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

Mapping striatal functional gradients and associated gene expression in Parkinson's disease with continuous cognitive impairment

Cognitive impairment in Parkinson's disease is closely tied to striatal dysfunction, yet the neurobiological interface between macroscale connectivity and molecular signatures remains unexplored. This study characterizes striatal gradient organization and its genetic underpinnings across PD cognitive trajectories. We analyzed functional connectivity gradients in 126 PD patients (spanning the cognitive spectrum from normal cognition to dementia) and 40 healthy controls, correlating spatial patterns with neurotransmitter architecture and transcriptomic profiles. Three distinct striatal gradients emerged: Gradient 1 remains stable throughout disease progression and partially aligns with canonical striatal subdivisions. Gradient 2 represents a spatial continuum closely linked to dopaminergic innervation and becomes most pronounced in the dementia stage. Gradient 3 corresponds to cortico-striatal connectivity patterns implicated in both early and advanced cognitive deficits. Spatial transcriptomic and neuroimaging correlation analyses identified significant associations between cortico-striatal gradient disruptions and specific gene expression patterns. These findings provide valuable insights into striatal macro- and microstructural changes in PD and their role in cognitive impairment.

Managing impulse control and related behavioral disorders in Parkinson's disease: where we are in 2025?

INTRODUCTION

Impulse control and related behavioral disorders (ICBDs) commonly complicate Parkinson's disease (PD) course. The ICBDs spectrum encompasses two groups of conditions, with distinct pathophysiology: proper 'impulse control disorders (ICDs)' (e.g. gambling) and the 'ICDs related disorders (ICDs-RD)' (e.g. punding). Behavioral disturbances are associated with dopamine replacement therapies. ICBDs affect quality of life of patients and caregivers, making their management essential for reducing PD overall burden.

AREAS COVERED

This article reviews current management strategies for ICBDs in PD. The authors highlight strengths and limitations of these strategies, and explore the potential role of emerging treatment options, giving particular focus to new compounds and invasive therapies.

EXPERT OPINION

Prevention, close monitoring, and caregiver involvement are essential in managing ICBDs in PD. Treatment approaches should be tailored to ICBDs' functional impact and aimed to reduce the pulsatile stimulation of dopamine receptors, especially D2. Dopamine agonist (DA) tapering remains the primary therapeutic approach, alongside psychotherapy and second-line agents, like atypical antipsychotics and serotonin-noradrenaline reuptake inhibitors. Insights into ICDs pathophysiology and DA-specific pharmacodynamics indicate safer profiles for certain preparations (e.g. rotigotine patches) and possibly for D1/D5 agonists like tavapadon. Invasive treatments, including deep brain stimulation and infusion therapies, should be prioritized in advanced-stage PD complicated by ICBDs.

Serotonergic dysfunction in patients with impulse control disorders in Parkinson's disease

Impulse control disorders (ICDs) are frequent and particularly distressing neuropsychiatric symptoms in patients with Parkinson's disease (PD) which are related to impaired behavioural inhibition. Multiple PET imaging studies indicate that striatal dopaminergic abnormalities contribute to hyperdopaminergic functioning in PD patients with ICD (PDICD+) and to the dysregulation of the limbic fronto-striatal networks which are critical for reward-related decision impulsivity. However, the serotonergic system is central to response inhibition and plays a critical role in neuropsychiatric symptoms in PD, but its role remains undetermined in PDICD. We hypothesized that PDICD+ patients exhibit serotonergic dysfunction within the cortico-striato-pallido-thalamic circuits involved in the inhibitory control of behaviour and decided to investigate the pre- and post-synaptic serotonergic innervation using two highly-specific PET tracers for the serotonin transporter (SERT) using [11C]DASB and the 5-HT2A receptor using [18F]altanserin. In this prospective, case-control, double-tracer PET study, we recruited 15 PDICD+ patients, 15 PDICD- patients and 15 healthy controls, matched for age and sex, and compared the availability of [11C]DASB and [18F]altanserin using permutation-based analysis. PDICD+ patients had one (n=9) or multiple ICDs (n=6), consisting in hypersexuality (n=8), compulsive eating (n=6), compulsive shopping (n=5) and pathological gambling (n=4) and were characterized by greater choice impulsivity (impaired delay discounting for monetary rewards) and greater urgency with more severe depressive and anxious symptoms. We demonstrate that PDICD+ patients had greater [11C]DASB binding in the posterior putamen and pallidum in comparison to PDICD- patients, corresponding to relatively preserved presynaptic SERT availability within the subcortical sensorimotor network involved in response inhibition. In addition, cortical [18F]altanserin binding was greater in PDICD+ patients in the bilateral supplementary motor area, precentral gyrus and right dorsolateral prefrontal cortex, involving the sensorimotor and associative networks which regulate behavioural inhibition. Furthermore, we show that pre- and post-synaptic serotonergic dysfunction subserving action versus decision impulsivity in PD patients specifically followed the distinctive functional organization of the sensorimotor and associative fronto-striatal networks. Altogether, we demonstrate that serotonergic dysfunction related to ICDs in PD specifically involve the sensorimotor and associative cortico-striato-pallido-thalamic circuits involved in inhibitory control. Thus, serotonergic dysfunction contributes to the mechanisms related to the vulnerability and development of ICDs in PD patients, beyond the known dopaminergic abnormalities in the limbic fronto-striatal circuit.

Clinically probable RBD is an early predictor of malignant non-motor Parkinson's disease phenotypes

Non-motor symptoms (NMS) in Parkinson's disease (PD) significantly impact quality of life, especially in later stages. REM sleep behavior disorder (RBD) affects approximately 42% of all PD patients and frequently precedes motor PD symptoms. RBD is linked to increased rates of depression and cognitive decline. This study explores how early RBD can predict the development of NMS profiles in patients, comparing those with and without early RBD. We identified a unique NMS profile associated with early RBD. These patients had a higher rate of cognitive impairment (M2 = 326.84, p < 0.001), apathy (M2 = 332.93, p < 0.001), hallucinations (M2 = 480.05, p < 0.001), depression (M2 = 480.05, p < 0.0001), anxiety (corrected p < 0.01), impulse control disorders (M2 = 77.577, p < 0.001), and autonomic dysfunction (F = 251.8, p < 0001). A survival analysis revealed an association between early RBD and faster progression to cognitive impairment. These NMS profiles may play a critical role in stratifying patients for targeted interventions.

Impulse control disorders in Parkinson's disease: What's new?

Impulse Control Disorders (ICDs) are increasingly recognized as a significant non-motor complication in Parkinson's disease (PD), impacting patients and their caregivers. ICDs in PD are primarily associated with dopaminergic treatments, particularly dopamine agonists, though not all patients develop these disorders, indicating a role for genetic and other clinical factors. Studies over the past few years suggest that the mesocorticolimbic reward system, a core neural substrate for impulsivity, is a key contributor to ICDs in PD. Recent advances in neuroimaging have begun to unravel the neurobiological diversity of ICD subtypes. Moreover, recent studies provide valuable insights into the clinical and biologic risk factors for ICDs that could be used as indicators for the development of future preventive strategies or targeted interventions. Indeed, current treatment strategies, which often involve reducing or discontinuing dopamine agonists, are limited in efficacy. Emerging therapies, including behavioral interventions and continuous drug delivery methods, show promise, though further research is needed. This paper provides an updated review of ICD prevalence, mechanisms, assessment, and novel management approaches.

Imaging of impulse control disorders in Parkinson's disease

Impulse control disorders (ICD) are frequent and cumbersome behavioral disorders in patients with Parkinson's disease (PD). Understanding their pathophysiological underpinnings is crucial. Molecular imaging using positron emission tomography (PET) and single-photon emission computed tomography (SPECT) clearly indicates preexisting vulnerability and abnormal sensitization of the pre- and postsynaptic dopaminergic system. Functional magnetic resonance imaging (fMRI) studies reveal abnormal connectivity within the reward system involving the ventral striatum and orbitofrontal cortex. These alterations pinpoint the dysfunction of reinforcement learning in ICD, which is biased toward the overvaluation of reward and underestimation of risk, and the deficit in inhibitory control mechanisms related to abnormal connectivity within and between the limbic and the associative and motor networks.

