Ventral striatal activation during reward anticipation correlates with impulsivity in alcoholics

Variable activation in striatal subregions across components of a social influence task in young adult cannabis users

INTRODUCTION

Decades of research have demonstrated the importance of social influence in initiation and maintenance of drug use, but little is known about neural mechanisms underlying social influence in young adults who use recreational drugs.

METHODS

To better understand whether the neural and/or behavioral response to social influence differs in young adults using illicit drugs, 20 marijuana-using young adults (MJ) aged 18-25, and 20 controls (CON) performed a decision-making task in the context of social influence, while they underwent functional magnetic resonance imaging scans. A priori analyses focused on the nucleus accumbens (NAc), with post hoc analyses in the rest of the striatum. In this task, participants could choose to either follow or go against group influence.

RESULTS

When subjects applied social information to response choice selection (independent of following or going against group influence), we observed activation in the middle striatum (caudate), in the MJ group only, that extended ventrally into the NAc. MJ users but not CON showed greater activation in the NAc but not the caudate while making choices congruent with group influence as opposed to choices going against group influence. Activation in the NAc when following social influence was associated with amount of drug use reported. In contrast, during the feedback phase of the task we observed significant NAc activation in both MJ and CON, along with dorsal caudate activation only in MJ participants. This NAc activation did not correlate with drug use.

CONCLUSIONS

This study shows that MJ users, but not CON, show differential brain activation across striatal subregions when applying social information to make a decision, following versus going against a group of peers, or receiving positive feedback. The current work suggests that differential neural sensitivity to social influence in regions such as the striatum may contribute to the development and/or maintenance of marijuana use.

Individual differences in regulatory focus predict neural response to reward

Although goal pursuit is related to both functioning of the brain's reward circuits and psychological factors, the literatures surrounding these concepts have often been separate. Here, we use the psychological construct of regulatory focus to investigate individual differences in neural response to reward. Regulatory focus theory proposes two motivational orientations for personal goal pursuit: (1) promotion, associated with sensitivity to potential gain, and (2) prevention, associated with sensitivity to potential loss. The monetary incentive delay task was used to manipulate reward circuit function, along with instructional framing corresponding to promotion and prevention in a within-subject design. We observed that the more promotion oriented an individual was, the lower their ventral striatum response to gain cues. Follow-up analyses revealed that greater promotion orientation was associated with decreased ventral striatum response even to no-value cues, suggesting that promotion orientation may be associated with relatively hypoactive reward system function. The findings are also likely to represent an interaction between the cognitive and motivational characteristics of the promotion system with the task demands. Prevention orientation did not correlate with ventral striatum response to gain cues, supporting the discriminant validity of regulatory focus theory. The results highlight a dynamic association between individual differences in self-regulation and reward system function.

Mouse and Human Genetic Analyses Associate Kalirin with Ventral Striatal Activation during Impulsivity and with Alcohol Misuse

Impulsivity is associated with a spectrum of psychiatric disorders including drug addiction. To investigate genetic associations with impulsivity and initiation of drug taking, we took a two-step approach. First, we identified genes whose expression level in prefrontal cortex, striatum and accumbens were associated with impulsive behavior in the 5-choice serial reaction time task across 10 BXD recombinant inbred (BXD RI) mouse strains and their progenitor C57BL/6J and DBA2/J strains. Behavioral data were correlated with regional gene expression using GeneNetwork (www.genenetwork.org), to identify 44 genes whose probability of association with impulsivity exceeded a false discovery rate of < 0.05. We then interrogated the IMAGEN database of 1423 adolescents for potential associations of SNPs in human homologs of those genes identified in the mouse study, with brain activation during impulsive performance in the Monetary Incentive Delay task, and with novelty seeking scores from the Temperament and Character Inventory, as well as alcohol experience. There was a significant overall association between the human homologs of impulsivity-related genes and percentage of premature responses in the MID task and with fMRI BOLD-response in ventral striatum (VS) during reward anticipation. In contrast, no significant association was found between the polygenic scores and anterior cingulate cortex activation. Univariate association analyses revealed that the G allele (major) of the intronic SNP rs6438839 in the KALRN gene was significantly associated with increased VS activation. Additionally, the A-allele (minor) of KALRN intronic SNP rs4634050, belonging to the same haplotype block, was associated with increased frequency of binge drinking.

PER1 rs3027172 Genotype Interacts with Early Life Stress to Predict Problematic Alcohol Use, but Not Reward-Related Ventral Striatum Activity

Increasing evidence suggests that the circadian and stress regulatory systems contribute to alcohol use disorder (AUD) risk, which may partially arise through effects on reward-related neural function. The C allele of the PER1 rs3027172 single nucleotide polymorphism (SNP) reduces PER1 expression in cells incubated with cortisol and has been associated with increased risk for adult AUD and problematic drinking among adolescents exposed to high levels of familial psychosocial adversity. Using data from undergraduate students who completed the ongoing Duke Neurogenetics Study (DNS) (n = 665), we tested whether exposure to early life stress (ELS; Childhood Trauma Questionnaire) moderates the association between rs3027172 genotype and later problematic alcohol use (Alcohol Use Disorders Identification Test) as well as ventral striatum (VS) reactivity to reward (card-guessing task while functional magnetic resonance imaging data were acquired). Initial analyses found that PER1 rs3027172 genotype interacted with ELS to predict both problematic drinking and VS reactivity; minor C allele carriers, who were also exposed to elevated ELS reported greater problematic drinking and exhibited greater ventral striatum reactivity to reward-related stimuli. When gene × covariate and environment × covariate interactions were controlled for, the interaction predicting problematic alcohol use remained significant (p < 0.05, corrected) while the interaction predicting VS reactivity was no longer significant. These results extend our understanding of relationships between PER1 genotype, ELS, and problematic alcohol use, and serve as a cautionary tale on the importance of controlling for potential confounders in studies of moderation including gene × environment interactions.

Problematic Internet Users Show Impaired Inhibitory Control and Risk Taking with Losses: Evidence from Stop Signal and Mixed Gambles Tasks

According to the balance model of self-regulation, dysfunction of the inhibitory control and reward processing might be a behavioral marker for addiction and problematic behaviors. Although several studies have separately examined the inhibitory control or reward processing of individuals exhibiting problematic Internet use (PIU), no study has explored these two functions simultaneously to examine the potential imbalance of these functions. This study aimed to investigate whether the self-regulatory failure of PIU individuals results from deficits in both inhibitory control [indexed with the stop signal reaction time (SSRT) in a stop signal task] and risk taking with losses (measured as the acceptance rates of risky gables or the ratio of win/loss in a mixed gambles task). The results revealed that PIU individuals, compared with controls, showed decreased SSRT and increased error rates as well as reduced risk taking with losses. Correlational analyses revealed a significant positive relationship between the SSRT and risk taking with losses. These findings suggest that both the inhibitory control and reward functions are impaired in PIU individuals and reveal an association between these two systems. These results strengthen the balance model of self-regulation theory's argument that deficits in inhibitory control and risk taking with losses may assist in identifying risk markers for early diagnosis, progression, and prediction of PIU.

Ginseng and Ginkgo Biloba Effects on Cognition as Modulated by Cardiovascular Reactivity: A Randomised Trial

Background

There is some evidence to suggest that ginseng and Ginkgo biloba can improve cognitive performance, however, very little is known about the mechanisms associated with such improvement. Here, we tested whether cardiovascular reactivity to a task is associated with cognitive improvement.

