Differential executive control impairments in early Parkinson’s disease

Serum glial cell line-derived neurotrophic factor (GDNF) a potential biomarker of executive function in Parkinson's disease

Objective

Evidence shows that the impairment of executive function (EF) is mainly attributed to the degeneration of frontal-striatal dopamine pathway. Glial cell line-derived neurotrophic factor (GDNF), as the strongest protective neurotrophic factor for dopaminergic neurons (DANs), may play a role in EF to some extent. This study mainly explored the correlation between serum GDNF concentration and EF performance in Parkinson's disease (PD).

Methods

This study recruited 45 healthy volunteers (health control, HC) and 105 PD patients, including 44 with mild cognitive impairment (PD-MCI), 20 with dementia (PD-D), and 20 with normal cognitive function (PD-N). Neuropsychological tests were performed to evaluate EF (working memory, inhibitory control, and cognitive flexibility), attention, language, memory, and visuospatial function. All subjects were tested for serum GDNF and homovanillic acid (HVA) levels by ELISA and LC-ESI-MS/MS, respectively.

Results

PD-MCI patients showed impairments in the trail making test (TMT) A (TMT-A), TMT-B, clock drawing test (CDT) and semantic fluency test (SFT), whereas PD-D patients performed worse in most EF tests. With the deterioration of cognitive function, the concentration of serum GDNF and HVA in PD patients decreased. In the PD group, the serum GDNF and HVA levels were negatively correlated with TMT-A (r _GDNF = -0.304, P < 0.01; r _HVA = -0.334, P < 0.01) and TMT-B (r _GDNF = -0.329, P < 0.01; r _HVA = -0.323, P < 0.01) scores. Serum GDNF levels were positively correlated with auditory verbal learning test (AVLT-H) (r = 0.252, P < 0.05) and SFT (r = 0.275, P < 0.05) scores. Serum HVA levels showed a positively correlation with digit span test (DST) (r = 0.277, P < 0.01) scores. Stepwise linear regression analysis suggested that serum GDNF and HVA concentrations and UPDRS-III were the influence factors of TMT-A and TMT-B performances in PD patients.

Conclusion

The decrease of serum GDNF concentration in PD patients was associated with impaired inhibitory control, cognitive flexibility, and attention performances. The changes of GDNF and HVA might synergistically participate in the occurrence and development of executive dysfunction in PD patients.

Alternate fluency in Parkinson’s disease: A machine learning analysis

Objective

The aim of the present study was to investigate whether patients with Parkinson’s Disease (PD) had changes in their level of performance in extra-dimensional shifting by implementing a novel analysis method, utilizing the new alternate phonemic/semantic fluency test.

Method

We used machine learning (ML) in order to develop high accuracy classification between PD patients with high and low scores in the alternate fluency test.

Results

The models developed resulted to be accurate in such classification in a range between 80% and 90%. The predictor which demonstrated maximum efficiency in classifying the participants as low or high performers was the semantic fluency test. The optimal cut-off of a decision rule based on this test yielded an accuracy of 86.96%. Following the removal of the semantic fluency test from the system, the parameter which best contributed to the classification was the phonemic fluency test. The best cut-offs were identified and the decision rule yielded an overall accuracy of 80.43%. Lastly, in order to evaluate the classification accuracy based on the shifting index, the best cut-offs based on an optimal single rule yielded an overall accuracy of 83.69%.

Conclusion

We found that ML analysis of semantic and phonemic verbal fluency may be used to identify simple rules with high accuracy and good out of sample generalization, allowing the detection of executive deficits in patients with PD.

[Guidelines for the Neuropsychological Assessment of Patients with Parkinson's Disease]

BACKGROUND

Presence of mild cognitive impairment is currently the best predictor for the development of Parkinson's disease dementia. Diagnostic criteria for both Parkinson's with mild cognitive impairment and Parkinson's disease dementia have been suggested by the Movement Disorder Society. However, not all cognitive tests recommended are available in the German language with proper standard values.

