Dynamic Interaction between Cortico-Brainstem Pathways during Training-Induced Recovery in Stroke Model Rats

High-Frequency repetitive transcranial magnetic stimulation enhances white matter integrity in a rat model of ischemic stroke: A diffusion tensor imaging study using tract-based spatial statistics

Ischemic stroke leads to white matter damage and neurological deficits. Previous studies have revealed that high-frequency repetitive transcranial magnetic stimulation (HF-rTMS) has beneficial effects on white matter reorganization and neurological recovery after stroke. However, the characteristics of poststroke white matter repair after treatment with HF-rTMS remain unclear. Therefore, this study used diffusion tensor imaging (DTI) to investigate the impact of HF-rTMS on white matter integrity following middle cerebral artery occlusion (MCAO) in a rat model. The modified neurological severity score (mNSS) and T2-weighted imaging data were used to assess neurological function and infarct size. We used a tract-based spatial statistics (TBSS) approach to analyze changes in fractional anisotropy (FA) across various white matter tracts. Furthermore, we performed Luxol fast blue (LFB) staining and transmission electron microscopy (TEM) to detect white matter and myelin damage. The results revealed that compared with the tMCAO group, the tMCAO+rTMS group presented a significant decrease in infarct size and the mNSS, as well as significantly greater FA values, mostly in the left external capsule, left internal capsule, left optic tract, left deep cerebral white matter, left stria terminalis and right external capsule. The LFB staining and electron microscopy results are consistent with the DTI results. These findings suggest that HF-rTMS contributes to the recovery of white matter integrity and neurological function. This study underscores the importance of HF-rTMS as a noninvasive intervention for enhancing poststroke neurological recovery by improving white matter integrity.

Post-Stroke Recovery in Relation to Parvalbumin-Positive Interneurons and Perineuronal Nets

BACKGROUND

There is a critical time window of post-stroke neuroplasticity when spontaneous behavioral recovery occurs. Potential factors responsible for this heightened plasticity are the reduction of parvalbumin-immunoreactive (PV+) interneuron inhibitory signaling and the disappearance of extracellular matrix synaptic stabilizers called perineuronal net(s; PNN/PNNs).

OBJECTIVE

This study investigated whether behavioral recovery during this critical period following stroke is associated with changes in densities of PV+ interneurons and PNNs.MethodsMale, Sprague-Dawley rats received forelimb motor cortex stroke (n = 43) using endothelin-1, or vehicle injections (n = 44). Cohorts of rats underwent a battery of motor tests and were sacrificed within the post-stroke critical window on day 1, and 1, 2, 4, and 6 weeks. Using immunofluorescent labeling, PNNs (wisteria floribunda agglutinin; WFA+ cells), PV+ interneurons, and cells expressing both PV and PNNs were quantified in contra- and ipsilesional cortices to elucidate their spatial-temporal profiles following stroke.ResultsPV+ interneuron density decreased significantly at 1-day post-stroke in the lateral ipsilesional cortex, while the density of PNNs was significantly lower up to 4 weeks post-stroke in the lateral ipsilesional cortex and at 1 and 2 weeks post-stroke in the medial ipsilesional cortex. Reduction of combined PV+/PNN signaling coincided with spontaneous behavioral recovery.ConclusionsThese results suggest that post-stroke behavioral recovery corresponds to an early reduction in PV+/PNN co-labeled cells in conjunction with an early temporally-dependent reduction in PV+ interneuron signaling and chronic disappearance of PNNs. Interventions targeting PNNs or PV+ interneuron signaling have significant potential for extending the critical window of recovery following stroke.

Developmental molecular signatures define de novo cortico-brainstem circuit for skilled forelimb movement

Skilled movement relies on descending cortical projections to the brainstem and spinal cord. While corticospinal neurons (CSN) have long been recognized for their role in fine motor control, the contribution of cortical projections to the brainstem remains poorly understood. Here, we identify a previously unrecognized direct cortico-brainstem circuit that emerges early in development and persists into adulthood. A subset of subcerebral projection neurons (SCPN) limit their projections to the brainstem from the earliest stages of axon extension without ever extending to the spinal cord. Using FACS purification and single-cell RNA sequencing, we show that these cortico-brainstem neurons (CBN) can be prospectively identified by the expression of Neuropeptide Y (Npy) in development. Functional silencing of Npy+ CBN in adulthood leads to impaired skilled forelimb reaching, demonstrating their essential role in adult motor control. Npy+ CBN project preferentially to rostral brainstem regions, including the midbrain reticular formation. These findings reveal developmental molecular signatures that define cortico-brainstem pathways for adult skilled movement. Our work provides new insights into the developmental logic that establishes descending cortical circuits and opens avenues for targeted investigation of their roles in motor function and recovery after injury.

