Side of lesion influences bilateral activation in chronic, post-stroke hemiparesis

The role of the contralesional primary motor cortex in upper limb recovery after stroke: a scoping review following PRISMA-ScR guidelines

BACKGROUND

Stroke often results in motor impairments, with recovery involving complex interactions between the lesioned (ipsilesional) and non-lesioned (contralesional) hemispheres. This scoping review investigates the role of the contralesional primary motor cortex (M1) in motor recovery of the paretic upper limb following stroke, examining its structural and functional changes and compensatory roles.

METHODS

A systematic search for scoping review was conducted in PubMed, Embase, Web of Science, and Google Scholar following PRISMA-ScR guidelines. Studies examining contralesional M1 contributions to upper limb recovery in humans and animal models were included. Data were extracted, synthesized qualitatively, and assessed for risk of bias using SYRCLE and Cochrane tools.

RESULTS

A total of 38 studies were included in the analysis, consisting of 34 focused on stroke patients and 4 utilizing animal models. The findings revealed the dual and task-specific role of the contralesional primary motor cortex (M1) in upper limb recovery after stroke. In patients with severe motor impairments, contralesional M1 supported recovery through compensatory mechanisms, such as increased neuronal recruitment and functional reorganization. However, in cases with mild impairments, its activation was associated with inhibitory effects on ipsilesional reorganization, potentially delaying optimal recovery. Animal studies provided evidence of structural and functional plasticity, including dendritic remodeling and enhanced neuronal connectivity, which paralleled improvements in motor function. In human studies, contralesional M1 activation was task-dependent, with pronounced engagement during demanding tasks and unimanual movements. Ipsilateral motor deficits, including reduced dexterity, strength, and coordination, were commonly reported and underscored the disrupted interhemispheric dynamics influencing recovery. Neuromodulation techniques showed promise in modulating interhemispheric interactions and enhancing motor outcomes. These results emphasize the complex interplay between compensatory and inhibitory processes mediated by contralesional M1 in stroke recovery.

CONCLUSION

The contralesional M1 plays a complex, task-specific role in upper limb recovery after stroke, acting as both a compensatory resource and a potential inhibitory factor. Future research should stratify patients by impairment severity to refine therapeutic approaches.

CLINICAL TRIAL NUMBER

Not applicable.

Evaluation of objective methods for analyzing ipsilateral motor evoked potentials in stroke survivors with chronic upper extremity motor impairment

Objective.Ipsilateral motor evoked potentials (iMEPs) are believed to represent cortically evoked excitability of uncrossed brainstem-mediated pathways. In the event of extensive injury to (crossed) corticospinal pathways, which can occur following a stroke, uncrossed ipsilateral pathways may serve as an alternate resource to support the recovery of the paretic limb. However, iMEPs, even in neurally intact people, can be small, infrequent, and noisy, so discerning them in stroke survivors is very challenging. This study aimed to investigate the inter-rater reliability of iMEP features (presence/absence, amplitude, area, onset, and offset) to evaluate the reliability of existing methods for objectively analyzing iMEPs in stroke survivors with chronic upper extremity (UE) motor impairment.Approach.Two investigators subjectively measured iMEP features from thirty-two stroke participants with chronic UE motor impairment. Six objective methods based on standard deviation (SD) and mean consecutive differences (MCD) were used to measure the iMEP features from the same 32 participants. IMEP analysis used both trial-by-trial (individual signal) and average-signal analysis approaches. Inter-rater reliability of iMEP features and agreement between the subjective and objective methods were analyzed (percent agreement-PA and intraclass correlation coefficient-ICC).Main results.Inter-rater reliability was excellent for iMEP detection (PA > 85%), amplitude, and area (ICC > 0.9). Of the six objective methods we tested, the 1SD method was most appropriate for identifying and analyzing iMEP amplitude and area (ICC > 0.9) in both trial-by-trial and average signal analysis approaches. None of the objective methods were reliable for analyzing iMEP onset and offset. Results also support using the average-signal analysis approach over the trial-by-trial analysis approach, as it offers excellent reliability for iMEP analysis in stroke survivors with chronic UE motor impairment.Significance.Findings from our study have relevance for understanding the role of ipsilateral pathways that typically survive unilateral severe white matter injury in people with stroke.

Static and dynamic interactions within the triple-network model in stroke patients with multidomain cognitive impairments

BACKGROUND

Internal capsule strokes often result in multidomain cognitive impairments across memory, attention, and executive function, typically due to disruptions in brain network connectivity. Our study examines these impairments by analyzing interactions within the triple-network model, focusing on both static and dynamic aspects.

