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Dopamine depletion effects on cognitive flexibility as modulated by tDCS of the dlPFC. Brain Stimul 2019; 13:105-108. [PMID: 31494070 DOI: 10.1016/j.brs.2019.08.016] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2019] [Revised: 08/27/2019] [Accepted: 08/28/2019] [Indexed: 01/27/2023] Open
Abstract
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.
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Hellberg SN, Russell TI, Robinson MJF. 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. COGNITIVE, AFFECTIVE & BEHAVIORAL NEUROSCIENCE 2019; 19:737-758. [PMID: 30357661 PMCID: PMC6482104 DOI: 10.3758/s13415-018-00662-3] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
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.
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Affiliation(s)
- Samantha N Hellberg
- Psychology Department and the Neuroscience and Behavior Program, Wesleyan University, 207 High Street, Middletown, CT, 06457, USA
- University of North Carolina Chapel Hill, Chapel Hill, NC, USA
| | - Trinity I Russell
- Psychology Department and the Neuroscience and Behavior Program, Wesleyan University, 207 High Street, Middletown, CT, 06457, USA
- National Institutes on Drug Abuse, Baltimore, MD, USA
| | - Mike J F Robinson
- Psychology Department and the Neuroscience and Behavior Program, Wesleyan University, 207 High Street, Middletown, CT, 06457, USA.
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Dopamine Depletion Reduces Food-Related Reward Activity Independent of BMI. Neuropsychopharmacology 2016; 41:1551-9. [PMID: 26450814 PMCID: PMC4832016 DOI: 10.1038/npp.2015.313] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/03/2015] [Revised: 09/02/2015] [Accepted: 09/21/2015] [Indexed: 01/09/2023]
Abstract
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.
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Robinson MJF, Fischer AM, Ahuja A, Lesser EN, Maniates H. Roles of "Wanting" and "Liking" in Motivating Behavior: Gambling, Food, and Drug Addictions. Curr Top Behav Neurosci 2016; 27:105-136. [PMID: 26407959 DOI: 10.1007/7854_2015_387] [Citation(s) in RCA: 92] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
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.
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Affiliation(s)
- M J F Robinson
- Department of Psychology, Wesleyan University, 207 High Street, Judd Hall, Middletown, CT, 06459, USA.
| | - A M Fischer
- Department of Psychology, Wesleyan University, 207 High Street, Judd Hall, Middletown, CT, 06459, USA
| | - A Ahuja
- Department of Psychology, Wesleyan University, 207 High Street, Judd Hall, Middletown, CT, 06459, USA
| | - E N Lesser
- Department of Psychology, Wesleyan University, 207 High Street, Judd Hall, Middletown, CT, 06459, USA
| | - H Maniates
- Department of Psychology, Wesleyan University, 207 High Street, Judd Hall, Middletown, CT, 06459, USA
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5
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Abstract
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.
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Freeman TP, Das RK, Kamboj SK, Curran HV. Dopamine, urges to smoke, and the relative salience of drug versus non-drug reward. Soc Cogn Affect Neurosci 2014; 10:85-92. [PMID: 24526184 DOI: 10.1093/scan/nsu026] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
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.
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Affiliation(s)
- Tom P Freeman
- Clinical Psychopharmacology Unit, University College London, Gower St, London WC1E 6BT, United Kingdom
| | - Ravi K Das
- Clinical Psychopharmacology Unit, University College London, Gower St, London WC1E 6BT, United Kingdom
| | - Sunjeev K Kamboj
- Clinical Psychopharmacology Unit, University College London, Gower St, London WC1E 6BT, United Kingdom
| | - H Valerie Curran
- Clinical Psychopharmacology Unit, University College London, Gower St, London WC1E 6BT, United Kingdom
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Leyton M, Vezina P. Striatal ups and downs: their roles in vulnerability to addictions in humans. Neurosci Biobehav Rev 2013; 37:1999-2014. [PMID: 23333263 PMCID: PMC3743927 DOI: 10.1016/j.neubiorev.2013.01.018] [Citation(s) in RCA: 135] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2012] [Revised: 01/03/2013] [Accepted: 01/07/2013] [Indexed: 01/05/2023]
Abstract
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.
