Should stereotypic movement synergies in hemiparetic patients be considered adaptive?

Safety and Feasibility of Cervical and Thoracic Transcutaneous Spinal Cord Stimulation to Improve Hand Motor Function in Children With Chronic Spinal Cord Injury

OBJECTIVE

In adults with cervical spinal cord injury (SCI), transcutaneous spinal stimulation (scTS) has improved upper extremity strength and control. This novel noninvasive neurotherapeutic approach combined with training may modulate the inherent developmental plasticity of children with SCI, providing even greater improvements than training or stimulation alone. Because children with SCI represent a vulnerable population, we first must establish the safety and feasibility of any potential novel therapeutic approach. The objectives of this pilot study were to determine the safety, feasibility, and proof of principle of cervical and thoracic scTS for short-term effect on upper extremity strength in children with SCI.

MATERIALS AND METHODS

In this nonrandomized, within-subject repeated measure design, seven participants with chronic cervical SCI performed upper extremity motor tasks without and with cervical (C3-C4 and C6-C7) and thoracic (T10-T11) site scTS. Safety and feasibility of using cervical and thoracic sites scTS were determined by the frequency count of anticipated and unanticipated risks (eg, pain, numbness). Proof-of-principle concept was tested via change in force production during hand motor tasks.

RESULTS

All seven participants tolerated cervical and thoracic scTS across the three days, with a wide range of stimulation intensities (cervical sites = 20-70 mA and thoracic site = 25-190 mA). Skin redness at the stimulation sites was observed in four of 21 assessments (19%) and dissipated in a few hours. No episode of autonomic dysreflexia was observed or reported. Hemodynamic parameters (systolic blood pressure and heart rate) remained within stable limits (p > 0.05) throughout the assessment time points at baseline, with scTS, and after the experiment. Hand-grip and wrist-extension strength increased (p < 0.05) with scTS.

CONCLUSIONS

We indicated that short-term application of scTS via two cervical and one thoracic site is safe and feasible in children with SCI and resulted in immediate improvements in hand-grip and wrist-extension strength in the presence of scTS.

CLINICAL TRIAL REGISTRATION

The Clinicaltrials.gov registration number for the study is NCT04032990.

Alterations in motor modules and their contribution to limitations in force control in the upper extremity after stroke

The generation of isometric force at the hand can be mediated by activating a few motor modules. Stroke induces alterations in motor modules underlying steady-state isometric force generation in the human upper extremity (UE). However, how the altered motor modules impact task performance (force production) remains unclear as stroke survivors develop and converge to the three-dimensional (3D) target force. Thus, we tested whether stroke-specific motor modules would be activated from the onset of force generation and also examined how alterations in motor modules would induce changes in force representation. During 3D isometric force development, electromyographic (EMG) signals were recorded from eight major elbow and shoulder muscles in the paretic arm of 10 chronic hemispheric stroke survivors and both arms of six age-matched control participants. A non-negative matrix factorization algorithm identified motor modules in four different time windows: three “exploratory” force ramping phases (Ramps 1–3; 0–33%, 33–67%, and 67–100% of target force magnitude, respectively) and the stable force match phase (Hold). Motor module similarity and between-force coupling were examined by calculating the scalar product and Pearson correlation across the phases. To investigate the association between the end-point force representation and the activation of the motor modules, principal component analysis (PCA) and multivariate multiple linear regression analyses were applied. In addition, the force components regressed on the activation profiles of motor modules were utilized to model the feasible force direction. Both stroke and control groups developed exploratory isometric forces with a non-linear relationship between EMG and force. During the force matching, only the stroke group showed abnormal between-force coupling in medial-lateral and backward-forward and medial-lateral and downward-upward directions. In each group, the same motor modules, including the abnormal deltoid module in stroke survivors, were expressed from the beginning of force development instead of emerging during the force exploration. The PCA and the multivariate multiple linear regression analyses showed that alterations in motor modules were associated with abnormal between-force coupling and limited feasible force direction after stroke. Overall, these results suggest that alterations in intermuscular coordination contribute to the abnormal end-point force control under isometric conditions in the UE after stroke.

