Metabolic abnormalities associated with mild cognitive impairment in Parkinson disease

Functional neuroimaging in Parkinson's disease

The use of functional imaging in neurodegenerative diseases has increased in recent years, with applications in research into the underlying pathophysiology, aiding in diagnosis, or evaluating new treatments. In Parkinson's disease (PD), these imaging methods have expanded our understanding of the disease beyond dopaminergic deficits. Moreover, functional imaging methods have described alterations in functional networks relating not only to the motor symptoms, but also to many nonmotor features of PD, such as cognitive dysfunction. From a clinical viewpoint, functional imaging methods can assist in monitoring disease progression, such as in the context of clinical trials, and holds the potential to aid in early diagnosis of PD and differentiation from other parkinsonian disorders.

Characterization of disease-related covariance topographies with SSMPCA toolbox: effects of spatial normalization and PET scanners

To generate imaging biomarkers from disease-specific brain networks, we have implemented a general toolbox to rapidly perform scaled subprofile modeling (SSM) based on principal component analysis (PCA) on brain images of patients and normals. This SSMPCA toolbox can define spatial covariance patterns whose expression in individual subjects can discriminate patients from controls or predict behavioral measures. The technique may depend on differences in spatial normalization algorithms and brain imaging systems. We have evaluated the reproducibility of characteristic metabolic patterns generated by SSMPCA in patients with Parkinson's disease (PD). We used [(18) F]fluorodeoxyglucose PET scans from patients with PD and normal controls. Motor-related (PDRP) and cognition-related (PDCP) metabolic patterns were derived from images spatially normalized using four versions of SPM software (spm99, spm2, spm5, and spm8). Differences between these patterns and subject scores were compared across multiple independent groups of patients and control subjects. These patterns and subject scores were highly reproducible with different normalization programs in terms of disease discrimination and cognitive correlation. Subject scores were also comparable in patients with PD imaged across multiple PET scanners. Our findings confirm a very high degree of consistency among brain networks and their clinical correlates in PD using images normalized in four different SPM platforms. SSMPCA toolbox can be used reliably for generating disease-specific imaging biomarkers despite the continued evolution of image preprocessing software in the neuroimaging community. Network expressions can be quantified in individual patients independent of different physical characteristics of PET cameras.

Parkinson's disease cognitive network correlates with caudate dopamine

Prior evidence has suggested a link between caudate dopaminergic functioning and cognition in Parkinson's disease (PD). In this dual tracer study we analyzed the relationship between nigrostriatal dopaminergic dysfunction and the expression of the previously validated PD cognition-related metabolic pattern (PDCP). In this study, 17 non-demented PD patients underwent positron emission tomography (PET) imaging with [(18)F]-fluorodeoxyglucose to measure PDCP expression, and [(18)F]-fluoropropyl-β-CIT (FPCIT) to measure dopamine transporter (DAT) binding. Automated voxel-by-voxel searches of the FPCIT PET volumes were performed to identify regions in which DAT binding significantly correlated with PDCP expression values. The findings were validated using prespecified anatomical regions-of-interest (ROIs). Voxel-wise interrogation of the FPCIT PET scans revealed a single significant cluster in which DAT binding correlated with PDCP expression (p<0.05, corrected). This cluster was localized to the left caudate nucleus; an analogous correlation (r=-0.63, p<0.01) was also present in the "mirror" region of the right hemisphere. These findings were confirmed by the presence of a significant correlation (r=-0.67, p<0.005) between PDCP expression and DAT binding in caudate ROIs, which survived adjustment for age, disease duration, and clinical severity ratings. Correlation between caudate DAT binding and subject expression of the PD motor-related metabolic pattern was not significant (p>0.21). In summary, this study demonstrates a significant relationship between loss of dopaminergic input to the caudate nucleus and the expression of a cognition-related disease network in unmedicated PD patients. These baseline measures likely function in concert to determine the cognitive effects of dopaminergic therapy in PD.

Neuroimaging of brain changes associated with cognitive impairment in Parkinson's disease

Cognitive impairment occurs frequently in Parkinson's disease (PD) and the concept of Mild Cognitive Impairment in PD (PD-MCI) has recently emerged. Patients with mild impairment are at risk of developing dementia, and thus it is a topic of growing interest. Many previous studies have investigated the neural correlates of cognitive impairment, in particular executive dysfunction, in PD patients without dementia using neuroimaging techniques including structural MRI, functional MRI and PET imaging. These studies, which have provided a foundation for understanding which brain regions and neurotransmitter systems may be involved in executive dysfunction in PD, will be reviewed. Recent neuroimaging studies that have used specific criteria to classify patients as PD-MCI, in the hopes of gaining further insight into the underlying neural mechanisms will also be discussed. In particular, this review will cover key findings involving structural MRI investigating grey and white matter changes, functional MRI to examine changes in neural activation and PET imaging to investigate metabolic and neurochemical changes that have led to an improved understanding of pathology associated with executive dysfunction in PD without dementia and PD-MCI.

Cognitive impairment in patients with Parkinson's disease: diagnosis, biomarkers, and treatment

Dementia is one of the most common and important aspects of Parkinson's disease and has consequences for patients and caregivers, and has health-related costs. Mild cognitive impairment is also common and frequently progresses to dementia. The underlying mechanisms of dementia associated with Parkinson's disease are only partly known and no mechanism-based treatments are available. Both dysmetabolism of α-synuclein and amyloid-protein and cholinergic deficits contribute to cognitive impairment in Parkinson's disease, and preliminary findings show that imaging and neurophysiological and peripheral biomarkers could be useful in diagnosis and prognosis. Rivastigmine is the only licensed treatment for dementia in Parkinson's disease, but emerging evidence suggests that memantine might also be useful. Whether these or other treatments can delay the progression from mild cognitive impairment to dementia in Parkinson's disease is a key research question.

