Personality and addictive behaviours in early Parkinson's disease and REM sleep behaviour disorder

Behavioral disorders in Parkinson disease: current view

Patients with Parkinson disease (PD) frequently experience several behavioral symptoms, such as anxiety, apathy, irritability, agitation, impulsive control and obsessive-compulsive or REM sleep behavior disorders, which can cause severe psychosocial problems and impair quality of life. Occurring in 30-70% of PD patients, these symptoms can manifest at early stages of the disease, sometimes even before the appearance of classic motor symptoms, while others can develop later. Behavioral changes in PD show distinct patterns of brain atrophy, dopaminergic and serotonergic deterioration, altered neuronal connectivity in frontostriatal, corticolimbic, default mode and other networks due to a cascade linking molecular pathologies and deficits in multiple behavior domains. The changes suggest a multi-system neurodegenerative process in the context of a specific α-synucleinopathy inducing a variety of biochemical and functional changes, the neurobiological basis and clinical relevance of which await further elucidation. This paper is intended to review the recent literature with focus on the main behavioral disturbances in PD patients, their epidemiology, clinical features, risk factors, animal models, neuroimaging findings, pathophysiological backgrounds, and treatment options of these deleterious lesions.

Causal associations between modifiable risk factors and isolated REM sleep behavior disorder: a mendelian randomization study

Objectives

This Mendelian randomization (MR) study identified modifiable risk factors for isolated rapid eye movement sleep behavior disorder (iRBD).

Methods

Genome-wide association study (GWAS) datasets for 29 modifiable risk factors for iRBD in discovery and replication stages were used. GWAS data for iRBD cases were obtained from the International RBD Study Group. The inverse variance weighted (IVW) method was primarily employed to explore causality, with supplementary analyses used to verify the robustness of IVW findings. Co-localization analysis further substantiated causal associations identified via MR. Genetic correlations between mental illness and iRBD were identified using trait covariance, linkage disequilibrium score regression, and co-localization analyses.

Results

Our study revealed causal associations between sun exposure-related factors and iRBD. Utilizing sun protection (odds ratio [OR] = 0.31 [0.14, 0.69], p = 0.004), ease of sunburn (OR = 0.70 [0.57, 0.87], p = 0.001), childhood sunburn occasions (OR = 0.58 [0.39, 0.87], p = 0.008), and phototoxic dermatitis (OR = 0.78 [0.66, 0.92], p = 0.003) decreased iRBD risk. Conversely, a deep skin color increased risk (OR = 1.42 [1.04, 1.93], p = 0.026). Smoking, alcohol consumption, low education levels, and mental illness were not risk factors for iRBD. Anxiety disorders and iRBD were genetically correlated.

Conclusion

Our study does not corroborate previous findings that identified smoking, alcohol use, low education, and mental illness as risk factors for iRBD. Moreover, we found that excessive sun exposure elevates iRBD risk. These findings offer new insights for screening high-risk populations and devising preventive measures.

Insulin and Disorders of Behavioural Flexibility

Behavioural inflexibility is a symptom of neuropsychiatric and neurodegenerative disorders such as Obsessive-Compulsive Disorder, Autism Spectrum Disorder and Alzheimer's Disease, encompassing the maintenance of a behaviour even when no longer appropriate. Recent evidence suggests that insulin signalling has roles apart from its regulation of peripheral metabolism and mediates behaviourally-relevant central nervous system (CNS) functions including behavioural flexibility. Indeed, insulin resistance is reported to generate anxious, perseverative phenotypes in animal models, with the Type 2 diabetes medication metformin proving to be beneficial for disorders including Alzheimer's Disease. Structural and functional neuroimaging studies of Type 2 diabetes patients have highlighted aberrant connectivity in regions governing salience detection, attention, inhibition and memory. As currently available therapeutic strategies feature high rates of resistance, there is an urgent need to better understand the complex aetiology of behaviour and develop improved therapeutics. In this review, we explore the circuitry underlying behavioural flexibility, changes in Type 2 diabetes, the role of insulin in CNS outcomes and mechanisms of insulin involvement across disorders of behavioural inflexibility.

Alcohol and Parkinson's Disease: A Systematic Review and Meta-Analysis

BACKGROUND

A substantial body of research has examined the relationship between alcohol consumption and risk of Parkinson's disease (PD).

