Training of isometric force tracking to improve motor control of the wrist after incomplete spinal cord injury: a case study.

OBJECTIVE: Upper limb function is a high priority for people with cervical spinal cord injury (SCI). This case report describes an application of technology to activate spared neural pathways and improve wrist motor control. CASE DESCRIPTION: A 73-year-old man with chronic incomplete C5 SCI completed 24 training sessions over 92 days. Each session included 2 maximal contractions, 6 test trials, and 10 training trials of a visuomotor force tracking task. The participant attempted to match a sinusoidal target force curve, using isometric wrist flexor and extensor contractions. Electromyography (EMG) and force signals were recorded. OUTCOMES: Errors were elevated initially and improved with training, similarly during extension and flexion phases of the force tracking task. Improvement in both phases was associated with greater flexor activation in flexion phases and greater extensor relaxation in flexion phases. Errors were not related to EMG modulation during the extensor phases. Small improvements in active range of motion, grip force, spasticity, touch sensation, and corticospinal excitability were also observed. CONCLUSIONS: Motor skill training improved motor control after incomplete SCI, within the range of residual force production capacity. Performance gains were associated with specific adjustments in muscle activation and relaxation, and increased corticospinal excitability.

Corticospinal modulation of vibration-induced H-reflex depression.

The purpose of this study was to examine corticospinal modulation of spinal reflex excitability, by determining the effect of transcranial magnetic stimulation (TMS) on soleus H-reflexes while they were almost completely suppressed by lower extremity vibration. In 15 healthy adults, a novel method of single-limb vibration (0.6 g, 30 Hz, 0.33 mm displacement) was applied to the non-dominant leg. Soleus muscle responses were examined in six stimulation conditions: (1) H-reflex elicited by tibial nerve stimulation, (2) tibial nerve stimulation during vibration, (3) subthreshold TMS, (4) subthreshold TMS during vibration, (5) tibial nerve stimulation 10 ms after a subthreshold TMS pulse, and (6) tibial nerve stimulation 10 ms after a subthreshold TMS pulse, during vibration. With or without vibration, subthreshold TMS produced no motor evoked potentials and had no effect on soleus electromyography (p > 0.05). In the absence of vibration, H-reflex amplitudes were not affected by subthreshold TMS conditioning (median (md) 35, interquartile range (IQ) 18-56 vs. md 46, IQ 22-59% of the maximal M wave (Mmax), p > 0.05). During vibration, however, unconditioned H-reflexes were nearly abolished, and a TMS conditioning pulse increased the H-reflex more than fourfold (md 0.3, IQ 0.1-0.7 vs. md 2, IQ 0.9-5.0% of Mmax, p < 0.008). Limb vibration alone had no significant effect on corticospinal excitability. In the absence of vibration, a subthreshold TMS pulse did not influence the soleus H-reflex. During limb vibration, however, while the H-reflex was almost completely suppressed, a subthreshold TMS pulse partially restored the H-reflex. This disinhibition of the H-reflex by a corticospinal signal may represent a mechanism involved in the control of voluntary movement. Corticospinal signals that carry the descending motor command may also reduce presynaptic inhibition, temporarily increasing the impact of sensory inputs on motoneuron activation.

A cortical injury model in a non-human primate to assess execution of reach and grasp actions: implications for recovery after traumatic brain injury.

BACKGROUND: Technological advances in developing experimentally controlled models of traumatic brain injury (TBI) are prevalent in rodent models and these models have proven invaluable in characterizing temporal changes in brain and behavior after trauma. To date no long-term studies in non-human primates (NHPs) have been published using an experimentally controlled impact device to follow behavioral performance over time. NEW METHOD: We have employed a controlled cortical impact (CCI) device to create a focal contusion to the hand area in primary motor cortex (M1) of three New World monkeys to characterize changes in reach and grasp function assessed for 3 months after the injury. RESULTS: The CCI destroyed most of M1 hand representation reducing grey matter by 9.6 mm3, 12.9 mm3, and 15.5 mm3 and underlying corona radiata by 7.4 mm3, 6.9 mm3, and 5.6 mm3 respectively. Impaired motor function was confined to the hand contralateral to the injury. Gross hand-use was only mildly affected during the first few days of observation after injury while activity requiring skilled use of the hand was impaired over three months. COMPARISON WITH EXISTING METHOD(S): This study is unique in establishing a CCI model of TBI in an NHP resulting in persistent impairments in motor function evident in volitional use of the hand. CONCLUSIONS: Establishing an NHP model of TBI is essential to extend current rodent models to the complex neural architecture of the primate brain. Moving forward this model can be used to investigate novel therapeutic interventions to improve or restore impaired motor function after trauma.