Functional brain networks in movement disorders: recent advances

PURPOSE OF REVIEW

Different neuroimaging techniques have been used to identify disease-specific functional brain networks in Parkinson's disease, atypical parkinsonian syndromes, and other movement disorders. This review highlights recent advances in network imaging and its clinical applications in movement disorders.

RECENT FINDINGS

Positron emission tomography and functional MRI studies have revealed distinct, abnormal metabolic brain networks and altered interregional connectivity in Parkinson's disease and related movement disorders. Network-level functional changes have been found to correlate with disease severity and progression. Moreover, network-based categorization algorithms are proving useful in enhancing the accuracy of clinical diagnosis in patients with early symptoms and in providing objective evidence of treatment response.

SUMMARY

Although in most movement disorders the predominant histopathology involves the basal ganglia, including the substantia nigra, functional changes in relevant neural circuits are not limited to these structures. The current advances in functional brain imaging have contributed to a better pathophysiological understanding of movement disorders as complex alterations of widespread functional brain networks. The promising findings from recent studies may help to establish new and reliable biomarkers to monitor disease progression and treatment effects in future clinical trials.

The neurobiology and neural circuitry of cognitive changes in Parkinson's disease revealed by functional neuroimaging

Patients with Parkinson's disease (PD) often develop a spectrum of cognitive symptoms that can evolve into dementia. Dopamine (DA) replacement medications, though improving motor symptoms, can exert both positive and negative effects on cognitive ability, depending on the severity of the disease and the specific skill being tested. By considering the behavioral and clinical aspects of disease- and treatment-mediated changes in cognition alongside the pathophysiology of PD, an understanding of the factors that govern the heterogeneous expression of cognitive impairment in PD is beginning to emerge. Here, we review the neuroimaging studies revealing the neural correlates of cognitive changes after DA loss and DA replacement as well as those that may accompany the conversion from milder stages of cognitive impairment to frank dementia.

Neurochemistry and the non-motor aspects of PD

Parkinson disease (PD) is a systemic disease with variegated non-motor deficits and neurological symptoms, including impaired olfaction, autonomic failure, cognitive impairment and psychiatric symptoms, in addition to the classical motor symptoms. Many non-motor symptoms appear before or in parallel with motor deficits and then worsen with disease progression. Although there is a relationship, albeit not causal, between motor symptoms and the presence of Lewy bodies (LBs) and neurites filled with abnormal α-synuclein, other neurological alterations are independent of the amount of α-synuclein inclusions in neurons and neurites, thereby indicating that different mechanisms probably converge in the degenerative process. This may apply to complex alterations interfering with olfactory and autonomic nervous systemfunctions, emotions, sleep regulation, and behavioral, cognitive and mental performance. Involvement of the cerebral cortex leading to impaired behavior and cognition is related to several convergent altered factors including: a. dopaminergic, noradrenergic, serotoninergic and cholinergic cortical innervation; b. synapses; c. cortical metabolism; d. mitochondrial function and energy production; e. oxidative damage; f. transcription; g. protein expression; h. lipid composition; and i. ubiquitin–proteasome system and autophagy, among others. This complex situation indicates that multiple subcellular failure in selected cell populations is difficult to reconcilewith a reductionistic scenario of a single causative cascade of events leading to non-motor symptoms in PD. Furthermore, these alterationsmay appear at early stages of the disease and may precede the appearance of substantial irreversible cell loss by years. These observations have important implications in the design of therapeutic approaches geared to prevention and treatment of PD.

Metabolic brain networks in translational neurology: concepts and applications

Over the past 2 decades, functional imaging techniques have become commonplace in the study of brain disease. Nevertheless, very few validated analytical methods have been developed specifically to identify and measure systems-level abnormalities in living patients. Network approaches are particularly relevant for translational research in the neurodegenerative disorders, which often involve stereotyped abnormalities in brain organization. In recent years, spatial covariance mapping, a multivariate analytical tool applied mainly to metabolic images acquired in the resting state, has provided a useful means of objectively assessing brain disorders at the network level. By quantifying network activity in individual subjects on a scan-by-scan basis, this technique makes it possible to objectively assess disease progression and the response to treatment on a system-wide basis. To illustrate the utility of network imaging in neurological research, we review recent applications of this approach in the study of Parkinson disease and related movement disorders. Novel uses of the technique are discussed, including the prediction of cognitive responses to dopaminergic therapy, evaluation of the effects of placebo treatment on network activity, assessment of preclinical disease progression, and the use of automated pattern-based algorithms to enhance diagnostic accuracy.

[Imaging non motor signs in Parkinson's disease]

Parkinson's disease is mainly considered as a motor disorder defined by a motor triad. However, various non-motor manifestations may be encountered in Parkinson's disease, including hyposmia, pain, fatigue, sleep disorders, cognitive and behavioral disorders. The pathophysiology of these signs is complex, not univocal and remains poorly understood. Functional imaging techniques either by positron emission tomography, single photon emission tomography or functional magnetic resonance imaging provide an invaluable opportunity to better understand the pathophysiology of these signs. In this paper, we present a review of the recent advances provided by functional imaging in this area.