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Affiliation(s)
- Marco Leyton
- Department of Psychiatry, McGill University, 1033 Pine Avenue West, Montreal, Quebec, H3A 1A1 Canada.
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Saunders BT, Robinson TE. Individual variation in resisting temptation: implications for addiction. Neurosci Biobehav Rev 2013; 37:1955-75. [PMID: 23438893 PMCID: PMC3732519 DOI: 10.1016/j.neubiorev.2013.02.008] [Citation(s) in RCA: 114] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2012] [Revised: 01/28/2013] [Accepted: 02/12/2013] [Indexed: 11/29/2022]
Abstract
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.
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Affiliation(s)
| | - Terry E. Robinson
- Department of Psychology (Biopsychology Program), University of Michigan
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Hardman CA, Rogers PJ, Etchells KA, Houstoun KVE, Munafò MR. The effects of food-related attentional bias training on appetite and food intake. Appetite 2013; 71:295-300. [PMID: 24025548 DOI: 10.1016/j.appet.2013.08.021] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2013] [Revised: 07/31/2013] [Accepted: 08/30/2013] [Indexed: 11/17/2022]
Abstract
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.
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Affiliation(s)
- Charlotte A Hardman
- Nutrition and Behaviour Unit, School of Experimental Psychology, University of Bristol, UK; Department of Psychological Sciences, University of Liverpool, Eleanor Rathbone Building, Bedford Street South, Liverpool L69 7ZA, UK.
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10
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Saunders BT, Yager LM, Robinson TE. Cue-evoked cocaine "craving": role of dopamine in the accumbens core. J Neurosci 2013; 33:13989-4000. [PMID: 23986236 PMCID: PMC3756749 DOI: 10.1523/jneurosci.0450-13.2013] [Citation(s) in RCA: 110] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2013] [Revised: 07/02/2013] [Accepted: 07/20/2013] [Indexed: 11/21/2022] Open
Abstract
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.
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Affiliation(s)
- Benjamin T. Saunders
- Biopsychology Program, Department of Psychology, University of Michigan, Ann Arbor, Michigan 48109
| | - Lindsay M. Yager
- Biopsychology Program, Department of Psychology, University of Michigan, Ann Arbor, Michigan 48109
| | - Terry E. Robinson
- Biopsychology Program, Department of Psychology, University of Michigan, Ann Arbor, Michigan 48109
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Luijten M, Veltman DJ, Hester R, Smits M, Pepplinkhuizen L, Franken IHA. Brain activation associated with attentional bias in smokers is modulated by a dopamine antagonist. Neuropsychopharmacology 2012; 37:2772-9. [PMID: 22850734 PMCID: PMC3499728 DOI: 10.1038/npp.2012.143] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
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.
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Affiliation(s)
- Maartje Luijten
- Institute of Psychology, Erasmus University Rotterdam, Rotterdam, The Netherlands.
