Molecular insights into chronotype and time-of-day effects on decision-making

Sex- and Substance-Specific Associations of Circadian-Related Genes with Addiction in the UK Biobank Cohort Implicate Neuroplasticity Pathways

BACKGROUND/OBJECTIVES

The circadian clockwork is implicated in the etiology of addiction, with circadian rhythm disruptions bidirectionally linked to substance abuse, but the molecular mechanisms that underlie this connection are not well known.

METHODS

Here, we use machine learning to reveal sex- and substance-specific associations with addiction in variants from 51 circadian-related genes (156,702 SNPs) in 98,800 participants from a UK Biobank cohort. We further analyze SNP associations in a subset of the cohort for substance-specific addictions (alcohol, illicit drugs (narcotics), and prescription drugs (opioids)).

RESULTS

We find robust (OR > 10) and novel sex-specific and substance-specific associations with variants in synaptic transcription factors (ZBTB20, CHRNB3) and hormone receptors (RORA), particularly in individuals addicted to narcotics and opioids. Circadian-related gene variants associated with male and female addiction were non-overlapping; variants in males primarily involve dopaminergic pathways, while variants in females factor in metabolic and inflammation pathways, with a novel gene association of female addiction with DELEC1, a gene of unknown function.

CONCLUSIONS

Our findings underscore the complexity of genetic pathways associated with addiction, involving core clock genes and circadian-regulated pathways, and reveal novel circadian-related gene associations that will aid the development of targeted, sex-specific therapeutic interventions for substance abuse.

Hilaire MA, Arrona-Palacios A, Czeisler CA, Duffy JF. Time of Day and Sleep Deprivation Effects on Risky Decision Making

Previous research has revealed that daily variations in human neurobehavioral functions are driven in part by the endogenous circadian system. The objective of this study was to explore whether there exists a circadian influence on performance regarding a risky decision-making task and to determine whether the performance changes with sleep deprivation (SD). Thirteen participants underwent a 39 h constant routine (CR) protocol, during which they remained awake in constant conditions and performed the BART (balloon analogue risk task) every two hours. The mean pumps (gains) (p < 0.001) and balloons popped (losses) (p = 0.003) exhibited variation during the CR. The reaction time (RT) also showed significant variation across the CR (p < 0.001), with slower mean RTs in the morning hours following SD. A greater risk propensity was observed around midday before SD and a lower risk propensity after 29.5 h of being awake. The sensitivity to punishment varied during the CR, but did not follow a predictable trend. Further research using real monetary incentives and neurophysiological measures is warranted to elucidate these findings.

Ethological computational psychiatry: Challenges and opportunities

Studying the intricacies of individual subjects' moods and cognitive processing over extended periods of time presents a formidable challenge in medicine. While much of systems neuroscience appropriately focuses on the link between neural circuit functions and well-constrained behaviors over short timescales (e.g., trials, hours), many mental health conditions involve complex interactions of mood and cognition that are non-stationary across behavioral contexts and evolve over extended timescales. Here, we discuss opportunities, challenges, and possible future directions in computational psychiatry to quantify non-stationary continuously monitored behaviors. We suggest that this exploratory effort may contribute to a more precision-based approach to treating mental disorders and facilitate a more robust reverse translation across animal species. We conclude with ethical considerations for any field that aims to bridge artificial intelligence and patient monitoring.

For Whom (and When) the Time Bell Tolls: Chronotypes and the Synchrony Effect

Circadian rhythms are powerful timekeepers that drive physiological and intellectual functioning throughout the day. These rhythms vary across individuals, with morning chronotypes rising and peaking early in the day and evening chronotypes showing a later rise in arousal, with peaks in the afternoon or evening. Chronotype also varies with age from childhood to adolescence to old age. As a result of these differences, the time of day at which people are best at attending, learning, solving analytical problems, making complex decisions, and even behaving ethically varies. Across studies of attention and memory and a range of allied areas, including academic achievement, judgment and decision-making, and neuropsychological assessment, optimal outcomes are found when performance times align with peaks in circadian arousal, a finding known as the synchrony effect. The benefits of performing in synchrony with one's chronotype (and the costs of not doing so) are most robust for individuals with strong morning or evening chronotypes and for tasks that require effortful, analytical processing or the suppression of distracting information. Failure to take the synchrony effect into consideration may be a factor in issues ranging from replication difficulties to school timing to assessing intellectual disabilities and apparent cognitive decline in aging.

