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

Neural and behavioral substrates of subtypes of Parkinson's disease

Parkinson’s disease (PD) is a neurological disorder, associated with rigidity, bradykinesia, and resting tremor, among other motor symptoms. In addition, patients with PD also show cognitive and psychiatric dysfunction, including dementia, mild cognitive impairment (MCI), depression, hallucinations, among others. Interestingly, the occurrence of these symptoms—motor, cognitive, and psychiatric—vary among individuals, such that a subgroup of PD patients might show some of the symptoms, but another subgroup does not. This has prompted neurologists and scientists to subtype PD patients depending on the severity of symptoms they show. Neural studies have also mapped different motor, cognitive, and psychiatric symptoms in PD to different brain networks. In this review, we discuss the neural and behavioral substrates of most common subtypes of PD patients, that are related to the occurrence of: (a) resting tremor (vs. nontremor-dominant); (b) MCI; (c) dementia; (d) impulse control disorders (ICD); (e) depression; and/or (f) hallucinations. We end by discussing the relationship among subtypes of PD subgroups, and the relationship among motor, cognitive, psychiatric factors in PD.

Impulsive and compulsive behaviors in Parkinson's disease

Impulsive-compulsive behaviors (ICBs) in Parkinson's disease (PD) are a common and devastating side effect of dopamine replacement therapy. In this review we describe the phenomenology, prevalence, and risk factors of patients with PD. Results of behavioral studies assessing the neuropsychological profile of patients with PD emphasize that the ICBs, which are behavioral addictions, are not hedonically motivated. Rather, other factors such as the inability to cope with uncertainty may be triggering ICBs. New insights from functional imaging studies, strengthening the incentive salience hypothesis, are discussed, and therapeutic guidelines for the management of ICBs in PD are given.

Pathological gambling in Parkinson's disease: subthalamic oscillations during economics decisions

Pathological gambling develops in up to 8% of patients with Parkinson's disease. Although the pathophysiology of gambling remains unclear, several findings argue for a dysfunction in the basal ganglia circuits. To clarify the role of the subthalamic nucleus in pathological gambling, we studied its activity during economics decisions. We analyzed local field potentials recorded from deep brain stimulation electrodes in the subthalamic nucleus while parkinsonian patients with (n = 8) and without (n = 9) pathological gambling engaged in an economics decision-making task comprising conflictual trials (involving possible risk-taking) and non conflictual trials. In all parkinsonian patients, subthalamic low frequencies (2-12 Hz) increased during economics decisions. Whereas, in patients without gambling, low-frequency oscillations exhibited a similar pattern during conflictual and non conflictual stimuli, in those with gambling, low-frequency activity increased significantly more during conflictual than during non conflictual stimuli. The specific low-frequency oscillatory pattern recorded in patients with Parkinson's disease who gamble could reflect a subthalamic dysfunction that makes their decisional threshold highly sensitive to risky options. When parkinsonian patients process stimuli related to an economics task, low-frequency subthalamic activity increases. This task-related change suggests that the cognitive-affective system that drives economics decisional processes includes the subthalamic nucleus. The specific subthalamic neuronal activity during conflictual decisions in patients with pathological gambling supports the idea that the subthalamic nucleus is involved in behavioral strategies and in the pathophysiology of gambling.

Uncertainty about mapping future actions into rewards may underlie performance on multiple measures of impulsivity in behavioral addiction: evidence from Parkinson's disease

A subset of patients with Parkinson's disease (PD) develops behavioral addictions, which may be due to their dopamine replacement therapy. Recently, several groups have been comparing PD patients with and without behavioral addictions on tasks that are thought to measure aspects of impulsivity. Several of these experiments, including information sampling, a bias toward novel stimuli and temporal discounting, have shown differences between PD patients with and without behavioral addictions. We have developed a unifying theoretical framework that allows us to model behavior in all three of these tasks. By exploring the performance of the patient groups on the three tasks with a single framework, we can ask questions about common mechanisms that underlie all three. Our results suggest that the effects seen in all three tasks can be accounted for by uncertainty about the ability to map future actions into rewards. More specifically, the modeling is consistent with the hypothesis that the group with behavioral addictions behaves as if they cannot use information provided within the experimental context to improve future reward guided actions. Future studies will be necessary to more firmly establish (or refute) this hypothesis. We discuss this result in light of what is known about the pathology that underlies the behavioral addictions in the PD patients.

