Motor sequencing in Parkinson's disease: relationship to executive function and motor rigidity

Cortical Thickness Correlates of Go/No-go and Motor Sequencing in Mild Cognitive Impairment and Suspected Alzheimer Disease Dementia

BACKGROUND

While the cognitive hallmark of typical Alzheimer disease (AD) is impaired memory consolidation, increasing evidence suggests that the frontal lobes and associated executive functions are also impacted.

OBJECTIVE

We examined two neurobehavioral executive function tasks and associations with cortical thickness in patients diagnosed with mild cognitive impairment (MCI), suspected AD dementia, and a healthy control group.

METHODS

First, we compared group performances on a go/no-go (GNG) task and on Luria's Fist-Edge-Palm (FEP) motor sequencing task. We then examined correlations between neurobehavioral task performance and the thickness of frontal cortical regions, AD signature regions, broader unbiased brain regions, and white matter hyperintensities (WMH).

RESULTS

Participants with MCI performed worse than healthy controls, but better than participants with suspected AD dementia on both tasks. Both GNG and FEP (to a slightly greater extent) tasks showed diffuse associations with most AD signature regions and multiple additional regions within the temporal, parietal, and occipital cortices. Similarly, both tasks showed significant associations with all other cognitive tasks examined. Of the frontal regions examined, only the middle frontal gyrus and pars opercularis were associated with performance on these tasks. Interactions between the precuneus and transtemporal gyri were most predictive of GNG task performance, while the interaction between superior temporal and lingual gyri was most predictive of FEP task performance.

CONCLUSION

This study replicates difficulties with both GNG and FEP tasks in participants with MCI and AD dementia. Both tasks showed widespread associations with the cortical thickness of various brain structures rather than localizing to frontal regions, consistent with the diffuse nature of AD.

Impaired executive functioning mediates the association between aging and deterministic sequence learning

Sensitivity to the fixed ordering of actions and events, or deterministic sequence learning, is an important skill throughout adulthood. Yet, it remains unclear whether age deficits in sequencing exist, and we lack a firm understanding of which factors might contribute to age-related impairments when they arise. Though debated, executive functioning, governed by the frontal lobe, may underlie age-related sequence learning deficits in older adults. The present study asked if age predicts errors in deterministic sequence learning across the older adult lifespan (ages 55-89), and whether executive functioning accounts for any age-related declines. Healthy older adults completed a comprehensive measure of frontal-based executive abilities as well as a deterministic sequence learning task that required the step-by-step acquisition of associations through trial-and-error feedback. Among those who met a performance-based criterion, increasing age was positively correlated with higher sequencing errors; however, this relationship was no longer significant after controlling for executive functioning. Moreover, frontal-based executive abilities mediated the relationship between age and sequence learning performance. These findings suggest that executive or frontal functioning may underlie age deficits in learning judgment-based, deterministic serial operations.

Altered alpha and theta oscillations correlate with sequential working memory in Parkinson's disease

Daily activities such as preparing a meal rely on the ability to arrange thoughts and actions in the right order. Patients with Parkinson's disease have difficulties in sequencing tasks. Their deficits in sequential working memory have been associated with basal ganglia dysfunction. Here we demonstrate that altered parietal alpha and theta oscillations correlate with sequential working memory in Parkinson's disease. We included 15 patients with Parkinson's disease (6 women, mean age: 66.0 years), 24 healthy young (14 women, mean age: 24.1 years), and 16 older participants (7 women, mean age: 68.6 years). All participants completed a picture ordering task with scalp electroencephalogram (EEG) recording, where they arranged five pictures in a specific order and memorized them over a delay. When encoding and maintaining picture sequences, patients with Parkinson's disease showed a lower baseline alpha peak frequency with higher alpha power than healthy young and older participants. Patients with a higher baseline alpha power responded more slowly for ordered trials. When manipulating picture sequences, patients with Parkinson's disease showed a lower frequency of maximal power change for random versus ordered trials than healthy young and older participants. Healthy older participants showed a higher frequency of maximal power change than healthy young participants. Compared with patients with frequency of maximal power change in the alpha band (8-15 Hz), patients with frequency of maximal power change in the theta band (4-7 Hz) showed a higher ordering-related accuracy cost (random versus ordered) in the main task and tended to respond more slowly and less accurately in an independent working memory test. In conclusion, altered baseline alpha oscillations and task-dependent modulation of alpha and theta oscillations may be neural markers of poor sequential working memory in Parkinson's disease.

