Positron emission tomography shows that impaired frontal lobe functioning in Parkinson's disease is related to dopaminergic hypofunction in the caudate nucleus

Quantifying cerebral blood flow changes using arterial spin labeling: A comparative study of idiopathic rapid eye movement sleep behavior disorder and Parkinson's disease

INTRODUCTION

Idiopathic rapid eye movement sleep behavior disorder (iRBD) and Parkinson's disease (PD) have been found to have changes in cerebral perfusion and overlap of some of the lesioned brain areas. However, a consensus regarding the specific location and diagnostic significance of these cerebral blood perfusion alternations remains elusive in both iRBD and PD. The present study evaluated the patterns of cerebral blood flow changes in iRBD and PD.

MATERIAL AND METHODS

A total of 59 right-handed subjects were enrolled, including 15 patients with iRBD, 20 patients with PD, and 24 healthy controls (HC). They were randomly divided into groups at a ratio of 4 to 1 for training and testing. A PASL sequence was employed to obtain quantitative cerebral blood flow (CBF) maps. The CBF values were calculated from these acquired maps. In addition, AutoGluon was employed to construct a classifier for CBF features selection and classification. An independent t-test was performed for CBF variations, with age and sex as nuisance variables. The performance of the feature was evaluated using receiver operating characteristic (ROC) curves. A significance level of P < 0.05 was considered significant. CBF in several brain regions, including the left median cingulate and paracingulate gyri and the right middle occipital gyrus (MOG), showed significant differences between PD and HC, demonstrating good classification performance. The combined model that integrates all features achieved even higher performance with an AUC of 0.9380. Additionally, CBF values in multiple brain regions, including the right MOG and the left angular gyrus, displayed significant differences between PD and iRBD. Particularly, CBF values in the left angular gyrus exhibited good performance in classifying PD and iRBD. The combined model achieved improved performance, with an AUC of 0.8533. No significant differences were found in brain regions when comparing CBF values between iRBD and HC subjects.

CONCLUSIONS

ASL-based quantitative CBF change features can offer reliable biomarkers to assist in the diagnosis of PD. Regarding the characteristic of CBF in the right MOG, it is anticipated to serve as an imaging biomarker for predicting the progression of iRBD to PD.

Topological alteration of the brain structural network in Parkinson's disease with apathy

BACKGROUND

Apathy is a common neuropsychiatric manifestations in Parkinson's disease (PD), but neural network mechanisms still remain elusive. We aim to investigate the topological alteration of the brain structural network in PD with apathy.

METHOD

In the present study, a total of 47 apathetic PD (aPD) patients, 37 non-apathetic PD (naPD) patients, and 40 healthy controls (HCs) were enrolled. Diffusion tensor imaging (DTI) in conjunction with graph-theoretic approaches were used to explore the alterations of topological properties of the WM structural network arising from apathy in PD. One-way analysis of covariance and post hoc analyses were performed to explore differences among the three groups. Correlations were ascertained to examine relationships between the Starkstein Apathy Scale (AS) scores and significantly different network metrics among the three groups.

RESULTS

Both aPD and naPD patients remained small-world topology. However, compared with the naPD patients, aPD patients showed increased clustering coefficient (Cp) at the global level. At the regional level, aPD exhibited decreased nodal properties, mainly in the right dorsolateral prefrontal cortex (DLPFC), the right caudate nucleus (CAU), the right hippocampus, and the right superior parietal gyrus. Further, AS scores were negatively correlated with degree centrality of the right DLPFC (r = -0.254, p = 0.020) and the right CAU ( r = -0.357, p = 0.001) in the pooled patients with PD.

CONCLUSIONS

The findings suggested that apathy in PD presented relatively optimized global topological properties of the brain structural network and disrupted topological organization of the regional network, particularly involving the fronto-striatal-limbic circuits. The altered topological properties of abnormal brain regions might be used to understand the physiopathologic mechanism of the neural network in aPD patients.

Slowing of EEG waves correlates with striatal [18 F]fluorodopa PET/CT uptake and executive dysfunction in Parkinson's disease

Parkinson's disease (PD) research on specific neuroimaging and neurophysiological biomarkers revealing executive dysfunction mechanisms is limited, necessitating validation. Thus, our study aimed to assess associations between electroencephalographic power spectral density (PSD-EEG), striatal [18 F]Fluorodopa uptake and neuropsychological executive function (EF) testing parameters in PD, while also estimating their diagnostic accuracy. We compared resting PSD-EEG, striatal [18 F]Fluorodopa uptake ratios based on positron emission computed tomography ([18 F]FDOPA PET/CT) and neuropsychological EF tests outcomes [Trail Making Test (TMT) and Stroop Test (ST)] between PD patients and healthy controls (HCO) and then calculated correlations among these measures separately for each group. Additionally, we estimated PD diagnostic accuracy of the PSD-EEG and [18 F]FDOPA PET/CT parameters. In PD patients, we observed the following: (i) slower EEG waves, reflected in increased power of the EEG theta and lower-alpha bands in frontal lobe areas; (ii) reduced [18 F]FDOPA PET/CT uptake in the putaminal and caudate nuclei, along with a decreased putamen-to-caudate ratio ([18 F]FDOPA PET/CT PCR); and (iii) longer performance times evident in nearly all EF tests' parameters. Slower EEG waves correlated negatively with [18 F]FDOPA PET/CT PCR and positively with most of the EF test parameters. Furthermore, we found negative correlations between [18 F]FDOPA PET/CT PCR and certain EF measures related to ST. [18 F]FDOPA PET/CT ratios and several PSD-EEG parameters, particularly those from the prefrontal cortex, demonstrated clinically reasonable diagnostic accuracy for PD. In conclusion, EEG waves slowing in the frontal lobe were correlated with striatal dopaminergic deficiency and impaired executive function in mild PD patients and showed promise as a biomarker of PD-related executive dysfunction.

Striatal dopamine transporter uptake, parkinsonism and cognition in Alzheimer's disease

BACKGROUND AND PURPOSE

The correlates of motor parkinsonism in Alzheimer's disease (AD) remain controversial. The effects of nigrostriatal dopaminergic degeneration on parkinsonism and cognition in biomarker-validated patients with AD were evaluated.

METHODS

This study recruited 116 patients with AD who underwent dual-phase 18 F-N-(3-fluoropropyl)-2β-carbon ethoxy-3β-(4-iodophenyl) nortropane positron emission tomography, 18 F-florbetaben positron emission tomography, 3 T brain magnetic resonance imaging, and Unified Parkinson's Disease Rating Scale (UPDRS) and neuropsychological tests. The mean cortical thickness in the frontal, temporal, parietal and occipital cortices, and the dopamine transporter (DAT) uptake in the caudate, anterior/posterior putamen and substantia nigra were quantified. The relationship between DAT uptake, mean lobar cortical thickness, UPDRS motor score and cognition was investigated using general linear models (GLMs) after controlling for age, sex, education, intracranial volume, and deep and periventricular white matter hyperintensities. A path analysis was performed for the UPDRS motor score with the same covariates.

RESULTS

Path analysis and multivariable GLMs for UPDRS motor score showed that lower caudate DAT uptake was directly associated with a higher UPDRS motor score, whereas caudate DAT uptake confounded the association between mean frontal/parietal thickness and UPDRS motor score. Multivariable GLMs for cognitive scores showed that lower caudate DAT uptake was associated with visuospatial/executive dysfunction independent of mean frontal or parietal thickness.

CONCLUSIONS

Nigrostriatal dopaminergic dysfunction is associated with parkinsonism and visuospatial/executive dysfunction in patients with AD.

Longitudinal striatal dopamine transporter binding and cerebrospinal fluid alpha-synuclein, amyloid beta, total tau, and phosphorylated tau in Parkinson's disease

BACKGROUND

Previous studies investigated CSF levels of α-synuclein (α-syn), amyloid-β (Aβ1-42), total tau (t-tau), and phosphorylated tau (p-tau) with clinical progression of Parkinson's disease (PD). However, there is limited data on the association between CSF biomarkers and dopamine uptake status in PD.

AIM

In the current study, we aim to investigate the longitudinal association between striatal dopaminergic neuronal loss assessed by dopamine active transporter single photon emission computerized tomography (DaTSCAN) imaging with CSF α-syn, t-tau, p-tau, and Aβ1-42.

METHODS

A total of 413 early-stage PD patients and 187 healthy controls (HCs) from the PPMI. Striatal binding ratios (SBRs) of DaTSCAN images in caudate and putamen nuclei were calculated. We investigated the cross-sectional and longitudinal association between CSF biomarkers and dopamine uptake using partial correlation models adjusted for the effect of age, sex, and years of education over 24 months of follow-up.

