Models to Tailor Brain Stimulation Therapies in Stroke

Brain-Hand Function Relationships Based on Level of Grasp Function in Chronic Left-Hemisphere Stroke

BACKGROUND AND OBJECTIVE

The biomarkers of hand function may differ based on level of motor impairment after stroke. The objective of this study was to determine the relationship between resting state functional connectivity (RsFC) and unimanual contralesional hand function after stroke and whether brain-behavior relationships differ based on level of grasp function.

METHODS

Sixty-two individuals with chronic, left-hemisphere stroke were separated into three functional levels based on Box and Blocks Test performance with the contralesional hand: Low (moved 0 blocks), Moderate (moved >0% but <90% of blocks relative to the ipsilesional hand), and High (moved ≥90% of blocks relative to the ipsilesional hand).

RESULTS

RsFC in the ipsilesional and interhemispheric motor networks was reduced in the Low group compared to the Moderate and High groups. While interhemispheric RsFC correlated with hand function (grip strength and Stroke Impact Scale Hand) across the sample, contralesional RsFC correlated with hand function in the Low group and no measures of connectivity correlated with hand function in the Moderate and High groups. Linear regression modeling found that contralesional RsFC significantly predicted hand function in the Low group, while no measure correlated with hand function in the High group. Corticospinal tract integrity was the only predictor of hand function for the Moderate group and in an analysis across the entire sample.

CONCLUSIONS

Differences in brain-hand function relationships based on level of motor impairment may have implications for predictive models of treatment response and the development of intervention protocols aimed at improving hand function after stroke.

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

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

Pyramidal and parvalbumin neurons modulate the process of electroacupuncture stimulation for stroke rehabilitation

Electroacupuncture (EA) stimulation has been shown to be beneficial in stroke rehabilitation; however, little is known about the neurological mechanism by which this peripheral stimulation approach treats for stroke. This study showed that both pyramidal and parvalbumin (PV) neuronal activity increased in the contralesional primary motor cortex forelimb motor area (M1FL) after ischemic stroke induced by focal unilateral occlusion in the M1FL. EA stimulation reduced pyramidal neuronal activity and increased PV neuronal activity. These results were obtained by a combination of fiber photometry recordings, in vivo and in vitro electrophysiological recordings, and immunofluorescence. Moreover, EA was found to regulate the expression/function of N-methyl-D-aspartate receptors (NMDARs) altered by stroke pathology. In summary, our findings suggest that EA could restore disturbed neuronal activity through the regulation of the activity of pyramidal and PV neurons. Furthermore, NMDARs we shown to play an important role in EA-mediated improvements in sensorimotor ability during stroke rehabilitation.

Inhibiting metabotropic glutamate receptor 5 after stroke restores brain function and connectivity

Stroke results in local neural disconnection and brain-wide neuronal network dysfunction leading to neurological deficits. Beyond the hyper-acute phase of ischaemic stroke, there is no clinically-approved pharmacological treatment that alleviates sensorimotor impairments. Functional recovery after stroke involves the formation of new or alternative neuronal circuits including existing neural connections. The type-5 metabotropic glutamate receptor (mGluR5) has been shown to modulate brain plasticity and function and is a therapeutic target in neurological diseases outside of stroke. We investigated whether mGluR5 influences functional recovery and network reorganization rodent models of focal ischaemia. Using multiple behavioural tests, we observed that treatment with negative allosteric modulators (NAMs) of mGluR5 (MTEP, fenobam and AFQ056) for 12 days, starting 2 or 10 days after stroke, restored lost sensorimotor functions, without diminishing infarct size. Recovery was evident within hours after initiation of treatment and progressed over the subsequent 12 days. Recovery was prevented by activation of mGluR5 with the positive allosteric modulator VU0360172 and accelerated in mGluR5 knock-out mice compared with wild-type mice. After stroke, multisensory stimulation by enriched environments enhanced recovery, a result prevented by VU0360172, implying a role of mGluR5 in enriched environment-mediated recovery. Additionally, MTEP treatment in conjunction with enriched environment housing provided an additive recovery enhancement compared to either MTEP or enriched environment alone. Using optical intrinsic signal imaging, we observed brain-wide disruptions in resting-state functional connectivity after stroke that were prevented by mGluR5 inhibition in distinct areas of contralesional sensorimotor and bilateral visual cortices. The levels of mGluR5 protein in mice and in tissue samples of stroke patients were unchanged after stroke. We conclude that neuronal circuitry subserving sensorimotor function after stroke is depressed by a mGluR5-dependent maladaptive plasticity mechanism that can be restored by mGluR5 inhibition. Post-acute stroke treatment with mGluR5 NAMs combined with rehabilitative training may represent a novel post-acute stroke therapy.

Noninvasive cerebellar stimulation and behavioral interventions: A crucial synergy for post-stroke motor rehabilitation

BACKGROUND

Improvement of functional movements after supratentorial stroke occurs through spontaneous biological recovery and training-induced reorganization of remnant neural networks. The cerebellum, through its connectivity with the cortex, brainstem and spinal cord, is actively engaged in both recovery and reorganization processes within the cognitive and sensorimotor systems. Noninvasive cerebellar stimulation (NiCBS) offers a safe, clinically feasible and potentially effective way to modulate the excitability of spared neural networks and promote movement recovery after supratentorial stroke. NiCBS modulates cerebellar connectivity to the cerebral cortex and brainstem, as well as influences the sensorimotor and frontoparietal networks.

OBJECTIVE

Our objective was twofold: (a) to conduct a scoping review of studies that employed NiCBS to influence motor recovery and learning in individuals with stroke, and (b) to present a theory-driven framework to inform the use of NiCBS to target distinct stroke-related deficits.

METHODS

A scoping review of current research up to August 2023 was conducted to determine the effect size of NiCBS effect on movement recovery of upper extremity function, balance, walking and motor learning in humans with stroke.

RESULTS

Calculated effect sizes were moderate to high, offering promise for improving upper extremity, balance and walking outcomes after stroke. We present a conceptual framework that capitalizes on cognitive-motor specialization of the cerebellum to formulate a synergy between NiCBS and behavioral interventions to target specific movement deficits.

CONCLUSION

NiCBS enhances recovery of upper extremity impairments, balance and walking after stroke. Physiologically-informed synergies between NiCBS and behavioral interventions have the potential to enhance recovery. Finally, we propose future directions in neurophysiological, behavioral, and clinical research to move NiCBS through the translational pipeline and augment motor recovery after stroke.

Effects of repetitive transcranial magnetic stimulation over the contralesional dorsal premotor cortex on upper limb function in severe ischaemic stroke: study protocol for a randomised controlled trial

INTRODUCTION

Repetitive transcranial magnetic stimulation (rTMS) is an evidence-based treatment widely recommended to promote hand motor recovery after ischaemic stroke. However, the therapeutic efficacy of rTMS over the motor cortex in stroke patients is currently restricted and heterogeneous. This study aimed to determine whether excitatory rTMS over the contralesional dorsal premotor cortex (cPMd) facilitates the functional recovery of the upper limbs during the postacute stage of severe ischaemic stroke.

METHODS AND ANALYSIS

This study will be conducted as a single-blind, controlled, randomised study, in which 44 patients with poststroke hemiplegia with a course of disease ranging from 1 week to 3 months and Fugl-Meyer upper limb score ≤22 will be enrolled. The study participants will be randomly assigned to groups A (n=22) and B (n=22). The two groups are based on routine rehabilitation training and drug treatment; group A will be treated with low-frequency (1 Hz) rTMS over the contralesional primary motor cortex (cM1), and group B will be treated with high-frequency (10 Hz) rTMS over cPMd. For 2 weeks, rTMS will be administered once a day, 5 days a week. The primary outcome is the Fugl-Meyer assessment of the upper limb. The secondary outcomes include the Arm Subscore of the Motricity Index, Hong Kong edition of Functional Test for the Hemiplegic Upper Extremity, Modified Barthel Index and Modified Ashworth Scale score of the paralysed pectoralis major and biceps brachii. Furthermore, data of diffusion tensor imaging and functional MRI will be collected. These outcomes will be assessed before and after the completion of the intervention.