Constraint-Induced Movement Therapy Promotes Contralesional Red Nucleus Plasticity and Increases Bilateral Motor Cortex-to-Red Nucleus Projections After a Large-Area Stroke

For decades, scientists have explored the patterns of neural network remodeling that occur after a stroke. Several studies have shown that both motor cortexes (MCs) undergo crucial remodeling after cerebral ischemia. However, the mechanism by which corticofugal fibers are remodeled is not well understood. Therefore, this study was aimed at investigating the changes in the bilateral red nucleus (RN) and MC-RN projections during recovery from a large-area stroke in a rat stroke model with or without constraint-induced movement therapy (CIMT). A large-area middle cerebral artery occlusion (MCAO) model was established in rats using the Longa method. CIMT was initiated 7 days after MCAO and continued for 1, 2, or 3 weeks. Rats in the control group underwent spontaneous recovery. Locomotor impairment was evaluated using the CatWalk automated gait analysis system, and overall neurological function was evaluated with the modified neurological severity score. Bilateral MC-RN projections were visualized by labeling fiber tracts with an anterograde tracer. Postsynaptic density 95 (PSD95), growth-associated protein 43 (GAP43), and synaptophysin expression levels in the RN were detected using western blotting and immunohistochemistry. The results showed that CIMT promoted motor recovery after a stroke, increased levels of GAP43 and PSD95 in the contralesional but not ipsilesional RN, and increased projections from the MC to the bilateral RN. Thus, CIMT promotes neuroplasticity after a large-area stroke by stimulating axon outgrowth, improving postsynaptic membrane function in the contralesional RN, and increasing bilateral projections of the MC-RN. These results provide evidence for the therapeutic efficacy of CIMT in restoring motor function and help with understanding RN plasticity after a large-area stroke.

The diversity and plasticity of descending motor pathways rewired after stroke and trauma in rodents

Descending neural pathways to the spinal cord plays vital roles in motor control. They are often damaged by brain injuries such as stroke and trauma, which lead to severe motor impairments. Due to the limited capacity for regeneration of neural circuits in the adult central nervous system, currently no essential treatments are available for complete recovery. Notably, accumulating evidence shows that residual circuits of the descending pathways are dynamically reorganized after injury and contribute to motor recovery. Furthermore, recent technological advances in cell-type classification and manipulation have highlighted the structural and functional diversity of these pathways. Here, we focus on three major descending pathways, namely, the corticospinal tract from the cerebral cortex, the rubrospinal tract from the red nucleus, and the reticulospinal tract from the reticular formation, and summarize the current knowledge of their structures and functions, especially in rodent models (mice and rats). We then review and discuss the process and patterns of reorganization induced in these pathways following injury, which compensate for lost connections for recovery. Understanding the basic structural and functional properties of each descending pathway and the principles of the induction and outcome of the rewired circuits will provide therapeutic insights to enhance interactive rewiring of the multiple descending pathways for motor recovery.

Hyperactive delta isoform of PI3 kinase enables long-distance regeneration of adult rat corticospinal tract

Neurons in the CNS lose regenerative potential with maturity, leading to minimal corticospinal tract (CST) axon regrowth after spinal cord injury (SCI). In young rodents, knockdown of PTEN, which antagonizes PI3K signaling by hydrolyzing PIP3, promotes axon regeneration following SCI. However, this effect diminishes in adults, potentially due to lower PI3K activation leading to reduced PIP3. This study explores whether increased PIP3 generation can promote long-distance regeneration in adults. We used a hyperactive PI3K, PI3Kδ (PIK3CD), to boost PIP3 levels in mature cortical neurons and assessed CST regeneration after SCI. Adult rats received AAV1-PIK3CD and AAV1-eGFP, or AAV1-eGFP alone, in the sensorimotor cortex concurrent with a C4 dorsal SCI. Transduced neurons showed increased pS6 levels, indicating elevated PI3K/Akt/mTOR signaling. CST regeneration, confirmed with retrograde tracing, was evaluated up to 16 weeks post injury. At 12 weeks, ∼100 axons were present at lesion sites, doubling to 200 by 16 weeks, with regeneration indices of 0.1 and 0.2, respectively. Behavioral tests showed significant improvements in paw reaching, grip strength, and ladder-rung walking in PIK3CD-treated rats, corroborated by electrophysiological recordings of cord dorsum potentials and distal flexor muscle electromyography. Thus, PI3Kδ upregulation in adult cortical neurons enhances axonal regeneration and functional recovery post SCI.

Experience-driven competition in neural reorganization after stroke

Behavioural experiences interact with regenerative responses to shape patterns of neural reorganization after stroke. This review is focused on the competitive nature of these behavioural experience effects. Interactions between learning-related plasticity and regenerative reactions have been found to underlie the establishment of new compensatory behaviours and the efficacy of motor rehabilitative training in rodent stroke models. Learning in intact brains depends on competitive and cooperative mechanisms of synaptic plasticity. Synapses are added in response to learning and selectively maintained and strengthened via activity-dependent competition. Long-term memories for experiences that occur closely in time can be weakened or enhanced by competitive or cooperative interactions in the time-dependent process of stabilizing synaptic changes. Rodent stroke model findings suggest that compensatory reliance on the non-paretic hand after stroke can shape and stabilize synaptic reorganization patterns in both hemispheres, to compete with the capacity for experiences of the paretic side to do so. However, the competitive edge of the non-paretic side can be countered by overlapping experiences of the paretic hand, and might even be shifted in a cooperative direction with skilfully coordinated bimanual experience. Advances in the basic understanding of learning-related synaptic competition are helping to inform the basis of experience-dependent variations in stroke outcome.

