Neurophysiology of gait: from the spinal cord to the frontal lobe

Cognitive load reduces the effects of optic flow on gait and electrocortical dynamics during treadmill walking

During navigation of complex environments, the brain must continuously adapt to both external demands, such as fluctuating sensory inputs, and internal demands, such as engagement in a cognitively demanding task. Previous studies have demonstrated changes in behavior and gait with increased sensory and cognitive load, but the underlying cortical mechanisms remain largely unknown. In the present study, in a mobile brain/body imaging (MoBI) approach, 16 young adults walked on a treadmill with high-density EEG while 3-dimensional (3D) motion capture tracked kinematics of the head and feet. Visual load was manipulated with the presentation of optic flow with and without continuous mediolateral perturbations. The effects of cognitive load were assessed by the performance of a go/no-go task on half of the blocks. During increased sensory load, participants walked with shorter and wider strides, which may indicate a more restrained pattern of gait. Interestingly, cognitive task engagement attenuated these effects of sensory load on gait. Using an independent component analysis and dipole-fitting approach, we found that cautious gait was accompanied by neuro-oscillatory modulations localized to frontal (supplementary motor area, anterior cingulate cortex) and parietal (inferior parietal lobule, precuneus) areas. Our results show suppression in alpha/mu (8-12 Hz) and beta (13-30 Hz) rhythms, suggesting enhanced activation of these regions with unreliable sensory inputs. These findings provide insight into the neural correlates of gait adaptation and may be particularly relevant to older adults who are less able to adjust to ongoing cognitive and sensory demands while walking. NEW & NOTEWORTHY The neural underpinnings of gait adaptation in humans are poorly understood. To this end, we recorded high-density EEG combined with three-dimensional body motion tracking as participants walked on a treadmill while exposed to full-field optic flow stimulation. Perturbed visual input led to a more cautious gait pattern with neuro-oscillatory modulations localized to premotor and parietal regions. Our findings show a possible brain-behavior link that might further our understanding of gait and mobility impairments.

Resting-state functional connectivity of subcortical locomotor centers explains variance in walking capacity

Walking capacity influences the quality of life and disability in normal aging and neurological disease, but the neural correlates remain unclear and subcortical locomotor regions identified in animals have been more challenging to assess in humans. Here we test whether resting-state functional MRI connectivity (rsFC) of midbrain and cerebellar locomotor regions (MLR and CLR) is associated with walking capacity among healthy adults. Using phenotypic and MRI data from the Nathan Kline Institute Rockland Sample (n =119, age 18-85), the association between walking capacity (6-min walk test distance) and rsFC was calculated from subcortical locomotor regions to 81 other gait-related regions of interest across the brain. Additional analyses assessed the independence and specificity of the results. Walking capacity was associated with higher rsFC between the MLR and superior frontal gyrus adjacent to the anterior cingulate cortex, higher rsFC between the MLR and paravermal cerebellum, and lower rsFC between the CLR and primary motor cortex foot area. These rsFC correlates were more strongly associated with walking capacity than phenotypic variables such as age, and together explained 25% of the variance in walking capacity. Results were specific to locomotor regions compared with the other brain regions. The rsFC of locomotor centers correlates with walking capacity among healthy adults. These locomotion-related biomarkers may prove useful in future work aimed at helping patients with reduced walking capacity.

A functional limitation to the lower limbs affects the neural bases of motor imagery of gait

Studies on athletes or neurological patients with motor disorders have shown a close link between motor experience and motor imagery skills. Here we evaluated whether a functional limitation due to a musculoskeletal disorder has an impact on the ability to mentally rehearse the motor patterns of walking, an overlearned and highly automatic behaviour. We assessed the behavioural performance (measured through mental chronometry tasks) and the neural signatures of motor imagery of gait in patients with chronic knee arthrosis and in age-matched, healthy controls. During fMRI, participants observed (i) stationary or (ii) moving videos of a path in a park shown in the first-person perspective: they were asked to imagine themselves (i) standing on or (ii) walking along the path, as if the camera were “their own eyes” (gait imagery (GI) task). In half of the trials, participants performed a dynamic gait imagery (DGI) task by combining foot movements with GI. Behavioural tests revealed a lower degree of isochrony between imagined and performed walking in the patients, indicating impairment in the ability to mentally rehearse gait motor patterns. Moreover, fMRI showed widespread hypoactivation during GI in motor planning (premotor and parietal) brain regions, the brainstem, and the cerebellum. Crucially, the performance of DGI had a modulatory effect on the patients and enhanced activation of the posterior parietal, brainstem, and cerebellar regions that the healthy controls recruited during the GI task. These findings show that functional limitations of peripheral origin may impact on gait motor representations, providing a rationale for cognitive rehabilitation protocols in patients with gait disorders of orthopaedic nature. The DGI task may be a suitable tool in this respect.

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Patients with chronic knee arthrosis show impairment in gait motor imagery

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Impairment is selective for gait and paralleled by hypoactivation in premotor areas

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Peripheral limitation of lower limb movements affects central gait motor control

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Dynamic motor imagery favours the recruitment of a motor strategy during imagery

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Mental motor training might help to restore gait control in orthopaedic patients

Tracking the Re-organization of Motor Functions After Disconnective Surgery: A Longitudinal fMRI and DTI Study

Objective: Mechanisms of motor plasticity are critical to maintain motor functions after cerebral damage. This study explores the mechanisms of motor reorganization occurring before and after surgery in four patients with drug-refractory epilepsy candidate to disconnective surgery.

Methods: We studied four patients with early damage, who underwent tailored hemispheric surgery in adulthood, removing the cortical motor areas and disconnecting the corticospinal tract (CST) from the affected hemisphere. Motor functions were assessed clinically, with functional MRI (fMRI) tasks of arm and leg movement and Diffusion Tensor Imaging (DTI) before and after surgery with assessments of up to 3 years. Quantifications of fMRI motor activations and DTI fractional anisotropy (FA) color maps were performed to assess the lateralization of motor network. We hypothesized that lateralization of motor circuits assessed preoperatively with fMRI and DTI was useful to evaluate the motor outcome in these patients.

Results: In two cases preoperative DTI-tractography did not reconstruct the CST, and FA-maps were strongly asymmetric. In the other two cases, the affected CST appeared reduced compared to the contralateral one, with modest asymmetry in the FA-maps. fMRI showed different degrees of lateralization of the motor network and the SMA of the intact hemisphere was mostly engaged in all cases. After surgery, patients with a strongly lateralized motor network showed a stable performance. By contrast, a patient with a more bilateral pattern showed worsening of the upper limb function. For all cases, fMRI activations shifted to the intact hemisphere. Structural alterations of motor circuits, observed with FA values, continued beyond 1 year after surgery.

Conclusion: In our case series fMRI and DTI could track the longitudinal reorganization of motor functions. In these four patients the more the paretic limbs recruited the intact hemisphere in primary motor and associative areas, the greater the chances were of maintaining elementary motor functions after adult surgery. In particular, DTI-tractography and quantification of FA-maps were useful to assess the lateralization of motor network. In these cases reorganization of motor connectivity continued for long time periods after surgery.

Gait Disorders

Walking is an extraordinarily complex task requiring integration of the entire nervous system, making gait susceptible to a variety of underlying neurologic abnormalities. Gait disorders are particularly prevalent in the elderly and increase fall risk. In this review we discuss an approach to the examination of gait and highlight key features of common gait disorders and their underlying causes. We review gaits due to lesions of motor systems (spasticity and neuromuscular weakness), the cerebellum and sensory systems (ataxia), parkinsonism, and frontal lobes and discuss the remarkably diverse phenomenology of functional (psychogenic) gait disorders. We offer a pragmatic approach to the diagnosis and management of neurologic gait disorders, because prompt recognition and intervention may improve quality of life in affected individuals.

