Applications of Repetitive Transcranial Magnetic Stimulation to Improve Upper Limb Motor Performance After Stroke: A Systematic Review

Predicting response to non-invasive brain stimulation in post-stroke upper extremity motor impairment: the importance of neurophysiological and clinical biomarkers

BACKGROUND

Non-invasive brain stimulation (NIBS) is a promising approach to enhance upper extremity motor impairment (UEMI) recovery in post-stroke individuals. However, variability in treatment response poses a significant challenge. Identifying neurophysiological and clinical biomarkers that predict NIBS response could improve personalization and treatment efficacy.

OBJECTIVES

This study aims to determine the predictive relevance of neurophysiological and clinical biomarkers for responses to NIBS in post-stroke UEMI using a machine learning model.

METHODS

This secondary analysis involved 63 post-stroke individuals with UEMI (age 56.9 ± 11.1 years). A support vector machine model was used to assess the importance of two neurophysiological biomarkers-brain activity in the lesioned hemisphere quantified using quantitative electroencephalography (power ratio index, PRI) and corticospinal tract (CST) integrity assessed via transcranial magnetic stimulation-and one clinical biomarker-the level of UEMI assessed with Fugl-Meyer upper extremity (FMA-UE)-in predicting responders (ΔFMA-UE ≥ 5 points) and those with excellent response (ΔFMA-UE ≥ 10 points) to NIBS based on the change of FMA-UE before and after treatment.

RESULTS

Of the 63 participants, 42 (65%) were classified as responders, and 14 (22%) demonstrated excellent responses. Predictive importance for responders was 0.78 for PRI-LH, 0.21 for UEMI level, and 0.01 for CST integrity. For predicting excellent responses, PRI-LH had an importance of 0.39, UEMI level 0.37, and CST integrity 0.24.

CONCLUSIONS

The study highlights the importance of electrical brain activity in the LH and UEMI level in predicting NIBS responders and excellent responses, with CST integrity being particularly valuable for excellent outcomes.

Corticomotor pathway function and recovery after stroke: a look back and a way forward

Stroke is a leading cause of adult disability that results in motor deficits and reduced independence. Regaining independence relies on motor recovery, particularly regaining function of the hand and arm. This review presents evidence from human studies that have used transcranial magnetic stimulation (TMS) to identify neurophysiological mechanisms underlying upper limb motor recovery early after stroke. TMS studies undertaken at the subacute stage after stroke have identified several neurophysiological factors that can drive motor impairment, including membrane excitability, the recruitment of corticomotor neurons, and glutamatergic and GABAergic neurotransmission. However, the inherent variability and subsequent poor reliability of measures derived from motor evoked potentials (MEPs) limit the use of TMS for prognosis at the individual patient level. Currently, prediction tools that provide the most accurate information about upper limb motor outcomes for individual patients early after stroke combine clinical measures with a simple neurophysiological biomarker based on MEP presence or absence, i.e. MEP status. Here, we propose a new compositional framework to examine MEPs across several upper limb muscles within a threshold matrix. The matrix can provide a more comprehensive view of corticomotor function and recovery after stroke by quantifying the evolution of subthreshold and suprathreshold MEPs through compositional analyses. Our contention is that subthreshold responses might be the most sensitive to reduced output of corticomotor neurons, desynchronized firing of the remaining neurons, and myelination processes that occur early after stroke. Quantifying subthreshold responses might provide new insights into post-stroke neurophysiology and improve the accuracy of prediction of upper limb motor outcomes.

Noninvasive brain stimulation to improve motor outcomes after stroke

PURPOSE OF REVIEW

This review highlights recent developments in noninvasive brain stimulation (NIBS) techniques and applications for improving motor outcomes after stroke. Two promising areas of development relate to deep brain neuromodulation and the use of single-pulse transcranial magnetic stimulation (TMS) within a prediction tool for predicting upper limb outcome for individual patients.

RECENT FINDINGS

Systematic reviews highlight the inconsistent effect sizes of interventional NIBS for motor outcome after stroke, as well as limited evidence supporting the interhemispheric competition model. To improve the therapeutic efficacy of NIBS, studies have leveraged metaplasticity and priming approaches. Transcranial temporal interference stimulation (tTIS) and low-intensity focused ultrasound stimulation (LIFUS) are emerging NIBS techniques with potential for modulating deeper brain structures, which may hold promise for stroke neurorehabilitation. Additionally, motor evoked potential (MEP) status obtained with single-pulse TMS is a prognostic biomarker that could be used to tailor NIBS for individual patients.