Remodeling and Characterization Analysis of Corticospinal Tract in Patients with Intracerebral Hemorrhage in the Basal Ganglia

To investigate corticospinal tract (CST) injury and remodeling in patients with basal ganglia intracerebral hemorrhage (ICH) and explore the characterization capabilities of the corresponding parameters. In this prospective study, baseline, scale, and diffusion-weighted imaging (DWI) data were collected from patient cohorts. Participants were stratified into favorable (0-3 points) and unfavorable (4-6 points) prognosis groups, based on Modified Rankin Scale (mRS) after 3-6 months. The analysis of DWI data was conducted employing FSL and DSI Studio software to compare CST injury between the prognosis groups and CST remodeling features. A partial correlation model was deployed to elucidate the characterization capability of CST-related parameters. Additionally, logistic regression analysis was applied to identify factors significantly influencing prognosis. A total of 65 patients were enrolled with a mean age of 53.52 years and a median hematoma volume of 23.60 ml. The 44 patients were classified within the favorable prognosis group, demonstrating a statistically significant difference in their lower mean age (P = 0.002). Additionally, 10 patients underwent DWI review with a mean age of 50.30 years and a median hematoma volume of 18.56 ml. The investigation uncovered evidence of CST damage versus remodeling at the group level, respectively, with statistical significance (FDR-corrected P < 0.05, 10,000 permutations). The fractional anisotropy (FA) ratio in the internal capsule region exhibited moderate correlation with motor function (r = 0.507, P < 0.001) and the 3- to 6-month mRS scores (r =  - 0.318, P < 0.013). Furthermore, binary logistic regression analysis identified the FA rate in the internal capsule as a significant influencing factor of prognosis (odds ratio = 1.027, 95% confidence interval = 1.003-1.052, P = 0.025). Basal ganglia ICH can coincide with injury to the CST, which could undergo repair over time. Additionally, the FA ratio of the internal capsule is a potential biomarker to characterize residual motor function and provide prognostic information.

Corticospinal and corticoreticulospinal projections have discrete but complementary roles in chronic motor behaviors after stroke

After corticospinal tract (CST) stroke, several motor deficits can emerge in the upper extremity (UE), including diminished muscle strength, motor control, and muscle individuation. Both the ipsilesional CST and contralesional corticoreticulospinal tract (CReST) innervate the paretic UE, but their relationship to motor behaviors after stroke remains uncertain. In this cross-sectional study of 14 chronic stroke and 27 healthy subjects, we examined two questions: whether the ipsilesional CST and contralesional CReST differentially relate to chronic motor behaviors in the paretic arm and hand and whether the severity of motor deficits differs by proximal versus distal location. In the paretic biceps and first dorsal interosseous muscles, we used transcranial magnetic stimulation to measure the projection strengths of the ipsilesional CST and contralesional CReST. We also used quantitative testing to measure strength, motor control, and muscle individuation in each muscle. We found that stroke subjects had muscle strength comparable to healthy subjects but poorer motor control and muscle individuation. In both paretic muscles, stronger ipsilesional CST projections related to better motor control, whereas stronger contralesional CReST projections related to better muscle strength. Stronger CST projections related to better individuation in the biceps alone. The severity of motor control and individuation deficits was comparable in the arm and hand. These findings suggest that the ipsilesional CST and contralesional CReST have specialized but complementary roles in motor behaviors of the paretic arm and hand. They also suggest that deficits in motor control and muscle individuation are not segmentally biased, underscoring the functional extent and efficacy of these pathways.NEW & NOTEWORTHY The corticospinal (CST) and corticoreticulospinal (CReST) tracts are two major descending motor pathways. We examined their relationships to motor behaviors in paretic arm and hand muscles in chronic stroke. Stronger ipsilesional CST projections related to better motor control, whereas stronger contralesional CReST projections related to better muscle strength. Stronger CST projections are also uniquely related to better biceps individuation. These findings support the notion of specialized but complementary contributions of these pathways to human motor function.

Corticospinal and corticoreticulospinal projections benefit motor behaviors in chronic stroke

After corticospinal tract (CST) stroke, several motor deficits in the upper extremity (UE) emerge, including diminished muscle strength, motor control, and muscle individuation. Both the ipsilesional CST and contralesional corticoreticulospinal tract (CReST) innervate the paretic UE and may have different innervation patterns for the proximal and distal UE segments. These patterns may underpin distinct pathway relationships to separable motor behaviors. In this cross-sectional study of 15 chronic stroke patients and 28 healthy subjects, we examined two key questions: (1) whether segmental motor behaviors differentially relate to ipsilesional CST and contralesional CReST projection strengths, and (2) whether motor behaviors segmentally differ in the paretic UE. We measured strength, motor control, and muscle individuation in a proximal (biceps, BIC) and distal muscle (first dorsal interosseous, FDI) of the paretic UE. We measured the projection strengths of the ipsilesional CST and contralesional CReST to these muscles using transcranial magnetic stimulation (TMS). Stroke subjects had abnormal motor control and muscle individuation despite strength comparable to healthy subjects. In stroke subjects, stronger ipsilesional CST projections were linked to superior motor control in both UE segments, whereas stronger contralesional CReST projections were linked to superior muscle strength and individuation in both UE segments. Notably, both pathways also shared associations with behaviors in the proximal segment. Motor control deficits were segmentally comparable, but muscle individuation was worse for distal motor performance. These results suggest that each pathway has specialized contributions to chronic motor behaviors but also work together, with varying levels of success in supporting chronic deficits.

Key points summary

Individuals with chronic stroke typically have deficits in strength, motor control, and muscle individuation in their paretic upper extremity (UE). It remains unclear how these altered behaviors relate to descending motor pathways and whether they differ by proximal and distal UE segment.In this study, we used transcranial magnetic stimulation (TMS) to examine projection strengths of the ipsilesional corticospinal tract (CST) and contralesional corticoreticulospinal tract (CReST) with respect to quantitated motor behaviors in chronic stroke.We found that stronger ipsilesional CST projections were associated with better motor control in both UE segments, whereas stronger contralesional CReST projections were associated with better strength and individuation in both UE segments. In addition, projections of both pathways shared associations with motor behaviors in the proximal UE segment.We also found that deficits in strength and motor control were comparable across UE segments, but muscle individuation was worse with controlled movement in the distal UE segment.These results suggest that the CST and CReST have specialized contributions to chronic motor behaviors and also work together, although with different degrees of efficacy.

