Experimentally imposed circadian misalignment alters the neural response to monetary rewards and response inhibition in healthy adolescents

Later ("evening") circadian preference is associated with poorer executive, academic, and attentional functioning in adolescents with and without ADHD

BACKGROUND

Adolescents vary considerably in their circadian phase preference; those with greater "eveningness" (also known as "night owls") have later bedtimes, wake times, and peak arousal compared to those with greater "morningness." Prior research suggests that (a) greater eveningness is associated with worse academic, executive, and attentional functioning; and (b) adolescents with attention-deficit/hyperactivity disorder (ADHD) tend to be high in eveningness and to have deficits in these school-related constructs. However, few studies have examined circadian preference alongside two potential confounds-sleep duration and sleep quality-as predictors of daytime functioning, or whether the strength of associations differs across adolescents with and without ADHD.

METHODS

Participants were 302 adolescents (Mage = 13.17 years; 44.7% female; 81.8% White); approximately half (52%) had ADHD. A multi-method, multi-informant design was used. Specifically, adolescents reported on their circadian preference, school night sleep duration, and sleep quality. Adolescents provided ratings of their academic motivation (intrinsic, extrinsic, and amotivation) and were administered standardized achievement tests in reading and math. Adolescents and parents completed ratings of daily life executive functioning (behavioral, emotion, and cognitive regulation), and they and teachers also provided ratings of ADHD inattentive symptoms.

RESULTS

Above and beyond sleep duration, sleep quality, and covariates (sex, family income, pubertal development, medication use), greater eveningness was uniquely associated with poorer academic, executive, and attentional functioning across most measures. Sleep quality was uniquely associated with a handful of outcomes, and sleep duration was not significantly uniquely associated with any outcome in the regression analyses. ADHD status did not moderate effects.

CONCLUSIONS

This study provides compelling evidence that poorer academic, executive, and attentional functioning are more closely associated with greater eveningness than with sleep duration or quality in adolescents. Findings suggest that targeting circadian preference may be important to reduce these problems in adolescents, especially in clinical samples such as ADHD for whom academic, executive, and attentional difficulties are exceptionally common.

The Relationship Between Intraindividual Sleep-Wake Variability and Mental Health in Adolescents

OBJECTIVE

We investigated the relationship between irregular sleep-wake patterns and other aspects of sleep and mental health among adolescents.

METHODS

Community-based sample of adolescents (n = 200, mean age 16.8; 61.7% female) completed baseline assessment (i.e. sleep quality, daytime sleepiness, depressive symptoms, social anhedonia, problematic alcohol use), and 7-8 consecutive days of wearing wrist actigraphy. Irregular sleep-wake patterns were assessed via two methods, both based on actigraphy, to capture day-to-day irregularity (intraindividual variability, IIV) and weekly irregularity (social jet lag, SJL). The Bayesian variability method was performed to calculate IIV in total sleep time (TST), sleep onset, and offset time. SJL was quantified as the actual difference in the sleep midpoint on school days versus non-school days.

RESULTS

Greater IIV in TST was associated with poorer sleep quality (B = 1.66, 95% CI, 0.14, 3.31, p < .05), and greater depressive symptoms (B = 0.72, 95% CI, 0.17, 1.35, p < .05), while greater IIV in sleep offset time was associated greater depressive symptoms (B = 0.63, 95% CI, 0.03, 1.28, p < .05), and greater problematic alcohol use (B = 0.70, 95% CI, 0.12, 1.35, p < .05), all after adjusting for age, sex, family SES, alcohol drinks, and SJL. No significant association was found with sleep onset time. Greater SJL was associated with poorer sleep quality (B = 0.40, 95% CI, 0.27, 0.54, p < .001) and fewer problematic alcohol uses (B = -0.05, 95% CI, -0.09, -0.00, p < .05), when adjusting for age, sex, family SES, and alcohol drinks.

CONCLUSION

Our findings add to a growing body of research on irregularity in sleep-wake patterns and clinical implications.

The Role of Chronotypes and Perceived Stress on Sleep Quality in Undergraduates in Taiwan

INTRODUCTION

Chronotypes and perceived stress can predict psychiatric symptoms and affect sleep quality, though the relationships between these factors are not completely described. This study explores the influence of chronotypes and perceived stress on sleep quality among undergraduates.