RESULTS

The level of CSF α-syn, Aβ1-42, t-tau, and p-tau was significantly higher in HCs compared to PD groups at any time point. We found that higher CSF α-syn was associated with a higher SBR score in the left caudate at baseline (P = 0.038) and after 12 months (P = 0.012) in PD patients. Moreover, SBR scores in the left caudate and CSF Aβ1-42 were positively correlated at baseline (P = 0.021), 12 months (P = 0.006), and 24 months (P = 0.014) in patients with PD. Our findings demonstrated that change in CSF Aβ1-42 was positively correlated with change in SBR score in the left caudate after 24 months in the PD group (P = 0.043).

CONCLUSION

We found that cross-sectional levels of α-syn and Aβ1-42 could reflect the degree of dopaminergic neuron loss in the left caudate nucleus. Interestingly, longitudinal changes in CSF Aβ1-42 could predict the severity of left caudal dopaminergic neuron loss throughout the disease. This suggested that Aβ pathology might precede dopaminergic loss in striatal nuclei in this case left caudate and subsequently cognitive impairment in PD patients, although future studies are needed to confirm our results and expand the understanding of the pathophysiology of cognitive dysfunction in PD.

The Protein-Rich Fraction from Spirulina platensis Exerts Neuroprotection in Hemiparkinsonian Rats by Decreasing Brain Inflammatory-Related Enzymes and Glial Fibrillary Acidic Protein Expressions

Spirulina platensis is a cyanobacterium with high protein content and presenting neuroprotective effects. Now, we studied a protein-enriched fraction (SPF), on behavior, neurochemical and immunohistochemical (IHC) assays in hemiparkinsonian rats, distributed into the groups: SO (sham-operated), 6-hydroxydopamine (6-OHDA), and 6-OHDA (treated with SPF, 5 and 10 mg/kg, p.o., 15 days). Afterward, animals were subjected to behavioral tests and euthanized, and brain areas used for neurochemical and IHC assays. SPF partly reversed the changes in the apomorphine-induced rotations, open field and forced swim tests, and also the decrease in striatal dopamine and 3,4-dihydroxyphenylacetic acid contents seen in hemiparkinsonian rats. Furthermore, SPF reduced brain oxidative stress and increased striatal expressions of tyrosine hydroxylase and dopamine transporter and significantly reduced hippocampal inducible nitric oxide synthase, cyclooxygenase-2 and glial fibrillary acidic protein expressions. The data suggest that the protein fraction from S. platensis, through its brain anti-inflammatory and antioxidative actions, exerts neuroprotective effects that could benefit patients affected by neurodegenerative diseases, like Parkinson's disease.

Altered Intrinsic Regional Spontaneous Brain Activity in Patients With Severe Obesity and Meibomian Gland Dysfunction: A Resting-State Functional Magnetic Resonance Imaging Study

Purpose

To evaluate potential regional homogeneity (ReHo) cerebrum function lesions in people with severe obesity and meibomian gland dysfunction (SM) and probe the connection between aberrant cerebrum activity and clinical manifestations.

Patients and Methods

An aggregation of 12 patients with SM, and 12 healthy controls (HCs) closely matched in age and gender were enrolled. We applied corneal confocal microscopy and fundus angiography to compare imaging distinctions between the two groups. SMs were required to carefully fill out the Hospital Anxiety Depression Scale (HADS) forms, and a correlation analysis was performed. ReHo was also utilized to appraise partial differences in spontaneous cerebrum function. Receiver operating characteristic (ROC) curves were created to partition ReHo values between patients with SM and the HCs.

Results

ReHo values for the left cerebellum (LC), right fusiform gyrus (RFG), left inferior temporal gyrus (LITG), left rectus gyrus (LRG), right thalamus (RT), right caudate (RC), left insula (LI), and left thalamus (LT) of subjects with SM were notably higher than those of the HCs (P < 0.05). ReHo values of the right middle frontal gyrus (RMFG) in subjects with SM were decreased notably compared to the HCs (P < 0.05). ReHo values for the RMFG showed a negative correlation with the anxiety scores (ASs; r = −0.961, P < 0.001) and ReHo values for the RFG showed a positive correlation with the depression scores (DSs; r = 0.676, P = 0.016). The areas under the ROC curve were 1.000 (P < 0.001) for the RMFG, LC, LITG, LRG, RC, LI, and LT and 0.993 (P < 0.001) for the RFG and RT. The results from the ROC curve analysis indicated that changes in the ReHo values of some brain regions may help diagnose SM.

Conclusion

Our research emphasized that patients with SM had lesions in synchronized neural activity in many encephalic areas. Our discoveries may provide beneficial information for exploring the neuromechanics of SM.

Neurofunctional characteristics of executive control in older people with HIV infection: a comparison with Parkinson's disease

Expression of executive dysfunctions is marked by substantial heterogeneity in people living with HIV infection (PLWH) and attributed to neuropathological degradation of frontostriatal circuitry with age and disease. We compared the neurophysiology of executive function in older PLWH and Parkinson's disease (PD), both affecting frontostriatal systems. Thirty-one older PLWH, 35 individuals with PD, and 28 older healthy controls underwent executive task-activated fMRI, neuropsychological testing, and a clinical motor exam. fMRI task conditions distinguished cognitive control operations, invoking a lateral frontoparietal network, and motor control operations, activating a cerebellar-precentral-medial prefrontal network. HIV-specific findings denoted a prominent sensorimotor hypoactivation during cognitive control and striatal hypoactivation during motor control related to CD4⁺ T cell count and HIV disease duration. Activation deficits overlapped for PLWH and PD, relative to controls, in dorsolateral frontal, medial frontal, and middle cingulate cortices for cognitive control, and in limbic, frontal, parietal, and cerebellar regions for motor control. Thus, despite well-controlled HIV infection, frontostriatal and sensorimotor activation deficits occurred during executive control in older PLWH. Overlapping activation deficits in posterior cingulate and hippocampal regions point toward similarities in mesocorticolimbic system aberrations among older PLWH and PD. The extent of pathophysiology in PLWH was associated with variations in immune system health, neural signature consistent with subclinical parkinsonism, and mild neurocognitive impairment. The failure to adequately engage these pathways could be an early sign for cognitive and motor functional decline in the aging population of PLWH.

Diabetes and Cognitive Impairment: A Role for Glucotoxicity and Dopaminergic Dysfunction

Diabetes mellitus (DM) is a chronic metabolic disorder characterized by hyperglycemia, responsible for the onset of several long-term complications. Recent evidence suggests that cognitive dysfunction represents an emerging complication of DM, but the underlying molecular mechanisms are still obscure. Dopamine (DA), a neurotransmitter essentially known for its relevance in the regulation of behavior and movement, modulates cognitive function, too. Interestingly, alterations of the dopaminergic system have been observed in DM. This review aims to offer a comprehensive overview of the most relevant experimental results assessing DA’s role in cognitive function, highlighting the presence of dopaminergic dysfunction in DM and supporting a role for glucotoxicity in DM-associated dopaminergic dysfunction and cognitive impairment. Several studies confirm a role for DA in cognition both in animal models and in humans. Similarly, significant alterations of the dopaminergic system have been observed in animal models of experimental diabetes and in diabetic patients, too. Evidence is accumulating that advanced glycation end products (AGEs) and their precursor methylglyoxal (MGO) are associated with cognitive impairment and alterations of the dopaminergic system. Further research is needed to clarify the molecular mechanisms linking DM-associated dopaminergic dysfunction and cognitive impairment and to assess the deleterious impact of glucotoxicity.

Frontoparietal network resilience is associated with protection against cognitive decline in Parkinson's disease

Though Parkinson's disease is primarily defined as a movement disorder, it is also characterized by a range of non-motor symptoms, including cognitive decline. The onset and progression of cognitive decline in individuals with Parkinson's disease is variable, and the neurobiological mechanisms that contribute to, or protect against, cognitive decline in Parkinson's disease are poorly understood. Using resting-state functional magnetic resonance imaging data collected from individuals with Parkinson's disease with and without cognitive decline, we examined the relationship between topological brain-network resilience and cognition in Parkinson's disease. By leveraging network attack analyses, we demonstrate that relative to individuals with Parkinson's disease experiencing cognitive decline, the frontoparietal network in cognitively stable individuals with Parkinson's disease is significantly more resilient to network perturbation. Our findings suggest that the topological robustness of the frontoparietal network is associated with the absence of cognitive decline in individuals with Parkinson's disease.

