Motor impairment factors related to brain injury timing in early hemiparesis. Part I: expression of upper-extremity weakness

Development of handedness and other lateralized functions during infancy and early childhood

Using a historical or "development from" approach to study the development of hand-use preferences in infants and children, we show how various sensorimotor experiential events shape the cascade from initial to subsequent hand-use preferences. That cascade represents, creates, and shapes the lateralized asymmetry of neural circuits in the cerebral hemispheres. The control of the preferred hand requires neural circuits in the contralateral hemisphere that are capable of processing the organization of finely timed, sequentially organized movements and detecting haptic information derived from high-frequency transitions in the stimulus. We propose that the lateralized differences in these neural circuits underlie processes contributing to the development of other forms of hemispheric specialization of function. We show how the development of hand-use preferences contributes to the development of language skills, tool use, spatial skills, and other cognitive abilities during infancy and early childhood. Such evidence supports the proposal of Michael Corballis that the phylogeny of human language emerged during the evolution of hominins from the co-option of those neural circuits employed in the expression of manual skills involved in tool use, tool manufacture, and communication. Finally, we summarize evidence from children with cerebral palsy, which shows that their difficulties with sensorimotor processing, visuomotor coordination, anticipatory motor planning, and other cognitive abilities may stem from disturbances in the development of their hand-use preferences and hence the functional specialization of their hemispheres.

Neural Correlates of Mobility in Children with Cerebral Palsy: A Systematic Review

Recent advances in brain mapping tools have enabled the study of brain activity during functional tasks, revealing neuroplasticity after early brain injuries and resulting from rehabilitation. Understanding the neural correlates of mobility limitations is crucial for treating individuals with cerebral palsy (CP). The aim is to summarize the neural correlates of mobility in children with CP and to describe the brain mapping methods that have been utilized in the existing literature. This systematic review was conducted based on PRISMA guidelines and was registered on PROSPERO (n° CRD42021240296). The literature search was conducted in the PubMed and Embase databases. Observational studies involving participants with CP, with a mean age of up to 18 years, that utilized brain mapping techniques and correlated these with mobility outcomes were included. The results were analyzed in terms of sample characteristics, brain mapping methods, mobility measures, and main results. The risk of bias was evaluated using a checklist previously created by our research group, based on STROBE guidelines, the Cochrane Handbook, and the Critical Appraisal Skills Programme (CASP). A total of 15 studies comprising 313 children with CP and 229 with typical development using both static and mobile techniques met the inclusion criteria. The studies indicate that children"with'CP have increased cerebral activity and higher variability in brain reorganization during mobility activities, such as gait, quiet standing, cycling, and gross motor tasks when compared with children with typical development. Altered brain activity and reorganization underline the importance of conducting more studies to investigate the neural correlates during mobility activities in children with CP. Such information could guide neurorehabilitation strategies targeting brain neuroplasticity for functional gains.

Children with bilateral cerebral palsy use their hip joint to complete a step-up task

Performance in stair-climbing is largely associated with disruptions to mobility and community participation in children with cerebral palsy (CP). It is important to understand the nature of motor impairments responsible for making stairs a challenge in children with bilateral CP to clarify underlying causes of impaired mobility. In pediatric clinical populations, sensitive measurements of movement quality can be captured during the initial step of stair ascent. Thus, the purpose of this study was to quantify the lower limb joint moments of children with bilateral CP during the stance phases of a step-up task. Participants performed multiple stepping trials in a university gait laboratory. Outcome measures included extensor support moments (the sum of hip, knee, and ankle sagittal plane moments), hip abduction moments, and their timing. We recruited seven participants per group. We found that peak support and hip abduction moments were similar in the bilateral CP group compared to the typical development (TD) group. We also found that children with bilateral CP timed their peak moments closer together and increasingly depended on the hip joint to complete the task, especially in their more affected (MA) lower limb. Our investigation highlights some underlying causes that may make stair climbing a challenge for the CP population, including a loss of selective voluntary motor control (SVMC), and provides a possible treatment approach to strengthen lower limb muscles.

