Cognitive impairment and dementia in Parkinson's disease

Effects of happy and sad facial expressions on the perception of time in Parkinson's disease patients with mild cognitive impairment

INTRODUCTION

Parkinson's disease (PD) is a movement disorder caused by deterioration of the dopaminergic system. Previous studies have demonstrated temporal as well as emotional facial recognition impairment in PD patients. Moreover, it has been demonstrated that emotional facial expressions alter temporal judgments. In the present study, we investigate the magnitude of temporal distortions caused by the presentation of emotional facial expressions (happiness, sadness, and neutral) in PD patients with mild cognitive impairment (PD-MCI) and controls.

METHOD

Seventeen older adults with PD-MCI and 22 healthy older adults took part in the present study. Participants were tested with a time bisection task with standard intervals lasting 400 ms and 1600 ms. Moreover, a complete neuropsychological evaluation was conducted to characterize the sample.

RESULTS

Differences between groups were observed indicating a general underestimation of time in PD-MCI patients. Temporal impairments in PD-MCI patients seem to be caused mainly by a dysfunction at the level of reference memory. The effect of emotional facial expressions on time perception was evident in both PD patients and controls, with an overestimation of perceived duration when happiness was presented and an underestimation when sadness was presented.

CONCLUSION

Overall, our results indicate that reduced cognitive abilities might be responsible for the lower temporal ability observed in PD-MCI patients. Moreover, similar effects of emotional stimuli were observed in both PD-MCI patients and controls.

Consensus on the Definition of Advanced Parkinson's Disease: A Neurologists-Based Delphi Study (CEPA Study)

To date, no consensus exists on the key factors for diagnosing advanced Parkinson disease (APD). To obtain consensus on the definition of APD, we performed a prospective, multicenter, Spanish nationwide, 3-round Delphi study (CEPA study). An ad hoc questionnaire was designed with 33 questions concerning the relevance of several clinical features for APD diagnosis. In the first-round, 240 neurologists of the Spanish Movement Disorders Group participated in the study. The results obtained were incorporated into the questionnaire and both, results and questionnaire, were sent out to and fulfilled by 26 experts in Movement Disorders. Review of results from the second-round led to a classification of symptoms as indicative of “definitive,” “probable,” and “possible” APD. This classification was confirmed by 149 previous participating neurologists in a third-round, where 92% completely or very much agreed with the classification. Definitive symptoms of APD included disability requiring help for the activities of daily living, presence of motor fluctuations with limitations to perform basic activities of daily living without help, severe dysphagia, recurrent falls, and dementia. These results will help neurologists to identify some key factors in APD diagnosis, thus allowing users to categorize the patients for a homogeneous recognition of this condition.

Review: Parkinson's disease: from synaptic loss to connectome dysfunction

Parkinson's disease (PD) is a common neurodegenerative disorder with prominent loss of nigro-striatal dopaminergic neurons. The resultant dopamine (DA) deficiency underlies the onset of typical motor symptoms (MS). Nonetheless, individuals affected by PD usually show a plethora of nonmotor symptoms (NMS), part of which may precede the onset of motor signs. Besides DA neuron degeneration, a key neuropathological alteration in the PD brain is Lewy pathology. This is characterized by abnormal intraneuronal (Lewy bodies) and intraneuritic (Lewy neurites) deposits of fibrillary aggregates mainly composed of α-synuclein. Lewy pathology has been hypothesized to progress in a stereotypical pattern over the course of PD and α-synuclein mutations and multiplications have been found to cause monogenic forms of the disease, thus raising the question as to whether this protein is pathogenic in this disorder. Findings showing that the majority of α-synuclein aggregates in PD are located at presynapses and this underlies the onset of synaptic and axonal degeneration, coupled to the fact that functional connectivity changes correlate with disease progression, strengthen this idea. Indeed, by altering the proper action of key molecules involved in the control of neurotransmitter release and re-cycling as well as synaptic and structural plasticity, α-synuclein deposition may crucially impair axonal trafficking, resulting in a series of noxious events, whose pressure may inevitably degenerate into neuronal damage and death. Here, we provide a timely overview of the molecular features of synaptic loss in PD and disclose their possible translation into clinical symptoms through functional disconnection.

Evaluating Recall and Recognition Memory Using the Montreal Cognitive Assessment: Applicability for Alzheimer's and Huntington's Diseases

We sought to investigate whether the Montreal Cognitive Assessment (MoCA) could provide a brief assessment of recall and recognition using Huntington disease (HD) and Alzheimer disease (AD) as disorders characterized by different memory deficits. This study included 80 participants with HD, 64 participants with AD, and 183 community-dwelling control participants. Random-effects hierarchical logistic regressions were performed to assess the relative performance of the normal control (NC), participants with HD, and participants with AD on verbal free recall, cued recall, and multiple-choice recognition on the MoCA. The NC participants performed significantly better than participants with AD at all the 3 levels of assessment. No difference existed between participants with HD and NC for cued recall, but NC participants performed significantly better than participants with HD on free recall and recognition. The participants with HD performed significantly better than participants with AD at all the 3 levels of assessment. The MoCA appears to be a valuable, brief cognitive assessment capable of identifying specific memory deficits consistent with known differences in memory profiles.

Cognitive impairment in patients with Parkinson's disease: A 30-month follow-up study

OBJECTIVE

A longitudinal (30-month) study of the cognitive changes in Parkinson's disease patients and analysis of influencing factors.

METHODS

The cognitive function and related symptoms of 102 patients with idiopathic Parkinson's disease were assessed using the Montreal Cognitive Assessment (MoCA), Mini-Mental State Examination (MMSE), and relevant scales, at baseline and 30-month follow-up. The t-test, nonparametric tests, and regression analyses were used to evaluate cognitive decline and investigate risk factors for cognitive impairment.

RESULTS

From baseline to follow-up, the MMSE and MoCA scores significantly decreased, respectively, from 28.16±2.29 to 26.18±3.64, and from 24.60±4.23 to 21.94±5.47 (both P<0.001). Impairment was observed in multiple cognitive areas, significantly in naming, delayed recall, and orientation (P<0.01). Patients at baseline with postural instability and gait disturbance (PIGD), lower MoCA scores, or depression had a higher risk of cognitive impairment at follow-up (P<0.01).