Voxel-based correlation of 18F-THK5351 accumulation with gray matter structural networks in cognitively normal older adults

Objective

The aim of this study was to evaluate tau-related structural network metrics derived from gray matter magnetic resonance imaging (MRI) scans in cognitively normal (CN) older adults.

Methods

We recruited 47 amyloid-negative CN older adults (mean age ± standard deviation, 65.0 ± 7.9 years; 26 women). All participants underwent 3D T1-weighted MRI and ¹¹C-Pittsburgh compound-B and ¹⁸F-THK5351 positron emission tomography scans. Four local network metrics (betweenness centrality, clustering coefficient, characteristic path length, and degree) were computed and rendered on individual brain images. We then evaluated the correlations between ¹⁸F-THK5351 positron emission tomography images and local network metric images at the voxel level.

Results

Significant positive correlations of the four local network metrics with ¹⁸F-THK5351 were detected in the bilateral caudate.

Conclusion

Our findings suggest that tau and neuroinflammation in CN older adults may influence the gray matter structural network in the caudate.

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Local correlation of ¹⁸F-THK5351 and network metrics images in healthy elderly.

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Positive correlation between ¹⁸F-THK5351and network changes in the caudate.

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Tau and neuroinflammation may influence structural network in the caudate.

Disrupted metabolic connectivity in dopaminergic and cholinergic networks at different stages of dementia from 18F-FDG PET brain persistent homology network

Dementia is related to the cellular accumulation of β-amyloid plaques, tau aggregates, or α-synuclein aggregates, or to neurotransmitter deficiencies in the dopaminergic and cholinergic pathways. Cellular and neurochemical changes are both involved in dementia pathology. However, the role of dopaminergic and cholinergic networks in metabolic connectivity at different stages of dementia remains unclear. The altered network organisation of the human brain characteristic of many neuropsychiatric and neurodegenerative disorders can be detected using persistent homology network (PHN) analysis and algebraic topology. We used 18F-fluorodeoxyglucose positron emission tomography (18F-FDG PET) imaging data to construct dopaminergic and cholinergic metabolism networks, and used PHN analysis to track the evolution of these networks in patients with different stages of dementia. The sums of the network distances revealed significant differences between the network connectivity evident in the Alzheimer's disease and mild cognitive impairment cohorts. A larger distance between brain regions can indicate poorer efficiency in the integration of information. PHN analysis revealed the structural properties of and changes in the dopaminergic and cholinergic metabolism networks in patients with different stages of dementia at a range of thresholds. This method was thus able to identify dysregulation of dopaminergic and cholinergic networks in the pathology of dementia.

Timing variability and midfrontal ~4 Hz rhythms correlate with cognition in Parkinson's disease

Patients with Parkinson's disease (PD) can have significant cognitive dysfunction; however, the mechanisms for these cognitive symptoms are unknown. Here, we used scalp electroencephalography (EEG) to investigate the cortical basis for PD-related cognitive impairments during interval timing, which requires participants to estimate temporal intervals of several seconds. Time estimation is an ideal task demand for investigating cognition in PD because it is simple, requires medial frontal cortical areas, and recruits basic executive processes such as working memory and attention. However, interval timing has never been systematically studied in PD patients with cognitive impairments. We report three main findings. First, 71 PD patients had increased temporal variability compared to 37 demographically matched controls, and this variability correlated with cognitive dysfunction as measured by the Montreal Cognitive Assessment (MOCA). Second, PD patients had attenuated ~4 Hz EEG oscillatory activity at midfrontal electrodes in response to the interval-onset cue, which was also predictive of MOCA. Finally, trial-by-trial linear mixed-effects modeling demonstrated that cue-triggered ~4 Hz power predicted subsequent temporal estimates as a function of PD and MOCA. Our data suggest that impaired cue-evoked midfrontal ~4 Hz activity predicts increased timing variability that is indicative of cognitive dysfunction in PD. These findings link PD-related cognitive dysfunction with cortical mechanisms of cognitive control, which could advance novel biomarkers and neuromodulation for PD.

Theta-Burst Stimulation for Cognitive Enhancement in Parkinson's Disease With Mild Cognitive Impairment: A Randomized, Double-Blind, Sham-Controlled Trial

Background: Mild cognitive impairment is a common non-motor symptom of Parkinson's disease (PD-MCI) and has minimal treatment options.

Objective: In this double-blind, randomized, sham-controlled trial, we assessed the effect of repeated sessions of intermittent theta-burst stimulation over the left dorsolateral prefrontal cortex on cognition and brain connectivity in subjects with PD-MCI.

Methods: Forty-one subjects were randomized to receive real (n = 21) or sham stimulation (n = 20). All subjects underwent neuropsychological assessments before, 1 day, and 1 month after stimulation. Subjects also underwent resting-state functional magnetic resonance imaging before and 48 h after stimulation. The primary outcome was the change in the cognitive domain (executive function, attention, memory, language, and visuospatial abilities) z-scores across time.

Results: There was an insignificant effect on cognitive domain z-scores across time when comparing real with sham stimulation and correcting for multiple comparisons across cognitive domains (p > 0.05 Bonferroni correction). However, the real stimulation group demonstrated a trend toward improved executive functioning scores at the 1-month follow-up compared with sham (p < 0.05 uncorrected). After real stimulation, the connectivity of the stimulation site showed decreased connectivity to the left caudate head. There was no change in connectivity within or between the stimulation network (a network of cortical regions connected to the stimulation site) and the striatal network. However, higher baseline connectivity between the stimulation network and the striatal network was associated with improved executive function scores at 1 month.

Conclusions: These results suggest that intermittent theta-burst stimulation over the dorsolateral prefrontal cortex in subjects with PD-MCI has minimal effect on cognition compared with sham, although there were trends toward improved executive function. This intervention may be more effective in subjects with higher baseline connectivity between the stimulation network and the striatal network. This trial supports further investigation focusing on executive function and incorporating connectivity-based targeting.

Clinical Trial Registration:www.ClinicalTrials.gov, identifier NCT03243214.

Novel PET Biomarkers to Disentangle Molecular Pathways across Age-Related Neurodegenerative Diseases

There is a need to disentangle the etiological puzzle of age-related neurodegenerative diseases, whose clinical phenotypes arise from known, and as yet unknown, pathways that can act distinctly or in concert. Enhanced sub-phenotyping and the identification of in vivo biomarker-driven signature profiles could improve the stratification of patients into clinical trials and, potentially, help to drive the treatment landscape towards the precision medicine paradigm. The rapidly growing field of neuroimaging offers valuable tools to investigate disease pathophysiology and molecular pathways in humans, with the potential to capture the whole disease course starting from preclinical stages. Positron emission tomography (PET) combines the advantages of a versatile imaging technique with the ability to quantify, to nanomolar sensitivity, molecular targets in vivo. This review will discuss current research and available imaging biomarkers evaluating dysregulation of the main molecular pathways across age-related neurodegenerative diseases. The molecular pathways focused on in this review involve mitochondrial dysfunction and energy dysregulation; neuroinflammation; protein misfolding; aggregation and the concepts of pathobiology, synaptic dysfunction, neurotransmitter dysregulation and dysfunction of the glymphatic system. The use of PET imaging to dissect these molecular pathways and the potential to aid sub-phenotyping will be discussed, with a focus on novel PET biomarkers.

Elevated caudate connectivity in cognitively normal Parkinson's disease patients

Mild cognitive impairment (MCI) is common in Parkinson’s disease patients. However, its underlying mechanism is not well understood, which has hindered new treatment discoveries specific to MCI. The aim of this study was to investigate functional connectivity changes of the caudate nucleus in cognitively impaired Parkinson’s patients. We recruited 18 Parkinson’s disease patients—10 PDNC [normal cognition Parkinson’s disease; Montreal Cognitive Assessment (MoCA) ≥ 26], 8 PDLC (low cognition Parkinson’s disease; MoCA < 26) —and 10 age-matched healthy controls. All subjects were scanned with resting-state functional magnetic resonance imaging (MRI) and perfusion MRI. We analyzed these data for graph theory metrics and Alzheimer’s disease-like pattern score, respectively. A strong positive correlation was found between the functional connectivity of the right caudate nucleus and MoCA scores in Parkinson’s patient groups, but not in healthy control subjects. Interestingly, PDNC’s functional connectivity of the right caudate was significantly higher than both PDLC and healthy controls, while PDLC and healthy controls were not significantly different from each other. We found that Alzheimer’s disease-like metabolic/perfusion pattern score correlated with MoCA scores in healthy controls, but not in Parkinson’s disease. Increased caudate connectivity may be related to a compensatory mechanism found in cognitively normal patients with Parkinson’s disease. Our findings support and complement the dual syndrome hypothesis.