Risk taking for potential losses but not gains increases with time of day

Humans exhibit distinct risk preferences when facing choices involving potential gains and losses. These preferences are believed to be subject to neuromodulatory influence, particularly from dopamine and serotonin. As neuromodulators manifest circadian rhythms, this suggests decision making under risk might be affected by time of day. Here, in a large subject sample collected using a smartphone application, we found that risky options with potential losses were increasingly chosen over the course of the day. We observed this result in both a within-subjects design (N = 2599) comparing risky options chosen earlier and later in the day in the same individuals, and in a between-subjects design (N = 26,720) showing our effect generalizes across ages and genders. Using computational modelling, we show this diurnal change in risk preference reflects a decrease in sensitivity to increasing losses, but no change was observed in the relative impacts of gains and losses on choice (i.e., loss aversion). Thus, our findings reveal a striking diurnal modulation in human decision making, a pattern with potential importance for real-life decisions that include voting, medical decisions, and financial investments.

Hair Follicles as a Critical Model for Monitoring the Circadian Clock

Clock (circadian) genes are heterogeneously expressed in hair follicles (HFs). The genes can be modulated by both the central circadian system and some extrinsic factors, such as light and thyroid hormones. These circadian genes participate in the regulation of several physiological processes of HFs, including hair growth and pigmentation. On the other hand, because peripheral circadian genes are synchronized with the central clock, HFs could provide a noninvasive and practical method for monitoring and evaluating multiple circadian-rhythm-related conditions and disorders among humans, including day and night shifts, sleep-wake disorders, physical activities, energy metabolism, and aging. However, due to the complexity of circadian biology, understanding how intrinsic oscillation operates using peripheral tissues only may be insufficient. Combining HF sampling with multidimensional assays such as detection of body temperature, blood samples, or certain validated questionnaires may be helpful in improving HF applications. Thus, HFs can serve as a critical model for monitoring the circadian clock and can help provide an understanding of the potential mechanisms of circadian-rhythm-related conditions; furthermore, chronotherapy could support personalized treatment scheduling based on the gene expression profile expressed in HFs.

Machine learning and expression analyses reveal circadian clock features predictive of anxiety

Mood disorders, including generalized anxiety disorder, are associated with disruptions in circadian rhythms and are linked to polymorphisms in circadian clock genes. Molecular mechanisms underlying these connections may be direct-via transcriptional activity of clock genes on downstream mood pathways in the brain, or indirect-via clock gene influences on the phase and amplitude of circadian rhythms which, in turn, modulate physiological processes influencing mood. Employing machine learning combined with statistical approaches, we explored clock genotype combinations that predict risk for anxiety symptoms in a deeply phenotyped population. We identified multiple novel circadian genotypes predictive of anxiety, with the PER3(rs17031614)-AG/CRY1(rs2287161)-CG genotype being the strongest predictor of anxiety risk, particularly in males. Molecular chronotyping, using clock gene expression oscillations, revealed that advanced circadian phase and robust circadian amplitudes are associated with high levels of anxiety symptoms. Further analyses revealed that individuals with advanced phases and pronounced circadian misalignment were at higher risk for severe anxiety symptoms. Our results support both direct and indirect influences of clock gene variants on mood: while sex-specific clock genotype combinations predictive of anxiety symptoms suggest direct effects on mood pathways, the mediation of PER3 effects on anxiety via diurnal preference measures and the association of circadian phase with anxiety symptoms provide evidence for indirect effects of the molecular clockwork on mood. Unraveling the complex molecular mechanisms underlying the links between circadian physiology and mood is essential to identifying the core clock genes to target in future functional studies, thereby advancing the development of non-invasive treatments for anxiety-related disorders.

