Why Some People Discount More than Others: Baseline Activation in the Dorsal PFC Mediates the Link between COMT Genotype and Impatient Choice

Genome-wide association studies (GWAS) and post-GWAS analyses of impulsivity: A systematic review

Impulsivity is related to a host of mental and behavioral problems. It is a complex construct with many different manifestations, most of which are heritable. The genetic compositions of these impulsivity manifestations, however, remain unclear. A number of genome-wide association studies (GWAS) and post-GWAS analyses have tried to address this issue. We conducted a systematic review of all GWAS and post-GWAS analyses of impulsivity published up to December 2023. Available data suggest that single nucleotide polymorphisms (SNPs) in more than a dozen of genes (e.g., CADM2, CTNNA2, GPM6B) are associated with different measures of impulsivity at genome-wide significant levels. Post-GWAS analyses further show that different measures of impulsivity are subject to different degrees of genetic influence, share few genetic variants, and have divergent genetic overlap with basic personality traits such as extroversion and neuroticism, cognitive ability, psychiatric disorders, substance use, and obesity. These findings shed light on controversies in the conceptualization and measurement of impulsivity, while providing new insights on the underlying mechanisms that yoke impulsivity to psychopathology.

Interindividual differences in intergenerational sustainable behavior are associated with cortical thickness of the dorsomedial and dorsolateral prefrontal cortex

Intergenerational sustainability requires people of the present generation to make sacrifices today to benefit others of future generations (e.g. mitigating climate change, reducing public debt). Individuals vary greatly in their intergenerational sustainability, and the cognitive and neural sources of these interindividual differences are not yet well understood. We here combined neuroscientific and behavioral methods by assessing interindividual differences in cortical thickness and by using a common-pool resource paradigm with intergenerational contingencies. This enabled us to look for objective, stable, and trait-like neural markers of interindividual differences in consequential intergenerational behavior. We found that individuals behaving sustainably (vs. unsustainably) were marked by greater cortical thickness of the dorsomedial and dorsolateral prefrontal cortex. Given that these brain areas are involved in perspective-taking and self-control and supported by mediation analyses, we speculate that greater cortical thickness of these brain areas better enable individuals to take the perspective of future generations and to resist temptations to maximize personal benefits that incur costs for future generations. By meeting recent calls for the contribution of neuroscience to sustainability research, it is our hope that the present study advances the transdisciplinary understanding of interindividual differences in intergenerational sustainability.

Local slow-wave activity over the right prefrontal cortex reveals individual risk preferences

In everyday life, we have to make decisions under varying degrees of risk. Even though previous research has shown that the manipulation of sleep affects risky decision-making, it remains unknown whether individual, temporally stable neural sleep characteristics relate to individual differences in risk preferences. Here, we collected sleep data under normal conditions in fifty-four healthy adults using a portable high-density EEG at participants' home. Whole-brain corrected for multiple testing, we found that lower slow-wave activity (SWA, an indicator of sleep depth) in a cluster of electrodes over the right prefrontal cortex (PFC) is associated with higher individual risk propensity. Importantly, the association between local sleep depth and risk preferences remained significant when controlling for total sleep time and for time spent in deep sleep, i.e., sleep stages N2 and N3. Moreover, the association between risk preferences and SWA over the right PFC was very similar in all sleep cycles. Because the right PFC plays a central role in cognitive control functions, we speculate that local sleep depth in this area, as reflected by SWA, might serve as a dispositional indicator of self-regulatory ability, which in turn reflects risk preferences.

Neural signatures of heterogeneity in risk-taking and strategic consistency

People display a high degree of heterogeneity in risk-taking behaviour, but this heterogeneity remains poorly understood. Here, we use a neural trait approach to examine if task-independent, brain-based differences can help uncover the sources of heterogeneity in risky decision-making. We extend prior research in two key ways. First, we disentangled risk-taking and strategic consistency using novel measures afforded by the Balloon Analogue Risk Task. Second, we applied a personality neuroscience framework to explore why personality traits are typically only weakly related to risk-taking behaviour. We regressed participants' (N = 104) source localized resting-state electroencephalographic activity on risk-taking and strategic consistency. Results revealed that higher levels of resting-state delta-band current density (reflecting reduced cortical activation) in the left dorsal anterior cingulate cortex and the left dorsolateral prefrontal cortex were associated with increased risk-taking and decreased strategic consistency, respectively. These results suggest that heterogeneity in risk-taking behaviour is associated with neural dispositions related to sensitivity to the risk of loss, whereas heterogeneity in strategic consistency is associated with neural dispositions related to strategic decision-making. Finally, extraversion, neuroticism, openness, and self-control were broadly associated with both of the identified neural traits, which in turn mediated indirect associations between personality traits and behavioural measures. These results provide an explanation for the weak direct relationships between personality traits and risk-taking behaviour, supporting a personality neuroscience framework of traits and decision-making.