The Dorsal Column Lesion Model of Spinal Cord Injury and Its Use in Deciphering the Neuron-Intrinsic Injury Response

The neuron‐intrinsic response to axonal injury differs markedly between neurons of the peripheral and central nervous system. Following a peripheral lesion, a robust axonal growth program is initiated, whereas neurons of the central nervous system do not mount an effective regenerative response. Increasing the neuron‐intrinsic regenerative response would therefore be one way to promote axonal regeneration in the injured central nervous system. The large‐diameter sensory neurons located in the dorsal root ganglia are pseudo‐unipolar neurons that project one axon branch into the spinal cord, and, via the dorsal column to the brain stem, and a peripheral process to the muscles and skin. Dorsal root ganglion neurons are ideally suited to study the neuron‐intrinsic injury response because they exhibit a successful growth response following peripheral axotomy, while they fail to do so after a lesion of the central branch in the dorsal column. The dorsal column injury model allows the neuron‐intrinsic regeneration response to be studied in the context of a spinal cord injury. Here we will discuss the advantages and disadvantages of this model. We describe the surgical methods used to implement a lesion of the ascending fibers, the anatomy of the sensory afferent pathways and anatomical, electrophysiological, and behavioral techniques to quantify regeneration and functional recovery. Subsequently we review the results of experimental interventions in the dorsal column lesion model, with an emphasis on the molecular mechanisms that govern the neuron‐intrinsic injury response and manipulations of these after central axotomy. Finally, we highlight a number of recent advances that will have an impact on the design of future studies in this spinal cord injury model, including the continued development of adeno‐associated viral vectors likely to improve the genetic manipulation of dorsal root ganglion neurons and the use of tissue clearing techniques enabling 3D reconstruction of regenerating axon tracts. © 2018 The Authors. Developmental Neurobiology Published by Wiley Periodicals, Inc. Develop Neurobiol 00: 000–000, 2018

Day-to-Day Variability of Postural Sway and Its Association With Cognitive Function in Older Adults: A Pilot Study

Introduction: Increased variability in motor function has been observed during the initial stages of cognitive decline. However, the natural variability of postural control, as well as its association with cognitive status and decline, remains unknown. The objective of this pilot study was to characterize the day-to-day variability in postural sway in non-demented older adults. We hypothesized that older adults with a lower cognitive status would have higher day-to-day variability in postural sway. Materials and Methods: A Nintendo Wii balance board (WBB) was used to quantify postural sway in the home twice daily for 30 days in 20 non-demented, community-dwelling older adults: once under a single-task condition and once under a dual-task condition (using a daily word search task administered via a Nook tablet). Mean sway distance, velocity, area, centroidal frequency and frequency dispersion were derived from the center of pressure data acquired from the WBB. Results: Linear relationships were observed between the day-to-day variability in postural sway and cognitive status (indexed by cognitive global z-scores). More variability in time-domain postural sway (sway distance and area) and less variability in frequency-domain postural sway (centroidal sway frequency) were associated with a lower cognitive status under both the single- and dual-task conditions. Additionally, lower cognitive performance rates on the daily word search task were related to a lower cognitive status. Discussion: This small pilot study conducted on a short time scale motivates large-scale implementations over more extended time periods. Tracking longitudinal changes in postural sway may further our understanding of early-stage postural decline and its association with cognitive decline and, in turn, may aid in the early detection of dementia during preclinical stages when the utility of disease-modifying therapies would be greatest.

Cortical activity during walking and balance tasks in older adults and in people with Parkinson's disease: A structured review

An emerging body of literature has examined cortical activity during walking and balance tasks in older adults and in people with Parkinson's disease, specifically using functional near infrared spectroscopy (fNIRS) or electroencephalography (EEG). This review provides an overview of this developing area, and examines the disease-specific mechanisms underlying walking or balance deficits. Medline, PubMed, PsychInfo and Scopus databases were searched. Articles that described cortical activity during walking and balance tasks in older adults and in those with PD were screened by the reviewers. Thirty-seven full-text articles were included for review, following an initial yield of 566 studies. This review summarizes study findings, where increased cortical activity appears to be required for older adults and further for participants with PD to perform walking and balance tasks, but specific activation patterns vary with the demands of the particular task. Studies attributed cortical activation to compensatory mechanisms for underlying age- or PD-related deficits in automatic movement control. However, a lack of standardization within the reviewed studies was evident from the wide range of study protocols, instruments, regions of interest, outcomes and interpretation of outcomes that were reported. Unstandardized data collection, processing and reporting limited the clinical relevance and interpretation of study findings. Future work to standardize approaches to the measurement of cortical activity during walking and balance tasks in older adults and people with PD with fNIRS and EEG systems is needed, which will allow direct comparison of results and ensure robust data collection/reporting. Based on the reviewed articles we provide clinical and future research recommendations.

Do depressive symptoms affect balance in older adults with mild cognitive impairment? Results from the "gait and brain study"

BACKGROUND

Mild cognitive impairment (MCI) and depression independently affect balance control in older adults. However, it is uncertain whether depressive symptoms would amplify balance problems in older adults with MCI.

AIM

To evaluate if the presence of significant depressive symptoms affects postural sway under somatosensory challenges in a MCI population.

METHODS

Eighty two participants (mean of 75.3 ± 6.4 years of age; 46% women) with MCI completed cognitive and balance assessments. Participants were grouped by severity of depressive symptoms using the Geriatric Depression Scale-15, as MCI with depressive symptoms (MCI-D = 14, score ≥ 5) and MCI without depressive symptoms (MCI = 68, score < 5). Postural sway area was evaluated during eyes open (EO) and eyes closed (EC) while standing on a rigid flat force plate platform, and compared across groups. Analyses were controlled for age, sex, comorbidities, anti-depressant medication use, executive function, and baseline sway.

RESULTS

MCI-D showed larger postural sway area when compared with MCI irrespective of visual feedback conditions (p = 0.03). This difference remained significant after adjusting for anti-depressant use and executive function performance. The lack of interaction between groups and visual condition was associated with group differences in postural sway during EO condition (Beta = 0.08, CI -257.5-621.9; p = 0.41) and by comparable sway increase from EO to EC in both groups.

CONCLUSION

Depressive symptoms in individuals with MCI worsened postural stability during both eyes open and eyes closed conditions independently of cognitive function. Significant depressive symptoms may affect balance in MCI populations, potentially increasing the risk of falls.

Brain mapping for long-term recovery of gait after supratentorial stroke: A retrospective cross-sectional study

The recovery of independent gait after stroke is a main goal of patients and understanding the relationship between brain lesions and the recovery of gait can help physicians set viable rehabilitation plans. Our study investigated the association between variables of gait parameters and brain lesions.Fifty poststroke patients with a mean age of 67.5 ± 1.3 years and an average duration after onset of 62.2 ± 7.9 months were included. Three-dimensional gait analysis and magnetic resonance imaging were conducted for all patients. Twelve quantified gait parameters of temporal-spatial, kinematic, and kinetic data were used. To correlate gait parameters with specific brain lesions, we used a voxel-based lesion symptom mapping analysis. Statistical significance was set to an uncorrected P value <.005 and cluster size >10 voxels.Based on the location of a brain lesion, the following results were obtained: The posterior limb of the internal capsule was significantly associated with gait speed and increased knee extension in the stance phase. The hippocampus and frontal lobe were significantly associated with cadence. The proximal corona radiata was significantly associated with stride length and affected the hip maximal extension angle in the stance phase. The paracentral lobule was significantly associated with the affected knee maximal flexion angle in the swing phase and with the affected ankle maximal dorsiflexion angle in the stance phase. The frontal lobe, thalamus, and the lentiform nucleus were associated with kinetic gait parameters.Cortical, proximal white matter, and learning-related and motor-related areas are mainly associated with one's walking ability after stroke.