OBJECTIVE

To provide an updated systematic review and meta-analysis of observational studies examining the relationship between alcohol consumption and risk of PD.

METHODS

Eligible studies comparing PD risk in ever vs. never alcohol drinkers were sourced from six databases. Outcomes were pooled using standard meta-analysis techniques. Separate female and male estimates were generated from studies reporting sex-specific data. Additionally, cohort studies stratifying participants by quantity of alcohol intake were integrated in a dose-response analysis.

RESULTS

52 studies were included, totaling 63,707 PD patients and 9,817,924 controls. Our meta-analysis supported a statistically significant overrepresentation of never drinkers among PD subjects; odds ratio (OR) for ever drinking alcohol 0.84 (95% confidence interval (CI) 0.76 - 0.92). A subgroup analysis revealed similar effect estimates in females and males. A further synthesis of seven cohort studies suggested a negative, dose-dependent association between alcohol and risk of PD.

CONCLUSION

In the absence of a known neuroprotective pathway, there may be reason to doubt a true biological effect. The role of survivor bias, selection and recall bias, misclassification, and residual confounding requires consideration. Alternatively, observations might be attributable to reverse causation if those predestined for PD alter their alcohol habits during the preclinical phase. Major limitations of our study include high between-study heterogeneity (I2 = 93.2%) and lack of adjustment for key confounders, namely smoking status.

Personality profile and its association with conversion to neurodegenerative disorders in idiopathic REM sleep behavior disorder

Patients with Parkinson’s disease (PD) were described less extraverted and more neurotic. It remained unclear whether similar personality traits could be found in idiopathic rapid eye movement sleep behavior disorder (iRBD), a prodromal stage of PD, and could predict phenoconversion to neurodegenerative disorders. We aimed to investigate the personality profile and its association with future neurodegenerative phenoconversion in iRBD patients. One hundred and eighty-five video-polysomnography confirmed iRBD patients and 91 age- and sex-matched controls underwent personality assessment using the NEO five-factor inventory, and 171 iRBD patients were followed up. Our results showed that iRBD was marginally negatively associated with extraverted personality trait (B = −0.28, 95% confidence interval (CI) = −0.55, −0.001). During a median follow-up of 5.9 years, 47 iRBD patients (27.5%) had phenoconversion. More neurotic (adjusted hazard ratio (HR) = 2.0, 95% CI = 1.3, 3.1) and less extraverted personality traits (adjusted HR = 0.53, 95% CI = 0.36, 0.77) were associated with an increased risk of phenoconversion in iRBD patients. Our findings suggest that personality profile may be a potential prodromal marker of iRBD.

Lippia grata essential oil complexed with β-cyclodextrin ameliorates biochemical and behavioral deficits in an animal model of progressive parkinsonism

Parkinson's disease (PD) is identified by the loss of dopaminergic neurons in the Substantia Nigra pars compacta (SNpc), and is correlated to aggregates of proteins such as α-synuclein, Lewy's bodies. Although the PD etiology remains poorly understood, evidence suggests a main role of oxidative stress on this process. Lippia grata Schauer, known as "alecrim-do-mato", "alecrim-de-vaqueiro", "alecrim-da-chapada", is a native bush from tropical areas mainly distributed throughout the Central and South America. This plant species is commonly used in traditional medicine for relief of pain and inflammation conditions, and that has proven antioxidant effects. We evaluated the effects of essential oil of the L. grata after its complexed with β-cyclodextrin (LIP) on PD animal model induced by reserpine (RES). Behavioral assessments were performed across the treatment. Upon completion the treatment, the animals were euthanized, afterwards their brains were isolated and processed for immunohistochemical and oxidative stress analysis. The LIP treatment delayed the onset of the behavior of catalepsy, decreased the number of oral movements and prevented the memory impairment on the novel object recognition task. In addition, the treatment with LIP protected against dopaminergic depletion in the SNpc and dorsal striatum (STRd), and decreased the α-syn immunoreactivity in the SNpc and hippocampus (HIP). Moreover, there was reduction of the oxidative stability index. These findings demonstrated that the LIP treatment has neuroprotective effect in a progressive parkinsonism model, suggesting that LIP could be an important source for novel treatment approaches in PD.