ETHICS AND DISSEMINATION

This study has been approved by the Ethics Committee of the First Affiliated Hospital of Nanjing Medical University (2020 SR-266). The findings of this study will be spread through networks of scientists, professionals and the general public as well as peer-reviewed scientific papers and presentations at pertinent conferences.

TRIAL REGISTRATION NUMBER

ChiCTR2000038049.

The behavioral and neural effects of parietal theta burst stimulation on the grasp network are stronger during a grasping task than at rest

Repetitive transcranial magnetic stimulation (TMS) is widely used in neuroscience and clinical settings to modulate human cortical activity. The effects of TMS on neural activity depend on the excitability of specific neural populations at the time of stimulation. Accordingly, the brain state at the time of stimulation may influence the persistent effects of repetitive TMS on distal brain activity and associated behaviors. We applied intermittent theta burst stimulation (iTBS) to a region in the posterior parietal cortex (PPC) associated with grasp control to evaluate the interaction between stimulation and brain state. Across two experiments, we demonstrate the immediate responses of motor cortex activity and motor performance to state-dependent parietal stimulation. We randomly assigned 72 healthy adult participants to one of three TMS intervention groups, followed by electrophysiological measures with TMS and behavioral measures. Participants in the first group received iTBS to PPC while performing a grasping task concurrently. Participants in the second group received iTBS to PPC while in a task-free, resting state. A third group of participants received iTBS to a parietal region outside the cortical grasping network while performing a grasping task concurrently. We compared changes in motor cortical excitability and motor performance in the three stimulation groups within an hour of each intervention. We found that parietal stimulation during a behavioral manipulation that activates the cortical grasping network increased downstream motor cortical excitability and improved motor performance relative to stimulation during rest. We conclude that constraining the brain state with a behavioral task during brain stimulation has the potential to optimize plasticity induction in cortical circuit mechanisms that mediate movement processes.

Neural Plasticity Changes Induced by Motor Robotic Rehabilitation in Stroke Patients: The Contribution of Functional Neuroimaging

Robotic rehabilitation is one of the most advanced treatments helping people with stroke to faster recovery from motor deficits. The clinical impact of this type of treatment has been widely defined and established using clinical scales. The neurofunctional indicators of motor recovery following conventional rehabilitation treatments have already been identified by previous meta-analytic investigations. However, a clear definition of the neural correlates associated with robotic neurorehabilitation treatment has never been performed. This systematic review assesses the neurofunctional correlates (fMRI, fNIRS) of cutting-edge robotic therapies in enhancing motor recovery of stroke populations in accordance with PRISMA standards. A total of 7, of the initial yield of 150 articles, have been included in this review. Lessons from these studies suggest that neural plasticity within the ipsilateral primary motor cortex, the contralateral sensorimotor cortex, and the premotor cortices are more sensitive to compensation strategies reflecting upper and lower limbs' motor recovery despite the high heterogeneity in robotic devices, clinical status, and neuroimaging procedures. Unfortunately, the paucity of RCT studies prevents us from understanding the neurobiological differences induced by robotic devices with respect to traditional rehabilitation approaches. Despite this technology dating to the early 1990s, there is a need to translate more functional neuroimaging markers in clinical settings since they provide a unique opportunity to examine, in-depth, the brain plasticity changes induced by robotic rehabilitation.

Evaluation of fMRI activation in post-stroke patients with movement disorders after repetitive transcranial magnetic stimulation: a scoping review

Background

Movement disorders are one of the most common stroke residual effects, which cause a major stress on their families and society. Repetitive transcranial magnetic stimulation (rTMS) could change neuroplasticity, which has been suggested as an alternative rehabilitative treatment for enhancing stroke recovery. Functional magnetic resonance imaging (fMRI) is a promising tool to explore neural mechanisms underlying rTMS intervention.

Object

Our primary goal is to better understand the neuroplastic mechanisms of rTMS in stroke rehabilitation, this paper provides a scoping review of recent studies, which investigate the alteration of brain activity using fMRI after the application of rTMS over the primary motor area (M1) in movement disorders patients after stroke.

Method

The database PubMed, Embase, Web of Science, WanFang Chinese database, ZhiWang Chinese database from establishment of each database until December 2022 were included. Two researchers reviewed the study, collected the information and the relevant characteristic extracted to a summary table. Two researchers also assessed the quality of literature with the Downs and Black criteria. When the two researchers unable to reach an agreement, a third researcher would have been consulted.

Results

Seven hundred and eleven studies in all were discovered in the databases, and nine were finally enrolled. They were of good quality or fair quality. The literature mainly involved the therapeutic effect and imaging mechanisms of rTMS on improving movement disorders after stroke. In all of them, there was improvement of the motor function post-rTMS treatment. Both high-frequency rTMS (HF-rTMS) and low-frequency rTMS (LF-rTMS) can induce increased functional connectivity, which may not directly correspond to the impact of rTMS on the activation of the stimulated brain areas. Comparing real rTMS with sham group, the neuroplastic effect of real rTMS can lead to better functional connectivity in the brain network in assisting stroke recovery.

Conclusion

rTMS allows the excitation and synchronization of neural activity, promotes the reorganization of brain function, and achieves the motor function recovery. fMRI can observe the influence of rTMS on brain networks and reveal the neuroplasticity mechanism of post-stroke rehabilitation. The scoping review helps us to put forward a series of recommendations that might guide future researchers exploring the effect of motor stroke treatments on brain connectivity.

Anodal Contralesional tDCS Enhances CST Excitability Bilaterally in an Adolescent with Hemiparetic Cerebral Palsy: A Brief Report

Hemiparetic cerebral palsy (HCP), weakness on one side of the body typically caused by perinatal stroke, is characterized by lifelong motor impairments related to alterations in the corticospinal tract (CST). CST reorganization could be a useful biomarker to guide applications of neuromodulatory interventions, such as transcranial direct current stimulation (tDCS), to improve the effectiveness of rehabilitation therapies. We evaluated an adolescent with HCP and CST reorganization who demonstrated persistent heightened CST excitability in both upper limbs following anodal contralesional tDCS. The results support further investigation of targeted tDCS as an adjuvant therapy to traditional neurorehabilitation for upper limb function.

Applying transcranial magnetic stimulation to rehabilitation of poststroke lower extremity function and an improvement: Individual-target TMS

Stroke is the leading cause of disability globally in need of novel and effective methods of rehabilitation. Intermittent theta burst stimulation (iTBS) has been adopted as a Level B recommendation for lower limb spasticity in guidelines on the therapeutic use of repetitive transcranial magnetic stimulation (rTMS). Nonetheless, the methodological differences and deficits of existing work bring about heterogenous results and therefore limit the universal clinical use of rTMS in lower extremity (LE) rehabilitation. The variation of stimulated targets across motor cortex contributes mainly to these heterogeneities. This narrative review includes studies of rTMS on LE motor function rehabilitation in patients after stroke until now. Some analyses of brain imaging and electromagnetic simulation and quantification through computational modeling were also performed. rTMS appears capable of fostering LE motor rehabilitation after stroke, but the actually stimulated targets are considerably bias making it difficult to confirm effectiveness. The main reason for this phenomenon is probably inaccurate targeting of motor cortical leg representation. An underlying updated method is proposed as Individual-Target TMS (IT-TMS) combined with brain imaging. rTMS is a promising validated method for LE function regaining. Future studies should systematically compare the effects of IT-TMS with traditional rTMS using large samples in random clinical trials. This article is categorized under: Neuroscience > Clinical Neuroscience.

Bimanual motor skill learning after stroke: Combining robotics and anodal tDCS over the undamaged hemisphere: An exploratory study

Background

Since a stroke can impair bimanual activities, enhancing bimanual cooperation through motor skill learning may improve neurorehabilitation. Therefore, robotics and neuromodulation with transcranial direct current stimulation (tDCS) are promising approaches. To date, tDCS has failed to enhance bimanual motor control after stroke possibly because it was not integrating the hypothesis that the undamaged hemisphere becomes the major poststroke hub for bimanual control.

