The impact of Parkinson’s disease on sequence learning: Perceptual pattern learning and executive function

Research progress on the application of anti-gravity treadmill in the rehabilitation of Parkinson's disease patients: a mini review

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by motor and non-motor symptoms. It is the second most common chronic progressive neurodegenerative disease. PD still lacks a known cure or prophylactic medication. Current treatments primarily address symptoms without halting the progression of PD, and the side effects of dopaminergic therapy become more apparent over time. In contrast, physical therapy, with its lower risk of side effects and potential cardiovascular benefits, may provide greater benefits to patients. The Anti-Gravity Treadmill is an emerging rehabilitation therapy device with high safety, which minimizes patients' fear and allows them to focus more on a normal, correct gait, and has a promising clinical application. Based on this premise, this study aims to summarize and analyze the relevant studies on the application of the anti-gravity treadmill in PD patients, providing a reference for PD rehabilitation practice and establishing a theoretical basis for future research in this area.

High-frequency multimodal training with a focus on Tai Chi in people with Parkinson's disease: a pilot study

Background and objectives

Cognitive decline is an important and common complication in patients with Parkinson's disease (PD) since it significantly reduces the quality of life. A breakthrough in treating and preventing cognitive decline in PD remains to be achieved. This study aimed to evaluate the effectiveness of high-frequency and intensive multimodal training in improving motor and cognitive function.

Methods

Twenty-eight patients diagnosed with idiopathic PD completed a comprehensive neuropsychological test battery and were neurologically examined. The patients of the intervention group (n = 15) underwent 2 weekly sessions of Tai Chi therapy over 4 weeks and participated in an individually tailored training program consisting of two modules (smartphone-based speech training and cognitive training). A matched control group consisted of n = 13 patients with PD who received computer-assisted cognitive training. The data were analyzed with repeated-measures ANOVA.

Results

Four weeks of high-frequency training showed significant effects on verbal and figural episodic memory and visuospatial function in the intervention group. Compared to the control group, the cognitive performance of the intervention group improved significantly in visuospatial function and figural episodic memory. A significant improvement was also shown in the intervention group in the Tinetti Mobility Test and the Epworth Sleepiness Scale. The significant effects in the Tinetti mobility test remained after the 6 months follow-up. After the intervention, the patients reported high motivation and satisfaction with the multimodal training.

Conclusion

In patients with PD, a multimodal training program not only improves gait and stability but may also contribute to improving cognition.

Clinical trial registration

ClinicalTrials.gov Identifier: NCT04103255; https://register.clinicaltrials.gov/prs/app/action/LoginUser?ts=1&cx=-jg9qo4.

Impaired perceptual phonetic plasticity in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative condition primarily associated with its motor consequences. Although much of the focus within the speech domain has focused on PD's consequences for production, people with PD have been shown to differ in the perception of emotional prosody, loudness, and speech rate from age-matched controls. The current study targeted the effect of PD on perceptual phonetic plasticity, defined as the ability to learn and adjust to novel phonetic input, both in second language and native language contexts. People with PD were compared to age-matched controls (and, for three of the studies, a younger control population) in tasks of explicit non-native speech learning and adaptation to variation in native speech (compressed rate, accent, and the use of timing information within a sentence to parse ambiguities). The participants with PD showed significantly worse performance on the task of compressed rate and used the duration of an ambiguous fricative to segment speech to a lesser degree than age-matched controls, indicating impaired speech perceptual abilities. Exploratory comparisons also showed people with PD who were on medication performed significantly worse than their peers off medication on those two tasks and the task of explicit non-native learning.

