Are ADHD symptoms associated with delay aversion or choice impulsivity? A general population study

Behavioral and neurofunctional profiles of delay aversion in children with attention-deficit hyperactivity disorder

Despite substantial efforts to unravel cognitive heterogeneity in ADHD, the examination of motivational variability, particularly delay aversion, remains limited. This study aimed to identify homogeneous delay-averse profiles in children with ADHD to understand motivational deficits. Delay-averse profiles were examined in a clinically well-characterized sample of 43 children with ADHD and 47 control participants using cluster analyses on an experiential delay discounting task. External validation analyses included parents' and teachers' clinical ratings, and fNIRS-based resting-state functional connectivity (rsFC) from the frontoparietal (FPN) and the default mode (DMN) networks. A five-profile solution best fit the data. Two clusters, labeled Conventional and Conventional-steeper, exhibited a conventional reward discount with increased delay but differed in the discounting slope. Three clusters demonstrated altered discounting: Steep discounting (abrupt devaluation of the reward), Shallow discounting (shallow discounting), and Zero discounting (no devaluation across delay durations). 77.78% of ADHD-C children clustered into steep discounting profiles, while 41.67% of ADHD-IN children were found in Shallow and Zero profiles, showing a significant disparity in the distribution of categorical presentations. External validation showed no differences in clinical ratings. However, clusters showing Zero and Shallow discounting demonstrated hypoconnectivity within and between FPN and DMN nodes. Delay aversion in ADHD spans a continuum from decreased to increased discounting rather than being solely defined by steeper discounting. These findings highlight the relevance of dimensional approaches in capturing ADHD's motivational heterogeneity and identifying distinct neurobiological substrates, with implications for improving diagnostic protocols and intervention strategies through the incorporation of behavioral measures of reward processing.

Examining the association between delay discounting, delay aversion and physical activity in Chinese adults with type-2 diabetes mellitus

BACKGROUND

The role of physical activity in diabetes is critical, influencing this disease's development, man-agement, and overall outcomes. In China, 22.3% of adults do not meet the minimum level of physical activity recommended by the World Health Organization. Therefore, it is imperative to identify the factors that contributing to lack of physical activity must be identified.

AIM

To investigate the relationship among delay discounting, delay aversion, glycated hemoglobin (HbA1c), and various levels of physical activity in Chinese adults diagnosed with type 2 diabetes mellitus (T2DM).

METHODS

In 2023, 400 adults with T2DM were recruited from the People's Hospital of Linxia Hui Autonomous Prefecture of Gansu Province. A face-to-face questionnaire was used to gather demographic data and details on physical activity, delay discounting, and delay aversion. In addition, HbA1c levels were measured in all 400 participants. The primary independent variables considered were delay discounting and delay aversion. The outcome variables included HbA1c levels and different intensity levels of physical activity, including walking, moderate physical activity, and vigorous physical activity. Multiple linear regression models were utilized to assess the relationship between delay discounting, delay aversion, and HbA1c levels, along with the intensity of different physical activity measured in met-hours per week.

RESULTS

After controlling for the sample characteristics, delay discounting was negatively associated with moderate physical activity (β = -2.386, 95%CI: -4.370 to -0.401). Meanwhile, delay aversion was negatively associated with the level of moderate physical activity (β = -3.527, 95% CI: -5.578 to -1.476) in the multiple linear regression model, with statistically significant differences.

CONCLUSION

Elevated delay discounting and increased delay aversion correlated with reduced levels of moderate physical activity. Result suggests that delay discounting and aversion may influence engagement in moderate physical activity. This study recommends that health administration and government consider delay discounting and delay aversion when formulating behavioral intervention strategies and treatment guidelines involving physical activity for patients with T2DM, which may increase participation in physical activity. This study contributes a novel perspective to the research on physical activity in adults with T2DM by examining the significance of future health considerations and the role of emotional responses to delays.

An experimental task to measure preschool children's frustration induced by having to wait unexpectedly: The role of sensitivity to delay and culture

The ability to manage frustration induced by having to wait for valued outcomes emerges across childhood and is an important marker of self-regulatory capacity. However, approaches to measure this capacity in preschool children are lacking. In this study, we introduced a new task, the Preschool Delay Frustration Task (P-DeFT), designed specifically to identify children's behavioral and emotional markers of waiting-induced frustration during the imposed wait period and after the release from waiting. We then explored how waiting-induced frustration relates to individual differences in delay sensitivity and whether it differs between two cultural groups thought to have different attitudes toward children's conduct and performance: Hong Kong (HK) and the United Kingdom (UK). A total of 112 preschool children (mean age = 46.22 months) completed the P-DeFT in a quiet laboratory. Each trial had two stages; first, a button press elicited a Go signal; second, this Go signal allowed children to go to a "supermarket" to pick a target toy. On most trials, the Go signal occurred immediately on the first press. On 6 trials, an unexpected/unsignaled 5- or 10-s pre-Go-signal period was imposed. Frustration was indexed by performance (button presses and press duration), behavioral agitation, and negative affect during the pre-Go-signal wait period and the post-Go-signal shopping task. Parents rated their children's delay sensitivity. Waiting-related frustration expressed during both the pre-Go-signal wait period and the post-Go-signal task varied with (a) the length of wait and (b) individual differences in parent-rated delay sensitivity. UK children displayed more negative affect during delay than their HK counterparts, although the relationship between delay sensitivity and frustration was culturally invariant.

Do Executive Dysfunction, Delay Aversion, and Time Perception Deficit Predict ADHD Symptoms and Early Academic Performance in Preschoolers

Children with attention deficit/hyperactivity disorder (ADHD) are commonly observed to have learning difficulties. This study examined how three neuropsychological constructs—executive dysfunction, delay aversion, and time perception—were associated with ADHD symptoms and early academic performance in preschoolers at risk of ADHD. One hundred and thirty-one preschoolers (70 boys, 53%) aged 4 to 6 (M = 5.31 years) were assessed on their ADHD-related behaviors, neuropsychological functioning, word reading, and math abilities at two time points one year apart. Factor analysis indicated that inhibitory and attentional control deficit, delay aversion, and time perception/working memory deficit were three dissociable factors. Among the three factors, inhibitory and attentional control measured at Time 1 was the strongest predictor of ADHD symptoms at both Time 1 and Time 2. Time perception was closely related to working memory, and they predicted word reading and numeration across time most strongly among other neuropsychological constructs. Our findings suggested that inhibitory and attentional control, delay aversion, and time perception are dissociable neuropsychological deficits underlying ADHD symptoms in preschoolers. Poor time perception may serve as a marker for the early identification of preschoolers with potential learning problems, and a possible target of intervention for ADHD.

Anxiety predicts impulsive-compulsive behaviours in Parkinson's disease: Clinical relevance and theoretical implications

Patients with Parkinson's disease (PD) often present symptoms of anxiety, depression and apathy. These negative affect manifestations have been recently associated with the presence of impulsive compulsive behaviours (ICBs). However, their relation with the use of dopamine replacement therapy (DRT), a renewed risk factor for ICBs, is still not fully understood. Elucidating the role of these different ICBs predictors in PD could inform both prevention/intervention recommendations as well as theoretical models. In the present study, we have analysed data collected in 417 PD patients, 50 patients with Parkinsonian symptoms but with scan without evidence of dopaminergic deficit (SWEDD), and 185 healthy controls (HC). We examined each patient's clinical profile over a two-year time window, investigating the role of both negative affect and DRT on ICBs. Results confirmed the presence of higher levels of anxiety in both the clinical groups, and of higher level of ICBs in SWEDD patients, respect to both PD and HC. Mixed model analyses revealed a statistically significant association between anxiety and ICBs in the SWEDD patients who did not take any DRT. Findings suggest the independence between anxiety and DRT in ICBs development, and provide new evidence for the motivational opponency theoretical framework.

