Applying incentive sensitization models to behavioral addiction

Separating desire from prediction of outcome value

Individuals typically want what they expect to like, often based on memories of previous positive experiences. However, in some situations desire can decouple completely from memories and from learned predictions of outcome value. The potential for desire to separate from prediction arises from independent operating rules that control motivational incentive salience. Incentive salience, or 'wanting', is a type of mesolimbic desire that evolved for adaptive goals, but can also generate maladaptive addictions. Two proof-of-principle examples are presented here to show how motivational 'wanting' can soar above memory-based predictions of outcome value: (i) 'wanting what is remembered to be disgusting', and (ii) 'wanting what is predicted to hurt'. Consequently, even outcomes remembered and predicted to be negatively aversive can become positively 'wanted'. Similarly, in human addictions, people may experience powerful cue-triggered cravings for outcomes that are not predicted to be enjoyable.

Neurocognitive predictors of addiction-related outcomes: A systematic review of longitudinal studies

It is well-established that addiction is typically associated with a distinct pattern of neurocognitive functioning with a consensus that it is typified by impaired top-down executive control and aberrant risk-reward processing. Despite a consensus that neurocognition plays an important role in characterizing and maintaining addictive disorders, there is a lack of systematic, bottom-up synthesis of quantitative evidence showing that neurocognition predicts addictive behaviors, and which neurocognitive constructs have the best predictive validity. This systematic review aimed to assess whether cognitive control and risk-reward processes as defined by the Research Domain Criteria (RDoC) predict the development and maintenance of addictive behaviors specifically, consumption, severity, and relapse. The findings from this review expose the substantial lack of evidence for neurocognition predicting addiction outcomes. However, there is evidence that suggests reward-related neurocognitive processes may be important for the detection of early risk for addiction, as well as a potentially viable target for designing novel, more effective interventions.

Computational reinforcement learning, reward (and punishment), and dopamine in psychiatric disorders

In the DSM-5, psychiatric diagnoses are made based on self-reported symptoms and clinician-identified signs. Though helpful in choosing potential interventions based on the available regimens, this conceptualization of psychiatric diseases can limit basic science investigation into their underlying causes. The reward prediction error (RPE) hypothesis of dopamine neuron function posits that phasic dopamine signals encode the difference between the rewards a person expects and experiences. The computational framework from which this hypothesis was derived, temporal difference reinforcement learning (TDRL), is largely focused on reward processing rather than punishment learning. Many psychiatric disorders are characterized by aberrant behaviors, expectations, reward processing, and hypothesized dopaminergic signaling, but also characterized by suffering and the inability to change one's behavior despite negative consequences. In this review, we provide an overview of the RPE theory of phasic dopamine neuron activity and review the gains that have been made through the use of computational reinforcement learning theory as a framework for understanding changes in reward processing. The relative dearth of explicit accounts of punishment learning in computational reinforcement learning theory and its application in neuroscience is highlighted as a significant gap in current computational psychiatric research. Four disorders comprise the main focus of this review: two disorders of traditionally hypothesized hyperdopaminergic function, addiction and schizophrenia, followed by two disorders of traditionally hypothesized hypodopaminergic function, depression and post-traumatic stress disorder (PTSD). Insights gained from a reward processing based reinforcement learning framework about underlying dopaminergic mechanisms and the role of punishment learning (when available) are explored in each disorder. Concluding remarks focus on the future directions required to characterize neuropsychiatric disorders with a hypothesized cause of underlying dopaminergic transmission.

