The morbid anatomy of dementia in Parkinson's disease

Hippocampal subfields: volume, neuropathological vulnerability and cognitive decline in Alzheimer's and Parkinson's disease

BACKGROUND

The hippocampus is highly affected in neurodegenerative diseases, including Alzheimer's disease (AD) and Parkinson's disease (PD). The relationship between neuropathology and atrophy in hippocampal subfields is complex due to differences in the selective neuronal vulnerability to distinct protein aggregates that underlie cognitive impairment. The aim of the current study was to investigate the relation between hippocampal subfield volumes, neuropathological burden (amyloid-β, p-tau and α-synuclein) and cognitive performance in AD, PD and control brain donors, using a cross-disease and within-subject post-mortem in situ MRI and neuropathology approach.

METHODS

A total of 60 brain donors, including 14 non-neurological controls, 27 AD and 19 PD, underwent post-mortem in situ MRI. From 3D-T1 images hippocampal subfield and entorhinal cortex volumes were derived using FreeSurfer-based subfield segmentation. Hippocampal tissue was obtained at subsequent autopsy, fixed and immunostained for amyloid-β, p-tau and pSer129-αSyn. Immunoreactivity in hippocampal subfields was quantified as area% load using QuPath. Clinical Dementia Rating scores were extracted from the clinical files when available.

RESULTS

AD showed atrophy and increased p-tau, but not amyloid-β, burden in the CA1, subiculum and entorhinal cortex compared to controls, however MRI and neuropathology did not correlate. Controls and PD had similar hippocampal subfield volumes and pathology load. In PD, p-tau pathology, rather than pSer129-αSyn, was associated with lower total hippocampal volume (r=-0.68, p = 0.045), predominantly in PD with dementia (PDD) (r=-0.99, p = 0.013). Cross-disease, volume loss of the subiculum (r=-0.68, p = 0.001) and entorhinal cortex (r=-0.73, p = 0.004) strongly associated with cognitive impairment. Moreover, p-tau pathology had the strongest effect on subfield atrophy, most pronounced in the subiculum (β=-0.570, p < 0.001), but could only explain 22-44% of the volumetric variance.

CONCLUSIONS

Even though p-tau was the strongest predictor of hippocampal subfield atrophy, AD-pathology (p-tau and amyloid-β) only partially accounted for volumetric differences in hippocampal subfields, highlighting the significance of other pathologies or mechanisms. The increased sensitivity of subicular and entorhinal cortical atrophy compared to total hippocampal atrophy highlights the potential clinical value of incorporating hippocampal subfield atrophy in monitoring disease progression.

Subregional analysis of the amygdala, thalamus, and hypothalamus at the pre-decline stage in Parkinson's disease with later cognitive impairment

Cognitive decline in Parkinson's disease (PD) significantly impacts patients' quality of life, yet early detection remains challenging. While structural brain abnormalities in cortical regions have been widely documented using magnetic resonance imaging (MRI), subcortical regions have received less analytical attention despite their potential role as early biomarkers. This study investigated changes in specific subregions of the amygdala, thalamus, and hypothalamus in patients with PD before cognitive decline development. We analyzed MRI data from 163 participants (97 healthy controls [HC] and 66 patients with PD) from the Parkinson's Progression Markers Initiative database. The patients with PD were classified based on cognitive status during a four-year follow-up: 21 who developed cognitive impairment (PDCI) and 45 who maintained normal cognition (PDNC). Cognitive function was assessed using the Montreal Cognitive Assessment and domain-specific tests. The PDCI group showed significantly lower corrected brain volumes in specific subregions of the amygdala (left basal nucleus), thalamus (bilateral lateral geniculate nuclei, right medial dorsal nucleus, and right anterior pulvinar nucleus), and hypothalamus (bilateral anterior-superior and left superior tubular parts) compared to that of HC. A significant difference between the PDCI and PDNC groups was observed only in the left lateral geniculate nucleus. In contrast, widespread structural changes were observed in cortical regions in the PDCI group, which showed stronger correlations with memory, attention, executive function, and visuospatial abilities. Hazard ratio analysis confirmed that structural changes in multiple cortical regions were significant predictors of cognitive decline. Although structural alterations were observed in subcortical regions, cortical changes demonstrated stronger associations with cognitive decline. These findings suggest that structural abnormalities may appear in the cerebral cortex before the stage proposed by conventional α-synuclein propagation models, potentially involving multiple mechanisms beyond α-synuclein, including global neural circuit dysfunction, disruption of neurotransmitter systems, breakdown of compensatory mechanisms, and coexisting pathologies (beta-amyloid and tau proteins). This study provides insights into early brain changes in PD and emphasizes the need for a comprehensive approach considering multiple mechanisms in early diagnosis and intervention strategies for PD-related cognitive impairment.

The Role of the Claustrum in Parkinson's Disease and Vascular Parkinsonism: A Matter of Network?

BACKGROUND

The mechanisms underlying extrapyramidal disorders and their anatomical substrate have been extensively investigated. Recently, the role of the claustrum in Parkinson's disease and other neurodegenerative conditions has been better detailed. The main aim of this review was to summarize the supporting evidence for the role of the claustrum in degenerative and vascular parkinsonism.

METHODS

The anatomy, biology, vascular supply, and connections of the claustrum in humans were identified and described, providing the substrate for the vascular involvement of the claustrum in large- and small-vessel disease. The vascular supply of the claustrum includes up to three different sources from a single artery, the middle cerebral artery, and it is known as territory with an intermediate hemodynamic risk. The connections of the claustrum make it a sensory integrator and a relevant point in several networks, from consciousness to movement planning.

CONCLUSIONS

The claustrum is still an incompletely explained structure. However, recent description of its multiple connections indicate that it is involved in several diseases, including Parkinson's disease. The evidence underlying its potential role in vascular parkinsonism is still scarce, but it might be a field warranting future investigations.

Pathobiology of Cognitive Impairment in Parkinson Disease: Challenges and Outlooks

Cognitive impairment (CI) is a characteristic non-motor feature of Parkinson disease (PD) that poses a severe burden on the patients and caregivers, yet relatively little is known about its pathobiology. Cognitive deficits are evident throughout the course of PD, with around 25% of subtle cognitive decline and mild CI (MCI) at the time of diagnosis and up to 83% of patients developing dementia after 20 years. The heterogeneity of cognitive phenotypes suggests that a common neuropathological process, characterized by progressive degeneration of the dopaminergic striatonigral system and of many other neuronal systems, results not only in structural deficits but also extensive changes of functional neuronal network activities and neurotransmitter dysfunctions. Modern neuroimaging studies revealed multilocular cortical and subcortical atrophies and alterations in intrinsic neuronal connectivities. The decreased functional connectivity (FC) of the default mode network (DMN) in the bilateral prefrontal cortex is affected already before the development of clinical CI and in the absence of structural changes. Longitudinal cognitive decline is associated with frontostriatal and limbic affections, white matter microlesions and changes between multiple functional neuronal networks, including thalamo-insular, frontoparietal and attention networks, the cholinergic forebrain and the noradrenergic system. Superimposed Alzheimer-related (and other concomitant) pathologies due to interactions between α-synuclein, tau-protein and β-amyloid contribute to dementia pathogenesis in both PD and dementia with Lewy bodies (DLB). To further elucidate the interaction of the pathomechanisms responsible for CI in PD, well-designed longitudinal clinico-pathological studies are warranted that are supported by fluid and sophisticated imaging biomarkers as a basis for better early diagnosis and future disease-modifying therapies.

