Hand motor recovery after stroke: a transcranial magnetic stimulation mapping study of motor output areas and their relation to functional status

Influence of clinical and tumor-specific factors on the resting motor threshold in navigated transcranial magnetic stimulation

OBJECTIVE

Preoperative non-invasive mapping of motor function with navigated transcranial magnetic stimulation (nTMS) has become a widely used diagnostic procedure. Determination of the patient-individual resting motor threshold (rMT) is of great importance to achieve reliable results when conducting nTMS motor mapping. Factors which contribute to differences in rMT of brain tumor patients have not been fully investigated.

METHODS

We included adult patients with all types of de novo and recurrent intracranial lesions, suspicious for intra-axial brain tumors. The outcome measure was the rMT of the upper extremity, defined as the stimulation intensity eliciting motor evoked potentials with amplitudes greater than 50µV in 50 % of applied stimulations.

RESULTS

Eighty nTMS examinations in 75 patients (37.5 % female) aged 57.9 ± 14.9 years were evaluated. In non-parametric testing, rMT values were higher in patients with upper extremity paresis (p = 0.024) and lower in patients with high grade gliomas (HGG) (p = 0.001). rMT inversely correlated with patient age (rs=-0.28, p = 0.013) and edema volume (rs=-0.28, p = 0.012) In regression analysis, infiltration of the precentral gyrus (p<0.001) increased rMT values. Values of rMT were reduced in high grade gliomas (p<0.001), in patients taking Levetiracetam (p = 0.019) and if perilesional edema infiltrated motor eloquent brain (p<0.001). Subgroup analyses of glioma patients revealed similar results. Values of rMT did not differ between hand and forearm muscles.

CONCLUSION

Most factors confounding rMT in our study were specific to the lesion. These factors contributed to the variability in cortical excitability and must be considered in clinical work with nTMS to achieve reliable results with nTMS motor mapping.

Resting motor threshold in the course of hand motor recovery after stroke: a systematic review

Background

Resting motor threshold is an objective measure of cortical excitability. Numerous studies indicate that the success of motor recovery after stroke is significantly determined by the direction and extent of cortical excitability changes. A better understanding of this topic (particularly with regard to the level of motor impairment and the contribution of either cortical hemisphere) may contribute to the development of effective therapeutical strategies in this cohort.

Objectives

This systematic review collects and analyses the available evidence on resting motor threshold and hand motor recovery in stroke patients.

Methods

PubMed was searched from its inception through to 31/10/2020 on studies investigating resting motor threshold of the affected and/or the non-affected hemisphere and motor function of the affected hand in stroke cohorts.

Results

Overall, 92 appropriate studies (including 1978 stroke patients and 377 healthy controls) were identified. The analysis of the data indicates that severe hand impairment is associated with suppressed cortical excitability within both hemispheres and with great between-hemispheric imbalance of cortical excitability. Favorable motor recovery is associated with an increase of ipsilesional motor cortex excitability and reduction of between-hemispheric imbalance. The direction of change of contralesional motor cortex excitability depends on the amount of hand motor impairment. Severely disabled patients show an increase of contralesional motor cortex excitability during motor recovery. In contrast, recovery of moderate to mild hand motor impairment is associated with a decrease of contralesional motor cortex excitability.

Conclusions

This data encourages a differential use of rehabilitation strategies to modulate cortical excitability. Facilitation of the ipsilesional hemisphere may support recovery in general, whereas facilitation and inhibition of the contralesional hemisphere may enhance recovery in severe and less severely impaired patients, respectively.

Hand Focused Upper Extremity Rehabilitation in the Subacute Phase Post-stroke Using Interactive Virtual Environments