Simultaneous Recording of Motor Evoked Potentials in Hand, Wrist and Arm Muscles to Assess Corticospinal Divergence.

The purpose of this study was to further develop methods to assess corticospinal divergence and muscle coupling using transcranial magnetic stimulation (TMS). Ten healthy right-handed adults participated (7 females, age 34.0 ± 12.9 years). Monophasic single pulses were delivered to 14 sites over the right primary motor cortex at 40, 60, 80 and 100% of maximum stimulator output (MSO), using MRI-based neuronavigation. Motor evoked potentials (MEPs) were recorded simultaneously from 9 muscles of the contralateral hand, wrist and arm. For each intensity, corticospinal divergence was quantified by the average number of muscles that responded to TMS per cortical site, coactivation across muscle pairs as reflected by overlap of cortical representations, and correlation of MEP amplitudes across muscle pairs. TMS to each muscle's most responsive site elicited submaximal MEPs in most other muscles. The number of responsive muscles per cortical site and the extent of coactivation increased with increasing intensity (ANOVA, p < 0.001). In contrast, correlations of MEP amplitudes did not differ across the 60, 80 and 100% MSO intensities (ANOVA, p = 0.34), but did differ across muscle pairs (ANOVA, p < 0.001). Post hoc analysis identified 4 sets of muscle pairs (Tukey homogenous subsets, p < 0.05). Correlations were highest for pairs involving two hand muscles and lowest for pairs that included an upper arm muscle. Correlation of MEP amplitudes may quantify varying levels of muscle coupling. In future studies, this approach may be a biomarker to reveal altered coupling induced by neural injury, neural repair and/or motor learning.

Novel human models for elucidating mechanisms of rate-sensitive H-reflex depression.

BACKGROUND: This study used novel human neurophysiologic models to investigate whether the mechanism of rate-sensitive H-reflex depression lies in the pre-synaptic or post-synaptic locus in humans. We hypothesized that pre-synaptic inhibition would suppress Ia afferents and H-reflexes without suppressing alpha motor neurons or motor evoked potentials (MEPs). In contrast, post-synaptic inhibition would suppress alpha motor neurons, thereby reducing H-reflexes and MEPs. METHODS: We recruited 23 healthy adults with typical rate-sensitive H-reflex depression, 2 participants with acute sensory-impaired spinal cord injury (SCI) (to rule out influence of sensory stimulation on supra-spinal excitability), and an atypical cohort of 5 healthy adults without rate-sensitive depression. After a single electrical stimulation to the tibial nerve, we administered either a testing H-reflex or a testing MEP at 50-5000 ms intervals. RESULTS: Testing MEPs were not diminished in healthy subjects with or without typical rate-sensitive H-reflex depression, or in subjects with sensory-impaired SCI. MEP responses were similar in healthy subjects with versus without rate-sensitive H-reflex depression. CONCLUSIONS: Results from these novel in vivo human models support a pre-synaptic locus of rate-sensitive H-reflex depression for the first time in humans. Spinal reflex excitability can be modulated separately from descending corticospinal influence. Each represents a potential target for neuromodulatory intervention.

Cortical control of intraspinal microstimulation: Toward a new approach for restoration of function after spinal cord injury.

Approximately 6 million people in the United States are currently living with paralysis in which 23% of the cases are related to spinal cord injury (SCI). Miniaturized closed-loop neural interfaces have the potential for restoring function and mobility lost to debilitating neural injuries such as SCI by leveraging recent advancements in bioelectronics and a better understanding of the processes that underlie functional and anatomical reorganization in an injured nervous system. This paper describes our current progress toward developing a miniaturized brain-machine-spinal cord interface (BMSI) that converts in real time the neural command signals recorded from the cortical motor regions to electrical stimuli delivered to the spinal cord below the injury level. Using a combination of custom integrated circuit (IC) technology for corticospinal interfacing and field-programmable gate array (FPGA)-based technology for embedded signal processing, we demonstrate proof-of-concept of distinct muscle pattern activation via intraspinal microstimulation (ISMS) controlled in real time by intracortical neural spikes in an anesthetized laboratory rat.

Towards a miniaturized brain-machine-spinal cord interface (BMSI) for restoration of function after spinal cord injury.