Prolonged visual fixation as a surrogate marker of cholinergic deficit in Parkinson's disease: A 2-year follow-up study

INTRODUCTION

The search for biomarkers of cognitive impairment in Parkinson's disease is driven by the potential clinical applications in disease prognostication. Various eye tracking studies on cognitive functions in Parkinson's disease suggest a promising role of eye movement parameters as a biomarker for cognitive decline but the clinical utility has not been validated in longitudinal studies. The present study aims to investigate the longitudinal progression of eye fixation duration in a visual search task and its correlation with domain-specific cognitive impairment.

METHOD

This is a 2-year follow-up study on a group of non-demented Parkinson's disease patients, with baseline eye movement metrics and multi-domain cognitive functions measured, to assess the association between domain-specific cognitive impairment and progression of visual fixation duration.

RESULTS

A total of 49 from the original 62 non-demented Parkinson's disease patients were re-examined at a 2-year follow-up. 15 cases (31%) were classified as having mild cognitive impairment. Visual fixation duration was significantly prolonged after 2 years. Using repeated measures ANOVA, impairment in semantic verbal fluency, visual and verbal recognition memory and orienting function of attention had a significant effect on prolonging visual fixation over time.

CONCLUSION

Correlation between prolonged visual fixation and multiple domains of cognitive impairment related to cholinergic dysfunction in repeated measures over two years provides preliminary evidence for the eye tracking paradigm as a surrogate marker for cholinergic deficit in Parkinson's disease. The clinical utility in terms of disease prognostication is yet to be confirmed in prospective longitudinal studies with longer follow-up periods.

The longitudinal associations between cognition, mood and striatal dopaminergic binding in Parkinson's Disease

Cognitive decline and mood symptoms are common in Parkinson's disease (PD). Reductions in striatal dopaminergic binding have been associated with worse cognition and mood. We investigated whether this association persists throughout the disease progression in newly diagnosed PD. Four-year data from Parkinson's Progression Markers Initiative (PPMI) were used. Groups consisted of left and right limb dominantly affected PD patients, and controls. Longitudinal relationships between cognition, mood and striatal binding ratios were assessed by repeated measures correlations. Reduced binding was associated with general cognitive decline in controls, reduced processing speed and increased mood symptoms in PD. Anxiety was associated with striatum only in left limb dominantly affected PD. Dominantly affected limb side did not impact striatum and cognition association. There are longitudinal associations between striatum, processing speed and anxiety. Dopamine transporter availability imaging may have some prognostic value for cognition and mood in PD.

Parietal Perfusion Alterations in Parkinson's Disease Patients Without Dementia

Fronto-parietal regions are involved in cognitive processes that are commonly affected in Parkinson's disease (PD). The aims of this study were to investigate cerebral blood flow (CBF) and gray matter (GM) volume within the regions belonging to the fronto-parietal circuit in people with PD (pwPD) without dementia, and to assess their association with cognitive performance. Twenty-seven pwPD without dementia (mean [SD] age = 67.4 [8.1] years, 20 males, mean [SD] Montreal Cognitive Assessment, MoCA score = 24.2 [2.9], median [IQR] Hoehn and Yahr scale = 1.5 [1–2]) and twenty-six age- and sex-matched healthy controls (HC) were scanned with arterial spin labeling (ASL) and T1-weighted magnetic resonance imaging (MRI) sequences to investigate CBF and GM volume, respectively. The cognitive performance of the enrolled pwPD was assessed with MoCA, Trail Making Test (TMT, part A, B, B-A), phonemic fluency and semantic fluency tests. The scores were adjusted for age and education. After standard preprocessing, CBF differences between pwPD and HC were tested with a voxel-wise approach. Voxel-based morphometry was used to compare pwPD and HC in terms of GM volume. Both voxel-wise comparisons between pwPD and HC were restricted to regions of the fronto-parietal circuit. The following additional voxel-wise analyses were performed within regions showing either perfusion or GM volume alterations: (1) correlation with neuropsychological test scores; (2) subgroup comparison after median split on each neuropsychological test score. Family-wise error-corrected (FWE) p-values lower than 0.05 were considered significant. Significant hypoperfusion was identified in the left inferior parietal lobule (IPL, p_peak = 0.037) and in the bilateral superior parietal lobule (SPL, left hemisphere: p_peak = 0.037; right hemisphere: p_peak = 0.049) of pwPD when compared to HC. No significant GM atrophy was observed. Local hypoperfusion did not correlate with any neuropsychological test scores. However, significantly lower CBF was observed in the left SPL and IPL of the pwPD subgroup who performed poorer on TMT part A in comparison with the pwPD subgroup that performed better. Perfusion alterations may occur in parietal regions of pwPD without dementia, and may be associated with lower visuomotor skills. Parietal CBF may be considered as a suitable early biomarker for longitudinal studies investigating cognitive decline in PD.

Processing speed is related to striatal dopamine transporter availability in Parkinson's disease

BACKGROUND

Parkinson's disease (PD) affects the integrity of the dopamine and serotonin system, and is characterized by a plethora of different symptoms, including cognitive impairments of which the pathophysiology is not yet fully elucidated.

OBJECTIVES

Investigate the role of the integrity of the dopaminergic and serotonergic system in cognitive functioning in early-stage PD using Single Photon Emission Computed Tomography (SPECT) combined with the radiotracer 123I-N-ω-fluoropropyl-2β-carbomethoxy-3β-(4-iodophenyl)nortropane (123I-FP-CIT).

METHODS

We studied the association between cognitive functions and dopamine transporter (DAT) availability in the caudate nucleus and putamen - as a proxy for striatal dopaminergic integrity - and serotonin transporter (SERT) availability as a proxy for serotonergic integrity in the thalamus and hippocampus using bootstrapped multiple regression. One-hundred-and-twenty-nine (129) PD patients underwent a 123I-FP-CIT SPECT scan and a neuropsychological assessment.

RESULTS

We showed a positive association between DAT availability in the head of the caudate nucleus and the Stroop Color Word Task - card I (reading words; β = 0.32, P = 0.001) and a positive association between DAT availability in the anterior putamen and the Trail Making Test part A (connecting consecutively numbered circles; β = 0.25, P = 0.02). These associations remained after adjusting for motor symptom severity or volume of the region-of-interest and were most pronounced in medication-naïve PD patients. There were no associations between cognitive performance and SERT availability in the thalamus or hippocampus.

CONCLUSIONS

We interpret these results as a role for striatal dopamine - and its PD-related decline - in aspects of processing speed.

Cognition Deficits in Parkinson's Disease: Mechanisms and Treatment

Parkinson's disease (PD) is the second most common progressive neurodegenerative disorder mainly in middle-elderly population, which represents diverse nonmotor symptoms (NMS) besides such well-documented motor symptoms as bradykinesia, resting tremor, rigidity, and postural instability. With the advancement of aging trend worldwide, the global prevalence of PD is mounting up year after year. Nowadays, accumulating lines of studies have given a comprehensive and thorough coverage of motor symptoms in PD. Yet much less attention as compared has been paid to the nonmotor symptoms of PD, such as cognition deficits. Of note, a patient with PD who suffers from cognitive impairment may harbour a statistically significantly higher risk of progressing toward dementia, which negatively affects their life expectancy and daily functioning and overall lowers the global quality of life. Furthermore, it is a widely held view that cognitive dysfunction does not just occur in the late stage of PD. On the basis of numerous studies, mild cognitive impairment (MCI) is a harbinger of dementia in PD, which is observed as an intermediate state with considerable variability; some patients remain stable and some even revert to normal cognition. Considered that the timing, profile, and rate of cognitive impairment vary greatly among PD individuals, it is extremely urgent for researchers and clinicians alike to identify and predict future cognitive decline in this population. Simultaneously, early screening and canonical management of PD with cognitive deficits are very imperative to postpone the disease progression and improve the prognosis of patients. In our review, we focus on a description of cognitive decline in PD, expound emphatically the pathological mechanisms underlying cognition deficits in PD, then give a comprehensive overview of specific therapeutic strategies, and finally dissect what fresh insights may bring new exciting prospect for the subfield.