Cerebrospinal fluid GFAP is a predictive biomarker for conversion to dementia and Alzheimer's disease-associated biomarkers alterations among de novo Parkinson's disease patients: a prospective cohort study

BACKGROUND

Dementia is a prevalent non-motor manifestation among individuals with advanced Parkinson's disease (PD). Glial fibrillary acidic protein (GFAP) is an inflammatory marker derived from astrocytes. Research has demonstrated the potential of plasma GFAP to forecast the progression to dementia in PD patients with mild cognitive impairment (PD-MCI). However, the predictive role of cerebrospinal fluid (CSF) GFAP on future cognitive transformation and alterations in Alzheimer's disease (AD)-associated CSF biomarkers in newly diagnosed PD patients has not been investigated.

METHODS

210 de novo PD patients from the Parkinson's Progression Markers Initiative were recruited. Cognitive progression in PD participants was evaluated using Cox regression. Cross-sectional and longitudinal associations between baseline CSF GFAP and cognitive function and AD-related CSF biomarkers were evaluated using multiple linear regression and generalized linear mixed model.

RESULTS

At baseline, the mean age of PD participants was 60.85 ± 9.78 years, including 142 patients with normal cognition (PD-NC) and 68 PD-MCI patients. The average follow-up time was 6.42 ± 1.69 years. A positive correlation was observed between baseline CSF GFAP and age (β = 0.918, p < 0.001). There was no statistically significant difference in baseline CSF GFAP levels between PD-NC and PD-MCI groups. Higher baseline CSF GFAP predicted greater global cognitive decline over time in early PD patients (Montreal Cognitive Assessment, β = - 0.013, p = 0.014). Furthermore, Cox regression showed that high baseline CSF GFAP levels were associated with a high risk of developing dementia over an 8-year period in the PD-NC group (adjusted HR = 3.070, 95% CI 1.119-8.418, p = 0.029). In addition, the baseline CSF GFAP was positively correlated with the longitudinal changes of not only CSF α-synuclein (β = 0.313, p < 0.001), but also CSF biomarkers associated with AD, namely, amyloid-β 42 (β = 0.147, p = 0.034), total tau (β = 0.337, p < 0.001) and phosphorylated tau (β = 0.408, p < 0.001).

CONCLUSIONS

CSF GFAP may be a valuable prognostic tool that can predict the severity and progression of cognitive deterioration, accompanied with longitudinal changes in AD-associated pathological markers in early PD.

Hippocampal, basal ganglia and olfactory connectivity contribute to cognitive impairments in Parkinson's disease

Cognitive impairment is increasingly recognized as a characteristic feature of Parkinson's disease (PD), yet relatively little is known about its underlying neurobiology. Previous investigations suggest that dementia in PD is associated with subcortical atrophy, but similar studies in PD with mild cognitive impairment have been mixed. Variability in cognitive phenotypes and diversity of PD symptoms suggest that a common neuropathological origin results in a multitude of impacts within the brain. These direct and indirect impacts of disease pathology can be investigated using network analysis. Functional connectivity, for instance, may be more sensitive than atrophy to decline in specific cognitive domains in the PD population. Fifty-eight participants with PD underwent a neuropsychological test battery and scanning with structural and resting state functional MRI in a comprehensive whole-brain association analysis. To investigate atrophy as a potential marker of impairment, structural gray matter atrophy was associated with cognitive scores in each cognitive domain using voxel-based morphometry. To investigate connectivity, large-scale networks were correlated with voxel time series and associated with cognitive scores using distance covariance. Structural atrophy was not associated with any cognitive domain, with the exception of visuospatial measures in primary sensory and motor cortices. In contrast, functional connectivity was associated with attention, executive function, language, learning and memory, visuospatial, and global cognition in the bilateral hippocampus, left putamen, olfactory cortex, and bilateral anterior temporal poles. These preliminary results suggest that cognitive domain-specific networks in PD are distinct from each other and could provide a network signature for different cognitive phenotypes.

Morphological basis of Parkinson disease-associated cognitive impairment: an update

Cognitive impairment is one of the most salient non-motor symptoms of Parkinson disease (PD) that poses a significant burden on the patients and carers as well as being a risk factor for early mortality. People with PD show a wide spectrum of cognitive dysfunctions ranging from subjective cognitive decline and mild cognitive impairment (MCI) to frank dementia. The mean frequency of PD with MCI (PD-MCI) is 25.8% and the pooled dementia frequency is 26.3% increasing up to 83% 20 years after diagnosis. A better understanding of the underlying pathological processes will aid in directing disease-specific treatment. Modern neuroimaging studies revealed considerable changes in gray and white matter in PD patients with cognitive impairment, cortical atrophy, hypometabolism, dopamine/cholinergic or other neurotransmitter dysfunction and increased amyloid burden, but multiple mechanism are likely involved. Combined analysis of imaging and fluid markers is the most promising method for identifying PD-MCI and Parkinson disease dementia (PDD). Morphological substrates are a combination of Lewy- and Alzheimer-associated and other concomitant pathologies with aggregation of α-synuclein, amyloid, tau and other pathological proteins in cortical and subcortical regions causing destruction of essential neuronal networks. Significant pathological heterogeneity within PD-MCI reflects deficits in various cognitive domains. This review highlights the essential neuroimaging data and neuropathological changes in PD with cognitive impairment, the amount and topographical distribution of pathological protein aggregates and their pathophysiological relevance. Large-scale clinicopathological correlative studies are warranted to further elucidate the exact neuropathological correlates of cognitive impairment in PD and related synucleinopathies as a basis for early diagnosis and future disease-modifying therapies.

Glymphatic System Dysfunction in Central Nervous System Diseases and Mood Disorders

The glymphatic system, a recently discovered macroscopic waste removal system in the brain, has many unknown aspects, especially its driving forces and relationship with sleep, and thus further explorations of the relationship between the glymphatic system and a variety of possible related diseases are urgently needed. Here, we focus on the progress in current research on the role of the glymphatic system in several common central nervous system diseases and mood disorders, discuss the structural and functional abnormalities of the glymphatic system which may occur before or during the pathophysiological progress and the possible underlying mechanisms. We emphasize the relationship between sleep and the glymphatic system under pathological conditions and summarize the common imaging techniques for the glymphatic system currently available. The perfection of the glymphatic system hypothesis and the exploration of the effects of aging and endocrine factors on the central and peripheral regulatory pathways through the glymphatic system still require exploration in the future.

Mutant glucocerebrosidase impairs α-synuclein degradation by blockade of chaperone-mediated autophagy

The most common genetic risk factors for Parkinson's disease (PD) are a set of heterozygous mutant (MT) alleles of the GBA1 gene that encodes β-glucocerebrosidase (GCase), an enzyme normally trafficked through the ER/Golgi apparatus to the lysosomal lumen. We found that half of the GCase in lysosomes from postmortem human GBA-PD brains was present on the lysosomal surface and that this mislocalization depends on a pentapeptide motif in GCase used to target cytosolic protein for degradation by chaperone-mediated autophagy (CMA). MT GCase at the lysosomal surface inhibits CMA, causing accumulation of CMA substrates including α-synuclein. Single-cell transcriptional analysis and proteomics of brains from GBA-PD patients confirmed reduced CMA activity and proteome changes comparable to those in CMA-deficient mouse brain. Loss of the MT GCase CMA motif rescued primary substantia nigra dopaminergic neurons from MT GCase-induced neuronal death. We conclude that MT GBA1 alleles block CMA function and produce α-synuclein accumulation.

Predictors of Pain Severity and its Impact on Quality of Life in Patients with Parkinson's Disease

Background

Pain is a common and distressing symptom of Parkinson's disease (PD). The relation of pain, its predictors, and its impact on quality of life (QoL) in PD has not been studied in Indian PD patients.