Introduction: Innovative motor therapies have attempted to reduce upper extremity impairment after stroke but have not made substantial improvement as over 50% of people post-stroke continue to have sensorimotor deficits affecting their self-care and participation in daily activities. Intervention studies have focused on the role of increased dosing, however recent studies have indicated that timing of rehabilitation interventions may be as important as dosing and importantly, that dosing and timing interact in mediating effectiveness. This study is designed to empirically test dosing and timing. Methods and Analysis: In this single-blinded, interventional study, subjects will be stratified on two dimensions, impairment level (Fugl-Meyer Upper Extremity Assessment (FM) and presence or absence of Motor Evoked Potentials (MEPs) as follows; (1) Severe, FM score 10-19, MEP+, (2) Severe, FM score 10-19, MEP-, (3) Moderate, FM score 20-49, MEP+, (4) Moderate, FM score 20-49, MEP-. Subjects not eligible for TMS will be assigned to either group 2 (if severe) or group 3 (if moderate). Stratified block randomization will then be used to achieve a balanced assignment. Early Robotic/VR Therapy (EVR) experimental group will receive in-patient usual care therapy plus an extra 10 h of intensive upper extremity therapy focusing on the hand using robotically facilitated rehabilitation interventions presented in virtual environments and initiated 5-30 days post-stroke. Delayed Robotic/VR Therapy (DVR) experimental group will receive the same intervention but initiated 30-60 days post-stroke. Dose-matched usual care group (DMUC) will receive an extra 10 h of usual care initiated 5-30 days post-stroke. Usual Care Group (UC) will receive the usual amount of physical/occupational therapy. Outcomes: There are clinical, neurophysiological, and kinematic/kinetic measures, plus measures of daily arm use and quality of life. Primary outcome is the Action Research Arm Test (ARAT) measured at 4 months post-stroke. Discussion: Outcome measures will be assessed to determine whether there is an early time period in which rehabilitation will be most effective, and whether there is a difference in the recapture of premorbid patterns of movement vs. the development of an efficient, but compensatory movement strategy. Ethical Considerations: The IRBs of New Jersey Institute of Technology, Rutgers University, Northeastern University, and Kessler Foundation reviewed and approved all study protocols. Study was registered in https://ClinicalTrials.gov (NCT03569059) prior to recruitment. Dissemination will include submission to peer-reviewed journals and professional presentations.

Does Resting Motor Threshold Predict Motor Hand Recovery After Stroke?

Background: Resting Motor threshold (rMT) is one of the measurement obtained by Transcranial Magnetic Stimulation (TMS) that reflects corticospinal excitability. As a functional marker of the corticospinal pathway, the question arises whether rMT is a suitable biomarker for predicting post-stroke upper limb function. To that aim, we conducted a systematic review of relevant studies that investigated the clinical significance of rMT in stroke survivors by using correlations between upper limb motor scores and rMT. Methods: Studies that reported correlations between upper limb motor function and rMT as a measure of corticospinal excitability in distal arm muscle were identified via a literature search in stroke patients. Two authors extracted the data using a home-made specific form. Subgroup analyses were carried out with patients classified with respect to time post-stroke onset (early vs. chronic stage) and stroke location (cortical, subcortical, or cortico-subcortical). Methodological quality of the study was also evaluated by a published checklist. Results: Eighteen studies with 22 groups (n = 508 stroke patients) were included in this systematic review. Mean methodological quality score was 14.75/24. rMT was often correlated with motor function or hand dexterity (n = 15/22, 68%), explaining on average 31% of the variance of the motor score. Moreover, the results did not seem impacted if patients were examined at the early or chronic stages of stroke. Two findings could not be properly interpreted: (i) the fact that the rMT is an independent predictor of motor function as several confounding factors are well-established, and, (ii) whether the stroke location impacts this prediction. Conclusion: Most of the studies found a correlation between rMT and upper limb motor function after stroke. However, it is still unclear if rMT is an independent predictor of upper limb motor function when taking into account for age, time post stroke onset and level of corticospinal tract damage as confounding factors. Clear-cut conclusions could not be drawn at that time but our results suggest that rMT could be a suitable candidate although future investigations are needed. Systematic Review Registration Number: (https://www.crd.york.ac.uk/prospero/): ID 114317.

Abnormal cortical asymmetry as a target for neuromodulation in neuropsychiatric disorders: A narrative review and concept proposal

Recent advances in knowledge relating to the organization of neural circuitry in the human brain have increased understanding of disorders involving brain circuit asymmetry. These asymmetries, which can be measured and identified utilizing EEG and LORETA analysis techniques, may be a factor in mental disorders. New treatments involving non-invasive brain stimulation (NIBS), including trans-cranial magnetic stimulation, direct current stimulation and vagal nerve stimulation, have emerged in recent years. We propose that EEG identification of circuit asymmetry geometries can direct non-invasive brain stimulation more specifically for treatments of mental disorders. We describe as a narrative review new NIBS therapies that have been developed and delivered, and suggest that they are proving effective in certain patient groups. A brief narrative of influence of classical and operant conditioning of neurofeedback on EEG coherence, phase, abnormalities and Loreta's significance is provided. We also discuss the role of Heart rate variability and biofeedback in influencing EEG co-relates. Clinical evidence is at an early stage, but the basic science evidence and early case studies suggest that this may be a promising new modality for treating mental disorders and merits further research.