| | - Dick J Veltman
- Department of Psychiatry, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands,Department of Psychiatry, VU University Medical Center, Amsterdam, The Netherlands
| | - Robert Hester
- Department of Psychological Sciences, University of Melbourne, Melbourne, Victoria, Australia
| | - Marion Smits
- Department of Radiology, Erasmus MC—University Medical Center Rotterdam, Rotterdam, The Netherlands
| | | | - Ingmar H A Franken
- Institute of Psychology, Erasmus University Rotterdam, Rotterdam, The Netherlands,Department of Child and Adolescent Psychiatry, Erasmus MC—Sophia Children's Hospital, University Medical Center Rotterdam, Rotterdam, The Netherlands
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Dopamine and food reward: Effects of acute tyrosine/phenylalanine depletion on appetite. Physiol Behav 2012; 105:1202-7. [DOI: 10.1016/j.physbeh.2011.12.022] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2011] [Accepted: 12/20/2011] [Indexed: 01/03/2023]
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de Wit S, Standing HR, Devito EE, Robinson OJ, Ridderinkhof KR, Robbins TW, Sahakian BJ. Reliance on habits at the expense of goal-directed control following dopamine precursor depletion. Psychopharmacology (Berl) 2012; 219:621-31. [PMID: 22134475 PMCID: PMC3249188 DOI: 10.1007/s00213-011-2563-2] [Citation(s) in RCA: 81] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/16/2011] [Accepted: 10/28/2011] [Indexed: 12/03/2022]
Abstract
RATIONALE Dopamine is well known to play an important role in learning and motivation. Recent animal studies have implicated dopamine in the reinforcement of stimulus-response habits, as well as in flexible, goal-directed action. However, the role of dopamine in human action control is still not well understood. OBJECTIVES We present the first investigation of the effect of reducing dopamine function in healthy volunteers on the balance between habitual and goal-directed action control. METHODS The dietary intervention of acute dietary phenylalanine and tyrosine depletion (APTD) was adopted to study the effects of reduced global dopamine function on action control. Participants were randomly assigned to either the APTD or placebo group (ns = 14) to allow for a between-subjects comparison of performance on a novel three-stage experimental paradigm. In the initial learning phase, participants learned to respond to different stimuli in order to gain rewarding outcomes. Subsequently, an outcome-devaluation test and a slips-of-action test were conducted to assess whether participants were able to flexibly adjust their behaviour to changes in the desirability of the outcomes. RESULTS APTD did not prevent stimulus-response learning, nor did we find evidence for impaired response-outcome learning in the subsequent outcome-devaluation test. However, when goal-directed and habitual systems competed for control in the slips-of-action test, APTD tipped the balance towards habitual control. These findings were restricted to female volunteers. CONCLUSIONS We provide direct evidence that the balance between goal-directed and habitual control in humans is dopamine dependent. The results are discussed in light of gender differences in dopamine function and psychopathologies.
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Affiliation(s)
- Sanne de Wit
- Behavioral and Clinical Neuroscience Institute, University of Cambridge, Cambridge, UK.
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Badawy AAB, Dougherty DM, Richard DM. Specificity of the acute tryptophan and tyrosine plus phenylalanine depletion and loading tests I. Review of biochemical aspects and poor specificity of current amino Acid formulations. Int J Tryptophan Res 2011; 2010:23-34. [PMID: 20676231 PMCID: PMC2911801 DOI: 10.4137/ijtr.s5134] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
The acute tryptophan or tyrosine plus phenylalanine depletion and loading tests are powerful tools for studying the roles of serotonin, dopamine and noradrenaline in normal subjects and those with behavioural disorders. The current amino acid formulations for these tests, however, are associated with undesirable decreases in ratios of tryptophan or tyrosine plus phenylalanine to competing amino acids resulting in loss of specificity. This could confound biochemical and behavioural findings. Compositions of current formulations are reviewed, the biochemical principles underpinning the tests are revisited and examples of unintended changes in the above ratios and their impact on monoamine function and behaviour will be demonstrated from data in the literature. The presence of excessive amounts of the 3 branched-chain amino acids Leu, Ile and Val is responsible for these unintended decreases and the consequent loss of specificity. Strategies for enhancing the specificity of the different formulations are proposed.
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Venugopalan VV, Casey KF, O'Hara C, O'Loughlin J, Benkelfat C, Fellows LK, Leyton M. Acute phenylalanine/tyrosine depletion reduces motivation to smoke cigarettes across stages of addiction. Neuropsychopharmacology 2011; 36:2469-76. [PMID: 21775977 PMCID: PMC3194074 DOI: 10.1038/npp.2011.135] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
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.