Characterization of Atypical Corticospinal Tract Microstructure and Hand Impairments in Early-Onset Hemiplegic Cerebral Palsy: Preliminary Findings

Unilateral brain injuries occurring before at or shortly after full-term can result in hemiplegic cerebral palsy (HCP). HCP affects one side of the body and can be characterized in the hand with measures of weakness and a loss of independent hand control resulting in mirror movements. Hand impairment severity is extremely heterogeneous across individuals with HCP and the neural basis for this variability is unclear. We used diffusion MRI and tractography to investigate the relationship between structural morphology of the supraspinal corticospinal tract (CST) and the severity of two typical hand impairments experienced by individuals with HCP, grasp weakness and mirror movements. Results from nine children with HCP and eight children with typical development show that there is a significant hemispheric association between CST microstructure and hand impairment severity that may be explained by atypical development and fiber distribution of motor pathways. Further analysis in the non-lesioned (dominant) hemisphere shows significant differences for CST termination in the cortex between participants with HCP and those with typical development. These findings suggest that structural disparities at the cellular level in the seemingly unaffected hemisphere after early unilateral brain injury may be the cause of heterogeneous hand impairments seen in this population.Clinical Relevance- Quantitative measurement of the variability in hand function in individuals with HCP is necessary to represent the distinct impairments experienced by each person. Further understanding of the structural neural morphology underlying distal upper extremity motor deficits after early unilateral brain injury will help lead to the development of more specific targeted interventions that increase functional outcomes.

Quantifying intra- and interlimb use during unimanual and bimanual tasks in persons with hemiparesis post-stroke

Background

Individuals with hemiparesis post-stroke often have difficulty with tasks requiring upper extremity (UE) intra- and interlimb use, yet methods to quantify both are limited.

Objective

To develop a quantitative yet sensitive method to identify distinct features of UE intra- and interlimb use during task performance.

Methods

Twenty adults post-stroke and 20 controls wore five inertial sensors (wrists, upper arms, sternum) during 12 seated UE tasks. Three sensor modalities (acceleration, angular rate of change, orientation) were examined for three metrics (peak to peak amplitude, time, and frequency). To allow for comparison between sensor data, the resultant values were combined into one motion parameter, per sensor pair, using a novel algorithm. This motion parameter was compared in a group-by-task analysis of variance as a similarity score (0–1) between key sensor pairs: sternum to wrist, wrist to wrist, and wrist to upper arm. A use ratio (paretic/non-paretic arm) was calculated in persons post-stroke from wrist sensor data for each modality and compared to scores from the Adult Assisting Hand Assessment (Ad-AHA Stroke) and UE Fugl-Meyer (UEFM).

Results

A significant group × task interaction in the similarity score was found for all key sensor pairs. Post-hoc tests between task type revealed significant differences in similarity for sensor pairs in 8/9 comparisons for controls and 3/9 comparisons for persons post stroke. The use ratio was significantly predictive of the Ad-AHA Stroke and UEFM scores for each modality.

Conclusions

Our algorithm and sensor data analyses distinguished task type within and between groups and were predictive of clinical scores. Future work will assess reliability and validity of this novel metric to allow development of an easy-to-use app for clinicians.

Clinical Characteristics Associated with Reduced Selective Voluntary Motor Control in the Upper Extremity of Individuals with Spastic Cerebral Palsy

BACKGROUND

Selective voluntary motor control (SVMC) in the upper extremity is often impaired in individuals with cerebral palsy (CP) and can be assessed quantitatively and qualitatively using the Test of Arm Selective Control (TASC).

METHODS

Fifty-six individuals with spastic CP (5-18 years old) were included. Descriptors associated with administration of the TASC were analyzed according to the type of CP and arm joint using Chi-square and Kruskal-Wallis tests. ABILHAND-Kids scores were compared between participants with and without mirror movements using a t-test.

RESULTS

All groups of children with spastic CP had incidence of TASC movement descriptors. There was a main effect of topography of CP on extra movements, decreased active range of motion, tightness, spasticity, and mirroring, and an additional main effect of joint on mirroring. Participants with mirroring had lower ABILHAND-Kids scores than those without mirroring.

CONCLUSIONS

Systematically observing arm movements using the TASC revealed differences across participants.