Altered event processing in persons with Parkinson's disease

Persons with Parkinson's disease (PD) often show particular problems in seemingly simple routines despite relatively preserved cognitive function. We therefore investigated the processing of everyday events on behavioral and neurophysiological levels in a PD and control group. The participants had to indicate via button press whether three sequentially presented sub-events described a previously defined event (e.g., going grocery shopping). Sub-event sequences were either correct or included an event that did not belong to the event (content violation), or events were chronologically wrong (temporal violation). During task execution event-related potentials (ERPs) were recorded. Generally, the PD group showed less accurate performance independently from task conditions, and reaction times to temporal violations were particularly slow compared to the control group. Regarding ERP results, the control group showed a right lateralized N400 effect in response to content violations, which was absent in the PD group indicating altered content event processing. Concerning the reanalysis of content event violations, the expression of late positive components (LPCs) was similar between both groups. Upon temporal violations, both groups also showed a LPC with a tendentially earlier onset in the PD group, resembling positive components indicative of novelty processing. Together, these findings suggest poor event prediction in PD, which may originate from weak event representation or retrieval and possibly relate to prevalent behavioral dysfunctions in everyday life in PD.

Altered neural oscillations during complex sequential movements in patients with Parkinson's disease

The sequelae of Parkinson's disease (PD) includes both motor- and cognitive-related symptoms. Although traditionally considered a subcortical disease, there is increasing evidence that PD has a major impact on cortical function as well. Prior studies have reported alterations in cortical neural function in patients with PD during movement, but to date such studies have not examined whether the complexity of multicomponent movements modulate these alterations. In this study, 23 patients with PD (medication "off" state) and 27 matched healthy controls performed simple and complex finger tapping sequences during magnetoencephalography (MEG), and the resulting MEG data were imaged to identify the cortical oscillatory dynamics serving motor performance. The patients with PD were significantly slower than controls at executing the sequences overall, and both groups took longer to complete the complex sequences than the simple. In terms of neural differences, patients also exhibited weaker beta complexity-related effects in the right medial frontal gyrus and weaker complexity-related alpha activity in the right posterior and inferior parietal lobules, suggesting impaired motor sequence execution. Characterizing the cortical pathophysiology of PD could inform current and future therapeutic interventions that address both motor and cognitive symptoms.

Fist-Edge-Palm (FEP) test has a high sensitivity in differentiating dementia from normal cognition in Parkinson's disease

BACKGROUND

The Fist-Edge-Palm (FEP) test takes 0.5-3 min to complete and is highly sensitive in differentiating Alzheimer's disease and frontotemporal dementia from normal cognition, but it has not yet been studied in Parkinson's disease (PD).

OBJECTIVE

To determine the sensitivity and specificity of the FEP test in screening patients with PD for cognitive impairment and dementia.

METHODS

PD patients were recruited and divided into three groups based on cognitive status: normal cognition, mild cognitive impairment (MCI) and dementia according to 2015 MDS clinical diagnostic criteria for PD and clinical dementia rating scale (CDR) assessment for cognitive status. MMSE, FEP and clock drawing test (CDT) were tested in all recruited PD patients. Chi-square test was used to compare the sensitivity of FEP and CDT in detecting PDD and PD-MCI.

RESULTS

A total of 108 PD patients were included: 52 normal cognition, 28 MCI, and 28 dementia. The sensitivity of FEP in differentiating PDD from PD-NC was 96.4% and the sensitivity for PD-MCI from PD-NC was 71.4%. The sensitivity of CDT in differentiating PDD from PD-NC was 71.4% and PD-MCI from PD-NC was 53.6%. The sensitivities of FEP and CDT were 83.9% and 62.5%, respectively, in identifying cognitive impairment (CDR ≥ 0.5) in PD patients.

CONCLUSION

FEP is a sensitive screening tool in differentiating PDD or PD-MCI from PD-NC, and it is much faster than MMSE and more sensitive than CDT. FEP may be a practical screening tool for daily clinical practice.

Examination of the Prefrontal Cortex Hemodynamic Responses to the Fist-Edge-Palm Task in Naïve Subjects Using Functional Near-Infrared Spectroscopy

The Fist-Edge-Palm (FEP) task, a manual hand task, has been used to detect frontal dysfunctions in clinical situations: its performance failures are observed in various prefrontal cortex (PFC)-related disorders, including schizophrenia. However, previous imaging studies reported that the performance of the FEP task activated motor-related areas, but not the PFC. Here, we aimed to investigate the relationships between the performance of the FEP task and PFC functions. Hemodynamic activity in the PFC, including the dorsolateral PFC (area 46) and frontal pole (area 10), was recorded. Healthy young subjects performed the FEP task as well as a palm tapping (PT) task (control task) three times. The subjects also completed a Wisconsin Card Sorting Test (WCST) and Schizotypal Personality Scale (STA) questionnaire. We found that hemodynamic activity (Oxy-Hb) in the PFC increased in the first trial of the FEP task but decreased considerably in the second and third trials compared to the PT task. The number of performance errors in the FEP task also decreased in the second and third trials. Error reduction (i.e., learning) in the FEP task between the first and second trials was negatively correlated with schizotypal trait and the number of perseveration errors in the WCST. Furthermore, changes in the PFC hemodynamic activity between the first and second trials were positively correlated with error reduction in the FEP task between the first and second trials, and negatively correlated with the number of perseveration errors in the WCST. These results suggest that learning in the FEP task requires PFC activation, which is negatively associated with perseveration errors in the WCST. The results further suggest that the FEP task, in conjunction with near-infrared spectroscopy, may be useful as a diagnostic method for various disorders with PFC dysfunction.