METHODS

We collected resting-state fMRI data from 62 left (CI_L) and 56 right (CI_R) internal capsule stroke patients, along with 57 healthy controls (HC). Using independent component analysis to extract the default mode (DMN), executive control (ECN), and salience networks (SAN), we conducted static and dynamic functional network connectivity analyses (DFNC) to identify differences between stroke patients and controls. For DFNC, we used k-means clustering to focus on temporal properties and multilayer network analysis to examine integration and modularity Q, where integration represents dynamic interactions between networks, and modularity Q measures how well the network is divided into distinct modules. We then calculated the correlations between SFNC/DFNC properties with significant inter-group differences and cognitive scales.

RESULTS

Compared to HC, both CI_L and CI_R patients showed increased static FCs between SAN and DMN and decreased dynamic interactions between ECN and other networks. CI_R patients also had heightened static FCs between SAN and ECN and maintained a state with strongly positive FNCs across all networks in the triple-network model. Additionally, CI_R patients displayed decreased modularity Q.

CONCLUSION

These findings highlight that stroke can result in the disruption of static and dynamic interactions in the triple network model, aiding our understanding of the neuropathological basis for multidomain cognitive deficits after internal capsule stroke.

Goal conceptualization has distinct effects on spatial and temporal bimanual coordination after left- and right- hemisphere stroke

Perception of task goal influences motor performance and coordination. In bimanual actions, it is unclear how one's perception of task goals influences bimanual coordination and performance in individuals with unilateral stroke. We characterized inter-limb coordination differences in individuals with chronic right- and left-hemisphere damaged (RCVA: n = 24, LCVA: n = 24) stroke and age-matched neurotypical controls (n = 24) as they completed bimanual reaching tasks under distinct goal conditions. In the dual-goal condition, participants reached to move two virtual bricks (cursors) assigned to each hand toward independent targets. In the common-goal condition, they moved a central common virtual brick representing both hands to a single, central target. Spatial and temporal coordination (cross-correlation coefficients of hand velocity and their time-lag), the redundant axis deviations (the hand deviations in the axis orthogonal to the axis along the cursor-target direction), and the contribution ratio of the paretic hand were measured. Compared to the dual-goal condition, reaching actions to the common-goal demonstrated better spatial bimanual coordination in all three participant groups. Temporal coordination was better during common-goal than dual-goal actions only for the LCVA group. Additionally, and novel to this field, sex, as a biological variable, differently influenced movement time and redundant axis deviation in participants with stroke under the common-goal condition. Specifically, female stroke survivors showed larger movements in the redundant axes and, consequently, longer movement times, which was more prominent in the LCVA group. Our results indicate that perception of task goals influences bimanual coordination, with common goal improving spatial coordination in neurotypical individuals and individuals with unilateral stroke and providing additional advantage for temporal coordination in those with LCVA. Sex influences bimanual performance in stroke survivors and needs to be considered in future investigations.

The impact of lesion side on bilateral upper limb coordination after stroke

BACKGROUND

A stroke frequently results in impaired performance of activities of daily life. Many of these are highly dependent on effective coordination between the two arms. In the context of bimanual movements, cyclic rhythmical bilateral arm coordination patterns can be classified into two fundamental modes: in-phase (bilateral homologous muscles contract simultaneously) and anti-phase (bilateral muscles contract alternately) movements. We aimed to investigate how patients with left (LHS) and right (RHS) hemispheric stroke are differentially affected in both individual-limb control and inter-limb coordination during bilateral movements.

METHODS

We used kinematic measurements to assess bilateral coordination abilities of 18 chronic hemiparetic stroke patients (9 LHS; 9 RHS) and 18 age- and sex-matched controls. Using KINARM upper-limb exoskeleton system, we examined individual-limb control by quantifying trajectory variability in each hand and inter-limb coordination by computing the phase synchronization between hands during anti- and in-phase movements.

RESULTS

RHS patients exhibited greater impairment in individual- and inter-limb control during anti-phase movements, whilst LHS patients showed greater impairment in individual-limb control during in-phase movements alone. However, LHS patients further showed a swap in hand dominance during in-phase movements.

CONCLUSIONS

The current study used individual-limb and inter-limb kinematic profiles and showed that bilateral movements are differently impaired in patients with left vs. right hemispheric strokes. Our results demonstrate that both fundamental bilateral coordination modes are differently controlled in both hemispheres using a lesion model approach. From a clinical perspective, we suggest that lesion side should be taken into account for more individually targeted bilateral coordination training strategies.

