Risk and learning in impulsive and nonimpulsive patients with Parkinson's disease

Impulse Control Disorders in Parkinson's Disease: An Overview of Risk Factors, Pathogenesis and Pharmacological Management

Impulse control disorders in Parkinson's disease are relatively common drug-induced addictive behaviours that are usually triggered by the dopamine agonists pramipexole, ropinirole and rotigotine. This narrative review aimed to provide a comprehensive overview of the current knowledge of impulse control disorders in Parkinson's disease. We summarised the prevalence, clinical features, risk factors and potential underlying mechanisms of impulse control disorders in Parkinson's disease. Moreover, recent advances in behavioural and imaging characteristics and management strategies are discussed. Early detection as well as a tailored multidisciplinary approach, which typically includes careful adjustment of the dopaminergic therapy and the treatment of associated neuropsychiatric symptoms, are necessary. In some cases, a continuous delivery of levodopa via a pump or the dopamine D1 receptor agonist, apomorphine, can be considered. In selected patients without cognitive or speech impairment, deep brain stimulation of the subthalamic nucleus can also improve addictions. Finding the right balance of tapering dopaminergic dose (usually dopamine agonists) without worsening motor symptoms is essential for a beneficial long-term outcome.

Subjective feelings associated with expectations and rewards during risky decision-making in impulse control disorder

Impulse Control Disorder (ICD) in Parkinson's disease is a behavioral addiction induced by dopaminergic therapies, but otherwise unclear etiology. The current study investigates the interaction of reward processing variables, dopaminergic therapy, and risky decision-making and subjective feelings in patients with versus without ICD. Patients with (n = 18) and without (n = 12) ICD performed a risky decision-making task both 'on' and 'off' standard-of-care dopaminergic therapies (the task was performed on 2 different days with the order of on and off visits randomized for each patient). During each trial of the task, participants choose between two options, a gamble or a certain reward, and reported how they felt about decision outcomes. Subjective feelings of 'pleasure' are differentially driven by expectations of possible outcomes in patients with, versus without ICD. While off medication, the influence of expectations about risky-decisions on subjective feelings is reduced in patients with ICD versus without ICD. While on medication, the influence of expected outcomes in patients with ICD versus without ICD becomes similar. Computational modeling of behavior supports the idea that latent decision-making factors drive subjective feelings in patients with Parkinson's disease and that ICD status is associated with a change in the relationship between factors associated with risky behavior and subjective feelings about the experienced outcomes. Our results also suggest that dopaminergic medications modulate the impact expectations have on the participants' subjective reports. Altogether our results suggest that expectations about risky decisions may be decoupled from subjective feelings in patients with ICD, and that dopaminergic medications may reengage these circuits and increase emotional reactivity in patients with ICD.

Exploration versus exploitation decisions in the human brain: A systematic review of functional neuroimaging and neuropsychological studies

Thoughts and actions are often driven by a decision to either explore new avenues with unknown outcomes, or to exploit known options with predictable outcomes. Yet, the neural mechanisms underlying this exploration-exploitation trade-off in humans remain poorly understood. This is attributable to variability in the operationalization of exploration and exploitation as psychological constructs, as well as the heterogeneity of experimental protocols and paradigms used to study these choice behaviours. To address this gap, here we present a comprehensive review of the literature to investigate the neural basis of explore-exploit decision-making in humans. We first conducted a systematic review of functional magnetic resonance imaging (fMRI) studies of exploration-versus exploitation-based decision-making in healthy adult humans during foraging, reinforcement learning, and information search. Eleven fMRI studies met inclusion criterion for this review. Adopting a network neuroscience framework, synthesis of the findings across these studies revealed that exploration-based choice was associated with the engagement of attentional, control, and salience networks. In contrast, exploitation-based choice was associated with engagement of default network brain regions. We interpret these results in the context of a network architecture that supports the flexible switching between externally and internally directed cognitive processes, necessary for adaptive, goal-directed behaviour. To further investigate potential neural mechanisms underlying the exploration-exploitation trade-off we next surveyed studies involving neurodevelopmental, neuropsychological, and neuropsychiatric disorders, as well as lifespan development, and neurodegenerative diseases. We observed striking differences in patterns of explore-exploit decision-making across these populations, again suggesting that these two decision-making modes are supported by independent neural circuits. Taken together, our review highlights the need for precision-mapping of the neural circuitry and behavioural correlates associated with exploration and exploitation in humans. Characterizing exploration versus exploitation decision-making biases may offer a novel, trans-diagnostic approach to assessment, surveillance, and intervention for cognitive decline and dysfunction in normal development and clinical populations.

Consensus on Feedback Statements That Create Responsibility Among People With Parkinson's Disease: A Delphi Study

IMPORTANCE

Sense of agency is associated with a sense of responsibility, which is essential to performing goal-directed occupations.

OBJECTIVE

To reach consensus on a set of extrinsic feedback statements that have the potential to create a sense of responsibility among patients with neurological disorders in the course of performing daily or social occupations.

DESIGN

Anonymous Delphi study with two rounds with international experts and one round with Irani patients with Parkinson's disease (PD).

SETTING

Electronic survey.

PARTICIPANTS

One hundred experts and 73 patients with idiopathic PD.

OUTCOMES AND MEASURES

Experts and patients anonymously rated (5 = strongly agree/very effective, 4 = agree/effective, 3 = neither agree nor disagree/uncertain, 2 = disagree/ineffective, 1 = strongly disagree/very ineffective) their level of agreement with each survey statement and the effectiveness of each statement in creating a sense of responsibility in the course of performing daily or social occupations. Consensus was set as an interquartile range of ≤1 and ≥70% agreement in two adjacent categories of a Likert scale.

RESULTS

In the experts' first round, consensus was reached on the level of agreement and effectiveness of 18 statements. In the second round, final consensus was achieved on all statements. In the one patient round, patients reached consensus on all statements. Finally, 34 statements were rated as 4 or 5 in terms of agreement and effectiveness, based on the opinions of experts and patients.

CONCLUSIONS AND RELEVANCE

This study has produced a collection of feedback statements that might be useful in occupation-based interventions. What This Article Adds: Extrinsic responsibility feedback delivered while administering occupation-based interventions may increase volition, motivation, and engagement.