Expanding the therapeutic potential of neuro(active)steroids: a promising strategy for hyperdopaminergic behavioral phenotypes

Imbalances in dopamine activity significantly contribute to the pathophysiology of several neuropsychiatric disorders, including addiction, ADHD, schizophrenia, impulse control disorders, and Parkinson's Disease. Neuro(active)steroids, comprising endogenous steroids that finely modulate neuronal activity, are considered crucial regulators of brain function and behavior, with implications in various physiological processes and pathological conditions. Specifically, subclasses of Neuro(active)steroids belonging to the 5α reductase pathway are prominently involved in brain disorders characterized by dopaminergic signaling imbalances. This review highlights the neuromodulatory effects of Neuro(active)steroids on the dopamine system and related aberrant behavioral phenotypes. We critically appraise the role of pregnenolone, progesterone, and allopregnanolone on dopamine signaling. Additionally, we discuss the impact of pharmacological interventions targeting 5α reductase activity in neuropsychiatric conditions characterized by excessive activation of the dopaminergic system, ranging from psychotic (endo)phenotypes and motor complications to decision-making problems and addiction.

Dynamic properties in functional connectivity changes and striatal dopamine deficiency in Parkinson's disease

Recent studies in Parkinson's disease (PD) patients reported disruptions in dynamic functional connectivity (dFC, i.e., a characterization of spontaneous fluctuations in functional connectivity over time). Here, we assessed whether the integrity of striatal dopamine terminals directly modulates dFC metrics in two separate PD cohorts, indexing dopamine-related changes in large-scale brain network dynamics and its implications in clinical features. We pooled data from two disease-control cohorts reflecting early PD. From the Parkinson's Progression Marker Initiative (PPMI) cohort, resting-state functional magnetic resonance imaging (rsfMRI) and dopamine transporter (DaT) single-photon emission computed tomography (SPECT) were available for 63 PD patients and 16 age- and sex-matched healthy controls. From the clinical research group 219 (KFO) cohort, rsfMRI imaging was available for 52 PD patients and 17 age- and sex-matched healthy controls. A subset of 41 PD patients and 13 healthy control subjects additionally underwent 18F-DOPA-positron emission tomography (PET) imaging. The striatal synthesis capacity of 18F-DOPA PET and dopamine terminal quantity of DaT SPECT images were extracted for the putamen and the caudate. After rsfMRI pre-processing, an independent component analysis was performed on both cohorts simultaneously. Based on the derived components, an individual sliding window approach (44 s window) and a subsequent k-means clustering were conducted separately for each cohort to derive dFC states (reemerging intra- and interindividual connectivity patterns). From these states, we derived temporal metrics, such as average dwell time per state, state attendance, and number of transitions and compared them between groups and cohorts. Further, we correlated these with the respective measures for local dopaminergic impairment and clinical severity. The cohorts did not differ regarding age and sex. Between cohorts, PD groups differed regarding disease duration, education, cognitive scores and L-dopa equivalent daily dose. In both cohorts, the dFC analysis resulted in three distinct states, varying in connectivity patterns and strength. In the PPMI cohort, PD patients showed a lower state attendance for the globally integrated (GI) state and a lower number of transitions than controls. Significantly, worse motor scores (Unified Parkinson's Disease Rating Scale Part III) and dopaminergic impairment in the putamen and the caudate were associated with low average dwell time in the GI state and a low total number of transitions. These results were not observed in the KFO cohort: No group differences in dFC measures or associations between dFC variables and dopamine synthesis capacity were observed. Notably, worse motor performance was associated with a low number of bidirectional transitions between the GI and the lesser connected (LC) state across the PD groups of both cohorts. Hence, in early PD, relative preservation of motor performance may be linked to a more dynamic engagement of an interconnected brain state. Specifically, those large-scale network dynamics seem to relate to striatal dopamine availability. Notably, most of these results were obtained only for one cohort, suggesting that dFC is impacted by certain cohort features like educational level, or disease severity. As we could not pinpoint these features with the data at hand, we suspect that other, in our case untracked, demographical features drive connectivity dynamics in PD. PRACTITIONER POINTS: Exploring dopamine's role in brain network dynamics in two Parkinson's disease (PD) cohorts, we unraveled PD-specific changes in dynamic functional connectivity. Results in the Parkinson's Progression Marker Initiative (PPMI) and the KFO cohort suggest motor performance may be linked to a more dynamic engagement and disengagement of an interconnected brain state. Results only in the PPMI cohort suggest striatal dopamine availability influences large-scale network dynamics that are relevant in motor control.

Topological features of functional brain networks and subclinical impulsivity: an investigation in younger and older adults

Impulsive traits (i.e., the tendency to act without forethought regardless of negative outcomes) are frequently found in healthy populations. When exposed to risk factors, individuals may develop debilitating disorders of impulse control (addiction, substance abuse, gambling) characterized by behavioral and cognitive deficits, eventually leading to huge socioeconomic costs. With the far-reaching aim of preventing the onset of impulsive disorders, it is relevant to investigate the topological organization of functional brain networks associated with impulsivity in sub-clinical populations. Taking advantage of the open-source LEMON dataset, we investigated the topological features of resting-state functional brain networks associated with impulsivity in younger (n = 146, age: 20-35) and older (n = 61, age: 59-77) individuals, using a graph-theoretical approach. Specifically, we computed indices of segregation and integration at the level of specific circuits and nodes known to be involved in impulsivity (frontal, limbic, and striatal networks). In younger individuals, results revealed that impulsivity was associated with a more widespread, less clustered and less efficient functional organization, at all levels of analyses and in all selected networks. Conversely, impulsivity in older individuals was associated with reduced integration and increased segregation of striatal regions. Speculatively, such alterations of functional brain networks might underlie behavioral and cognitive abnormalities associated with impulsivity, a working hypothesis worth being tested in future research. Lastly, differences between younger and older individuals might reflect the implementation of age-specific adaptive strategies, possibly accounting for observed differences in behavioral manifestations. Potential interpretations, limitations and implications are discussed.

Increased Cortical Thickness in Alzheimer's Disease

OBJECTIVE

Patients with Alzheimer's disease (AD) have diffuse brain atrophy, but some regions, such as the anterior cingulate cortex (ACC), are spared and may even show increase in size compared to controls. The extent, clinical significance, and mechanisms associated with increased cortical thickness in AD remain unknown. Recent work suggested neural facilitation of regions anticorrelated to atrophied regions in frontotemporal dementia. Here, we aim to determine whether increased thickness occurs in sporadic AD, whether it relates to clinical symptoms, and whether it occur in brain regions functionally connected to-but anticorrelated with-locations of atrophy.

METHODS

Cross-sectional clinical, neuropsychological, and neuroimaging data from the Alzheimer's Disease Neuroimaging Initiative were analyzed to investigate cortical thickness in AD subjects versus controls. Atrophy network mapping was used to identify brain regions functionally connected to locations of increased thickness and atrophy.

RESULTS

AD patients showed increased thickness in the ACC in a region-of-interest analysis and the visual cortex in an exploratory analysis. Increased thickness in the left ACC was associated with preserved cognitive function, while increased thickness in the left visual cortex was associated with hallucinations. Finally, we found that locations of increased thickness were functionally connected to, but anticorrelated with, locations of brain atrophy (r = -0.81, p < 0.05).

INTERPRETATION

Our results suggest that increased cortical thickness in Alzheimer's disease is relevant to AD symptoms and preferentially occur in brain regions functionally connected to, but anticorrelated with, areas of brain atrophy. Implications for models of compensatory neuroplasticity in response to neurodegeneration are discussed. ANN NEUROL 2024;95:929-940.

Impulse Control Disorders in Parkinson's Disease and Atypical Parkinsonian Syndromes-Is There a Difference?

