Split-belt locomotion in Parkinson’s disease with and without freezing of gait

Knowledge mapping of freezing of gait in Parkinson's disease: a bibliometric analysis

Objective

Among the disturbing motor symptoms in Parkinson's disease (PD), freezing of gait (FOG) stands out as one of the most severe challenges. It typically arises during the initiation of gait or when turning. This phenomenon not only impose a heavy burden on patients, but also on their families. We conduct a bibliometric analysis to summarize current research hotspots and trends concerning freezing of gait in Parkinson's disease (PD-FOG) over past two decades.

Methods

We retrieved articles and reviews published in English about PD-FOG in the Web of science Core Collection database from 2000 to 2023 on November 30,2023. The tools VOSviewer and CiteSpace facilitated a visual analysis covering various aspects such as publications, countries/regions, organizations, authors, journals, cited references, and keywords.

Result

This study includes 1,340 articles from 64 countries/regions. There is a growth in publications related to PD-FOG over the past two decades, maintaining a stable high output since 2018, indicating a promising research landscape in the field of PD-FOG. The United States holds a leading position in this field, with Nieuwboer A and Giladi N being two of the most influential researchers. Over the past two decades, the research hotspots for PD-FOG have primarily encompassed the kinematic characteristics, diagnosis and detection, cognitive deficits and neural connectivity, as well as therapy and rehabilitation of PD-FOG. Topics including functional connectivity, virtual reality, deep learning and machine learning will be focal points of future research.

Conclusion

This is the first bibliometric analysis of PD-FOG. We construct this study to summarize the research in this field over past two decades, visually show the current hotspots and trends, and offer scholars in this field concepts and strategies for subsequent studies.

Propulsive Force Modulation Drives Split-Belt Treadmill Adaptation in People with Multiple Sclerosis

Most people with multiple sclerosis (PwMS) experience significant gait asymmetries between their legs during walking, leading to an increased risk of falls. Split-belt treadmill training, where the speed of each limb is controlled independently, alters each leg's stepping pattern and can improve gait symmetry in PwMS. However, the biomechanical mechanisms of this adaptation in PwMS remain poorly understood. In this study, 32 PwMS underwent a 10 min split-belt treadmill adaptation paradigm with the more affected (MA) leg moving twice as fast as the less affected (LA) leg. The most noteworthy biomechanical adaptation observed was increased peak propulsion asymmetry between the limbs. A kinematic analysis revealed that peak dorsiflexion asymmetry and the onset of plantarflexion in the MA limb were the primary contributors to the observed increases in peak propulsion. In contrast, the joints in the LA limb underwent only immediate reactive adjustments without subsequent adaptation. These findings demonstrate that modulation during gait adaptation in PwMS occurs primarily via propulsive forces and joint motions that contribute to propulsive forces. Understanding these distinct biomechanical changes during adaptation enhances our grasp of the rehabilitative impact of split-belt treadmill training, providing insights for refining therapeutic interventions aimed at improving gait symmetry.

Triggers for freezing of gait in individuals with Parkinson's disease: a systematic review

Background

Freezing of Gait (FOG) is a motor symptom frequently observed in advanced Parkinson's disease. However, due to its paroxysmal nature and diverse presentation, assessing FOG in a clinical setting can be challenging. Before FOG can be fully investigated, it is critical that a reliable experimental setting is established in which FOG can be evoked in a standardized manner, but the efficacy of various gait tasks and triggers for eliciting FOG remains unclear.

Objectives

This study aimed to conduct a systematic review of the existing literature and evaluate the available evidence for the relationship between specific motor tasks, triggers, and FOG episodes in individuals with Parkinson's disease (PwPD).

Methods

We conducted a literature search on four online databases (PubMed, Web of Science, EMBASE, and Cochrane Library) using the keywords "Parkinson's disease," "Freezing of Gait", "triggers" and "tasks". A total of 128 articles met the inclusion criteria and were included in our analysis.

Results

The review found that a wide range of gait tasks were employed in studies assessing FOG among PD patients. However, three tasks (turning, dual tasking, and straight walking) emerged as the most frequently used. Turning (28%) appears to be the most effective trigger for eliciting FOG in PwPD, followed by walking through a doorway (14%) and dual tasking (10%).

Conclusion

This review thereby supports the utilisation of turning, especially a 360-degree turn, as a reliable trigger for FOG in PwPD. This finding could be beneficial to clinicians conducting clinical evaluations and researchers aiming to assess FOG in a laboratory environment.

Advances in the study of cholinergic circuits in the central nervous system

OBJECTIVE

Further understanding of the function and regulatory mechanism of cholinergic neural circuits and related neurodegenerative diseases.

METHODS

This review summarized the research progress of the central cholinergic nervous system, especially for the cholinergic circuit of the medial septal nucleus-hippocampus, vertical branch of diagonal band-hippocampus, basal nucleus of Meynert-cerebral cortex cholinergic loop, amygdala, pedunculopontine nucleus, and striatum-related cholinergic loops.

RESULTS

The extensive and complex fiber projection of cholinergic neurons form the cholinergic neural circuits, which regulate several nuclei in the brain through neurotransmission and participate in learning and memory, attention, emotion, movement, etc. The loss of cholinergic neurotransmitters, the reduction, loss, and degeneration of cholinergic neurons or abnormal theta oscillations and cholinergic neural circuits can induce cognitive disorders such as AD, PD, PDD, and DLB.

INTERPRETATION

The projection and function of cholinergic fibers in some nuclei and the precise regulatory mechanisms of cholinergic neural circuits in the brain remain unclear. Further investigation of cholinergic fiber projections in various brain regions and the underlying mechanisms of the neural circuits are expected to open up new avenues for the prevention and treatment of senile neurodegenerative diseases.

Differential gait adaptation patterns in Parkinson's disease - a split belt treadmill pilot study

BACKGROUND

Interventions using split belt treadmills (SBTM) aim to improve gait symmetry (GA) in Parkinson's disease (PD). Comparative effects in conjugated SBTM conditions were not studied systematically despite potentially affecting intervention outcomes. We compared gait adaptation effects instigated by SBTM walking with respect to the type (increased\decreased speed) and the side (more/less affected) of the manipulated belt in PD.

METHODS

Eight individuals with PD performed four trials of SBTM walking, each consisted of baseline tied belt configuration, followed by split belt setting - either WS or BS belt's speed increased or decreased by 50% from baseline, and final tied belt configuration. Based on the disease's motor symptoms, a 'worst' side (WS) and a 'best' side (BS) were defined for each participant.

