Shaping Early Reorganization of Neural Networks Promotes Motor Function after Stroke

Investigating functional connectivity related to stroke recovery: A systematic review

INTRODUCTION

Stroke recovery is a complex process influenced by various factors, including specific neural reorganization. The objective of this systematic review was to identify important functional connectivity (FC) changes in resting-state fMRI data that were often correlated with motor, emotional, and cognitive outcome improvement.

METHOD

A systematic search using PubMed and SCOPUS databases was conducted to identify relevant studies published between 2010 and 2023.

RESULTS

A total of 766 studies were identified, of which 20 studies (602 S individuals) met the inclusion criteria. Fourteen studies focussed on motor recovery while six on cognitive recovery. All studies reported interhemispheric FC to be strongly associated with motor and cognitive recovery. The preservation and changes of M1-M1 (eight incidences) and M1-SMA (nine incidences) FC were found to be strongly correlated with motor function improvement. For cognitive recovery, restoration and preservation of FC with and between default mode network (DMN)-related regions were important for the process.

CONCLUSIONS

This review identified specific patterns of FC that were consistently reported with recovery of motor and cognitive function. The findings may serve in refining future management strategies to enhance patient outcomes.

Neuromodulatory transcranial magnetic stimulation (TMS) changes functional connectivity proportional to the electric-field induced by the TMS pulse

OBJECTIVE

Transcranial magnetic stimulation (TMS) can efficiently and robustly modulate synaptic plasticity, but little is known about how TMS affects functional connectivity (rs-fMRI). Accordingly, this project characterized TMS-induced rsFC changes in depressed patients who received 3 days of left prefrontal intermittent theta burst stimulation (iTBS).

METHODS

rs-fMRI was collected from 16 subjects before and after iTBS. Correlation matrices were constructed from the cleaned rs-fMRI data. Electric-field models were conducted and used to predict pre-post changes in rs-fMRI. Site by orientation heatmaps were created for vectors centered on the stimulation site and a control site (contralateral motor cortex).

RESULTS

For the stimulation site, there was a clear relationship between both site and coil orientation, and connectivity changes. As distance from the stimulation site increased, prediction accuracy decreased. Similarly, as eccentricity from the optimal orientation increased, prediction accuracy decreased. The systematic effects described above were not apparent in the heatmap centered on the control site.

CONCLUSIONS

These results suggest that rs-fMRI following iTBS changes systematically as a function of the distribution of electrical energy delivered from the TMS pulse, as represented by the e-field model.

SIGNIFICANCE

This finding lays the groundwork for future studies to individualize TMS targeting based on how predicted rs-fMRI changes might impact psychiatric symptoms.

Theta burst stimulation for enhancing upper extremity motor functions after stroke: a systematic review of clinical and mechanistic evidence

This systematic review aimed to evaluate the effects of different theta burst stimulation (TBS) protocols on improving upper extremity motor functions in patients with stroke, their associated modulators of efficacy, and the underlying neural mechanisms. We conducted a meta-analytic review of 29 controlled trials published from January 1, 2000, to August 29, 2023, which investigated the effects of TBS on upper extremity motor, neurophysiological, and neuroimaging outcomes in poststroke patients. TBS significantly improved upper extremity motor impairment (Hedge's g = 0.646, p = 0.003) and functional activity (Hedge's g = 0.500, p < 0.001) compared to controls. Meta-regression revealed a significant relationship between the percentage of patients with subcortical stroke and the effect sizes of motor impairment (p = 0.015) and functional activity (p = 0.018). Subgroup analysis revealed a significant difference in the improvement of upper extremity motor impairment between studies using 600-pulse and 1200-pulse TBS (p = 0.002). Neurophysiological studies have consistently found that intermittent TBS increases ipsilesional corticomotor excitability. However, evidence to support the regional effects of continuous TBS, as well as the remote and network effects of TBS, is still mixed and relatively insufficient. In conclusion, TBS is effective in enhancing poststroke upper extremity motor function. Patients with preserved cortices may respond better to TBS. Novel TBS protocols with a higher dose may lead to superior efficacy compared with the conventional 600-pulse protocol. The mechanisms of poststroke recovery facilitated by TBS can be primarily attributed to the modulation of corticomotor excitability and is possibly caused by the recruitment of corticomotor networks connected to the ipsilesional motor cortex.

Comparison of Bilateral Versus Unilateral 5 Hz or 1 Hz Repetitive Transcranial Magnetic Stimulation in Subacute Stroke: Assessment of Motor Function in a Randomized Controlled Study

PURPOSE

Repetitive transcranial magnetic stimulation (rTMS) can enhance brain plasticity after stroke. At low frequencies, rTMS has an inhibitory effect, whereas at high frequencies, it has an excitatory effect. Combining both frequencies in bilateral stimulation is a new rTMS protocol under investigation, especially in the subacute stage.

METHODS

Fifty-five patients with subacute stroke were divided into four groups according to the rTMS protocol delivered: bilateral, inhibitory, excitatory, and control groups. All groups received concomitant task-oriented physiotherapy. Pretreatment to posttreatment assessment was performed twice, immediately after sessions and 1 month later. Volitional motor control was evaluated by Fugl-Meyer and Wolf motor function tests, and for spasticity, the Ashworth scale was used.

RESULTS

All groups showed significant improvement. Bilateral, inhibitory, and excitatory groups showed same efficacy, but the bilateral protocol was superior in spasticity. No correlations were found between improvement and stroke duration and site except for spasticity.

CONCLUSIONS

Bilateral rTMS shows a comparable effect to inhibitory and excitatory rTMS in improving motor disability in subacute stroke. However, it is superior for spasticity.

Priming constraint-induced movement therapy with intermittent theta burst stimulation to enhance upper extremity recovery in patients with stroke: protocol for a randomized controlled study

BACKGROUND

The treatments based on motor control and motor learning principles have gained popularity in the last 20 years, as well as non-invasive brain stimulations that enhance neuroplastic changes after stroke. However, the effect of intermittent theta burst stimulation (iTBS) in addition to evidence-based, intensive neurorehabilitation approaches such as modified constraint-induced movement therapy (mCIMT) is yet to be investigated.

AIM

We aim to establish a protocol for a randomized controlled study investigating the efficiency of mCIMT primed with iTBS after stroke.

METHODS

In this randomized controlled, single-blind study, patients with stroke (N = 17) will be divided into 3 groups: (a) mCIMT + real iTBS, (b) mCIMT + sham iTBS, and (c) mCIMT alone. 600-pulse iTBS will be delivered to the primary motor cortex on the ipsilesional hemisphere, and then, patients will receive mCIMT for 1 h/session, 3 sessions/week for 5 weeks. Upper extremity recovery will be assessed with Fugl-Meyer Test-Upper Extremity and Wolf Motor Function Test. Electrophysiological assessments, such as Motor-Evoked Potentials, Resting Motor Threshold, Short-Intracortical Inhibition, and Intracortical Facilitation, will also be included.

CONCLUSIONS

In this study, a protocol of an ongoing intervention study investigating the effectiveness of iTBS on ipsilesional M1 prior to the mCIMT in patients with stroke is proposed. This will be the first study to research priming mCIMT with iTBS and it may have the potential to reveal the true effect of the iTBS when it is added to the high-quality neurorehabilitation approaches.

TRIAL REGISTRATION

Trial registration number: NCT05308667.

Age- and sex-related changes in motor functions: a comprehensive assessment and component analysis

Age-related motor impairments often cause caregiver dependency or even hospitalization. However, comprehensive investigations of the different motor abilities and the changes thereof across the adult lifespan remain sparse. We, therefore, extensively assessed essential basic and complex motor functions in 444 healthy adults covering a wide age range (range 21 to 88 years). Basic motor functions, here defined as simple isolated single or repetitive movements in one direction, were assessed by means of maximum grip strength (GS) and maximum finger-tapping frequency (FTF). Complex motor functions, comprising composite sequential movements involving both proximal and distal joints/muscle groups, were evaluated with the Action Research Arm Test (ARAT), the Jebsen-Taylor Hand Function Test (JTT), and the Purdue Pegboard Test. Men achieved higher scores than women concerning GS and FTF, whereas women stacked more pins per time than men during the Purdue Pegboard Test. There was no significant sex effect regarding JTT. We observed a significant but task-specific reduction of basic and complex motor performance scores across the adult lifespan. Linear regression analyses significantly predicted the participants' ages based on motor performance scores (R2 = 0.502). Of note, the ratio between the left- and right-hand performance remained stable across ages for all tests. Principal Component Analysis (PCA) revealed three motor components across all tests that represented dexterity, force, and speed. These components were consistently present in young (21-40 years), middle-aged (41-60 years), and older (61-88 years) adults, as well as in women and men. Based on the three motor components, K-means clustering analysis differentiated high- and low-performing participants across the adult life span. The rich motor data set of 444 healthy participants revealed age- and sex-dependent changes in essential basic and complex motor functions. Notably, the comprehensive assessment allowed for generating robust motor components across the adult lifespan. Our data may serve as a reference for future studies of healthy subjects and patients with motor deficits. Moreover, these findings emphasize the importance of comprehensively assessing different motor functions, including dexterity, force, and speed, to characterize human motor abilities and their age-related decline.

The effects of rTMS on motor recovery after stroke: a systematic review of fMRI studies

Repetitive transcranial magnetic stimulation (rTMS) has been widely used in motor rehabilitation after stroke, and functional magnetic resonance imaging (fMRI) has been used to investigate the neural mechanisms of motor recovery during stroke therapy. However, there is no review on the mechanism of rTMS intervention for motor recovery after stroke based on fMRI explicitly. We aim to reveal and summarize the neural mechanism of the effects of rTMS on motor function after stroke as measured by fMRI. We carefully performed a literature search using PubMed, EMBASE, Web of Science, and Cochrane Library databases from their respective inceptions to November 2022 to identify any relevant randomized controlled trials. Researchers independently screened the literature, extracted data, and qualitatively described the included studies. Eleven studies with a total of 420 poststroke patients were finally included in this systematic review. A total of 338 of those participants received fMRI examinations before and after rTMS intervention. Five studies reported the effects of rTMS on activation of brain regions, and four studies reported results related to brain functional connectivity (FC). Additionally, five studies analyzed the correlation between fMRI and motor evaluation. The neural mechanism of rTMS in improving motor function after stroke may be the activation and FCs of motor-related brain areas, including enhancement of the activation of motor-related brain areas in the affected hemisphere, inhibition of the activation of motor-related brain areas in the unaffected hemisphere, and changing the FCs of intra-hemispheric and inter-hemispheric motor networks.