Exploring the impact of visual and movement based priming on a motor intervention in the acute phase post-stroke in persons with severe hemiparesis of the upper extremity

PURPOSE

Explore the potential benefits of using priming methods prior to an active hand task in the acute phase post-stroke in persons with severe upper extremity hemiparesis.

METHODS

Five individuals were trained using priming techniques including virtual reality (VR) based visual mirror feedback and contralaterally controlled passive movement strategies prior to training with an active pinch force modulation task. Clinical, kinetic, and neurophysiological measurements were taken pre and post the training period. Clinical measures were taken at six months post training.

RESULTS

The two priming simulations and active training were well tolerated early after stroke. Priming effects were suggested by increased maximal pinch force immediately after visual and movement based priming. Despite having no clinically observable movement distally, the subjects were able to volitionally coordinate isometric force and muscle activity (EMG) in a pinch tracing task. The Root Mean Square Error (RMSE) of force during the pinch trace task gradually decreased over the training period suggesting learning may have occurred. Changes in motor cortical neurophysiology were seen in the unaffected hemisphere using Transcranial Magnetic Stimulation (TMS) mapping. Significant improvements in motor recovery as measured by the Action Research Arm Test (ARAT) and the Upper Extremity Fugl Meyer Assessment (UEFMA) were demonstrated at six months post training by three of the five subjects.

CONCLUSION

This study suggests that an early hand-based intervention using visual and movement based priming activities and a scaled motor task allows participation by persons without the motor control required for traditionally presented rehabilitation and testing. Implications for Rehabilitation Rehabilitation of individuals with severely paretic upper extremities after stroke is challenging due to limited movement capacity and few options for therapeutic training. Long-term functional recovery of the arm after stroke depends on early return of active hand control, establishing a need for acute training methods focused distally. This study demonstrates the feasibility of an early hand-based intervention using virtual reality based priming and scaled motor activities which can allow for participation by persons without the motor control required for traditionally presented rehabilitation and testing.

Motor Recovery of the Affected Hand in Subacute Stroke Correlates with Changes of Contralesional Cortical Hand Motor Representation

Objective. To investigate the relationship between changes of cortical hand motor representation and motor recovery of the affected hand in subacute stroke. Methods. 17 patients with motor impairment of the affected hand were enrolled in an in-patient neurological rehabilitation program. Hand motor function tests (Wolf Motor Function Test, Action Research Arm Test) and neurophysiological evaluations (resting motor threshold, motor evoked potentials, motor map area size, motor map area volume, and motor map area location) were obtained from both hands and hemispheres at baseline and two, four, and six weeks of in-patient rehabilitation. Results. There was a wide spectrum of hand motor impairment at baseline and hand motor recovery over time. Hand motor function and recovery correlated significantly with (i) reduction of cortical excitability, (ii) reduction in size and volume of cortical hand motor representation, and (iii) a medial and anterior shift of the center of gravity of cortical hand motor representation within the contralesional hemisphere. Conclusion. Recovery of motor function of the affected hand after stroke is accompanied by definite changes in excitability, size, volume, and location of hand motor representation over the contralesional primary motor cortex. These measures may serve as surrogate markers for the outcome of hand motor rehabilitation after stroke.

Mapping cortical hand motor representation using TMS: A method to assess brain plasticity and a surrogate marker for recovery of function after stroke?

OBJECTIVE

Stroke is associated with reorganization within motor areas of both hemispheres. Mapping the cortical hand motor representation using transcranial magnetic stimulation may help to understand the relationship between motor cortex reorganization and motor recovery of the affected hand after stroke.

METHODS

A standardized review of the pertinent literature was performed.

RESULTS

We identified 20 trials, which analyzed the relationship between the extent and/or location of cortical hand motor representation using transcranial magnetic stimulation and motor function and recovery of the affected hand. Several correlations were found between cortical reorganization and measures of hand motor impairment and recovery.

CONCLUSION

A better understanding of the relationships between the extent and location of cortical hand motor representation and the motor impairment and motor recovery of the affected hand after stroke may contribute to a targeted use of non-invasive brain stimulation protocols. In the future motor mapping may help to guide brain stimulation techniques to the most effective motor area in an affected individual.

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.

Downregulating Aberrant Motor Evoked Potential Synergies of the Lower Extremity Post Stroke During TMS of the Contralesional Hemisphere

BACKGROUND

Growing evidence demonstrates unique synergistic signatures in the lower limb (LL) post-stroke, with specific across-plane and across-joint representations. While the inhibitory role of the ipsilateral hemisphere in the upper limb (UL) has been widely reported, examination of the contralesional hemisphere (CON-H) in modulating LL expressions of synergies following stroke is lacking.