The Relationship Among Chronotype, Hardiness, Affect, and Talent and Their Effects on Performance in a Military Context

Individual preference for morning or evening activities (chronotype), affect, hardiness, and talent are associated with a variety of performance outcomes. This longitudinal study was designed to investigate the degree to which these variables are associated with academic, physical, and military performance. Self-reported measures of chronotype, affect, and hardiness were collected from 1149 cadets from the Class of 2016 upon entry to the United States Military Academy. Talent, a composite of academic, leadership, and physical fitness scores were drawn from cadet records. Academic, military, and physical performance measures were collected at graduation 4 years later. The results indicated that a morning orientation was associated with better physical and military performance. Higher talent scores, as well as lower levels of negative affect, were associated with better performance across all three performance measures. Hardiness was only associated with military performance. The findings suggest that a morning orientation and less negative affect may result in better performance overall within a challenging and structured military environment. Future studies of chronotype shifts may provide further insight into associated performance benefits.

Minimally Invasive Ways of Determining Circadian Rhythms in Humans

Circadian rhythm exerts a critical role in mammalian health and disease. A malfunctioning circadian clock can be a consequence, as well as the cause of several pathophysiologies. Clinical therapies and research may also be influenced by the clock. Since the most suitable manner of revealing this rhythm in humans is not yet established, we discuss existing methods and seek to determine the most feasible ones.

Associations between diurnal preference, impulsivity and substance use in a young-adult student sample

A diurnal preference for eveningness is common in young adulthood and previous research has associated eveningness with anxiety symptoms as well as increased smoking and alcohol use behaviors. There is some evidence that impulsivity might be an important explanatory variable in these associations, but this has not been comprehensively researched. Here we used both subjective and objective measures of impulsivity to characterize impulsive tendencies in young adults and investigated whether trait impulsivity or trait anxiety could mediate the link between eveningness and substance use. A total of 191 university students (169 females), age range 18-25 y, completed the study. Diurnal preference, sleep quality, anxiety, impulsivity, and substance use were assessed by questionnaire. Impulsivity was also measured using a delay discounting task. Eveningness correlated with trait anxiety and trait impulsivity, and these associations were still significant after controlling for sleep quality. On the delayed discounting task, eveningness correlated with a tendency to prefer smaller immediate rewards over delayed, larger ones. Evening types also reported higher levels of alcohol and cigarette use even after controlling for sleep quality. These associations were found to be completely mediated by self-reported impulsivity; anxiety did not contribute. The current results could help inform interventions aiming to reduce substance use in young adult populations.

Diurnal Preference and Grey Matter Volume in a Large Population of Older Adults: Data from the UK Biobank

Eveningness (a diurnal preference for evening time) is associated with a number of negative health outcomes and risk and prevalence for psychiatric disorder. Our understanding of the anatomical substrates of diurnal preference, however, is limited. The current study used Voxel-Based Morphometry to compare grey matter volume in a large sample (N = 3730) of healthy adults determined by questionnaire to be either definite morning-type or definite evening-type. Eveningness was associated with increased grey matter volume in precuneus, brain regions implicated in risk and reward processing (bilateral nucleus accumbens, caudate, putamen and thalamus) and orbitofrontal cortex. These results indicate an anatomical-basis for diurnal preference which may underlie reported differences in behaviour and brain function observed in these individuals.

Ideal Time of Day for Risky Decision Making: Evidence from the Balloon Analogue Risk Task

BACKGROUND

Previous studies have demonstrated that individuals showed higher risk preference in the afternoon than in the morning. However, few studies aimed to explore the alteration of feedback learning effect during risky decision making, which is one of the important psychological processes of real risk behaviors. Moreover, cognitive function altered at the off-peak time due to impaired inhibitory control. The present study is to investigate the time-of-day effect on risky decision making and inhibitory control and whether the alteration of inhibitory control causes the differences in risky decision making across one day.

PARTICIPANTS AND METHODS

We adopted a within-participants design without extremely chronotype individuals to measure the time-of-day (9 am vs 3 pm) effect on risky decision making by using the Balloon Analogue Risk Task. At the same time, we measured the inhibitory control by using the Go/no-go task.