[Changes in walking in the elderly]

The article addresses gait disturbances in the elderly. It emphasizes that the system that maintains the balance in resting conditions and gait is based on the hierarchical principle and its function depends on the maintenance of integration between vestibular, visual and somatosensory information as well as on cognitive functions. Walking depends on the integrity of frontal-subcortical neuronal circles that support regulatory functions. The main pathogenetic mechanisms of age-related disturbances of balance and gait are a decrease in the efficacy of spinal motorneurons activation caused by Ia-afferentation, a decrease in cortical activation and excitability of corticospinal pathways and in the intensity of intracortical inhibition. The causes of age-related changes in walking are not confined to a single system (e.g., one sensory modality) but have a multisystem character and are involved in many structures. The author analyses the results of recent studies that use functional neuroimaging methods.

Profiling walking dysfunction in multiple sclerosis: characterisation, classification and progression over time

Gait dysfunction is a common and relevant symptom in multiple sclerosis (MS). This study aimed to profile gait pathology in gait-impaired patients with MS using comprehensive 3D gait analysis and clinical walking tests. Thirty-seven patients with MS walked on the treadmill at their individual, sustainable speed while 20 healthy control subjects walked at all the different patient's paces, allowing for comparisons independent of walking velocity. Kinematic analysis revealed pronounced restrictions in knee and ankle joint excursion, increased gait variability and asymmetry along with impaired dynamic stability in patients. The most discriminative single gait parameter, differentiating patients from controls with an accuracy of 83.3% (χ2 test; p = 0.0001), was reduced knee range of motion. Based on hierarchical cluster and principal component analysis, three principal pathological gait patterns were identified: a spastic-paretic, an ataxia-like, and an unstable gait. Follow-up assessments after 1 year indicated deterioration of walking function, particularly in patients with spastic-paretic gait patterns. Our findings suggest that impaired knee/ankle control is common in patients with MS. Personalised gait profiles and clustering algorithms may be promising tools for stratifying patients and to inform patient-tailored exercise programs. Responsive, objective outcome measures are important for monitoring disease progression and treatment effects in MS trials.

Neuromodulatory procedures for gait disorders in Parkinson's disease

The neurophysiology of gait is complex and involves numerous structures in the central nervous system. Gait disorders occur frequently in Parkinson's disease (PD), and their management may become cumbersome, especially in the more advanced stages. Neuromodulatory treatments, including deep brain stimulation, cortical stimulation and spinal cord stimulation, are reviewed with respect to their effectiveness to improve gait in PD patients. Although positive effects have been reported for all of these procedures, many issues remain in view of methodological heterogeneity, variability in outcome measures and sample size. Gait in PD remains a difficult issue with a tremendous impact on quality of life, for which future research is badly needed.

Assessing Brain-Muscle Connectivity in Human Locomotion through Mobile Brain/Body Imaging: Opportunities, Pitfalls, and Future Directions

Assessment of the cortical role during bipedalism has been a methodological challenge. While surface electroencephalography (EEG) is capable of non-invasively measuring cortical activity during human locomotion, it is associated with movement artifacts obscuring cerebral sources of activity. Recently, statistical methods based on blind source separation revealed potential for resolving this issue, by segregating non-cerebral/artifactual from cerebral sources of activity. This step marked a new opportunity for the investigation of the brains' role while moving and was tagged mobile brain/body imaging (MoBI). This methodology involves simultaneous mobile recording of brain activity with several other body behavioral variables (e.g., muscle activity and kinematics), through wireless recording wearable devices/sensors. Notably, several MoBI studies using EEG-EMG approaches recently showed that the brain is functionally connected to the muscles and active throughout the whole gait cycle and, thus, rejecting the long-lasting idea of a solely spinal-driven bipedalism. However, MoBI and brain/muscle connectivity assessments during human locomotion are still in their fledgling state of investigation. Mobile brain/body imaging approaches hint toward promising opportunities; however, there are some remaining pitfalls that need to be resolved before considering their routine clinical use. This article discusses several of these pitfalls and proposes research to address them. Examples relate to the validity, reliability, and reproducibility of this method in ecologically valid scenarios and in different populations. Furthermore, whether brain/muscle connectivity within the MoBI framework represents a potential biomarker in neuromuscular syndromes where gait disturbances are evident (e.g., age-related sarcopenia) remains to be determined.

Pisa Syndrome in Parkinson's Disease: Pathogenic Roles of Verticality Perception Deficits

We elucidated whether verticality misperception is associated with the generation of Pisa syndrome (PS) in patients with Parkinson's disease (PD). To examine the heterogenous influence of verticality perception, we also identified the characteristics distinguishing between PD patients with PS who tilted toward the deviation of perceived verticality and those who did not. Subjective visual vertical (SVV) testing was performed in 54 PD patients with PS and 36 without PS to measure verticality perception. Other potential risk factors for PS were evaluated by assessing the asymmetry of motor symptoms, EMG activities of paraspinal muscles, bithermal caloric tests, back pain history, and Berg Balance Scale. Abnormal SVV (odds ratio (OR) 18.40, p = 0.006), postural imbalance (OR 0.71, p = 0.046), and unilateral EMG hyperactivity of paraspinal muscles (OR 39.62, p = 0.027) were independent contributors to PS. In subgroup analysis, EMG hyperactivity of paraspinal muscles contralateral to the leaning side and postural imbalance were associated with PD patients with PS who tilted toward the SVV deviation, whereas back pain was more frequent in those who did not. Verticality misperception is a potent risk factor for PS in PD and contributes differentially to PS depending on the congruence between its direction and PS direction, indicating distinct pathogenic roles.

Gait

Gait is one of the keys to functional independence. For a long-time, walking was considered an automatic process involving minimal higher-level cognitive input. Indeed, walking does not take place without muscles that move the limbs and the "lower-level" control that regulates the timely activation of the muscles. However, a growing body of literature suggests that walking can be viewed as a cognitive process that requires "higher-level" cognitive control, especially during challenging walking conditions that require executive function and attention. Two main locomotor pathways have been identified involving multiple brain areas for the control of posture and gait: the dorsal pathway of cognitive locomotor control and the ventral pathway for emotional locomotor control. These pathways may be distinctly affected in different pathologies that have important implications for rehabilitation and therapy. The clinical assessment of gait should be a focused, simple, and cost-effective process that provides both quantifiable and qualitative information on performance. In the last two decades, gait analysis has gradually shifted from analysis of a few steps in a restricted space to long-term monitoring of gait using body fixed sensors, capturing real-life and routine behavior in the home and community environment. The chapter also describes this evolution and its implications.

Local dynamic stability during treadmill walking can detect children with developmental coordination disorder

OBJECTIVE

Developmental coordination disorder (DCD) is an innate impairment of motor coordination that affects basic locomotion and balance. This study investigated local dynamic stability of trunk accelerations during treadmill walking as an objective evaluation of gait stability and the sensitivity and specificity of this measure to discriminate children with DCD from typically developing children.

METHOD

Eight children with DCD and ten age- and gender-matched typically developing children (TD) walked four minutes on a treadmill. Trunk accelerations in vertical, medio-lateral and anterior-posterior directions were recorded with a sternum mounted accelerometer at 256Hz. Short term local dynamic stability (λs), root mean square (RMS) and relative root mean square (RMSR) were calculated from measures of orthogonal trunk accelerations. Receiver operating characteristic curve (ROC) analysis was performed to discriminate between groups based on short term local dynamic stability.