Theta-burst stimulation as a therapeutic tool in neurological pathology: a systematic review

TBS (theta-burst stimulation) is a novel therapeutic approach in a wide range of neurological diseases. The present systematic review aims to identify the various protocols used in the last years, to assess study quality and to offer a general overview of the current state of the literature. The systematic review was conducted according to the Preferred Reporting Item for Systematic Review and Meta-Analyses (PRISMA) guidelines. We applied the following inclusion criteria: (1) population over 18 years old with diagnosed neurological disorders, (2) patients treated with sessions of theta-burst stimulation, (3) randomized-controlled clinical trials, (4) articles in the English language, and (5) studies that report response and score reduction on a validated scale of the investigated disorder or remission rates. We included in the final analysis 56 randomized controlled trials focusing on different neurological pathologies (stroke, Parkinson`s disease, multiple sclerosis, tinnitus, dystonia, chronic pain, essential tremor and tic disorder), and we extracted data regarding study design, groups and comparators, sample sizes, type of coil, stimulation parameters (frequency, number of pulses, intensity, stimulation site etc.), number of sessions, follow-up, assessment through functional connectivity and neurological scales used. We observed a great interstudy heterogenicity that leads to a difficulty in drawing plain conclusions. TBS protocols have shown promising results in improving various symptoms in patients with neurological disorders, but larger and more coherent studies, using similar stimulation protocols and evaluation scales, are needed to establish guideline recommendations.

Effects of Priming Intermittent Theta Burst Stimulation With High-Definition tDCS on Upper Limb Function in Hemiparetic Patients With Stroke: A Randomized Controlled Study

BACKGROUND

Preconditioning with cathodal high-definition transcranial direct current stimulation (HD-tDCS) can potentiate cortical plasticity induced by intermittent theta burst stimulation (iTBS) and enhance the after-effects of iTBS in healthy people. However, it is unclear whether this multi-modal protocol can enhance upper limb function in patients with stroke.

OBJECTIVE

The aim of this study was to investigate whether priming iTBS with cathodal HD-tDCS over the ipsilesional M1 can augment upper limb motor recovery in poststroke patients.

METHODS

A total of 66 patients with subacute stroke were randomly allocated into 3 groups. Group 1 received priming iTBS with HD-tDCS (referred to as the tDCS + iTBS group), Group 2 received non-priming iTBS (the iTBS group), and Group 3 received sham stimulation applied to the ipsilesional M1. One session was performed per day, 5 days per week, for 3 consecutive weeks. In Group 1, iTBS was preceded by a 20-minute session of cathodal HD-tDCS at a 10-minute interval. The primary outcome measure was the Fugl-Meyer Assessment-Upper Extremity (FMA-UE) score. Moreover, the secondary outcome measures for muscle strength and spasticity were the Motricity Index-Upper Extremity (MI-UE) and the Modified Ashworth Scale Upper-Extremity (MAS-UE), respectively, and the Hong Kong Version of the Functional Test for the Hemiplegic Upper Extremity (FTHUE-HK) and the Modified Barthel Index (MBI) for activity and participation.

RESULTS

Significant differences were detected in the changes in FMA-UE, MI-UE, and MBI scores between the 3 groups from baseline to post-intervention (χ2FMA-UE = 10.856, P = .004; χ2MI-UE = 6.783, P = .034; χ2MBI = 9.608, P = .008). Post hoc comparisons revealed that the priming iTBS group demonstrated substantial improvements in FMA-UE (P = .004), MI-UE (P = .028), and MBI (P = 0.006) compared with those in the sham group. However, no significant difference was observed between the iTBS group and the sham group. Moreover, no significant differences were found in the changes in MAS-UE or FTHUE-HK between the groups.

CONCLUSIONS

Priming iTBS with HD-tDCS over the ipsilesional M1 cortex had beneficial effects on augmenting upper limb motor recovery and enhancing daily participation among subacute stroke patients.

Theta burst stimulation: what role does it play in stroke rehabilitation? A systematic review of the existing evidence

Various post-stroke dysfunctions often result in poor long-term outcomes for stroke survivors, but the effect of conventional treatments is limited. In recent years, lots of studies have confirmed the effect of repetitive transcranial magnetic stimulation (rTMS) in stroke rehabilitation. As a new pattern of rTMS, theta burst stimulation (TBS) was proved recently to yield more pronounced and long-lasting after-effects than the conventional pattern at a shorter stimulation duration. To explore the role of TBS in stroke rehabilitation, this review summarizes the existing evidence from all the randomized controlled trials (RCTs) so far on the efficacy of TBS applied to different post-stroke dysfunctions, including cognitive impairment, visuospatial neglect, aphasia, dysphagia, spasticity, and motor dysfunction. Overall, TBS promotes the progress of stroke rehabilitation and may serve as a preferable alternative to traditional rTMS. However, it's hard to recommend a specific paradigm of TBS due to the limited number of current studies and their heterogeneity. Further high-quality clinical RCTs are needed to determine the optimal technical settings and intervention time in stroke survivors.

Effects of robot-assisted upper limb training combined with intermittent theta burst stimulation (iTBS) on cortical activation in stroke patients: A functional near-infrared spectroscopy study

BACKGROUND

The therapeutic effect and mechanism of robot-assisted upper limb training (RT) combined with intermittent theta burst stimulation (iTBS) for stroke patients are unclear.

OBJECTIVE

The purpose of this study was to evaluate changes in brain activation after combination therapy and RT alone using functional near-infrared spectroscopy (fNIRS).

METHODS

Patients were randomly assigned to two groups (iTBS + RT Group, n = 18, and RT Group, n = 18). Training was conducted five times a week for four weeks. fNIRS was used to measure changes in oxyhemoglobin in both the primary motor cortex (M1) and pre-motor and supplementary motor area (pSMA) during affected limb movement. Fugl-Meyer Assessment-Upper Extremity (FMA-UE) was employed for evaluating the function of upper limbs.

RESULTS

Thirty-two patients with subacute stroke completed the study. The cortex of both hemispheres was extensively activated prior to treatment in the RT group. After training, overactivation decreased. The brain activation of the combined treatment group transferred to the affected side after the treatment. There was a notable enhancement in the FMA-UE scores for both groups, with the combined group's progress significantly surpassing that of the RT group.

CONCLUSION

RT combined with iTBS can improve the motor function of stroke patients and promote the balance between cerebral hemispheres.

The effectiveness of intermittent theta burst stimulation for upper limb motor recovery after stroke: a systematic review and meta-analysis of randomized controlled trials

Background

Intermittent theta burst stimulation (iTBS) is a promising noninvasive therapy to restore the excitability of the cortex, and subsequently improve the function of the upper extremities. Several studies have demonstrated the effectiveness of iTBS in restoring upper limb function and modulating cortical excitability. We aimed to evaluate the effects of iTBS on upper limb motor recovery after stroke.

Objective

The purpose of this article is to evaluate the influence of intermittent theta-burst stimulation on upper limb motor recovery and improve the quality of life.

Method

A literature search was conducted using PubMed, EMBASE, MEDLINE, The Cochrane Library, Web of Science, and CBM, including only English studies, to identify studies that investigated the effects of iTBS on upper limb recovery, compared with sham iTBS used in control groups. Effect size was reported as standardized mean difference (SMD) or weighted mean difference (WMD).

Results

Ten studies were included in the meta-analysis. The results of the meta-analysis indicated that when compared to the control group, the iTBS group had a significant difference in the Fugl-Meyer Assessment (FMA) and Action Research Arm Test (ARAT) (WMD: 3.20, 95% CI: 1.42 to 4.97; WMD: 3.72, 95% CI: 2.13 to 5.30, respectively). In addition, there was also a significant improvement in the modified Ashworth scale (MAS) compared to the sham group (WMD: -0.56; 95% CI: -0.85 to -0.28). More evidence is still needed to confirm the effect of Barthel Index (BI) scores after interventions. However, no significant effect was found for the assessment of Motor Evoked Potential (MEP) amplitude and MEP latency (SMD: 0.35; 95% CI: -0.21 to 0.90; SMD: 0.35, 95% CI: -0.18 to 0.87; SMD: 0.03, 95% CI: -0.49 to 0.55; respectively).

Conclusion

Our results showed that iTBS significantly improved motor impairment, functional activities, and reduced muscle tone of upper limbs, thereby increasing the ability to perform Activities of Daily Living (ADL) in stroke patients, while there were no significant differences in MEPs. In conclusion, iTBS is a promising non-invasive brain stimulation as an adjunct to therapy and enhances the therapeutic effect of conventional physical therapy. In the future, more randomized controlled trials with large sample sizes, high quality, and follow-up are necessary to explore the neurophysiological effects.

Systematic review registration

https://www.crd.york.ac.uk/PROSPERO/, identifier CRD42023392739.

Different doses of intermittent theta burst stimulation for upper limb motor dysfunction after stroke: a study protocol for a randomized controlled trial

Background

Upper limb motor recovery is one of the important goals of stroke rehabilitation. Intermittent theta burst stimulation (iTBS), a new type of repetitive transcranial magnetic stimulation (rTMS), is considered a potential therapy. However, there is still no consensus on the efficacy of iTBS for upper limb motor dysfunction after stroke. Stimulus dose may be an important factor affecting the efficacy of iTBS. Therefore, we aim to investigate and compare the effects and neural mechanisms of three doses of iTBS on upper limb motor recovery in stroke patients, and our hypothesis is that the higher the dose of iTBS, the greater the improvement in upper limb motor function.