Objective

We tested the following hypotheses: (I) In patients with chronic hemiparetic stroke training on a robotic device, anodal tDCS applied over the primary motor cortex of the undamaged hemisphere enhances bimanual motor skill learning compared to sham tDCS. (II) The severity of impairment correlates with the effect of tDCS on bimanual motor skill learning. (III) Bimanual motor skill learning is less efficient in patients than in healthy individuals (HI).

Methods

A total of 17 patients with chronic hemiparetic stroke and 7 healthy individuals learned a complex bimanual cooperation skill on the REAplan® neurorehabilitation robot. The bimanual speed/accuracy trade-off (biSAT), bimanual coordination (biCo), and bimanual force (biFOP) scores were computed for each performance. In patients, real/sham tDCS was applied in a crossover, randomized, double-blind approach.

Results

Compared to sham, real tDCS did not enhance bimanual motor skill learning, retention, or generalization in patients, and no correlation with impairment was noted. The healthy individuals performed better than patients on bimanual motor skill learning, but generalization was similar in both groups.

Conclusion

A short motor skill learning session with a robotic device resulted in the retention and generalization of a complex skill involving bimanual cooperation. The tDCS strategy that would best enhance bimanual motor skill learning after stroke remains unknown.

Clinical trial registration

https://clinicaltrials.gov/ct2/show/NCT02308852, identifier: NCT02308852.

Motor overflow in the lower limb after stroke: insights into mechanisms

Motor overflow (involuntary muscle activation) is common after stroke, particularly in the non-paretic upper limb. Two potential cortical mechanisms are: 1) the contralesional hemisphere controls both limbs, and 2) inhibition from the ipsilesional to the contralesional hemisphere is diminished. Few studies have differentiated between these hypotheses or investigated motor overflow in the lower limb after stroke. To investigate these potential mechanisms, individuals with chronic stroke performed unilateral isometric and dynamic dorsiflexion. Motor overflow was quantified in the contralateral, resting (non-target) ankle. Transcranial magnetic stimulation was applied, and responses were measured in both legs. Relations between motor overflow, excitability of ipsilateral motor pathways, and interhemispheric inhibition were assessed. Non-target muscle activity (motor overflow) was greater during isometric and dynamic conditions than rest in both legs (p≤0.001) and was higher in the non-paretic than the paretic leg (p=0.03). Some participants (25%) had motor overflow >4SD above the group mean in the non-paretic leg. Greater motor overflow in the non-paretic leg was associated with lesser inhibition from the ipsilesional to the contralesional hemisphere (p=0.04). In both legs, non-target TMS responses were greater during the isometric and dynamic than the rest condition (p≤0.01), but not when normalized to background muscle activity. Overall, motor overflow occurred in both legs after stroke, suggesting a common bilateral mechanism. Our correlational results suggest that alterations in interhemispheric inhibition may contribute to motor overflow. Furthermore, the lack of differences in non-target MEPs between rest, isometric, and dynamic conditions, suggests that subcortical and/or spinal pathways may contribute to motor overflow.

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.

Effects of Repetitive Peripheral Sensory Stimulation in the Subacute and Chronic Phases After Stroke: Study Protocol for a Pilot Randomized Trial

Background

Repetitive peripheral nerve sensory stimulation (RPSS) is a potential add-on intervention to motor training for rehabilitation of upper limb paresis after stroke. Benefits of RPSS were reported in subjects in the chronic phase after stroke, but there is limited information about the effects of this intervention within the 1st weeks or months. The primary goal of this study is to compare, in a head-to-head proof-of-principle study, the impact of a single session of suprasensory vs. subsensory RPSS on the upper limb motor performance and learning in subjects at different phases after stroke subacute and chronic phases and mild upper limb motor impairments after stroke. In addition, we examine the effects of RPSS on brain perfusion, functional imaging activation, and γ-aminobutyric acid (GABA) levels. Subjects with mild upper limb motor impairments will be tested with MRI and clinical assessment either at an early (7 days to 3 months post-stroke) or at a chronic (>6 months) stage after stroke.

Methods

In this multicenter, randomized, parallel-group, proof-of-principle clinical trial with blinded assessment of outcomes, we compare the effects of one session of suprasensory or subsensory RPSS in patients with ischemic or hemorrhagic stroke and upper limb paresis. Clinical assessment and MRI will be performed only once in each subject (either at an early or at a chronic stage). The primary outcome is the change in performance in the Jebsen–Taylor test. Secondary outcomes: hand strength, cerebral blood flow assessed with arterial spin labeling, changes in the blood oxygenation level-dependent (BOLD) effect in ipsilesional and contralesional primary motor cortex (M1) on the left and the right hemispheres assessed with functional MRI (fMRI) during a finger-tapping task performed with the paretic hand, and changes in GABA levels in ipsilesional and contralesional M1 evaluated with spectroscopy. The changes in outcomes will be compared in four groups: suprasensory, early; subsensory, early; suprasensory, chronic; and subsensory, chronic.

Discussion

The results of this study are relevant to inform future clinical trials to tailor RPSS to patients more likely to benefit from this intervention.

Trial Registration

NCT03956407.

Efficacy of mechanisms of neuroplasticity after a stroke

BACKGROUND

The sequelae of stoke, including the loss and recovery of function, are strongly linked to the mechanisms of neuroplasticity. Rehabilitation and non-invasive brain stimulation (NIBS) paradigms have shown promise in modulating corticomotor neuroplasticity to promote functional recovery in individuals post-stroke. However, an important limitation to these approaches is that while stroke recovery depends on the mechanisms of neuroplasticity, those mechanisms may themselves be altered by a stroke.

OBJECTIVE

Compare Transcranial Magnetic Stimulation (TMS)-based assessments of efficacy of mechanism of neuroplasticity between individuals post-stroke and age-matched controls.

METHODS

Thirty-two participants (16 post-stroke, 16 control) underwent an assessment of mechanisms of neuroplasticity, measured by the change in amplitude of motor evoked potentials elicited by single-pulse TMS 10-20 minutes following intermittent theta-burst stimulation (iTBS), and dual-task effect (DTE) reflecting cognitive-motor interference (CMI). In stroke participants, we further collected: time since stroke, stroke type, location, and Stroke Impact Scale 16 (SIS-16).

RESULTS

Although there was no between-group difference in the efficacy of TMS-iTBS neuroplasticity mechanism (p = 0.61, η2 = 0.01), the stroke group did not exhibit the expected facilitation to TMS-iTBS (p = 0.60, η2 = 0.04) that was shown in the control group (p = 0.016, η2 = 0.18). Sub-cohort analysis showed a trend toward a difference between those in the late-stage post-stroke and the control group (p = 0.07, η2 = 0.12). Within the post-stroke group, we found significant relationships between TMS-iTBS neuroplasticity and time since stroke onset, physical function (SIS-16), and CMI (all rs > |0.53| and p-values < 0.05).

CONCLUSIONS

In this proof-of-principle study, our findings suggested altered mechanisms of neuroplasticity in post-stroke patients which were dependent on time since stroke and related to motor function. TMS-iTBS neuroplasticity assessment and its relationship with clinical functional measures suggest that TMS may be a useful tool to study post-stroke recovery. Due to insufficient statistical power and high variability of the data, generalization of the findings will require replication of the results in a larger, better-characterized cohort.

Effects of Combining Online Anodal Transcranial Direct Current Stimulation and Gait Training in Stroke Patients: A Systematic Review and Meta-Analysis

Objective: Combining transcranial direct current stimulation (tDCS) and repetitive gait training may be effective for gait performance recovery after stroke; however, the timing of stimulation to obtain the best outcomes remains unclear. We performed a systematic review and meta-analysis to establish evidence for changes in gait performance between online stimulation (tDCS and repetitive gait training simultaneously) and offline stimulation (gait training after tDCS). Methods: We comprehensively searched the electronic databases Medline, Cochrane Central Register of Controlled Trials, Physiotherapy Evidence Database, and Cumulative Index to Nursing and Allied Health Literature, and included studies that combined cases of anodal tDCS with motor-related areas of the lower limbs and gait training. Nine studies fulfilled the inclusion criteria and were included in the systematic review, of which six were included in the meta-analysis. Result: The pooled effect estimate showed that anodal tDCS significantly improved the 10-m walking test (p = 0.04; I ² = 0%) and 6-min walking test (p = 0.001; I ² = 0%) in online stimulation compared to sham tDCS. Conclusion: Our findings suggested that simultaneous interventions may effectively improve walking ability. However, we cannot draw definitive conclusions because of the small sample size. More high-quality studies are needed on the effects of online stimulation, including various stimulation parameters.