METHODS

An online survey was administered to a convenience sample of 110 undergraduates aged 18-23 years (mean age 20.32 ± 1.00) at a university in southern Taiwan, predominantly women and senior students. Three self-reporting instruments were used: the Munich Chronotype Questionnaire, the Perceived Stress Scale, and the Pittsburgh Sleep Quality Index. Multivariate regression analysis was performed to investigate the influence of chronotype and perceived stress on sleep quality in undergraduates.

RESULTS

Sixty-one per cent of the respondents were poor-quality sleepers. Moreover, 85.5% of the respondents were classified as "neither" chronotype, whereas 13.6% were "evening" chronotype. Sleep quality was associated with both chronotype and perceived stress level (r = 0.41, 0.43, p < 0.01). Multiple regression revealed higher MCTQ scores (continuous or categorical) and higher perceived stress were significantly associated with poorer sleep quality, explaining approximately 30% of the variance (p < 0.001).

CONCLUSIONS

The findings of this study showed evening-type undergraduates with higher perceived stress exhibited poorer sleep quality. Highlight the importance of considering chronotype in health promotion among individuals transitioning to adulthood. Early interventions may help align an individual's chronotype with their external time schedule, mitigate the negative impacts of misaligned later chronotypes, enhance sleep quality, and help to manage perceived stress levels in undergraduates.

Looking beyond sleep duration in understanding obesity risk in adolescents: the role of circadian timing and misalignment on adolescent dietary outcomes, physical activity, and body mass index

Study Objectives

This study evaluated the differences in obesity-related outcomes across multiple adolescent sleep health domains, including circadian misalignment (CM), circadian timing, and sleep duration.

Methods

53 adolescents (aged 14-18; body mass index [BMI] percentile < 95%; 53.7% female) completed a cross-sectional study that included baseline assessment of height; weight; demographics; and 10 days assessment of sleep, physical activity, and dietary outcomes. Sleep duration, sleep timing, and physical activity data were collected from all participants using wrist-worn and waist-worn actigraphs. Dietary intake was measured using the Automated Self-Administered 24 Hours dietary recalls on 3 randomized days. Circadian timing was measured using dim-light melatonin onset (DLMO), and CM was calculated as the distance of time between DLMO and the average sleep onset time. Participants were categorized into groups (early vs late circadian timing, aligned vs misaligned circadian timing, and adequate sleep vs short sleep), and differences in dietary outcomes, physical activity, and BMI were analyzed using t-tests.

Results

Adolescents with later DLMO (M = 21:30 ± 1:11) had 0.63 higher BMI and 0.47% less averaged daily percent fat consumption than adolescents with early DLMO. Adolescents with CM (M = 1:42 ± 1:06) consumed 451.77 more averaged daily kcal consumption compared with those with circadian alignment. No statistically significant differences were found in any obesity-related outcome between sleep duration groups.

Conclusions

Our cross-sectional findings indicate that focusing on sleep timing and circadian alignment, beyond sleep duration, may promote better health outcomes for healthy adolescents. The findings of this study could enhance sleep education and inform clinical models for prevention efforts for pediatric obesity.

Waking up on the wrong side of the bed: Depression severity moderates daily associations between sleep duration and morning affect

Mornings are salient times for disrupted affect that may be impacted by prior sleep. The current study extends work linking sleep disruptions with negative affect by examining how nightly changes in sleep duration, timing, and quality relative to a person's average impact morning affect. We further tested whether depression severity moderated the relationship between nightly variations in sleep and morning affect. This is a secondary analysis of participants ages 18-65 years with varying levels of depression (N = 91) who wore an Actiwatch for 3-17 days (n = 73) while reporting morning affect using a visual analogue scale. Multilevel models tested the previous night's sleep duration, timing, or quality as a predictor of morning affect. Sleep measures were group-mean centred to account for nightly variation in participants' sleep. A cross-level interaction between depression severity and nightly sleep was entered. Sleeping longer (b = 0.1; p < 0.001) and later (b = 1.8; p = 0.01) than usual were both associated with better morning mood. There was a significant interaction between nightly actigraphic sleep duration and depression severity on morning affect (b = 0.003; p = 0.003). Participants with higher depression severity reported worse affect upon waking after sleeping less than their usual. In comparison, sleeping less than usual did not affect morning affect ratings for participants with lower depression. A similar interaction was found for sleep quality (b = 0.02; p < 0.001). There was no interaction for midsleep timing. Sleeping less than usual impacted morning affect in individuals with greater depression, potentially suggesting a pathway by which sleep disturbances perpetuate depression.

Do sleep and circadian characteristics predict alcohol use in adult drinkers?

