Ventral striatal dopamine synthesis capacity predicts financial extravagance in Parkinson's disease

Latent profile analysis of gambling

Early age of gambling onset, ease of gambling with technological developments and lack of controlling online gambling games have led to unmanageable risk of gambling. Individual-centered approaches play a significant role in managing the risk that gambling poses on public health and discerning the heterogeneity of gambling addiction. Therefore, this study employed Latent Profile Analysis (LPA), one of the individual-centered approaches, to model the interactions across the psychosocial characteristics of gamblers. The study aims to reveal the latent profiles of gambling addiction. Unlike variable-centered approaches, LPA is a contemporary technique that provides objective information regarding individual psychological processes and behaviors. The profile indicators of the study involve psychosocial characteristics such as resilience, motives to gamble (excitement/fun, avoidance, making money, socializing), purposefulness, responsibility and worthiness. Data were collected from 317 volunteers (M = 68.9%; F = 31.1%; mean age = 25.16 ± 6.46) through the Brief Resilience Scale (BRS), Gambling Motives Scale (GMS) and Personal Virtues Scale (PVS). The emerging profiles were defined as adventurous players (14.2%), social gamblers (9.8%), professional gamblers (32.8%), problem gamblers (24.6%) and avoidant gamblers (18.6%). The individual-centered modeling is congruent with the literature on gambling and provides a complementary perspective to understand the heterogeneous structure of gambling. The results are expected to assist mental health professionals in developing educational and clinical intervention programs for gambling behavior. Finally yet importantly, it is recommended that new LPA models be offered through the use of different indicators related to gambling addiction.

Unlucky punches: the vulnerability-stress model for the development of impulse control disorders in Parkinson's disease

Impulse-control disorders are commonly observed during dopamine-replacement therapy in Parkinson’s disease, but the majority of patients seems “immune” to this side effect. Epidemiological evidence suggests that a major risk factor may be a specific difference in the layout of the dopaminergic-reinforcement system, of which the ventral striatum is a central player. A series of imaging studies of the dopaminergic system point toward a presynaptic reduction of dopamine-reuptake transporter density and dopamine synthesis capacity. Here, we review current evidence for a vulnerability-stress model in which a relative reduction of dopaminergic projections to the ventral striatum and concomitant sensitization of postsynaptic neurons represent a predisposing (hypodopaminergic) vulnerability. Stress (hyperdopaminergic) is delivered when dopamine replacement therapy leads to a relative overdosing of the already-sensitized ventral striatum. These alterations are consistent with consecutive changes in reinforcement mechanisms, which stimulate learning from reward and impede learning from punishment, thereby fostering the development of impulse-control disorders. This vulnerability-stress model might also provide important insights into the development of addictions in the non-Parkinsonian population.

Dopamine metabolism of the nucleus accumbens and fronto-striatal connectivity modulate impulse control

