Gabry W. Mies

The neural correlates of temporal reward discounting.

Temporal reward discounting (TD) refers to the decrease in subjective value of a reward when the delay to that reward increases. In recent years, a growing number of studies on the neural correlates of temporal reward discounting have been conducted. This article focuses on functional magnetic resonance imaging (fMRI) studies on TD in humans. First, we describe the different types of tasks (also from behavioral studies) and the dependent variables. Subsequently, we discuss the evidence for three neurobiological models of TD: the dual-systems model, the single-system model and the self-control model. Further, studies in which nontraditional tasks (e.g., with nonmonetary rewards) were used to study TD are reviewed. Finally, we discuss the neural correlates of individual differences in discounting, and its development across the lifespan. We conclude that the evidence for each of the three neurobiological models of TD is mixed, in that all models receive (partial) support, and several studies provide support for multiple models. Because of large differences between studies in task design and analytical approach, it is difficult to draw a firm conclusion regarding which model provides the best explanation of the neural correlates of temporal discounting. We propose that some components of these models can complement each other, and future studies should test the predictions offered by different models against each other. Several future research directions are suggested, including studying the connectivity between brain regions in relation to discounting, and directly comparing the neural mechanisms involved in discounting of monetary and primary rewards. WIREs Cogn Sci 2013, 4:523-545. doi: 10.1002/wcs.1246 CONFLICT OF INTEREST: The authors have declared no conflicts of interest for this article. For further resources related to this article, please visit the WIREs website.

The prevalence of food addiction in a large sample of adolescents and its association with addictive substances

The prevalence of overweight and obesity is increasing, due to, among other factors, increased availability of highly palatable food (food high in fat, salt and/or sugar). It has been proposed that certain foods and/or eating behaviours may be addictive, to a degree comparable to substances of abuse. The Yale Food Addiction Scale (YFAS) measures food addiction by translating the diagnostic criteria for substance use disorder to eating behaviour. So far, only a few studies have examined the prevalence of food addiction in children with the YFAS for children (YFAS-C). Large-scale studies, especially among adolescents, are lacking. Adolescence is of particular interest because it is a period wherein unhealthy eating behaviours or addictive tendencies are likely to develop. The current study examines the prevalence of food addiction using the YFAS-C in a large group of Dutch adolescents (Nxa0=xa02653) aged 14-21 years. With Generalized Estimation Equation (GEE) analysis we tested the relationship between food addiction symptoms and smoking, cannabis use, alcohol use, and sugar intake through drinks, while controlling for gender, age, educational level and weight class. In the total sample 2.6% met the criteria for a food addiction diagnosis, and the average symptom count was 1.0 (SDxa0=xa01.3, range 0-7). Symptoms of food addiction were positively associated with smoking, alcohol use, cannabis use and sugar intake. We propose that future studies focus on possible genetic/(neuro)biological mechanisms involved in both food addiction and substance use and that longitudinal designs are needed to examine possible causal pathways.

Ventral striatal hyperconnectivity during rewarded interference control in adolescents with ADHD

OBJECTIVEnAttention-deficit/hyperactivity disorder (ADHD) is characterized by cognitive deficits (e.g., interference control) and altered reward processing. Cognitive control is influenced by incentive motivation and according to current theoretical models, ADHD is associated with abnormal interactions between incentive motivation and cognitive control. However, the neural mechanisms by which reward modulates cognitive control in individuals with ADHD are unknown.nnnMETHODnWe used event-related functional resonance imaging (fMRI) to study neural responses during a rewarded Stroop color-word task in adolescents (14-17 years) with ADHD (nxa0=xa025; 19 boys) and healthy controls (nxa0=xa033; 22 boys).nnnRESULTSnAdolescents with ADHD showed increased reward signaling within the superior frontal gyrus and ventral striatum (VS) relative to controls. Importantly, functional connectivity analyses revealed a hyperconnectivity between VS and motor control regions in the ADHD group, as a function of reward-cognitive control integration. Connectivity was associated with performance improvement in controls but not in the ADHD group, suggesting inefficient connectivity.nnnCONCLUSIONnAdolescents with ADHD show increased neural sensitivity to rewards and its interactions with interference control in VS and motor regions, respectively. The findings support theoretical models of altered reward-cognitive control integration in individuals with ADHD.