The Role of Impulsivity and Reward Deficiency in "Liking" and "Wanting" of Potentially Problematic Behaviors and Substance Uses

A few studies have examined the changes in substance- and behavior-related "wanting" and "liking" of human subjects, the key properties of Incentive Sensitization Theory (IST). The aim of this study was to examine the dissociation between "wanting" and "liking" as a function of usage frequency, intensity, and subjective severity in individuals across four substances (alcohol, nicotine, cannabis, and other drugs) and ten behaviors (gambling, overeating, gaming, pornography use, sex, social media use, Internet use, TV-series watching, shopping, and work). Also, the potential roles of impulsivity and reward deficiency were investigated in "wanting," "liking," and wellbeing. The sex differences between "wanting" and "liking" were also examined. Based on our findings using structural equation modeling with 749 participants (503 women, M age = 35.7 years, SD = 11.84), who completed self-report questionnaires, "wanting" increased with the severity, frequency, and intensity of potentially problematic use, while "liking" did not change. Impulsivity positively predicted "wanting," and "wanting" positively predicted problem uses/behaviors. Reward deficiency positively predicted problem uses/behaviors, and both impulsivity and problem uses/behaviors negatively predicted wellbeing. Finally, women showed higher levels of "wanting," compared to men. These findings demonstrate the potential roles of incentive sensitization in both potentially problematic substance uses and behaviors.

Neural correlates of cue-induced changes in decision-making distinguish subjects with gambling disorder from healthy controls

In addiction, there are few human studies on the neural basis of cue-induced changes in value-based decision making (Pavlovian-to-instrumental transfer, PIT). It is especially unclear whether neural alterations related to PIT are due to the physiological effects of substance abuse or rather related to learning processes and/or other etiological factors related to addiction. We have thus investigated whether neural activation patterns during a PIT task help to distinguish subjects with gambling disorder (GD), a nonsubstance-based addiction, from healthy controls (HCs). Thirty GD and 30 HC subjects completed an affective decision-making task in a functional magnetic resonance imaging (fMRI) scanner. Gambling-associated and other emotional cues were shown in the background during the task. Data collection and feature modeling focused on a network of nucleus accumbens (NAcc), amygdala, and orbitofrontal cortex (OFC) (derived from PIT and substance use disorder [SUD] studies). We built and tested a linear classifier based on these multivariate neural PIT signatures. GD subjects showed stronger PIT than HC subjects. Classification based on neural PIT signatures yielded a significant area under the receiver operating curve (AUC-ROC) (0.70, p = 0.013). GD subjects showed stronger PIT-related functional connectivity between NAcc and amygdala elicited by gambling cues, as well as between amygdala and OFC elicited by negative and positive cues. HC and GD subjects were thus distinguishable by PIT-related neural signatures including amygdala-NAcc-OFC functional connectivity. Neural PIT alterations in addictive disorders might not depend on the physiological effect of a substance of abuse but on related learning processes or even innate neural traits.

Maladaptive consequences of repeated intermittent exposure to uncertainty

Recently we reported that nucleus accumbens (NAcc) dopamine (DA) tracks uncertainty during operant responding for non-caloric saccharin. We also showed that repeated intermittent exposure to this uncertainty, like exposure to drugs of abuse, leads to sensitization of the locomotor and NAcc DA effects of amphetamine and promotes the subsequent self-administration of the drug. Here we review these findings together with others showing that NAcc glutamate signaling is similarly affected by uncertainty. Extracellular levels of glutamate in this site also track uncertainty in a task in which nose poking for saccharin on an escalating variable ratio schedule of reinforcement is associated with progressively increasing variance between performance of the operant and payout. Furthermore, sensitized behavioral responding to and for amphetamine following exposure to uncertainty is accompanied by increased levels of Ca2+/calmodulin-dependent protein kinase II (CaMKII) and protein kinase C (PKC) phosphorylation as well as altered protein levels of the transcription factor ∆FosB (increased) and glutamate transporter 1 (GLT1; decreased) in NAcc tissues. Notably, phosphorylation by CaMKII and PKC regulates AMPA receptor trafficking and function in this site, is elevated following psychostimulant exposure, and is necessary for the expression of enhanced drug taking. Increased ∆FosB and decreased GLT1 levels are observed following psychostimulant exposure, are associated with increased drug taking and seeking, and are known to modulate AMPA receptors and extracellular glutamate levels respectively. These adaptations in glutamate transmission as well as those observed with DA following repeated intermittent exposure to uncertainty are similar to those produced by exposure to abused drugs. Together, they point to the recruitment of both DA and glutamate signaling pathways in the NAcc in both drug and behavioral addictions. As uncertainty is central to games of chance, these findings have particular relevance for gambling disorders known to exhibit comorbidity with drug abuse.