Cognition and motor learning in a Parkinson's disease cohort: importance of recall in episodic memory

Impaired motor learning in individuals with Parkinson's disease is often attributed to deficits in executive function, which serves as an important cognitive process supporting motor learning. However, less is known about the role of other cognitive domains and its association with motor learning in Parkinson's disease. The objective of this study was to investigate the associations between motor learning and multiple domains of cognitive performance in individuals with Parkinson's disease. Twenty-nine participants with Parkinson's disease received comprehensive neuropsychological testing, followed by practice of a bimanual finger sequence task. A retention test of the finger sequence task was completed 24 h later. Hierarchical linear regressions were used to examine the associations between motor learning (acquisition rate and retention) and cognitive performance in five specific cognitive domains, while controlling for age, sex, and years of Parkinson's disease diagnosis. We found that a higher acquisition rate was associated with better episodic memory, specifically better recall in visual episodic memory, in individuals with Parkinson's disease. No significant associations were observed between retention and cognitive performance in any domains. The association between motor acquisition and episodic memory indicates an increased dependency on episodic memory as a potential compensatory cognitive strategy used by individuals with Parkinson's disease during motor learning.

The Four Square Step Test for Assessing Cognitively Demanding Dynamic Balance in Parkinson's Disease Patients

Objective

The Four Square Step Test (FSST) is a tool that assesses dynamic balance during obstacle step-over. To date, few studies have used the FSST to measure balance in patients with Parkinson’s disease (PD). This study aimed to verify that patients with PD, even at the de novo early stage, take more time to perform the FSST and identify which factors, cognitive status or cardinal motor symptoms, are related most to FSST scores.

Methods

Thirty-five newly diagnosed drug-naïve patients with PD and 17 controls completed the FSST. The Unified Parkinson’s Disease Rating Scale (UPDRS), Hoehn and Yahr (H&Y) stage, spatiotemporal gait parameters, and neuropsychological test battery were also assessed in the PD group.

Results

Mean FSST performance time was 8.20 ± 1.61 seconds in patients with PD, which was significantly more than the control group (7.13 ± 1.10 seconds, p = 0.018). UPDRS part III total score and H&Y stage were not significantly associated with FSST, but among the UPDRS subscores, only the postural instability/gait disturbance subscore showed a significant association. Regarding the association between FSST and cognition, the Trail Making Test-B and the Color Word Stroop Test showed strongly inverse correlations with FSST (rho = -0.598 and -0.590, respectively). With respect to gait parameters, double support time was significantly associated with FSST score (rho = 0.342, p = 0.044); however, other parameters, including velocity and step length, were not associated with the FSST.

Conclusion

The FSST can be used in the clinic to assess dynamic balance with cognitive demands even in the early stages of PD.

Determinants of Dual-Task Training Effect Size in Parkinson Disease: Who Will Benefit Most?

BACKGROUND AND PURPOSE

Dual-task interventions show positive effects in people with Parkinson disease (PD), but it remains unclear which factors determine the size of these benefits. As a secondary analysis of the DUALITY trial, the aim of this study was to assess the determinants of the effect size after 2 types of dual-task practice.

METHODS

We randomly allocated 121 participants with PD to receive either integrated or consecutive dual-task training. Dual-task walking performance was assessed during (i) a backward digit span task (digit), (ii) an auditory Stroop task (Stroop), and (iii) a functional mobile phone task. Baseline descriptive, motor, and cognitive variables were correlated with the change in dual-task gait velocity after the intervention. Factors correlated with the change in dual-task gait velocity postintervention (P < 0.20) were entered into a stepwise forward multiple linear regression model.

RESULTS

Lower dual-task gait velocity and higher cognitive capacity (Scales for Outcomes in Parkinson's Disease-Cognition [ScopaCog]) at baseline were related to larger improvements in dual-task gait velocity after both integrated and consecutive dual-task training for all 3 tasks (β[gait] = -0.45, β[ScopaCog] = 0.34, R = 0.23, P < 0.001, for digit; β[gait] = -0.52, β[ScopaCog] = 0.29, R = 0.26, P < 0.001, for Stroop; and β[gait] = -0.40, β[ScopaCog] = 0.30, R = 0.18, P < 0.001, for mobile phone task).

DISCUSSION AND CONCLUSIONS

Participants with PD who showed a slow dual-task gait velocity and good cognitive functioning at baseline benefited most from the dual-task training, irrespective of the type of training and type of dual-task outcome.Video Abstract available for more insights from the authors (see Video, Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A242).