CONCLUSION

Cognitive impairment is highly prevalent in Parkinson's disease patients, especially for those with lower MoCA scores, PIGD, and depression.

Subtypes of mild cognitive impairment in patients with Parkinson's disease: evidence from the LANDSCAPE study

OBJECTIVE

Inconsistent results exist regarding the cognitive profile in patients with Parkinson's disease with mild cognitive impairment (PD-MCI). We aimed at providing data on this topic from a large cohort of patients with PD-MCI.

METHODS

Sociodemographic, clinical and neuropsychological baseline data from patients with PD-MCI recruited in the multicentre, prospective, observational DEMPARK/LANDSCAPE study were analysed.

RESULTS

269 patients with PD-MCI (age 67.8±7.4, Unified Parkinson's Disease Rating Scale (UPDRS-III) scores 23.2±11.6) were included. PD-MCI subtypes were 39.4% non-amnestic single domain, 30.5% amnestic multiple domain, 23.4% non-amnestic multiple domain and 6.7% amnestic single domain. Executive functions were most frequently impaired. The most sensitive tests to detect cognitive dysfunctions were the Modified Card Sorting Test, digit span backwards and word list learning direct recall. Multiple stepwise regression analyses showed that global cognition, gender and age, but not education or disease-related parameters predicted PD-MCI subtypes.

CONCLUSIONS

This study with the so far largest number of prospectively recruited patients with PD-MCI indicates that non-amnestic PD-MCI is more frequent than amnestic PD-MCI; executive dysfunctions are the most typical cognitive symptom in PD-MCI; and age, gender and global cognition predict the PD-MCI subtype. Longitudinal data are needed to test the hypothesis that patients with PD-MCI with specific cognitive profiles have different risks to develop dementia.

The Perceive, Recall, Plan and Perform (PRPP) system for persons with Parkinson's disease: a psychometric study

BACKGROUND

The Perceive, Recall, Plan & Perform (PRPP) system of task analysis might be feasible to evaluate occupational performance and information processing strategies for persons with Parkinson's disease (PD).

AIM

To evaluate: (1) the random error between raters (inter-rater study), (2) the random error within raters (intra-rater study), and (3) the internal consistency of the PRPP.

MATERIALS AND METHODS

(1) video-recorded performance of meaningful activities of 13 Dutch persons with PD, scored independently by 38 Dutch PRPP trained occupational therapists were included in the analysis. The random error between raters was analyzed with two-way random Intraclass Correlation Coefficients (ICC). (2) Four videos were scored twice by 30 raters (6 week time interval). The random error within raters was analyzed using one-way random ICC's. (3) Internal consistency study: data of 190 persons with PD were analyzed using Cronbach's alpha (α).

RESULTS

Inter-rater reliability ranged from slight to moderate (ICC= 0.06-0.43). The mean intra-rater reliability ranged from moderate to almost perfect (ICC= 0.60-0.83). Internal consistency is good (α = 0.60-0.86).

CONCLUSION

The limited inter-rater reliability but adequate intra-rater reliability and internal consistency show the feasibility of the PRPP when used for persons with PD. Implications for reliable clinical use are discussed.

Cognitive decline in Parkinson's disease: the complex picture

Mild cognitive impairment (PD-MCI) and dementia (PDD) are among the most frequent non-motor symptoms in Parkinson's disease (PD). PD-MCI is six times more likely than age-matched controls to develop dementia and the PDD prevalence is 80% after 15-20 years of disease. Therefore, research has focused on the identification of early dementia biomarkers including specific cognitive at-risk profiles hoping to implement therapeutic interventions when they are most likely to be efficacious. However, given the heterogeneous neuropathological, neurochemical, and neuropsychological nature of cognitive deficits, definition of a comprehensive cognitive model of PDD is a challenge. Evidence from neuroimaging studies using different methods and techniques suggests that in addition to degeneration of the dopaminergic system, other mechanisms have a role including β-amyloid and tau deposition, and that specific cognitive scales could help identifying a malignant profile. Prospective studies combining neuroimaging techniques and specific cognitive tests are required to define the interplay between the various neurodegenerative processes and the contribution of structural disconnection in brain functional networks, heralding the development of dementia in PD.

Parkinson Disease and Dementia

Dementia is a frequent complication of Parkinson disease (PD) with a yearly incidence of around 10% of patients with PD. Lewy body pathology is the most important factor in the development of Parkinson disease dementia (PDD) and there is evidence for a synergistic effect with β-amyloid. The clinical phenotype in PDD extends beyond the dysexecutive syndrome that is often present in early PD and encompasses deficits in recognition memory, attention, and visual perception. Sleep disturbances, hallucinations, neuroleptic sensitivity, and fluctuations are often present. This review provides an update on current knowledge of PDD including aspects of epidemiology, pathology, clinical presentation, management, and prognosis.

Screening for Cognitive Impairment in Parkinson's Disease: Improving the Diagnostic Utility of the MoCA through Subtest Weighting

Background

Given the high prevalence of cognitive impairment in Parkinson’s disease (PD), cognitive screening is important in clinical practice. The Montreal Cognitive Assessment (MoCA) is a frequently used screening test in PD to detect mild cognitive impairment (PD-MCI) and Parkinson’s disease dementia (PD-D). However, the proportion in which the subtests are represented in the MoCA total score does not seem reasonable. We present the development and preliminary evaluation of an empirically based alternative scoring system of the MoCA which aims at increasing the overall diagnostic accuracy.

Methods

In study 1, the MoCA was administered to 40 patients with PD without cognitive impairment (PD-N), PD-MCI, or PD-D, as defined by a comprehensive neuropsychological test battery. The new MoCA scoring algorithm was developed by defining Areas under the Curve (AUC) for MoCA subtests in a Receiver Operating Characteristic (ROC) and by weighting the subtests according to their sensitivities and specificities. In study 2, an independent sample of 24 PD patients (PD-N, PD-MCI, or PD-D) was tested with the MoCA. In both studies, diagnostic accuracy of the original and the new scoring procedure was calculated.

Results

Diagnostic accuracy increased with the new MoCA scoring algorithm. In study 1, the sensitivity to detect cognitive impairment increased from 62.5% to 92%, while specificity decreased only slightly from 77.7% to 73%; in study 2, sensitivity increased from 68.8% to 81.3%, while specificity stayed stable at 75%.