An evaluation of the effect of methylphenidate on working memory, time perception, and choice impulsivity in children with ADHD

Individuals with Attention-Deficit Hyperactivity Disorder (ADHD) consistently exhibit a stronger preference for immediate rewards than for larger rewards available following a delay on tasks measuring choice impulsivity (CI). Despite this, however, there remains a dearth of studies examining the impact of stimulant treatment on CI as well as associated higher order (e.g., working memory [WM]) and perceptual (e.g., time perception) cognitive processes. The present study examines the effect of osmotic release oral system methylphenidate (OROS-MPH) on CI, WM and time perception processes as well as the relation among these processes before and after taking a regimen of OROS-MPH. Thirty-five children (aged 7-12 years) with a diagnosis of ADHD participating in a concurrent stimulant medication study were recruited to complete computerized assessments of CI, WM, and time perception. Children completed the assessments after administration of a placebo as well as their lowest effective dose of OROS-MPH following a 2-week titration period. The results from one-sample t-tests indicated that OROS-MPH improves both CI and WM in youth with ADHD but does not impact time perception. Further, results revealed no significant association among the various indices of cognitive performance while taking placebo or OROS-MPH. Overall, the findings suggest that while OROS-MPH improves both CI and WM in youth with ADHD, improvements in CI as a result of OROS-MPH are unlikely to be associated with the improvements in WM given the lack of association among the two. Future studies should consider alternate cognitive, emotional, and motivational mechanisms that may account for the impact of OROS-MPH on CI. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Motor cortex modulation and reward in children with attention-deficit/hyperactivity disorder

Attention-deficit/hyperactivity disorder, the most prevalent developmental disorder in childhood, is a biologically heterogenous condition characterized by impaired attention and impulse control as well as motoric hyperactivity and anomalous motor skill development. Neuropsychological testing often demonstrates impairments in motivation and reward-related decision making in attention-deficit/hyperactivity disorder, believed to indicate dysfunction of the dopamine reward pathway. Development of reliable, non-invasive, easily obtained and quantitative biomarkers correlating with the presence and severity of clinical symptoms and impaired domains of function could aid in identifying meaningful attention-deficit/hyperactivity disorder subgroups and targeting appropriate treatments. To this end, 55 (37 male) 8–12-year-old children with attention-deficit/hyperactivity disorder and 50 (32 male) age-matched, typically-developing controls were enrolled in a transcranial magnetic stimulation protocol—used previously to quantify cortical disinhibition in both attention-deficit/hyperactivity disorder and Parkinson’s Disease—with a child-friendly reward motivation task. The primary outcomes were reward task-induced changes in short interval cortical inhibition and up-modulation of motor evoked potential amplitudes, evaluated using mixed model, repeated measure regression. Our results show that both reward cues and reward receipt reduce short-interval cortical inhibition, and that baseline differences by diagnosis (less inhibition in attention-deficit/hyperactivity disorder) were no longer present when reward was cued or received. Similarly, both reward cues and reward receipt up-modulated motor evoked potential amplitudes, but, differentiating the two groups, this Task-Related-Up-Modulation was decreased in children with attention-deficit/hyperactivity disorder. Furthermore, more severe hyperactive/impulsive symptoms correlated significantly with less up-modulation with success in obtaining reward. These results suggest that in children with attention-deficit/hyperactivity disorder, short interval cortical inhibition may reflect baseline deficiencies as well as processes that normalize performance under rewarded conditions. Task-Related-Up-Modulation may reflect general hypo-responsiveness in attention-deficit/hyperactivity disorder to both reward cue and, especially in more hyperactive/impulsive children, to successful reward receipt. These findings support transcranial magnetic stimulation evoked cortical inhibition and task-induced excitability as biomarkers of clinically relevant domains of dysfunction in childhood attention-deficit/hyperactivity disorder.

Examining the Relationship Between Delay Discounting, Delay Aversion, Diabetes Self-care Behaviors, and Diabetes Outcomes in U.S. Adults With Type 2 Diabetes

OBJECTIVE

Delay discounting and delay aversion are emerging areas for understanding diabetes management; however, few data exist on their relationship with multiple diabetes self-care behaviors and diabetes outcomes.

RESEARCH DESIGN AND METHODS

This cross-sectional study included 356 adults with type 2 diabetes across three racial/ethnic groups receiving care from two primary care clinics. The primary predictors were delay discounting and delay aversion. Outcomes included self-care behaviors, quality of life (QOL; mental health component score [MCS], physical component score), and A1C. Multiple linear regression models were run to examine the association between predictors and the outcomes, A1C, QOL, and each self-care behavior.

RESULTS

Higher delay discounting was associated with lower engagement in self-care behaviors for general diet (B = -0.06; 95% CI -0.12; -0.01), specific diet (B = -0.07; 95% CI -0.12; -0.03), and foot care (B = -0.10; 95% CI -0.17; -0.02). Higher delay aversion was associated with lower engagement in self-care behaviors for general diet (B = -0.06; 95% CI -0.10; -0.01), specific diet (B = -0.03; 95% CI -0.07; -0.01), foot care (B = -0.11; 95% CI -0.17; -0.05), and lower MCS (B = -0.38; 95% CI -0.71; -0.06).

CONCLUSIONS

In a diverse sample of adults with type 2 diabetes, higher delay discounting and higher delay aversion were significantly related to lower engagement in self-care behaviors. High delay aversion was specifically related to lower QOL. These findings offer new knowledge by highlighting the role that delay-related behaviors may have in the performance of self-care behaviors and the impact on QOL. Work is needed to further elucidate these relationships. Specifically, these results highlight the importance of targeting value and decision-making for diabetes self-management.

A Meta-Analytic Review of Sex Differences on Delay of Gratification and Temporal Discounting Tasks in ADHD and Typically Developing Samples

Objective: To examine whether males and females with ADHD differ in their preferences for delayed rewards, since there is some evidence that suggests a sex difference with typically developing (TD) samples. Method: We used meta-analyses to examine sex differences on delay of gratification and temporal discounting tasks in both TD and ADHD samples. We identified 28 papers with 52 effect sizes for children and adults, and calculated the average effect size for sex comparisons within TD and ADHD samples. Results: The estimated mean difference between TD males and TD females was negligible, but males with ADHD were more likely to choose the larger delayed rewards than females with ADHD. Meta-regressions indicated that task type, age, and reward type did not significantly predict sex differences. Conclusion: These findings suggest that females referred for ADHD may make less adaptive choices by preferring smaller immediate rewards over larger delayed rewards more often than males with ADHD. Implications of our findings are discussed.

Delay aversion in school-aged children with attention-deficit hyperactivity disorder

This study considered whether children with attention-deficit hyperactivity disorder displayed a stronger preference for smaller, more immediate rewards over larger, but delayed rewards (delay aversion) when compared to typically developing controls and, furthermore, whether age and gender influenced their preference in any way. Children, between 6 and 15 years of age, living in Limpopo province of South Africa, participated in the study. Two hundred sixteen children in total (108 with attention-deficit hyperactivity disorder and 108 matched controls without attention-deficit hyperactivity disorder symptoms) were assessed, on a task of delay aversion. The Two Choice Impulsivity Paradigm, which assesses immediate and delayed responses, was administered to both the attention-deficit hyperactivity disorder and control groups. The performance of both groups was compared on the Two Choice Impulsivity Paradigm, and the scores were analysed as a function of gender and age. The attention-deficit hyperactivity disorder group chose significantly more immediate, smaller responses than the neurotypical control group, which preferred significantly more delayed but larger responses. Gender and age did not affect the response choices for both immediate and delayed measurements. Children with attention-deficit hyperactivity disorder show a greater need for more immediate gratification, even if the reward is smaller, than the neurotypical control group who could delay gratification to receive a larger reward. Gender and age did not influence their preferences.