SUMMARY

Trials of interventional NIBS to improve stroke outcomes may be improved by applying NIBS in a more targeted manner. This could be achieved by taking advantage of NIBS techniques that can be targeted to deeper brain structures, using biomarkers of structural and functional reserve to stratify patients, and recruiting patients in more homogeneous time windows.

Examining the effectiveness of motor imagery combined with non-invasive brain stimulation for upper limb recovery in stroke patients: a systematic review and meta-analysis of randomized clinical trials

BACKGROUND

Transcranial direct current stimulation (tDCS) and repetitive transcranial magnetic stimulation (rTMS) are common non-invasive brain stimulation (NIBS) methods for functional recovery after stroke. Motor imagery (MI) can be used in the rehabilitation of limb motor function after stroke, but its effectiveness remains to be rigorously established. Furthermore, there is a growing interest in the combined application of NIBS with MI, yet the evidence regarding its impact on the recovery of upper limb function after stroke is inconclusive. This meta-analysis aimed to demonstrate whether combining the two is superior to NIBS alone or MI alone to provide a reference for clinical decision-making.

METHODS

PubMed, EMBASE, Cochrane Library, Web of Science, Science Direct, CNKI, WANFANG, and VIP databases were searched for randomized controlled trials on the effects of MI combined NIBS in motor function recovery after stroke until February 2024. The outcomes of interest were associated with body functions or structure (impairment) and activity (functional). The primary outcome was assessed with the Fugl-Meyer assessment of the upper extremity (FMA-UE) for motor function of the upper limbs and the modified Barthel Index (MBI) for the ability to perform daily living activities. For secondary outcomes, functional activity level was measured using wolf motor function test (WMFT) and action research arm test (ARAT), and cortical excitability was assessed using cortical latency of motor evoked potential (MEP-CL) and central motor conduction time (CMCT). The methodological quality of the selected studies was evaluated using the evidence‑based Cochrane Collaboration's tool. A meta-analysis was performed to calculate the mean differences (MD) or the standard mean differences (SMD) and 95% confidence intervals (CI) with random-effect models.

RESULTS

A total of 14 articles, including 886 patients, were reviewed in the meta-analysis. In comparison with MI or NIBS alone, the combined therapy significantly improved the motor function of the upper limbs (MD = 5.43; 95% CI 4.34-6.53; P < 0.00001) and the ability to perform activities of daily living (MD = 11.07; 95% CI 6.33-15.80; P < 0.00001). Subgroup analyses showed an interaction between the stage of stroke, the type of MI, and the type of NIBS with the effect of the combination therapy.

CONCLUSION

The combination of MI and NIBS may be a promising therapeutic approach to enhance upper limb motor function, functional activity, and activities of daily living after stroke.

SYSTEMATIC REGISTRATION

PROSPERO registration CRD42023493073.

Resting-State Functional Magnetic Resonance Imaging Reveals the Effects of rTMS on Neural Activity and Brain Connectivity After Experimental Stroke

AIMS

Limited understanding of neurobiological mechanisms of repetitive transcranial magnetic stimulation (rTMS) prevents us from choosing optimal therapeutic regimen for patients to improve therapeutic efficiency. Resting-state functional magnetic resonance imaging (rs-fMRI) has been demonstrated to obtain comparable functional readouts across species.

METHODS

Intermittent and continuous theta burst stimulation were used to stimulate ipsilesional and contralesional hemisphere, respectively, during the subacute phase after stroke. We used a rat middle cerebral artery occlusion stroke model. The amplitude of low-frequency fluctuations and functional connectivity analyses of rs-fMRI were chosen to detect neuron activity and functional connectivity. The expression of neuron activation marker c-Fos and axonal plasticity marker GAP43 was examined by an immunochemistry method to corroborate the results of rs-fMRI.

RESULTS

iTBS altered the long-term neuronal activity in bilateral sensorimotor cortex, whereas cTBS influenced immediate neuronal activity of bilateral sensorimotor cortex. In addition, cTBS enhanced interhemispheric and intrahemisheric functional connectivity in contralesional hemisphere, accompanied by axonal and dendritic remodeling in the perilesional cortical areas and contralesional homologous areas after large stroke.

CONCLUSION

rTMS exerted complex effects on brain structural and functional connectivity in addition to affecting cortical excitability. cTBS promoted the compensatory effect of contralesional hemisphere after stroke with large lesions.