OBJECTIVES

To define evidence-based guidelines for neuropsychological assessment of patients with Parkinson's disease in German.

METHODS

Two systematic literature searches were conducted. First, articles that presented international guidelines (consensus papers or reviews) for the application of standardized neuropsychological assessments for the diagnosis of cognitive impairment in Parkinson's disease were selected. Of those, only neuropsychological assessments in German language with normative values referring either to a German, Austrian, or Swiss population were considered. Second, articles comparing test performances of healthy controls vs. Parkinson's disease and/or different cognitive Parkinson's disease subtypes (e.g. no cognitive impairment, Parkinson's with mild cognitive impairment, Parkinson's disease dementia) were selected. Effect sizes for group differentiation were calculated.

RESULTS

Out of 127 full-text articles reviewed, 48 tests were identified during the first literature search. In the second search, 1716 articles were reviewed and 23 papers selected. The strongest effect sizes for group discrimination were revealed for tests assessing executive function, attention, and visuo-cognitive abilities. Based on the results of the two literature searches, consensus guidelines were defined by the authors, allowing for Level-II diagnosis for Parkinson's with mild cognitive impairment and Parkinson's disease dementia.

CONCLUSIONS

The presented guidelines may have the potential to standardize and improve the neuropsychological assessment of Parkinson's disease patients in German speaking countries.

Do importance instructions improve time-based prospective remembering in autism spectrum conditions?

This study explored the impact of motivation on the memory for delayed intentions (so-called, prospective memory, PM) in autistic individuals. Specifically, we were interested in the effects of personal (i.e., receiving a reward) as compared to social motivation (i.e., performing a favour for someone). Given the well-established theory of mind deficits in autism, we expected autistic individuals to benefit more strongly from personal than social importance manipulations, whereas the opposite pattern was predicted for controls. Sixty-one adolescents with autism and 61 typically developing adolescents participated, with each group distributed equally to one of the three motivation conditions of standard, social and personal reward. Participants worked on a 2-back picture-based ongoing task in which a time-based PM task was embedded. A mixed 2 (Group) x 3 (Motivation condition) analysis of covariance with age, verbal and non-verbal abilities as covariates and correct PM responses as dependent variable indicated solely a main effect of group, with controls outperforming the autism group. In contrast to our expectations, there was no main effect of condition, no significant interaction, and none of the covariates had any significant impact. However, further planned analyses revealed that controls only outperformed autistic individuals in the personal reward condition. Controls performed significantly best when a personal reward was promised, whereas there were no significant differences between the motivation conditions for autistic individuals. Findings are discussed in terms of underlying processes.

Visuospatial functioning is associated with sleep disturbance and hallucinations in nondemented patients with Parkinson's disease

Introduction: Cognitive impairment is a common symptom of Parkinson's disease (PD) associated with reduced quality of life and a more severe disease state. Previous research has shown an association between visuospatial dysfunction and worse disease course; however, it is not clear whether this is separable from executive dysfunction and/or dementia. This study sought to determine whether distinct cognitive factors could be measured in a large PD cohort, and if those factors were differentially associated with other PD-related features, specifically to provide insight into visuospatial dysfunction. Methods: Non-demented participants with PD from the Pacific Udall Center were enrolled (n = 197). Co-participants (n = 104) completed questionnaires when available. Principal components factor analysis (PCFA) was utilized to group the neuropsychological test scores into independent factors by considering those with big factor loading (≥.40). Linear and logistic regression analyses were performed to examine the relationship between the cognitive factors identified in the PCFA and other clinical features of PD. Results: Six factors were extracted from the PCFA: 1) executive/processing speed, 2) visual learning & memory/visuospatial, 3) auditory working memory, 4) contextual verbal memory, 5) semantic learning & memory, and 6) visuospatial. Motor severity (p = 0.001), mood (p < 0.001), and performance on activities of daily living scores (informant: p < 0.001, patient: p = 0.009) were primarily associated with frontal and executive factors. General sleep disturbance (p < 0.006) and hallucinations (p = 0.002) were primarily associated with visuospatial functioning and visual learning/memory. Conclusions: Motor symptoms, mood, and performance on activities of daily living were primarily associated with frontal/executive factors. Sleep disturbance and hallucinations were associated with visuospatial functioning and visual learning/memory only, over and above executive functioning and regardless of cognitive disease severity. These findings support that visuospatial function in PD may indicate a more severe disease course, and that symptom management should be guided accordingly.

