Freezing of gait and executive functions in patients with Parkinson's disease

Attentional set-shifting in Parkinson's disease patients with freezing of gait-acquisition and discrimination set learning deficits at the background?

Cognitive loading aggravates the freezing of gait (FoG), which is observed in approximately 50% of patients with Parkinson's disease (PD) in the advanced stages. To investigate whether a specific pattern of executive deficits, that is, attentional set-shifting and/or inhibitory control, are associated with FoG in PD, 30 PD patients with FoG (PD-FoG+) and 36 PD patients without FoG (PD-FoG-) and 22 control healthy subjects were examined with a comprehensive neuropsychological battery. Intra-Extra Dimensional Set shifting Test (IED) and Stop Signal Task (SST), selected from the Cambridge Automated Neuropsychological Battery (CANTAB battery), were administered to analyze set-shifting and motor inhibition, respectively. The IED task was significantly sensitive for differentiating between PD-FoG+ and PD-FoG- groups (p<.01), as well Adenbrook's clock drawing task (p=.033). By contrast, no differences emerged on any aspect of the SST task and other cognitive tasks. The attrition rate during the IED task showed that the problem in the PD-FoG+ group appeared at the pre-ID level, on the discrimination-learning set; the 32% PD-FoG+ subjects did not achieve the ID level of the task in comparison to negligible 4% of the PD-FoG- patients (p=.011). The logistic regression analysis, indicated the higher the IED stage successfully completed, the less likely presence of FoG in PD subjects. These results demonstrate that the complex cognitive-motor interplay might be responsible for FoG in PD and have had real life implication for the patients.

Freezing of gait subtypes have different cognitive correlates in Parkinson's disease

BACKGROUND

Freezing of gait (FOG) is a major concern for Parkinson's disease (PD) patients because it is a leading cause of falls and is associated with poor quality of life. The pathophysiology is unknown but it is hypothesized that it relates to cognitive abnormalities; particularly executive and visuospatial dysfunction. However, prior results have been discrepant. Pharmacologic subtypes of FOG include those that are responsive and unresponsive to levodopa.

OBJECTIVE

To determine whether executive and visuospatial dysfunction are associated specifically with the levodopa unresponsive subtype of FOG.

METHODS

135 PD subjects completed a single assessment included FOG questionnaire, UPDRS motor scale, comprehensive cognitive battery and measure of hallucinations. Analyses compared unresponsive (n = 16), responsive (n = 20) and no FOG (n = 99) subtypes.

RESULTS

The unresponsive subtype had a significantly older age of onset of PD than the responsive group (p = .03) and had worse motor scores (p = .003) than the no FOG group. Longer disease duration was associated with the responsive group compared to the no FOG group (p = .002). The unresponsive FOG group had significantly poorer visuospatial ability (p = .001) and executive functioning (p = .02) than both the no and responsive FOG subgroups. These latter groups were not significantly different. The responsive FOG group was associated with the presence of hallucinations.

CONCLUSION

Aside from pharmacological differences, unresponsive FOG is associated with executive and visuospatial dysfunction implicating frontostriatal pathways while responsive FOG is associated with hallucinations suggesting involvement of posterior cortical regions. Further study and treatment of FOG should include appropriate subtype classification.

Freezing of gait in Chinese patients with Parkinson disease

A total of 474 Chinese Parkinson disease (PD) patients were evaluated to explore the prevalence and clinical correlates of freezing of gait (FOG) in this cross-sectional study. Two hundred and twenty-one PD patients (46.62%) reported FOG (freezers). FOG occurred more frequently in older patients and patients with low limbs as the site of onset, longer disease duration and higher Hoehn and Yahr (H&Y) stage (P<0.05). After adjusting for confounding factors, the freezers had higher scores for the Unified PD Rating Scale (UPDRS) part III, Non-Motor Symptoms Scale (NMSS), PD Questionnaire 39 (PDQ-39), Hamilton Depression Scale (HAMD) and Hamilton Anxiety Scale (HAMA), and lower scores for the Mini-Mental status examination (MMSE), frontal assessment battery (FAB) and Montreal Cognitive Assessment (MoCA) compared with the non-freezers (P<0.05). The binary logistic regression analysis indicated that festination, falls, a high daily dose of levodopa, the use of a dopamine receptor agonist, a high H&Y stage, the severity of urinary symptoms and a high HAMD score were associated with FOG. FOG is a relatively common disabling symptom in Chinese PD patients. Patients that were older, or reported a longer disease duration, low limbs as the site of onset and a more severe disability were more likely to experience FOG. Non-motor symptoms, especially urinary symptoms and depression, may also be related to FOG.

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.