BACKGROUND AND OBJECTIVES

Impulse control disorders (ICDs) are characterized by potentially harmful actions resulting from disturbances in the self-control of emotions and behavior. ICDs include disorders such as gambling, hypersexuality, binge eating, and compulsive buying. ICDs are known non-motor symptoms in Parkinson's disease (PD) and are associated primarily with the use of dopaminergic treatment (DRT) and especially dopamine agonists (DA). However, in atypical parkinsonism (APS), such as progressive supranuclear palsy (PSP) or multiple system atrophy (MSA), there are only single case reports of ICDs without attempts to determine the risk factors for their occurrence. Moreover, numerous reports in the literature indicate increased impulsivity in PSP. Our study aimed to determine the frequency of individual ICDs in APS compared to PD and identify potential factors for developing ICDs in APS.

MATERIALS AND METHODS

Our prospective study included 185 patients with PD and 35 with APS (27 patients with PSP and 9 with MSA) hospitalized between 2020 and 2023 at the Neurological Department of University Central Hospital in Katowice. Each patient was examined using the Questionnaire for Impulsive-Compulsive Disorders in Parkinson's Disease (QUIP) to assess ICDs. Additionally, other scales were used to assess the advancement of the disease, the severity of depression, and cognitive impairment. Information on age, gender, age of onset, disease duration, and treatment used were collected from medical records and patient interviews.

RESULTS

ICDs were detected in 23.39% of patients with PD (including binge eating in 11.54%, compulsive buying in 10.44%, hypersexuality in 8.79%, and pathological gambling in 4.40%), in one patient with MSA (hypersexuality and pathological gambling), and in 18.52% of patients with PSP (binge eating in 3.70%, compulsive buying in 7.41%, and hypersexuality in 11.11%). We found no differences in the frequency of ICDs between individual diseases (p = 0.4696). We confirmed that the use of higher doses of DA and L-dopa in patients with PD, as well as a longer disease duration and the presence of motor complications, were associated with a higher incidence of ICDs. However, we did not find any treatment effect on the incidence of ICDs in APS.

CONCLUSIONS

ICDs are common and occur with a similar frequency in PD and APS. Well-described risk factors for ICDs in PD, such as the use of DRT or longer disease duration, are not fully reflected in the risk factors for ICDs in APS. This applies especially to PSP, which, unlike PD and MSA, is a tauopathy in which, in addition to the use of DRT, other mechanisms related to the disease, such as disorders in neuronal loops and neurotransmitter deficits, may influence the development of ICDs. Further prospective multicenter studies recruiting larger groups of patients are needed to fully determine the risk factors and mechanisms of ICD development in APS.

Glucose-6-Phosphatase-Dehydrogenase activity as modulative association between Parkinson's disease and periodontitis

The association between periodontitis (PD) and Parkinson's disease (PK) is discussed due to the inflammatory component of neurodegenerative processes. PK severity and affected areas were determined using the following neuropsychological tests: Unified Parkinson's Disease Rating Score (UPDRS) and Hoehn and Yahr; non-motoric symptoms by Non-Motor Symptoms Scale (NMSS), and cognitive involvement by Mini-Mental State Examination (MMSE). Neuroinflammation and the resulting Glucose-6-Phosphatase-Dehydrogenase (G6PD) dysfunction are part of the pathophysiology of PK. This study aimed to evaluate these associations in periodontal inflammation. Clinical data and saliva-, serum-, and RNA-biobank samples of 50 well-characterized diametric patients with PK and five age- and sex-matched neurologically healthy participants were analyzed for G6PD function, periodontal pathogens (Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, Tannerella forsythia, Treponema denticola, Prevotella intermedia, Campylobacter rectus, Fusobacterium nucleatum, and Filifactor alocis), monocyte chemoattractant protein (MCP) 1, and interleukin (IL) 1-beta. Regression analysis was used to identify associations between clinical and behavioral data, and t-tests were used to compare health and disease. Compared with PK, no pathogens and lower inflammatory markers (p < 0.001) were detectible in healthy saliva and serum, PK-severity/UPDRS interrelated with the occurrence of Prevotella intermedia in serum as well as IL1-beta levels in serum and saliva (p = 0.006, 0.019, 0.034), Hoehn and Yahr correlated with Porphyromonas gingivalis, Prevotella intermedia, RNA IL1-beta regulation, serum, and saliva IL1-beta levels, with p-values of 0.038, 0.011, 0.008, <0.001, and 0.010, while MMSE was associated with Aggregatibacter actinomycetemcomitans, Fusobacterium nucleatum, serum MCP 1 levels, RNA IL1-beta regulation and G6PD serum activity (p = 0.036, 0.003, 0.045, <0.001, and 0.021). Cognitive and motor skills seem to be important as representative tests are associated with periodontal pathogens and oral/general inflammation, wherein G6PD-saliva dysfunction might be involved.

Clinical trial registration

https://www.bfarm.de/DE/Das-BfArM/Aufgaben/Deutsches-Register-Klinischer-Studien/_node.html, identifier DRKS00005388.

Prefrontal Dopamine in Flexible Adaptation to Environmental Changes: A Game for Two Players

Deficits in cognitive flexibility have been characterized in affective, anxiety, and neurodegenerative disorders. This paper reviews data, mainly from studies on animal models, that support the existence of a cortical-striatal brain circuit modulated by dopamine (DA), playing a major role in cognitive/behavioral flexibility. Moreover, we reviewed clinical findings supporting misfunctioning of this circuit in Parkinson's disease that could be responsible for some important non-motoric symptoms. The reviewed findings point to a role of catecholaminergic transmission in the medial prefrontal cortex (mpFC) in modulating DA's availability in the nucleus accumbens (NAc), as well as a role of NAc DA in modulating the motivational value of natural and conditioned stimuli. The review section is accompanied by a preliminary experiment aimed at testing weather the extinction of a simple Pavlovian association fosters increased DA transmission in the mpFC and inhibition of DA transmission in the NAc.

Impulsive-compulsive behaviour in early Parkinson's disease is determined by apathy and dopamine receptor D3 polymorphism

Impulsive-compulsive behaviour (ICB) is a frequently observed non-motor symptom in early Parkinson's disease after initiating dopamine replacement therapy. At the opposite end of the motivated behaviour spectrum, apathy occurs in early Parkinson's disease even before dopamine replacement is started. The co-occurrence of these behavioural conditions in Parkinson's disease raises questions about their relationship and underlying pathophysiological determinants. In previous imaging or genetic studies, both conditions have been associated with the limbic dopaminergic system. The risk variant of the Ser9Gly polymorphism of the dopamine receptor D3 (DRD3) is linked to increased dopamine affinity in the limbic striatum. With this in mind, we investigated how ICB expression is explained by apathy and DRD3 polymorphisms and their effects on grey matter volume and dopamine synthesis capacity. Fifty-four patients with early Parkinson's disease took part in anatomical T1-weighted MRI. Forty of them also underwent dynamic PET imaging using [18F]DOPA to measure striatal dopamine synthesis capacity. Further, Ser9Gly (rs6280) gene polymorphism influencing the DRD3 dopamine-binding affinity was determined in all patients. The severity of impulsive-compulsive behaviour and apathy was assessed using the Questionnaire for Impulsive-Compulsive Disorders Rating Scale and the Apathy Evaluation Scale. ICB and the severity of apathy were indeed positively correlated. Apathy and the DRD3 polymorphism were interactive risk factors for ICB severity. Apathy was significantly linked to atrophy of the bilateral putamen. Patients with the DRD3 risk type had reduced dopamine synthesis capacity in the putamen and limbic striatum, apathy was associated with reduced dopamine synthesis capacity in the limbic striatum. The results of [18F]DOPA reached only trend significance. Apathy in drug-naïve PD patients might be a consequence of impaired striatal dopaminergic tone. This may represent a predisposing factor for the development of ICB after the initiation of dopamine replacement therapy. The risk type of DRD3 could further amplify this predisposition due to its higher affinity to dopamine.