Conclusion

This pilot study demonstrates that the sensitivity of the MoCA can be enhanced substantially by an empirically based weighting procedure and that the proposed scoring algorithm may serve the MoCA’s actual purpose as a screening tool in the detection of cognitive dysfunction in PD patients better than the original scoring of the MoCA. Further research with larger sample sizes is necessary to establish efficacy of the alternate scoring system.

Cognitive Changes following Bilateral Deep Brain Stimulation of Subthalamic Nucleus in Parkinson's Disease: A Meta-Analysis

Background. Nowadays, it has been largely acknowledged that deep brain stimulation of subthalamic nucleus (STN DBS) can alleviate motor symptoms of Parkinson's disease, but its effects on cognitive function remain unclear, which are not given enough attention by many clinical doctors and researchers. To date, 3 existing meta-analyses focusing on this issue included self-control studies and have not drawn consistent conclusions. The present study is the first to compare effect sizes of primary studies that include control groups, hoping to reveal the net cognitive outcomes after STN DBS and the clinical significance. Methods. A structured literature search was conducted using strict criteria. Only studies with control group could be included. Data on age, duration of disease, levodopa equivalent dosage (LED), and multiple cognitive scales were collected and pooled. Results. Of 172 articles identified, 10 studies (including 3 randomized controlled trials and 7 nonrandomized controlled studies) were eligible for inclusion. The results suggest that STN DBS results in decreased global cognition, memory, verbal fluency, and executive function compared with control group. No significant difference is found in other cognitive domains. Conclusions. STN DBS seems relatively safe with respect to cognitive function, and further studies should focus on the exact mechanisms of possible verbal deterioration after surgery in the future.

Profiling cognitive and neuropsychiatric heterogeneity in Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is a highly heterogeneous disease, in which motor symptom subtypes are often-described. While it is recognized that motor, cognitive and affective neuropsychiatric symptoms negatively influence the patients' quality of life, it is currently unknown how these symptoms contribute to phenotypic subtypes. The objective of this study was to assess subtypes of motor, cognitive and affective symptoms in PD.

METHODS

A hierarchical cluster analysis was conducted on clinical data of 226 PD patients screened at the VU University Medical Center using comprehensive assessment of cognitive, affective and motor symptoms. Subsequent linear discriminant analyses were conducted to investigate discriminating constructs between clusters.

RESULTS

The cluster analysis yielded four clusters: (1) a young-age (59.9 years), mildly affected cluster (N = 86), (2) an old-age (72.3 years) cluster with severe motor and non-motor symptoms (N = 15), (3) a cluster (age 64.7 years) with mild motor symptoms, below-average executive functioning and affective symptoms (N = 46) and (4) a cluster (age 64.8 years) with severe motor symptoms, affective symptoms and below-average verbal memory (N = 79).

CONCLUSIONS

Cluster 1 and 2 seem to represent opposite ends of the PD disease stages. Patients in clusters 3 and 4 had similar age, educational level and disease duration but different symptom profiles - we therefore suggest that these clusters represent different pathways of disease progression, presumably with distinct underlying pathology localization. Future research on the neuropathophysiological characteristics of these two clusters and monitoring of disease progression is required.

Default mode network differences between rigidity- and tremor-predominant Parkinson's disease

BACKGROUND

Parkinson's disease (PD) traditionally is characterized by tremor, rigidity, and bradykinesia, although cognitive impairment also is a common symptom. The clinical presentation of PD is heterogeneous and associated with different risk factors for developing cognitive impairment. PD patients with primary akinetic/rigidity (PDAR) are more likely to develop cognitive deficits compared to those with tremor-predominant symptoms (PDT). Because cognitive impairment in PD appears to be related to changes in the default mode network (DMN), this study tested the hypothesis that DMN integrity is different between PDAR and PDT subtypes.

METHOD

Resting state fMRI (rs-fMRI) and whole brain volumetric data were obtained from 17 PDAR, 15 PDT and 24 healthy controls (HCs) using a 3T scanner. PD patients were matched closely to HCs for demographic and cognitive variables, and showed no symptoms of dementia. Voxel-based morphometry (VBM) was used to examine brain gray matter (GM) volume changes between groups. Independent component analysis (ICA) interrogated differences in the DMN among PDAR, PDT, and HC.

RESULTS

There was decreased activity in the left inferior parietal cortex (IPC) and the left posterior cingulate cortex (PCC) within the DMN between PDAR and both HC and PDT subjects, even after controlling for multiple comparisons, but not between PDT and HC. GM volume differences between groups were detected at a lower threshold (p < 0.001, uncorrected). Resting state activity in IPC and PCC were correlated with some measures of cognitive performance in PD but not in HC.

CONCLUSION

This is the first study to demonstrate DMN differences between cognitively comparable PDAR and PDT subtypes. The DMN differences between PD and HC appear to be driven by the PDAR subtype. Further studies are warranted to understand the underlying neural mechanisms and their relevance to clinical and cognitive outcomes in PDAR and PDT subtypes.

Cognitive predictors of balance in Parkinson's disease

Postural instability is one of the most incapacitating symptoms of Parkinson's disease (PD) and appears to be related to cognitive deficits. This study aims to determine the cognitive factors that can predict deficits in static and dynamic balance in individuals with PD. A sociodemographic questionnaire characterized 52 individuals with PD for this work. The Trail Making Test, Rule Shift Cards Test, and Digit Span Test assessed the executive functions. The static balance was assessed using a plantar pressure platform, and dynamic balance was based on the Timed Up and Go Test. The results were statistically analysed using SPSS Statistics software through linear regression analysis. The results show that a statistically significant model based on cognitive outcomes was able to explain the variance of motor variables. Also, the explanatory value of the model tended to increase with the addition of individual and clinical variables, although the resulting model was not statistically significant The model explained 25-29% of the variability of the Timed Up and Go Test, while for the anteroposterior displacement it was 23-34%, and for the mediolateral displacement it was 24-39%. From the findings, we conclude that the cognitive performance, especially the executive functions, is a predictor of balance deficit in individuals with PD.