Premorbid performances determine the deleterious effects of nigrostriatal degeneration and pramipexole on behavioural flexibility

Subtle cognitive impairment can occur early in the course of Parkinson's disease (PD) and may manifest under different forms of executive dysfunction such as impaired cognitive flexibility. The precise contribution of nigrostriatal dopaminergic neurodegeneration to these non-motor features of the disease is poorly known. Whether such cognitive impairment associated with the disease process may also predate and contribute to the development of neuropsychiatric side-effects following dopamine replacement therapy remains largely unknown. To address these issues, we investigated the respective contributions of nigrostriatal degeneration and chronic treatment with the dopamine D3-preferring agonist pramipexole on behavioral flexibility in a rat model of PD. Flexible, intermediate and inflexible rats were identified based on baseline assessment of behavioral flexibility using an operant set-shifting task. Nigrostriatal degeneration was induced by bilateral viral-mediated expression of A53T mutated human α-synuclein in the substantia nigra pars compacta and behavioral flexibility was assessed after induction of nigrostriatal degeneration, and during chronic pramipexole treatment. Nigrostriatal degeneration impaired behavioral flexibility in flexible but not in inflexible rats. Pramipexole induced a decrease of behavioral flexibility that was exacerbated in lesioned rats and in the most flexible individuals. Furthermore, the deficits induced by pramipexole in lesioned rats affected different components of the task between flexible and inflexible individuals. This study demonstrates that nigrostriatal degeneration and pramipexole unequally impair behavioral flexibility, suggesting that the susceptibility to develop non-motor impairments upon treatment initiation could primarily depend on premorbid differences in behavioral flexibility.

Characteristics of behavioural addiction in Parkinson's disease patients with self-reported impulse control disorder and controls matched for levodopa equivalent dose: a matched case-control study

Impulse control disorders (ICD) in Parkinson's disease (PD) frequently occur, not always as a direct consequence of dopaminergic medication. This study investigated premorbid personality traits and behavioural characteristics in non-demented PD patients with self-reported symptoms of ICD (PD-srICD). From a total of 200 non-demented PD patients who filled out questionnaires assessing symptoms and severity of ICD, those were classified as PD-srICD (n = 32) who reported current occurrence of at least one compulsive behaviour (gambling, sexual behaviour, buying behaviour, or eating). As a control group, 32 patients with no self-reported ICD symptoms were matched for levodopa equivalent daily dose. The demographic, clinical, and premorbid personality profiles were compared between both groups. Frequency of psychological characteristics indicating substance use disorder was evaluated in patients with PD-srICD. Patients with PD-srICD were more frequently male, younger at examination, had earlier PD onset, more depression, higher non-motor burden, less quality of life (p < 0.05, respectively), and more frequently reported premorbid sensation seeking/novelty orientation (p = 0.03) and joyful experience of stress (p = 0.04) than patients in the control group. Of patients with PD-srICD, 90.6% reported at least one behavioural characteristic of substance use disorder, most frequently positive expectations following ICD behaviour and illusional beliefs about its behavioural control. Signs of addiction were common among patients with PD-srICD. Therefore, the profile of psychological characteristics in patients with PD-srICD resembled that of patients with substance use disorder. It can be concluded that dopamine replacement therapy (DRT) alone does not account for PD-srICD and that thorough psychological diagnostics are recommended.

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

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

Recovering Reliable Idiographic Biological Parameters from Noisy Behavioral Data: the Case of Basal Ganglia Indices in the Probabilistic Selection Task

Behavioral data, despite being a common index of cognitive activity, is under scrutiny for having poor reliability as a result of noise or lacking replications of reliable effects. Here, we argue that cognitive modeling can be used to enhance the test-retest reliability of the behavioral measures by recovering individual-level parameters from behavioral data. We tested this empirically with the Probabilistic Stimulus Selection (PSS) task, which is used to measure a participant’s sensitivity to positive or negative reinforcement. An analysis of 400,000 simulations from an Adaptive Control of Thought-Rational (ACT-R) model of this task showed that the poor reliability of the task is due to the instability of the end-estimates: because of the way the task works, the same participants might sometimes end up having apparently opposite scores. To recover the underlying interpretable parameters and enhance reliability, we used a Bayesian Maximum A Posteriori (MAP) procedure. We were able to obtain reliable parameters across sessions (intraclass correlation coefficient ≈ 0.5). A follow-up study on a modified version of the task also found the same pattern of results, with very poor test-retest reliability in behavior but moderate reliability in recovered parameters (intraclass correlation coefficient ≈ 0.4). Collectively, these results imply that this approach can further be used to provide superior measures in terms of reliability, and bring greater insights into individual differences.

Aberrant Salient and Corticolimbic Connectivity in Hypersexual Parkinson's Disease

Introduction: Impulse control disorders (ICDs) represent a side effect of dopaminergic medication in Parkinson's disease (PD). Patients experience an excessive desire toward natural rewards paired with uncontrolled actions. Yet, the precise neural and behavioral mechanisms associated with ICDs and, importantly, each specific subdomain remain unclear. We aim to decipher resting-state and corticolimbic functional connectivity in PD patients with and without hypersexual ICD. Materials and Methods: Seventeen PD patients with hypersexuality (PD+HS) and 15 PD patients without hypersexuality (PD-HS) underwent two sessions (with and without medication) of resting-state functional magnetic resonance imaging and were compared with 17 healthy controls. Dual-regression independent component analyses extracted salience, sensorimotor, default-mode, and central executive networks. Seed-based functional connectivity with three striatal subdivisions (motor, associative, and limbic) was obtained and significant changes were correlated with key impulsivity and inhibitory measures. Results: Enhanced salience network (SN) activity represented by a significant rise in the right inferior frontal gyrus was found in PD+HS compared with PD-HS. Connectivity analyses revealed a functional disconnection between associative and limbic striatum with precuneus and superior parietal lobe in PD+HS, some connections explained by abnormal sexual behavior and inhibition in PD+HS. Conclusions: Hypersexual ICD is associated with enhanced SN signaling and corticolimbic disconnections, including striatal associative and limbic loops that contribute to altered control of sexually driven behavior and overall severity in PD and ICD.

Impulse Control Disorders in Parkinson's Disease: Epidemiology, Pathogenesis and Therapeutic Strategies

Impulse control disorders (ICDs) in Parkinson's disease (PD) are aberrant behavior such as pathological gambling, hypersexuality, binge eating, and compulsive buying, which typically occur as a result of dopaminergic therapy. Numerous studies have focused on the broad spectrum of ICDs-related behaviors and their tremendous impact on patients and their family members. Recent advances have improved our understanding of ICDs. In this review, we discuss the epidemiology, pathogenesis and treatment of ICDs in the setting of PD.

Dopaminergic influences on risk preferences of Parkinson's disease patients

Clinicians are increasingly recognizing impulse control disorders (ICDs) as a complication of dopaminergic treatment in Parkinson's disease (PD). Considering the pivotal role of dopamine in reward information processing, ICDs may originate from dysregulation of reward-oriented behavior, and the behavioral changes may be reflected in shifts of psychological risk preference during decision-making. We used a behavioral economics paradigm to evaluate quantitatively the risk preferences of PD patients in levodopa on and off states. We also examined age-matched healthy controls. We found that levodopa increased the subjective value and prolonged the decision time in PD patients. These effects are apparently not explained by kinematic improvements but are attributed to psychological shifts of risk preferences and increased attention during risky decision-making. The risk preferences of healthy controls were similar to those of PD on levodopa treatment. The risk preferences of PD patients were not correlated with the scores of routine cognitive batteries, suggesting that dopamine-sensitive risk preferences are independent of cognitive capacities as measured by conventional batteries, including general intelligence, memory, and frontal functioning. By contrast, apathy and ICD partially predicted the risk attitude in PD patients, suggesting a common background of limbic origin behind these properties. The present results demonstrated that dopamine deficiency in off-state PD leads to risk-avoiding behavior and levodopa treatment increases the risk preferences. Behavioral economics framework is useful to evaluate short-term psychological changes in response to levodopa in PD patients.