BACKGROUND

While sleep and circadian rhythms are recognized contributors to the risk for alcohol use and related problems, few studies have examined whether objective sleep and circadian measures can predict future alcohol use in humans, and no such studies have been conducted in adults. This study examined whether any baseline sleep and/or circadian characteristics of otherwise healthy adults predicted their alcohol use over the subsequent 12 months.

METHODS

Participants (21-42 years) included 28 light and 50 heavy drinkers. At baseline, a comprehensive range of self-reported and objective sleep/circadian measures was assessed via questionnaires, wrist actigraphy, and measurement of dim light melatonin onset and circadian photoreceptor responsivity. Following this, the number of alcoholic drinks per week and binge drinking episodes per month were assessed quarterly over the subsequent 12 months. Anticipated effects of alcohol (stimulation, sedation, and rewarding aspects) were also assessed quarterly over the 12 months. Analyses included generalized linear mixed-effects models and causal mediation analysis.

RESULTS

Across the range of measures, only self-reported insomnia symptoms and a longer total sleep time at baseline predicted more drinks per week and binges per month (ps <0.02). There was a trend for the anticipated alcohol effect of wanting more alcohol at the 6-month timepoint to mediate the relationship between insomnia symptoms at baseline and drinks per week at 12 months (p = 0.069).

CONCLUSIONS

These results suggest that in otherwise healthy adults, insomnia symptoms, even if subclinical, are a significant predictor of future drinking, and appear to outweigh the influence of circadian factors on future drinking, at least in otherwise healthy adults. Insomnia symptoms may be a modifiable target for reducing the risk of alcohol misuse.

Sleep-Related Predictors of Risk for Alcohol Use and Related Problems in Adolescents and Young Adults

PURPOSE

Growing evidence supports sleep and circadian rhythms as influencing alcohol use and the course of alcohol use disorder (AUD). Studying sleep/circadian-alcohol associations during adolescence and young adulthood may be valuable for identifying sleep/circadian-related approaches to preventing and/or treating AUD. This paper reviews current evidence for prospective associations between sleep/circadian factors and alcohol involvement during adolescence and young adulthood with an emphasis on the effects of sleep/circadian factors on alcohol use.

SEARCH METHODS

The authors conducted a literature search in PsycInfo, PubMed, and Web of Science using the search terms "sleep" and "alcohol" paired with "adolescent" or "adolescence" or "young adult" or "emerging adult," focusing on the title/abstract fields, and restricting to English-language articles. Next, the search was narrowed to articles with a prospective/longitudinal or experimental design, a sleep-related measure as a predictor, an alcohol-related measure as an outcome, and confirming a primarily adolescent and/or young adult sample. This step was completed by a joint review of candidate article abstracts by two of the authors.

SEARCH RESULTS

The initial search resulted in 720 articles. After review of the abstracts, the list was narrowed to 27 articles reporting on observational longitudinal studies and three articles reporting on intervention trials. Noted for potential inclusion were 35 additional articles that reported on studies with alcohol-related predictors and sleep-related outcomes, and/or reported on candidate moderators or mediators of sleep-alcohol associations. Additional articles were identified via review of relevant article reference lists and prior exposure based on the authors' previous work in this area.

DISCUSSION AND CONCLUSIONS

Overall, the review supports a range of sleep/circadian characteristics during adolescence and young adulthood predicting the development of alcohol use and/or alcohol-related problems. Although sleep treatment studies in adolescents and young adults engaging in regular and/or heavy drinking show that sleep can be improved in those individuals, as well as potentially reducing alcohol craving and alcohol-related consequences, no studies in any age group have yet demonstrated that improving sleep reduces drinking behavior. Notable limitations include relatively few longitudinal studies and only two experimental studies, insufficient consideration of different assessment timescales (e.g., day-to-day vs. years), insufficient consideration of the multidimensional nature of sleep, a paucity of objective measures of sleep and circadian rhythms, and insufficient consideration of how demographic variables may influence sleep/circadian-alcohol associations. Examining such moderators, particularly those related to minoritized identities, as well as further investigation of putative mechanistic pathways linking sleep/circadian characteristics to alcohol outcomes, are important next steps.