Impulsive-compulsive behaviours like pathological gambling or hypersexuality are a frequent side effect of dopamine replacement therapy in patients with Parkinson's disease. Multiple imaging studies suggest a significant reduction of presynaptic dopamine transporters in the nucleus accumbens to be a predisposing factor, reflecting either a reduction of mesolimbic projections or, alternatively, a lower presynaptic dopamine transporter expression per se. Here, we aimed to test the hypothesis of fewer mesolimbic projections as a risk factor by using dopamine synthesis capacity as a proxy of dopaminergic terminal density. Furthermore, previous studies have demonstrated a reduction of fronto-striatal connectivity to be associated with increased risk of impulsive-compulsive behaviour in Parkinson's disease. Therefore, another aim of this study was to investigate the relationship between severity of impulsive-compulsive behaviour, dopamine synthesis capacity and fronto-striatal connectivity. Eighty participants underwent resting state functional MRI and anatomical T1-weighted images [mean age: 68 ± 9.9 years, 67% male (patients)]. In 59 participants, 18F-DOPA-PET was obtained and voxel-wise Patlak slopes indicating dopamine synthesis capacity were calculated. All participants completed the QUIP-RS questionnaire, a well validated test to quantify severity of impulsive-compulsive behaviour in Parkinson's disease. A voxel-wise correlation analysis between dopamine synthesis capacity and QUIP-RS score was calculated for striatal regions. To investigate the relationship between symptom severity and functional connectivity, voxel-wise correlations were performed. A negative correlation was found between dopamine synthesis capacity and QUIP-RS score in the nucleus accumbens (r = -0.57, P = 0.001), a region functionally connected to the rostral anterior cingulate cortex. The connectivity strength was modulated by QUIP-RS, i.e. patients with more severe impulsive-compulsive behaviours had a weaker functional connectivity between rostral anterior cingulate cortex and the nucleus accumbens. In addition, cortical thickness and severity of impulsive-compulsive behaviour were positively correlated in the subgenual rostral anterior cingulate cortex. We found three factors to be associated with severity of impulsive-compulsive behaviour: (i) decreased dopamine synthesis capacity in the nucleus accumbens; (ii) decreased functional connectivity of the rostral anterior cingulate cortex with the nucleus accumbens; and (iii) increased cortical thickness of the subgenual rostral anterior cingulate cortex. Rather than a downregulation of dopamine transporters, a reduction of mesolimbic dopaminergic projections in conjunction with a dysfunctional rostral anterior cingulate cortex-a region known to play a key role in impulse control-could be the most crucial neurobiological risk factor for the development of impulsive-compulsive behaviours in patients with Parkinson's disease under dopamine replacement therapy.

Gambling Dual Disorder: A Dual Disorder and Clinical Neuroscience Perspective

Several behaviors, including compulsive gambling, have been considered non-substance-related addictive disorders. Categorical mental disorders (e.g., DSM-5) are usually accompanied by very different symptomatic expressions (affective, behavioral, cognitive, substance abuse, personality traits). When these mental disorders occur with addictive disorders, either concomitantly or sequentially over the life span, this clinical condition is called a dual disorder. Gambling disorder (GD) has been associated with other categorical psychiatric diagnoses: attention deficit hyperactivity disorder, depression, bipolar disorder, social anxiety, schizophrenia, substance use disorder, antisocial personality disorder; and dimensional symptoms including higher impulsivity, poorer emotional wellbeing, cognitive distortion, psychosis, deficient self-regulation, suicide, poorer family environment, and greater mental distress. We are calling this clinical condition Gambling Dual Disorder. From a clinical perspective, it is clear that Gambling Dual Disorder is not the exception but rather the expectation, and this holds true not just for GD, but also for other mental disorders including other addictions. Mental disorders are viewed as biological disorders that involve brain circuits that implicate specific domains of cognition, emotion, and behavior. This narrative review presents the state of the art with respect to GD in order to address current matters from a dual disorder, precision psychiatry, and clinical neuroscience perspective, rather than the more subjective approach of symptomatology and clinical presentation. This review also presents Gambling Dual Disorder as a brain and neurodevelopmental disorder, including from the perspectives of evolutionary psychiatry, genetics, impulsivity as an endophenotype, the self-medication hypothesis, and sexual biological differences. The wide vision of the disease advances a paradigm shift, highlighting how GD and dual disorders should be conceptualized, diagnosed, and treated. Rethinking GD as part of a dual disorder is crucial for its appropriate conceptualization from the perspective of clinical neuroscience and precision psychiatry.

Gambling disorder

Gambling disorder is characterized by a persistent, recurrent pattern of gambling that is associated with substantial distress or impairment. The prevalence of gambling disorder has been estimated at 0.5% of the adult population in the United States, with comparable or slightly higher estimates in other countries. The aetiology of gambling disorder is complex, with implicated genetic and environmental factors. Neurobiological studies have implicated cortico-striato-limbic structures and circuits in the pathophysiology of this disorder. Individuals with gambling disorder often go unrecognized and untreated, including within clinical settings. Gambling disorder frequently co-occurs with other conditions, particularly other psychiatric disorders. Behavioural interventions, particularly cognitive-behavioural therapy but also motivational interviewing and Gamblers Anonymous, are supported in the treatment of gambling disorder. No pharmacological therapy has a formal indication for the treatment of gambling disorder, although placebo-controlled trials suggest that some medications, such as opioid-receptor antagonists, may be helpful. Given the associations with poor quality of life and suicide, improved identification, prevention, policy and treatment efforts are needed to help people with gambling disorder.