Delay aversion and immediate choice in Sepedi-speaking primary school children with attention-deficit/hyperactivity disorder

Motivational factors play a significant role in the pathology of attention-deficit/hyperactivity disorder and are associated with altered reinforcement sensitivity. Delay aversion as a motivational style is characterised by a negative emotional reaction to the burden of delay. Children with attention-deficit/hyperactivity disorder have a stronger need to seek smaller immediate rewards rather than larger delayed rewards. This study ascertains whether children with attention-deficit/hyperactivity disorder have different responses when asked to choose between a larger delayed reward and a smaller immediate reward. Furthermore, it determines whether there are differences in response among the attention-deficit/hyperactivity disorder presentations. A sample ( N = 188) of attention-deficit/hyperactivity disorder participants ( n = 94) was compared with that of a group of children ( n = 94) without attention-deficit/hyperactivity disorder. These children attended primary school in Limpopo Province, South Africa. The Two-Choice Impulsivity Paradigm computer task was administered. The results showed that children with attention-deficit/hyperactivity disorder–combined presentation selected significantly smaller immediate rewards over larger delayed rewards in comparison to the control group, whereas children with attention-deficit/hyperactivity disorder–predominantly inattentive and attention-deficit/hyperactivity disorder–hyperactive/impulsive presentations did not demonstrate a significant difference in choice compared to the control group. In addition, no effect for gender was found. Children with attention-deficit/hyperactivity disorder seem to present with impulsive responses, which lead them to complete the concerned task faster and thereby escape delay. The study confirmed that children with attention-deficit/hyperactivity disorder–combined presentation may face problems with waiting for delayed rewards, which could have negative consequences in social and academic situations.

Prenatal testosterone exposure is associated with delay of gratification and attention problems/overactive behavior in 3-year-old boys

Sex differences in self-control become apparent during preschool years. Girls are better able to delay their gratification and show less attention problems and overactive behavior than boys. In this context, organizational effects of gonadal steroids affecting the neural circuitry underlying self-control could be responsible for these early sex differences. In the present study testosterone levels measured in amniotic fluid (via ultra performance liquid chromatography and tandem mass spectrometry) were used to examine the role of organizational sex hormones on self-control. One hundred and twenty-two 40-month-old children participated in a delay of gratification task (DoG task) and their parents reported on their attention problems and overactive behavior. Girls waited significantly longer for their preferred reward than boys, and significantly more girls than boys waited the maximum period of time, providing evidence for sex differences in delay of gratification. Boys that were rated as suffering from more attention problems and overactive behavior waited significantly shorter in the DoG task. Amniotic testosterone measures were reliable in boys only. Most importantly, boys who waited shorter in the DoG task and boys who were reported to suffer from more attention problems and overactive behavior had higher prenatal testosterone levels. These findings extend our knowledge concerning organizational effects of testosterone on the brain circuitry underlying self-control in boys, and are of relevance for understanding how sex differences in behavioral disorders are connected with a lack of self-control.

Attention-deficit/hyperactivity disorder: An integrated developmental psychopathology and Research Domain Criteria (RDoC) approach

Attention-deficit/hyperactivity disorder (ADHD) is characterized by heterogeneous behaviors and symptoms, developmental trajectories, and treatment response. Isolating intermediate phenotypes that are superior to current DSM-based nosology in order to explain such heterogeneity is integral to enhancing etiological theory, improving clinical assessment, predicting treatment response, and developing tailored treatments. To this end, this review provides an integrated developmental psychopathology and National Institute of Mental Health Research Domain Criteria (RDoC) approach to ADHD. In particular, associations between ADHD and RDoC domains of cognition (specifically working memory) and positive valence (reward anticipation/delay/receipt) are discussed. These domains are examined across behavioral and neurocircuitry levels of analysis and placed within a developmental context via examining associations among RDoC domains, relevant features of ADHD, and environmental correlates implicated across development. Limitations of the existing literature and proposed future directions are explored. Importantly, future work should focus on novel approaches that account for developmental shifts in functioning of relevant RDoC domains over time, as well as further examination of the interaction across RDoC domains and levels of analysis.

Prefrontal cortex dysfunction in hypoxic-ischaemic encephalopathy contributes to executive function impairments in rats: Potential contribution for attention-deficit/hyperactivity disorder

OBJECTIVES

The attention-deficit/hyperactivity disorder (ADHD) compromises the quality of life of individuals including adaptation to the social environment. ADHD aetiology includes perinatal conditions such as hypoxic-ischaemic events; preclinical studies have demonstrated attentional deficits and impulsive-hyperactive outcomes after neonatal hypoxic and/or ischaemic intervention, but data are missing to understand this relationship. Thus, the aim of this study was to evaluate executive function (EF) and impulsivity, and tissue integrity and dopaminergic function in the prefrontal cortex (PFC) of rats submitted to hypoxia-ischaemia (HI).

METHODS

At postnatal day (PND) 7, male Wistar rats were divided into control (n = 10) and HI groups (n = 11) and the HI procedure was conducted. At PND60, the animals were tested in the attentional set-shifting (ASS) task to EF and in the tolerance to delay of reward for assessment of impulsivity. After, morphological analysis and the dopaminergic system were evaluated in the PFC.

RESULTS

Animals subjected to HI had impairments in EF evidenced by a behavioural inflexibility that was correlated to PFC atrophy. Moreover, HI animals presented reduced D2 receptors in the ipsilateral side of ischaemia in the PFC.

CONCLUSIONS

Animals submitted to HI presented impaired EF associated with tissue atrophy and dopaminergic disturbance in the PFC.

Preference for Smaller Sooner Over Larger Later Rewards in ADHD: Contribution of Delay Duration and Paradigm Type

OBJECTIVE

Individuals with ADHD preferentially choose smaller sooner (SS) over larger later (LL) rewards, termed impulsive choice. This has been observed to different degrees on single-choice and more complex discounting tasks using various types of rewards and durations of delays. There has been no direct comparison of performance of ADHD children using these two paradigms.

METHOD

Two experimental paradigms, single-choice and temporal discounting, each including two delay conditions (13 and 25 s), were administered to 7- to 9-year-old children with ADHD ( n = 17) and matched controls ( n = 24).

RESULTS

Individuals with ADHD chose more SS rewards than controls on both tasks, but in the long delay condition only.

CONCLUSION

These findings demonstrate that delay durations rather than paradigm types determine laboratory-based measures of choice impulsivity in ADHD.

Risky decision-making in children with and without ADHD: A prospective study

Learning from past decisions can enhance successful decision-making. It is unclear whether difficulties in learning from experience may contribute to risky decision-making, which may be altered among individuals with attention-deficit/hyperactivity disorder (ADHD). This study follows 192 children with and without ADHD aged 5 to 10 years for approximately 2.5 years and examines their risky decision-making using the Balloon Emotional Learning Task (BELT), a computerized assessment of sequential risky decision-making in which participants pump up a series of virtual balloons for points. The BELT contains three task conditions: one with a variable explosion point, one with a stable and early explosion point, and one with a stable and late explosion point. These conditions may be learned via experience on the task. Contrary to expectations, ADHD status was not found to be related to greater risk-taking on the BELT, and among younger children ADHD status is in fact associated with reduced risk-taking. In addition, the typically-developing children without ADHD showed significant learning-related gains on both stable task conditions. However, the children with ADHD demonstrated learning on the condition with a stable and early explosion point, but not on the condition with the stable and late explosion point, in which more pumps are required before learning when the balloon will explode. Learning during decision-making may be more difficult for children with ADHD. Because adapting to changing environmental demands requires the use of feedback to guide future behavior, negative outcomes associated with childhood ADHD may partially reflect difficulties in learning from experience.