Relation between cognitive and behavioral aspects of dysexecutive functioning in normal aging

The aim of this study was to investigate the relation between cognitive and behavioral symptoms of dysexecutive functioning, understood as two aspects of dysexecutive syndrome, in an elderly nonclinical sample. Most previous studies have concentrated on clinical population. However, nonclinical population of elderly adults is, in this context, a group of special interest due to a large body of evidence indicating that executive functions decrease pronouncedly in the course of normal aging. The data were collected from 40 participants aged 67-86 years. None presented symptoms of cognitive disorder or depression or reported psychiatric or neurological problems. The Dysexecutive Questionnaire was used as a measure of behavioral aspect of dysexecutive syndrome. Participants also performed experimental tasks referring to three cognitive aspects of executive functioning (i.e., updating, inhibition, and attentional shifting). Analysis resulted in weak and nonsignificant correlations between cognitive and behavioral aspects of dysexecutive syndrome. Results are discussed in the context of previous research and diagnostic criteria of dysexecutive syndrome.

Sensitivity and Specificity of the ECAS in Parkinson's Disease and Progressive Supranuclear Palsy

Disentangling Parkinson's disease (PD) and progressive supranuclear palsy (PSP) may be a diagnostic challenge. Cognitive signs may be useful, but existing screens are often insufficiently sensitive or unsuitable for assessing people with motor disorders. We investigated whether the newly developed ECAS, designed to be used with people with even severe motor disability, was sensitive to the cognitive impairment seen in PD and PSP and able to distinguish between these two disorders. Thirty patients with PD, 11 patients with PSP, and 40 healthy controls were assessed using the ECAS, as well as an extensive neuropsychological assessment. The ECAS detected cognitive impairment in 30% of the PD patients, all of whom fulfilled the diagnostic criteria for mild cognitive impairment. The ECAS was also able to detect cognitive impairment in PSP patients, with 81.8% of patients performing in the impaired range. The ECAS total score distinguished between the patients with PSP and healthy controls with high sensitivity (91.0) and specificity (86.8). Importantly, the ECAS was also able to distinguish between the two syndromes, with the measures of verbal fluency offering high sensitivity (82.0) and specificity (80.0). In sum, the ECAS is a quick, simple, and inexpensive test that can be used to support the differential diagnosis of PSP.

French Version of the Hayling Sentence Completion Test, Part II: Clinical Utility in Schizophrenia and Parkinson's Disease

Objective

We previously developed normative data for a French version of the Hayling Sentence Completion Test (f-HSCT) for adults and elderly people. The present study aimed to evaluate the clinical utility of the f-HSCT norms in two clinical populations in which inhibition dysfunction has been largely documented, i.e., Parkinson's disease (PD) and schizophrenia.

Method

Eighty-five non-demented patients with idiopathic PD and 64 out-patients with schizophrenia completed the automatic and inhibition conditions of the f-HSCT. Time latencies and errors raw data of each patient were compared to the norms previously developed by the authors.

Results

In the automatic condition, errors were rare in both clinical groups and time latencies on this condition felt within the normative data range. Compared with the standardized norms, 46% of patients with PD and 61% of patients with schizophrenia had a deviant performance (i.e., borderline or deficit) for the inhibition error score. The proportion of patients with a deviant performance on the inhibition response time score was similar in both clinical samples (respectively, 25% and 23%). Finally, slightly more than half of patients with PD and more than two-thirds of patients with schizophrenia had a deviant performance on at least one of the f-HSCT inhibition measures.