Resting-state functional connectivity of the striatum in early-stage Parkinson's disease: Cognitive decline and motor symptomatology

Parkinson's disease is a neurodegenerative disorder characterized by changes to dopaminergic function in the striatum and a range of cognitive and motor deficits. Neuroimaging studies have repeatedly shown differences in activation and functional connectivity patterns of the striatum between symptomatic individuals with Parkinson's disease and healthy controls. However, the presence and severity of cognitive and motor symptoms seem to differ dramatically among individuals with Parkinson's disease at the early-stages. To investigate the neural basis of such heterogeneity, we examined the resting state functional connectivity patterns of caudate and putamen subdivisions in relation to cognitive and motor impairments among 62 early-stage individuals with Parkinson's disease (21 females, 23 drug naive, ages 39-77 years, average UPDRS motor scores off medication = 18.56, average H&Y stage = 1.66). We also explored how changes in striatal connectivity relate to changes in symptomatology over a year. There are two main findings. First, higher motor deficit rating was associated with weaker coupling between anterior putamen and midbrain including substantia nigra. Intriguingly, steeper declines in functional connectivity between these regions were associated with greater declines in motor function over the course of 1 year. Second, decline in cognitive function, particularly in the memory and visuospatial domains, was associated with stronger coupling between the dorsal caudate and the rostral anterior cingulate cortex. These findings remained significant after controlling for age, medication, gender, and education. In sum, our findings suggest that cognitive decline and motor deficit are each associated with a differentiable pattern of functional connectivity of striatal subregions. Hum Brain Mapp 37:648-662, 2016. © 2015 Wiley Periodicals, Inc.

Gait in Parkinson's disease: A visuo-cognitive challenge

Vision and cognition have both been related to gait impairment in Parkinson's disease (PD) through separate strands of research. The cumulative and interactive effect of both (which we term visuo-cognition) has not been previously investigated and little is known about the influence of cognition on vision with respect to gait. Understanding the role of vision, cognition and visuo-cognition in gait in PD is critical for data interpretation and to infer and test underlying mechanisms. The purpose of this comprehensive narrative review was to examine the interdependent and interactive role of cognition and vision in gait in PD and older adults. Evidence from a broad range of research disciplines was reviewed and summarised. A key finding was that attention appears to play a pivotal role in mediating gait, cognition and vision, and should be considered emphatically in future research in this field.

Event-Related Potentials in Parkinson’s Disease Patients with Visual Hallucination

Using neuropsychological investigation and visual event-related potentials (ERPs), we aimed to compare the ERPs and cognitive function of nondemented Parkinson's disease (PD) patients with and without visual hallucinations (VHs) and of control subjects. We recruited 12 PD patients with VHs (PD-H), 23 PD patients without VHs (PD-NH), and 18 age-matched controls. All subjects underwent comprehensive neuropsychological assessment and visual ERPs measurement. A visual odd-ball paradigm with two different fixed interstimulus intervals (ISI) (1600 ms and 5000 ms) elicited visual ERPs. The frontal test battery was used to assess attention, visual-spatial function, verbal fluency, memory, higher executive function, and motor programming. The PD-H patients had significant cognitive dysfunction in several domains, compared to the PD-NH patients and controls. The mean P3 latency with ISI of 1600 ms in PD-H patients was significantly longer than that in controls. Logistic regression disclosed UPDRS-on score and P3 latency as significant predictors of VH. Our findings suggest that nondemented PD-H patients have worse cognitive function and P3 measurements. The development of VHs in nondemented PD patients might be implicated in executive dysfunction with altered visual information processing.

The Behavior of Migraine in Patients with Parkinson's Disease

Parkinson’s disease (PD) is characterized by the degeneration of dopaminergic systems in the central nervous system. In migraine it is supposed to occur hyperactivation of central dopaminergic pathways. We verified the hypothesis of improved migraine in patients who manifest PD. We evaluated 109 patients with PD over 40 years (57 men and 52 women) about the presence throughout the life of migraine, as well as the possibility of improvement in migraine after the onset of motor symptoms of PD. This group was compared to a control group of 152 people (41 men and 152 women) without PD regarding the presence of migraine and its improvement. Twenty-one patients manifested migraine in the group with PD (16 women and 5 men) in which 13 reported improvement in migraine after the onset of symptoms of PD. Among the controls, 37 interviewed had migraine history (32 women and 5 men) among which 20 showed improvement. There was no significant difference when comparing the two groups (χ²_1:0,05=0.337; P<0.382). We were unable to relate the improvement of migraine with the emergence of PD motor signs, despite the degeneration of dopaminergic pathways of the central nervous system.

Brain mediators of systemic oxidative stress on perceptual impairments in Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is well documented to be associated with elevated systemic oxidative stress and perceptual impairments. Furthermore, the striatum and extrastriatal cortical areas, which are involved in the coordination of perceptual functions, are impaired at an early stage of the disease. However, the possible pathophysiology involved in perceptual impairments remains unclear. This raises the possibility that structural abnormalities might mediate the relationship between oxidative stress and perceptual impairments.

METHODS

We explored the differences between 27 patients with PD and 25 healthy controls in terms of serum oxidative stress, perceptual functions, and regional gray matter. A single-level three-variable mediation model was used to investigate the possible relationships between serum oxidative stress, regional gray matter volume, and different domains of perceptual functioning.

RESULTS

The results demonstrate that increased serum oxidative stress (as indicated by thiobarbituric acid reactive substances) was associated with declined perceptual functioning in PD patients. We further explored significant gray matter volume reductions in the bilateral temporal gyri (middle temporal gyrus and fusiform gyrus), bilateral frontal gyri, limbic lobe (hippocampus and uncus), left inferior parietal lobule, right caudate nucleus, and insula in PD. Further mediation analysis showed that gray matter volumes in the middle temporal gyrus, inferior parietal lobule, hippocampus, and insula served as brain mediators between elevated serum oxidative stress and perceptual impairments.

CONCLUSIONS

These results suggest that higher oxidative stress levels adversely impact perceptual functions by causing temporal and mesolimbic abnormalities.

