White matter integrity of premotor-motor connections is associated with motor output in chronic stroke patients

Radiomic white matter parameters of functional integrity of the corticospinal tract in high-grade glioma

Tractography has become a widely available tool for the planning of neurosurgical operations as well as for neuroscientific research. The absence of patient interaction makes it easily applicable. However, it leaves uncertainty about the functional relevance of the identified bundles. We retrospectively analyzed the correlation of white matter markers with their clinical function in 24 right-handed patients who underwent first surgery for high-grade glioma. Morphological affection of the corticospinal tract (CST) and grade of paresis were assessed before surgery. Tractography was performed manually with MRTrix3 and automatically with TractSeg. Median and mean fractional anisotropy (FA) from manual tractography showed a significant correlation with CST affection (p = 0.008) and paresis (p = 0.015, p = 0.026). CST affection correlated further most with energy, and surface-volume ratio (p = 0.014) from radiomic analysis. Paresis correlated most with maximum 2D column diameter (p = 0.005), minor axis length (p = 0.006), and kurtosis (p = 0.008) from radiomic analysis. Streamline count yielded no significant correlations. In conclusion, mean or median FA can be used for the assessment of CST integrity in high-grade glioma. Also, several radiomic parameters are suited to describe tract integrity and may be used to quantitatively analyze white matter in the future.

The mouse motor system contains multiple premotor areas and partially follows human organizational principles

While humans are known to have several premotor cortical areas, secondary motor cortex (M2) is often considered to be the only higher-order motor area of the mouse brain and is thought to combine properties of various human premotor cortices. Here, we show that axonal tracer, functional connectivity, myelin mapping, gene expression, and optogenetics data contradict this notion. Our analyses reveal three premotor areas in the mouse, anterior-lateral motor cortex (ALM), anterior-lateral M2 (aM2), and posterior-medial M2 (pM2), with distinct structural, functional, and behavioral properties. By using the same techniques across mice and humans, we show that ALM has strikingly similar functional and microstructural properties to human anterior ventral premotor areas and that aM2 and pM2 amalgamate properties of human pre-SMA and cingulate cortex. These results provide evidence for the existence of multiple premotor areas in the mouse and chart a comparative map between the motor systems of humans and mice.

Adaptation of the Concept of Brain Reserve for the Prediction of Stroke Outcome: Proxies, Neural Mechanisms, and Significance for Research

The prediction of stroke outcome is challenging due to the high inter-individual variability in stroke patients. We recently suggested the adaptation of the concept of brain reserve (BR) to improve the prediction of stroke outcome. This concept was initially developed alongside the one for the cognitive reserve for neurodegeneration and forms a valuable theoretical framework to capture high inter-individual variability in stroke patients. In the present work, we suggest and discuss (i) BR-proxies-quantitative brain characteristics at the time stroke occurs (e.g., brain volume, hippocampus volume), and (ii) proxies of brain pathology reducing BR (e.g., brain atrophy, severity of white matter hyperintensities), parameters easily available from a routine MRI examination that might improve the prediction of stroke outcome. Though the influence of these parameters on stroke outcome has been partly reported individually, their independent and combined impact is yet to be determined. Conceptually, BR is a continuous measure determining the amount of brain structure available to mitigate and compensate for stroke damage, thus reflecting individual differences in neural resources and a capacity to maintain performance and recover after stroke. We suggest that stroke outcome might be defined as an interaction between BR at the time stroke occurs and lesion load. BR in stroke can potentially be influenced, e.g., by modifying cardiovascular risk factors. In addition to the potential power of the BR concept in a mechanistic understanding of inter-individual variability in stroke outcome and establishing individualized therapeutic approaches, it might help to strengthen the synergy of preventive measures in stroke, neurodegeneration, and healthy aging.