Are psychiatric comorbidities and associated cognitive functions related to treatment response to methylphenidate in boys with attention-deficit/hyperactivity disorder?

BACKGROUND

Methylphenidate (MPH) has been found to be an effective medication for attention-deficit/hyperactivity disorder (ADHD). However, there are neither consistent nor sufficient findings on whether psychiatric comorbidities and associated cognitive functions of ADHD are related to treatment response to MPH in ADHD children.

OBJECTIVES

This study investigated whether psychiatric comorbidities, IQ, and neurocognitive deficits are related to treatment response to MPH in ADHD children. In some ways, it is preferable to have a drug that the effectiveness of which to a disorder is not affected by its associated cognitive functions and psychiatric comorbidities. On the other hand, it is likely that the baseline symptom severity of ADHD is associated with the effectiveness of MPH treatment on the symptoms post treatment.

METHODS

A total of 149 Chinese boys (aged 6-12 years) with ADHD, combined type, and normal IQ participated in this study. Assessment of ADHD symptom severity was conducted pre and post MPH treatment, while assessment of psychiatric comorbidities, IQ, and neurocognitive deficits was performed in a non-medicated condition. Treatment response was defined as the ADHD symptom severity post MPH treatment.

RESULTS

Results indicated that MPH treatment was effective, significantly improving the ADHD condition. Yet, comorbid disorders, IQ, and neurocognitive deficits were not related to MPH treatment response on ADHD symptoms. These findings indicated that the effectiveness of MPH was not affected by psychiatric comorbidities and associated cognitive functions of ADHD. Instead, as expected, it was the baseline symptom severity that was mainly related to the treatment response, ie, the milder the baseline condition, the better the treatment response.

CONCLUSION

The current findings positively endorse the widespread clinical use of MPH for treating ADHD. It improves the behavioral symptoms of ADHD regardless of varying psychiatric comorbidities, IQ, and neurocognitive deficits.

Neural Systems Underlying Individual Differences in Intertemporal Decision-making

Excessively choosing immediate over larger future rewards, or delay discounting (DD), associates with multiple clinical conditions. Individual differences in DD likely depend on variations in the activation of and functional interactions between networks, representing possible endophenotypes for associated disorders, including alcohol use disorders (AUDs). Numerous fMRI studies have probed the neural bases of DD, but investigations of large-scale networks remain scant. We addressed this gap by testing whether activation within large-scale networks during Now/Later decision-making predicts individual differences in DD. To do so, we scanned 95 social drinkers (18-40 years old; 50 women) using fMRI during hypothetical choices between small monetary amounts available "today" or larger amounts available later. We identified neural networks engaged during Now/Later choice using independent component analysis and tested the relationship between component activation and degree of DD. The activity of two components during Now/Later choice correlated with individual DD rates: A temporal lobe network positively correlated with DD, whereas a frontoparietal-striatal network negatively correlated with DD. Activation differences between these networks predicted individual differences in DD, and their negative correlation during Now/Later choice suggests functional competition. A generalized psychophysiological interactions analysis confirmed a decrease in their functional connectivity during decision-making. The functional connectivity of these two networks negatively correlates with alcohol-related harm, potentially implicating these networks in AUDs. These findings provide novel insight into the neural underpinnings of individual differences in impulsive decision-making with potential implications for addiction and related disorders in which impulsivity is a defining feature.

Planning to make economic decisions in the future, but choosing impulsively now: are preference reversals related to symptoms of ADHD and depression?

A preference for smaller immediate rewards over larger delayed rewards (delay discounting, DD) is common in attention deficit hyperactivity disorder (ADHD), but rarely investigated in depression. Whether this preference is due to sensitivity to reward immediacy or delay aversion remains unclear. To investigate this, we examined whether ADHD and depressive symptoms are associated with preference reversals: a switch from smaller immediate rewards to larger delayed rewards when smaller rewards are also delayed. We also examined whether these symptoms differentially affect DD of losses. In Study 1 undergraduates completed a questionnaire about ADHD symptoms, and performed a hypothetical DD task. In the NOW condition, participants were presented with choices between a small reward available today and a large reward available after one year. In the FUTURE condition both rewards were delayed with +1 year. In Study 2 undergraduates completed questionnaires about ADHD and depressive symptoms and performed a DD task with gains and losses. Participants showed preference reversals in both studies and tasks. Losses were less steeply discounted than gains. ADHD and depressive symptoms did not influence these effects. Depressive symptoms, but not ADHD symptoms, were associated with less economic choices in general. These findings suggest that impulsive choice in depression is not explained by sensitivity to reward immediacy. Copyright © 2016 John Wiley & Sons, Ltd.

Satiety and the Self-Regulation of Food Take in Children: a Potential Role for Gene-Environment Interplay

Child eating self-regulation refers to behaviors that enable children to start and stop eating in a manner consistent with maintaining energy balance. Perturbations in these behaviors, manifesting as poorer child eating self-regulation, are associated with higher child weight status. Initial research into child eating self-regulation focused on the role of parent feeding styles and behaviors. However, we argue that child eating self-regulation is better understood as arising from a complex interplay between the child and their feeding environment, and highlight newer research into the heritable child characteristics, such as cognitive ability, that play an important role in this dynamic. Therefore, child eating self-regulation arises from gene-environment interactions. Identifying the genes and environmental influences contributing to these will help us tailor our parental feeding advice to the unique nature of the child. In this way, we will devise more effective advice for preventing childhood obesity.

A Computational Analysis of Aberrant Delay Discounting in Psychiatric Disorders

Impatience for reward is a facet of many psychiatric disorders. We draw attention to a growing literature finding greater discounting of delayed reward, an important aspect of impatience, across a range of psychiatric disorders. We propose these findings are best understood by considering the goals and motivation for discounting future reward. We characterize these as arising from either the opportunity costs of waiting or the uncertainty associated with delayed reward. We link specific instances of higher discounting in psychiatric disorder to heightened subjective estimates of either of these factors. We propose these costs are learned and represented based either on a flexible cognitive model of the world, an accumulation of previous experience, or through evolutionary specification. Any of these can be considered suboptimal for the individual if the resulting behavior results in impairments in personal and social functioning and/or in distress. By considering the neurochemical and neuroanatomical implementation of these processes, we illustrate how this approach can in principle unite social, psychological and biological conceptions of impulsive choice.

Cognitive heterogeneity in adult attention deficit/hyperactivity disorder: A systematic analysis of neuropsychological measurements

Attention Deficit/Hyperactivity Disorder (ADHD) in childhood is associated with impaired functioning in multiple cognitive domains: executive functioning (EF), reward and timing. Similar impairments have been described for adults with persistent ADHD, but an extensive investigation of neuropsychological functioning in a large sample of adult patients is currently lacking. We systematically examined neuropsychological performance on tasks measuring EF, delay discounting, time estimation and response variability using univariate ANCOVA's comparing patients with persistent ADHD (N=133, 42% male, mean age 36) and healthy adults (N=132, 40% male, mean age 36). In addition, we tested which combination of variables provided the highest accuracy in predicting ADHD diagnosis. We also estimated for each individual the severity of neuropsychological dysfunctioning. Lastly, we investigated potential effects of stimulant medication and a history of comorbid major depressive disorder (MDD) on performance. Compared to healthy adults, patients with ADHD showed impaired EF, were more impulsive, and more variable in responding. However, effect sizes were small to moderate (range: 0.05-0.70) and 11% of patients did not show neuropsychological dysfunctioning. The best fitting model predicting ADHD included measures from distinct cognitive domains (82.1% specificity, 64.9% sensitivity). Furthermore, patients receiving stimulant medication or with a history of MDD were not distinctively impaired. To conclude, while adults with ADHD as a group are impaired on several cognitive domains, the results confirm that adult ADHD is neuropsychologically heterogeneous. This provides a starting point to investigate individual differences in terms of impaired cognitive pathways.