Peak Activation Shifts in the Sensorimotor Cortex of Chronic Stroke Patients Following Robot-assisted Rehabilitation Therapy

Background:

Ischemic stroke is the most common cause of complex chronic disability and the third leading cause of death worldwide. In recovering stroke patients, peak activation within the ipsilesional primary motor cortex (M1) during the performance of a simple motor task has been shown to exhibit an anterior shift in many studies and a posterior shift in other studies.

Objective:

We investigated this discrepancy in chronic stroke patients who completed a robot-assisted rehabilitation therapy program.

Methods:

Eight chronic stroke patients with an intact M1 and 13 Healthy Control (HC) volunteers underwent 300 functional magnetic resonance imaging (fMRI) scans while performing a grip task at different force levels with a robotic device. The patients were trained with the same robotic device over a 10-week intervention period and their progress was evaluated serially with the Fugl-Meyer and Modified Ashworth scales. Repeated measure analyses were used to assess group differences in locations of peak activity in the sensorimotor cortex (SM) and the relationship of such changes with scores on the Fugl-Meyer Upper Extremity (FM UE) scale.

Results:

Patients moving their stroke-affected hand had proportionally more peak activations in the primary motor area and fewer peak activations in the somatosensory cortex than the healthy controls (P=0.009). They also showed an anterior shift of peak activity on average of 5.3-mm (P<0.001). The shift correlated negatively with FM UE scores (P=0.002).

Conclusion:

A stroke rehabilitation grip task with a robotic device was confirmed to be feasible during fMRI scanning and thus amenable to be used to assess plastic changes in neurological motor activity. Location of peak activity in the SM is a promising clinical neuroimaging index for the evaluation and monitoring of chronic stroke patients.

Contralesional Cathodal Transcranial Direct Current Stimulation Does Not Enhance Upper Limb Function in Subacute Stroke: A Pilot Randomized Clinical Trial

Transcranial direct current stimulation (tDCS) has the potential to improve upper limb motor outcomes after stroke. According to the assumption of interhemispheric inhibition, excessive inhibition from the motor cortex of the unaffected hemisphere to the motor cortex of the affected hemisphere may worsen upper limb motor recovery after stroke. We evaluated the effects of active cathodal tDCS of the primary motor cortex of the unaffected hemisphere (ctDCSM1_UH) compared to sham, in subjects within 72 hours to 6 weeks post ischemic stroke. Cathodal tDCS was intended to inhibit the motor cortex of the unaffected hemisphere and hence decrease the inhibition from the unaffected to the affected hemisphere and enhance motor recovery. We hypothesized that motor recovery would be greater in the active than in the sham group. In addition, greater motor recovery in the active group might be associated with bigger improvements in measures in activity and participation in the active than in the sham group. We also explored, for the first time, changes in cognition and sleep after ctDCSM1_UH. Thirty subjects were randomized to six sessions of either active or sham ctDCSM1_UH as add-on interventions to rehabilitation. The NIH Stroke Scale (NIHSS), Fugl-Meyer Assessment of Motor Recovery after Stroke (FMA), Barthel Index (BI), Stroke Impact Scale (SIS), and Montreal Cognitive Assessment (MoCA) were assessed before, after treatment, and three months later. In the intent-to-treat (ITT) analysis, there were significant GROUP∗TIME interactions reflecting stronger gains in the sham group for scores in NIHSS, FMA, BI, MoCA, and four SIS domains. At three months post intervention, the sham group improved significantly compared to posttreatment in FMA, NIHSS, BI, and three SIS domains while no significant changes occurred in the active group. Also at three months, NIHSS improved significantly in the sham group and worsened significantly in the active group. FMA scores at baseline were higher in the active than in the sham group. After adjustment of analysis according to baseline scores, the between-group differences in FMA changes were no longer statistically significant. Finally, none of the between-group differences in changes in outcomes after treatment were considered clinically relevant. In conclusion, active CtDCSM1_UH did not have beneficial effects, compared to sham. These results were consistent with other studies that applied comparable tDCS intensities/current densities or treated subjects with severe upper limb motor impairments during the first weeks post stroke. Dose-finding studies early after stroke are necessary before planning larger clinical trials.

Mapping causal circuit dynamics in stroke using simultaneous electroencephalography and transcranial magnetic stimulation

BACKGROUND

Motor impairment after stroke is due not only to direct tissue loss but also to disrupted connectivity within the motor network. Mixed results from studies attempting to enhance motor recovery with Transcranial Magnetic Stimulation (TMS) highlight the need for a better understanding of both connectivity after stroke and the impact of TMS on this connectivity. This study used TMS-EEG to map the causal information flow in the motor network of healthy adult subjects and define how stroke alters these circuits.

METHODS

Fourteen stroke patients and 12 controls received TMS to two sites (bilateral primary motor cortices) during two motor tasks (paretic/dominant hand movement vs. rest) while EEG measured the cortical response to TMS pulses. TMS-EEG based connectivity measurements were derived for each hemisphere and the change in connectivity (ΔC) between the two motor tasks was calculated. We analyzed if ΔC for each hemisphere differed between the stroke and control groups or across TMS sites, and whether ΔC correlated with arm function in stroke patients.

RESULTS

Right hand movement increased connectivity in the left compared to the right hemisphere in controls, while hand movement did not significantly change connectivity in either hemisphere in stroke. Stroke patients with the largest increase in healthy hemisphere connectivity during paretic hand movement had the best arm function.

CONCLUSIONS

TMS-EEG measurements are sensitive to movement-induced changes in brain connectivity. These measurements may characterize clinically meaningful changes in circuit dynamics after stroke, thus providing specific targets for trials of TMS in post-stroke rehabilitation.

White matter integrity of contralesional and transcallosal tracts may predict response to upper limb task-specific training in chronic stroke

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Increase in upper limb function post task specific training in chronic stroke.

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Motor improvements were not accompanied by changes in white matter integrity.

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Integrity in contralesional fibers predicted larger motor recovery in Responders.

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Non-responders had more severe damage of transcallosal fibers than Responders.

Objective

To investigate white matter (WM) plasticity induced by intensive upper limb (UL) task specific training (TST) in chronic stroke.

Methods

Diffusion tensor imaging data and UL function measured by the Action Research Arm Test (ARAT) were collected in 30 individuals with chronic stroke prior to and after intensive TST. ANOVAs tested the effects of training on the entire sample and on the Responders [ΔARAT ≥ 5.8, N = 13] and Non-Responders [ΔARAT < 5.8, N = 17] groups. Baseline fractional anisotropy (FA) values were correlated with ARATpost TST controlling for baseline ARAT and age to identify voxels predictive of response to TST. Results.

While ARAT scores increased following training (p < 0.0001), FA changes within major WM tracts were not significant at p < 0.05. In the Responder group, larger baseline FA of both contralesional (CL) and transcallosal tracts predicted larger ARAT scores post-TST. Subcortical lesions and more severe damage to transcallosal tracts were more pronounced in the Non-Responder than in the Responder group.

Conclusions

The motor improvements post-TST in the Responder group may reflect the engagement of interhemispheric processes not available to the Non-Responder group. Future studies should clarify differences in the role of CL and transcallosal pathways as biomarkers of recovery in response to training for individuals with cortical and subcortical stroke. This knowledge may help to identify sources of heterogeneity in stroke recovery, which is necessary for the development of customized rehabilitation interventions.