Early Parkinson's Disease Phenotypes Tailored by Personality, Behavior, and Motor Symptoms

BACKGROUND

Previous studies described a parkinsonian personality characterized as rigid, introverted, and cautious; however, little is known about personality traits in de novo Parkinson's disease (PD) patients and their relationships with motor and neuropsychiatric symptoms.

OBJECTIVE

To investigate personality in de novo PD and explore its relationship with PD symptoms.

METHODS

Using Cloninger's biosocial model, we assessed personality in 193 de novo PD patients. Motor and non-motor symptoms were measured using several validated scales. Cluster analysis was conducted to investigate the interrelationship of personality traits, motor, and non-motor symptoms.

RESULTS

PD patients showed low novelty seeking, high harm avoidance, and normal reward dependence and persistence scores. Harm avoidance was positively correlated with the severity of depression, anxiety, and apathy (rs = [0.435, 0.676], p < 0.001) and negatively correlated with quality of life (rs = -0.492, p < 0.001). Novelty seeking, reward dependence, and persistence were negatively correlated with apathy (rs = [-0.274, -0.375], p < 0.001). Classification of patients according to personality and PD symptoms revealed 3 distinct clusters: i) neuropsychiatric phenotype (with high harm avoidance and low novelty seeking, hypodopaminergic neuropsychiatric symptoms and higher impulsivity), ii) motor phenotype (with low novelty seeking and higher motor severity), iii) benign phenotype (with low harm avoidance and high novelty seeking, reward dependence, and persistence traits clustered with lower symptoms severity and low impulsivity).

CONCLUSION

Personality in early PD patients allows us to recognize 3 patients' phenotypes. Identification of such subgroups may help to better understand their natural history. Their longitudinal follow-up will allow confirming whether some personality features might influence disease evolution and treatment.

Obsessive–compulsive personality disorder in rapid eye movement sleep behavior disorder

Rapid eye movement sleep behavior disorder (RBD) is a common prodromic non-motor symptom of Parkinson’s disease (PD). Only few studies have evaluated the personality of RBD patients with conflicting results. Aim of the study was to evaluate the frequency of Personality Disorders (PeDs)in RBD. RBD patients, PD patients and healthy controls (HC) were enrolled. All the enrolled subjects underwent a full neurological examination. Motor symptoms were evaluated with the UPDRS-Motor Examination. PeDs were assessed with the Structured Clinical Interview for DSM-IV Personality Disorders (SCID-II). Twenty-nine RBD patients [14 men (48.3%); mean age 55.6 ± 11.1], 30 PD patients [17 men (56.7%); mean age 65.7 ± 10.7] and 30 HC [12 men (40%); mean age 65.7 ± 5.4] were enrolled in the study. PD patients had a disease duration of 4.5 ± 4.6 and presented a mean UPDRS-ME score of 26.7 ± 9.4. The most frequent PeDs was the Obsessive–Compulsive one (OCPeD); OCPeD was significantly more frequent in RBD (55.2%) patients than HC (13.3%; p-value < 0.001). No significant differences were found comparing the frequency of OCPeD in RBD patients to that in PD. In the present study, the prevalence of OCPeD in RBD patients was close to that reported in PD patients. Our data could suggest the existence of a common disease-specific RBD-PD personality profile.

Neuroticism, Smoking, and the Risk of Parkinson's Disease

Background:

The relationship among neuroticism, smoking, and Parkinson’s disease (PD) is less examined.

Objective:

To examine the causal associations between neuroticism, smoking initiation, and the risk of PD.

Methods:

We performed a two-sample Mendelian randomization (MR) design in a network framework. Summary statistics from meta-analyses of genome-wide association studies (GWAS) were based on large cohorts of European ancestry. Study participants were from various cohort studies for neuroticism and smoking initiation, and case-control studies or cohort studies of PD from previously published GWAS meta-analyses. Patients with PD were ascertained from either clinical visit or self-reported.

Results:

The two-sample MR analysis showed no evidence for a causal association between neuroticism and PD risk (odds ratio [OR] 0.86, 95%confidence intervals [CIs] 0.67 to 1.12). While we did not find a significant association between neuroticism and PD, one SNP, rs58879558 (located in MAPT region), was associated with both neuroticism and PD. We found a significant association of neuroticism on smoking initiation (OR: 1.10, 95%CI: 1.05 to 1.14). Further, our results provided evidence for a protective effect of smoking initiation on the risk of PD (OR: 0.75, 95%CI: 0.62 to 0.91).