Parkinson's disease dementia: a neural networks perspective

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

Clinical predictors of cognitive impairment and psychiatric complications in Parkinson’s disease

Objective To estimate the clinical and demographics aspects that may contribute to cognitive impairment and psychiatric symptoms in Parkinson’s disease (PD). Method All patients answered a structured standardized clinical questionnaire. Two movement disorders specialists performed the following scale: Unified Parkinson’s disease rating score (UPDRS), the modified Hoehn and Yahr staging, Schwab and England Scale, SCOPA cognition (SCOPA-COG), SCOPA-Psychiatric complications (SCOPA-PC) and Non-Motor Symptoms Scale (NMSS). We built a generalized linear model to assess predictors for the SCOPA-COG and SCOPA-PC scores. Results Almost 37% of our patients were demented as per SCOPA-COG scores. Level of education and the UPDRS-Subscale III were predictors of cognitive impairment. Higher scores in domain 3 of NMSS and male gender were associated with psychiatric complications as assessed per the SCOPA-PC. Conclusion Level of education and disease severity are predictors of dementia in PD. Psychiatric complications are more commonly observed in men.

Education-corrected CERAD identifies MCI and dementia in Parkinson's disease

OBJECTIVES

This study examined whether controlling for educational background in the CERAD cognitive screening battery would affect the likelihood of patients with Parkinson's disease to fulfill criteria for mild cognitive impairment (PD-MCI) and dementia (PDD).

MATERIALS & METHODS

One-hundred seventeen patients with PD were studied. Cognitive impairment was determined as two subtest scores falling below either the standard cutoff scores or education-corrected cutoff scores. The presence of dementia was determined by clinical interview or Clinical Dementia Rating. Patients were then classified as PD-MCI and PDD according to cognitive test performance and presence/absence of dementia.

RESULTS

The number of cognitively impaired patients (PD-MCI or PDD) was significantly higher when education-controlled cutoff scores were used (62.5% vs 38%). Correspondingly, the number of false negatives (demented PD patients performing normally in CERAD) was significantly lower when education-corrected cutoff scores were used (4% vs 10%).

CONCLUSIONS

Controlling for education increases the sensitivity of the CERAD for PD-MCI and PDD.

Nigral proteasome inhibition in mice leads to motor and non-motor deficits and increased expression of Ser129 phosphorylated α-synuclein

Parkinson's disease is a neurodegenerative disorder characterized by motor and non-motor disturbances. Various pathogenic pathways drive disease progression including oxidative stress, mitochondrial dysfunction, α-synuclein aggregation and impairment of protein degradation systems. Dysfunction of the ubiquitin-proteasome system in the substantia nigra of Parkinson's disease patients is believed to be one of the causes of protein aggregation and cell death associated with this disorder. Lactacystin, a potent inhibitor of the proteasome, was previously delivered to the nigrostriatal pathway of rodents to model nigrostriatal degeneration. Although lactacystin-treated animals develop parkinsonian motor impairment, it is currently unknown whether they also develop non-motor symptoms characteristic of this disorder. In order to further describe the proteasome inhibition model of Parkinson's disease, we characterized the unilateral lactacystin model, performed by stereotaxic injection of the toxin in the substantia nigra of mice. We studied the degree of neurodegeneration and the behavioral phenotype 1 and 3 weeks after lactacystin lesion both in terms of motor impairment, as well as non-motor symptoms. We report that unilateral administration of 3 μg lactacystin to the substantia nigra of mice leads to partial (~40%) dopaminergic cell loss and concurrent striatal dopamine depletion, accompanied by increased expression of Ser129-phosphorylated α-synuclein. Behavioral characterization of the model revealed parkinsonian motor impairment, as well as signs of non-motor disturbances resembling early stage Parkinson's disease including sensitive and somatosensory deficits, anxiety-like behavior, and perseverative behavior. The consistent finding of good face validity, together with relevant construct validity, warrant a further evaluation of proteasome inhibition models of Parkinson's disease in pre-clinical research and validation of therapeutic targets.

Antipsychotic-induced parkinsonism is associated with working memory deficits in schizophrenia-spectrum disorders

In view of the significant cognitive deficits in schizophrenia and their impact on patients' social and occupational functioning, and considering that the influence potential influence of antipsychotic-induced extrapyramidal symptoms on cognition in schizophrenia remains poorly understood, the current study sought to identify the clinical, socio-demographic and neurologic predictors of the cognitive performance of schizophrenia patients. Eighty-two schizophrenia-spectrum (DSM-IV criteria) outpatients were recruited. Psychiatric symptoms were evaluated with the Positive And Negative Syndrome Scale and the Calgary Depression Scale for Schizophrenia. Extrapyramidal symptoms were evaluated with the Extrapyramidal Symptoms Rating Scale, while spatial working, planning abilities and visual paired associates learning were evaluated with the CAmbridge Neuropsychological Tests Automated Battery. The Stroop test was also administered. Multivariate hierarchic linear regression analyses were performed. We found that negative symptoms were associated with cognitive flexibility, planning, visual learning and working memory performance in schizophrenia. Age, sex, number of hospitalizations and antipsychotic type also emerged as significant predictors. More importantly, we found a significant association between antipsychotic-induced parkinsonism and working memory performance. The fact that negative symptoms and socio-demographic variables predicted cognitive performance in schizophrenia is consistent with the previous literature on the topic. The finding of an association between parkinsonism and working memory may have clinical implications, since working memory deficits are considered putative endophenotypes of schizophrenia and are known to impair patients' social and occupational functioning. Our results will need to be replicated in longitudinal studies involving larger samples of patients.

Telencephalic neurocircuitry and synaptic plasticity in rodent spatial learning and memory

Spatial learning and memory in rodents represent close equivalents of human episodic declarative memory, which is especially sensitive to cerebral aging, neurodegeneration, and various neuropsychiatric disorders. Many tests and protocols are available for use in laboratory rodents, but Morris water maze and radial-arm maze remain the most widely used as well as the most valid and reliable spatial tests. Telencephalic neurocircuitry that plays functional roles in spatial learning and memory includes hippocampus, dorsal striatum and medial prefrontal cortex. Prefrontal-hippocampal circuitry comprises the major associative system in the rodent brain, and is critical for navigation in physical space, whereas interconnections between prefrontal cortex and dorsal striatum are probably more important for motivational or goal-directed aspects of spatial learning. Two major forms of synaptic plasticity, namely long-term potentiation, a lasting increase in synaptic strength between simultaneously activated neurons, and long-term depression, a decrease in synaptic strength, have been found to occur in hippocampus, dorsal striatum and medial prefrontal cortex. These and other phenomena of synaptic plasticity are probably crucial for the involvement of telencephalic neurocircuitry in spatial learning and memory. They also seem to play a role in the pathophysiology of two brain pathologies with episodic declarative memory impairments as core symptoms, namely Alzheimer's disease and schizophrenia. Further research emphasis on rodent telencephalic neurocircuitry could be relevant to more valid and reliable preclinical research on these most devastating brain disorders. This article is part of a Special Issue entitled SI: Brain and Memory.