OBJECTIVE

We hypothesize that stimulation of lesioned and contralesional motor cortices will differentially regulate paretic LL motor outflow. We propose a novel TMS paradigm to identify synergistic motor evoked potential (MEP) patterns across multiple muscles.

METHODS

Amplitude and background activation matched adductor MEPs were elicited using single pulse TMS of L-H and CON-H (control ipsilateral) during an adductor torque matching task from 11 stroke and 10 control participants. Associated MEPs of key synergistic muscles were simultaneously observed.

RESULTS

By quantifying CON-H/L-H MEP ratios, we characterized a significant targeted inhibition of aberrant MEP coupling between ADD and VM (p = 0.0078) and VL (p = 0.047) exclusive to the stroke group (p = 0.028) that was muscle dependent (p = 0.039). We find TA inhibition in both groups following ipsilateral hemisphere stimulation (p = 0.0014; p = 0.015).

CONCLUSION

We argue that ipsilaterally mediated attenuation of abnormal synergistic activations post stroke may reflect an adaptive intracortical inhibition. The predominance of sub 3ms interhemispheric MEP latency differences implicates LL ipsilateral corticomotor projections. These findings provide insight into the association between CON-H reorganization and post-stroke LL recovery. While a prevailing view of driving L-H disinhibition for UL recovery seems expedient, presuming analogous LL neuromodulation may require further examination for rehabilitation. This study provides a step toward this goal.

Sensorimotor cortex reorganization in subacute and chronic stroke: A neuronavigated TMS study

The integrity of the corticospinal system is an important biomarker for recovery from stroke. However, mapping the topography of the corticospinal system in subacute stroke is not trivial and how it changes over the course of recovery is poorly understood. We intend to use a transcranial magnetic stimulation (TMS) based mapping approach to quantify the topographic landscape of corticospinal activation in the ipsi- and contralesional sensorimotor cortices in the subacute and chronic phase of stroke. Mapping was conducted before (PRE) and after (POST), intervention in 10 chronic subjects and 8 subacute subjects. Reorganization was quantified in a unique way by dissociating reorganization attributed to changes in the expanse (area) of the sensorimotor territory, from that attributed to changes in the robustness of the activation (amplitude). In doing so, we observed differences in reorganization in the subacute and chronic stages indicating that recovery in different stages may not be guided by similar neurophysiological mechanisms of neuroplasticity.

Differential patterns of cortical reorganization following constraint-induced movement therapy during early and late period after stroke: A preliminary study

OBJECTIVE

Constraint-induced movement therapy (CIMT) has been shown to improve upper extremity voluntary movement and change cortical movement representation after stroke. Direct comparison of the differential degree of cortical reorganization according to chronicity in stroke subjects receiving CIMT has not been performed and was the purpose of this study. We hypothesized that a higher degree of cortical reorganization would occur in the early (less than 9 months post-stroke) compared to the late group (more than 12 months post-stroke).

METHODS

17 early and 9 late subjects were enrolled. Each subject was evaluated using transcranial magnetic stimulation (TMS) and the Wolf Motor Function Test (WMFT) and received CIMT for 2 weeks.

RESULTS

The early group showed greater improvement in WMFT compared with the late group. TMS motor maps showed persistent enlargement in both groups but the late group trended toward more enlargement. The map shifted posteriorly in the late stroke group. The main limitation was the small number of TMS measures that could be acquired due to high motor thresholds, particularly in the late group.

CONCLUSION

CIMT appears to lead to greater improvement in motor function in the early phase after stroke. Greater cortical reorganization in map size and position occurred in the late group in comparison.

SIGNIFICANCE

The contrast between larger functional gains in the early group vs larger map changes in the late group may indicate that mechanisms of recovery change over the several months following stroke or that map changes are a time-dependent epiphenomenon.

Functional Neuroimaging in Motor Recovery After Stroke

Neuroimaging techniques provide information on the neural substrates underlying functional recovery after stroke, the number one cause of long-term disability. Despite the methodological difficulties, they promise to offer insight into the mechanisms by which therapeutic interventions can modulate human cortical plasticity. This information should lead to the development of new, targeted interventions to maximize recovery.