Multichannel bridges and NSC synergize to enhance axon regeneration, myelination, synaptic reconnection, and recovery after SCI

Regeneration in the injured spinal cord is limited by physical and chemical barriers. Acute implantation of a multichannel poly(lactide-co-glycolide) (PLG) bridge mechanically stabilizes the injury, modulates inflammation, and provides a permissive environment for rapid cellularization and robust axonal regrowth through this otherwise inhibitory milieu. However, without additional intervention, regenerated axons remain largely unmyelinated (<10%), limiting functional repair. While transplanted human neural stem cells (hNSC) myelinate axons after spinal cord injury (SCI), hNSC fate is highly influenced by the SCI inflammatory microenvironment, also limiting functional repair. Accordingly, we investigated the combination of PLG scaffold bridges with hNSC to improve histological and functional outcome after SCI. In vitro, hNSC culture on a PLG scaffold increased oligodendroglial lineage selection after inflammatory challenge. In vivo, acute PLG bridge implantation followed by chronic hNSC transplantation demonstrated a robust capacity of donor human cells to migrate into PLG bridge channels along regenerating axons and integrate into the host spinal cord as myelinating oligodendrocytes and synaptically integrated neurons. Axons that regenerated through the PLG bridge formed synaptic circuits that connected the ipsilateral forelimb muscle to contralateral motor cortex. hNSC transplantation significantly enhanced the total number of regenerating and myelinated axons identified within the PLG bridge. Finally, the combination of acute bridge implantation and hNSC transplantation exhibited robust improvement in locomotor recovery. These data identify a successful strategy to enhance neurorepair through a temporally layered approach using acute bridge implantation and chronic cell transplantation to spare tissue, promote regeneration, and maximize the function of new axonal connections.

Recovery of Forearm and Fine Digit Function After Chronic Spinal Cord Injury by Simultaneous Blockade of Inhibitory Matrix Chondroitin Sulfate Proteoglycan Production and the Receptor PTPσ

Spinal cord injuries (SCI), for which there are limited effective treatments, result in enduring paralysis and hypoesthesia, in part because of the inhibitory microenvironment that develops and limits regeneration/sprouting, especially during chronic stages. Recently, we discovered that targeted enzymatic removal of the inhibitory chondroitin sulfate proteoglycan (CSPG) component of the extracellular and perineuronal net (PNN) matrix via Chondroitinase ABC (ChABC) rapidly restored robust respiratory function to the previously paralyzed hemi-diaphragm after remarkably long times post-injury (up to 1.5 years) following a cervical level 2 lateral hemi-transection. Importantly, ChABC treatment at cervical level 4 in this chronic model also elicited improvements in gross upper arm function. In the present study, we focused on arm and hand function, seeking to highlight and optimize crude as well as fine motor control of the forearm and digits at lengthy chronic stages post-injury. However, instead of using ChABC, we utilized a novel and more clinically relevant systemic combinatorial treatment strategy designed to simultaneously reduce and overcome inhibitory CSPGs. Following a 3-month upper cervical spinal hemi-lesion using adult female Sprague Dawley rats, we show that the combined treatment had a profound effect on functional recovery of the chronically paralyzed forelimb and paw, as well as on precision movements of the digits. The regenerative and immune system related events that we describe deepen our basic understanding of the crucial role of CSPG-mediated inhibition via the PTPσ receptor in constraining functional synaptic plasticity at lengthy time points following SCI, hopefully leading to clinically relevant translational benefits.

Motor skills training-induced activation of descending pathways mediating cortical command to hindlimb motoneurons in experimental diabetic rats

Diabetes disrupts the corticospinal tract (CST) system components that control hindlimb and trunk movement, resulting in weakness of the lower extremities. However, there is no information about a method to improve these disorders. This study aimed to investigate the rehabilitative effects of 2 weeks of aerobic training (AT) and complex motor skills training (ST) on motor disorders in streptozotocin-induced type 1 diabetic rats. In this study, electrophysiological mapping of the motor cortex showed that the diabetes mellitus (DM)-ST group had a larger motor cortical area compared to the DM-AT group and sedentary diabetic animals. Moreover, hand grip strength and rotarod latency increased in the DM-ST group; however, these two parameters did not change in the DM-AT group, as well as in control and sedentary diabetic rats. Furthermore, in the DM-ST group, cortical stimulation-induced and motor-evoked potentials were preserved after the interception of the CST; however, this potential disappeared after additional lesions were made on lateral funiculus, suggesting that their function extends to activating motor descending pathways other than the CST locating lateral funiculus. According to immunohistochemical analysis, the larger fibers present on the dorsal part of the lateral funiculus, which corresponds to the rubrospinal tract of the DM-ST group, expressed the phosphorylated growth-associated protein, 43 kD, which is a specific marker of axons with plastic changes. Additionally, electrical stimulation of the red nucleus revealed expansion of the hindlimb-responsible area and increased motor-evoked potentials of the hindlimb in the DM-ST group, suggesting a strengthening of synaptic connections between the red nucleus and spinal interneurons driving motoneurons. These results reveal that ST induces plastic changes in the rubrospinal tract in a diabetic model, which can compensate for diabetes by disrupting the CST system components that control the hindlimb. This finding suggests that ST can be a novel rehabilitation strategy to improve motor dysfunctions in diabetic patients.