Individual Differences in Intertemporal Choice

Intertemporal choice involves deciding between smaller, sooner and larger, later rewards. People tend to prefer smaller rewards that are available earlier to larger rewards available later, a phenomenon referred to as temporal or delay discounting. Despite its ubiquity in human and non-human animals, temporal discounting is subject to considerable individual differences. Here, we provide a critical narrative review of this literature and make suggestions for future work. We conclude that temporal discounting is associated with key socio-economic and health-related variables. Regarding personality, large-scale studies have found steeper temporal discounting to be associated with higher levels of self-reported impulsivity and extraversion; however, effect sizes are small. Temporal discounting correlates negatively with future-oriented cognitive styles and inhibitory control, again with small effect sizes. There are consistent associations between steeper temporal discounting and lower intelligence, with effect sizes exceeding those of personality or cognitive variables, although socio-demographic moderator variables may play a role. Neuroimaging evidence of brain structural and functional correlates is not yet consistent, neither with regard to areas nor directions of effects. Finally, following early candidate gene studies, recent Genome Wide Association Study (GWAS) approaches have revealed the molecular genetic architecture of temporal discounting to be more complex than initially thought. Overall, the study of individual differences in temporal discounting is a maturing field that has produced some replicable findings. Effect sizes are small-to-medium, necessitating future hypothesis-driven work that prioritizes large samples with adequate power calculations. More research is also needed regarding the neural origins of individual differences in temporal discounting as well as the mediating neural mechanisms of associations of temporal discounting with personality and cognitive variables.

Theta resting EEG in the right TPJ is associated with individual differences in implicit intergroup bias

Why are some people more biased than others in their implicit evaluations during social interaction? The dispositional determinants of individual differences in implicit intergroup bias are poorly understood. Here, we explored whether such variability might be explained by stable neural traits. For that purpose, we used the source-localized resting electroencephalograms of 83 members of naturalistic social groups to explain their bias in an in-/outgroup implicit association test. Lower levels of resting theta current density in the right temporo-parietal junction (TPJ) were associated with stronger implicit intergroup bias and explained unique variability in bias beyond relevant personality questionnaires. These findings demonstrate the added value of the neural trait approach in predicting inter-individual differences in implicit social cognition. Given that low levels of resting theta current density during wakefulness likely reflect increased cortical activation, our results suggest that individuals with an efficiently working right TPJ possess capacities to mediate specific cognitive processes that predispose them towards stronger implicit intergroup bias. As the human species has evolved living in distinct social groups, the capacity to quickly differentiate friend from foe became highly adaptive and might thus constitute an essential part of human nature.

Linking Delay Discounting and Substance Use Disorders: Genotypes and Phenotypes

Research supports the idea that "delay discounting," also known as temporal discounting, intertemporal choice, or impulsive choice, is a transdisease process with a strong connection to substance use disorders (SUDs) and other psychopathologies, like attention deficit hyperactivity disorder and depression. This article briefly reviews the evidence used to conclude that delay discounting is heritable and should be considered to be an endophenotype, as well as evidence of its behavioral and genetic associations with SUDs. It also discusses the limitations that should be considered when evaluating the strength of these associations. Finally, this article briefly describes research examining relationships among delay discounting and SUD-associated intermediate phenotypes to better understand the conceptual relationships underlying the links between SUDs and delay discounting, and identifies research gaps that should be addressed.

Excessive discounting of delayed reinforcers as a trans-disease process: Update on the state of the science

Delay discounting, or the process by which reinforcers lose value with delay to their receipt, has been identified as a trans-disease process underlying addiction, other disorders, and maladaptive health behaviors. Delay discounting has been identified as an endophenotype for multiple psychiatric disorders including substance use disorder, ADHD, and major depressive disorder, with this endophenotype being linked to deficits in dopaminergic and serotonergic neurotransmission. In addition, neuroanatomical and neurophysiological deficits in areas of the executive and impulsive systems have been associated with both steeper discounting and substance use disorders. Delay discounting constitutes a novel target for interventions to change health behaviors. A new theory, termed reinforcer pathology, has been developed uniting these findings and setting the stage for future research.

Genetic influences on delayed reward discounting: A genome-wide prioritized subset approach

Delayed reward discounting (DRD) is a behavioral economic measure of impulsivity that has been consistently associated with addiction. It has also been identified as a promising addiction endophenotype, linking specific sources of genetic variation to individual risk. A challenge in the studies to date is that levels of DRD are often confounded with prior drug use, and previous studies have also had limited genomic scope. The current investigation sought to address these issues by studying DRD in healthy young adults with low levels of substance use (N = 986; 62% female, 100% European ancestry) and investigating genetic variation genome-wide. The genome-wide approach used a prioritized subset design, organizing the tests into theoretically and empirically informed categories and apportioning power accordingly. Three subsets were used: (a) a priori loci implicated by previous studies; (b) high-value addiction (HVA) markers from the recently developed SmokeScreen array; and (c) an atheoretical genome-wide scan. Among a priori loci, a nominally significant association was present between DRD and rs521674 in ADRA2A. No significant HVA loci were detected. One statistically significant genome-wide association was detected (rs13395777, p = 2.8 × 10-8), albeit in an intergenic region of unknown function. These findings are generally not supportive of the previous candidate gene studies and suggest that DRD has a complex genetic architecture that will require considerably larger samples to identify genetic associations more definitively. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Frequency of everyday pro-environmental behaviour is explained by baseline activation in lateral prefrontal cortex