Cognitive contributions to gait and falls: evidence and implications

Dementia and gait impairments often coexist in older adults and patients with neurodegenerative disease. Both conditions represent independent risk factors for falls. The relationship between cognitive function and gait has recently received increasing attention. Gait is no longer considered merely automated motor activity but rather an activity that requires executive function and attention as well as judgment of external and internal cues. In this review, we intend to: (1) summarize and synthesize the experimental, neuropsychological, and neuroimaging evidence that supports the role played by cognition in the control of gait; and (2) briefly discuss the implications deriving from the interplay between cognition and gait. In recent years, the dual task paradigm has been widely used as an experimental method to explore the interplay between gait and cognition. Several neuropsychological investigations have also demonstrated that walking relies on the use of several cognitive domains, including executive-attentional function, visuospatial abilities, and even memory resources. A number of morphological and functional neuroimaging studies have offered additional evidence supporting the relationship between gait and cognitive resources. Based on the findings from 3 lines of studies, it appears that a growing body of evidence indicates a pivotal role of cognition in gait control and fall prevention. The interplay between higher-order neural function and gait has a number of clinical implications, ranging from integrated assessment tools to possible innovative lines of interventions, including cognitive therapy for falls prevention on one hand and walking program for reducing dementia risk on the other.

Clinical syndromes: Parkinsonian gait

Disturbances of gait manifest in almost all cases of Parkinson's disease (PD), often leading to loss of mobility and increased mortality. In this review a clinically oriented approach to gait disorders in different stages of PD is presented. In addition, interactions between motor behavior and mental processing will be discussed. Analyzing the clinical features of gait can be helpful to differentiate PD from atypical forms of parkinsonism. Bedside tests to distinguish parkinsonian gait disorders are reviewed. There is still an unmet need to effectively treat complex gait disturbances, which are frequently not responsive to dopamine replacement medication. We thus present current approaches for the management of dopa-refractory gait disorders.

Gait disorders

PURPOSE OF REVIEW

This article provides insight and reviews useful tools for the clinical assessment, understanding, and management of neurologic gait disorders.

RECENT FINDINGS

In recent years, our understanding of the physiology of human walking has steadily increased. The recognition of gait as a complex, "higher-order" form of motor behavior with prominent influence of mental processes has been an important new insight, and the clinical implications of gait disorders are increasingly being recognized. Better classification schemes, the redefinition of established entities (eg, senile gait), and new insights from research on degenerative disorders primarily affecting gait (eg, primary progressive freezing of gait) have become available.

SUMMARY

Gait disorders are directly correlated with poor quality of life and increased mortality. Because gait is very sensitive to any insult to the nervous system, its assessment should be carried out carefully in routine clinical practice. Disorders of locomotion are easily discernible to the naked eye. However, when examining gait, clinicians should bear in mind that the clinical phenotype is the net result of changes induced by the disease itself plus any compensations adopted by the patient to improve stability. This review presents a clinically oriented approach to gait disorders based on the dominant phenomenology and underlying pathophysiology, which are tightly connected. The authors conclude by proposing a practical management approach.

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.

Early phenotypic differences between Parkinson's disease patients with and without freezing of gait

BACKGROUND

Previous studies have associated freezing of gait in Parkinson's disease with the presence of specific phenotypic features such as mood disturbances, REM sleep behavior disorder and selective cognitive impairments. However, it is not clear whether these features are present in the earlier stages of disease or simply represent a more general pattern of progression. To investigate this issue, the current study evaluated motor, cognitive, affective and autonomic features as well as REM sleep behavior disorder in Parkinson's disease patients in the early stages of the condition.

METHODS

Thirty-eight freezers and fifty-three non-freezers with disease duration of less than five years and a Hoehn and Yahr stage of less than three were included in this study. The groups were matched on a number of key disease features including age, disease duration, motor severity and dopamine dose equivalence. Furthermore, patients were assessed on measures of motor, cognitive, affective and autonomic features, as well as REM sleep behavior disorder.

RESULTS

Compared to non-freezers, patients with freezing of gait had significantly more non-tremor symptoms and a selective impairment on executive functions, such as set-shifting ability and working memory. Freezers and non-freezers did not differ on measures of tremor, autonomic function, REM sleep behavior disorder, mood or more general cognition.

CONCLUSION

These results suggest the pathophysiological mechanisms underlying freezing of gait in the early clinical stages of Parkinson's disease are likely to be related to specific changes in the frontostriatal pathways rather than being due to brainstem or more diffuse neuropathology.

Gait-related brain activity in people with Parkinson disease with freezing of gait