Neurostimulation for Stroke Rehabilitation

Neurological injuries such as strokes can lead to important loss in motor function. Thanks to neuronal plasticity, some of the lost functionality may be recovered over time. However, the recovery process is often slow and incomplete, despite the most effective conventional rehabilitation therapies. As we improve our understanding of the rules governing activity-dependent plasticity, neuromodulation interventions are being developed to harness neural plasticity to achieve faster and more complete recovery. Here, we review the principles underlying stimulation-driven plasticity as well as the most commonly used stimulation techniques and approaches. We argue that increased spatiotemporal precision is an important factor to improve the efficacy of neurostimulation and drive a more useful neuronal reorganization. Consequently, closed-loop systems and optogenetic stimulation hold theoretical promise as interventions to promote brain repair after stroke.

Does Cathodal vs. Sham Transcranial Direct Current Stimulation Over Contralesional Motor Cortex Enhance Upper Limb Motor Recovery Post-stroke? A Systematic Review and Meta-analysis

Background: During recovery from stroke, the contralesional motor cortex (M1) may undergo maladaptive changes that contribute to impaired interhemispheric inhibition (IHI). Transcranial direct current stimulation (tDCS) with the cathode over contralesional M1 may inhibit this maladaptive plasticity, normalize IHI, and enhance motor recovery.

Objective: The objective of this systematic review and meta-analysis was to evaluate available evidence to determine whether cathodal tDCS on contralesional M1 enhances motor re-learning or recovery post-stroke more than sham tDCS.

Methods: We searched OVID Medline, Embase, and the Cochrane Central Register of Controlled Trials for participants with stroke (>1 week post-onset) with motor impairment and who received cathodal or sham tDCS to contralesional M1 for one or more sessions. The outcomes included a change in any clinically validated assessment of physical function, activity, or participation, or a change in a movement performance variable (e.g., time, accuracy). A meta-analysis was performed by pooling five randomized controlled trials (RCTs) and comparing the change in Fugl–Meyer upper extremity scores between cathodal and sham tDCS groups.

Results: Eleven studies met the inclusion criteria. Qualitatively, four out of five cross-over design studies and three out of six RCTs reported a significant effect of cathodal vs. sham tDCS. In the quantitative synthesis, cathodal tDCS (n = 65) did not significantly reduce motor impairment compared to sham tDCS (n = 67; standardized mean difference = 0.33, z = 1.79, p = 0.07) with a little observed heterogeneity (I² = 5%).

Conclusions: The effects of cathodal tDCS to contralesional M1 on motor recovery are small and consistent. There may be sub-populations that may respond to this approach; however, further research with larger cohorts is required.

Ipsilateral Motor Pathways and Transcallosal Inhibition During Lower Limb Movement After Stroke

BACKGROUND

Stroke rehabilitation may be improved with a better understanding of the contribution of ipsilateral motor pathways to the paretic limb and alterations in transcallosal inhibition. Few studies have evaluated these factors during dynamic, bilateral lower limb movements, and it is unclear whether they relate to functional outcomes.

OBJECTIVE

Determine if lower limb ipsilateral excitability and transcallosal inhibition after stroke depend on target limb, task, or number of limbs involved, and whether these factors are related to clinical measures.

METHODS

In 29 individuals with stroke, ipsilateral and contralateral responses to transcranial magnetic stimulation were measured in the paretic and nonparetic tibialis anterior during dynamic (unilateral or bilateral ankle dorsiflexion/plantarflexion) and isometric (unilateral dorsiflexion) conditions. Relative ipsilateral excitability and transcallosal inhibition were assessed. Fugl-Meyer, ankle movement accuracy, and walking characteristics were assessed.

RESULTS

Relative ipsilateral excitability was greater during dynamic than isometric conditions in the paretic limb (P ≤ .02) and greater in the paretic than the nonparetic limb during dynamic conditions (P ≤ .004). Transcallosal inhibition was greater in the ipsilesional than contralesional hemisphere (P = .002) and during dynamic than isometric conditions (P = .03). Greater ipsilesional transcallosal inhibition was correlated with better ankle movement accuracy (R² = 0.18, P = .04). Greater contralateral excitability to the nonparetic limb was correlated with improved walking symmetry (R² = 0.19, P = .03).

CONCLUSIONS

Ipsilateral pathways have increased excitability to the paretic limb, particularly during dynamic tasks. Transcallosal inhibition is greater in the ipsilesional than contralesional hemisphere and during dynamic than isometric tasks. Ipsilateral pathways and transcallosal inhibition may influence walking asymmetry and ankle movement accuracy.

Ipsilateral motor pathways to the lower limb after stroke: Insights and opportunities

Stroke-related damage to the crossed lateral corticospinal tract causes motor deficits in the contralateral (paretic) limb. To restore functional movement in the paretic limb, the nervous system may increase its reliance on ipsilaterally descending motor pathways, including the uncrossed lateral corticospinal tract, the reticulospinal tract, the rubrospinal tract, and the vestibulospinal tract. Our knowledge about the role of these pathways for upper limb motor recovery is incomplete, and even less is known about the role of these pathways for lower limb motor recovery. Understanding the role of ipsilateral motor pathways to paretic lower limb movement and recovery after stroke may help improve our rehabilitative efforts and provide alternate solutions to address stroke-related impairments. These advances are important because walking and mobility impairments are major contributors to long-term disability after stroke, and improving walking is a high priority for individuals with stroke. This perspective highlights evidence regarding the contributions of ipsilateral motor pathways from the contralesional hemisphere and spinal interneuronal pathways for paretic lower limb movement and recovery. This perspective also identifies opportunities for future research to expand our knowledge about ipsilateral motor pathways and provides insights into how this information may be used to guide rehabilitation.

From adults to pediatrics: A review noninvasive brain stimulation (NIBS) to facilitate recovery from brain injury

Stroke is a major problem worldwide that impacts over 100 million adults and children annually. Rehabilitation therapy is the current standard of care to restore functional impairments post-stroke, however its effects are limited and many patients suffer persisting functional impairments and life-long disability. Noninvasive Brain Stimulation (NIBS) has emerged as a potential rehabilitation treatment option in both adults and children with brain injury. In the last decade, Transcranial Magnetic Stimulation (TMS), Transcranial Direct Current Stimulation (tDCS) and Transcutaneous Auricular Vagus Nerve Stimulation (taVNS) have been investigated to improve motor recovery in adults post-stroke. These promising adult findings using NIBS, however, have yet to be widely translated to the area of pediatrics. The limited studies exploring NIBS in children have demonstrated safety, feasibility, and utility of stimulation-augmented rehabilitation. This chapter will describe the mechanism of NIBS therapy (cortical excitability, neuroplasticity) that underlies its use in stroke and motor function and how TMS, tDCS, and taVNS are applied in adult stroke treatment paradigms. We will then discuss the current state of NIBS in early pediatric brain injury and will provide insight regarding practical considerations and future applications of NIBS in pediatrics to make this promising treatment option a viable therapy in children.

Combining transcranial direct current stimulation with aerobic exercise to optimize cortical priming in stroke

Aerobic exercise (AE) and transcranial direct current stimulation (tDCS) are priming techniques that have been studied for their potential neuromodulatory effects on corticomotor excitability (CME); however, the synergistic effects of AE and tDCS are not explored in stroke. Here we investigated the synergistic effects of AE and tDCS on CME, intracortical and transcallosal inhibition, and motor control for the lower limb in stroke. Twenty-six stroke survivors participated in 3 sessions: tDCS, AE, and AE+tDCS. AE included moderate-intensity exercise and tDCS included 1 mA of anodal tDCS to the lower limb motor cortex with or without AE. Outcomes included measures of CME, short-interval intracortical inhibition (SICI), ipsilateral silent period (iSP) (an index of transcallosal inhibition) for the tibialis anterior, and ankle reaction time. Ipsilesional CME significantly decreased for AE compared with AE+tDCS and tDCS. No differences were noted in SICI, iSP measures, or reaction time between all 3 sessions. Our findings suggest that a combination of exercise and tDCS, and tDCS demonstrate greater excitability of the ipsilesional hemisphere compared with exercise only; however, these effects were specific to the descending corticomotor pathways. No additive priming effects of exercise and tDCS over tDCS was observed. Novelty: An exercise and tDCS paradigm upregulated the descending motor pathways from the ipsilesional lower limb primary motor cortex compared with exercise. Exercise or tDCS administered alone or in combination did not affect intracortical or transcallosal inhibition or reaction time.