Methods

This prospective, randomized, controlled trial will recruit 56 stroke patients with upper limb motor dysfunction. All participants will be randomized in a 1:1:1:1 ratio to receive 21 sessions of 600 pulses active iTBS, 1,200 pulses active iTBS, 1,800 pulses active iTBS, or 1,800 pulses sham iTBS in addition to conventional rehabilitation training. The primary outcome is the Fugl-Meyer Assessment of the Upper Extremity (FMA-UE) score from baseline to end of intervention, and the secondary outcomes are the Wolf Motor Function Test (WMFT), Grip Strength (GS), Modified Barthel Index (MBI), and Stroke Impact Scale (SIS). The FMA-UE, MBI, and SIS are assessed pre-treatment, post-treatment, and at the 3-weeks follow-up. The WMFT, GS, and resting-state functional magnetic resonance imaging (rs-fMRI) data will be obtained pre- and post-treatment.

Discussion

The iTBS intervention in this study protocol is expected to be a potential method to promote upper limb motor recovery after stroke, and the results may provide supportive evidence for the optimal dose of iTBS intervention.

Evidence of rTMS for Motor or Cognitive Stroke Recovery: Hype or Hope?

BACKGROUND

Evidence of efficacy of repetitive transcranial magnetic stimulation (rTMS) for stroke recovery is hampered by an unexplained variability of reported effect sizes and an insufficient understanding of mechanisms of action. We aimed to (1) briefly summarize evidence of efficacy, (2) identify critical factors to explain the reported variation in effects, and (3) provide mechanism-based recommendations for future trials.

METHODS

We performed a systematic review of the literature according to Cochrane and PRISMA Protocols. We included trials with ≥10 patients per treatment group. We classified outcome measures according to the International Classification of Functioning, Disability, and Health. Meta-analysis was done when at least 3 trials were reported on the same construct. In case of significant summary effect sizes with significant heterogeneity, we used sensitivity analyses to test for correlations and differences between found individual effect sizes and possible effect modifiers such as patient-, repetitive transcranial magnetic stimulation-, and trial characteristics.

RESULTS

We included 57 articles (N=2595). Funnel plots showed no publication bias. We found significant effect sizes at the level of body function (upper limb synergies, muscle strength, language functioning, global cognitive functioning, visual/spatial inattention) with repetitive transcranial magnetic stimulation within or beyond 3 months after stroke. We also found significant effect sizes at the level of activities. We found no subgroup differences or significant correlations between individual summary effect sizes and any tested possible effect modifier.

CONCLUSIONS

Repetitive transcranial magnetic stimulation holds the potential to benefit a range of motor and cognitive outcomes after stroke, but the evidence of efficacy is challenged by unexplained heterogeneity across many small sampled trials. We propose large trials with the collection of individual patient data on baseline severity and brain network integrity with sufficiently powered subgroup analyses, as well as protocolized time-locked training of the target behavior. Additional neurophysiological and biomechanical data may help in understanding mechanisms and identifying biomarkers of treatment efficacy.

REGISTRATION

URL: https://www.

CLINICALTRIALS

gov; Unique identifier: CRD42022300330.

Brain Topological Reorganization Associated with Visual Neglect After Stroke

Background/Purpose: To identify brain hubs that are behaviorally relevant for neglect after stroke as well as to characterize their functional architecture of communication. Methods: Twenty acute right hemisphere damaged patients underwent neuropsychological and resting-state functional magnetic resonance imaging sessions. Spatial neglect was assessed by means of the Center of Cancellation on the Bells Cancellation Test. For each patient, resting-state functional connectivity matrices were derived by adopting a brain parcellation scheme consisting of 153 nodes. For every node, we extracted its betweenness centrality (BC) defined as the portion of all shortest paths in the connectome involving such node. Then, neglect hubs were identified as those regions showing a high correlation between their BC and neglect scores. Results: A first set of neglect hubs was identified in multiple systems including dorsal attention and ventral attention, default mode, and frontoparietal executive-control networks within the damaged hemisphere as well as in the posterior and anterior cingulate cortex. Such cortical regions exhibited a loss of BC and increased (i.e., less efficient) weighted shortest path length (WSPL) related to severe neglect. Conversely, a second group of neglect hubs found in visual and motor networks, in the undamaged hemisphere, exhibited a pathological increase of BC and reduction of WSPL associated with severe neglect. Conclusion: The topological reorganization of the brain in neglect patients might reflect a maladaptive shift in processing spatial information from higher level associative-control systems to lower level visual and sensory-motor processing areas after a right hemisphere lesion.

Top-down and bottom-up stimulation techniques combined with action observation treatment in stroke rehabilitation: a perspective

Stroke is a central nervous system disease that causes structural lesions and functional impairments of the brain, resulting in varying types, and degrees of dysfunction. The bimodal balance-recovery model (interhemispheric competition model and vicariation model) has been proposed as the mechanism of functional recovery after a stroke. We analyzed how combinations of motor observation treatment approaches, transcranial electrical (TES) or magnetic (TMS) stimulation and peripheral electrical (PES) or magnetic (PMS) stimulation techniques can be taken as accessorial physical therapy methods on symptom reduction of stroke patients. We suggest that top-down and bottom-up stimulation techniques combined with action observation treatment synergistically might develop into valuable physical therapy strategies in neurorehabilitation after stroke. We explored how TES or TMS intervention over the contralesional hemisphere or the lesioned hemisphere combined with PES or PMS of the paretic limbs during motor observation followed by action execution have super-additive effects to potentiate the effect of conventional treatment in stroke patients. The proposed paradigm could be an innovative and adjunctive approach to potentiate the effect of conventional rehabilitation treatment, especially for those patients with severe motor deficits.

Connectomic insight into unique stroke patient recovery after rTMS treatment

An improved understanding of the neuroplastic potential of the brain has allowed advancements in neuromodulatory treatments for acute stroke patients. However, there remains a poor understanding of individual differences in treatment-induced recovery. Individualized information on connectivity disturbances may help predict differences in treatment response and recovery phenotypes. We studied the medical data of 22 ischemic stroke patients who received MRI scans and started repetitive transcranial magnetic stimulation (rTMS) treatment on the same day. The functional and motor outcomes were assessed at admission day, 1 day after treatment, 30 days after treatment, and 90 days after treatment using four validated standardized stroke outcome scales. Each patient underwent detailed baseline connectivity analyses to identify structural and functional connectivity disturbances. An unsupervised machine learning (ML) agglomerative hierarchical clustering method was utilized to group patients according to outcomes at four-time points to identify individual phenotypes in recovery trajectory. Differences in connectivity features were examined between individual clusters. Patients were a median age of 64, 50% female, and had a median hospital length of stay of 9.5 days. A significant improvement between all time points was demonstrated post treatment in three of four validated stroke scales utilized. ML-based analyses identified distinct clusters representing unique patient trajectories for each scale. Quantitative differences were found to exist in structural and functional connectivity analyses of the motor network and subcortical structures between individual clusters which could explain these unique trajectories on the Barthel Index (BI) scale but not on other stroke scales. This study demonstrates for the first time the feasibility of using individualized connectivity analyses in differentiating unique phenotypes in rTMS treatment responses and recovery. This personalized connectomic approach may be utilized in the future to better understand patient recovery trajectories with neuromodulatory treatment.

Effects of repetitive transcranial magnetic stimulation and their underlying neural mechanisms evaluated with magnetic resonance imaging-based brain connectivity network analyses

Repetitive transcranial magnetic stimulation (rTMS) is a noninvasive brain modulation and rehabilitation technique used in patients with neuropsychiatric diseases. rTMS can structurally remodel or functionally induce activities of specific cortical regions and has developed to an important therapeutic method in such patients. Magnetic resonance imaging (MRI) provides brain data that can be used as an explanation tool for the neural mechanisms underlying rTMS effects; brain alterations related to different functions or structures may be reflected in changes in the interaction and influence of brain connections within intrinsic specific networks. In this review, we discuss the technical details of rTMS and the biological interpretation of brain networks identified with MRI analyses, comprehensively summarize the neurobiological effects in rTMS-modulated individuals, and elaborate on changes in the brain network in patients with various neuropsychiatric diseases receiving rehabilitation treatment with rTMS. We conclude that brain connectivity network analysis based on MRI can reflect alterations in functional and structural connectivity networks comprising adjacent and separated brain regions related to stimulation sites, thus reflecting the occurrence of intrinsic functional integration and neuroplasticity. Therefore, MRI is a valuable tool for understanding the neural mechanisms of rTMS and practically tailoring treatment plans for patients with neuropsychiatric diseases.

Brain-oscillation-synchronized stimulation to enhance motor recovery in early subacute stroke: a randomized controlled double-blind three- arm parallel-group exploratory trial comparing personalized, non- personalized and sham repetitive transcranial magnetic stimulation (Acronym: BOSS-STROKE)

BACKGROUND

Stroke is a major cause of death and the most frequent cause of permanent disability in western countries. Repetitive transcranial brain stimulation (rTMS) has been used to enhance neuronal plasticity after stroke, yet with only moderate effect sizes. Here we will apply a highly innovative technology that synchronizes rTMS to specific brain states identified by real-time analysis of electroencephalography.

METHODS

One hundred forty-four patients with early subacute ischemic motor stroke will be included in a multicenter 3-arm parallel, randomized, double-blind, standard rTMS and sham rTMS-controlled exploratory trial in Germany. In the experimental condition, rTMS will be synchronized to the trough of the sensorimotor µ-oscillation, a high-excitability state, over ipsilesional motor cortex. In the standard rTMS control condition the identical protocol will be applied, but non-synchronized to the ongoing µ-oscillation. In the sham condition, the same µ-oscillation-synchronized protocol as in experimental condition will be applied, but with ineffective rTMS, using the sham side of an active/placebo TMS coil. The treatment will be performed over five consecutive work days (1,200 pulses per day, 6,000 pulses total). The primary endpoint will be motor performance after the last treatment session as measured by the Fugl-Meyer Assessment Upper Extremity.

DISCUSSION

This study investigates, for the first time, the therapeutic efficacy of personalized, brain-state-dependent rTMS. We hypothesize that synchronization of rTMS with a high-excitability state will lead to significantly stronger improvement of paretic upper extremity motor function than standard or sham rTMS. Positive results may catalyze a paradigm-shift towards personalized brain-state-dependent stimulation therapies.

TRIAL REGISTRATION

This study was registered at ClinicalTrials.gov (NCT05600374) on 10-21-2022.