Increased neural responses to reward in adolescents and young adults with attention-deficit/hyperactivity disorder and their unaffected siblings

OBJECTIVE

Attention-deficit/hyperactivity disorder (ADHD) is a heritable neuropsychiatric disorder associated with abnormal reward processing. Limited and inconsistent data exist about the neural mechanisms underlying this abnormality. Furthermore, it is not known whether reward processing is abnormal in unaffected siblings of participants with ADHD.

METHOD

We used event-related functional magnetic resonance imaging (fMRI) to investigate brain responses during reward anticipation and receipt with an adapted monetary incentive delay task in a large sample of adolescents and young adults with ADHD (n = 150), their unaffected siblings (n = 92), and control participants (n = 108), all of the same age.

RESULTS

Participants with ADHD showed, relative to control participants, increased responses in the anterior cingulate, anterior frontal cortex, and cerebellum during reward anticipation, and in the orbitofrontal, occipital cortex and ventral striatum. Responses of unaffected siblings were increased in these regions as well, except for the cerebellum during anticipation and ventral striatum during receipt.

CONCLUSION

ADHD in adolescents and young adults is associated with enhanced neural responses in frontostriatal circuitry to anticipation and receipt of reward. The findings support models emphasizing aberrant reward processing in ADHD, and suggest that processing of reward is subject to familial influences. Future studies using standard monetary incentive delay task parameters are needed to replicate our findings.

Hot executive function following moderate-to-late preterm birth: altered delay discounting at 4 years of age

Interest in monitoring long-term neurodevelopmental outcomes of children born moderate-to-late preterm (32-36 weeks gestation) is increasing. Moderate-to-late preterm birth has a negative impact on academic achievement, which may relate to differential development of executive function (EF). Prior studies reporting deficits in EF in preterm children have almost exclusively assessed EF in affectively neutral contexts in high-risk preterm children (< 32 weeks gestation). Disrupted function in motivational or emotionally charged contexts (hot EF) following preterm birth remains uninvestigated, despite evidence that preterm children show differential development of neural circuitry subserving hot EF, including reduced orbitofrontal cortex volume. The present study is the first to examine whether low-risk, healthy children born moderate-to-late preterm exhibit impairments in the development of hot EF. Preterm children at age 4.5 years were less likely to choose larger, delayed rewards across all levels of reward magnitude on a delay discounting task using tangible rewards, but performed more similarly to their full-term peers on a delay aversion task involving abstract rewards and on measures of cool EF. The relationship between gestational age at birth and selection of delayed rewards extended across the entire gestational age range of the sample (32-42 weeks), and remained significant after controlling for intelligence and processing speed. Results imply that there is not a finite cut-off point at which children are spared from potential long-term neurodevelopmental effects of PT birth. Further investigation of reward processing and hot EF in individuals with a history of PT birth is warranted given the susceptibility of prefrontal cortex development to early environmental variations.

Reconsidering "inattention" in attention-deficit hyperactivity disorder: implications for neuropsychological assessment and intervention

Attention-deficit hyperactivity disorder (ADHD) does not exist. This explicit statement needs elucidation of course given ADHD is a common neurodevelopmental disorder, but it provides the reader with the impetus to reconsider long-held beliefs about this condition and its treatment. Surely, there is a disorder called ADHD from which this thesis is framed, but primary attention and hyperactivity-impulsivity problems are mediated by different albeit interrelated brain systems. Like many neurodevelopmental disorders (e.g., learning disabilities, autism spectrum disorder), the medical and psychological professions have used a single, large inclusive ADHD diagnostic category to represent children with different etiologies for their overt symptoms. Despite neurobiological differences among children diagnosed with ADHD, the clinical position that attention-deficit or primary attention problems are sufficient for ADHD identification undermines clinical practice. This commonly accepted dubious position not only undermines the diagnostic utility of our neuropsychological measures, but it attenuates treatment effects as well. Supported with evidence from our ongoing ADHD research program, this data-based review will support these contentions and provide implications for diagnosis and treatment of children with attention problems.

Childhood predictors of adolescent and young adult outcome in ADHD

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) often persists into adulthood, but it remains unclear which childhood factors predict future outcome.

AIM

To identify childhood predictors of ADHD outcome using both dimensional and categorical approaches.

METHODS

116 adolescents and young adults with childhood ADHD were followed up on average 6.6 years later. ADHD outcome variables were interview-based parent-reported ADHD symptoms and impairment. Childhood predictors included parent- and teacher-rated ADHD symptoms and co-occurring behaviours; actigraph measures of activity level; socio-economic status (SES); and cognitive measures previously associated with ADHD.

RESULTS

Of the sample, 79% continued to meet clinical criteria of ADHD in adolescence and young adulthood. Higher parent-rated ADHD symptoms and movement intensity in childhood, but not teacher-rated symptoms, predicted ADHD symptoms at follow up. Co-occurring symptoms of oppositional behaviours, anxiety, social and emotional problems were also significant predictors, but these effects disappeared after controlling for ADHD symptoms. IQ and SES were significant predictors of both ADHD symptoms and impairment at follow up, but no other cognitive measures significantly predicted outcome.

CONCLUSIONS

SES and IQ emerge as potential moderators for the prognosis of ADHD. Childhood severity of ADHD symptoms, as measured by parent ratings and actigraph movement intensity, also predicts later ADHD outcome. These factors should be considered when identifying ADHD children at most risk of poor long-term outcomes and for the development of interventions to improve prognosis.

Models of ADHD: Five ways smaller sooner is better

BACKGROUND

In the delay discounting paradigm choices are made between a good of small utility available soon (SS) vs. a good of greater utility available later (LL). Versions of the task may be used with human and non-human subjects, they generate characteristic data, and are of relevance the topic of this special issue, the imputed impulsivity of organisms categorized as ADHD, and animal models of ADHD.

METHOD

Mathematical models of judgment were formulated. The first model adds the utility of a good to the utility of the delay. It provides distinct information about future perspective, the marginal utility of the goods offered, and the relative weight on delay. It grounds hyperbolic discounting. It predicts slower rates of discount for more preferred goods. It can reduce to an exponential function on future perspective time. When choice is mediated by conditioning, not judgment, a model of conditioned reinforcement strength is written. For studies where only the degree of preference for the LL is reported, a Thurstonian model of discrimination provides a shell that embraces all of the earlier models, providing additional information about the precision and bias of those preferential judgments.

COMPARISON WITH OTHER MODELS

All other prominent models are nested within, or approximations to, the models described here.

RESULTS

The models are fit to exemplary data. They provide some support for theories of delay aversion, and explanations for some inconsistencies in the literature. They involve parameters of general utility and provide connection to economic models.

Impulsivity in cocaine-dependent individuals with and without attention-deficit/hyperactivity disorder

BACKGROUND

Cocaine-dependent individuals (CDI) display increased impulsivity. However, despite its multifactorial nature most studies in CDI have treated impulsivity monolithically. Moreover, the impact of attention-deficit/hyperactivity disorder (ADHD) has often not been taken into account. This study investigates whether CDI with ADHD (CDI+ADHD) differ from CDI without an ADHD diagnosis and healthy controls (HC) on several impulsivity measures.

METHODS

Thirty-four CDI, 25 CDI+ADHD and 28 HC participated in this study. Trait impulsivity was assessed with the motor, attentional and non-planning subscales of the Barratt Impulsiveness Scale (BIS-11). Neurocognitive dimensions of impulsivity were examined with the stop signal task (SST), delay discounting task (DDT) and information sampling task (IST).