Objective

To assess the predictors of pain and investigate its impact on QoL among Indian PD patients.

Methodology

We conducted a cross-sectional study on 100 PD patients. The cases were diagnosed according to the UK brain bank criteria. Unified PD Rating Scale (UPDRS) parts III, V, and VI were employed to assess the severity of the disease. King's Parkinson Disease Pain Scale (KPPS) and PD questionnaire-8 (PDQ-8) were used to evaluate pain and QoL, respectively.

Results

Prevalence of different pain types in patients with PD was 70%, mainly including musculoskeletal (53%), fluctuation-related (35%), and nocturnal pain (27%). Subjects with pain developed PD symptoms at a younger age and had a longer duration of the disease. A positive correlation was found between KPPS scores and UPDRS parts III and V, while a negative correlation was observed with UPDRS part VI. Pain in PD subjects had a significant impact on the QoL.

Conclusions

Most of the PD patients suffered some form of pain with significant correlations with motor disability and poor QoL. Predictors of pain severity among PD patients included a longer disease duration, younger age of disease onset, and a higher levodopa equivalent daily dose (LEDD).

Locus Coeruleus Pathology Indicates a Continuum of Lewy Body Dementia

BACKGROUND

Lewy body dementia (LBD) has two main phenotypes of LBD, Parkinson's disease dementia (PDD) and dementia with Lewy bodies (DLB), separated by the 'one-year-rule'. They also show different symptom profiles: core DLB features include fluctuating cognition, REM-sleep behaviur disorder, and visual hallucinations. These symptoms are sometimes present in PDD, representing an intermediate 'PDD-DLB' phenotype.

OBJECTIVE

DLB-like features may reflect deficits in the functions of the noradrenergic nucleus locus coeruleus (LC). Therefore, we compared the LC in the LBD phenotypes, PD, and controls.

METHODS

38 PD, 56 PDD, 22 DLB, and 11 age-matched control cases from the Parkinson's UK tissue bank were included. LC tissue sections were immunostained for tyrosine-hydroxylase (TH), α-synuclein, tau, and amyloid-β. TH-neurons were quantified and pathologic burden calculated by %-coverage method.

RESULTS

The LC shows a stepwise reduction in neuron count from controls, PD, PDD, to DLB. PDD-DLB cases showed an intermediate clinical phenotype that was reflected pathologically. Cell counts were significantly reduced in DLB compared to PDD after correction for demographic factors. LC degeneration contributed significantly to the onset of all DLB symptoms. While α-synuclein was not significantly different between PDD and DLB cases, DLB exhibited significantly less tau pathology.

CONCLUSION

DLB and DLB-like symptoms represent noradrenergic deficits resulting from neuronal loss in the LC. PDD and DLB are likely to represent a clinical continuum based on the presence or absence of DLB-like symptoms mirrored by a pathological continuum in the LC.

Significance of cerebral amyloid angiopathy and other co-morbidities in Lewy body diseases

Lewy body dementia (LBD) and Parkinson's disease-dementia (PDD) are two major neurocognitive disorders with Lewy bodies (LB) of unknown etiology. There is considerable clinical and pathological overlap between these two conditions that are clinically distinguished based on the duration of Parkinsonism prior to development of dementia. Their morphology is characterized by a variable combination of LB and Alzheimer's disease (AD) pathologies. Cerebral amyloid angiopathy (CAA), very common in aged persons and particularly in AD, is increasingly recognized for its association with both pathologies and dementia. To investigate neuropathological differences between LB diseases with and without dementia, 110 PDD and 60 LBD cases were compared with 60 Parkinson's disease (PD) cases without dementia (PDND). The major demographic and neuropathological data were assessed retrospectively. PDD patients were significantly older than PDND ones (83.9 vs 77.8 years; p < 0.05); the age of LB patients was in between both groups (mean 80.2 years), while the duration of disease was LBD < PDD < PDND (mean 6.7 vs 12.5 and 14.3 years). LBD patients had higher neuritic Braak stages (mean 5.1 vs 4.5 and 4.0, respectively), LB scores (mean 5.3 vs 4.2 and 4.0, respectively), and Thal amyloid phases (mean 4.1 vs 3.0 and 2.3, respectively) than the two other groups. CAA was more common in LBD than in the PDD and PDND groups (93 vs 50 and 21.7%, respectively). Its severity was significantly greater in LBD than in PDD and PDND (p < 0.01), involving mainly the occipital lobes. Moreover, striatal Aβ deposition highly differentiated LBD brains from PDD. Braak neurofibrillary tangle (NFT) stages, CAA, and less Thal Aβ phases were positively correlated with LB pathology (p < 0.05), which was significantly higher in LBD than in PDD < PDND. Survival analysis showed worse prognosis in LBD than in PDD (and PDND), which was linked to both increased Braak tau stages and more severe CAA. These and other recent studies imply the association of CAA-and both tau and LB pathologies-with cognitive decline and more rapid disease progression that distinguishes LBD from PDD (and PDND).

Striatal dopamine transporters and cognitive function in Parkinson's disease

BACKGROUND

Idiopathic Parkinson's disease (PD) is characterized by clinical motor symptoms including hypokinesia, rigidity and tremor. In addition to the movement disorder, cognitive deficits are commonly described. In the present study, we applied FP-CIT SPECT to investigate the impact of nigrostriatal dopaminergic degeneration on cognitive function in PD patients.

METHODS

Fifty-four PD patients underwent [¹²³I]FP-CIT SPECT and CERAD (Consortium to Establish a Registry for Alzheimer's Disease) testing. FP-CIT SPECT visualized the density of presynaptic dopamine transporters in both striata, each subdivided into a limbic, executive and sensorimotor subregion according to the atlas of Tziortzi et al (Cereb Cortex 24, 2014, 1165). CERAD testing quantified cognitive function.

RESULTS

In the CERAD testing, PD patients exhibited deficits in the domains of semantic memory, attention, visuospatial function, non-verbal memory and executive function. After correction for multiple testing, the performance of the subtests Figure Recall and Trail-Making Test A correlated significantly with FP-CIT uptake into the ipsilateral executive subregion. The performance of the subtest Figure Saving correlated significantly with FP-CIT uptake into the contralateral executive subregion.

CONCLUSIONS

The significant correlation between cognitive function and density of nigrostriatal dopamine transporters, as assessed by FP-CIT SPECT, indicate that striatal dopaminergic pathways-primarily the executive striatal subregion-are relevant to cognitive processing in PD.

Grey matter abnormalities are associated only with severe cognitive decline in early stages of Parkinson's disease

Cognitive impairment is common in Parkinson's disease (PD), yet with large heterogeneity in the range and course of deficits. In a cross-sectional study, 124 PD patients underwent extensive clinical and neuropsychological assessment as well as a 3T MRI scan of the brain. Our aim was to identify differences in grey matter volume and thickness, as well as cortical folding, across different cognitive profiles as defined through a data-driven exploratory cluster analysis of neuropsychological data. The identified cognitive groups ranged from cognitively intact patients to patients with severe deficits in all cognitive domains, whilst showing comparable levels of motor disability and disease duration. Each group was compared to the cognitively intact PD group using voxel- and vertex-based morphometry. Results revealed widespread age-related grey matter abnormalities associated with progressive worsening of cognitive functions in mild PD. When adjusted for age, significant differences were only seen between cognitively intact and severely affected PD patients and these were restricted to the right posterior cingulate and the right precuneus. Reduced cortical thickness was seen in the right inferior temporal gyrus and reduced folding in the right temporal region. As these differences were not associated with age, we assume that they are associated with underlying pathology of the cognitive decline. Given the limited involvement of grey matter differences, and the absence of differences in vascular changes across the groups, we hypothesize a more important role for white matter tract changes in cognitive decline in PD.