Effects of transcranial combined with peripheral repetitive magnetic stimulation on limb spasticity and resting-state brain activity in stroke patients

Background and objective

Transcranial magnetic stimulation and peripheral repetitive magnetic stimulation (rPMS), as non-invasive neuromodulation techniques, can promote functional recovery in patients with post-stroke spasticity (PSS), but the effects of transcranial magnetic stimulation combined with peripheral magnetic stimulation on PSS remain largely unknown. Therefore, we examined the effects of low-frequency repetitive transcranial magnetic stimulation (LF-rTMS) combined with rPMS on PSS patients and its potential neural correlates to behavioral improvements.

Methods

Forty-nine PSS patients were divided randomly into three groups: a combined group (n = 20), a LF-rTMS group (n = 15), and a control group (n = 14). The combined group received LF-rTMS and rPMS treatment, the rTMS group received LF-rTMS treatment, and the control group received only routine rehabilitation. All patients underwent Ashworth Spasm Scale (MAS), upper extremity Fugl-Meyer (FMA-UE), and modified Barthel Index (MBI) assessments before and after intervention. In addition, resting-state functional magnetic resonance imaging data were collected pre- and post-treatment to observe changes in the amplitude of low-frequency fluctuation (ALFF).

Results

The MAS score was decreased, FMA-UE score and MBI scores were increased in the three groups after therapy than before therapy (all P &lt; 0.05). In particular, the combined group showed significant effect on improved motor function and relieved spasticity in PSS (P &lt; 0.01). Moreover, the combined treatment increased ALFF values mainly in the right supplementary motor area, right middle frontal gyrus, and right cerebellum, while reduced ALFF values mainly in the right post-central gyrus compared with pre-treatment. Compared with the LF-rTMS and control groups, the combined treatment increased ALFF values in the right cerebellum and reduced ALFF values mainly in the frontoparietal cortex. Improvements in the MAS score were positively correlated with the change in ALFF values in the right cerebellum (r = 0.698, P = 0.001) and the right supplementary motor area (r = 0.700, P = 0.001) after combined treatment.

Conclusion

Transcranial combined with peripheral repetitive magnetic stimulation could improve spastic state and motor function in PSS patients, and this effect may be associated with altered cerebellar and frontoparietal cortical activity.

Clinical trial registration

http://www.chictr.org.cn/index.aspx, identifier ChiCTR1800019452.

The role of corticospinal and extrapyramidal pathways in motor impairment after stroke

Anisotropy of descending motor pathways has repeatedly been linked to the severity of motor impairment following stroke-related damage to the corticospinal tract. Despite promising findings consistently tying anisotropy of the ipsilesional corticospinal tract to motor outcome, anisotropy is not yet utilized as a biomarker for motor recovery in clinical practice as several methodological constraints hinder a conclusive understanding of degenerative processes in the ipsilesional corticospinal tract and compensatory roles of other descending motor pathways. These constraints include estimating anisotropy in voxels with multiple fibre directions, sampling biases and confounds due to ageing-related atrophy. The present study addressed these issues by combining diffusion spectrum imaging with a novel compartmentwise analysis approach differentiating voxels with one dominant fibre direction (one-directional voxels) from voxels with multiple fibre directions. Compartmentwise anisotropy for bihemispheric corticospinal and extrapyramidal tracts was compared between 25 chronic stroke patients, 22 healthy age-matched controls, and 24 healthy young controls and its associations with motor performance of the upper and lower limbs were assessed. Our results provide direct evidence for Wallerian degeneration along the entire length of the ipsilesional corticospinal tract reflected by decreased anisotropy in descending fibres compared with age-matched controls, while ageing-related atrophy was observed more ubiquitously across compartments. Anisotropy of descending ipsilesional corticospinal tract voxels showed highly robust correlations with various aspects of upper and lower limb motor impairment, highlighting the behavioural relevance of Wallerian degeneration. Moreover, anisotropy measures of two-directional voxels within bihemispheric rubrospinal and reticulospinal tracts were linked to lower limb deficits, while anisotropy of two-directional contralesional rubrospinal voxels explained gross motor performance of the affected hand. Of note, the relevant extrapyramidal structures contained fibres crossing the midline, fibres potentially mitigating output from brain stem nuclei, and fibres transferring signals between the extrapyramidal system and the cerebellum. Thus, specific parts of extrapyramidal pathways seem to compensate for impaired gross arm and leg movements incurred through stroke-related corticospinal tract lesions, while fine motor control of the paretic hand critically relies on ipsilesional corticospinal tract integrity. Importantly, our findings suggest that the extrapyramidal system may serve as a compensatory structural reserve independent of post-stroke reorganization of extrapyramidal tracts. In summary, compartment-specific anisotropy of ipsilesional corticospinal tract and extrapyramidal tracts explained distinct aspects of motor impairment, with both systems representing different pathophysiological mechanisms contributing to motor control post-stroke. Considering both systems in concert may help to develop diffusion imaging biomarkers for specific motor functions after stroke.

Alterations of static and dynamic functional network connectivity in acute ischemic brainstem stroke

Background

Prior studies have shown abnormal brain functional network changes in patients with acute ischemic stroke. However, the alterations of dynamic functional network connectivity (FNC) in brainstem strokes have not been elucidated.

Purpose

To assess alterations of static and dynamic FNCs and determine the relationships between these and upper limb movement performance in patients with acute brainstem ischemic stroke.

Material and Methods

In total, 50 patients with acute brainstem ischemic stroke and 50 age- and sex-matched healthy controls were enrolled in the present study and underwent resting-state functional magnetic resonance imaging (rs-fMRI). Independent component analysis was conducted to assess static and dynamic FNC patterns based on seven resting-state networks, namely, the default mode network (DMN), executive control network (ECN), attention network (AN), somatomotor network (SMN), visual network (VN), auditory network (AUN), and cerebellum network (CN).

Results

Compared with controls, patients with acute brainstem ischemic stroke exhibited wide aberrations of static FNC, including increased FNC in DMN–ECN, DMN–VN, ECN–VN, ECN–AN and AN–AUN pairs. Patients with acute brainstem ischemic stroke showed aberrant dynamic FNC in State 1, involving increased FNC aberrance in the DMN with AN, DMN with ECN, and reduced FNC in SMN–VN pairs. In State 5, patients with acute brainstem ischemic stroke showed increased FNC in DMN–VN and AN–AUN, and decreased FNC in AN–SMN pairs.

Conclusion

This study suggests that static and dynamic FNC impairment and aberrant connections exist in acute brainstem ischemic stroke, which expands what is known regarding the relationship between stroke and FNC from static and dynamic perspectives.

Rewiring Cortico-Muscular Control in the Healthy and Poststroke Human Brain with Proprioceptive β-Band Neurofeedback

In severely affected stroke survivors, cortico-muscular control is disturbed and volitional upper limb movements often absent. Mental rehearsal of the impaired movement in conjunction with sensory feedback provision are suggested as promising rehabilitation exercises. Knowledge about the underlying neural processes, however, remains vague. In male and female chronic stroke patients with hand paralysis, a brain-computer interface controlled a robotic orthosis and turned sensorimotor β-band desynchronization during motor imagery (MI) of finger extension into contingent hand opening. Healthy control subjects performed the same task and received the same proprioceptive feedback with a robotic orthosis or visual feedback only. Only when proprioceptive feedback was provided, cortico-muscular coherence (CMC) increased with a predominant information flow from the sensorimotor cortex to the finger extensors. This effect (1) was specific to the β frequency band, (2) transferred to a motor task (MT), (3) was proportional to subsequent corticospinal excitability (CSE) and correlated with behavioral changes in the (4) healthy and (5) poststroke condition; notably, MI-related enhancement of β-band CMC in the ipsilesional premotor cortex correlated with motor improvements after the intervention. In the healthy and injured human nervous system, synchronized activation of motor-related cortical and spinal neural pools facilitates, in accordance with the communication-through-coherence hypothesis, cortico-spinal communication and may, thereby, be therapeutically relevant for functional restoration after stroke, when voluntary movements are no longer possible.SIGNIFICANCE STATEMENT This study provides insights into the neural processes that transfer effects of brain-computer interface neurofeedback to subsequent motor behavior. Specifically, volitional control of cortical oscillations and proprioceptive feedback enhances both cortical activity and behaviorally relevant connectivity to the periphery in a topographically circumscribed and frequency-specific way. This enhanced cortico-muscular control can be induced in the healthy and poststroke brain. Thereby, activating the motor cortex with mental rehearsal of the impaired movement and closing the loop by robot-assisted feedback synchronizes ipsilesional premotor cortex and spinal neural pools in the β frequency band. This facilitates, in accordance with the communication-through-coherence hypothesis, cortico-spinal communication and may, thereby, be therapeutically relevant for functional restoration after stroke, when voluntary movements are no longer possible.

Specific subsystems of the inferior parietal lobule are associated with hand dysfunction following stroke: A cross-sectional resting-state fMRI study

AIM

The inferior parietal lobule (IPL) plays important roles in reaching and grasping during hand movements, but how reorganizations of IPL subsystems underlie the paretic hand remains unclear. We aimed to explore whether specific IPL subsystems were disrupted and associated with hand performance after chronic stroke.

METHODS

In this cross-sectional study, we recruited 65 patients who had chronic subcortical strokes and 40 healthy controls from China. Each participant underwent the Fugl-Meyer Assessment of Hand and Wrist and resting-state fMRI at baseline. We mainly explored the group differences in resting-state effective connectivity (EC) patterns for six IPL subregions in each hemisphere, and we correlated these EC patterns with paretic hand performance across the whole stroke group and stroke subgroups. Moreover, we used receiver operating characteristic curve analysis to distinguish the stroke subgroups with partially (PPH) and completely (CPH) paretic hands.

RESULTS

Stroke patients exhibited abnormal EC patterns with ipsilesional PFt and bilateral PGa, and five sensorimotor-parietal/two parietal-temporal subsystems were positively or negatively correlated with hand performance. Compared with CPH patients, PPH patients exhibited abnormal EC patterns with the contralesional PFop. The PPH patients had one motor-parietal subsystem, while the CPH patients had one sensorimotor-parietal and three parietal-occipital subsystems that were associated with hand performance. Notably, the EC strength from the contralesional PFop to the ipsilesional superior frontal gyrus could distinguish patients with PPH from patients with CPH.