Methodology/Principal findings

Using a double-blind, placebo controlled, crossover design, participants (N = 24) received two doses of Panax Ginseng (500, 1000 mg) or Ginkgo Biloba (120, 240 mg) (N = 24), and underwent a series of cognitive tests while systolic, diastolic, and heart rate readings were taken. Ginkgo Biloba improved aspects of executive functioning (Stroop and Berg tasks) in females but not in males. Ginseng had no effect on cognition. Ginkgo biloba in females reversed the initial (i.e. placebo) increase in cardiovascular reactivity (systolic and diastolic readings increased compared to baseline) to cognitive tasks. This effect (reversal) was most notable after those tasks (Stroop and Iowa) that elicited the greatest cardiovascular reactivity during placebo. In males, although ginkgo also decreased cardiovascular readings, it did so from an initial (placebo) blunted response (i.e. decrease or no change from baseline) to cognitive tasks. Ginseng, on the contrary, increased cardiovascular readings compared to placebo.

Conclusions/Significance

These results suggest that cardiovascular reactivity may be a mechanism by which ginkgo but not ginseng, in females is associated with certain forms of cognitive improvement.

Trial Registration

ClinicalTrials.gov NCT02386852

Blunted striatal response to monetary reward anticipation during smoking abstinence predicts lapse during a contingency-managed quit attempt

RATIONALE

Tobacco smoking is associated with dysregulated reward processing within the striatum, characterized by hypersensitivity to smoking rewards and hyposensitivity to non-smoking rewards. This bias toward smoking reward at the expense of alternative rewards is further exacerbated by deprivation from smoking, which may contribute to difficulty maintaining abstinence during a quit attempt.

OBJECTIVE

We examined whether abstinence-induced changes in striatal processing of rewards predicted lapse likelihood during a quit attempt supported by contingency management (CM), in which abstinence from smoking was reinforced with money.

METHODS

Thirty-six non-treatment-seeking smokers participated in two functional MRI (fMRI) sessions, one following 24-h abstinence and one following smoking as usual. During each scan, participants completed a rewarded guessing task designed to elicit striatal activation in which they could earn smoking and monetary rewards delivered after the scan. Participants then engaged in a 3-week CM-supported quit attempt.

RESULTS

As previously reported, 24-h abstinence was associated with increased striatal activation in anticipation of smoking reward and decreased activation in anticipation of monetary reward. Individuals exhibiting greater decrements in right striatal activation to monetary reward during abstinence (controlling for activation during non-abstinence) were more likely to lapse during CM (p < 0.025), even when controlling for other predictors of lapse outcome (e.g., craving); no association was seen for smoking reward.

CONCLUSIONS

These results are consistent with a growing number of studies indicating the specific importance of disrupted striatal processing of non-drug reward in nicotine dependence and highlight the importance of individual differences in abstinence-induced deficits in striatal function for smoking cessation.

Reflection impulsivity in binge drinking: behavioural and volumetric correlates

The degree to which an individual accumulates evidence prior to making a decision, also known as reflection impulsivity, can be affected in psychiatric disorders. Here, we study decisional impulsivity in binge drinkers, a group at elevated risk for developing alcohol use disorders, comparing two tasks assessing reflection impulsivity and a delay discounting task, hypothesizing impairments in both subtypes of impulsivity. We also assess volumetric correlates of reflection impulsivity focusing on regions previously implicated in functional magnetic resonance imaging studies. Sixty binge drinkers and healthy volunteers were tested using two different information-gathering paradigms: the beads task and the Information Sampling Task (IST). The beads task was analysed using a behavioural approach and a Bayesian model of decision making. Delay discounting was assessed using the Monetary Choice Questionnaire. Regression analyses of primary outcomes were conducted with voxel-based morphometry analyses. Binge drinkers sought less evidence prior to decision in the beads task compared with healthy volunteers in both the behavioural and computational modelling analysis. There were no group differences in the IST or delay discounting task. Greater impulsivity as indexed by lower evidence accumulation in the beads task was associated with smaller dorsolateral prefrontal cortex and inferior parietal volumes. In contrast, greater impulsivity as indexed by lower evidence accumulation in the IST was associated with greater dorsal cingulate and precuneus volumes. Binge drinking is characterized by impaired reflection impulsivity suggesting a deficit in deciding on the basis of future outcomes that are more difficult to represent. These findings emphasize the role of possible therapeutic interventions targeting decision-making deficits.

Altered Striatal Response During Effort-Based Valuation and Motivation in Alcohol-Dependent Individuals

AIMS

To use functional magnetic resonance imaging (fMRI) to investigate the neural circuitry behind effort-related valuation and motivation in a population of alcohol-dependent participants and healthy controls.

METHODS

Seventeen alcohol-dependent participants and a comparison group of 17 healthy control participants completed an effort-based motivation paradigm during an fMRI scan, in which they were required to exert effort at varying levels in order to earn a monetary reward.

RESULTS

We found that alcohol-dependent participants were less motivated during trials requiring high levels of effort. The whole-brain fMRI analysis revealed that alcohol-dependent participants displayed an increased blood-oxygen-level dependent (BOLD) signal during low and unknown effort cues in the dorsal and ventral striatum compared with healthy controls.

CONCLUSION

These findings provide the first evidence that alcohol-dependent participants and healthy controls differ in their effort-based valuation and motivation processing. Alcohol-dependent participants displayed a hyperactive mesolimbic reward circuitry recruited by non-drug rewards, potentially reflecting a sensitization to reward in this patient population.

Binge drinking impacts dorsal striatal response during decision making in adolescents

Adolescence is a time of both increased risk taking and increased vulnerability to the neurotoxic effects of alcohol. However, it is unclear whether brain functioning abnormalities in adolescent binge drinkers are a result of alcohol use itself or whether they represent premorbid risk characteristics. The current study addresses this question by using a modified version of the Wheel of Fortune (WOF) task, during functional magnetic resonance imaging (fMRI), at both baseline, while all subjects were alcohol-naïve, and revisit, when half of the subjects had emerged into regular binge drinking (n=13) and half remained alcohol and substance-naïve (n=13). Region of interest (ROI) analysis revealed that during decision making, there was a significant binge-drinking related reduction in brain activation in the dorsal striatum, an effect associated with degree of recent use. Furthermore, whole-brain analysis revealed a decrease in fronto-parietal brain activation prior to initiation of alcohol use, in adolescents who went on to binge drink. Additionally, there were numerous regions, both cortical and subcortical, in which there was a significant time-related developmental change, across groups. These results demonstrate how abnormalities in decision-making related circuitry might both lead to and perpetuate alcohol drinking behavior. These findings help aid in our ability to disentangle consequences of binge drinking from potential risk markers for future binge drinking, and may help guide future prevention and intervention strategies.