Preserved White Matter Integrity and Recovery After Brain Tumor Surgery: A Prospective Pilot Study on the Frontal Aslant Tract

Introduction: Damage to white matter tracts can cause severe neurological deficits, which are often hardly predictable before brain tumor surgery. To explore the possibility of assessing white matter integrity and its preservation, we chose the frontal aslant tract (FAT) due to its involvement in multiple neurological functions such as speech and movement initiation. Methods: Right-handed patients with left hemispheric intracerebral tumors underwent FAT tractography within 7 days before and 3 days after surgery. Neurological performance score and aphasia score were assessed within 7 days before and after surgery, as well as at follow-up 3 months postoperatively. Results: Fifteen patients were prospectively analyzed. After multivariate analysis and receiver operating characteristic analysis, we found that preoperative fractional anisotropy (FA) of the left FAT indicated the preoperative aphasia score (cutoff 0.40, p = 0.015). Aphasia scores 3 months postoperatively were predicted by both postoperative FA of the left FAT (cutoff 0.35, p = 0.005) and postoperatively preserved FA of the left FAT (cutoff 95.8%, p = 0.017). Postoperatively preserved right FAT FA inversely predicted postoperative aphasia score (cutoff 95.1%, p = 0.016). Discussion: Assessment of white matter integrity preservation is possible and correlates with outcome after brain tumor surgery. It may be useful for patient counseling and assessment of rehabilitation potential, as well as to investigate relevant brain networks in the future. Clinical Trial Registration: The trial was prospectively registered at ClinicalTrials.gov (NCT04302857).

Interhemispheric Structural Connectivity Underlies Motor Recovery after Stroke

OBJECTIVE

Although ample evidence highlights that the ipsilesional corticospinal tract (CST) plays a crucial role in motor recovery after stroke, studies on cortico-cortical motor connections remain scarce and provide inconclusive results. Given their unique potential to serve as structural reserve enabling motor network reorganization, the question arises whether cortico-cortical connections may facilitate motor control depending on CST damage.

METHODS

Diffusion spectrum imaging (DSI) and a novel compartment-wise analysis approach were used to quantify structural connectivity between bilateral cortical core motor regions in chronic stroke patients. Basal and complex motor control were differentially assessed.

RESULTS

Both basal and complex motor performance were correlated with structural connectivity between bilateral premotor areas and ipsilesional primary motor cortex (M1) as well as interhemispheric M1 to M1 connectivity. Whereas complex motor skills depended on CST integrity, a strong association between M1 to M1 connectivity and basal motor control was observed independent of CST integrity especially in patients who underwent substantial motor recovery. Harnessing the informational wealth of cortico-cortical connectivity facilitated the explanation of both basal and complex motor control.

INTERPRETATION

We demonstrate for the first time that distinct aspects of cortical structural reserve enable basal and complex motor control after stroke. In particular, recovery of basal motor control may be supported via an alternative route through contralesional M1 and non-crossing fibers of the contralesional CST. Our findings help to explain previous conflicting interpretations regarding the functional role of the contralesional M1 and highlight the potential of cortico-cortical structural connectivity as a future biomarker for motor recovery post-stroke. ANN NEUROL 2023;94:785-797.

White Matter Integrity and Chronic Poststroke Upper Limb Function: An ENIGMA Stroke Recovery Analysis

BACKGROUND

Integrity of the corticospinal tract (CST) is an important biomarker for upper limb motor function following stroke. However, when structurally compromised, other tracts may become relevant for compensation or recovery of function.

METHODS

We used the ENIGMA Stroke Recovery data set, a multicenter, retrospective, and cross-sectional collection of patients with upper limb impairment during the chronic phase of stroke to test the relevance of tracts in individuals with less and more severe (laterality index of CST fractional anisotropy ≥0.25) CST damage in an observational study design. White matter integrity was quantified using fractional anisotropy for the CST, the superior longitudinal fascicle, and the callosal fibers interconnecting the primary motor cortices between hemispheres. Optic radiations served as a control tract as they have no a priori relevance for the motor system. Pearson correlation was used for testing correlation with upper limb motor function (Fugl-Meyer upper extremity).

RESULTS

From 1235 available data sets, 166 were selected (by imaging, Fugl-Meyer upper extremity, covariates, stroke location, and stage) for analyses. Only individuals with severe CST damage showed a positive association of fractional anisotropy in both callosal fibers interconnecting the primary motor cortices (r[21]=0.49; P=0.025) and superior longitudinal fascicle (r[21]=0.51; P=0.018) with Fugl-Meyer upper extremity.

CONCLUSIONS

Our data support the notion that individuals with more severe damage of the CST depend on residual pathways for achieving better upper limb outcome than those with less affected CST.