RESULTS

λs was significantly greater in children with DCD in the main movement direction (AP) (DCD: 1.69±0.17 λs; TD:1.41±0.17 λs; p=0.005), indicating reduced local dynamic stability. RMS and RMSR accelerations showed no difference between children with DCD and TD children in any direction. The ROC analysis of λs in separate directions and in two dimensions showed an excellent accuracy of discriminating between children with DCD and TD children. Anterior-posterior direction in combination with medio-lateral or vertical showed best performance with an area under the curve (AUC) of 0.91.

CONCLUSION

We have shown that children with developmental coordination disorder have general reduced local dynamic stability and that the short term Lyapunov exponent has good power of discrimination between DCD and TD.

Contextual interference during adaptation to asymmetric split-belt treadmill walking results in transfer of unique gait mechanics

When humans make errors in stepping during walking due to a perturbation, they may adapt their gait as a way to correct for discrepancies between predicted and actual sensory feedback. This study sought to determine if increased contextual interference during acquisition of a novel asymmetric gait pattern would change lower-limb mechanical strategies generalized to different walking contexts. Such knowledge could help to clarify the role of contextual interference in locomotor adaptation, and demonstrate potential use in future gait rehabilitation paradigms. One belt on a split-belt treadmill was driven at a constant velocity while the other was driven at changing velocities according to one of three practice paradigms: serial, random blocked, or random training. Subjects returned to complete one of two different transfer tests. Results indicate that during acquisition, random practice requires unique gait mechanics to adapt to a challenging walking environment. Also, results from one transfer test close to that of the acquisition experience did not seem to demonstrate any contextual interference effect. Finally, random blocked practice resulted in highly unique changes in step length symmetry on a second, more challenging, transfer test. This perhaps indicates that a moderate level of contextual interference causes unique locomotor generalization strategies.

Summary: Specific biomechanical gait adaptations occur as a result of variance of stepping errors during walking. Humans optimize a novel gait pattern based on different levels of error variance.

Reversible Cooling-induced Deactivations to Study Cortical Contributions to Obstacle Memory in the Walking Cat

On complex, naturalistic terrain, sensory information about an environmental obstacle can be used to rapidly adjust locomotor movements for avoidance. For example, in the cat, visual information about an impending obstacle can modulate stepping for avoidance. Locomotor adaptation can also occur independent of vision, as sudden tactile inputs to the leg by an expected obstacle can modify the stepping of all four legs for avoidance. Such complex locomotor coordination involves supraspinal structures, such as the parietal cortex. This protocol describes the use of reversible, cooling-induced cortical deactivation to assess parietal cortex contributions to memory-guided obstacle locomotion in the cat. Small cooling loops, known as cryoloops, are specially shaped to deactivate discrete regions of interest to assess their contributions to an overt behavior. Such methods have been used to elucidate the role of parietal area 5 in memory-guided obstacle avoidance in the cat.

Characteristics associated with freezing of gait in actual daily living in Parkinson's disease

[Purpose] Parkinson’s disease (PD) patients often freeze in actual daily living but seldom in clinical setting. This study aimed to identify the factors contributing to freezing of gait (FOG). [Subjects and Methods] The participants included 28 adults with PD. Principal component analysis was used to investigate the characteristics of 14 common FOG situations adopted from previous studies. Cluster analysis classified the subjects into four groups. Kruskal-Wallis test was performed to compare the PD Questionnaire-39 mobility dimension between the groups. [Results] The major variables of the first principal component in 14 FOG situations were unfamiliar places, unpredictable schedule changes, entering an automatic door, when another person suddenly crossed, and change in the walking surface. These situations were unrelated to the second principal component. Getting on/off a public transport and crowded places were major variables for the second principal component, and related to both the first and second principal components. Although fatigue was the most frequent FOG situation, not all principal components were influenced. The values of the PD Questionnaire-39 revealed significant differences between the groups. [Conclusion] Actual FOG situations may be categorized into (1) task complexity, (2) both task complexity and emotional factors, and (3) fatigue as decreased attentional resources.

Transcranial Doppler and Lower Extremity Function in Older Adults: Einstein Aging Study

OBJECTIVES

To determine whether transcranial Doppler ultrasound (TCD) measures of mean blood flow velocity (MBFV) in the major cerebral arteries are associated with measures of lower extremity function in community-dwelling older adults.

DESIGN

Cross-sectional study.

SETTING

Community sample.

PARTICIPANTS

Individuals aged 70 and older (mean 79.5, 54% female) without dementia participating in the Einstein Aging Study (N = 200).

MEASUREMENTS

All participants underwent TCD assessments and tests of lower extremity function at an annual clinic visit. Average MBFV for anterior (left and right anterior and middle cerebral arteries (MCAs)) and posterior (vertebral (VA) and basilar (BA) artery) circulation was measured using a standardized TCD protocol. Lower extremity function was characterized according to gait speed (cm/s) measured using an instrumented walkway, balance according to unipedal stance time (UPST, seconds), and lower extremity strength according to timed repeated chair rise (seconds).

RESULTS

Multiple regression models adjusted for age, sex, race, education, and medical comorbidities showed that lower MBFV in the MCA was associated with slower gait speed and chair rise time but not with UPST. Ordinal regression models showed that lower MBFV in the VA and BA is associated with shorter UPST.

CONCLUSION

Low MBFV in the anterior and posterior cerebral circulation was associated with worse lower extremity function and balance in older adults. This might be indicative of the importance of age-related changes in cerebral hemodynamics in the function of brain regions involved in specific aspects of physical performance.

Brain lesions affecting gait recovery in stroke patients

OBJECTIVES

Gait recovery is an important goal in stroke patients. Several studies have sought to uncover relationships between specific brain lesions and the recovery of gait, but the effects of specific brain lesions on gait remain unclear. Thus, we investigated the effects of stroke lesions on gait recovery in stroke patients.

MATERIALS AND METHODS

In total, 30 subjects with stroke were assessed in a retrograde longitudinal observational study. To assess gait function, the functional ambulation category (FAC) was tested four times: initially (within 2 weeks) and 1, 3, and 6 months after the onset of the stroke. Brain lesions were analyzed via overlap, subtraction, and voxel-based lesion symptom mapping (VLSM).

RESULTS

Ambulation with FAC improved significantly with time. Subtraction analysis showed that involvement of the corona radiata, internal capsule, globus pallidus, and putamen were associated with poor recovery of gait throughout 6 months after onset. The caudate nucleus did influence poor recovery of gait at 6 months after onset. VLSM revealed that corona radiata, internal capsule, globus pallidus, putamen and cingulum were related with poor recovery of gait at 3 months after onset. Corona radiata, internal capsule, globus pallidus, putamen, primary motor cortex, and caudate nucleus were related with poor recovery of gait at 6 months after onset.

CONCLUSION

Results identified several important brain lesions for gait recovery in patients with stroke. These results may be useful for planning rehabilitation strategies for gait and understanding the prognosis of gait in stroke patients.