Learning to lose control: A process-based account of behavioral addiction

Learning psycho(bio)logy has developed a solid corpus of evidence and theory regarding behavior control modes. The present article briefly reviews that literature and its influence on recent models in which the transition from goal-directed to compulsive behavior is identified as the main process underlying substance use disorders. This literature is also relevant to non-substance addictive disorders, and serves as basis to propose a restricted definition of behavioral addiction relying on the presence of behavior-specific compulsivity. Complementarily, we consider whether some activities can become disordered while remaining mostly goal-driven. Based on reinforcement learning models, relative outcome utility computation is proposed as an alternative mechanism through which dysfunctional behaviors (even not qualifying as addictive) can override adaptive ones, causing functional impairment. Beyond issues of conceptual delimitation, recommendations are made regarding the importance of identifying individual etiological pathways to dysregulated behavior, the necessity of accurately profiling at-risk individuals, and the potential hazards of symptom-based diagnosis. In our view, the validity of these recommendations does not depend on the position one takes in the nosological debate.

Striatal presynaptic dopaminergic dysfunction in gambling disorder: A 123 I-FP-CIT SPECT study

Although the involvement of dopamine in gambling disorder (GD) has long been hypothesized, its precise role remains unclear. The action of dopamine in the synapses is regulated by the dopamine transporter (DAT). We hereinafter present significant differences between a sample of 15 treatment-seeking GD subjects and 17 healthy controls in terms of striatal DAT availability, and we explore its association with reward-based decision making. We performed ¹²³ I-FP-CIT Single-photon emission computed tomography (SPECT) and correlated DAT binding ratios in the bilateral caudate and putamen with gambling symptoms (G-SAS, PG-YBOCS) and behaviors, as well as other psychometric variables (anhedonia and impulsivity). Gambling disorder (GD) subjects were also administered a computerized version of the Iowa gambling task (IGT) to assess reward-based decision making. We found reduced DAT availability in GD subjects compared with healthy controls (-13.30% in right caudate, -11.11% in right putamen, -11.44% in left caudate, and -11.46% in the left putamen). We also found that striatal DAT availability was inversely correlated with days spent gambling and IGT performance in GD subjects. These results provide evidence for a presynaptic dopaminergic dysfunction in striatal regions of GD subjects. Functional DAT down-regulation possibly sustains the transition towards compulsive gambling addiction, characterized both by hyperdopaminergic and hypodopaminergic states in the context of a sensitized dopaminergic system.

Relative insensitivity to time-out punishments induced by win-paired cues in a rat gambling task

RATIONALE

Pairing rewarding outcomes with audiovisual cues in simulated gambling games increases risky choice in both humans and rats. However, the cognitive mechanism through which this sensory enhancement biases decision-making is unknown.

OBJECTIVES

To assess the computational mechanisms that promote risky choice during gambling, we applied a series of reinforcement learning models to a large dataset of choices acquired from rats as they each performed one of two variants of a rat gambling task (rGT), in which rewards on "win" trials were delivered either with or without salient audiovisual cues.

METHODS

We used a sampling technique based on Markov chain Monte Carlo to obtain posterior estimates of model parameters for a series of RL models of increasing complexity, in order to assess the relative contribution of learning about positive and negative outcomes to the latent valuation of each choice option on the cued and uncued rGT.

RESULTS

Rats which develop a preference for the risky options on the rGT substantially down-weight the equivalent cost of the time-out punishments during these tasks. For each model tested, the reduction in learning from the negative time-outs correlated with the degree of risk preference in individual rats. We found no apparent relationship between risk preference and the parameters that govern learning from the positive rewards.