Humankind faces a plethora of environmental problems, many of which are directly influenced by individual human behaviour. To better understand pro-environmental behaviour, we here try to identify interindividual markers that explain variance in the frequency of every-day pro-environmental behaviour. So far, research on this topic has mainly relied on subjective self-report measures and has yielded mixed results. In this study, we applied a neural trait approach to assess stable, objective individual differences. Using source-localised electroencephalography, we measured cortical activation at rest and combined our neural task-independent data with an ecologically valid assessment of everyday pro-environmental behaviour. We find whole-brain-corrected evidence that task-independent baseline activation in the right lateral prefrontal cortex, a brain area known to be involved in cognitive control and self-control processes, explains individual differences in pro-environmental behaviour. The higher the cortical baseline activation in this area, the higher the frequency of everyday pro-environmental behaviour. Implications for the promotion of pro-environmental behaviour are discussed.

Theta resting EEG in TPJ/pSTS is associated with individual differences in the feeling of being looked at

Direct eye gaze is a powerful stimulus in social interactions, yet people vary considerably in the range of gaze lines that they accept as being direct (cone of direct gaze, CoDG). Here, we searched for a possible neural trait marker of these individual differences. We measured the width of the CoDG in 137 healthy participants and related their individual CoDG to their neural baseline activation as measured with resting electroencephalogram. Using a source-localization technique, we found that resting theta current density in the left temporo-parietal junction (TPJ) and adjacent posterior superior temporal sulcus (pSTS) was associated with the width of CoDG. Our findings suggest that the higher the baseline cortical activation in the left TPJ/pSTS, the wider the CoDG and thus the more liberal the individuals’ judgments were in deciding whether a looker stimulus was making eye contact or not. This is a first demonstration of the neural signatures underlying individual differences in the feeling of being looked at.

Peer influence, Frontostriatal connectivity, and delay discounting in African American emerging adults

Prior research has demonstrated the importance of delay discounting in adverse health behaviors, such as addiction, attention deficit hyperactivity disorder, risk taking, and obesity. Nevertheless, the functional connectivity of neural circuitry associated with delay discounting and the ways in which the social environment may influence frontostriatal connectivity remain largely unknown, particularly in African Americans. Building on recent literature implicating frontostriatal connectivity during active delay discounting decision making and at rest, we used functional magnetic resonance imaging to assess the association between delay discounting and frontostriatal resting state connectivity (rsFC). We also examined the capacity of social relationships with parents and peers to longitudinally predict frontostriatal rsFC. The study cohort was composed of 91 rural African American emerging adults followed over a 6-year period. Greater (i.e., more positive) frontostriatal rsFC was associated with decreased delay discounting (i.e., less impulsive decision making). In addition, peer relationships at ages 20 and 21 significantly predicted frontostriatal rsFC at age 25 above and beyond parental influence. A significant indirect effect of peer affiliation on delay discounting through frontostriatal rsFC also emerged. These results indicate a role of frontostriatal connectivity in delay discounting decision making and highlight peers' unique influence on decision making behaviors through frontostriatal rsFC during emerging adulthood.

Understanding Individual Differences in Domain-General Prosociality: A Resting EEG Study

Prosocial behavior is of vital importance for the smooth functioning of society. However, the propensity to behave in a prosocial manner is characterized by vast individual differences. In order to reveal the sources of these differences, some studies have used objective, task-independent neural traits, for instance resting electroencephalography (EEG). Despite providing valuable insights into the neural signatures of several domains of prosociality, each of these studies has only focused on one single domain. Here, we exposed 137 participants to different social dilemma situations in order to obtain a measure of the individuals’ domain-general prosociality and recorded multi-channel task-independent, resting EEG. Using a source-localization technique, we found that resting current density within the temporo-parietal junction in two beta bands (beta2 and beta3) was positively associated with domain-general prosociality. This is the first demonstration of neural signatures underlying individual differences in the propensity to behave in a prosocial manner across different social situations.

Dissociable functional activities of cortical theta and beta oscillations in the lateral prefrontal cortex during intertemporal choice

The lateral prefrontal cortex (LPFC) plays an important role in the neural networks involved in intertemporal choice. However, little is known about how the neural oscillation of LPFC functions during intertemporal choice, owing to the technical limitations of functional magnetic resonance imaging and event-related brain potential recordings. Electrocorticography (ECoG) is a novel neuroimaging technique that has high spatial and temporal resolution. In this study, we used ECoG and projected the ECoG data onto individual brain spaces to investigate human intracranial cortex activity and how neural oscillations of the LPFC impact intertemporal choice. We found that neural activity of theta oscillation was significantly higher during impulsive decisions, while beta oscillation activity was significantly higher during non-impulsive ones. Our findings suggest a functional dissociation between cortical theta and beta oscillations during decision-making processes involved in intertemporal choice, and that decision outcomes may be determined by LPFC modulation, which involves neural oscillations at different frequencies.