Increased reflection impulsivity in patients with ephedrone-induced Parkinsonism

AIMS

To examine a syndrome of chronic manganism that occurs in drug addicts in eastern Europe who use intravenous methcathinone (ephedrone) contaminated with potassium permanganate. In many cases the basal ganglia, especially the globus pallidus and the putamen, are damaged irreversibly. Routine neuropsychological assessment has revealed no cognitive deficits, despite widespread abnormalities on brain imaging studies and severe extrapyramidal motor handicap on clinical examination.

DESIGN

Case-control study.

SETTING

Ephedrone patients and patients with opioid dependence were recruited from Lviv, Ukraine.

PARTICIPANTS

We tested 15 patients with ephedrone-induced toxicity, 13 opiate-dependent patients who were receiving opioid replacement therapy and 18 matched healthy volunteers.

MEASUREMENTS

The 'beads task', an information-gathering task to assess reflection impulsivity, was used and feedback learning, working memory and risk-taking were also assessed.

FINDINGS

Opiate-dependent patients differed from controls on three of four tasks, whereas ephedrone patients differed from controls on only one task. More specifically, both patient groups were more impulsive and made more irrational choices on the beads task than controls (P < 0.001). However, ephedrone patients had no deficits in working memory (P > 0.1) or risk-taking (P > 0.1) compared with controls. Opioid-dependent patients had significantly worse working memory (P < 0.001) and were significantly more risk-prone than controls (P = 0.002).

CONCLUSIONS

Ephedrone patients may have similar deficits in information-gathering and decision-making to opiate-dependent patients, with preservation of working memory and risk-taking. This may reflect specific damage to anterior cingulate- basal ganglia loops.

Decision making, impulsivity, and addictions: do Parkinson's disease patients jump to conclusions?

Links between impulsive-compulsive behaviors (ICBs) in treated Parkinson's disease (PD), behavioral addictions, and substance abuse have been postulated, but no direct comparisons have been carried out so far. We directly compared patients with PD with and without ICBs with illicit drug abusers, pathological gamblers, and age-matched healthy controls using the beads task, a test of reflection impulsivity, and a working memory task. We found that all patients with PD made more impulsive and irrational choices than the control group. PD patients who had an ICB showed similar behavior to illicit substance abusers, whereas patients without ICBs more closely resembled pathological gamblers. In contrast, we found no difference in working memory performance within the PD groups. However, PD patients without ICBs remembered distractors significantly less than all other patients during working memory tests. We were able to correctly classify 96% of the PD patients with respect to whether or not they had an ICB by analyzing three trials of the 80/20 loss condition of the beads task with a negative prediction value of 92.3%, and we propose that this task may prove to be a powerful screening tool to detect an ICB in PD. Our results also suggest that intact cortical processing and less distractibility in PD patients without ICBs may protect them from developing behavioral addictions.

Effects of dopamine on sensitivity to social bias in Parkinson's disease

Patients with Parkinson's disease (PD) sometimes develop impulsive compulsive behaviours (ICBs) due to their dopaminergic medication. We compared 26 impulsive and 27 non-impulsive patients with PD, both on and off medication, on a task that examined emotion bias in decision making. No group differences were detected, but patients on medication were less biased by emotions than patients off medication and the strongest effects were seen in patients with ICBs. PD patients with ICBs on medication also showed more learning from negative feedback and less from positive feedback, whereas off medication they showed the opposite effect.

Impulsivity and Parkinson's disease: more than just disinhibition

In the last few years it has become clear that impulsivity is a complex behaviour composed of different domains and dependent on different neural networks. The proposed pathogenetic mechanisms for the emergence of impulsivity disorders in Parkinson's Disease (PD) can be broadly separated into three potentially interacting processes: the contribution of premorbid susceptibility to impulsivity, the contribution of the disease itself to the behaviour and the potential contribution of therapeutic agents. Growing evidence suggests that dopamine and the subthalamic nucleus are playing a certain role in the pathophysiology of different aspects of impulsivity. In this review, we summarise the main concepts defining various components of impulsivity both in healthy subjects and patients affected by PD.