Psychiatric aspects of Parkinson's disease

Parkinson's disease (PD) is essentially characterized by the motor symptoms in the form of resting tremor, rigidity and bradykinesia. However, over the years it has been recognized that motor symptoms are just the "tip of the iceberg" of clinical manifestations of PD. Besides motor symptoms, PD characterized by many non-motor symptoms, which include cognitive decline, psychiatric disturbances (depression, psychosis and impulse control), sleep difficulties, autonomic failures (gastrointestinal, cardiovascular, urinary, thermoregulation) and pain syndrome. This review evaluates the various aspects of psychiatric disorders including cognitive decline and sleep disturbances in patients with PD. The prevalence rate of various psychiatric disorders is high in patients with PD. In terms of risk factors, various demographic, clinical and treatment-related variables have been shown to be associated with higher risk of development of psychiatric morbidity. Evidence also suggests that the presence of psychiatric morbidity is associated with poorer outcome. Randomized controlled trials, evaluating the various pharmacological and non-pharmacological treatments for management of psychiatric morbidity in patients with PD are meager. Available evidence suggests that tricyclic antidepressants like desipramine and nortriptyline are efficacious for management of depression. Among the antipsychotics, clozapine is considered to be the best choice for management of psychosis in patients with PD. Among the various cognitive enhancers, evidence suggest efficacy of rivastigmine in management of dementia in patients with PD. To conclude, this review suggests that psychiatric morbidity is highly prevalent in patients with PD. Hence, a multidisciplinary approach must be followed to improve the overall outcome of PD. Further studies are required to evaluate the efficacy of various other measures for management of psychiatric morbidity in patients with PD.

The neurobiological basis of cognitive impairment in Parkinson's disease

The recent formalization of clinical criteria for Parkinson's disease with dementia (PDD) codifies many studies on this topic, including those assessing biological correlates. These studies show that the emergence of PDD occurs on the background of severe dopamine deficits with, the main pathological drivers of cognitive decline being a synergistic effect between alpha-synuclein and Alzheimer's disease pathology. The presence of these pathologies correlates with a marked loss of limbic and cortically projecting dopamine, noradrenaline, serotonin, and acetylcholine neurons, although the exact timing of these relationships remains to be determined. Genetic factors, such as triplications in the α-synuclein gene, lead to a clear increased risk of PDD, whereas others, such as parkin mutations, are associated with a reduced risk of PDD. The very recent formalization of clinical criteria for PD with mild cognitive impairment (PD-MCI) allows only speculation on its biological and genetic bases. Critical assessment of animal models shows that chronic low-dose MPTP treatment in primates recapitulates PD-MCI over time, enhancing the current biological concept of PD-MCI as having enhanced dopamine deficiency in frontostriatal pathways as well as involvement of other neurotransmitter systems. Data from other animal models support multiple transmitter involvement in cognitive impairment in PD. Whereas dopamine dysfunction has been highlighted because of its obvious role in PD, the role of the other neurotransmitter systems, neurodegenerative pathologies, and genetic factors in PD-MCI remains to be fully elucidated.

Virtual multiple errands test (VMET): a virtual reality-based tool to detect early executive functions deficit in Parkinson's disease

INTRODUCTION

Several recent studies have pointed out that early impairment of executive functions (EFs) in Parkinson's Disease (PD) may be a crucial marker to detect patients at risk for developing dementia. The main objective of this study was to compare the performances of PD patients with mild cognitive impairment (PD-MCI) with PD patients with normal cognition (PD-NC) and a control group (CG) using a traditional assessment of EFs and the Virtual Multiple Errands Test (VMET), a virtual reality (VR)-based tool. In order to understand which subcomponents of EFs are early impaired, this experimental study aimed to investigate specifically which instrument best discriminates among these three groups.

MATERIALS AND METHODS

The study included three groups of 15 individuals each (for a total of 45 participants): 15 PD-NC; 15 PD-MCI, and 15 cognitively healthy individuals (CG). To assess the global neuropsychological functioning and the EFs, several tests (including the Mini Mental State Examination (MMSE), Clock Drawing Test, and Tower of London test) were administered to the participants. The VMET was used for a more ecologically valid neuropsychological evaluation of EFs.

RESULTS

Findings revealed significant differences in the VMET scores between the PD-NC patients vs. the controls. In particular, patients made more errors in the tasks of the VMET, and showed a poorer ability to use effective strategies to complete the tasks. This VMET result seems to be more sensitive in the early detection of executive deficits because these two groups did not differ in the traditional assessment of EFs (neuropsychological battery).

CONCLUSION

This study offers initial evidence that a more ecologically valid evaluation of EFs is more likely to lead to detection of subtle executive deficits.

SK channel blockade reverses cognitive and motor deficits induced by nigrostriatal dopamine lesions in rats

Parkinson's disease has traditionally been viewed as a motor disorder caused by the loss of dopamine (DA) neurons. However, emotional and cognitive syndromes can precede the onset of the motor deficits and provide an opportunity for therapeutic intervention. Potassium channels have recently emerged as potential new targets in the treatment of Parkinson's disease. The selective blockade of small conductance calcium-activated K+ channels (SK channels) by apamin is known to increase burst firing in midbrain DA neurons and therefore DA release. We thus investigated the effects of systemic administration of apamin on the motor, cognitive deficits and anxiety present after bilateral nigrostriatal 6-hydroxydopamine (6-OHDA) lesions in rats. Apamin administration (0.1 or 0.3 mg/kg i.p.) counteracted the depression, anxiety-like behaviors evaluated on sucrose consumption and in the elevated plus maze, social recognition and spatial memory deficits produced by partial 6-OHDA lesions. Apamin also reduced asymmetric motor deficits on circling behavior and postural adjustments in the unilateral extensive 6-OHDA model. The partial 6-OHDA lesions (56% striatal DA depletion) produced 20% decrease of iodinated apamin binding sites in the substantia nigra pars compacta in correlation with the loss of tyrosine hydroxylase positive cells, without modifying apamin binding in brain regions receiving DAergic innervation. Striatal extracellular levels of DA, not detectable after 6-OHDA lesions, were enhanced by apamin treatment as measured by in vivo microdialysis. These results indicate that blocking SK channels may reinstate minimal DA activity in the striatum to alleviate the non-motor symptoms induced by partial striatal DA lesions.