Using fMRI to study reward processing in humans: past, present, and future

Functional magnetic resonance imaging (fMRI) is a noninvasive tool used to probe cognitive and affective processes. Although fMRI provides indirect measures of neural activity, the advent of fMRI has allowed for1) the corroboration of significant animal findings in the human brain, and2) the expansion of models to include more common human attributes that inform behavior. In this review, we briefly consider the neural basis of the blood oxygenation level dependent signal to set up a discussion of how fMRI studies have applied it in examining cognitive models in humans and the promise of using fMRI to advance such models. Specifically, we illustrate the contribution that fMRI has made to the study of reward processing, focusing on the role of the striatum in encoding reward-related learning signals that drive anticipatory and consummatory behaviors. For instance, we discuss how fMRI can be used to link neural signals (e.g., striatal responses to rewards) to individual differences in behavior and traits. While this functional segregation approach has been constructive to our understanding of reward-related functions, many fMRI studies have also benefitted from a functional integration approach that takes into account how interconnected regions (e.g., corticostriatal circuits) contribute to reward processing. We contend that future work using fMRI will profit from using a multimodal approach, such as combining fMRI with noninvasive brain stimulation tools (e.g., transcranial electrical stimulation), that can identify causal mechanisms underlying reward processing. Consequently, advancements in implementing fMRI will promise new translational opportunities to inform our understanding of psychopathologies.

Neurobiological phenotypes associated with a family history of alcoholism

BACKGROUND

Individuals with a family history of alcoholism are at much greater risk for developing an alcohol use disorder (AUD) than youth or adults without such history. A large body of research suggests that there are premorbid differences in brain structure and function in family history positive (FHP) individuals relative to their family history negative (FHN) peers.

METHODS

This review summarizes the existing literature on neurobiological phenotypes present in FHP youth and adults by describing findings across neurophysiological and neuroimaging studies.

RESULTS

Neuroimaging studies have shown FHP individuals differ from their FHN peers in amygdalar, hippocampal, basal ganglia, and cerebellar volume. Both increased and decreased white matter integrity has been reported in FHP individuals compared with FHN controls. Functional magnetic resonance imaging studies have found altered inhibitory control and working memory-related brain response in FHP youth and adults, suggesting neural markers of executive functioning may be related to increased vulnerability for developing AUDs in this population. Additionally, brain activity differences in regions involved in bottom-up reward and emotional processing, such as the nucleus accumbens and amygdala, have been shown in FHP individuals relative to their FHN peers.

CONCLUSIONS

It is critical to understand premorbid neural characteristics that could be associated with cognitive, reward-related, or emotional risk factors that increase risk for AUDs in FHP individuals. This information may lead to the development of neurobiologically informed prevention and intervention studies focused on reducing the incidence of AUDs in high-risk youth and adults.

[An effect of cabergoline on alcohol consumption and DRD2 expression in the brain of rats with chronic alcohol intoxication]

AIM

Cabergoline is a high selective agonist of dopamine D2 receptors (D2R). The activation of D2R plays an important role in the regulation of dopamine transmission, the imbalance of which is thought to underlie the development of alcohol motivation. To examine this possibility, cabergoline effects on alcohol consumption and brain DRD2 expression in rats with chronic alcohol intoxication were studied.

MATERIAL AND METHODS

Male Wister rats were studied using the following methods: modelling of chronic alcohol intoxication, testing in «10% alcohol vs water» choice regimen, quantitative RT-PCR.

RESULTS

Systemic administration of 0.5 mg/kg of cabergoline significantly decreases alcohol intake in alcohol-preferring rats. At the same time, cabergoline elevates the DRD2 expression in the midbrain and striatum of high-alcohol-preferring rats but not in intact (alcohol-naïve) animals.

CONCLUSION

The involvement of cabergoline in the DRD2 expression may lead to the decrease in alcohol motivation. These findings indicate that cabergoline needs further investigations as a new potential medication for alcohol use disorder.

Relationships Between Impulsivity, Anxiety, and Risk-Taking and the Neural Correlates of Attention in Adolescents

Although impulsivity, anxiety, and risk-taking may relate to attentional processes, little research has directly investigated how each may be associated with specific facets of attentional processes and their underlying neural correlates. Nineteen adolescents performed a functional magnetic resonance imaging task involving simple, selective, and divided attention. Out-of-scanner-assessed impulsivity, anxiety, and risk-taking scores were not correlated with each other and showed task-phase-specific patterns of association. Results are discussed in light of research and theory suggesting a relationship between these domains and attention and may serve to focus future research aiming to understand these relationships.

Does incentive-elicited nucleus accumbens activation differ by substance of abuse? An examination with adolescents

Numerous questions surround the nature of reward processing in the developing adolescent brain, particularly in regard to polysubstance use. We therefore sought to examine incentive-elicited brain activation in the context of three common substances of abuse (cannabis, tobacco, and alcohol). Due to the role of the nucleus accumbens (NAcc) in incentive processing, we compared activation in this region during anticipation of reward and loss using a monetary incentive delay (MID) task. Adolescents (ages 14-18; 66% male) were matched on age, gender, and frequency of use of any common substances within six distinct groups: cannabis-only (n=14), tobacco-only (n=34), alcohol-only (n=12), cannabis+tobacco (n=17), cannabis+tobacco+alcohol (n=17), and non-using controls (n=38). All groups showed comparable behavioral performance on the MID task. The tobacco-only group showed decreased bilateral nucleus accumbens (NAcc) activation during reward anticipation as compared to the alcohol-only group, the control group, and both polysubstance groups. Interestingly, no differences emerged between the cannabis-only group and any of the other groups. Results from this study suggest that youth who tend toward single-substance tobacco use may possess behavioral and/or neurobiological characteristics that differentiate them from both their substance-using and non-substance-using peers.

Neurobiological features of binge eating disorder

Biobehavioral features associated with binge-eating disorder (BED) have been investigated; however, few systematic reviews to date have described neuroimaging findings from studies of BED. Emerging functional and structural studies support BED as having unique and overlapping neural features as compared with other disorders. Neuroimaging studies provide evidence linking heightened responses to palatable food cues with prefrontal areas, particularly the orbitofrontal cortex (OFC), with specific relationships to hunger and reward-sensitivity measures. While few studies to date have investigated non-food-cue responses; these suggest a generalized hypofunctioning in frontostriatal areas during reward and inhibitory control processes. Early studies applying neuroimaging to treatment efforts suggest that targeting neural function underlying motivational processes may prove important in the treatment of BED.

Delay discounting without decision-making: medial prefrontal cortex and amygdala activations reflect immediacy processing and correlate with impulsivity and anxious-depressive traits

Humans value rewards less when these are delivered in the future as opposed to immediately, a phenomenon referred to as delay discounting. While delay discounting has been studied during the anticipation of rewards and in the context of intertemporal decision-making, little is known about its neural correlates in the outcome phase (during reward delivery) and their relation to personality. Personality traits that have been associated with increased delay discounting include impulsivity and, potentially, anxious-depressive traits. Here we performed functional magnetic resonance imaging (fMRI) in 72 healthy participants while they carried out a monetary incentive delay (MID) task with a delay manipulation. In sixty percent of the experimental trials, participants won rewards that differed in magnitude (0.05€, 0.50€ or 1€) and delay until delivery (immediately, 10 days, or 100 days). A factor analysis on questionnaires yielded two factors reflecting Impulsivity and Anxiety/Depression, which we used to examine potential relationships between personality and delay discounting. When winning a reward, medial prefrontal cortex (mPFC) activation was higher for immediate compared to delayed rewards. Moreover, amygdala activation correlated with reward magnitude for immediate but not for delayed rewards. Amygdala activation to winning immediate rewards was higher in more impulsive participants, while mPFC activation to winning immediate rewards was higher in more anxious-depressed participants. Our results uncover neural correlates of delay discounting during reward delivery, and suggest that impulsivity and subclinical anxious-depressive traits are related to stronger neural responses for winning immediate relative to delayed rewards.

