Greater activation of secondary motor areas is related to less arm use after stroke

Cortical activity in patients with high-functioning ischemic stroke during the Purdue Pegboard Test: insights into bimanual coordinated fine motor skills with functional near-infrared spectroscopy

After stroke, even high-functioning individuals may experience compromised bimanual coordination and fine motor dexterity, leading to reduced functional independence. Bilateral arm training has been proposed as a promising intervention to address these deficits. However, the neural basis of the impairment of functional fine motor skills and their relationship to bimanual coordination performance in stroke patients remains unclear, limiting the development of more targeted interventions. To address this gap, our study employed functional near-infrared spectroscopy to investigate cortical responses in patients after stroke as they perform functional tasks that engage fine motor control and coordination. Twenty-four high-functioning patients with ischemic stroke (7 women, 17 men; mean age 64.75 ± 10.84 years) participated in this cross-sectional observational study and completed four subtasks from the Purdue Pegboard Test, which measures unimanual and bimanual finger and hand dexterity. We found significant bilateral activation of the sensorimotor cortices during all Purdue Pegboard Test subtasks, with bimanual tasks inducing higher cortical activation than the assembly subtask. Importantly, patients with better bimanual coordination exhibited lower cortical activation during the other three Purdue Pegboard Test subtasks. Notably, the observed neural response patterns varied depending on the specific subtask. In the unaffected hand task, the differences were primarily observed in the ipsilesional hemisphere. In contrast, the bilateral sensorimotor cortices and the contralesional hemisphere played a more prominent role in the bimanual task and assembly task, respectively. While significant correlations were found between cortical activation and unimanual tasks, no significant correlations were observed with bimanual tasks. This study provides insights into the neural basis of bimanual coordination and fine motor skills in high-functioning patients after stroke, highlighting task-dependent neural responses. The findings also suggest that patients who exhibit better bimanual performance demonstrate more efficient cortical activation. Therefore, incorporating bilateral arm training in post-stroke rehabilitation is important for better outcomes. The combination of functional near-infrared spectroscopy with functional motor paradigms is valuable for assessing skills and developing targeted interventions in stroke rehabilitation.

Neuroscience meets behavior: A systematic literature review on magnetic resonance imaging of the brain combined with real-world digital phenotyping

A primary goal of neuroscience is to understand the relationship between the brain and behavior. While magnetic resonance imaging (MRI) examines brain structure and function under controlled conditions, digital phenotyping via portable automatic devices (PAD) quantifies behavior in real-world settings. Combining these two technologies may bridge the gap between brain imaging, physiology, and real-time behavior, enhancing the generalizability of laboratory and clinical findings. However, the use of MRI and data from PADs outside the MRI scanner remains underexplored. Herein, we present a Preferred Reporting Items for Systematic Reviews and Meta-Analysis systematic literature review that identifies and analyzes the current state of research on the integration of brain MRI and PADs. PubMed and Scopus were automatically searched using keywords covering various MRI techniques and PADs. Abstracts were screened to only include articles that collected MRI brain data and PAD data outside the laboratory environment. Full-text screening was then conducted to ensure included articles combined quantitative data from MRI with data from PADs, yielding 94 selected papers for a total of N = 14,778 subjects. Results were reported as cross-frequency tables between brain imaging and behavior sampling methods and patterns were identified through network analysis. Furthermore, brain maps reported in the studies were synthesized according to the measurement modalities that were used. Results demonstrate the feasibility of integrating MRI and PADs across various study designs, patient and control populations, and age groups. The majority of published literature combines functional, T1-weighted, and diffusion weighted MRI with physical activity sensors, ecological momentary assessment via PADs, and sleep. The literature further highlights specific brain regions frequently correlated with distinct MRI-PAD combinations. These combinations enable in-depth studies on how physiology, brain function and behavior influence each other. Our review highlights the potential for constructing brain-behavior models that extend beyond the scanner and into real-world contexts.

Optimizing Epoch Length and Activity Count Threshold Parameters in Accelerometry: Enhancing Upper Extremity Use Quantification in Cerebral Palsy

Various accelerometry protocols have been used to quantify upper extremity (UE) activity, encompassing diverse epoch lengths and thresholding methods. However, there is no consensus on the most effective approach. The aim of this study was to delineate the optimal parameters for analyzing accelerometry data to quantify UE use in individuals with unilateral cerebral palsy (CP).

METHODS

A group of adults with CP (n = 15) participated in six activities of daily living, while a group of children with CP (n = 14) underwent the Assisting Hand Assessment. Both groups performed the activities while wearing ActiGraph GT9X-BT devices on each wrist, with concurrent video recording. Use ratio (UR) derived from accelerometry and video analysis and accelerometer data were compared for different epoch lengths (1, 1.5, and 2 s) and activity count (AC) thresholds (between 2 and 150).

RESULTS

In adults, results are comparable across epoch lengths, with the best AC thresholds being ≥ 100. In children, results are similar across epoch lengths of 1 and 1.5 (optimal AC threshold = 50), while the optimal threshold is higher with an epoch length of 2 (AC = 75).