Report from a randomized control trial: improved alignment between circadian biology and sleep-wake behavior as a mechanism of depression symptom improvement in evening-type adolescents with depressive symptoms

STUDY OBJECTIVES

An evening circadian preference is common among adolescents. It is characterized by a behavioral predilection for later sleep and wake timing and is associated with higher rates of Major Depressive Disorder (MDD). The present study aims to (a) test the effectiveness of a cognitive behavioral sleep intervention (Transdiagnostic Sleep and Circadian Intervention; TranS-C) in a sample of adolescents with an evening circadian preference and clinically significant depressive symptoms and (b) evaluate improved alignment between circadian biology and sleep-wake behavior as a potential mechanism in the relationship between sleep and depression symptom improvement.

METHODS

Adolescents with an evening circadian preference and clinically significant depressive symptoms were randomized to receive TranS-C (n = 24) or a psychoeducation condition (PE; n = 18). Alignment between circadian biology and sleep-wake behavior was measured using objective biological measurement. Measures of sleep and circadian rhythm were taken at pre- and posttreatment, and depression symptoms were measured at pre- and posttreatment and 6- and 12-month follow-up.

RESULTS

Mixed effects modeling revealed that compared with an active control condition, TranS-C resulted in a significant reduction in MDD severity at 12-month follow-up. A MacArthur mediation analysis conducted to explore alignment between circadian biology and sleep-wake behavior as a mediator of depression severity reduction through 12-month follow-up revealed a significant interaction between change in alignment between circadian biology and sleep-wake behavior and treatment arm, indicating that improved alignment between circadian biology and sleep-wake behavior at posttreatment was associated with improvements in depression outcomes at 12-month follow-up under the treatment condition.

CONCLUSIONS

These results provide novel evidence for improved alignment between circadian biology and sleep-wake behavior as a specific mechanism of depression improvement, provide key clues into the complex relationship between sleep and depression, and have significant clinical implications for adolescents with depression.

Preliminary evidence that misalignment between sleep and circadian timing alters risk-taking preferences

Decision-making has been shown to suffer when circadian preference is misaligned with time of assessment; however, little is known about how misalignment between sleep timing and the central circadian clock impacts decision-making. This study captured naturally occurring variation in circadian alignment (i.e., alignment of sleep-wake timing with the central circadian clock) to examine if greater misalignment predicts worse decision-making. Over the course of 2 weeks, 32 late adolescent drinkers (aged 18-22 years; 61% female; 69% White) continuously wore actigraphs and completed two overnight in-laboratory visits (Thursday and Sunday) in which both dim-light melatonin onset (DLMO) and behavioural decision-making (risk taking, framing, and strategic reasoning tasks) were assessed. Sleep-wake timing was assessed by actigraphic midsleep from the 2 nights prior to each in-laboratory visit. Alignment was operationalised as the phase angle (interval) between average DLMO and average midsleep. Multilevel modelling was used to predict performance on decision-making tasks from circadian alignment during each in-laboratory visit; non-linear associations were also examined. Shorter DLMO-midsleep phase angle predicted greater risk-taking under conditions of potential loss (B = -0.11, p = 0.06), but less risk-taking under conditions of potential reward (B = 0.14, p = 0.03) in a curvilinear fashion. Misalignment did not predict outcomes in the framing and strategic reasoning tasks. Findings suggest that shorter alignment in timing of sleep with the central circadian clock (e.g., phase-delayed misalignment) may impact risky decision-making, further extending accumulating evidence that sleep/circadian factors are tied to risk-taking. Future studies will need to replicate findings and experimentally probe whether manipulating alignment influences decision-making.

Sleep and circadian differences between light and heavy adult alcohol drinkers

Background

Numerous studies have reported that eveningness is associated with increased alcohol consumption. However, biological markers of circadian timing, such as dim light melatonin onset (DLMO) and circadian photoreceptor responsivity (post‐illumination pupil response, PIPR), have rarely been assessed in the context of habitual alcohol consumption. This study aimed to examine sleep, circadian timing, and photoreceptor responsivity in adult alcohol drinkers.

Methods

Participants (21 to 45 years) included 28 light and 50 heavy drinkers. The 8‐day study consisted of a week of adlib sleep monitored with wrist actigraphy, followed by a 9‐h laboratory session with a photoreceptor responsivity and circadian phase assessment.

Results

The heavy drinkers obtained on average 28 more minutes of sleep (p = 0.002) and reported more eveningness than the light drinkers (p = 0.029). There was a trend for a shorter DLMO‐midsleep interval (p = 0.059) in the heavy drinkers, reflecting a tendency for them to sleep at an earlier circadian phase. The PIPR in the heavy drinkers was significantly smaller than in the light drinkers (p = 0.032), suggesting reduced circadian photoreceptor responsivity in the heavy drinkers. A larger PIPR was significantly associated with a later DLMO in the light drinkers (r = 0.44, p = 0.019), but this relationship was absent in the heavy drinkers (r = −0.01, p = 0.94).