The Metabolic Activity of Caudate and Prefrontal Cortex Negatively Correlates with the Severity of Idiopathic Parkinson's Disease

Positron emission tomography (PET) scan with tracer [¹⁸F]-fluorodeoxy-glucose (¹⁸F-FDG) is widely used to measure the glucose metabolism in neurodegenerative disease such as Idiopathic Parkinson’s disease (IPD). Previous studies using ¹⁸F-FDG PET mainly focused on the motor or non-motor symptoms but not the severity of IPD. In this study, we aimed to determine the metabolic patterns of ¹⁸F-FDG in different stages of IPD defined by Hoehn and Yahr rating scale (H-Y rating scale) and to identify regions in the brain that play critical roles in disease progression. Fifty IPD patients were included in this study. They were 29 men and 21 women (mean±SD, age 57.7±11.1 years, disease duration 4.0±3.8 years, H-Y 2.2±1.1). Twenty healthy individuals were included as normal controls. Following ¹⁸F-FDG PET scan, image analysis was performed using Statistical Parametric Mapping (SPM) and Resting-State fMRI Data Analysis Toolkit (REST). The metabolic feature of IPD and regions-of-interests (ROIs) were determined. Correlation analysis between ROIs and H-Y stage was performed. SPM analysis demonstrated a significant hypometabolic activity in bilateral putamen, caudate and anterior cingulate as well as left parietal lobe, prefrontal cortex in IPD patients. In contrast, hypermetabolism was observed in the cerebellum and vermis. There was a negative correlation (p=0.007, r=-0.412) between H-Y stage and caudate metabolic activity. Moreover, the prefrontal area also showed a negative correlation with H-Y (P=0.033, r=-0.334). Thus, the uptake of FDG in caudate and prefrontal cortex can potentially be used as a surrogate marker to evaluate the severity of IPD.

Machine learning identified an Alzheimer's disease-related FDG-PET pattern which is also expressed in Lewy body dementia and Parkinson's disease dementia

Utilizing the publicly available neuroimaging database enabled by Alzheimer's disease Neuroimaging Initiative (ADNI; http://adni.loni.usc.edu/ ), we have compared the performance of automated classification algorithms that differentiate AD vs. normal subjects using Positron Emission Tomography (PET) with fluorodeoxyglucose (FDG). General linear model, scaled subprofile modeling and support vector machines were examined. Among the tested classification methods, support vector machine with Iterative Single Data Algorithm produced the best performance, i.e., sensitivity (0.84) × specificity (0.95), by 10-fold cross-validation. We have applied the same classification algorithm to four different datasets from ADNI, Health Science Centre (Winnipeg, Canada), Dong-A University Hospital (Busan, S. Korea) and Asan Medical Centre (Seoul, S. Korea). Our data analyses confirmed that the support vector machine with Iterative Single Data Algorithm showed the best performance in prediction of future development of AD from the prodromal stage (mild cognitive impairment), and that it was also sensitive to other types of dementia such as Parkinson's Disease Dementia and Dementia with Lewy Bodies, and that perfusion imaging using single photon emission computed tomography may achieve a similar accuracy to that of FDG-PET.

Can neuroimaging predict dementia in Parkinson's disease?

Dementia in Parkinson's disease affects 50% of patients within 10 years of diagnosis but there is wide variation in severity and timing. Thus, robust neuroimaging prediction of cognitive involvement in Parkinson's disease is important: (i) to identify at-risk individuals for clinical trials of potential new treatments; (ii) to provide reliable prognostic information for individuals and populations; and (iii) to shed light on the pathophysiological processes underpinning Parkinson's disease dementia. To date, neuroimaging has not made major contributions to predicting cognitive involvement in Parkinson's disease. This is perhaps unsurprising considering conventional methods rely on macroscopic measures of topographically distributed neurodegeneration, a relatively late event in Parkinson's dementia. However, new technologies are now emerging that could provide important insights through detection of other potentially relevant processes. For example, novel MRI approaches can quantify magnetic susceptibility as a surrogate for tissue iron content, and increasingly powerful mathematical approaches can characterize the topology of brain networks at the systems level. Here, we present an up-to-date overview of the growing role of neuroimaging in predicting dementia in Parkinson's disease. We discuss the most relevant findings to date, and consider the potential of emerging technologies to detect the earliest signs of cognitive involvement in Parkinson's disease.

Repetitive transcranial magnetic stimulation of the dorsolateral prefrontal cortex to alleviate depression and cognitive impairment associated with Parkinson's disease: A review and clinical implications

The rapid methodological development and growing availability of neuromodulation techniques have spurred myriad studies investigating their clinical effectiveness. Repetitive transcranial magnetic stimulation (rTMS) of the dorsolateral prefrontal cortex (DLPFC) has in many instances been proven to exert antidepressant-like effects superior to placebo and equivalent to standard psychopharmacological treatment. Due to the similar neuroanatomy and neurophysiology of executive and affective control processes, rTMS to the DLPFC may be able to address multiple issues simultaneously. This review pools available literature on the therapeutic usage of rTMS on non-motor symptoms of Parkinson's disease associated with the DLPFC (i.e. mood disturbance and cognitive impairment). To the best of the author's knowledge, it is one of the few available of its' kind, up to this date. Most studies included in the review found beneficial effects of high frequency prefrontal rTMS on PD-related depression. In regard to the usability of rTMS to alleviate cognitive impairment associated with PD, definitive claims are yet to be established.

Motor cognition in patients treated with subthalamic nucleus deep brain stimulation: Limits of compensatory overactivity in Parkinson's disease

Recent fMRI findings revealed that impairment in a serial prediction task in patients suffering from Parkinson's disease (PD) results from hypoactivity of the SMA. Furthermore, hyperactivity of the lateral premotor cortex sustained performance after withdrawal of medication. To further explore these findings, we here examined the impact of deep brain stimulation of the subthalamic nucleus on the activity of the putamen and premotor areas while performing the serial prediction task. To this end, we measured eight male PD patients ON and OFF deep brain stimulation and eight healthy age-matched male controls using [¹⁵O] water positron emission tomography to measure regional cerebral blood flow. As expected, PD patients showed poorer performance than healthy controls while performance did not differ between OFF and ON stimulation. Hypoactivity of the putamen and hyperactivity of the left lateral premotor cortex was found in patients compared to controls. Lateral premotor hyperactivity further increased OFF compared to ON stimulation and was positively related to task performance. These results confirm that the motor loop's dysfunction has impact on cognitive processes (here: prediction of serial stimuli) in PD. Extending prior data regarding the role of the lateral premotor cortex in cognitive compensation, our results indicate that lateral premotor cortex hyperactivity, while beneficial in moderate levels of impairment, might fail to preserve performance in more severe stages of the motor loop's degeneration.

A model-based quantification of action control deficits in Parkinson's disease

Basal ganglia dysfunction in Parkinson's disease (PD) is thought to generate deficits in action control, but the characterization of these deficits have been qualitative rather than quantitative. Patients with PD typically show prolonged response times on tasks that instantiate a conflict between goal-directed processing and automatic response tendencies. In the Simon task, for example, the irrelevant location of the stimulus automatically activates a corresponding lateralized response, generating a potential conflict with goal-directed choices. We applied a new computational model of conflict processing to two sets of behavioral data from the Simon task to quantify the effects of PD and dopaminergic (DA) medication on action control mechanisms. Compared to healthy controls (HC) matched in age gender and education, patients with PD showed a deficit in goal-directed processing, and the magnitude of this deficit positively correlated with cognitive symptoms. Analyses of the time-course of the location-based automatic activation yielded mixed findings. In both datasets, we found that the peak amplitude of the automatic activation was similar between PD and HC, demonstrating a similar degree of response capture. However, PD patients showed a prolonged automatic activation in only one dataset. This discrepancy was resolved by theoretical analyses of conflict resolution in the Simon task. The reduction of interference generated by the automatic activation appears to be driven by a mixture of passive decay and top-down inhibitory control, the contribution of each component being modulated by task demands. Our results suggest that PD selectively impairs the inhibitory control component, a deficit likely remediated by DA medication. This work advances our understanding of action control deficits in PD, and illustrates the benefit of using computational models to quantitatively measure cognitive processes in clinical populations.

Parkinson disease-related cortical and striatal cognitive patterns in dual time F-18 FP CIT: evidence for neural correlates between the caudate and the frontal lobe

BACKGROUND

Using dual time F-18 FP-CIT, we evaluated cortical perfusion, striatal binding and neuropsychological performance simultaneously in Parkinson disease (PD) with and without mild cognitive impairment (MCI), to investigate neural correlates between caudate and frontal cortex.