RESULTS

Our results confirmed that individuals showed higher risk preference in the afternoon than in the morning. In addition, we found that individuals were insensitive to loss and the previous negative feedback in the afternoon. Critically, the results did not reveal any significant correlation between risky decision making and inhibitory control under the regulation of the time-of-day effects, although individuals performed worse on inhibitory control in the afternoon.

CONCLUSION

The current findings revealed that the time-of-day effect regulated risky decision making and inhibitory control. Individuals act with higher risk preference, less sensitivity to loss as negative feedback, and lower inhibitory control in the afternoon than in the morning. This may reflect the effects of time-of-day on risk propensity and inhibitory control is relatively independent.

Circadian clock genes and circadian phenotypes in patients with myocardial infarction

PURPOSE

Human physiological activities and diseases are under the control of the circadian rhythm. There are strong epidemiological associations between disrupted circadian rhythms, sleep duration and diseases. Sleep disorders are associated with vascular outcomes, such as myocardial infarction (MI).

METHODS

We conducted an association study of genotype-phenotype interaction, to determine which circadian clock gene variants might be associated with the circadian phenotypes in patients with MI. In the present study, we analyzed the allele frequencies of 10 single nucleotide polymorphisms in four circadian clock genes in two independent samples: MI patients and controls. Chronotype was assessed using the Morningness - Eveningness Questionnaire (MEQ) and daytime sleepiness using the Epworth Sleepiness Scale (ESS).

RESULTS

Chronotype was associated with the ARNTL genetic variant rs12363415 in MI patients. The polymorphisms rs11932595 of the CLOCK gene and rs934945 of the PER2 gene were associated with daytime sleepiness in the patient group.

CONCLUSION

Our data suggest that genetic variations in some circadian clock genes might be related to circadian phenotype (i.e., chronotype and daytime sleepiness) in patients with myocardial infarction.

Chronotype mediates gender differences in risk propensity and risk-taking

Risk-taking is a complex form of decision-making that involves calculated assessments of potential costs and rewards that may be immediate or delayed. Thus, making predictions about inter-individual variation in risk-taking due to personality traits, decision styles or other attributes can be difficult. The association of risk-taking with gender is well-supported; males report higher propensity for risk-taking and show higher risk-taking on tasks measuring actual risk-taking behavior. Risk-taking also appears to be associated with circadian phenotypes (chronotypes), with evening-types reporting higher levels of risk-taking—but this association may be confounded by the fact that, in certain age groups, males are more likely to be evening-types. Here, we test for gender by chronotype effects on risk-taking in young adults (n = 610) using a self-reported risk propensity questionnaire, the health domain of the DOSPERT, and a behavioral task measuring risk-taking, the Balloon Analog Risk Task (BART). Our results show that males report and take significantly more risks than females in this population. In addition, evening-type individuals have significantly higher self-reported risk propensity and tend to take more risks on the BART. Interestingly, there is no significant difference in risk propensity or risk-taking behavior across male circadian phenotypes, but evening-type females significantly report and take more risk than female intermediate and morning types. In regression analyses, we found both gender and chronotype predict risk propensity and risk-taking. Path analysis confirms that chronotype has an indirect effect on gender differences in both risk propensity and risk-taking. Furthermore, we found that trait anxiety (STAI) and sleep disturbance (PROMIS), significantly correlate with chronotype and gender in the complete dataset, but do not independently predict differences in female risk-taking. These results suggest that chronotype mediates gender effects on risk-taking and that these effects are driven primarily by morning-type females, but are not related to gender-specific differences in trait anxiety or sleep quality.

In vivo molecular chronotyping, circadian misalignment, and high rates of depression in young adults

BACKGROUND

Young adults are disproportionately affected by depression and related mental disorders. Circadian misalignment (a phase advance or delay in the body's internal clock timing) is thought to exert adverse effects on downstream physiological processes regulating mood. Circadian disruption may represent an additional, under-appreciated risk factor affecting young adults. Here, we test the hypothesis that depression in young adults is associated with circadian misalignment-the lack of concordance between an individual's endogenous rhythm and their external social and academic environment.