TRIAL REGISTRATION

the current experiment is not a health care intervention study.

Bimanual coordination during reach-to-grasp actions is sensitive to task goal with distinctions between left- and right-hemispheric stroke

The perceptual feature of a task such as how a task goal is perceived influences performance and coordination of bimanual actions in neurotypical adults. To assess how bimanual task goal modifies paretic and non-paretic arm performance and bimanual coordination in individuals with stroke affecting left and right hemispheres, 30 participants with hemispheric stroke (15 right-hemisphere damage-RHD); 15 left-hemisphere damage-LHD) and 10 age-matched controls performed reach-to-grasp and pick-up actions under bimanual common-goal (i.e., two physically coupled dowels), bimanual independent-goal (two physically uncoupled dowels), and unimanual conditions. Reach-to-grasp time and peak grasp aperture indexed motor performance, while time lags between peak reach velocities, peak grasp apertures, and peak pick-up velocities of the two hands characterized reach, grasp, and pick-up coordination, respectively. Compared to unimanual actions, bimanual actions significantly slowed non-paretic arm speed to match paretic arm speed, thus affording no benefit to paretic arm performance. Detriments in non-paretic arm performance during bimanual actions was more pronounced in the RHD group. Under common-goal conditions, movements were faster with smaller peak grasp apertures compared to independent-goal conditions for all groups. Compared to controls, individuals with stroke demonstrated poor grasp and pick-up coordination. Of the patient groups, patients with LHD showed more pronounced deficits in grasp coordination between hands. Finally, grasp coordination deficits related to paretic arm motor deficits (upper extremity Fugl-Meyer score) for LHD group, and to Trail-Making Test performance for RHD group. Findings suggest that task goal and distinct clinical deficits influence bimanual performance and coordination in patients with left- and right-hemispheric stroke.

Evaluation of signal analysis algorithms for ipsilateral motor-evoked potentials induced by transcranial magnetic stimulation

OBJECTIVE

Evaluating ipsilateral motor-evoked potentials (iMEP) induced by transcranial magnetic stimulation (TMS) is challenging. In healthy adults, isometric contraction is necessary to facilitate iMEP induction; therefore, the signal may be masked by the concurrent muscle activity. Signal analysis algorithms for iMEP evaluation need to be benchmarked and evaluated.

APPROACH

An open analysis toolbox for iMEP evaluation was implemented on the basis of eleven previously reported algorithms, which were all threshold based, and a new template-based method based on data-driven signal decomposition. The reliability and validity of these algorithms were evaluated with a dataset of 4244 iMEP from 55 healthy adults.

MAIN RESULTS

iMEP estimation varies drastically between algorithms. Several algorithms exhibit high reliability, but some appear to be influenced by background activity of muscle preactivation. Especially in healthy subjects, template-based approaches might be more valid than threshold-based ones. Measurement of iMEP persistence requires algorithms that reject some trials as MEP negative. The stricter the algorithms reject trials, the less reliable they generally are. Our evaluation identifies an optimally strict and reliable algorithm.

SIGNIFICANCE

We show different benchmarks and propose application for different use cases.

Corticoreticulospinal tract neurophysiology in an arm and hand muscle in healthy and stroke subjects

KEY POINTS

The corticoreticulospinal tract (CReST) is a descending motor pathway that reorganizes after corticospinal tract (CST) injury in animals. In humans, the pattern of CReST innervation to upper limb muscles has not been carefully examined in healthy individuals or individuals with CST injury. In the present study, we assessed CReST projections to an arm and hand muscle on the same side of the body in healthy and chronic stoke subjects using transcranial magnetic stimulation. We show that CReST connection strength to the muscles differs between healthy and stroke subjects, with stronger connections to the hand than arm in healthy subjects, and stronger connections to the arm than hand in stroke subjects. These results help us better understand CReST innervation patterns in the upper limb, and may point to its role in normal motor function and motor recovery in humans.

