Effects of acute tyrosine/phenylalanine depletion on the selective processing of smoking-related cues and the relative value of cigarettes in smokers

Cholinergic and dopaminergic-mediated motivated behavior in healthy states and in substance use and mood disorders

Acetylcholine is an important neuromodulator of the mesolimbic dopamine (DA) system, which itself is a mediator of motivated behavior. Motivated behavior can be described by two primary components, termed directional and activational motivation, both of which can be examined and dissociated using effort-choice tasks. The directional component refers to motivated behavior directed towards reinforcing stimuli and away from aversive stimuli. Behaviors characterized by increased vigor, persistence, and work output are considered to reflect activational components of motivation. Disruption of DA signaling has been shown to decrease activational components of motivation, while leaving directional features intact. Facilitation of DA release promotes the activational aspects of motivated behavior. In this review, we discuss cholinergic and DA regulation of motivated behaviors. We place emphasis on effort-choice processes and the ability of effort-choice tasks to examine and dissociate changes of motivated behavior in the context of substance use and mood disorders. Furthermore, we consider how altered cholinergic transmission impacts motivated behavior across disease states, and the possible role of cholinergic dysregulation in the etiology of these illnesses. Finally, we suggest that treatments targeting cholinergic activity may be useful in ameliorating motivational disruptions associated with substance use and comorbid substance use and mood disorders.

Acute depletion of dopamine precursors in the human brain: effects on functional connectivity and alcohol attentional bias

Individuals who abuse alcohol often show exaggerated attentional bias (AB) towards alcohol-related cues, which is thought to reflect reward conditioning processes. Rodent studies indicate that dopaminergic pathways play a key role in conditioned responses to reward- and alcohol-associated cues. However, investigation of the dopaminergic circuitry mediating this process in humans remains limited. We hypothesized that depletion of central dopamine levels in adult alcohol drinkers would attenuate AB and that these effects would be mediated by altered function in frontolimbic circuitry. Thirty-four male participants (22-38 years, including both social and heavy drinkers) underwent a two-session, placebo-controlled, double-blind dopamine precursor depletion procedure. At each visit, participants consumed either a balanced amino acid (control) beverage or an amino acid beverage lacking dopamine precursors (order counterbalanced), underwent resting-state fMRI, and completed behavioral testing on three AB tasks: an alcohol dot-probe task, an alcohol attentional blink task, and a task measuring AB to a reward-conditioned cue. Dopamine depletion significantly diminished AB in each behavioral task, with larger effects among subjects reporting higher levels of binge drinking. The depletion procedure significantly decreased resting-state functional connectivity among ventral tegmental area, striatum, amygdala, and prefrontal regions. Beverage-related AB decreases were mediated by decreases in functional connectivity between the fronto-insular cortex and striatum and, for alcohol AB only, between anterior cingulate cortex and amygdala. The results support a substantial role for dopamine in AB, and suggest specific dopamine-modulated functional connections between frontal, limbic, striatal, and brainstem regions mediate general reward AB versus alcohol AB.

Effects of acute distress and tobacco cues on tobacco demand

INTRODUCTION

Cigarette demand, or relative value, can be assessed via analysis of performance on a hypothetical behavioral economic cigarette purchase task (CPT). Substance purchase tasks are highly amenable to manipulation, namely, external stimuli, instructional changes, or acute stressors. In this regard, the current secondary analysis evaluates the role a novel, computerized stress induction paradigm, the Contextual-Frustration Intolerance Typing Task (C-FiTT), plays in eliciting varying levels of stress and resulting demand.

METHOD

Daily smokers (n = 484) completed the C-FiTT wherein they were randomly assigned to one of five distress conditions: combination of task difficulty (low or high difficulty) with neutral or withdrawal cues, and a neutral control group. Tobacco demand was assessed immediately following the distress task using the hypothetical CPT.

RESULTS

The C-FiTT distress-induction task significantly increased key cigarette demand indices, including price at maximum expenditure (Pmax) and first price where consumption was suppressed to zero (breakpoint). Moreover, demand increased with severity of C-FiTT condition, with the high-difficulty condition resulting in significantly higher breakpoint and Pmax, compared to other conditions. C-FiTT condition was not related to a significant increase in Omax, intensity, or elasticity.

DISCUSSION

The novel C-FiTT paradigm produced comparable effects on tobacco demand relative to in vivo withdrawal induction, indicating that the C-FiTT is a viable procedure by which to influence demand. Reduction of internal and external stressors may be effective in lowering motivation for tobacco. These results highlight the importance of state distress in tobacco demand, and offer a potential avenue for intervention.

The Effects of Anger on Alcohol Demand and Subjective Alcohol Craving

BACKGROUND

Anger and anger-related traits have been related to alcohol use in both cross-sectional and prospective studies. However, only a small number of studies have experimentally manipulated anger to examine whether the manipulation of anger influences alcohol craving or the relative reinforcing value of alcohol.

METHODS

Participants (N = 231) recruited through Amazon's MTurk were randomly assigned to a provocation condition or a neutral condition prior to completing both the Alcohol Purchase Task and a self-report measure of alcohol craving. Linear regression analyses were conducted to examine the effects of the anger induction, trait hostility, frequency of alcohol use in the past month, and relevant demographic characteristics (gender, age, income) on alcohol craving and indices of alcohol demand.

RESULTS

Participants assigned to the provocation condition had greater P_Max (B = 0.17, p = 0.012) and breakpoint (B = 0.18, p = 0.006) values, less elastic demand (B = -0.15, p = 0.020), and lower drinking intensity (B = -0.14, p = 0.025) than participants assigned to the neutral condition. Trait hostility was positively related to O_Max (B = 0.22, p = 0.001), intensity of demand (B = 0.27, p < 0.001), and subjective alcohol craving posttask (B = 0.32, p < 0.001), but did not moderate the relationship between condition and outcomes.

CONCLUSIONS

Although most persistence indices of alcohol demand were sensitive to the anger induction, we did not observe higher scores on amplitude indices or subjective craving in the provocation condition relative to the neutral condition. Further investigation into the role which anger plays in alcohol use is warranted.

Preliminary evidence for an association between intake of high-fat high-sugar diet, variations in peripheral dopamine precursor availability and dopamine-dependent cognition in humans

Obesity is associated with alterations in dopaminergic transmission and cognitive function. Rodent studies suggest that diets rich in saturated fat and refined sugars (HFS), as opposed to diets diets low in saturated fat and refined sugars (LFS), change the dopamine system independent of excessive body weight. However, the impact of HFS on the human brain has not been investigated. Here, we compared the effect of dietary dopamine depletion on dopamine-dependent cognitive task performance between two groups differing in habitual intake of dietary fat and sugar. Specifically, we used a double-blind within-subject cross-over design to compare the effect of acute phenylalanine/tyrosine depletion on a reinforcement learning and a working memory task, in two groups that are on opposite ends of the spectrum of self-reported HFS intake (low vs high intake: LFS vs HFS group). We tested 31 healthy young women matched for body mass index (mostly normal weight to overweight) and IQ. Depletion of peripheral precursors of dopamine reduced the working memory specific performance on the operation span task in the LFS, but not in the HFS group (P = 0.016). Learning from positive- and negative-reinforcement (probabilistic selection task) was increased in both diet groups after dopamine depletion (P = 0.049). As a secondary exploratory research question, we measured peripheral dopamine precursor availability (pDAP) at baseline as an estimate for central dopamine levels. The HFS group had a significantly higher pDAP at baseline compared to the LFS group (P = 0.025). Our data provide the first evidence indicating that the intake of HFS is associated with changes in dopamine precursor availability, which is suggestive of changes in central dopamine levels in humans. The observed associations are present in a sample of normal to overweight participants (ie, in the absence of obesity), suggesting that the consumption of a HFS might already be associated with altered behaviours. Alternatively, the effects of HFS diet and obesity might be independent.