RESULTS

SB initial change in GA was significant regardless of condition (p ≤ 0.02). This change was however more pronounced for BS-decrease compared with its matching condition WS-increase (p = 0.016). Similarly, the same was observed for WS-decrease compared to BS-increase (p = 0.013). Upon returning to tied belt condition, both BS-decrease and WS-increased resulted in a significant change in GA (p = 0.04). Upper limb asymmetry followed a similar trend of GA reversal, although non-significant.

CONCLUSIONS

Stronger effects on GA were obtained by decreasing the BS belt's speed of the best side, rather than increasing the speed of the worst side. Albeit a small sample size, which limits the generalisability of these results, we propose that future clinical studies would benefit from considering such methodological planning of SBTM intervention, for maximising of intervention outcomes. Larger samples may reveal arm swinging asymmetries alterations to match SBTM adaptation patterns. Finally, further research is warranted to study post-adaption effects in order to define optimal adaptation schemes to maximise the therapeutic effect of SBTM based interventions.

Cognition and freezing of gait in Parkinson's disease: A systematic review and meta-analysis

Freezing of gait (FOG) is a common and disabling symptom in people with Parkinson's Disease (PwPD). Although cognition is thought to be worse in PwPD who freeze, a comprehensive analysis of this relationship will inform future research and clinical care. This systematic review and meta-analysis compared cognition between PwPD who do and do not exhibit FOG across a range of cognitive domains and assessed the impact of disease severity and medication status on this relationship. 145 papers (n = 9010 participants) were included in the analysis, with 144 and 138 articles meeting the criteria to assess moderating effects of disease severity and medication status, respectively. PwPD who freeze exhibited worse cognition than PwPD without FOG across global cognition, executive function/attention, language, memory, and visuospatial domains. Greater disease severity and "ON" levodopa medication status moderated the FOG status-cognition relationship in global cognitive performance but not in other cognitive domains. This meta-analysis confirmed that cognition is worse in PwPD with FOG and highlights the importance of disease severity and medication status in this relationship.

Cognition affects gait adaptation after split-belt treadmill training in Parkinson's disease

BACKGROUND

Split-belt treadmill (SBTM) training has been proposed to improve gait symmetry and overall gait performance of patients with Parkinson's disease (PD).

OBJECTIVES

To determine whether patient's baseline features affect gait adaptation to SBTM in PD with freezing of gait (FOG).

METHODS

Twenty participants with idiopathic PD and treatment-resistant FOG underwent several clinical assessments including the Toronto Cognitive Assessment (TorCA) prior to treadmill training. Velocity of the treadmill was adjusted to over-ground walking speed. During SBTM training, the belt velocity on the least-affected side was reduced by 25%.

RESULTS

Participants who adapted to SBTM training demonstrated cognitively intact TorCA scores (p < 0.001), particularly intact working memory (p < 0.001). After-effects correlated with normal total TorCA (p = 0.02), working memory and visuospatial (p < 0.001) function.

CONCLUSIONS

Cognitive impairment, particularly impaired working memory, reduces gait adaptation and after-effects in PD with FOG. This is informative for trials studying prolonged effects of SBTM training in FOG.

Modulation of the gait pattern during split-belt locomotion after lateral spinal cord hemisection in adult cats

Most previous studies investigated the recovery of locomotion in animals and people with incomplete spinal cord injury (SCI) during relatively simple tasks (e.g., walking in a straight line on a horizontal surface or a treadmill). We know less about the recovery of locomotion after incomplete SCI in left-right asymmetric conditions, such as turning or stepping along circular trajectories. To investigate this, we collected kinematic and electromyography data during split-belt locomotion at different left-right speed differences before and after a right thoracic lateral spinal cord hemisection in nine adult cats. After hemisection, although cats still performed split-belt locomotion, we observed several changes in the gait pattern compared with the intact state at early (1-2 wk) and late (7-8 wk) time points. Cats with larger lesions showed new coordination patterns between the fore- and hindlimbs, with the forelimbs taking more steps. Despite this change in fore-hind coordination, cats maintained consistent phasing between the fore- and hindlimbs. Adjustments in cycle and phase (stance and swing) durations between the slow and fast sides allowed animals to maintain 1:1 left-right coordination. Periods of triple support involving the right (ipsilesional) hindlimb decreased in favor of quad support and triple support involving the other limbs. Step and stride lengths decreased with concurrent changes in the right fore- and hindlimbs, possibly to avoid interference. The above adjustments in the gait pattern allowed cats to retain the ability to locomote in asymmetric conditions after incomplete SCI. We discuss potential plastic neuromechanical mechanisms involved in locomotor recovery in these conditions.NEW & NOTEWORTHY Everyday locomotion often involves left-right asymmetries, when turning, walking along circular paths, stepping on uneven terrains, etc. To show how incomplete spinal cord injury affects locomotor control in asymmetric conditions, we collected data before and after a thoracic lateral spinal hemisection on a split-belt treadmill with one side stepping faster than the other. We show that adjustments in kinematics and muscle activity allowed cats to retain the ability to perform asymmetric locomotion after hemisection.

Split-Belt Adaptation and Savings in People With Parkinson Disease

BACKGROUND AND PURPOSE

Upper extremity studies suggest that implicit adaptation is less impaired than explicit learning in persons with Parkinson disease (PD). Little work has explored implicit locomotor adaptation and savings in this population, yet implicit locomotor learning is critical for everyday function. This cross-sectional study examined adaptation and savings in individuals with PD during split-belt treadmill walking.

METHODS

Fourteen participants completed the following treadmill protocol: Baseline (6 minutes belts tied), Adaptation (10 minutes split), Washout (10 minutes tied), and Readaptation (10 minutes split). Step length and step symmetry index (SSI) were calculated to determine magnitude and rate of adaptation and savings. Rate was calculated as strides to reach SSI plateau during Adaptation and Readaptation.

RESULTS

During Early Adaptation and Early Readaptation, SSI was perturbed from Baseline ( P < 0.001 and P = 0.002, respectively). Less perturbation in Early Readaptation ( P < 0.001) demonstrated savings. In Late Adaptation and Late Readaptation, participants returned to Baseline symmetry ( P = 0.026 and P = 0.022, respectively, with adjusted level of significance = 0.007). Adaptation was also seen in reverse asymmetry observed in Early Washout ( P = 0.003 vs Baseline). Readaptation rate was faster than in Adaptation ( P = 0.015), demonstrating savings.

DISCUSSION AND CONCLUSIONS

Individuals with PD showed locomotor adaptation in an implicit sensorimotor adaptation task. They also demonstrated savings, with less perturbation and faster adaptation during the second split-belt exposure. However, performance was variable; some individuals showed minimal adaptation. Variations in learning, savings, and clinical presentation highlight the need to further explore characteristics of individuals with PD most likely to benefit from adaptation-based locomotor training.Video Abstract available for more insights from the authors (see the Video, Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A395 ).