Convergence of EEG and fMRI measures of reward anticipation

Deficits in reward anticipation are putative mechanisms for multiple psychopathologies. Research indicates that these deficits are characterized by reduced left (relative to right) frontal electroencephalogram (EEG) activity and blood oxygenation level-dependent (BOLD) signal abnormalities in mesolimbic and prefrontal neural regions during reward anticipation. Although it is often assumed that these two measures capture similar mechanisms, no study to our knowledge has directly examined the convergence between frontal EEG alpha asymmetry and functional magnetic resonance imaging (fMRI) during reward anticipation in the same sample. Therefore, the aim of the current study was to investigate if and where in the brain frontal EEG alpha asymmetry and fMRI measures were correlated in a sample of 40 adults. All participants completed two analogous reward anticipation tasks--once during EEG data collection and the other during fMRI data collection. Results indicated that the two measures do converge and that during reward anticipation, increased relative left frontal activity is associated with increased left anterior cingulate cortex (ACC)/medial prefrontal cortex (mPFC) and left orbitofrontal cortex (OFC) activation. This suggests that the two measures may similarly capture PFC functioning, which is noteworthy given the role of these regions in reward processing and the pathophysiology of disorders such as depression and schizophrenia.

Brain Imaging in Gambling Disorder

Gambling disorder recently was reclassified under the category “substance-related and addictive disorders.” With regard to the diagnostic criteria, it overlaps a great deal with substance use disorder, i.e., loss of control, craving/withdrawal, and neglect of other areas of life. However, the gambling disorder symptom “chasing one’s losses” is the only criterion absent from substance use disorder. Therefore, special forms of reward (i.e., gain/loss) processing, such as the processing of loss avoidance and loss aversion, have just recently attracted attention among gambling disorder researchers. Because gambling disorder might be considered an addiction in its “pure” form, i.e., without the influence of a drug of abuse, investigating brain volume changes in people with this behavioral addiction is an important task for neuroimaging researchers in exploring the neural signatures of addiction. Because the brain is a complex network, investigation of alterations in functional connectivity has gained interest among gambling disorder researchers in order to get a more complete picture of functional brain changes in people with gambling disorder. However, only a few studies on brain structure and functional connectivity in gambling disorder have been performed so far. This review focuses on brain imaging studies of reward and loss processing, with an emphasis on loss avoidance and aversion as well as brain volume and functional connectivity in gambling disorder.

The Imperial College Cambridge Manchester (ICCAM) platform study: An experimental medicine platform for evaluating new drugs for relapse prevention in addiction. Part A: Study description

Drug and alcohol dependence are global problems with substantial societal costs. There are few treatments for relapse prevention and therefore a pressing need for further study of brain mechanisms underpinning relapse circuitry. The Imperial College Cambridge Manchester (ICCAM) platform study is an experimental medicine approach to this problem: using functional magnetic resonance imaging (fMRI) techniques and selective pharmacological tools, it aims to explore the neuropharmacology of putative relapse pathways in cocaine, alcohol, opiate dependent, and healthy individuals to inform future drug development. Addiction studies typically involve small samples because of recruitment difficulties and attrition. We established the platform in three centres to assess the feasibility of a multisite approach to address these issues. Pharmacological modulation of reward, impulsivity and emotional reactivity were investigated in a monetary incentive delay task, an inhibitory control task, and an evocative images task, using selective antagonists for µ-opioid, dopamine D3 receptor (DRD3) and neurokinin 1 (NK1) receptors (naltrexone, GSK598809, vofopitant/aprepitant), in a placebo-controlled, randomised, crossover design. In two years, 609 scans were performed, with 155 individuals scanned at baseline. Attrition was low and the majority of individuals were sufficiently motivated to complete all five sessions (n=87). We describe herein the study design, main aims, recruitment numbers, sample characteristics, and explain the test hypotheses and anticipated study outputs.

Functional coherence of insula networks is associated with externalizing behavior

The externalizing spectrum encompasses a range of maladaptive behaviors, including substance-use problems, impulsivity, and aggression. Although previous literature has linked externalizing behaviors with prefrontal and amygdala abnormalities, recent studies suggest insula functionality is implicated. This study investigated the relation between insula functional coherence and externalizing in a large community sample (N = 244). Participants underwent a resting functional MRI scan. Three nonartifactual intrinsic connectivity networks (ICNs) substantially involving the insula were identified after completing independent components analysis. Three externalizing domains-general disinhibition, substance abuse, and callous aggression-were measured with the Externalizing Spectrum Inventory. Regression models tested whether within-network coherence for the 3 insula ICNs was related to each externalizing domain. Posterior insula coherence was positively associated with general disinhibition and substance abuse. Anterior insula/ventral striatum/anterior cingulate network coherence was negatively associated with general disinhibition. Insula coherence did not relate to the callous aggression domain. Follow-up analyses indicated specificity for insula ICNs in their relation to general disinhibition and substance abuse as compared with other frontal and limbic ICNs. This study found insula network coherence was significantly associated with externalizing behaviors in community participants. Frontal and limbic ICNs containing less insular cortex were not related to externalizing. Thus, the neural synchrony of insula networks may be central for understanding externalizing psychopathology.

Brain pathways to recovery from alcohol dependence

This article highlights the research presentations at the satellite symposium on "Brain Pathways to Recovery from Alcohol Dependence" held at the 2013 Society for Neuroscience Annual Meeting. The purpose of this symposium was to provide an up to date overview of research efforts focusing on understanding brain mechanisms that contribute to recovery from alcohol dependence. A panel of scientists from the alcohol and addiction research field presented their insights and perspectives on brain mechanisms that may underlie both recovery and lack of recovery from alcohol dependence. The four sessions of the symposium encompassed multilevel studies exploring mechanisms underlying relapse and craving associated with sustained alcohol abstinence, cognitive function deficit and recovery, and translational studies on preventing relapse and promoting recovery. Gaps in our knowledge and research opportunities were also discussed.

HIV infection results in ventral-striatal reward system hypo-activation during cue processing

OBJECTIVE

Functional MRI has thus far demonstrated that HIV has an impact on frontal-striatal systems involved in executive functioning. The potential impact of HIV on frontal-striatal systems involved in reward processing has yet to be examined by functional MRI. This study therefore aims to investigate the effects of HIV infection on reward processing by examining the function of the ventral-striatal reward system during a monetary incentive delay task.

DESIGN

This is a cross-sectional case-control study.

METHODS

Eighteen combined antiretroviral therapy-naive HIV-positive (HIV+) participants, as well as 16 matched healthy controls, performed a monetary incentive delay task. This paradigm assesses behaviour as well as functional brain activity-associated reward anticipation and reward outcome.

RESULTS

HIV+ participants showed a general decrease in activation associated with both neutral as well as potentially rewarding cues in their ventral striatum. We found normal activity related to reward outcome in the orbito-frontal cortex. Despite HIV+ participants' reaction times being significantly slower when independently measured from the reward paradigm, this performance deficit normalized during the performance of the reward task.

CONCLUSION

HIV caused a decrease in activity during cue processing in the ventral striatum, with normal cortical functioning during reward outcome processing. Our results therefore suggest that HIV not only has an impact on fronto-striatal systems involved in executive functioning, but also has a direct impact on the function of the ventral-striatal reward system.