Behavioral and Neuroanatomical Account of Impulsivity in Parkinson's Disease

Impulse control disorder (ICD) is a major non-motor complication of Parkinson's disease (PD) with often devastating consequences for patients' quality of life. In this study, we aimed to characterize the phenotype of impulsivity in PD and its neuroanatomical correlates.

Methods: Thirty-seven PD patients (15 patients with ICD, 22 patients without ICD) and 36 healthy controls underwent a neuropsychological battery. The test battery consisted of anxiety and depression scales, self-report measures of impulsivity (Barratt scale and UPPS-P), behavioral measures of impulsive action (Go/No-Go task, Stop signal task) and impulsive choice (Delay discounting, Iowa gambling task), and measures of cognitive abilities (working memory, attention, executive function). Patients and controls underwent structural MRI scanning.

Results: Patients with ICD had significantly higher levels of self-reported impulsivity (Barratt scale and Lack of perseverance from UPPS-P) in comparison with healthy controls and non-impulsive PD patients, but they performed similarly in behavioral tasks, except for the Iowa gambling task. In this task, patients with ICD made significantly less risky decisions than patients without ICD and healthy controls. Patients without ICD did not differ from healthy controls in self-reported impulsivity or behavioral measurements. Both patient groups were more anxious and depressive than healthy controls. MRI scanning revealed structural differences in cortical areas related to impulse control in both patient groups. Patients without ICD had lower volumes and cortical thickness of bilateral inferior frontal gyrus. Patients with ICD had higher volumes of right caudal anterior cingulate and rostral middle frontal cortex.

Conclusions: Despite the presence of ICD as confirmed by both clinical follow-up and self-reported impulsivity scales and supported by structural differences in various neural nodes related to inhibitory control and reward processing, patients with ICD performed no worse than healthy controls in various behavioral tasks previously hypothesized as robust impulsivity measures. These results call for caution against impetuous interpretation of behavioral tests, since various factors may and will influence the ultimate outcomes, be it the lack of sensitivity in specific, limited ICD subtypes, excessive caution of ICD patients during testing due to previous negative experience rendering simplistic tasks insufficient, or other, as of now unknown aspects, calling for further research.

Trait Impulsivity Is Independent of Mild Cognitive Impairment in a Parkinson's Disease Cohort

Introduction

Patients with Parkinson's disease (PD) commonly experience cognitive deficits and some also develop impulse control disorders (ICDs); however, the relationship between impulsivity and cognitive dysfunction remains unclear. This study investigated whether trait impulsivity associates with mild cognitive impairment (MCI), or is altered in a PD patient cohort with MCI.

Methods

A total of 302 patients with idiopathic PD were recruited sequentially from three Australian Movement Disorder clinics. Based on cognitive scores, participants were divided into two groups, one defined as having mild cognitive impairment (PD-MCI; n = 113) and the other with normal cognitive function (PD-C; n = 189). Trait impulsivity was evaluated using the Barrett Impulsiveness Scale 11 (BIS-11). Total impulsivity scores, as well as subscale scores, were compared between PD-C and PD-MCI groups.

Results

The PD-MCI cohort had significantly lower scores in all cognitive domains, and mirrored expected clinical differences in medication, motor symptoms, and disease duration, when compared to the PD-C cohort. Self-reported impulsivity was not significantly different between groups, nor was there a difference within first-order subscale scores: attention (p=0.137), cognitive instability (p=0.787), self-control (p=0.503), cognitive complexity (p=0.157), motor impulsivity (p=0.559), or perseverance (p=0.734) between the PD-MCI and PD-C groups.

Conclusions

These findings suggest that impulsive traits and behaviors are independent of changes in cognitive state and are not altered in PD patients with mild cognitive impairment.

Nigrostriatal dopamine transporter availability, and its metabolic and clinical correlates in Parkinson's disease patients with impulse control disorders

PURPOSE

Previous studies in patients with Parkinson's disease (PD) and impulse control disorders (ICDs) have produced heterogeneous results regarding striatal dopamine transporter (DaT) binding and activity in the mesocorticolimbic network. Our aim here was to study the relationship between striatal DaT availability and cortical metabolism, as well as motor, behavioural and cognitive features of PD patients with ICD.

METHODS

In a group of PD patients with ICD (PD-ICD, n = 16) and 16 matched PD patients without ICD (PD-noICD, n = 16), DaT single-photon emission computed tomography (SPECT) imaging (DaTSCAN) was used to study DaT availability in predefined striatal volumes of interest (VOIs): putamen, caudate nucleus and ventral striatum (VS). In addition, the specific association of striatal DaT binding with cortical limbic and associative metabolic activity was evaluated by ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography (PET) in PD-ICD patients and investigated using statistical parametric mapping (SPM8). Finally, associations between DaT availability and motor, behavioural and cognitive features were assessed.

RESULTS

PD-ICD patients had a significantly lower DaT density in the VS than PD-noICD patients, which was inversely associated with ICD severity. Lower DaT availability in the VS was associated with lower FDG uptake in several cortical areas belonging to the limbic and associative circuits, and in other regions involved in reward and inhibition processes (p < 0.0001 uncorrected; k > 50 voxels). No significant results were observed using a higher conservative threshold (p < 0.05; FDR corrected). PD-ICD patients also displayed impairment in interference and attentional Stroop Task execution, and more anxiety, all associated with reduced DaT availability in the VS and caudate nucleus.

CONCLUSIONS

ICDs in PD patients are related to reduced DaT binding in the VS, which accounts for dysfunction in a complex cortico-subcortical network that involves areas of the mesolimbic and mesocortical systems, being associated with reward evaluation, salience attribution and inhibitory control processes.

Dopamine replacement remediates risk aversion in Parkinson's disease in a value-independent manner

INTRODUCTION

Clinical evidence suggests that Parkinson's Disease (PD) patients are risk averse. Dopaminergic therapy has been reported to increase risk tolerance, but the underlying mechanisms are unclear. Some studies have suggested an amplification of subjective reward value, consistent with the role of dopamine in reward value coding. Others have reported value-independent risk enhancement. We evaluated the value-dependence of the effects of PD and its therapy on risk using tasks designed to sensitively measure risk over a wide range of expected values.

METHOD

36 patients with idiopathic PD receiving levodopa monotherapy and 36 healthy matched controls performed two behavioural economic tasks aimed at quantifying 1) risk tolerance/aversion in the gain frame and 2) valuation of potential gains relative to losses. PD patients performed the tasks on and off their usual dose of levodopa in randomized order; controls performed the same tasks twice.