The Upper Extremity Flexion Synergy Is Minimally Expressed in Young Individuals With Unilateral Cerebral Palsy Following an Early Brain Injury

Hemiparetic stroke in adulthood often results in the grouped movement pattern of the upper extremity flexion synergy thought to arise from an increased reliance on cortico-reticulospinal pathways due to a loss of lateral corticospinal projections. It is well established that the flexion synergy induces reaching constraints in individuals with adult-onset hemiplegia. The expression of the flexion synergy in individuals with brain injuries onset earlier in the lifespan is currently unknown. An early unilateral brain injury occurring prior to six months post full-term may preserve corticospinal projections which can be used for independent joint control and thus minimizing the expression of the flexion synergy. This study uses kinematics of a ballistic reaching task to evaluate the expression of the flexion synergy in individuals with pediatric hemiplegia (PH) ages six to seventeen years. Fifteen individuals with brain injuries before birth (n = 8) and around full-term (n = 7) and nine age-matched controls with no known neurological impairment completed a set of reaches in an admittance controlled robotic device. Descending drive, and the possible expression of the upper extremity flexion synergy, was modulated by increasing shoulder abduction loading. Individuals with early-onset PH achieved lower peak velocities when reaching with the paretic arm compared to controls; however, no differences in reaching distance were found between groups. Relative maintenance in reaching seen in individuals with early brain injuries highlights minimal expression of the flexion synergy. We interpret this conservation of independent control of the paretic shoulder and elbow as the use of more direct corticospinal projections instead of indirect cortico-reticulospinal pathways used in individuals with adult-onset hemiplegia.

Functional near-infrared spectroscopy to assess sensorimotor cortical activity during hand squeezing and ankle dorsiflexion in individuals with and without bilateral and unilateral cerebral palsy

Significance: Our study is the first comparison of brain activation patterns during motor tasks across unilateral cerebral palsy (UCP), bilateral cerebral palsy (BCP), and typical development (TD) to elucidate neural mechanisms and inform rehabilitation strategies. Aim: Cortical activation patterns were compared for distal upper and lower extremity tasks in UCP, BCP, and TD using functional near-infrared spectroscopy (fNIRS) and related to functional severity. Approach: Individuals with UCP ( n = 10 , 18.8 ± 6.8    years ), BCP ( n = 14 , 17.5 ± 9.6    years ), and TD ( n = 16 , 17.3 ± 9.1    years ) participated in this cross-sectional cohort study. The fNIRS was used to noninvasively monitor the hemodynamic response to task-related cortical activation. The block design involved repetitive nondominant hand squeezing and ankle dorsiflexion. Results: Individuals with UCP demonstrated the highest levels of activation for the squeeze task ( UCP > BCP q = 0.049 ; BCP > TD q < 0.001 ; and UCP > TD q = 0.001 ) and more activity in the ipsilateral versus contralateral hemisphere. Individuals with BCP showed the highest levels of cortical activation in the dorsiflexion task ( BCP > UCP q < 0.001 ; BCP > TD ). Conclusions: Grouping by CP subtype and manual function or mobility level demonstrated significant differences from TD, even for individuals with the mildest forms of CP. Hemispheric activation patterns showed hypothesized but nonsignificant trends.

A Method to Quantify Multi-Degree-of-Freedom Lower Limb Isometric Joint Torques in Children with Hemiplegia

Pediatric hemiplegia, caused by a unilateral brain injury during childhood, can lead to motor deficits such as weakness and abnormal joint torque coupling patterns which may result in a loss of independent joint control. It is hypothesized that these motor impairments are present in the paretic lower extremity, especially at the hip joint where extension may be abnormally coupled with adduction. Previous studies investigating lower extremity isometric joint torques in children with spastic cerebral palsy used tools that limited data collection to one degree of freedom, making it impossible to quantify these coupling patterns. We describe the adaptation of a multi-joint lower extremity isometric torque measurement device to allow for quantification of weakness and abnormal joint torque coupling patterns at the hip in the pediatric population. We also present preliminary data in three children without hemiplegia to highlight how the presence of atypical femoral bony geometry, often observed in childhood hemiplegia, can be accounted for in the Jacobian transformations and affect joint torque measurements at the hip.