Subthalamic Nucleus Stimulation Impairs Sequence Processing in Patients with Parkinson's Disease

BACKGROUND

Maintaining and manipulating sequences online is essential for language and memory. In Parkinson's disease (PD), poor performance in sequencing tasks has been associated with basal ganglia dysfunction, especially subthalamic hyperactivity.

OBJECTIVE

This study is aimed to investigate the impact of high-frequency subthalamic nucleus (STN) deep brain stimulation (DBS) on sequence processing in PD.

METHODS

Twenty-nine patients with PD (17 women) completed a 'before/after' sentence task and a digit ordering task with STN DBS ON and OFF. In the sentence task, patients read a sequence of events expressed in the actual order of occurrence ('after' sentences) or reversed order ('before' sentences) for comprehension. In the digit task, patients recalled a sequence of ordered digits (ordered trials) or reordered and recalled random digits in ascending order (random trials). Volumes of tissue activated (VTAs) were estimated for the motor and associative STN.

RESULTS

Patients were slower with STN DBS ON versus OFF in both tasks, although their motor symptoms were significantly improved under DBS. In the sentence task, patients showed higher ordering-related reaction time costs ('before' > 'after') with DBS ON versus OFF. Moreover, patients with larger left associative VTAs, smaller total motor VTAs, and more daily exposure to dopaminergic drugs tended to show larger reaction time cost increases under DBS. In the digit ordering task, patients with too large or too small right associative VTAs tended to show larger reaction time cost increases under DBS.

CONCLUSION

Stimulating the STN, especially its associative part, might impair sequence processing in language and memory.

Effectiveness of sorting tests for detecting cognitive decline in older adults with dementia and other common neurodegenerative disorders: A meta-analysis

The demand for simple, accurate and time-efficient screens to detect cognitive decline at point-of-care is increasing. Sorting tests are often used to detect the 'executive' deficits that are commonly associated with behavioural-variant frontotemporal dementia (bvFTD), but their potential for use as a cognitive screen with older adults is unclear. A comprehensive search of four databases identified 142 studies that compared the sorting test performance (e.g. WCST, DKEFS-ST) of adults with a common neurodegenerative disorder (e.g. Alzheimer's disease, vascular dementia, bvFTD, Parkinson's disease) and cognitively-healthy controls. Hedges' g effect sizes were used to compare the groups on five common test scores (Category, Total, Perseveration, Error, Description). The neurodegenerative disorders (combined) showed large deficits on all scores (g -1.0 to -1.3), with dementia (combined subtypes) performing more poorly (g -1.2 to -2.1), although bvFTD was not disproportionately worse than the other dementias. Overall, sorting tests detected the cognitive impairments caused by common neurodegenerative disorders, especially dementia, highlighting their potential suitability as a cognitive screen for older adults.

Disentangling motor planning and motor execution in unmedicated de novo Parkinson's disease patients: An fMRI study

Many studies have used functional magnetic resonance imaging to unravel the neuronal underpinnings of motor system abnormalities in Parkinson's disease, indicating functional inhibition at the level of basal ganglia-thalamo-cortical motor networks. The study aim was to extend the characterization of functional motor changes in Parkinson's Disease by dissociating between two phases of action (i.e. motor planning and motor execution) during an automated unilateral finger movement sequence with the left and right hand, separately. In essence, we wished to identify neuronal dysfunction and potential neuronal compensation before (planning) and during (execution) automated sequential motor behavior in unmedicated early stage Parkinson's Disease patients. Twenty-two Parkinson's Disease patients (14 males; 53 ± 11 years; Hoehn and Yahr score 1.4 ± 0.6; UPDRS (part 3) motor score 16 ± 6) and 22 healthy controls (14 males; 49 ± 12 years) performed a pre-learnt four finger sequence (index, ring, middle and little finger, in order), either self-initiated (FREE) or externally triggered (REACT), within an 8-second time window. Findings were most pronounced during FREE with the clinically most affected side, where motor execution revealed significant underactivity of contralateral primary motor cortex, contralateral posterior putamen (sensorimotor territory), ipsilateral anterior cerebellum / cerebellar vermis, along with underactivity in supplementary motor area (based on ROI analyses only), corroborating previous findings in Parkinson's Disease. During motor planning, Parkinson's Disease patients showed a significant relative overactivity in dorsolateral prefrontal cortex (DLPFC), suggesting a compensatory overactivity. To a variable extent this relative overactivity in the DLPFC went along with a relative overactivity in the precuneus and the ipsilateral anterior cerebellum/cerebellar vermis Our study illustrates that a refined view of disturbances in motor function and compensatory processes can be gained from experimental designs that try to dissociate motor planning from motor execution, emphasizing that compensatory mechanisms are triggered in Parkinson's Disease when voluntary movements are conceptualized for action.