Gait bradykinesia in Parkinson's disease: a change in the motor program which controls the synergy of gait

This study examined how gait bradykinesia is changed by the motor programming in Parkinson's disease. Thirty-five idiopathic Parkinson's disease patients and nine age-matched healthy subjects participated in this study. After the patients fixated on a visual-fixation target (conditioning-stimulus), the voluntary-gait was triggered by a visual on-stimulus. While the subject walked on a level floor, soleus, tibialis anterior EMG latencies, and the y-axis-vector of the sole-floor reaction force were examined. Three paradigms were used to distinguish between the off-/on-latencies. The gap-task: the visual-fixation target was turned off; 200 ms before the on-stimulus was engaged (resulting in a 200 ms-gap). EMG latency was not influenced by the visual-fixation target. The overlap-task: the on-stimulus was turned on during the visual-fixation target presentation (200 ms-overlap). The no-gap-task: the fixation target was turned off and the on-stimulus was turned on simultaneously. The onset of EMG pause following the tonic soleus EMG was defined as the off-latency of posture (termination). The onset of the tibialis anterior EMG burst was defined as the on-latency of gait (initiation). In the gap-task, the on-latency was unchanged in all of the subjects. In Parkinson's disease, the visual-fixation target prolonged both the off-/on-latencies in the overlap-task. In all tasks, the off-latency was prolonged and the off-/on-latencies were unsynchronized, which changed the synergic movement to a slow, short-step-gait. The synergy of gait was regulated by two independent sensory-motor programs of the off- and on-latency levels. In Parkinson's disease, the delayed gait initiation was due to the difficulty in terminating the sensory-motor program which controls the subject's fixation. The dynamic gait bradykinesia was involved in the difficulty (long off-latency) in terminating the motor program of the prior posture/movement.

Long-term Monitoring Gait Analysis Using a Wearable Device in Daily Lives of Patients with Parkinson's Disease: The Efficacy of Selegiline Hydrochloride for Gait Disturbance

Objective

The aim of this study was to assess quantitatively the gait disorders in the daily lives of patients with Parkinson’s disease (PD) using with a newly developed portable gait rhythmogram (PGR), which has a trunk-mounted acceleration sensor and automatic gait-detection algorithm.

Methods

Using the PGR, we recorded the daily walking profiles of 14 PD patients before and after the addition or increase in dose of an MAO-B inhibitor (selegiline, average dose: 4.0 mg/day) as part of their medicine regimen, and evaluated their gait using the unified Parkinson’s disease rating scale (UPDRS) and scores from a freezing of gait (FOG) questionnaire.

Results

Before treatment with selegiline, the overall movements per 24 h was decreased below 0.41 m/s² (mean − 1.5 SD) in eight patients. The mean gait acceleration was decreased below 1.94 m/s² (mean − 2 SD) in 10 patients. The slope of the linear regression line was increased to 1.6 (mean + 1.5 SD) in eight patients. The cadence was increased to 124 steps/min (mean + 1.5 SD) in four patients. Based on continuous PGR recordings in the daily lives of the patients for 24 h, the addition or increase in dose of selegiline increased the amplitudes of gait accelerations in 4 of 10 patients (40.0%), widened the range of gait accelerations in 5 of 8 patients (62.5%), diminished the cadence in 4 of 4 patients (100%), and diminished the fluctuations in gait throughout the day in 12 of 14 patients (85.7%). The UPDRS III and FOG scores significantly improved after the addition or increase in dose of selegiline (p < 0.005, p < 0.01, respectively). However, changes in gait-related scores of UPDRS were not detected in six patients.

Conclusion

Improvements in the gait fluctuations of PD patients after the addition or increase in dose of selegiline were detected using the PGR in the daily lives of the patients for 24 h. The PGR had a higher sensitivity for detecting the improvements than UPDRS scores.

Effects of Subthalamic and Nigral Stimulation on Gait Kinematics in Parkinson's Disease

Conventional subthalamic deep brain stimulation for Parkinson's disease (PD) presumably modulates the spatial component of gait. However, temporal dysregulation of gait is one of the factors that is tightly associated with freezing of gait (FOG). Temporal locomotor integration may be modulated differentially at distinct levels of the basal ganglia. Owing to its specific descending brainstem projections, stimulation of the substantia nigra pars reticulata (SNr) area might modulate spatial and temporal parameters of gait differentially compared to standard subthalamic nucleus (STN) stimulation. Here, we aimed to characterize the differential effect of STN or SNr stimulation on kinematic gait parameters. We analyzed biomechanical parameters during unconstrained over ground walking in 12 PD patients with subthalamic deep brain stimulation and FOG. Patients performed walking in three therapeutic conditions: (i) Off stimulation, (ii) STN stimulation (alone), and (iii) SNr stimulation (alone). SNr stimulation was achieved by stimulating the most caudal contact of the electrode. We recorded gait using three sensors (each containing a tri-axial accelerometer, gyroscope, and magnetometer) attached on both left and right ankle, and to the lumbar spine. STN stimulation improved both the spatial features (stride length, stride length variability) and the temporal parameters of gait. SNr stimulation improved temporal parameters of gait (swing time asymmetry). Correlation analysis suggested that patients with more medial localization of the SNr contact associated with a stronger regularization of gait. These results suggest that SNr stimulation might support temporal regularization of gait integration.

Unidirectional brain to muscle connectivity reveals motor cortex control of leg muscles during stereotyped walking

In lower mammals, locomotion seems to be mainly regulated by subcortical and spinal networks. On the contrary, recent evidence suggests that in humans the motor cortex is also significantly engaged during complex locomotion tasks. However, a detailed understanding of cortical contribution to locomotion is still lacking especially during stereotyped activities. Here, we show that cortical motor areas finely control leg muscle activation during treadmill stereotyped walking. Using a novel technique based on a combination of Reliable Independent Component Analysis, source localization and effective connectivity, and by combining electroencephalographic (EEG) and electromyographic (EMG) recordings in able-bodied adults we were able to examine for the first time cortical activation patterns and cortico-muscular connectivity including information flow direction. Results not only provided evidence of cortical activity associated with locomotion, but demonstrated significant causal unidirectional drive from contralateral motor cortex to muscles in the swing leg. These insights overturn the traditional view that human cortex has a limited role in the control of stereotyped locomotion, and suggest useful hypotheses concerning mechanisms underlying gait under other conditions.

ONE SENTENCE SUMMARY

Motor cortex proactively drives contralateral swing leg muscles during treadmill walking, counter to the traditional view of stereotyped human locomotion.

Mental steps: Differential activation of internal pacemakers in motor imagery and in mental imitation of gait

Gait imagery and gait observation can boost the recovery of locomotion dysfunctions; yet, a neurologically justified rationale for their clinical application is lacking as much as a direct comparison of their neural correlates. Using functional magnetic resonance imaging, we measured the neural correlates of explicit motor imagery of gait during observation of in-motion videos shot in a park with a steady cam (Virtual Walking task). In a 2 × 2 factorial design, we assessed the modulatory effect of gait observation and of foot movement execution on the neural correlates of the Virtual Walking task: in half of the trials, the participants were asked to mentally imitate a human model shown while walking along the same route (mental imitation condition); moreover, for half of all the trials, the participants also performed rhythmic ankle dorsiflexion as a proxy for stepping movements. We found that, beyond the areas associated with the execution of lower limb movements (the paracentral lobule, the supplementary motor area, and the cerebellum), gait imagery also recruited dorsal premotor and posterior parietal areas known to contribute to the adaptation of walking patterns to environmental cues. When compared with mental imitation, motor imagery recruited a more extensive network, including a brainstem area compatible with the human mesencephalic locomotor region (MLR). Reduced activation of the MLR in mental imitation indicates that this more visually guided task poses less demand on subcortical structures crucial for internally generated gait patterns. This finding may explain why patients with subcortical degeneration benefit from rehabilitation protocols based on gait observation. Hum Brain Mapp 38:5195-5216, 2017. © 2017 Wiley Periodicals, Inc.