ABSTRACT

The corticoreticulospinal tract (CReST) is a major descending motor pathway in many animals, but little is known about its innervation patterns in proximal and distal upper extremity muscles in humans. The contralesional CReST furthermore reorganizes after corticospinal tract (CST) injury in animals, but it is less clear whether CReST innervation changes after stroke in humans. We thus examined CReST functional connectivity, connection strength, and modulation in an arm and hand muscle of healthy (n = 15) and chronic stroke (n = 16) subjects. We delivered transcranial magnetic stimulation to the contralesional hemisphere (assigned in healthy subjects) to elicit ipsilateral motor evoked potentials (iMEPs) from the paretic biceps (BIC) and first dorsal interosseous (FDI) muscle. We operationalized CReST functional connectivity as iMEP presence/absence, CReST projection strength as iMEP size and CReST modulation as change in iMEP size by head rotation. We found comparable CReST functional connectivity to the BICs and FDIs in both subject groups. However, the pattern of CReST connection strength to the muscles diverged between groups, with stronger connections to FDIs than BICs in healthy subjects and stronger connections to BICs than FDIs in stroke subjects. Head rotation modulated only FDI iMEPs of healthy subjects. Our findings indicate that the healthy CReST does not have a proximal innervation bias, and its strong FDI connections may have functional relevance to finger individuation. The reversed CReST innervation pattern in stroke subjects confirms its reorganization after CST injury, and its strong BIC connections may indicate upregulation for particular upper extremity muscles or their functional actions.

Bimanual Coordination Functions between Paretic and Nonparetic Arms: A Systematic Review and Meta-analysis

BACKGROUND

Bimanual coordination is essential for performing many everyday interlimb actions that require successful spatiotemporal interactions between the 2 arms. This systematic review and meta-analysis investigates bimanual coordination function of the upper extremities in patients with stroke.

METHODS

Seventeen studies that compared bimanual coordination functions in patients with stroke and age-matched healthy controls qualified for this meta-analysis. We categorized 25 comparisons from the 17 qualified studies into 6 types of bimanual actions based on 3 task constraints: (1), symmetry versus asymmetry movements, (2) parallel versus cooperative movements, and (3) independent goals versus a common goal.

RESULTS

Random effects meta-analysis revealed that patients with stroke had impaired kinematic (Hedges's g = -1.232 and P < .0001) and kinetic (Hedges's g = -.712 and P = .001) control of bimanual coordination as compared with the age-matched healthy controls. The moderator variable analysis on the 6 types of bimanual actions showed that bimanual coordination impairments after stroke appeared while performing both asymmetrical bimanual movements and symmetrical bimanual movements to achieve a common goal. Moreover, we observed a potential relationship between greater time since stroke onset and increased interlimb coordination impairments for chronic patients.

CONCLUSIONS

These findings suggest that restoring interlimb coordination functions after stroke may be a crucial rehabilitation goal for facilitating progress toward stroke motor recovery.

Constraint induced movement therapy promotes contralesional-oriented structural and bihemispheric functional neuroplasticity after stroke

The mechanism behind constraint-induced movement therapy (CIMT) in promoting motor recovery after stroke remains unclear. We explored the bilateral structural and functional reorganization of the brain induced by CIMT after left middle cerebral artery occlusion (MCAO) in rats. CIMT started on the 8^th day (D8) after MCAO surgery and lasted for 3 weeks. Skilled walking was assessed by Foot-Fault tests. The efferent neuron network innervating the paralyzed forelimb was labeled by pseudorabies virus (PRV) to explore neuron recruitment. Synapsin Ⅰ was used as an indicator of the number of synapses. Additionally, C-fos expression 1 h after walking was detected to explore the activation of the brain. As a result, CIMT significantly improved skilled walking and elicited more neuron recruitment into the innervating network of a paralyzed forelimb in the contralesional rather than the ipsilesional motor cortex and red nucleus. CIMT also increased the synapse number in the contralesional cortex but there was no corresponding effect in the intact ipsilesional cortex. Furthermore, MCAO decreased ipsilesional motor cortex activation, but CIMT partially compensated for this by increasing the number of activated neurons (c-fos⁺) in both the left and right motor cortex. In conclusion, the contralesional motor cortex and red nucleus might play more important roles than corresponding ipsilesional regions in structural reorganization during CIMT-induced motor recovery after stroke. However, CIMT promotes bilateral motor cortex activity without a side preference.

Gray matter volume changes in chronic subcortical stroke: A cross-sectional study

This study aimed to investigate the effects of lesion side and degree of motor recovery on gray matter volume (GMV) difference relative to healthy controls in right-handed subcortical stroke. Structural MRI data were collected in 97 patients with chronic subcortical ischemic stroke and 79 healthy controls. Voxel-wise GMV analysis was used to investigate the effects of lesion side and degree of motor recovery on GMV difference in right-handed chronic subcortical stroke patients. Compared with healthy controls, right-lesion patients demonstrated GMV increase (P < 0.05, voxel-wise false discovery rate correction) in the bilateral paracentral lobule (PCL) and supplementary motor area (SMA) and the right middle occipital gyrus (MOG); while left-lesion patients did not exhibit GMV difference under the same threshold. Patients with complete and partial motor recovery showed similar degree of GMV increase in right-lesion patients. However, the motor recovery was correlated with the GMV increase in the bilateral SMA in right-lesion patients. These findings suggest that there exists a lesion-side effect on GMV difference relative to healthy controls in right-handed patients with chronic subcortical stroke. The GMV increase in the SMA may facilitate motor recovery in subcortical stroke patients.