Conclusion:

These findings do not support a causal association of neuroticism on PD risk. However, they provide evidence for a causal relationship between neuroticism and smoking initiation and a strong causal effect of smoking initiation on a reduced risk of PD.

Impulsivity in Parkinson's disease patients treated with subthalamic nucleus deep brain stimulation-An exploratory study

BACKGROUND

Deep brain stimulation of the subthalamic nucleus (STN-DBS) is a recognized treatment in Parkinson's disease (PD). Knowledge is still limited regarding the possible impact of STN-DBS on personality traits and the personality characteristics of PD patients who undergo surgery.

METHODS

To assess personality traits in relation to STN-DBS we did an ancillary protocol as part of a prospective randomized study that compared two surgical strategies. Patients were assessed with the Temperament and Character Inventory (TCI), the Urgency, Premeditation, Perseverance and Sensation Seeking impulse behavior scale, the Eysenck Personality Questionnaire (EPQ) and the Toronto Alexithymia Scale preoperatively and after one year of STN-DBS. EPQ and TCI baseline scores were compared with mean scores of healthy reference populations.

RESULTS

After 12-months of STN-DBS, there was a significant decline in Persistence compared to baseline. Preoperatively, the STN-DBS patients had significantly lower Persistence and Self-Transcendence scores, and significantly higher scores on Novelty-Seeking, Self-Directedness, Cooperativeness and on Social Conformity than referenced populations. No difference was found in Neuroticism or Harm-Avoidance scores. The baseline prevalence of alexithymia was low and at 1-year follow-up there was no significant change in alexithymia scores.

CONCLUSIONS

We found a higher baseline level of impulsivity in PD patients who underwent STN-DBS. After one year of STN-DBS, our results indicated that the treatment may affect the patients' personality by increasing certain aspects of impulsivity. There was no effect on alexithymia. The preoperative personality profile of PD patients might influence the outcome of STN-DBS.

Limbic hypoconnectivity in idiopathic REM sleep behaviour disorder with impulse control disorders

INTRODUCTION

Current neuroimaging research has revealed several brain alterations in idiopathic REM sleep behaviour disorder (iRBD) that mirror and precede those reported in PD. However, none have specifically addressed the presence of changes across the reward system, and their role in the emergence of impulse control disorders (ICDs). We aimed to compare the volumetric and functional connectivity characteristics of the reward system in relation to the psychobehavioral profile of patients with iRBD versus healthy controls and PD patients.

METHODS

Twenty patients with polysomnography confirmed iRBD along with 17 PD patients and 14 healthy controls (HC) underwent structural and functional resting-state brain MRI analysis. Participants completed the questionnaire for impulsive-compulsive disorders in PD (QUIP), the short UPPS-P impulsive behaviour scale, as well as neuropsychological testing of cognitive function.

RESULTS

A higher percentage of iRBD patients reported hypersexuality, compared to HC and PD (p = 0.008). Whole-brain and striatal voxel-based morphometry analyses showed no significant clusters of reduced grey matter volume between groups. However, iRBD compared to HC demonstrated functional hypoconnectivity between the limbic striatum and temporo-occipital regions. Furthermore, the presence of ICDs correlated with hypoconnectivity between the limbic striatum and clusters located in cuneus, lingual and fusiform gyrus.

CONCLUSION

Altered functional connectivity between the limbic striatum and posterior cortical regions was associated with increased hypersexuality in iRBD. It is possible that this change may ultimately predispose individuals to the emergence of ICDs when they receive dopaminergic medications, after transitioning to PD.

Olfactory Testing in Parkinson Disease and REM Behavior Disorder: A Machine Learning Approach

OBJECTIVE

We sought to identify an abbreviated test of impaired olfaction amenable for use in busy clinical environments in prodromal (isolated REM sleep behavior disorder [iRBD]) and manifest Parkinson disease (PD).