Immersive Technology for Cognitive-Motor Training in Parkinson’s Disease

Background: Parkinson’s disease (PD) is a neurodegenerative disease in which the progressive loss of dopaminergic neurons (DA) leads to initially sporadic and eventually widespread damage of the nervous system resulting in significant musculoskeletal and cognitive deterioration. Loss of motor function alongside increasing cognitive impairment is part of the natural disease progression. Gait is often considered an automatic activity; however, walking is the result of a delicate balance of multiple systems which maintain the body’s center of mass over an ever-changing base of support. It is a complex motor behavior that requires components of attention and memory to prevent falls and injury. In addition, evidence points to the critical role of salient visual information to gait adaptability. There is a growing understanding that treatment for PD needs to address movement as it occurs naturally and walking needs to be practiced in more complex environments than traditional therapy has provided.

Locomotor Adaptation Deficits in Older Individuals With Cognitive Impairments: A Pilot Study

Gait dysfunction and fall risk have been well documented in people with Alzheimer's Disease (AD) and individuals with mild cognitive impairment (MCI). Normal locomotor adaptation may be an important prerequisite for normal and safe community walking function, especially in older adults with age-related neural, musculoskeletal, or cardiovascular changes and cognitive impairments. The split-belt walking task is a well-studied and robust method to evaluate locomotor adaptation (e.g., the ability to adjust stepping movements to changing environmental demands). Here, we capitalized on the split-belt adaptation task to test our hypothesis that a decreased capacity for locomotor adaptation may be an important contributing factor and indicator of increased fall risk and cognitive decline in older individuals with MCI and AD. The objectives of this study were to (1) compare locomotor adaptation capacity in MCI and AD compared to healthy older adults (HOA) during split-belt treadmill walking, and (2) evaluate associations between locomotor adaptation and cognitive impairments. Our results demonstrated a significant decrease in split-belt locomotor adaptation magnitude in older individuals with MCI and AD compared to HOA. In addition, we found significant correlations between the magnitude of early adaptation and de-adaptation vs. cognitive test scores, demonstrating that individuals with greater cognitive impairment also display a reduced capacity to adapt their walking in response to the split-belt perturbation. Our study takes an important step toward understanding mechanisms underlying locomotor dysfunction in older individuals with cognitive impairment.

Adaptation of bilateral coordination of gait during split belt walking as reflected by the phase coordination index

BACKGROUND

The Split belt treadmill (SBTM) has recently been used in research and rehabilitation to study and utilize gait adaptations. The Phase coordination index (PCI) is useful in assessing bilateral coordination of gait by quantifying the consistency and accuracy in generating the anti-phased left-right stepping pattern. Recently we proposed that 23 strides are sufficient to reliably characterize PCI values from regular over ground and treadmill walking RESEARCH QUESTION: Can we detect the effect of SBTM on PCI using only 23 gait cycles also from SBTM walking?

METHODS

Young healthy participants (n = 13) with right side motor dominance performed SBTM walking trials. Experiment protocol began by walking in tied belt (TB) mode, followed by an incremental speed increase of one of the belts by 50 % - split belt (SB) mode. This was performed for each side. Two 1-minute segments were analyzed per participant, TB and SB. PCI analysis was carried out upon fewer strides (n = 23) and compared to PCI that was obtained based on all available strides (n = 56 ± 5).

RESULTS

Clear SBTM walking effects on PCI were seen in both experiments, for example, PCI increased from 4.46 ± 1.5 % (TB) to 10.07 ± 3.6 % (SB) for left belt speed increase. Twenty three strides from each trail were sufficient to demonstrate the effect.

SIGNIFICANCE

PCI can be a useful metric to characterize changes in bilateral coordination of gait during SBTM gait adaptations. The fact that 23 strides are sufficient for its reliable estimation, contribute to the continued monitoring through the adaptation process (i.e., by using time windows).

On Nonlinear Regression for Trends in Split-Belt Treadmill Training

Single and double exponential models fitted to step length symmetry series are used to evaluate the timecourse of adaptation and de-adaptation in instrumented split-belt treadmill tasks. Whilst the nonlinear regression literature has developed substantially over time, the split-belt treadmill training literature has not been fully utilising the fruits of these developments. In this research area, the current methods of model fitting and evaluation have three significant limitations: (i) optimisation algorithms that are used for model fitting require a good initial guess for regression parameters; (ii) the coefficient of determination (R2) is used for comparing and evaluating models, yet it is considered to be an inadequate measure of fit for nonlinear regression; and, (iii) inference is based on comparison of the confidence intervals for the regression parameters that are obtained under the untested assumption that the nonlinear model has a good linear approximation. In this research, we propose a transformed set of parameters with a common language interpretation that is relevant to split-belt treadmill training for both the single and double exponential models. We propose parameter bounds for the exponential models which allow the use of particle swarm optimisation for model fitting without an initial guess for the regression parameters. For model evaluation and comparison, we propose the use of residual plots and Akaike's information criterion (AIC). A method for obtaining confidence intervals that does not require the assumption of a good linear approximation is also suggested. A set of MATLAB (MathWorks, Inc., Natick, MA, USA) functions developed in order to apply these methods are also presented. Single and double exponential models are fitted to both the group-averaged and participant step length symmetry series in an experimental dataset generating new insights into split-belt treadmill training. The proposed methods may be useful for research involving analysis of gait symmetry with instrumented split-belt treadmills. Moreover, the demonstration of the suggested statistical methods on an experimental dataset may help the uptake of these methods by a wider community of researchers that are interested in timecourse of motor training.

The Adapted Resistance Training with Instability Randomized Controlled Trial for Gait Automaticity

BACKGROUND

Deficits in the cerebellar locomotor region (CLR) have been associated with loss of gait automaticity in individuals with freezing of gait in Parkinson's disease (freezers); however, exercise interventions that restore gait automaticity in freezers are lacking. We evaluated the effects of the adapted resistance training with instability ([ARTI] complex exercises) compared with traditional motor rehabilitation (without complex exercises) on gait automaticity and attentional set-shifting. We also verified associations between gait automaticity change and CLR activation change previously published.

METHODS

Freezers were randomized either to the experimental group (ARTI, n = 17) or to the active control group (traditional motor rehabilitation, n = 15). Both training groups performed exercises 3 times a week for 12 weeks. Gait automaticity (dual-task and dual-task cost [DTC] on gait speed and stride length), single-task gait speed and stride length, attentional set-shifting (time between Trail Making Test parts B and A), and CLR activation during a functional magnetic resonance imaging protocol of simulated step initiation task were evaluated before and after interventions.