Prediction of post-stroke motor recovery benefits from measures of sub-acute widespread network damages

Following a stroke in regions of the brain responsible for motor activity, patients can lose their ability to control parts of their body. Over time, some patients recover almost completely, while others barely recover at all. It is known that lesion volume, initial motor impairment and cortico-spinal tract asymmetry significantly impact motor changes over time. Recent work suggested that disabilities arise not only from focal structural changes but also from widespread alterations in inter-regional connectivity. Models that consider damage to the entire network instead of only local structural alterations lead to a more accurate prediction of patients' recovery. However, assessing white matter connections in stroke patients is challenging and time-consuming. Here, we evaluated in a data set of 37 patients whether we could predict upper extremity motor recovery from brain connectivity measures obtained by using the patient's lesion mask to introduce virtual lesions in 60 healthy streamline tractography connectomes. This indirect estimation of the stroke impact on the whole brain connectome is more readily available than direct measures of structural connectivity obtained with magnetic resonance imaging. We added these measures to benchmark structural features, and we used a ridge regression regularization to predict motor recovery at 3 months post-injury. As hypothesized, accuracy in prediction significantly increased (R ² = 0.68) as compared to benchmark features (R ² = 0.38). This improved prediction of recovery could be beneficial to clinical care and might allow for a better choice of intervention.

Transcranial direct current stimulation for gait recovery following stroke: A systematic review of current literature and beyond

Background

Over the last decade, transcranial direct current stimulation (tDCS) has set promise contributing to post-stroke gait rehabilitation. Even so, results are still inconsistent due to low sample size, heterogeneity of samples, and tDCS design differences preventing comparability. Nonetheless, updated knowledge in post-stroke neurophysiology and stimulation technologies opens up opportunities to massively improve treatments.

Objective

The current systematic review aims to summarize the current state-of-the-art on the effects of tDCS applied to stroke subjects for gait rehabilitation, discuss tDCS strategies factoring individual subject profiles, and highlight new promising strategies.

Methods

MEDLINE, SCOPUS, CENTRAL, and CINAHL were searched for stroke randomized clinical trials using tDCS for the recovery of gait before 7 February 2022. In order to provide statistical support to the current review, we analyzed the achieved effect sizes and performed statistical comparisons.

Results

A total of 24 records were finally included in our review, totaling n = 651 subjects. Detailed analyses revealed n = 4 (17%) studies with large effect sizes (≥0.8), n = 6 (25%) studies with medium ones (≥0.5), and n = 6 (25%) studies yielding low effects sizes (≤ 0.2). Statistically significant negative correlations (rho = −0.65, p = 0.04) and differences (p = 0.03) argued in favor of tDCS interventions in the sub-acute phase. Finally, significant differences (p = 0.03) were argued in favor of a bifocal stimulation montage (anodal M1 ipsilesional and cathodal M1 contralesional) with respect to anodal ipsilesional M1.

Conclusion

Our systematic review highlights the potential of tDCS to contribute to gait recovery following stroke, although also the urgent need to improve current stimulation strategies and subject-customized interventions considering stroke severity, type or time-course, and the use of network-based multifocal stimulation approaches guided by computational biophysical modeling.

Systematic review registration

PROSPERO: CRD42021256347.

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

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

Usefulness and Limits of Tractography for Surgery in the Precentral Gyrus—A Case Report

The resection of tumors within the primary motor cortex is a constant challenge. Although tractography may help in preoperative planning, it has limited application. While it can give valuable information on subcortical fibers, it is less accurate in the cortical layer of the brain. A 38-year-old patient presented with paresis of the right hand and focal epileptic seizures due to a tumor in the left precentral gyrus. Transcranial magnetic stimulation was not applicable due to seizures, so microsurgical resection was performed with preoperative tractography and intraoperative direct electrical stimulation. A histopathological assessment revealed a diagnosis of glioblastoma. Postoperative magnetic resonance imaging (MRI) showed complete resection. The paresis dissolved completely during follow-up. Surgery within the precentral gyrus is of high risk and requires multimodal functional planning. If interpreted with vigilance and consciousness of the underlying physical premises, tractography can provide helpful information within its limitations, which is especially subcortically. However, it may also help in the identification of functional cortex columns of the brain in the presence of a tumor.

Biomarkers of plasticity for stroke recovery

Stroke is the commonest cause of physical disability in the world. Our understanding of the biologic mechanisms involved in recovery and repair has advanced to the point that therapeutic opportunities to promote recovery through manipulation of post-stroke plasticity have never been greater. This work has almost exclusively been carried out in rodent models of stroke with little translation into human studies. The challenge ahead is to develop a mechanistic understanding of recovery from stroke in humans. Advances in neuroimaging techniques can now provide the appropriate intermediate level of description to bridge the gap between a molecular and cellular account of recovery and a behavioral one. Clinical trials can then be designed in a stratified manner taking into account when an intervention should be delivered and who is most likely to benefit. This approach is most likely to lead to the step-change in how restorative therapeutic strategies are delivered in human stroke patients.