METHODS

According to the neuropsychological scores, subjects were classified into 26 healthy controls (HC), 38 PD-MCI (executive) (PE), 24 PD-MCI (non-executive) (PN) and 21 PD (motor) (PM). Scans were acquired at 10 minutes and 2 hours. Group differences of early perfusion and delayed binding were compared using SPM and volume of interest method. The relationships between neuropsychological variables and the striatal binding were investigated with correlation and regression analysis.

RESULTS

Compared with PM, PE showed decreased prefrontal perfusion and binding of both caudates (right: P=0.0010, left: P=0.014), but not of both putamens. Compared with PN, PE showed decreased binding of both caudates (right: P=0.001, left: P=0.005), but not in both putamens. Binding of both caudates correlated with the Stroop z-score, but not of both putamens. Executive score was a contributing factor to binding of the caudate, and not the putamen.

CONCLUSIONS

PE showed decreased prefrontal perfusion and caudate binding, supporting neural correlates between the caudate and the prefrontal cortex. Dopaminergic binding of the caudate, but not of the putamen, was related to executive scores. Caudate hypofunction was specific to executive domain. This is the first study that elucidated the clinical use of dual time F-18 FP-CIT for integrative evaluation of cognitive and motor function in PD.

Cognitive performance correlates with the degree of dopaminergic degeneration in the associative part of the striatum in non-demented Parkinson's patients

Parkinson's disease (PD) patients show cognitive deficits that are relevant in terms of prognosis and quality of life. Degeneration of striatal dopaminergic afferents proceeds from dorsal/caudal to anterior/ventral and is discussed to account for some of these symptoms. Treatment with dopamine (DA) has differential effects on cognitive dysfunctions, improving some and worsening others. We hypothesized that cognitive performance during the dopaminergic OFF state correlates with DAT availability in the associative striatum. 16 PD patients underwent motor and cognitive examination ON and OFF DA. Global cognition was measured using the Montréal Cognitive Assessment (MoCA) test and executive functioning using a Stroop test. Nigrostriatal dopaminergic innervation was characterized with [¹²³I]FP-CIT SPECT. A connectivity atlas of the striatum was used to assess DAT availability in functionally defined striatal subregions. Correlations between imaging data and behavioral data OFF medication were calculated. Correlations between DAT availability and MoCA performance in the dopaminergic OFF state was strongest in the associative part of the striatum (r = 0.674, p = 0.004). MoCA test performance did not differ between the ON and the OFF state. There was no correlation of DAT availability with Stroop performance in the OFF state but performance was significantly better during the ON state. Not only motor but also cognitive dysfunctions in PD are associated with striatal dopaminergic depletion. Cognitive decline in non-demented PD patients goes along with nigrostriatal degeneration, most pronounced in the associative subdivision of the striatum. In addition, the present findings suggest that executive dysfunctions are ameliorated by DA whereas global cognition is not improved by dopaminergic medication.

Cognitive Dysfunction in Parkinson’s Disease: The Role of Frontostriatal Circuitry

It has been known for many years that the classic motor symptoms of Parkinson’s disease are accompanied by deficits of executive function that resemble those seen after frontal lobe damage in humans. What is less clear is how different components of frontostriatal circuitry contribute to these impairments. Recently, improved methods of clinical assessment and classification, combined with novel technical approaches, such as functional neuroimaging, have led to great advances in our understanding of the fundamental mechanisms that drive frontostriatal circuitry. As a direct result, it has been possible to redefine impairments of executive function in Parkinson’s disease more precisely in terms of the specific neuropsychological, neuroanatomical, and psychopharmacological mechanisms involved.

Parkinson's disease and the Stroop color word test: processing speed and interference algorithms

OBJECTIVE

Processing speed alters the traditional Stroop calculations of interference. Consequently, alternative algorithms for calculating Stroop interference have been introduced to control for processing speed, and have done so in a multiple sclerosis sample. This study examined how these processing speed correction algorithms change interference scores for individuals with idiopathic Parkinson's disease (PD, n = 58) and non-PD peers (n = 68).

METHOD

Linear regressions controlling for demographics predicted group (PD vs. non-PD) differences for Jensen's, Golden's, relative, ratio, and residualized interference scores. To examine convergent and divergent validity, interference scores were correlated with standardized measures of processing speed and executive function.

RESULTS

PD-non-PD differences were found for Jensen's interference score, but not Golden's score, or the relative, ratio, and residualized interference scores. Jensen's score correlated significantly with standardized processing speed but not executive function measures. Relative, ratio, and residualized scores correlated with executive function but not processing speed measures. Golden's score did not correlate with any other standardized measures.

CONCLUSIONS

The relative, ratio, and residualized scores were comparable for measuring Stroop interference in processing speed-impaired populations. Overall, the ratio interference score may be the most useful calculation method to control for processing speed in this population.

Catecholamines and cognition after traumatic brain injury

Cognitive problems are one of the main causes of ongoing disability after traumatic brain injury. The heterogeneity of the injuries sustained and the variability of the resulting cognitive deficits makes treating these problems difficult. Identifying the underlying pathology allows a targeted treatment approach aimed at cognitive enhancement. For example, damage to neuromodulatory neurotransmitter systems is common after traumatic brain injury and is an important cause of cognitive impairment. Here, we discuss the evidence implicating disruption of the catecholamines (dopamine and noradrenaline) and review the efficacy of catecholaminergic drugs in treating post-traumatic brain injury cognitive impairments. The response to these therapies is often variable, a likely consequence of the heterogeneous patterns of injury as well as a non-linear relationship between catecholamine levels and cognitive functions. This individual variability means that measuring the structure and function of a person’s catecholaminergic systems is likely to allow more refined therapy. Advanced structural and molecular imaging techniques offer the potential to identify disruption to the catecholaminergic systems and to provide a direct measure of catecholamine levels. In addition, measures of structural and functional connectivity can be used to identify common patterns of injury and to measure the functioning of brain ‘networks’ that are important for normal cognitive functioning. As the catecholamine systems modulate these cognitive networks, these measures could potentially be used to stratify treatment selection and monitor response to treatment in a more sophisticated manner.

Biomarkers for dementia and mild cognitive impairment in Parkinson's disease

Cognitive decline is one of the most frequent and disabling nonmotor features of Parkinson's disease. Around 30% of patients with Parkinson's disease experience mild cognitive impairment, a well-established risk factor for the development of dementia. However, mild cognitive impairment in patients with Parkinson's disease is a heterogeneous entity that involves different types and extents of cognitive deficits. Because it is not currently known which type of mild cognitive impairment confers a higher risk of progression to dementia, it would be useful to define biomarkers that could identify these patients to better study disease progression and possible interventions. In this sense, the identification among patients with Parkinson's disease and mild cognitive impairment of biomarkers associated with dementia would allow the early detection of this process. This review summarizes studies from the past 25 years that have assessed the potential biomarkers of dementia and mild cognitive impairment in Parkinson's disease patients. Despite the potential importance, no biomarker has as yet been validated. However, features such as low levels of epidermal and insulin-like growth factors or uric acid in plasma/serum and of Aß in CSF, reduction of cerebral cholinergic innervation and metabolism measured by PET mainly in posterior areas, and hippocampal atrophy in MRI might be indicative of distinct deficits with a distinct risk of dementia in subgroups of patients. Longitudinal studies combining the existing techniques and new approaches are needed to identify patients at higher risk of dementia. © 2016 International Parkinson and Movement Disorder Society.

Endocannabinoid 2-Arachidonoylglycerol Suppresses LPS-Induced Inhibition of A-Type Potassium Channel Currents in Caudate Nucleus Neurons Through CB1 Receptor

Inflammation plays a pivotal role in the pathogenesis of many diseases in the central nervous system. Caudate nucleus (CN), the largest nucleus in the brain, is also implicated in many neurological disorders. 2-Arachidonoylglycerol (2-AG), the most abundant endogenous cannabinoid, has been shown to exhibit neuroprotective effects through its anti-inflammatory action from some proinflammatory stimuli. However, the neuroprotective mechanism of 2-AG is complex and has not been fully understood. A-type K(+) channels critically regulate neuronal excitability and have been demonstrated to be associated with some nervous system diseases. The aim of this study was to explore whether A-type K(+) channels were involved in neurotoxicity of lipopolysaccharides (LPS) and the neuroprotective mechanism of 2-AG in CN neurons. Whole cell patch clamp recording was used to investigate the influence of LPS on the function of A-type K(+) channels and its modulation by 2-AG in primary cultured rat CN neurons. Our findings showed that in cultured CN neurons, LPS significantly decreased the A-type potassium currents (I A) in a voltage-insensitive way. The further data demonstrated that an elevation of 2-AG levels by directly applying exogenous 2-AG or inhibiting monoacylglycerol lipase (MAGL) to prevent 2-AG hydrolysis was capable of suppressing the LPS-induced inhibition of IA and the action of 2-AG is mediated through CB1 receptor-dependant way. The study provides a better understanding of inflammation-related neurological disorders and suggests the therapeutic potential for 2-AG for the treatment of these diseases.