RESULTS

Relative to HC, both CDI and CDI+ADHD scored higher on all BIS-11 subscales, required more time to inhibit their responses (SST) and sampled less information before making a decision (IST). Greater discounting of delayed rewards (DDT) was only found among CDI+ADHD. Compared to CDI without ADHD, CDI+ADHD scored higher on the BIS-11 non-planning and total scale and showed higher discounting rates.

CONCLUSION

CDI score higher on several indices of impulsivity relative to HC, regardless of whether they have concomitant ADHD or not. CDI+ADHD are specifically characterized by a lack of future orientation compared to CDI without ADHD. © 2015 S. Karger AG, Basel.

Clinical utility of guanfacine extended release in the treatment of ADHD in children and adolescents

Attention deficit hyperactivity disorder (ADHD) is the most common psychiatric illness in children and adolescents. Several stimulant medications, such as methylphenidate and amphetamine derivatives, are available to treat ADHD in pediatric patients. Nonstimulant medications are more preferred by some parents, other caregivers, and patients because they lack the abuse potential of stimulant medications. In the US, one available nonstimulant option is guanfacine extended release (XR). As a selective α2A adrenergic receptor, guanfacine acts on the central noradrenergic pathways and cortical noradrenergic targets to improve working memory and attention. The XR formulation of guanfacine, compared with the immediate-release formulation, is more effective for the long-term management of ADHD and is associated with fewer adverse effects. Available data also indicate that guanfacine XR is superior to atomoxetine and is as effective as the nonselective α2 adrenergic receptor agonist, clonidine XR. The most common adverse effects associated with guanfacine XR are somnolence, fatigue, bradycardia, and hypotension. Somnolence is the most often cited reason for discontinuation. Guanfacine XR is also labeled for use as an adjuvant to stimulant treatment for ADHD. A similar profile of adverse effects as reported with monotherapy is reported when guanfacine XR is "added on" to stimulant therapy with somnolence as the most commonly reported adverse event. This review discusses the clinical efficacy and patient preference of guanfacine XR based on available published data on the safety, relative effectiveness, and tolerance of this medication to treat ADHD.

Shared cognitive impairments and aetiology in ADHD symptoms and reading difficulties

Background

Twin studies indicate that the frequent co-occurrence of attention deficit hyperactivity disorder (ADHD) symptoms and reading difficulties (RD) is largely due to shared genetic influences. Both disorders are associated with multiple cognitive impairments, but it remains unclear which cognitive impairments share the aetiological pathway, underlying the co-occurrence of the symptoms. We address this question using a sample of twins aged 7–10 and a range of cognitive measures previously associated with ADHD symptoms or RD.

Methods

We performed multivariate structural equation modelling analyses on parent and teacher ratings on the ADHD symptom domains of inattention and hyperactivity, parent ratings on RD, and cognitive data on response inhibition (commission errors, CE), reaction time variability (RTV), verbal short-term memory (STM), working memory (WM) and choice impulsivity, from a population sample of 1312 twins aged 7–10 years.

Results

Three cognitive processes showed significant phenotypic and genetic associations with both inattention symptoms and RD: RTV, verbal WM and STM. While STM captured only 11% of the shared genetic risk between inattention and RD, the estimates increased somewhat for WM (21%) and RTV (28%); yet most of the genetic sharing between inattention and RD remained unaccounted for in each case.

Conclusion

While response inhibition and choice impulsivity did not emerge as important cognitive processes underlying the co-occurrence between ADHD symptoms and RD, RTV and verbal memory processes separately showed significant phenotypic and genetic associations with both inattention symptoms and RD. Future studies employing longitudinal designs will be required to investigate the developmental pathways and direction of causality further.

The decimal effect: behavioral and neural bases for a novel influence on intertemporal choice in healthy individuals and in ADHD

We identify a novel contextual variable that alters the evaluation of delayed rewards in healthy participants and those diagnosed with attention deficit/hyperactivity disorder (ADHD). When intertemporal choices are constructed of monetary outcomes with rounded values (e.g., $25.00), discount rates are greater than when the rewards have nonzero decimal values (e.g., $25.12). This finding is well explained within a dual system framework for temporal discounting in which preferences are constructed from separate affective and deliberative processes. Specifically, we find that round dollar values produce greater positive affect than do nonzero decimal values. This suggests that relative involvement of affective processes may underlie our observed difference in intertemporal preferences. Furthermore, we demonstrate that intertemporal choices with rounded values recruit greater brain responses in the nucleus accumbens to a degree that correlates with the size of the behavioral effect across participants. Our demonstration that a simple contextual manipulation can alter self-control in ADHD has implications for treatment of individuals with disorders of impulsivity. Overall, the decimal effect highlights mechanisms by which the properties of a reward bias perceived value and consequent preferences.

Replication and external validation of a bi-factor parameterization of attention deficit/hyperactivity symptomatology

This study evaluated the fit and criterion validity of a recently proposed bi-factor structure for attention deficit/hyperactivity disorder (ADHD) symptoms. Participants were 1,093 children, drawn from an ongoing prospective longitudinal study, whose ADHD symptoms were rated by parents and teachers when children were in 1st grade. The criterion validity of the bi-factor model was established using a range of school-based outcomes that included treatment utilization, teacher perceptions of the need for treatment, academic functioning, and peer and teacher relationship quality. Results indicated that a bi-factor model parameterization provided an equally good fit to parent, teacher, and combined reports of ADHD symptoms as did traditional 1-, 2-, and 3-factor models. However, in contrast to traditional models, the bi-factor parameterization acknowledged both the unity and diversity of ADHD symptoms. The general ADHD latent factor explained the vast majority of the observed variation in every symptom. Whereas the general ADHD latent factor was significantly associated with all 15 outcomes, the specific Inattentive factor explained unique variation in 9 (primarily the academically oriented) outcomes and the specific Hyperactive-Impulsive factor explained unique variation in 2 outcomes. The general ADHD factor was more strongly correlated with each of the observed ADHD symptom scores (total, inattentive, hyperactive-impulsive) than was either specific factor. Results are discussed with respect to how changes in the conceptualization of the factor structure correspond to recent changes to the diagnostic criteria for ADHD, as well as whether/how individual differences in inattention and hyperactivity-impulsivity might be used to differentiate children who are diagnosed with ADHD.

Steep temporal reward discounting in ADHD-Combined type: acting upon feelings

Difficulty waiting plays a primary role in symptoms of attention-deficit/hyperactivity disorder (ADHD), in particular, impulsivity. Current theories suggest that relatively strong preferences for small immediate rewards as observed in ADHD-Combined type are the result of delay-related negative feelings. However, the measurement of difficulty waiting is typically limited to objective choices between small immediate and large delayed rewards. This study aimed at extending the measurement of difficulty waiting in ADHD-Combined type with ratings about subjective feelings. Children and adolescents (ages 6-17) with ADHD-Combined type (n=25), ADHD-Inattentive type (n=20) and matched typically developing participants (n=37) performed temporal reward discounting tasks, and completed a Visual Analogue Scale of subjectively experienced ease/difficulty waiting. Although those with ADHD-Combined type demonstrated relatively steep temporal reward discounting, as reported elsewhere (Scheres et al., 2010), there were no group differences for subjectively experienced ease/difficulty waiting. Additionally, correlations between subjective and objective measures of difficulty waiting were significantly higher in the ADHD-Combined type group than in the control group. These findings suggest that (a) those with ADHD-Combined type do not choose impulsively because they have more negative feelings about waiting than controls; (b) choices in the ADHD-Combined type group are more in accordance with/driven by their feelings than choices made by participants in the control group.