Haptic feedback system for postural adaptation during robotic rehabilitation of upper limb

Although trunk compensation during stroke rehabilitation is widely studied, the proposed solutions primarily include a trunk constraint, which has several disadvantages. In this study, we have proposed a haptic feedback-based system for postural training during upper-limb motor rehabilitation. We have tested the proposed system on six healthy people in this preliminary study. Participants performed a simple 1-dimensional reaching task while their posture was being monitored. They received haptic feedback based on their trunk posture. Preliminary results revealed a significant decline in postural error (p<0.05) after the haptic-based training. The reduction in error was maintained even after haptic feedback was turned off. This study shows that haptic feedback could be a viable alternative to the traditional constraint-based methods for postural adaptation. Additional studies need to be conducted to further evaluate the influence of using such feedback strategies.

Correlation Evaluation of Functional Corticomuscular Coupling With Abnormal Muscle Synergy After Stroke

OBJECTIVE

While neuroplasticity and functional reorganization during motor recovery can be indirectly reflected and evaluated by functional corticomuscular coupling (fCMC), little work has been published regarding the cortical origin of abnormal muscle synergy and compensatory mechanism in the separation movement of stroke patients.

METHODS

In this study, we proposed to use extended partial directed coherence (ePDC) combined with an optimal spatial filtering approach to estimate fCMC in stroke patients and healthy controls, and further established muscle synergy model (MSM) to jointly explore the modulation mechanism between cortex and muscles.

RESULTS

Compared to healthy controls, stroke patients had significantly reduced coupling strength in both descending and ascending pathway. Moreover, the MSM were abnormal with high variability and low similarity in the separation stage of stroke patients. Further exploration of the positive relationship between fCMC characteristics and MSM parameters proved the possibility of using fCMC-MSM-based correlation indicator to evaluate abnormality of the cortical related synergy movement as well as the rehabilitation level of stroke patients.

CONCLUSION

We developed a computational procedure to evaluate the correlation between fCMC and MSM in stroke patients.

SIGNIFICANCE

This article provides a quantitative evaluation metrics based on fCMC to reveal the deficits during poststroke motor restoration and a promising approach to help patients correct abnormal movement habits, paving the way for neurophysiological assessment of neuromuscular control in conjunction with clinical scores.

Motor Learning, Neuroplasticity, and Strength and Skill Training: Moving From Compensation to Retraining in Behavioral Management of Dysphagia

Purpose Learning a motor skill and regaining a motor skill after it is lost are key tenets to the field of speech-language pathology. Motor learning and relearning have many theoretical underpinnings that serve as a foundation for our clinical practice. This review article applies selective motor learning theories and principles to feeding and swallowing across the life span. Conclusion In reviewing these theoretical fundamentals, clinical exemplars surrounding the roles of strength, skill, experience, compensation, and retraining, and their influence on motor learning and plasticity in regard to swallowing/feeding skills throughout the life span are discussed.

Optimizing functional outcome endpoints for stroke recovery studies

Novel therapeutic intervention that aims to enhance the endogenous recovery potential of the brain during the subacute phase of stroke has produced promising results. The paradigm shift in treatment approaches presents new challenges to preclinical and clinical researchers alike, especially in the functional endpoints domain. Shortcomings of the "neuroprotection" era of stroke research are yet to be fully addressed. Proportional recovery observed in clinics, and potentially in animal models, requires a thorough reevaluation of the methods used to assess recovery. To this end, this review aims to give a detailed evaluation of functional outcome measures used in clinics and preclinical studies. Impairments observed in clinics and animal models will be discussed from a functional testing perspective. Approaches needed to bridge the gap between clinical and preclinical research, along with potential means to measure the moving target recovery, will be discussed. Concepts such as true recovery of function and compensation and methods that are suitable for distinguishing the two are examined. Often-neglected outcomes of stroke, such as emotional disturbances, are discussed to draw attention to the need for further research in this area.

Recovery and compensation after robotic assisted gait training in chronic stroke survivors

Background: Gait re-education is a primary rehabilitation goal after stroke. In the last decades, robots with different mechanical structures have been extensively used in the clinical practice for gait training of stroke survivors. However, the effectiveness of robotic training is still controversial, especially for chronic subjects. In this study, we investigated the short-term effects of gait training assisted by an endpoint robot in a population of chronic stroke survivors.Methods: Subjects were evaluated before and after training with clinical scales and instrumented gait analysis. Our primary outcome indicator was the walking speed. Next, we investigated the changes in kinetic and kinematic gait patterns as well as the intersegmental coordination at the level of the lower limbs.Results: Most subjects improved their speed in over-ground walking, by modifying the temporal more than the spatial gait parameters. These changes led to an improvement in the ankle power for both sides and to a slight reduction of the inclination of the pelvis during the swing phase, mainly due to a decreased knee flexion and an increased hip extension on the unimpaired leg.Conclusions: These results indicate that the proposed training induced mainly a functional change rather than an improvement of the quality of gait.Implication for RehabilitationGait re-education is a primary goal in stroke rehabilitation.Nowadays several robotic devices for gait rehabilitation are used in the clinical practice, but their effectiveness is controversial, especially for chronic survivors.After a 20-session training with an endpoint robot the chronic stroke survivors showed an improvement in overground gait speed.The increased gait speed was mainly due to functional changes of the temporal parameters and of the kinetic variables at the level of both ankle joints, as well as to a reduction of compensatory strategies observable in the unimpaired side.