GABAergic Neurons in the Nucleus Accumbens are Involved in the General Anesthesia Effect of Propofol

The mechanism underlying the hypnosis effect of propofol is still not fully understood. In essence, the nucleus accumbens (NAc) is crucial for regulating wakefulness and may be directly engaged in the principle of general anesthesia. However, the role of NAc in the process of propofol-induced anesthesia is still unknown. We used immunofluorescence, western blotting, and patch-clamp to access the activities of NAc GABAergic neurons during propofol anesthesia, and then we utilized chemogenetic and optogenetic methods to explore the role of NAc GABAergic neurons in regulating propofol-induced general anesthesia states. Moreover, we also conducted behavioral tests to analyze anesthetic induction and emergence. We found out that c-Fos expression was considerably dropped in NAc GABAergic neurons after propofol injection. Meanwhile, patch-clamp recording of brain slices showed that firing frequency induced by step currents in NAc GABAergic neurons significantly decreased after propofol perfusion. Notably, chemically selective stimulation of NAc GABAergic neurons during propofol anesthesia lowered propofol sensitivity, prolonged the induction of propofol anesthesia, and facilitated recovery; the inhibition of NAc GABAergic neurons exerted opposite effects. Furthermore, optogenetic activation of NAc GABAergic neurons promoted emergence whereas the result of optogenetic inhibition was the opposite. Our results demonstrate that NAc GABAergic neurons modulate propofol anesthesia induction and emergence.

Impulsivity Traits in Parkinson's Disease: A Systematic Review and Meta-Analysis

Background

In Parkinson's disease (PD), impulsivity as a personality trait may be linked to the risk of developing impulse control disorders (ICDs) during dopaminergic therapy. However, studies evaluating differences in trait impulsivity between patients with PD and healthy controls or between patients with PD with and without ICDs reported partly inconsistent findings.

Objectives

We conducted a systematic review and meta-analysis (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) of studies comparing Barratt Impulsiveness Scale (BIS-11) scores between patients with PD and healthy controls and between patients with PD with and without ICDs.

Methods

Eligible studies were identified through a systematic search in 3 databases. Mean differences with 95% confidence intervals (CIs) for BIS-11 total and subscale scores were separately calculated for studies comparing patients with PD and healthy controls and patients with PD with and without ICDs. Meta-regressions were performed to explore sources of heterogeneity (percentage of men, age, disease duration, and levodopa equivalent daily dose).

Results

A total of 40 studies were included in the quantitative analyses. BIS-11 total scores were significantly higher in patients with PD compared with healthy controls (mean difference 2.43; 95% CI, 1.03, 3.83), and in patients with PD with active ICDs compared with patients without ICDs (6.62; 95% CI, 5.01, 8.23). No significant moderators emerged by meta-regression analyses.

Conclusions

The present meta-analysis supports that impulsivity, as a personality trait, may characterize patients with PD, even in the absence of ICDs. Moreover, these data corroborate findings of clinical studies reporting higher levels of trait impulsivity in PD patients with ICDs compared with patients without ICDs.

Tissue specific LRRK2 interactomes reveal a distinct striatal functional unit

Mutations in LRRK2 are the most common genetic cause of Parkinson's disease. Despite substantial research efforts, the physiological and pathological role of this multidomain protein remains poorly defined. In this study, we used a systematic approach to construct the general protein-protein interactome around LRRK2, which was then evaluated taking into consideration the differential expression patterns and the co-expression behaviours of the LRRK2 interactors in 15 different healthy tissue types. The LRRK2 interactors exhibited distinct expression features in the brain as compared to the peripheral tissues analysed. Moreover, a high degree of similarity was found for the LRRK2 interactors in putamen, caudate and nucleus accumbens, thus defining a potential LRRK2 functional cluster within the striatum. The general LRRK2 interactome paired with the expression profiles of its members constitutes a powerful tool to generate tissue-specific LRRK2 interactomes. We exemplified the generation of the tissue-specific LRRK2 interactomes and explored the functions highlighted by the "core LRRK2 interactors" in the striatum in comparison with the cerebellum. Finally, we illustrated how the LRRK2 general interactome reported in this manuscript paired with the expression profiles can be used to trace the relationship between LRRK2 and specific interactors of interest, here focusing on the LRRK2 interactors belonging to the Rab protein family.

Neural correlates of impulse control behaviors in Parkinson's disease: Analysis of multimodal imaging data

BACKGROUND

Impulse control behaviors (ICB) are frequently observed in patients with Parkinson's disease (PD) and are characterized by compulsive and repetitive behavior resulting from the inability to resist internal drives.

OBJECTIVES

In this study, we aimed to provide a better understanding of structural and functional brain alterations and clinical parameters related to ICB in PD patients.

METHODS

We utilized a dataset from the Parkinson's Progression Markers Initiative including 36 patients with ICB (PDICB+) compared to 76 without ICB (PDICB-) and 61 healthy controls (HC). Using multimodal MRI data we assessed gray matter brain volume, white matter integrity, and graph topological properties at rest.

RESULTS

Compared with HC, PDICB+ showed reduced gray matter volume in the bilateral superior and middle temporal gyrus and in the right middle occipital gyrus. Compared with PDICB-, PDICB+ showed volume reduction in the left anterior insula. Depression and anxiety were more prevalent in PDICB+ than in PDICB- and HC. In PDICB+, lower gray matter volume in the precentral gyrus and medial frontal cortex, and higher axial diffusivity in the superior corona radiata were related to higher depression score. Both PD groups showed disrupted functional topological network pattern within the cingulate cortex compared with HC. PDICB+ vs PDICB- displayed reduced topological network pattern in the anterior cingulate cortex, insula, and nucleus accumbens.

CONCLUSIONS

Our results suggest that structural alterations in the insula and abnormal topological connectivity pattern in the salience network and the nucleus accumbens may lead to impaired decision making and hypersensitivity towards reward in PDICB+. Moreover, PDICB+ are more prone to suffer from depression and anxiety.

Drug-Induced Gambling Disorder: Epidemiology, Neurobiology, and Management

Problematic gambling has been suggested to be a possible consequence of dopaminergic medications used mainly in neurological conditions, i.e. pramipexole and ropinirole, and possibly by one antipsychotic compound, aripiprazole. Patients with Parkinson's disease, restless legs syndrome and other conditions potentially treated with dopamine agonists, as well as patients treated for psychotic disorders, are vulnerable patient groups with theoretically increased risk of developing gambling disorder (GD), for example due to higher rates of mental ill-health in these groups. The aim of the present paper is to review the epidemiological, clinical, and neurobiological evidence of the association between dopaminergic medications and GD, and to describe risk groups and treatment options. The neurobiology of GD involves the reward and reinforcement system, based mainly on mesocorticolimbic dopamine projections, with the nucleus accumbens being a crucial area for developing addictions to substances and behaviors. The addictive properties of gambling can perhaps be explained by the reward uncertainty that activates dopamine signaling in a pathological manner. Since reward-related learning is mediated by dopamine, it can be altered by dopaminergic medications, possibly leading to increased gambling behavior and a decreased impulse control. A causal relationship between the medications and GD seems likely, but the molecular mechanisms behind this association have not been fully described yet. More research is needed in order to fully outline the clinical picture of GD developing in patient groups with dopaminergic medications, and data are needed on the differentiation of risk in different compounds. In addition, very few interventional studies are available on the management of GD induced by dopaminergic medications. While GD overall can be treated, there is need for treatment studies testing the effectiveness of tapering of the medication or other gambling-specific treatment modalities in these patient groups.