Approximately 50% of people with Parkinson disease experience freezing of gait, described as a transient inability to produce effective stepping. Complex gait tasks such as turning typically elicit freezing more commonly than simple gait tasks, such as forward walking. Despite the frequency of this debilitating and dangerous symptom, the brain mechanisms underlying freezing remain unclear. Gait imagery during functional magnetic resonance imaging permits investigation of brain activity associated with locomotion. We used this approach to better understand neural function during gait-like tasks in people with Parkinson disease who experience freezing--"FoG+" and people who do not experience freezing--"FoG-". Nine FoG+ and nine FoG- imagined complex gait tasks (turning, backward walking), simple gait tasks (forward walking), and quiet standing during measurements of blood oxygen level dependent (BOLD) signal. Changes in BOLD signal (i.e. beta weights) during imagined walking and imagined standing were analyzed across FoG+ and FoG- groups in locomotor brain regions including supplementary motor area, globus pallidus, putamen, mesencephalic locomotor region, and cerebellar locomotor region. Beta weights in locomotor regions did not differ for complex tasks compared to simple tasks in either group. Across imagined gait tasks, FoG+ demonstrated significantly lower beta weights in the right globus pallidus with respect to FoG-. FoG+ also showed trends toward lower beta weights in other right-hemisphere locomotor regions (supplementary motor area, mesencephalic locomotor region). Finally, during imagined stand, FoG+ exhibited lower beta weights in the cerebellar locomotor region with respect to FoG-. These data support previous results suggesting FoG+ exhibit dysfunction in a number of cortical and subcortical regions, possibly with asymmetric dysfunction towards the right hemisphere.

Practical approach to freezing of gait in Parkinson's disease

Freezing of gait in Parkinson's disease and related disorders is common and very disabling. It usually occurs in the advanced stages, although mild forms may develop earlier. Freezing can occur on turning, in narrow spaces, immediately before reaching a destination, and in stressful situations. Dual tasking (motor or cognitive load) aggravates the problem. Freezing of gait in Parkinson's disease usually occurs in the 'off' rather than in the 'on' state. It is, therefore, not entirely drug-resistant; the first step in medical treatment is to ensure adequate dopaminergic stimulation to reduce the 'off' state. There is no good evidence for any specific drug to alleviate freezing. Visual or auditory cues are very helpful as behavioural therapy. Assistive devices, such as a wheeled walker sometimes help. Deep brain stimulation of the subthalamic nucleus may alleviate freezing in the 'off' state. Because of the complexity of freezing, individual patients need a careful assessment-particularly in relation to motor fluctuation-to optimise their treatment.

Low frontal assessment battery score as a risk factor for falling in patients with Hoehn-Yahr Stage III Parkinson's disease: a 2-year prospective study

BACKGROUND

Recently, we evaluated factors responsible for falling, including walking speed evaluated with the use of originally designed, suddenly narrowed paths, in patients with Hoehn-Yahr stage III PD. We prospectively studied the same cohort of patients with PD who were followed up for 2 years, to determine predictors of future falls.

METHODS

We performed clinical assessments and evaluated balance in 26 patients. A total of 19 variables including PD-related independent variables, balance investigation-related independent variables and gait independent-related variables were evaluated.

RESULTS

The Frontal Assessment Battery (FAB) score (p = 0.002), Tinetti balance (p = 0.009), and gait velocity (p = 0.001) were higher in fallers than in non-fallers. On multiple logistic regression analysis, the FAB score was related to falling (odds ratio = 3.328, p = 0.033, 95% confidence interval = 1.104-10.03). On the FAB, the scores of 'inhibitory control' and 'sensitivity to interference' were significantly lower in fallers than in non-fallers.

CONCLUSIONS

The use of the originally designed, suddenly narrowed path was the primary reason for demonstrating for the first time that a low FAB score is a risk factor for future falls. Calculation of the FAB score may be useful for predicting the risk of future falls.

Gait control and executive dysfunction in early schizophrenia

Dysexecutive functioning, which is described as an enduring core feature of schizophrenia, has been associated with gait disorders. However, few studies have reported gait disorders in schizophrenia patients. The objective of this study was to examine the association between executive dysfunction and gait performance in recent-onset schizophrenia patients using the dual task paradigm. Thirty-two subjects participated to the study: 17 with recent-onset schizophrenia and 15 healthy age-matched controls. Executive functions were evaluated using the Frontal Assessment Battery, Stroop and Trail-Making tests. Mean values and coefficients of variation (CV) of the temporal gait parameters while single tasking (just walking) and while dual tasking (walking and forward counting, walking and backward counting, walking and verbal fluency) were measured using the SMTEC(®)-footswitch system. We focused on the CV of stride time as this measure has been shown to be the most representative parameter of higher gait control. A strong effect of the stride time was found in the group factor for the verbal fluency dual-task when compared to controls (Cohen's d mean = 1.28 and CV = 1.05). The effect was lower in the other dual tasks, and insignificant in the single task of walking. This study shows that patients exhibit higher stride-to-stride variability while dual tasking than controls. It also shows a stronger impact of verbal fluency on gait regularity compared to the other dual tasks revealing a relationship between the executive dysfunction and gait modification. Those results are in line with the idea that schizophrenia implies not only cognitive but also motor functioning and coordination impairment.