Assessment of bilateral motor skills and visuospatial attention in children with perinatal stroke using a robotic object hitting task

Background

While motor deficits are the hallmark of hemiparetic cerebral palsy, children may also experience impairments in visuospatial attention that interfere with participation in complex activities, including sports or driving. In this study, we used a robotic object hitting task to assess bilateral sensorimotor control and visuospatial skills in children with hemiparesis due to perinatal arterial ischemic stroke (AIS) or periventricular venous infarct (PVI). We hypothesized that performance would be impaired bilaterally and be related to motor behavior and clinical assessment of visuospatial attention.

Methods

Forty-nine children with perinatal stroke and hemiparetic cerebral palsy and 155 typically developing (TD) children participated in the study. Participants performed a bilateral object hitting task using the KINARM Exoskeleton Robot, in which they used virtual paddles at their fingertips to hit balls that fell from the top of the screen with increasing speed and frequency over 2.3 min. We quantified performance across 13 parameters including number of balls hit with each hand, movement speed and area, biases between hands, and spatial biases. We determined normative ranges of performance accounting for age by fitting 95% prediction bands to the TD children. We compared parameters between TD, AIS, and PVI groups using ANCOVAs accounting for age effects. Lastly, we performed regression analysis between robotic and clinical measures.

Results

The majority of children with perinatal stroke hit fewer balls with their affected arm compared to their typically developing peers. We also found deficits with the ipsilesional (“unaffected”) arm. Children with AIS had greater impairments than PVI. Despite hitting fewer balls, we only identified 18% of children as impaired in hand speed or movement area. Performance on the Behavioral Inattention Test accounted for 21–32% of the variance in number of balls hit with the unaffected hand.

Conclusions

Children with perinatal stroke-induced hemiparetic cerebral palsy may have complex bilateral deficits reflecting a combination of impairments in motor skill and visuospatial attention. Clinical assessments and interventions should address the interplay between motor and visuospatial skills.

Frequency distribution in intraoperative stimulation-evoked EMG responses during selective dorsal rhizotomy in children with cerebral palsy-part 2: gender differences and left-biased asymmetry

INTRODUCTION

Spinal reflexes reorganize in cerebral palsy (CP), producing hyperreflexia and spasticity. CP is more common among male infants, and gender might also influence brain and spinal-cord reorganization. This retrospective study investigated the frequency of higher-graded EMG responses elicited by electrical nerve-root stimulation during selective dorsal rhizotomy (SDR), prior to partial nerve- root deafferentation, considering not only segmental level and body side, but also gender.

METHODS

Intraoperative neuromonitoring (IOM) was used in SDR to pinpoint the rootlets most responsible for exacerbated stimulation-evoked EMG patterns recorded from lower-limb muscle groups. Responses were graded according to an objective response-classification system, ranging from no abnormalities (grade 0) to highly abnormal (grade 4+), based on ipsilateral spread and contralateral involvement. Non-parametric analysis of data with repeated measures was primarily used in investigating the frequency distribution of these various EMG response grades. Over 7000 rootlets were stimulated, and the results for 65 girls and 81 boys were evaluated, taking changes in the composition of patient groups into account when considering GMFCS levels.

RESULTS

The distribution of graded EMG responses varied according to gender, laterality, and level. Higher-graded EMG responses were markedly more frequent in the boys and at lower segmental levels (L5, S1). Left-biased asymmetry in higher-graded rootlets was also more noticeable in the boys and in patients with GMFCS level I. A close link was observed between higher-grade assessments and left-biased asymmetry.

CONCLUSIONS

Detailed insight into the patient's initial spinal-neurofunctional state prior to deafferentation suggests that differences in asymmetrical spinal reorganization might be attributable to a hemispheric imbalance.

Sustained involuntary muscle activity in cerebral palsy and stroke: same symptom, diverse mechanisms