The benefits and mechanisms of exercise training for Parkinson's disease

Parkinson's disease (PD) is a significantly progressive neurodegenerative disease characterised by both motor and nonmotor disorders. The main pathological characteristics of PD consist of the loss of dopaminergic neurons and the formation of alpha-synuclein-containing Lewy bodies in the substantia nigra. Currently, the main therapeutic method for PD is anti-Parkinson medications, including levodopa, madopar, sirelin, and so on. However, the effect of pharmacological treatment has its own limitations, the most significant of which is that the therapeutic effect of dopaminergic treatments gradually diminishes with time. Exercise training, as an adjunctive treatment and complementary therapy, can improve the plasticity of cortical striatum and increase the release of dopamine. Exercise training has been proven to effectively improve motor disorders (including balance, gait, risk of falls and physical function) and nonmotor disorders (such as sleep impairments, cognitive function and quality of life) in PD patients. In recent years, various types of exercise training have been used to treat PD. In this review, we summarise the exercise therapy mechanisms and the protective effects of different types of exercise training on PD patients.

Auditory entrainment of motor responses in older adults with and without Parkinson's disease: An MEG study

Medical therapies applied to Parkinson's disease (PD) have advanced tremendously since the 1960's based on advances in our understanding of the underlying neurophysiology. Behavioral therapies, such as rhythmic auditory stimulation (RAS), have been developed more recently and demonstrated efficacy. However, the neural mechanisms of RAS are only vaguely understood. In this study, we examined the neurophysiology of RAS using magnetoencephalography (MEG) in a sample of older adults with (21 people) and without PD (23 participants). All participants underwent high-density MEG during a beat-based cued tapping task with rhythmic and non-rhythmic patterns, and the resulting data were analyzed using a Bayesian image reconstruction method. Complex wavelet based time-frequency decomposition was used to compute inter-trial phase locking factor (PLF) to auditory stimuli for left and right signal space projection vectors. Tapping with a rhythm compared to a non-rhythmic sequence resulted in differential brain activity in each group: (i) a greater activation of temporal, motor and parietal areas was found in healthy adults; (ii) a greater reliance on parietal and frontal gyri was found in PD participants. During rhythmic tapping, older adults without PD had significantly stronger neural activity in bilateral frontal, supplementary and primary motor areas compared to those with PD. Conversely, older adults with PD exhibited significantly stronger activity in the bilateral parietal regions, as well as the rolandic operculum and bilateral supramarginal gyri, relative to their healthy peers. These data suggest that RAS mobilizes diverse oscillatory networks; Healthy controls may shift to frontal areas mobilization whereas PD patients rely on parietal areas to a greater extent, which may reflect frontal network dysfunction with compensation in PD, and could serve as specific regions of interest for further RAS studies.

Dual vs. Single Tasking During Circular Walking: What Better Reflects Progression in Parkinson's Disease?

Background and Aim: Reliable, valid and sensitive measures of dual-task-associated impairments in patients with Parkinson's disease (PD) may reveal progressive deficits unnoticed under single-task walking. The aim of this study was to quantitatively identify markers of progressive gait deficits in idiopathic PD while walking over a circular trajectory condition in single-task walking and in different dual-task conditions: (1) circular walking while checking boxes on a paper sheet as fast as possible and (2) circular walking while performing subtraction of 7 as fast as possible. In addition, we aimed to study the added value of dual-tasking assessment over single (circular) walking task assessment in the study of PD progression.

Methods: The assessments were performed every 6 months over a (up to) 5 years period for 22 patients in early-stage PD, 27 patients in middle-stage PD and 25 healthy controls (HC). Longitudinal changes of 27 gait features extracted from accelerometry were compared between PD groups and HCs using generalized estimating equations analysis, accounting for gait speed, age, and levodopa medication state confounders when required. In addition, dual-task-interference with gait and cognitive performance was assessed, as well as their combination.

Results: The results support the validity and robustness of some of the gait features already identified in our previous work as progression markers of the disease in single-task circular walking. However, fewer gait features from dual-task than from single-task assessments were identified as markers of progression in PD. Moreover, we did not clearly identify progressive worsening of dual-task-interference in patients with PD, although some group differences between early and middle stages of PD vs. the control group were observed for dual-task interference with the gait task and with the concurrent tasks.