Behavioral economic measurement of cigarette demand: A descriptive review of published approaches to the cigarette purchase task

The cigarette purchase task (CPT) is a behavioral economic method for assessing demand for cigarettes. Growing interest in behavioral correlates of tobacco use in clinical and general populations as well as empirical efforts to inform policy has seen an increase in published articles employing the CPT. Accordingly, an examination of the published methods and procedures for obtaining these behavioral economic metrics is timely. The purpose of this investigation was to provide a review of published approaches to using the CPT. We searched specific Boolean operators (["behavioral economic" AND "purchase task"] OR ["demand" AND "cigarette"]) and identified 49 empirical articles published through the year 2018 that reported administering a CPT. Articles were coded for participant characteristics (e.g., sample size, population type, age), CPT task structure (e.g., price framing, number and sequence of prices; vignettes, contextual factors), and data analytic approach (e.g., method of generating indices of cigarette demand). Results of this review indicate no standard approach to administering the CPT and underscore the need for replicability of these behavioral economic measures for the purpose of guiding clinical and policy decisions. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Experimental manipulations of behavioral economic demand for addictive commodities: a meta-analysis

BACKGROUND AND AIMS

Reinforcing value, an index of motivation for a drug, is commonly measured using behavioral economic purchase tasks. State-oriented purchase tasks are sensitive to phasic manipulations, but with heterogeneous methods and findings. The aim of this meta-analysis was to characterize the literature examining manipulations of reinforcing value, as measured by purchase tasks and multiple-choice procedures, to inform etiological models and treatment approaches METHODS: A random-effects meta-analysis of published findings in peer-reviewed articles. Following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) protocol, studies were gathered through searches in PsycINFO and PubMed/MEDLINE (published 22 May 2018). Searches returned 34 unique studies (aggregate sample n = 2402; average sample size = 68.94) yielding 126 effect sizes. Measurements included change (i.e. Cohen's d) in six behavioral economic indices (intensity, breakpoint, O_max , P_max , elasticity, cross-over point) in relation to six experimental manipulations (cue exposure, stress/negative affect, reinforcer magnitude, pharmacotherapy, behavioral interventions, opportunity cost).

RESULTS

Cue exposure (d range = 0.25-0.44, all Ps < 0.05) and reinforcer magnitude [d = 0.60; 95% confidence interval (CI) = 0.18, 1.01; P < 0.005] manipulations resulted in significant increases in behavioral economic demand across studies. Stress/negative affect manipulations also resulted in a small, significant increase in O_max (d = 0.18; 95% CI = 0.01, 0.34; P = 0.03); all other effect sizes for negative affect/stress were non-significant, albeit similar in size (d range = 0.14-0.18). In contrast, pharmacotherapy (d range = -0.37 to -0.49; Ps < 0.04), behavioral intervention (d = -0.36 to -1.13) and external contingency (d = -1.42; CI = -2.30, -0.54; P = 0.002) manipulations resulted in a significant decrease in intensity. Moderators (substance type) explained some of the heterogeneity in findings across meta-analyses.

CONCLUSIONS

In behavioral economic studies, purchase tasks and multiple-choice procedures appear to provide indices that are sensitive to manipulations found to influence motivation to consume addictive substances in field experiments.

From sign-tracking to attentional bias: Implications for gambling and substance use disorders

Sign-tracking behavior in Pavlovian autoshaping is known to be a relevant index of the incentive salience attributed to reward-related cues. Evidence has accumulated to suggest that animals that exhibit a sign-tracker phenotype are especially vulnerable to addiction and relapse due to their proneness to attribute incentive salience to drug cues, and their relatively weak cognitive and attentional control over their behavior. Interestingly, sign-tracking is also influenced by reward uncertainty in a way that may promote gambling disorder. Research indicates that reward uncertainty sensitizes sign-tracking responses and favors the development of a sign-tracker phenotype, compatible with the conditioned attractiveness of lights and sounds in casinos for problem gamblers. The study of attentional biases in humans (an effect akin to sign-tracking in animals) leads to similar observations, notably that the propensity to develop attraction for conditioned stimuli (CSs) is predictive of addictive behavior. Here we review the literature on drug addiction and gambling disorder, highlighting the similarities between studies of sign-tracking and attentional biases.

Behavioral economic tobacco demand in relation to cigarette consumption and nicotine dependence: a meta-analysis of cross-sectional relationships

BACKGROUND AND AIMS

A cigarette purchase task (CPT) aims to characterize individual variation in the reinforcing value of tobacco. This meta-analysis estimated the associations between cigarette demand, tobacco consumption and nicotine dependence using this task.

DESIGN

A meta-analysis of cross-sectional studies identified by PubMed and PsycINFO databases was conducted. Fixed- and random-effects models were used. The study also examined the model used to derive elasticity of demand (exponential or exponentiated) as a potential moderator. Publication bias was assessed using 'fail-safe N', Begg-Mazumdar test, Egger's test, Tweedie's trim-and-fill approach and meta-regression of publication year with effect size.

SETTING

Studies from any setting that reported coefficient correlations on the tested associations.

PARTICIPANTS

Daily cigarette users (i.e. 5 to 38 cigarettes per day; n = 7649).

MEASUREMENTS

Cigarette consumption, nicotine dependence and five tobacco demand indicators: intensity (i.e. consumption at no cost), elasticity (i.e. sensitivity to rises in costs), Omax (maximum expenditure), Pmax (i.e. price at which consumption becomes elastic) and breakpoint (i.e. price at which consumption ceases).

FINDINGS

Twenty-three studies met inclusion criteria. All the CPT indices were significantly correlated with smoking behavior (rs = 0.044-0.572, Ps = 0.012-10-8 ). Medium-to-large effect size associations were present for intensity, Omax, and elasticity, whereas small effects were obtained for breakpoint and Pmax . Evidence of a moderating effect of the different elasticity modeling approaches was not present. There was limited evidence of publication bias.

CONCLUSIONS

All five demand indices derived from the cigarette purchase task by (CPT) were robustly associated with cigarette consumption and tobacco dependence. Of the demand indices, maximum expenditure, intensity and elasticity exhibited the largest magnitude associations.

The Acute Effects of a Dopamine D3 Receptor Preferring Agonist on Motivation for Cigarettes in Dependent and Occasional Cigarette Smokers

Background

Dopaminergic functioning is thought to play critical roles in both motivation and addiction. There is preliminary evidence that dopamine agonists reduce the motivation for cigarettes in smokers. However, the effects of pramipexole, a dopamine D3 receptor preferring agonist, have not been investigated.

The aim of this study was to examine the effects of an acute dose of pramipexole on the motivation to earn cigarettes and nondrug rewards.

Methods

Twenty dependent and 20 occasional smokers received 0.5 mg pramipexole using a double-blind, placebo-controlled crossover design. Motivation for cigarettes and consummatory nondrug rewards was measured using the DReaM-Choice task, in which participants earned, and later “consumed,” cigarettes, music, and chocolate. Demand for cigarettes was measured using the Cigarette Purchase Task (CPT). Self-reported craving, withdrawal, and drug effects were also recorded.

Results

Dependent smokers chose (p < .001) and button-pressed for (p < .001) cigarettes more, and chose chocolate less (p < .001), than occasional smokers. Pramipexole did not affect the number of choices for or amount of button-pressing for any reward including cigarettes, which was supported by a Bayesian analysis. The dependent smokers had greater demand for cigarettes than occasional smokers across all CPT outcomes (ps < .021), apart from elasticity. Pramipexole did not affect demand for cigarettes, and this was supported by Bayesian analyses. Pramipexole produced greater subjective “feel drug” and “dislike drug” effects than placebo.