The effect of swallowing treatments on corticobulbar excitability: a review of transcranial magnetic stimulation induced motor evoked potentials

Transcranial magnetic stimulation (TMS) has been used extensively as a method of investigating the corticomotor physiology of many motor tasks, including healthy and disordered swallowing. Changes in excitability of cortical projections to various swallowing muscles have been documented in response to treatments with TMS induced motor evoked potentials (MEPs). These studies have provided valuable insight into CNS response to swallowing impairment, and more importantly, the adaptations associated with functional recovery. However, unique obstacles are presented when investigating corticobulbar neurophysiology associated with the complex task of swallowing. Stringent methodological control and supplementary outcome measures are required to ensure robust and clinically applicable findings. This article offers a tutorial for the researcher who may be considering the use of TMS for investigating changes in cortical excitability associated with various swallowing paradigms. Included is a review of the mechanisms of TMS and what can be measured with this technique, a summary of existing research using MEPs to investigate swallowing, a review of methodological factors that may influence outcomes, and proposed directions for new areas of research.

Age-related weakness of proximal muscle studied with motor cortical mapping: a TMS study

Aging-related weakness is due in part to degeneration within the central nervous system. However, it is unknown how changes to the representation of corticospinal output in the primary motor cortex (M1) relate to such weakness. Transcranial magnetic stimulation (TMS) is a noninvasive method of cortical stimulation that can map representation of corticospinal output devoted to a muscle. Using TMS, we examined age-related alterations in maps devoted to biceps brachii muscle to determine whether they predicted its age-induced weakness. Forty-seven right-handed subjects participated: 20 young (22.6±0.90 years) and 27 old (74.96±1.35 years). We measured strength as force of elbow flexion and electromyographic activation of biceps brachii during maximum voluntary contraction. Mapping variables included: 1) center of gravity or weighted mean location of corticospinal output, 2) size of map, 3) volume or excitation of corticospinal output, and 4) response density or corticospinal excitation per unit area. Center of gravity was more anterior in old than in young (p<0.001), though there was no significant difference in strength between the age groups. Map size, volume, and response density showed no significant difference between groups. Regardless of age, center of gravity significantly predicted strength (β = −0.34, p = 0.005), while volume adjacent to the core of map predicted voluntary activation of biceps (β = 0.32, p = 0.008). Overall, the anterior shift of the map in older adults may reflect an adaptive change that allowed for the maintenance of strength. Laterally located center of gravity and higher excitation in the region adjacent to the core in weaker individuals could reflect compensatory recruitment of synergistic muscles. Thus, our study substantiates the role of M1 in adapting to aging-related weakness and subtending strength and muscle activation across age groups. Mapping from M1 may offer foundation for an examination of mechanisms that preserve strength in elderly.

Behavioral, Neurophysiological, and Descriptive Changes After Occupation-Based Intervention

OBJECTIVE. We evaluated the effects of occupation-based intervention on poststroke upper-extremity (UE) motor recovery, neuroplastic change, and occupational performance in 1 research participant.

METHOD. A 55-yr-old man with chronic stroke and moderately impaired UE motor function participated in 15 sessions of occupation-based intervention in a hospital setting designed to simulate a home environment. We tested behavioral motor function (Fugl-Meyer Assessment, Stroke Impact Scale, Canadian Occupational Performance Measure) and neuroplasticity (transcranial magnetic stimulation [TMS]) at baseline and at completion of intervention. We collected descriptive data on occupational participation throughout the study.

RESULTS. All behavioral outcomes indicated clinically relevant improvement. TMS revealed bihemispheric corticomotor reorganization. Descriptive data revealed enhanced occupational performance.

CONCLUSION. Occupation-based intervention delivered in a hospital-based, homelike environment can lead to poststroke neuroplastic change, increased functional use of the affected UE, and improved occupational performance.

Transcranial magnetic stimulation as an investigative tool for motor dysfunction and recovery in stroke: an overview for neurorehabilitation clinicians

RATIONALE

An improved understanding of motor dysfunction and recovery after stroke has important clinical implications that may lead to the design of more effective rehabilitation strategies for patients with hemiparesis.

SCOPE

Transcranial magnetic stimulation (TMS) is a safe and painless tool that has been used in conjunction with other existing diagnostic tools to investigate motor pathophysiology in stroke patients. Since TMS emerged more than two decades ago, its application in clinical and basic neuroscience has expanded worldwide. TMS can quantify the corticomotor excitability properties of clinically affected and unaffected muscles and can probe local cortical networks as well as remote but functionally related areas. This provides novel insight into the physiology of neural circuits underlying motor dysfunction and brain reorganization during the motor recovery process. This important tool needs to be used with caution by clinical investigators, its limitations need to be understood, and the results should to be interpreted along with clinical evaluation in this patient population.