Degeneration of Dopaminergic Neurons Due to Metabolic Alterations and Parkinson's Disease

The rates of metabolic diseases, such as type 2 diabetes mellitus (T2DM), obesity, and cardiovascular disease (CVD), markedly increase with age. In recent years, studies have reported an association between metabolic changes and various pathophysiological mechanisms in the central nervous system (CNS) in patients with metabolic diseases. Oxidative stress and hyperglycemia in metabolic diseases lead to adverse neurophysiological phenomena, including neuronal loss, synaptic dysfunction, and improper insulin signaling, resulting in Parkinson’s disease (PD). In addition, several lines of evidence suggest that alterations of CNS environments by metabolic changes influence the dopamine neuronal loss, eventually affecting the pathogenesis of PD. Thus, we reviewed recent findings relating to degeneration of dopaminergic neurons during metabolic diseases. We highlight the fact that using a metabolic approach to manipulate degeneration of dopaminergic neurons can serve as a therapeutic strategy to attenuate pathology of PD.

Gray and White Matter Contributions to Cognitive Frontostriatal Deficits in Non-Demented Parkinson's Disease

Objective

This prospective investigation examined: 1) processing speed and working memory relative to other cognitive domains in non-demented medically managed idiopathic Parkinson’s disease, and 2) the predictive role of cortical/subcortical gray thickness/volume and white matter fractional anisotropy on processing speed and working memory.

Methods

Participants completed a neuropsychological protocol, Unified Parkinson’s Disease Rating Scale, brain MRI, and fasting blood draw to rule out vascular contributors. Within group a priori anatomical contributors included bilateral frontal thickness, caudate nuclei volume, and prefrontal white matter fractional anisotropy.

Results

Idiopathic Parkinson’s disease (n = 40; Hoehn & Yahr stages 1–3) and non-Parkinson’s disease ‘control’ peers (n = 40) matched on demographics, general cognition, comorbidity, and imaging/blood vascular metrics. Cognitively, individuals with Parkinson’s disease were significantly more impaired than controls on tests of processing speed, secondary deficits on working memory, with subtle impairments in memory, abstract reasoning, and visuoperceptual/spatial abilities. Anatomically, Parkinson’s disease individuals were not statistically different in cortical gray thickness or subcortical gray volumes with the exception of the putamen. Tract Based Spatial Statistics showed reduced prefrontal fractional anisotropy for Parkinson’s disease relative to controls. Within Parkinson’s disease, prefrontal fractional anisotropy and caudate nucleus volume partially explained processing speed. For controls, only prefrontal white matter was a significant contributor to processing speed. There were no significant anatomical predictors of working memory for either group.

Conclusions

Caudate nuclei volume and prefrontal fractional anisotropy, not frontal gray matter thickness, showed unique and combined significance for processing speed in Parkinson’s disease. Findings underscore the relevance for examining gray-white matter interactions and also highlight clinical processing speed metrics as potential indicators of early cognitive impairment in PD.

Neuroimaging studies of striatum in cognition part II: Parkinson's disease

In recent years a gradual shift in the definition of Parkinson's disease (PD) has been established, from a classical akinetic-rigid movement disorder to a multi-system neurodegenerative disease. While the pathophysiology of PD is complex and goes much beyond the nigro-striatal degeneration, the striatum has been shown to be responsible for many cognitive functions. Patients with PD develop impairments in multiple cognitive domains and the PD model is probably the most extensively studied regarding striatum dysfunction and its influence on cognition. Up to 40% of PD patients present cognitive impairment even in the early stages of disease development. Thus, understanding the key patterns of striatum and connecting regions' influence on cognition will help develop more specific approaches to alleviate cognitive impairment and slow down its decline. This review focuses on the contribution of neuroimaging studies in understanding how striatum impairment affects cognition in PD.

Motor loop dysfunction causes impaired cognitive sequencing in patients suffering from Parkinson's disease

Cognitive impairment in Parkinson's disease (PD) is often attributed to dopamine deficiency in the prefrontal-basal ganglia-thalamo-cortical loops. Although recent studies point to a close interplay between motor and cognitive abilities in PD, the so-called "motor loop" connecting supplementary motor area (SMA) and putamen has been considered solely with regard to the patients' motor impairment. Our study challenges this view by testing patients with the serial prediction task (SPT), a cognitive task that requires participants to predict stimulus sequences and particularly engages premotor sites of the motor loop. We hypothesised that affection of the motor loop causes impaired SPT performance, especially when the internal sequence representation is challenged by suspension of external stimuli. As shown for motor tasks, we further expected this impairment to be compensated by hyperactivity of the lateral premotor cortex (PM). We tested 16 male PD patients ON and OFF dopaminergic medication and 16 male age-matched healthy controls in an functional Magnetic Resonance Imaging study. All subjects performed two versions of the SPT: one with on-going sequences (SPT0), and one with sequences containing non-informative wildcards (SPT+) increasing the demands on mnemonic sequence representation. Patients ON (compared to controls) revealed an impaired performance coming along with hypoactivity of SMA and putamen. Patients OFF compared to ON medication, while showing poorer performance, exhibited a significantly increased PM activity for SPT+ vs. SPT0. Furthermore, patients' performance positively co-varied with PM activity, corroborating a compensatory account. Our data reveal a contribution of the motor loop to cognitive impairment in PD, and suggest a close interplay of SMA and PM beyond motor control.

Effect of Homocysteine on Voltage-Gated Sodium Channel Currents in Primary Cultured Rat Caudate Nucleus Neurons and Its Modulation by 2-Arachidonylglycerol

Homocysteine (Hcy) is an important risk factor for Alzheimer's disease (AD) and other neurodegenerative diseases. Caudate nucleus (CN), the largest nucleus in the brain, is also implicated in many neurological disorders. 2-Arachidonoylglycerol (2-AG), the most abundant endogenous cannabinoid, has been shown to exhibit neuroprotective effects from many stimuli in the central nervous system (CNS). Furthermore, it has been reported that voltage-gated sodium channels (VGSCs) are the common targets of many neuronal damages and drugs. However, it is still not clear whether VGSCs are involved in the neurotoxicity of Hcy and the neuroprotective effect of 2-AG in CN neurons. In the present study, whole-cell patch clamp recording was used to invest the action of Hcy on sodium currents in primary cultured rat CN neurons and its modulation by 2-AG. The results showed that in cultured CN neurons, pathological concentration of Hcy (100 μM) significantly increased the voltage-gated sodium currents (I(Na)) and produced a hyperpolarizing shift in the activation-voltage curve of I(Na). The further data demonstrated 2-AG is capable of suppressing elevation of Hcy-induced increase in I(Na) and hyperpolarizing shift of activation curves most partly through CB1 receptor-dependent way. Our study provides a better understanding of Hcy-associated neurological disorders and suggests the therapeutic potential for 2-AG for the treatment of these diseases.

Parkinson's disease dementia: a neural networks perspective

In the long-term, with progression of the illness, Parkinson's disease dementia affects up to 90% of patients with Parkinson's disease. With increasing life expectancy in western countries, Parkinson's disease dementia is set to become even more prevalent in the future. However, current treatments only give modest symptomatic benefit at best. New treatments are slow in development because unlike the pathological processes underlying the motor deficits of Parkinson's disease, the neural mechanisms underlying the dementing process and its associated cognitive deficits are still poorly understood. Recent insights from neuroscience research have begun to unravel the heterogeneous involvement of several distinct neural networks underlying the cognitive deficits in Parkinson's disease dementia, and their modulation by both dopaminergic and non-dopaminergic transmitter systems in the brain. In this review we collate emerging evidence regarding these distinct brain networks to give a novel perspective on the pathological mechanisms underlying Parkinson's disease dementia, and discuss how this may offer new therapeutic opportunities.

Cognitive performances and DAT imaging in early Parkinson's disease with mild cognitive impairment: a preliminary study

OBJECTIVES

Mild cognitive impairment (MCI) is a common feature in Parkinson's disease (PD). We performed an exploratory study to investigate dopaminergic nigrostriatal innervation and its cognitive correlates in early untreated PD patients with MCI as compared to cognitively intact patients.