CONCLUSIONS

The emergence of risk-preferring choice on the rGT derives from a relative insensitivity to the cost of the time-out punishments, as opposed to a relative hypersensitivity to rewards. This hyposensitivity to punishment is more likely to be induced in individual rats by the addition of salient audiovisual cues to rewards delivered on win trials.

The gambling craving experience questionnaire: Psychometric properties of a new scale based on the elaborated intrusion theory of desire

Both research and clinical practice acknowledge the importance of craving as a maintenance and relapse factor in gambling disorder. The elaborated intrusion theory (EIT; Kavanagh et al., 2005) of desire has been extensively investigated in relation to psychoactive substance or food cravings but, to date, has scarcely been studied in relation to gambling. In such a context, developing an assessment tool of gambling craving based on the EIT is warranted. To fill this gap in the literature, we aimed to develop and test the psychometric properties of a gambling-adapted version of the Craving Experience Questionnaire (CEQ; May et al., 2014), which is the best established measure of craving theoretically anchored in the EIT. An online survey that included the gambling CEQ (g-CEQ) and a craving induction procedure was administered to 274 community participants involved in gambling at least a few times a year. Concurrent and convergent validity were explored through correlations with a scale that measured gambling urge and with a series of questionnaires that measured disordered gambling symptoms, gambling cognitions, and gambling motives. The confirmatory factor analyses supported the validity of the expected three-factor model of the "strength" and "frequency" forms of the g-CEQ and showed better model fit than a one-factor solution, corroborating the initial structure of the CEQ. Furthermore, the scale has good internal consistency and its validity is supported by correlations with gambling-related constructs. The g-CEQ is thus a theoretically and psychometrically sound instrument to measure gambling craving based on the EIT.

Disentangling Reward Processing in Trichotillomania: 'Wanting' and 'Liking' Hair Pulling Have Distinct Clinical Correlates

Trichotillomania (TTM; hair-pulling disorder) is characterized by an irresistible urge or desire to pull out one's own hair, and a sense of pleasure when hair is pulled out. Evidence from translational neuroscience has shown that 'wanting' (motivation to seek a reward) and 'liking' (enjoyment when reward is received) are each mediated by overlapping but distinct neural circuitry, and that 'wanting' contributes to addictive/compulsive behaviors more so than 'liking'. In the present study, we developed the Hair Pulling Reward Scale (HPRS), a self-report measure that consists of two subscales designed to assess (a) cue-triggered urges and appetitive motivation to pull hair (i.e., putative correlates of 'wanting'), and (b) momentary pleasure and gratification during pulling episodes (i.e., putative correlates of 'liking'). We administered the HPRS to 259 individuals with TTM and examined its psychometric properties. Confirmatory factor analysis supported a two-factor model reflecting correlated Wanting and Liking scales. Consistent with predictions, Wanting, much more than Liking, had robust correlations with TTM severity, impulsiveness, difficulties in emotion regulation, psychiatric symptoms, and sleep dysfunction. The results suggest that the HPRS is a psychometrically sound instrument that can be used as a symptom-level measure of reward processing in TTM.

Cued for risk: Evidence for an incentive sensitization framework to explain the interplay between stress and anxiety, substance abuse, and reward uncertainty in disordered gambling behavior