RESULTS

Both training groups improved gait parameters in single task (P < 0.05), but ARTI was more effective than traditional motor rehabilitation in improving DTC on gait speed, DTC on stride length, dual-task stride length, and CLR activation (P < 0.05). Changes in CLR activation were associated with changes in DTC on stride length (r = 0.68, P = 0.002) following ARTI. Only ARTI improved attentional set-shifting at posttraining (P < 0.05).

CONCLUSIONS

ARTI restores gait automaticity and improves attentional set-shifting in freezers attributed to the usage of exercises with high motor complexity. © 2020 International Parkinson and Movement Disorder Society.

The Effect of One Session Split-Belt Treadmill Training on Gait Adaptation in People With Parkinson's Disease and Freezing of Gait

BACKGROUND

Freezing of gait (FOG) in Parkinson's disease (PD) is associated with gait asymmetry and switching difficulty. A split-belt treadmill may potentially address those deficits.

OBJECTIVE

To investigate the immediate and retention effects of one-session split-belt treadmill training (SBT) in contrast to regular tied-belt treadmill training (TBT) on gait asymmetry and adaptation in people with PD and FOG (PD + FOG) and healthy controls (HC). Additionally, to investigate differential effects of 3 SBT protocols and compare different gait adaptation outcomes.

METHODS

PD + FOG (n = 45) and HC (n = 36) were randomized to 1 of 3 SBT groups (belt speeds' ratio 0.75:1; 0.5:1 or changing ratios) or TBT group. Participants were tested at Pre, Post, and Retention after one treadmill training session. Gait asymmetry was measured during a standardized adaptation test on the split-belt treadmill.

RESULTS

SBT proved beneficial for gait adaptation in PD + FOG and HC (P < .0001); however, HC improved more. SBT with changing ratios demonstrated significant effects on gait adaptation from Pre to Post in PD + FOG, supported by strong effect sizes (d = 1.14) and improvements being retained for 24 hours. Mean step length asymmetry during initial exposure was lower in HC compared with PD + FOG (P = .035) and differentiated best between the groups.

CONCLUSIONS

PD + FOG improved gait adaptation after a single SBT session although effects were smaller than in HC. SBT with changing ratios was the most effective to ameliorate gait adaptation in PD + FOG. These promising results warrant future study on whether long-term SBT strengthens adaptation in PD + FOG and has potential to induce a better resilience to FOG. Clinical trial ID: NCT03725215.

Age-related differences in interlimb coordination during typical gait: An observational study

BACKGROUND

Arm movements during gait are known to alter with increasing age during the slow maturation phase (>3years). It is unclear whether coordination between the arms and legs (i.e. interlimb coordination), which is a measure of gait quality, shows a similar pattern.

RESEARCH QUESTION

to investigate age-related differences in interlimb coordination during gait in typically developing children and adults.

METHODS

In this observational study, 98 typically developing participants were divided into five age-groups: preschool children (G1; 2.9-5.9 years[n = 18]), children (G2; 6.0-9.9 years[n = 22]), pubertal children (G3; 10.0-13.9 years[n = 26]), adolescents (G4; 14.0-18.9 years[n = 14]) and adults (G5; 19.0-35.2 years[n = 18]). Participants walked barefoot at a self-selected walking speed along a 10-m walkway during three-dimensional total-body gait analysis. To examine interlimb coordination, mean continuous relative phase over the gait cycle (MRP) and its variability (sdMRP) were calculated for each combination of limb pairs in the sagittal plane.

RESULTS

MRP increased towards more anti-phase coordination with increasing age in following limb pair combinations: left arm-right arm (median[interquartile range]; G1: 152.0°[126.6;160.7°]-G5: 171.5°[170.0;175.3°]), left arm-left leg (G1: 155.0°[131.3;167.6°]-G5: 170.8°[165.3;173.5°]) and right arm-right leg (G1: 155.7°[135.5;166.0°]-G5: 170.0°[166.4;173.5°]). MRP decreased towards more in-phase coordination from G1 to G5 in left arm-right leg (G1: 24.4°[15.3;45.8°]-G5: 10.5°[6.1;15.6°]) and right arm-left leg (G1: 25.0°[13.7;41.1°]-G5: 9.7°[5.2;16.8°]). sdMRP decreased from G1 to G5 for all limb pair combinations.

SIGNIFICANCE

Interlimb coordination altered with increasing age. First, coordination between the legs and right arm-left leg appeared mature in G1 (aged 2.9-5.9 years). Next, coordination between the ipsilateral limbs seemed mature at 9.9 years, followed by a mature coordination between left arm-right leg at 13.9years. Coordination between the two arms showed ongoing differences until adulthood. These data provide an age-related framework and normative dataset to distinguish age-related differences from pathology in children with neuromotor disorders in clinical practice.

A Randomized, Controlled Trial of Exercise for Parkinsonian Individuals With Freezing of Gait

BACKGROUND

Exercises with motor complexity induce neuroplasticity in individuals with Parkinson's disease (PD), but its effects on freezing of gait are unknown. The objective of this study was to verify if adapted resistance training with instability - exercises with motor complexity will be more effective than traditional motor rehabilitation - exercises without motor complexity in improving freezing-of-gait severity, outcomes linked to freezing of gait, and brain function.

METHODS

Freezers were randomized either to the adapted resistance training with instability group (n = 17) or to the active control group (traditional motor rehabilitation, n = 15). Both training groups performed exercises 3 times a week for 12 weeks. The primary outcome was the New Freezing of Gait Questionnaire. Secondary outcomes were freezing of gait ratio (turning task), cognitive inhibition (Stroop-III test), motor signs (Unified Parkinson's Disease Rating Scale part-III [UPDRS-III]), quality of life (PD Questionnaire 39), anticipatory postural adjustment (leg-lifting task) and brain activation during a functional magnetic resonance imaging protocol of simulated anticipatory postural adjustment task. Outcomes were evaluated before and after interventions.

RESULTS

Only adapted resistance training with instability improved all the outcomes (P < 0.05). Adapted resistance training with instability was more effective than traditional motor rehabilitation (in improving freezing-of-gait ratio, motor signs, quality of life, anticipatory postural adjustment amplitude, and brain activation; P < 0.05). Our results are clinically relevant because improvement in the New Freezing of Gait Questionnaire (-4.4 points) and UPDRS-III (-7.4 points) scores exceeded the minimally detectable change (traditional motor rehabilitation group data) and the moderate clinically important difference suggested for PD, respectively. The changes in mesencephalic locomotor region activation and in anticipatory postural adjustment amplitude explained the changes in New Freezing of Gait Questionnaire scores and in freezing-of-gait ratio following adapted resistance training with instability, respectively.