METHODS

We screened 528 individuals for morningness-eveningness diurnal preference and sleep-wake chronotype. We selected individuals with extreme scores (n = 130) for estimation of circadian phase by measuring clock gene mRNA oscillations in hair follicles (a peripheral clock). Using an independent, data-driven cluster analysis, we define the circadian misalignment of both advanced- and delayed-phase individuals from clock gene mRNA expression levels. We compare depression (BDI-II), anxiety (STAI), social jetlag, sleep duration, and sleep disturbance (PROMIS) scores between misaligned individuals and control individuals of intermediate chronotype (n = 173).

RESULTS

We demonstrate that depression scores in young adults are significantly higher in individuals with circadian phase delays and in individuals with a mismatch between circadian behavioral phenotypes and circadian molecular phase. Evening-type individuals with circadian phase delays are 20 times more likely and mismatched individuals are 5-8 times more likely to be depressed than control individuals. Sleep disturbance shows a similar relationship with circadian phenotypes, but the mood effects described in this study are independent of sleep duration, social jetlag and gender.

LIMITATIONS

Our study examined peripheral clock genes that represents a circadian rhythm potentially influenced by both intrinsic and external, environmental factors. Our study population spanned a limited age-group and our results cannot distinguish between cause and effect of circadian, sleep and mood variables.

CONCLUSIONS

Our study validates previous theoretical predictions of circadian effects on mood disorders and highlights a critical, hidden risk factor affecting mood in young adults-circadian disruption.

Understanding suicide: Focusing on its mechanisms through a lithium lens

BACKGROUND

Current intervention strategies have been slow in reducing suicide rates, particularly in mood disorders. Thus, for intervention and prevention, a new approach is necessary. Investigating the effects of a medication known for its anti-suicidal properties on neurobiological and neurocognitive substrates of suicidal thinking may provide a deeper and more meaningful understanding of suicide.

METHOD

A literature search of recognised databases was conducted to examine the intersection of suicide, mood disorders, and the mechanisms of lithium.

RESULTS

This review synthesises the extant evidence of putative suicide biomarkers and endophenotypes and melds these with known actions of lithium to provide a comprehensive picture of processes underlying suicide. Specifically, the central importance of glycogen synthase kinase-3β (GSK3β) is discussed in detail because it modulates multiple systems that have been repeatedly implicated in suicide, and which lithium also exerts effects on.

LIMITATIONS

Suicide also occurs outside of mood disorders but we limited our discussion to mood because of our focus on lithium and extending our existing model of suicidal thinking and behaviour that is contextualised within mood disorders.

CONCLUSIONS

Focusing on the neurobiological mechanisms underpinning suicidal thinking and behaviours through a lithium lens identifies important targets for assessment and intervention. The use of objective measures is critical and using these within a framework that integrates findings from different perspectives and domains of research is likely to yield replicable and validated markers that can be employed both clinically and for further investigation of this complex phenomenon.

Circadian Effects on Performance and Effort in Collegiate Swimmers

Although individual athletic performance generally tends to peak in the evening, individuals who exhibit a strong diurnal preference perform better closer to their circadian peak. Time-of-day performance effects are influenced by circadian phenotype (diurnal preference and chronotype-sleep-wake patterns), homeostatic energy reserves and, potentially, genotype, yet little is known about how these factors influence physiological effort. Here, we investigate the effects of time of day, diurnal preference, chronotype, and PER3 (a circadian clock gene) genotype on both effort and performance in a population of Division I collegiate swimmers (n = 27). Participants competed in 200m time trials at 7:00 and 19:00 and were sampled pre- and post-trial for salivary α-amylase levels (as a measure of physiological effort), allowing for per-individual measures of performance and physiological effort. Hair samples were collected for genotype analysis (a variable-number tandem-repeat (VNTR) and a single nucleotide polymorphism (SNP) in PER3). Our results indicate significant and parallel time-of-day by circadian phenotype effects on swim performance and effort; evening-type swimmers swam on average 6% slower with 50% greater α-amylase levels in the morning than they did in the evening, and morning types required 5-7 times more effort in the evening trial to achieve the same performance result as the morning trial. In addition, our results suggest that these performance effects may be influenced by gene (circadian clock gene PER3 variants) by environment (time of day) interactions. Participants homozygous for the PER3^4,4 length variant (rs57875989) or who possess a single G-allele at PER3 SNP rs228697 swam 3-6% slower in the morning. Overall, these results suggest that intra-individual variation in athletic performance and effort with time of day is associated with circadian phenotype and PER3 genotype.