Force control in chronic stroke

Force control deficits are common dysfunctions after a stroke. This review concentrates on various force control variables associated with motor impairments and suggests new approaches to quantifying force control production and modulation. Moreover, related neurophysiological mechanisms were addressed to determine variables that affect force control capabilities. Typically, post stroke force control impairments include: (a) decreased force magnitude and asymmetrical forces between hands, (b) higher task error, (c) greater force variability, (d) increased force regularity, and (e) greater time-lag between muscular forces. Recent advances in force control analyses post stroke indicated less bimanual motor synergies and impaired low-force frequency structure. Brain imaging studies demonstrate possible neurophysiological mechanisms underlying force control impairments: (a) decreased activation in motor areas of the ipsilesional hemisphere, (b) increased activation in secondary motor areas between hemispheres, (c) cerebellum involvement, and (d) relatively greater interhemispheric inhibition from the contralesional hemisphere. Consistent with identifying neurophysiological mechanisms, analyzing bimanual motor synergies as well as low-force frequency structure will advance our understanding of post stroke force control.

Functional evaluation of robot end-point assisted gait re-education in chronic stroke survivors

Gait re-education is a primary rehabilitation goal after stroke. In this study, we used instrumented gait analysis for evaluating the outcomes of gait training assisted by an endpoint robot in a population of six chronic stroke survivors. The preliminary results, based on spatial-temporal and kinematic analysis, suggest that (a) self-placed walking speed increases, with an improvement of both length and duration of the stride, (b) balance increases during standing and walking, (c) the non-affected side becomes less involved in attempting to correct for the deficiencies of the affected side, thus reducing the importance of compensatory strategies.

What Do Motor “Recovery” and “Compensation” Mean in Patients Following Stroke?

There is a lack of consistency among researchers and clinicians in the use of terminology that describes changes in motor ability following neurological injury. Specifically, the terms and definitions of motor compensation and motor recovery have been used in different ways, which is a potential barrier to interdisciplinary communication. This Point of View describes the problem and offers a solution in the form of definitions of compensation and recovery at the neuronal, motor performance, and functional levels within the framework of the International Classification of Functioning model.

Virtual reality environments for post-stroke arm rehabilitation

INTRODUCTION

Optimal practice and feedback elements are essential requirements for maximal motor recovery in patients with motor deficits due to central nervous system lesions.

METHODS

A virtual environment (VE) was created that incorporates practice and feedback elements necessary for maximal motor recovery. It permits varied and challenging practice in a motivating environment that provides salient feedback.

RESULTS

The VE gives the user knowledge of results feedback about motor behavior and knowledge of performance feedback about the quality of pointing movements made in a virtual elevator. Movement distances are related to length of body segments.

CONCLUSION

We describe an immersive and interactive experimental protocol developed in a virtual reality environment using the CAREN system. The VE can be used as a training environment for the upper limb in patients with motor impairments.

Improvement of Arm Movement Patterns and Endpoint Control Depends on Type of Feedback During Practice in Stroke Survivors

Background. A major challenge in stroke rehabilitation is restoration of arm motor function. Therapy-induced improvements in arm function may occur via restoration of premorbid movement patterns (recovery) or development of compensatory movement strategies. However, it is unclear whether the learning benefits of practice might be enhanced by incorporating different forms of feedback, focusing on movement outcomes or on specific arm movement patterns. Objective. To determine if manipulation of attentional focus by providing either knowledge of results (KR) feedback, focusing on movement outcomes, or knowledge of performance (KP) feedback, focusing on arm movement patterns during repetitive practice of a pointing movement, may lead to arm motor recovery. Methods. Twenty-eight chronic stroke survivors were randomly assigned to 2 groups that practiced 10 sessions of 75 pointing movements. During practice, groups received either 20% KR about movement precision or faded (26.6% average) KP about arm joint movements. A nondisabled control group (n = 5) practiced the same task with KR. Results. Motor patterns recovered only in KP, as evidenced by immediate and long-term increases in joint range, better interjoint coordination in early movement phases, and generalization of gains. Improvements in clinical impairment and function were related to decreases in compensation (trunk rotation) and recovery of interjoint coordination in mid-movement phases. Conclusions. In stroke survivors, when the learners' attention was directed to the movements themselves (KP), motor improvements reflect recovery compared to when attention was directed toward movement outcomes (KR).