Neural signatures of different behavioral types in fairness norm compliance

Fairness norm compliance is critical in any society. However, norm compliant behavior is very heterogeneous. Some people are reliably fair (voluntary compliers). Some are fair to avoid sanctions (sanction-based compliers), and some are reliably unfair (non-compliers). These types play divergent roles in society. However, they remain poorly understood. Here, we combined neural measures (resting electroencephalography and event-related potentials) and economic paradigms to better understand these types. We found that voluntary compliers are characterized by higher baseline activation in the right temporo-parietal junction, suggesting better social cognition capacity compared to sanction-based compliers and non-compliers. The latter two types are differentiated by (a) baseline activation in the dorso-lateral prefrontal cortex, a brain area known to be involved in self-control processes, and (b) event-related potentials in a classic self-control task. Both results suggest that sanction-based compliers have better self-control capacity than non-compliers. These findings improve our understanding of fairness norm compliance. Broadly, our findings suggest that established training techniques that boost self-control might help non-compliers adhere to fairness norms.

Elevated outcome-anticipation and outcome-evaluation ERPs associated with a greater preference for larger-but-delayed rewards

Although waiting for a reward reduces or discounts its value, some people have a stronger tendency to wait for larger rewards and forgo smaller-but-immediate rewards. This ability to delay gratification is captured by individual differences in so-called intertemporal choices in which individuals are asked to choose between larger-but-delayed versus smaller-but-immediate rewards. The current study used event-related potentials (ERPs) to examine whether enhancement in two neurocognitive processes, outcome anticipation and outcome evaluation, modulate individual variability in intertemporal responses. After completing a behavioral intertemporal choice task, 34 participants performed an ERP gambling task. From this ERP task, we separately examined individual differences in outcome anticipation (stimulus-preceding negativity; SPN), early outcome valuation (feedback-related negativity; FRN), and late outcome evaluation (P3). We observed that both elevated outcome-anticipation (SPN) and late outcome-evaluation (P3) neural processes predicted a stronger preference toward larger-but-delayed rewards. No relationship was observed between intertemporal responses and early outcome evaluation (FRN), indicating that the relationship between outcome evaluation and intertemporal responses was specific to the late outcome-evaluation processing stream. Moreover, multiple regression analyses indicated that the SPN and P3 independently modulate individual differences in intertemporal responses, suggesting separate mechanisms underlie the relationship between these two neurocognitive processes and intertemporal responses. Accordingly, we identify two potential neurocognitive modulators of individual variability in intertemporal responses. We discuss the mechanisms underlying these modulators in terms of anticipation-related processing (SPN) and a saliency bias toward gain (compared to loss) outcomes (P3).

Decline of prefrontal cortical-mediated executive functions but attenuated delay discounting in aged Fischer 344 × brown Norway hybrid rats

Despite the fact that prefrontal cortex (PFC) function declines with age, aged individuals generally show an enhanced ability to delay gratification, as evident by less discounting of delayed rewards in intertemporal choice tasks. The present study was designed to evaluate relationships between 2 aspects of PFC-dependent cognition (working memory and cognitive flexibility) and intertemporal choice in young (6 months) and aged (24 months) Fischer 344 × brown Norway F1 hybrid rats. Rats were also evaluated for motivation to earn rewards using a progressive ratio task. As previously reported, aged rats showed attenuated discounting of delayed rewards, impaired working memory, and impaired cognitive flexibility compared with young. Among aged rats, greater choice of delayed reward was associated with preserved working memory, impaired cognitive flexibility, and less motivation to work for food. These relationships suggest that age-related changes in PFC and incentive motivation contribute to variance in intertemporal choice within the aged population. Cognitive impairments mediated by PFC are unlikely, however, to fully account for the enhanced ability to delay gratification that accompanies aging.

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

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.

Does Power Increase Self-Control? Episodic Priming May Not Provide the Answer

Powerful people (e.g., political and business leaders) should be able to control their impulses and act in line with long-term rather than short-term interests. However, theories of power suggest different answers to the question whether the basic experience of feeling powerful decreases (e.g., Keltner, Gruenfeld, & Anderson, 2003) or increases self-control performance (e.g., Magee & Smith, 2013). We conducted a pre-registered direct replication of the only experiment testing the effects of power on self-control (Joshi & Fast, 2013, Study 3). In contrast to the original results, social power, operationalized by episodic priming, did not affect temporal discounting. A possible explanation is the fact that the power priming failed to elevate participants’ sense of power. Thus, the null findings challenge the power priming paradigm rather than the two theories from which opposite predictions were derived. In order to understand how power affects self-control, future research may need to rely on other manipulations.