Cortical priming strategies for gait training after stroke: a controlled, stratified trial

BACKGROUND

Stroke survivors experience chronic gait impairments, so rehabilitation has focused on restoring ambulatory capacity. High-intensity speed-based treadmill training (HISTT) is one form of walking rehabilitation that can improve walking, but its effectiveness has not been thoroughly investigated. Additionally, cortical priming with transcranial direct current stimulation (tDCS) and movement may enhance HISTT-induced improvements in walking, but there have been no systematic investigations. The objective of this study was to determine if motor priming can augment the effects of HISTT on walking in chronic stroke survivors.

METHODS

Eighty-one chronic stroke survivors participated in a controlled trial with stratification into four groups: 1) control-15 min of rest (n = 20), 2) tDCS-15 min of stimulation-based priming with transcranial direct current stimulation (n = 21), 3) ankle motor tracking (AMT)-15 min of movement-based priming with targeted movements of the ankle and sham tDCS (n = 20), and 4) tDCS+AMT-15 min of concurrent tDCS and AMT (n = 20). Participants performed 12 sessions of HISTT (40 min/day, 3 days/week, 4 weeks). Primary outcome measure was walking speed. Secondary outcome measures included corticomotor excitability (CME). Outcomes were measured at pre, post, and 3-month follow-up assessments.

RESULTS

HISTT improved walking speed for all groups, which was partially maintained 3 months after training. No significant difference in walking speed was seen between groups. The tDCS+AMT group demonstrated greater changes in CME than other groups. Individuals who demonstrated up-regulation of CME after tDCS increased walking speed more than down-regulators.

CONCLUSIONS

Our results support the effectiveness of HISTT to improve walking; however, motor priming did not lead to additional improvements. Upregulation of CME in the tDCS+AMT group supports a potential role for priming in enhancing neural plasticity. Greater changes in walking were seen in tDCS up-regulators, suggesting that responsiveness to tDCS might play an important role in determining the capacity to respond to priming and HISTT.

TRIAL REGISTRATION

ClinicalTrials.gov , NCT03492229. Registered 10 April 2018 - retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT03492229 .

Interhemispheric asymmetry of the motor cortex excitability in stroke: relationship with sensory-motor impairment and injury chronicity

OBJECTIVE

To compare the interhemispheric asymmetry of the motor cortex excitability of chronic stroke patients with healthy and to observe if the magnitude of this asymmetry is associated to sensory-motor impairment and stroke chronicity.

METHODS

This cross-sectional study was performed with chronic stroke and aged and sex-matched healthy individuals. The interhemispheric asymmetry index was calculated by the difference of rest motor threshold (rMT) of the brain hemispheres. The rMT was assessed by transcranial magnetic stimulation over the cortical representation of the first dorsal interosseous muscle. To investigate the relationship of the asymmetry with sensory-motor impairment and injury chronicity, the stroke patients were grouped according to the level of sensory-motor impairment (mild/moderate, moderate/severe, and severe) and different chronicity stages (> 3-12, 13-24, 25-60, and > 60 months since stroke).

RESULTS

Fifty-six chronic stroke and twenty-six healthy were included. We found higher interhemispheric asymmetry in stroke patients (mean, 27.1 ± 20.9) compared to healthy (mean, 4.9 ± 4.7). The asymmetry was higher in patients with moderate/severe (mean, 35.4 ± 20.4) and severe (mean, 32.9 ± 22.7) impairment. No difference was found between patients with mild/moderate impairment (mean, 15.5 ± 12.5) and healthy. There were no differences of the interhemispheric asymmetry between patients with different times since stroke (> 3-12, mean, 32 ± 18.1; > 13-24, mean, 20.7 ± 16.2; > 25-60, mean, 29.6 ± 18.1; > 60 months, mean, 25.9 ± 17.5).

CONCLUSION

Stroke patients showed higher interhemispheric asymmetry of the motor cortex excitability when compared to healthy, and the magnitude of this asymmetry seems to be correlated with the severity of sensory-motor impairment, but not with stroke chronicity.

SIGNIFICANCE

Higher interhemispheric asymmetry was found in stroke patients with greatest sensory-motor impairment.

Possible Contributions of Ipsilateral Pathways From the Contralesional Motor Cortex to the Voluntary Contraction of the Spastic Elbow Flexors in Stroke Survivors: A TMS Study

OBJECTIVE

The contribution of the contralesional motor cortex to the impaired limbs is still controversial. The aim of this study was to investigate the role of descending projections from the contralesional hemisphere during voluntary elbow flexion on the paretic side.

DESIGN

Eleven healthy and 10 stroke subjects performed unilateral isometric elbow flexion tasks at various submaximal levels. Transcranial magnetic stimulation was delivered to the hotspot of biceps muscles ipsilateral to the target side (paretic side in stroke subjects or right side in controls) at rest and during elbow flexion tasks. Motor-evoked potential amplitudes of the contralateral resting biceps muscles, transcranial magnetic stimulation-induced ipsilateral force increment, and reflex torque and weakness of spastic elbow flexors were quantified.

RESULTS

The normalized motor-evoked potential amplitude increased with force level in both healthy and stroke subjects. However, stroke subjects exhibited significantly higher force increment compared with healthy subjects only at low level of elbow flexion but similar at moderate to high levels. The greater force increment significantly correlated with reflex torque of the spastic elbow flexors, but not weakness.

CONCLUSIONS

These results provide novel evidence that ipsilateral projections are not likely to contribute to strength but are correlated to spasticity of spastic-paretic elbow flexors after stroke.

Contralesional motor cortex is causally engaged during more dexterous actions of the paretic hand after stroke-A Preliminary report

Bilateral activation in motor cortex is observed during paretic hand performance after stroke; however the functional significance of contralesional motor cortex (C-M1) activation is highly debated. Particularly, it is not known if task characteristics such as dexterity influence the causal engagement of C-M1 during paretic hand performance. Transcranial magnetic stimulation (TMS) was used to quantify motor corticospinal physiology of the CM1 projecting to the contralateral resting extensor carpi radialis brevis (ECRB) and first dorsal interosseous (FDI) while eleven participants with unilateral stroke performed unimanual tasks of differing dexterity with their paretic hand. The novel finding was that compared to rest and less dexterous task (LDT), more dexterous task (MDT) performance led to increased corticospinal excitability and decreased intracortical inhibition of the C-M1 projecting to the resting FDI, but not resting ECRB. Further, using trains of repetitive TMS during MDT and LDT, we tested the behavioral relevance of C-M1 for paretic hand performance. Online rTMS perturbation to C-M1, but not to the vertex or sham stimulation led to significantly more movement errors during MDT without consistently affecting LDT performance. The present results argue for a beneficial role of C-M1 for accurate performance during dexterous motor actions with the paretic hand after stroke.

Individualized functional networks reconfigure with cognitive state

There is extensive evidence that functional organization of the human brain varies dynamically as the brain switches between task demands, or cognitive states. This functional organization also varies across subjects, even when engaged in similar tasks. To date, the functional network organization of the brain has been considered static. In this work, we use fMRI data obtained across multiple cognitive states (task-evoked and rest conditions) and across multiple subjects, to measure state- and subject-specific functional network parcellation (the assignment of nodes to networks). Our parcellation approach provides a measure of how node-to-network assignment (NNA) changes across states and across subjects. We demonstrate that the brain's functional networks are not spatially fixed, but that many nodes change their network membership as a function of cognitive state. Such reconfigurations are highly robust and reliable to the extent that they can be used to predict cognitive state with up to 97% accuracy. Our findings suggest that if functional networks are to be defined via functional clustering of nodes, then it is essential to consider that such definitions may be fluid and cognitive-state dependent.