Compensatory strategies for reaching in stroke

A major prerequisite for successful rehabilitation therapy after stroke is the understanding of the mechanisms underlying motor deficits common to these patients. Studies have shown that in stroke patients multijoint pointing movements are characterized by decreased movement speed and increased movement variability, by increased movement segmentation and by spatial and temporal incoordination between adjacent arm joints with respect to healthy subjects. We studied how the damaged nervous system recovers or compensates for deficits in reaching, and correlated reaching deficits with the level of functional impairment. Nine right-hemiparetic subjects and nine healthy subjects participated. All subjects were right-hand dominant. Data from the affected arm of hemiparetic subjects were compared with those from the arm in healthy subjects. Seated subjects made 40 pointing movements with the right arm in a single session. Movements were made from an initial target, for which the arm was positioned alongside the trunk. Then the subject lifted the arm and pointed to the final target, located in front of the subject in the contralateral workspace. Kinematic data from the arm and trunk were recorded with a three-dimensional analysis system. Arm movements in stroke subjects were longer, more segmented, more variable and had larger movement errors. Elbow-shoulder coordination was disrupted and the range of active joint motion was decreased significantly compared with healthy subjects. Some aspects of motor performance (duration, segmentation, accuracy and coordination) were significantly correlated with the level of motor impairment. Despite the fact that stroke subjects encountered all these deficits, even subjects with the most severe motor impairment were able to transport the end-point to the target. All but one subject involved the trunk to accomplish this motor task. In others words, they recruited new degrees of freedom typically not used by healthy subjects. The use of compensatory strategies may be related to the degree of motor impairment: severely to moderately impaired subjects recruited new degrees of freedom to compensate for motor deficits while mildly impaired subjects tended to employ healthy movement patterns. We discuss the possibility that there is a critical level of recovery at which patients switch from a strategy employing new degrees of freedom to one in which motor recovery is produced by improving the management of degrees of freedom characteristic of healthy performance. Our data also suggest that stroke subjects may be able to exploit effectively the redundancy of the motor system.

Spatial zones for muscle coactivation and the control of postural stability

It is hypothesized that, depending on the motor task, the angular range of a joint may be subdivided into zones in which agonist and antagonist muscles are coactive, only one group of muscles is active or neither group is active. It is further hypothesized that central commands may change the size and location of these spatial zones. We investigated whether spatial zones are used by the nervous system and how they may be changed to provide postural stability of the elbow. We compared responses to sudden unloading of the elbow flexors in neurologically normal subjects with those in patients with postural control deficits due to unilateral hemispheric and/or subcortical lesions. By studying responses in patients, we sought to determine whether the specification of zones of agonist/antagonist muscle coactivation ("coactivation zones") may be essential for postural stability. At an initial elbow angle (130 degrees; full extension is 180 degrees), flexors were pre-activated by compensating an initial load which was equal to approximately 30% of the subject's maximal isometric voluntary contraction effort. Subjects were instructed not to correct the arm displacement elicited by a sudden decrease in the load. Data from 10 trials were collected at each of 4-6 final load levels (separated by 1.5-2 Nm) in order to map out the relationship between torque and angle in each subject. The procedure was repeated from a more flexed initial position of the elbow (100 degrees). EMG activity from two elbow flexors and two elbow extensors, as well as torque, velocity and joint position were recorded. Healthy control subjects and patients with mild clinical symptoms had coactivation zones or small silent zones around the final positions established after unloading. In these subjects, final positions of the limb were stable. Voluntary movement, i.e., transition of the limb from one initial position to another, was associated with a change in the location of the zone in articular space. The presence of large silent zones in patients with moderate or severe symptoms was correlated with postural instability and oscillations about the final position of the arm after unloading. The comparison of results from healthy and hemiparetic subjects implies that the central specification of the size and the location of a coactivation zone may be fundamental for the control of posture and movement.