Obstacle avoidance during human walking: H-reflex modulation during motor learning

Abstract.: The goal of this study was to investigate changes of H-reflex amplitudes during a motor learning task. Subjects with reduced vision were instructed to step over an obstacle on a treadmill as low as possible, while the soleus H-reflex was elicited. Acoustic warning and feedback signals about performance were provided. Performance improvement was associated with a decrease of muscle activity, needed to step over the obstacle (rectus femoris, biceps femoris, tibialis anterior and gastrocnemius medialis muscles), and of foot clearance, while joint angle trajectories from knee and ankle became more stable. The experiment consisted of five runs, three with normal treadmill walking and two with randomly stepping over the obstacle (100 times). H-reflexes were elicited at early and late stance phase before stepping over the obstacle. H/M ratio, latency and duration were determined. The values of these measures were calculated for the onset and end of a run and their course over time was evaluated using a correlation coefficient. The largest adaptations with a significant increase of reflex amplitude occurred during the first obstacle run. This increase lasted only briefly and the reflex amplitudes decreased to their previous values. During the later obstacle run, no H-reflex modulation occurred. It is concluded that a motor learning task causes adaptational effects not only on performance, but also on H-reflex responses. The results indicate that most of the modulation of H-reflexes is probably due to supraspinal influences on reflex transmission. The observations made are probably less specific for this motor task (stepping over the obstacle), but rather associated with the increased attention required by the motor learning task during the first obstacle ru

Ankle dexterity remains intact in patients with incomplete spinal cord injury in contrast to stroke patients

Patients with either incomplete spinal cord injury (iSCI) or stroke suffer from muscle weakness in the lower limb and impaired ambulation. The assessment of motor function in iSCI has so far focused on measures of muscle strength, while in stroke extensive research has been directed towards upper limb motor control. Slowness of movements was reported to be a common motor impairment of patients with lesions of the central nervous system (CNS). It may result from muscle weakness and deficits in dexterity, which is two aspects of motor control that are dependent on cortico-spinal tract (CST) integrity and are crucial to ambulation. Thus, this study investigated the impact of CST damage either at spinal (iSCI) or cortical level (stroke) on ankle dexterity and maximal movement velocity (MMV). Twelve iSCI, stroke and control subjects were tested. The patients were matched for gender, age and maximal voluntary contraction (MVC) in ankle dorsi- and plantar-flexion muscles. Dexterity and MMV were tested in the supine position. CST function was assessed by motor evoked potentials (MEPs). In both groups of patients, MMV and MEP latencies were comparably deteriorated. However, dexterity was preserved in iSCI, but impaired in the hemiparetic stroke leg. Therefore, iSCI patients showed a high dexterity within the preserved muscle strength, but suffered primarily from reduced MMV. In stroke patients, both dexterity and MMV were reduced. These differences might be considered in rehabilitation programs and regeneration therapie

Ankle dexterity is less impaired than muscle strength in incomplete spinal cord lesion

Background : Motor assessment after incomplete spinal cord injury (iSCI) currently consists of tests for muscle strength (manual muscle testing) and gait. The ability to adequately time a movement, an aspect of dexterity, is not tested. Thus, this study assessed the timing of ankle dorsiflexion in iSCI patients in the supine position and during gait and examined its relation to measures for muscle strength, corticospinal conductivity and gait speed. Methods : In 12 subjects with iSCI and 12 matched controls, timing of ankle dorsiflexion was tested by means of auditory-paced dorsiand plantar-flexion movements at three frequencies in the supine position and by determining initiation and termination of dorsiflexion in swing during gait. In addition, maximal movement velocity (MMV) in the ankle task, maximal voluntary contraction (MVC), corticospinal conductivity (motor evoked potentials (MEP)) and gait speed (10 Meter Walk Test) were assessed. Results : The groups did not significantly differ in timing of ankle dorsiflexion, neither in the supine position nor in gait. However, they significantly differed in MMV at all frequencies, MEP latency, MEP amplitude and gait speed. In contrast to ankle timing in the supine position, the onset of dorsiflexion in swing during gait significantly correlated to the dynamic MEP parameters. Conclusions : Although MMV and gait speed were significantly reduced, timing of ankle dorsiflexion, both in the supine position and during gait,was less impaired in iSCI patients. This indicates that the loss of strength, particularly of dynamic strength, is the major motor impairment in iSCI, which might be considered when assessing treatment intervention

Arc-Standard Spinal Parsing with Stack-LSTMs

We present a neural transition-based parser for spinal trees, a dependency representation of constituent trees. The parser uses Stack-LSTMs that compose constituent nodes with dependency-based derivations. In experiments, we show that this model adapts to different styles of dependency relations, but this choice has little effect for predicting constituent structure, suggesting that LSTMs induce useful states by themselves.Comment: IWPT 201

Obstacle stepping in patients with Parkinson's disease: Complexity does influence performance

Patients with Parkinson's disease (PD) have difficulties in performing complex bimanual movements. Here we have examined acquisition and performance of a bilateral obstacle stepping task to see whether these difficulties are also present during bipedal movements. Subjects had to minimize foot clearance when repeatedly stepping on a treadmill over randomly approaching obstacles on either side. The subjects had full vision and received acoustic feedback information about task performance. Foot clearance improved in healthy and PD subjects during the acquisition of the task. However, PD subjects showed a slower improvement and achieved a poorer performance level. Thus, in contrast to unilateral obstacle stepping, where no deficits in performance after task repetition were found in PD subjects, bilateral obstacle stepping was poorer in these subjects compared to healthy subjects. The present results extend findings from upper to lower limb movements, namely that PD subjects have difficulties in the performance of bilateral motor task