Amphetamine-induced dopamine release and impulsivity in Parkinson's disease

Impulsive-compulsive behaviours manifest in a substantial proportion of subjects with Parkinson's disease. Reduced ventral striatum dopamine receptor availability, and increased dopamine release is noted in patients with these symptoms. Prior studies of impulsivity suggest that midbrain D2 autoreceptors regulate striatal dopamine release in a feedback inhibitory manner, and in healthy populations, greater impulsivity is linked to poor proficiency of this inhibition. This has not been assessed in a Parkinson's disease population. Here, we applied 18F-fallypride PET studies to assess striatal and extrastriatal D2-like receptor uptake in a placebo-controlled oral dextroamphetamine sequence. We hypothesized that Parkinson's disease patients with impulsive-compulsive behaviours would have greater ventral striatal dopaminergic response to dextroamphetamine, and that an inability to attenuate ventral striatal dopamine release via midbrain D2 autoreceptors would underlie this response. Twenty patients with Parkinson's disease (mean age = 64.1 ± 5.8 years) both with (n = 10) and without (n = 10) impulsive-compulsive behaviours, participated in a single-blind dextroamphetamine challenge (oral; 0.43 mg/kg) in an OFF dopamine state. All completed PET imaging with 18F-fallypride, a high-affinity D2-like receptor ligand, in the placebo and dextroamphetamine state. Both voxelwise and region of interest analyses revealed dextroamphetamine-induced endogenous dopamine release localized to the ventral striatum, and the caudal-medial orbitofrontal cortex. The endogenous dopamine release observed in the ventral striatum correlated positively with patient-reported participation in reward-based behaviours, as quantified by the self-reported Questionnaire for Impulsivity in Parkinson's disease Rating Scale. In participants without impulsive-compulsive behaviours, baseline midbrain D2 receptor availability negatively correlated with ventral striatal dopamine release; however, this relationship was absent in those with impulsive-compulsive behaviours. These findings emphasize that reward-based behaviours in Parkinson's disease are regulated by ventral striatal dopamine release, and suggest that loss of inhibitory feedback from midbrain autoreceptors may underlie the manifestation of impulsive-compulsive behaviours.

Imaging the Limbic System in Parkinson's Disease-A Review of Limbic Pathology and Clinical Symptoms

The limbic system describes a complex of brain structures central for memory, learning, as well as goal directed and emotional behavior. In addition to pathological studies, recent findings using in vivo structural and functional imaging of the brain pinpoint the vulnerability of limbic structures to neurodegeneration in Parkinson's disease (PD) throughout the disease course. Accordingly, dysfunction of the limbic system is critically related to the symptom complex which characterizes PD, including neuropsychiatric, vegetative, and motor symptoms, and their heterogeneity in patients with PD. The aim of this systematic review was to put the spotlight on neuroimaging of the limbic system in PD and to give an overview of the most important structures affected by the disease, their function, disease related alterations, and corresponding clinical manifestations. PubMed was searched in order to identify the most recent studies that investigate the limbic system in PD with the help of neuroimaging methods. First, PD related neuropathological changes and corresponding clinical symptoms of each limbic system region are reviewed, and, finally, a network integration of the limbic system within the complex of PD pathology is discussed.

Neural correlates and predictors of subjective cognitive decline in patients with Parkinson's disease

BACKGROUND

Subjective cognitive decline (SCD) may occur very early in the course of Parkinson's disease (PD) before the onset of objective cognitive decline. Data on neural correlates and determinants of SCD in PD are rare.

OBJECTIVE

The aim of the present study was to identify neural correlates as well as sociodemographic, clinical, and neuropsychological predictors of SCD in patients with PD.

METHODS

We retrospectively analyzed 30 patients with PD without cognitive impairment (23% female, 66.90 ± 7.20 years, UPDRS-III: 19.83 ± 9.29), of which n = 12 patients were classified as having no SCD (control group, PD-CG) and n = 18 as having SCD (PD-SCD). Neuropsychological testing and 18-fluoro-2-deoxyglucose positron emission tomography (FDG-PET) were conducted. SCD was assessed using a questionnaire covering multiple cognitive domains.

RESULTS

SCD subscores differed significantly between PD-CG and PD-SCD and correlated significantly with other scales measuring related concepts. FDG-PET whole-brain voxel-wise regression analysis revealed hypometabolism in middle frontal, middle temporal, and occipital areas, and the angular gyrus as neural correlates of SCD in PD. Next to this hypometabolism, depressive symptoms were an independent significant determinant of SCD in a stepwise regression analysis (adjusted R2 = 50.3%).

CONCLUSION

This study strengthens the hypothesis of SCD being an early manifestation of future cognitive decline in PD and, more generally, early pathological changes in PD. The early identification of the vulnerability for future cognitive decline constitutes the basis for successful prevention and delay of this non-motor symptom.

Dopamine-induced changes to thalamic GABA concentration in impulsive Parkinson disease patients

Impulsivity is inherent to behavioral disorders such as substance abuse and binge eating. While the role of dopamine in impulse behavior is well established, γ-aminobutyric acid (GABA) therapies have promise for the treatment of maladaptive behaviors. In Parkinson disease (PD), dopaminergic therapies can result in the development of impulsive and compulsive behaviors, and this clinical syndrome shares similar pathophysiology to that seen in addiction, substance abuse, and binge-eating disorders. We hypothesized that impulsive PD patients have a reduced thalamic GABAergic response to dopamine therapy. To test this hypothesis, we employed GABA magnetic resonance spectroscopy, D2-like receptor PET imaging, and clinical and quantitative measures of impulsivity in PD patients (n = 33), before and after dopamine agonist administration. We find a blunted thalamic GABA response to dopamine agonists in patients with elevated impulsivity (p = 0.027). These results emphasize how dopamine treatment differentially augments thalamic GABA concentrations, which may modify behavioral impulsivity.

More than Addiction—The Nucleus Accumbens Contribution to Development of Mental Disorders and Neurodegenerative Diseases

Stress and negative emotions evoked by social relationships and working conditions, frequently accompanied by the consumption of addictive substances, and metabolic and/or genetic predispositions, negatively affect brain function. One of the affected structures is nucleus accumbens (NAc). Although its function is commonly known to be associated with brain reword responses and addiction, a growing body of evidence also suggests its role in some mental disorders, such as depression and schizophrenia, as well as neurodegenerative diseases, such as Alzheimer’s, Huntington’s, and Parkinson’s. This may result from disintegration of the extensive connections based on numerous neurotransmitter systems, as well as impairment of some neuroplasticity mechanisms in the NAc. The consequences of NAc lesions are both morphological and functional. They include changes in the NAc’s volume, cell number, modifications of the neuronal dendritic tree and dendritic spines, and changes in the number of synapses. Alterations in the synaptic plasticity affect the efficiency of synaptic transmission. Modification of the number and structure of the receptors affects signaling pathways, the content of neuromodulators (e.g., BDNF) and transcription factors (e.g., pCREB, DeltaFosB, NFκB), and gene expression. Interestingly, changes in the NAc often have a different character and intensity compared to the changes observed in the other parts of the basal ganglia, in particular the dorsal striatum. In this review, we highlight the role of the NAc in various pathological processes in the context of its structural and functional damage, impaired connections with the other brain areas cooperating within functional systems, and progression of the pathological processes.

Assessment of Repetitive and Compulsive Behaviors Induced by Pramipexole in Rats: Effect of Alpha-Synuclein-Induced Nigrostriatal Degeneration

Treatment with dopamine agonists in Parkinson’s disease (PD) is associated with debilitating neuropsychiatric side-effects characterized by impulsive and compulsive behaviors. The vulnerability to develop such impairments is thought to involve interactions between individual vulnerability traits, types of antiparkinsonian medications, and the neurodegenerative process. We investigated the effect of the dopamine D3/D2 agonist pramipexole (PPX) and selective nigrostriatal degeneration achieved by viral-mediated expression of alpha-synuclein on the expression of repetitive and compulsive-like behaviors in rats. In a task assessing spontaneous food hoarding behavior, PPX increased the time spent interacting with food pellets at the expense of hoarding. This disruption of hoarding behavior was identical in sham and lesioned rats. In an operant post-training signal attenuation task, the combination of nigrostriatal lesion and PPX decreased the number of completed trials and increased the number of uncompleted trials. The lesion led to an increased compulsive behavior after signal attenuation, and PPX shifted the overall behavioral output towards an increased proportion of compulsive lever-presses. Given the magnitude of the behavioral effects and the lack of strong interaction between PPX and nigral degeneration, these results suggest that extra-nigral pathology may be critical to increase the vulnerability to develop compulsive behaviors following treatment with D3/D2 agonists.