CONCLUSIONS

The combination of epoch length and AC thresholds should be chosen carefully as both influence the validity of the quantification of UE use.

Effects of robot-assisted task-oriented upper limb motor training on neuroplasticity in stroke patients with different degrees of motor dysfunction: A neuroimaging motor evaluation index

Introduction

Although robot-assisted task-oriented upper limb (UL) motor training had been shown to be effective for UL functional rehabilitation after stroke, it did not improve UL motor function more than conventional therapy. Due to the lack of evaluation of neurological indicators, it was difficult to confirm the robot treatment parameters and clinical efficacy in a timely manner. This study aimed to explore the changes in neuroplasticity induced by robot-assisted task-oriented UL motor training in different degrees of dysfunction patients and extract neurological evaluation indicators to provide the robot with additional parameter information.

Materials and methods

A total of 33 adult patients with hemiplegic motor impairment after stroke were recruited as participants in this study, and a manual muscle test divided patients into muscle strength 0–1 level (severe group, n = 10), 2–3 level (moderate group, n = 14), and 4 or above level (mild group, n = 9). Tissue concentration of oxyhemoglobin and deoxyhemoglobin oscillations in the bilateral prefrontal cortex, dorsolateral prefrontal cortex (DLPFC), superior frontal cortex (SFC), premotor cortex, primary motor cortex (M1), primary somatosensory cortex (S1), and occipital cortex were measured by functional near-infrared spectroscopy (fNIRS) in resting and motor training state. The phase information of a 0.01 −0.08 Hz signal was identified by the wavelet transform method. The wavelet amplitude, lateralization index, and wavelet phase coherence (WPCO) were calculated to describe the frequency-specific cortical changes.

Results

Compared with the resting state, significant increased cortical activation was observed in ipsilesional SFC in the mild group and bilateral SFC in the moderate group during UL motor training. Patients in the mild group demonstrated significantly decreased lateralization of activation in motor training than resting state. Moreover, the WPCO value of motor training between contralesional DLPFC and ipsilesional SFC, bilateral SFC, contralesional, S1, and ipsilesional M1 showed a significant decrease compared with the resting state in the mild group.

Conclusion

Robot-assisted task-oriented UL motor training could modify the neuroplasticity of SFC and contribute to control movements and continuous learning motor regularity for patients. fNIRS could provide a variety of real-time sensitive neural evaluation indicators for the robot, which was beneficial to formulating more reasonable and effective personalized prescriptions during motor training.

Functional connectivity drives stroke recovery: shifting the paradigm from correlation to causation

Stroke is a leading cause of disability, with deficits encompassing multiple functional domains. The heterogeneity underlying stroke poses significant challenges in the prediction of post-stroke recovery, prompting the development of neuroimaging-based biomarkers. Structural neuroimaging measurements, particularly those reflecting corticospinal tract injury, are well-documented in the literature as potential biomarker candidates of post-stroke motor recovery. Consistent with the view of stroke as a 'circuitopathy', functional neuroimaging measures probing functional connectivity may also prove informative in post-stroke recovery. An important step in the development of biomarkers based on functional neural network connectivity is the establishment of causality between connectivity and post-stroke recovery. Current evidence predominantly involves statistical correlations between connectivity measures and post-stroke behavioural status, either cross-sectionally or serially over time. However, the advancement of functional connectivity application in stroke depends on devising experiments that infer causality. In 1965, Sir Austin Bradford Hill introduced nine viewpoints to consider when determining the causality of an association: (i) strength; (ii) consistency; (iii) specificity; (iv) temporality; (v) biological gradient; (vi) plausibility; (vii) coherence; (viii) experiment; and (ix) analogy. Collectively referred to as the Bradford Hill Criteria, these points have been widely adopted in epidemiology. In this review, we assert the value of implementing Bradford Hill's framework to stroke rehabilitation and neuroimaging. We focus on the role of neural network connectivity measurements acquired from task-oriented and resting-state functional MRI, EEG, magnetoencephalography and functional near-infrared spectroscopy in describing and predicting post-stroke behavioural status and recovery. We also identify research opportunities within each Bradford Hill tenet to shift the experimental paradigm from correlation to causation.

Limited capacity for ipsilateral secondary motor areas to support hand function post-stroke

KEY POINTS

Ipsilateral-projecting corticobulbar pathways, originating primarily from secondary motor areas, innervate the proximal and even distal portions, although they branch more extensively at the spinal cord. It is currently unclear to what extent these ipsilateral secondary motor areas and subsequent cortical projections may contribute to hand function following stroke-induced damage to one hemisphere. In the present study, we provide both structural and functional evidence indicating that individuals increasingly rely on ipsilateral secondary motor areas, although at the detriment of hand function. Increased activity in ipsilateral secondary motor areas was associated with increased involuntary coupling between shoulder abduction and finger flexion, most probably as a result of the low resolution of these pathways, making it increasingly difficult to open the hand. These findings suggest that, although ipsilateral secondary motor areas may support proximal movements, they do not have the capacity to support distal hand function, particularly for hand opening.