METHODS

Eight hundred ninety individuals with PD and 313 controls in the Discovery cohort study underwent Sniffin' Stick odor identification assessment. Random forests were initially trained to distinguish individuals with poor (functional anosmia/hyposmia) and good (normosmia/super-smeller) smell ability using all 16 Sniffin' Sticks. Models were retrained using the top 3 sticks ranked by order of predictor importance. One randomly selected 3-stick model was tested in a second independent PD dataset (n = 452) and in 2 iRBD datasets (Discovery n = 241, Marburg n = 37) before being compared to previously described abbreviated Sniffin' Stick combinations.

RESULTS

In differentiating poor from good smell ability, the overall area under the curve (AUC) value associated with the top 3 sticks (anise/licorice/banana) was 0.95 in the Development dataset (sensitivity 90%, specificity 92%, positive predictive value 92%, negative predictive value 90%). Internal and external validation confirmed AUCs ≥0.90. The combination of the 3-stick model determined poor smell, and an RBD screening questionnaire score of ≥5 separated those with iRBD from controls with a sensitivity, specificity, positive predictive value, and negative predictive value of 65%, 100%, 100%, and 30%.

CONCLUSIONS

Our 3-Sniffin'-Stick model holds potential utility as a brief screening test in the stratification of individuals with PD and iRBD according to olfactory dysfunction.

CLASSIFICATION OF EVIDENCE

This study provides Class III evidence that a 3-Sniffin'-Stick model distinguishes individuals with poor and good smell ability and can be used to screen for individuals with iRBD.

Risk stratification for REM sleep behavior disorder in patients with Parkinson's disease: A PRISMA-compliant meta-analysis and systematic review

This study aimed to compare whether the characteristics of Parkinson's disease (PD) patients between probably rapid eye movement sleep behavior disorder (RBD) and confirmed RBD versus non-RBD are differing using a meta-analytic approach. We systematically searched PubMed, EmBase, and the Cochrane library for eligible studies throughout October 2018 in this meta-analysis. The clinical characteristics of PD patients presented with probably RBD, confirmed RBD, or non-RBD were analyzed. The pooled odds ratios and weighted mean differences with corresponding 95 % confidence intervals were calculated for categories and continuous data, respectively. All the pooled analyses were conducted using random-effects model. Forty-seven studies recruited a total of 8019 PD patients were included in the final meta-analysis. The summary results indicated significant differences between probable RBD and non-RBD for PD duration, levodopa dosage daily, Hoehn-Yahr stage, UPDRS-III, UPDRS-motor score, UPDRS activity of daily living, Epworth Sleepiness scale, male percentage, dyskinesia, orthostatic hypotension, constipation, and fluctuations present. Moreover, confirmed RBD versus non-RBD showed significant differences for age, PD duration, levodopa dosage daily, Mini-Mental State Examination, Hoehn-Yahr stage, UPDRS-motor score, Epworth Sleepiness scale, male percentage, dyskinesia, hallucination, insomnia, dementia, orthostatic hypotension, falls, and fluctuations present. Furthermore, the difference of confirmed RBD versus non-RBD was significantly elderly than probable RBD versus non-RBD. Moreover, PD patients with confirmed RBD with lower Mini-Mental State Examination as compared with probable RBD corresponding PD patients without RBD. In addition, PD patients with confirmed RBD versus probable RBD was associated with high Hoehn-Yahr stage as compared with non-RBD. Finally, patients with confirmed RBD with high incidence of insomnia as compared with probable RBD corresponding PD patients without RBD. The results provide the comprehensive differences in the patients' characteristics among probable RBD, confirmed RBD, and non-RBD in PD patients.

Spectrum of impulse control behaviours in Parkinson's disease: pathophysiology and management

Impulse control behaviours (ICBs) are a range of behaviours linked by their reward-based, repetitive natures. They can be precipitated in Parkinson's disease (PD) by dopamine replacement therapy, often with detrimental consequences for patients and caregivers. While now a well-recognised non-motor feature of treated PD, much remains unknown about the influence of risk factors, pathophysiological mechanisms, vulnerability factors for specific types of behaviour and the optimal management strategies. Imaging studies have identified structural and functional changes in striatal and prefrontal brain regions, among others. Gene association studies indicate a role for genetic predisposition to PD-ICB. Clinical observational studies have identified potential modifiable and non-modifiable risk factors. Psychological studies shed light on the neurocognitive domains implicated in PD-ICBs and identify psychosocial determinants that may perpetuate the cycle of impulsive and harm-avoidance behaviours. Based on these results, a range of pharmacological and non-pharmacological management strategies have been trialled in PD-ICBs with varying success. The purpose of this review is to update clinicians on the evidence around the pathophysiology of PD-ICB. We aim to translate our findings into an interpretable biopsychosocial model that can be applied to the clinical assessment and management of individual cases of PD-ICB.