Upper and Lower Limb Motor Function Correlates with Ipsilesional Corticospinal Tract and Red Nucleus Structural Integrity in Chronic Stroke: A Cross-Sectional, ROI-Based MRI Study

Background

Structural integrity of the ipsilesional corticospinal tract (CST) is important for upper limb motor recovery after stroke. However, additional neuromechanisms associated with motor function poststroke are less well understood, especially regarding the lower limb.

Objective

To investigate the neural basis of upper/lower limb motor deficits poststroke by correlating measures of motor function with diffusion tensor imaging-derived indices of white matter integrity (fractional anisotropy (FA), mean diffusivity (MD)) in primary and secondary motor tracts/structures.

Methods

Forty-three individuals with chronic stroke (time poststroke, 64.4 ± 58.8 months) underwent a comprehensive motor assessment and MRI scanning. Correlation and multiple regression analyses were performed to examine relationships between FA/MD in a priori motor tracts/structures and motor function.

Results

FA in the ipsilesional CST and red nucleus (RN) was positively correlated with motor function of both the affected upper and lower limb (r = 0.36‐0.55, p ≤ 0.01), while only ipsilesional RN FA was associated with gait speed (r = 0.50). Ipsilesional CST FA explained 37.3% of the variance in grip strength (p < 0.001) and 31.5% of the variance in Arm Motricity Index (p = 0.004). Measures of MD were not predictors of motor performance.

Conclusions

Microstructural integrity of the ipsilesional CST is associated with both upper and lower limb motor function poststroke, but appears less important for gait speed. Integrity of the ipsilesional RN was also associated with motor performance, suggesting increased contributions from secondary motor areas may play a role in supporting chronic motor function and could become a target for interventions.

Stimulation of frontal pathways disrupts hand muscle control during object manipulation

The activity of frontal motor areas during hand-object interaction is coordinated by dense communication along specific white matter pathways. This architecture allows the continuous shaping of voluntary motor output and, despite extensively investigated in non-human primate studies, remains poorly understood in humans. Disclosure of this system is crucial for predicting and treatment of motor deficits after brain lesions. For this purpose, we investigated the effect of direct electrical stimulation on white matter pathways within the frontal lobe on hand-object manipulation. This was tested in thirty-four patients (15 left hemisphere, mean age 42 years, 17 male, 15 with tractography) undergoing awake neurosurgery for frontal lobe tumour removal with the aid of the brain mapping technique. The stimulation outcome was quantified based on hand-muscle activity required by task execution. The white matter pathways responsive to stimulation with an interference on muscles were identified by means of probabilistic density estimation of stimulated sites, tract-based lesion-symptom (disconnectome) analysis and diffusion tractography on the single patient level. Finally, we assessed the effect of permanent tracts disconnection on motor outcome in the immediate postoperative period using a multivariate lesion-symptom mapping approach. The analysis showed that stimulation disrupted hand-muscle activity during task execution in 66 sites within the white matter below dorsal and ventral premotor regions. Two different EMG interference patterns associated with different structural architectures emerged: 1) an arrest pattern, characterised by complete impairment of muscle activity associated with an abrupt task interruption, occurred when stimulating a white matter area below the dorsal premotor region. Local mid-U-shaped fibres, superior fronto-striatal, corticospinal and dorsal fronto-parietal fibres intersected with this region. 2) a clumsy pattern, characterised by partial disruption of muscle activity associated with movement slowdown and/or uncoordinated finger movements, occurred when stimulating a white matter area below the ventral premotor region. Ventral fronto-parietal and inferior fronto-striatal tracts intersected with this region. Finally, only resections partially including the dorsal white matter region surrounding the supplementary motor area were associated with transient upper-limb deficit (p = 0.05; 5000 permutations). Overall, the results identify two distinct frontal white matter regions possibly mediating different aspects of hand-object interaction via distinct sets of structural connectivity. We suggest the dorsal region, associated with arrest pattern and post-operative immediate motor deficits, to be functionally proximal to motor output implementation, while the ventral region may be involved in sensorimotor integration required for task execution.