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There is a lesion-side effect on gray matter volume in subcortical stroke patients.

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Right-sided stroke patients show more extensive GMV changes than left-sided ones.

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GMV increase in the SMA may facilitate to motor recovery after stroke.

Correlations between arm motor behavior and brain function following bilateral arm training after stroke: a systematic review

BACKGROUND

Bilateral training (BT) of the upper limb (UL) might enhance recovery of arm function after stroke. To better understand the therapeutic potential of BT, this study aimed to determine the correlation between arm motor behavior and brain structure/function as a result of bilateral arm training poststroke.

METHODS

A systematic review of quantitative studies of BT evaluating both UL motor behavior and neuroplasticity was conducted. Eleven electronic databases were searched. Two reviewers independently selected studies, extracted data and assessed methodological quality, using the Effective Public Health Practice Project (EPHPP) tool.

RESULTS

Eight studies comprising 164 participants met the inclusion criteria. Only two studies rated "strong" on the EPHPP tool. Considerable heterogeneity of participants, BT modes, comparator interventions and measures contraindicated pooled outcome analysis. Modes of BT included: in-phase and anti-phase; functional movements involving objects; and movements only. Movements were mechanically coupled, free, auditory-cued, or self-paced. The Fugl-Meyer Assessment (UL section) was used in six of eight studies, however, different subsections were used by different studies. Neural correlates were measured using fMRI and TMS in three and five studies, respectively, using a wide variety of variables. Associations between changes in UL function and neural plasticity were inconsistent and only two studies reported a statistical correlation following BT.

CONCLUSIONS

No clear pattern of association between UL motor and neural response to BT was apparent from this review, indicating that the neural correlates of motor behavior response to BT after stroke remain unknown. To understand the full therapeutic potential of BT and its different modes, further investigation is required.

Recovery Potential After Acute Stroke

In acute stroke, the major factor for recovery is the early use of thrombolysis aimed at arterial recanalization and reperfusion of ischemic brain tissue. Subsequently, neurorehabilitative training critically improves clinical recovery due to augmention of postlesional plasticity. Neuroimaging and electrophysiology studies have revealed that the location and volume of the stroke lesion, the affection of nerve fiber tracts, as well as functional and structural changes in the perilesional tissue and in large-scale bihemispheric networks are relevant biomarkers of post-stroke recovery. However, associated disorders, such as mood disorders, epilepsy, and neurodegenerative diseases, may induce secondary cerebral changes or aggravate the functional deficits and, thereby, compromise the potential for recovery.

Ipsilateral motor pathways after stroke: implications for non-invasive brain stimulation

In humans the two cerebral hemispheres have essential roles in controlling the upper limb. The purpose of this article is to draw attention to the potential importance of ipsilateral descending pathways for functional recovery after stroke, and the use of non-invasive brain stimulation (NBS) protocols of the contralesional primary motor cortex (M1). Conventionally NBS is used to suppress contralesional M1, and to attenuate transcallosal inhibition onto the ipsilesional M1. There has been little consideration of the fact that contralesional M1 suppression may also reduce excitability of ipsilateral descending pathways that may be important for paretic upper limb control for some patients. One such ipsilateral pathway is the cortico-reticulo-propriospinal pathway (CRPP). In this review we outline a neurophysiological model to explain how contralesional M1 may gain control of the paretic arm via the CRPP. We conclude that the relative importance of the CRPP for motor control in individual patients must be considered before using NBS to suppress contralesional M1. Neurophysiological, neuroimaging, and clinical assessments can assist this decision making and facilitate the translation of NBS into the clinical setting.

Motor planning in chronic upper-limb hemiparesis: evidence from movement-related potentials

Background

Chronic hemiplegia is a common long-term consequence of stroke, and subsequent motor recovery is often incomplete. Neurophysiological studies have focused on motor execution deficits in relatively high functioning patients. Much less is known about the influence exerted by processes related to motor preparation, particularly in patients with poor motor recovery.