A behavioral neuroenergetics theory of ADHD

Energetic insufficiency in neurons due to inadequate lactate supply is implicated in several neuropathologies, including attention-deficit/hyperactivity disorder (ADHD). By formalizing the mechanism and implications of such constraints on function, the behavioral Neuroenergetics Theory (NeT) predicts the results of many neuropsychological tasks involving individuals with ADHD and kindred dysfunctions, and entails many novel predictions. The associated diffusion model predicts that response times will follow a mixture of Wald distributions from the attentive state, and ex-Wald distributions after attentional lapses. It is inferred from the model that ADHD participants can bring only 75-85% of the neurocognitive energy to bear on tasks, and allocate only about 85% of the cognitive resources of comparison groups. Parameters derived from the model in specific tasks predict performance in other tasks, and in clinical conditions often associated with ADHD. The primary action of therapeutic stimulants is to increase norepinephrine in active regions of the brain. This activates glial adrenoceptors, increasing the release of lactate from astrocytes to fuel depleted neurons. The theory is aligned with other approaches and integrated with more general theories of ADHD. Therapeutic implications are explored.

Impulsive choice behavior in four strains of rats: evaluation of possible models of Attention-Deficit/Hyperactivity Disorder

Several studies have examined impulsive choice behavior in spontaneously hypertensive rats (SHRs) as a possible pre-clinical model for Attention-Deficit/Hyperactivity Disorder (ADHD). However, this strain was not specifically selected for the traits of ADHD and as a result their appropriateness as a model has been questioned. The present study investigated whether SHRs would exhibit impulsive behavior in comparison to their control strain, Wistar Kyoto (WKY) rats. In addition, we evaluated a strain that has previously shown high levels of impulsive choice, the Lewis (LEW) rats and compared them with their source strain, Wistar (WIS) rats. In the first phase, rats could choose between a smaller-sooner (SS) reward of 1 pellet after 10 s and a larger-later (LL) reward of 2 pellets after 30 s. Subsequently, the rats were exposed to increases in LL reward magnitude and SS delay. These manipulations were designed to assess sensitivity to magnitude and delay within the choice task to parse out possible differences in using the strains as models of specific deficits associated with ADHD. The SHR and WKY strains did not differ in their choice behavior under either delay or magnitude manipulations. In comparison to WIS, LEW showed deficits in choice behavior in the delay manipulation, and to a lesser extent in the magnitude manipulation. An examination of individual differences indicated that the SHR strain may not be sufficiently homogeneous in their impulsive choice behavior to be considered as a viable model for impulse control disorders such as ADHD. The LEW strain may be worthy of further consideration for their suitability as an animal model.

Neuropsychological correlates of emotional lability in children with ADHD

BACKGROUND

Emotional lability (EL) is commonly seen in patients with attention-deficit/hyperactivity disorder (ADHD). The reasons for this association remain currently unknown. To address this question, we examined the relationship between ADHD and EL symptoms, and performance on a range of neuropsychological tasks to clarify whether EL symptoms are predicted by particular cognitive and/or motivational dysfunctions and whether these associations are mediated by the presence of ADHD symptoms.

METHODS

A large multi-site sample of 424 carefully diagnosed ADHD cases and 564 unaffected siblings and controls aged 6-18 years performed a broad neuropsychological test battery, including a Go/No-Go Task, a warned four-choice Reaction Time task, the Maudsley Index of Childhood Delay Aversion and Digit span backwards. Neuropsychological variables were aggregated as indices of processing speed, response variability, executive functions, choice impulsivity and the influence of energetic and/or motivational factors. EL and ADHD symptoms were regressed on each neuropsychological variable in separate analyses controlling for age, gender and IQ, and, in subsequent regression analyses, for ADHD and EL symptoms respectively.

RESULTS

Neuropsychological variables significantly predicted ADHD and EL symptoms with moderate-to-low regression coefficients. However, the association between neuropsychological parameters on EL disappeared entirely when the effect of ADHD symptoms was taken into account, revealing that the association between the neuropsychological performance measures and EL is completely mediated statistically by variations in ADHD symptoms. Conversely, neuropsychological effects on ADHD symptoms remained after EL symptom severity was taken into account.

CONCLUSIONS

The neuropsychological parameters examined, herein, predict ADHD more strongly than EL. They cannot explain EL symptoms beyond what is already accounted for by ADHD symptom severity. The association between EL and ADHD cannot be explained by these cognitive or motivational deficits. Alternative mechanisms, including overlapping genetic influences (pleiotropic effects) and/or alternative neuropsychological processes need to be considered.

Age modulates the effect of COMT genotype on delay discounting behavior

RATIONALE AND OBJECTIVE

A form of impulsivity, the tendency to choose immediate over delayed rewards (delay-discounting) has been associated with a single nucleotide polymorphism (SNP) in the catechol-O-methyltransferase (COMT) gene (COMTval¹⁵⁸met; rs4680). However, the existing data regarding the nature of this association are in conflict. We have previously reported that adults homozygous for valine (val) at the COMTval¹⁵⁸met SNP demonstrate greater delay-discounting than do methionine (met) allele carriers (Boettiger et al., J Neurosci 27:14383-14391, 2007). In contrast, a recent study of adolescent males found that those with the met/met genotype demonstrate greater delay-discounting than do val-allele carriers (Paloyelis et al., Neuropsychopharmacology 35:2414-2426, 2010). Based on reported age-related changes in frontal dopamine function and COMT expression, we hypothesized that the association of COMT genotype with delay-discounting behavior is modulated by age from late adolescence to young adulthood.

METHODS

To test this hypothesis, we genotyped late adolescents (18-21 years; n = 72) and adults (22-40 years; n = 70) for the COMTval¹⁵⁸met polymorphism, measured their delay-discounting behavior, and tested for an interaction between age group and COMT genotype.

RESULTS

This cross-sectional study found that age modulates COMTval¹⁵⁸met genotype effects on delay-discounting behavior. Among met-carriers, delay-discounting was negatively correlated with age from late adolescence to adulthood, while among val/val individuals delay-discounting was positively correlated with age across this range.

CONCLUSIONS

These results confirm our previous finding of enhanced delay-discounting among val/val adults relative to met-allele carriers, and help reconcile existing literature. We propose a single U-shaped model of the relationship between frontal DA levels and impulsive choice that accounts for both adolescent and adult data.

Animal models to guide clinical drug development in ADHD: lost in translation?

We review strategies for developing animal models for examining and selecting compounds with potential therapeutic benefit in attention-deficit hyperactivity disorder (ADHD). ADHD is a behavioural disorder of unknown aetiology and pathophysiology. Current understanding suggests that genetic factors play an important role in the aetiology of ADHD. The involvement of dopaminergic and noradrenergic systems in the pathophysiology of ADHD is probable. We review the clinical features of ADHD including inattention, hyperactivity and impulsivity and how these are operationalized for laboratory study. Measures of temporal discounting (but not premature responding) appear to predict known drug effects well (treatment validity). Open-field measures of overactivity commonly used do not have treatment validity in human populations. A number of animal models have been proposed that simulate the symptoms of ADHD. The most commonly used are the spontaneously hypertensive rat (SHR) and the 6-hydroxydopamine-lesioned (6-OHDA) animals. To date, however, the SHR lacks treatment validity, and the effects of drugs on symptoms of impulsivity and inattention have not been studied extensively in 6-OHDA-lesioned animals. At the present stage of development, there are no in vivo models of proven effectiveness for examining and selecting compounds with potential therapeutic benefit in ADHD. However, temporal discounting is an emerging theme in theories of ADHD, and there is good evidence of increased value of delayed reward following treatment with stimulant drugs. Therefore, operant behaviour paradigms that measure the effects of drugs in situations of delayed reinforcement, whether in normal rats or selected models, show promise for the future.