SUMMARY

In this review, we provide an overview of the rationale, implementation, and limitations of TMS to study stroke motor physiology. This knowledge may be useful to guide future rehabilitation treatments by assessing and promoting functional plasticity.

Probing modifications of cortical excitability during stroke recovery with navigated transcranial magnetic stimulation

OBJECTIVE

To follow cortical excitability changes during recovery from stroke with navigated transcranial magnetic stimulation (nTMS), in particular, to characterize changes of short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF), to correlate them with recovery of upper extremity function, and to detect possible shifts of cortical hand representations.

METHODS

Single and paired pulse nTMS were delivered to the hemisphere with infarction and to the hemisphere without infarction in 14 first-ever stroke patients at 1 (T1) and 3 months (T2) after stroke. Electromyographic responses to nTMS stimulation were recorded from the first dorsal interosseus muscles. nTMS was used to ensure an accurate coil repositioning in repeated measurements. Hand function recovery was clinically evaluated using the Action Research Arm Test (ARAT) and 9-hole peg test (9-HPT).

RESULTS

SICI and ICF were modulated in both hemispheres during recovery. Inhibition in the hemisphere without infarction correlated significantly with the affected hand performance at T2; stronger disinhibition (poor inhibition) was associated with worse hand performance. Location of hand muscle representations was shifted in 3 well-recovered patients out of 14 patients at T2.

CONCLUSIONS

In line with earlier studies, disinhibition in the hemisphere without infarction may be related to poor recovery of the affected hand. Usage of the affected hand during stroke recovery seems to influence these cortical excitability changes. nTMS is a valuable tool for tracking muscle cortical representation changes during brain reorganization.

Age dependence of excitatory-inhibitory balance following stroke

The mechanisms which mediate cortical map plasticity and functional recovery following stroke remain a matter of debate. Readjustment of the excitatory-inhibitory balance may support cortical map plasticity in perilesional areas. Here we studied cortical net inhibition in the vicinity of photothrombotically-induced cortical lesions in young adult (3 months) and aged (24 months) male rats. Field potentials were recorded in cortical layer II/III following application of paired-pulse stimulation at layer VI/white matter in coronal brain slices. Additionally, we analyzed the regional distribution of 5 major gamma-aminobutyric acid A (GABA(A)) receptor subunits (α1, α2, α3, α5, and γ2) by immunohistochemistry. Paired-pulse inhibition in the perilesional parietal cortex was decreased in young rats but was increased in aged rats. As a consequence of the diminished intrinsic net inhibition in aged control animals, the excitatory-inhibitory balance was readjusted to an age-independent similar level in young and aged lesioned rats in a homeostatic-like fashion. These physiological changes in neuronal activity were accompanied by age-specific laminar alterations of the gamma-aminobutyric acid A (GABA(A)) receptor subunit composition, most prominently of the subunit α5. The present study suggests that the mechanisms underlying functional reorganization in aged animals may be distinctly different from those in young animals.

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.

Constraint-induced movement therapy results in increased motor map area in subjects 3 to 9 months after stroke

BACKGROUND

Constraint-induced movement therapy (CIMT) has received considerable attention as an intervention to enhance motor recovery and cortical reorganization after stroke.

OBJECTIVE

The present study represents the first multi-center effort to measure cortical reorganization induced by CIMT in subjects who are in the subacute stage of recovery.

METHODS

A total of 30 stroke subjects in the subacute phase (>3 and <9 months poststroke) were recruited and randomized into experimental (receiving CIMT immediately after baseline evaluation) and control (receiving CIMT after 4 months) groups. Each subject was evaluated using transcranial magnetic stimulation (TMS) at baseline, 2 weeks after baseline, and at 4-month follow-up (ie, after CIMT in the experimental groups and before CIMT in the control groups). The primary clinical outcome measure was the Wolf Motor Function Test.

RESULTS

Both experimental and control groups demonstrated improved hand motor function 2 weeks after baseline. The experimental group showed significantly greater improvement in grip force after the intervention and at follow-up (P = .049). After adjusting for the baseline measures, the experimental group had an increase in the TMS motor map area compared with the control group over a 4-month period; this increase was of borderline significance (P = .053).

CONCLUSIONS

Among subjects who had a stroke within the previous 3 to 9 months, CIMT produced statistically significant and clinically relevant improvements in arm motor function that persisted for at least 4 months. The corresponding enlargement of TMS motor maps, similar to that found in earlier studies of chronic stroke subjects, appears to play an important role in CIMT-dependent plasticity.