Nearly 6 million people in the United States are currently living with paralysis in which 23% of the cases are related to spinal cord injury (SCI). Miniaturized closed-loop neural interfaces have the potential for restoring function and mobility lost to debilitating neural injuries such as SCI by leveraging recent advancements in bioelectronics and a better understanding of the processes that underlie functional and anatomical reorganization in an injured nervous system. This paper describes our current progress towards developing a miniaturized brain-machine-spinal cord interface (BMSI) that is envisioned to convert in real time the neural command signals recorded from the brain to electrical stimuli delivered to the spinal cord below the injury level. Specifically, the paper reports on a corticospinal interface integrated circuit (IC) as a core building block for such a BMSI that is capable of low-noise recording of extracellular neural spikes from the cerebral cortex as well as muscle activation using intraspinal microstimulation (ISMS) in a rat with contusion injury to the thoracic spinal cord. The paper further presents results from a neurobiological study conducted in both normal and SCI rats to investigate the effect of various ISMS parameters on movement thresholds in the rat hindlimb. Coupled with proper signal-processing algorithms in the future for the transformation between the cortically recorded data and ISMS parameters, such a BMSI has the potential to facilitate functional recovery after an SCI by re-establishing corticospinal communication channels lost due to the injury.

Overground body-weight-supported gait training for children and youth with neuromuscular impairments.

The aim of this investigation was to determine if body-weight-supported (BWS) overground gait training has the potential to improve the walking abilities of children and youth with childhood onset motor impairments and intellectual disabilities. Eight participants (mean age of 16.3 years) completed 12 weeks of BWS overground gait training that was performed two times a week. BWS was provided during the training sessions by an overhead harness system that rolls overground. There was a significant improvement in the preferred walking speed after the training (p < .01; pre = 0.51 ± 0.2 m/s; post = 0.67 ± 0.3 m/s; Cohen's d = 0.80) and cadence (p = .04; pre = 37 ± 7 steps/min; post = 43 ± 8 steps/min; Cohen's d = 0.94). Our results indicate that overground BWS gait training may be an effective treatment strategy for improving the preferred walking speed of children and youth with motor impairments.

Comparison of unilateral versus bilateral upper extremity task performance after stroke.

BACKGROUND: Previous studies have suggested that practicing functional tasks bilaterally instead of unilaterally may improve paretic limb performance after stroke. OBJECTIVE: The purposes of this study were to determine whether the bilateral movement condition alters paretic limb performance of a functional task in people with poststroke hemiparesis and to identify specifically which parameters of performance may be affected. METHODS: In this single-session study, we examined immediate effects of the bilateral versus unilateral movement condition on performance of a reach-grasp-lift-release task at preferred speed in 16 people with mild to moderate poststroke hemiparesis and in 12 healthy control subjects. Performance was quantified by using motion analysis variables, including duration of the reach and grasp phases, reach path straightness, maximum thumb-index finger aperture, efficiency of finger movement, peak grip force, and timing of release. RESULTS: We found no evidence of immediate improvement in paretic limb performance in the bilateral condition. In both groups, release timing occurred later when participants moved bilaterally instead of unilaterally, possibly representing a divided attention effect. Other variables did not differ across conditions. CONCLUSIONS: Our findings suggest little immediate impact of the bilateral condition on motor performance of a reach-grasp-lift-release task at preferred speed in people with mild to moderate hemiparesis.

Grip type and task goal modify reach-to-grasp performance in post-stroke hemiparesis.

This study investigated whether grip type and/or task goal influenced reaching and grasping performance in poststroke hemiparesis. Sixteen adults with poststroke hemiparesis and twelve healthy adults reached to and grasped a cylindrical object using one of two grip types (3-finger or palmar) to achieve one of two task goals (hold or lift). Performance of the stroke group was characteristic of hemiparetic limb movement during reach-to-grasp, with more curved handpaths and slower velocities compared with the control group. These effects were present regardless of grip type or task goal. Other measures of reaching (reach time and reach velocity at object contact) and grasping (peak thumb-index finger aperture during the reach and peak grip force during the grasp) were differentially affected by grip type, task goal, or both, despite the presence of hemiparesis, providing new evidence that changes in motor patterns after stroke may occur to compensate for stroke-related motor impairment.

The bilateral movement condition facilitates maximal but not submaximal paretic-limb grip force in people with post-stroke hemiparesis.