What motivates individuals with ADHD? A qualitative analysis from the adolescent’s point of view

Individuals with ADHD appear to respond differently to incentives than their peers. This could be due to a general altered sensitivity to reinforcers. However, apart from differences in the degree of motivation, individuals with ADHD might also be motivated by qualitatively different factors. This study aimed to harvest a range of motivational factors and identify ADHD-related qualitative differences in motivation, from the adolescent’s point of view. Semi-structured interviews allowing participants to describe what motivates them in daily life were conducted with young adolescents (9–16xa0years) with and without ADHD. Thematic analysis was undertaken using NVivo software. Major themes relating to motivation were identified from the interview data. These were: (1) achieving a sense of togetherness; (2) feeling competent; (3) fulfilling a need for variation; (4) gaining pleasure from applying effort to achieve a goal; (5) valuing social reinforcement; (6) desiring to be absorbed/forget problems; (7) feeling free and independent, (8) attaining material reinforcement; and (9) an enjoyment of bodily stimulation. The theme structure was very similar for both groups. However, individuals with ADHD differed in some specifics: their focus on the passing of time, the absence of preference for predictable and familiar tasks, and their less elaborate description of the togetherness theme. A broad range of motivational themes was identified, stretching beyond the current focus of ADHD research and motivational theories. Similarities and differences in motivational values of individuals with and without ADHD should be taken into account in reward sensitivity research, and in psychological treatment.

Neural mechanisms of individual differences in temporal discounting of monetary and primary rewards in adolescents

Abstract Adolescents are generally characterized as impulsive. However, impulsivity is a multi‐dimensional construct that involves multiple component processes. Which of these components contribute to adolescent impulsivity is currently unclear. This study focused on the neural mechanisms underlying individual differences in distinct components of temporal discounting (TD), i.e., the preference for smaller immediate rewards over larger delayed rewards. Participants were 58 adolescents (12–16 years‐old) who performed an fMRI TD task with both monetary and snack rewards. Using mixed‐effects modeling, we determined participants’ average impatience, and further decomposed TD choices into: 1) amount sensitivity (unique contribution of the magnitude of the immediate reward); and 2) delay sensitivity (unique contribution of delay duration). Adolescents’ average impatience was positively correlated with frontoparietal and ventral striatal activity during delayed reward choices, and with ventromedial prefrontal cortex activity during immediate reward choices. Adolescents’ amount sensitivity was positively associated with ventral striatal and dorsal anterior cingulate cortex activity during immediate reward choices. Delay sensitivity was positively correlated with inferior parietal cortex activity during delayed reward choices. As expected, snacks were discounted more steeply than money, and TD of both reward types was associated with overlapping activation in the inferior parietal cortex. Exploring whether testosterone or estradiol were associated with TD and its neural correlates revealed no significant associations. These findings indicate that distinct components contribute uniquely to TD choice and that individual differences in amount sensitivity are uniquely associated with activation of reward valuation areas, while individual differences in delay sensitivity are uniquely associated with activation of cognitive control areas. HighlightsWe examined individual differences in temporal discounting in adolescents.We determined adolescents’ average impatience and amount and delay sensitivity.Average impatience was positively associated with frontoparietal and striatal activity.Amount sensitivity was positively associated with ventral striatum activity.Delay sensitivity was positively associated with parietal cortex activity.

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

Quick Delay Questionnaire: Reliability, validity, and relations to functional impairments in adults with attention-deficit/hyperactivity disorder (ADHD)

The Quick Delay Questionnaire (QDQ) is a self-report measure of delay-related behaviors in adults, and the present study aimed at investigating the psychometric properties of QDQ scores, how well they can discriminate between ADHD adults and both clinical and nonclinical controls, as well as their relations to measures of functional impairments. In the present study, QDQ ratings, a laboratory measure of delay discounting, and ratings of functional impairments were collected from adults diagnosed with attention-deficit/hyperactivity disorder (ADHD; n = 51), a clinical control group with other psychiatric disorders (n = 46), and a nonclinical control group (n = 105). Results showed that the QDQ scores showed adequate reliability. Adults with ADHD had higher scores compared with normal controls on both QDQ subscales, and they also reported higher levels of delay aversion than the clinical controls. Logistic regression analyses showed high specificity but low sensitivity when trying to discriminate between adults with ADHD and nonclinical controls. QDQ scores were not associated with a laboratory measure of delay discounting, but with functional impairments such as substance use, criminality, and money management. Our findings indicate that QDQ scores are reliable, but this instrument should be regarded as a complement rather than as a replacement for laboratory measures. The relatively low sensitivity of QDQ scores is in line with current models of heterogeneity stating that only a subgroup of individuals with ADHD has high levels of delay-related behaviors. Our findings further indicate that this subgroup may be at particularly high risk for problems in everyday life.