Conclusions: Overall, the results showed that dual-tasking did not have added value in the study of PD progression from circular gait assessments. Our analyses suggest that, while single-task walking might be sensitive enough, dual-tasking may introduce additional (error) variance to the data and may represent complex composite measures of cognitive and motor performance.

Impaired cognitive modification for estimating time duration in Parkinson's disease

Parkinson's disease (PD) is associated with various cognitive impairments. However, the nature of cognitive modification in patients with PD remains to be elucidated. In the present study, we examined whether patients with PD could correct and maintain subjective time duration and line length estimation. After training sessions, in which participants repeatedly memorized either a duration or a length, we compared a learning performance in 20 PD patients with 20 healthy controls. In the case of duration in the PD patients, the learned durations immediately returned to baseline of pre-training within a few minutes. However, the patients’ ability to learn length estimation remained unimpaired. In contrast, healthy controls were able to retain the learned duration and length estimations. Time compression in PD's internal clock may become entrained to their altered duration estimation even after learning of accurate time duration. These deficits may be associated with disrupting cognitive modification in PD.

A Single Bout of Aerobic Exercise Improves Motor Skill Consolidation in Parkinson's Disease

Background: Motor learning is impaired in Parkinson’s disease (PD), with patients demonstrating deficits in skill acquisition (online learning) and consolidation (offline learning) compared to healthy adults of similar age. Recent studies in young adults suggest that single bouts of aerobic exercise (AEX), performed in close temporal proximity to practicing a new motor task, may facilitate motor skill learning. Thus, we aimed at investigating the effects of a single bout of aerobic cycling on online and offline learning in PD patients.

Methods: 17 PD patients (Hoehn and Yahr 1 – 2.5, age: 64.4 ± 6.2) participated in this crossover study. Immediately prior to practicing a novel balance task, patients either performed 30 min of (i) moderate intensity (60–70% VO_2max) aerobic cycling, or (ii) seated rest (order counterbalanced). The task required patients to stabilize a balance platform (stabilometer) in a horizontal position for 30 s. For each experimental condition, patients performed 15 acquisition trials, followed by a retention test 24 h later. We calculated time in balance (platform within ± 5° from horizontal) for each trial, and analyzed within- and between-subjects differences in skill acquisition (online learning) and skill retention (offline learning) using mixed repeated-measures ANOVA.

Results: We found that the exercise bout had no effect on performance level or online gains during acquisition, despite affecting the time course of skill improvements (larger initial and reduced late skill gains). Aerobic cycling significantly improved offline learning, as reflected by larger 24-h skill retention compared to the rest condition.

Conclusion: Our results suggest that a single bout of moderate-intensity AEX is effective in improving motor skill consolidation in PD patients. Thus, acute exercise may represent an effective strategy to enhance motor memory formation in this population. More work is necessary to understand the underlying mechanisms, the optimal scheduling of exercise, and the applicability to other motor tasks. Further, the potential for patients in later disease stages need to be investigated. The study was a priori registered at ClinicalTrials.gov (NCT03245216).

Protocol for a randomized comparison of integrated versus consecutive dual task practice in Parkinson's disease: the DUALITY trial

Background

Multiple tasking is an integral part of daily mobility. Patients with Parkinson’s disease have dual tasking difficulties due to their combined motor and cognitive deficits. Two contrasting physiotherapy interventions have been proposed to alleviate dual tasking difficulties: either to discourage simultaneous execution of dual tasks (consecutive training); or to practice their concurrent use (integrated training). It is currently unclear which of these training methods should be adopted to achieve safe and consolidated dual task performance in daily life. Therefore, the proposed randomized controlled trial will compare the effects of integrated versus consecutive training of dual tasking (tested by combining walking with cognitive exercises).