Salivary cortisol levels in Parkinson's disease and its correlation to risk behaviour

OBJECTIVE

To investigate salivary cortisol samples in patients with Parkinson's disease (PD) with and without impulsive compulsive behaviours (ICB) during a risk task.

METHODS

Salivary cortisol levels were measured in 13 PD patients without ICB (PD-ICB) and in 15 PD patients with ICB (PD+ICB) before, after medication and throughout the day, and were compared with results with 14 healthy controls. All participants also performed a gambling task to assess risk taking behaviour.

RESULTS

Significantly higher diurnal cortisol levels were found in the PD-ICB group compared with healthy controls but no differences were seen between the PD+ICB and the control group. Increased cortisol levels were significantly correlated with increased risk taking in PD+ICB patients but no interaction was found in the PD-ICB group.

CONCLUSIONS

The findings are in keeping with previous studies which have linked low cortisol levels with antisocial behaviour. The higher cortisol levels during the risk task in the PD+ICB group are consistent with reports in pathological gamblers during gambling and addicts during drug abuse. The results support the hypothesis that cortisol plays an important role in risk taking in ICBs.

Impulse control disorders in Parkinson's disease: recent advances

PURPOSE OF REVIEW

The aim is to review the recent advances in the epidemiology and pathophysiology of impulse control disorders (ICDs) in Parkinson's disease.

RECENT FINDINGS

Large cross-sectional and case-control multicentre studies show that ICDs in Parkinson's disease are common, with a frequency of 13.6%. These behaviours are associated with impaired functioning and with depressive, anxiety and obsessive symptoms, novelty seeking and impulsivity. Behavioural subtypes demonstrate differences in novelty seeking and impulsivity, suggesting pathophysiological differences. Observational and neurophysiological studies point towards a potential mechanistic overlap between behavioural (ICDs) and motor (dyskinesias) dopaminergic sequelae. Converging data suggest dopamine agonists in ICDs appear to enhance learning from rewarding outcomes and impulsive choice. ICD patients also have enhanced risk preference and impaired working memory. Neuroimaging data point towards enhanced bottom-up ventral striatal dopamine release to incentive cues, gambling tasks and reward prediction, and possible inhibition of top-down orbitofrontal influences. Dopamine agonist-related ventral striatal hypoactivity to risk is consistent with impaired risk evaluation.

SUMMARY

Recent large-scale studies and converging findings are beginning to provide an understanding of mechanisms underlying ICDs in Parkinson's disease, which can guide prevention of these behaviours and optimize therapeutic approaches.

Dopamine agonists and risk: impulse control disorders in Parkinson's disease

Impulse control disorders are common in Parkinson's disease, occurring in 13.6% of patients. Using a pharmacological manipulation and a novel risk taking task while performing functional magnetic resonance imaging, we investigated the relationship between dopamine agonists and risk taking in patients with Parkinson's disease with and without impulse control disorders. During functional magnetic resonance imaging, subjects chose between two choices of equal expected value: a 'Sure' choice and a 'Gamble' choice of moderate risk. To commence each trial, in the 'Gain' condition, individuals started at $0 and in the 'Loss' condition individuals started at -$50 below the 'Sure' amount. The difference between the maximum and minimum outcomes from each gamble (i.e. range) was used as an index of risk ('Gamble Risk'). Sixteen healthy volunteers were behaviourally tested. Fourteen impulse control disorder (problem gambling or compulsive shopping) and 14 matched Parkinson's disease controls were tested ON and OFF dopamine agonists. Patients with impulse control disorder made more risky choices in the 'Gain' relative to the 'Loss' condition along with decreased orbitofrontal cortex and anterior cingulate activity, with the opposite observed in Parkinson's disease controls. In patients with impulse control disorder, dopamine agonists were associated with enhanced sensitivity to risk along with decreased ventral striatal activity again with the opposite in Parkinson's disease controls. Patients with impulse control disorder appear to have a bias towards risky choices independent of the effect of loss aversion. Dopamine agonists enhance sensitivity to risk in patients with impulse control disorder possibly by impairing risk evaluation in the striatum. Our results provide a potential explanation of why dopamine agonists may lead to an unconscious bias towards risk in susceptible individuals.