OBJECTIVES: Although healthy individuals have less force production capacity during bilateral muscle contractions compared to unilateral efforts, emerging evidence suggests that certain aspects of paretic upper limb task performance after stroke may be enhanced by moving bilaterally instead of unilaterally. We investigated whether the bilateral movement condition affects grip force differently on the paretic side of people with post-stroke hemiparesis, compared to their non-paretic side and both sides of healthy young adults. METHODS: Within a single session, we compared: (1) maximal grip force during unilateral vs. bilateral contractions on each side, and (2) force contributed by each side during a 30% submaximal bilateral contraction. RESULTS: Healthy controls produced less grip force in the bilateral condition, regardless of side (-2.4% difference), and similar findings were observed on the non-paretic side of people with hemiparesis (-4.5% difference). On the paretic side, however, maximal grip force was increased by the bilateral condition in most participants (+11.3% difference, on average). During submaximal bilateral contractions in each group, the two sides each contributed the same percentage of unilateral maximal force. CONCLUSIONS: The bilateral condition facilitates paretic limb grip force at maximal, but not submaximal levels. SIGNIFICANCE: In some people with post-stroke hemiparesis, the paretic limb may benefit from bilateral training with high force requirements.

Person-specific changes in motor performance accompany upper extremity functional gains after stroke.

In animal models, hundreds of repetitions of upper extremity (UE) task practice promote neural adaptation and functional gain. Recently, we demonstrated improved UE function following a similar intervention for people after stroke. In this secondary analysis, computerized measures of UE task performance were used to identify movement parameters that changed as function improved. Ten people with chronic poststroke hemiparesis participated in high-repetition UE task-specific training 3 times per week for 6 weeks. Before and after training, we assessed UE function with the Action Research Arm Test (ARAT), and evaluated motor performance using computerized motion capture during a reach-grasp-transport-release task. Movement parameters included the duration of each movement phase, trunk excursion, peak aperture, aperture path ratio, and peak grip force. Group results showed an improvement in ARAT scores (p = .003). Although each individual changed significantly on at least one movement parameter, across the group there were no changes in any movement parameter that reached or approached significance. Changes on the ARAT were not closely related to changes in movement parameters. Since aspects of motor performance that contribute to functional change vary across individuals, an individualized approach to upper extremity motion analysis appears warranted.

Need for speed: better movement quality during faster task performance after stroke.

BACKGROUND: . Although slow and insufficient muscle activation is a hallmark of hemiparesis poststroke, movement speed is rarely emphasized during upper-extremity rehabilitation. Moving faster may increase the intensity of task-specific training, but positive and/or negative effects on paretic-limb movement quality are unknown. OBJECTIVE: . To determine whether moving quickly instead of at a preferred speed either enhances or impairs paretic-limb task performance after stroke. METHODS: . A total of 16 people with poststroke hemiparesis and 11 healthy controls performed reach-grasp-lift movements at their preferred speed and as fast as possible, using palmar and 3-finger grip types. The authors measured durations of the reach and grasp phases, straightness of the reach path, thumb-index finger separation (aperture), efficiency of finger movement, and grip force. RESULTS: . Reach and grasp phase durations decreased in the fast condition in both groups, showing that participants were able to move more quickly when asked. When moving fast, the hemiparetic group had reach durations equal to those of healthy controls moving at their preferred speed. Movement quality also improved. Reach paths were straighter, and peak apertures were greater in both groups in the fast condition. The group with hemiparesis also showed improved efficiency of finger movement. Differences in peak grip force across speed conditions did not reach significance. CONCLUSIONS: . People with hemiparesis who can perform reach-grasp-lift movements with a 3-finger grip can move faster than they choose to, and when they do, movement quality improves. Simple instructions to move faster could be a cost-free and effective means of increasing rehabilitation intensity after stroke.

Body weight supported treadmill training improves the regularity of the stepping kinematics in children with cerebral palsy.

OBJECTIVE: To examine if body weight supported treadmill training (BWSTT) improves the regularity of stepping kinematics in children with cerebral palsy (CP). METHODS: Twelve children with CP who had Gross Motor Function Classification Scores that ranged from II-IV participated in 12 weeks of body weight supported treadmill training that was performed 2 days a week. The primary outcome measure was the regularity of the stepping kinematics, which was assessed with Fourier analysis methods. The secondary measures were the preferred walking speed, step length, lower extremity strength and section E of the GMFM. RESULTS: BWSTT improved the rhythmical control of the stepping kinematics, preferred walking speed, step length and GMFM score. The improvements in the regularity of the stepping kinematics were strongly correlated with changes in the preferred walking speed, step length and GMFM score. CONCLUSION: BWSTT can improve the motor control of the walk performance of children with CP.

Mechanical work performed by the legs of children with spastic diplegic cerebral palsy.