Rsu1 regulates ethanol consumption in Drosophila and humans

Alcohol abuse is highly prevalent, but little is understood about the molecular causes. Here, we report that Ras suppressor 1 (Rsu1) affects ethanol consumption in flies and humans. Drosophila lacking Rsu1 show reduced sensitivity to ethanol-induced sedation. We show that Rsu1 is required in the adult nervous system for normal sensitivity and that it acts downstream of the integrin cell adhesion molecule and upstream of the Ras-related C3 botulinum toxin substrate 1 (Rac1) GTPase to regulate the actin cytoskeleton. In an ethanol preference assay, global loss of Rsu1 causes high naïve preference. In contrast, flies lacking Rsu1 only in the mushroom bodies of the brain show normal naïve preference but then fail to acquire ethanol preference like normal flies. Rsu1 is, thus, required in distinct neurons to modulate naïve and acquired ethanol preference. In humans, we find that polymorphisms in RSU1 are associated with brain activation in the ventral striatum during reward anticipation in adolescents and alcohol consumption in both adolescents and adults. Together, these data suggest a conserved role for integrin/Rsu1/Rac1/actin signaling in modulating reward-related phenotypes, including ethanol consumption, across phyla.

Too difficult to stop: mechanisms facilitating relapse in alcohol dependence

BACKGROUND

In alcohol and other substance dependencies, patients often suffer relapse despite better knowledge and their intention to remain abstinent. A variety of neurotransmitter systems and their respective alterations due to the chronic drug intake are involved in mechanisms that facilitate relapse. It has been postulated that these neurotransmitter systems are related to changes in motivational and learning mechanisms, and engender a shift from goal-directed to habitual behavior in dependent patients that facilitates drug-seeking behavior.

METHODS

We review learning mechanisms facilitating relapse, as identified and tested to date. We focus on studies examining the interaction between alcohol-related changes in monoaminergic neurotransmission and their respective effects on pavlovian and operant learning mechanisms in alcohol dependence.

RESULTS

Animal experiments and first human studies suggest that chronic alcohol intake impairs goal-directed behavior and facilitates habitual drug intake. Key symptoms of alcohol dependence such as tolerance development, withdrawal, craving and reduced control of alcohol intake can be explained by alcohol-induced alteration of dopaminergic neurotransmission and its GABAergic and glutamatergic modulation and their respective effects on pavlovian and operant conditioning as well as pavlovian-to-instrumental transfer.

CONCLUSION

Chronic alcohol intake impairs neurotransmitter systems that regulate prefrontal-striatal circuits and interfere with goal-directed decision-making and the acquisition of new, non-drug-related behavior patterns. Alcohol craving induced by pavlovian conditioned cues can facilitate habitual drug intake. Such learning mechanisms and their alterations by chronic alcohol intake might be targeted by specific interventions.

From symptoms to neurobiology: pathological gambling in the light of the new classification in DSM-5

Pathological gambling (PG), as defined until recently in the DSM-IV, shares many clinical characteristics with substance use disorders (SUDs), such as craving and loss of control. Moreover, an increasing body of literature also revealed neurobiological similarities between PG and substance-related addictions. Further, specific treatments for SUD are also effective in pathological gamblers. These observations resulted in a recent change in the diagnostic classification of PG in DSM-5: maladaptive gambling behavior is now subsumed as 'gambling disorder' (GD) under the category 'substance-related and addictive disorders'. On the basis of similarities in clinical characteristics between GD and SUDs, this article proposes 3 main clusters of diagnostic criteria: 'loss of control', 'craving/withdrawal' and 'neglect of other areas in life'. These symptom clusters can then be related to the experimental paradigms commonly used in the neuroscience of addiction, including neuropsychological, neurophysiological and neuroimaging studies. In this paper, we present the neurobiological evidence for PG by focusing on key functional magnetic resonance imaging studies related to these 3 symptom clusters. It is concluded that these symptom clusters provide a useful framework for systematic comparisons of new evidence in GD and SUDs in the future.

How do we 'learn' addiction? Risk factors and mechanisms getting addicted to alcohol

BACKGROUND

Alcohol dependence is one of the leading contributors to the burden of disease in the world. A range of genetic and environmental risk factors has been identified to date, and preclinical and clinical studies including imaging studies have identified neuronal networks involved in the development of alcohol dependence.

METHODS

We review genetic and environmental risk factors for the development of alcohol addiction as well as structural and neuronal changes, including their transmitter systems, due to regular alcohol intake.

RESULTS

Stress as well as family background and, in juveniles, the peer group could be identified as environmental risk factors for alcohol dependence. Heritability is estimated at around 50%, and it seems to be comparable in women and men. There is ongoing research on a broad range of putative endophenotypes such as tolerance of the effects of alcohol intake or personal traits like 'impulsivity'. On the neurobiological level, chronic alcohol intake seems to render mesolimbic circuits hypersensitive to alcohol and alter the motivational reward system including dopaminergic neurotransmission.

CONCLUSION

Environmental and genetic risk factors, and especially their interaction, facilitate the development of alcohol dependence. Ongoing alcohol intake results in profound alterations of neuronal systems crucial for motivation, learning, memory and cognition control. Future studies should further combine the knowledge of neurobiological mechanisms and risk factors to develop new prevention strategies.

Model-based and model-free decisions in alcohol dependence

BACKGROUND

Human and animal work suggests a shift from goal-directed to habitual decision-making in addiction. However, the evidence for this in human alcohol dependence is as yet inconclusive.

METHODS

Twenty-six healthy controls and 26 recently detoxified alcohol-dependent patients underwent behavioral testing with a 2-step task designed to disentangle goal-directed and habitual response patterns.

RESULTS

Alcohol-dependent patients showed less evidence of goal-directed choices than healthy controls, particularly after losses. There was no difference in the strength of the habitual component. The group differences did not survive controlling for performance on the Digit Symbol Substitution Task.

CONCLUSION

Chronic alcohol use appears to selectively impair goal-directed function, rather than promoting habitual responding. It appears to do so particularly after nonrewards, and this may be mediated by the effects of alcohol on more general cognitive functions subserved by the prefrontal cortex.

Impulsivity relates to striatal gray matter volumes in humans: evidence from a delay discounting paradigm

Time-stable personality traits, such as impulsivity and its relationship with functional and structural brain alterations, have gained much attention in the recent literature. Evidence from functional neuroimaging data implies an association between impulsivity and cortical as well as subcortical areas of the reward system. Discounting future rewards during impulsive decisions can be related to activation in the orbitofrontal cortex and striatum. Cortical structural changes in prefrontal regions have been found for introspective impulsivity measures. The present study focuses on brain regions associated with delay discounting to investigate structural manifestations of trait impulsivity. To test this, seventy subjects underwent structural magnetic resonance imaging (MRI) followed by a behavioral delay discounting task outside of the scanner to measure impulsivity with questions like: "Would you like to have 3€ immediately or 10€ in 5 days?". The amount of smaller-but-sooner decisions was calculated and used as a measure of behavioral impulsivity. Furthermore, we estimated subject's individual delay discounting parameter K reflecting the tendency to discount future rewards. Behaviorally, we found strong evidence in favor of a discounting utility model compared to a standard hyperbolic model of choice valuation. Neuronally, we focused on cortical and subcortical brain structure and investigated the association of behavioral impulsivity with delay discounting tendencies and gray matter volume. Voxel-based morphometric analyses showed positive correlations between delay discounting and gray matter volume in the striatum. Additional analyses using Freesurfer provided evidence for a positive correlation between delay discounting and gray matter volume of the caudate. Taken together, our study provides strong evidence for a structural manifestation of time-stable trait impulsivity in the human brain.