Conclusions

Our results suggest that the f-HSCT has a strong potential for characterizing inhibition of prepotent responses in PD and schizophrenia. Furthermore, it requires only a short administration time so it may be ideal to detect response inhibition in clinical populations with cognitive fatigue.

Self-Reported Executive Functioning in Everyday Life in Parkinson's Disease after Three Months of Subthalamic Deep Brain Stimulation

Objective. Studies on the effect of subthalamic deep brain stimulation (STN-DBS) on executive functioning in Parkinson's disease (PD) are still controversial. In this study we compared self-reported daily executive functioning in PD patients before and after three months of STN-DBS. We also examined whether executive functioning in everyday life was associated with motor symptoms, apathy, and psychiatric symptoms. Method. 40 PD patients were examined with the Behavior Rating Inventory of Executive Function-Adult Version (BRIEF-A), the Symptom Checklist 90-Revised (SCL-90-R), and the Apathy Evaluation Scale (AES-S). Results. PD patients reported significant improvement in daily life executive functioning after 3 months of STN-DBS. Anxiety scores significantly declined, while other psychiatric symptoms remained unchanged. The improvement of self-reported executive functioning did not correlate with motor improvement after STN-DBS. Apathy scores remained unchanged after surgery. Only preoperative depressed mood had predictive value to the improvement of executive function and appears to prevent potentially favorable outcomes from STN-DBS on some aspects of executive function. Conclusion. PD patients being screened for STN-DBS surgery should be evaluated with regard to self-reported executive functioning. Depressive symptoms in presurgical PD patients should be treated. Complementary information about daily life executive functioning in PD patients might enhance further treatment planning of STN-DBS.

Executive dysfunction in Parkinson's disease: a review

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

Relation between freezing of gait and frontal function in Parkinson's disease

INTRODUCTION

Freezing of gait (FOG) is a common symptom of Parkinson's disease (PD). Although the pathophysiological mechanism of FOG is unknown, previous studies have suggested that frontal dysfunction is associated with FOG. The Behavioral Assessment of the Dysexecutive Syndrome (BADS) battery, which is wide-ranging neurological battery composed of six subtests, evaluates frontal function and is more sensitive to executive dysfunction (ED) than other tools in PD patients. This is the first study to assess the relation between FOG in the 'on' state and frontal dysfunction evaluated using BADS.

METHODS

Subjects were 65 patients with PD. Multiple logistic regression analysis was used to compare the age-controlled standardized BADS score, age, disease duration, Hoehn and Yahr (HY) stage, levodopa-equivalent daily dose, and Mini-Mental State Examination (MMSE) score across patients with FOG (n = 43) and patients without FOG (n = 22). Score on each of the six BADS subtests were compared across patients with and without FOG using the Mann-Whitney U test.

RESULTS

Multiple logistic regression analysis revealed that FOG was related to lower age-controlled standardized BADS score (P = 0.022) and higher HY stage (P = 0.009) but not to disease duration, levodopa equivalent daily dose, or MMSE score. Among the six BADS subtests, score on the Zoo Map Test, which evaluates problem solving and planning, was lower in patients with FOG than in patients without FOG.

CONCLUSION

These results support a relation between on-state FOG and frontal dysfunction in PD patients.

Pattern of executive impairment in mild to moderate Parkinson's disease

BACKGROUND/AIMS

The exact pattern of impairment in executive functions (EF) among people with Parkinson's disease (PD) is still debated. Using a data-driven approach we investigated which areas of EF are particularly problematic in mild to moderate PD.

METHODS

Thirty-four patients with mild to moderate PD, who scored in the normal range on general cognition screening tests, but displayed frontal-type deficits indicated by Frontal Assessment Battery screening, completed the 9 tests that comprise the Delis-Kaplan Executive Function System. Patterns of performance were explored using cluster analysis and principal component analysis (PCA), and the frequency of impairments was established using normative data.