FUNCTION MONITORING AND RECOVERY METHODS IN THE REHABILITATION OF TENNIS PLAYERS

ABSTRACT Introduction Sports injury is a common injury among professional tennis players compared to other sports. Updated rehabilitation methods can accelerate players’ recovery and ensure a return to sporting activity. However, contemporary rehabilitation monitoring practices want updated reporting. Objective Monitoring tennis players’ function and recovery methods during rehabilitation training after injury. Methods The tennis player underwent arthroscopic capsulotomy of the left ankle joint, free body removal, and synovectomy. The athlete’s body composition, blood routine, biochemistry, nutritional indices, and physiological indicators were monitored. Data were collected before, during, and at the end of the four months (6-10 months) of rehabilitation after the operation. Results 1 month after the operation, weight and lean mass decreased significantly; body fat percentage increased; static heart rate increased significantly (P<0.05). Three months after surgery, the athlete’s lean mass increased significantly to 43.7 kg; body fat percentage decreased to 24.5% (P<0.05); hemoglobin, serum iron, total protein, and albumin improved; in rehabilitation during October, blood routine and biochemical blood indices were regular; Resting, maintained-load and recovery heart rate decreased significantly (P<0.05). Conclusion Tennis players should begin function monitoring, rehabilitation training, and nutritional recovery as soon as possible after ankle joint surgery. Evidence Level II; Therapeutic Studies - Investigating the result.

Restoring After Central Nervous System Injuries: Neural Mechanisms and Translational Applications of Motor Recovery

Central nervous system (CNS) injuries, including stroke, traumatic brain injury, and spinal cord injury, are leading causes of long-term disability. It is estimated that more than half of the survivors of severe unilateral injury are unable to use the denervated limb. Previous studies have focused on neuroprotective interventions in the affected hemisphere to limit brain lesions and neurorepair measures to promote recovery. However, the ability to increase plasticity in the injured brain is restricted and difficult to improve. Therefore, over several decades, researchers have been prompted to enhance the compensation by the unaffected hemisphere. Animal experiments have revealed that regrowth of ipsilateral descending fibers from the unaffected hemisphere to denervated motor neurons plays a significant role in the restoration of motor function. In addition, several clinical treatments have been designed to restore ipsilateral motor control, including brain stimulation, nerve transfer surgery, and brain–computer interface systems. Here, we comprehensively review the neural mechanisms as well as translational applications of ipsilateral motor control upon rehabilitation after CNS injuries.

Grid-Based Estimation of Transformation Between Partial Relationships Using a Genetic Algorithm

Human motor learning is characterized by adaptation, wherein information obtained in the past is transferred to a different situation. In this study, we investigate a grid-based computation for explaining the reuse of the information of an existing controller for adaptation to a partial malfunction of a controller. To this end, a motor learning scheme is adopted based on the detection and estimation of partial relationships. The transformation between the partial relationships is estimated based on a grid-based estimation of the two coordinate systems. In this estimation, the coordinate systems are optimized using a genetic algorithm. Two arms in a reflection are considered, and it is confirmed that the transformation of the differential kinematics (Jacobian), as an example of the partial relationships, can be estimated by the proposed method.

Modulation of neural co-firing to enhance network transmission and improve motor function after stroke

Stroke is a leading cause of disability. While neurotechnology has shown promise for improving upper limb recovery after stroke, efficacy in clinical trials has been variable. Our central thesis is that to improve clinical translation, we need to develop a common neurophysiological framework for understanding how neurotechnology alters network activity. Our perspective discusses principles for how motor networks, both healthy and those recovering from stroke, subserve reach-to-grasp movements. We focus on neural processing at the resolution of single movements, the timescale at which neurotechnologies are applied, and discuss how this activity might drive long-term plasticity. We propose that future studies should focus on cross-area communication and bridging our understanding of timescales ranging from single trials within a session to across multiple sessions. We hope that this perspective establishes a combined path forward for preclinical and clinical research with the goal of more robust clinical translation of neurotechnology.

Muscle synergy analysis yields an efficient and physiologically relevant method of assessing stroke

The Fugl-Meyer Assessment is widely used to test motor function in stroke survivors. In the Fugl-Meyer Assessment, stroke survivors perform several movement tasks and clinicians subjectively rate the performance of each task item. The individual task items in the Fugl-Meyer Assessment are selected on the basis of clinical experience, and their physiological relevance has not yet been evaluated. In the present study, we aimed to objectively rate the performance of task items by measuring the muscle activity of 41 muscles from the upper body while stroke survivors and healthy participants performed 37 Fugl-Meyer Assessment upper extremity task items. We used muscle synergy analysis to compare muscle activity between subjects and found that 13 muscle synergies in the healthy participants (which we defined as standard synergies) were able to reconstruct all of the muscle activity in the Fugl-Meyer Assessment. Among the standard synergies, synergies involving the upper arms, forearms and fingers were activated to varying degrees during different task items. In contrast, synergies involving posterior trunk muscles were activated during all tasks, which suggests the importance of posterior trunk muscle synergies throughout all sequences. Furthermore, we noted the inactivation of posterior trunk muscle synergies in stroke survivors with severe but not mild impairments, suggesting that lower trunk stability and the underlying activity of posterior trunk muscle synergies may have a strong influence on stroke severity and recovery. By comparing the synergies of stroke survivors with standard synergies, we also revealed that some synergies in stroke survivors corresponded to merged standard synergies; the merging rate increased with the impairment of stroke survivors. Moreover, the degrees of severity-dependent changes in the merging rate (the merging rate–severity relationship) were different among different task items. This relationship was significant for 26 task items only and not for the other 11 task items. Because muscle synergy analysis evaluates coordinated muscle activities, this different dependency suggests that these 26 task items are appropriate for evaluating muscle coordination and the extent of its impairment in stroke survivors. Overall, we conclude that the Fugl-Meyer Assessment reflects physiological function and muscle coordination impairment and suggest that it could be performed using a subset of the 37 task items.