Gambling disorder is an impairing condition confounded by psychiatric co-morbidity, particularly with substance use and anxiety disorders. Yet, our knowledge of the mechanisms that cause these disorders to coalesce remains limited. The Incentive Sensitization Theory suggests that sensitization of neural "wanting" pathways, which attribute incentive salience to rewards and their cues, is responsible for the excessive desire for drugs and cue-triggered craving. The resulting hyper-reactivity of the "wanting' system is believed to heavily influence compulsive drug use and relapse. Notably, evidence for sensitization of the mesolimbic dopamine pathway has been seen across gambling and substance use, as well as anxiety and stress-related pathology, with stress playing a major role in relapse. Together, this evidence highlights a phenomenon known as cross-sensitization, whereby sensitization to stress, drugs, or gambling behaviors enhance the sensitivity and dopaminergic response to any of those stimuli. Here, we review the literature on how cue attraction and reward uncertainty may underlie gambling pathology, and examine how this framework may advance our understanding of co-mordidity with substance-use disorders (e.g., alcohol, nicotine) and anxiety disorders. We argue that reward uncertainty, as seen in slot machines and games of chance, increases dopaminergic activity in the mesolimbic pathway and enhances the incentive value of reward cues. We propose that incentive sensitization by reward uncertainty may interact with and predispose individuals to drug abuse and stress, creating a mechanism through which co-mordidity of these disorders may emerge.

The potential involvement of miR-204-3p-axon guidance network in methamphetamine-induced locomotor sensitization of mice

MicroRNAs (miRNAs) are gene expression regulators that play an important role in drug addiction. We previously reported miR-204-3p was the only up-regulated miRNA in the nucleus accumbens (NAc) in methamphetamine (METH)-sensitized mice. In this study, we are reporting a miR-204-3p potential mechanism in METH sensitization. We first measured the expression changes of miR-204-3p in the NAc of METH- sensitized mice. Then we predicted the targets of miR-204-3p by bioinformatics tools and combined the potential targets with the METH-responsive genes from the ArrayExpress database. KEGG pathway analyses were performed to investigate the prospective mechanisms and four enriched genes were validated by RT-PCR. As a result, miR-204-3p showed a shift from down-regulation to up-regulation in the NAc from the development to the expression of METH sensitization. Bioinformatics analysis predicted 1834 putative targets, 259 of which were differentially expressed in the NAc in response to METH. These targets were significantly enriched in axon guidance (P = 9.59 × 10^-6). Four putative targets (Sema3A, Plxna4, Rac1, and Pak3) enriched in axon guidance also exhibited significant changes in the NAc after METH challenge injection. Moreover, expression levels of miR-204-3p, Sema3A and Plxna4 exhibited a negative association in the expression of METH sensitization. It appeared that miR-204-3p may be involved in the expression of METH sensitization by regulating the expression of Sema3A and Plxna4. Our study provided a potential network of miR-204-3p-axon guidance in the NAc in the expression of METH-induced behavioral sensitization.

Exposure to conditions of uncertainty promotes the pursuit of amphetamine

Prior exposure to abused drugs leads to long-lasting neuroadaptations culminating in excessive drug intake. Given the comorbidity between substance use and gambling disorders, surprisingly little is known about the effects of exposure to reinforcement contingencies experienced during games of chance. As it is a central feature of these games, we characterized the effects of exposure to uncertainty on biochemical and behavioral effects normally observed in rats exposed to amphetamine. Rats in different groups were trained to nose-poke for saccharin under certain [fixed-ratio (FR)] or uncertain conditions [variable-ratio (VR)] for 55 1-h sessions. Ratios were escalated on successive sessions and rats maintained on the last ratio (FR/VR 20) for 20-25 days. Two to three weeks later, rats were tested for their locomotor or nucleus accumbens dopamine (NAcc DA) response to amphetamine or self-administration of the drug using a lever press operant. NAcc DA overflow was also assessed in additional rats during the saccharin sessions. Rats exposed to uncertainty subsequently showed a higher locomotor and NAcc DA response to amphetamine and self-administered more drug infusions relative to rats exposed to predictable reinforcement. NAcc DA levels during the saccharin sessions tracked the variance of the scheduled ratios (a measure of uncertainty). VR rats showed escalating DA overflow with increasing ratios. Exposure to uncertainty triggered neuroadaptations similar to those produced by exposure to abused drugs. As these were produced in drug naive rats both during and after exposure to uncertainty, they provide a novel common pathway to drug and behavioral addictions.