CONCLUSIONS

Adapted resistance training with instability is able to cause significant clinical improvement and brain plasticity in freezers. © 2020 International Parkinson and Movement Disorder Society.

Double obstacles increase gait asymmetry during obstacle crossing in people with Parkinson's disease and healthy older adults: A pilot study

Gait asymmetry during unobstructed walking in people with Parkinson’s disease (PD) has been well documented. However, under complex situations, such as environments with double obstacles, gait asymmetry remains poorly understood in PD. Therefore, the aim of this study was to analyze inter-limb asymmetry while crossing a single obstacle and double obstacles (with different distances between them) in people with PD and healthy older adults. Nineteen people with PD and 19 healthy older people performed three conditions: (i) walking with one obstacle (Single); (ii) walking with two obstacles with a 50 cm distance between them (Double-50); (iii) walking with two obstacles with a 108 cm distance between them (Double-108). The participants performed the obstacle crossing with both lower limbs. Asymmetry Index was calculated. We found that people with PD presented higher leading and trailing toe clearance asymmetry than healthy older people. In addition, participants increased asymmetry in the Double-50 compared to Single condition. It can be concluded that people with PD show higher asymmetry during obstacle crossing compared to healthy older people, independently of the number of obstacles. In addition, a challenging environment induces asymmetry during obstacle crossing in both people with PD and healthy older people.

Neural correlates and gait characteristics for hypoxic-ischemic brain injury induced freezing of gait

OBJECTIVE

To investigate gait characteristics in patients with freezing of gait (FOG) after hypoxic-ischemic brain injury (HIBI) and to elucidate neural correlates for FOG using F-18 fluoro-2-deoxy-d-glucose positron emission tomography.

METHODS

We enrolled 12 patients with FOG after HIBI and 17 patients without FOG after HIBI. We performed three-dimensional gait analyses and compared each parameter and gait variability. Brain metabolism was measured, and we compared regional brain metabolism using a voxel-by-voxel-based statistical mapping analysis.

RESULTS

The FOG group revealed a significantly decreased joint range of motion (ROM), particularly in the sagittal plane for three-joint summated ROM (p < 0.0025). Spatiotemporal results demonstrated that stride length and step length were decreased in the with FOG group (p < 0.005). FOG severity was negatively correlated with brain metabolism in the left thalamus, and three-joint summated ROM in the sagittal plane was positively associated with brain metabolism in the left thalamus and midbrain (p < 0.05).

CONCLUSIONS

Central organizational level amplitude disorder may play an important role in the pathophysiology, and disturbance in the cholinergic pathway might contribute to the development of FOG in patients with HIBI.

SIGNIFICANCE

These findings contribute to understanding FOG in HIBI.

The functional network signature of heterogeneity in freezing of gait

Freezing of gait is a complex, heterogeneous, and highly variable phenomenon whose pathophysiology and neural signature remains enigmatic. Evidence suggests that freezing is associated with impairments across cognitive, motor and affective domains; however, most research to date has focused on investigating one axis of freezing of gait in isolation. This has led to inconsistent findings and a range of different pathophysiological models of freezing of gait, due in large part to the tendency for studies to investigate freezing of gait as a homogeneous entity. To investigate the neural mechanisms of this heterogeneity, we used an established virtual reality paradigm to elicit freezing behaviour in 41 Parkinson's disease patients with freezing of gait and examined individual differences in the component processes (i.e. cognitive, motor and affective function) that underlie freezing of gait in conjunction with task-based functional MRI. First, we combined three unique components of the freezing phenotype: impaired set-shifting ability, step time variability, and self-reported anxiety and depression in a principal components analysis to estimate the severity of freezing behaviour with a multivariate approach. By combining these measures, we were then able to interrogate the pattern of task-based functional connectivity associated with freezing (compared to normal foot tapping) in a sub-cohort of 20 participants who experienced sufficient amounts of freezing during task functional MRI. Specifically, we used the first principal component from our behavioural analysis to classify patterns of functional connectivity into those that were associated with: (i) increased severity; (ii) increased compensation; or (iii) those that were independent of freezing severity. Coupling between the cognitive and limbic networks was associated with 'worse freezing severity', whereas anti-coupling between the putamen and the cognitive and limbic networks was related to 'increased compensation'. Additionally, anti-coupling between cognitive cortical regions and the caudate nucleus were 'independent of freezing severity' and thus may represent common neural underpinnings of freezing that are unaffected by heterogenous factors. Finally, we related these connectivity patterns to each of the individual components (cognitive, motor, affective) in turn, thus exposing latent heterogeneity in the freezing phenotype, while also identifying critical functional network signatures that may represent potential targets for novel therapeutic intervention. In conclusion, our findings provide confirmatory evidence for systems-level impairments in the pathophysiology of freezing of gait and further advance our understanding of the whole-brain deficits that mediate symptom expression in Parkinson's disease.

Split-belt treadmill walking in patients with Parkinson's disease: A systematic review

BACKGROUND

Walking on a split-belt treadmill (SBT) can help to modulate an asymmetric gait, particularly for people with neurological conditions, such as Parkinson's disease (PD), where asymmetry plays a role due to the laterality of the disease.

RESEARCH QUESTION

This systematic review critically evaluates the literature on SBT in PD. First, different SBT paradigms and methodological approaches were evaluated. Second, the review explored how people with PD adapt their gait to different SBT conditions compared to healthy controls (HC).

METHODS

We conducted a systematic search of the PubMED, PsychINFO, and Web of Knowledge databases. Original research articles, published in English and investigating SBT walking in people with PD, were included.

RESULTS

From the 925 studies originally identified, seven met the inclusion criteria and were selected for evaluation (n = 118 individuals with PD of whom 44 had freezing of gait (FOG)). The SBT paradigms varied across studies regarding the SBT settings, definitions of gait variables, and criteria for determining dominance of body side. Gait variability and bilateral coordination were found to adapt to the SBT condition similarly in people with PD and healthy controls (HC). Inconsistent results were found with respect to the adaptation of gait asymmetry, for the differences between PD and HC participants. The subgroup of people with PD and FOG showed reduced accuracy in detecting belt speed differences and slower adaptation to SBT conditions.

CONCLUSION

Individuals with mild to moderately severe PD adapted similarly to HCs to SBT walking for gait variability and bilateral gait coordination. However, those with FOG had impaired perception of belt speed differences and did not adapt their gait so readily. Although SBT can be useful for modulating gait asymmetry in some people with PD, it was not beneficial for all. We recommend standardization of SBT protocols for clinical practice in future studies.