RESULTS

Relative to the controls, unmedicated PD patients showed significant value-independent risk aversion in the gain frame, which was normalized by levodopa. PD patients did not differ from controls in their valuation of gains relative to losses. However, across both tasks and regardless of medication, choices of the patients were more determined by expected values of the prospects than those of controls.

CONCLUSION

Dopamine deficiency in PD was associated with risk aversion, and levodopa promoted riskier choice in a value-independent manner. PD patients also showed an increased sensitivity to expected value, which was independent of levodopa and does not appear to result directly from dopamine deficiency.

Why not try harder? Computational approach to motivation deficits in neuro-psychiatric diseases

Motivation deficits, such as apathy, are pervasive in both neurological and psychiatric diseases. Even when they are not the core symptom, they reduce quality of life, compromise functional outcome and increase the burden for caregivers. They are currently assessed with clinical scales that do not give any mechanistic insight susceptible to guide therapeutic intervention. Here, we present another approach that consists of phenotyping the behaviour of patients in motivation tests, using computational models. These formal models impose a precise and operational definition of motivation that is embedded in decision theory. Motivation can be defined as the function that orients and activates the behaviour according to two attributes: a content (the goal) and a quantity (the goal value). Decision theory offers a way to quantify motivation, as the cost that patients would accept to endure in order to get the benefit of achieving their goal. We then review basic and clinical studies that have investigated the trade-off between the expected cost entailed by potential actions and the expected benefit associated with potential rewards. These studies have shown that the trade-off between effort and reward involves specific cortical, subcortical and neuromodulatory systems, such that it may be shifted in particular clinical conditions, and reinstated by appropriate treatments. Finally, we emphasize the promises of computational phenotyping for clinical purposes. Ideally, there would be a one-to-one mapping between specific neural components and distinct computational variables and processes of the decision model. Thus, fitting computational models to patients' behaviour would allow inferring of the dysfunctional mechanism in both cognitive terms (e.g. hyposensitivity to reward) and neural terms (e.g. lack of dopamine). This computational approach may therefore not only give insight into the motivation deficit but also help personalize treatment.

Impact of Cognitive Profile on Impulse Control Disorders Presence and Severity in Parkinson's Disease

Background: Impulse control disorders (ICDs) and related behaviors are frequent in Parkinson's disease (PD). Mild cognitive impairment (PD-MCI) and dementia (PDD), both characterized by heterogeneous cognitive phenotypes, are also commonly reported in PD. However, the frequency and severity of ICD within PD cognitive states is unknown.

Methods: Three hundred and twenty-six PD patients completed a comprehensive neuropsychological assessment and were classified as PD-MCI, PDD, or without cognitive alterations (PD-NC). The Minnesota impulsive disorders interview was used to ascertain the presence (ICD+) or absence (ICD–) of ICD. The Questionnaire for Impulsive-Compulsive Disorders in Parkinson's Disease-Rating Scale was used to assess ICD severity. A subsample of 286 patients evaluated with the same cognitive tasks was selected in order to investigate the characteristics of ICD in PD cognitive phenotypes.

Results: ICDs were present in 55% of PD-NC, in 50% of PD-MCI, and in 42% of PDD patients. Frequencies of ICD+ with attentive (ICD+: 20% vs. ICD–: 4%; p = 0.031) and executive impairments (ICD+: 44% vs. ICD–: 30%; p = 0.027) were higher in the PD-MCI and PDD subgroups, respectively. As expected, no differences were observed in the PD-NC. PD-MCI with attentive impairments presented higher percentage of ICD+ with deficits in the Trail Making Test B-A but not in the Digit Span Sequencing task. In PDD, executive failures concerned Similarities task (ICD+: 67%; ICD–: 29%; p = 0.035), with no differences between ICD+ and ICD– in the Stroop task.

Conclusions: Prevalence and severity of ICDs and related behaviors do not differ in PD with different cognitive states. However, ICD+ are more likely to show deficits, respectively in attentive and in executive domains, specifically in the Trail Making Test B-A task for the attention and working memory domain in PD-MCI and in the Similarities task for the executive function domain in PDD. Prospective studies should evaluate if these tests can be used as screening tool for ICDs in PD.

Impulse Control Disorder in Parkinson's Disease: A Meta-Analysis of Cognitive, Affective, and Motivational Correlates

Background: In Parkinson's disease (PD), impulse control disorders (ICDs) develop as side-effect of dopaminergic replacement therapy (DRT). Cognitive, affective, and motivational correlates of ICD in medicated PD patients are debated. Here, we systematically reviewed and meta-analyzed the evidence for an association between ICD in PD and cognitive, affective, and motivational abnormalities. Methods: A systematic review and meta-analysis was performed on PubMed, Science Direct, ISI Web of Science, Cochrane, EBSCO for studies published between 1-1-2000 and 8-3-2017 comparing cognitive, affective, and motivational measures in PD patients with ICD (ICD+) vs. those without ICD (ICD-). Exclusion criteria were conditions other than PD, substance and/or alcohol abuse, dementia, drug naïve patients, cognition assessed by self-report tools. Standardized mean difference (SMD) was used, and random-effect model applied. Results: 10,200 studies were screened (title, abstract), 79 full-texts were assessed, and 25 were included (ICD+: 625 patients; ICD-: 938). Compared to ICD-, ICD+ showed worse performance reward-related decision-making (0.42 [0.02, 0.82], p = 0.04) and set-shifting tasks (SMD = -0.49 [95% CI -0.78, -0.21], p = 0.0008). ICD in PD was also related to higher self-reported rate of depression (0.35 [0.16, 0.54], p = 0.0004), anxiety (0.43 [0.18, 0.68], p = 0.0007), anhedonia (0.26 [0.01, 0.50], p = 0.04), and impulsivity (0.79 [0.50, 1.09], p < 0.00001). Heterogeneity was low to moderate, except for depression (I² = 61%) and anxiety (I² = 58%). Conclusions: ICD in PD is associated with worse set-shifting and reward-related decision-making, and increased depression, anxiety, anhedonia, and impulsivity. This is an important area for further studies as ICDs have negative impact on the quality of life of patients and their caregivers.

Neurocognitive correlates of medication-induced addictive behaviours in Parkinson's disease: A systematic review

Dopaminergic medication can induce severe addictive behaviours (e.g., pathological gambling) in susceptible Parkinson's disease (PD) patients. It is still unknown which particular neurocognitive processes become exacerbated or dysfunctional in PD patients with addictive behaviours. We sought to systematically review the relevant literature to identity potential neurocognitive correlates of medication-induced addictive behaviours in PD. We framed our review around neurocognitive processes central to four dominant accounts of substance addiction: 'aberrant learning', 'incentive sensitization', 'impulsivity to compulsivity' and 'impaired response inhibition and salience attribution'. Searches of the PubMed and Scopus databases were completed on June 23, 2017. To be included, studies were required to involve: (a) medicated PD patients, without a history of deep brain stimulation, with and without addictive behaviours; (b) a reward-related or decision-making task; and (c) statistical comparison of addictive and non-addictive groups' 'on' medication performance on the task(s). Studies were summarised qualitatively with statistically significant (p<.05) group differences and effect sizes (Cohen's d) highlighted. 35 studies were included. Findings showed that the extant literature is highly heterogeneous. The domains of reward and punishment learning, reflection impulsivity and disadvantageous decision-making exemplify this. More homogeneity exists in domains in which (a) neurocognitive dysfunction is not apparent (motor control, cognitive/attentional flexibility and cognitive control) or (b) typical neurocognitive processes appear exacerbated by medication (reward motivation and choice impulsivity). Future large-scale neurocognitive studies are still required to develop our scientific understanding of addictive behaviours in PD and aid their clinical treatment and prediction.