Mapping the human corticoreticular pathway with multimodal delineation of the gigantocellular reticular nucleus and high-resolution diffusion tractography

The corticoreticular pathway (CRP) is a major motor tract that transmits cortical input to the reticular formation motor nuclei and may be an important mediator of motor recovery after central nervous system damage. However, its cortical origins, trajectory and laterality are incompletely understood in humans. This study aimed to map the human CRP and generate an average CRP template in standard MRI space. Following recently established guidelines, we manually delineated the primary reticular formation motor nucleus (gigantocellular reticular nucleus [GRN]) using several group-mean MRI contrasts from the Human Connectome Project (HCP). CRP tractography was then performed with HCP diffusion-weighted MRI data (N = 1065) by selecting diffusion streamlines that reached both the cortex and GRN. Corticospinal tract (CST) tractography was also performed for comparison. Results suggest that the human CRP has widespread origins, which overlap with the CST across most of the motor cortex and include additional exclusive inputs from the medial and anterior prefrontal cortices. The estimated CRP projected through the anterior and posterior limbs of the internal capsule before partially decussating in the midbrain tegmentum and converging bilaterally on the pontomedullary reticular formation. Thus, the CRP trajectory appears to partially overlap the CST, while being more distributed and anteromedial to the CST in the cerebrum before moving posterior to the CST in the brainstem. These findings have important implications for neurophysiologic testing, cortical stimulation and movement recovery after brain lesions. We expect that our GRN and tract maps will also facilitate future CRP research.

Effective brain network analysis in unilateral and bilateral upper limb exercise training in subjects with stroke

PURPOSE

Knowing the patterns of brain activation that occur and networks involved under different interventions is important for motor recovery in subjects with stroke. This study aimed to study the patterns of brain activation and networks in two interventions, affected upper limb side and bilateral exercise training, using concurrent functional near-infrared spectroscopy (fNIRS) imaging.

METHODS

Thirty-two patients in the early subacute stage were randomly divided into two groups: unilateral and bilateral groups. The patients in the unilateral group underwent isokinetic muscle strength training on the affected upper limb side and patients in the bilateral group underwent bilateral upper limb training. Oxyhemoglobin and deoxyhemoglobin concentration changes (ΔHbO₂ and ΔHbR, respectively) were recorded in the ipsilateral and contralateral prefrontal cortex (IPFC and CPFC, respectively) and ipsilateral and contralateral motor cortex (IMC and CMC, respectively) by fNIRS equipment in the resting state and training conditions. The phase information of a 0.01-0.08 Hz fNIRS signal was extracted by the wavelet transform method. Dynamic Bayesian inference was adopted to calculate the coupling strength and direction of effective connectivity. The network threshold was determined by surrogate signal method, the global (weighted clustering coefficient, global efficiency and small-worldness) and local (degree, betweenness centrality and local efficiency) network metrics were calculated. The degree of cerebral lateralization was also compared between the two groups.

RESULTS

The results of covariance analysis showed that, compared with bilateral training, the coupling effect of CMC→IMC was significantly enhanced (p = 0.03); also, the local efficiency of the IMC (p = 0.01), IPFC (p<0.001), and CPFC (p = 0.006) and the hemispheric autonomy index of IPFC (p = 0.007) were significantly increased in unilateral training. In addition, there was a significant positive correlation between the coupling intensity of the inter-hemispheric motor area and the shifted local efficiency.

CONCLUSIONS

The results indicated that unilateral upper limb training could more effectively promote the interaction and balance of bilateral motor hemispheres and help brain reorganization in the IMC and prefrontal cortex in stroke patients. The method provided in this study could be used to evaluate dynamic brain activation and network reorganization under different interventions, thus improving the strategy of rehabilitation intervention in a timely manner and resulting in better motor recovery. This article is protected by copyright. All rights reserved.

Clinical Effects of Acupuncture for Stroke Patients Recovery

Stroke is assumed as one of the common cerebrovascular diseases that endangers human health and life. Its incidence and mortality rates are high, while survivors (50% to 70%) suffer from different degrees of disability. Hemiplegia is a common disability after stroke, mainly manifested as muscle weakness of the affected side, limb spasm, and limited activity, which severely impacts a patient's daily life. There are various rehabilitation methods for stroke hemiplegia, including modern rehabilitation medicine, motor therapy, acupuncture, and rehabilitation robot. The cost and effect of different rehabilitation methods are not the same. It is the focus to find an economical and effective rehabilitation method. In this paper, 128 stroke patients aged 41 to 73 hospitalized between January 2019 and January 2021 were analyzed. The intervention group used standard physical therapy and traditional acupuncture therapy, and the control group only used standard physical therapy. We used RStudio 1.1.419 (RStudio Corporation) for analysis. Experimental results show that the short-term efficacy of the intervention group is better than that of the control group. The intervention group was better than the control group in recovery from injury during rehabilitation, degree of muscle spasm, self-care ability in daily life, and overall degree of damage. In the long-term efficacy analysis, we can see that with the increase in the number of acupuncture, the efficacy of the intervention group is still better than that of the control group. Compared with physical rehabilitation alone, acupuncture has better short-term, and long-term clinical effects for stroke patients improves motor dysfunction and improves the quality of life and independence of stroke patients. With the increase in the number of acupuncture treatments, the patient's rehabilitation effect will be better.