Simultaneous Damage of the Cingulate Cortex Zone II and Fronto-Striatal Circuit Causes Prolonged Selective Attentional Deficits

Selective attention is essential for successful cognitive performance. Although several brain areas are known to be involved in selective attention, damage to some of these areas does not necessarily cause attentional deficits. In the current study, we hypothesized that damage to specific parts of the right cerebral hemisphere, especially the cingulate cortex (CC), causes prolonged selective attentional deficits, and examined the influence of focal brain damage on selective attention. We recruited 36 patients with right cerebral hemispheric WHO grade 2 and 3 brain tumors who underwent surgery. We assessed selective attention over time from pre-operation to 3 months postoperatively using the cancelation test and color Stroop test, and calculated the percentage of deficit. Additionally, two types of imaging analyses were performed: voxel-based lesion symptom mapping (VLSM) and multiple logistic regression analysis, to reveal related brain regions for selective attention. Consequently, we found that the CC and deep part of the middle frontal gyrus were associated with deficits in selective attention via VLSM. Using multiple logistic regression analysis, the CC zone II at the cortical level (p < 0.0001) and the fronto-striatal tract (FST) at the subcortical level (p = 0.0079) were associated with attentional deficit among several regions identified in the VLSM. At 3 months postoperatively, selective attention was impaired in patients who underwent resection of these regions. Moreover, only patients with simultaneous damage of the CC zone II and FST had prolonged attentional deficits until the chronic phase. Our results suggest that the right CC zone II and FST are critical areas for the selective attentional networks.

The neuropsychiatry of Parkinson's disease: advances and challenges

In people with Parkinson's disease, neuropsychiatric signs and symptoms are common throughout the disease course. These symptoms can be disabling and as clinically relevant as motor symptoms, and their presentation can be similar to, or distinct from, their counterparts in the general population. Correlates and risk factors for developing neuropsychiatric signs and symptoms include demographic, clinical, and psychosocial characteristics. The underlying neurobiology of these presentations is complex and not well understood, with the strongest evidence for neuropathological changes associated with Parkinson's disease, mechanisms linked to dopaminergic therapy, and effects not specific to Parkinson's disease. Assessment instruments and formal diagnostic criteria exist, but there is little routine screening of these signs and symptoms in clinical practice. Mounting evidence supports a range of pharmacological and non-pharmacological interventions, but relatively few efficacious treatment options exist. Optimising the management of neuropsychiatric presentations in people with Parkinson's disease will require additional research, raised awareness, specialised training, and development of innovative models of care.

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

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

Imaging Cognitive Impairment and Impulse Control Disorders in Parkinson's Disease

Dementia and mild forms of cognitive impairment as well as neuropsychiatric symptoms (i. e., impulse control disorders) are frequent and disabling non-motor symptoms of Parkinson's disease (PD). The identification of changes in neuroimaging studies for the early diagnosis and monitoring of the cognitive and neuropsychiatric symptoms associated with Parkinson's disease, as well as their pathophysiological understanding, are critical for the development of an optimal therapeutic approach. In the current literature review, we present an update on the latest structural and functional neuroimaging findings, including high magnetic field resonance and radionuclide imaging, assessing cognitive dysfunction and impulse control disorders in PD.

Impulse control disorders are associated with lower ventral striatum dopamine D3 receptor availability in Parkinson's disease: A [11C]-PHNO PET study

INTRODUCTION

Reduced postsynaptic D3 dopaminergic receptor availability has been reported in the ventral striatum of pathological gamblers without Parkinson's disease (PD) and in patients with PD and impulse control disorders (ICD). However, a direct relationship between ventral striatum D3 dopaminergic receptors and the severity of ICD in PD patients has not yet been proven using a validated tool for ICD in PD, such as the Questionnaire for Impulsive-Compulsive Disorders in Parkinson's disease-Rating Scale (QUIP-RS). In this pilot study, we investigated the relationship between ventral striatum D3 dopamine receptor availability and severity of impulse control disorder (ICD) in Parkinson's disease (PD).

METHODS

Twelve patients were assessed with PET and the high affinity dopamine D3 receptor radioligand [¹¹C]-PHNO. Severity of ICD was assessed with the QUIP-RS.

RESULTS

We found that lower ventral striatum D3 receptor availability measured with [¹¹C]-PHNO PET was associated with greater severity of ICD, as measured by the QUIP-RS score (rho = -0.625, p = 0.03).

CONCLUSION

These findings suggest that the occurrence and severity of ICD in Parkinson's disease may be linked to reductions in ventral striatum dopamine D3 receptor availability. Further studies in larger cohort of patients need to be performed in order to confirm our findings and clarify whether lower ventral striatum D3 receptor may reflect a pharmacological downregulation to higher dopamine release in ventral striatum of patients with ICD or a patients' predisposition to ICD.

Impulse Control Disorders in Parkinson's Disease: From Bench to Bedside

Parkinson’s disease (PD) is a neurodegenerative disorder that is characterized by symptoms that impact both motor and non-motor domains. Outside of motor impairments, PD patients are at risk for impulse control disorders (ICDs), which include excessively disabling impulsive and compulsive behaviors. ICD symptoms in PD (PD + ICD) can be broadly conceptualized as a synergistic interaction between dopamine agonist therapy and the many molecular and circuit-level changes intrinsic to PD. Aside from discontinuing dopamine agonist treatment, there remains a lack of consensus on how to best address ICD symptoms in PD. In this review, we explore recent advances in the molecular and neuroanatomical mechanisms underlying ICD symptoms in PD by summarizing a rapidly accumulating body of clinical and preclinical studies, with a special focus on the utility of rodent models in gaining new insights into the neurochemical basis of PD + ICD. We also discuss the relevance of these findings to the broader problem of impulsive and compulsive behaviors that impact a range of neuropsychiatric syndromes.

The relationship between apathy and impulsivity in large population samples

Apathy and impulsivity are debilitating conditions associated with many neuropsychiatric conditions, and expressed to variable degrees in healthy people. While some theories suggest that they lie at different ends of a continuum, others suggest their possible co-existence. Surprisingly little is known, however, about their empirical association in the general population. Here, gathering data from six large studies (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$n = 3755$$\end{document}n=3755), we investigated the relationship between measures of apathy and impulsivity in young adults. The questionnaires included commonly used self-assessment tools—Apathy Evaluation Scale, Barratt Impulsiveness Scale (BIS-11) and UPPS-P Scale—as well as a more recent addition, the Apathy Motivation Index (AMI). Remarkably, across datasets and assessment tools, global measures of apathy and impulsivity correlated positively. However, analysis of sub-scale scores revealed a more complex relationship. Although most dimensions correlated positively with one another, there were two important exceptions revealed using the AMI scale. Social apathy was mostly negatively correlated with impulsive behaviour, and emotional apathy was orthogonal to all other sub-domains. These results suggest that at a global level, apathy and impulsivity do not exist at distinct ends of a continuum. Instead, paradoxically, they most often co-exist in young adults. Processes underlying social and emotional apathy, however, appear to be different and dissociable from behavioural apathy and impulsivity.

Inhibitory control dysfunction in parkinsonian impulse control disorders

Impulse control disorders (ICDs) in Parkinson's disease have been associated with dysfunctions in the control of value- or reward-based responding (choice impulsivity) and abnormalities in mesocorticolimbic circuits. The hypothesis that dysfunctions in the control of response inhibition (action impulsivity) also play a role in Parkinson's disease ICDs has recently been raised, but the underlying neural mechanisms have not been probed directly. We used high-resolution EEG recordings from 41 patients with Parkinson's disease with and without ICDs to track the spectral and dynamical signatures of different mechanisms involved in inhibitory control in a simple visuomotor task involving no selection between competing responses and no reward to avoid potential confounds with reward-based decision. Behaviourally, patients with Parkinson's disease with ICDs proved to be more impulsive than those without ICDs. This was associated with decreased beta activity in the precuneus and in a region of the medial frontal cortex centred on the supplementary motor area. The underlying dynamical patterns pinpointed dysfunction of proactive inhibitory control, an executive mechanism intended to gate motor responses in anticipation of stimulation in uncertain contexts. The alteration of the cortical drive of proactive response inhibition in Parkinson's disease ICDs pinpoints the neglected role the precuneus might play in higher order executive functions in coordination with the supplementary motor area, specifically for switching between executive settings. Clinical perspectives are discussed in the light of the non-dopaminergic basis of this function.