Increased Striatal Dopamine Synthesis Capacity in Gambling Addiction

BACKGROUND

The hypothesis that dopamine plays an important role in the pathophysiology of pathological gambling is pervasive. However, there is little to no direct evidence for a categorical difference between pathological gamblers and healthy control subjects in terms of dopamine transmission in a drug-free state. Here we provide evidence for this hypothesis by comparing dopamine synthesis capacity in the dorsal and ventral parts of the striatum in 13 pathological gamblers and 15 healthy control subjects.

METHODS

This was achieved using [¹⁸F]fluoro-levo-dihydroxyphenylalanine dynamic positron emission tomography scans and striatal regions of interest that were hand-drawn based on visual inspection of individual structural magnetic resonance imaging scans.

RESULTS

Our results show that dopamine synthesis capacity was increased in pathological gamblers compared with healthy control subjects. Dopamine synthesis was 16% higher in the caudate body, 17% higher in the dorsal putamen, and 17% higher in the ventral striatum in pathological gamblers compared with control subjects. Moreover, dopamine synthesis capacity in the dorsal putamen and caudate head was positively correlated with gambling distortions in pathological gamblers.

CONCLUSIONS

Taken together, these results provide empirical evidence for increased striatal dopamine synthesis in pathological gambling.

Do Patients With Parkinson's Disease Exhibit Reduced Cheating Behavior? A Neuropsychological Study

Parkinson's disease (PD) is a common neurodegenerative disorder characterized by loss of dopamine neurons. Since a seminal report was published in the early twentieth century, a growing body of literature has suggested that patients with PD display characteristic personality traits, such as cautiousness and inflexibility. Notably, PD patients have also been described as "honest," indicating that they have a remarkable tendency to avoid behaving dishonestly. In this study, we predicted that PD patients show reduced cheating behavior in opportunities for dishonest gain due to dysfunction of the dopaminergic reward system. Thirty-two PD patients without dementia and 20 healthy controls (HC) completed an incentivized prediction task where participants were rewarded based on their self-reported accuracy, affording them the opportunity to behave dishonestly. Compared with HC, PD patients showed significantly lower accuracy in the prediction task. Furthermore, the mean accuracy of PD patients was virtually equivalent to the chance level. These results indicate that PD patients exhibit reduced cheating behavior when confronted with opportunities for dishonest gain.

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

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

The relationships between androgens and novelty seeking in healthy Japanese men

Androgens are associated with behavioral traits, such as sensation seeking, extraversion, and novelty seeking in humans and other animals. This study investigated whether the levels of total testosterone, free testosterone, and dehydroepiandrosterone sulfate (DHEA-S) in serum were associated with personality traits related to novelty seeking (NS) and its subscales in healthy Japanese male subjects (n=178). Novelty seeking was assessed using Cloninger׳s Temperament and Character Inventory (TCI). The values of the three hormones were log transformed to normalize the data and to allow the use of parametric statistics. Statistical analysis was performed using multiple stepwise regression analysis. There were no associations between the total scores of NS and total testosterone, free testosterone, or DHEA-S. However, free testosterone was slightly but significantly associated with extravagance (NS3), a subscale of novelty seeking. These results indicate the possibility that free testosterone has a small influence on novelty seeking in healthy Japanese male subjects, whereas total testosterone and DHEA-S have no influence. Additional TCI-based studies of the association between novelty seeking and androgens are needed to confirm our findings.