Conclusions

These results are consistent with earlier reports of more eveningness and a shorter DLMO‐midsleep interval being associated with heavier alcohol drinking. The novel finding of reduced circadian photoreceptor responsivity in heavy drinkers is consistent with prior rodent studies. Future studies should explore the impact of habitual alcohol consumption on other measures of circadian photoreceptor responsivity.

Circadian preference is associated with multiple domains of trait and state level impulsivity

Impulsivity is a multidimensional construct with well-documented risk for substance use problems at both the trait- and state levels. A circadian preference towards eveningness has been linked to trait-level, global impulsivity, but whether this association holds true across multiple dimensions of impulsivity and whether actual sleep timing shows parallel associations with impulsivity remain unclear. Here, we extend existing literature by investigating whether eveningness is associated with multiple facets of both trait- and state-level impulsivity. We also examined these associations utilizing daily measures of sleep timing and duration and explored whether they differed by sex and/or race. All participants were moderate-to-heavy social drinkers aged 21-35. Primary analyses included 78 participants (100% White male participants: Sample 1) with circadian preference data (Composite Scale of Morningness: CSM) and sleep timing (midsleep) and duration assessed via daily self-report over 10 days. Five facets of impulsivity were assessed via the UPPS-P, both at baseline (full scale; trait-level) and up to 6 times per day over 10 days (reduced scale; state-level). Linear regression and mixed-effects models were used to examine between- and within-person associations of impulsivity with measures of circadian preference, timing, and duration, accounting for covariates. Exploratory analyses combined Sample 1 with an additional more diverse sample (Sample 2), resulting in a total of 182 participants (29.1% self-identified as Black, 29.7% as female) with daily self-report sleep timing and duration only (no circadian preference). Primary between-person models found that eveningness was associated with multiple facets of impulsivity, at trait (lack of perseverance) and state levels (negative and positive urgency, lack of perseverance, and lack of premeditation), while average midsleep and duration were generally unrelated to impulsivity. Primary within-person models largely paralleled the between-person findings. Exploratory analyses in the larger combined Samples 1 and 2 (without circadian preference) found that later midsleep timing was associated with greater mean state-level impulsivity across multiple facets, associations that may differ by race and sex. In a sample of White male participants, circadian preference for eveningness was strongly associated with multiple facets of impulsivity, at both trait- and state-levels, which may contribute to risk for substance use. Preliminary findings suggest sex and race differences in sleep-impulsivity associations, but future research with objective sleep/circadian measures in larger, more diverse samples will be important to clarify implications for sleep-focused prevention and/or treatment of substance use.

Self-reported sleep and circadian characteristics predict alcohol and cannabis use: A longitudinal analysis of the National Consortium on Alcohol and Neurodevelopment in Adolescence Study

BACKGROUND

Growing evidence indicates that sleep characteristics predict future substance use and related problems. However, most prior studies assessed a limited range of sleep characteristics, studied a narrow age span, and included few follow-up assessments. Here, we used six annual assessments from the National Consortium on Alcohol and Neurodevelopment in Adolescence (NCANDA) study, which spans adolescence and young adulthood with an accelerated longitudinal design, to examine whether multiple sleep characteristics in any year predict alcohol and cannabis use the following year.

METHODS

The sample included 831 NCANDA participants (423 females; baseline age 12-21 years). Sleep variables included circadian preference, sleep quality, daytime sleepiness, the timing of midsleep (weekday/weekend), and sleep duration (weekday/weekend). Using generalized linear mixed models (logistic for cannabis; ordinal for binge severity), we tested whether each repeatedly measured sleep characteristic (years 0-4) predicted substance use (alcohol binge severity or cannabis use) the following year (years 1-5), covarying for age, sex, race, visit, parental education, and previous year's substance use.

RESULTS

Greater eveningness, more daytime sleepiness, later weekend sleep timing, and shorter sleep duration (weekday/weekend) all predicted more severe alcohol binge drinking the following year. Only greater eveningness predicted a greater likelihood of any cannabis use the following year. Post-hoc stratified exploratory analyses indicated that some associations (e.g., greater eveningness and shorter weekend sleep duration) predicted binge severity only in female participants, and that middle/high school versus post-high school adolescents were more vulnerable to sleep-related risk for cannabis use.