Posterior parietooccipital hypometabolism may differentiate mild cognitive impairment from dementia in Parkinson's disease

PURPOSE

Patients with Parkinson's disease (PD) may have normal cognition, mild cognitive impairment (MCI) or dementia. We investigated differences in cerebral metabolism associated with these three cognitive states and the relationship between metabolism and cognitive dysfunction.

METHODS

FDG PET and a battery of neuropsychological tests were used to study PD patients with dementia (n = 19), MCI (n = 28) and normal cognition (n = 21), and control subjects (n = 20). Regional glucose metabolism in patients and controls was analysed using statistical parametric mapping (SPM8) corrected for age, motor severity and depression. Correlations between the mini-mental state examination score and Z-score values of the different cognitive domains with respect to cerebral FDG uptake were assessed using SPM8.

RESULTS

PD patients with MCI (PD-MCI patients) exhibited decreased FDG uptake in the frontal lobe, and to a lesser extent in parietal areas compared with cognitively normal patients. Patients with dementia showed reduced metabolism in the parietal, occipital and temporal areas and a less extensive reduction in the frontal lobe compared with PD-MCI patients, while widespread hypometabolism was seen in comparison with patients with normal cognition. PD-MCI patients exhibited reduced FDG uptake in the parietal and occipital lobes and in localized areas of the frontal and temporal lobes compared with controls, whereas patients with dementia showed a widespread reduction of cortical metabolism. Mini-mental state examination score correlated positively with metabolism in several lobes, executive function with metabolism in the parietooccipitotemporal junction and frontal lobe, memory with temporoparietal metabolism, visuospatial function with occipitoparietal and temporal metabolism, and language with frontal metabolism.

CONCLUSION

PD patients with MCI exhibited hypometabolism in several cortical regions compared with controls, and in the frontal and parietal regions compared with cognitively normal patients. Hypometabolism was higher in patients with dementia than in those with MCI, mainly in the posterior cortical areas where it was correlated with visuospatial, memory and executive functions.

Clinical differences among mild cognitive impairment subtypes in Parkinson's disease

Mild cognitive impairment is increasingly recognized as a construct in Parkinson's disease (PD) and occurs in about 25% of nondemented PD patients. Although executive dysfunction is the most frequent type of cognitive deficit in PD, the cognitive phenotype of PD mild cognitive impairment (PD-MCI) is broad. PD-MCI subtypes are represented by amnestic and nonamnestic domain impairment as well as single- and multiple-domain impairment. However, it is unclear whether patients with different PD-MCI subtypes also differ in other clinical characteristics in addition to cognitive profile. We studied 128 PD-MCI subjects at our Movement Disorders center, comparing clinical, motor, and behavioral characteristics across the PD-MCI subtypes. We found varying proportions of impairment subtypes: nonamnestic single domain, 47.7%; amnestic multiple domain, 24.2%; amnestic single domain, 18.8%; and nonamnestic multiple domain, 9.5%. Attentional/executive functioning and visuospatial abilities were the most frequently impaired domains. PD-MCI subtypes differed in their motor features, with nonamnestic multiple-domain PD-MCI subjects showing particularly pronounced problems with postural instability and gait. Differences among PD-MCI subtypes in age, PD duration, medication use, mood or behavioral disturbances, and vascular disease were not significant. Thus, in addition to differing cognitive profiles, PD-MCI subtypes differed in motor phenotype and severity but not in mood, behavioral, or vascular comorbidities. Greater postural instability and gait disturbances in the nonamnestic multiple-domain subtype emphasize shared nondopaminergic neural substrates of gait and cognition in PD. Furthermore, increased burden of cognitive dysfunction, rather than type of cognitive deficit, may be associated with greater motor impairment in PD-MCI.

The motor system and its disorders

The motor system has been intensively studied using the emerging neuroimaging technologies over the last twenty years. These include early applications of positron emission tomography of brain perfusion, metabolic rate and receptor function, as well as functional magnetic resonance imaging, tractography from diffusion weighted imaging, and transcranial magnetic stimulation. Motor system research has the advantage of the existence of extensive electrophysiological and anatomical information from comparative studies which enables cross-validation of new methods. We review the impact of neuroimaging on the understanding of diverse motor functions, including motor learning, decision making, inhibition and the mirror neuron system. In addition, we show how imaging of the motor system has supported a powerful platform for bidirectional translational neuroscience. In one direction, it has provided the opportunity to study safely the processes of neuroplasticity, neural networks and neuropharmacology in stroke and movement disorders and offers a sensitive tool to assess novel therapeutics. In the reverse direction, imaging of clinical populations has promoted innovations in cognitive theory, experimental design and analysis. We highlight recent developments in the analysis of structural and functional connectivity in the motor system; the advantages of integration of multiple methodologies; and new approaches to experimental design using formal models of cognitive-motor processes.

Functional brain networks and abnormal connectivity in the movement disorders

Clinical manifestations of movement disorders, such as Parkinson's disease (PD) and dystonia, arise from neurophysiological changes within the cortico-striato-pallidothalamocortical (CSPTC) and cerebello-thalamo-cortical (CbTC) circuits. Neuroimaging techniques that probe connectivity within these circuits can be used to understand how these disorders develop as well as identify potential targets for medical and surgical therapies. Indeed, network analysis of (18)F-fluorodeoxyglucose (FDG) positron emission tomography (PET) has identified abnormal metabolic networks associated with the cardinal motor symptoms of PD, such as akinesia and tremor, as well as PD-related cognitive dysfunction. More recent task-based and resting state functional magnetic resonance imaging studies have reproduced several of the altered connectivity patterns identified in these abnormal PD-related networks. A similar network analysis approach in dystonia revealed abnormal disease related metabolic patterns in both manifesting and non-manifesting carriers of dystonia mutations. Other multimodal imaging approaches using magnetic resonance diffusion tensor imaging in patients with primary genetic dystonia suggest abnormal connectivity within the CbTC circuits mediate the clinical manifestations of this inherited neurodevelopmental disorder. Ongoing developments in functional imaging and future studies in early patients are likely to enhance our understanding of these movement disorders and guide novel targets for future therapies.