Conclusions

Dependent and occasional cigarette smokers differed in their motivation for cigarettes but not for the nondrug rewards. Pramipexole did not acutely alter motivation for cigarettes. These findings question the role of dopamine D3 receptors in cigarette-seeking behavior in dependent and occasional smokers.

Implications

This study adds to the growing literature about cigarette versus nondrug reward processing in nicotine dependence and the role of dopamine in cigarette-seeking behavior. Our results suggest nicotine dependence is associated with a hypersensitivity to cigarette rewards but not a hyposensitivity to nondrug rewards. Furthermore, our results question the importance of dopamine D3 receptors in motivational processing of cigarettes in occasional and dependent smokers.

Dopamine depletion effects on cognitive flexibility as modulated by tDCS of the dlPFC

BACKGROUND

Recent evidence suggests that transcranial direct current stimulation (tDCS) may interact with the dopaminergic system to affect cognitive flexibility. Objective/hypotheses: We examined whether putative reduction of dopamine levels through the acute phenylalanine/tyrosine depletion (APTD) procedure and excitatory anodal tDCS of the dorsolateral prefrontal cortex (dlPFC) are causally related to cognitive flexibility as measured by task switching and reversal learning.

METHOD

A double-blind, sham-controlled, randomised trial was conducted to test the effects of combining anodal tDCS and depletion of catecholaminergic precursor tyrosine on cognitive flexibility.

RESULTS

Anodal tDCS and tyrosine depletion had a significant effect on task switching, but not reversal learning. Whilst perseverative errors were significantly improved by anodal tDCS, the APTD impaired reaction times. Importantly, the combination of APTD and anodal tDCS resulted in cognitive performance which did not statistically differ to that of the control condition.

CONCLUSIONS

Our results suggest that the effects of tDCS on cognitive flexibility are modulated by dopaminergic tone.

Behavioral Economic Purchase Tasks to Estimate Demand for Novel Nicotine/tobacco Products and Prospectively Predict Future Use: Evidence From The Netherlands

INTRODUCTION

The demand for alternative nicotine/tobacco products is not well established. This paper uses a behavioral economic approach to test whether smokers have differential demand for conventional factory-made, electronic, and very low nicotine content cigarettes (FMCs/ECs/VLNCs) and uses the prospective cohort design to test the predictive validity of demand indices on subsequent use of commercially available FMCs and ECs.

METHODS

Daily smokers (≥16 years) from the Netherlands completed an online survey in April 2014 (N = 1215). Purchase tasks were completed for FMCs, ECs, and VLNCs. Participants indicated the number of cigarettes they would consume in 24 h, across a range of prices (0-30 euro). The relationship between consumption and price was quantified into four indices of demand (intensity, Pmax, breakpoint, and essential value). A follow-up survey in July 2015 measured FMC and EC use.

RESULTS

At baseline, greater demand was observed for FMCs relative to ECs and VLNCs across all demand indices, with no difference between ECs and VLNCs. At follow-up, greater baseline FMC demand (intensity, essential value) was associated with lower quit rates and higher relapse. EC demand (Pmax, breakpoint, essential value) was positively associated with any EC use between survey waves, past 30 day EC use, and EC purchase between waves.

CONCLUSIONS

Smokers valued FMCs more than ECs or VLNCs, and FMCs were less sensitive to price increases. Demand indices predicted use of commercially available products over a 15 month period. To serve as viable substitutes for FMCs, ECs and VLNCs will need to be priced lower than FMCs.

IMPLICATIONS

Purchase tasks can be adapted for novel nicotine/tobacco products as a means to efficiently quantify demand and predict use. Among current daily smokers, the demand for ECs and VLNCs is lower than FMCs.

Validation of a behavioral economic purchase task for assessing drug abuse liability

Behavioral economic purchase tasks quantify drug demand (i.e. reinforcing value of a drug) and have been used extensively to assess the value of various drugs among current users. However, purchase tasks have been rarely used with unfamiliar drugs to address a compound's abuse liability, and the current study sought to validate the paradigm in this capacity. Using a double-blind placebo-controlled within-subjects drug challenge design, the study evaluated differential drug demand on an experimental drug purchase task for a 20 mg dose of oral D-amphetamine (versus placebo), a prototypic psychostimulant, in 98 stimulant-naïve participants. Compared with placebo, amphetamine significantly increased intensity, breakpoint and O_max , and significantly decreased elasticity. Mechanistic analyses revealed that O_max and breakpoint mediated the relationship between subjective drug effects and 'willingness to take again', a putative indicator of liability via motivation for future drug-seeking behavior. These findings validate the purchase task paradigm for quantifying the reinforcing value and, in turn, abuse liability of unfamiliar compounds, providing a foundation for a variety of future applications.

Tobacco demand, delay discounting, and smoking topography among smokers with and without psychopathology

INTRODUCTION

Tobacco demand (i.e., relative value attributed to a given reinforcer) and delay discounting (i.e., relative preference for smaller immediate rewards over larger delayed rewards) are two behavioral economic processes that are linked to the progression of problematic substance use. These processes have not been studied among those with psychopathology, a vulnerable group of smokers. The current study examined differences in tobacco demand and delay discounting, and their association with smoking topography among smokers with (n=43) and without (n=64) past-year psychopathology.

METHOD

Adult daily smokers (n=107,Mage=43.5; SD=9.7) participated in a study on "smoking behavior." Past-year psychological disorders were assessed via a clinician-administered diagnostic assessment. All subjects participated in an ad libitum smoking trial and then completed an assessment of delay discounting (Monetary Choice Questionnaire) and tobacco demand (Cigarette Purchase Task) approximately 45-60min post-smoking.

RESULTS

Smokers with psychopathology, compared to those without, had significantly higher demand intensity and maximum expenditure on tobacco (Omax), but did not differ on other demand indices or delay discounting. Smokers with psychopathology had shorter average inter-puff intervals and shorter time to cigarette completion than smokers without psychopathology. Tobacco demand and delay discounting measures were significantly intercorrelated among smokers with psychopathology, but not those without. Both behavioral economic measures were associated with specific aspects of smoking topography in smokers with psychopathology.

DISCUSSION

The association between tobacco demand and delay discounting is evident among smokers with psychopathology and both measures were most consistently related to smoking behavior.

Psychopathology and tobacco demand

INTRODUCTION

Behavioral economic measurement of the relative value of tobacco (Cigarette Purchase Task; CPT) is used to examine individual differences in motivation for tobacco under certain contexts. Smokers with psychopathology, relative to those without, may demonstrate stronger demand for tobacco following a period of smoking deprivation, which could account for disparate rates of smoking and cessation among this subgroup.

METHOD

Participants (n=111) were community-recruited adult daily smokers who completed the CPT after a deprivation period of approximately 60min. Presence of psychopathology was assessed via clinical interview; 40.5% (n=45) of the sample met criteria for past-year psychological diagnosis. Specifically, 31.5% (n=35) had an emotional disorder (anxiety/depressive disorder), 17.1% (n=19) had a substance use disorder, and 19.1% of the sample had more than one disorder.

RESULTS

Smokers with any psychopathology showed significantly higher intensity (demand at unrestricted cost; $0) and O_max (peak expenditure for a drug) relative to smokers with no psychopathology. Intensity was significantly higher among smokers with an emotional disorder compared to those without. Smokers with a substance use disorder showed significantly higher intensity and O_max, and lower elasticity, reflecting greater insensitivity to price increases. Having≥2 disorders was associated with higher intensity relative to having 1 or no disorders.

DISCUSSION

Findings suggest that presence of psychopathology may be associated with greater and more persistent motivation to smoke. Future work is needed to explore the mechanism linking psychopathology to tobacco demand.