PATIENTS AND METHODS

A consecutive series of 34-de-novo, drug-naïve patients with PD were enrolled. They underwent [123-I] FP-CIT SPECT and comprehensive neuropsychological battery. MCI was identified in 15 of 34 patients with PD.

RESULTS

The two groups did not show any statistically significant difference in age, sex, disease duration, education, lateralization, and H&Y and Hospital Anxiety and Depression Scale scores. Logistic regression analysis showed that UPDRS-III was weakly associated with MCI (P = 0.034). Partial correlation analysis controlling for UPDRS-III and age suggested that in PD patients with MCI reduced V3″ values in the more affected caudate were correlated with reduced performances in frontal assessment battery, Trail Making Test: part B minus Part A and copy task of the Rey-Osterrieth complex figure test. Reduced V3″ values in the more and less affected putamen were significantly related with reduced performance in frontal assessment battery and in copy task of Rey-Osterrieth complex figure test, respectively. No correlation was found between neuropsychological scores and DAT availability in PD patients without MCI.

CONCLUSIONS

Although preliminary, our results suggest that striatal dopamine depletion may contribute to some cognitive deficit in early never treated PD patients with MCI.

Brain (18)F-DOPA PET and cognition in de novo Parkinson's disease

PURPOSE

The role of mesocortical dopaminergic pathways in the cognitive function of patients with early Parkinson's disease (PD) needs to be further clarified.

METHODS

The study groups comprised 15 drug-naive patients with de novo PD and 10 patients with essential tremor (controls) who underwent (18)F-DOPA PET (static acquisition, normalization on mean cerebellar counts) and an extended neuropsychological test battery. Factor analysis with varimax rotation was applied to the neuropsychological test scores, to yield five factors from 16 original scores, which explained 82 % of the total variance. Correlations between cognitive factors and (18)F-DOPA uptake were assessed with SPM8, taking age and gender as nuisance variables.

RESULTS

(18)F-DOPA uptake was significantly lower in PD patients than in controls in the bilateral striatum, mainly in the more affected (right) hemisphere, and in a small right temporal region. Significant positive correlations were found only in PD patients between the executive factor and (18)F-DOPA uptake in the bilateral anterior cingulate cortex (ACC) and the middle frontal gyrus, between the verbal fluency factor and (18)F-DOPA uptake in left BA 46 and the bilateral striatum, and between the visuospatial factor and (18)F-DOPA uptake in the left ACC and bilateral striatum. No correlations were found between (18)F-DOPA uptake and either the verbal memory factor or the abstraction-working memory factor.

CONCLUSION

These data clarify the role of the mesocortical dopaminergic pathways in cognitive function in early PD, highlighting the medial frontal lobe, anterior cingulate, and left BA 46 as the main sites of cortical correlation with executive and language functions.

Monoacylglycerol lipase inhibitor protects primary cultured neurons against homocysteine-induced impairments in rat caudate nucleus through COX-2 signaling

AIMS

URB602 is a selective inhibitor of monoacylglycerol lipase (MAGL), a serine hydrolase involved in the biological deactivation of the endocannabinoid 2-arachidonoyl glycerol (2-AG). It has been described that URB602 significantly enhances depolarization-induced increases in 2-AG. A high level of homocysteine (Hcy) is a modifiable risk factor for developing Alzheimer's disease (AD). The aim of this study was to investigate the protective effects of URB602 on Hcy-induced impairments underlying its cellular and molecular mechanism in primary cultured caudate nucleus (CN) neurons.

MAIN METHODS

The expressions of cyclooxygenase-2 (COX-2), ERK1/2, NF-κB and IκB-α as well as cleaved caspase-3 and p-Bcl-2 in Hcy-, URB602 or SR1 (a selective inhibitor of CB1 receptor)-treated primary cultured neurons in CN were measured by immunoblotting technique and neurotoxicity assays were performed by using Hoechst staining.

KEY FINDINGS

The MAGL inhibitor URB602 exerted a neuroprotective effect on Hcy-induced impairment through suppression of cyclooxygenase-2 (COX-2) elevation and ERK1/2 and NF-κB phosphorylation as well as suppressions of IκB-α degradation in a CB1 receptor-dependent way. Moreover, anti-neuronal impairments of URB602 were mediated by modulating down-regulation of cleaved caspase-3 expression and up-regulation of p-Bcl-2 expression in a CB1 receptor-dependent manner in primary cultured CN neurons.

SIGNIFICANCE

These data suggest that the MAGL inhibitor is a promising therapeutic target for some neurodegenerative disorders, such as AD, via the COX-2 signaling pathway.

Dopamine signals and physiological origin of cognitive dysfunction in Parkinson's disease

The pathological hallmark of Parkinson's disease (PD) is the degeneration of midbrain dopamine neurons. Cognitive dysfunction is a feature of PD patients even at the early stages of the disease. Electrophysiological studies on dopamine neurons in awake animals provide contradictory accounts of the role of dopamine. These studies have established that dopamine neurons convey a unique signal associated with rewards rather than cognitive functions. Emphasizing their role in reward processing leads to difficulty in developing hypothesis as to how cognitive impairments in PD are associated with the degeneration of dopamine circuitry. A hint to resolve this contradiction came from recent electrophysiological studies reporting that dopamine neurons transmit more diverse signals than previously thought. These studies suggest that dopamine neurons are divided into at least two functional subgroups, one signaling "motivational value" and the other signaling "salience." The former subgroup fits well with the conventional reward theory, whereas the latter subgroup has been shown to transmit signals related to salient but non-rewarding experiences such as aversive stimulations and cognitively demanding situations. This article reviews recent advances in understanding the non-reward functions of dopamine, and then discusses the possibility that cognitive dysfunction in PD is at least partially caused by the degeneration of the dopamine neuron subgroup signaling the salience of events in the environment.

The role of executive control in bilingual language production: A study with Parkinson's disease individuals

The basal ganglia are critically involved in language control (LC) processes, allowing a bilingual to utter correctly in one language without interference from the non-requested language. It has been hypothesized that the neural mechanism of LC closely resembles domain-general executive control (EC). The purpose of the present study is to investigate the integrity of bilingual LC and its overlap with domain-general EC in a clinical population such as individuals with Parkinson's disease (PD), notoriously associated with structural damage in the basal ganglia. We approach these issues in two ways. First, we employed a language switching task to investigate the integrity of LC in a group of Catalan-Spanish bilingual individuals with PD, as compared to a group of matched healthy controls. Second, to test the relationship between domain-general EC and LC we compared the performances of individuals with PD and healthy controls also in a non-linguistic switching task. We highlight that, compared to controls, individuals with PD report decreased processing speed, less accuracy and larger switching costs in terms of RT and errors in the language switching task, whereas in the non-linguistic switching task PD patients showed only increased switching cost in terms of errors. However, we report a positive correlation between the magnitudes of linguistic and non-linguistic mixing costs in individuals with PD. Taken together, these results support the notion of a critical role of the basal ganglia and connected structures in LC, and suggest a possible link between LC and domain-general EC.

Striatal and extrastriatal dopamine transporter levels relate to cognition in Lewy body diseases: an (11)C altropane positron emission tomography study

Introduction

The biological basis of cognitive impairment in parkinsonian diseases is believed to be multifactorial. We investigated the contribution of dopamine deficiency to cognition in Parkinson disease (PD) and dementia with Lewy bodies (DLB) with dopamine transporter (DAT) imaging.

Methods

We acquired ¹¹C altropane PET, magnetic resonance imaging and cognitive testing in 19 nondemented subjects with PD, 10 DLB and 17 healthy control subjects (HCS). We analyzed DAT concentration in putamen, caudate, anterior cingulate (AC), orbitofrontal and prefrontal regions, using the Standardized Uptake Volume Ratio with partial volume correction, and we related DAT concentration and global cortical thickness to neuropsychological performance.

Results

DAT concentration in putamen and in caudate were similar in PD and DLB groups and significantly lower than in HCS. Reduced caudate DAT concentration was associated with worse Clinical Dementia Rating Scale–sum of boxes (CDR-SB) scores and visuospatial skills in DLB but not in PD or HCS groups. Adjusting for putamen DAT concentration, as a measure of severity of motor disease, caudate DAT concentration was lower in DLB than in PD. Higher AC DAT concentration was associated with lower putamen DAT concentration in DLB and with higher putamen DAT concentration in PD. Higher AC DAT concentration in DLB correlated with greater impairment in semantic memory and language.

Conclusions

Caudate and AC dopamine dysfunction contribute in opposing directions to cognitive impairment in DLB.