Effects of personal and task constraints on limb coordination during walking: A systematic review and meta-analysis

BACKGROUND

In human behaviour, emergence of movement patterns is shaped by different, interacting constraints and consequently, individuals with motor disorders usually display distinctive lower limb coordination modes.

OBJECTIVES

To review existing evidence on the effects of motor disorders and different task constraints on emergent coordination patterns during walking, and to examine the clinical significance of task constraints on gait coordination in people with motor disorders.

METHODS

The search included CINHAL Plus, MEDLINE, HSNAE, SPORTDiscus, Scopus, Pubmed and AMED. We included studies that compared intra-limb and inter-limb coordination during gait between individuals with a motor disorder and able-bodied individuals, and under different task constraints. Two reviewers independently examined the quality of studies by using the Newcastle Ottawa Scale-cohort study.

FINDINGS

From the search results, we identified 1416 articles that studied gait patterns and further analysis resulted in 33 articles for systematic review and 18 articles for meta-analysis-1, and 10 articles for meta-analysis-2. In total, the gait patterns of 539 patients and 358 able-bodied participants were analysed in the sampled studies. Results of the meta-analysis for group comparisons revealed a low effect size for group differences (ES = -0.24), and a moderate effect size for task interventions (ES = -0.53), on limb coordination during gait.

INTERPRETATION

Findings demonstrated that motor disorders can be considered as an individual constraint, significantly altering gait patterns. These findings suggest that gait should be interpreted as functional adaptation to changing personal constraints, rather than as an abnormality. Results imply that designing gait interventions, through modifying locomotion tasks, can facilitate the emergent re-organisation of inter-limb coordination patterns during rehabilitation.

Quantifying Dynamic Balance in Young, Elderly and Parkinson's Individuals: A Systematic Review

Introduction: Falling is one of the primary concerns for people with Parkinson's Disease and occurs predominately during dynamic movements, such as walking. Several methods have been proposed to quantify dynamic balance and to assess fall risk. However, no consensus has been reached concerning which method is most appropriate for examining walking balance during unperturbed and perturbed conditions, particularly in Parkinson's Disease individuals. Therefore, this systematic review aimed to assess the current literature on quantifying dynamic balance in healthy young, elderly and Parkinson's individuals during unperturbed and perturbed walking. Methods: The PubMed database was searched by title and abstract for publications quantifying dynamic balance during unperturbed and mechanically perturbed walking conditions in elderly adults and PD. Inclusion criteria required publications to be published in English, be available in full-text, and implement a dynamic balance quantification method. Exclusion criteria included clinical dynamic balance measures, non-mechanical perturbations, pathologies other than PD, and dual-tasking conditions. The initial database search yielded 280 articles, however, only 81 articles were included after title, abstract and full-text screening. Methodological quality and data were extracted from publications included in the final synthesis. Results: The dynamic balance articles included 26 Coefficient of Variation of Spatiotemporal Variability, 10 Detrended Fluctuation Analysis, 20 Lyapunov Exponent, 7 Maximum Floquet Multipliers, 17 Extrapolated Center of Mass, 11 Harmonic Ratios, 4 Center of Mass-Center of Pressure Separation, 2 Gait Stability Ratio, 1 Entropy, 3 Spatiotemporal Variables, 2 Center of Gravity and Center of Pressure, and 2 Root Mean Square in the final synthesis. Assessment of methodological quality determined that 58 articles had a low methodological rating, a 22 moderate rating, and 1 having a high rating. Conclusion: Careful consideration must be given when selecting a method to quantify dynamic balance because each method defines balance differently, reflects a unique aspect of neuromuscular stability mechanisms, and is dependent on the walking condition (unperturbed vs. perturbed). Therefore, each method provides distinct information into stability impairment in elderly and PD individuals.

Freezing-related perception deficits of asymmetrical walking in Parkinson's disease

Patients with Parkinson's disease (PD), and especially those with freezing of gait (FOG), are known to experience impairments in gait rhythmicity, symmetry, and bilateral coordination between both legs. In the current study, we investigated whether deficits in perception of gait speed between limbs were more pronounced in freezers than in non-freezers and could explain some of these gait impairments. We also assessed cognitive ability and proprioception. Twenty-five PD patients (13 freezers, 12 non-freezers) and 12 healthy controls walked on a split-belt treadmill, while the speed of one of the belts was gradually increased. Participants had to indicate the moment at which they perceived belt speeds to be different. The main outcome variables were the number of correct responses (perception accuracy) and the difference in belt speeds at the moment the participants perceived belt speeds to be different (perception threshold). In addition, gait characteristics during both split- and tied-belt walking were determined. Results showed significantly lower perception accuracy in freezers, whereas the perception threshold did not differ between groups. During tied-belt walking, freezers exhibited more asymmetrical step lengths and limb excursions than non-freezers and healthy controls. Greater step length and limb excursions were associated with better perception, whereas more variable gait was associated with more impaired perception. The results confirm the hypothesis that freezers have impaired perception of locomotor asymmetry. While proprioceptive and cognitive ability did not explain these findings, the possible causal link with the occurrence of FOG needs further corroboration.

Split-belt locomotion in Parkinson's disease links asymmetry, dyscoordination and sequence effect

BACKGROUND

The pathophysiology behind gait impairments seen in Parkinson's disease (PD), in particular freezing of gait (FOG), is not fully understood. Here we study the interplay between several gait features related to FOG during different split-belt treadmill (SBTM) conditions.

METHODS

We investigated the spatiotemporal properties, the phenomenon of sequence effect and the inter-limb symmetry and temporal coordination of gait during different split-belt conditions in 20 patients with advanced Parkinson's disease and different severities of freezing. Subjects were tested in four belt configurations: tied, split while reducing the velocity of leg with the shorter (worst side reduction, WSR) and longer (best side reduction, BSR) step length, and tied again to measure the after-effect.

RESULTS

We found that in spite of an improvement of spatial symmetry, the BSR led to a worsening of coordination (i.e. the left-right anti-phased stepping) and an increased sequence effect (i.e. progressive shortening of the step length). By contrast, in spite of a worsened spatial symmetry, WSR improved inter-limbs coordination and reduced the sequence effect. After prolonged split-belt walking gait was differently modulated according to the reduction of the best or worst leg velocity: BSR led to positive after effects in symmetry, bilateral coordination and sequence effect.

CONCLUSIONS

These findings support the hypothesis that the irregularity of inter-limb coordination and defective amplitude generation leading to sequence effect might be coupled and result from the same maladaptive motor behavior. Furthermore, our results show that SBTM can be an effective tool to improve parkinsonian gait.