ABSTRACT

Recent findings have shown connections of ipsilateral cortico-reticulospinal tract (CRST), predominantly originating from secondary motor areas to not only proximal, but also distal muscles of the arm. Following a unilateral stroke, CRST from the ipsilateral side remains intact and thus has been proposed as a possible backup system for post-stroke rehabilitation even for the hand. We argue that, although CRST from ipsilateral secondary motor areas can provide control for proximal joints, it is insufficient to control either hand or coordinated shoulder and hand movements as a result of its extensive spinal branching compared to contralateral corticospinal tract. To address this issue, we combined magnetic resonance imaging, high-density EEG, and robotics in 17 individuals with severe chronic hemiparetic stroke and 12 age-matched controls. We tested for changes in structural morphometry of the sensorimotor cortex and found that individuals with stroke demonstrated higher grey matter density in secondary motor areas ipsilateral to the paretic arm compared to controls. We then measured cortical activity when participants were attempting to generate hand opening either supported on a table or when lifting against a shoulder abduction load. The addition of shoulder abduction during hand opening increased reliance on ipsilateral secondary motor areas in stroke, but not controls. Crucially, the increased use of ipsilateral secondary motor areas was associated with decreased hand opening ability when lifting the arm as a result of involuntary coupling between the shoulder and wrist/finger flexors. Taken together, this evidence implicates a compensatory role for ipsilateral (i.e. contralesional) secondary motor areas post-stroke, although with no apparent capacity to support hand function.

Increased Sensorimotor Cortex Activation With Decreased Motor Performance During Functional Upper Extremity Tasks Poststroke

BACKGROUND AND PURPOSE

Current literature has focused on identifying neuroplastic changes associated with stroke through tasks and in positions that are not representative of functional rehabilitation. Emerging technologies such as functional near-infrared spectroscopy (fNIRS) provide new methods of expanding the area of neuroplasticity within rehabilitation. This study determined the differences in sensorimotor cortex activation during unrestrained reaching and gripping after stroke.

METHODS

Eleven individuals with chronic stroke and 11 neurologically healthy individuals completed reaching and gripping tasks under 3 conditions using their (1) stronger, (2) weaker, and (3) both arms together. Performance and sensorimotor cortex activation using fNIRS were collected. Group and arm differences were calculated using mixed analysis of covariance (covariate: age). Pairwise comparisons were used for post hoc analyses. Partial Pearson correlations between performance and activation were assessed for each task, group, and hemisphere.

RESULTS

Larger sensorimotor activations in the ipsilesional hemisphere were found for the stroke compared with healthy group for reaching and gripping conditions despite poorer performance. Significant correlations were observed between gripping performance (with the weaker arm and both arms simultaneously) and sensorimotor activation for the stroke group only.

DISCUSSION AND CONCLUSIONS

Stroke leads to significantly larger sensorimotor activation during functional reaching and gripping despite poorer performance. This may indicate an increased sense of effort, decreased efficiency, or increased difficulty after stroke. fNIRS can be used for assessing differences in brain activation during movements in functional positions after stroke. This can be a promising tool for investigating possible neuroplastic changes associated with functional rehabilitation interventions in the stroke population.Video Abstract available for more insights from the authors (see Video Abstract, Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A269).

Right Hemisphere Contributions to Bilateral Force Control in Chronic Stroke: A Preliminary Report

BACKGROUND

Bilateral motor control deficits poststroke may be lateralized by hemisphere damage. This preliminary study investigated bilateral force control between left and right hemisphere-damaged groups at baseline and after coupled bilateral movement training with neuromuscular stimulation.

METHODS

Stroke participants (8 left hemisphere and 6 right hemisphere cerebrovascular accidents) performed a bilateral isometric force control task at 3 submaximal force levels (5%, 25%, and 50% of maximum voluntary contraction [MVC]) before and after training. Force accuracy, force variability, and interlimb force coordination were analyzed in 3-way mixed design ANOVAs (2 × 2 × 3; Group × Test Session × Force Level) with repeated measures on test session and force level.

RESULTS

The findings indicated that force accuracy and variability at 50% of MVC in the right hemisphere-damaged group were more impaired than lower targeted force levels at baseline, and the impairment at the highest target level was improved after coupled bilateral movement training. However, these patterns were not observed in the left hemisphere-damaged group.

CONCLUSIONS

Current findings support a proposition that the right hemisphere presumably contributes to controlling bilateral force production.