Dopaminergic Drug Effects on Probability Weighting during Risky Decision Making

Dopamine has been associated with risky decision-making, as well as with pathological gambling, a behavioral addiction characterized by excessive risk-taking behavior. However, the specific mechanisms through which dopamine might act to foster risk-taking and pathological gambling remain elusive. Here we test the hypothesis that this might be achieved, in part, via modulation of subjective probability weighting during decision making. Human healthy controls (n = 21) and pathological gamblers (n = 16) played a decision-making task involving choices between sure monetary options and risky gambles both in the gain and loss domains. Each participant played the task twice, either under placebo or the dopamine D₂/D₃ receptor antagonist sulpiride, in a double-blind counterbalanced design. A prospect theory modelling approach was used to estimate subjective probability weighting and sensitivity to monetary outcomes. Consistent with prospect theory, we found that participants presented a distortion in the subjective weighting of probabilities, i.e., they overweighted low probabilities and underweighted moderate to high probabilities, both in the gain and loss domains. Compared with placebo, sulpiride attenuated this distortion in the gain domain. Across drugs, the groups did not differ in their probability weighting, although gamblers consistently underweighted losing probabilities in the placebo condition. Overall, our results reveal that dopamine D₂/D₃ receptor antagonism modulates the subjective weighting of probabilities in the gain domain, in the direction of more objective, economically rational decision making.

Personality Traits and Cortical Activity Affect Gambling Behavior in Parkinson's Disease

BACKGROUND

Pathological gambling (PG) in Parkinson's disease (PD) manifests as a persistent and uncontrollable gambling behavior, characterized by dysfunctional decision-making and emotional impairment related to high-risk decisions.

OBJECTIVE

The aim of this study was to explore the relationship between personality traits and prefrontal cortex activity in PD patients with or without PG.

METHODS

Thus, hemodynamic cortical activity measured by functional near-infrared spectroscopy (fNIRS) and Iowa Gambling Task (IGT) performance were recorded in forty-six PD patients, divided into three groups according to their gambling status: PD patients with active gambling behavior (PDG); PD patients who remitted from PG (PDNG); and a control group (CG) composed by patients with PD only.

RESULTS

Results indicates that gambling behavior in PD patients is strongly predictive of dysfunctional cognitive strategy; affecting anomalous cortical response with a left hemispheric unbalance in dorsal areas; and it is related to more reward sensitivity than impulsivity personality components.

CONCLUSIONS

PDG patients differed from PDNG and CG from both behavioral and brain response to decision-making. Overall, these effects confirm a pathological condition related to cognitive and emotional aspects which makes the patients with PGD victims of their dysfunctional behavior.

Impulse control disorders in Parkinson's disease

Impulse control disorders (ICD) are frequent side effects of dopamine replacement therapy (DRT) used in Parkinson's disease (PD) with devastating consequences on the patients and caregivers. ICD are behavioural addictions including compulsive gambling, shopping, sexual behaviour, and binge eating that are mainly associated with dopamine D2/D3 agonists. Their management is a real clinical challenge due to the lack of therapeutic alternative. Clinical studies have identified demographic and clinical risk factors for ICD such as younger age at disease onset, male gender, prior history of depression or substance abuse, REM sleep behaviour disorders and higher rate of dyskinesia. PD patients with ICD may also have a specific pattern of dopaminergic denervation in the ventral striatum. Specific evaluation tools have now been designed to better evaluate the severity and impact of ICD in PD. Patients with ICD display altered processing of reward and loss, and decisional bias associated with altered activity in cortical and subcortical areas such as the orbitofrontal cortex, amygdala, insula, anterior cingular cortex, and ventral striatum. Preclinical studies have demonstrated that D2/D3 agonists induce impairments in behavioural processes likely relevant to ICD such as risk-taking behaviour, preference for uncertainty, perseverative responding and sustained drive to engage in gambling-like behaviour. Whether interactions between dopamine denervation and DRT significantly contribute to the pathogenesis of ICD remains poorly understood so far, although features unique to PD have been identified in patients with ICD. Large-scale longitudinal studies are needed to better identify subjects with increased risk to develop ICD and develop therapeutic options.

Brain structural and functional signatures of impulsive-compulsive behaviours in Parkinson's disease

This study assessed brain structural and functional alterations in patients with Parkinson's disease and impulsive-compulsive behaviours (PD-ICB) compared with controls and PD no-ICB cases. Eighty-five PD patients (35 PD-ICB) and 50 controls were recruited. All subjects underwent three-dimensional T1-weighted, diffusion tensor (DT), and resting state functional magnetic resonance imaging (RS fMRI). We assessed cortical thickness with surface-based morphometry, subcortical volumes using FIRST, DT MRI metrics using region of interest and tractography approaches, and RS fMRI using a model free approach. Compared with controls, both PD groups showed a pattern of brain structural alterations in the basal ganglia (more evident in PD no-ICB patients), sensorimotor and associative systems. Compared with PD no-ICB, PD-ICB cases showed left precentral and superior frontal cortical thinning, and motor and extramotor white matter tract damage. Compared with controls, all patients had an increased functional connectivity within the visual network. Additionally, PD no-ICB showed increased functional connectivity of bilateral precentral and postcentral gyri within the sensorimotor network compared with controls and PD-ICB. Severity and duration of PD-ICB modulated the functional connectivity between sensorimotor, visual and cognitive networks. Relative to PD no-ICB, PD-ICB patients were characterised by a more severe involvement of frontal, meso-limbic and motor circuits. These data suggest ICB in PD as the result of a disconnection between sensorimotor, associative and cognitive networks with increasing motor impairment, psychiatric symptoms, and ICB duration. These findings may have important implications in understanding the neural substrates underlying ICB in PD.

Risky decision-making and affective features of impulse control disorders in Parkinson's disease

Impulse control disorders (ICDs) in Parkinson’s disease (PD) are considered dopaminergic treatment side effects. Cognitive and affective factors may increase the risk of ICD in PD. The aim is to investigate risky decision-making and associated cognitive processes in PD patients with ICDs within a four-stage conceptual framework. Relationship between ICDs and affective factors was explored. Thirteen PD patients with ICD (ICD+), 12 PD patients without ICD (ICD−), and 17 healthy controls were recruited. Overall risky decision-making and negative feedback effect were examined with the Balloon Analogue Risk Task (BART). A cognitive battery dissected decision-making processes according to the four-stage conceptual framework. Affective and motivational factors were measured. ANOVA showed no effect of group on overall risky decision-making. However, there was a group × feedback interaction [F (2, 39) = 3.31, p = 0.047]. ICD+, unlike ICD− and healthy controls, failed to reduce risky behaviour following negative feedback. A main effect of group was found for anxiety and depression [F(2, 38) = 8.31, p = 0.001], with higher symptoms in ICD+ vs. healthy controls. Groups did not differ in cognitive outcomes or affective and motivational metrics. ICD+ may show relatively preserved cognitive function, but reduced sensitivity to negative feedback during risky decision-making and higher symptoms of depression and anxiety.