Simulating future value in intertemporal choice

The laboratory study of how humans and other animals trade-off value and time has a long and storied history, and is the subject of a vast literature. However, despite a long history of study, there is no agreed upon mechanistic explanation of how intertemporal choice preferences arise. Several theorists have recently proposed model-based reinforcement learning as a candidate framework. This framework describes a suite of algorithms by which a model of the environment, in the form of a state transition function and reward function, can be converted on-line into a decision. The state transition function allows the model-based system to make decisions based on projected future states, while the reward function assigns value to each state, together capturing the necessary components for successful intertemporal choice. Empirical work has also pointed to a possible relationship between increased prospection and reduced discounting. In the current paper, we look for direct evidence of a relationship between temporal discounting and model-based control in a large new data set (n = 168). However, testing the relationship under several different modeling formulations revealed no indication that the two quantities are related.

I can't wait! Neural reward signals in impulsive individuals exaggerate the difference between immediate and future rewards

Waiting for rewards is difficult, and highly impulsive individuals with low self-control have an especially hard time with it. Here, we investigated whether neural responses to rewards in a delayed gratification task predict impulsivity and self-control. The EEG was recorded from participants engaged in a guessing game in which on each trial they could win either a large or small reward, paid either now or after 6 months. Ratings confirmed that participants preferred immediate, large rewards over small, delayed rewards. Electrophysiological reward signals reflecting the difference between immediate and future rewards predicted self-report measures of impulsivity and self-control. Further, these signals were highly reliable across two sessions over a 1-week interval, showing high temporal stability like stable personality traits. These results suggest that greater valuation of immediate rewards causes impulsive individuals to redirect control away from delayed rewards, indicating why it is so hard for them to wait.

Willing to wait: Elevated reward-processing EEG activity associated with a greater preference for larger-but-delayed rewards

While almost everyone discounts the value of future rewards over immediate rewards, people differ in their so-called delay-discounting. One of the several factors that may explain individual differences in delay-discounting is reward-processing. To study individual-differences in reward-processing, however, one needs to consider the heterogeneity of neural-activity at each reward-processing stage. Here using EEG, we separated reward-related neural activity into distinct reward-anticipation and reward-outcome stages using time-frequency characteristics. Thirty-seven individuals first completed a behavioral delay-discounting task. Then reward-processing EEG activity was assessed using a separate reward-learning task, called a reward time-estimation task. During this EEG task, participants were instructed to estimate time duration and were provided performance feedback on a trial-by-trial basis. Participants received monetary-reward for accurate-performance on Reward trials, but not on No-Reward trials. Reward trials, relative to No-Reward trials, enhanced EEG activity during both reward-anticipation (including, cued-locked delta power during cue-evaluation and pre-feedback alpha suppression during feedback-anticipation) and reward-outcome (including, feedback-locked delta, theta and beta power) stages. Moreover, all of these EEG indices correlated with behavioral performance in the time-estimation task, suggesting their essential roles in learning and adjusting performance to maximize winnings in a reward-learning situation. Importantly, enhanced EEG power during Reward trials, as reflected by stronger 1) pre-feedback alpha suppression, 2) feedback-locked theta and 3) feedback-locked beta, was associated with a greater preference for larger-but-delayed rewards in a separate, behavioral delay-discounting task. Results highlight the association between a stronger preference toward larger-but-delayed rewards and enhanced reward-processing. Moreover, our reward-processing EEG indices detail the specific stages of reward-processing where these associations occur.

Dopamine Modulation of Intertemporal Decision-making: Evidence from Parkinson Disease

Choosing between smaller prompt rewards and larger later rewards is a common choice problem, and studies widely agree that frontostriatal circuits heavily innervated by dopamine are centrally involved. Understanding how dopamine modulates intertemporal choice has important implications for neurobiological models and for understanding the mechanisms underlying maladaptive decision-making. However, the specific role of dopamine in intertemporal decisions is not well understood. Dopamine may play a role in multiple aspects of intertemporal choices--the valuation of choice outcomes and sensitivity to reward delays. To assess the role of dopamine in intertemporal decisions, we tested Parkinson disease patients who suffer from dopamine depletion in the striatum, in either high (on medication, PDON) or low (off medication, PDOFF) dopaminergic states. Compared with both PDOFF and healthy controls, PDON made more farsighted choices and reduced their valuations less as a function of increasing time to reward. Furthermore, reduced discounting in the high dopaminergic state was robust across multiple measures, providing new evidence for dopamine's role in making decisions about the future.