Freezing of gait in Parkinson's disease is associated with functional decoupling between the cognitive control network and the basal ganglia

Recent neuroimaging evidence has led to the proposal that freezing of gait in Parkinson's disease is due to dysfunctional interactions between frontoparietal cortical regions and subcortical structures, such as the striatum. However, to date, no study has employed task-based functional connectivity analyses to explore this hypothesis. In this study, we used a data-driven multivariate approach to explore the impaired communication between distributed neuronal networks in 10 patients with Parkinson's disease and freezing of gait, and 10 matched patients with no clinical history of freezing behaviour. Patients performed a virtual reality gait task on two separate occasions (once ON and once OFF their regular dopaminergic medication) while functional magnetic resonance imaging data were collected. Group-level independent component analysis was used to extract the subject-specific time courses associated with five well-known neuronal networks: the motor network, the right- and left cognitive control networks, the ventral attention network and the basal ganglia network. We subsequently analysed both the activation and connectivity of these neuronal networks between the two groups with respect to dopaminergic state and cognitive load while performing the virtual reality gait task. During task performance, all patients used the left cognitive control network and the ventral attention network and in addition, showed increased connectivity between the bilateral cognitive control networks. However, patients with freezing demonstrated functional decoupling between the basal ganglia network and the cognitive control network in each hemisphere. This decoupling was also associated with paroxysmal motor arrests. These results support the hypothesis that freezing behaviour in Parkinson's disease is because of impaired communication between complimentary yet competing neural networks.

Abnormal patterns of theta frequency oscillations during the temporal evolution of freezing of gait in Parkinson's disease

OBJECTIVE

We sought to characterize the electrophysiological signature of Freezing of gait in Parkinson's disease.

METHODS

We examined 24 patients with idiopathic Parkinson's disease and significant freezing of gait as they performed a series of timed up-and-go tasks in their 'off' state while electroencephalographic data was collected from four scalp leads. Fast Fourier Transformation was utilized to explore the power spectral density between periods of normal walking and periods of freezing, as well as during the transition between the two states. In addition, Cross Spectrum and Cross Frequency analyses were used to explore the role of impaired temporal and spatial connectivity.

RESULTS

When compared to walking, episodes of freezing were associated with a significant increase in theta band power within the central and frontal leads. The transition from normal walking to freezing of gait was also associated with increased theta frequency coupling between the central and frontal leads, along with an increase in cross-frequency coupling in the central lead.

CONCLUSIONS

Episodes of freezing of gait in Parkinson's disease are associated with abnormal oscillatory activity in the brain.

SIGNIFICANCE

These results provide novel insights into the pattern of spatiotemporal dynamics underlying freezing of gait and may provide a potential means for therapeutic prediction and alleviation of freezing episodes in susceptible patients.

The role of frontostriatal impairment in freezing of gait in Parkinson's disease

Freezing of gait (FOG) is a disabling symptom of advanced Parkinson's disease (PD) that leads to an increased risk of falls and nursing home placement. Interestingly, multiple lines of evidence suggest that the manifestation of FOG is related to specific deficits in cognition, such as set shifting and the ability to process conflict-related signals. These findings are consistent with the specific patterns of abnormal cortical processing seen during functional neuroimaging experiments of FOG, implicating increased neural activation within cortical structures underlying cognition, such as the Cognitive Control Network. In addition, these studies show that freezing episodes are associated with abnormalities in the BOLD response within key structures of the basal ganglia, such as the striatum and the subthalamic nucleus. In this article, we discuss the implications of these findings on current models of freezing behavior and propose an updated model of basal ganglia impairment during FOG episodes that integrates the neural substrates of freezing from the cortex and the basal ganglia to the cognitive dysfunctions inherent in the condition.

Intravenous amantadine on freezing of gait in Parkinson's disease: a randomized controlled trial

To compare the effects of intravenous amantadine and placebo therapy on freezing of gait in patients with Parkinson's disease, this randomized, double-blind, placebo-controlled, multicenter trial compared the efficacy of 5 days intravenous amantadine and placebo treatments on freezing of gait in 42 subjects randomly allocated 2:1 to amantadine or placebo groups. Changes in freezing of gait questionnaire (FOG-Q) scores and in unified Parkinson's disease rating scale (UPDRS) scores, from baseline to immediately (V1) and 1 month (V2) after treatments, were assessed. Among the 42 patients (amantadine n = 29, placebo n = 13, a mean age 65.5 ± 9.4 years and a mean FOG-Q score 17.4 ± 3.2), 40 subjects completed treatment. There was no significant group difference on the primary outcome measure as total FOG-Q score changes at V1. However a significant beneficial effect of amantadine on freezing was seen at V2 in the UPDRS Part II freezing and FOG-Q item 3 scores, and there was significant improvement in the UPDRS Part IV total score and in the UPDRS Part II getting out of bed score in the amantadine group at both V1 and V2. There was no serious adverse event reported during the study. The intravenous amantadine therapy did not show a significant improvement on overall FOG-Q scores in patients with moderate-to-severe freezing; however, it might be beneficial by attenuating freezing severity and improving patients' mobility. To prove this finding further studies with larger sample sizes are warranted in the future.

Influence of educational status on executive function and functional balance in individuals with Parkinson disease

OBJECTIVE

This study investigated whether educational status influenced how people with Parkinson disease (PD) performed on Parts A, B, and DELTA of the Trail Making Test (TMT) and on the Berg Balance Scale (BBS).