Visual feedback alters force control and functional activity in the visuomotor network after stroke

Modulating visual feedback may be a viable option to improve motor function after stroke, but the neurophysiological basis for this improvement is not clear. Visual gain can be manipulated by increasing or decreasing the spatial amplitude of an error signal. Here, we combined a unilateral visually guided grip force task with functional MRI to understand how changes in the gain of visual feedback alter brain activity in the chronic phase after stroke. Analyses focused on brain activation when force was produced by the most impaired hand of the stroke group as compared to the non-dominant hand of the control group. Our experiment produced three novel results. First, gain-related improvements in force control were associated with an increase in activity in many regions within the visuomotor network in both the stroke and control groups. These regions include the extrastriate visual cortex, inferior parietal lobule, ventral premotor cortex, cerebellum, and supplementary motor area. Second, the stroke group showed gain-related increases in activity in additional regions of lobules VI and VIIb of the ipsilateral cerebellum. Third, relative to the control group, the stroke group showed increased activity in the ipsilateral primary motor cortex, and activity in this region did not vary as a function of visual feedback gain. The visuomotor network, cerebellum, and ipsilateral primary motor cortex have each been targeted in rehabilitation interventions after stroke. Our observations provide new insight into the role these regions play in processing visual gain during a precisely controlled visuomotor task in the chronic phase after stroke.

Cortical contributions to sensory gating in the ipsilateral somatosensory cortex during voluntary activity

KEY POINTS

It has long been known that the somatosensory cortex gates sensory inputs from the contralateral side of the body. Here, we examined the contribution of the ipsilateral somatosensory cortex (iS1) to sensory gating during index finger voluntary activity. The amplitude of the P25/N33, but not other somatosensory evoked potential (SSEP) components, was reduced during voluntary activity compared with rest. Interhemispheric inhibition between S1s and intracortical inhibition in the S1 modulated the amplitude of the P25/N33. Note that changes in interhemispheric inhibition between S1s correlated with changes in cortical circuits in the ipsilateral motor cortex. Our findings suggest that cortical circuits, probably from somatosensory and motor cortex, contribute to sensory gating in the iS1 during voluntary activity in humans.

ABSTRACT

An important principle in the organization of the somatosensory cortex is that it processes afferent information from the contralateral side of the body. The role of the ipsilateral somatosensory cortex (iS1) in sensory gating in humans remains largely unknown. Using electroencephalographic (EEG) recordings over the iS1 and electrical stimulation of the ulnar nerve at the wrist, we examined somatosensory evoked potentials (SSEPs; P14/N20, N20/P25 and P25/N33 components) and paired-pulse SSEPs between S1s (interhemispheric inhibition) and within (intracortical inhibition) the iS1 at rest and during tonic index finger voluntary activity. We found that the amplitude of the P25/N33, but not other SSEP components, was reduced during voluntary activity compared with rest. Interhemispheric inhibition increased the amplitude of the P25/N33 and intracortical inhibition reduced the amplitude of the P25/N33, suggesting a cortical origin for this effect. The P25/N33 receives inputs from the motor cortex, so we also examined the contribution of distinct sets of cortical interneurons by testing the effect of ulnar nerve stimulation on motor-evoked potentials (MEPs) elicited by transcranial magnetic stimulation over the ipsilateral motor cortex with the coil in the posterior-anterior (PA) and anterior-posterior (AP) orientation. Afferent input attenuated PA, but not AP, MEPs during voluntary activity compared with rest. Notably, changes in interhemispheric inhibition correlated with changes in PA MEPs. Our novel findings suggest that interhemispheric projections between S1s and intracortical circuits, probably from somatosensory and motor cortex, contribute to sensory gating in the iS1 during voluntary activity in humans.

Hemispheric asymmetry in myelin after stroke is related to motor impairment and function

The relationships between impairment, function, arm use and underlying brain structure following stroke remain unclear. Although diffusion weighted imaging is useful in broadly assessing white matter structure, it has limited utility in identifying specific underlying neurobiological components, such as myelin. The purpose of the present study was to explore relationships between myelination and impairment, function and activity in individuals with chronic stroke. Assessments of paretic upper-extremity impairment and function were administered, and 72-hour accelerometer based activity monitoring was conducted on 19 individuals with chronic stroke. Participants completed a magnetic resonance imaging protocol that included a high resolution T₁ anatomical scan and a multi-component T₂ relaxation imaging scan to quantify myelin water fraction (MWF). MWF was automatically parcellated from pre- and post-central subcortical regions of interest and quantified as an asymmetry ratio (contralesional/ipsilesional). Cluster analysis was used to group more and less impaired individuals based on Fugl-Meyer upper extremity scores. A significantly higher precentral MWF asymmetry ratio was found in the more impaired group compared to the less impaired group (p < 0.001). There were no relationships between MWF asymmetry ratio and upper-limb use. Stepwise multiple linear regression identified precentral MWF asymmetry as the only variable to significantly predict impairment and motor function in the upper extremity (UE). These results suggest that asymmetric myelination in a motor specific brain area is a significant predictor of upper-extremity impairment and function in individuals with chronic stroke. As such, myelination may be utilized as a more specific marker of the neurobiological changes that predict long term impairment and recovery from stroke.