Spatiotemporal Characteristics of Freezing of Gait in Patients After Hypoxic-Ischemic Brain Injury: A Pilot Study

The objective of this study was to investigate spatiotemporal characteristics with gait variability in patients with freezing of gait (FOG) after hypoxic-ischemic brain injury (HIBI).Eleven patients showing FOG after HIBI and 15 normal controls were consecutively enrolled. We performed gait analysis using a computerized gait system (VICON MX-T10 Motion Analysis System) and compared spatiotemporal characteristics and gait variability in both groups. Additionally, we performed correlation analysis to identify the gait parameters associated with severity of freezing, which we measured based on unified Parkinson disease Rating Scale subscore.Spatiotemporal characteristic of FOG patients showed increased stance time and double support phase and decreased swing time, single support phase, stride length, step length, and gait velocity compared with normal controls (P < 0.05). Besides baseline spatiotemporal characteristics, step time asymmetry and step length asymmetry were significantly increased in HIBI patients with FOG (P < 0.05). The coefficient of variation, which reflects the variability of each parameter, demonstrated increased cadence, stride time, swing time, single support phase, stride length, step length, and gait velocity variability in HIBI patients with FOG compared with normal controls (P < 0.05). Correlation analysis between FOG severity and spatiotemporal parameters revealed gait velocity, step length, and single support phase to be spatiotemporal parameters related to FOG severity (P < 0.05).Our findings suggest that bilateral gait coordination deterioration plays a considerable role for pathophysiology of FOG in HIBI patients. Additional studies with a larger number of subjects are needed to further investigate the neural mechanism of FOG after HIBI.

Reduced after-effects following podokinetic adaptation in people with Parkinson's disease and freezing of gait

INTRODUCTION

Gait dysfunction is common in people with Parkinson's disease (PD). Freezing of gait (FOG) is one such gait disturbance that significantly impacts mobility and quality of life in PD. Recent evidence suggests that cerebellar connectivity may differ in people with PD and FOG (PD+FOG) relative to those without FOG (PD-FOG). Investigation of gait adaptation, or the ability to change gait patterns in response to external perturbations, is cerebellum-dependent, is a practical means of probing cerebellar integrity and may provide additional insights regarding the FOG phenomenon.

METHODS

In this study, we investigated gait adaptation in PD and FOG by measuring after-effects, namely whole-body rotation, following stepping on a rotating disc in PD+FOG compared to PD-FOG and older healthy adults. We refer to the period of stepping on the rotating disc as the podokinetic (PK) stimulation and after-effects as podokinetic after-rotation (PKAR). Our primary measure of adaptation was the magnitude and rate of decay of the after-effects.

RESULTS

We noted that PKAR was diminished in PD+FOG compared to the other groups, indicating reduced storage of the adapted gait pattern in PD+FOG. In the PD groups, FOG explained about 20% of the variability in peak velocity. Furthermore, these differences were independent of stepping cadence or motor sign severity.

CONCLUSION

Our results show that gait adaptation is impaired in PD+FOG, suggesting the cerebellum may be differentially impacted in PD+FOG compared to PD-FOG. This supports previous neuroimaging evidence of cerebellar dysfunction in PD+FOG. Overall, these data further our understanding of gait deficits in PD+FOG.

Gait asymmetry during early split-belt walking is related to perception of belt speed difference

Gait adaptation is essential for humans to walk according to the different demands of the environment. Although locomotor adaptation has been studied in different contexts and in various patient populations, the mechanisms behind locomotor adaptation are still not fully understood. The aim of the present study was to test two opposing hypotheses about the control of split-belt walking, one based on avoidance of limping and the other on avoiding limb excursion asymmetry. We assessed how well cerebellar patients with focal lesions and healthy control participants could sense differences between belt speeds during split-belt treadmill walking and correlated this to split-belt adaptation parameters. The ability to perceive differences between belt speeds was similar between the cerebellar patients and the healthy controls. After combining all participants, we observed a significant inverse correlation between stance time symmetry and limb excursion symmetry during the early phase of split-belt walking. Participants who were better able to perceive belt speed differences (e.g., they had a lower threshold and hence were able to detect a smaller speed difference) walked with the smallest asymmetry in stance time and the largest asymmetry in limb excursion. Our data support the hypothesis that humans aim to minimize (temporal) limping rather than (spatial) limb excursion asymmetry when using their perception of belt speed differences in the early phase of adaptation to split-belt walking.

Adaptation and aftereffects of split-belt walking in cerebellar lesion patients

To walk efficiently and stably on different surfaces under various constrained conditions, humans need to adapt their gait pattern substantially. Although the mechanisms behind locomotor adaptation are still not fully understood, the cerebellum is thought to play an important role. In this study we aimed to address the specific localization of cerebellar involvement in split-belt adaptation by comparing performance in patients with stable focal lesions after cerebellar tumor resection and in healthy controls. We observed that changes in symmetry of those parameters that were most closely related to interlimb coordination (such as step length and relative double stance time) were similar between healthy controls and cerebellar patients during and after split-belt walking. In contrast, relative stance times (proportions of stance in the gait cycle) were more asymmetric for the patient group than for the control group during the early phase of the post-split-belt condition. Patients who walked with more asymmetric relative stance times were more likely to demonstrate lesions in vermal lobules VI and Crus II. These results confirm that deficits in gait adaptation vary with ataxia severity and between patients with different types of cerebellar damage.

Prism adaptation in Parkinson disease: comparing reaching to walking and freezers to non-freezers

Visuomotor adaptation to gaze-shifting prism glasses requires recalibration of the relationship between sensory input and motor output. Healthy individuals flexibly adapt movement patterns to many external perturbations; however, individuals with cerebellar damage do not adapt movements to the same extent. People with Parkinson disease (PD) adapt normally, but exhibit reduced after-effects, which are negative movement errors following the removal of the prism glasses and are indicative of true spatial realignment. Walking is particularly affected in PD, and many individuals experience freezing of gait (FOG), an episodic interruption in walking, that is thought to have a distinct pathophysiology. Here, we examined how individuals with PD with (PD + FOG) and without (PD - FOG) FOG, along with healthy older adults, adapted both reaching and walking patterns to prism glasses. Participants completed a visually guided reaching and walking task with and without rightward-shifting prism glasses. All groups adapted at similar rates during reaching and during walking. However, overall walking adaptation rates were slower compared to reaching rates. The PD - FOG group showed smaller after-effects, particularly during walking, compared to PD + FOG, independent of adaptation magnitude. While FOG did not appear to affect characteristics of prism adaptation, these results support the idea that the distinct neural processes governing visuomotor adaptation and storage are differentially affected by basal ganglia dysfunction in PD.