Methods and design

Hundred and twenty patients with Parkinson’s disease will be recruited to participate in this multi-centered, single blind, randomized controlled trial. Patients in Hoehn & Yahr stage II-III, with or without freezing of gait, and who report dual task difficulties will be included. All patients will undergo a six-week control period without intervention after which they will be randomized to integrated or consecutive task practice. Training will consist of standardized walking and cognitive exercises delivered at home four times a week during six weeks. Treatment is guided by a physiotherapist twice a week and consists of two sessions of self-practice using an MP3 player. Blinded testers will assess patients before and after the control period, after the intervention period and after a 12-week follow-up period. The primary outcome measure is dual task gait velocity, i.e. walking combined with a novel untrained cognitive task to evaluate the consolidation of learning. Secondary outcomes include several single and dual task gait and cognitive measures, functional outcomes and a quality of life scale. Falling will be recorded as a possible adverse event using a weekly phone call for the entire study period.

Discussion

This randomized study will evaluate the effectiveness and safety of integrated versus consecutive task training in patients with Parkinson’s disease. The study will also highlight whether dual task gait training leads to robust motor learning effects, and whether these can be retained and carried-over to untrained dual tasks and functional mobility.

Trial registration

Clinicaltrials.gov NCT01375413.

Implicit perceptual-motor skill learning in mild cognitive impairment and Parkinson's disease

OBJECTIVE

Implicit skill learning is hypothesized to depend on nondeclarative memory that operates independent of the medial temporal lobe (MTL) memory system and instead depends on cortico striatal circuits between the basal ganglia and cortical areas supporting motor function and planning. Research with the Serial Reaction Time (SRT) task suggests that patients with memory disorders due to MTL damage exhibit normal implicit sequence learning. However, reports of intact learning rely on observations of no group differences, leading to speculation as to whether implicit sequence learning is fully intact in these patients. Patients with Parkinson's disease (PD) often exhibit impaired sequence learning, but this impairment is not universally observed.

METHOD

Implicit perceptual-motor sequence learning was examined using the Serial Interception Sequence Learning (SISL) task in patients with amnestic Mild Cognitive Impairment (MCI; n = 11) and patients with PD (n = 15). Sequence learning in SISL is resistant to explicit learning and individually adapted task difficulty controls for baseline performance differences.

RESULTS

Patients with MCI exhibited robust sequence learning, equivalent to healthy older adults (n = 20), supporting the hypothesis that the MTL does not contribute to learning in this task. In contrast, the majority of patients with PD exhibited no sequence-specific learning in spite of matched overall task performance. Two patients with PD exhibited performance indicative of an explicit compensatory strategy suggesting that impaired implicit learning may lead to greater reliance on explicit memory in some individuals.

CONCLUSION

The differences in learning between patient groups provides strong evidence in favor of implicit sequence learning depending solely on intact basal ganglia function with no contribution from the MTL memory system.

Incidental encoding of the serial order of visual-spatial events in working memory

We investigated the incidental encoding in working memory of event serial order in tasks in which the relevant dimension was visual appearance, spatial location, or visual-spatial conjunction. The participants (n = 60) were asked whether two sequences were identical based on the relevant dimension, and to ignore changes in the irrelevant dimension, that is the order of events. Changes in serial order impaired the performance when sequences were identical; this effect was more pronounced in spatial sequences. It is suggested that the order was incidentally encoded with the relevant information to the task in an earlier stage in the information processing, which explains a different pattern of serial order effect according to the relevant dimension. Although encoded, the serial order may not have affected the visual storage in working memory because it might have been kept in a distinct subcomponent rather than the one that stores the visual characteristic. Moreover, the order may have affected spatial storage because the maintenance of this dimension might be related to a rehearsal mechanism based on serial order of sequence. This conclusion qualifies models that admit the architecture of working memory based on the specificity of encoding and functional interaction between subcomponents of storage.

Video game play (Dance Dance Revolution) as a potential exercise therapy in Huntington's disease: a controlled clinical trial

OBJECTIVE

To investigate the feasibility, acceptability, and safety of a supervised video game exercise program administered via Dance Dance Revolution in individuals with Huntington's disease.

DESIGN

A cross-over, controlled, single-blinded, six-week trial.

SETTING

Home-based.

PARTICIPANTS

Eighteen ambulatory individuals with Huntington's disease (seven male, mean age 50.7 SD 14.7).

INTERVENTIONS

Participants played the Dance Dance Revolution game with supervision and the handheld game without supervision for 45 minutes, two days per week for six weeks.