Impulse Control and Related Disorders in Parkinson's Disease

Impulse control disorders (ICDs), such as compulsive gambling, buying, sexual, and eating behaviors, are a serious and increasingly recognized complication in Parkinson's disease (PD), occurring in up to 20% of PD patients over the course of their illness. Related behaviors include punding (stereotyped, repetitive, purposeless behaviors), dopamine dysregulation syndrome (DDS) (compulsive medication overuse), and hobbyism (e.g., compulsive internet use, artistic endeavors, and writing). These disorders have a significant impact on quality of life and function, strain interpersonal relationships, and worsen caregiver burden, and are associated with significant psychiatric comorbidity. ICDs have been most closely related to the use of dopamine agonists (DAs), while DDS is primarily associated with shorter acting, higher potency dopamine replacement therapy (DRT), such as levodopa. However, in preliminary research ICDs have also been reported to occur with monoamine oxidase inhibitor-B and amantadine treatment, and after deep brain stimulation (DBS) surgery. Other risk factors for ICDs may include sex (e.g., male sex for compulsive sexual behavior, and female sex for compulsive buying behavior); younger age overall at PD onset; a pre-PD history of an ICD; personal or family history of substance abuse, bipolar disorder, or gambling problems; and impulsive personality traits. Dysregulation of the mesocorticolimbic dopamine system is thought to be the major neurobiological substrate for ICDs in PD, but there is preliminary evidence for alterations in opiate and serotonin systems too. The primary treatment of ICDs in PD is discontinuation of the offending treatment, but not all patients can tolerate this due to worsening motor symptoms or DA withdrawal syndrome. While psychiatric medications and psychosocial treatments are frequently used to treat ICDs in the general population, there is limited empirical evidence for their use in PD, so it is critical for patients to be monitored closely for ICDs from disease onset and routine throughout its course. In the future, it may be possible to use a precision medicine approach to decrease the incidence of ICDs in PD by avoiding DA use in patients determined to be at highest risk based on their clinical and neurobiological (e.g., motor presentation, behavioral measures of medication response, genetics, dopamine transporter neuroimaging) profile. Additionally, as empirically validated treatments for ICDs and similar disorders (e.g., substance use disorders) emerge, it will also be important to examine their efficacy and tolerability in individuals with comorbid PD.

The relationship between Impulse Control Disorders and cognitive dysfunctions in Parkinson's Disease: A meta-analysis

Impulse Control Disorders (ICD) are associated with impairment in cognitive flexibility and cortical inhibition. In Parkinson's Disease (PD) the relationship between ICD and cognitive dysfunctions is still unclear: some studies found different cognitive profiles between Parkinsonians with and without ICD, whereas others did not. Moreover, findings from studies on ICD in PD are conflicting on which cognitive function is altered. A meta-analysis of 34 studies was performed to shed light on relationship between ICD and cognitive dysfunctions and to reveal the cognitive function compromised in Parkinsonians with ICD. Data were analysed in global cognitive functioning, memory, executive functions, attention/working memory, language, and visuospatial functions. Significant relationship between ICD and dysfunction of abstraction ability/concept formation, set-shifting, visuospatial/constructional abilities and decision-making was found. These findings suggested that people affected by PD with specific frontal dysfunctions are more vulnerable to develop ICD when they take antiparkinsonian drug. Evaluation of specific cognitive functions in routine clinical practice might help to detect those people with PD susceptible to ICD before treating them with antiparkinsonian drugs.

Pramipexole enhances disadvantageous decision-making: Lack of relation to changes in phasic dopamine release

Pramipexole (PPX) is a high-affinity D₂-like dopamine receptor agonist, used in the treatment of Parkinson's disease (PD) and restless leg syndrome. Recent evidence indicates that PPX increases the risk of problem gambling and impulse-control disorders in vulnerable patients. Although the molecular bases of these complications remain unclear, several authors have theorized that PPX may increase risk propensity by activating presynaptic dopamine receptors in the mesolimbic system, resulting in the reduction of dopamine release in the nucleus accumbens (NAcc). To test this possibility, we subjected rats to a probability-discounting task specifically designed to capture the response to disadvantageous options. PPX enhanced disadvantageous decision-making at a dose (0.3 mg/kg/day, SC) that reduced phasic dopamine release in the NAcc. To test whether these modifications in dopamine efflux were responsible for the observed neuroeconomic deficits, PPX was administered in combination with the monoamine-depleting agent reserpine (RES), at a low dose (1 mg/kg/day, SC) that did not affect baseline locomotor and operant responses. Contrary to our predictions, RES surprisingly exacerbated the effects of PPX on disadvantageous decision-making, even though it failed to augment PPX-induced decreases in phasic dopamine release. These results collectively suggest that PPX impairs the discounting of probabilistic losses and that the enhancement in risk-taking behaviors secondary to this drug may be dissociated from dynamic changes in mesolimbic dopamine release.

Executive functioning and risk-taking behavior in Parkinson's disease patients with impulse control disorders

Impulse control disorders (ICD) are common in Parkinson's disease (PD) and are associated with dopaminergic medication. The purpose of this study was to investigate executive function and risk-taking behavior in PD patients with ICD. 17 PD patients with ICD (ICD-PD) were compared to 20 PD patients without ICD (CTRL-PD) using neuropsychological and experimental tasks. Executive functions were assessed using standard executive testing (Conner's Performance Test, Modified Wisconsin Card Sorting Test, Trail Making Test and phonological verbal fluency). Subjects were also submitted to an experimental gambling task consisted of three decks of money cards: neutral deck (equal opportunity for gains as losses), winning deck (small amount of money with a positive balance) and loser deck (high amount of money with a negative balance), evaluating risk-taking behavior (number of cards picked in each deck) and valuation of the reward (subjective appreciation of the value of each deck). There was no significant difference in executive functioning between groups. Both groups selected more cards in the losing deck (high amount of money) as compared to the neutral deck (Mann-Whitney test, ICD-PD, p = 0.02; CTRL-PD, p = 0.003) and to the winning deck (Mann-Whitney test, ICD-PD p = 0.0001; CTRL-PD p = 0.003), suggesting an increased risk-taking behavior. Interestingly, we found that ICD-PD patients estimated the value of decks differently from CTRL-PD patients, taking into account mainly the positive reinforced value of the decks (Mann-Whitney test, p = 0.04). This study showed that executive pattern and risk-taking behavior are similar between ICD-PD and CTRL-PD patients. However, ICD-PD patients showed a specific deficit of the subjective estimation of the reward. Links between this deficit and metacognitive skills are discussed.