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Dissociated activations in early stage PD for motor planning and motor execution

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PD patients show frontal-parietal network compensation during self-initiated movement.

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Compensation for an impaired basal ganglia-premotor circuit occurs during planning.

Greater naturally occurring expressive suppression is associated with poorer executive functioning and motor-sequence learning among older adults

Objectives: Unusually high engagement in expressive suppression (i.e., purposeful regulation of overt affect) has been associated with poorer performance on executive functioning (EF) and motor-sequence learning tasks. As such, expressive suppression represents one possible source of fluctuations in executive test performance. However, the relationship between expressive suppression and EF and motor performance has not yet been examined in older adults, who are more prone to EF and motor fluctuations than are younger adults. The purpose of this study was to test whether greater self-reported, naturally occurring expressive suppression is related to poorer EF performance and motor-sequence learning in older adults. Method: One hundred and ten community-dwelling older adults completed a self-report measure of expressive suppression, a battery of EF tests, and a computer-based measure of motor-sequence learning. Results: As expected, higher self-reported burden of expressive suppression in the 24 hours prior to testing was related to poorer performance on EF tests and on multiple aspects of motor-sequence learning (action planning latencies and sequencing errors) even after accounting for age, depressive symptoms, and component processes (e.g., processing speed). Conclusions: The current results suggest that naturally occurring expressive suppression depletes EF, which builds on previous findings from experimental studies that show that expressive suppression leads to reduced EF performance. Furthermore, this effect can be captured using self-report methods. These findings highlight expressive suppression as one source of intraindividual fluctuations in executive and motor functioning, which likely place older adults at risk for both functional and motor lapses (e.g., medication mistakes, falls).

Impaired serial ordering in nondemented patients with mild Parkinson's disease

The ability to arrange thoughts and actions in an appropriate serial order (the problem of serial order) is essential to complex behaviors such as language, reasoning and cognitive planning. Patients with Parkinson’s disease (PD) perform poorly in tasks that rely on the successful rearrangement of working memory representations. We hypothesized that serial ordering is impaired in nondemented patients with mild PD. We recruited 49 patients with mild idiopathic PD (Hoehn and Yahr Scale 1–2.5) and 51 matched healthy adults. Nineteen patients had normal global cognition (PD-NC, Montreal Cognitive Assessment, MoCA≥26/30) and thirty patients had mild cognitive impairment (PD-MCI, 21≤MoCA≤25). All participants underwent three working memory assessments: two experimental tests that require reordering random digits following a particular rule (adaptive digit ordering test and digit span backward test) and a control test that requires maintaining but no reordering (digit span forward test). PD-NC and PD-MCI patients performed significantly worse (with lower test scores and larger ordering costs) than healthy controls in both digit ordering and backward tests, although they performed normally in the forward test. The ordering cost increased as a function of age across groups, indicating an aging-related decline in the ability of serial ordering. However, individual patients’ task performances were not correlated with their severity or duration of motor symptoms, or daily exposure to dopaminergic drugs. These results suggested that serial ordering deficits exist in early stages of PD, prior to subtle changes in global cognition and in parallel with motor symptoms.

Implicit Motor Sequence Learning in Individuals with Parkinson Disease: A Meta-Analysis

BACKGROUND

Deficits in implicit motor sequence learning (IMSL) in individuals with Parkinson disease (PD) compared to age matched healthy controls (HC) are unclear.

OBJECTIVE

The purpose of this paper is to present results of a systematic review with a meta-analysis examining the hypothesis that IMSL is impaired in individuals with PD when compared to HC.

METHODS

Fifteen articles met our final criteria and assessed 299 individuals with PD and 244 HC. Raw mean and standard deviation data for the final block of repeated and final block of random practice trials were obtained to calculate sequence-specific learning (SSL) for individuals with PD and HC. Forest plots were used to depict the comparison of the groups by assessing standardized mean difference with random effect size.

RESULTS

A significant and moderate effect size, 0.83 was found suggesting that individuals with PD demonstrated impaired SSL of motor sequences compared to HC.

CONCLUSIONS

Individuals with PD demonstrate a deficit compared with HC in their ability to implicitly learn motor tasks. Existing research lacks detail on the factors which may alter IMSL, either negatively or positively, such as the design features of current IMSL paradigms utilized and disease-specific characteristics. Successful motor rehabilitation of functional tasks in persons with PD is highly dependent on IMSL; therefore, an improved knowledge of the influence of these additional variables is critical.