Methodology/Principal Findings

The current study investigates motor preparation using a modified response-priming experiment in a large sample of patients (n = 50) with moderate-to-severe chronic hemiparesis. The behavioural results revealed that hemiparetic patients had an increased response-priming effect compared to controls, but that their response times were markedly slower for both hands. Patients also demonstrated significantly enhanced midline late contingent negative variation (CNV) during paretic hand preparation, despite the absence of overall group differences when compared to controls. Furthermore, increased amplitude of the midline CNV correlated with a greater response-priming effect. We propose that these changes might reflect greater anticipated effort to respond in patients, and consequently that advance cueing of motor responses may be of benefit in these individuals. We further observed significantly reduced CNV amplitudes over the lesioned hemisphere in hemiparetic patients compared to controls during non-paretic hand preparation, preparation of both hands and no hand preparation. Two potential explanations for these CNV reductions are discussed: alterations in anticipatory attention or state changes in motor processing, for example an imbalance in inter-hemispheric inhibition.

Conclusions/Significance

Overall, this study provides evidence that movement preparation could play a crucial role in hemiparetic motor deficits, and that advance motor cueing may be of benefit in future therapeutic interventions. In addition, it demonstrates the importance of monitoring both the non-paretic and paretic hand after stroke and during therapeutic intervention.

Age- and stroke-related skeletal muscle changes: a review for the geriatric clinician

Independently, aging and stroke each have a significant negative impact on skeletal muscle, but the potential cumulative effects of aging and stroke have not been explored. Optimal interventions for individuals post stroke may include those that specifically target skeletal muscle. Addressing changes in muscles may minimize activity limitations and enhance participation post stroke. This article reviews the impact of aging and stroke on muscle morphology and composition, including fiber atrophy, reductions in muscle cross-sectional area, changes in muscle fiber distributions, and increases in intramuscular fat. Relationships between changes in muscle structure, muscle function, and physical mobility are reviewed. Clinical recommendations that preserve and enhance skeletal muscle in the aging adult and individuals post stroke are discussed. Future research directions that include systematic comparison of the differences in skeletal muscle between younger and older adults who have sustained a stroke are suggested.

Maladaptive plasticity for motor recovery after stroke: mechanisms and approaches

Many studies in human and animal models have shown that neural plasticity compensates for the loss of motor function after stroke. However, neural plasticity concerning compensatory movement, activated ipsilateral motor projections and competitive interaction after stroke contributes to maladaptive plasticity, which negatively affects motor recovery. Compensatory movement on the less-affected side helps to perform self-sustaining activity but also creates an inappropriate movement pattern and ultimately limits the normal motor pattern. The activated ipsilateral motor projections after stroke are unable to sufficiently support the disruption of the corticospinal motor projections and induce the abnormal movement linked to poor motor ability. The competitive interaction between both hemispheres induces abnormal interhemispheric inhibition that weakens motor function in stroke patients. Moreover, widespread disinhibition increases the risk of competitive interaction between the hand and the proximal arm, which results in an incomplete motor recovery. To minimize this maladaptive plasticity, rehabilitation programs should be selected according to the motor impairment of stroke patients. Noninvasive brain stimulation might also be useful for correcting maladaptive plasticity after stroke. Here, we review the underlying mechanisms of maladaptive plasticity after stroke and propose rehabilitation approaches for appropriate cortical reorganization.

Contralesional hemisphere control of the proximal paretic upper limb following stroke

Cathodal transcranial direct current stimulation (c-tDCS) can reduce excitability of neurons in primary motor cortex (M1) and may facilitate motor recovery after stroke. However, little is known about the neurophysiological effects of tDCS on proximal upper limb function. We hypothesized that suppression of contralesional M1 (cM1) excitability would produce neurophysiological effects that depended on the severity of upper limb impairment. Twelve patients with varying upper limb impairment after subcortical stroke were assessed on clinical scales of upper limb spasticity, impairment, and function. Magnetic resonance imaging was used to determine lesion size and fractional anisotropy (FA) within the posterior limbs of the internal capsules indicative of corticospinal tract integrity. Excitability within paretic M1 biceps brachii representation was determined from motor-evoked potentials during selective isometric tasks, after cM1 sham stimulation and after c-tDCS. These neurophysiological data indicate that c-tDCS improved selective proximal upper limb control for mildly impaired patients and worsened it for moderate to severely impaired patients. The direction of the neurophysiological after effects of c-tDCS was strongly related to upper limb spasticity, impairment, function, and FA asymmetry between the posterior limbs of the internal capsules. These results indicate systematic variation of cM1 for proximal upper limb control after stroke and that suppression of cM1 excitability is not a "one size fits all" approach.