Mild cognitive impairment in Parkinson's disease

Parkinson's disease (PD) traditionally has been defined by its characteristic motor hallmarks, but non-motor features such as cognitive impairment and dementia are increasingly recognized as part of PD. Mild cognitive impairment (MCI) is common in non-demented PD patients, occurring in about 20-50%. Frequency estimates and clinical features of mild cognitive impairment in PD (PD-MCI), however, vary across studies due to methodological differences and lack of uniform diagnostic criteria for PD-MCI. Overall, PD-MCI patients exhibit nonamnestic deficits in cognitive domains such as executive function, attention, and visuospatial function; however, the cognitive phenotype of PD-MCI is heterogeneous with some patients demonstrating greater amnestic deficits. PD-MCI patients, particularly those with posterior cortical profiles, may be at high risk for developing dementia. Various biomarkers studied in PD-MCI including cerebrospinal fluid, genetic analyses, and neuroimaging suggest that there may be distinct PD-MCI profiles. Future studies using uniform PD-MCI diagnostic criteria and incorporating biomarkers and longitudinal follow-up of PD-MCI cohorts are needed to understand PD-MCI as a transitional state between normal cognition and dementia.

Alzheimer's disease pattern of brain atrophy predicts cognitive decline in Parkinson's disease

Research suggests overlap in brain regions undergoing neurodegeneration in Parkinson's and Alzheimer's disease. To assess the clinical significance of this, we applied a validated Alzheimer's disease-spatial pattern of brain atrophy to patients with Parkinson's disease with a range of cognitive abilities to determine its association with cognitive performance and decline. At baseline, 84 subjects received structural magnetic resonance imaging brain scans and completed the Dementia Rating Scale-2, and new robust and expanded Dementia Rating Scale-2 norms were applied to cognitively classify participants. Fifty-nine non-demented subjects were assessed annually with the Dementia Rating Scale-2 for two additional years. Magnetic resonance imaging scans were quantified using both a region of interest approach and voxel-based morphometry analysis, and a method for quantifying the presence of an Alzheimer's disease spatial pattern of brain atrophy was applied to each scan. In multivariate models, higher Alzheimer's disease pattern of atrophy score was associated with worse global cognitive performance (β = -0.31, P = 0.007), including in non-demented patients (β = -0.28, P = 0.05). In linear mixed model analyses, higher baseline Alzheimer's disease pattern of atrophy score predicted long-term global cognitive decline in non-demented patients [F(1, 110) = 9.72, P = 0.002], remarkably even in those with normal cognition at baseline [F(1, 80) = 4.71, P = 0.03]. In contrast, in cross-sectional and longitudinal analyses there was no association between region of interest brain volumes and cognitive performance in patients with Parkinson's disease with normal cognition. These findings support involvement of the hippocampus and parietal-temporal cortex with cognitive impairment and long-term decline in Parkinson's disease. In addition, an Alzheimer's disease pattern of brain atrophy may be a preclinical biomarker of cognitive decline in Parkinson's disease.

Neuropathology of sporadic Parkinson's disease: evaluation and changes of concepts

Parkinson's disease (PD), one of the most frequent neurodegenerative disorders, is no longer considered a complex motor disorder characterized by extrapyramidal symptoms, but a progressive multisystem or-more correctly-multiorgan disease with variegated neurological and nonmotor deficiencies. It is morphologically featured not only by the degeneration of the dopaminergic nigrostriatal system, responsible for the core motor deficits, but by multifocal involvement of the central, peripheral and autonomic nervous system and other organs associated with widespread occurrence of Lewy bodies and dystrophic Lewy neurites. This results from deposition of abnormal α-synuclein (αSyn), the major protein marker of PD, and other synucleinopathies. Recent research has improved both the clinical and neuropathological diagnostic criteria of PD; it has further provided insights into the development and staging of αSyn and Lewy pathologies and has been useful in understanding the pathogenesis of PD. However, many challenges remain, for example, the role of Lewy bodies and the neurobiology of axons in the course of neurodegeneration, the relation between αSyn, Lewy pathology, and clinical deficits, as well as the interaction between αSyn and other pathologic proteins. Although genetic and experimental models have contributed to exploring the causes, pathomechanisms, and treatment options of PD, there is still a lack of an optimal animal model, and the etiology of this devastating disease is far from being elucidated.

Milestones in neuroimaging

In the last 25 years there have been enormous advances in brain imaging. In addition to utility in diagnosis, these have led to novel insights into the pathogenesis of basal ganglia disease and the role of dopamine and the basal ganglia in normal health. The authors review highlights of this work, with a focus on advances in Parkinson's disease, the dystonias, Huntington's disease, and the role of dopamine in cognition and reward signaling. Emerging areas for future development include studies of functional connectivity, the analysis of default mode networks, studies of novel neurochemical pathways, methods to study disease pathogenesis, and the application of imaging techniques to investigate animal models of disease.