Further examination of the temporal stability of alcohol demand

Demand, or the amount of a substance consumed as a function of price, is a central dependent measure in behavioral economic research and represents the relative valuation of a substance. Although demand is often utilized as an index of substance use severity and is assumed to be relatively stable, recent experimental and clinical research has identified conditions in which demand can be manipulated, such as through craving and stress inductions, and treatment. Our study examines the 1-month reliability of the alcohol purchase task in a sample of heavy drinking college students. We also analyzed reliability in subgroup of individuals whose consumption decreased, increased, or stayed the same over the 1-month period, and in individuals with moderate/severe Alcohol Use Disorder (AUD) vs. those with no/mild AUD. Reliability was moderate in the full sample, high in the group with stable consumption, and did not differ appreciably between AUD groups. Observed indices and indices derived from an exponentiated equation (Koffarnus et al., 2015) were generally comparable, although P_max observed had very low reliability. Area under the curve, O_max derived, and essential value showed the greatest reliability in the full sample (rs=0.75-0.77). These results provide evidence for the relative stability over time of demand and across AUD groups, particularly in those whose consumption remains stable.

The Neuroeconomics of Tobacco Demand: An Initial Investigation of the Neural Correlates of Cigarette Cost-Benefit Decision Making in Male Smokers

How the brain processes cigarette cost-benefit decision making remains largely unknown. Using functional magnetic resonance imaging (fMRI), this study investigated the neural correlates of decisions for cigarettes (0–10 cigarettes) at varying levels of price during a Cigarette Purchase Task (CPT) in male regular smokers (N = 35). Differential neural activity was examined between choices classified as inelastic, elastic, and suppressed demand, operationalized as consumption unaffected by cost, partially suppressed by cost, and entirely suppressed by cost, respectively. Decisions reflecting elastic demand, putatively the most effortful decisions, elicited greater activation in regions associated with inhibition and planning (e.g., middle frontal gyrus and inferior frontal gyrus), craving and interoceptive processing (anterior insula), and conflict monitoring (e.g., anterior cingulate cortex). Exploratory examination in a harmonized dataset of both cigarette and alcohol demand (N = 59) suggested common neural activation patterns across commodities, particularly in the anterior insula, caudate, anterior cingulate, medial frontal gyrus, and dorsolateral prefrontal cortex. Collectively, these findings provide initial validation of a CPT fMRI paradigm; reveal the interplay of brain regions associated with executive functioning, incentive salience, and interoceptive processing in cigarette decision making; and add to the literature implicating the insula as a key brain region in addiction.

Individual and combined effects of cannabis and tobacco on drug reward processing in non-dependent users

RATIONALE

Cannabis and tobacco are often smoked simultaneously in joints, and this practice may increase the risks of developing tobacco and/or cannabis use disorders. Currently, there is no human experimental research on how these drugs interact on addiction-related measures.

OBJECTIVES

This study aimed to investigate how cannabis and tobacco, each alone and combined together in joints, affected individuals' demand for cannabis puffs and cigarettes, explicit liking of drug and non-drug-related stimuli and craving.

METHOD

A double-blind, 2 (active cannabis, placebo cannabis) × 2 (active tobacco, placebo tobacco) crossover design was used with 24 non-dependent cannabis and tobacco smokers. They completed a pleasantness rating task (PRT), a marijuana purchase task (MPT) and a cigarette purchase task (CPT) alongside measures of craving pre- and post-drug administration.

RESULTS

Relative to placebo cannabis, active cannabis reduced liking of cannabis-associated stimuli and increased response time to all stimuli except cigarette-related stimuli. Relative to placebo cannabis, active cannabis decreased demand for cannabis puffs (trends for breakpoint and elasticity) and cigarettes (breakpoint, P _max, O _max) on several characteristics of the purchase tasks. We found no evidence that active tobacco, both alone or combined with cannabis, had an effect on liking, demand or craving.

CONCLUSIONS

Acutely, cannabis reduced liking of cannabis-related stimuli and demand for cannabis itself. Acute cannabis also reduced demand for cigarettes on the CPT. Acute tobacco administration did not affect demand or pleasantness ratings for cigarettes themselves or cannabis. In non-dependent cannabis and tobacco co-users, tobacco did not influence the rewarding effects of cannabis.

Cue-elicited increases in incentive salience for marijuana: Craving, demand, and attentional bias

BACKGROUND

Incentive salience is a multidimensional construct that includes craving, drug value relative to other reinforcers, and implicit motivation such as attentional bias to drug cues. Laboratory cue reactivity (CR) paradigms have been used to evaluate marijuana incentive salience with measures of craving, but not with behavioral economic measures of marijuana demand or implicit attentional processing tasks.

METHODS

This within-subjects study used a new CR paradigm to examine multiple dimensions of marijuana's incentive salience and to compare CR-induced increases in craving and demand. Frequent marijuana users (N=93, 34% female) underwent exposure to neutral cues then to lit marijuana cigarettes. Craving, marijuana demand via a marijuana purchase task, and heart rate were assessed after each cue set. A modified Stroop task with cannabis and control words was completed after the marijuana cues as a measure of attentional bias.

RESULTS

Relative to neutral cues, marijuana cues significantly increased subjective craving and demand indices of intensity (i.e., drug consumed at $0) and Omax (i.e., peak drug expenditure). Elasticity significantly decreased following marijuana cues, reflecting sustained purchase despite price increases. Craving was correlated with demand indices (r's: 0.23-0.30). Marijuana users displayed significant attentional bias for cannabis-related words after marijuana cues. Cue-elicited increases in intensity were associated with greater attentional bias for marijuana words.

CONCLUSIONS

Greater incentive salience indexed by subjective, behavioral economic, and implicit measures was observed after marijuana versus neutral cues, supporting multidimensional assessment. The study highlights the utility of a behavioral economic approach in detecting cue-elicited changes in marijuana incentive salience.

Dopamine Depletion Reduces Food-Related Reward Activity Independent of BMI

Reward sensitivity and possible alterations in the dopaminergic-reward system are associated with obesity. We therefore aimed to investigate the influence of dopamine depletion on food-reward processing. We investigated 34 female subjects in a randomized placebo-controlled, within-subject design (body mass index (BMI)=27.0 kg/m(2) ±4.79 SD; age=28 years ±4.97 SD) using an acute phenylalanine/tyrosine depletion drink representing dopamine depletion and a balanced amino acid drink as the control condition. Brain activity was measured with functional magnetic resonance imaging during a 'wanting' and 'liking' rating of food items. Eating behavior-related traits and states were assessed on the basis of questionnaires. Dopamine depletion resulted in reduced activation in the striatum and higher activation in the superior frontal gyrus independent of BMI. Brain activity during the wanting task activated a more distributed network than during the liking task. This network included gustatory, memory, visual, reward, and frontal regions. An interaction effect of dopamine depletion and the wanting/liking task was observed in the hippocampus. The interaction with the covariate BMI was significant in motor and control regions but not in the striatum. Our results support the notion of altered brain activity in the reward and prefrontal network with blunted dopaminergic action during food-reward processing. This effect is, however, independent of BMI, which contradicts the reward-deficiency hypothesis. This hints to the hypothesis suggesting a different or more complex mechanism underlying the dopaminergic reward function in obesity.

Initial Development of a Brief Behavioral Economic Assessment of Alcohol Demand

Due to difficulties with definition and measurement, the role of conscious craving in substance use disorders remains contentious. To address this, behavioral economics is increasingly being used to quantify aspects of an individual's acute motivation to use a substance. Doing so typically involves the use of a purchase task, in which participants make choices about consuming alcohol or other substances at various prices and multiple indices of alcohol demand are generated. However, purchase tasks can be limited by the time required to administer and score them. In the current study, a brief 3-item measure, designed to capture three important indices of demand that are derived from demand curve modeling (intensity, O_max, and breakpoint), was investigated in a group of 84 heavy drinkers. Participants underwent a cue-reactivity paradigm that is established to increase both conscious craving and alcohol demand on traditional purchase tasks. All three indices of demand for alcohol measured using the abbreviated measure increased significantly in response to alcohol cues, analogous to what has been observed using a traditional purchase task. Additionally, the correlations between these indices and subjective craving were modest-to-moderate, as has been found in studies comparing craving to the indices derived from purchase tasks. These findings suggest that this abbreviated measure may be a useful and efficient way to capture important and distinct aspects of motivation for alcohol. If these results are confirmed, this measure may be able to help increase the portability of behavioral economic indices of demand into novel research and clinical contexts.