CONCLUSIONS

The IPL subsystems manifest specific functional reorganization and are associated with hand dysfunction following chronic stroke.

Increased cerebral cortex activation in stroke patients during electrical stimulation of cerebellar fastigial nucleus with functional near-infrared spectroscopy

Background

Electrical stimulation of the cerebellar fastigial nucleus (FNS) has been shown to protect animals against cerebral ischemic injury. However, the changes in cortical activation as a response to FNS have not been illustrated in humans.

Objective

This study aims to detect functional connectivity changes in the brain of stroke patients, and investigate the cortical activation caused by FNS through measuring the oxygenated hemoglobin concentration (HBO) in the cerebral cortex of stroke patients and healthy controls (HCs).

Methods

This study recruited 20 patients with stroke and 20 HCs with all the following factors matched: age, gender and BMI. The experiment session was made up of the pre-task baseline, FNS task period, and post-task baseline. FNS task period contains 5 blocks, each block encompassing the resting state (30 s) and the FNS state (30 s). HBO signals were acquired by functional near-infrared spectroscopy (fNIRS) from the Prefrontal Cortex (PFC), the Motor Cortex (MC) and the Occipital Cortex (OC) throughout the experiment. The Pearson correlation coefficient was used to calculate the resting-state functional connectivity strength between the two groups, and the general linear model (GLM) was used to calculate the activation of 39 fNIRS channels during FNS in stroke patients and HCs, respectively.

Results

The coupling strength of stroke patients were significantly decreased in the following regions: right MC and left MC (t = 4.65, p = 0.0007), right MC and left OC (t = 2.93, p = 0.04), left MC and left OC (t = 2.81, p = 0.04). In stroke patients, the changes in cerebral oxygenated hemoglobin (ΔHBO) among 12 channels (CH) in the bilateral PFC and bilateral MC regions were significantly increased during the FNS state (FDR corrected p < 0.05) compared with the resting state. In HCs, only 1 channel was increased (FDR corrected p < 0.05) in the left PFC during FNS.

Conclusion

By using the FNS and fNIRS techniques, the characteristics of functional connectivity were found to decrease in stroke patients. It was also noticed that FNS activates the PFC and MC regions. These findings may help to guide functional rehabilitation in stroke patients.

Stimulus-Evoked Activity Modulation of In Vitro Engineered Cortical and Hippocampal Networks

The delivery of electrical stimuli is crucial to shape the electrophysiological activity of neuronal populations and to appreciate the response of the different brain circuits involved. In the present work, we used dissociated cortical and hippocampal networks coupled to Micro-Electrode Arrays (MEAs) to investigate the features of their evoked response when a low-frequency (0.2 Hz) electrical stimulation protocol is delivered. In particular, cortical and hippocampal neurons were topologically organized to recreate interconnected sub-populations with a polydimethylsiloxane (PDMS) mask, which guaranteed the segregation of the cell bodies and the connections among the sub-regions through microchannels. We found that cortical assemblies were more reactive than hippocampal ones. Despite both configurations exhibiting a fast (<35 ms) response, this did not uniformly distribute over the MEA in the hippocampal networks. Moreover, the propagation of the stimuli-evoked activity within the networks showed a late (35−500 ms) response only in the cortical assemblies. The achieved results suggest the importance of the neuronal target when electrical stimulation experiments are performed. Not all neuronal types display the same response, and in light of transferring stimulation protocols to in vivo applications, it becomes fundamental to design realistic in vitro brain-on-a-chip devices to investigate the dynamical properties of complex neuronal circuits.

The Effectiveness of Intermittent Theta Burst Stimulation for Stroke Patients With Upper Limb Impairments: A Systematic Review and Meta-Analysis

Background

Upper limb impairments are one of the most common health problems of stroke, affecting both motor function and independence in daily life. It has been demonstrated that intermittent theta burst stimulation (iTBS) increases brain excitability and improves upper limb function. Our study sought to determine the role of iTBS in stroke recovery.

Objective

The purpose of this study was to determine the efficacy of iTBS in individuals with upper limb impairments following stroke.

Methods

The databases used included Cumulative Index to PubMed, EMBASE, ESCBOhost, The Cochrane Library, Chinese Biomedical Database, Web of Science, China Biology Medicine (CBM), China National Knowledge Infrastructure (CNKI), Technology Periodical Database (VIP), and WanFang Database. Studies published before November 2021 were included. Each participant received an iTBS-based intervention aimed at improving activity levels or impairment, which was compared to usual care, a sham intervention, or another intervention. The primary outcome measure was a change in upper limb function assessment. Secondary outcomes included impairment, participation, and quality of life measures.

Result

A total of 18 studies (n = 401 participants) that met the inclusion criteria were included in this study. There was a slight change in the upper limb function of the iTBS group compared with the control group, as measured by the Fugl-Meyer Assessment-Upper Extremity (FMA-UE) score (mean difference 2.70, 95% CI −0.02 to 5.42, p = 0.05). Significant improvement in resting motor threshold (RMT) and motor-evoked potential (MEP) was also observed in the meta-analysis of iTBS (MD 3.46, 95% CI 2.63 to 4.28, p < 0.00001); (MD 1.34, 95% CI 1.17 to 1.51, P < 0.00001). In addition, we got similar results when the studies were using the Modified Barthel Index (MBI) assessment (mean difference of 7.34, 95% CI 0.47 to 14.21, p = 0.04).

Conclusion

Our study established the efficacy of iTBS in improving motor cortical plasticity, motor function, and daily functioning in stroke patients. However, the review requires evidence from additional randomized controlled trials and high-quality research.

Systematic Review Registration

https://www.crd.york.ac.uk/PROSPERO/

Toward an Adapted Neurofeedback for Post-stroke Motor Rehabilitation: State of the Art and Perspectives

Stroke is a severe health issue, and motor recovery after stroke remains an important challenge in the rehabilitation field. Neurofeedback (NFB), as part of a brain–computer interface, is a technique for modulating brain activity using on-line feedback that has proved to be useful in motor rehabilitation for the chronic stroke population in addition to traditional therapies. Nevertheless, its use and applications in the field still leave unresolved questions. The brain pathophysiological mechanisms after stroke remain partly unknown, and the possibilities for intervention on these mechanisms to promote cerebral plasticity are limited in clinical practice. In NFB motor rehabilitation, the aim is to adapt the therapy to the patient’s clinical context using brain imaging, considering the time after stroke, the localization of brain lesions, and their clinical impact, while taking into account currently used biomarkers and technical limitations. These modern techniques also allow a better understanding of the physiopathology and neuroplasticity of the brain after stroke. We conducted a narrative literature review of studies using NFB for post-stroke motor rehabilitation. The main goal was to decompose all the elements that can be modified in NFB therapies, which can lead to their adaptation according to the patient’s context and according to the current technological limits. Adaptation and individualization of care could derive from this analysis to better meet the patients’ needs. We focused on and highlighted the various clinical and technological components considering the most recent experiments. The second goal was to propose general recommendations and enhance the limits and perspectives to improve our general knowledge in the field and allow clinical applications. We highlighted the multidisciplinary approach of this work by combining engineering abilities and medical experience. Engineering development is essential for the available technological tools and aims to increase neuroscience knowledge in the NFB topic. This technological development was born out of the real clinical need to provide complementary therapeutic solutions to a public health problem, considering the actual clinical context of the post-stroke patient and the practical limits resulting from it.

Excitatory Repetitive Transcranial Magnetic Stimulation Over the Ipsilesional Hemisphere for Upper Limb Motor Function After Stroke: A Systematic Review and Meta-Analysis

Background

Repetitive transcranial magnetic stimulation (rTMS) is a promising therapy to promote recovery of the upper limb after stroke. According to the regulation of cortical excitability, rTMS can be divided into excitatory rTMS and inhibitory rTMS, and excitatory rTMS includes high-frequency rTMS (HF-rTMS) or intermittent theta-burst stimulation (iTBS). We aimed to evaluate the effects of excitatory rTMS over the ipsilesional hemisphere on upper limb motor recovery after stroke.

Methods

Databases of PubMed, Embase, ISI Web of Science, and the Cochrane Library were searched for randomized controlled trials published before 31 December 2021. RCTs on the effects of HF-rTMS or iTBS on upper limb function in patients diagnosed with stroke were included. Two researchers independently screened the literature, extracted the data, and assessed quality. The meta-analysis was performed by using Review Manager Version 5.4 software.

Results

Fifteen studies with 449 participants were included in this meta-analysis. This meta-analysis found that excitatory rTMS had significant efficacy on upper limb motor function (MD = 5.88, 95% CI, 3.32–8.43, P < 0.001), hand strength (SMD = 0.53, 95% CI, 0.04–1.01, P = 0.03), and hand dexterity (SMD = 0.76, 95% CI, 0.39–1.14, P < 0.001). Subgroup analyses based on different types of rTMS showed that both iTBS and HF-rTMS significantly promoted upper limb motor function (iTBS, P < 0.001; HF-rTMS, P < 0.001) and hand dexterity (iTBS, P = 0.01; HF-rTMS, P < 0.001) but not hand strength (iTBS, P = 0.07; HF-rTMS, P = 0.12). Further subgroup analysis based on the duration of illness demonstrated that applying excitatory rTMS during the first 3 months (<1 month, P = 0.01; 1–3 months, P = 0.001) after stroke brought significant improvement in upper limb motor function but not in the patients with a duration longer than 3 months (P = 0.06). We found that HF-rTMS significantly enhanced the motor evoked potential (MEP) amplitude of affected hemisphere (SMD = 0.82, 95% CI, 0.32–1.33, P = 0.001).

Conclusion

Our study demonstrated that excitatory rTMS over the ipsilesional hemisphere could significantly improve upper limb motor function, hand strength, and hand dexterity in patients diagnosed with stroke. Both iTBS and HF-rTMS which could significantly promote upper limb motor function and hand dexterity, and excitatory rTMS were beneficial to upper limb motor function recovery only when applied in the first 3 months after stroke. HF-rTMS could significantly enhance the MEP amplitude of the affected hemisphere. High-quality and large-scale randomized controlled trials in the future are required to confirm our conclusions.