Cognitive impairment in nondemented Parkinson's disease

A substantial percentage of patients with newly diagnosed Parkinson's disease without dementia are reported to be affected by cognitive impairment (CI). In practice, however, CI is underrecognized, as the signs may not be apparent in early-stage disease and many routine assessment tools lack the sensitivity to detect subtle cognitive dysfunction. Patients with PD and mild CI (MCI) may have a higher risk of developing dementia than cognitively intact PD patients; however, it is not currently known which patients with CI are at increased risk of developing dementia. This review summarizes current knowledge about CI in nondemented PD; it discusses the structural and functional changes associated with CI and addresses areas of unmet needs. We focus on questions that should be addressed in future studies to achieve consensus on its characteristics and definition, pathophysiology, epidemiology, diagnosis and assessment, and treatment and management.

Network correlates of the cognitive response to levodopa in Parkinson disease

OBJECTIVE

Cognitive dysfunction is common in Parkinson disease (PD), even early in its clinical course. This disease manifestation has been associated with impaired verbal learning performance as well as abnormal expression of a specific PD-related cognitive spatial covariance pattern (PDCP). It is not known, however, how this metabolic network relates to the cognitive response to dopaminergic therapy on the individual patient level.

METHODS

We assessed treatment-mediated changes in verbal learning and PDCP expression in 17 patients with PD without dementia who underwent cognitive testing and metabolic imaging in the unmedicated and levodopa-treated conditions. We also determined whether analogous changes were present in 12 other patients with PD without dementia who were evaluated before and during the treatment of cognitive symptoms with placebo.

RESULTS

Levodopa-mediated changes in verbal learning correlated with concurrent changes in PDCP expression (r = -0.60, p < 0.01). The subset of patients with meaningful cognitive improvement on levodopa (n = 8) exhibited concurrent reductions in PDCP expression (p < 0.01) with treatment; network modulation was not evident in the remaining subjects. Notably, the levodopa cognitive response correlated with baseline PDCP levels (r = 0.70, p = 0.002). By contrast, placebo did not affect PDCP expression, even in the subjects (n = 7) with improved verbal learning during treatment.

CONCLUSIONS

These findings suggest that cognitive dysfunction in PD may respond to treatment depending upon the degree of baseline PDCP expression. Quantification of treatment-mediated network changes can provide objective information concerning the efficacy of new agents directed at the cognitive manifestations of this disease.

Radionuclide brain imaging correlates of cognitive impairment in Parkinson's disease (PD)

A subtle cognitive impairment can be detected early in the course of Parkinson's disease (PD). Executive, memory and visuospatial functions are specifically affected, but the underlying pathophysiological basis is not well elucidated yet and may be heterogeneous. The recent identification of a PD-related cognitive metabolic pattern (PDCP), including hypometabolism in associative frontal, parietal and posterior limbic structures, has integrated the classical notion of a striato-frontal syndrome at the basis of cognitive dys-function. Recent evidence suggests that whilst executive dys-function is seen in virtually all PD patients, visuospatial and memory impairment may share a higher risk for the subsequent development of dementia. By means of perfusion SPECT and [18F]FDG-PET, cortical dys-function may be highlighted since the early stages, it is more evident in PD patients with Mild Cognitive Impairment (MCI), and reaches the maximum in PD dementia (PDD). Posterior temporo-parieto-occipital dys-function in associative and limbic cortex, closely resembling that found in Alzheimer's disease patients, is found in PDD, with a more severe occipital hypometabolism and a relatively milder hypometabolism in medial temporal lobe structures. Furthermore, deficit of acetylcholinesterase (AchE) can be found by means of [11C]MP4A-PET already in early stage of PD, especially in posterior regions, then becoming more severe in PDD and in dementia with Lewy bodies (DLB). Administration of AchE inhibitors to PDD patients increased brain metabolism in bilateral frontal and left parietal regions, and left posterior cingulate. Finally, the recent availability of radiopharmaceuticals able to disclose amyloid brain deposition has allowed to demonstrate amyloid load in a part of patients with PDD, possibly due to diffuse rather than neuritic plaques. Brain PET and SPECT have strongly contributed to the understanding of the pathophysiology of cognitive impairment in PD and may serve as probes to monitor the effects of therapeutic interventions.

MDS Task Force on mild cognitive impairment in Parkinson's disease: critical review of PD-MCI

There is controversy regarding the definition and characteristics of mild cognitive impairment in Parkinson's disease. The Movement Disorder Society commissioned a Task Force to critically evaluate the literature and determine the frequency and characteristics of Parkinson's disease-mild cognitive impairment and its association with dementia. A comprehensive PubMed literature review was conducted using systematic inclusion and exclusion criteria. A mean of 26.7% (range, 18.9%-38.2%) of nondemented patients with Parkinson's disease have mild cognitive impairment. The frequency of Parkinson's disease-mild cognitive impairment increases with age, disease duration, and disease severity. Impairments occur in a range of cognitive domains, but single domain impairment is more common than multiple domain impairment, and within single domain impairment, nonamnestic is more common than amnestic impairment. A high proportion of patients with Parkinson's disease-mild cognitive impairment progress to dementia in a relatively short period of time. The primary conclusions of the Task Force are that: (1) Parkinson's disease-mild cognitive impairment is common, (2) there is significant heterogeneity within Parkinson's disease-mild cognitive impairment in the number and types of cognitive domain impairments, (3) Parkinson's disease-mild cognitive impairment appears to place patients at risk of progressing to dementia, and (4) formal diagnostic criteria for Parkinson's disease-mild cognitive impairment are needed.