The purpose of this investigation was to evaluate the work performed on the center of mass by the legs of children with cerebral palsy. 10 children that were diagnosed as having cerebral palsy with spastic diplegia (Age=9.1+/-2 years), and 10 healthy children with no walking disabilities participated (Age=9.4+/-2 years). We collected individual leg ground reaction forces from four force platforms, and calculated the mechanical work performed on the center of mass by the lead and trail legs. The normalized walking speeds were not significantly (p=0.33) different between the children with cerebral palsy (0.26+/-0.07) and the controls (0.28+/-0.06). The children with cerebral palsy performed significantly more negative work by the lead leg during double support (p=0.0004), and significantly less positive work by the trail leg (p<0.00001). During single support, the children with cerebral palsy performed significantly more positive work on the center of mass (p<0.00001). No significant differences were found for the amount of negative work performed by the leg in single support (p=0.84). Children with spastic diplegic cerebral palsy show a diminished ability to appropriately perform mechanical work by the legs to lift and redirect the center of mass. The altered mechanical work performed by the legs on the center of mass may play a role in the higher metabolic cost for walking noted in children with cerebral palsy.

Use of information entropy measures of sitting postural sway to quantify developmental delay in infants.

BACKGROUND: By quantifying the information entropy of postural sway data, the complexity of the postural movement of different populations can be assessed, giving insight into pathologic motor control functioning. METHODS: In this study, developmental delay of motor control function in infants was assessed by analysis of sitting postural sway data acquired from force plate center of pressure measurements. Two types of entropy measures were used: symbolic entropy, including a new asymmetric symbolic entropy measure, and approximate entropy, a more widely used entropy measure. For each method of analysis, parameters were adjusted to optimize the separation of the results from the infants with delayed development from infants with typical development. RESULTS: The method that gave the widest separation between the populations was the asymmetric symbolic entropy method, which we developed by modification of the symbolic entropy algorithm. The approximate entropy algorithm also performed well, using parameters optimized for the infant sitting data. The infants with delayed development were found to have less complex patterns of postural sway in the medial-lateral direction, and were found to have different left-right symmetry in their postural sway, as compared to typically developing infants. CONCLUSION: The results of this study indicate that optimization of the entropy algorithm for infant sitting postural sway data can greatly improve the ability to separate the infants with developmental delay from typically developing infants.

Pre- and post-operative gait analysis for evaluation of neck pain in chronic whiplash.

INTRODUCTION: Chronic neck pain after whiplash is notoriously refractory to conservative treatment, and positive radiological findings to explain the symptoms are scarce. The apparent disproportionality between subjective complaints and objective findings is significant for the planning of treatment, impairment ratings, and judicial questions on causation. However, failure to identify a symptom's focal origin with routine imaging studies does not invalidate the symptom per se. It is therefore of a general interest both to develop effective therapeutic strategies in chronic whiplash, and to establish techniques for objectively evaluation of treatment outcomes. METHODS: Twelve patients with chronic neck pain after whiplash underwent pre- and postoperative computerized 3D gait analysis. RESULTS: Significant improvement was found in all gait parameters, cervical range-of-motion, and self reported pain (VAS). CONCLUSION: Chronic neck pain is associated with abnormal cervical spine motion and gait patterns. 3D gait analysis is a useful instrument to assess the outcome of treatment for neck pain.

Recovery of thumb and finger extension and its relation to grasp performance after stroke.

This study investigated how the ability to extend the fingers and thumb recovers early after stroke and how the ability to extend all of the digits affects grasping performance. We studied 24 hemiparetic patients at 3 and 13 wk post stroke. At each visit, we tested the subjects' ability to actively extend all five digits of their contralesional, affected hand against gravity and to perform a grasp movement with the same hand. Three-dimensional motion analysis captured: 1) maximal voluntary extension excursion of each digit and 2) grasp performance variables of movement time, peak aperture, peak aperture rate, and aperture path ratio. We found that finger and thumb extension improved from 3 to 13 wk, with average improvements ranging from 12 to 19 degrees across the five digits. Grasp performance improved on two of the four variables measured. Peak apertures and peak aperture rates improved from 3 to 13 wk, but self-selected movement time and aperture path ratio did not. Stepwise multiple regression models showed that the majority of variance in grasp performance at 13 wk could be predicted by the ability to extend the index or middle finger at 3 wk, plus the change in the ability to extend the index finger from 3 to 13 wk. R2 values ranged from 0.55 to 0.89. Our data indicate that the amount of recovery in finger and thumb extension and grasping is small from 3 to 13 wk post stroke. In people with relatively pure motor hemiparesis, one important factor underlying deficits in hand shaping during grasping is the inability to extend the fingers and thumb. Without sufficient volitional control of finger and thumb extension, successful grasping of objects will not occur.