Luck, come here! Automatic approach tendencies toward gambling cues in moderate- to high-risk gamblers

BACKGROUND AND AIMS

Similar to substance addictions, reward-related cognitive motivational processes, such as selective attention and positive memory biases, have been found in disordered gambling. Despite findings that individuals with substance use problems are biased to approach substance-related cues automatically, no study has yet focused on automatic approach tendencies for motivationally salient gambling cues in problem gamblers. We tested if moderate- to high-risk gamblers show a gambling approach bias and whether this bias was related prospectively to gambling behaviour and problems.

DESIGN

Cross-sectional assessment study evaluating the concurrent and longitudinal correlates of gambling approach bias in moderate- to high-risk gamblers compared with non-problem gamblers.

SETTING

Online study throughout the Netherlands.

PARTICIPANTS

Twenty-six non-treatment-seeking moderate- to high-risk gamblers and 26 non-problem gamblers community-recruited via the internet.

MEASUREMENTS

Two online assessment sessions 6 months apart, including self-report measures of gambling problems and behaviour (frequency, duration and expenditure) and the gambling approach avoidance task, with stimuli tailored to individual gambling habits.

FINDINGS

Relative to non-problem gamblers, moderate- to high-risk gamblers revealed a stronger approach bias towards gambling-related stimuli than neutral stimuli (P = 0.03). Gambling approach bias was correlated positively with past-month gambling expenditure at baseline (P = 0.03) and with monthly frequency of gambling at follow-up (P = 0.02). In multiple hierarchical regressions, baseline gambling approach bias predicted monthly frequency positively (P = 0.03) and total duration of gambling episodes (P = 0.01) 6 months later, but not gambling problems or expenditure.

CONCLUSIONS

In the Netherlands, relative to non-problem gamblers, moderate- to high-risk gamblers appear to have a stronger tendency to approach rather than to avoid gambling-related pictures compared with neutral ones. This gambling approach bias is associated concurrently with past-month gambling expenditure and duration of gambling and has been found to predict persistence in gambling behaviour over time.

Cognitive distortions and gambling near-misses in Internet Gaming Disorder: A preliminary study

Increased cognitive distortions (i.e. biased processing of chance, probability and skill) are a key psychopathological process in disordered gambling. The present study investigated state and trait aspects of cognitive distortions in 22 individuals with Internet Gaming Disorder (IGD) and 22 healthy controls. Participants completed the Gambling Related Cognitions Scale as a trait measure of cognitive distortions, and played a slot machine task delivering wins, near-misses and full-misses. Ratings of pleasure (“liking”) and motivation to play (“wanting”) were taken following the different outcomes, and gambling persistence was measured after a mandatory phase. IGD was associated with elevated trait cognitive distortions, in particular skill-oriented cognitions. On the slot machine task, the IGD group showed increased “wanting” ratings compared with control participants, while the two groups did not differ regarding their “liking” of the game. The IGD group displayed increased persistence on the slot machine task. Near-miss outcomes did not elicit stronger motivation to play compared to full-miss outcomes overall, and there was no group difference on this measure. However, a near-miss position effect was observed, such that near-misses stopping before the payline were rated as more motivating than near-misses that stopped after the payline, and this differentiation was attenuated in the IGD group, suggesting possible counterfactual thinking deficits in this group. These data provide preliminary evidence for increased incentive motivation and cognitive distortions in IGD, at least in the context of a chance-based gambling environment.

Effectiveness of two web-based cognitive bias modification interventions targeting approach and attentional bias in gambling problems: study protocol for a pilot randomised controlled trial

BACKGROUND

Disordered gamblers have phenotypical and pathological similarities to those with substance use disorders (SUD), including exaggerated automatic cognitive processing of motivationally salient gambling cues in the environment (i.e., attentional and approach bias). Cognitive bias modification (CBM) is a family of computerised interventions that have proved effective in successfully re-training these automatic cognitive biases in SUD. CBM interventions can, in principle, be administered online, thus showing potential of being a low-cost, low-threshold addition to conventional treatments. This paper presents the design of a pilot randomised controlled trial exploring the effectiveness of two web-based CBM interventions targeting attentional and approach bias towards gambling cues in a sample of Dutch and Belgian problematic and pathological gamblers.