BACKGROUND

Recent studies have shown that educational status may influence cognitive and motor test performance.

METHODS

We gave the TMT and the BBS to assess executive function and functional balance in 28 people with PD (Hoehn and Yahr score between 2 and 3) and 30 healthy elderly people. Participants reported their number of years of formal education. We divided each group of participants by educational status: low (4 to 10 years of education) or high (≥11 years).

RESULTS

In both the PD (P=0.018) and control (P=0.003) groups, participants with low educational status performed worse on the TMT Part B than did those with high educational status. Within the PD group, the less-educated participants scored worse on the BBS than did the more educated (P<0.001); this difference was not significant between the more- and less-educated controls (P=0.976).

CONCLUSIONS

Whether or not they had PD, less-educated people performed worse than more-educated people on the TMT Part B. Educational status affected executive function, but PD status did not. Among individuals with PD, educational status influenced functional balance.

Asymmetric pedunculopontine network connectivity in parkinsonian patients with freezing of gait

Freezing of gait is one of the most debilitating symptoms in Parkinson's disease as it causes falls and reduces mobility and quality of life. The pedunculopontine nucleus is one of the major nuclei of the mesencephalic locomotor region and has neurons related to anticipatory postural adjustments preceding step initiation as well as to the step itself, thus it may be critical for coupling posture and gait to avoid freezing. Because freezing of gait and postural impairments have been related to frontal lesions and frontal dysfunction such as executive function, we hypothesized that freezing is associated with disrupted connectivity between midbrain locomotor regions and medial frontal cortex. We used diffusion tensor imaging to quantify structural connectivity of the pedunculopontine nucleus in patients with Parkinson's disease with freezing of gait, without freezing, and healthy age-matched controls. We also included behavioural tasks to gauge severity of freezing of gait, quantify gait metrics, and assess executive cognitive functions to determine whether between-group differences in executive dysfunction were related to pedunculopontine nucleus structural network connectivity. Using seed regions from the pedunculopontine nucleus, we were able to delineate white matter connections between the spinal cord, cerebellum, pedunculopontine nucleus, subcortical and frontal/prefrontal cortical regions. The current study is the first to demonstrate differences in structural connectivity of the identified locomotor pathway in patients with freezing of gait. We report reduced connectivity of the pedunculopontine nucleus with the cerebellum, thalamus and multiple regions of the frontal cortex. Moreover, these structural differences were observed solely in the right hemisphere of patients with freezing of gait. Finally, we show that the more left hemisphere-lateralized the pedunculopontine nucleus tract volume, the poorer the performance on cognitive tasks requiring the initiation of appropriate actions and/or the inhibition of inappropriate actions, specifically within patients with freezing. These results support the notion that freezing of gait is strongly related to structural deficits in the right hemisphere's locomotor network involving prefrontal cortical areas involved in executive inhibition function.

Modeling freezing of gait in Parkinson's disease with a virtual reality paradigm

Freezing of gait is a paroxysmal and disabling symptom that commonly affects patients in the latter stages of Parkinson's disease, however the intermittent nature of this symptom makes it difficult to study in the clinical setting. Our research group has previously reported a correlation between self-reported freezing of gait symptoms and performance on a seated virtual reality gait task. In this study, we sought to determine whether behavioral measures recorded on this task were correlated with actual clinical measures of freezing of gait recorded in a cohort of 38 Parkinson's disease patients whilst in their clinically defined 'off' state. Firstly, patients with freezing of gait had a significantly larger frequency of spontaneous motor arrests recorded on the virtual reality gait task than 'non-freezers'. In addition, in those 24 patients with clinically proven freezing of gait, the number and percentage of time spent with freezing on the virtual reality task were both moderately correlated with the duration of freezing of gait recorded on the timed up-and-go tasks. These findings suggest that the freezing behavior observed during a virtual reality gait task may share similar neural substrates to freezing of gait. Such a relationship could offer a potential avenue for modeling the phenomenon of freezing of gait in Parkinson's disease, allowing for the exploration of the neural correlates of freezing.

Exploring the cortical and subcortical functional magnetic resonance imaging changes associated with freezing in Parkinson's disease

Freezing of gait is a devastating symptom of advanced Parkinson's disease yet the neural correlates of this phenomenon remain poorly understood. In this study, severity of freezing of gait was assessed in 18 patients with Parkinson's disease on a series of timed 'up and go' tasks, in which all patients suffered from episodes of clinical freezing of gait. The same patients also underwent functional magnetic resonance imaging with a virtual reality gait paradigm, performance on which has recently been shown to correlate with actual episodes of freezing of gait. Statistical parametric maps were created that compared the blood oxygen level-dependent response associated with paroxysmal motor arrests (freezing) to periods of normal motor output. The results of a random effects analysis revealed that these events were associated with a decreased blood oxygen level-dependent response in sensorimotor regions and an increased response within frontoparietal cortical regions. These signal changes were inversely correlated with the severity of clinical freezing of gait. Motor arrests were also associated with decreased blood oxygen level-dependent signal bilaterally in the head of caudate nucleus, the thalamus and the globus pallidus internus. Utilizing a mixed event-related/block design, we found that the decreased blood oxygen level-dependent response in the globus pallidus and the subthalamic nucleus persisted even after controlling for the effects of cognitive load, a finding which supports the notion that paroxysmal increases in basal ganglia outflow are associated with the freezing phenomenon. This method also revealed a decrease in the blood oxygen level-dependent response within the mesencephalic locomotor region during motor arrests, the magnitude of which was positively correlated with the severity of clinical freezing of gait. These results provide novel insights into the pathophysiology underlying freezing of gait and lend support to models of freezing of gait that implicate dysfunction across coordinated neural networks.