MRI Biomarkers for Hand-Motor Outcome Prediction and Therapy Monitoring following Stroke

Several biomarkers have been identified which enable a considerable prediction of hand-motor outcome after cerebral damage already in the subacute stage after stroke. We here review the value of MRI biomarkers in the evaluation of corticospinal integrity and functional recruitment of motor resources. Many of the functional imaging parameters are not feasible early after stroke or for patients with high impairment and low compliance. Whereas functional connectivity parameters have demonstrated varying results on their predictive value for hand-motor outcome, corticospinal integrity evaluation using structural imaging showed robust and high predictive power for patients with different levels of impairment. Although this is indicative of an overall higher value of structural imaging for prediction, we suggest that this variation be explained by structure and function relationships. To gain more insight into the recovering brain, not only one biomarker is needed. We rather argue for a combination of different measures in an algorithm to classify fine-graded subgroups of patients. Approaches to determining biomarkers have to take into account the established markers to provide further information on certain subgroups. Assessing the best therapy approaches for individual patients will become more feasible as these subgroups become specified in more detail. This procedure will help to considerably save resources and optimize neurorehabilitative therapy.

Spontaneous and Therapeutic-Induced Mechanisms of Functional Recovery After Stroke

With increasing rates of survival throughout the past several years, stroke remains one of the leading causes of adult disability. Following the onset of stroke, spontaneous mechanisms of recovery at the cellular, molecular, and systems levels ensue. The degree of spontaneous recovery is generally incomplete and variable among individuals. Typically, the best recovery outcomes entail the restitution of function in injured but surviving neural matter. An assortment of restorative therapies exists or is under development with the goal of potentiating restitution of function in damaged areas or in nearby ipsilesional regions by fostering neuroplastic changes, which often rely on mechanisms similar to those observed during spontaneous recovery. Advancements in stroke rehabilitation depend on the elucidation of both spontaneous and therapeutic-driven mechanisms of recovery. Further, the implementation of neural biomarkers in research and clinical settings will enable a multimodal approach to probing brain state and predicting the extent of post-stroke functional recovery. This review will discuss spontaneous and therapeutic-induced mechanisms driving post-stroke functional recovery while underscoring several potential restorative therapies and biomarkers.

Role of contralesional hemisphere in paretic arm reaching in patients with severe arm paresis due to stroke: A preliminary report

Stroke is highly prevalent and a leading cause of serious, long-term disability among American adults. Impaired movement (i.e. paresis) of the stroke-affected arm is a major contributor to post-stroke disability, yet the mechanisms of upper extremity motor recovery are poorly understood, particularly in severely impaired patients who lack hand function. To address this problem, we examined the functional relevance of the contralesional hemisphere in paretic arm motor performance in individuals with severe arm paresis. Twelve individuals with severe stroke-induced arm paresis (Upper Extremity Fugl-Meyer Assessment=17.1 ± 8.5; maximum score=66) participated in the study. Participants performed a reaching response time task with their paretic arm. At varying time intervals following a 'Go' cue, a pair of transcranial magnetic stimulation (TMS) pulses were delivered to contralesional hemisphere primary motor (M1) or dorsal pre-motor cortex (PMd) to momentarily disrupt the pattern of neural firing. Response time components and hand-path characteristics were compared across the 2 sites for trials with and without TMS disruption. There was no significant effect of TMS disruption on overall Response time or Reaction time, but Movement time was significantly longer (i.e. slower) with disruption of the contralesional hemisphere (p=0.015), regardless of which area was stimulated. Peak hand-path velocity and hand-path smoothness were also significantly lower (p=0.005 and p<0.0001, respectively) with TMS disruption of the contralesional hemisphere. The data from this study provide evidence supporting a functionally relevant role of contralesional hemisphere motor areas in paretic arm reaching movements in individuals with severe post-stroke arm impairment.

Functional versus Nonfunctional Rehabilitation in Chronic Ischemic Stroke: Evidences from a Randomized Functional MRI Study

Motor rehabilitation of stroke survivors may include functional and/or nonfunctional strategy. The present study aimed to compare the effect of these two rehabilitation strategies by means of clinical scales and functional Magnetic Resonance Imaging (fMRI). Twelve hemiparetic chronic stroke patients were selected. Patients were randomly assigned a nonfunctional (NFS) or functional (FS) rehabilitation scheme. Clinical scales (Fugl-Meyer, ARA test, and modified Barthel) and fMRI were applied at four moments: before rehabilitation (P1) and immediately after (P2), 1 month after (P3), and three months after (P4) the end of rehabilitation. The NFS group improved significantly and exclusively their Fugl-Meyer scores at P2, P3, and P4, when compared to P1. On the other hand, the FS group increased significantly in Fugl-Meyer at P2, when compared to P1, and also in their ARA and Barthel scores. fMRI inspection at the individual level revealed that both rehabilitation schemes most often led to decreased activation sparseness, decreased activity of contralesional M1, increased asymmetry of M1 activity to the ipsilesional side, decreased perilesional activity, and decreased SMA activity. Increased M1 asymmetry with rehabilitation was also confirmed by Lateralization Indexes. Our clinical analysis revealed subtle differences between FS and NFS.