The default mode network and cognition in Parkinson's disease: A multimodal resting-state network approach

Involvement of the default mode network (DMN) in cognitive symptoms of Parkinson's disease (PD) has been reported by resting-state functional MRI (rsfMRI) studies. However, the relation to metabolic measures obtained by [18F]-fluorodeoxyglucose positron emission tomography (FDG-PET) is largely unknown. We applied multimodal resting-state network analysis to clarify the association between intrinsic metabolic and functional connectivity abnormalities within the DMN and their significance for cognitive symptoms in PD. PD patients were classified into normal cognition (n = 36) and mild cognitive impairment (MCI; n = 12). The DMN was identified by applying an independent component analysis to FDG-PET and rsfMRI data of a matched subset (16 controls and 16 PD patients) of the total cohort. Besides metabolic activity, metabolic and functional connectivity within the DMN were compared between the patients' groups and healthy controls (n = 16). Glucose metabolism was significantly reduced in all DMN nodes in both patient groups compared to controls, with the lowest uptake in PD-MCI (p < .05). Increased metabolic and functional connectivity along fronto-parietal connections was identified in PD-MCI patients compared to controls and unimpaired patients. Functional connectivity negatively correlated with cognitive composite z-scores in patients (r = -.43, p = .005). The current study clarifies the commonalities of metabolic and hemodynamic measures of brain network activity and their individual significance for cognitive symptoms in PD, highlighting the added value of multimodal resting-state network approaches for identifying prospective biomarkers.

Prenatal Alcohol Exposure in Rats Diminishes Postnatal Cxcl16 Chemokine Ligand Brain Expression

Maternal ethanol consumption during pregnancy is one of the main causes of Neurodevelopmental disorders (NDD). Prenatal alcohol exposure (PAE) produces several adverse manifestations. Even low or moderate intake has been associated with long-lasting behavioral and cognitive impairment in offspring. In this study we examined the gene expression profile in the rat nucleus accumbens using microarrays, comparing animals exposed prenatally to ethanol and controls. Microarray gene expression showed an overall downward regulatory effect of PAE. Gene cluster analysis reveals that the gene groups most affected are related to transcription regulation, transcription factors and homeobox genes. We focus on the expression of the C-X-C motif chemokine ligand 16 (Cxcl16) which was differentially expressed. There is a significant reduction in the expression of this chemokine throughout the brain under PAE conditions, evidenced here by quantitative polymerase chain reaction qPCR and immunohistochemistry. Chemokines are involved in neuroprotection and implicated in alcohol-induced brain damage and neuroinflammation in the developing central nervous system (CNS), therefore, the significance of the overall decrease in Cxcl16 expression in the brain as a consequence of PAE may reflect a reduced ability in neuroprotection against subsequent conditions, such as excitotoxic damage, inflammatory processes or even hypoxic-ischemic insult.

Non-motor symptom burden in patients with Parkinson's disease with impulse control disorders and compulsive behaviours: results from the COPPADIS cohort

The study was aimed at analysing the frequency of impulse control disorders (ICDs) and compulsive behaviours (CBs) in patients with Parkinson's disease (PD) and in control subjects (CS) as well as the relationship between ICDs/CBs and motor, nonmotor features and dopaminergic treatment in PD patients. Data came from COPPADIS-2015, an observational, descriptive, nationwide (Spain) study. We used the validated Questionnaire for Impulsive-Compulsive Disorders in Parkinson's Disease-Rating Scale (QUIP-RS) for ICD/CB screening. The association between demographic data and ICDs/CBs was analyzed in both groups. In PD, this relationship was evaluated using clinical features and treatment-related data. As result, 613 PD patients (mean age 62.47 ± 9.09 years, 59.87% men) and 179 CS (mean age 60.84 ± 8.33 years, 47.48% men) were included. ICDs and CBs were more frequent in PD (ICDs 12.7% vs. 1.6%, p < 0.001; CBs 7.18% vs. 1.67%, p = 0.01). PD patients had more frequent previous ICDs history, premorbid impulsive personality and antidepressant treatment (p < 0.05) compared with CS. In PD, patients with ICDs/CBs presented younger age at disease onset, more frequent history of previous ICDs and premorbid personality (p < 0.05), as well as higher comorbidity with nonmotor symptoms, including depression and poor quality of life. Treatment with dopamine agonists increased the risk of ICDs/CBs, being dose dependent (p < 0.05). As conclusions, ICDs and CBs were more frequent in patients with PD than in CS. More nonmotor symptoms were present in patients with PD who had ICDs/CBs compared with those without. Dopamine agonists have a prominent effect on ICDs/CBs, which could be influenced by dose.

Incentive-driven decision-making networks in de novo and drug-treated Parkinson's disease patients with impulsive-compulsive behaviors: A systematic review of neuroimaging studies

BACKGROUND

In Parkinson's disease (PD), impulsive-compulsive behaviors (ICBs) may develop as side-effect of dopaminergic medications. Abnormal incentive-driven decision-making, which is supported by the cognitive control and motivation interaction, may represent an ICBs signature. This systematic review explored whether structural and/or functional brain differences between PD patients with vs without ICBs encompass incentive-driven decision-making networks.

METHODS

Structural and functional neuroimaging studies comparing PD patients with and without ICBs, either de novo or medicated, were included.

RESULTS

Thirty articles were identified. No consistent evidence of structural alteration both in de novo and medicated PD patients were found. Differences in connectivity within the default mode, the salience and the central executive networks predate ICBs development and remain stable once ICBs are fully developed. Medicated PD patients with ICBs show increased metabolism and cerebral blood flow in orbitofrontal and cingulate cortices, ventral striatum, amygdala, insula, temporal and supramarginal gyri. Abnormal ventral striatum connectivity with anterior cingulate cortex and limbic structures was reported in PD patients with ICBs.

DISCUSSION

Functional brain signatures of ICBs in PD encompass areas involved in cognitive control and motivational encoding networks of the incentive-driven decision-making. Functional alterations predating ICBs may be related to abnormal synaptic plasticity in these networks.

GBA Variants in Parkinson's Disease: Clinical, Metabolomic, and Multimodal Neuroimaging Phenotypes

BACKGROUND

Alterations in the GBA gene (NM_000157.3) are the most important genetic risk factor for Parkinson's disease (PD). Biallelic GBA mutations cause the lysosomal storage disorder Gaucher's disease. The GBA variants p.E365K and p.T408M are associated with PD but not with Gaucher's disease. The pathophysiological role of these variants needs to be further explored.

OBJECTIVE

This study analyzed clinical, neuropsychological, metabolic, and neuroimaging phenotypes of patients with PD carrying the GBA variants p.E365K and p.T408M.

METHODS

GBA was sequenced in 56 patients with mid-stage PD. Carriers of GBA variants were compared with noncarriers regarding clinical history and symptoms, neuropsychological features, metabolomics, and multimodal neuroimaging. Blood plasma gas chromatography coupled to mass spectrometry, 6-[¹⁸ F]fluoro-L-Dopa positron emission tomography (PET), [¹⁸ F]fluorodeoxyglucose PET, and resting-state functional magnetic resonance imaging were performed.

RESULTS

Sequence analysis detected 13 heterozygous GBA variant carriers (7 with p.E365K, 6 with p.T408M). One patient carried a GBA mutation (p.N409S) and was excluded. Clinical history and symptoms were not significantly different between groups. Global cognitive performance was lower in variant carriers. Metabolomic group differences were suggestive of more severe PD-related alterations in carriers versus noncarriers. Both PET scans showed signs of a more advanced disease; [¹⁸ F]fluorodeoxyglucose PET and functional magnetic resonance imaging showed similarities with Lewy body dementia and PD dementia in carriers.