Ageing and the Ipsilateral M1 BOLD Response: A Connectivity Study

Young people exhibit a negative BOLD response in ipsilateral primary motor cortex (M1) when making unilateral movements, such as button presses. This negative BOLD response becomes more positive as people age. In this study, we investigated why this occurs, in terms of the underlying effective connectivity and haemodynamics. We applied dynamic causal modeling (DCM) to task fMRI data from 635 participants aged 18-88 from the Cam-CAN dataset, who performed a cued button pressing task with their right hand. We found that connectivity from contralateral supplementary motor area (SMA) and dorsal premotor cortex (PMd) to ipsilateral M1 became more positive with age, explaining 44% of the variability across people in ipsilateral M1 responses. In contrast, connectivity from contralateral M1 to ipsilateral M1 was weaker and did not correlate with individual differences in rM1 BOLD. Neurovascular and haemodynamic parameters in the model were not able to explain the age-related shift to positive BOLD. Our results add to a body of evidence implicating neural, rather than vascular factors as the predominant cause of negative BOLD-while emphasising the importance of inter-hemispheric connectivity. This study provides a foundation for investigating the clinical and lifestyle factors that determine the sign and amplitude of the M1 BOLD response in ageing, which could serve as a proxy for neural and vascular health, via the underlying neurovascular mechanisms.

Intact procedural learning and motor intracortical inhibition in adult neurofibromatosis type 1 gene carriers

OBJECTIVE

Neurofibromatosis type 1 (NF1)¹ is known to cause learning deficits in affected individuals. There has been evidence linking altered gamma-aminobutyric acid (GABA)² mediated inhibition to learning impairments in rodent models and humans with NF1. Still, evidence on the role of GABA in learning deficits associated with NF1 is inconclusive.

METHODS

We examined procedural learning and motor cortex excitability through intracortical facilitation and short interval intracortical inhibition and its activity dependent modulation while performing a procedural sequence learning task in 16 asymptomatic NF1 gene carriers. We aimed to analyze potential brain-behavior correlations in a carefully selected sample of gene carriers in order to minimize confounding factors.

RESULTS

Gene carriers did not differ from healthy controls when learning the task with their non-dominant hand over three days of training. Electrophysiological data did not reveal alterations in patients' inhibitory function of the motor cortex.

CONCLUSIONS

In contrast with previous publications reporting various cognitive deficits in clinically asymptomatic individuals with NF1, here asymptomatic gene carriers did not show major neuropsychological or behavioral abnormalities.

SIGNIFICANCE

Our results support the concept that gene carriers may not always be impaired by the condition and the population of individuals with NF1 most likely comprises different subgroups according to patients' phenotype severity.

Relation between rich-club organization versus brain functions and functional recovery after acute ischemic stroke

Studies have shown the brain's rich-club organization may underpin brain function and be associated with various brain disorders. In this study, we aimed to investigate the relation between poststroke brain functions and functional recovery versus the rich-club organization of the structural brain network of patients after first-time acute ischemic stroke. A cohort of 16 acute ischemic stroke patients (11 males) was recruited. Structural brain networks were measured using diffusion tensor imaging within 1 week and at 1, 3 and 6 months after stroke. Motor impairment was assessed using the Upper-Extremity Fugl-Meyer motor scale and activities of daily living using the Barthel Index at the same time points as MRI. The rich-club regions that were stable over the course of stroke recovery included the bilateral dorsolateral superior frontal gyri, right supplementary motor area, and left median cingulate and paracingulate gyri. The network properties that correlated with poststroke brain functions were mainly the ratio between communication cost ratio and density ratio of rich-club, feeder and local connections. The recovery of both motor functions and activities of daily living were correlated with higher normalized rich club coefficients and a shorter length of local connections within a week after stroke. The communication cost ratio of feeder connections, the length of rich-club and local connections, and normalized rich club coefficients were found to be potential prognostic indicators of stroke recovery. Our results provide additional support to the notion that different types of network connections play different roles in brain functions as well as functional recovery.

Complete monoplegia due to limb-kinetic apraxia in a patient with traumatic brain injury: A case report

RATIONALE

Limb-kinetic apraxia (LKA) is a disorder of movement execution that is a result of injury to the corticofugal tracts (CFTs) from the secondary motor area. We report on a patient with traumatic brain injury (TBI) and complete monoplegia due to LKA, which was mainly ascribed to injury of the CFT from the secondary motor area using diffusion tensor tractography.