Patients with schizophrenia show increased aversion to angry faces in an associative learning task

BACKGROUND

We were interested in examining the relationship between socially relevant stimuli and decision processes in patients with schizophrenia.

METHOD

We tested patients with schizophrenia and healthy controls on a stochastically rewarded associative learning task. Participants had to determine, through trial and error, which of two faces was associated with a higher chance of reward: one face was angry, the other happy.

RESULTS

Both patients and healthy controls were able to perform the task at above-chance accuracy, and there was no significant difference in overall accuracy between the groups. Both groups also reliably preferred the happy face, such that they selected it more often than the angry face on the basis of the same amount of positive versus negative feedback. However, patients were significantly more averse to the angry face, such that they chose it less often than control participants when the reward feedback strongly supported the angry face as the best choice.

CONCLUSIONS

Patients show an increased aversion to angry faces, in a task in which they must learn to associate rewards with expressions.

Novelty seeking behaviour in Parkinson's disease

Novelty seeking can be a positive trait leading to creativity and innovation, but it is also related to increased risk of damaging addictive behaviour. We have assessed novelty seeking with a three armed bandit task, in which novel stimuli were occasionally introduced, replacing choice options from which the participants had been choosing. This allowed us to assess whether or not they would be prone to selecting novel stimuli. We tested 25 non impulsive patients with Parkinson's disease (PD) and 27 PD patients with impulsive compulsive behaviours (ICBs). Both patient groups were examined "on" and "off" dopaminergic medication in a counterbalanced order and their behaviour was compared with 24 healthy controls. We found that PD patients with ICBs were significantly more prone to choose novel options than either non impulsive PD patients or controls, regardless of medication status. Our findings suggest that attraction to novelty is a personality trait in all PD patients with ICBs which is independent of medication status.

Pathological gambling in Parkinson's disease--a review of the literature

The prevalence of pathological gambling is 3.4% to 6% in treated Parkinson's disease, which is higher than the background population rate. In this review we discuss current evidence to indicate that dopamine agonists are much more likely to trigger this behavior than either L-dopa or selective monoamine oxidase B inhibitor monotherapy. New insights from recent behavioral and functional imaging studies and possible treatment approaches are also covered. A PubMed literature search using the terms "gambling" and "Parkinson's disease," "impulse control disorder," "impulsive compulsive behaviour," "dopamine agonist," of individual dopamine agonists, and of ongoing drug trials, using http://www.clinicaltrials.gov, was carried out for the period up to January 2011.

Pathological behaviors provoked by dopamine agonist therapy of Parkinson's disease

The dopamine agonist medications, pramipexole and ropinirole, are commonly used to treat Parkinson's disease. These two drugs have a highly specific affinity for cerebral D3 receptors, known to be localized to the mesolimbic system. Herein is described a common side effect of these drugs, encountered in our routine clinical practice: pathological behaviors. This includes excessive gambling, hypersexuality, shopping, hyperphagia or obsessive hobbying, which may develop in up to 30% of people taking higher agonist doses. In contrast, treatment with the dopamine precursor, levodopa, in the absence of D3 agonist therapy very rarely provokes such behavioral syndromes. Although these agonist-induced behaviors have been called "impulse control disorders", the problem is not simply loss of impulse control, but rather a novel obsessive-compulsion directed at one or a few behaviors, often taking on pathological proportions. This experience points to the dopamine D3 receptor as a potential therapeutic target for gambling, sex or other addictions occurring spontaneously in the general population.