Jumping to conclusions in untreated patients with Parkinson's disease

BACKGROUND

Jumping to conclusions due to impulsivity has been shown to be a sensitive marker for dopamine dysregulation and addictive behaviour patterns in treated patients with Parkinson's disease (PD). It is unknown whether drug naïve PD patients, who have never received dopaminergic therapy also have deficits in information sampling.

METHODS

Twenty five de novo PD patients and twenty matched healthy controls were recruited and tested on the beads task, which is a validated information sampling task to assess reflection impulsivity and a temporal discounting questionnaire.

RESULTS

Patients gathered significantly less information and made more irrational choices than matched controls. There was, however, no group difference on the temporal discounting questionnaire.

CONCLUSIONS

Poor information sampling and irrational decision making may be an inherent component of the neuropsychological deficit in Parkinson's disease. These findings suggest that underlying impulsivity detected by a metric task is common in de novo PD.

Psychiatric Conditions in Parkinson Disease: A Comparison With Classical Psychiatric Disorders

Psychiatric conditions often complicate the outcome of patients affected by Parkinson disease (PD), but they differ from classical psychiatric disorders in terms of underlying biological mechanisms, clinical presentation, and treatment response. The purpose of the present review is to illustrate the biological and clinical aspects of psychiatric conditions associated with PD, with particular reference to the differences with respect to classical psychiatric disorders. A careful search of articles on main databases was performed in order to obtain a comprehensive review about the main psychiatric conditions associated with PD. A manual selection of the articles was then performed in order to consider only those articles that concerned with the topic of the review. Psychiatric conditions in patients with PD present substantial differences with respect to classical psychiatric disorders. Their clinical presentation does not align with the symptom profiles represented by Diagnostic and Statistical Manual for Mental Disorders and International Classification of Diseases. Furthermore, psychiatry treatment guidelines are of poor help in managing psychiatric symptoms of patients with PD. Specific diagnostic tools and treatment guidelines are needed to allow early diagnosis and adequate treatment of psychiatric conditions in comorbidity with PD.

Clinical Heterogeneity in Cerebral Hemiatrophy Syndromes

Background

Cerebral hemiatrophy syndromes can present with variable neurological symptoms. In childhood epilepsy, mental retardation and neuropsychiatric disorders are common while in adults movement disorders, such as highly asymmetric parkinsonism or hemidystonia as well as neuropsychiatric problems have been reported.

Methods

Here, we present three adult patients with features that expand the clinical spectrum and give an overview of the most common clinical signs associated with this rare condition.

Results

All three patients had prominent neuropsychiatric symptoms such as mood swings and increased irritability. Furthermore, one patient developed hemichorea which can be a rare presentation of cerebral hemiatrophy.

Conclusions

Cerebral hemiatrophy syndromes are a heterogeneous group of disorders that may also present with neuropsychiatric symptoms or hemichorea.

Impact of Impulse Control Disorders on Sleep-Wake Regulation in Parkinson's Disease

Sleep disturbances are common in patients with Parkinson's disease (PD) and are even more prevalent in patients with behavioural addictions, such as pathological gambling, compulsive sexual behaviour, compulsive buying, binge eating, punding, and the compulsive use of dopamine replacement therapy. An overview of the relationship between these impulse control disorders and sleep disturbances is given and potential underlying mechanisms and treatment strategies are covered.

Pathophysiology of L-dopa-induced motor and non-motor complications in Parkinson's disease

Involuntary movements, or dyskinesia, represent a debilitating complication of levodopa (L-dopa) therapy for Parkinson's disease (PD). L-dopa-induced dyskinesia (LID) are ultimately experienced by the vast majority of patients. In addition, psychiatric conditions often manifested as compulsive behaviours, are emerging as a serious problem in the management of L-dopa therapy. The present review attempts to provide an overview of our current understanding of dyskinesia and other L-dopa-induced dysfunctions, a field that dramatically evolved in the past twenty years. In view of the extensive literature on LID, there appeared a critical need to re-frame the concepts, to highlight the most suitable models, to review the central nervous system (CNS) circuitry that may be involved, and to propose a pathophysiological framework was timely and necessary. An updated review to clarify our understanding of LID and other L-dopa-related side effects was therefore timely and necessary. This review should help in the development of novel therapeutic strategies aimed at preventing the generation of dyskinetic symptoms.

Decision-making impairments in Parkinson's disease as a by-product of defective cost-benefit analysis and feedback processing

Studies examining decision-making in people with Parkinson's disease (PD) show impaired performance on a variety of tasks. However, there are also demonstrations that patients with PD can make optimal decisions just like healthy age-matched controls. We propose that the reason for these mixed findings is that PD does not produce a generalized impairment of decision-making, but rather affects sub-components of this process. In this review we evaluate this hypothesis by considering the empirical evidence examining decision-making in PD. We suggest that of the various stages of the decision-making process, the most affected in PD are (1) the cost-benefit analysis stage and (2) the outcome evaluation stage. We consider the implications of this proposal for research in this area.

Theory of choice in bandit, information sampling and foraging tasks

Decision making has been studied with a wide array of tasks. Here we examine the theoretical structure of bandit, information sampling and foraging tasks. These tasks move beyond tasks where the choice in the current trial does not affect future expected rewards. We have modeled these tasks using Markov decision processes (MDPs). MDPs provide a general framework for modeling tasks in which decisions affect the information on which future choices will be made. Under the assumption that agents are maximizing expected rewards, MDPs provide normative solutions. We find that all three classes of tasks pose choices among actions which trade-off immediate and future expected rewards. The tasks drive these trade-offs in unique ways, however. For bandit and information sampling tasks, increasing uncertainty or the time horizon shifts value to actions that pay-off in the future. Correspondingly, decreasing uncertainty increases the relative value of actions that pay-off immediately. For foraging tasks the time-horizon plays the dominant role, as choices do not affect future uncertainty in these tasks.

Linking neuroscience with modern concepts of impulse control disorders in Parkinson's disease

Patients with Parkinson's disease (PD) may experience impulse control disorders (ICDs) when on dopamine agonist therapy for their motor symptoms. In the last few years, a rapid growth of interest for the recognition of these aberrant behaviors and their neurobiological correlates has occurred. Recent advances in neuroimaging are helping to identify the neuroanatomical networks responsible for these ICDs, and together with psychopharmacological assessments are providing new insights into the brain status of impulsive behavior. The genetic associations that may be unique to ICDs in PD are also being identified. Complementing human studies, electrophysiological and biochemical studies in animal models are providing insights into neuropathological mechanisms associated with these disorders. New animal models of ICDs in PD patients are being implemented that should provide critical means to identify efficacious therapies for PD-related motor deficits while avoiding ICD side effects. Here, we provide an overview of these recent advances, with a particular emphasis on the neurobiological correlates reported in animal models and patients along with their genetic underpinnings.