Imaging cognitive and behavioral symptoms in Parkinson's disease

Non-motor symptoms are a major and often unrecognized cause of morbidity of Parkinson's disease. In the past few years, imaging technology, such as functional MRI and PET, have provided a large bulk of information about the phenomena. Here, we provide an overview of those imaging studies that may help us understand the neuronal correlates associated with non-motor symptoms in Parkinson's disease, with a particular focus on cognitive and neuropsychiatric deficits.

A précis of recent advances in the neuropsychology of mild cognitive impairment(s) in Parkinson's disease and a proposal of preliminary research criteria

Cognitive changes of Parkinson's disease (PD) manifest earlier and are more heterogeneous than previously appreciated. Approximately one-third of patients have at least mild cognitive changes at PD diagnosis, and subtle changes might be appreciable among those at risk for PD. Executive dysfunction is the most common cognitive change, but other phenotypes exist. Pathobiologic and potential prognostic differences among cognitive phenotypes remain poorly understood. Progress in the neuropsychology, epidemiology and pathobiology of mild cognitive impairment (MCI) in PD is hampered by lack of diagnostic criteria. This study proposes preliminary research criteria for two categories of PD non-dementia cognitive impairment.

Abnormal metabolic brain networks in Tourette syndrome

OBJECTIVES

To identify metabolic brain networks that are associated with Tourette syndrome (TS) and comorbid obsessive-compulsive disorder (OCD).

METHODS

We utilized [(18)F]-fluorodeoxyglucose and PET imaging to examine brain metabolism in 12 unmedicated patients with TS and 12 age-matched controls. We utilized a spatial covariance analysis to identify 2 disease-related metabolic brain networks, one associated with TS in general (distinguishing TS subjects from controls), and another correlating with OCD severity (within the TS group alone).

RESULTS

Analysis of the combined group of patients with TS and healthy subjects revealed an abnormal spatial covariance pattern that completely separated patients from controls (p < 0.0001). This TS-related pattern (TSRP) was characterized by reduced resting metabolic activity of the striatum and orbitofrontal cortex associated with relative increases in premotor cortex and cerebellum. Analysis of the TS cohort alone revealed the presence of a second metabolic pattern that correlated with OCD in these patients. This OCD-related pattern (OCDRP) was characterized by reduced activity of the anterior cingulate and dorsolateral prefrontal cortical regions associated with relative increases in primary motor cortex and precuneus. Subject expression of OCDRP correlated with the severity of this symptom (r = 0.79, p < 0.005).

CONCLUSION

These findings suggest that the different clinical manifestations of TS are associated with the expression of 2 distinct abnormal metabolic brain networks. These, and potentially other disease-related spatial covariance patterns, may prove useful as biomarkers for assessing responses to new therapies for TS and related comorbidities.

Neuropathology and neurochemistry of nonmotor symptoms in Parkinson's disease

Parkinson disease (PD) is no longer considered a complex motor disorder characterized by Parkinsonism but rather a systemic disease with variegated non-motor deficits and neurological symptoms, including impaired olfaction, autonomic failure, cognitive impairment, and psychiatric symptoms. Many of these alterations appear before or in parallel with motor deficits and then worsen with disease progression. Although there is a close relation between motor symptoms and the presence of Lewy bodies (LBs) and neurites filled with abnormal α-synuclein, other neurological alterations are independent of the amount of α-synuclein inclusions in neurons and neurites, thereby indicating that different mechanisms probably converge in the degenerative process. Involvement of the cerebral cortex that may lead to altered behaviour and cognition are related to several convergent factors such as (a) abnormal α-synuclein and other proteins at the synapses, rather than LBs and neurites, (b) impaired dopaminergic, noradrenergic, cholinergic and serotoninergic cortical innervation, and (c) altered neuronal function resulting from reduced energy production and increased energy demands. These alterations appear at early stages of the disease and may precede by years the appearance of cell loss and cortical atrophy.

Parkinson's disease dementia and potential therapeutic strategies

Dementia in Parkinson's disease (PD-D) has only been acknowledged in the recent three decades, but research in this field has accelerated. The purpose of this review was to discuss advances in PD-D regarding biomarker correlates and potential therapeutic targets. Attention and executive dysfunction, memory deficits that improve with cueing, and visual hallucinations are characteristic in PD-D. PD-D dramatically increases the disability and misery of the disease. Current treatment for PD-D is symptomatic, modest, and only transiently effective. There is wide agreement that more effective treatment is needed, but this will require more knowledge about PD-D pathophysiology. Advances in the pathogenesis of PD have focused on the substantia nigra, which is the location from where the pathophysiology of motor symptoms primarily arises in initial stages. In contradistinction, pathology studies have suggested that cognitive decline correlates with cortical and subcortical-cortical projection pathway abnormalities. There is evidence that substantia nigra mechanisms, including protein aggregation of α-synuclein (e.g., Lewy bodies) may also play a role in cortical neuron degeneration. Other different mechanisms, such as Alzheimer's disease pathology (e.g., Aβ aggregation) may be operant for PD-D. Biomarkers of various types are being proposed for the study of PD-D as well as for objective measures of PD-D prediction and progression. Therapeutic targets are currently derived mostly from general PD neurodegeneration research rather than cortical PD neurodegeneration per se. Protein aggregation, genes that are associated with PD, oxidative stress, inflammation, and trophic factors constitute the major classes of therapeutic targets for PD-D. More research is needed on the specific aspects of cortical dysfunction and degeneration that create PD-D.