Using the Montreal Cognitive Assessment Scale to screen for dementia in Chinese patients with Parkinson's Disease

Background

Dementia is one of the most distressing and burdensome health problems associated with Parkinson's Disease (PD). The Montreal Cognitive Assessment scale (MoCA) is widely used to screen for dementia in PD patients, but the appropriate diagnostic cutoff score when used with Chinese PD patients is not known.

Aim

Determine a diagnostic cutoff value of the Chinese version of the MoCA (MoCA-C) for Chinese PD patients and describe the characteristics of PD patients screened positive for dementia using the MoCA-C.

Methods

The presence of dementia in 616 PD patients and 85 community controls was determined using the Movement Disorder Society Task Force criteria (the gold standard diagnosis). We administered the MoCA-C to these individuals and used a receiver operating characteristic (ROC) curve to identify the cutoff score of the MoCA-C that most efficiently identified dementia in both PD patients and community controls. Demographic and clinical characteristics of PD patients who were screened positive or negative for dementia using the MoCA-C were compared.

Results

A MoCA-C score of 23 was the optimal cutoff score for dementia in both patients and controls. Using this cutoff score, the sensitivity and specificity of the MoCA-C in PD patients were 0.70 and 0.77, respectively; the positive and negative predictive values were 0.59 and 0.85, respectively; and the overall concordance (kappa [95% confidence interval]) was 0.45 (0.39-0.52). The corresponding kappa value (concordance) in community controls was only 0.25 (0.05-0.45). Compared to PD patients who screened negative for dementia, those who screened positive for dementia were significantly impaired in all cognitive domains, including visuospatial and executive functioning, naming, attention, language, abstraction, delayed recall and orientation (all p<0.001). Among the PD patients, screening positive for dementia was independently associated with old age, low educational attainment, female gender and more severe motor impairment.

Conclusions

The commonly recommended cutoff screening score for dementia of 26 on the MoCA it too high for PD patients in China; a cutoff score of 23 is more appropriate. Potential risk factors for dementia in Chinese PD patients include older age, less education, and more severe motor symptoms of PD.

Pacific Northwest Udall Center of excellence clinical consortium: study design and baseline cohort characteristics

BACKGROUND

The substantial proportion of individuals with Parkinson's disease (PD) who have or are expected to develop concomitant cognitive impairment emphasizes the need for large, well-characterized participant cohorts to serve as a basis for research into the causes, manifestations, and potential treatments of cognitive decline in those with PD.

OBJECTIVE

To establish a multi-site clinical core that cognitively and clinically characterizes patients with PD by obtaining quality longitudinal clinical, neuropsychological, and validated biomarker data.

METHODS

Six hundred nineteen participants with idiopathic PD (68.0 ± 9.1 years, 7.1 ± 6.2 years since diagnosis, 70% males) were enrolled in the Pacific Northwest Udall Center (PANUC), one of the Morris K. Udall Centers of Excellence for Parkinson's Research, Clinical Consortium and underwent comprehensive clinical and neuropsychological assessment. Participants were diagnosed with no cognitive impairment (PD-NCI), mild cognitive impairment (PD-MCI), or dementia (PDD) at a diagnostic consensus conference.

RESULTS

A substantial proportion of the overall sample was diagnosed with cognitive impairment at baseline: 22% with PDD and 59% with PD-MCI. A higher rate of cognitive impairment was observed in men than women (87% vs. 68%, p < 0.0001), despite a higher level of education. Most patients older than 50 years at the time of diagnosis and with disease duration greater than 10 years were cognitively impaired or demented.

CONCLUSIONS

The PANUC Clinical Consortium is a clinically and cognitively well-characterized cohort of patients with PD. Baseline cohort characteristics demonstrate a high rate of cognitive impairment in the sample, as well as potential sex differences with regard to cognitive diagnosis. The PANUC Clinical Consortium, with its access to biomarker, genetic, and autopsy data, provides an excellent foundation for detailed research related to cognitive impairment in PD.

Imaging changes associated with cognitive abnormalities in Parkinson's disease

The current study investigates both gray and white matter changes in non-demented Parkinson's disease (PD) patients with varying degrees of mild cognitive deficits and elucidates the relationships between the structural changes and clinical sequelae of PD. Twenty-six PD patients and 15 healthy controls (HCs) were enrolled in the study. Participants underwent T1-weighted and diffusion tensor imaging (DTI) scans. Their cognition was assessed using a neuropsychological battery. Compared with HCs, PD patients showed significant cortical thinning in sensorimotor (left pre- and postcentral gyri) and cognitive (left dorsolateral superior frontal gyrus [DLSFG]) regions. The DLSFG cortical thinning correlated with executive and global cognitive impairment in PD patients. PD patients showed white matter abnormalities as well, primarily in bilateral frontal and temporal regions, which also correlated with executive and global cognitive impairment. These results seem to suggest that both gray and white matter changes in the frontal regions may constitute an early pathological substrate of cognitive impairment of PD providing a sensitive biomarker for brain changes in PD.

Initial cognitive decline is associated with cortical thinning in early Parkinson disease

OBJECTIVES

Our aim was to assess cortical thickness in a large multicenter cohort of drug-naive patients with early Parkinson disease (PD), with and without mild cognitive impairment (MCI), and explore the cognitive correlates of regional cortical thinning.

METHODS

One hundred twenty-three newly diagnosed patients with PD and 56 healthy controls with 3-tesla structural MRI scans and complete neuropsychological assessment from the Parkinson's Progression Markers Initiative were included. Modified Movement Disorders Society Task Force level II criteria were applied to diagnose MCI in PD. FreeSurfer image processing and analysis software was used to measure cortical thickness across groups and the association with cognitive domains and tests.