Targeting Sensory and Motor Integration for Recovery of Movement After CNS Injury

The central nervous system (CNS) integrates sensory and motor information to acquire skilled movements, known as sensory-motor integration (SMI). The reciprocal interaction of the sensory and motor systems is a prerequisite for learning and performing skilled movement. Injury to various nodes of the sensorimotor network causes impairment in movement execution and learning. Stimulation methods have been developed to directly recruit the sensorimotor system and modulate neural networks to restore movement after CNS injury. Part 1 reviews the main processes and anatomical interactions responsible for SMI in health. Part 2 details the effects of injury on sites critical for SMI, including the spinal cord, cerebellum, and cerebral cortex. Finally, Part 3 reviews the application of activity-dependent plasticity in ways that specifically target integration of sensory and motor systems. Understanding of each of these components is needed to advance strategies targeting SMI to improve rehabilitation in humans after injury.

Double viral vector intersectional approaches for pathway-selective manipulation of motor functions and compensatory mechanisms

Selective manipulation of particular subcomponent of neural circuits is crucial for understanding the functional architecture of neural systems and for development of the future therapeutic strategies against neurological disorders. In this article, I review how the intersectional approaches with double viral vector technique was introduced for the pathway-selective manipulation of spinal circuits. In this technique, a retrograde gene transfer vector is injected into the terminal area of the targeted neurons and an anterograde vector is injected at the location of their somata. Either by using the Tet-transactivator or Cre-loxP system, the experimenter can chemogenetically or optogenetically manipulate the transmission of the target pathway originated from the double-infected neurons. This technique was first developed for manipulation of spinal cord interneurons in the macaque monkeys by selective expression of tetanus neurotoxin and successfully affected the dexterous hand movements. Currently, this technique is widely used on a variety of neural pathways both in rodents and primates in combination with a variety of retrograde vectors and a variety of optogenetic and chemogenetic tools. The advantage of this technique is that it is not necessary to generate transgenic animals. Knowledge of the cell-type specific promotors is not needed. Manipulation is achieved primarily by injection of two viral vectors based on the anatomical knowledge and it is applicable in a variety of animal species including primates. The pros, cons and future direction of this technique are discussed.

Mapping the corticoreticular pathway from cortex-wide anterograde axonal tracing in the mouse

The corticoreticular pathway (CRP) has been implicated as an important mediator of motor recovery and rehabilitation after central nervous system damage. However, its origins, trajectory and laterality are not well understood. This study mapped the mouse CRP in comparison with the corticospinal tract (CST). We systematically searched the Allen Mouse Brain Connectivity Atlas (© 2011 Allen Institute for Brain Science) for experiments that used anterograde tracer injections into the right isocortex in mice. For each eligible experiment (N = 607), CRP and CST projection strength were quantified by the tracer volume reaching the reticular formation motor nuclei (RF_motor ) and pyramids, respectively. Tracer density in each brain voxel was also correlated with RF_motor versus pyramids projection strength to explore the relative trajectories of the CRP and CST. We found significant CRP projections originating from the primary and secondary motor cortices, anterior cingulate, primary somatosensory cortex, and medial prefrontal cortex. Compared with the CST, the CRP had stronger projections from each region except the primary somatosensory cortex. Ipsilateral projections were stronger than contralateral for both tracts (above the pyramidal decussation), but the CRP projected more bilaterally than the CST. The estimated CRP trajectory was anteromedial to the CST in the internal capsule and dorsal to the CST in the brainstem. Our findings reveal a widespread distribution of CRP origins and confirm strong bilateral CRP projections, theoretically increasing the potential for partial sparing after brain lesions and contralesional compensation after unilateral injury.

Lesion Area in the Cerebral Cortex Determines the Patterns of Axon Rewiring of Motor and Sensory Corticospinal Tracts After Stroke

The corticospinal tract (CST) is an essential neural pathway for reorganization that recovers motor functions after brain injuries such as stroke. CST comprises multiple pathways derived from different sensorimotor areas of the cerebral cortex; however, the patterns of reorganization in such complex pathways postinjury are largely unknown. Here we comprehensively examined the rewiring patterns of the CST pathways of multiple cerebral origins in a mouse stroke model that varied in size and location in the sensorimotor cortex. We found that spared contralesional motor and sensory CST axons crossed the midline and sprouted into the denervated side of the cervical spinal cord after stroke in a large cortical area. In contrast, the contralesional CST fibers did not sprout in a small stroke, whereas the ipsilesional axons from the spared motor area grew on the denervated side. We further showed that motor and sensory CST axons did not innervate the projecting areas mutually when either one was injured. The present results reveal the basic principles that generate the patterns of CST rewiring, which depend on stroke location and CST subtype. Our data indicate the importance of targeting different neural substrates to restore function among the types of injury.