Establishing a framework for neuropathological correlates and glymphatic system functioning in Parkinson's disease

Recent evidence has advanced our understanding of the function of sleep to include removal of neurotoxic protein aggregates via the glymphatic system. However, most research on the glymphatic system utilizes animal models, and the function of waste clearance processes in humans remains unclear. Understanding glymphatic function offers new insight into the development of neurodegenerative diseases that result from toxic protein inclusions, particularly those characterized by neuropathological sleep dysfunction, like Parkinson's disease (PD). In PD, we propose that glymphatic flow may be compromised due to the combined neurotoxic effects of alpha-synuclein protein aggregates and deteriorated dopaminergic neurons that are linked to altered REM sleep, circadian rhythms, and clock gene dysfunction. This review highlights the importance of understanding the functional role of glymphatic system disturbance in neurodegenerative disorders and the subsequent clinical and neuropathological effects on disease progression. Future research initiatives utilizing noninvasive brain imaging methods in human subjects with PD are warranted, as in vivo identification of functional biomarkers in glymphatic system functioning may improve clinical diagnosis and treatment of PD.

Neuropathology and pathogenesis of extrapyramidal movement disorders: a critical update-I. Hypokinetic-rigid movement disorders

Extrapyramidal movement disorders include hypokinetic rigid and hyperkinetic or mixed forms, most of them originating from dysfunction of the basal ganglia (BG) and their information circuits. The functional anatomy of the BG, the cortico-BG-thalamocortical, and BG-cerebellar circuit connections are briefly reviewed. Pathophysiologic classification of extrapyramidal movement disorder mechanisms distinguish (1) parkinsonian syndromes, (2) chorea and related syndromes, (3) dystonias, (4) myoclonic syndromes, (5) ballism, (6) tics, and (7) tremor syndromes. Recent genetic and molecular-biologic classifications distinguish (1) synucleinopathies (Parkinson's disease, dementia with Lewy bodies, Parkinson's disease-dementia, and multiple system atrophy); (2) tauopathies (progressive supranuclear palsy, corticobasal degeneration, FTLD-17; Guamian Parkinson-dementia; Pick's disease, and others); (3) polyglutamine disorders (Huntington's disease and related disorders); (4) pantothenate kinase-associated neurodegeneration; (5) Wilson's disease; and (6) other hereditary neurodegenerations without hitherto detected genetic or specific markers. The diversity of phenotypes is related to the deposition of pathologic proteins in distinct cell populations, causing neurodegeneration due to genetic and environmental factors, but there is frequent overlap between various disorders. Their etiopathogenesis is still poorly understood, but is suggested to result from an interaction between genetic and environmental factors. Multiple etiologies and noxious factors (protein mishandling, mitochondrial dysfunction, oxidative stress, excitotoxicity, energy failure, and chronic neuroinflammation) are more likely than a single factor. Current clinical consensus criteria have increased the diagnostic accuracy of most neurodegenerative movement disorders, but for their definite diagnosis, histopathological confirmation is required. We present a timely overview of the neuropathology and pathogenesis of the major extrapyramidal movement disorders in two parts, the first one dedicated to hypokinetic-rigid forms and the second to hyperkinetic disorders.

Hippocampal CA2 Lewy pathology is associated with cholinergic degeneration in Parkinson's disease with cognitive decline

Although the precise neuropathological substrates of cognitive decline in Parkinson's disease (PD) remain elusive, it has long been regarded that pathology in the CA2 hippocampal subfield is characteristic of Lewy body dementias, including dementia in PD (PDD). Early non-human primate tracer studies demonstrated connections from the nucleus of the vertical limb of the diagonal band of Broca (nvlDBB, Ch2) to the hippocampus. However, the relationship between Lewy pathology of the CA2 subfield and cholinergic fibres has not been explored. Therefore, in this study, we investigated the burden of pathology in the CA2 subsector of PD cases with varying degrees of cognitive impairment and correlated this with the extent of septohippocampal cholinergic deficit. Hippocampal sections from 67 PD, 34 PD with mild cognitive impairment and 96 PDD cases were immunostained for tau and alpha-synuclein, and the respective pathology burden was assessed semi-quantitatively. In a subset of cases, the degree of CA2 cholinergic depletion was quantified using confocal microscopy and correlated with cholinergic neuronal loss in Ch2. We found that only cases with dementia have a significantly greater Lewy pathology, whereas cholinergic fibre depletion was evident in cases with mild cognitive impairment and this was significantly correlated with loss of cholinergic neurons in Ch2. In addition, multiple antigen immunofluorescence demonstrated colocalisation between cholinergic fibres and alpha-synuclein but not tau pathology. Such specific Lewy pathology targeting the cholinergic system within the CA2 subfield may contribute to the unique memory retrieval deficit seen in patients with Lewy body disorders, as distinct from the memory storage deficit seen in Alzheimer's disease.

Imaging Markers of Progression in Parkinson's Disease

Background

Parkinson's disease (PD) is the second-most common neurodegenerative disorder after Alzheimer's disease; however, to date, there is no approved treatment that stops or slows down disease progression. Over the past decades, neuroimaging studies, including molecular imaging and MRI are trying to provide insights into the mechanisms underlying PD.

Methods

This work utilized a literature review.

Results

It is now becoming clear that these imaging modalities can provide biomarkers that can objectively detect brain changes related to PD and monitor these changes as the disease progresses, and these biomarkers are required to establish a breakthrough in neuroprotective or disease-modifying therapeutics.

Conclusions

Here, we provide a review of recent observations deriving from PET, single-positron emission tomography, and MRI studies exploring PD and other parkinsonian disorders.

The impact of Apolipoprotein E alleles on cognitive performance in patients with Parkinson's disease

Apolipoprotein E (ApoE) is a vital component of several lipoproteins and plays a major role in lipid metabolism. APOE gene comprises of three alleles determined by two single nucleotide polymorphisms (rs429358 and rs7412) resulting in the protein isoforms, among which ApoE4 is a confirmed risk factor for Alzheimer's Disease. However, the impact of APOE genotypes on Parkinson's Disease Dementia (PDD) is still inconclusive. The PDD diagnostic criteria are very inconsistent, and could be complemented with genetic factors. Our study covers a total of 237 patients diagnosed with Parkinson's Disease (PD) according to UK PD Brain Bank criteria, who were classified as subjects with (PDD, n equals 73) and without (nPDD, n equals 164) dementia, using neuropsychological assessment tests. TaqMan real-time PCR assays were used to determine APOE allele. No statistically significant differences in APOE alleles frequencies between nPDD and PDD patients have been observed. The study results revealed that the APOE polymorphism is not associated with cognitive status in PD patients.

Basal ganglia and beyond: The interplay between motor and cognitive aspects in Parkinson's disease rehabilitation

Parkinson's disease (PD) is characterized by motor and cognitive dysfunctions, affecting the motor behaviour. We summarize evidence that the interplay between motor and cognitive approaches is crucial in PD rehabilitation. Rehabilitation is complementary to pharmacological therapy and effective in reducing the PD disturbances, probably acting by inducing neuroplastic effects. The motor behaviour results from a complex integration between cortical and subcortical areas, underlying the motor, cognitive and motivational aspects of movement. The close interplay amongst these areas makes possible to learn, control and express habitual-automatic actions, which are dysfunctional in PD. The physiopathology of PD could be considered the base for the development of effective rehabilitation treatments. As the volitional action control is spared in early-medium stages of disease, rehabilitative approaches engaging cognition permit to achieve motor benefits and appear to be the most effective for PD. We will point out data supporting the relevance of targeting both motor and cognitive aspects in PD rehabilitation. Finally, we will discuss the role of cognitive engagement in motor rehabilitation for PD.