Reorganization of brain function during force production after stroke: a systematic review of the literature

BACKGROUND AND PURPOSE

Damage to motor areas of the brain caused by stroke can produce devastating motor deficits, including aberrant control of force. Reorganization of brain function is a fundamental mechanism involved in recovery of motor control after stroke, and recent advances in neuroimaging have enabled study of this reorganization. This review focuses on neuroimaging studies that have examined reorganization of brain function during force production and force modulation after stroke.

METHODS

The type and extent of reorganization after stroke were characterized by three factors: severity of injury, time after stroke, and impact of therapeutic interventions on brain activation during force production. Twenty-six studies meeting the inclusion criteria could be identified in MEDLINE (1980-2007).

RESULTS

Relevant characteristics of studies (lesion location, chronicity of stroke, and motor task) and mapping techniques varied. During force production, increased activation in secondary motor areas occurred in persons with more severe strokes. Reduced recruitment of secondary motor areas during force production was found as a function of increased time since stroke. During force modulation, increased activation in motor areas occurred with greater force generation. Persons with more severe stroke showed greater activation with increasing force compared with persons with less severe stroke. Alteration of brain activation during and after rehabilitative interventions was identified in some studies.

DISCUSSION AND CONCLUSION

This systematic review establishes that reorganization of brain function during force production and force modulation can occur after stroke. These findings imply that therapeutic strategies may target brain reorganization to improve force control and functional recovery after stroke.

Transcranial direct current stimulation: a noninvasive tool to facilitate stroke recovery

Electrical brain stimulation, a technique developed many decades ago and then largely forgotten, has re-emerged recently as a promising tool for experimental neuroscientists, clinical neurologists and psychiatrists in their quest to causally probe cortical representations of sensorimotor and cognitive functions and to facilitate the treatment of various neuropsychiatric disorders. In this regard, a better understanding of adaptive and maladaptive plasticity in natural stroke recovery over the last decade and the idea that brain polarization may modulate neuroplasticity has led to the use of transcranial direct current stimulation (tDCS) as a potential enhancer of natural stroke recovery. We will review tDCS's successful utilization in pilot and proof-of-principle stroke recovery studies, the different modes of tDCS currently in use, and the potential mechanisms underlying the neural effects of tDCS.

Informing dose-finding studies of repetitive transcranial magnetic stimulation to enhance motor function: a qualitative systematic review

OBJECTIVE

Repetitive transcranial magnetic stimulation (rTMS) of the lesioned hemisphere might enhance motor recovery after stroke, but the appropriate dose (parameters of rTMS) remains uncertain. The present review collates evidence of the effect of rTMS on corticospinal pathway excitability and motor function in healthy adults and in people after stroke.

METHODS

The authors searched MEDLINE and EMBASE (1996 to April 2007), their own collection of peer-reviewed articles, and the reference lists of included studies. They included healthy adults or people with stroke who received rTMS to the primary motor cortex to facilitate or inhibit contralateral corticospinal excitability or movement control.

FINDINGS

Of the 625 references identified, 37 studies were included with 455 healthy adults (34 studies) and 69 people with stroke (3 studies). For healthy adults, the effects of rTMS on corticospinal pathway excitability varied within each frequency, for example, 1 Hz rTMS was found to facilitate, inhibit, and have no effect on amplitude of motor-evoked potentials (MEPs). After stroke there was a trend for recovery of MEPs (ie, presence of MEPs) after 10 daily sessions of 3 Hz rTMS (one study). Motor function in healthy adults might be adversely affected by 1 Hz rTMS (two studies), whereas combined frequency rTMS was found to have no effect (one study).

INTERPRETATION

There is as yet insufficient published evidence to guide the dose of rTMS to the lesioned hemisphere after stroke to improve recovery of a paretic limb. Moreover, it is apparent that there is variability in response to rTMS in healthy adults. Dose-finding studies in groups of well-characterized stroke patients are needed.

Constraint-induced movement therapy during early stroke rehabilitation

BACKGROUND

Limited data are available about the effectiveness of early rehabilitation after stroke.

OBJECTIVE

This is the 1st randomized controlled trial of constraint-induced movement therapy (CIMT) in subacute stroke to investigate neurophysiologic mechanisms and long-term outcome.

METHODS

Within 2 weeks after stroke, 23 patients with upper extremity (UE) weakness were randomized to 2 weeks of CIMT or traditional therapy at an equal frequency of up to 3 h/day. Motor function of the affected UE was blindly assessed before treatment, after treatment, and 3 months after stroke. Transcranial magnetic stimulation (TMS) measured the cortical area evoking movement of the affected hand.