The effects of nicotine dependence and acute abstinence on the processing of drug and non-drug rewards

RATIONALE

Drug addiction may be characterised by a hypersensitivity to drug rewards and a hyposensitivity to non-drug rewards. This imbalance may become further polarised during acute abstinence.

OBJECTIVES

(i) Examine the differences between dependent and occasional smokers in choices for, motivation for and self-reported wanting and liking of cigarette and non-drug rewards. (ii) Examine the effects of 12-h nicotine abstinence on these metrics.

METHODS

Dependent (n = 20) and occasional, non-dependent smokers (n = 20) were tested after ad libitum smoking and ≥12-h of nicotine abstinence. A novel task was developed (Drug, Reward and Motivation-Choice (DReaM-Choice)) in which different rewards (cigarettes, music and chocolate) could be won. In each trial, participants chose between two rewards and then could earn the chosen reward via repeated button-pressing. Participants subsequently 'consumed' and rated subjective liking of the rewards they had won.

RESULTS

Compared with occasional smokers, dependent smokers made more choices for (p < 0.001), pressed more for (p = 0.046) and reported more wanting (p = 0.007) and liking (p < 0.001) of cigarettes, and also made fewer choices for chocolate (p = 0.005). There were no differences between the groups on button-pressing for chocolate or music. However, the balance between drug and non-drug reward processing was different between the groups across all metrics. Twelve-hour nicotine abstinence led to more cigarette choices (p < 0.001) and fewer music choices (p = 0.042) in both groups.

CONCLUSIONS

Nicotine dependence was associated with a hypersensitivity to cigarette rewards, but we found little evidence indicating a hyposensitivity to non-drug rewards. Our findings question the moderating influence of dependence on how acute nicotine abstinence affects reward processing.

Mapping brain volumetric abnormalities in never-treated pathological gamblers

Several magnetic resonance imaging (MRI) studies to date have investigated brain abnormalities in association with the diagnosis of pathological gambling (PG), but very few of these have specifically searched for brain volume differences between PG patients and healthy volunteers (HV). To investigate brain volume differences between PG patients and HV, 30 male never-treated PG patients (DSM-IV-TR criteria) and 30 closely matched HV without history of psychiatric disorders in the past 2 years underwent structural magnetic resonance imaging with a 1.5-T instrument. Using Freesurfer software, we performed an exploratory whole-brain voxelwise volume comparison between the PG group and the HV group, with false-discovery rate correction for multiple comparisons (p < 0.05). Using a more flexible statistical threshold (p < 0.01, uncorrected for multiple comparisons), we also measured absolute and regional volumes of several brain structures separately. The voxelwise analysis showed no clusters of significant regional differences between the PG and HV groups. The additional analyses of absolute and regional brain volumes showed increased absolute global gray matter volumes in PG patients relative to the HV group, as well as relatively decreased volumes specifically in the left putamen, right thalamus and right hippocampus (corrected for total gray matter). Our findings indicate that structural brain abnormalities may contribute to the functional changes associated with the symptoms of PG, and they highlight the relevance of the brain reward system to the pathophysiology of this disorder.

Reduced cerebellar brain activity during reward processing in adolescent binge drinkers

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Adolescent binge drinkers have reduced cerebellar activity during reward outcome.

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Average drinks consumed/drinking day was negatively related to brain activity.

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Salience of rewards may be blunted because of alcohol-induced neurotoxicity.

Due to ongoing development, adolescence may be a period of heightened vulnerability to the neurotoxic effects of alcohol. Binge drinking may alter reward-driven behavior and neurocircuitry, thereby increasing risk for escalating alcohol use. Therefore, we compared reward processing in adolescents with and without a history of recent binge drinking. At their baseline study visit, all participants (age = 14.86 ± 0.88) were free of heavy alcohol use and completed a modified version of the Wheel of Fortune (WOF) functional magnetic resonance imaging task. Following this visit, 17 youth reported binge drinking on ≥3 occasions within a 90 day period and were matched to 17 youth who remained alcohol and substance-naïve. All participants repeated the WOF task during a second visit (age = 16.83 ± 1.22). No significant effects were found in a region of interest analysis of the ventral striatum, but whole-brain analyses showed significant group differences in reward response at the second study visit in the left cerebellum, controlling for baseline visit brain activity (p/α < 0.05), which was negatively correlated with mean number of drinks consumed/drinking day in the last 90 days. These findings suggest that binge drinking during adolescence may alter brain activity during reward processing in a dose-dependent manner.

Subjective illusion of control modulates striatal reward anticipation in adolescence

The perception of control over the environment constitutes a fundamental biological adaptive mechanism, especially during development. Previous studies comparing an active choice condition with a passive no-choice condition showed that the neural basis of this mechanism is associated with increased activity within the striatum and the prefrontal cortex. In the current study, we aimed to investigate whether subjective belief of control in an uncertain gambling situation induces elevated activation in a cortico-striatal network. We investigated 79 adolescents (age range: 13-16years) during reward anticipation with a slot machine task using functional magnetic resonance imaging. We assessed post-experimentally whether the participants experienced a subjective illusion of control on winning or losing in this task that was objectively not given. Nineteen adolescents experienced an illusion of control during slot machine gambling. This illusion of control group showed an increased neural activity during reward anticipation within a cortico-striatal network including ventral striatum (VS) as well as right inferior frontal gyrus (rIFG) relative to the group reporting no illusion of control. The rIFG activity was inversely associated with impulsivity in the no illusion of control group. The subjective belief about control led to an elevated ventral striatal activity, which is known to be involved in the processing of reward. This finding strengthens the notion that subjectively perceived control, not necessarily the objective presence of control, affects striatal reward-related processing.

Cumulative gains enhance striatal response to reward opportunities in alcohol-dependent patients

Substance use disorder is characterized by a transition from volitional to compulsive responding for drug reward. A possible explanation for this transition may be that alcohol-dependent patients (ADP) show a general propensity for a history of rewarded instrumental responses, and these rewarded responses may boost the activation of motivational neurocircuitry for additional reward. Brain imaging studies of decision-making have demonstrated that ADP relative to controls (CON) often show altered neural activation in response to anticipating and receiving rewards, but the majority of studies have not investigated how past performance affects activation. A potential exists for ADP to show increased sensitivity to reward as a function of reward delivery history. In the current study, we used functional magnetic resonance imaging to investigate the neural correlates of risky decision-making in ADP (n = 18) and CON (n = 18) while they played a two-choice monetary risk-taking game. In addition to investigating general neural recruitment by risky decision-making, we also modeled each participant's running total of monetary earnings in order to determine areas of activation that correlated with cumulative reward. We found that ADP and CON showed few differences in behavior or in mesolimbic activation by choice for, and receipt of, risky gains. However, when including a cumulative-earnings covariate, ADP exhibited heightened striatal activation that correlated with total earnings during the choice event in the task. The heightened contextual sensitivity of striatal responses to cumulative earnings in ADP may represent a general neurobiological affective substrate for development of automatized instrumental behavior.