OUTCOME MEASURES

Game play performance and adherence, participant perceptions of the game, safety (vital signs, adverse health changes), spatiotemporal gait measures, Four-Square Step Test, Tinetti Mobility Test, Activities-Specific Balance Confidence Scale, and World Health Organization Quality of Life - Bref, before and after each intervention.

RESULTS

Most participants improved on game play, enjoyed playing the game, and wanted to continue playing after study completion. After playing Dance Dance Revolution, participants showed significant reductions in double support percentage (adjusted mean difference (95% confidence intervals): -2.54% (-4.75, -0.34) for forward walking and -4.18 (-6.89, -0.48) for backward walking) and those with less severe motor symptoms had reductions in heel-to-heel base of support during forward walking. The remaining measures were not significantly impacted by the intervention.

CONCLUSION

Dance Dance Revolution appears to be a feasible, motivating, and safe exercise intervention for individuals with Huntington's disease.

Diminished activation of motor working-memory networks in Parkinson's disease

Parkinson's disease (PD) is characterized by typical extrapyramidal motor features and increasingly recognized non-motor symptoms such as working memory (WM) deficits. Using functional magnetic resonance imaging (fMRI), we investigated differences in neuronal activation during a motor WM task in 23 non-demented PD patients and 23 age- and gender-matched healthy controls. Participants had to memorize and retype variably long visuo-spatial stimulus sequences after short or long delays (immediate or delayed serial recall). PD patients showed deficient WM performance compared to controls, which was accompanied by reduced encoding-related activation in WM-related regions. Mirroring slower motor initiation and execution, reduced activation in motor structures such as the basal ganglia and superior parietal cortex was detected for both immediate and delayed recall. Increased activation in limbic, parietal and cerebellar regions was found during delayed recall only. Increased load-related activation for delayed recall was found in the posterior midline and the cerebellum. Overall, our results demonstrate that impairment of WM in PD is primarily associated with a widespread reduction of task-relevant activation, whereas additional parietal, limbic and cerebellar regions become more activated relative to matched controls. While the reduced WM-related activity mirrors the deficient WM performance, the additional recruitment may point to either dysfunctional compensatory strategies or detrimental crosstalk from “default-mode” regions, contributing to the observed impairment.

Nonmotor manifestations in Parkinson disease

BACKGROUND

Although the diagnosis of Parkinson disease (PD) still relies mainly on the appearance of its classical motor features of resting tremor, rigidity, bradykinesia, and postural instability, nonmotor manifestations in PD are now recognized as an integral component of this multisystem disorder.

REVIEW SUMMARY

Nonmotor complications in PD occur commonly. The current understanding of cognitive dysfunction; neuropsychiatric manifestations including psychosis, impulsive control, and compulsive disorders, depression, anxiety and apathy; autonomic complications such as hypotension, erectile dysfunction, and urinary complications; sleep disorders and other nonmotor manifestations are summarized in this review.

CONCLUSION

Nonmotor complications often carry a greater impact than motor features in PD. Therefore, heightened awareness and proper recognition of these features are critical in improving a Parkinson patient's quality of life.

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.

Difficulty processing temporary syntactic ambiguities in Lewy body spectrum disorder

While grammatical aspects of language are preserved, executive deficits are prominent in Lewy body spectrum disorder (LBSD), including Parkinson's disease (PD), Parkinson's dementia (PDD) and dementia with Lewy bodies (DLB). We examined executive control during sentence processing in LBSD by assessing temporary structural ambiguities. Using an on-line word detection procedure, patients heard sentences with a syntactic structure that has high-compatibility or low-compatibility with the main verb's statistically preferred syntactic structure, and half of the sentences were lengthened strategically between the onset of the ambiguity and its resolution. We found selectively slowed processing of lengthened ambiguous sentences in the PDD/DLB subgroup. This correlated with impairments on measures of executive control. Regression analyses related the working memory deficit during ambiguous sentence processing to significant cortical thinning in frontal and parietal regions. These findings emphasize the role of prefrontal disease in the executive limitations that interfere with processing ambiguous sentences in LBSD.

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.