Recent advances in cholinergic imaging and cognitive decline-Revisiting the cholinergic hypothesis of dementia

PURPOSE OF REVIEW

Although the cholinergic hypothesis of dementia provided a successful paradigm for the development of new drugs for dementia, this hypothesis has waned in popularity. Cholinergic brain imaging may provide novel insights into the viability of this hypothesis.

RECENT FINDINGS

Cholinergic receptor and forebrain volumetric studies suggest an important role of the cholinergic system in maintaining brain network integrity that may deteriorate with cognitive decline in Alzheimer disease (AD) and Lewy body disorders (LBD). Bidirectional changes in regional receptor expression may suggest the presence of compensatory responses to neurodegenerative injury. Cholinergic system changes are more complex in LBD because of additional subcortical degenerations compared to AD. Cholinergic-dopaminergic interactions affect attentional, verbal learning and executive functions, and impairments in these two transmitter systems may jointly increase the risk of dementia in Parkinson disease.

SUMMARY

The cholinergic hypothesis is evolving from a primary focus on memory toward expanded cognitive functions modulated by regionally more complex and interactive brain networks. Cholinergic network adaptation may serve as a novel research target in neurodegeneration.

Critical appraisal of pathology transmission in the α-synuclein fibril model of Lewy body disorders

Lewy body disorders are characterized by the emergence of α-synucleinopathy in many parts of the central and peripheral nervous systems, including in the telencephalon. Dense α-synuclein+ pathology appears in regio inferior of the hippocampus in both Parkinson's disease and dementia with Lewy bodies and may disturb cognitive function. The preformed α-synuclein fibril model of Parkinson's disease is growing in use, given its potential for seeding the self-propagating spread of α-synucleinopathy throughout the mammalian brain. Although it is often assumed that the spread occurs through neuroanatomical connections, this is generally not examined vis-à-vis the uptake and transport of tract-tracers infused at precisely the same stereotaxic coordinates. As the neuronal connections of the hippocampus are historically well defined, we examined the first-order spread of α-synucleinopathy three months following fibril infusions centered in the mouse regio inferior (CA2+CA3), and contrasted this to retrograde and anterograde transport of the established tract-tracers FluoroGold and biotinylated dextran amines (BDA). Massive hippocampal α-synucleinopathy was insufficient to elicit memory deficits or loss of cells and synaptic markers in this model of early disease processes. However, dense α-synuclein+ inclusions in the fascia dentata were negatively correlated with memory capacity. A modest compensatory increase in synaptophysin was evident in the stratum radiatum of cornu Ammonis in fibril-infused animals, and synaptophysin expression correlated inversely with memory function in fibril but not PBS-infused mice. No changes in synapsin I/II expression were observed. The spread of α-synucleinopathy was somewhat, but not entirely consistent with FluoroGold and BDA axonal transport, suggesting that variables other than innervation density also contribute to the materialization of α-synucleinopathy. For example, layer II entorhinal neurons of the perforant pathway exhibited somal α-synuclein+ inclusions as well as retrogradely labeled FluoroGold+ somata. However, some afferent brain regions displayed dense retrograde FluoroGold label and no α-synuclein+ inclusions (e.g. medial septum/diagonal band), supporting the selective vulnerability hypothesis. The pattern of inclusions on the contralateral side was consistent with specific spread through commissural connections (e.g. stratum pyramidale of CA3), but again, not all commissural projections exhibited α-synucleinopathy (e.g. hilar mossy cells). The topographical extent of inclusions is displayed here in high-resolution images that afford viewers a rich opportunity to dissect the potential spread of pathology through neural circuitry. Finally, the results of this expository study were leveraged to highlight the challenges and limitations of working with preformed α-synuclein fibrils.

The catecholaminergic innervation of the claustrum of the pig

Over the past decades, the number of studies employing the pig brain as a model for neurochemical studies has dramatically increased. The key translational features of the pig brain are the similarities with the cortical and subcortical structures of the human brain. In addition, the caudalmost part of the pig claustrum (CL) is characterized by a wide enlargement called posterior puddle, an ideal structure for physiological recordings. Several hypotheses have been proposed for CL function, the key factor being its reciprocal connectivity with most areas of the cerebral cortex and selected subcortical structures. However, afferents from the brainstem could also be involved. The brainstem is the main source of catecholaminergic axons that play an important neuromodulatory action in different brain functions. To study a possible role of the CL in catecholaminergic pathways, we analyzed the presence and the distribution of afferents immunostained with antibodies against tyrosine hydroxylase (TH) and dopamine betahydroxylase (DBH) in the pig CL. Here we show that the CL contains significant TH immunoreactive axons contacting perikarya, whereas projections staining for DBH are very scarce. Our findings hint at the possibility that brainstem catecholaminergic afferents project to the CL, suggesting (i) a possible role of this nucleus in functions controlled by brainstem structures; and, consequently, (ii) its potential involvement in the pathophysiology of neurodegenerative pathologies, including Parkinson's disease (PD).

Mild cognitive impairment in Parkinson's disease: a distinct clinical entity?

BACKGROUND

Mild cognitive impairment in Parkinson's disease (PD-MCI) is a common clinical condition. Understanding its pathology and clinical features is important for early intervention before the onset of dementia. In the past, variable definitions and differences in neuropsychological batteries generated divergent results of the affected cognitive patterns.

MAIN BODY

The introduction of PD-MCI criteria by the Movement Disorders Society (MDS) Task Force provides a more uniform system for defining and measuring PD-MCI and may improve the validity of future research. PD-MCI is likely to be heterogeneous since it can coexist with Alzheimer's disease and/ or Lewy body pathologies in PD. Pathogeneses of neuropsychiatric disturbances, such as depression, anxiety and apathy, are associated with PD with or without MCI. In addition, cognitive reserve formed by patients' unique life experiences may influence the outward cognitive performance despite the presence of the aforementioned pathogeneses and hence alter the diagnosis of MCI.

CONCLUSION

The overlap of cognitive impairment across different neurodegenerative diseases suggests that PD-MCI is likely to result from a mixture of complex pathophysiologies, rather than being a distinct pathologic entity. Differentiating MCI from other organic symptoms in PD would facilitate novel therapeutic strategies.

Molecular Imaging and Updated Diagnostic Criteria in Lewy Body Dementias

PURPOSE OF REVIEW

The aims of the study were to review recent advances in molecular imaging in the Lewy body dementias (LBD) and determine if these may support the clinical but contested temporal profile distinction between Parkinson disease (PD) with dementia (PDD) versus dementia with Lewy bodies (DLB).

RECENT FINDINGS

There do not appear to be major regional cerebral metabolic or neurotransmitter distinctions between PDD and DLB. However, recent studies highlight the relative discriminating roles of Alzheimer proteinopathies. PDD patients have lower cortical β-amyloid deposition than DLB. Preliminary tau PET studies suggest a gradient of increasing tau binding from cognitively normal PD (absent to lowest) to cognitively impaired PD (low) to DLB (intermediate) to Alzheimer disease (AD; highest). However, tau binding in DLB, including the medial temporal lobe, is substantially lower than in AD. Alzheimer-type proteinopathies appear to be more common in DLB compared to PDD with relative but no absolute differences. Given the spectrum of overlapping pathologies, future α-synuclein ligands are expected to have the best potential to distinguish the LBD from pure AD.