METHODS/DESIGN

Participants (N = 182) are community-recruited adults experiencing gambling problems, who have gambled at least twice in the past 6 months and are motivated to change their gambling behaviour. After a baseline assessment session, participants are randomly assigned to one of four experimental conditions (attentional or approach bias training, or the placebo version of the two trainings) and complete six sessions of training. At baseline and before each training session, participants receive automated personalised feedback on their gambling motives and reasons to quit or reduce gambling. The post-intervention, 1-month, and 3-month follow-up assessments will examine changes in gambling behaviour, with frequency and expenditure as primary outcomes, and depressive symptoms and gambling-related attentional and approach biases as secondary outcomes. Secondary analyses will explore possible moderators (interference control capacity and trait impulsivity) and mediators (change in cognitive bias) of training effects on the primary outcomes.

DISCUSSION

This study is the first to explore the effectiveness of an online CBM intervention for gambling problems. The results of this study can be extremely valuable for developing e-health interventions for gambling problems and further understanding the role of motivational implicit cognitive processes underlying problematic gambling behaviour.

TRIAL REGISTRATION

Netherlands Trial Register, NTR5096 . Registered on 11 March 2015.

Cue-induced craving for Internet among Internet addicts

Intense craving is a core feature of addictive disorder, and cue-induced craving is believed to be a key factor in the maintenance and relapse of addictive behaviors. With the rapid development of the Internet, Internet addiction has become a widespread behavioral problem accompanied by many negative effects. This study used the cue-reactivity paradigm to examine cue-induced craving for the Internet among Internet addicts and non-addicts. Participants were exposed to Internet-related words, and asked to report their craving for the Internet. Results indicated that Internet-related words aroused cue-induced craving for the Internet among both Internet addicts and non-addicts; however, the craving was more intense among Internet addicts. These results suggest that craving may not be a unipolar, all or none state found only in addicts, but may also be present among non-addicts. They indicate that Internet-related words may be able to induce craving for the Internet, and that Internet addiction and other addictions may share similar underlying mechanisms. This finding has important implications for designing interventions for Internet addiction.

Behavioural addiction-A rising tide?

The term 'addiction' was traditionally used in relation to centrally active substances, such as cocaine, alcohol, or nicotine. Addiction is not a unitary construct but rather incorporates a number of features, such as repetitive engagement in behaviours that are rewarding (at least initially), loss of control (spiralling engagement over time), persistence despite untoward functional consequences, and physical dependence (evidenced by withdrawal symptoms when intake of the substance diminishes). It has been suggested that certain psychiatric disorders characterized by maladaptive, repetitive behaviours share parallels with substance addiction and therefore represent 'behavioural addictions'. This perspective has influenced the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), which now has a category 'Substance Related and Addictive Disorders', including gambling disorder. Could other disorders characterised by repetitive behaviours, besides gambling disorder, also be considered 'addictions'? Potential examples include kleptomania, compulsive sexual behaviour, 'Internet addiction', trichotillomania (hair pulling disorder), and skin-picking disorder. This paper seeks to define what is meant by 'behavioural addiction', and critically considers the evidence for and against this conceptualisation in respect of the above conditions, from perspectives of aetiology, phenomenology, co-morbidity, neurobiology, and treatment. Research in this area has important implications for future diagnostic classification systems, neurobiological models, and novel treatment directions.