LFP Oscillations in the Mesencephalic Locomotor Region during Voluntary Locomotion

Oscillatory rhythms in local field potentials (LFPs) are thought to coherently bind cooperating neuronal ensembles to produce behaviors, including locomotion. LFPs recorded from sites that trigger locomotion have been used as a basis for identification of appropriate targets for deep brain stimulation (DBS) to enhance locomotor recovery in patients with gait disorders. Theta band activity (6–12 Hz) is associated with locomotor activity in locomotion-inducing sites in the hypothalamus and in the hippocampus, but the LFPs that occur in the functionally defined mesencephalic locomotor region (MLR) during locomotion have not been determined. Here we record the oscillatory activity during treadmill locomotion in MLR sites effective for inducing locomotion with electrical stimulation in rats. The results show the presence of oscillatory theta rhythms in the LFPs recorded from the most effective MLR stimulus sites (at threshold ≤60 μA). Theta activity increased at the onset of locomotion, and its power was correlated with the speed of locomotion. In animals with higher thresholds (>60 μA), the correlation between locomotor speed and theta LFP oscillations was less robust. Changes in the gamma band (previously recorded in vitro in the pedunculopontine nucleus (PPN), thought to be a part of the MLR) were relatively small. Controlled locomotion was best achieved at 10–20 Hz frequencies of MLR stimulation. Our results indicate that theta and not delta or gamma band oscillation is a suitable biomarker for identifying the functional MLR sites.

Effect of tDCS stimulation of motor cortex and cerebellum on EEG classification of motor imagery and sensorimotor band power

Background

Transcranial direct current stimulation (tDCS) is a technique for brain modulation that has potential to be used in motor neurorehabilitation. Considering that the cerebellum and motor cortex exert influence on the motor network, their stimulation could enhance motor functions, such as motor imagery, and be utilized for brain-computer interfaces (BCIs) during motor neurorehabilitation.

Methods

A new tDCS montage that influences cerebellum and either right-hand or feet motor area is proposed and validated with a simulation of electric field. The effect of current density (0, 0.02, 0.04 or 0.06 mA/cm²) on electroencephalographic (EEG) classification into rest or right-hand/feet motor imagery was evaluated on 5 healthy volunteers for different stimulation modalities: 1) 10-minutes anodal tDCS before EEG acquisition over right-hand or 2) feet motor cortical area, and 3) 4-seconds anodal tDCS during EEG acquisition either on right-hand or feet cortical areas before each time right-hand or feet motor imagery is performed. For each subject and tDCS modality, analysis of variance and Tukey-Kramer multiple comparisons tests (p <0.001) are used to detect significant differences between classification accuracies that are obtained with different current densities. For tDCS modalities that improved accuracy, t-tests (p <0.05) are used to compare μ and β band power when a specific current density is provided against the case of supplying no stimulation.

Results

The proposed montage improved the classification of right-hand motor imagery for 4 out of 5 subjects when the highest current was applied for 10 minutes over the right-hand motor area. Although EEG band power changes could not be related directly to classification improvement, tDCS appears to affect variably different motor areas on μ and/or β band.

Conclusions

The proposed montage seems capable of enhancing right-hand motor imagery detection when the right-hand motor area is stimulated. Future research should be focused on applying higher currents over the feet motor cortex, which is deeper in the brain compared to the hand motor cortex, since it may allow observation of effects due to tDCS. Also, strategies for improving analysis of EEG respect to accuracy changes should be implemented.

Modulation of the sensorimotor system by sustained manual pressure stimulation

In Vojta physiotherapy, also known as reflex locomotion therapy, prolonged peripheral pressure stimulation induces complex generalized involuntary motor responses and modifies subsequent behavior, but its neurobiological basis remains unknown. We hypothesized that the stimulation would induce sensorimotor activation changes in functional magnetic resonance imaging (fMRI) during sequential finger opposition. Thirty healthy volunteers (mean age 24.2) underwent two randomized fMRI sessions involving manual pressure stimulation applied either at the right lateral heel according to Vojta, or at the right lateral ankle (control site). Participants were scanned before and after the stimulation when performing auditory-paced sequential finger opposition with their right hand. Despite an extensive activation decrease following both stimulation paradigms, the stimulation of the heel specifically led to an increase in task-related activation in the predominantly contralateral pontomedullary reticular formation and bilateral posterior cerebellar hemisphere and vermis. Our findings suggest that sustained pressure stimulation of the foot is associated with differential short-term changes in hand motor task-related activation depending on the stimulation. This is the first evidence for brainstem modulation after peripheral pressure stimulation, suggesting that the after-effects of reflex locomotion physiotherapy involve a modulation of the pontomedullary reticular formation.

Functional Neuroanatomy for Posture and Gait Control

Here we argue functional neuroanatomy for posture-gait control. Multi-sensory information such as somatosensory, visual and vestibular sensation act on various areas of the brain so that adaptable posture-gait control can be achieved. Automatic process of gait, which is steady-state stepping movements associating with postural reflexes including headeye coordination accompanied by appropriate alignment of body segments and optimal level of postural muscle tone, is mediated by the descending pathways from the brainstem to the spinal cord. Particularly, reticulospinal pathways arising from the lateral part of the mesopontine tegmentum and spinal locomotor network contribute to this process. On the other hand, walking in unfamiliar circumstance requires cognitive process of postural control, which depends on knowledges of self-body, such as body schema and body motion in space. The cognitive information is produced at the temporoparietal association cortex, and is fundamental to sustention of vertical posture and construction of motor programs. The programs in the motor cortical areas run to execute anticipatory postural adjustment that is optimal for achievement of goal-directed movements. The basal ganglia and cerebellum may affect both the automatic and cognitive processes of posturegait control through reciprocal connections with the brainstem and cerebral cortex, respectively. Consequently, impairments in cognitive function by damages in the cerebral cortex, basal ganglia and cerebellum may disturb posture-gait control, resulting in falling.

The developmental dynamics of gait maturation with a focus on spatiotemporal measures

Gait analysis is recognised as a powerful clinical tool for studying relationships between motor control and brain function. By drawing on the literature investigating gait in individuals with neurological disorders, this review provides insight into the neural processes that contribute to and regulate specific spatiotemporal sub-components of gait and how they may mature across early to late childhood. This review also discusses the roles of changing anthropomorphic characteristics, and maturing sensory and higher-order cognitive processes in differentiating the developmental trajectories of the sub-components of gait. Importantly, although studies have shown that cognitive-gait interference is larger in children compared to adults, the contributing neurocognitive mechanisms may vary across age groups who have different types of attentional or cognitive vulnerabilities. These findings have implications for current models of gait maturation by highlighting the need for a dynamic model that focuses on the integration of various factors that contribute to gait though experience and practice. This is essential to elucidating why gait and other motor deficits are often contiguous with cognitive neurodevelopmental disorders.

Bipedal Hopping Reveals Evidence of Advanced Neuromuscular Aging Among People With Mild Multiple Sclerosis

Measures of walking such as the timed 25-ft walk test (T25FWT) may not be able to detect subtle impairment in lower limb function among people with multiple sclerosis (MS). We examined bipedal hopping to determine to what extent people with mild (Expanded Disease Severity Scale ≤ 3.5) MS (n = 13) would differ compared to age-, gender-, and education-matched controls (n = 9) and elderly participants (n = 13; ≥ 70 years old). We estimated lower limb power (e.g., hop length, velocity), consistency (e.g., variability of hop length, time), and symmetry (ratio of left to right foot). Participants completed the T25FWT and, after a rest, they then hopped using both feet 4 times along the walkway. We found that although all groups scored below the 6 -s cutoff for T25FWT, the elderly group had significantly shorter hop lengths, more variability, and more asymmetry than the controls. The results of the MS group were not significantly different from the elderly or controls in most measures and most of their values fell between the control and elderly groups. Hop length, but not measures of walking predicted Expanded Disease Severity Scale score (R² = .38, p = .02). Bipedal hopping is a potentially useful measure of lower limb neuromuscular performance.