Abnormal metabolic brain networks in Parkinson's disease from blackboard to bedside

Metabolic imaging in the rest state has provided valuable information concerning the abnormalities of regional brain function that underlie idiopathic Parkinson's disease (PD). Moreover, network modeling procedures, such as spatial covariance analysis, have further allowed for the quantification of these changes at the systems level. In recent years, we have utilized this strategy to identify and validate three discrete metabolic networks in PD associated with the motor and cognitive manifestations of the disease. In this chapter, we will review and compare the specific functional topographies underlying parkinsonian akinesia/rigidity, tremor, and cognitive disturbance. While network activity progressed over time, the rate of change for each pattern was distinctive and paralleled the development of the corresponding clinical symptoms in early-stage patients. This approach is already showing great promise in identifying individuals with prodromal manifestations of PD and in assessing the rate of progression before clinical onset. Network modulation was found to correlate with the clinical effects of dopaminergic treatment and surgical interventions, such as subthalamic nucleus (STN) deep brain stimulation (DBS) and gene therapy. Abnormal metabolic networks have also been identified for atypical parkinsonian syndromes, such as multiple system atrophy (MSA) and progressive supranuclear palsy (PSP). Using multiple disease-related networks for PD, MSA, and PSP, we have developed a novel, fully automated algorithm for accurate classification at the single-patient level, even at early disease stages.

Enhanced glutamate, IP3 and cAMP activity in the cerebral cortex of unilateral 6-hydroxydopamine induced Parkinson's rats: effect of 5-HT, GABA and bone marrow cell supplementation

Parkinson's disease is characterized by progressive cell death in the substantia nigra pars compacta, which leads to dopamine depletion in the striatum and indirectly to cortical dysfunction. Increased glutamatergic transmission in the basal ganglia is implicated in the pathophysiology of Parkinson's disease and glutamate receptor mediated excitotoxicity has been suggested to be one of the possible causes of the neuronal degeneration. In the present study, the effects of serotonin, gamma-aminobutyric acid and bone marrow cells infused intranigrally to substantia nigra individually and in combination on unilateral 6-hydroxydopamine induced Parkinson's rat model was analyzed. Scatchard analysis of total glutamate and NMDA receptor binding parameters showed a significant increase in B_max (P < 0.001) in the cerebral cortex of 6-hydroxydopamine infused rat compared to control. Real Time PCR amplification of NMDA2B, mGluR5, bax, and ubiquitin carboxy-terminal hydrolase were up regulated in cerebral cortex of 6-hydroxydopamine infused rats compared to control. Gene expression studies of GLAST, ά-Synuclien and Cyclic AMP response element-binding protein showed a significant (P < 0.001) down regulation in 6-OHDA infused rats compared to control. Behavioural studies were carried out to confirm the biochemical and molecular studies. Serotonin and GABA along with bone marrow cells in combination showed reversal of glutamate receptors and behaviour abnormality shown in the Parkinson's rat model. The therapeutic significance in Parkinson's disease is of prominence.

The epidemiology of dementia associated with Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative illness after Alzheimer's disease (AD). Cognitive impairment and dementia are common features in PD and characterized by a wide range of cognitive deficits distinct from those seen in AD. Mild cognitive impairment occurs even early in PD and is associated with shorter time to dementia. The purpose of this review is to present recent findings on clinical aspects of dementia in PD and to elucidate underlying clinical and neurobiological risk factors.

Biomarkers for cognitive impairment in Parkinson disease

Cognitive impairment, including dementia, is commonly seen in those afflicted with Parkinson disease (PD), particularly at advanced disease stages. Pathologically, PD with dementia (PD-D) is most often associated with the presence of cortical Lewy bodies, as is the closely related dementia with Lewy bodies (DLB). Both PD-D and DLB are also frequently complicated by the presence of neurofibrillary tangles and amyloid plaques, features most often attributed to Alzheimer disease. Biomarkers are urgently needed to differentiate among these disease processes and predict dementia in PD as well as monitor responses of patients to new therapies. A few clinical assessments, along with structural and functional neuroimaging, have been utilized in the last few years with some success in this area. Additionally, a number of other strategies have been employed to identify biochemical/molecular biomarkers associated with cognitive impairment and dementia in PD, e.g. targeted analysis of candidate proteins known to be important to PD pathogenesis and progression in cerebrospinal fluid or blood. Finally, interesting results are emerging from preliminary studies with unbiased and high throughput genomic, proteomic and metabolomic techniques. The current findings and perspectives of applying these strategies and techniques are reviewed in this article, together with potential areas of advancement.

Neuroimaging and cognition in Parkinson's disease dementia

The prevalence of cognitive impairment and dementia in Parkinson's disease (PD) is high and can potentially occur as the result of multiple differing pathologies. Neuroimaging has provided evidence of decreased cortical volume, increased white matter diffusion changes, and decreased resting metabolic activity that appears to begin prior to the onset of dementia in PD patients. Cognitive impairment has been found to be associated with multiple neurotransmitter transmission deficiencies, including dopamine and acetylcholine, indicating a widespread neurotransmitter dysfunction in PD-related dementia. Findings of increased Pittsburgh Compound B (PiB) binding in subjects with Lewy Body Disease (LBD) compared with Parkinson's disease and dementia (PDD) may explain phenotype differences in the spectrum of Dementia with Lewy Bodies (DLB), and show promise in guiding future therapeutic trials aimed at this disease. Advances in neuroimaging now allow for the detection of volumetric, pharmacologic, and pathological changes that may assist in the diagnosis and prediction of cognitive impairment in Parkinson's patients so that better evaluation of disease progression and treatment can be obtained.