RESULTS

Both cluster analysis and PCA identified two distinct groups of EF tests. The first group included tests requiring time-efficient attentional control (e.g. the Trail Making test). The second group included tests measuring abstract reasoning and concept formation abilities (e.g. the 20 Questions test). Impairment was more frequent on the attentional control tests than on the abstract thinking tests.

CONCLUSION

PD pathology in the mild to moderate PD appears to affect the attentional control aspect of EF to a greater extent than abstract reasoning. Understanding the nature of executive deficits in PD is important for the development of targeted pharmacological and cognitive interventions for cognitive disturbances.

Impairment of script comprehension in Lewy body spectrum disorders

A disabling impairment of higher-order language function can be seen in patients with Lewy body spectrum disorders such as Parkinson's disease (PD), Parkinson's disease dementia (PDD), and dementia with Lewy bodies (DLB). We focus on script comprehension in patients with Lewy body spectrum disorders. While scripts unfold sequentially, constituent events are thought to contain an internal organization. Executive dysfunction in patients with Lewy body spectrum disorders may interfere with comprehension of this internal structure. We examined 42 patients (30 non-demented PD and 12 mildly demented PDD/DLB patients) and 12 healthy seniors. We presented 22 scripts (e.g., "going fishing"), each consisting of six events. Pilot data from young controls provided the basis for organizing associated events into clusters and arranging them hierarchically into scripts. We measured accuracy and latency to judge the order of adjacent events in the same cluster versus adjacent events in different clusters. PDD/DLB patients were less accurate in their ordering judgments than PD patients and controls. Healthy seniors and PD patients were significantly faster to judge correctly the order of highly associated within-cluster event pairs relative to less closely associated different-cluster event pairs, while PDD/DLB patients did not consistently distinguish between these event-pair types. This relative insensitivity to the clustered-hierarchical organization of events was related to executive impairment and to frontal atrophy as measured by volumetric MRI. These findings extend prior work on script processing to patients with Lewy body spectrum disorders and highlight the potential impact of frontal/executive dysfunction on the daily lives of affected patients.

Efficacy of tailored computer-based neurorehabilitation for improvement of movement initiation in Parkinson's disease

While Parkinson's disease (PD) is considered a motor disorder, motor signs of PD can be exacerbated by cognitive dysfunction. We evaluated the efficacy of a computer-based cognitive rehabilitation training program designed to improve motor-related executive function. Thirty people with PD and 21 controls participated in the 10-day training. Training consisted of a two-phase button press task. First, subjects produced an externally cued (EC) digit sequence, typing numbers displayed on the computer screen. Second, subjects were prompted to generate the same sequence in the absence of the number display (internally represented sequence, IR). Sequence length was automatically adjusted to maintain 87% correct performance. Participants were evaluated before and after training using a fixed version of the training task, and generalization of training was assessed using measures involving IR motor sequencing, switching and activities of daily living. PD participants were divided into two groups, those who showed impairment in IR motor sequence production prior to training (N=14) and those whose performance was similar to controls (N=16). Following training the impaired PD group showed significantly greater reduction in sequence initiation and completion time and in error rate for IR conditions compared to the unimpaired PD and control groups. All groups improved on Trails B-A, and pre-training Trails B was identified as a predictor of training-based improvement in IR sequence completion time and error rate. Our findings highlight the importance of neurorehabilitation tailored to the specific cognitive deficits of the PD patient.