CONCLUSIONS

This is the first study to comprehensively assess (neuro-)biological phenotypes of GBA variants in PD. Metabolomics and neuroimaging detected more significant group differences than clinical and behavioral evaluation. These alterations could be promising to monitor effects of disease-modifying treatments targeting glucocerebrosidase metabolism. © 2020 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Linking brain activity during sequential gambling to impulse control in Parkinson's disease

Dopaminergic treatment may impair the ability to suppress impulsive behaviours in patients with Parkinson's disease, triggering impulse control disorders. It is unclear how dopaminergic medication affects the neural networks that contribute to withholding inappropriate actions. To address this question, we mapped task-related brain activity with whole-brain functional magnetic resonance imaging at 3 Tesla in 26 patients with Parkinson's disease. Patients performed a sequential gambling task while being ON and OFF their regular dopaminergic treatment. During a gambling round, patients repeatedly decided between the option to continue with gambling and accumulate more monetary reward under increasing risk or the option to bank the current balance and start a new round. 13 patients had an impulse control disorder (ICD + group). These patients did not differ in risk-taking attitude during sequential gambling from 13 patients without impulse control disorder (ICD - group), but they displayed differences in gambling-related activity in cortico-subcortical brain areas supporting inhibitory control. First, the ICD + group showed reduced "continue-to-gamble" activity in right inferior frontal gyrus and subthalamic nucleus. Second, the individual risk-attitude scaled positively with "continue-to-gamble" activity in right subthalamic nucleus and striatum in the ICD - group only. Third, ICD + patients differed in their functional neural responses to dopaminergic treatment from ICD - patients: dopaminergic therapy reduced functional connectivity between inferior frontal gyrus and subthalamic nucleus during "continue-to-gamble" decisions and attenuated striatal responses towards accumulating reward and risk. Together, the medication-independent (trait) and medication-related (state) differences in neural activity may set a permissive stage for the emergence of impulse control disorders during dopamine replacement therapy in Parkinson's disease.

Lower nucleus accumbens α-synuclein load and D3 receptor levels in Parkinson's disease with impulsive compulsive behaviours

Impulsive compulsive behaviours in Parkinson's disease have been linked to increased dopaminergic release in the ventral striatum and excessive stimulation of dopamine D3 receptors. Thirty-one patients with impulsive compulsive behaviours and Parkinson's disease who donated their brains to the Queen Square Brain Bank for Neurological Disorders were assessed for α-synuclein neuropathological load and tyrosine hydroxylase levels in the nucleus accumbens, dorsal putamen and caudate using immunohistochemistry. Dopamine D2 and dopamine D3 receptors protein levels in the nucleus accumbens, frontal cortex and putamen were determined using western blotting. Results were compared to 29 Parkinson's disease cases without impulsive compulsive behaviours matched by age, sex, disease duration, age at Parkinson's disease onset and disease duration. The majority of patients with impulsive compulsive behaviours had dopamine dysregulation syndrome. Patients with Parkinson's disease and impulsive compulsive behaviours had lower α-synuclein load and dopamine D3 receptor levels in the nucleus accumbens. No differences were seen between groups in the other brain areas and in the analysis of tyrosine hydroxylase and dopamine D2 receptor levels. Lower α-synuclein load in the nucleus accumbens of individuals with Parkinson's disease and impulsive compulsive behaviours was confirmed on western blotting. Downregulation of the dopamine D3 receptor levels may have occurred either as a consequence of the degenerative process or of a pre-morbid trait. The lower levels of α-synuclein may have contributed to an excessive stimulation of the ventral striatum resulting in impulsive compulsive behaviours.

The adverse effects of pramipexole on probability discounting are not reversed by acute D2 or D3 receptor antagonism

Pramipexole (PPX) is a D₂ and D₃ dopamine receptor agonist approved for clinical use, which is associated with a higher risk of impulse-control disorders. Using a rat model, we recently found that low doses of the monoamine-depleting agent reserpine (RES; 1 mg/kg/day, SC) dramatically increased the untoward effects of PPX (0.3 mg/kg/day, SC) on probability discounting, a key impulsivity function. To further understand the neurobehavioral mechanisms underlying these effects, we first tested whether the combination of PPX and RES may lead to a generalized enhancement in risk taking, as tested in the suspended wire-beam paradigm. The association of RES and PPX did not augment the proclivity of rats to cross the bridge in order to obtain a reward, suggesting that the effects of RES and PPX on probability discounting do not reflect a generalized increase in impulsivity. We then studied what receptors mediate the effects of PPX in RES-treated rats. The combination of RES and PPX increased membrane expression and binding of D₃, but not D₂ dopamine receptors, in the nucleus accumbens. However, the behavioral effects of PPX and RES were not reduced by acute treatments with the D₂/D₃ receptor antagonist raclopride (0.01-0.05 mg/kg, SC), the highly selective D₂ receptor antagonist L-741,626 (0.1-1 mg/kg, SC) or the D₃ receptor antagonists GR 103691 (0.1-0.3 mg/kg, SC) and SB 277011A (1-10 mg/kg, SC). These findings collectively suggest that the effects of PPX in probability discounting do not reflect generalized enhancements in impulsivity or acute dopamine D₂ or D₃ receptor activation.

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.

Human Brain Imaging Links Dopaminergic Systems to Impulsivity

Molecular and functional imaging techniques have been used and combined with pharmacological probes to evaluate the role of dopamine in impulsivity. Overall, strong evidence links striatal dopaminergic function with impulsivity, measured by self-reports and laboratory tests of cognitive control and reward-based decision-making. The combination of molecular imaging using positron emission tomography (PET) with functional magnetic resonance imaging (fMRI) specifically implicates striatal D2-type dopamine receptors (i.e., D2 and D3) and corticostriatal connectivity in cognitive control. Low levels of striatal and midbrain D2-type receptor availability correlate with self-reported impulsivity, whereas striatal D2-type receptor availability shows positive correlation with motor response inhibition and cognitive flexibility. Impulsive choice on reward-based decision-making tasks also is related to deficits in striatal D2-type dopamine receptor availability, and there is evidence for an inverted U-shaped function in this relationship, reflecting an optimum of striatal dopaminergic activity. Findings from studies of clinical populations that present striatal dopamine D2-type receptor deficits as well as healthy control research participants identify D2-type receptors as therapeutic targets to improve cognitive control.

Brain Imaging and Impulse Control Disorders in Parkinson's Disease

Purpose of Review

Parkinson’s disease (PD) has a wide spectrum of symptoms including the presence of psychiatric disease. At present, most treatment plans, comprised of dopaminergic drugs, are chronic and complex. Though dopaminergic agents are quite efficient in managing the motor aspects of the disease, chronic pharmacotherapy specifically with dopamine receptor agonists has been highly linked to the occurrence of Impulse Compulsive disorder (ICD), which can be problematic for individual patients.

Recent Findings

Much of what is known today about PD-related ICD stems from brain imaging studies, however, evidence is not quite conclusive. Research in the field has been focused on identifying the underlying mechanisms of PD-related ICD and understanding the functions of the structures involved in the reward network.

Summary

This article presents an update of recent findings from key neuroimaging studies in PD-related ICD, discusses results from controversial studies, and identifies areas for future research in the field.

Connectomics and molecular imaging in neurodegeneration

Our understanding on human neurodegenerative disease was previously limited to clinical data and inferences about the underlying pathology based on histopathological examination. Animal models and in vitro experiments have provided evidence for a cell-autonomous and a non-cell-autonomous mechanism for the accumulation of neuropathology. Combining modern neuroimaging tools to identify distinct neural networks (connectomics) with target-specific positron emission tomography (PET) tracers is an emerging and vibrant field of research with the potential to examine the contributions of cell-autonomous and non-cell-autonomous mechanisms to the spread of pathology. The evidence provided here suggests that both cell-autonomous and non-cell-autonomous processes relate to the observed in vivo characteristics of protein pathology and neurodegeneration across the disease spectrum. We propose a synergistic model of cell-autonomous and non-cell-autonomous accounts that integrates the most critical factors (i.e., protein strain, susceptible cell feature and connectome) contributing to the development of neuronal dysfunction and in turn produces the observed clinical phenotypes. We believe that a timely and longitudinal pursuit of such research programs will greatly advance our understanding of the complex mechanisms driving human neurodegenerative diseases.