Scaled subprofile modeling of resting state imaging data in Parkinson's disease: methodological issues

Consistent functional brain abnormalities in Parkinson's disease (PD) are difficult to pinpoint because differences from the normal state are often subtle. In this regard, the application of multivariate methods of analysis has been successful but not devoid of misinterpretation and controversy. The Scaled Subprofile Model (SSM), a principal components analysis (PCA)-based spatial covariance method, has yielded critical information regarding the characteristic abnormalities of functional brain organization that underlie PD and other neurodegenerative disorders. However, the relevance of disease-related spatial covariance patterns (metabolic brain networks) and the most effective methods for their derivation has been a subject of debate. We address these issues here and discuss the inherent advantages of proper application as well as the effects of the misapplication of this methodology. We show that ratio pre-normalization using the mean global metabolic rate (GMR) or regional values from a "reference" brain region (e.g. cerebellum) that may be required in univariate analytical approaches is obviated in SSM. We discuss deviations of the methodology that may yield erroneous or confounding factors.

Diffuse occipital hypometabolism on [18 F]-FDG PET scans in patients with idiopathic REM sleep behavior disorder: prodromal dementia with Lewy bodies?

BACKGROUND

Previous longitudinal studies have revealed that specific patterns on [(18) F]-fluoro-d-glucose (FDG) positron emission tomography (PET) scans in patients with amnesic mild cognitive impairment can predict Alzheimer's disease (AD). However, the significance of particular patterns on [(18) F]-FDG PET scans in prodromal patients with dementia with Lewy bodies (DLB) remains unclear.

METHODS

Based on the prevailing evidence that rapid eye movement (REM) sleep behavior disorder (RBD) often precedes the onset of DLB, [(18) F]-FDG PET scans of nine non-demented patients reporting recurrent nocturnal dream-enactment behavior in our memory clinic were compared with the normative database using three-dimensional stereotactic surface projection (3D-SSP) images. All patients underwent clinical and neuropsychological examinations as well as cardiac [(123) I]-metaiodobenzylguanidine ([(123) I]-MIBG) scintigraphy.

RESULTS

Four patients were found to have diffuse areas of reduced cerebral metabolic rate of glucose (CMRglc), predominantly in the occipital lobe, which is the preferentially affected region in DLB patients. In contrast, five patients showed no such occipital hypometabolism; instead, these five patients showed hypometabolism in the left anterior cingulate gyrus (Broadmann area (BA) 24), right frontal lobe (BA 32) and right anterior temporal lobe (BA 38), which are the preferentially affected regions in Parkinson's disease rather than DLB. The extent of the reduction in CMRglc in the left occipital lobe was correlated with scores on the Bender Gestalt Test, which reflects visuospatial ability, but not with global cognitive measures. All patients showed reduced cardiac [(123) I]-MIBG levels, consistent with underlying Lewy body disease.

CONCLUSION

These variations in [(18) F]-FDG PET scans raise the possibility that the specific pattern of CMRglc reduction may predict developing DLB in patients with idiopathic RBD. Further follow-up studies are needed, particularly on patients with diffuse occipital hypometabolism.

Functional connectivity of cortical motor areas in the resting state in Parkinson's disease

Parkinson's disease (PD) patients have difficulty in initiating movements. Previous studies have suggested that the abnormal brain activity may happen not only during performance of self-initiated movements but also in the before movement (baseline or resting) state. In the current study, we investigated the functional connectivity of brain networks in the resting state in PD. We chose the rostral supplementary motor area (pre-SMA) and bilateral primary motor cortex (M1) as "seed" regions, because the pre-SMA is important in motor preparation, whereas the M1 is critical in motor execution. FMRIs were acquired in 18 patients and 18 matched controls. We found that in the resting state, the pattern of connectivity with both the pre-SMA or the M1 was changed in PD. Connectivity with the pre-SMA in patients with PD compared to normal subjects was increased connectivity to the right M1 and decreased to the left putamen, right insula, right premotor cortex, and left inferior parietal lobule. We only found stronger connectivity in the M1 with its own local region in patients with PD compared to controls. Our findings demonstrate that the interactions of brain networks are abnormal in PD in the resting state. There are more connectivity changes of networks related to motor preparation and initiation than to networks of motor execution in PD. We postulate that these disrupted connections indicate a lack of readiness for movement and may be partly responsible for difficulty in initiating movements in PD.

Executive functions deficit in Parkinson's disease with amnestic mild cognitive impairment

Recent studies suggest that onset of dementia in Parkinson's disease (PD) is preceded by a phase known as mild cognitive impairment (MCI). Different clinical subtypes of MCI in PD were found. The objective of this study was to investigate whether patients with PD diagnosed with amnestic MCI (aPD-MCI) have also subtle deficits in other cognitive domains and especially in attention/executive functions and, therefore to clarify whether all subcomponents of executive control are equally affected in aPD-MCI. We investigated 23 patients with aPD-MCI (modified Petersen's criteria) and 25 normal controls. Relative to controls, the aPD-MCI group showed significant deficits with reference to tasks that encompass various aspects of attention/executive functions, including Trail Making Test, Stroop test, Modified Card Sorting Test, and digit span backward, as well as phonemic and semantic verbal fluency. This suggests that executive dysfunction is consistently presented in PD with MCI, even in ''amnestic'' PD-MCI due to cortical-subcortical dysfunction.