Pathological gambling and alcohol dependence: neural disturbances in reward and loss avoidance processing

Pathological gambling (PG) shares clinical characteristics such as craving and loss of control with substance use disorders and is thus considered a behavioral addiction. While functional alterations in the mesolimbic reward system have been correlated with craving and relapse in substance use disorders, only a few studies have examined this brain circuit in PG, and no direct comparison has been conducted so far. Thus, we investigated the neuronal correlates of reward processing in PG in contrast to alcohol-dependent (AD) patients and healthy subjects. Eighteen PG patients, 15 AD patients and 17 controls were investigated with a monetary incentive delay task, in which visual cues predict the consequence (monetary gain, avoidance of loss, none) of a fast response to a subsequent target stimulus. Functional magnetic resonance imaging data were analyzed to account for possible confounding factors such as local gray matter volume. Activity in the right ventral striatum during loss anticipation was increased in PG patients compared with controls and AD patients. Moreover, PG patients showed decreased activation in the right ventral striatum and right medial prefrontal cortex during successful loss avoidance compared with controls, which was inversely associated with severity of gambling behavior. Thus, despite neurobiological similarities to substance use disorders in reward processing, as reported by previous studies, we found relevant differences with respect to the anticipation of loss as well as its avoidance (negative reinforcement), which further contributes to the understanding of PG.

No differences in ventral striatum responsivity between adolescents with a positive family history of alcoholism and controls

Individuals with alcohol-dependent parents show an elevated risk of developing alcohol-related problems themselves. Modulations of the mesolimbic reward circuit have been postulated as a pre-existing marker of alcoholism. We tested whether a positive family history of alcoholism is correlated with ventral striatum functionality during a reward task. All participants performed a modified version of the monetary incentive delay task while their brain responses were measured with functional magnetic resonance imaging. We compared 206 healthy adolescents (aged 13-15) who had any first- or second-degree relative with alcoholism to 206 matched controls with no biological relative with alcoholism. Reward anticipation as well as feedback of win recruited the ventral striatum in all participants, but adolescents with a positive family history of alcoholism did not differ from their matched peers. Also we did not find any correlation between family history density and reward anticipation or feedback of win. This finding of no differences did not change when we analyzed a subsample of 77 adolescents with at least one parent with alcohol use disorder and their matched controls. Because this result is in line with another study reporting no differences between children with alcohol-dependent parents and controls at young age, but contrasts with studies of older individuals, one might conclude that at younger age the effect of family history has not yet exerted its influence on the still developing mesolimbic reward circuit.

Influence of dorsolateral prefrontal cortex and ventral striatum on risk avoidance in addiction: a mediation analysis

BACKGROUND

Alterations in frontal and striatal function are hypothesized to underlie risky decision making in drug users, but how these regions interact to affect behavior is incompletely understood. We used mediation analysis to investigate how prefrontal cortex and ventral striatum together influence risk avoidance in abstinent drug users.

METHOD

Thirty-seven abstinent substance-dependent individuals (SDI) and 43 controls underwent fMRI while performing a decision-making task involving risk and reward. Analyses of a priori regions-of-interest tested whether activity in dorsolateral prefrontal cortex (DLPFC) and ventral striatum (VST) explained group differences in risk avoidance. Whole-brain analysis was conducted to identify brain regions influencing the negative VST-risk avoidance relationship.

RESULTS

Right DLPFC (RDLPFC) positively mediated the group-risk avoidance relationship (p < 0.05); RDLPFC activity was higher in SDI and predicted higher risk avoidance across groups, controlling for SDI vs.

CONTROLS

Conversely, VST activity negatively influenced risk avoidance (p < 0.05); it was higher in SDI, and predicted lower risk avoidance. Whole-brain analysis revealed that, across group, RDLPFC and left temporal-parietal junction positively (p ≤ 0.001) while right thalamus and left middle frontal gyrus negatively (p < 0.005) mediated the VST activity-risk avoidance relationship.

CONCLUSION

RDLPFC activity mediated less risky decision making while VST mediated more risky decision making across drug users and controls. These results suggest a dual pathway underlying decision making, which, if imbalanced, may adversely influence choices involving risk. Modeling contributions of multiple brain systems to behavior through mediation analysis could lead to a better understanding of mechanisms of behavior and suggest neuromodulatory treatments for addiction.

Hypothalamic-pituitary-adrenal axis activity in patients with pathological gambling and internet use disorder

Alterations in secretion of stress hormones within the hypothalamic-pituitary-adrenal (HPA) axis have repeatedly been found in substance-related addictive disorders. It has been suggested that glucocorticoids might contribute to the development and maintenance of substance use disorders by facilitatory effects on behavioral responses to substances of abuse. The objective of this pilot study was to investigate HPA axis activity in patients with non-substance-related addictive disorders, i.e. pathological gambling and internet use disorder. We measured plasma levels of copeptin, a vasopressin surrogate marker, adrenocorticotropic hormone (ACTH) and cortisol in male patients with pathological gambling (n=14), internet use disorder (n=11) and matched healthy controls for pathological gambling (n=13) and internet use disorder (n=10). Plasma levels of copeptin, ACTH and cortisol in patients with pathological gambling or internet use disorder did not differ among groups. However, cortisol plasma levels correlated negatively with the severity of pathological gambling as measured by the PG-YBOCS. Together with our findings of increased serum levels of brain-derived neurotrophic factor (BDNF) in pathological gambling but not internet use disorder, these results suggest that the pathophysiology of pathological gambling shares some characteristics with substance-related addictive disorders on a neuroendocrinological level, whereas those similarities could not be observed in internet use disorder.

[³H]Ifenprodil binding in post-mortem brains of Cloninger type 1 and 2 alcoholics: a whole-hemisphere autoradiography study

The glutamate N-methyl-d-aspartate (NMDA) receptor NR2B subunits are sensitive to ethanol and are found in brain areas related to ethanol addiction, dependence, development of alcohol tolerance, and alcohol withdrawal syndrome. Previous studies indicate that early-onset Cloninger type 2 alcoholics have an intact, responsive, dopaminergic system in the nucleus accumbens (NAC), whereas type 1 alcoholics have dopaminergic defects. NR2B-containing NMDA receptors in the NAC are involved in both non-opioid and opioid receptor-mediated reward. Our aim was to evaluate the putative [(3)H]ifenprodil binding alterations of NR2B receptors in limbic, hippocampal, and cortical brain areas of type 1 alcoholics (n=8), type 2 alcoholics (n=8), and control subjects (n=10) by postmortem whole hemisphere autoradiography. We found significantly different binding levels among these three subject groups, and the main difference was localized in the decreased binding in type 2 alcoholics and controls in the nucleus accumbens. Although preliminary and from relatively small diagnostic groups, these results suggest pathological alterations in the NR2B-mediated reward system of type 2 alcoholics.