Individuals with lesions of central motor pathways frequently suffer from sustained involuntary muscle activity. This symptom shares clinical characteristics with dystonia but is observable in individuals classified as spastic. The term spastic dystonia has been introduced, although the underlying mechanisms of involuntary activity are not clarified and vary between individuals depending on the disorder. This study aimed to investigate the nature and pathophysiology of sustained involuntary muscle activity in adults with cerebral palsy and stroke. Seventeen adults with cerebral palsy (Gross Motor Function Classification System I–V), 8 adults with chronic stroke and 14 control individuals participated in the study. All individuals with cerebral palsy or stroke showed increased resistance to passive movement with Modified Ashworth Scale >1. Two-minute surface EMG recordings were obtained from the biceps muscle during attempted rest in three positions of the elbow joint; a maximally flexed position, a 90-degree position and a maximally extended position. Cross-correlation analysis of sustained involuntary muscle activity from individuals with cerebral palsy and stroke, and recordings of voluntary isometric contractions from control individuals were performed to examine common synaptic drive. In total, 13 out of 17 individuals with cerebral palsy and all 8 individuals with stroke contained sustained involuntary muscle activity. In individuals with cerebral palsy, the level of muscle activity was not affected by the joint position. In individuals with stroke, the level of muscle activity significantly (P < 0.05) increased from the flexed position to the 90 degree and extended position. Cumulant density function indicated significant short-term synchronization of motor unit activities in all recordings. All groups exhibited significant coherence in the alpha (6–15 Hz), beta (16–35 Hz) and early gamma band (36–60 Hz). The cerebral palsy group had lower alpha band coherence estimates, but higher gamma band coherence estimates compared with the stroke group. Individuals with increased resistance to passive movement due to cerebral palsy or stroke frequently suffer sustained involuntary muscle activity, which cannot exclusively be described by spasticity. The sustained involuntary muscle activity in both groups originated from a common synaptic input to the motor neuron pool, but the generating mechanisms could differ between groups. In cerebral palsy it seemed to originate more from central mechanisms, whereas peripheral mechanisms likely play a larger role in stroke. The sustained involuntary muscle activity should not be treated simply like the spinal stretch reflex mediated symptom of spasticity and should not either be treated identically in both groups.

Spinal Hyper-Excitability and Altered Muscle Structure Contribute to Muscle Hypertonia in Newborns After Antenatal Hypoxia-Ischemia in a Rabbit Cerebral Palsy Model

Rabbit kits after global antenatal hypoxic-ischemic injury exhibit motor deficits similar to humans with cerebral palsy. We tested several mechanisms previously implicated in spinal hyper-excitability after perinatal brain injury that may explain muscle hypertonia in newborns. Stiffness of hind limb muscles during passive stretch, electromyogram, and spinal excitability by Hoffman reflex, were assessed in rabbit kits with muscle hypertonia after global hypoxic-ischemic brain injury and naïve controls. Affected muscle architecture, motoneuron morphology, primary afferents density, gliosis, and KCC2 expression transporter in the spinal cord were also examined. Decrease knee stiffness after anesthetic administration was larger, but residual stiffness was higher in hypertonic kits compared to controls. Hypertonic kits exhibited muscle shortening and atrophy, in both agonists and antagonists. Sarcomere length was longer in tibialis anterior in hypertonic kits than in controls. Hypertonic kits had decreased rate dependent depression and increased H_max/M_max in H-reflex. Motor neuron soma sizes, primary afferent density were not different between controls and hypertonic kits. Length of dendritic tree and ramification index were lower in hypertonic group. Gene expression of KCC2 was lower in hypertonic kits, but protein content was not different between the groups. In conclusion, while we found evidence of decreased supraspinal inhibitory control and increased excitability by H-reflex that may contribute to neuronal component in hypertonia, increased joint resistance to stretch was explained predominantly by changes in passive properties of muscles and joints. We did not find structural evidence of increased sensory afferent input or morphological changes in motoneurons that might explain increased excitability. Gliosis, observed in spinal gray matter, may contribute to muscle hypertonia.

Nonsurgical Treatment Options for Upper Limb Spasticity

There are many nonsurgical treatment options for patients with upper limb spasticity. This article presents an algorithmic approach to management, encompassing evidence-based rehabilitation therapies, medications, and promising new orthotic and robotic innovations.

Evaluation of a toolkit for standardizing clinical measures of muscle tone

OBJECTIVE

To evaluate a new portable toolkit for quantifying upper and lower extremity muscle tone in patients with upper motor neuron syndrome (UMNS).

APPROACH

Cross-sectional, multi-site, observational trial to test and validate a new technology.

SETTING

Neurorehabilitation clinics at tertiary care hospitals.