Neuropathology of Nonmotor Symptoms of Parkinson's Disease

Parkinson's disease (PD), a multiorgan neurodegenerative disorder associated with α-synuclein deposits throughout the nervous system and many organs, is clinically characterized by motor and nonmotor features, many of the latter antedating motor dysfunctions by 20 or more years. The causes of the nonmotor manifestations such as olfactory, autonomic, sensory, neuropsychiatric, visuospatial, sleep, and other disorders are unlikely to be related to single lesions. They are mediated by the involvement of both dopaminergic and nondopaminergic systems, and diverse structures outside the nigrostriatal system that is mainly responsible for the motor features of PD. The nonmotor alterations appear in early/prodromal stages of the disease and its further progression, suggesting a topographical and chronological spread of the lesions. This lends further support for the notion that PD is a multiorgan proteinopathy, although the exact relationship between presymptomatic and later developing nonmotor features of PD and neuropathology awaits further elucidation.

Effects of dual tasks and dual-task training on postural stability: a systematic review and meta-analysis

The use of dual-task training paradigm to enhance postural stability in patients with balance impairments is an emerging area of interest. The differential effects of dual tasks and dual-task training on postural stability still remain unclear. A systematic review and meta-analysis were conducted to analyze the effects of dual task and training application on static and dynamic postural stability among various population groups. Systematic identification of published literature was performed adhering to Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) guidelines, from inception until June 2016, on the online databases Scopus, PEDro, MEDLINE, EMBASE, and SportDiscus. Experimental studies analyzing the effects of dual task and dual-task training on postural stability were extracted, critically appraised using PEDro scale, and then summarized according to modified PEDro level of evidence. Of 1,284 records, 42 studies involving 1,480 participants met the review’s inclusion criteria. Of the studies evaluating the effects of dual-task training on postural stability, 87.5% of the studies reported significant enhancements, whereas 30% of the studies evaluating acute effects of dual tasks on posture reported significant enhancements, 50% reported significant decrements, and 20% reported no effects. Meta-analysis of the pooled studies revealed moderate but significant enhancements of dual-task training in elderly participants (95% CI: 1.16–2.10) and in patients suffering from chronic stroke (−0.22 to 0.86). The adverse effects of complexity of dual tasks on postural stability were also revealed among patients with multiple sclerosis (−0.74 to 0.05). The review also discusses the significance of verbalization in a dual-task setting for increasing cognitive–motor interference. Clinical implications are discussed with respect to practical applications in rehabilitation settings.

Nonmotor Symptoms in Parkinson Disease: A Descriptive Review on Social Cognition Ability

Parkinson disease (PD) is a neurodegenerative disorder characterized by motor and nonmotor symptoms. Nonmotor symptoms include cognitive deficits and impairment in emotions recognition ability associated with loss of dopaminergic neurons in the substantia nigra and with alteration in frontostriatal circuits. In this review, we analyzed the studies on social cognition ability in patients with PD. We searched on PubMed and Web of Science databases and screening references of included studied and review articles for additional citations. From initial 260 articles, only 18 met search criteria. A total of 496 patients were compared with 514 health controls, through 16 different tests that assessed some subcomponents of social cognition, such as theory of mind, decision-making, and emotional face recognition. Studies on cognitive function in patients with PD have focused on executive function. Patients with PD showed impairment in social cognition from the earliest stages of disease. This ability seems to not be significantly associated with other cognitive functions.

Dysfunction of the Default Mode Network in Drug-Naïve Parkinson's Disease with Mild Cognitive Impairments: A Resting-State fMRI Study

Objective: Cognitive impairments are common in Parkinson's disease (PD) and can even occur in the early stages. The default mode network (DMN) is highly relevant for cognitive processes; however, it remains largely unknown if changes in the DMN connectivity are related to the cognitive decline in drug-naïve early stage PD patients with a mild cognitive impairment (MCI). This study used resting-state functional MRI (fMRI) to explore the brain connectivity of the DMN in early stage drug-naïve PD patients with MCI. Method: We recruited 32 early stage drug-naïve PD patients and 22 matched healthy controls (HC). Among the PD patients, 14 were classified as having MCI (PD-MCI) and 18 were classified as having unimpaired cognition (PD-CU). The functional integration of the DMN was evaluated by a seed-based correlation approach. Results: The brain connectivity analysis revealed reduced functional connectivity (FC) in both PD subgroups compared with HC. The PD-MCI group showed a significant reduction in FC between the DMN and a set of regions, including the precentral gyrus, middle temporal gyrus, insula, anterior inferior parietal lobule and middle frontal gyrus. Compared to the PD-CU group, the PD-MCI group demonstrated a significantly decreased FC in the middle frontal and middle temporal gyri. Additionally, compared to HC, the PD-MCI group had a significantly decreased FC within the DMN, mainly in the FC between the hippocampal formation and inferior frontal gyrus, between the posterior cingulate cortex and posterior inferior parietal lobule, and between the anterior temporal lobe and inferior frontal gyrus. Compared to the PD-CU group, the only significantly decreased FC within the DMN in the PD-MCI group was between the anterior temporal lobe and inferior frontal gyrus. In all PD patients, the decreased FC between anterior temporal lobe and middle temporal gyrus was positively correlated with attention/working performance, and the reduced FC between the hippocampal formation and inferior frontal gyrus was also positively correlated with memory function. Conclusion: Our findings suggest that an altered DMN connectivity characterizes PD-MCI patients. These findings may be helpful for facilitating the further understanding of the potential mechanisms underlying MCI in PD. However, our results are preliminary, and further investigation is needed.

Microtubule Dynamics in Neuronal Development, Plasticity, and Neurodegeneration

Neurons are the basic information-processing units of the nervous system. In fulfilling their task, they establish a structural polarity with an axon that can be over a meter long and dendrites with a complex arbor, which can harbor ten-thousands of spines. Microtubules and their associated proteins play important roles during the development of neuronal morphology, the plasticity of neurons, and neurodegenerative processes. They are dynamic structures, which can quickly adapt to changes in the environment and establish a structural scaffold with high local variations in composition and stability. This review presents a comprehensive overview about the role of microtubules and their dynamic behavior during the formation and maturation of processes and spines in the healthy brain, during aging and under neurodegenerative conditions. The review ends with a discussion of microtubule-targeted therapies as a perspective for the supportive treatment of neurodegenerative disorders.

Beta-amyloid deposition in chronic traumatic encephalopathy

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease associated with repetitive mild traumatic brain injury. It is defined pathologically by the abnormal accumulation of tau in a unique pattern that is distinct from other tauopathies, including Alzheimer's disease (AD). Although trauma has been suggested to increase amyloid β peptide (Aβ) levels, the extent of Aβ deposition in CTE has not been thoroughly characterized. We studied a heterogeneous cohort of deceased athletes and military veterans with neuropathologically diagnosed CTE (n = 114, mean age at death = 60) to test the hypothesis that Aβ deposition is altered in CTE and associated with more severe pathology and worse clinical outcomes. We found that Aβ deposition, either as diffuse or neuritic plaques, was present in 52 % of CTE subjects. Moreover, Aβ deposition in CTE occurred at an accelerated rate and with altered dynamics in CTE compared to a normal aging population (OR = 3.8, p < 0.001). We also found a clear pathological and clinical dichotomy between those CTE cases with Aβ plaques and those without. Aβ deposition was significantly associated with the presence of the APOE ε4 allele (p = 0.035), older age at symptom onset (p < 0.001), and older age at death (p < 0.001). In addition, when controlling for age, neuritic plaques were significantly associated with increased CTE tauopathy stage (β = 2.43, p = 0.018), co-morbid Lewy body disease (OR = 5.01, p = 0.009), and dementia (OR = 4.45, p = 0.012). A subset of subjects met the diagnostic criteria for both CTE and AD, and in these subjects both Aβ plaques and total levels of Aβ1-40 were increased at the depths of the cortical sulcus compared to the gyral crests. Overall, these findings suggest that Aβ deposition is altered and accelerated in a cohort of CTE subjects compared to normal aging and that Aβ is associated with both pathological and clinical progression of CTE independent of age.