The role of dopamine in risk taking: a specific look at Parkinson's disease and gambling

An influential model suggests that dopamine signals the difference between predicted and experienced reward. In this way, dopamine can act as a learning signal that can shape behaviors to maximize rewards and avoid punishments. Dopamine is also thought to invigorate reward seeking behavior. Loss of dopamine signaling is the major abnormality in Parkinson’s disease. Dopamine agonists have been implicated in the occurrence of impulse control disorders in Parkinson’s disease patients, the most common being pathological gambling, compulsive sexual behavior, and compulsive buying. Recently, a number of functional imaging studies investigating impulse control disorders in Parkinson’s disease have been published. Here we review this literature, and attempt to place it within a decision-making framework in which potential gains and losses are evaluated to arrive at optimum choices. We also provide a hypothetical but still incomplete model on the effect of dopamine agonist treatment on these value and risk assessments. Two of the main brain structures thought to be involved in computing aspects of reward and loss are the ventral striatum (VStr) and the insula, both dopamine projection sites. Both structures are consistently implicated in functional brain imaging studies of pathological gambling in Parkinson’s disease.

Ventral striatal dopamine synthesis capacity is associated with individual differences in behavioral disinhibition

Pathological gambling, alongside addictive and antisocial disorders, forms part of a broad psychopathological spectrum of externalizing disorders, which share an underlying genetic vulnerability. The shared externalizing propensity is a highly heritable, continuously varying trait. Disinhibitory personality traits such as impulsivity and novelty seeking (NS) function as indicators of this broad shared externalizing tendency, which may reflect, at the neurobiological level, variation in the reactivity of dopaminergic (DAergic) brain reward systems centered on the ventral striatum (VS). Here, we examined whether individual differences in ventral striatal dopamine (DA) synthesis capacity were associated with individual variation in disinhibitory personality traits. Twelve healthy male volunteers underwent 6-[¹⁸F]Fluoro-L-DOPA (FDOPA) positron emission tomography (PET) scanning to measure striatal DA synthesis capacity, and completed a measure of disinhibited personality (NS). We found that levels of ventral, but not dorsal, striatal DA synthesis capacity were significantly correlated with inter-individual variation in disinhibitory personality traits, particularly a propensity for financial extravagance and irresponsibility. Our results are consistent with preclinical models of behavioral disinhibition and addiction proneness, and provide novel insights into the neurobiology of personality based vulnerability to pathological gambling and other externalizing disorders.

Inhibitory deficits in euthymic bipolar disorder patients assessed in the human behavioral pattern monitor

BACKGROUND

Bipolar disorder (BD) is associated with inhibitory deficits characterized by a reduced ability to control inappropriate actions or thoughts. While aspects of inhibition such as exaggerated novelty-seeking and perseveration are quantified in rodent exploration of novel environments, similar models are rarely applied in humans. The human Behavioral Pattern Monitor (hBPM), a cross-species exploratory paradigm, has identified a pattern of impaired inhibitory function in manic BD participants, but this phenotype has not been examined across different BD phases. The objective of this study was to determine if euthymic BD individuals demonstrate inhibitory deficits in the hBPM, supporting disinhibition as an endophenotype for the disorder.

METHODS

25 euthymic BD outpatients and 51 healthy comparison subjects were assessed in the hBPM, where activity was recorded by a concealed videocamera and an ambulatory monitoring sensor.

RESULTS

Euthymic BD individuals, similar to manic subjects, demonstrated increased motor activity, greater interaction with novel objects, and more frequent perseverative behavior relative to comparison participants. The quantity of locomotion was also reduced in BD individuals treated with mood stabilizers compared to other patients.

LIMITATIONS

Low sample size for treatment subgroups limits the evaluation of specific medication regimens.

CONCLUSIONS

Our results suggest that BD is distinguished by both trait- and state-dependent inhibitory deficits optimally assessed with sophisticated multivariate measures. These data support the use of the hBPM as a tool to elucidate the effects of BD across various illness states, facilitate the development of BD animal models, and advance our understanding of the neurobiology underlying the disorder.