Dietary chromium supplementation for targeted treatment of diabetes patients with comorbid depression and binge eating

Dietary chromium supplementation for the treatment of diabetes remains controversial. The prevailing view that chromium supplementation for glucose regulation is unjustified has been based upon prior studies showing mixed, modest-sized effects in patients with type 2 diabetes (T2DM). Based on chromium's potential to improve insulin, dopamine, and serotonin function, we hypothesize that chromium has a greater glucoregulatory effect in individuals who have concurrent disturbances in dopamine and serotonin function--that is, complex patients with comorbid diabetes, depression, and binge eating. We propose, as suggested by the collective data to date, the need to go beyond the "one size fits all" approach to chromium supplementation and put forth a series of experiments designed to link physiological and neurobehavioral processes in the chromium response phenotype.

Using Behavior Economics to Understand Alcohol Use Disorders: A Concise Review and Identification of Research Priorities

We review recent advances in the application of behavioral economics to alcohol use disorders (AUDs). Specifically, we review individual differences in alcohol demand (i.e., the relative reinforcing value of alcohol) and delayed reward discounting (i.e., impulsive decision making) in relation to AUDs. Additionally, we review the efficacy of reinforcement-based clinical applications. What emerges from the literature is an extensive body of cross-sectional research implicating alcohol demand and delayed reward discounting with alcohol misuse. However, more research is needed to examine these domains across the lifespan in order to understand their longitudinal trajectories. Similarly, clinical research is consistently supportive of reinforcement-based clinical interventions, but the number of randomized controlled trials to date is relatively small and there has been limited examination of the putative mechanisms of behavior change.

Metabolome-wide association study of phenylalanine in plasma of common marmosets

Little systematic knowledge exists concerning the impacts of cumulative lifelong exposure, termed the exposome, on requirements for nutrients. Phenylalanine (Phe) is an essential dietary amino acid with an aromatic ring structure similar to endogenous metabolites, dietary compounds and environmental agents. Excess plasma Phe in genetic disease or nutritional deficiency of Phe has adverse health consequences. In principle, structurally similar chemicals interfering with Phe utilization could alter Phe requirement at an individual level. As a strategy to identify components of the exposome that could interfere with Phe utilization, we tested for metabolites correlating with Phe concentration in plasma of a non-human primate species, common marmosets (Callithrix jacchus). The results of tests for more than 5,000 chemical features detected by high-resolution metabolomics showed 17 positive correlations with Phe metabolites and other amino acids. Positive and negative correlations were also observed for 33 other chemicals, which included matches to endogenous metabolites and dietary, microbial and environmental chemicals in database searches. Chemical similarity analysis showed many of the matches had high structural similarity to Phe. Together, the results show that chemicals in marmoset plasma could impact Phe utilization. Such chemicals could contribute to early lifecycle developmental disorders when neurological development is vulnerable to Phe levels.

Pharmacological interventions to modulate attentional bias in addiction

Attentional bias in substance-dependent patients is the tendency to automatically direct attention to substance-related cues in the environment. Preclinical models suggest that attentional bias emerges as a consequence of dopaminergic activity evoked by substance-related cues. The aim of the current review is to describe pharmacological mechanisms underlying attentional bias in humans and to critically review empirical studies that aimed to modulate attentional bias in substance-dependent patients by using pharmacological agents. The findings of the reviewed studies suggest that attentional bias and related brain activation may be modulated by dopamine. All of the reviewed studies investigated acute effects of pharmacological agents, while measurements of chronic pharmacological treatments on attentional bias and clinically relevant measures such as relapse are yet lacking. Therefore, the current findings should be interpreted as a proof of principle concerning the role of dopamine in attentional bias. At the moment, there is too little evidence for clinical applications. While the literature search was not limited to dopamine, there is a lack of studies investigating the role of non-dopaminergic neurotransmitter systems in substance-related attentional bias. A focus on neurotransmitter systems such as acetylcholine and noradrenaline could provide new insights regarding the pharmacology of substance-related attentional bias.

Using a drug-word Stroop task to differentiate recreational from dependent drug use

Distinguishing dependent from recreational drug use can be a surprisingly difficult task, and the current means for identifying substance abuse can be inadequate or even misleading. In subjective self-reports, those who are most at risk may down play their consumption, not admitting to the full extent of their habit, and measures purely of quantity of use rarely capture the true nature of an individual's relationship to the drug, such as a psychological dependence on the substance. This trend is particularly true for heavy stimulant use, which is absent of the physical withdrawal symptoms that can help identify opiate or alcohol dependence. As such, a simple objective measure to help identify substance abuse, particularly in individuals who might not otherwise raise suspicion, would be a valuable tool in both clinical and experimental settings. We propose that the drug-word Stroop task, an objective assessment of attentional bias and distraction to salient drug-related stimuli, would be a valuable tool in helping to make these categorizations. This measure has been shown to correlate with drug craving, as well as to successfully distinguish dependent from recreational stimulant users and to help to predict outcomes in treatment-seeking individuals. Here, we survey prior literature on the drug-word Stroop task and provide a perspective on using the assessment as a potential diagnostic for drug use severity.

Tyrosine-free amino acid mixtures reduce physiologically-evoked release of dopamine in a selective and activity-dependent manner

Depletion of the catecholamine precursor tyrosine using tyrosine-free amino acid mixtures is an important tool in neuropsychological studies, and often considered dopamine selective on the basis of neuropharmacological studies. However, little is known of the effects of tyrosine depletion when catecholamine neurons are activated physiologically. Here we investigated the effect of tyrosine-free amino acid mixtures on catecholamine release evoked in vivo using a stimulation paradigm aimed to approximate the phasic firing pattern of these neurons that accompanies cognitive and behavioural change. Dopamine and noradrenaline release was monitored by microdialysis in rat medial prefrontal cortex (mPFC) and striatum (chloral hydrate anaesthesia, perfusion medium containing 1 µM cocaine). Electrical stimulation of the medial forebrain bundle (MFB) caused a short-lasting, frequency-dependent increase in dopamine and noradrenaline. A full tyrosine-free amino acid mixture reduced the release of dopamine in mPFC and striatum, across a range of stimulation frequencies, and the effect was greater as stimulation frequency increased. Similar results were obtained using a smaller tyrosine-free amino acid mixture. In the same experiments showing decreased dopamine, neither tyrosine-free mixture of amino acids significantly altered stimulation-evoked release of noradrenaline. These results show that tyrosine depletion using tyrosine-free amino acid mixtures causes a selective, activity-dependent decrease in dopamine release when dopamine neurons are driven physiologically.

Dopamine, urges to smoke, and the relative salience of drug versus non-drug reward

When addicted individuals are exposed to drug-related stimuli, dopamine release is thought to mediate incentive salience attribution, increasing attentional bias, craving and drug seeking. It is unclear whether dopamine acts specifically on drug cues versus other rewards, and if these effects correspond with craving and other forms of cognitive bias. Here, we administered the dopamine D2/D3 agonist pramipexole (0.5 mg) to 16 tobacco smokers in a double-blind placebo-controlled crossover design. Visual fixations on smoking and money images were recorded alongside smoking urges and fluency tasks. Pramipexole attenuated a marked bias in initial orienting towards smoking relative to money but did not alter a maintained attentional bias towards smoking. Pramipexole decreased urges to smoke retrospectively after the task but not on a state scale. Fewer smoking words were generated after pramipexole but phonological and semantic fluency were preserved. Although these treatment effects did not correlate with each other, changes in initial orienting towards smoking and money were inversely related to baseline scores. In conclusion, pramipexole can reduce the salience of an addictive drug compared with other rewards and elicit corresponding changes in smoking urges and cognitive bias. These reward-specific and baseline-dependent effects support an 'inverted-U' shaped profile of dopamine in addiction.