Mesocorticolimbic dopamine functioning in primary psychopathy: A source of within-group heterogeneity

Despite similar emotional deficiencies, primary psychopathic individuals can be situated on a continuum that spans from controlled to disinhibited. The constructs on which primary psychopaths are found to diverge, such as self-control, cognitive flexibility, and executive functioning, are crucially regulated by dopamine (DA). As such, the goal of this review is to examine which specific alterations in the meso-cortico-limbic DA system and corresponding genes (e.g., TH, DAT, COMT, DRD2, DRD4) might bias development towards a more controlled or disinhibited expression of primary psychopathy. Based on empirical data, it is argued that primary psychopathy is generally related to a higher tonic and population activity of striatal DA neurons and lower levels of D2-type DA receptors in meso-cortico-limbic projections, which may boost motivational drive towards incentive-laden goals, dampen punishment sensitivity, and increase future reward-expectancy. However, increasingly higher levels of DA activity in the striatum (moderate versus pathological elevations), lower levels of DA functionality in the prefrontal cortex, and higher D1-to-D2-type receptor ratios in meso-cortico-limbic projections may lead to increasingly disinhibited and impetuous phenotypes of primary psychopathy. Finally, in order to provide a more coherent view on etiological mechanisms, we discuss interactions between DA and serotonin that are relevant for primary psychopathy.

Genetic influences on delay discounting in smokers: examination of a priori candidates and exploration of dopamine-related haplotypes

RATIONALE

Delay discounting is a behavioral economic index of impulsivity that reflects a person's relative preference for small immediate rewards versus larger delayed rewards. Elevated delay discounting is robustly linked to addictive disorders and has been increasingly investigated as a viable endophenotype for genetic influences on addiction.

OBJECTIVE

The aim of this study is to examine associations between delay discounting and two a priori loci, rs4680 in COMT and rs1800497 in ANKK1, and three exploratory haplotypes proximal to rs1800497 in a sample of daily smokers.

METHODS

Participants were 713 (60.2 % male) daily smokers of European ancestry who completed a delay discounting assessment and provided a DNA sample.

RESULTS

Significant associations were detected between greater discounting of medium magnitude rewards (~$55) and the G allele of rs4680, as well as the T allele of rs1800497. Exploratory haplotype analyses identified two haplotypes (rs1160467/rs1800497; rs6277/rs1079597) significantly associated with delay discounting rates. However, the rs1160467/rs1800497 haplotype associations appeared to be entirely attributable to variation in rs1800497, suggesting that the association of rs1800497 with discounting is best understood at the individual SNP level. Similarly, the rs6277/rs1079597 haplotype findings suggested that the association was specific to rs1079597.

CONCLUSIONS

This study provides further evidence that rs4680 and rs1800497 genotypes are significantly associated with delay discounting preferences and does so among smokers for the first time. The study also provides evidence of specificity for the rs1800497 association and identifies a novel locus, rs1079597, as a genetic contributor to higher delay discounting rates.

The effect of cognitive challenge on delay discounting

Recent findings suggest that the dorsolateral prefrontal cortex (DLPFC), a region consistently associated with impulse control, is vulnerable to transient suppression of its activity and attendant functions by excessive stress and/or cognitive demand. Using functional magnetic resonance imaging, we show that a capacity-exceeding cognitive challenge induced decreased DLPFC activity and correlated increases in the preference for immediately available rewards. Consistent with growing evidence of a link between working memory capacity and delay discounting, the effect was inversely proportional to baseline performance on a working memory task. Subjects who performed well on the working memory task had unchanged, or even decreased, delay discounting rates, suggesting that working memory ability may protect cognitive control from cognitive challenge.

COMT Associations with Disordered Gambling and Drinking Measures

Disordered gambling and alcohol dependence are influenced by unique and shared genetic factors. Although the evidence is mixed, some research has linked catechol-O-methyltransferase (COMT) rs4680 (or COMT Val158Met) to the development of gambling or drinking problems; however, no molecular genetic study has jointly examined gambling and drinking problems. Furthermore, the majority of past studies examined gambling or drinking problems using a case-control design. The purpose of the current study was to examine associations of COMT rs4680 with dimensionally and categorically measured gambling and drinking problems in a nonclinical sample (139 Caucasian adults). The current study found that COMT rs4680 was related to both dimensionally and categorically measured gambling and drinking problems. It appears that the COMT Met/Met genotype may be a genetic risk factor that contributes to the development of both gambling and drinking problems.

Impulsive delayed reward discounting as a genetically-influenced target for drug abuse prevention: a critical evaluation

This review evaluates the viability of delayed reward discounting (DRD), an index of how much an individual devalues a future reward based on its delay in time, for genetically-informed drug abuse prevention. A review of the literature suggests that impulsive DRD is robustly associated with drug addiction and meets most of the criteria for being an endophenotype, albeit with mixed findings for specific molecular genetic influences. Several modes of experimental manipulation have been demonstrated to reduce DRD acutely. These include behavioral strategies, such as mindfulness, reward bundling, and episodic future thinking; pharmacological interventions, including noradrenergic agonists, adrenergic agonists, and multiple monoamine agonists; and neuromodulatory interventions, such as transcranial magnetic stimulation and transcranial direct current stimulation. However, the generalization of these interventions to positive clinical outcomes remains unclear and no studies to date have examined interventions on DRD in the context of prevention. Collectively, these findings suggest it would be premature to target DRD for genetically-informed prevention. Indeed, given the evidence of environmental contributions to impulsive DRD, whether genetically-informed secondary prevention would ever be warranted is debatable. Progress in identifying polymorphisms associated with DRD profiles could further clarify the underlying biological systems for pharmacological and neuromodulatory interventions, and, as a qualitatively different risk factor from existing prevention programs, impulsive DRD is worthy of investigation at a more general level as a novel and promising drug abuse prevention target.