RESULTS

In patients with MCI, atrophy was found in temporal, parietal, frontal, and occipital areas compared with controls. Specific regional thinning in the right inferior temporal cortex was also found in cognitively normal patients. Memory, executive, and visuospatial performance was associated with temporoparietal and superior frontal thinning, suggesting a relationship between cognitive impairment and both anterior and posterior cortical atrophy in the whole patient sample.

CONCLUSIONS

These findings confirm that MCI is associated with widespread cortical atrophy. In addition, they suggest that regional cortical thinning is already present at the time of diagnosis in patients with early, untreated PD who do not meet the criteria for MCI. Together, the results indicate that cortical thinning can serve as a marker for initial cognitive decline in early PD.

Reading comprehension in Parkinson's disease

PURPOSE

Although individuals with Parkinson's disease (PD) self-report reading problems and experience difficulties in cognitive-linguistic functions that support discourse-level reading, prior research has primarily focused on sentence-level processing and auditory comprehension. Accordingly, the authors investigated the presence and nature of reading comprehension in PD, hypothesizing that (a) individuals with PD would display impaired accuracy and/or speed on reading comprehension tests and (b) reading performances would be correlated with cognitive test results.

METHOD

Eleven adults with PD and 9 age- and education-matched control participants completed tests that evaluated reading comprehension; general language and cognitive abilities; and aspects of attention, memory, and executive functioning.

RESULT

The PD group obtained significantly lower scores on several, but not all, reading comprehension, language, and cognitive measures. Memory, language, and disease severity were significantly correlated with reading comprehension for the PD group.

CONCLUSION

Individuals in the early stages of PD without dementia or broad cognitive deficits can display reading comprehension difficulties, particularly for high- versus basic-level reading tasks. These reading difficulties are most closely related to memory, high-level language, and PD symptom severity status. The findings warrant additional research to delineate further the types and nature of reading comprehension impairments experienced by individuals with PD.

Exploring recollection and familiarity impairments in Parkinson's disease

There is conflicting evidence on whether patients diagnosed with Parkinson's disease (PD) have cognitive deficits associated with episodic memory and particularly with recognition memory. The aim of the present study was to explore whether PD patients exhibit deficits in recollection and familiarity, the two processes involved in recognition. A sample of young healthy participants (22) was tested to verify that the experimental tasks were useful estimators of recognition processes. Two further samples--one of elderly controls (16) and one of PD patients (20)--were the main focus of this research. All participants were exposed to an associative recognition test aimed at estimating recollection followed by a two-alternative forced-choice (2AFC) test designed to estimate familiarity. The analyses showed a deficit in associative recognition in PD patients and no difference between elderly controls and PD patients in the 2AFC test. By contrast, young healthy participants were better than elderly controls and PD patients in both components of recognition. Further analyses of results of the 2AFC test indicated that the measure chosen to estimate conceptual familiarity was adequate.

Evaluation of mild cognitive impairment subtypes in Parkinson's disease

Mild cognitive impairment in Parkinson's disease (PD-MCI) is common and increases the risk for dementia. Establishing distinct PD-MCI cognitive subtypes could be valuable for eventually predicting those most likely to convert to dementia. However, the study of PD-MCI subtypes has not yielded consistent results among cohorts. To determine whether there are distinct cognitive subtypes among participants diagnosed with PD-MCI in the Pacific Northwest Udall Center Clinical Consortium, we cognitively subtyped 95 patients with PD-MCI, using the Movement Disorders Society Task Force diagnostic guidelines. Psychometric test scores were then subjected to principle components factor analysis to determine whether similar cognitive subgroups could be identified using statistical methodology. Multiple-domain PD-MCI was diagnosed in 95% of the sample, and a range of cognitive impairments were noted. Factor analysis yielded seven factors and demonstrated overlap of phonemic verbal fluency on two factors, as well as the loading of verbal fluency on the same factor as a visuospatial measure; however, these factors did not partition the sample into distinct cognitive subtypes. Separation of cognitive subtypes based on the current PD-MCI criteria, or via statistical methods, may not provide sufficient information to describe distinct PD groups. Future efforts to validate the PD-MCI criteria and identify combinations of genetic or other risk factors for cognitive impairment are warranted.

Cerebrospinal fluid α-synuclein predicts cognitive decline in Parkinson disease progression in the DATATOP cohort

Most patients with Parkinson disease (PD) develop both cognitive and motor impairment, and biomarkers for progression are urgently needed. Although α-synuclein is altered in cerebrospinal fluid of patients with PD, it is not known whether it predicts motor or cognitive deterioration. We examined clinical data and α-synuclein in >300 unmedicated patients with PD who participated in the deprenyl and tocopherol antioxidative therapy of parkinsonism (DATATOP) study, with up to 8 years of follow-up. Longitudinal measures of motor and cognitive function were studied before (phase 1) and during (phase 2) levodopa therapy; cerebrospinal fluid was collected at the beginning of each phase. Correlations and linear mixed models were used to assess α-synuclein association with disease severity and prediction of progression in the subsequent follow-up period. Despite decreasing α-synuclein (phase 1 to phase 2 change of -0.05 ± 0.21 log-transformed values, P < 0.001), no correlations were observed between α-synuclein and motor symptoms. Longitudinally, lower α-synuclein predicted better preservation of cognitive function by several measures [Selective Reminding Test total recall α-synuclein × time interaction effect coefficient, -0.12 (P = 0.037); delayed recall, -0.05 (P = 0.002); New Dot Test, -0.03 (P = 0.002)]. Thus, α-synuclein, although not clinically useful for motor progression, might predict cognitive decline, and future longitudinal studies should include this outcome for further validation.

Perceived and performance-based executive dysfunction in Parkinson's disease

Executive dysfunction is common in early stage Parkinson's disease (PD). We evaluated the relationship between self- and informant-report measurement of real-world executive functions as well as performance-based neuropsychological measures in mildly cognitively impaired individuals with PD and healthy controls. The PD group reported more difficulty with initiation of complex tasks compared to caregiver ratings, and processing speed was a strong predictor of self-reported executive dysfunction for the PD group, followed by depression. Processing speed and semantic verbal fluency predicted informant-reported executive dysfunction in PD. These findings highlight the contribution of speeded processing for performance of everyday executive tasks in PD.