PARTICIPANTS

Four cohorts UMNS patient, >6 mo post acquired brain injury, spinal cord injury, multiple sclerosis and cerebral palsy, and a sample of healthy age-matched adult controls.

MEASURES

Strength: grip, elbow flexor and extensor, and knee extensor; range of motion (ROM): passive ROM (contracture) and passive-active ROM (paresis); objective spasticity: stretch-reflex test for elbow, and pendulum test for knee; subjective spasticity: modified Ashworth scale scores for elbow and knee flexors and extensors.

RESULTS

Measures were acquired for 103 patients from three rehabilitation clinics. Results for patient cohorts were consistent with the literature. Grip strength correlated significantly with elbow muscle strength and all patient populations were significantly weaker in upper- and lower-extremity compared to controls. Strength and paresis were correlated for elbow and knee but neither correlated with contracture. Elbow spasticity correlated with strength and paresis but not contracture. Knee spasticity correlated with strength, and subjective spasticity correlated with contracture.

SIGNIFICANCE

The BioTone^™ toolkit provided comprehensive objective measures for assessing muscle tone in patients with UMNS. The toolkit could be useful for standardizing outcomes measures in clinical trials and for routine practice.

Motor system plasticity after unilateral injury in the developing brain

In maturity, motor skills depend on the corticospinal tract (CST) and brainstem pathways that together synapse on interneurons and motoneurons in the spinal cord. Descending signals to spinal neurons that mediate voluntary control can be distinguished from peripheral sensory signals, primarily for feedback control. These motor system circuits depend initially on developmental genetic mechanisms to establish their connections and neural activity- and use-dependent synaptic refinement during the early postnatal period to enable motor skills to develop. In this review we consider four key activity-dependent developmental mechanisms that provide insights into how the motor systems establish the proper connections for skilled movement control and how the same mechanisms also inform the mechanisms of motor impairments and developmental plasticity after corticospinal system injury: (1) synaptic competition between the CSTs from each hemisphere; (2) interactions between the CST and spinal cord neurons; (3) synaptic competition between the CST and proprioceptive sensory fibres; and (4) interactions between the developing corticospinal motor system and the rubrospinal tract. Our findings suggest that the corticospinal motor system effectively 'oversees' development of its subcortical targets through synaptic competition and trophic-like interactions and this has important implications for motor impairments after perinatal cortical stroke.

WHAT THIS PAPER ADDS

Neural activity-dependent processes inform the brain and spinal cord response to injury. The corticospinal motor system may 'oversee' development of its downstream subcortical targets through activity, trophic-like interactions, and synaptic competition.

On Denny-Brown's 'spastic dystonia' - What is it and what causes it?

In this review, we will work around two simple definitions of two different entities, which most often co-exist in patients with lesions to central motor pathways: Spasticity is "Enhanced excitability of velocity-dependent responses to phasic stretch at rest", which will not be the subject of this review, while Spastic dystonia is tonic, chronic, involuntary muscle contraction in the absence of any stretch or any voluntary command (Gracies, 2005). Spastic dystonia is a much less well understood entity that will be the subject this review. Denny-Brown (1966) observed involuntary sustained muscle activity in monkeys with lesions restricted to the motor cortices . He further observed that such involuntary muscle activity persisted following abolition of sensory input to the spinal cord and concluded that a central mechanism rather than exaggerated stretch reflex activity had to be involved. He coined the term spastic dystonia to describe this involuntary tonic activity in the context of otherwise exaggerated stretch reflexes. Sustained involuntary muscle activity in the absence of any stretch or any voluntary command contributes to burdensome and disabling body deformities in patients with spastic paresis. Yet, little has been done since Denny-Brown's studies to determine the pathophysiology of this non- stretch or effort related sustained involuntary muscle activity following motor lesions and there is a clear need for research studies in order to improve current therapy. The purpose of the present review is to discuss some of the possible mechanisms that may be involved in the hope that this may guide future research. We discuss the existence of persistent inward currents in spinal motoneurones and present the evidence that the channels involved may be upregulated following central motor lesions. We also discuss a possible contribution from alterations in synaptic inputs from surviving or abnormally branched sensory and descending fibres leading to over-activity and lack of motor coordination. We finally discuss evidence of alterations in motor cortical representational maps and basal ganglia lesions.