Reported Expressive Suppression in Daily Life Is Associated with Slower Action Planning

Objectives Growing evidence demonstrates that (a) executive functioning (EF) becomes deleteriously affected by engagement in the emotion regulation strategy known as expressive suppression and (b) EF shows considerable functional and neuroanatomical overlap with motor output. The current study aimed to bridge these two literatures by examining the relationships between naturally occurring expressive suppression and several different aspects of motor output, including action planning, action learning, and motor-control speed and accuracy. In addition, we investigated whether any identified relationships could be explained by EF. Methods Fifty-one healthy young adults completed selected subtests from the Delis-Kaplan Executive Function System as indices of EF, a self-report measure of expressive suppression, and a computerized motor sequencing task (Push Turn Taptap task; PTT) designed to assess action planning, action learning, and motor control speed and accuracy. Results Hierarchical regressions using each aspect of PTT performance as the dependent variable revealed that higher than usual self-reported expressive suppression on the day of testing (relative to the 2 weeks preceding testing) was associated with longer action-planning latencies. This relationship was fully explained by EF. No other PTT variables related to expressive suppression on the day of testing. Conclusions These results suggest that increased expressive suppression in daily life is associated with slower action planning, an aspect of motor output that is reliant on EF, highlighting the importance of factors that lead to intra-individual fluctuations in EF and motor performance. (JINS, 2016, 22, 671-681).

Influence of dual-task on sit-to-stand-to-sit postural control in Parkinson's disease

Postural control deficits are the most disabling aspects of Parkinson's disease (PD), resulting in decreased mobility and functional independence. The aim of this study was to assess the postural control stability, revealed by variables based on the centre of pressure (CoP), in individuals with PD while performing a sit-to-stand-to-sit sequence under single- and dual-task conditions. An observational, analytical and cross-sectional study was performed. The sample consisted of 9 individuals with PD and 9 healthy controls. A force platform was used to measure the CoP displacement and velocity during the sit-to-stand-to-sit sequence. The results were statistically analysed. Individuals with PD required greater durations for the sit-to-stand-to-sit sequence than the controls (p < 0.05). The anteroposterior and mediolateral CoP displacement were higher in the individuals with PD (p < 0.05). However, only the anteroposterior CoP velocity in the stand-to-sit phase (p = 0.006) was lower in the same individuals. Comparing the single- and dual-task conditions in both groups, the duration, the anteroposterior CoP displacement and velocity were higher in the dual-task condition (p < 0.05). The individuals with PD presented reduced postural control stability during the sit-to-stand-to-sit sequence, especially when under the dual-task condition. These individuals have deficits not only in motor performance, but also in cognitive performance when performing the sit-to-stand-to-sit sequence in their daily life tasks. Moreover, both deficits tend to be intensified when two tasks are performed simultaneously.

Basal ganglia and cortical networks for sequential ordering and rhythm of complex movements

Voluntary actions require the concurrent engagement and coordinated control of complex temporal (e.g., rhythm) and ordinal motor processes. Using high-resolution functional magnetic resonance imaging (fMRI) and multi-voxel pattern analysis (MVPA), we sought to determine the degree to which these complex motor processes are dissociable in basal ganglia and cortical networks. We employed three different finger-tapping tasks that differed in the demand on the sequential temporal rhythm or sequential ordering of submovements. Our results demonstrate that sequential rhythm and sequential order tasks were partially dissociable based on activation differences. The sequential rhythm task activated a widespread network centered around the supplementary motor area (SMA) and basal-ganglia regions including the dorsomedial putamen and caudate nucleus, while the sequential order task preferentially activated a fronto-parietal network. There was also extensive overlap between sequential rhythm and sequential order tasks, with both tasks commonly activating bilateral premotor, supplementary motor, and superior/inferior parietal cortical regions, as well as regions of the caudate/putamen of the basal ganglia and the ventro-lateral thalamus. Importantly, within the cortical regions that were active for both complex movements, MVPA could accurately classify different patterns of activation for the sequential rhythm and sequential order tasks. In the basal ganglia, however, overlapping activation for the sequential rhythm and sequential order tasks, which was found in classic motor circuits of the putamen and ventro-lateral thalamus, could not be accurately differentiated by MVPA. Overall, our results highlight the convergent architecture of the motor system, where complex motor information that is spatially distributed in the cortex converges into a more compact representation in the basal ganglia.

Apraxic agraphia following bithalamic damage

OBJECTIVES

Apraxic agraphia (AA) is a peripheral writing disorder generally considered to result from a causative lesion in the parietal and/or prefrontal lobe of the language dominant hemisphere (De Smet, Engelborghs, Paquier, De Deyn, & Mariën, 2011). De Smet et al. (2011), however, confirmed that AA might be associated with lesions outside the typical language areas such as the cerebellum or the thalamus. We report a 32-year-old ambidextrous patient with a left frontal lobectomy who following bilateral thalamic damage developed AA.

METHOD

Detailed neurolinguistic and neurocognitive test results were obtained after resection of an extensive left frontal lobe tumour by means of a set of standardised tests. Repeated investigations were performed after a bithalamic stroke. Functional imaging was performed by means of quantified SPECT.

RESULTS

Normal neurolinguistic test results were obtained after tumour resection. Neurocognitive test results, however, showed a dysexecutive syndrome and frontal behavioural deficits, including response inhibition. AA occurred after a bithalamic stroke while non-handwriting written language skills, such as typing, were normal. Quantified SPECT showed a significant bifrontal hypoperfusion.