Replication study implicates COMT val158met polymorphism as a modulator of probabilistic reward learning

Previous studies suggest that a single nucleotide polymorphism in the catechol-O-methyltransferase (COMT) gene (val158met) may modulate reward-guided decision making in healthy individuals. The polymorphism affects dopamine catabolism and thus modulates prefrontal dopamine levels, which may lead to variation in individual responses to risk and reward. We previously showed, using tasks that index reward responsiveness (measured by responses bias towards reinforced stimuli) and risk taking (measured by the Balloon Analogue Risk Task), that COMT met homozygotes had increased reward responsiveness and, thus, an increased propensity to seek reward. In this study, we sought to replicate these effects in a larger, independent cohort of Caucasian UK university students and staff with similar demographic characteristics (n = 101; 54 females, mean age: 22.2 years). Similarly to our previous study, we observed a significant trial × COMT genotype interaction (P = 0.047; η(2) = 0.052), which was driven by a significant effect of COMT on the incremental acquisition of response bias [response bias at block 3 - block 1 (met/met > val/val: P = 0.028) and block 3 - block 2 (met/met > val/val: P = 0.007)], suggesting that COMT met homozygotes demonstrated higher levels of reward responsiveness by the end of the task. However, we failed to see main effects of COMT genotype on overall response bias or risk-seeking behaviour. These results provide additional evidence that prefrontal dopaminergic variation may have a role in reward responsiveness, but not risk-seeking behaviour. Our findings may have implications for neuropsychiatric disorders characterized by clinical deficits in reward processing such as anhedonia.

Modulation of the COMT Val(158)Met polymorphism on resting-state EEG power

The catechol-O-methyltransferase (COMT) Val(158)Met polymorphism impacts cortical dopamine (DA) levels and may influence cortical electrical activity in the human brain. This study investigated whether COMT genotype influences resting-state electroencephalogram (EEG) power in the frontal, parietal and midline regions in healthy volunteers. EEG recordings were conducted in the resting-state in 13 postmenopausal healthy woman carriers of the Val/Val genotype and 11 with the Met/Met genotype. The resting EEG spectral absolute power in the frontal (F3, F4, F7, F8, FC3 and FC4), parietal (CP3, CP4, P3 and P4) and midline (Fz, FCz, Cz, CPz, Pz and Oz) was analyzed during the eyes-open and eyes-closed conditions. The frequency bands considered were the delta, theta, alpha1, alpha2, beta1 and beta2. EEG data of the Val/Val and Met/Met genotypes, brain regions and conditions were analyzed using a general linear model analysis. In the individuals with the Met/Met genotype, delta activity was increased in the eyes-closed condition, theta activity was increased in the eyes-closed and in the eyes-open conditions, and alpha1 band, alpha2 band and beta1band activity was increased in the eyes-closed condition. A significant interaction between COMT genotypes and spectral bands was observed. Met homozygote individuals exhibited more delta, theta and beta1 activity than individuals with the Val/Val genotype. No significant interaction between COMT genotypes and the resting-state EEG regional power and conditions were observed for the three brain regions studied. Our findings indicate that the COMT Val(158)Met polymorphism does not directly impact resting-state EEG regional power, but instead suggest that COMT genotype can modulate resting-state EEG spectral power in postmenopausal healthy women.

Interindividual variability in functional connectivity as long-term correlate of temporal discounting

During intertemporal choice (IT) future outcomes are usually devaluated as a function of the delay, a phenomenon known as temporal discounting (TD). Based on task-evoked activity, previous neuroimaging studies have described several networks associated with TD. However, given its relevance for several disorders, a critical challenge is to define a specific neural marker able to predict TD independently of task execution. To this aim, we used resting-state functional connectivity MRI (fcMRI) and measured TD during economic choices several months apart in 25 human subjects. We further explored the relationship between TD, impulsivity and decision uncertainty by collecting standard questionnaires on individual trait/state differences. Our findings indicate that fcMRI within and between critical nodes of task-evoked neural networks associated with TD correlates with discounting behavior measured a long time afterwards, independently of impulsivity. Importantly, the nodes form an intrinsic circuit that might support all the mechanisms underlying TD, from the representation of subjective value to choice selection through modulatory effects of cognitive control and episodic prospection.

A neural trait approach to exploring individual differences in social preferences

Research demonstrates that social preferences are characterized by significant individual differences. An important question, often overlooked, is from where do these individual differences originate? And what are the processes that underlie such differences? In this paper, we outline the neural trait approach to uncovering sources of individual differences in social preferences, particularly as evidenced in economic games. We focus on two primary methods—resting-state electroencephalography and structural magnetic resonance imaging (MRI)—used by researchers to quantify task-independent, brain-based characteristics that are stable over time. We review research that has employed these methods to investigate social preferences with an emphasis on a key psychological process in social decision-making; namely, self-control. We then highlight future opportunities for the neural trait approach in cutting-edge decision-making research. Finally, we explore the debate about self-control in social decision-making and the potential role neural trait research could play in this issue.