Learning a Bimanual Cooperative Skill in Chronic Stroke Under Noninvasive Brain Stimulation: A Randomized Controlled Trial

Background. Transcranial direct current stimulation (tDCS) has been suggested to improve poststroke recovery. However, its effects on bimanual motor learning after stroke have not previously been explored. Objective. We investigated whether dual-tDCS of the primary motor cortex (M1), with cathodal and anodal tDCS applied over undamaged and damaged hemispheres, respectively, improves learning and retention of a new bimanual cooperative motor skill in stroke patients. Method. Twenty-one chronic hemiparetic patients were recruited for a randomized, double-blinded, cross-over, sham-controlled trial. While receiving real or sham dual-tDCS, they trained on a bimanual cooperative task called CIRCUIT. Changes in performance were quantified via bimanual speed/accuracy trade-off (Bi-SAT) and bimanual coordination factor (Bi-Co) before, during, and 0, 30, and 60 minutes after dual-tDCS, as well as one week later to measure retention. A generalization test then followed, where patients were asked to complete a new CIRCUIT layout. Results. The patients were able to learn and retain the bimanual cooperative skill. However, a general linear mixed model did not detect a significant difference in retention between the real and sham dual-tDCS conditions for either Bi-SAT or Bi-Co. Similarly, no difference in generalization was detected for Bi-SAT or Bi-Co. Conclusion. The chronic hemiparetic stroke patients learned and retained the complex bimanual cooperative task and generalized the newly acquired skills to other tasks, indicating that bimanual CIRCUIT training is promising as a neurorehabilitation approach. However, bimanual motor skill learning was not enhanced by dual-tDCS in these patients.

Is There a Future for Non-invasive Brain Stimulation as a Therapeutic Tool?

Several techniques and protocols of non-invasive transcranial brain stimulation (NIBS), including transcranial magnetic and electrical stimuli, have been developed in the past decades. These techniques can induce long lasting changes in cortical excitability by promoting synaptic plasticity and thus may represent a therapeutic option in neuropsychiatric disorders. On the other hand, despite these techniques have become popular, the fragility and variability of the after effects are the major challenges that non-invasive transcranial brain stimulation currentlyfaces. Several factors may account for such a variability such as biological variations, measurement reproducibility, and the neuronal state of the stimulated area. One possible strategy, to reduce this variability is to monitor the neuronal state in real time using EEG and trigger TMS pulses only at pre-defined state. In addition, another strategy under study is to use the spaced application of multiple NIBS protocols within a session to improve the reliability and extend the duration of NIBS effects. Further studies, although time consuming, are required for improving the so far limited effect sizes of NIBS protocols for treatment of neurological or psychiatric disorders.

Home-based transcranial direct current stimulation plus tracking training therapy in people with stroke: an open-label feasibility study

Background

Transcranial direct current stimulation (tDCS) is an effective neuromodulation adjunct to repetitive motor training in promoting motor recovery post-stroke. Finger tracking training is motor training whereby people with stroke use the impaired index finger to trace waveform-shaped lines on a monitor. Our aims were to assess the feasibility and safety of a telerehabilitation program consisting of tDCS and finger tracking training through questionnaires on ease of use, adverse symptoms, and quantitative assessments of motor function and cognition. We believe this telerehabilitation program will be safe and feasible, and may reduce patient and clinic costs.

Methods

Six participants with hemiplegia post-stroke [mean (SD) age was 61 (10) years; 3 women; mean (SD) time post-stroke was 5.5 (6.5) years] received five 20-min tDCS sessions and finger tracking training provided through telecommunication. Safety measurements included the Digit Span Forward Test for memory, a survey of symptoms, and the Box and Block test for motor function. We assessed feasibility by adherence to treatment and by a questionnaire on ease of equipment use. We reported descriptive statistics on all outcome measures.

Results

Participants completed all treatment sessions with no adverse events. Also, 83.33% of participants found the set-up easy, and all were comfortable with the devices. There was 100% adherence to the sessions and all recommended telerehabilitation.

Conclusions

tDCS with finger tracking training delivered through telerehabilitation was safe, feasible, and has the potential to be a cost-effective home-based therapy for post-stroke motor rehabilitation.

Trial registration

NCT02460809 (ClinicalTrials.gov).

Modulation of Cerebellar Cortical Plasticity Using Low-Intensity Focused Ultrasound for Poststroke Sensorimotor Function Recovery

BACKGROUND

Stroke affects widespread brain regions through interhemispheric connections by influencing bilateral motor activity. Several noninvasive brain stimulation techniques have proved their capacity to compensate the functional loss by manipulating the neural activity of alternative pathways. Over the past few decades, brain stimulation therapies have been tailored within the theoretical framework of modulation of cortical excitability to enhance adaptive plasticity after stroke.

OBJECTIVE

However, considering the vast difference between animal and human cerebral cortical structures, it is important to approach specific neuronal target starting from the higher order brain structure for human translation. The present study focuses on stimulating the lateral cerebellar nucleus (LCN), which sends major cerebellar output to extensive cortical regions.

METHODS

In this study, in vivo stroke mouse LCN was exposed to low-intensity focused ultrasound (LIFU). After the LIFU exposure, animals underwent 4 weeks of rehabilitative training.

RESULTS

During the cerebellar LIFU session, motor-evoked potentials (MEPs) were generated in both forelimbs accompanying excitatory sonication parameter. LCN stimulation group on day 1 after stroke significantly enhanced sensorimotor recovery compared with the group without stimulation. The recovery has maintained for a 4-week period in 2 behavior tests. Furthermore, we observed a significantly decreased level of brain edema and tissue swelling in the affected hemisphere 3 days after the stroke.

CONCLUSIONS

This study provides the first evidence showing that LIFU-induced cerebellar modulation could be an important strategy for poststroke recovery. A longer follow-up study is, however, necessary in order to fully confirm the effects of LIFU on poststroke recovery.

Bilateral Motor Cortex Plasticity in Individuals With Chronic Stroke, Induced by Paired Associative Stimulation

Background: In the chronic phase after stroke, cortical excitability differs between the cerebral hemispheres; the magnitude of this asymmetry depends on degree of motor impairment. It is unclear whether these asymmetries also affect capacity for plasticity in corticospinal tract excitability or whether hemispheric differences in plasticity are related to chronic sensorimotor impairment. Methods: Response to paired associative stimulation (PAS) was assessed bilaterally in 22 individuals with chronic hemiparesis. Corticospinal excitability was measured as the area under the motor-evoked potential (MEP) recruitment curve (AUC) at baseline, 5 minutes, and 30 minutes post-PAS. Percentage change in contralesional AUC was calculated and correlated with paretic motor and somatosensory impairment scores. Results: PAS induced a significant increase in AUC in the contralesional hemisphere ( P = .041); in the ipsilesional hemisphere, there was no significant effect of PAS ( P = .073). Contralesional AUC showed significantly greater change in individuals without an ipsilesional MEP ( P = .029). Percentage change in contralesional AUC between baseline and 5 m post-PAS correlated significantly with FM score ( r = −0.443; P = .039) and monofilament thresholds ( r = 0.444, P = .044). Discussion: There are differential responses to PAS within each cerebral hemisphere. Contralesional plasticity was increased in individuals with more severe hemiparesis, indicated by both the absence of an ipsilesional MEP and a greater degree of motor and somatosensory impairment. These data support a body of research showing compensatory changes in the contralesional hemisphere after stroke; new therapies for individuals with chronic stroke could exploit contralesional plasticity to help restore function.

Combining robotic training and inactivation of the healthy hemisphere restores pre-stroke motor patterns in mice

Focal cortical stroke often leads to persistent motor deficits, prompting the need for more effective interventions. The efficacy of rehabilitation can be increased by ‘plasticity-stimulating’ treatments that enhance experience-dependent modifications in spared areas. Transcallosal pathways represent a promising therapeutic target, but their role in post-stroke recovery remains controversial. Here, we demonstrate that the contralesional cortex exerts an enhanced interhemispheric inhibition over the perilesional tissue after focal cortical stroke in mouse forelimb motor cortex. Accordingly, we designed a rehabilitation protocol combining intensive, repeatable exercises on a robotic platform with reversible inactivation of the contralesional cortex. This treatment promoted recovery in general motor tests and in manual dexterity with remarkable restoration of pre-lesion movement patterns, evaluated by kinematic analysis. Recovery was accompanied by a reduction of transcallosal inhibition and ‘plasticity brakes’ over the perilesional tissue. Our data support the use of combinatorial clinical therapies exploiting robotic devices and modulation of interhemispheric connectivity.