Corpus Callosum Structural Integrity Is Associated With Postural Control Improvement in Persons With Multiple Sclerosis Who Have Minimal Disability

BACKGROUND

Improvement of postural control in persons with multiple sclerosis (PwMS) is an important target for neurorehabilitation. Although PwMS are able to improve postural performance with training, the neural underpinnings of these improvements are poorly understood.

OBJECTIVE

To understand the neural underpinnings of postural motor learning in PwMS.

METHODS

Supraspinal white matter structural connectivity in PwMS was correlated with improvements in postural performance (balancing on an oscillating surface over 25 trials) and retention of improvements (24 hours later).

RESULTS

Improvement in postural performance was directly correlated to microstructural integrity of white matter tracts, measured as radial diffusivity, in the corpus callosum, posterior parieto-sensorimotor fibers and the brainstem in PwMS. Within the corpus callosum, the genu and midbody (fibers connecting the prefrontal and primary motor cortices, respectively) were most strongly correlated to improvements in postural control. Twenty-four-hour retention was not correlated to radial diffusivity.

CONCLUSION

PwMS who exhibited poorer white matter tract integrity connecting the cortical hemispheres via the corpus callosum showed the most difficulty learning to control balance on an unstable surface. Prediction of improvements in postural control through training (ie, motor learning) via structural imaging of the brain may allow for identification of individuals who are particularly well suited for postural rehabilitation interventions.

Gait function and locus coeruleus Lewy body pathology in 51 Parkinson's disease patients

INTRODUCTION

Gait impairment in Parkinson's Disease (PD) is often severely disabling, yet frequently remains refractory to treatment. The locus coeruleus (LC) has diffuse noradrenergic projections that are thought to play a role in gait function. Enhancement of norepinephrine transmission may improve gait in some PD patients. We hypothesized that the severity of PD pathology, and more specifically, Lewy bodies and neuronal loss in the LC, would correlate with the severity of gait dysfunction in PD.

METHODS

Autopsy data from 51 patients, collected through the Morris K. Udall Parkinson's Disease Research Center, were correlated with clinical gait-related measures, including individual Unified Parkinson's Disease Rating Scale (UPDRS) Part II and III questions, total UPDRS Part III scores, and timed up-and-go speed (TUG).

RESULTS

Neither the presence nor degree of Lewy body pathology in the LC on autopsy was associated with a higher UPDRS part III gait score. LC tau deposition and frontal Lewy body deposition were not correlated with any of the assessed gait measures. The degree of Lewy body pathology, independent of Braak stage, was positively associated with the severity of motor symptoms overall (UPDRS Part III total score).

CONCLUSION

Neither the degree of Lewy body nor tau pathology in the LC is associated with severity of gait disorders in PD. This finding may have implications for targeted noradrenergic therapies in patients with refractory gait disorders.

Structural Validity of the Mini-Balance Evaluation Systems Test (Mini-BESTest) in People With Mild to Moderate Parkinson Disease

BACKGROUND

The Mini-Balance Evaluation Systems Test (Mini-BESTest) is a clinical balance test comprising 14 items assumed to reflect the unidimensional construct "dynamic balance."

OBJECTIVE

The study objective was to examine the dimensionality of the test and the properties of each item and their interrelationships in elderly people with mild to moderate Parkinson disease (PD).

DESIGN

This was a cross-sectional study in a laboratory setting.

METHODS

A total of 112 participants (mean age=73 years) with idiopathic PD (Hoehn and Yahr stages 1-3) were assessed by physical therapists. Local independence among items was examined with Rasch modeling. Unidimensionality was tested by running a principal component analysis on the residuals. An exploratory factor analysis was used to examine the structure of the test, and a confirmatory factor analysis was used to evaluate the fit of the derived model.

RESULTS

The first residual component of the principal component analysis, with an eigenvalue of greater than 2, superseded the assumption of unidimensionality. After the omission of item 7 because of convergence problems, the exploratory factor analysis suggested that a 3-factor solution best fit the data. A confirmatory factor analysis demonstrated acceptable fit of the final model, although item 14 loaded poorly on its factor.

LIMITATIONS

The sample size was on the lower end of what is generally recommended.

CONCLUSIONS

This study could not confirm that the Mini-BESTest is unidimensional. Gait items were dispersed over all factors, indicating that they may reflect different constructs. Nonetheless, as there arguably is no clinical balance test superior to the Mini-BESTest today, we recommend using the total score for assessing gross balance in this population and individual items to identify specific weaknesses. Moreover, dual tasks should be assessed separately because they are an important aspect of balance control in people with PD, reflected in only one item of the test.

Cerebral Small Vessel Disease and Motoric Cognitive Risk Syndrome: Results from the Kerala-Einstein Study

BACKGROUND

The contribution of cerebral small vessel disease to cognitive decline, especially in non-Caucasian populations, is not well established.

OBJECTIVE

We examined the relationship between cerebral small vessel disease and motoric cognitive risk syndrome (MCR), a recently described pre-dementia syndrome, in Indian seniors.

METHODS

139 participants (mean age 66.6 ± 5.4 y, 33.1% female) participating in the Kerala-Einstein study in Southern India were examined in a cross-sectional study. The presence of cerebral small vessel disease (lacunar infarcts and cerebral microbleeds (CMB)) and white matter hyperintensities on MRI was ascertained by raters blinded to clinical information. MCR was defined by the presence of cognitive complaints and slow gait in older adults without dementia or mobility disability.

RESULTS

Thirty-eight (27.3%) participants met MCR criteria. The overall prevalence of lacunar infarcts and CMB was 49.6% and 9.4% , respectively. Lacunar infarcts in the frontal lobe, but no other brain regions, were associated with MCR even after adjusting for vascular risk factors and presence of white matter hyperintensities (adjusted Odds Ratio (aOR): 4.67, 95% CI: 1.69-12.94). Frontal lacunar infarcts were associated with slow gait (aOR: 3.98, 95% CI: 1.46-10.79) and poor performance on memory test (β: -1.24, 95% CI: -2.42 to -0.05), but not with cognitive complaints or non-memory tests. No association of CMB was found with MCR, individual MCR criterion or cognitive tests.

CONCLUSIONS

Frontal lacunar infarcts are associated with MCR in Indian seniors, perhaps, by contributing to slow gait and poor memory function.

The influence of walking-aids on the plasticity of spinal interneuronal networks, central-pattern-generators and the recovery of gait post-stroke. A literature review and scholarly discussion

BACKGROUND

Many aspects of post-stroke gait-rehabilitation are based on low-level evidence or expert opinion. Neuroscientific principles are often not considered when evaluating the impact of interventions. The use of walking-aids including canes and rollators, although widely used for long periods, has primarily been investigated to assess the immediate kinetic, kinematic or physiological effects. The long-term impact on neural structures und functions remains unclear.

METHODS

A literature review of the function of and factors affecting plasticity of spinal interneuronal-networks and central-pattern-generators (CPG) in healthy and post-stroke patients. The relevance of these mechanisms for gait recovery and the potential impact of walking-aids is discussed.

RESULTS

Afferent-input to spinal-networks influences motor-output and spinal and cortical plasticity. Disrupted input may adversely affect post-stroke plasticity and functional recovery. Joint and muscle unloading and decoupling from four-limb CPG control may be particularly relevant.

CONCLUSIONS

Canes and rollators disrupt afferent-input and may negatively affect the recovery of gait.