Enhancement of bend sensor properties as applied in a glove for use in neurorehabilitation settings

Following hand function impairment caused by a neurological disorder, the functional level of the upper extremities has to be assessed in the clinical and rehabilitation settings. Current hand function evaluation tests are somewhat imprecise. Instrumented gloves allow finger motion monitoring during the performance of skilled tasks, such as grasping objects. As a result, they provide an objective tool for evaluating slight changes in the fine motor skills of the hand. Numerous gloves are based on resistive bend sensors, given that this is an easy to handle, low-cost, and reliable sensing element. When bending is not applied homogeneously along such a sensor, as is the case with finger-joint bending, its output response varies with the sensor's longitudinal position. Our goal is to determine the optimal sensor position with respect to the finger-joint in order to enhance the resolution of the sensors embedded in a glove. The validity of the integrated sensors is evaluated and the accuracy values are given

Standardized assessment of walking capacity after spinal cord injury: the European network approach

OBJECTIVES: After a spinal cord injury (SCI), walking function is an important outcome measure for rehabilitation and new treatment interventions. The current status of four walking capacity tests that are applied to SCI subjects is presented: the revised walking index for spinal cord injury (WISCI II), the 6 minute walk test (6MinWT), 10 meter walk test (10MWT) and the timed up and go (TUG) test. Then, we investigated which categories of the WISCI II apply to SCI subjects who participated in the European Multicenter Study of Human Spinal Cord Injury (EM-SCI), and the relationship between the 10MWT and the TUG. METHODS: In the EM-SCI, the walking tests were applied 2 weeks and 1, 3, 6 and 12 months after SCI. We identified the WISCI II categories that applied to the EM-SCI subjects at each time point and quantified the relationship between the 10MWT and the TUG using Spearman's correlation coefficients (rho) and linear regression. RESULTS: Five WISCI II categories applied to 71% of the EM-SCI subjects with walking ability, while 11 items applied to 11% of the subjects. The 10MWT correlated excellently with the TUG at each time point (rho>0.80). However, this relationship changed over time. One year after SCI, the time needed to accomplish the TUG was 1.25 times greater than the 10MWT time. DISCUSSION: Some categories of the WISCI II appear to be redundant, while some discriminate to an insufficient degree. In addition, there appear to be ceiling effects, which limit its usefulness. The relationship between the 10MWT and TUG is high, but changes over time. We suggest that, at present, the 10MWT appears to be the best tool to assess walking capacity in SCI subjects. Additional valuable information is provided by assessing the needs for walking aids or personal assistance. To ensure comparability of study results, proposals for standardized instructions are presented

Vertical perturbations of human gait: organisation and adaptation of leg muscle responses

During the last several years, evidence has arisen that the neuronal control of human locomotion depends on feedback from load receptors. The aim of the present study was to determine the effects and the course of sudden and unexpected changes in body load (vertical perturbations) on leg muscle activity patterns during walking on a treadmill. Twenty-two healthy subjects walking with 25% body weight support (BWS) were repetitively and randomly loaded to 5% or unloaded to 45% BWS during left mid-stance. At the new level of BWS, the subjects performed 3-11 steps before returning to 25% BWS (base level). EMG activity of upper and lower leg muscles was recorded from both sides. The bilateral leg muscle activity pattern changed following perturbations in the lower leg muscles and the net effect of the vertical perturbations showed onset latencies with a range of 90-105ms. Body loading enhanced while unloading diminished the magnitude of ipsilateral extensor EMG amplitude, compared to walking at base level. Contralateral leg flexor burst activity was shortened following loading and prolonged following unloading perturbation while flexor EMG amplitude was unchanged. A general decrease in EMG amplitudes occurred during the course of the experiment. This is assumed to be due to adaptation. Only the muscles directly activated by the perturbations did not significantly change EMG amplitude. This is assumed to be due to the required compensation of the perturbations by polysynaptic spinal reflexes released following the perturbations. The findings underline the importance of load receptor input for the control of locomotio

The amplitude of lower leg motor evoked potentials is a reliable measure when controlled for torque and motor task

Abstract : Objectives : Motor evoked potential (MEP) amplitudes have the disadvantage of a high variability when repeatedly assessed. This affects the reliability of MEP amplitude measurements taken during the course of motor incomplete spinal cord injury (iSCI). The study investigated the reliability of anterior tibial (TA) MEP measures controlled for dorsal flexion torque and motor task. Methods : TA MEPs were recorded at 10, 20, 40 and 60% of maximal voluntary contraction (MVC) during a static and dynamic (isometric increase of dorsal flexion torque) motor task. To determine reliability, 20 healthy and five chronic iSCI subjects were tested twice (≥7 days) by the same investigator. Intraclass correlation coefficients (ICCs) were calculated. MEP amplitudes and latencies were compared between 20 healthy and 29 iSCI subjects. Results : The reliability of MEP amplitude was in general good (ICC ≥ 0.52) and was highest during the static task at 40% MVC (ICC = 0.77). The increased facilitation by the dynamic motor task showed the best reliability at 20% MVC (ICC = 0.48). The reliability was good to excellent for MEP latency (0.46 ≥ ICC ≥ 0.81), MVC (ICC ≥ 0.90) and for the TMS threshold required to evoke a MEP response (ICC ≥ 0.77). The torque generated by the MEP response ()0.02 ≥ ICC ≥ 0.55) and the duration of the silent period (0.07 ≥ ICC ≥ 0.50) were not reliable. Both MEP amplitudes and latencies differed significantly between healthy and iSCI subjects. Conclusions : Controlling for torque generation and motor task establishes a reliability of TA MEP amplitudes that is sufficient for longitudinal assessments in motor incomplete SC