Cue-induced striatal dopamine release in Parkinson's disease-associated impulsive-compulsive behaviours

Impulsive-compulsive behaviours are a significant source of morbidity for patients with Parkinson's disease receiving dopaminergic therapy. The development of these behaviours may reflect sensitization of the neural response to non-drug rewards, similar to that proposed for sensitization to drug rewards in addiction. Here, by using (11)C-raclopride positron emission tomography imaging, we investigated the effects of reward-related cues and L-dopa challenge in patients with Parkinson's disease with and without impulsive-compulsive behaviours on striatal levels of synaptic dopamine. Eighteen patients (11 with and seven without impulsive-compulsive behaviours) underwent three (11)C-raclopride positron emission tomography scans. The impulsive-compulsive behaviours included hypersexuality, binge eating, punding, compulsive use of dopamine replacement therapy, compulsive buying and pathological gambling, with eight patients exhibiting more than one impulsive-compulsive behaviour. There were no significant differences in baseline dopamine D2 receptor availability between the Parkinson's disease groups. No differences were found when comparing the percentage change of raclopride binding potential between the two Parkinson's disease groups following L-dopa challenge with neutral cues. The group with Parkinson's disease with impulsive-compulsive behaviours had a greater reduction of ventral striatum (11)C-raclopride binding potential following reward-related cue exposure, relative to neutral cue exposure, following L-dopa challenge (16.3% compared with 5.8% in Parkinson's disease controls, P = 0.016). The heightened response of striatal reward circuitry to heterogeneous reward-related visual cues among a group of patients with different impulsive-compulsive behaviours is consistent with a global sensitization to appetitive behaviours with dopaminergic therapy in vulnerable individuals. Our findings are relevant for the broader debate on the relation between impulsive-compulsive behaviours and addictions and may have important implications with regards to advertisement legislation in an effort to prevent the onset of behavioural addictions.

Stroop test performance in impulsive and non impulsive patients with Parkinson's disease

Impulsive personalities are considered to have a general impairment in cognitive flexibility and cortical inhibition. To examine this hypothesis we used a trial by trial Stroop task in impulsive and non impulsive patients with Parkinson's disease (PD) and recorded errors and reaction times (RT). We tested 28 impulsive PD (PD+ICB) and 24 non impulsive PD (PD-ICB) patients prior to and after dopaminergic medication. These results were compared with 24 age matched normal controls. We found an increased error rate in all PD patients prior to their usual medication which resolved after medication. Furthermore patients on medication showed enhanced cognitive flexibility and shorter RT. There was no difference between non impulsive and impulsive PD patients. This suggests that the impulsive behaviours may not affect response inhibition tasks and the response inhibition required in the Stroop test does not engage the same processes that differentiate impulsive and non-impulsive PD patients, which likely involve mesolimbic dopamine.

Oxytocin decreases aversion to angry faces in an associative learning task

Social and financial considerations are often integrated when real life decisions are made, and recent studies have provided evidence that similar brain networks are engaged when either social or financial information is integrated. Other studies, however, have suggested that the neuropeptide oxytocin can specifically affect social behaviors, which would suggest separable mechanisms at the pharmacological level. Thus, we examined the hypothesis that oxytocin would specifically affect social and not financial information in a decision making task, in which participants learned which of the two faces, one smiling and the other angry or sad, was most often being rewarded. We found that oxytocin specifically decreased aversion to angry faces, without affecting integration of positive or negative financial feedback or choices related to happy vs sad faces.

Altruistic punishment in patients with Parkinson's disease with and without impulsive behaviour

Punishing violators of social norms when there is personal cost is known as altruistic punishment. We tested patients with Parkinson's disease (PD) with and without impulsive-compulsive behaviours (ICBs) and matched control subjects, on and off their regular dopamine replacement therapy on a task, in which the patients decided whether or not to invest a sum of money with a trustee. The sum was then quadrupled and the trustee could decide whether or not to return a portion of the investment. Participants could punish the trustee after they were informed of the trustee's decision. We found that PD patients without ICBs on or off medication punished more often than controls, whereas PD patients with ICBs punished more than controls on medication, but similar to controls off medication. These results suggest a role for dopamine in altruistic punishment decisions in PD patients with impulsive compulsive behaviour.