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Ersche KD, Bullmore ET, Craig KJ, Shabbir SS, Abbott S, Müller U, Ooi C, Suckling J, Barnes A, Sahakian BJ, Merlo-Pich EV, Robbins TW. Influence of compulsivity of drug abuse on dopaminergic modulation of attentional bias in stimulant dependence. ARCHIVES OF GENERAL PSYCHIATRY 2010; 67:632-44. [PMID: 20530013 PMCID: PMC3664786 DOI: 10.1001/archgenpsychiatry.2010.60] [Citation(s) in RCA: 90] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
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.
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Affiliation(s)
- Karen D Ersche
- University of Cambridge, Behavioural and Clinical Neuroscience Institute, Department of Psychiatry, Cambridge, England.
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Bongiovanni R, Kirkbride B, Newbould E, Durkalski V, Jaskiw GE. Relationships between large neutral amino acid levels in plasma, cerebrospinal fluid, brain microdialysate and brain tissue in the rat. Brain Res 2010; 1334:45-57. [DOI: 10.1016/j.brainres.2010.03.111] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2009] [Revised: 03/29/2010] [Accepted: 03/31/2010] [Indexed: 11/30/2022]
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Field M, Munafò MR, Franken IHA. A meta-analytic investigation of the relationship between attentional bias and subjective craving in substance abuse. Psychol Bull 2009; 135:589-607. [PMID: 19586163 DOI: 10.1037/a0015843] [Citation(s) in RCA: 383] [Impact Index Per Article: 25.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
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.
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Affiliation(s)
- Matt Field
- School of Psychology, University of Liverpool, Liverpool, UK.
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Hitsman B, MacKillop J, Lingford-Hughes A, Williams TM, Ahmad F, Adams S, Nutt DJ, Munafò MR. Effects of acute tyrosine/phenylalanine depletion on the selective processing of smoking-related cues and the relative value of cigarettes in smokers. Psychopharmacology (Berl) 2008; 196:611-21. [PMID: 18038222 DOI: 10.1007/s00213-007-0995-5] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/16/2007] [Accepted: 10/18/2007] [Indexed: 11/28/2022]
Abstract
RATIONALE Acute tyrosine/phenylalanine depletion (ATPD) is a validated neurobiological challenge that results in reduced dopaminergic neurotransmission, allowing examination of the effects of a hypodopaminergic state on craving-related processes. OBJECTIVES We studied 16 nonabstaining smokers (>10 cigarettes/day; 9 males; age 20-33 years) to whom was administered a tyrosine/phenylalanine-free mixture (TYR/PHE-free) and a balanced amino acid mixture (BAL) in a double-blind, counterbalanced, crossover design. METHODS Subjective cigarette craving, attentional bias to smoking-related word cues, relative value of cigarettes, negative mood, and expired carbon monoxide (CO) levels were measured at various timepoints through 300 min. Participants smoked at hourly intervals to prevent acute nicotine withdrawal during testing. RESULTS The TYR/PHE-free mixture, as compared to the BAL mixture, was associated with a greater increase in CO levels from baseline (p = 0.01). Adjusting for the potential confounding influence of between-condition differences in CO levels across time, TYR/PHE-free mixture was associated with increased demand for cigarettes (p = 0.01) and decreased attentional bias toward smoking-related words (p = 0.003). There were no significant differences between conditions in either subjective craving or depressed or anxious mood (p values > 0.05). CONCLUSION Among nonabstaining daily smokers, acute dopaminergic depletion via ATPD may influence smoking behavior and indices of smoking-related motivation, such as attentional bias to smoking cues and relative cigarette value, which are not readily captured by subjective craving.
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Affiliation(s)
- Brian Hitsman
- Centers for Behavioral and Preventive Medicine, The Miriam Hospital and Brown Medical School, Coro Building, Suite 500, 1 Hoppin Street, Providence, RI 02903, USA.
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