Waiting and working for rewards: Attention-Deficit/Hyperactivity Disorder is associated with steeper delay discounting linked to amygdala activation, but not with steeper effort discounting

OBJECTIVEnChildren and adolescents with ADHD have a relatively strong preference for smaller immediate rewards over larger delayed rewards (steep delay discounting). It is unknown whether such steep discounting of rewards is specific for delayed rewards, i.e., supporting the delay aversion account of ADHD, or whether it is also present for effortful rewards, i.e., representing general reward insensitivity. Therefore, this study examined behavioral and BOLD responses during delay discounting (DD) and effort discounting (ED) in ADHD.nnnMETHODnThirty adolescents with ADHD and 28 controls (12-17 years) were scanned while performing a DD-ED task (fMRI findings were based on 21 and 25 participants, respectively). During DD, participants were presented with a series of choices between a small reward delivered immediately and a larger reward delivered after 5-25s. During ED, participants were presented with choices between a small reward that was delivered after exerting 15% of their maximal hand grip strength and a larger reward delivered after exerting 30-90% of their strength.nnnRESULTSnAnalyses on the subjective values of delayed and effortful rewards and on the Area Under the discounting Curves (AUCs) indicated that adolescents with ADHD showed steeper discounting than controls for DD, but not for ED. This was accompanied by a slightly stronger delay dose-response relationship in the amygdala for adolescents with ADHD who reported to be more delay averse in daily life.nnnCONCLUSIONnTogether, these results-steeper DD in the ADHD group and a stronger delay dose-response relationship in the amygdala, while no evidence for group differences in ED was found-support the delay aversion account of ADHD.

Does an attention bias to appetitive and aversive words modulate interference control in youth with ADHD

ABSTRACT Interference control refers to the ability to selectively attend to certain information while ignoring distracting information. This ability can vary as a function of distractor relevance. Distractors that are particularly relevant to an individual may attract more attention than less relevant distractors. This is referred to as attention bias. Weak interference control and altered reward sensitivity are both important features of attention deficit hyperactivity disorder (ADHD). However, interference control is typically studied in isolation. This study integrates both. Youths (aged 9 to 17 years) with ADHD (n = 37, 25 boys) and typically-developing controls (n = 38, 20 boys) completed a Stroop task using appetitive words and matched neutral words to assess whether appetitive distractors diminished interference control more in youths with ADHD than controls. In order to test for specificity, aversive words were also included. As expected, appetitive words disrupted interference control but this effect was not stronger for youths with ADHD than the controls. Aversive words, on the other hand, facilitated interference control. Dimensional analyses revealed that this facilitation effect increased substantially as a function of ADHD symptom severity. Possible mechanisms for this effect include up-regulation of interference control as a function of induced negative mood, or as a function of increased effort. In conclusion, appetitive words do not lead to worse interference control in youths with ADHD compared with controls. Interference control was modulated in a valence-specific manner, concurrent with mood-induced effects on cognitive control.

Polygenic risk for alcohol consumption and its association with alcohol-related phenotypes: Do stress and life satisfaction moderate these relationships?

BACKGROUNDnGenetic and environmental factors contribute about equally to alcohol-related phenotypes in adulthood. In the present study, we examined whether more stress at home or low satisfaction with life might be associated with heavier drinking or more alcohol-related problems in individuals with a high genetic susceptibility to alcohol use.nnnMETHODSnInformation on polygenic scores and drinking behavior was available in 6705 adults (65% female; 18-83 years) registered with the Netherlands Twin Register. Polygenic risk scores (PRSs) were constructed for all subjects based on the summary statistics of a large genome-wide association meta-analysis on alcohol consumption (grams per day). Outcome measures were quantity of alcohol consumption and alcohol-related problems assessed with the Alcohol Use Disorders Identification Test (AUDIT). Stress at home and life satisfaction were moderating variables whose significance was tested by Generalized Estimating Equation analyses taking familial relatedness, age and sex into account.nnnRESULTSnPRSs for alcohol were significantly associated with quantity of alcohol consumption and alcohol-related problems in the past year (R2=0.11% and 0.10% respectively). Participants who reported to have experienced more stress in the past year and lower life satisfaction, scored higher on alcohol-related problems (R2=0.27% and 0.29 respectively), but not on alcohol consumption. Stress and life satisfaction did not moderate the association between PRSs and the alcohol outcome measures.nnnCONCLUSIONSnThere were significant main effects of polygenic scores and of stress and life satisfaction on drinking behavior, but there was no support for PRS-by-stress or PRS-by-life satisfaction interactions on alcohol consumption and alcohol-related problems.