Sentence processing in Lewy body spectrum disorder: the role of working memory

Prior work has related sentence processing to executive deficits in non-demented patients with Parkinson's disease (PD). We extended this investigation to patients with dementia with Lewy bodies (DLB) and PD dementia (PDD) by examining grammatical and working memory components of sentence processing in the full range of patients with Lewy body spectrum disorder (LBSD). Thirty-three patients with LBSD were given a two-alternative, forced-choice sentence-picture matching task. Sentence type, working memory, and grammatical structure were systematically manipulated in the sentences. We found that patients with PDD and DLB were significantly impaired relative to non-demented PD patients and healthy controls. The deficit in PDD/DLB was most pronounced for sentences lengthened by the strategic placement of an additional prepositional phrase and for sentences with an additional proposition due to a center-embedded clause. However, there was no effect for subject-relative versus object-relative grammatical structure. An MRI voxel-based morphometry analysis in a subset of patients showed significant gray matter thinning in the frontal lobe bilaterally, and this extended to temporal, parietal and occipital regions. A regression analysis related sentence processing difficulty in LBSD to frontal neocortex, including inferior prefrontal, premotor, and dorsolateral prefrontal regions, as well as right superior temporal cortex. These findings are consistent with the hypothesis that patients with PDD and DLB have difficulty processing sentences with increased working memory demands and that this deficit is related in part to their frontal disease.

Executive functions in Parkinson's disease: systematic review and meta-analysis

Impairment of executive function (EF) is commonly reported as a feature of PD. However, the exact pattern of executive impairment remains unclear. Also, there is an ongoing discussion surrounding the definition and conceptualization of EF, which might affect the clarity of research evidence on cognition in PD. The aim of this systematic review was to describe the pattern of executive impairment in early-stage PD emerging from the research literature and to identify critical issues for improving consistency in this field. The PsychInfo, MEDLINE, Science Direct, CINAHL, and Cochrane Library databases were searched using the term "Parkinson's disease" combined with each of 14 cognitive abilities defined as representing aspects of EF. The review was limited to studies that investigated EF as the central variable in early-stage, nondemented PD patients. The review identified 33 studies of EF that were operationalized in terms of 30 abilities tested by 60 measures and variously interpreted. Many measures were used only once, so only a small part of the available research evidence could be synthesized in the meta-analysis. The meta-analysis was undertaken using data from five commonly used tests of EF drawn from 18 studies. This revealed consistent evidence for cognitive difficulties across all five EF tests. Research on EF in PD is characterized by a considerable lack of clarity with regard to measure selection and interpretation. The findings support the view that EF impairments are evident in PD. However, the clinical significance of the cognitive abnormalities reported has yet to be clarified.

Premotor cognitive status in a cohort of incident Parkinson disease patients (NEDICES)

BACKGROUND

A variety of symptoms may precede the classical motor features of Parkinson disease (PD). However, it is not known whether cognitive dysfunction precedes the motor phase of PD. We examined whether patients with incident PD had had global cognitive function disturbances three years prior to diagnosis when compared with matched controls in a cohort of community-dwelling subjects.

METHODS

All participants were age 65 years or older (median 76 years) and were enrolled in the Neurological Disorders in Central Spain (NEDICES) study in central Spain. We identified all participants with incident PD (N=23), diagnosed in the follow-up examination (1997-1998), who had performed an expanded 37-item version of the Mini-Mental State Examination (37-MMSE) at the baseline evaluation (1994-1995). These 23 were 1:4 matched to 92 controls.

RESULTS

Baseline 37-MMSE scores were 27.9±4.9 (28) in PD patients and 28.7±6.5 (31) in controls (p=0.212). There were no patient-control differences in orientation, immediate recall, attention and calculation, memory recall, language, or visuospatial copying. In analyses that adjusted for several possible confounding factors, there were no case-control differences.

CONCLUSIONS

In this population-based sample, patients with incident PD did not have evidence of significant global cognitive function disturbances three years prior to their diagnosis when compared with matched controls. Our data suggest that global cognitive dysfunction does not precede the diagnosis of PD.