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

KEY POINTS

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

ABSTRACT

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

Corticospinal vs Rubrospinal Revisited: An Evolutionary Perspective for Sensorimotor Integration

The knowledge about how different subsystems participate and interplay in sensorimotor control is fundamental to understand motor deficits associated with CNS injury and movement recovery. The role of corticospinal (CS) and rubrospinal (RS) projections in motor control has been extensively studied and compared, and it is clear that both systems are important for skilled movement. However, during phylogeny, the emerging cerebral cortex took a higher hierarchical role controlling rubro-cerebellar circuits. Here, we present anatomical, neurophysiological, and behavioral evidence suggesting that both systems modulate complex segmental neuronal networks in a parallel way, which is important for sensorimotor integration at spinal cord level. We also highlight that, although specializations exist, both systems could be complementary and potentially subserve motor recovery associated with CNS damage.

Pseudotyped lentiviral vectors for tract-targeting and application for the functional control of selective neural circuits

A lentiviral vector strategy for efficient gene transfer through retrograde axonal transport provides a powerful approach for studying the neural circuit mechanisms that mediate higher level functions of the central nervous system. Pseudotyping of human immunodeficiency virus type-1 with different types of fusion glycoproteins (FuGs), which are composed of segments of rabies virus glycoprotein (RV-G) and vesicular stomatitis virus glycoprotein (VSV-G), enhances the efficiency of retrograde gene transfer in both rodent and non-human primate brains. These pseudotyped lentiviral vectors are classified into two groups, highly efficient retrograde gene transfer (HiRet) and neuron-specific retrograde gene transfer (NeuRet) vectors, based on their properties of gene transduction. Combinatorial use of the pseudotyped vectors with various molecular tools for manipulating neural circuit functions (such as the cell targeting, synaptic silencing, and optogenetic or chemogenetic approaches) enables us to control the function of specific neural circuits, thus leading to a deeper understanding of the mechanism underlying various nervous system functions.

A Review of Exercise-Induced Neuroplasticity in Ischemic Stroke: Pathology and Mechanisms

After ischemic stroke, survivors experience motor dysfunction and deterioration of memory and cognition. These symptoms are associated with the disruption of normal neuronal function, i.e., the secretion of neurotrophic factors, interhemispheric connections, and synaptic activity, and hence the disruption of the normal neural circuit. Exercise is considered an effective and feasible rehabilitation strategy for improving cognitive and motor recovery following ischemic stroke through the facilitation of neuroplasticity. In this review, our aim was to discuss the mechanisms by which exercise-induced neuroplasticity improves motor function and cognitive ability after ischemic stroke. The associated mechanisms include increases in neurotrophins, improvements in synaptic structure and function, the enhancement of interhemispheric connections, the promotion of neural regeneration, the acceleration of neural function reorganization, and the facilitation of compensation beyond the infarcted tissue. We also discuss some common exercise strategies and a novel exercise therapy, robot-assisted movement, which might be widely applied in the clinic to help stroke patients in the future.

Corticospinal Pathways and Interactions Underpinning Dexterous Forelimb Movement of the Rodent

In 2013, Thomas Jessell published a paper with Andrew Miri and Eiman Azim that took on the task of examining corticospinal neuron function during movement (Miri et al., 2013). They took the view that a combination of approaches would be able to shed light on corticospinal function, and that this function must be considered in the context of corticospinal connectivity with spinal circuits. In this review, we will highlight recent developments in this area, along with new information regarding inputs and cross-connectivity of the corticospinal circuit with other circuits across the rodent central nervous system. The genetic and viral manipulations available in these animals have led to new insights into descending circuit interaction and function. As species differences exist in the circuitry profile that contributes to dexterous forelimb movements (Lemon, 2008; Yoshida and Isa, 2018), highlighting important advances in one model could help to compare and contrast with what is known about other models. We will focus on the circuitry underpinning dexterous forelimb movements, including some recent developments from systems besides the corticospinal tract, to build a more holistic understanding of sensorimotor circuits and their control of voluntary movement. The rodent corticospinal system is thus a central point of reference in this review, but not the only focus.

Constraint-induced movement therapy improves functional recovery after ischemic stroke and its impacts on synaptic plasticity in sensorimotor cortex and hippocampus

Constraint-induced movement therapy (CIMT) has proven to be an effective way to restore functional deficits following stroke in human and animal studies, but its underlying neural plasticity mechanism remains unknown. Accumulating evidence indicates that rehabilitation after stroke is closely associated with synaptic plasticity. We therefore investigated the impact of CIMT on synaptic plasticity in ipsilateral and contralateral brain of rats following stroke. Rats were subjected to 90 minutes of transient middle cerebral artery occlusion (MCAO). CIMT was performed from 7 days after stroke and lasted for two weeks. Modified Neurology Severity Score (mNSS) and the ladder rung walking task tests were conducted at 7,14 and 21 days after stroke. Golgi-Cox staining was used to observe the plasticity changes of dendrites and dendritic spines. The expression of glutamate receptors (GluR1, GluR2 and NR1) were examined by western blot. Our data suggest that the dendrites and dendritic spines are damaged to varying degrees in bilateral sensorimotor cortex and hippocampus after acute stroke. CIMT treatment enhances the plasticity of dendrites and dendritic spines in the ipsilateral and contralateral sensorimotor cortex, increases the expression of synaptic GluR2 in ipsilateral sensorimotor cortex, which may be mechanisms for CIMT to improve functional recovery after ischemic stroke.