Biological Clocks and Rhythms of Anger and Aggression

The body’s internal timekeeping system is an under-recognized but highly influential force in behaviors and emotions including anger and reactive aggression. Predictable cycles or rhythms in behavior are expressed on several different time scales such as circadian (circa diem, or approximately 24-h rhythms) and infradian (exceeding 24 h, such as monthly or seasonal cycles). The circadian timekeeping system underlying rhythmic behaviors in mammals is constituted by a network of clocks distributed throughout the brain and body, the activity of which synchronizes to a central pacemaker, or master clock. Our daily experiences with the external environment including social activity strongly influence the exact timing of this network. In the present review, we examine evidence from a number of species and propose that anger and reactive aggression interact in multiple ways with circadian clocks. Specifically, we argue that: (i) there are predictable rhythms in the expression of aggression and anger; (ii) disruptions of the normal functioning of the circadian system increase the likelihood of aggressive behaviors; and (iii) conversely, chronic expression of anger can disrupt normal rhythmic cycles of physiological activities and create conditions for pathologies such as cardiovascular disease to develop. Taken together, these observations suggest that a comprehensive perspective on anger and reactive aggression must incorporate an understanding of the role of the circadian timing system in these intense affective states.

Chronotype regulates the neural basis of response inhibition during the daytime

Studies have elucidated the various modulatory effects of chronotype and time-of-day on task-dependent brain activity, but it is unclear how chronotype and time-of-day regulate brain activity in response inhibition tasks. To address this question, we used functional magnetic resonance imaging (fMRI) to explore the effects of chronotype and time-of-day on response inhibition in normal day-night conditions. Morning-type (MT) and evening-type (ET) participants conducted the stop-signal task in morning (08:00-12:00 hours) and evening (19:00-23:00 hours) sessions. The results showed that inhibition-related cerebral responses in the medial frontal gyrus (MFG), middle cingulate cortex (MCC), thalamus and other typical regions for the execution of response inhibition significantly decreased from morning to evening in MT participants, whereas activity in the right inferior frontal gyrus (IFG)/insula, MFG, MCC and thalamus remained stable or increased in ET participants. The chronotypical differences in homeostatic sleep pressure may explain the observed individual differences in maintaining cognition-related cortical activation. These results suggest the importance of considering chronotype and time-of-day in the design and analysis of cognitive neuroscience studies.

Dad's Snoring May Have Left Molecular Scars in Your DNA: the Emerging Role of Epigenetics in Sleep Disorders

The sleep-wake cycle is a biological phenomena under the orchestration of neurophysiological, neurochemical, neuroanatomical, and genetical mechanisms. Moreover, homeostatic and circadian processes participate in the regulation of sleep across the light-dark period. Further complexity of the understanding of the genesis of sleep engages disturbances which have been characterized and classified in a variety of sleep-wake cycle disorders. The most prominent sleep alterations include insomnia as well as excessive daytime sleepiness. On the other side, several human diseases have been linked with direct changes in DNA, such as chromatin configuration, genomic imprinting, DNA methylation, histone modifications (acetylation, methylation, ubiquitylation or sumoylation, etc.), and activating RNA molecules that are transcribed from DNA but not translated into proteins. Epigenetic theories primarily emphasize the interaction between the environment and gene expression. According to these approaches, the environment to which mammals are exposed has a significant role in determining the epigenetic modifications occurring in chromosomes that ultimately would influence not only development but also the descendants' physiology and behavior. Thus, what makes epigenetics intriguing is that, unlike genetic variation, modifications in DNA are altered directly by the environment and, in some cases, these epigenetic changes may be inherited by future generations. Thus, it is likely that epigenetic phenomena might contribute to the homeostatic and/or circadian control of sleep and, possibly, have an undescribed link with sleep disorders. An exciting new horizon of research is arising between sleep and epigenetics since it represents the relevance of the study of how the genome learns from its experiences and modulates behavior, including sleep.