Upper extremity rehabilitation of children with cerebral palsy using accelerometer feedback on a multitouch display

Cerebral palsy is a non-progressive neurological disorder caused by disturbances to the developing brain. Physical and occupational therapy, if started at a young age, can help minimizing complications such as joint contractures, and can improve limb range of motion and coordination. While current forms of therapy for children with cerebral palsy are effective in minimizing symptoms, many children find them boring or repetitive. We have designed a system for use in upper-extremity rehabilitation sessions, making use of a multitouch display. The system allows children to be engaged in interactive gaming scenarios, while intensively performing desired exercises. It supports games which require completion of specific stretching or coordination exercises using one or both hands, as well as games which use physical, or "tangible" input mechanisms. To encourage correct posture during therapeutic exercises, we use a wireless kinematic sensor, worn on the patient's trunk, as a feedback channel for the games. The system went through several phases of design, incorporating input from observations of therapy and clinical sessions, as well as feedback from medical professionals. This paper describes the hardware platform, presents the design objectives derived from our iterative design phases and meetings with clinical personnel, discusses our current game designs and identifies areas of future work.

Current trends in stroke rehabilitation. A review with focus on brain plasticity

Current understanding of brain plasticity has lead to new approaches in ischemic stroke rehabilitation. Stroke units that combine good medical and nursing care with task-oriented intense training in an environment that provides confidence, stimulation and motivation significantly improve outcome. Repetitive trans-cranial magnetic stimulation (rTMS), and trans-cranial direct current stimulation (tDCS) are applied in rehabilitation of motor function. The long-term effect, optimal way of stimulation and possibly efficacy in cognitive rehabilitation need evaluation. Methods based on multisensory integration of motor, cognitive, and perceptual processes including action observation, mental training, and virtual reality are being tested. Different approaches of intensive aphasia training are described. Recent data on intensive melodic intonation therapy indicate that even patients with very severe non-fluent aphasia can regain speech through homotopic white matter tract plasticity. Music therapy is applied in motor and cognitive rehabilitation. To avoid the confounding effect of spontaneous improvement, most trials are preformed ≥3 months post stroke. Randomized controlled trials starting earlier after strokes are needed. More attention should be given to stroke heterogeneity, cognitive rehabilitation, and social adjustment and to genetic differences, including the role of BDNF polymorphism in brain plasticity.

Theta Burst Stimulation of Human Primary Motor Cortex Degrades Selective Muscle Activation in the Ipsilateral Arm

This study investigated whether repetitive transcranial magnetic stimulation (TMS) delivered as continuous theta burst stimulation (cTBS) to left M1 degraded selective muscle activation in the contralateral and ipsilateral upper limb in healthy participants. Contralateral motor-evoked potentials (cMEPs) were elicited in left and right biceps brachii (BB) before either elbow flexion or forearm pronation. A neurophysiological index, the excitability ratio (ER), was computed from the relative size of BB cMEPs before each type of movement. Short interval intracortical inhibition (SICI) was assessed in cMEPs of right BB with paired-pulse TMS of left M1. Ipsilateral MEPs (iMEPs) and silent periods (iSPs) were measured in left BB with single-pulse TMS of left M1. Low-intensity cTBS was expected to suppress corticospinal output from left M1. A sham condition was also included. Real but not sham cTBS caused increases in BB ER bilaterally. In the right arm, ER increased because BB cMEPs before flexion were less facilitated, whereas cMEPs in the pronation task were unaffected. This was accompanied by an increase in left M1 SICI. In the left arm, ER increased because BB cMEPs before pronation were facilitated but were unaffected in the flexion task. There was also facilitation of left BB iMEPs. These changes in the left arm are consistent with inappropriate facilitation of left BB α-motoneurons (αMNs) before pronation. This is the first demonstration that cTBS of M1 can alter excitability of neurons controlling ipsilateral proximal musculature and degrade ipsilateral upper limb motor control, providing evidence that ipsilateral and contralateral M1 shape the spatial and temporal characteristics of proximal muscle activation appropriate for the task at hand.

Task-Dependent Modulation of Inputs to Proximal Upper Limb Following Transcranial Direct Current Stimulation of Primary Motor Cortex

Cathodal transcranial DC stimulation (c-tDCS) suppresses excitability of primary motor cortex (M1) controlling contralateral hand muscles. This study assessed whether c-tDCS would have similar effects on ipsi- and contralateral M1 projections to a proximal upper limb muscle. Transcranial magnetic stimulation (TMS) of left M1 was used to elicit motor evoked potentials (MEPs) in the left and right infraspinatus (INF) muscle immediately before and after c-tDCS of left M1, and at 20 and 40 min, post-c-tDCS. TMS was delivered as participants preactivated each INF in isolation (left, right) or both INF together (bilateral). After c-tDCS, ipsilateral MEPs in left INF and contralateral MEPs in right INF were suppressed in the left task but not in the bilateral or right tasks, indicative of task-dependent modulation. Ipsilateral silent period duration in the left INF was reduced after c-tDCS, indicative of altered transcallosal inhibition. These findings may have implications for the use of tDCS as an adjunct to therapy for the proximal upper limb after stroke.