CONCLUSION

Neurolinguistic follow-up findings and SPECT evidence in this unique patient with bithalamic damage for the first time indicate that AA in the alphabetic script may result from diaschisis affecting the frontal writing centre. The findings suggest that the thalamus is critically implicated in the neural network subserving graphomotor processing.

The contribution of trail making to the prediction of performance-based instrumental activities of daily living in Parkinson's disease without dementia

Performance on Part B of the Trail Making Test (TMT) contributes to the prediction of ability to complete instrumental activities of daily living (IADLs) in Parkinson's disease (PD). Although this suggests that cognitive flexibility is important in the everyday functioning of individuals with PD, this may not be the case as the TMT is multifactorial, involving motor speed, visual scanning, sequencing, and cognitive flexibility. The purpose of the current study was to determine which elements of the task contribute to the prediction of IADLs in a sample of 30 nondemented individuals with PD. Correlational analyses indicated strong relationships between a performance-based measure of IADLs and measures involving scanning, sequencing, and cognitive flexibility from the Delis-Kaplan Executive Function System (D-KEFS) TMT. Results from standard regressions indicated that measures of sequencing and level of depression but not scanning, cognitive flexibility, or demographic variables made a significant, independent contribution to the prediction of IADLs. These results suggest that the sequencing element of the TMT is paramount in the prediction of IADLs in PD.

Parkinson's disease progression: implicit acquisition, cognitive and motor impairments, and medication effects

Parkinson's disease (PD) symptoms have been collectively ascribed to malfunctioning of dopamine-related nigro-striatal and cortico-striatal loops. However, some doubts about this proposition are raised by controversies about the temporal progression of the impairments, and whether they are concomitant or not. The present study consists of a systematic revision of literature data on both functional PD impairments and dopaminergic medication effects in order to draw a coherent picture about the disease progression. It was done in terms of an explanatory model for the disruption of implicit knowledge acquisition, motor and cognitive impairments, and the effects of dopaminergic medication on these functions. Cognitive impairments arise at early stages of PD and stabilizes while disruption of implicit knowledge acquisition and motor impairments, are still in progression; additionally, dopaminergic medication reduces motor impairments and increases disruption of implicit knowledge acquisition. Since this model revealed consistency and plausibility when confronted with data of others studies not included in model's formulation, it may turn out to be a useful tool for understanding the multifaceted characteristics of PD.

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.

Persistent but less severe ataxia in long-term versus short-term abstinent alcoholic men and women: a cross-sectional analysis

BACKGROUND

Disturbed gait and balance are among the most consistent and salient sequelae of chronic alcoholism. Results of small sample longitudinal investigations have provided evidence that partial recovery of gait and balance functions in alcoholics may be achieved with abstinence. However, abstinence durations reported have been limited, and their power and generalizability have suffered from small sample sizes.

METHODS

In this study, we employed a cross-sectional approach to assess gait and balance functions in short-term (6 to 15 weeks) abstinent alcoholics (STAA; n = 70) and long-term (minimum 18 months, mean = 7.38 years) abstinent alcoholics (LTAA; n = 82). STAA and LTAA did not differ with respect to lifetime alcohol consumption, family drinking density, or years of education. In addition, we examined the effects of gender and alcohol use variables.

RESULTS

Our main findings were: (i) persistent disturbed gait and balance in STAA and disturbed standing balance in LTAA; (ii) overall less impaired performance of LTAA compared with STAA on gait and balance measures; and (iii) worse performance of STAA (but not LTAA) women, compared with men, on standing balance without visual control.

CONCLUSIONS

Our results suggest that alcoholics' gait and balance can continue to recover with long abstinence from alcohol, but that deficits persist, especially in eyes-closed standing balance. In addition, our results are consistent with more severe alcohol-induced ataxia in women than in men but suggest that with extended abstinence, women recover gait and balance function to a level comparable with men.

Contrast sensitivity in children with and without attention deficit hyperactivity disorder symptoms

Dopamine regulation may play a role in attention-deficit hyperactivity disorder (ADHD). Visual contrast sensitivity has been proposed as a measure of retinal dopamine that may predict frontal lobe dopamine levels. Individuals with disorders involving dopamine dysregulation (e.g., Parkinson's disease, Phenylketonuria) have shown poor contrast sensitivity. In this study, 110 6- to 13-year-old children with and without ADHD completed a task measuring visual contrast sensitivity. As predicted, contrast sensitivity was significantly worse in children with ADHD-Combined Type than controls. Contrast sensitivity was significantly correlated with inattention and hyperactivity. However, unlike many neuropsychological studies of ADHD, only hyperactivity accounted for unique variance.