Roles of "Wanting" and "Liking" in Motivating Behavior: Gambling, Food, and Drug Addictions

The motivation to seek out and consume rewards has evolutionarily been driven by the urge to fulfill physiological needs. However in a modern society dominated more by plenty than scarcity, we tend to think of motivation as fueled by the search for pleasure. Here, we argue that two separate but interconnected subcortical and unconscious processes direct motivation: "wanting" and "liking." These two psychological and neuronal processes and their related brain structures typically work together, but can become dissociated, particularly in cases of addiction. In drug addiction, for example, repeated consumption of addictive drugs sensitizes the mesolimbic dopamine system, the primary component of the "wanting" system, resulting in excessive "wanting" for drugs and their cues. This sensitizing process is long-lasting and occurs independently of the "liking" system, which typically remains unchanged or may develop a blunted pleasure response to the drug. The result is excessive drug-taking despite minimal pleasure and intense cue-triggered craving that may promote relapse long after detoxification. Here, we describe the roles of "liking" and "wanting" in general motivation and review recent evidence for a dissociation of "liking" and "wanting" in drug addiction, known as the incentive sensitization theory (Robinson and Berridge 1993). We also make the case that sensitization of the "wanting" system and the resulting dissociation of "liking" and "wanting" occurs in both gambling disorder and food addiction.

Measuring anhedonia: impaired ability to pursue, experience, and learn about reward

Ribot’s (1896) long standing definition of anhedonia as “the inability to experience pleasure” has been challenged recently following progress in affective neuroscience. In particular, accumulating evidence suggests that reward consists of multiple subcomponents of wanting, liking and learning, as initially outlined by Berridge and Robinson (2003), and these processes have been proposed to relate to appetitive, consummatory and satiety phases of a pleasure cycle. Building on this work, we recently proposed to reconceptualize anhedonia as “impairments in the ability to pursue, experience, and/or learn about pleasure, which is often, but not always accessible to conscious awareness.” (Rømer Thomsen et al., 2015). This framework is in line with Treadway and Zald’s (2011) proposal to differentiate between motivational and consummatory types of anhedonia, and stresses the need to combine traditional self-report measures with behavioral measures or procedures. In time, this approach may lead to improved clinical assessment and treatment. In line with our reconceptualization, increasing evidence suggests that reward processing deficits are not restricted to impaired hedonic impact in major psychiatric disorders. Successful translations of animal models have led to strong evidence of impairments in the ability to pursue and learn about reward in psychiatric disorders such as major depressive disorder, schizophrenia, and addiction. It is of high importance that we continue to systematically target impairments in all phases of reward processing across disorders using behavioral testing in combination with neuroimaging techniques. This in turn has implications for diagnosis and treatment, and is essential for the purposes of identifying the underlying neurobiological mechanisms. Here I review recent progress in the development and application of behavioral procedures that measure subcomponents of anhedonia across relevant patient groups, and discuss methodological caveats as well as implications for assessment and treatment.

Reconceptualizing anhedonia: novel perspectives on balancing the pleasure networks in the human brain

Anhedonia, the lack of pleasure, has been shown to be a critical feature of a range of psychiatric disorders. Yet, it is currently measured primarily through subjective self-reports and as such has been difficult to submit to rigorous scientific analysis. New insights from affective neuroscience hold considerable promise in improving our understanding of anhedonia and for providing useful objective behavioral measures to complement traditional self-report measures, potentially leading to better diagnoses and novel treatments. Here, we review the state-of-the-art of hedonia research and specifically the established mechanisms of wanting, liking, and learning. Based on this framework we propose to conceptualize anhedonia as impairments in some or all of these processes, thereby departing from the longstanding view of anhedonia as solely reduced subjective experience of pleasure. We discuss how deficits in each of the reward components can lead to different expressions, or subtypes, of anhedonia affording novel ways of measurement. Specifically, we review evidence suggesting that patients suffering from depression and schizophrenia show impairments in wanting and learning, while some aspects of conscious liking seem surprisingly intact. Furthermore, the evidence suggests that anhedonia is heterogeneous across psychiatric disorders, depending on which parts of the pleasure networks are most affected. This in turn has implications for diagnosis and treatment of anhedonia.