Neuropathobiology of non-motor symptoms in Parkinson disease

Parkinson disease (PD) is a multisystem disorder associated with α-synuclein aggregates throughout the central, autonomic, and peripheral nervous system, clinically characterized by motor and non-motor (NM) symptoms. The NMS in PD, many of which antedating motor dysfunction and representing a preclinical phase spanning 20 or more years, are linked to widespread distribution of α-synuclein pathology not restricted to the dopaminergic nigrostriatal system that is responsible for core motor features of PD. The pathologic substrate of NM manifestations such as olfactory, autonomic (gastrointestinal, urogenital, cardia, respiratory), sensory, skin, sleep, visual, neuropsychiatric dysfunctions (cognitive, mood, dementia), and others are critically reviewed. In addition to non-nigral brainstem nuclei, α-synuclein pathology involves sympathetic and parasympathetic, enteric, cardiac and pelvic plexuses, and many other organs indicating a topographical and chronological spread, particularly in the prodromal stages of the disease. Few animal models recapitulate NMS in PD. The relationship between regional α-synuclein/Lewy pathology, neurodegeneration and the corresponding clinical deficits awaits further elucidation. Controlled clinicopathologic studies will refine the correlations between presymptomatic and late-developing NM features of PD and neuropathology, and new premotor biomarkers will facilitate early diagnosis of PD as a basis for more effective preventive and therapeutic options of this devastating disease.

Relationship and factor structure in multisystem neurodegeneration in Parkinson's disease

OBJECTIVES

Parkinson's disease (PD) is a multisystem neurodegenerative disease. We aimed to identify the relationship and factor structure among its different features.

MATERIALS & METHODS

Motor, olfactory and cognitive function, and cardiac sympathetic denervation were evaluated in 125 patients with PD using the Unified Parkinson's Disease Rating Scale (UPDRS) part III score, odor stick identification test for the Japanese (OSIT-J), Mini-Mental State Examination (MMSE), and [(123) I] meta-iodobenzylguanidine (MIBG) cardiac scintigraphy (heart-to-mediastinum (H/M) ratio). Pearson's correlation and multiple regression analysis were used to evaluate the association among the four measures with age, gender, and disease duration as the covariates. Exploratory factor analysis was used to identify the underlying factor structure among the measures and covariates.

RESULTS

Pearson's correlation and multiple regression analysis showed correlations between OSIT-J score and MIBG H/M ratio, OSIT-J and MMSE scores, UPDRS part III score and MIBG H/M ratio, UPDRS part III score and disease duration, and MMSE score and age. Factor analysis identified three factors: (i) age and MMSE score; (ii) MIBG H/M ratio and OSIT-J score; and (iii) UPDRS part III score and disease duration.

CONCLUSIONS

Our results suggest that aging, PD-related pathogenesis, and disease duration underlie the multisystem neurodegeneration present in PD. Moreover, age and disease duration are the major risk factors for cognitive impairment and motor symptoms, respectively. Olfactory impairment and cardiac sympathetic denervation are strongly associated in PD.

Executive dysfunction in Parkinson's disease: a review

Executive dysfunction can be present from the early stages of Parkinson's disease (PD). It is characterized by deficits in internal control of attention, set shifting, planning, inhibitory control, dual task performance, and on a range of decision-making and social cognition tasks. Treatment with dopaminergic medication has variable effects on executive deficits, improving some, leaving some unchanged, and worsening others. In this review, we start by defining the specific nature of executive dysfunction in PD and describe suitable neuropsychological tests. We then discuss how executive deficits relate to pathology in specific territories of the basal ganglia, consider the impact of dopaminergic treatment on executive function (EF) in this context, and review the changes in EFs with disease progression. In later sections, we summarize correlates of executive dysfunction in PD with motor performance (e.g., postural instability, freezing of gait) and a variety of psychiatric (e.g., depression, apathy) and other clinical symptoms, and finally discuss the implications of these for the patients' daily life.

Grey matter hypometabolism and atrophy in Parkinson's disease with cognitive impairment: a two-step process

The pathophysiological process underlying cognitive decline in Parkinson's disease is not well understood. Cerebral atrophy and hypometabolism have been described in patients with Parkinson's disease and dementia or mild cognitive impairment with respect to control subjects. However, the exact relationships between atrophy and hypometabolism are still unclear. To determine the extension and topographical distribution of hypometabolism and atrophy in the different cognitive states of Parkinson's disease, we examined 46 patients with Parkinson's disease (19 female, 27 male; 71.7 ± 5.9 years old; 14.6 ± 4.2 years of disease evolution; modified Hoehn and Yahr mean stage 3.1 ± 0.7). Cognitive status was diagnosed as normal in 14 patients, as mild cognitive impairment in 17 and as dementia in 15 patients. Nineteen normal subjects (eight female, 11 male; 68.1 ± 3.2 years old) were included as controls. (18)F-fluorodeoxyglucose positron emission tomography and magnetic resonance imaging scans were obtained, co-registered, corrected for partial volume effect and spatially normalized to the Montreal Neurological Institute space in each subject. Smoothing was applied to the positron emission tomography and magnetic resonance imaging scans to equalize their effective smoothness and resolution (10 mm and 12 mm full-width at half-maximum and Gaussian kernel, respectively). Z-score maps for atrophy and for hypometabolism were obtained by comparing individual images to the data set of control subjects. For each group of patients, a paired Student's t-test was performed to statistically compare the two Z-map modalities (P < 0.05 false discovery rate corrected) using the direct voxel-based comparison technique. In patients with mild cognitive impairment, hypometabolism exceeded atrophy in the angular gyrus, occipital, orbital and anterior frontal lobes. In patients with dementia, the hypometabolic areas observed in the group with mild cognitive impairment were replaced by areas of atrophy, which were surrounded by extensive zones of hypometabolism. Areas where atrophy was more extended than hypometabolism were found in the precentral and supplementary motor areas in both patients with mild cognitive impairment and with dementia, and in the hippocampus and temporal lobe in patients with dementia. These findings suggest that there is a gradient of severity in cortical changes associated with the development of cognitive impairment in Parkinson's disease in which hypometabolism and atrophy represent consecutive stages of the same process in most of the cortical regions affected.

Functional connectivity within the default mode network is associated with saccadic accuracy in Parkinson's disease: a resting-state FMRI and videooculographic study

In addition to the skeleto-motor deficits, patients with Parkinson's disease (PD) frequently present with oculomotor dysfunctions such as impaired smooth pursuit and saccadic abnormalities. There is increasing evidence for an impaired cortical function to be responsible for oculomotor deficits that are associated with lack of inhibitory control; however, these pathomechanisms still remain poorly understood. By means of "task-free" resting-state functional magnetic resonance imaging (rs-fMRI), functional connectivity changes in PD within the default mode network (DMN) have been reported. The aim of this study was to investigate whether altered functional connectivity within the DMN was correlated with oculomotor parameter changes in PD. Twelve PD patients and 13 matched healthy controls underwent rs-fMRI at 1.5 T and videooculography (VOG) using Eye-Link-System. Rs-fMRI seed-based region-to-region connectivity analysis was performed, including medial prefrontal cortex (mPFC), medial temporal lobe (MTL), posterior cingulate cortex (PCC), and hippocampal formation (HF); while VOG examination comprised ocular reactive saccades, smooth pursuit, and executive tests. Rs-fMRI analysis demonstrated a decreased region-to-region functional connectivity between mPFC and PCC as well as increased connectivity between bilateral HF in PD compared with controls. In VOG, patients and controls differed in terms of executive tests outcome, smooth pursuit eye movement, and visually guided reactive saccades but not in peak eye velocity. A significant relationship was observed between saccadic accuracy and functional connectivity strengths between MTL and PCC. These results suggest that PD-associated changes of DMN connectivity are correlated with PD-associated saccadic hypometria, in particular in the vertical direction.