Characteristics of executive function impairment in Parkinson's disease patients without dementia

Executive function impairments in Parkinson's disease (PD) are well documented. However, uncertainties remain regarding the impact of these deficits on other areas of cognitive functioning. The goal of this study was to provide a comprehensive assessment of cognitive characteristics in patients with PD without dementia and to assess how any such deficits affected other areas of cognitive functioning. Forty PD patients without dementia were compared to healthy controls using measures of attention and speed of processing and a comprehensive set of executive function tests including working memory, planning, and problem solving. Measures of memory/learning and visuospatial skills were also included to examine the relationship between aspects of executive function and other areas of cognition. Patients with PD showed deficits on measures of executive function, problem solving, and visuospatial skills. However, they were unimpaired on measures of planning, attention, and memory/learning. Deficits in problem solving were only evident for tasks with a high visuospatial content and were no longer significant when visuospatial skills were controlled for. While deficits in executive function and visuospatial skills were apparent for PD patients compared to controls, many aspects of cognition remained intact. These can provide a focus for cognitive intervention strategies that can be effective in delaying decline for PD patients.

[Gait disorders in Parkinson's disease: and pathophysiological approaches]

Gait disorders and axial symptoms are the main therapeutic challenges in advanced Parkinson's disease (PD). Gait disorders in PD are characterized by spatial and temporal dysfunction. Gait hypokinesia is the first to appear and is responsible for the decrease in velocity. A good sensitivity to the levodopa is well established. Morris et al. [Morris ME, Iansek R, Matyas TA, Summers JJ. Ability to modulate walking cadence remains intact in Parkinson's disease. J Neurol Neurosurg Psychiatry 1994a;57(12):1532-4; Morris ME, Iansek R, Matyas TA, Summers JJ. The pathogenesis of gait hypokinesia in Parkinson's disease. Brain 1994b;117(Pt. 5):1169-81; Morris ME, Iansek R, Matyas TA, Summers JJ. Stride length regulation in Parkinson's disease. Brain 1996;119:551-68] demonstrated that the ability to modulate walking cadence remains intact in PD, and could correspond to a compensatory mechanism. More advanced disease stages of the disease are characterized by abnormal temporal parameters (such as stride length variability, stride time variability and cadence elevation) which are unresponsive to levodopa therapy and may be correlated with the occurrence of falls and freezing of gait (FOG). Lastly, postural instability also results in falls and is poorly responsive to levodopa. A link between gait impairment and frontal disorders has recently been suggested. After a few years of evolution, paradoxical episodic phenomena are described: festination ("hastening gait" with rapid small, short steps) and FOG (involuntary and sudden cessation of gait). Both symptoms are often incapacitating for PD patients, because of their resultant loss of independence and their poor response to levodopa therapy. Kinematical studies of FOG revealed a decrease in velocity, stride length and an exponential increase in cadence, prior to a FOG episode. New approaches (functional MRI, wavelets...) should offer new perspectives concerning these disabling symptoms.

Role of working memory components in planning performance of individuals with Parkinson's disease

The current study investigated the involvement of all four components of Baddeley's [Baddeley, A. D. (2000). The episodic buffer: A new component of working memory? Trends in Cognitive Sciences, 4, 417-423] revised working memory model in deficits of planning accompanying Parkinson's disease (PD). PD resulted in poorer formulation and execution of plans, as measured by the Tower of London task. PD also reduced the efficiency of the episodic buffer and central executive components of working memory, but did not influence storage of verbal or visuospatial information. Planning deficits in PD were particularly linked to problems in integrating multimodal short-term information with long-term memory (episodic buffer). These results emphasize the importance of integrative and executive processing in cognitive problems in PD, rather than simple memory deficits.

A common cognitive profile in elderly fallers and in patients with Parkinson's disease: the prominence of impaired executive function and attention

The present study examined the cognitive profile of elderly fallers relative to healthy elderly controls and patients with Parkinson's disease (PD), a positive-control group, using a computerized battery. Fallers performed more poorly than controls on executive function, attention, and motor skills, but performed comparably on memory, information processing and the Mini-Mental State Examination. A similar profile was evident for PD patients. However, unlike PD patients, fallers were abnormally inconsistent in their reaction times. These findings indicate that elderly fallers may have a unique cognitive processing deficit (i.e., variability of response timing) and underscore the importance of executive function and attention as potential targets for fall risk screening and interventions.