Differential neural activation patterns in patients with Parkinson's disease and freezing of gait in response to concurrent cognitive and motor load

Freezing of gait is a devastating symptom of Parkinson's disease (PD) that is exacerbated by the processing of cognitive information whilst walking. To date, no studies have explored the neural correlates associated with increases in cognitive load whilst performing a motor task in patients with freezing. In this experiment, 14 PD patients with and 15 PD patients without freezing of gait underwent 3T fMRI while performing a virtual reality gait task. Directions to walk and stop were presented on the viewing screen as either direct cues or as more cognitively indirect pre-learned cues. Both groups showed a consistent pattern of BOLD response within the Cognitive Control Network during performance of the paradigm. However, a between group comparison revealed that those PD patients with freezing of gait were less able to recruit the bilateral anterior insula, ventral striatum and the pre-supplementary motor area, as well as the left subthalamic nucleus when responding to indirect cognitive cues whilst maintaining a motor output. These results suggest that PD patients with freezing of gait are unable to properly recruit specific cortical and subcortical regions within the Cognitive Control Network during the performance of simultaneous motor and cognitive functions.

Freezing of gait in Parkinson's disease: disturbances in automaticity and control

Recent studies emphasize a key role of controlled operations, such as set-shifting and inhibition, in the occurrence of freezing of gait (FOG) in Parkinson's disease (PD). However, FOG can also be characterized as a de-automatization disorder, showing impairments in both the execution and acquisition of automaticity. The observed deficits in automaticity and executive functioning indicate that both processes are malfunctioning in freezers. Therefore, to explain FOG from a cognitive-based perspective, we present a model describing the pathways involved in automatic and controlled processes prior to a FOG episode. Crucially, we focus on disturbances in automaticity and control, regulated by the frontostriatal circuitry. In complex situations, non-freezing PD patients may compensate for deficits in automaticity by switching to increased cognitive control. However, as both automatic and controlled processes are more severely impaired in freezers, this hampers cognitive compensation in FOG, resulting in a potential breakdown. Future directions for cognitive rehabilitation are proposed, based on the cognitive model we put forward.

Differential susceptibility to motor impulsivity among functional subtypes of Parkinson's disease

BACKGROUND AND OBJECTIVES

Parkinson's disease patients with predominant postural instability and gait difficulties (PIGD) may experience unique cognitive difficulties compared to patients with tremor predominant (TD) symptoms. PIGD patients are also at high risk for falling, and some of the worst fallers seem to react impulsively to their environment. We tested the hypothesis that PIGD patients show poorer control over motor impulses compared to TD patients.

METHODS

34 PD participants were divided into predominant PIGD (n=17) or TD (n=17) functional subtypes based on their presenting symptoms in their optimally treated motor state. All participants performed a speeded reaction task that quantified motor impulsivity and the proficiency of inhibiting prepotent motor impulses.

RESULTS

The groups showed similar reaction times, but compared to TD patients, PIGD patients made significantly more impulsive motor errors. Notably, when the initial impulsive erroneous response was avoided, PIGD and TD groups were similar in their ability to suppress the incorrect motor impulse from further interfering with the selection of a correct action.

CONCLUSIONS

PD patients with PIGD predominant symptoms show greater susceptibility to acting on prepotent motor impulses compared to TD patients. This finding may have direct implications for fall risk and also points to dissociable neurocognitive pathologies in TD and PIGD subtypes. Clinically, the use of specific cognitive instruments to assess the expression and inhibition of motor impulses may help identify PD patients who have difficulty 'thinking before they leap' and are at high risk of falling.

The differential yet concurrent contributions of motor, cognitive and affective disturbance to freezing of gait in Parkinson's disease

OBJECTIVES

We sought to concurrently examine the specific motor, cognitive and affective contributions to self-reported FOG symptoms.

PATIENTS AND METHODS

Ninety-six patients with Parkinson's disease completed the validated freezing of gait questionnaire and had their motor function scored on section three of the Unified Parkinson's Disease Rating Scale questionnaire. A 5-choice reaction time task was administered in order to measure cognitive processing speed and the Beck Depression Inventory was utilised to assess affective disturbance.