The instrumented timed up and go test: potential outcome measure for disease modifying therapies in Parkinson's disease

The Timed Up and Go (TUG) test has been used to assess balance and mobility in Parkinson's Disease (PD). However, it is not known if this test is sensitive to subtle abnormalities present in early stages of the disease, when balance and gait problems are not clinically evident but may be detected with instrumented analysis of movement. We hypothesise that postural transitions and arm swing during gait will be the most sensitive characteristics of the TUG for early PD. In the present study, we instrumented the TUG test (iTUG) using portable inertial sensors, and extended the walking distance from 3 m (traditional TUG) to 7 m. Twelve subjects with early-to-moderate, untreated PD and 12 healthy individuals participated. Our findings show that although the stopwatch measure of TUG duration did not detect any abnormalities in early-to-mid-stage PD, the peak arm swing velocity on the more affected side, average turning velocity, cadence and peak trunk rotation velocity were significantly slower. These iTUG parameters were also correlated with the Unified Parkinson's Disease Rating Motor Scale. Thus, the iTUG test is sensitive to untreated PD and could potentially detect progression of PD and response to symptomatic and disease-modifying treatments.

Estrogen, testosterone, and sequential movement in men

Behavioral and physiological data suggest that the striatal dopaminergic system is important in the production and execution of sequential movements. Striatal function is also modulated by sex hormones, and previous studies show that estradiol is related to sequential movement in women. The authors examined whether sex hormones are involved in the production of sequential movement in healthy older and younger men. Testosterone was modified for a 6-week period such that levels in older men matched those of younger men, the conversion of testosterone to estradiol was blocked, the production of testosterone was blocked, or the men received no treatment (placebo). Sequential movement was measured before and after hormone treatment. Older men were slower and more accurate than younger men on the sequential movement task pre- and posttreatment. Hormone manipulation had no effect on movement speed. Hormone levels were not correlated with sequential movement performance in either older or younger men, suggesting that sex hormones do not modulate sequential movement in men, and hormone replacement may not restore a loss of sequential movement ability in elderly men or men with Parkinson's disease.

Cognitive and behavioural impairment in Parkinson's disease

Although Parkinson's disease (PD) has been considered to primarily affect motor abilities, increasing emphasis is being placed on cognitive and behavioural impairment in this disorder. Depression, dementia, psychosis and impulse control disorders have a major impact on quality of life for both patients and families. This article reviews cognitive and behavioural disturbances in PD and their relation to affective and motor symptoms, treatment of dementia associated with PD, and treatment approaches to psychosis in PD. We also discuss similarities between the dementia of PD and dementia with Lewy bodies.

Disruption of reciprocal coordination by a medial frontal stroke sparing the corpus callosum

Aleksandr Luria described several tests of higher motor function, including the "reciprocal coordination" test of bimanual coordination. Although these tests are commonly used to assess frontal lobe function, their specific neuroanatomic underpinnings are not completely understood. We describe a man with a medial frontal stroke sparing the corpus callosum with a defect in Luria's reciprocal coordination test but otherwise intact motor abilities, including other tests of higher motor function.

The missing link between action and cognition

The study of the neural correlates of motor behaviour at the systems level has received increasing consideration in recent years. One emerging observation from this research is that neural regions typically associated with cognitive operations may also be recruited during the performance of motor tasks. This apparent convergence between action and cognition - domains that have most often been studied in isolation - becomes especially apparent when examining new complex motor skills such as those involving sequencing or coordination, and when taking into account external (environment-related) factors such as feedback availability and internal (performer-related) factors such as pathology. Neurally, overlap between action and cognition is prominent in frontal lobe areas linked to response selection and monitoring. Complex motor tasks are particularly suited to reveal the crucial link between action and cognition and the generic brain areas at the interface between these domains.

A scale-free systems theory of motivation and addiction

Scale-free organizations, characterized by uneven distributions of linkages between nodal elements, describe the structure and function of many life-based complex systems developing under evolutionary pressures. We explore motivated behavior as a scale-free map toward a comprehensive translational theory of addiction. Motivational and behavioral repertoires are reframed as link and nodal element sets, respectively, comprising a scale-free structure. These sets are generated by semi-independent information-processing streams within cortical-striatal circuits that cooperatively provide decision-making and sequential processing functions necessary for traversing maps of motivational links connecting behavioral nodes. Dopamine modulation of cortical-striatal plasticity serves a central-hierarchical mechanism for survival-adaptive sculpting and development of motivational-behavioral repertoires by guiding a scale-free design. Drug-induced dopamine activity promotes drug taking as a highly connected behavioral hub at the expense of natural-adaptive motivational links and behavioral nodes. Conceptualizing addiction as pathological alteration of scale-free motivational-behavioral repertoires unifies neurobiological, neurocomputational and behavioral research while addressing addiction vulnerability in adolescence and psychiatric illness. This model may inform integrative research in defining more effective prevention and treatment strategies for addiction.