Representing serial action and perception

This article presents a review on the representational base of sequence learning in the serial reaction time task. The first part of the article addresses the major questions and challenges that underlie the debate on implicit and explicit learning. In the second part, the informational content that underlies sequence representations is reviewed. The latter issue has produced a rich and equivocal literature. A taxonomy illustrates that substantial support exists for associations between successive stimulus features, between successive response features, and between successive response-to-stimulus compounds. We suggest that sequence learning is not predetermined with respect to one particular type of information but, rather, develops according to an overall principle of activation contingent on task characteristics. Moreover, substantiating such an integrative approach is proposed by a synthesis with the dual-system model (Keele, Ivry, Mayr, Hazeltine, & Heuer, 2003).

From the cell to the clinic: a comparative review of the partial D₂/D₃receptor agonist and α2-adrenoceptor antagonist, piribedil, in the treatment of Parkinson's disease

Though L-3,4-dihydroxyphenylalanine (L-DOPA) is universally employed for alleviation of motor dysfunction in Parkinson's disease (PD), it is poorly-effective against co-morbid symptoms like cognitive impairment and depression. Further, it elicits dyskinesia, its pharmacokinetics are highly variable, and efficacy wanes upon long-term administration. Accordingly, "dopaminergic agonists" are increasingly employed both as adjuncts to L-DOPA and as monotherapy. While all recognize dopamine D(2) receptors, they display contrasting patterns of interaction with other classes of monoaminergic receptor. For example, pramipexole and ropinirole are high efficacy agonists at D(2) and D(3) receptors, while pergolide recognizes D(1), D(2) and D(3) receptors and a broad suite of serotonergic receptors. Interestingly, several antiparkinson drugs display modest efficacy at D(2) receptors. Of these, piribedil displays the unique cellular signature of: 1), signal-specific partial agonist actions at dopamine D(2)and D(3) receptors; 2), antagonist properties at α(2)-adrenoceptors and 3), minimal interaction with serotonergic receptors. Dopamine-deprived striatal D(2) receptors are supersensitive in PD, so partial agonism is sufficient for relief of motor dysfunction while limiting undesirable effects due to "over-dosage" of "normosensitive" D(2) receptors elsewhere. Further, α(2)-adrenoceptor antagonism reinforces adrenergic, dopaminergic and cholinergic transmission to favourably influence motor function, cognition, mood and the integrity of dopaminergic neurones. In reviewing the above issues, the present paper focuses on the distinctive cellular, preclinical and therapeutic profile of piribedil, comparisons to pramipexole, ropinirole and pergolide, and the core triad of symptoms that characterises PD-motor dysfunction, depressed mood and cognitive impairment. The article concludes by highlighting perspectives for clarifying the mechanisms of action of piribedil and other antiparkinson agents, and for optimizing their clinical exploitation.

Effect of dopaminergic medications on the time course of explicit motor sequence learning in Parkinson's disease

The capacity to learn new motor sequences is fundamental to adaptive motor behavior. The early phase of motor sequence learning relies on the ventral and anterior striatal circuitry, whereas the late phase relies on the dorsal and posterior striatal circuitry. Early Parkinson's disease (PD) is mainly characterized by dopaminergic denervation of the dorsal and posterior striatum while sparing anterior and ventral regions. Dopaminergic medication improves dorsal and posterior striatum function by compensating for the loss of dopamine. However, previous work has shown that dopaminergic medication interferes with the ventral and anterior striatum function by overdosing this relatively intact structure in early-state PD. Here we test whether these effects are also observed over the time course of motor sequence learning. Fourteen PD patients ON and OFF dopaminergic medications and 11 healthy age-matched control participants performed an explicit motor sequence learning task. When sequence learning was compared across different learning phases in patients ON and OFF medication, a significant impairment associated with medication was observed in the early relative to later phases of learning. The rate of learning in the early phase measured trial by trial in patients ON medication was significantly slower than that in controls and when patients were OFF medication. No significant impairment was found in the later learning phases. These results demonstrate that dopaminergic medications may selectively impair early-phase motor sequence learning. These results extend and generalize the dopamine overdose effects previously reported for (antero)ventral striatum-mediated cognitive tasks to motor sequence learning.