High-density surface EMG decomposition allows for recording of motor unit discharge from proximal and distal flexion synergy muscles simultaneously in individuals with stroke

Analysis of motor unit discharge can provide insight into the neural control of movement in healthy and pathological states, but it is typically completed in one muscle at a time. For some research investigations, it would be advantageous to study motor unit discharge from multiple muscles simultaneously. One such example is investigation of the flexion synergy, an abnormal muscle co-activation pattern in post-stroke individuals in which activation of shoulder abductors is involuntarily coupled with that of elbow and finger flexors. However, limitations in available technology have hindered the ability to efficiently extract motor unit discharge from multiple muscles simultaneously. In this study, we propose the use of high-density surface EMG decomposition from proximal and distal flexion synergy muscles (deltoid, biceps, wrist/finger flexors) in combination with an isometric joint torque recording device in individuals with chronic stroke. This innovative approach provides the ability to efficiently analyze both motor units and joint torques that have been simultaneously recorded from the shoulder, elbow, and fingers. In preliminary experiments, 3 stroke and 5 control participants generated shoulder abduction, elbow flexion, and finger flexion torques at 10, 20, 30 and 40% of maximum torque. Motor unit spike trains could be extracted from all muscles at each torque level. Mean motor unit firing rates were significantly lower in the stroke group than in the control group for all three muscles. Within the stroke group, wrist/finger flexor motor units had the lowest coefficient of variation. Additionally, modulation of mean firing rates across torque levels was significantly impaired in all three paretic muscles. The implications of these findings and overall impact of this approach are discussed.

Faster Reaching in Chronic Spastic Stroke Patients Comes at the Expense of Arm-Trunk Coordination

Background. The velocity of reaching movements is often reduced in patients with stroke-related hemiparesis; however, they are able to voluntarily increase paretic hand velocity. Previous studies have proposed that faster speed improves movement quality. Objective. To investigate the combined effects of reaching distance and speed instruction on trunk and paretic upper-limb coordination. The hypothesis was that increased speed would reduce elbow extension and increase compensatory trunk movement. Methods. A single session study in which reaching kinematics were recorded in a group of 14 patients with spastic hemiparesis. A 3-dimensional motion analysis system was used to track the trajectories of 5 reflective markers fixed on the finger, wrist, elbow, acromion, and sternum. The reaching movements were performed to 2 targets at 60% and 90% arm length, respectively, at preferred and maximum velocity. The experiment was repeated with the trunk restrained by a strap. Results. All the patients were able to voluntarily increase reaching velocity. In the trunk free, faster speed condition, elbow extension velocity increased but elbow extension amplitude decreased and trunk movement increased. In the trunk restraint condition, elbow extension amplitude did not decrease with faster speed. Seven patients scaled elbow extension and elbow extension velocity as a function of reach distance, the other 7 mainly increased trunk compensation with increased task constraints. There were no clear clinical characteristics that could explain this difference. Conclusions. Faster speed may encourage some patients to use compensation. Individual indications for therapy could be based on a quantitative analysis of reaching coordination.

Efficacy of upper limb strengthening in children with Cerebral Palsy: A critical review

OBJECTIVE

This review focuses on the effects of strengthening interventions of the upper limb in children with Cerebral Palsy (CP). The strengthening intervention studies were divided in two categories: those based on stand-alone strength training, and those on strength training combined with other interventions.

DATA SOURCES AND EXTRACTION

A search in all relevant databases was performed.

DATA SYNTHESIS

Six articles were included: three randomized controlled trials (RCTs), two clinical trial (CT) and one case study. Effect sizes of strength training on muscle strength and function of the upper limb were calculated.

CONCLUSION

There are no coherent recommendations for strength training, based on these studies. The causes include too much variety of types of training, level of intensity and duration. All of the reported upper limb strength training studies found an increase in muscle strength. In addition, the quality of these studies was not high. More RCTs on strength training according to the official strength training guidelines are necessary to assess the impact and potential of strength training of the upper limb to improve the daily activities and participation in children with CP.