Clinical Trial Registration

www.crd.york.ac.uk/prospero/, identifier: CRD42022312288.

The effect of coupled inhibitory-facilitatory repetitive transcranial magnetic stimulation on shaping early reorganization of the motor network after stroke

Neural plasticity is a major factor driving cortical reorganization after stroke. This study aimed to evaluate functional connectivity (FC) changes in the cortical motor network after coupled inhibitory-facilitatory repetitive transcranial magnetic stimulation (rTMS) treatment and to assess the correlation between FC changes and functional recovery, further characterizing the neural mechanisms underlying the beneficial effects of rTMS. We randomly divided 63 patients with acute stroke into four groups: (1) Group A received coupled inhibitory-facilitatory rTMS [1 Hz over the contralesional primary motor cortex (M1) and 10 Hz over ipsilesional M1]; (2) Group B received a contralesional sham stimulation and ipsilesional 10 Hz stimulation; (3) Group C received a contralesional 1 Hz rTMS and ipsilesional sham stimulation; and (4) Group D received bilateral sham stimulation only. Standardized rehabilitation therapy was performed immediately after rTMS, and each group was treated with their respective treatment modalities for 4 weeks. Twenty-four hours before and after the intervention, participants underwent resting-state functional magnetic resonance imaging. Additional functional assessments were conducted at baseline, after treatment, and at the 3 month follow-up. The rTMS treatment significantly changed the FCs of intra- and inter-hemispheric cortical motor networks in the rTMS groups (A and B) compared with the sham group (Group D). This effect was more pronounced in Group A, which displayed a changed FC between the contralesional postcentral gyrus and contralesional superior parietal gyrus, between the contralesional precentral gyrus and contralesional postcentral gyrus, and between the ipsilesional postcentral gyrus and contralesional superior parietal gyrus, when compared with Groups B and C. Importantly, FC changes were significantly correlated with improvement of motor function. In the early stages of ischemic stroke, coupled rTMS was more conducive to motor recovery by modulating the FCs of intra-hemispheric and inter-hemispheric motor networks. Our results suggested that FC changes were related to motor function recovery for early-stage cerebral stroke patients treated with coupled rTMS. These findings could help to understand the mechanism of coupled rTMS and further the use of this therapy as an adjunct rehabilitation technique in motor recovery.

Recovered grasping performance after stroke depends on interhemispheric frontoparietal connectivity

Activity changes in the ipsi- and contralesional parietal cortex and abnormal interhemispheric connectivity between these regions are commonly observed after stroke, however, their significance for motor recovery remains poorly understood. We here assessed the contribution of ipsilesional and contralesional anterior intraparietal cortex (aIPS) for hand motor function in 18 recovered chronic stroke patients and 18 healthy control subjects using a multimodal assessment consisting of resting-state functional MRI, motor task functional MRI, online-repetitive transcranial magnetic stimulation (rTMS) interference, and 3D movement kinematics. Effects were compared against two control stimulation sites, i.e. contralesional M1 and a sham stimulation condition. We found that patients with good motor outcome compared to patients with more substantial residual deficits featured increased resting-state connectivity between ipsilesional aIPS and contralesional aIPS as well as between ipsilesional aIPS and dorsal premotor cortex. Moreover, interhemispheric connectivity between ipsilesional M1 and contralesional M1 as well as ipsilesional aIPS and contralesional M1 correlated with better motor performance across tasks. TMS interference at individual aIPS and M1 coordinates led to differential effects depending on the motor task that was tested, i.e. index finger-tapping, rapid pointing movements, or a reach-grasp-lift task. Interfering with contralesional aIPS deteriorated the accuracy of grasping, especially in patients featuring higher connectivity between ipsi- and contralesional aIPS. In contrast, interference with the contralesional M1 led to impaired grasping speed in patients featuring higher connectivity between bilateral M1. These findings suggest differential roles of contralesional M1 and aIPS for distinct aspects of recovered hand motor function, depending on the reorganization of interhemispheric connectivity.

Resting State EEG Directed Functional Connectivity Unveils Changes in Motor Network Organization in Subacute Stroke Patients After Rehabilitation

Brain plasticity and functional reorganization are mechanisms behind functional motor recovery of patients after an ischemic stroke. The study of resting-state motor network functional connectivity by means of EEG proved to be useful in investigating changes occurring in the information flow and find correlation with motor function recovery. In the literature, most studies applying EEG to post-stroke patients investigated the undirected functional connectivity of interacting brain regions. Quite recently, works started to investigate the directionality of the connections and many approaches or features have been proposed, each of them being more suitable to describe different aspects, e.g., direct or indirect information flow between network nodes, the coupling strength or its characteristic oscillation frequency. Each work chose one specific measure, despite in literature there is not an agreed consensus, and the selection of the most appropriate measure is still an open issue. In an attempt to shed light on this methodological aspect, we propose here to combine the information of direct and indirect coupling provided by two frequency-domain measures based on Granger’s causality, i.e., the directed coherence (DC) and the generalized partial directed coherence (gPDC), to investigate the longitudinal changes of resting-state directed connectivity associated with sensorimotor rhythms α and β, occurring in 18 sub-acute ischemic stroke patients who followed a rehabilitation treatment. Our results showed a relevant role of the information flow through the pre-motor regions in the reorganization of the motor network after the rehabilitation in the sub-acute stage. In particular, DC highlighted an increase in intra-hemispheric coupling strength between pre-motor and primary motor areas, especially in ipsi-lesional hemisphere in both α and β frequency bands, whereas gPDC was more sensitive in the detection of those connection whose variation was mostly represented within the population. A decreased causal flow from contra-lesional premotor cortex towards supplementary motor area was detected in both α and β frequency bands and a significant reinforced inter-hemispheric connection from ipsi to contra-lesional pre-motor cortex was observed in β frequency. Interestingly, the connection from contra towards ipsilesional pre-motor area correlated with upper limb motor recovery in α band. The usage of two different measures of directed connectivity allowed a better comprehension of those coupling changes between brain motor regions, either direct or mediated, which mostly were influenced by the rehabilitation, revealing a particular involvement of the pre-motor areas in the cerebral functional reorganization.

Interventional neurorehabilitation for promoting functional recovery post-craniotomy: a proof-of-concept

The human brain is a highly plastic ‘complex’ network—it is highly resilient to damage and capable of self-reorganisation after a large perturbation. Clinically, neurological deficits secondary to iatrogenic injury have very few active treatments. New imaging and stimulation technologies, though, offer promising therapeutic avenues to accelerate post-operative recovery trajectories. In this study, we sought to establish the safety profile for ‘interventional neurorehabilitation’: connectome-based therapeutic brain stimulation to drive cortical reorganisation and promote functional recovery post-craniotomy. In n = 34 glioma patients who experienced post-operative motor or language deficits, we used connectomics to construct single-subject cortical networks. Based on their clinical and connectivity deficit, patients underwent network-specific transcranial magnetic stimulation (TMS) sessions daily over five consecutive days. Patients were then assessed for TMS-related side effects and improvements. 31/34 (91%) patients were successfully recruited and enrolled for TMS treatment within two weeks of glioma surgery. No seizures or serious complications occurred during TMS rehabilitation and 1-week post-stimulation. Transient headaches were reported in 4/31 patients but improved after a single session. No neurological worsening was observed while a clinically and statistically significant benefit was noted in 28/31 patients post-TMS. We present two clinical vignettes and a video demonstration of interventional neurorehabilitation. For the first time, we demonstrate the safety profile and ability to recruit, enroll, and complete TMS acutely post-craniotomy in a high seizure risk population. Given the lack of randomisation and controls in this study, prospective randomised sham-controlled stimulation trials are now warranted to establish the efficacy of interventional neurorehabilitation following craniotomy.

Relationship Between Body-Specific Attention to a Paretic Limb and Real-World Arm Use in Stroke Patients: A Longitudinal Study

Learned nonuse is a major problem in upper limb (UL) rehabilitation after stroke. Among the various factors that contribute to learned nonuse, recent studies have focused on body representation of the paretic limb in the brain. We previously developed a method to measure body-specific attention, as a marker of body representation of the paretic limb and revealed a decline in body-specific attention to the paretic limb in chronic stroke patients by a cross-sectional study. However, longitudinal changes in body-specific attention and paretic arm use in daily life (real-world arm use) from the onset to the chronic phase, and their relationship, remain unknown. Here, in a longitudinal, prospective, observational study, we sought to elucidate the longitudinal changes in body-specific attention to the paretic limb and real-world arm use, and their relationship, by using accelerometers and psychophysical methods, respectively, in 25 patients with subacute stroke. Measurements were taken at baseline (TBL), 2 weeks (T2w), 1 month (T1M), 2 months (T2M), and 6 months (T6M) after enrollment. UL function was measured using the Fugl-Meyer Assessment (FMA) and Action Research Arm Test (ARAT). Real-world arm use was measured using accelerometers on both wrists. Body-specific attention was measured using a visual detection task. The UL function and real-world arm use improved up to T6M. Longitudinal changes in body-specific attention were most remarkable at T1M. Changes in body-specific attention up to T1M correlated positively with changes in real-world arm use up to T6M, and from T1M to T6M, and the latter more strongly correlated with changes in real-world arm use. Changes in real-world arm use up to T2M correlated positively with changes in FMA up to T2M and T6M. No correlation was found between body-specific attention and FMA scores. Thus, these results suggest that improved body-specific attention to the paretic limb during the early phase contributes to increasing long-term real-world arm use and that increased real-world use is associated with the recovery of UL function. Our results may contribute to the development of rehabilitation strategies to enhance adaptive changes in body representation in the brain and increase real-world arm use after stroke.

Effects of transcranial magnetic stimulation in modulating cortical excitability in patients with stroke: a systematic review and meta-analysis

Background

Transcranial magnetic stimulation (TMS) has attracted plenty of attention as it has been proved to be effective in facilitating motor recovery in patients with stroke. The aim of this study was to systematically review the effects of repetitive TMS (rTMS) and theta burst stimulation (TBS) protocols in modulating cortical excitability after stroke.

