aspects of the passed event both endogenous, including physiological arousal, level of wakefulness, attention, and surprise, as well as exogenous such as valence, salience, or context in the environment. There is some evidence that "time-giving" cues from the environment (zeitgebers) are coupled with time perception. The movement of the sun on the horizon was demonstrated to affect interval perception in a study conducted by Schatzschneider et al. (2016) claiming that the sun’s motion is a zeitgeber that influences time perception. In the present study, we undertake the first to our knowledge replication of this effect, extending the analysis to confounding aspects of the used paradigm. We aimed to test the effect of immersion, cognitive load, and changes in the speed of the sun on the horizon of the virtual environment on the perceived interval duration. We did not replicate the original effect, as reported by Schatzschneider et al., however, we did find that the perceived duration of an interval was affected by cognitive load, fatigue, and unpleasant symptoms caused by VR. In our analysis, we used Bayesian statistics to support our conclusion and offer its results as having some important consequences for the field.

The social evolution of sleep: sex differences, intragenomic conflicts and clinical pathologies

Sleep appears to be essential for most animals, including humans. Accordingly, individuals who sacrifice sleep are expected to incur costs and so should only be evolutionarily favoured to do this when these costs are offset by other benefits. For instance, a social group might benefit from having some level of wakefulness during the sleeping period if this guards against possible threats. Alternatively, individuals might sacrifice sleep in order to gain an advantage over mate competitors. Here, we perform a theoretical analysis of the social evolutionary pressures that drive investment into sleep versus wakefulness. Specifically, we: investigate how relatedness between social partners may modulate sleeping strategies, depending upon whether sleep sacrifice is selfish or altruistic; determine the conditions under which the sexes are favoured to adopt different sleeping strategies; identify the potential for intragenomic conflict between maternal-origin versus paternal-origin genes regarding an individual's sleeping behaviour; translate this conflict into novel and readily testable predictions concerning patterns of gene expression; and explore the concomitant effects of different kinds of mutations, epimutations, and uniparental disomies in relation to sleep disorders and other clinical pathologies. Our aim is to provide a theoretical framework for future empirical data and stimulate further research on this neglected topic.

The after-hours circadian mutant has reduced phenotypic plasticity in behaviors at multiple timescales and in sleep homeostasis

Circadian clock is known to adapt to environmental changes and can significantly influence cognitive and physiological functions. In this work, we report specific behavioral, cognitive, and sleep homeostatic defects in the after hours (Afh) circadian mouse mutant, which is characterized by lengthened circadian period. We found that the circadian timing irregularities in Afh mice resulted in higher interval timing uncertainty and suboptimal decisions due to incapability of processing probabilities. Our phenotypic observations further suggested that Afh mutants failed to exhibit the necessary phenotypic plasticity for adapting to temporal changes at multiple time scales (seconds-to-minutes to circadian). These behavioral effects of Afh mutation were complemented by the specific disruption of the Per/Cry circadian regulatory complex in brain regions that govern food anticipatory behaviors, sleep, and timing. We derive statistical predictions, which indicate that circadian clock and sleep are complementary processes in controlling behavioral/cognitive performance during 24 hrs. The results of this study have pivotal implications for understanding how the circadian clock modulates sleep and behavior.

Working-for-Food Behaviors: A Preclinical Study in Prader-Willi Mutant Mice

Abnormal feeding behavior is one of the main symptoms of Prader-Willi syndrome (PWS). By studying a PWS mouse mutant line, which carries a paternally inherited deletion of the small nucleolar RNA 116 (Snord116), we observed significant changes in working-for-food behavioral responses at various timescales. In particular, we report that PWS mutant mice show a significant delay compared to wild-type littermate controls in responding to both hour-scale and seconds-to-minutes-scale time intervals. This timing shift in mutant mice is associated with better performance in the working-for-food task, and results in better decision making in these mutant mice. The results of our study reveal a novel aspect of the organization of feeding behavior, and advance the understanding of the interplay between the metabolic functions and cognitive mechanisms of PWS.

Deletion of the Snord116/SNORD116 Alters Sleep in Mice and Patients with Prader-Willi Syndrome

STUDY OBJECTIVES

Sleep-wake disturbances are often reported in Prader-Willi syndrome (PWS), a rare neurodevelopmental syndrome that is associated with paternally-expressed genomic imprinting defects within the human chromosome region 15q11-13. One of the candidate genes, prevalently expressed in the brain, is the small nucleolar ribonucleic acid-116 (SNORD116). Here we conducted a translational study into the sleep abnormalities of PWS, testing the hypothesis that SNORD116 is responsible for sleep defects that characterize the syndrome.