Virtual reality applications in assessing the effect of anxiety on sensorimotor integration in human postural control

Falls are a leading cause of injury and mortality among adults over the age of 65 years. Given the strong relation between fear of falling and fall risk, identification of the mechanisms that underlie anxiety-related changes in postural control may pave the way to the development of novel therapeutic strategies aimed at reducing fall risk in older adults. First, we review potential mechanisms underlying anxiety-mediated changes in postural control in older adults with and without neurological conditions. We then present a system that allows for the simultaneous recording of neural, physiological, and behavioral data in an immersive virtual reality (VR) environment while implementing sensory and mechanical perturbations to evaluate alterations in sensorimotor integration under conditions with high postural threat. We also discuss applications of VR in minimizing falls in older adults and potential future studies.

Mechanisms for regulating step length while running towards and over an obstacle

The ability to run across uneven terrain with continuous stable movement is critical to the safety and efficiency of a runner. Successful step-to-step stabilization while running may be mediated by minor adjustments to a few key parameters (e.g., leg stiffness, step length, foot strike pattern). However, it is not known to what degree runners in relatively natural settings (e.g., trails, paved road, curbs) use the same strategies across multiple steps. This study investigates how three readily measurable running parameters - step length, foot placement, and foot strike pattern - are adjusted in response to encountering a typical urban obstacle - a sidewalk curb. Thirteen subjects were video-recorded as they ran at self-selected slow and fast paces. Runners targeted a specific distance before the curb for foot placement, and lengthened their step over the curb (p<0.0001) regardless of where the step over the curb was initiated. These strategies of adaptive locomotion disrupt step cycles temporarily, and may increase locomotor cost and muscle loading, but in the end assure dynamic stability and minimize the risk of injury over the duration of a run.

Influence of Transcranial Direct Current Stimulation to the Cerebellum on Standing Posture Control

Damage to the vestibular cerebellum results in dysfunctional standing posture control. Patients with cerebellum dysfunction have a larger sway in the center of gravity while standing compared with healthy subjects. Transcranial direct current stimulation (tDCS) is a noninvasive technique for selectively exciting or inhibiting specific neural structures with potential applications in functional assessment and treatment of neural disorders. However, the specific stimulation parameters for influencing postural control have not been assessed. In this study, we investigated the influence of tDCS when applied over the cerebellum on standing posture control. Sixteen healthy subjects received tDCS (20 min, 2 mA) over the scalp 2 cm below the inion. In Experiment 1, all 16 subjects received tDCS under three stimulus conditions, Sham, Cathodal, and Anodal, in a random order with the second electrode placed on the forehead. In Experiment 2, five subjects received cathodal stimulation only with the second electrode placed over the right buccinator muscle. Center of gravity sway was measured twice for 60 s before and after tDCS in a standing posture with eyes open and legs closed, and average total locus length, locus length per second, rectangular area, and enveloped area were calculated. In Experiment 1, total locus length and locus length per second decreased significantly after cathodal stimulation but not after anodal or sham stimulation, while no tDCS condition influenced rectangular or enveloped areas. In Experiment 2, cathodal tDCS again significantly reduced total locus length and locus length per second but not rectangular and enveloped areas. The effects of tDCS on postural control are polarity-dependent, likely reflecting the selective excitation or inhibition of cerebellar Purkinje cells. Cathodal tDCS to the cerebellum of healthy subjects can alter body sway (velocity).

Acute effects of walking at moderate normobaric hypoxia on gait and balance performance in healthy community-dwelling seniors: A randomized controlled crossover study

BACKGROUND

Hiking at moderate altitude is a popular outdoor activity in seniors. Acute exercise or altitude can diminish balance performance. Thus, the present study examined the combined effects of altitude and walking on static and dynamic balance.

METHODS

Thirty-six healthy seniors (age: 62 (SD: 4) y; BMI: 25 (5) kg/m(2)) were examined on three days. Firstly, walking velocity was determined at 85% of the first ventilatory threshold (VT1). Therefore, a ramp walking test on a treadmill was completed. On day two or three, a 40-minute treadmill walk under sea level or normobaric hypoxia (2600m) was performed using a random, double-blind study design. Balance performance was assessed on a force-plate during single leg stance with eyes open (SLEO, 10s on a force-plate) immediately before and after walking. Spatio-temporal gait characteristics were collected during walking at 5 and 35min.

RESULTS

Condition×time interaction effects were not found for either parameter (0.13<p<0.60; 0.007<ηp(2)<0.07). Only time effects were observed for cadence (-1.5%, p<0.001, ηp(2)=0.29), stride time (+2.3%, p=0.007, ηp(2)=0.28), and temporal gait variability (+22.6%, p=0.01, ηp(2)=0.16). A moderate time×condition effect was observed for postural sway during SLEO (p=0.04, ηp(2)=0.11). Subseqent post hoc testing revealed difference between hypoxia and normoxia at 35min (p=0.01) and between 5 and 35min testing during hypoxia and normoxia (both p<0.001).

CONCLUSION

Alterations of cadence, stride time, and temporal gait variability might be attributed to fatigue-induced changes of temporal gait adjustments. Normobaric hypoxia did not acutely impair gait patterns. We assume that demanding postural standing tasks that require more central control may be affected to a greater extent by altitude exposure.

Supraspinal control of automatic postural responses in people with multiple sclerosis

The neural underpinnings of delayed automatic postural responses in people with multiple sclerosis (PwMS) are unclear. We assessed whether white matter pathways of two supraspinal regions (the cortical proprioceptive Broadman's Area-3; and the balance/locomotor-related pedunculopontine nucleus) were related to delayed postural muscle response latencies in response to external perturbations. 19 PwMS (48.8±11.4years; EDSS=3.5 (range: 2-4)) and 12 healthy adults (51.7±12.2years) underwent 20 discrete, backward translations of a support surface. Onset latency of agonist (medial-gastrocnemius) and antagonist (tibialis anterior) muscles were assessed. Diffusion tensor imaging assessed white-matter integrity (i.e. radial diffusivity) of cortical proprioceptive and balance/locomotor-related tracts. Latency of the tibialis anterior, but not medial gastrocnemius was larger in PwMS than control subjects (p=0.012 and 0.071, respectively). Radial diffusivity of balance/locomotor tracts was higher (worse) in PwMS than control subjects (p=0.004), and was significantly correlated with tibialis (p=0.002), but not gastrocnemius (p=0.06) onset latency. Diffusivity of cortical proprioceptive tracts was not correlated with muscle onset. Lesions in supraspinal structures including the pedunculopontine nucleus balance/locomotor network may contribute to delayed onset of postural muscle activity in PwMS, contributing to balance deficits in PwMS.

Gait variability in people with neurological disorders: A systematic review and meta-analysis

There has been growing evidence showing gait variability provides unique information about gait characteristics in neurological disorders. This study systemically reviewed and quantitatively synthesized (via meta-analysis) existing evidence on gait variability in various neurological diseases, including Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), cerebellar ataxia (CA), Huntington's disease (HD), multiple sclerosis (MS), and Parkinson's disease (PD). Keyword search were conducted in PubMed, Web of science, Cumulative Index to Nursing and Allied Health Literature, and Cochrane Library. Meta-analysis was performed to estimate the pooled effect size for gait variability for each neurological group. Meta-regression was performed to compare gait variability across multiple groups with neurological diseases. Gait variability of 777 patients with AD, ALS, CA, HD, MS, or PD participating in 25 studies was included in meta-analysis. All pathological groups had increased amount of gait variability and loss of fractal structure of gait dynamics compared to healthy controls, and gait variability differentiated distinctive neurological conditions. The HD groups had the highest alterations in gait variability among all pathological groups, whereas the PD, AD and MS groups had the lowest. Interventions that aim to improve gait function in patients with neurological disorders should consider the heterogeneous relationship between gait variability and neurological conditions.