Effects of nicotine withdrawal on panic-like response to breath holding: a placebo-controlled, double-blind, crossover patch study

BACKGROUND

Cigarette smoking may increase the likelihood of developing panic disorder. Periods of nicotine withdrawal, in particular, may promote panic in individuals high in anxiety sensitivity. We examined the importance of nicotine withdrawal in the occurrence of smoking and panic.

METHODS

We utilized a placebo-controlled, double-blind, randomized, crossover design. Fifty smokers underwent a breath-holding (BH) challenge after the transdermal administration of nicotine on one test day and a placebo on another test day. Physiological and psychological variables were assessed at baseline as well as directly before and after the challenges.

RESULTS

Nicotine abstinence induced a decrease in heart rate and systolic blood pressure (BP) before the BH procedure (heart rate: 78.80 ± 11.43 under nicotine, 70.88 ± 10.83 under placebo; systolic BP: 124.90 ± 11.34 under nicotine, 121.18 ± 13.44 under placebo) and shorter BH duration relative to the nicotine patch condition. Nicotine abstinence did not, though, increase fear reactivity to the challenge.

CONCLUSIONS

The findings for heart rate and BP are consistent with the stimulant properties of nicotine. The reduced capacity to maintain apnea under placebo might be due to carbon dioxide (CO2 ) hypersensitivity during periods of nicotine abstinence. The negative findings regarding fear reactivity might be due to BH being a relatively weak anxiogen. Future researchers are encouraged to employ CO2 -inhalation procedures to study the relationship between nicotine withdrawal and panic.

Striatal ups and downs: their roles in vulnerability to addictions in humans

Susceptibility to addictive behaviors has been related to both increases and decreases in striatal function. Both profiles have been reported in humans as well as in animal models. Yet, the mechanisms underlying these opposing effects and the manner in which they relate to the behavioral development and expression of addiction remain unclear. In the present review of human studies, we describe a number of factors that could influence whether striatal hyper- or hypo-function is observed and propose a model that integrates the influence of these opposite responses on the expression of addiction related behaviors. Central to this model is the role played by the presence versus absence of addiction related cues and their ability to regulate responding to abused drugs and other rewards. Striatal function and incentive motivational states are increased in the presence of these cues and decreased in their absence. Alternations between these states might account for the progressive narrowing of interests as addictions develop and point to relevant processes to target in treatment.

Individual variation in resisting temptation: implications for addiction

When exposed to the sights, sounds, smells and/or places that have been associated with rewards, such as food or drugs, some individuals have difficulty resisting the temptation to seek out and consume them. Others have less difficulty restraining themselves. Thus, Pavlovian reward cues may motivate maladaptive patterns of behavior to a greater extent in some individuals than in others. We are just beginning to understand the factors underlying individual differences in the extent to which reward cues acquire powerful motivational properties, and therefore, the ability to act as incentive stimuli. Here we review converging evidence from studies in both human and non-human animals suggesting that a subset of individuals are more "cue reactive", in that certain reward cues are more likely to attract these individuals to them and motivate actions to get them. We suggest that those individuals for whom Pavlovian reward cues become especially powerful incentives may be more vulnerable to impulse control disorders, such as binge eating and addiction.

The effects of food-related attentional bias training on appetite and food intake

Obese and overweight individuals show a marked attentional bias to food cues. Food-related attentional bias may therefore play a causal role in over-eating. To test this possibility, the current study experimentally manipulated attentional bias towards food using a modified version of the visual probe task in which cake-stationery item image pairs were presented for 500 ms each. Participants (N=60) were either trained to attend to images of cake, trained to avoid images of cake, or assigned to a no-training control group. Hunger was measured before and after the training. Post-training, participants were given the opportunity to consume cake as well as a non-target food (crisps) that was not included in the training. There was weak evidence of an increase in attentional bias towards cake in the attend group only. We found no selective effects of the training on hunger or food intake, and little evidence for any gender differences. Our study suggests that attentional bias for food is particularly ingrained and difficult to modify. It also represents a first step towards elucidating the potential functional significance of food-related attentional biases and the lack of behavioural effects is broadly consistent with single-session attentional training studies from the addiction literature. An alternative hypothesis, that attentional bias represents a noncausal proxy for the motivational impact of appetitive stimuli, is considered.

Cue-evoked cocaine "craving": role of dopamine in the accumbens core

Drug-associated cues can acquire powerful motivational control over the behavior of addicts, and can contribute to relapse via multiple, dissociable mechanisms. Most preclinical models of relapse focus on only one of these mechanisms: the ability of drug cues to reinforce drug-seeking actions following a period of extinction training. However, in addicts, drug cues typically do not follow seeking actions; they precede them. They often produce relapse by evoking a conditioned motivational state ("wanting" or "craving") that instigates and/or invigorates drug-seeking behavior. Here we used a conflict-based relapse model to ask whether individual variation in the propensity to attribute incentive salience to reward cues predicts variation in the ability of a cocaine cue to produce conditioned motivation (craving) for cocaine. Following self-administration training, responding was curtailed by requiring rats to cross an electrified floor to take cocaine. The subsequent response-independent presentation of a cocaine-associated cue was sufficient to reinstate drug-seeking behavior, despite the continued presence of the adverse consequence. Importantly, there were large individual differences in the motivational properties of the cocaine cue, which were predicted by variation in the propensity to attribute incentive salience to a food cue. Finally, a dopamine antagonist injected into the nucleus accumbens core attenuated, and amphetamine facilitated, cue-evoked cocaine seeking, implicating dopamine signaling in cocaine cue-evoked craving. These data provide a promising preclinical approach for studying sources of individual variation in susceptibility to relapse due to conditioned craving and implicate mesolimbic dopamine in this process.

Brain activation associated with attentional bias in smokers is modulated by a dopamine antagonist

Attentional bias in substance-dependent individuals is the tendency to automatically direct the attention to substance-related cues in the environment. Attentional bias is known to be associated with clinical measures such as relapse or successful quitting in smokers. It has been suggested that attentional bias emerges as a consequence of dopaminergic activity evoked by substance-related cues. The current functional magnetic resonance imaging study employed a dopaminergic challenge in order to test whether brain activation associated with attentional bias in smokers could be modulated by a dopamine antagonist. A total of 25 smokers were compared with 24 controls. Participants were scanned twice while performing a pictorial attentional bias task. Haloperidol (2 mg), a selective D2/D3 dopamine antagonist, or placebo was orally administered 4 h before each scanning session in a double-blind randomized cross-over design. Imaging analyses were performed in a priori selected regions of interest. Results showed that smokers had enhanced brain activation compared with controls in the dorsal anterior cingulate cortex (dACC), right dorsolateral prefrontal cortex (r-DLPFC), and left superior parietal lobe (I-SPL) after placebo. Group × medication interactions were found in the dACC and r-DLPFC, with no differences between groups in these regions after haloperidol. The current findings suggest that a pharmacologically induced reduction in dopamine normalizes brain activation associated with attentional bias in the dACC and DLPFC in smokers, probably because salience of these cues is no longer detected when dopamine activity is reduced.