Comparing No-Show Rates of Neurology Outpatients with and without Parkinson's Disease: A Real-World Assessment of the Parkinsonian Personality Profile

BACKGROUND

Parkinson's disease (PD) has been hypothesized to be associated with certain personality traits, including conscientiousness and punctuality. However, research aimed at quantifying these traits is largely derived from questionnaire-based personality inventories rather than real-world observations.

OBJECTIVE

To explore the presence of a parkinsonian personality profile by assessing the no-show rate of patients with PD versus other neurological disorders.

METHODS

We extracted data from our electronic health record for all neurology appointments over a 78-month interval. Additionally, we obtained primary care appointment data for the same patients over the same timeframe. For each appointment we collected appointment date/time, check-in time, provider, age, sex, insurance type, days between appointment date and scheduling, diagnosis code, and no-show status.

RESULTS

19,433 unique patients (400 with PD) accounting for a total of 252,347 outpatient appointments were included in our analysis. The overall no-show rate for PD patients was 3% versus 7.4% for patients with other neurologic disorders (OND). No show rates for PD patients were lower than those with OND for both neurology appointments (2.7% versus 13.6%) and for primary care visits (3.1% versus 5.9%).

CONCLUSIONS

Patients with PD have lower no-show rates than patients with OND. Additionally, the no-show rate for patients with PD did not differ between their neurology and primary care appointments, confirming that patient's personality rather than provider traits account for this difference, and supporting the presence of a parkinsonian personality.

Risk factors for possible REM sleep behavior disorder: A CLSA population-based cohort study

OBJECTIVE

To assess sociodemographic, socioeconomic, and clinical correlates of idiopathic REM sleep behavior disorder (RBD) in a 30,097-person national cohort.

METHODS

Participants 45 to 85 years of age in Canada were collected as part of the Canadian Longitudinal Study on Aging. Possible RBD (pRBD) was screened with the REM Sleep Behavior Disorder Single-Question Screen, a questionnaire with 94% specificity and 87% sensitivity. To improve diagnostic accuracy, those screening positive for apnea or non-REM parasomnia (young-onset pRBD) and those self-reporting dementia or Parkinson disease were excluded. A series of sociodemographic, lifestyle, and mental health variables were analyzed cross-sectionally. Potential correlates were assessed via multivariable logistic regression.

RESULTS

Of 30,097 participants, 958 (3.2%) were identified as having pRBD. Male sex (odds ratio [OR] 2.09, 95% confidence interval [CI] 1.78-2.44) and lower education (OR 0.95, 95% CI 0.92-0.98) were associated with pRBD. Participants with pRBD had smoked more (pack-years OR 1.01, 95% CI 1.00-1.01) and were more likely to be moderate to heavy drinkers (OR 1.25, 95% CI 1.04-1.51). There was a strong association between pRBD and self-reported antidepressant treatment for depression (OR 2.77, 95% CI 2.23-3.45), psychological distress (OR 1.61, 95% CI 1.44-1.80), mental illness (OR 2.09, 95% CI 1.75-2.49), and posttraumatic stress disorder (OR 2.68, 95% CI 1.97-3.65).

CONCLUSIONS

Our study replicated previous reported associations between pRBD and smoking, low education, and male sex and found previously unreported links with alcohol use and psychological distress. Risk factors for pRBD differ from those previously defined for neurodegenerative synucleinopathies.

Sensorimotor subthalamic stimulation restores risk-reward trade-off in Parkinson's disease

BACKGROUND

STN-DBS effectively treats motor symptoms of advanced PD. Nonmotor cognitive symptoms, such as impaired impulse control or decision making, may either improve or worsen with DBS. A potential mediating factor of DBS-induced modulation of cognition is the electrode position within the STN with regard to functional subareas of parallel motor, cognitive, and affective basal ganglia loops. However, to date, the volume of tissue activated and weighted stimulation of STN motor versus nonmotor territories are yet to be linked to differential DBS effects on cognition.