METHODS

We studied sleep in mutant mice that carry a deletion of Snord116 at the orthologous locus (mouse chromosome 7) of the human PWS critical region (PWScr). In particular, we assessed EEG and temperature profiles, across 24-h, in PWScr (m+/p-) heterozygous mutants compared to wild-type littermates. High-resolution magnetic resonance imaging (MRI) was performed to explore morphoanatomical differences according to the genotype. Moreover, we complemented the mouse work by presenting two patients with a diagnosis of PWS and characterized by atypical small deletions of SNORD116. We compared the individual EEG parameters of patients with healthy subjects and with a cohort of obese subjects.

RESULTS

By studying the mouse mutant line PWScr(m+/p-), we observed specific rapid eye movement (REM) sleep alterations including abnormal electroencephalograph (EEG) theta waves. Remarkably, we observed identical sleep/EEG defects in the two PWS cases. We report brain morphological abnormalities that are associated with the EEG alterations. In particular, mouse mutants have a bilateral reduction of the gray matter volume in the ventral hippocampus and in the septum areas, which are pivotal structures for maintaining theta rhythms throughout the brain. In PWScr(m+/p-) mice we also observed increased body temperature that is coherent with REM sleep alterations in mice and human patients.

CONCLUSIONS

Our study indicates that paternally expressed Snord116 is involved in the 24-h regulation of sleep physiological measures, suggesting that it is a candidate gene for the sleep disturbances that most individuals with PWS experience.

Analysis of Genetic and Non-Genetic Factors Influencing Timing and Time Perception

Performance on different psychophysical tasks measuring the sense of time indicates a large amount of individual variation in the accuracy and precision of timing in the hundredths of milliseconds-to-minutes range. Quantifying factors with an influence on timing is essential to isolating a biological (genetic) contribution to the perception and estimation of time. In the largest timing study to date, 647 participants completed a duration-discrimination task in the sub-second range and a time-production task in the supra-second range. We confirm the stability of a participant's time sense across multiple sessions and substantiate a modest sex difference on time production. Moreover, we demonstrate a strong correlation between performance on a standardized cognitive battery and performance in both duration-discrimination and time-production tasks; we further show that performance is uncorrelated with age after controlling for general intelligence. Additionally, we find an effect of ethnicity on time sense, with African Americans and possibly Hispanics in our cohort differing in accuracy and precision from other ethnic groups. Finally, a preliminary genome-wide association and exome chip study was performed on 148 of the participants, ruling out the possibility for a single common variant or groups of low-frequency coding variants within a single gene to explain more than ~18% of the variation in the sense of time.

Parent-of-origin genetic background affects the transcriptional levels of circadian and neuronal plasticity genes following sleep loss

Sleep homoeostasis refers to a process in which the propensity to sleep increases as wakefulness progresses and decreases as sleep progresses. Sleep is tightly organized around the circadian clock and is regulated by genetic and epigenetic mechanisms. The homoeostatic response of sleep, which is classically triggered by sleep deprivation, is generally measured as a rebound effect of electrophysiological measures, for example delta sleep. However, more recently, gene expression changes following sleep loss have been investigated as biomarkers of sleep homoeostasis. The genetic background of an individual may affect this sleep-dependent gene expression phenotype. In this study, we investigated whether parental genetic background differentially modulates the expression of genes following sleep loss. We tested the progeny of reciprocal crosses of AKR/J and DBA/2J mouse strains and we show a parent-of-origin effect on the expression of circadian, sleep and neuronal plasticity genes following sleep deprivation. Thus, we further explored, by in silico, specific functions or upstream mechanisms of regulation and we observed that several upstream mechanisms involving signalling pathways (i.e. DICER1, PKA), growth factors (CSF3 and BDNF) and transcriptional regulators (EGR2 and ELK4) may be differentially modulated by parental effects. This is the first report showing that a behavioural manipulation (e.g. sleep deprivation) in adult animals triggers specific gene expression responses according to parent-of-origin genomic mechanisms. Our study suggests that the same mechanism may be extended to other behavioural domains and that the investigation of gene expression following experimental manipulations should take seriously into account parent-of-origin effects.