CONCLUSIONS

Our findings support the relevance of multiple sleep/circadian characteristics in the risk for future alcohol binge severity and cannabis use. Preliminary findings suggest that these risk factors vary based on developmental stage and sex. Results underscore a need for greater attention to sleep/circadian characteristics as potential risk factors for substance use in youth and may inform new avenues to prevention and intervention.

The Mind After Midnight: Nocturnal Wakefulness, Behavioral Dysregulation, and Psychopathology

Sufficient sleep with minimal interruption during the circadian/biological night supports daytime cognition and emotional regulation. Conversely, disrupted sleep involving significant nocturnal wakefulness leads to cognitive and behavioral dysregulation. Most studies to-date have examined how fragmented or insufficient sleep affects next-day functioning, but recent work highlights changes in cognition and behavior that occur when someone is awake during the night. This review summarizes the evidence for day-night alterations in maladaptive behaviors, including suicide, violent crime, and substance use, and examines how mood, reward processing, and executive function differ during nocturnal wakefulness. Based on this evidence, we propose the Mind after Midnight hypothesis in which attentional biases, negative affect, altered reward processing, and prefrontal disinhibition interact to promote behavioral dysregulation and psychiatric disorders.

Preliminary Evidence That Circadian Alignment Predicts Neural Response to Monetary Reward in Late Adolescent Drinkers

BACKGROUND

Robust evidence links sleep and circadian rhythm disturbances to alcohol use and alcohol-related problems, with a growing literature implicating reward-related mechanisms. However, the extant literature has been limited by cross-sectional designs, self-report or behavioral proxies for circadian timing, and samples without substantive alcohol use. Here, we employed objective measures of sleep and circadian rhythms, and an intensive prospective design, to assess whether circadian alignment predicts the neural response to reward in a sample of late adolescents reporting regular alcohol use.

METHODS

Participants included 31 late adolescents (18-22 y/o; 19 female participants) reporting weekly alcohol use. Participants completed a 14-day protocol including pre- and post-weekend (Thursday and Sunday) circadian phase assessments via the dim light melatonin onset (DLMO), in counterbalanced order. Sleep-wake timing was assessed via actigraphy. Circadian alignment was operationalized as the DLMO-midsleep interval; secondary analyses considered social jet lag based on weekday-weekend differences in midsleep or DLMO. Neural response to reward (anticipation and outcome) was assessed via a monetary reward fMRI task (Friday and Monday scans). Alcohol use was assessed at baseline and via ecological momentary assessment. Mean BOLD signal was extracted from two regions-of-interest (striatum and medial prefrontal cortex, mPFC) for analyses in regression models, accounting for age, sex, racial identity, and scan order.

RESULTS

In primary analyses, shorter DLMO-midsleep intervals (i.e., greater misalignment) on Thursday predicted lower striatal and mPFC responses to anticipated reward, but not reward outcome, on Friday. Lower neural (striatum and mPFC) responses to anticipated reward on Friday correlated with more binge-drinking episodes at baseline, but were not associated with alcohol use in the post-scan weekend. In secondary analyses, greater social jet lag (particularly larger weekend delays in midsleep or DLMO) was associated with lower neural responses to reward anticipation on Monday.

CONCLUSION

Findings provide preliminary evidence of proximal associations between objectively determined circadian alignment and the neural response to anticipated monetary reward, which is linked in turn to patterns of problematic drinking. Replication in a larger sample and experimental designs will be important next steps to determining the extent to which circadian misalignment influences risk for alcohol involvement via alterations in reward function.

Delayed circadian rhythms and substance abuse: dopamine transmission's time has come

Disrupted sleep and circadian rhythms are linked with substance abuse risk. Human studies that investigate relationships between sleep, circadian rhythm, and substance use reward generally rely on indirect means to infer dopaminergic function, such as functional magnetic resonance imaging. In this issue of the JCI, Zhang and colleagues used positron emission tomography (PET) to image striatal dopamine D1 (D1R) and D2/3 receptor (D/3R) availability in healthy adults. The authors assessed rest-activity rhythms, then conducted PET scans using radioligand antagonists selective for D1 receptors or D2/D3 receptors to measure D1R and D2/3R availability. They also measured the subjective drug effects of oral methylphenidate. Higher D1R availability in caudate and a greater methylphenidate reward sensitivity were associated with delayed rest-activity rhythms. Unexpectedly, lower overall activity was associated with higher D2/3R availability in the nucleus accumbens, which coincided with greater methylphenidate reward score. These findings may inform personalized prevention and/or treatment interventions.