RESULTS

The results showed that after controlling disease duration and dopaminergic medication dose, the triad of motor disability, cognitive processing speed and affective symptoms were all significant independent predictors of scores on the freezing of gait questionnaire.

CONCLUSIONS

These findings suggest the need to consider the interplay between distinct motor, cognitive and affective domains in aetiological studies of freezing and the development of future therapies.

Risk factors for freezing of gait in Parkinson's disease

Freezing of gait is an episodic gait disorder that may occur in patients with Parkinson's disease. The risk factors for this disorder are poorly understood. To determine the relevant risk factors for this condition, we screened 160 consecutive patients with Parkinson's disease for freezing of gait and assessed 36 potentially related variables. Freezers and non-freezers were compared using statistical univariate analysis, followed by bivariate and multivariate logistic regression, receiver operating characteristics curves and Kaplan-Meier estimates. Seventy-one patients (44.4%) reported freezing of gait. At onset, the mean disease duration was 8.1±6.3years. Freezers experienced falls more frequently than non-freezers (57.7% vs 23.6%, p<0.001). Disease duration was the independent variable most associated with freezing of gait (OR=1.10, 95% CI=1.01-1.19, p=0.020). Its specificity was 77%, but its sensitivity was low, and Hoehn and Yahr staging and the UPDRS (part III) score showed similar accuracy to that of disease duration in predicting freezers. Previous antiparkinsonian treatments and predominant motor signs (tremor/akinesia-rigidity subtypes) at the onset of Parkinson's disease were not related to freezing of gait. Patients who developed Parkinson's disease before the age of 60years experienced freezing of gait earlier than older patients (log-rank, p<0.005). Freezing of gait is a common and disabling motor complication of Parkinson's disease that is related to the progression of the disease. It is not primarily associated with dopamine replacement therapy and may occur early in young patients.

Comparisons of forward and backward gait between poorer and better attention capabilities in early Parkinson's disease

This study compared forward and backward gait between Parkinson's disease (PD) patients with poorer and better attention capabilities. PD and healthy control (HC) participants received a dual-stimuli attention task. The results were assessed using principal component analysis to quantify and rank attention capability. Accordingly, 22 PD and 42 HC subjects were equally divided into poorer (14 PD-P, 18 HC-P) and better (8 PD-B, 24 HC-B) attention capabilities. To analyze the spatiotemporal gait parameters, each participant walked forwards and backwards on a GAITRite(®) walkway. Compared to HC, PD performed worse in the dual task and exhibited slower velocity, less swing, and shorter stride in both walking directions. Notably, PD-P experienced all these gait defects, regardless of directions. PD-B walked worse than HC-B backwards, and displayed comparable gait to HC-P in both directions. In PD and HC, velocity, stride, and swing decreased perceptibly when walking backwards compared to forwards, and the same was true for velocity and stride in PD-P and PD-B. Backward strides were reduced evidently more in PD-P than in PD-B. However, backward swing reductions in PD-P and PD-B were statistically insignificant. Cadence in both directions was similar within the groups and between the groups, and there were little alterations between directions within each group and between groups. These results suggest that attention capability may affect PD gait. Poorer attention exacerbates gait defects and better attention improves gait in both directions. These results may support the application of cuing strategies in PD to enhance attention capability and improve walking gait.

Regional gray matter atrophy in patients with Parkinson disease and freezing of gait

BACKGROUND AND PURPOSE

FOG is a troublesome symptom of PD. Despite growing evidence suggesting that FOG in PD may be associated with cognitive dysfunction, the relationship between regional brain atrophy and FOG has been poorly investigated.

MATERIALS AND METHODS

Optimized VBM was applied to 3T brain MR images of 24 patients with PD and 12 HC. Patients were classified as either FOG- or FOG+ (n = 12) based on their responses to a validated FOG Questionnaire and clinical observation. All patients with PD also underwent a detailed neuropsychological evaluation.

RESULTS

The VBM analysis in patients with FOG+ showed a reduced GM volume in the left cuneus, precuneus, lingual gyrus, and posterior cingulate cortex compared with both patients with FOG- and HC. We did not detect any significant change of GM volume when comparing HC versus all patients with PD (FOG- and FOG+). FOG clinical severity was significantly correlated with GM loss in posterior cortical regions. Finally, patients with FOG+ scored lower on tests of frontal lobe function.

CONCLUSIONS

Our findings provide the first evidence that the development of FOG in patients with PD is associated with posterior GM atrophy, which may play a role in the complex pathophysiology of this disabling symptom.

Regional cerebral blood flow patterns in patients with freezing of gait due to lacunar infarction: SPECT study using three-dimensional stereotactic surface projections

BACKGROUND

Although freezing of gait (FOG) is reportedly caused by cerebrovascular disease, few studies have examined its pathology. We examined regional cerebral blood flow (rCBF) patterns in patients with FOG resulting from chronic lacunar infarction using single-photon emission computed tomography (SPECT).