Exploring the Role of Accelerometers in the Measurement of Real World Upper-Limb Use After Stroke

The ultimate goal of upper-limb rehabilitation after stroke is to promote real-world use, that is, use of the paretic upper-limb in everyday activities outside the clinic or laboratory. Although real-world use can be collected through self-report questionnaires, an objective indicator is preferred. Accelerometers are a promising tool. The current paper aims to explore the feasibility of accelerometers to measure upper-limb use after stroke and discuss the translation of this measurement tool into clinical practice. Accelerometers are non-invasive, wearable sensors that measure movement in arbitrary units called activity counts. Research to date indicates that activity counts are a reliable and valid index of upper-limb use. While most accelerometers are unable to distinguish between the type and quality of movements performed, recent advancements have used accelerometry data to produce clinically meaningful information for clinicians, patients, family and care givers. Despite this, widespread uptake in research and clinical environments remains limited. If uptake was enhanced, we could build a deeper understanding of how people with stroke use their arm in real-world environments. In order to facilitate greater uptake, however, there is a need for greater consistency in protocol development, accelerometer application and data interpretation.

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.

A Randomized Controlled Trial of the Effect of Early Upper-Limb Training on Stroke Recovery and Brain Activation

Background. Upper-limb (UL) dysfunction is experienced by up to 75% of patients poststroke. The greatest potential for functional improvement is in the first month. Following reperfusion, evidence indicates that neuroplasticity is the mechanism that supports this recovery. Objective. This preliminary study hypothesized increased activation of putative motor areas in those receiving intensive, task-specific UL training in the first month poststroke compared with those receiving standard care. Methods. This was a single-blinded, longitudinal, randomized controlled trial in adult patients with an acute, first-ever ischemic stroke; 23 participants were randomized to standard care (n = 12) or an additional 30 hours of task-specific UL training in the first month poststroke beginning week 1. Patients were assessed at 1 week, 1 month, and 3 months poststroke. The primary outcome was change in brain activation as measured by functional magnetic resonance imaging. Results. When compared with the standard-care group, the intensive-training group had increased brain activation in the anterior cingulate and ipsilesional supplementary motor areas and a greater reduction in the extent of activation ( P = .02) in the contralesional cerebellum. Intensive training was associated with a smaller deviation from mean recovery at 1 month (Pr>F0 = 0.017) and 3 months (Pr>F = 0.006), indicating more consistent and predictable improvement in motor outcomes. Conclusion. Early, more-intensive, UL training was associated with greater changes in activation in putative motor (supplementary motor area and cerebellum) and attention (anterior cingulate) regions, providing support for the role of these regions and functions in early recovery poststroke.

Reorganizing therapy: changing the clinical approach to upper limb recovery post-stroke

Stroke is the leading cause of adult disability, and as a consequence, most therapists will provide health care to patients with stroke during their professional careers. An increasing number of studies are investigating the association between upper limb recovery and changes in brain activation patterns following stroke. In this review, we explore the translational implications of this research for health professionals working in stroke recovery. We argue that in light of the most recent evidence, therapists should consider how best to take full advantage of the brain's natural ability to reorganize, when prescribing and applying interventions to those with a stroke-affected upper limb. The authors propose that stroke is a brain-based problem that needs a brain-based solution. This review addresses two topics, anticipating recovery and maximizing recovery. It proposes five practice-ready recommendations that are based on the evidence reviewed. The over-riding aim of this review and discussion is to challenge therapists to reconsider the health care they prescribe and apply to people with a stroke-affected upper limb.

Changes in brain functional network connectivity after stroke

Studies have shown that functional network connection models can be used to study brain network changes in patients with schizophrenia. In this study, we inferred that these models could also be used to explore functional network connectivity changes in stroke patients. We used independent component analysis to find the motor areas of stroke patients, which is a novel way to determine these areas. In this study, we collected functional magnetic resonance imaging datasets from healthy controls and right-handed stroke patients following their first ever stroke. Using independent component analysis, six spatially independent components highly correlated to the experimental paradigm were extracted. Then, the functional network connectivity of both patients and controls was established to observe the differences between them. The results showed that there were 11 connections in the model in the stroke patients, while there were only four connections in the healthy controls. Further analysis found that some damaged connections may be compensated for by new indirect connections or circuits produced after stroke. These connections may have a direct correlation with the degree of stroke rehabilitation. Our findings suggest that functional network connectivity in stroke patients is more complex than that in hea-lthy controls, and that there is a compensation loop in the functional network following stroke. This implies that functional network reorganization plays a very important role in the process of rehabilitation after stroke.