Methods

A literature search was carried out using PubMed, Medline, EMBASE, CINAHL, and PEDro, to identify studies that investigated the effects of four rTMS protocols—low and high frequency rTMS, intermittent and continuous TBS, on TMS measures of cortical excitability in stroke. A random-effects model was used for all meta-analyses.

Results

Sixty-one studies were included in the current review. Low frequency rTMS was effective in decreasing individuals’ resting motor threshold and increasing the motor-evoked potential of the non-stimulated M1 (affected M1), while opposite effects occurred in the stimulated M1 (unaffected M1). High frequency rTMS enhanced the cortical excitability of the affected M1 alone. Intermittent TBS also showed superior effects in rebalancing bilateral excitability through increasing and decreasing excitability within the affected and unaffected M1, respectively. Due to the limited number of studies found, the effects of continuous TBS remained inconclusive. Motor impairment was significantly correlated with various forms of TMS measures.

Conclusions

Except for continuous TBS, it is evident that these protocols are effective in modulating cortical excitability in stroke. Current evidence does support the effects of inhibitory stimulation in enhancing the cortical excitability of the affected M1.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12984-022-00999-4.

Insight Into the Effects of Clinical Repetitive Transcranial Magnetic Stimulation on the Brain From Positron Emission Tomography and Magnetic Resonance Imaging Studies: A Narrative Review

Repetitive transcranial magnetic stimulation (rTMS) has been proposed as a therapeutic tool to alleviate symptoms for neurological and psychiatric diseases such as chronic pain, stroke, Parkinson’s disease, major depressive disorder, and others. Although the therapeutic potential of rTMS has been widely explored, the neurological basis of its effects is still not fully understood. Fortunately, the continuous development of imaging techniques has advanced our understanding of rTMS neurobiological underpinnings on the healthy and diseased brain. The objective of the current work is to summarize relevant findings from positron emission tomography (PET) and magnetic resonance imaging (MRI) techniques evaluating rTMS effects. We included studies that investigated the modulation of neurotransmission (evaluated with PET and magnetic resonance spectroscopy), brain activity (evaluated with PET), resting-state connectivity (evaluated with resting-state functional MRI), and microstructure (diffusion tensor imaging). Overall, results from imaging studies suggest that the effects of rTMS are complex and involve multiple neurotransmission systems, regions, and networks. The effects of stimulation seem to not only be dependent in the frequency used, but also in the participants characteristics such as disease progression. In patient populations, pre-stimulation evaluation was reported to predict responsiveness to stimulation, while post-stimulation neuroimaging measurements showed to be correlated with symptomatic improvement. These studies demonstrate the complexity of rTMS effects and highlight the relevance of imaging techniques.

Intermittent Theta Burst Stimulation Increases Natural Oscillatory Frequency in Ipsilesional Motor Cortex Post-Stroke: A Transcranial Magnetic Stimulation and Electroencephalography Study

Objective

Intermittent theta burst stimulation (iTBS) has been widely used as a neural modulation approach in stroke rehabilitation. Concurrent use of transcranial magnetic stimulation and electroencephalography (TMS-EEG) offers a chance to directly measure cortical reactivity and oscillatory dynamics and allows for investigating neural effects induced by iTBS in all stroke survivors including individuals without recordable MEPs. Here, we used TMS-EEG to investigate aftereffects of iTBS following stroke.

Methods

We studied 22 stroke survivors (age: 65.2 ± 11.4 years; chronicity: 4.1 ± 3.5 months) with upper limb motor deficits. Upper-extremity component of Fugl-Meyer motor function assessment and action research arm test were used to measure motor function of stroke survivors. Stroke survivors were randomly divided into two groups receiving either Active or Sham iTBS applied over the ipsilesional primary motor cortex. TMS-EEG recordings were performed at baseline and immediately after Active or Sham iTBS. Time and time-frequency domain analyses were performed for quantifying TMS-evoked EEG responses.

Results

At baseline, natural frequency was slower in the ipsilesional compared with the contralesional hemisphere (P = 0.006). Baseline natural frequency in the ipsilesional hemisphere was positively correlated with upper limb motor function following stroke (P = 0.007). After iTBS, natural frequency in the ipsilesional hemisphere was significantly increased (P < 0.001).

Conclusions

This is the first study to investigate the acute neural adaptations after iTBS in stroke survivors using TMS-EEG. Our results revealed that natural frequency is altered following stroke which is related to motor impairments. iTBS increases natural frequency in the ipsilesional motor cortex in stroke survivors. Our findings implicate that iTBS holds the potential to normalize natural frequency in stroke survivors, which can be utilized in stroke rehabilitation.

First evidence of long-term effects of transcranial pulse stimulation (TPS) on the human brain

Background

With the high spatial resolution and the potential to reach deep brain structures, ultrasound-based brain stimulation techniques offer new opportunities to non-invasively treat neurological and psychiatric disorders. However, little is known about long-term effects of ultrasound-based brain stimulation. Applying a longitudinal design, we comprehensively investigated neuromodulation induced by ultrasound brain stimulation to provide first sham-controlled evidence of long-term effects on the human brain and behavior.

Methods

Twelve healthy participants received three sham and three verum sessions with transcranial pulse stimulation (TPS) focused on the cortical somatosensory representation of the right hand. One week before and after the sham and verum TPS applications, comprehensive structural and functional resting state MRI investigations and behavioral tests targeting tactile spatial discrimination and sensorimotor dexterity were performed.

Results

Compared to sham, global efficiency significantly increased within the cortical sensorimotor network after verum TPS, indicating an upregulation of the stimulated functional brain network. Axial diffusivity in left sensorimotor areas decreased after verum TPS, demonstrating an improved axonal status in the stimulated area.

Conclusions

TPS increased the functional and structural coupling within the stimulated left primary somatosensory cortex and adjacent sensorimotor areas up to one week after the last stimulation. These findings suggest that TPS induces neuroplastic changes that go beyond the spatial and temporal stimulation settings encouraging further clinical applications.

Selectively disrupted sensorimotor circuits in chronic stroke with hand dysfunction

Aim

To investigate the directional and selective disconnection of the sensorimotor cortex (SMC) subregions in chronic stroke patients with hand dysfunction.

Methods

We mapped the resting‐state fMRI effective connectivity (EC) patterns for seven SMC subregions in each hemisphere of 65 chronic stroke patients and 40 healthy participants and correlated these patterns with paretic hand performance.

Results

Compared with controls, patients demonstrated disrupted EC in the ipsilesional primary motor cortex_4p, ipsilesional primary somatosensory cortex_2 (PSC_2), and contralesional PSC_3a. Moreover, we found that EC values of the contralesional PSC_1 to contralesional precuneus, the ipsilesional inferior temporal gyrus to ipsilesional PSC_1, and the ipsilesional PSC_1 to contralesional postcentral gyrus were correlated with paretic hand performance across all patients. We further divided patients into partially (PPH) and completely (CPH) paretic hand subgroups. Compared with CPH patients, PPH patients demonstrated decreased EC in the ipsilesional premotor_6 and ipsilesional PSC_1. Interestingly, we found that paretic hand performance was positively correlated with seven sensorimotor circuits in PPH patients, while it was negatively correlated with five sensorimotor circuits in CPH patients.

Conclusion

SMC neurocircuitry was selectively disrupted after chronic stroke and associated with diverse hand outcomes, which deepens the understanding of SMC reorganization.

Synaptic plasticity mechanisms behind TMS efficacy: insights from its application to animal models

Neural plasticity is defined as a reshape of communication paths among neurons, expressed through changes in the number and weights of synaptic contacts. During this process, which occurs massively during early brain development but continues also in adulthood, specific brain functions are modified by activity-dependent processes, triggered by external as well as internal stimuli. Since transcranial magnetic stimulation (TMS) produces a non-invasive form of brain cells activation, many different TMS protocols have been developed to treat neurological and psychiatric conditions and proved to be beneficial. Although neural plasticity induction by TMS has been widely assessed on human subjects, we still lack compelling evidence about the actual biological and molecular mechanisms. To support a better comprehension of the involved phenomena, the main focus of this review is to summarize what has been found through the application of TMS to animal models. The hope is that such integrated view will shed light on why and how TMS so effectively works on human subjects, thus supporting a more efficient development of new protocols in the future.

Dynamic connectivity predicts acute motor impairment and recovery post-stroke

Thorough assessment of cerebral dysfunction after acute lesions is paramount to optimize predicting clinical outcomes. We here built random forest classifier-based prediction models of acute motor impairment and recovery post-stroke. Predictions relied on structural and resting-state fMRI data from 54 stroke patients scanned within the first days of symptom onset. Functional connectivity was estimated via static and dynamic approaches. Motor performance was phenotyped in the acute phase and 6 months later. A model based on the time spent in specific dynamic connectivity configurations achieved the best discrimination between patients with and without motor impairments (out-of-sample area under the curve, 95% confidence interval: 0.67 ± 0.01). In contrast, patients with moderate-to-severe impairments could be differentiated from patients with mild deficits using a model based on the variability of dynamic connectivity (0.83 ± 0.01). Here, the variability of the connectivity between ipsilesional sensorimotor cortex and putamen discriminated the most between patients. Finally, motor recovery was best predicted by the time spent in specific connectivity configurations (0.89 ± 0.01) in combination with the initial impairment. Here, better recovery was linked to a shorter time spent in a functionally integrated configuration. Dynamic connectivity-derived parameters constitute potent predictors of acute impairment and recovery, which, in the future, might inform personalized therapy regimens to promote stroke recovery.

The Effects of Intermittent Theta Burst Stimulation on Functional Brain Network Following Stroke: An Electroencephalography Study

Objective: Intermittent theta burst stimulation (iTBS) is a special form of repetitive transcranial magnetic stimulation (rTMS), which effectively increases cortical excitability and has been widely used as a neural modulation approach in stroke rehabilitation. As effects of iTBS are typically investigated by motor evoked potentials, how iTBS influences functional brain network following stroke remains unclear. Resting-state electroencephalography (EEG) has been suggested to be a sensitive measure for evaluating effects of rTMS on brain functional activity and network. Here, we used resting-state EEG to investigate the effects of iTBS on functional brain network in stroke survivors.