Diagnostic classification of schizophrenia patients on the basis of regional reward-related FMRI signal patterns

Functional neuroimaging has provided evidence for altered function of mesolimbic circuits implicated in reward processing, first and foremost the ventral striatum, in patients with schizophrenia. While such findings based on significant group differences in brain activations can provide important insights into the pathomechanisms of mental disorders, the use of neuroimaging results from standard univariate statistical analysis for individual diagnosis has proven difficult. In this proof of concept study, we tested whether the predictive accuracy for the diagnostic classification of schizophrenia patients vs. healthy controls could be improved using multivariate pattern analysis (MVPA) of regional functional magnetic resonance imaging (fMRI) activation patterns for the anticipation of monetary reward. With a searchlight MVPA approach using support vector machine classification, we found that the diagnostic category could be predicted from local activation patterns in frontal, temporal, occipital and midbrain regions, with a maximal cluster peak classification accuracy of 93% for the right pallidum. Region-of-interest based MVPA for the ventral striatum achieved a maximal cluster peak accuracy of 88%, whereas the classification accuracy on the basis of standard univariate analysis reached only 75%. Moreover, using support vector regression we could additionally predict the severity of negative symptoms from ventral striatal activation patterns. These results show that MVPA can be used to substantially increase the accuracy of diagnostic classification on the basis of task-related fMRI signal patterns in a regionally specific way.

Anticipatory reward processing in addicted populations: a focus on the monetary incentive delay task

Advances in brain imaging techniques have allowed neurobiological research to temporally analyze signals coding for the anticipation of reward. In addicted populations, both hyporesponsiveness and hyperresponsiveness of brain regions (e.g., ventral striatum) implicated in drug effects and reward system processing have been reported during anticipation of generalized reward. We discuss the current state of knowledge of reward processing in addictive disorders from a widely used and validated task: the monetary incentive delay task. Only studies applying the monetary incentive delay task in addicted and at-risk adult populations are reviewed, with a focus on anticipatory processing and striatal regions activated during task performance as well as the relationship of these regions with individual difference (e.g., impulsivity) and treatment outcome variables. We further review drug influences in challenge studies as a means to examine acute influences on reward processing in abstinent, recreationally using, and addicted populations. Generalized reward processing in addicted and at-risk populations is often characterized by divergent anticipatory signaling in the ventral striatum. Although methodologic and task variations may underlie some discrepant findings, anticipatory signaling in the ventral striatum may also be influenced by smoking status, drug metabolites, and treatment status in addicted populations. Divergent results across abstinent, recreationally using, and addicted populations demonstrate complexities in interpreting findings. Future studies would benefit from focusing on characterizing how impulsivity and other addiction-related features relate to anticipatory striatal signaling over time. Additionally, identifying how anticipatory signals recover or adjust after protracted abstinence will be important in understanding recovery processes.

Dimensional psychiatry: reward dysfunction and depressive mood across psychiatric disorders

RATIONALE

A dimensional approach in psychiatry aims to identify core mechanisms of mental disorders across nosological boundaries.

OBJECTIVES

We compared anticipation of reward between major psychiatric disorders, and investigated whether reward anticipation is impaired in several mental disorders and whether there is a common psychopathological correlate (negative mood) of such an impairment.

METHODS

We used functional magnetic resonance imaging (fMRI) and a monetary incentive delay (MID) task to study the functional correlates of reward anticipation across major psychiatric disorders in 184 subjects, with the diagnoses of alcohol dependence (n = 26), schizophrenia (n = 44), major depressive disorder (MDD, n = 24), bipolar disorder (acute manic episode, n = 13), attention deficit/hyperactivity disorder (ADHD, n = 23), and healthy controls (n = 54). Subjects' individual Beck Depression Inventory-and State-Trait Anxiety Inventory-scores were correlated with clusters showing significant activation during reward anticipation.

RESULTS

During reward anticipation, we observed significant group differences in ventral striatal (VS) activation: patients with schizophrenia, alcohol dependence, and major depression showed significantly less ventral striatal activation compared to healthy controls. Depressive symptoms correlated with dysfunction in reward anticipation regardless of diagnostic entity. There was no significant correlation between anxiety symptoms and VS functional activation.

CONCLUSION

Our findings demonstrate a neurobiological dysfunction related to reward prediction that transcended disorder categories and was related to measures of depressed mood. The findings underline the potential of a dimensional approach in psychiatry and strengthen the hypothesis that neurobiological research in psychiatric disorders can be targeted at core mechanisms that are likely to be implicated in a range of clinical entities.

Quantifying familial influences on brain activation during the monetary incentive delay task: an adolescent monozygotic twin study

Although altered brain activation during reward tasks has been found in a number of heritable psychiatric disorders and health outcomes, the familial nature of reward-related brain activation remains unexplored. In this study, we investigated the degree to which the magnitude of mesocorticolimbic reward system signal intensities in anticipation of reward during the monetary incentive delay (MID) task was similar within 46 pairs of adolescent, monozygotic twins. Significant within-pair correlations in brain activation during anticipation of gain were found in one third of the 18 reward-related regions investigated. These regions were the right nucleus accumbens, left and right posterior caudate, right anterior caudate, left insula, and anterior cingulate cortex. This serves as evidence for a shared familial contribution to individual differences in reward related brain activity in certain key reward processing regions.

Linking online gaming and addictive behavior: converging evidence for a general reward deficiency in frequent online gamers

Millions of people regularly play so-called massively multiplayer online role playing games (MMORPGs). Recently, it has been argued that MMORPG overuse is becoming a significant health problem worldwide. Symptoms such as tolerance, withdrawal, and craving have been described. Based on behavioral, resting state, and task-related neuroimaging data, we test whether frequent players of the MMORPG "World of Warcraft" (WoW) - similar to drug addicts and individuals with an increased risk for addictions - show a generally deficient reward system. In frequent players of the MMORPG "World of Warcraft" (WoW-players) and in a control group of non-gamers we assessed (1) trait sensitivity to reward (SR), (2) BOLD responses during monetary reward processing in the ventral striatum, and (3) ventral-striatal resting-state dynamics. We found a decreased neural activation in the ventral striatum during the anticipation of both small and large monetary rewards. Additionally, we show generally altered neurodynamics in this region independent of any specific task for WoW players (resting state). On the behavioral level, we found differences in trait SR, suggesting that the reward processing deficiencies found in this study are not a consequence of gaming, but predisposed to it. These findings empirically support a direct link between frequent online gaming and the broad field of behavioral and drug addiction research, thus opening new avenues for clinical interventions in addicted gamers and potentially improving the assessment of addiction-risk in the vast population of frequent gamers.

Reward processing in obesity, substance addiction and non-substance addiction

Similarities and differences between obesity and addiction are a prominent topic of ongoing research. We conducted an activation likelihood estimation meta-analysis on 87 studies in order to map the functional magnetic resonance imaging (fMRI) response to reward in participants with obesity, substance addiction and non-substance (or behavioural) addiction, and to identify commonalities and differences between them. Our study confirms the existence of alterations during reward processing in obesity, non-substance addiction and substance addiction. Specifically, participants with obesity or with addictions differed from controls in several brain regions including prefrontal areas, subcortical structures and sensory areas. Additionally, participants with obesity and substance addictions exhibited similar blood-oxygen-level-dependent fMRI hyperactivity in the amygdala and striatum when processing either general rewarding stimuli or the problematic stimuli (food and drug-related stimuli, respectively). We propose that these similarities may be associated with an enhanced focus on reward--especially with regard to food or drug-related stimuli--in obesity and substance addiction. Ultimately, this enhancement of reward processes may facilitate the presence of compulsive-like behaviour in some individuals or under some specific circumstances. We hope that increasing knowledge about the neurobehavioural correlates of obesity and addictions will lead to practical strategies that target the high prevalence of these central public health challenges.