Assessment of inter-hemispheric imbalance using imaging and noninvasive brain stimulation in patients with chronic stroke

OBJECTIVE

To determine how interhemispheric balance in stroke, measured using transcranial magnetic stimulation (TMS), relates to balance defined using neuroimaging (functional magnetic resonance [fMRI], diffusion-tensor imaging [DTI]) and how these metrics of balance are associated with clinical measures of upper-limb function and disability.

DESIGN

Cross sectional.

SETTING

Laboratory.

PARTICIPANTS

Patients with chronic stroke (N = 10; age, 63 ± 9 y) in a population-based sample with unilateral upper-limb paresis.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Interhemispheric balance was measured with TMS, fMRI, and DTI. TMS defined interhemispheric differences in the recruitment of corticospinal output, size of the corticomotor output maps, and degree of mutual transcallosal inhibition that they exerted on one another. fMRI studied whether cortical activation during the movement of the paretic hand was lateralized to the ipsilesional or to the contralesional primary motor cortex (M1), premotor cortex (PMC), and supplementary motor cortex (SMA). DTI was used to define interhemispheric differences in the integrity of the corticospinal tracts projecting from the M1. Clinical outcomes tested function (upper extremity Fugl-Meyer [UEFM]) and perceived disability in the use of the paretic hand (Motor Activity Log [MAL] amount score).

RESULTS

Interhemispheric balance assessed with TMS relates differently to fMRI and DTI. Patients with high fMRI lateralization to the ipsilesional hemisphere possessed stronger ipsilesional corticomotor output maps (M1: r = .831, P = .006; PMC: r = .797, P = .01) and better balance of mutual transcallosal inhibition (r = .810, P = .015). Conversely, we found that patients with less integrity of the corticospinal tracts in the ipsilesional hemisphere show greater corticospinal output of homologous tracts in the contralesional hemisphere (r = .850, P = .004). However, an imbalance in integrity and output do not relate to transcallosal inhibition. Clinically, although patients with less integrity of corticospinal tracts from the ipsilesional hemisphere showed worse impairments (UEFM) (r = -.768, P = .016), those with low fMRI lateralization to the ipsilesional hemisphere had greater perception of disability (MAL amount score) (M1: r = .883, P = .006; PMC: r = .817, P = .007; SMA: r = .633, P = .062).

CONCLUSIONS

In patients with chronic motor deficits of the upper limb, fMRI may serve to mark perceived disability and transcallosal influence between hemispheres. DTI-based integrity of the corticospinal tracts, however, may be useful in categorizing the range of functional impairments of the upper limb. Further, in patients with extensive corticospinal damage, DTI may help infer the role of the contralesional hemisphere in recovery.

Control of reach extent with the paretic and nonparetic arms after unilateral sensorimotor stroke II: planning and adjustments to control movement distance

Nondisabled adults utilize both planning and feedback-based compensatory adjustments to control actual distance moved for skilled reach actions. The purpose of this study was to determine whether individuals post-stroke utilize planning and compensatory adjustments to control movement distance for reaches to targets that vary in distance. Individuals with mild to moderate motor impairment after stroke and nondisabled adults reached with both arms to targets presented at three distances (8, 16, 24 cm). The control of movement distance was compared between arms (control, nonparetic, and paretic) as to the use of planning (correlation of peak acceleration with movement distance), compensatory adjustments prior to peak velocity (correlation of time to peak velocity with movement distance), and compensatory adjustments after peak velocity (variance in movement distance accounted for by deterministic statistical model). The correlation of peak acceleration with movement distance for reaches with the paretic arm was significantly less than controls suggesting a decreased reliance on planning. Feedback-based compensatory adjustments, however, were present prior to and after peak velocity that assisted in achievement of movement distance in a similar manner as controls. Overall reach performance with the paretic arm was impaired, however, as evidenced by greater endpoint error and longer movement times than controls. The decreased use of planning to control movement distance after stroke suggests that the selected motor command was suboptimal in producing the desired movement outcome and may be related to an inability to generate muscle force quickly, lack of knowledge of arm dynamics due to decreased arm use, or lesion characteristics.

Spasticity, weakness, force variability, and sustained spontaneous motor unit discharges of resting spastic-paretic biceps brachii muscles in chronic stroke

INTRODUCTION

The purpose of our study was to examine relations among spasticity, weakness, force variability, and sustained spontaneous motor unit discharges in spastic-paretic biceps brachii muscles in chronic stroke.

METHODS

Ten chronic stroke subjects produced submaximal isometric elbow flexion force on impaired and non-impaired sides. Intramuscular EMG (iEMG) was recorded from biceps and triceps brachii muscles.

RESULTS

We observed sustained spontaneous motor unit discharges in resting biceps on iEMG. Spontaneous discharges increased after voluntary activation only on the impaired side. The impaired side had greater matching errors and greater fluctuations in isometric force. Spontaneous discharges were not related functionally to spasticity, force variability, or weakness. However, greater strength on the impaired side correlated with less force variability.

CONCLUSION

Weakness rather than spasticity is a main factor interfering with voluntary force control in paretic-spastic biceps brachii muscles in chronic stroke.