Robotic exoskeletons: a perspective for the rehabilitation of arm coordination in stroke patients

Upper-limb impairment after stroke is caused by weakness, loss of individual joint control, spasticity, and abnormal synergies. Upper-limb movement frequently involves abnormal, stereotyped, and fixed synergies, likely related to the increased use of sub-cortical networks following the stroke. The flexible coordination of the shoulder and elbow joints is also disrupted. New methods for motor learning, based on the stimulation of activity-dependent neural plasticity have been developed. These include robots that can adaptively assist active movements and generate many movement repetitions. However, most of these robots only control the movement of the hand in space. The aim of the present text is to analyze the potential of robotic exoskeletons to specifically rehabilitate joint motion and particularly inter-joint coordination. First, a review of studies on upper-limb coordination in stroke patients is presented and the potential for recovery of coordination is examined. Second, issues relating to the mechanical design of exoskeletons and the transmission of constraints between the robotic and human limbs are discussed. The third section considers the development of different methods to control exoskeletons: existing rehabilitation devices and approaches to the control and rehabilitation of joint coordinations are then reviewed, along with preliminary clinical results available. Finally, perspectives and future strategies for the design of control mechanisms for rehabilitation exoskeletons are discussed.

Activity-Based Therapies for Repair of the Corticospinal System Injured during Development

This review presents the mechanistic underpinnings of corticospinal tract (CST) development, derived from animal models, and applies what has been learned to inform neural activity-based strategies for CST repair. We first discuss that, in normal development, early bilateral CST projections are later refined into a dense crossed CST projection, with maintenance of sparse ipsilateral projections. Using a novel mouse genetic model, we show that promoting the ipsilateral CST projection produces mirror movements, common in hemiplegic cerebral palsy (CP), suggesting that ipsilateral CST projections become maladaptive when they become abnormally dense and strong. We next discuss how animal studies support a developmental “competition rule” whereby more active/used connections are more competitive and overtake less active/used connections. Based on this rule, after unilateral injury the damaged CST is less able to compete for spinal synaptic connections than the uninjured CST. This can lead to a progressive loss of the injured hemisphere’s contralateral projection and a reactive gain of the undamaged hemisphere’s ipsilateral CST. Knowledge of the pathophysiology of the developing CST after injury informs interventional strategies. In an animal model of hemiplegic CP, promoting injured system activity or decreasing the uninjured system’s activity immediately after the period of a developmental injury both increase the synaptic competitiveness of the damaged system, contributing to significant CST repair and motor recovery. However, delayed intervention, despite significant CST repair, fails to restore skilled movements, stressing the need to consider repair strategies for other neural systems, including the rubrospinal and spinal interneuronal systems. Our interventional approaches harness neural activity-dependent processes and are highly effective in restoring function. These approaches are minimally invasive and are poised for translation to the human.

Motor impairments related to brain injury timing in early hemiparesis. Part II: abnormal upper extremity joint torque synergies

BACKGROUND

Extensive neuromotor development occurs early in human life, and the timing of brain injury may affect the resulting motor impairment. In Part I of this series, it was demonstrated that the distribution of weakness in the upper extremity depended on the timing of brain injury in individuals with childhood-onset hemiparesis.

OBJECTIVE

The goal of this study was to characterize how timing of brain injury affects joint torque synergies, or losses of independent joint control.

METHOD

Twenty-four individuals with hemiparesis were divided into 3 groups based on the timing of their injury: before birth (PRE-natal, n = 8), around the time of birth (PERI-natal, n = 8), and after 6 months of age (POST-natal, n = 8). Individuals with hemiparesis and 8 typically developing peers participated in maximal isometric shoulder, elbow, wrist, and finger torque generation tasks while their efforts were recorded by a multiple degree-of-freedom load cell. Motor output in 4 joints of the upper extremity was concurrently measured during 8 primary torque generation tasks to quantify joint torque synergies.

RESULTS

There were a number of significant coupling patterns identified in individuals with hemiparesis that differed from the typically developing group. POST-natal differences were most noted in the coupling of shoulder abductors with elbow, wrist, and finger flexors, while the PRE-natal group demonstrated significant distal joint coupling with elbow flexion.

CONCLUSION

The torque synergies measured provide indirect evidence for the use of bulbospinal pathways in the POST-natal group, while those with earlier injury may use relatively preserved ipsilateral corticospinal motor pathways.