METHODS

Among patients with chronic lacunar infarction treated at our outpatient unit, we performed N-isopropyl-p-[(123)I]-iodoamphetamine SPECT in seven patients with FOG (FOG group) and in 20 patients without FOG (non-FOG group). We analyzed and compared the SPECT data using three-dimensional stereotactic surface projections of the two groups.

RESULTS

On z-score maps, the FOG group showed a significant reduction in rCBF in the bilateral anterior cingulate cortices compared with the non-FOG group. The mean z-score for the bilateral cingulate gyri was significantly higher in the FOG group than in the non-FOG group (p < .01). When the cingulate gyrus data of the anterior and posterior subregions were analyzed on a region-by-region basis, the mean z-score for the left anterior cingulate gyrus was significantly higher than that for the right cingulate gyrus (p < .05).

CONCLUSION

These results suggest that anterior cingulate cortex dysfunction may be involved in the pathology of FOG in patients with chronic lacunar infarction.

Resting-state brain connectivity in patients with Parkinson's disease and freezing of gait

BACKGROUND

Freezing of gait is a common cause of disability and falls in patients with Parkinson's disease. We studied brain functional connectivity, by means of resting-state functional magnetic resonance imaging, in patients with Parkinson's disease and freezing of gait.

METHODS

Resting-state functional magnetic resonance imaging at 3 T was collected in 29 patients with Parkinson's disease, of whom 16 presented with freezing of gait as determined by a validated freezing of gait questionnaire, and 15 matched healthy controls. Single-subject and group-level independent component analysis was used to identify the main resting-state networks differing between Parkinson's disease patients with and without freezing of gait. Statistical analysis was performed using BrainVoyager QX.

RESULTS

Between-group differences in resting-state networks revealed that patients with freezing of gait exhibit significantly reduced functional connectivity within both "executive-attention" (in the right middle frontal gyrus and in the angular gyrus) and visual networks (in the right occipito-temporal gyrus) [p < 0.05 corrected for multiple comparisons]. Freezing of gait clinical severity was significantly correlated with decreased connectivity within the two networks. Consistent with their "executive-attention" network impairment, patients with freezing of gait scored lower on tests of frontal lobe functions (phonemic verbal fluency: p = 0.005; frontal assessment battery: p < 0.001; ten point clock test: p = 0.04).

CONCLUSIONS

Our findings suggest that a resting-state functional connectivity disruption of "executive-attention" and visual neural networks may be associated with the development of freezing of gait in patients with Parkinson's disease.

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.

Abnormalities and Cue Dependence of Rhythmical Upper-Limb Movements in Parkinson Patients With Freezing of Gait

Background. Freezing of gait (FOG) is a significant clinical problem in Parkinson disease (PD). Similar freezing-like episodes occur during finger movements, but little is known about ongoing motor problems during repetitive hand movements. Objective. To investigate if the regulation of bimanual movements is impaired in those with FOG and if withdrawal of an auditory cue amplifies this problem. Methods. A total of 23 PD patients (11 with and 12 without FOG) and 11 controls (CTRLs) performed repetitive finger movements, either externally paced or following cue withdrawal. Movement frequency, amplitude, and coordination pattern were manipulated. The stability and accuracy of movement were evaluated after exclusion of freezing trials. Results. With auditory pacing present, movement performance was comparable between groups. Following cue withdrawal, motor control deteriorated in those with FOG, resulting in smaller and less stable amplitudes, hastened and more variable frequency, and decreased coordination stability. Conversely, the performance of those without FOG remained mostly similar to that of CTRLs. Conclusions. Compared with those without FOG, those with FOG show greater continuous dyscontrol of bimanual movements, similar to the continuous timing and scaling difficulties during locomotion. Those with FOG also benefit from auditory cueing during upper-limb movements, but these are highly cue dependent. This implies that internal timekeeping functions are more disturbed in those with FOG, who may require rehabilitation strategies for repetitive upper-extremity tasks that include cueing and imagery.

Is freezing of gait in Parkinson's disease a result of multiple gait impairments? Implications for treatment

Several gait impairments have been associated with freezing of gait (FOG) in patients with Parkinson's disease (PD). These include deteriorations in rhythm control, gait symmetry, bilateral coordination of gait, dynamic postural control and step scaling. We suggest that these seemingly independent gait features may have mutual interactions which, during certain circumstances, jointly drive the predisposed locomotion system into a FOG episode. This new theoretical framework is illustrated by the evaluation of the potential relationships between the so-called "sequence effect", that is, impairments in step scaling, and gait asymmetry just prior to FOG. We further discuss what factors influence gait control to maintain functional gait. "Triggers", for example, such as attention shifts or trajectory transitions, may precede FOG. We propose distinct categories of interventions and describe examples of existing work that support this idea: (a) interventions which aim to maintain a good level of locomotion control especially with respect to aspects related to FOG; (b) those that aim at avoiding FOG "triggers"; and (c) those that merely aim to escape from FOG once it occurs. The proposed theoretical framework sets the stage for testable hypotheses regarding the mechanisms that lead to FOG and may also lead to new treatment ideas.