Rewiring the brain: potential role of the premotor cortex in motor control, learning, and recovery of function following brain injury

The brain is a plastic organ with a capability to reorganize in response to behavior and/or injury. Following injury to the motor cortex or emergent corticospinal pathways, recovery of function depends on the capacity of surviving anatomical resources to recover and repair in response to task-specific training. One such area implicated in poststroke reorganization to promote recovery of upper extremity recovery is the premotor cortex (PMC). This study reviews the role of distinct subdivisions of PMC: dorsal (PMd) and ventral (PMv) premotor cortices as critical anatomical and physiological nodes within the neural networks for the control and learning of goal-oriented reach and grasp actions in healthy individuals and individuals with stroke. Based on evidence emerging from studies of intrinsic and extrinsic connectivity, transcranial magnetic stimulation, functional neuroimaging, and experimental studies in animals and humans, the authors propose 2 distinct patterns of reorganization that differentially engage ipsilesional and contralesional PMC. Research directions that may offer further insights into the role of PMC in motor control, learning, and poststroke recovery are also proposed. This research may facilitate neuroplasticity for maximal recovery of function following brain injury.

Disparity between functional recovery and daily use of the upper and lower extremities during subacute stroke rehabilitation

BACKGROUND

Although inpatient rehabilitation may enhance an individual's functional ability after stroke, it is not known whether these improvements are accompanied by an increase in daily use of the arms and legs.

OBJECTIVES

To determine the change in daily use of the upper and lower extremities of stroke patients during rehabilitation and to compare these values with that of community-dwelling older adults.

METHODS

A total of 60 stroke patients underwent functional assessments and also wore 3 accelerometers for 3 consecutive weekdays on admission to rehabilitation and 3 weeks later prior to hospital discharge. The number of steps and upper-extremity activity counts were measured over the waking hours and during daily use for occupational therapy (OT) and physical therapy (PT) sessions. Healthy older adults (n = 40) also wore 3 accelerometers for 5 consecutive days.

RESULTS

Stroke patients demonstrated a significant increase in mobility function, and this was accompanied by an increase in daily walking over the entire day as well as in PT. However, increases in daily walking were found predominantly in patients who were wheelchair users (and not walkers) at the time of admission. Control walking values (5202 steps) were more than 17 times that of stroke patients. Despite significant improvements in paretic hand function, no increase in daily use of the paretic or nonparetic hand was found over the entire day or in PT.

CONCLUSIONS

A disparity between functional recovery and increases in daily use of the upper and lower extremities was found during inpatient stroke rehabilitation.

Arm-hand use in healthy older adults

OBJECTIVE

Our objectives were (1) to quantify arm-hand use of older adults without a disability and to determine the effects of hand dominance, gender, and day on hand usage and (2) to determine the factors that predict arm-hand use. This information will enhance understanding of the extent of the client's occupational performance.

METHOD

Twenty men and 20 women, ages 65-85, wore wrist and hip accelerometers for 7 consecutive days. Manual dexterity and grip strength were assessed. A three-way factorial analysis of variance and multiple linear regressions were conducted.

RESULTS

The activity kilocounts from both wrist accelerometers revealed a significant interaction effect between hand and gender (F[1, 190] = 24.4, p < .001). Enhanced manual dexterity of the right hand was associated with greater right-hand use.

CONCLUSION

Arm-hand use is a novel dimension of hand function measuring the extent of real-life occupational performance in the client's home.

Oscillatory MEG motor activity reflects therapy-related plasticity in stroke patients

BACKGROUND

A goal of stroke rehabilitation is to harness the capacity of the brain to reorganize following neurological damage and enable restoration of function.

OBJECTIVE

To understand how neural oscillatory motor responses change following a therapeutic intervention and to illuminate whether these neurophysiological alterations correlate with improvements on behavioral measurements.

METHODS

Magnetoencephalography (MEG) was used to evaluate plasticity in motor networks following 2 weeks of intensive task-oriented therapy, which was paired with sham or peripheral nerve stimulation (PNS). Patients completed unilateral finger tapping before and 3 weeks after therapy as whole-head MEG data were acquired. MEG data were imaged using beamforming, and the resulting event-related synchronizations and desynchronizations (ERSs/ERDs) were subjected to region-of-interest (ROI) analyses. For each ROI, the authors compared the baseline and postintervention MEG response amplitude, volume, and peak location for premovement β ERD, movement-onset γ ERS, and postmovement β ERS.

RESULTS

Following therapy, all patients showed reduced postmovement β ERS response amplitudes in bilateral precentral gyri and reduced γ ERS amplitudes in the precentral gyrus of the affected hemisphere. This latter response also distinguished treatment groups, as the posttherapy γ reduction was greater in patients who received PNS. Finally, both β and γ response amplitudes were significantly correlated with improvement on several behavioral indices of motor function.

DISCUSSION

These case-series data indicate that oscillatory MEG responses may be useful in gauging plasticity in motor cortices following therapy in stroke patients.