Effects of developmental nicotine exposure in rats on decision-making in adulthood

Exposure to tobacco smoke during pregnancy is associated with a range of adverse outcomes in offspring, including cognitive deficits and increased incidence of attention deficit-hyperactivity disorder, but there is a considerable controversy with regard to the causal role of tobacco smoke in these outcomes. To determine whether developmental exposure to the primary psychoactive ingredient in tobacco smoke, nicotine, may cause long-lasting behavioral alterations analogous to those in attention deficit-hyperactivity disorder, male Sprague-Dawley rats underwent a chronic neonatal nicotine administration regimen, which models third-trimester human exposure. Male rat pups were administered nicotine (6 mg/kg/day) by oral gastric intubation on postnatal days 1-7. In adulthood, rats were tested in two decision-making tasks (risky decision-making and delay discounting) as well as in free-operant responding for food reward and the elevated plus maze. Chronic neonatal nicotine attenuated weight gain during nicotine exposure, but there were no effects on performance in the decision-making task, and only a modest decrease in arm entries in the elevated plus maze in one subgroup of rats. These data are consistent with previous findings that developmental nicotine exposure has no effect on delay discounting, and they extend these findings to risky decision-making as well. They further suggest that at least some neurocognitive alterations associated with prenatal tobacco smoke exposure in humans may be due to genetic or other environmental factors, including non-nicotine components of tobacco smoke.

The genetic etiology of inhibitory control and behavior problems at 24 months of age

BACKGROUND

To investigate links between inhibitory control (IC) and behavior problems in early childhood, as well as genetic and environmental covariances between these two constructs.

METHODS

Parent and laboratory ratings of IC and parent ratings of externalizing and attention deficit hyperactivity disorder behaviors were administered at 24 months of age on a sample of 291 same-sex twin pairs (131 monozygotic, 160 dizygotic).

RESULTS

There were significant phenotypic associations between both IC assessments and the two areas of behavioral maladjustment (correlations ranged from -.13 to -.57). Multivariate analyses revealed that phenotypic covariance between IC and behavior problems could be substantially explained by common genetic influences (genetic correlations ranged from -.30 to -.74). Parent ratings of IC showed higher phenotypic and genetic correlations with behavior problems than lab ratings of IC.

CONCLUSIONS

This study is the first to examine the etiology of the covariance between IC and related behavioral difficulties in toddlerhood. Findings suggest that low levels of IC can be considered a genetic risk factor for the development of early emerging behavior problems.

Risk Taking and Sensitivity to Punishment in Children with ADHD, ODD, ADHD+ODD, and Controls

We used the Balloon Analog Risk Task (BART) to examine risk taking and sensitivity to punishment, two relevant aspects of behavioral inhibition, in 203 school-age children with attention-deficit/hyperactivity disorder (ADHD), oppositional defiant disorder (ODD), ADHD+ODD, and controls. Participants earned points on the BART by pumping 30 separate balloons that exploded at variable intervals. No points were earned on a trial when a balloon exploded. The number of pumps across all balloons estimated risk taking and the reduction in pumps following balloon explosions was interpreted as an indicator of sensitivity to negative punishment. We found that all groups significantly differed from one another on risk taking. The ADHD+ODD group pumped the most, followed by the ODD, ADHD, and the control group, respectively. For sensitivity to negative punishment, all groups performed differently, with the ODD group showing the least sensitivity to an exploded balloon, followed by the ADHD, control, and ADHD+ODD groups, respectively. Children with ADHD+ODD demonstrated significantly different patterns of risk taking and sensitivity to negative punishment than children with either ADHD-only or ODD-only. ADHD youth with comorbid ODD had the greatest levels of risk taking, but they were also the most sensitive to negative punishment. The relationship between ADHD and ODD, as well as the nature of comorbidity in constructs related to risk taking and related behaviors, are discussed.

The relationship between ADHD and key cognitive phenotypes is not mediated by shared familial effects with IQ

BACKGROUND

Twin and sibling studies have identified specific cognitive phenotypes that may mediate the association between genes and the clinical symptoms of attention deficit hyperactivity disorder (ADHD). ADHD is also associated with lower IQ scores. We aimed to investigate whether the familial association between measures of cognitive performance and the clinical diagnosis of ADHD is mediated through shared familial influences with IQ.

METHOD

Multivariate familial models were run on data from 1265 individuals aged 6-18 years, comprising 920 participants from ADHD sibling pairs and 345 control participants. Cognitive assessments included a four-choice reaction time (RT) task, a go/no-go task, a choice-delay task and an IQ assessment. The analyses focused on the cognitive variables of mean RT (MRT), RT variability (RTV), commission errors (CE), omission errors (OE) and choice impulsivity (CI).

RESULTS

Significant familial association (rF) was confirmed between cognitive performance and both ADHD (rF=0.41-0.71) and IQ (rF=-0.25 to -0.49). The association between ADHD and cognitive performance was largely independent (80-87%) of any contribution from etiological factors shared with IQ. The exception was for CI, where 49% of the overlap could be accounted for by the familial variance underlying IQ.

CONCLUSIONS

The aetiological factors underlying lower IQ in ADHD seem to be distinct from those between ADHD and RT/error measures. This suggests that lower IQ does not account for the key cognitive impairments observed in ADHD. The results have implications for molecular genetic studies designed to identify genes involved in ADHD.

Prenatal exposure to nicotine impairs performance of the 5-choice serial reaction time task in adult rats

Cigarette smoking is associated with a wide variety of adverse reproductive outcomes, including increased infant mortality and decreased birth weight. Prenatal exposure to tobacco smoke, of which nicotine is a major teratogenic component, has also been linked to the acceleration of the risk for different psychiatric disorders, including conduct disorder and attention deficit hyperactivity disorder (ADHD). Whether this increased risk is influenced by the direct effects of gestational nicotine exposure on the developing fetus remains uncertain. In this study we provide experimental evidence for the effects of prenatal nicotine exposure on measures of attention and impulsivity in adult male rats. Offspring of females exposed during pregnancy to 0.06 mg/ml nicotine solution as the only source of water (daily consumption: 69.6±1.4 ml/kg; nicotine blood level: 96.0±31.9 ng/ml) had lower birth weight and delayed sensorimotor development measured by negative geotaxis, righting reflex, and grip strength. In the 5-choice serial reaction time test, adult rats showed increased numbers of anticipatory responses and omissions errors, more variable response times, and lower accuracy with evidence of delayed learning of the task demands when the 1 s stimulus duration was introduced. In contrast, prenatal nicotine exposure had no effect on exploratory locomotion or delay-discounting test. Prenatal nicotine exposure increased expression of the D5 dopamine receptor gene in the striatum, but did not change expression of other dopamine-related genes (DRD4, DAT1, NR4A2, and TH) in either the striatum or the prefrontal cortex. These data suggest a direct effect of prenatal nicotine exposure on important aspects of attention, inhibitory control, or learning later in life.

Electrophysiological markers of genetic risk for attention deficit hyperactivity disorder

Attention deficit hyperactivity disorder (ADHD) is a highly heritable neurodevelopmental disorder with complex genetic aetiology. The identification of candidate intermediate phenotypes may facilitate the detection of susceptibility genes and neurobiological mechanisms underlying the disorder. Electroencephalography (EEG) is an ideal neuroscientific approach, providing a direct measurement of neural activity that demonstrates reliability, developmental stability and high heritability. This systematic review evaluates the utility of a subset of electrophysiological measures as potential intermediate phenotypes for ADHD: quantitative EEG indices of arousal and intraindividual variability, and functional investigations of attention, inhibition and performance monitoring using the event-related potential (ERP) technique. Each measure demonstrates consistent and meaningful associations with ADHD, a degree of genetic overlap with ADHD and potential links to specific genetic variants. Investigations of the genetic and environmental contributions to EEG/ERP and shared genetic overlap with ADHD might enhance molecular genetic studies and provide novel insights into aetiology. Such research will aid in the precise characterisation of the clinical deficits seen in ADHD and guide the development of novel intervention and prevention strategies for those at risk.