Parkinsonian deficits in context-dependent regulation of standing postural control

This study explored whether patients with Parkinson's disease alter the regulation of upright standing according to constraints imposed by the environmental context. The provision of context-dependent adaptations was inferred from the presence of adjustments to standing postural control that would serve to reduce fall risk when balance was challenged by a threatening environmental context. Participants were asked to stand as still as possible in two environmental context conditions that differed in the level of imposed postural threat: LOW threat and HIGH threat. Eight levodopa dependent patients with Parkinson's disease (PD) and eight age-matched control subjects (CTRL) provided the subject sample. PD patients were tested following a 12-h withdrawal of anti-Parkinsonian medications and approximately 1h post-medication. The CTRL group showed altered postural control in the HIGH threat condition, in a manner that was indicative of appropriate context-dependent regulation of standing. PD patients, in the non-medicated or medicated states, did not modify stance regulation when the environmental context heightened postural threat. Our results extend the current understanding of Parkinsonian deficits in the context-dependent regulation of postural control to include upright standing.

Quantitative measurement of trunk rigidity in parkinsonian patients

We aimed to develop an objective measurement to quantify trunk rigidity in patients with Parkinson's disease (PD), and to examine its reliability, validity and sensitivity in differentiating PD patients from control subjects. In Study 1, an isokinetic dynamometer was employed to assess trunk rigidity in 6 PD patients and 6 healthy controls. Passive trunk flexion and extension at 4 angular velocities were applied and resistive torques were recorded. Both work done and resistive peak torques to passive trunk flexion (Torque(PF)) and extension (Torque(PE)) were found to be highly reliable within a 2-day interval in PD patients and control subjects. In Study 2, trunk muscle tone was compared between 15 PD and 15 control subjects. Significantly higher muscle tone, as shown by increases in work done, and in Torque(PF) and Torque(PE )at higher movement speeds, was found in PD patients. Within each subject group, resistive trunk muscle tone was found to increase with increasing velocity of passive movement, but the extent of increase was greater in PD patients. Our results thus suggest that the objective method developed by us was reliable and could differentiate trunk rigidity in PD patients from that of healthy subjects.

On the genesis of unilateral micrographia of the progressive type

We report a patient who, following a focal ischemic lesion of the left basal ganglia, developed right hand micrographia characterised by progressive reduction of letter size during writing (progressive micrographia). The patient did not show relevant cognitive impairments, but achieved pathological scores in tests for verbal fluency, and cognitive flexibility and monitoring. A systematic investigation of the writing performances demonstrated that micrographia showed a clear length effect in whatever writing style or task, while it was not observed in drawing, or in left hand writing to a comparable extent. Right hand progressive micrographia was not affected by a concurrent motor and cognitive load; instead, switching between two kinds of allographic responses and presenting one letter at a time in copying tasks reduced severity of micrographia significantly. These findings support the view that progressive micrographia in our patient could be ascribed to a defect in regulating the motor output on the basis of self-generated strategies. This conclusion would be consistent with neuroimaging evidence about the role of the basal ganglia in the control of motor sequencing, and could suggest that progressive micrographia might be associated with specific executive defects.

Learning and retention of movement sequences in Parkinson's disease

The purpose of this study was to examine motor learning and retention given extensive practice in two fundamentally different movement sequences. One sequence was a memory-driven task (performing a series of whole body positions from memory) and the other a context-driven task (buttoning). Practice took place over 3 weeks, with performance measured weekly; retention was measured weekly for 3 weeks after practice. There were 7 people with Parkinson's disease (PD) and 7 age-matched neurologically healthy people who participated in this study. Both groups improved performance on both tasks with practice, with the majority of the change for the PD group occurring between 1 and 2 weeks of practice. Although those with PD did not necessarily perform as well as age-matched controls, they learned both sequences in a manner similar to age-matched controls, and exhibited retention across the 3-week retention interval. If people with PD are given sufficient practice they can learn and retain both memory-based and context-driven movement sequences as well as age-matched controls. The results provide support for maintaining physical activity and for intervention through movement therapy.

Striatal and forebrain nuclei volumes: contribution to motor function and working memory deficits in alcoholism

BACKGROUND

Striatal structures are involved in dopaminergic alcohol reward mechanisms and aspects of motor control. Basal forebrain structures hold cholinergic mechanisms influencing memory formation, vulnerable to chronic alcoholism; however, alcoholism's effect on volumes of these structures has seldom been considered with in vivo measurement.

METHODS

We measured bilateral volumes of caudate nucleus, putamen, nucleus accumbens, and medial septal/diagonal band (MS/DB) in 25 men with alcohol dependence and 51 age-matched control men. Six alcoholic subjects had been drinking recently, and 19 had been sober.

RESULTS

Volumes of caudate and putamen were smaller in the alcoholics than in the control subjects, regardless of length of sobriety. Recent drinkers showed greater deficits in nucleus accumbens than sober alcoholics. Putamen volume was positively correlated with grip strength; MS/DB volume was positively correlated with verbal working memory independently of the negative association between age-standardized MS/DB and age in alcoholics.

CONCLUSIONS

Caudate and putamen volume deficits occur and endure in chronic alcoholism. Nucleus accumbens might be especially sensitive to recent alcohol exposure. Striatal volumes should be considered in functional imaging studies of alcohol craving that target striatal brain regions. The age-alcohol interaction for MS/DB volumes is consistent with a cholinergic mechanism for the working memory impairment observed in the alcoholics.