OBJECTIVES

We aim to investigate whether STN-DBS influences risk-reward trade-off decisions and analyze its dependency on electrode placement.

METHODS

Seventeen PD patients ON and OFF STN-DBS and 17 age-matched healthy controls conducted a sequential decision-making task with escalating risk and reward. We computed the effect of STN-DBS on risk-reward trade-off decisions, localized patients' bilateral electrodes, and analyzed the predictive value of volume of tissue activated in STN motor and nonmotor territories on behavioral change.

RESULTS

We found that STN-DBS not only improves PD motor symptoms, but also normalizes overly risk-averse decision behavior in PD. Intersubject variance in electrode location could explain this behavioral change. Specifically, if STN-DBS activated preferentially STN motor territory, patients' risk-reward trade-off decisions more resembled those of healthy controls.

CONCLUSIONS

Our findings support the notion of convergence of different functional circuits within the STN and imply a positive effect of well-placed STN-DBS on nonmotor cognitive functioning in PD. © 2018 International Parkinson and Movement Disorder Society.

Pramipexole-induced impulsivity in mildparkinsonian rats: a model of impulse control disorders in Parkinson's disease

Treatment with dopaminergic agonists such as pramipexole (PPX) contributes to the development of impulse control disorders (ICDs) in patients with Parkinson's disease (PD). As such, animal models of abnormal impulse control in PD are needed to better study the pathophysiology of these behaviors. Thus, we investigated impulsivity and related behaviors using the 5-choice serial reaction time task, as well as FosB/ΔFosB expression, in rats with mild parkinsonism induced by viral-mediated substantia nigra overexpression of human A53T mutated α-synuclein, and following chronic PPX treatment (0.25 mg/kg/d) for 4 weeks. The bilateral loss of striatal dopamine transporters (64%) increased the premature response rate of these rats, indicating enhanced waiting impulsivity. This behavior persisted in the OFF state after the second week of PPX treatment and it was further exacerbated in the ON state throughout the treatment period. The enhanced rate of premature responses following dopaminergic denervation was positively correlated with the premature response rate following PPX treatment (both in the ON and OFF states). Moreover, the striatal dopaminergic deficit was negatively correlated with the premature response rate at all times (pretreatment, ON and OFF states) and it was positively correlated with the striatal FosB/ΔFosB expression. By contrast, PPX treatment was not associated with changes in compulsivity (perseverative responses rate). This model recapitulates some features of PD with ICD, namely the dopaminergic deficit of early PD and the impulsivity traits provoked by dopaminergic loss in association with PPX treatment, making this model a useful tool to study the pathophysiology of ICDs.

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.

Personality and Parkinson's disease: A meta-analysis

INTRODUCTION

Personality changes are considered pre-motor features of Parkinson's disease (PD). Cross-sectional studies revealed that PD patients were more introvert, apprehensive, and cautious than healthy subjects (HS), whereas other studies failed to disclose these behavioural traits. Some studies found mixed results concerning Novelty Seeking (NS) and Harm Avoidance (HA) profiles in PD patients. To better clarify the personality profile in PD we performed a meta-analysis on studies exploring such topic according to both Cloninger's Psychobiological Model (PM) and Big Five Model (BFM) METHODS: The meta-analysis included 17 studies evaluating the personality in PD patients compared with HS. The outcomes were the dimensions of the temperament and character of the PM and personality traits of BFM. Effect sizes from data reported in the primary studies were computed using Hedges'g unbiased approach. Heterogeneity among the studies and publication bias were assessed. Meta-regressions were conducted with age at evaluation, gender, schooling, and type of personality trait tools as moderators.

RESULTS

As for PM, PD patients scored higher on HA and lower on NS than HS. No difference was found on Reward Dependence, Perseverance/Persistence and on character level. As for BFM, higher levels of Neuroticism, but lower levels of Openness and Extraversion were associated with PD.

DISCUSSION

The personality profile in PD is characterized by high Neuroticism and HA, and by low Openness, Extraversion and NS. The personality profile delineated in the present study on PD patients seems to reflect the premorbid one and might contribute to development and persistence of affective disorders.