RESULTS

Long-term improvement in motor function of the affected UE did not differ significantly between patients who received CIMT versus intensive traditional therapy. All outcome comparisons showed trends favoring CIMT over intensive traditional therapy, but none was statistically significant except for improvements in the Fugl-Meyer (FM) UE motor scale immediately following treatment and in reported quality of hand function at 3 months. Improvement in UE motor function on the FM was associated with a greater number of sites on the affected cerebral hemisphere where responses of the affected hand were evoked by TMS.

CONCLUSIONS

Future trials of CIMT during early stroke rehabilitation need greater statistical power, more inclusive eligibility criteria, and improved experimental control over treatment intensity. The relationship between changes in motor function and in evoked motor responses suggests that motor recovery during the 1st 3 months after stroke is associated with increased motor excitability of the affected cerebral hemisphere.

Axonal sprouting into the denervated spinal cord and synaptic and postsynaptic protein expression in the spinal cord after transplantation of bone marrow stromal cell in stroke rats

We investigated whether compensatory reinnervation in the corticospinal tract (CST) and the corticorubral tract (CRT) is enhanced by the administration of bone marrow stromal cells (BMSCs) after experimental stroke. Adult male Wistar rats were subjected to permanent right middle cerebral artery occlusion (MCAo). Phosphate-buffered saline (PBS, control, n=7) or 3x10(6) BMSCs in PBS (n=8) were injected into a tail vein at 1 day postischemia. The CST of the left sensorimotor cortices was labeled with DiI 2 days prior to MCAo. Functional recovery was measured. Rats were sacrificed at 28 days after MCAo. The brain and spinal cord were removed and processed for vibratome sections for laser-scanning confocal analysis and paraffin sections for immunohistochemistry. Normal rats (n=4) exhibited a predominantly unilateral pattern of innervation of CST and CRT axons. After stroke, bilateral innervation occurred through axonal sprouting of the uninjured CRT and CST. Administration of BMSCs significantly increased the axonal restructuring on the de-afferented red nucleus and the denervated spinal motoneurons (p<0.05). BMSC treatment also significantly increased synaptic proteins in the denervated motoneurons. These results were highly correlated with improved functional outcome after stroke (r>0.81, p<0.01). We conclude that the transplantation of BMSCs enhances axonal sprouting and rewiring into the denervated spinal cord which may facilitate functional recovery after focal cerebral ischemia.

Arm function after stroke: Neurophysiological correlates and recovery mechanisms assessed by transcranial magnetic stimulation

Transcranial Magnetic Stimulation has been used for over 20 years to investigate recovery of motor function in stroke patients. In particular, it has been used to quantify the extent of damage to the corticospinal output, reorganisation of the cortical representation of the affected body parts and excitability of intracortical and cortico-cortical circuitries in both hemispheres. In this review, we provide a detailed account of most of the published data with particular reference to methodological issues that affect their interpretation.

Do alternate methods of analysing motor evoked potentials give comparable results?

This study assessed the reliability of alternate methods of analysis of motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS). We recorded two sets of MEPs (Time 1 and Time 2) at the optimal scalp sites for both the right first dorsal interosseous (FDI) and flexor carpi ulnaris (FCU) at two different stimulation intensities in 10 healthy subjects. MEP magnitude was determined in each of the following three ways: the mean peak-to-peak amplitude and area of the 20 individual responses; the amplitude and area of the ensemble averaged waveform; and the amplitude and area of the maximal response. There was no significant difference in amplitude or area for either muscle using any of the three methods between Time 1 and 2. However, the ensemble average (area and amplitude) was significantly smaller that the mean MEP, and the maximal MEP amplitude was significantly larger. Intraclass correlation analysis demonstrated that reliability of MEP measures over time was poor regardless of method. Reliability was similar between methods for FDI, but FCU had lower reliability values for the mean and ensemble average methods than the maximal method.

Stroke

The search for evidence-based treatments has resulted in an exciting new era for neurorehabilitation intervention strategies for stroke. Although stroke rehabilitation research poses many methodologic challenges, evaluation of stroke rehabilitation interventions is clearly moving beyond descriptive and observational studies toward well designed randomized clinical trials. The goals of this article are to summarize issues of trial design for stroke rehabilitation, to discuss promising stroke rehabilitation treatments currently undergoing rigorous evaluation, and to present treatments that may be candidates for randomized clinical trials in the future on the basis of promising preliminary data. Several examples of new developments in neuroscience research that are leading to possible rehabilitation interventions will be discussed. New modalities to evaluate the response of neural networks to rehabilitation interventions are also reviewed.