Training of executive functions in Parkinson's disease

Cognitive disturbances are common in Parkinson's disease (PD). Examination of cognitive function often reveals deficits in executive functions, including maintenance and inhibition of attention, flexibility in thinking, and planning. The involvement of the dopaminergic system in cognitive executive functions has been suggested by numerous studies. The aim of the present study was to analyze the effect of cognitive training on cognitive performance of PD-patients (N=26). Half of the patients participated in a cognitive training regimen, while the other patients only received standard treatment. The outcome showed improved performance of the group with cognitive treatment in two executive tasks after the training period, while no improvement was seen in the standard-treatment group. The results indicate that specific training is required for improvement of executive functions, while general rehabilitation is not sufficient. Thus, PD-patients might benefit from a short-term cognitive executive function training program that is tailored to the individual patient's needs.

Dual tasking, gait rhythmicity, and Parkinson's disease: Which aspects of gait are attention demanding?

Cognitive function and the performance of a secondary, dual task may affect certain aspects of gait, but the relationships between cognitive function and gait are not well understood. To better understand the motor control of gait and the relationship between cognitive function and gait, we studied cognitive function and the effects of different types of dual tasking on the gait of patients with Parkinson's disease (PD) and controls, contrasting measures of gait automaticity and rhythmicity with other features. Patients with idiopathic PD (n=30; mean age 71.8 year) with moderate disease severity (Hoehn and Yahr Stage 2--3) were compared to age and gender-matched healthy controls (n=28). Memory and executive function were also assessed. In both groups, gait speed decreased in response to dual tasking, in a parallel fashion. For the PD group only, gait variability increased compared to usual walking. Executive function was significantly worse in the PD group, while memory was not different in the two groups. Executive function measures were significantly correlated with gait variability during dual tasking, but not during usual walking. These findings demonstrate that regulation of gait variability and rhythmicity is apparently an automatic process that does not demand attention in healthy adults. In patients with PD, however, this ability becomes attention-demanding and worsens when subjects perform secondary tasks. Moreover, the associations between executive function and gait variability suggest that a decline in executive function in PD may exacerbate the effects of dual tasking on gait, potentially increasing fall risk.

Psychiatric aspects of Parkinson's disease

PURPOSE OF REVIEW

Recently, there has been much interest and rapid progress in understanding the neuropsychiatry of Parkinson's disease. This paper reviews the most important papers published during 2004 on dementia and cognitive impairment, depression and psychosis in Parkinson's disease.

RECENT FINDINGS

Many new studies of cognitive impairment and dementia in Parkinson's disease have been published during 2004. Cognitive impairment has been demonstrated even during the first 1-2 years after onset of disease. Whereas executive and attentional impairment is typical, learning deficits occur early in some patients. Both functional and structural imaging suggest that in addition to fronto-subcortical deficits, temporal and parietal changes occur early as well. In the first large placebo-controlled trial, the cholinesterase inhibitor rivastigmine improved cognition, daily functioning and psychiatric symptoms without worsening of parkinsonism. The frequency and characteristics of depression, anxiety and hallucinations have been explored in several studies. Unfortunately, there is still little scientific evidence available to guide the treatment of these important aspects of Parkinson's disease, and adequately designed clinical trials are needed. Although subthalamic stimulation, in addition to improvement of movement, is frequently associated with some affective and cognitive improvement, permanent and significant worsening may occur in some. Future studies should aim at identifying at-risk patients, as well as identifying the optimal pharmacological and stimulation treatments for individual patients.

SUMMARY

These findings provide a deeper understanding of the neurobiological substrate of cognitive impairment and dementia in Parkinson's disease, and provide new information regarding the assessment and management of dementia and other neuropsychiatric aspects of Parkinson's disease.