Methods: We studied thirty stroke survivors (age: 63.1 ± 12.1 years; chronicity: 4.0 ± 3.8 months; UE FMA: 26.6 ± 19.4/66) with upper limb motor dysfunction. Stroke survivors were randomly divided into two groups receiving either Active or Sham iTBS over the ipsilesional primary motor cortex. Resting-state EEG was recorded at baseline and immediately after iTBS to assess the effects of iTBS on functional brain network.

Results: Delta and theta bands interhemispheric functional connectivity were significantly increased after Active iTBS (P = 0.038 and 0.011, respectively), but were not significantly changed after Sham iTBS (P = 0.327 and 0.342, respectively). Delta and beta bands global efficiency were also significantly increased after Active iTBS (P = 0.013 and 0.0003, respectively), but not after Sham iTBS (P = 0.586 and 0.954, respectively).

Conclusion: This is the first study that used EEG to investigate the acute neuroplastic changes after iTBS following stroke. Our findings for the first time provide evidence that iTBS modulates brain network functioning in stroke survivors. Acute increase in interhemispheric functional connectivity and global efficiency after iTBS suggest that iTBS has the potential to normalize brain network functioning following stroke, which can be utilized in stroke rehabilitation.

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.

Motor Network Reorganization After Repetitive Transcranial Magnetic Stimulation in Early Stroke Patients: A Resting State fMRI Study

OBJECTIVE

To compare the effects of high-frequency (10 Hz) versus low-frequency (1 Hz) repetitive Transcranial Magnetic Stimulation (rTMS) on motor recovery and functional reorganization of the cortical motor network during the early phase of stroke.

METHODS

Forty-six hospitalized, first-ever ischemic stroke patients in early stage (within two weeks) with upper limb motor deficits were recruited. They were randomly allocated to three groups with 10 Hz ipsilesional rTMS, 1 Hz contralesional rTMS, and sham rTMS of five daily session. All patients underwent motor function (Upper Extremity Fugl-Meyer), neurophysiological and resting-state  functional Magnetic Resonance Imaging (fMRI) (rs-fMRI) assessments before and after rTMS intervention. Motor recovery (△Fugl-Meyer Assessment) was defined as motor function changes before and after rTMS intervention. Motor function assessment was reevaluated at time point of three month follow-up.

RESULTS

The two real rTMS groups manifested greater motor improvements than the sham group. The effect sustained for at least 3 months after the end of the treatment sessions. Compared with the sham group, 10 Hz ipsilesional rTMS group presented increased resting-state functional connectivity (FC) between ipsilesional primary motor cortex (M1) and contralesional M1 (P = .007), whereas 1 Hz contralesional rTMS group presented increased FC between contralesional M1 and ipsilesional supplementary motor area (P = .010), which were positively correlated with motor recovery (P < .05).

CONCLUSION

Beneficial effect of rTMS on motor recovery might be underlaid by increased FC between stimulating site and the remote motor areas, highlighting the motor network reorganization mechanism of rTMS in early post-stroke phase.

Early motor network connectivity after stroke: An interplay of general reorganization and state-specific compensation

Motor recovery after stroke relies on functional reorganization of the motor network, which is commonly assessed via functional magnetic resonance imaging (fMRI)-based resting-state functional connectivity (rsFC) or task-related effective connectivity (trEC). Measures of either connectivity mode have been shown to successfully explain motor impairment post-stroke, posing the question whether motor impairment is more closely reflected by rsFC or trEC. Moreover, highly similar changes in ipsilesional and interhemispheric motor network connectivity have been reported for both rsFC and trEC after stroke, suggesting that altered rsFC and trEC may capture similar aspects of information integration in the motor network reflecting principle, state-independent mechanisms of network reorganization rather than state-specific compensation strategies. To address this question, we conducted the first direct comparison of rsFC and trEC in a sample of early subacute stroke patients (n = 26, included on average 7.3 days post-stroke). We found that both rsFC and trEC explained motor impairment across patients, stressing the clinical potential of fMRI-based connectivity. Importantly, intrahemispheric connectivity between ipsilesional M1 and premotor areas depended on the activation state, whereas interhemispheric connectivity between homologs was state-independent. From a mechanistic perspective, our results may thus arise from two distinct aspects of motor network plasticity: task-specific compensation within the ipsilesional hemisphere and a more fundamental form of reorganization between hemispheres.

Paired associative stimulations: Novel tools for interacting with sensory and motor cortical plasticity

In the early 2000s, a novel non-invasive brain stimulation protocol, the paired associative stimulation (PAS), was introduced, allowing to induce and investigate Hebbian associative plasticity within the humans' motor system, with patterns resembling spike-timing-dependent plasticity properties found in cellular models. Since this evidence, PAS efficacy has been proved in healthy, and to a lesser extent, in clinical populations. Recently, novel 'modified' protocols targeting sensorimotor and crossmodal networks appeared in the literature. In the present work, we have reviewed recent advances using these 'modified' PAS protocols targeting sensory and motor cortical networks. To better categorize them, we propose a novel classification according to the nature of the peripheral and cortical stimulations (i.e., within-system, cross-systems, and cortico-cortical PAS). For each protocol of the categories mentioned above, we describe and discuss their main features, how they have been used to study and promote brain plasticity, and their advantages and disadvantages. Overall, current evidence suggests that these novel non-invasive brain stimulation protocols represent very promising tools to study the plastic properties of humans' sensorimotor and crossmodal networks, both in the healthy and in the damaged central nervous system.

Translating Functional Connectivity After Stroke: Functional Magnetic Resonance Imaging Detects Comparable Network Changes in Mice and Humans

[Figure: see text].

Ipsilateral BDNF mRNA expression in the motor cortex positively correlates with motor function of the affected forelimb after intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a subtype of stroke that causes major motor impairments. Brain-derived neurotrophic factor (BDNF) is known to have important roles in neuroplasticity and beneficially contributes to stroke recovery. This study aimed to characterize BDNF expression in the motor cortex after ICH and investigate the relationship between cortical BDNF expression and behavioral outcomes using an ICH rat model. Wistar rats were divided into two groups: a SHAM group (n = 7) and an ICH group (n = 8). ICH was induced by the injection of collagenase into the left striatum near the internal capsule. For behavioral assessments, the cylinder test and open field test were performed before surgery and 3 days, 1 week, 2 weeks, and 4 weeks after surgery. Following the behavioral assessments at 4 weeks, BDNF expression in the ipsilateral and contralateral motor cortex was assayed using RT-PCR and ELISA methods. There was no significant difference in either cortical BDNF mRNA or protein expression levels between the SHAM and ICH groups. However, the asymmetry index of BDNF mRNA expression between the ipsilateral and contralateral hemispheres shifted to the ipsilateral hemisphere after ICH. Furthermore, the ipsilateral cortical BDNF mRNA expression level positively correlated with motor function in the affected forelimb after ICH. This study describes for the first time that cortical BDNF mRNA expression is related to post-ICH motor impairment. These results highlight the importance of assessing the interhemispheric laterality of BDNF expression and could help develop novel treatment strategies for BDNF-dependent recovery after ICH.

TMS-Induced Central Motor Conduction Time at the Non-Infarcted Hemisphere Is Associated with Spontaneous Motor Recovery of the Paretic Upper Limb after Severe Stroke

Background: Stroke affects the neuronal networks of the non-infarcted hemisphere. The central motor conduction time (CMCT) induced by transcranial magnetic stimulation (TMS) could be used to determine the conduction time of the corticospinal tract of the non-infarcted hemisphere after a stroke. Objectives: Our primary aim was to demonstrate the existence of prolonged CMCT in the non-infarcted hemisphere, measured within the first 48 h when compared to normative data, and secondly, if the severity of motor impairment of the affected upper limb was significantly associated with prolonged CMCTs in the non-infarcted hemisphere when measured within the first 2 weeks post stroke. Methods: CMCT in the non-infarcted hemisphere was measured in 50 patients within 48 h and at 11 days after a first-ever ischemic stroke. Patients lacking significant spontaneous motor recovery, so-called non-recoverers, were defined as those who started below 18 points on the FM-UE and showed less than 6 points (10%) improvement within 6 months. Results: CMCT in the non-infarcted hemisphere was prolonged in 30/50 (60%) patients within 48 h and still in 24/49 (49%) patients at 11 days. Sustained prolonged CMCT in the non-infarcted hemisphere was significantly more frequent in non-recoverers following FM-UE. Conclusions: The current study suggests that CMCT in the non-infarcted hemisphere is significantly prolonged in 60% of severely affected, ischemic stroke patients when measured within the first 48 h post stroke. The likelihood of CMCT is significantly higher in non-recoverers when compared to those that show spontaneous motor recovery early post stroke.

Calhoun V, Grefkes C, Rost NS. Abnormal dynamic functional connectivity is linked to recovery after acute ischemic stroke

The aim of the current study was to explore the whole-brain dynamic functional connectivity patterns in acute ischemic stroke (AIS) patients and their relation to short and long-term stroke severity. We investigated resting-state functional MRI-based dynamic functional connectivity of 41 AIS patients two to five days after symptom onset. Re-occurring dynamic connectivity configurations were obtained using a sliding window approach and k-means clustering. We evaluated differences in dynamic patterns between three NIHSS-stroke severity defined groups (mildly, moderately, and severely affected patients). Furthermore, we built Bayesian hierarchical models to evaluate the predictive capacity of dynamic connectivity and examine the interrelation with clinical measures, such as white matter hyperintensity lesions. Finally, we established correlation analyses between dynamic connectivity and AIS severity as well as 90-day neurological recovery (ΔNIHSS). We identified three distinct dynamic connectivity configurations acutely post-stroke. More severely affected patients spent significantly more time in a configuration that was characterized by particularly strong connectivity and isolated processing of functional brain domains (three-level ANOVA: p < .05, post hoc t tests: p < .05, FDR-corrected). Configuration-specific time estimates possessed predictive capacity of stroke severity in addition to the one of clinical measures. Recovery, as indexed by the realized change of the NIHSS over time, was significantly linked to the dynamic connectivity between bilateral intraparietal lobule and left angular gyrus (Pearson's r = -.68, p = .003, FDR-corrected). Our findings demonstrate transiently increased isolated information processing in multiple functional domains in case of severe AIS. Dynamic connectivity involving default mode network components significantly correlated with recovery in the first 3 months poststroke.