Understanding naltrexone mechanism of action and pharmacogenetics in Asian Americans via behavioral economics: a preliminary study

A behavioral economic approach to understanding the relative value of alcohol may be useful for advancing medication development for alcoholism. Naltrexone is a heavily researched and moderately effective treatment for alcohol dependence making it a good candidate for a proof-of-concept study of behavioral economics and alcoholism pharmacotherapy. This study examines naltrexone efficacy and pharmacogenetics in terms of the relative value of alcohol, assessed via demand curve analysis. Participants were 35 heavy drinking (AUDIT ≥8) Asian Americans. A within-subjects cross-over medication design was used along with an intravenous alcohol challenge completed after 4 days of both naltrexone and placebo. At baseline and BrAC = 0.06g/dl, participants completed an Alcohol Purchase Task, which assessed estimated alcohol consumption along escalating prices. Behavioral economic demand curve analysis yielded measures of intensity, elasticity, maximum expenditure (O(max)), proportionate price insensitivity (P(max)) and breakpoint. Compared to placebo, naltrexone significantly reduced intensity, O(max) and breakpoint. There were also trend-level medication effects on P(max). BrAC was associated with increases in P(max) and breakpoint. A significant naltrexone × OPRM1 genotype interaction was observed for intensity of demand. The present study extends the literature on naltrexone's mechanisms through the application of a novel behavioral economic paradigm. These results indicate that naltrexone reduces several indices of demand for alcohol. This preliminary report provides further evidence for the effectiveness of naltrexone and supports the utility of a behavioral economic approach to alcoholism pharmacotherapy development.

Behavioral economic analysis of withdrawal- and cue-elicited craving for tobacco: an initial investigation

INTRODUCTION

The role of craving in nicotine dependence remains controversial and may be a function of measurement challenges. The current study used behavioral economic approach to test the hypotheses that subjective craving from acute withdrawal and exposure to tobacco cues dynamically increases the relative value of cigarettes.

METHODS

Using a 2 (1-hr/12-hr deprivation) × 2 (neutral/tobacco cues) within-subjects design, 33 nicotine dependent adults completed 2 laboratory sessions. Assessment included subjective craving and behavioral economic indices of cigarette demand, namely Intensity (i.e., cigarette consumption at zero cost), O(max) (i.e., maximum total expenditure), Breakpoint (i.e., highest acceptable price for cigarettes), P(max) (i.e., price at which consumption becomes sensitive to price), and elasticity (i.e., price sensitivity). Behavioral economic indices were generated using a Cigarette Purchase Task in which participants selected between cigarettes for a subsequent 2-hr self-administration period and money.

RESULTS

Main effects of deprivation and tobacco cues were present for subjective craving and multiple behavioral economic indices of cigarette demand. Interestingly, deprivation significantly increased Breakpoint (p ≤ .01) and P(max) (p ≤ .05) and had trend-level effects on Intensity and O(max) (p ≤ .10); whereas cues significantly reduced elasticity (p ≤ .01), reflecting lower sensitivity to increasing prices. Heterogeneous associations were evident among the motivational variables but with aggregations suggesting variably overlapping motivational channels.

CONCLUSIONS

These findings further support a behavioral economic approach to craving and a multidimensional conception of acute motivation for addictive drugs. Methodological considerations, including potential order effects, and the need for further refinement of these findings are discussed.

Acute phenylalanine/tyrosine depletion reduces motivation to smoke cigarettes across stages of addiction

The neurobiology of tobacco use is poorly understood, possibly in part because the relevant mechanisms might differ depending on past nicotine exposure and degree of addiction. In the present study we investigated whether these factors might affect the role of dopamine (DA). Using the acute phenylalanine/tyrosine depletion method (APTD), DA synthesis was transiently decreased in three groups of abstinent smokers (n=47): (1) early low-frequency smokers, who had smoked a maximum of five cigarettes per day for less than one year, (2) stable low-frequency smokers smoking at the same level as early low-frequency smokers for at least 3 years, and (3) stable high-frequency smokers, who smoked a minimum of 10 or more cigarettes per day for at least 5 years. Motivation to obtain tobacco was measured using a progressive ratio breakpoint schedule for nicotine-containing and de-nicotinized cigarettes. Compared with a nutritionally balanced control mixture, APTD decreased the self-administration of nicotine-containing cigarettes, and this occurred in all three groups of smokers. The results suggest that DA influenced the willingness to sustain effort for nicotine reward, and this was seen in participants at all three levels of cigarette addiction. In the transition from sporadic to addicted use, the role of DA in the motivation to seek drug may change less than previously proposed.

Is talk "cheap"? An initial investigation of the equivalence of alcohol purchase task performance for hypothetical and actual rewards

BACKGROUND

Behavioral economic alcohol purchase tasks (APTs) are self-report measures of alcohol demand that assess estimated consumption at escalating levels of price. However, the relationship between estimated performance for hypothetical outcomes and choices for actual outcomes has not been determined. The present study examined both the correspondence between choices for hypothetical and actual outcomes, and the correspondence between estimated alcohol consumption and actual drinking behavior. A collateral goal of the study was to examine the effects of alcohol cues on APT performance.

METHODS

Forty-one heavy-drinking adults (56% men) participated in a human laboratory protocol comprising APTs for hypothetical and actual alcohol and money, an alcohol cue reactivity paradigm, an alcohol self-administration period, and a recovery period.

RESULTS

Pearson correlations revealed very high correspondence between APT performance for hypothetical and actual alcohol (ps < 0.001). Estimated consumption on the APT was similarly strongly associated with actual consumption during the self-administration period (r = 0.87, p < 0.001). Exposure to alcohol cues significantly increased subjective craving and arousal and had a trend-level effect on intensity of demand, in spite of notable ceiling effects. Associations among motivational indices were highly variable, suggesting multidimensionality.

CONCLUSIONS

These results suggest there may be close correspondence both between value preferences for hypothetical alcohol and actual alcohol, and between estimated consumption and actual consumption. Methodological considerations and priorities for future studies are discussed.

Cigarette demand and delayed reward discounting in nicotine-dependent individuals with schizophrenia and controls: an initial study

RATIONALE

The high prevalence of smoking and low cessation rates among individuals with schizophrenia and similar conditions are not well understood. Behavioral economics has been extensively applied to studying addictive behavior and may contribute to understanding smoking in this subpopulation.

OBJECTIVES

This study compared smokers with schizophrenia or schizoaffective disorder (SS) and control smokers (CS) on indices of cigarette demand and delayed reward discounting, a behavioral economic index of impulsivity.

MATERIALS AND METHODS

The SS (n=25) and CS (n=24) groups participated in two sessions approximately 1 week apart. During the first session, delay discounting was assessed using the Monetary Choice Questionnaire. During the second session, participants smoked their usual brand ad libitum through a smoking topography assessment device, after which cigarette demand was assessed using a cigarette purchase task. Primary comparisons were of the hyperbolic discounting function, k, and indices of cigarette demand.

RESULTS

Compared to the CS group, the SS group exhibited significantly higher intensity of demand, and significantly greater consumption and expenditure across the inelastic portion of the demand curve, but no differences were evident on the other demand indices. No differences were evident for delay discounting. The SS group also exhibited heavier smoking topography and two indices of smoking topography were significantly correlated with demand.

CONCLUSIONS

These results provide further evidence of higher incentive value of cigarettes among SS individuals, but not greater impulsivity, as measured by discounting. Considerations include potentially important methodological factors and the role of satiation/withdrawal.

Influence of compulsivity of drug abuse on dopaminergic modulation of attentional bias in stimulant dependence

CONTEXT

There are no effective pharmacotherapies for stimulant dependence but there are many plausible targets for development of novel therapeutics. We hypothesized that dopamine-related targets are relevant for treatment of stimulant dependence, and there will likely be individual differences in response to dopaminergic challenges.

OBJECTIVE

To measure behavioral and brain functional markers of drug-related attentional bias in stimulant-dependent individuals studied repeatedly after short-term dosing with dopamine D(2)/D(3) receptor antagonist and agonist challenges.