Bilateral movement training and stroke motor recovery progress: a structured review and meta-analysis

The purpose was to conduct a structured review and meta-analysis to determine the cumulative effect of bilateral arm training on motor capabilities post stroke. Forty-eight stroke studies were selected from three databases with 25 comparisons qualifying for inclusion in our meta-analysis. We identified and coded four types of bilateral arm interventions with 366 stroke patients. A random effects model using the standardized mean difference technique determined a large and significant effect size (0.734; SE=0.125), high fail-safe N (532), and medium variability in the studies (I(2)=63%). Moderator variable analysis on the type of bilateral training revealed two large and significant effects: (a) BATRAC (0.842; SE=0.155) and (b) coupled bilateral and EMG-triggered neuromuscular stimulation (1.142; SE=0.176). These novel findings provide strong evidence supporting bilateral arm training with the caveat that two coupled protocols, rhythmic alternating movements and active stimulation, are most effective.

Intracortical inhibition and facilitation with unilateral dominant, unilateral nondominant and bilateral movement tasks in left- and right-handed adults

PURPOSE

To investigate intracortical inhibition and facilitation in response to unilateral dominant, nondominant and bilateral biceps activation and short-term upper extremity training in right- and left-handed adults.

METHODS

Paired-pulse transcranial magnetic stimulation was used to measure intracortical excitability in motor dominant and nondominant cortices of 26 nondisabled adults. Neural facilitation and inhibition were measured in each hemisphere during unilateral dominant, nondominant and bilateral arm activation and after training in each condition.

RESULTS

No differences were seen between right- and left-handed subjects. Intracortical facilitation and decreased inhibition were seen in each hemisphere with unilateral activation/training of contralateral muscles and bilateral muscle activation/training. Persistent intracortical inhibition was seen in each hemisphere with ipsilateral muscle activation/training. Inhibition was greater in the nondominant hemisphere during dominant hemisphere activation (dominant arm contraction).

CONCLUSION

Strongly dominant individuals show no difference in intracortical responses given handedness. Intracortical activity with unilateral and bilateral arm activation and short-term training differs based on hemispheric dominance, with the motor dominant hemisphere exerting a larger inhibitory influence over the nondominant hemisphere. Bilateral activation and training have a disinhibitory effect in both dominant and nondominant hemispheres.

Ipsilateral versus contralateral cortical motor projections to a shoulder adductor in chronic hemiparetic stroke: implications for the expression of arm synergies

An increase in ipsilateral descending motor pathway activity has been reported following hemiparetic stroke. In axial muscles, increased ipsilateral cortical activity has been correlated with good recovery whereas in distal arm muscles it is correlated with poor recovery. Currently, little is known about the control of proximal upper limb muscles following stroke. This muscle group is less impaired than the distal arm muscles following stroke, yet contributes to the abnormal motor coordination patterns associated with movements of the arm which can severely impair reaching ability. This study used transcranial magnetic stimulation (TMS) to evaluate the presence and magnitude of ipsilateral and contralateral projections to the pectoralis major (PMJ) muscle in stroke survivors. A laterality index (LI) was used to investigate the relationship between ipsilateral and contralateral projections and strength, clinical impairment level, and the degree of abnormal coordination expressed in the arm. The ipsilateral and contralateral hemispheres were stimulated using 90% TMS intensity while the subject generated shoulder adduction torques in both arms. Motor evoked potentials (MEPs) were measured in the paretic and non-paretic PMJ. The secondary torque at the elbow was measured during maximal adduction as an indicator of the degree of extensor synergy. Ipsilateral MEPs were most common in stroke survivors with moderate to severe motor deficits. The LI was correlated with clinical impairment level (P = 0.05) and the degree of extension synergy expressed in the arm (P = 0.03). The LI was not correlated with strength. These results suggest that increased excitability of ipsilateral pathways projecting to the proximal upper arm may contribute to the expression of the extension synergy following stroke. These findings are discussed in relation to a possible unmasking or upregulation of oligosynaptic cortico-bulbospinal pathways following stroke.