Time devours things: how impulsivity and time affect temporal decisions in pathological gamblers

Impulsivity is associated with several psychiatric disorders in which the loss of control of a specific behavior determines the syndrome itself. One particularly interesting population characterized by reported high impulsivity and problematic decision-making are those diagnosed with pathological gambling. However the association between impulsivity and decision making in pathological gambling has been only partially confirmed until now. We tested 23 normal controls and 23 diagnosed pathological gamblers in an intertemporal choice task, as well as other personality trait measurements. Results showed that gamblers scored higher on impulsivity questionnaires, and selected a higher percentage of impatient choices (higher percentage of smaller, sooner rewards), when compared to normal controls. Moreover, gamblers were faster in terms of reaction times at selecting the smaller, sooner options and discounted rewards more rapidly over time. Importantly, regression analyses clarified that self-reported measures of impulsivity played a significant role in biasing decisions towards small but more rapidly available rewards. In the present study we found evidence for impulsivity in personality traits and decisions in pathological gamblers relative to controls. We conclude by speculating on the need to incorporate impulsivity and decision biases in the conceptualization of pathological gambling for a better understanding and treatment of this pathology.

Activity in dlPFC and its effective connectivity to vmPFC are associated with temporal discounting

There is widespread interest in identifying computational and neurobiological mechanisms that influence the ability to choose long-term benefits over more proximal and readily available rewards in domains such as dietary and economic choice. We present the results of a human fMRI study that examines how neural activity relates to observed individual differences in the discounting of future rewards during an intertemporal monetary choice task. We found that a region of left dorsolateral prefrontal cortex (dlPFC) BA-46 was more active in trials where subjects chose delayed rewards, after controlling for the subjective value of those rewards. We also found that the connectivity from dlPFC BA-46 to a region of ventromedial prefrontal cortex (vmPFC) widely associated with the computation of stimulus values, increased at the time of choice, and especially during trials in which subjects chose delayed rewards. Finally, we found that estimates of effective connectivity between these two regions played a critical role in predicting out-of-sample, between-subject differences in discount rates. Together with previous findings in dietary choice, these results suggest that a common set of computational and neurobiological mechanisms facilitate choices in favor of long-term reward in both settings.

Catechol-O-methyltransferase Val158Met polymorphism modulates gray matter volume and functional connectivity of the default mode network

The effect of catechol-O-methyltransferase (COMT) Val158Met polymorphism on brain structure and function has been previously investigated separately and regionally; this prevents us from obtaining a full picture of the effect of this gene variant. Additionally, gender difference must not be overlooked because estrogen exerts an interfering effect on COMT activity. We examined 323 young healthy Chinese Han subjects and analyzed the gray matter volume (GMV) differences between Val/Val individuals and Met carriers in a voxel-wise manner throughout the whole brain. We were interested in genotype effects and genotype × gender interactions. We then extracted these brain regions with GMV differences as seeds to compute resting-state functional connectivity (rsFC) with the rest of the brain; we also tested the genotypic differences and gender interactions in the rsFCs. Val/Val individuals showed decreased GMV in the posterior cingulate cortex (PCC) compared with Met carriers; decreased GMV in the medial superior frontal gyrus (mSFG) was found only in male Val/Val subjects. The rsFC analysis revealed that both the PCC and mSFG were functionally correlated with brain regions of the default mode network (DMN). Both of these regions showed decreased rsFCs with different parts of the frontopolar cortex of the DMN in Val/Val individuals than Met carriers. Our findings suggest that the COMT Val158Met polymorphism modulates both the structure and functional connectivity within the DMN and that gender interactions should be considered in studies of the effect of this genetic variant, especially those involving prefrontal morphology.

Who is honest and why: baseline activation in anterior insula predicts inter-individual differences in deceptive behavior

Humans engage in deceptive behavior that negatively affects others. The propensity to deceive is, however, characterized by vast inter-individual heterogeneity that is poorly understood. Attempts to investigate the origins of this heterogeneity have so far mainly relied on subjective measures and have shown little predictive power. Here, we used resting electroencephalography to measure objective and stable individual differences in neural baseline activation in combination with an ecologically valid deception paradigm. Results showed that task-independent baseline activation in the anterior insula, a brain area implicated in mapping internal bodily states and in representing emotional arousal and conscious feelings, predicts individuals' propensity for deceptive behavior. The higher the neural baseline activation in this area is, the lower individuals' propensity to deceive. Moreover, results provide evidence that high baseline activation in the anterior insula is associated with negative affect and dispositional tendencies to avoid aversive emotional situations. These results provide converging neural and psychological evidence that individuals might avoid a deceptive act due to a highly active negative emotional system which would make a deceptive act too stressful and bothersome.