Brain state-dependent repetitive transcranial magnetic stimulation for motor stroke rehabilitation: a proof of concept randomized controlled trial

Background

In healthy subjects, repetitive transcranial magnetic stimulation (rTMS) targeting the primary motor cortex (M1) demonstrated plasticity effects contingent on electroencephalography (EEG)-derived excitability states, defined by the phase of the ongoing sensorimotor μ-oscillation. The therapeutic potential of brain state-dependent rTMS in the rehabilitation of upper limb motor impairment post-stroke remains unexplored.

Objective

Proof-of-concept trial to assess the efficacy of rTMS, synchronized to the sensorimotor μ-oscillation, in improving motor impairment and reducing upper-limb spasticity in stroke patients.

Methods

We conducted a parallel group, randomized double-blind controlled trial in 30 chronic stroke patients (clinical trial registration number: NCT05005780). The experimental intervention group received EEG-triggered rTMS of the ipsilesional M1 [1,200 pulses; 0.33 Hz; 100% of the resting motor threshold (RMT)], while the control group received low-frequency rTMS of the contralesional motor cortex (1,200 pulses; 1 Hz, 115% RMT), i.e., an established treatment protocol. Both groups received 12 rTMS sessions (20 min, 3× per week, 4 weeks) followed by 50 min of physiotherapy. The primary outcome measure was the change in upper-extremity Fugl-Meyer assessment (FMA-UE) scores between baseline, immediately post-treatment and 3 months' follow-up.

Results

Both groups showed significant improvement in the primary outcome measure (FMA-UE) and the secondary outcome measures. This included the reduction in spasticity, measured objectively using the hand-held dynamometer, and enhanced motor function as measured by the Wolf Motor Function Test (WMFT). There were no significant differences between the groups in any of the outcome measures.

Conclusion

The application of brain state-dependent rTMS for rehabilitation in chronic stroke patients is feasible. This pilot study demonstrated that the brain oscillation-synchronized rTMS protocol produced beneficial effects on motor impairment, motor function and spasticity that were comparable to those observed with an established therapeutic rTMS protocol.

Clinical Trial Registration

ClinicalTrials.gov, identifier [NCT05005780].

Facilitating Corticomotor Excitability of the Contralesional Hemisphere Using Non-Invasive Brain Stimulation to Improve Upper Limb Motor Recovery from Stroke-A Scoping Review

Upper limb weakness following stroke poses a significant global psychosocial and economic burden. Non-invasive brain stimulation (NIBS) is a potential adjunctive treatment in rehabilitation. However, traditional approaches to rebalance interhemispheric inhibition may not be effective for all patients. The supportive role of the contralesional hemisphere in recovery of upper limb motor function has been supported by animal and clinical studies, particularly for those with severe strokes. This review aims to provide an overview of the facilitation role of the contralesional hemisphere for post-stroke motor recovery. While more studies are required to predict responses and inform the choice of NIBS approach, contralesional facilitation may offer new hope for patients in whom traditional rehabilitation and NIBS approaches have failed.

Contralesional Anodal Transcranial Direct Current Stimulation Promotes Intact Corticospinal Tract Axonal Sprouting and Functional Recovery After Traumatic Brain Injury in Mice

BACKGROUND

Anodal transcranial direct current stimulation (AtDCS), a neuromodulatory technique, has been applied to treat traumatic brain injury (TBI) in patients and was reported to promote functional improvement. We evaluated the effect of contralesional AtDCS on axonal sprouting of the intact corticospinal tract (CST) and the underlying mechanism in a TBI mouse model to provide more preclinical evidence for the use of AtDCS to treat TBI.

METHODS

TBI was induced in mice by a contusion device. Then, the mice were subjected to contralesional AtDCS 5 days per week followed by a 2-day interval for 7 weeks. After AtDCS, motor function was evaluated by the irregular ladder walking, narrow beam walking, and open field tests. CST sprouting was assessed by anterograde and retrograde labeling of corticospinal neurons (CSNs), and the effect of AtDCS was further validated by pharmacogenetic inhibition of axonal sprouting using clozapine-N-oxide (CNO).

RESULTS

TBI resulted in damage to the ipsilesional cortex, while the contralesional CST remained intact. AtDCS improved the skilled motor functions of the impaired hindlimb in TBI mice by promoting CST axon sprouting, specifically from the intact hemicord to the denervated hemicord. Furthermore, electrical stimulation of CSNs significantly increased the excitability of neurons and thus activated the mechanistic target of rapamycin (mTOR) pathway.

CONCLUSIONS

Contralesional AtDCS improved skilled motor following TBI, partly by promoting axonal sprouting through increased neuronal activity and thus activation of the mTOR pathway.