Gait speed in Parkinson disease correlates with cholinergic degeneration

OBJECTIVE

We investigated dopaminergic and cholinergic correlates of gait speed in Parkinson disease (PD) and non-PD control subjects to test the hypothesis that gait dysfunction in PD may result from multisystem degeneration.

METHODS

This was a cross-sectional study. Subjects with PD but without dementia (n = 125, age 65.6 ± 7.3 years) and elderly subjects without PD (n = 32, age 66.0 ± 10.6 years) underwent [¹¹C]dihydrotetrabenazine dopaminergic and [(11)C]methyl-4-piperidinyl propionate acetylcholinesterase PET imaging, and cognitive and clinical testing, including an 8.5-m walk in the dopaminergic "off" state. The fifth percentile of cortical cholinergic activity in the elderly without PD was used to define normal-range activity in the subjects with PD.

RESULTS

Normal-range cortical cholinergic activity was present in 87 subjects with PD (69.6%). Analysis of covariance using gait speed as the dependent variable demonstrated a significant model (F = 6.70, p < 0.0001) with a significant group effect (F = 3.36, p = 0.037) and significant slower gait speed in the low cholinergic PD subgroup (0.97 ± 0.22 m/s) with no significant difference between the normal-range cholinergic PD subgroup (1.12 ± 0.20 m/s) and control subjects (1.17 ± 0.18 m/s). Covariate effects were significant for cognition (F = 6.58, p = 0.011), but not for striatal dopaminergic innervation, sex, or age.

CONCLUSION

Comorbid cortical cholinergic denervation is a more robust marker of slowing of gait in PD than nigrostriatal denervation alone. Gait speed is not significantly slower than normal in subjects with PD with relatively isolated nigrostriatal denervation.

Potential for misdiagnosis in community-acquired PET scans for dementia

We reviewed records of patients seen in a tertiary Neurobehavior Clinic to identify those who had community-acquired PET scans as part of their dementia diagnostic evaluation with the goal of assessing factors influencing diagnostic accuracy. We compared outside radiologist PET diagnoses to our consensus clinical diagnosis and collected data regarding clinical variables, ordering reasons, and specialties of interpreting and ordering physicians. Among 1,580 total patients seen in our clinic, 46 met our inclusion criteria. There was disagreement between outside diagnosis based on PET and our consensus diagnosis in 65% (n = 30) of patients. Community-acquired PET scans may have lower diagnostic value in dementia evaluation than suggested by prior research and may be associated with significant risks including misdiagnosis with an incurable neurodegenerative disease.

Neocortex and allocortex respond differentially to cellular stress in vitro and aging in vivo

In Parkinson’s and Alzheimer’s diseases, the allocortex accumulates aggregated proteins such as synuclein and tau well before neocortex. We present a new high-throughput model of this topographic difference by microdissecting neocortex and allocortex from the postnatal rat and treating them in parallel fashion with toxins. Allocortical cultures were more vulnerable to low concentrations of the proteasome inhibitors MG132 and PSI but not the oxidative poison H₂O₂. The proteasome appeared to be more impaired in allocortex because MG132 raised ubiquitin-conjugated proteins and lowered proteasome activity in allocortex more than neocortex. Allocortex cultures were more vulnerable to MG132 despite greater MG132-induced rises in heat shock protein 70, heme oxygenase 1, and catalase. Proteasome subunits PA700 and PA28 were also higher in allocortex cultures, suggesting compensatory adaptations to greater proteasome impairment. Glutathione and ceruloplasmin were not robustly MG132-responsive and were basally higher in neocortical cultures. Notably, neocortex cultures became as vulnerable to MG132 as allocortex when glutathione synthesis or autophagic defenses were inhibited. Conversely, the glutathione precursor N-acetyl cysteine rendered allocortex resilient to MG132. Glutathione and ceruloplasmin levels were then examined in vivo as a function of age because aging is a natural model of proteasome inhibition and oxidative stress. Allocortical glutathione levels rose linearly with age but were similar to neocortex in whole tissue lysates. In contrast, ceruloplasmin levels were strikingly higher in neocortex at all ages and rose linearly until middle age. PA28 levels rose with age and were higher in allocortex in vivo, also paralleling in vitro data. These neo- and allocortical differences have implications for the many studies that treat the telencephalic mantle as a single unit. Our observations suggest that the topographic progression of protein aggregations through the cerebrum may reflect differential responses to low level protein-misfolding stress but also reveal impressive compensatory adaptations in allocortex.

The relationship between motor symptom lateralization and cognitive performance in newly diagnosed drug-naïve patients with Parkinson's disease

The side of motor symptom predominance may influence cognitive performance in patients with Parkinson's disease (PD): PD patients with right-side motor symptom predominance typically present difficulties in tasks of language and verbal memory, whereas PD patients with left-side motor symptom predominance typically present difficulties in visuospatial tasks. The current study aimed at investigating the relationship between motor symptom lateralization and cognitive performance in PD patients without the possible confounding effect of dopaminergic drugs, which may enhance or impair cognition on the basis of assessed function and disease stage. From the initial sample of 137 consecutive newly diagnosed drug-naïve (de novo) PD patients, clinical follow-ups and neurological examinations identified 108 right-handed patients with a unilateral motor presentation or a clear motor asymmetry (59 right-PD: 54.6%; 49 left-PD: 45.4%). Any cognitive difference emerged between right-PD patients and left-PD patients at this disease stage. Scores of lateralized motor impairment severity correlated with some cognitive performances: Right motor impairment correlated with a measure of set shifting (Trail Making Test B-A), and left motor impairment correlated with phonemic fluency and tasks with visuospatial material (Colored Progressive Matrices of Raven, Rey-Osterrieth Complex Figure Copy and Immediate Recall). Findings of the current study supported the conclusion that the side of clinical motor predominance scarcely influences cognition in the early untreated stages of PD, suggesting that cognitive differences between subgroups of lateralized PD patients probably may appear in more advanced disease stages.

Cognitive dysfunction and depression in Parkinson's disease: what can be learned from rodent models?

Parkinson's disease (PD) has for decades been considered a pure motor disorder and its cardinal motor symptoms have been attributed to the loss of dopaminergic (DAergic) neurons in the substantia nigra pars compacta and to nigral Lewy body pathology. However, there has more recently been a shift in the conceptualization of the disease, and its pathological features have now been recognized as involving several other areas of the brain and indeed even outside the central nervous system. There are a corresponding variety of intrinsic non-motor symptoms such as autonomic dysfunction, cognitive impairment, sleep disturbances and neuropsychiatric problems, which cannot be explained exclusively by nigral pathology. In this review, we will focus on cognitive impairment and affective symptoms in PD, and we will consider whether, and how, these deficits can best be modelled in rodent models of the disorder. As only a few of the non-motor symptoms respond to standard DA replacement therapies, the quest for a broader therapeutic approach remains a major research effort, and success in this area in particular will be strongly dependent on appropriate rodent models. In addition, better understanding of the different models, as well as the advantages and disadvantages of the available behavioural tasks, will result in better tools for evaluating new treatment strategies for PD patients suffering from these neuropsychological symptoms.