DESIGN

Randomized, double-blind, placebo-controlled, parallel-groups, crossover design using pharmacological functional magnetic resonance imaging.

SETTING

Clinical research unit (GlaxoSmithKline) and local community in Cambridge, England.

PARTICIPANTS

Stimulant-dependent individuals (n = 18) and healthy volunteers (n = 18).

INTERVENTIONS

Amisulpride (400 mg), pramipexole dihydrochloride (0.5 mg), or placebo were administered in counterbalanced order at each of 3 repeated testing sessions.

MAIN OUTCOME MEASURES

Attentional bias for stimulant-related words was measured during functional magnetic resonance imaging by a drug-word Stroop paradigm; trait impulsivity and compulsivity of dependence were assessed at baseline by questionnaire.

RESULTS

Drug users demonstrated significant attentional bias for drug-related words, which was correlated with greater activation of the left prefrontal and right cerebellar cortex. Attentional bias was greater in people with highly compulsive patterns of stimulant abuse; the effects of dopaminergic challenges on attentional interference and related frontocerebellar activation were different between high- and low-compulsivity subgroups.

CONCLUSIONS

Greater attentional bias for and greater prefrontal activation by stimulant-related words constitute a candidate neurocognitive marker for dependence. Individual differences in compulsivity of stimulant dependence had significant effects on attentional bias, its brain functional representation, and its short-term modulation by dopaminergic challenges.

Effects of bupropion on simulated demand for cigarettes and the subjective effects of smoking

INTRODUCTION

The biobehavioral mechanism(s) mediating bupropion's efficacy are not well understood. Behavioral economic measures such as demand curves have proven useful in investigations of the reinforcing effects of drugs of abuse. Behavioral economic measures may also be used to measure the effect of pharmacotherapies on the reinforcing effects of drugs of abuse.

METHODS

The effects of bupropion on simulated demand for cigarettes were investigated in a placebo-controlled double-blind clinical trial. Participants reported the number of cigarettes they would purchase and consume in a single day at a range of prices. The effects of medication on the subjective effects of smoking were also explored.

RESULTS

Demand for cigarettes was well described by an exponential demand equation. Bupropion did not significantly decrease the maximum number of cigarettes that participants said they would smoke in a single day nor did it significantly alter the relation between price per cigarette and demand. Baseline demand elasticity did not predict smoking cessation, but changes in elasticity following 1 week of treatment did. Medication group had no effect on any subjective effects of smoking.

DISCUSSION

Bupropion had no significant effects on demand for cigarettes. The exponential demand equation, recently introduced in behavioral economics, proved amenable to human simulated demand and might be usefully employed in other pharmacotherapy studies as it provides a potentially useful measure of changes in the essential value of the drug as a reinforcer. Such changes may be useful in predicting the efficacy of medications designed to reduce drug consumption.

Measuring smoking-related preoccupation and compulsive drive: evaluation of the obsessive compulsive smoking scale

RATIONALE

Tobacco use for many people is compulsive in nature. Compelling theories of how smoking becomes compulsive exist but are largely based on extrapolation from neuroscience findings. Research on smokers is impeded, in part, by a lack of instruments that specifically measure compulsive smoking.

OBJECTIVE

This study evaluated the measurement structure and validity of the Obsessive Compulsive Smoking Scale (OCSS), a ten-item questionnaire designed to measure compulsive smoking.

METHODS

Participants were 239 daily smokers (>/=1 cigarette/day), including 142 students at a public university in Chicago and 97 veterans treated at the VA Boston Healthcare System. The OCSS and questionnaires measuring current and past smoking, cigarette craving, automatic smoking, and nicotine dependence were administered.

RESULTS

Factor analysis with maximum likelihood extraction and oblique rotation revealed two correlated underlying factors, interpreted as "Preoccupation with Smoking" and "Compulsive Drive." The measurement structure was consistent across students and veterans, and confirmed in an independent sample of adults (n = 95). Veterans exhibited higher OCSS scores (full scale and subscales) than students. Across groups, higher OCSS scores were positively correlated with smoking intensity, craving, and nicotine dependence. OCSS full-scale and compulsive drive scores, but not smoking preoccupation scores, were inversely correlated with past month smoking reduction and minutes since last cigarette.

CONCLUSIONS

The OCSS is a valid and reliable inventory for measuring the degree to which daily smokers are preoccupied with smoking and engage in compulsive tobacco use, and may be useful for advancing understanding of core smoking phenotypes or for tailoring cessation therapies.

Does smoking cue-induced craving tell us anything important about nicotine dependence?

Cue-reactivity, or self-reported craving response to drug-associated stimuli, is an active area of research on factors that maintain drug use, particularly cigarette smoking. A common rationale for this research is the expectation that treatments that extinguish cue-induced craving will be effective as smoking cessation interventions. Therefore, the importance of research on the variables that moderate and control cue-induced craving would seem to hinge upon the relevance of cue-induced craving to nicotine dependence, particularly its association with relapse risk. However, the limited relevant clinical research has not demonstrated clearly a link between smoking relapse risk and self-reported craving in response to smoking cues. Links between relapse and other responses to cues, such as heart rate or electrodermal activity, are inconsistent or not significant. The Food and Drug Administration (FDA)-approved smoking cessation medications have not been shown to alleviate cue-induced craving, although they do alleviate abstinence-induced craving, which has been associated with relapse risk. Nevertheless, other acute measures assessed in the laboratory have been shown to predict subsequent relapse risk in quitting smokers, demonstrating the feasibility of this type of study. Future research may benefit from using more reliable and valid multi-item craving measures, focusing upon more specific conditions under which cue-induced craving may predict relapse and, most importantly, considering dependent measures other than self-reported craving in response to cues, particularly actual smoking behavior. Without stronger evidence in support of the relevance of cue-induced craving response to the persistence of smoking behavior or other measures of dependence, it will be incumbent upon researchers in this area to justify why studies of cue-induced craving contribute to our understanding of dependence.

A meta-analytic investigation of the relationship between attentional bias and subjective craving in substance abuse

Theoretical models of addiction suggest that attentional bias for substance-related cues should be associated with self-reported craving. The authors evaluated the strength of the association by performing a meta-analysis on 68 independent data sets from which correlation coefficients between subjective craving and attentional bias indices were derived. Additional stratified analyses were conducted to identify any variables that might moderate the association between craving and attentional bias. The primary meta-analysis indicated a significant, albeit weak (r=.19), association between attentional bias and craving. Stratified analyses revealed that the association was larger for illicit drug and caffeine craving than for alcohol and tobacco craving, larger for direct measures of attention (eye movement measures and event-related potential measures) than for indirect behavioral measures of attentional bias, and larger when craving strength was high than when it was low (all ps<.05). The size of the correlation did not differ among patients in treatment and individuals who were not seeking treatment. These results suggest that attentional bias and craving are related phenomena, although the relationship is generally modest and appears to be moderated by various factors. Theoretical implications are discussed.

The role of attentional bias in mediating human drug-seeking behaviour

RATIONALE

The attentional bias for drug cues is believed to be a causal cognitive process mediating human drug seeking and relapse.

OBJECTIVES, METHODS AND RESULTS

To test this claim, we trained smokers on a tobacco conditioning procedure in which the conditioned stimulus (or S+) acquired parallel control of an attentional bias (measured with an eye tracker), tobacco expectancy and instrumental tobacco-seeking behaviour. Although this correlation between measures may be regarded as consistent with the claim that the attentional bias for the S+ mediated tobacco seeking, when a secondary task was added in the test phase, the attentional bias for the S+ was abolished, yet the control of tobacco expectancy and tobacco seeking remained intact.

CONCLUSIONS

This dissociation suggests that the attentional bias for drug cues is not necessary for the control that drug cues exert over drug-seeking behaviour. The question raised by these data is what function does the attentional bias serve if it does not mediate drug seeking?