Multisensory stimulation improves functional recovery and resting-state functional connectivity in the mouse brain after stroke

Stroke causes direct structural damage to local brain networks and indirect functional damage to distant brain regions. Neuroplasticity after stroke involves molecular changes within perilesional tissue that can be influenced by regions functionally connected to the site of injury. Spontaneous functional recovery can be enhanced by rehabilitative strategies, which provides experience-driven cell signaling in the brain that enhances plasticity. Functional neuroimaging in humans and rodents has shown that spontaneous recovery of sensorimotor function after stroke is associated with changes in resting-state functional connectivity (RS-FC) within and across brain networks. At the molecular level, GABAergic inhibitory interneurons can modulate brain plasticity in peri-infarct and remote brain regions. Among this cell-type, a decrease in parvalbumin (PV)-immunoreactivity has been associated with improved behavioral outcome. Subjecting rodents to multisensory stimulation through exposure to an enriched environment (EE) enhances brain plasticity and recovery of function after stroke. Yet, how multisensory stimulation relates to RS-FC has not been determined. In this study, we investigated the effect of EE on recovery of RS-FC and behavior in mice after stroke, and if EE-related changes in RS-FC were associated with levels of PV-expressing neurons. Photothrombotic stroke was induced in the sensorimotor cortex. Beginning 2 days after stroke, mice were housed in either standard environment (STD) or EE for 12 days. Housing in EE significantly improved lost tactile-proprioceptive function compared to mice housed in STD environment. RS-FC in the mouse was measured by optical intrinsic signal imaging 14 days after stroke or sham surgery. Stroke induced a marked reduction in RS-FC within several perilesional and remote brain regions. EE partially restored interhemispheric homotopic RS-FC between spared motor regions, particularly posterior secondary motor. Compared to mice housed in STD cages, EE exposure lead to increased RS-FC between posterior secondary motor regions and contralesional posterior parietal and retrosplenial regions. The increased regional RS-FC observed in EE mice after stroke was significantly correlated with decreased PV-immunoreactivity in the contralesional posterior motor region. In conclusion, experimental stroke and subsequent housing in EE induces dynamic changes in RS-FC in the mouse brain. Multisensory stimulation associated with EE enhances RS-FC among distinct brain regions relevant for recovery of sensorimotor function and controlled movements that may involve PV/GABA interneurons. Our results indicate that targeting neural circuitry involving spared motor regions across hemispheres by neuromodulation and multimodal sensory stimulation could improve rehabilitation after stroke.

Revisiting interhemispheric imbalance in chronic stroke: A tDCS study

OBJECTIVE

Chronic stroke patients with moderate-severe motor impairment may have an increased reliance on contralesional vs ipsilesional motor areas to control the paretic arm. We hypothesised that increasing contralesional excitability with anodal transcranial direct current stimulation (a-tDCS) would benefit motor performance in patients with moderate-severe impairment.

METHODS

Ten patients with motor impairment at the chronic stage after stroke received a-tDCS, cathodal (c-tDCS) and sham with the target electrode over contralesional motor cortex (M1). Motor performance was quantified from the circularity and size of planar movements made with the paretic arm. Contralateral and ipsilateral corticospinal excitability was inferred using transcranial magnetic stimulation. Corticospinal tract integrity and basal GABA concentration were assessed with magnetic resonance imaging and spectroscopy.

RESULTS

Anodal tDCS increased contralesional corticomotor excitability evident from motor evoked potentials in both wrist extensors (both P<0.043). Cathodal tDCS did not affect corticomotor excitability (P>0.37). The effect of tDCS on motor performance with the paretic limb was negatively associated with ipsilesional GABA concentration after c-tDCS (P=0.001).

CONCLUSIONS

Further investigation of noninvasive brain stimulation protocols that facilitate contralesional M1 is warranted.

SIGNIFICANCE

The inter-hemispheric imbalance model of stroke recovery may not apply to patients with more severe impairment.

Deep brain stimulation for stroke: Current uses and future directions

BACKGROUND

Survivors of stroke often experience significant disability and impaired quality of life related to ongoing maladaptive responses and persistent neurologic deficits. Novel therapeutic options are urgently needed to augment current approaches. One way to promote recovery and ameliorate symptoms may be to electrically stimulate the surviving brain. Various forms of brain stimulation have been investigated for use in stroke, including deep brain stimulation (DBS).

OBJECTIVE/METHODS

We conducted a comprehensive literature review in order to 1) review the use of DBS to treat post-stroke maladaptive responses including pain, dystonia, dyskinesias, and tremor and 2) assess the use and potential utility of DBS for enhancing plasticity and recovery from post-stroke neurologic deficits.

RESULTS/CONCLUSIONS

A large variety of brain structures have been targeted in post-stroke patients, including motor thalamus, sensory thalamus, basal ganglia nuclei, internal capsule, and periventricular/periaqueductal grey. Overall, the reviewed clinical literature suggests a role for DBS in the management of several post-stroke maladaptive responses. More limited evidence was identified regarding DBS for post-stroke motor deficits, although existing work tentatively suggests DBS-particularly DBS targeting the posterior limb of the internal capsule-may improve paresis in certain circumstances. Substantial future work is required both to establish optimal targets and parameters for treatment of maladapative responses and to further investigate the effectiveness of DBS for post-stroke paresis.

Therapeutic Applications of BCI Technologies

Brain-computer interface (BCI) technology can restore communication and control to people who are severely paralyzed. There has been speculation that this technology might also be useful for a variety of diverse therapeutic applications. This survey considers possible ways that BCI technology can be applied to motor rehabilitation following stroke, Parkinson's disease, and psychiatric disorders. We consider potential neural signals as well as the design and goals of BCI-based therapeutic applications. These diverse applications all share a reliance on neuroimaging and signal processing technologies. At the same time, each of these potential applications presents a series of unique challenges.

Inhibition versus facilitation of contralesional motor cortices in stroke: Deriving a model to tailor brain stimulation

OBJECTIVE

The standard approach to brain stimulation in stroke is based on the premise that ipsilesional M1 (iM1) is important for motor function of the paretic upper limb, while contralesional cortices compete with iM1. Therefore, the approach typically advocates facilitating iM1 and/or inhibiting contralesional M1 (cM1). But, this approach fails to elicit much improvement in severely affected patients, who on account of extensive damage to ipsilesional pathways, cannot rely on iM1. These patients are believed to instead rely on the undamaged cortices, especially the contralesional dorsal premotor cortex (cPMd), for support of function of the paretic limb. Here, we tested for the first time whether facilitation of cPMd could improve paretic limb function in severely affected patients, and if a cut-off could be identified to separate responders to cPMd from responders to the standard approach to stimulation.

METHODS

In a randomized, sham-controlled crossover study, fifteen patients received the standard approach of stimulation involving inhibition of cM1 and a new approach involving facilitation of cPMd using repetitive transcranial magnetic stimulation (rTMS). Patients also received rTMS to control areas. At baseline, impairment [Upper Extremity Fugl-Meyer (UEFM_PROXIMAL, max=36)] and damage to pathways [fractional anisotropy (FA)] was measured. We measured changes in time to perform proximal paretic limb reaching, and neurophysiology using TMS.

RESULTS

Facilitation of cPMd generated more improvement in severely affected patients, who had experienced greater damage and impairment than a cut-off value of FA (0.5) and UEFM_PROXIMAL (26-28). The standard approach instead generated more improvement in mildly affected patients. Responders to cPMd showed alleviation of interhemispheric competition imposed on iM1, while responders to the standard approach showed gains in ipsilesional excitability in association with improvement.

CONCLUSIONS

A preliminary cut-off level of severity separated responders for standard approach vs. facilitation of cPMd.

SIGNIFICANCE

Cut-offs identified here could help select candidates for tailored stimulation in future studies so patients in all ranges of severity could potentially achieve maximum benefit in function of the paretic upper limb.