Motor Switching and Motor Adaptation Deficits Contribute to Freezing of Gait in Parkinson’s Disease

Background. Patients with freezing of gait (FOG) have more difficulty with switching tasks as well as controlling the spatiotemporal parameters of gait than patients without FOG. Objective. To compare the ability of patients with and without FOG to adjust their gait to sudden speed switching and to prolonged walking in asymmetrical conditions. Methods. Gait characteristics of 10 freezers, 12 non-freezers, and 12 controls were collected during tied-belt conditions (3 and 4 km/h), motor switching and reswitching (increase of speed in one belt from 3 to 4 km/h and vice versa), and adaptation (adjustment to asymmetrical gait) and re-adaptation (returning to symmetrical gait) on a split-belt treadmill. Results. Following switching, freezers showed the largest increase of step length asymmetry ( P = .001). All groups gradually adapted their gait to asymmetrical conditions, but freezers were slower and demonstrated larger final asymmetry than the other 2 groups ( P = .001). After reswitching, freezers again showed the largest step length asymmetry ( P = .01). During re-adaptation, both controls and non-freezers reached symmetrical levels, but freezers did not. Interestingly, only immediately after switching did one episode of FOG and one episode of festination occur in 2 different patients. Conclusions. Freezers have more difficulties adapting their gait during both suddenly triggered and continued gait speed asymmetry. The impaired ability of freezers during both switching and reswitching would suggest that they have an adaptive deficit rather than difficulties with asymmetry per se. Future work needs to address whether these adaptation problems can be ameliorated with rehabilitation.

Spatiotemporal control of interlimb coordination during transverse split-belt locomotion with 1:1 or 2:1 coupling patterns in intact adult cats

Interlimb coordination must be flexible to adjust to an ever-changing environment. Here adjustments in interlimb coordination were quantified during tied-belt (equal speed of the fore- and hindlimbs) and transverse split-belt (unequal speed of the fore- and hindlimbs) locomotion in five intact adult cats. Cats performed tied-belt locomotion at 0.4 m/s and 0.8 m/s. For transverse split-belt locomotion, the forelimbs stepped at 0.4 m/s and 0.8 m/s while the hindlimbs stepped at 0.8 m/s (4F8H condition) and 0.4 m/s (8F4H condition), respectively. In the 8F4H condition, the forelimbs could take two steps within one hindlimb cycle, or a 2:1 forelimb-hindlimb relationship. The sequence of limbs contacting the ground and the duration of support periods were differentially modified if the forelimbs stepped faster or slower than the hindlimbs. During transverse split-belt locomotion, the hindlimbs performed longer strides when the forelimbs took shorter strides. In the 8F4H condition with a 2:1 forelimb-hindlimb relationship, phase and gap intervals for the first and second steps were found around certain values and were not randomly distributed, indicating that a new coupling pattern was established. However, temporal and spatial coordination indexes revealed that bilateral coordination between hindlimbs was less accurate and more variable with a 2:1 coupling pattern. Importantly, the animals did not stumble, indicating that spatial and temporal adjustments in interlimb coordination allowed the animals to maintain dynamic stability. The results provide a better understanding of the spatiotemporal adjustments that take place among the four limbs during locomotion when interlimb coordination is challenged.

Effects of dopaminergic therapy on locomotor adaptation and adaptive learning in persons with Parkinson's disease

Persons with Parkinson's disease (PD) are characterized by multifactorial gait deficits, though the factors which influence the abilities of persons with PD to adapt and store new gait patterns are unclear. The purpose of this study was to investigate the effects of dopaminergic therapy on the abilities of persons with PD to adapt and store gait parameters during split-belt treadmill (SBT) walking. Ten participants with idiopathic PD who were being treated with stable doses of orally-administered dopaminergic therapy participated. All participants performed two randomized testing sessions on separate days: once while optimally-medicated (ON meds) and once after 12-h withdrawal from dopaminergic medication (OFF meds). During each session, locomotor adaptation was investigated as the participants walked on a SBT for 10 min while the belts moved at a 2:1 speed ratio. We assessed locomotor adaptive learning by quantifying: (1) aftereffects during de-adaptation (once the belts returned to tied speeds immediately following SBT walking) and (2) savings during re-adaptation (as the participants repeated the same SBT walking task after washout of aftereffects following the initial SBT task). The withholding of dopaminergic medication diminished step length aftereffects significantly during de-adaptation. However, both locomotor adaptation and savings were unaffected by levodopa. These findings suggest that dopaminergic pathways influence aftereffect storage but do not influence locomotor adaptation or savings within a single session of SBT walking. It appears important that persons with PD should be optimally-medicated if walking on the SBT as gait rehabilitation.

Muscle activation patterns are bilaterally linked during split-belt treadmill walking in humans

There is growing evidence that human locomotion is controlled by flexibly combining a set of basic muscle activity patterns. To explore how these patterns are modified to cope with environmental constraints, 10 healthy young adults 1st walked on a split-belt treadmill at symmetric speeds of 4 and 6 km/h for 2 min. An asymmetric condition was then performed for 10 min in which treadmill speeds for the dominant (fast) and nondominant (slow) sides were 6 and 4 km/h, respectively. This was immediately followed by a symmetric speed condition of 4 km/h for 5 min. Gait kinematics and ground reaction forces were recorded. Electromyography (EMG) was collected from 12 lower limb muscles on each side of the body. Nonnegative matrix factorization was applied to the EMG signals bilaterally and unilaterally to obtain basic activation patterns. A cross-correlation analysis was then used to quantify temporal changes in the activation patterns. During the early (1st 10 strides) and late (final 10 strides) phases of the asymmetric condition, the patterns related to ankle plantar flexor (push-off) of the fast limb and quadriceps muscle (contralateral heel contact) of the slow limb occurred earlier in the gait cycle compared with the symmetric conditions. Moreover, a bilateral temporal alignment of basic patterns between limbs was still maintained in the split-belt condition since a similar shift was observed in the unilateral patterns. The results suggest that the temporal structure of these locomotor patterns is shaped by sensory feedback and that the patterns are bilaterally linked.

Stride length asymmetry in split-belt locomotion

The number of studies utilizing a split-belt treadmill is rapidly increasing in recent years. This has led to some confusion regarding the definitions of reported gait parameters. The purpose of this paper is to clearly present the definitions of the gait parameters that are commonly used in split-belt treadmill studies. We argue that the modified version of stride length for split-belt gait, which is different from the standard definition of stride length and actually is a measure of limb excursion, should be referred to as 'limb excursion' in future studies. Furthermore, the symmetry of stride length and stride time is specifically addressed.

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.