Sociodemographic, neuropsychiatric and cognitive characteristics of pathological gambling and impulse control disorders NOS in Parkinson's disease

Despite of previous evidence supporting the association between impulse control disorder (ICD) and several demographic, clinical and therapeutic features in Parkinson's disease (PD), the relationships between pathological gambling (PG) or other variants of ICD (ICD-NOS) and specific neuropsychiatric or cognitive domains are not entirely defined. In this study, 155 PD patients without dementia or cognitive impairment underwent: i. the ICD diagnoses, using the Questionnaire for Impulsive-Compulsive Disorders, ii. the mood and anxiety disorders diagnoses, according to the DSM-IV-TR criteria, and iii. a comprehensive battery for measuring severity of psychopathology and neuropsychology domains. Patients were divided in those with pathological gambling (PG), ICDs not otherwise specified (ICD-NOS), or the lack of ICD (No-ICD). There was a progression in age and age at onset from the younger PG subjects throughout ICD-NOS to No-ICD. PG and ICD-NOS subjects had longer disease duration and were taking significantly higher dosages of antiparkinsonian drugs than No-ICD ones. PG subjects had significantly higher severity of depressive and anxious symptoms with respect to the other 2 groups. Both PG and ICD-NOS subjects suffer from increased severity of psychotic symptoms than No-ICD ones. The 3 groups did not differ in any cognitive measure. Our results support the concept that the different sociodemographic and neuropsychiatric profiles of PD patients are associated with different ICDs. Moreover, we clearly demonstrate the lack of relationship between ICD and cognitive performances in undemented PD patients.

Psychiatric issues in cognitive impairment

Neuropsychiatric symptoms (NPS) such as depression, hallucinations and apathy commonly occur in Parkinson's disease (PD) and have major clinical consequences including a negative impact on quality of life. This review discusses the epidemiology, clinical features, diagnostic procedures and treatment issues of NPS in PD and related disorders in the perspective of cognitive impairment, focusing on depression, anxiety, visual hallucinations, apathy, sleep disturbances, impulse control disorder and non-motor fluctuations. The majority of NPS are more common in PD patients with dementia, possibly related to shared underlying pathologies. Recent studies also suggest that NPS are associated with mild cognitive impairment in PD, in particular with the amnestic type. Accurate diagnosis of NPS is important but can be difficult, due to overlapping symptoms and similar appearance of symptoms of motor symptoms of parkinsonism, cognitive impairment, mood disorders and apathy. There are few systematic studies focusing on the management of NPS in PD with cognitive impairment.

Perceptual decision-making in patients with Parkinson's disease

Impulsive choice and poor information sampling have been found to be key behavioural mechanisms linked to impulse control disorders (ICDs) in Parkinson's disease (PD). Perceptual decision-making is intimately related to information sampling. Therefore, we wanted to determine whether dopaminergic medication or ICDs influence perceptual decision-making in PD. All participants performed two tasks. One was a simple reaction time task, where subjects needed to respond as quickly as possible. The second was a perceptual decision-making task, in which participants had to estimate whether a stimulus contained either more red or more blue pixels. We tested three groups of patients, one treated with levodopa monotherapy, one additionally treated with dopamine agonists, and a third group had ICDs. Results were compared to healthy controls. We found that all patients made more errors than controls. Further, patients with ICDs responded fastest on the reaction time task and also in incorrect trials on the perceptual decision-making task. Similarly, patients with dopamine agonists responded faster than those on levodopa monotherapy and controls. Our results demonstrate that all patients have deficits in perceptual decision-making. However, patients treated with dopamine agonists closely resembled patients with ICDs.

Do Parkinson's Disease Patients Have Deficits in Sequential Sampling Tasks?

The aim of this study was to assess the neuropsychological behavior of Parkinson's disease (PD) patients with addictive behaviors. Characteristically, these patients have younger onset of PD, higher novelty-seeking personality traits, jump to conclusions, and often make irrational choices. We assessed whether PD patients with and without addictive behaviors have deficits in a sequential sampling task, often called the secretary problem. In this task, participants needed to pick the best out of multiple offers. Critically, once participants rejected a deal, this option became unavailable. Thus, decisions needed to be balanced not to stop too soon or sample for too long and miss the best deal. We tested 13 PD patients with and 13 patients without addictive behaviors. Results were compared to healthy volunteers. We found that all patients declined fewer options before committing to a deal. There was, however, no difference between the two patient groups. Furthermore, there was no difference in overall choice rank between patients and controls. These results suggest that, compared to controls, PD patients gather less evidence before committing to an offer, but have no deficits in recognizing the best deal out of many options, regardless of whether or not they have addictive behaviors.

Dopamine modulates novelty seeking behavior during decision making

Novelty seeking refers to the tendency of humans and animals to explore novel and unfamiliar stimuli and environments. The idea that dopamine modulates novelty seeking is supported by evidence that novel stimuli excite dopamine neurons and activate brain regions receiving dopaminergic input. In addition, dopamine is shown to drive exploratory behavior in novel environments. It is not clear whether dopamine promotes novelty seeking when it is framed as the decision to explore novel options versus the exploitation of familiar options. To test this hypothesis, we administered systemic injections of saline or GBR-12909, a selective dopamine transporter (DAT) inhibitor, to monkeys and assessed their novelty seeking behavior during a probabilistic decision making task. The task involved pseudorandom introductions of novel choice options. This allowed monkeys the opportunity to explore novel options or to exploit familiar options that they had already sampled. We found that DAT blockade increased the monkeys' preference for novel options. A reinforcement learning (RL) model fit to the monkeys' choice data showed that increased novelty seeking after DAT blockade was driven by an increase in the initial value the monkeys assigned to novel options. However, blocking DAT did not modulate the rate at which the monkeys learned which cues were most predictive of reward or their tendency to exploit that knowledge. These data demonstrate that dopamine enhances novelty-driven value and imply that excessive novelty seeking-characteristic of impulsivity and behavioral addictions-might be caused by increases in dopamine, stemming from less reuptake.

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.

The functional anatomy of impulse control disorders

Impulsive–compulsive disorders such as pathological gambling, hypersexuality, compulsive eating, and shopping are side effects of the dopaminergic therapy for Parkinson’s disease. With a lower prevalence, these disorders also appear in the general population. Research in the last few years has discovered that these pathological behaviors share features similar to those of substance use disorders (SUD), which has led to the term “behavioral addictions”. As in SUDs, the behaviors are marked by a compulsive drive toward and impaired control over the behavior. Furthermore, animal and medication studies, research in the Parkinson’s disease population, and neuroimaging findings indicate a common neurobiology of addictive behaviors. Changes associated with addictions are mainly seen in the dopaminergic system of a mesocorticolimbic circuit, the so-called reward system. Here we outline neurobiological findings regarding behavioral addictions with a focus on dopaminergic systems, relate them to SUD theories, and try to build a tentative concept integrating genetics, neuroimaging, and behavioral results.