PATIENT CONCERNS

A 35-year-old male was struck by a car from the side during riding an autocycle and received direct head trauma as a result of falling to ground. He lost consciousness for approximately 1 month and experienced continuous post-traumatic amnesia after the accident. The patient's Glasgow Coma Scale score was 3 and he showed quadriparesis including complete monoplegia of his left arm since the onset of TBI.

DIAGNOSES

The patient diagnosed complete monoplegia due to LKA after traumatic brain injury.

INTERVENTIONS

He underwent conservative management for TBI followed by rehabilitation at approximately 2 months after onset.

OUTCOMES

At 32-month after onset, weakness on left arm (Manual Muscle Test [MMT]:0) and partial weakness of left leg (MMT:3).

OUTCOMES

Results of electromyography and nerve conduction studies of left extremities were normal. Motor evoked potential values obtained from the abductor pollicis brevis muscle (APB) were: right APB latency 22.3msec, amplitude 1.6mV; left APB latency 22.8msec, amplitude 1.5mV. After 2 weeks of administration of dopaminergic drugs for improvement of LKA, left arm weakness had recovered to level that permitted movement against gravity (MMT:3). Diffusion tensor tractography at 32-month after onset showed right corticospinal tract discontinuation at the pontine level and partial tearing of the left corticospinal tract at the subcortical white matter. In addition, the left CFT from the supplementary motor area showed partial tearing at the subcortical white matter.

LESSONS

The LKA due to injury of the left supplementary motor area-CFT was demonstrated in a patient with complete monoplegia following TBI. Accurate diagnosis of LKA is important for successful rehabilitation because LKA is known to respond to dopaminergic drug treatment.

Effect of brain-computer interface training based on non-invasive electroencephalography using motor imagery on functional recovery after stroke - a systematic review and meta-analysis

Background

Training with brain-computer interface (BCI) technology in the rehabilitation of patients after a stroke is rapidly developing. Numerous RCT investigated the effects of BCI training (BCIT) on recovery of motor and brain function in patients after stroke.

Methods

A systematic literature search was performed in Medline, IEEE Xplore Digital Library, Cochrane library, and Embase in July 2018 and was repeated in March 2019. RCT or controlled clinical trials that included BCIT for improving motor and brain recovery in patients after a stroke were identified. Data were meta-analysed using the random-effects model. Standardized mean difference (SMD) with 95% confidence (95%CI) and 95% prediction interval (95%PI) were calculated. A meta-regression was performed to evaluate the effects of covariates on the pooled effect-size.

Results

In total, 14 studies, including 362 patients after ischemic and hemorrhagic stroke (cortical, subcortical, 121 females; mean age 53.0+/− 5.8; mean time since stroke onset 15.7+/− 18.2 months) were included. Main motor recovery outcome measure used was the Fugl-Meyer Assessment. Quantitative analysis showed that a BCI training compared to conventional therapy alone in patients after stroke was effective with an SMD of 0.39 (95%CI: 0.17 to 0.62; 95%PI of 0.13 to 0.66) for motor function recovery of the upper extremity. An SMD of 0.41 (95%CI: − 0.29 to 1.12) for motor function recovery of the lower extremity was found. BCI training enhanced brain function recovery with an SMD of 1.11 (95%CI: 0.64 to 1.59; 95%PI ranging from 0.33 to 1.89). Covariates such as training duration, impairment level of the upper extremity, and the combination of both did not show significant effects on the overall pooled estimate.

Conclusion

This meta-analysis showed evidence that BCI training added to conventional therapy may enhance motor functioning of the upper extremity and brain function recovery in patients after a stroke. We recommend a standardised evaluation of motor imagery ability of included patients and the assessment of brain function recovery should consider neuropsychological aspects (attention, concentration). Further influencing factors on motor recovery due to BCI technology might consider factors such as age, lesion type and location, quality of performance of motor imagery, or neuropsychological aspects.

Trial Registration

PROSPERO registration: CRD42018105832.

Supplementary information

Supplementary information accompanies this paper at 10.1186/s12883-020-01960-5.

The topographical organization of motor processing: An ALE meta-analysis on six action domains and the relevance of Broca's region

Action is a cover term used to refer to a large set of motor processes differing in domain specificities (e.g. execution or observation). Here we review neuroimaging evidence on action processing (N = 416; Subjects = 5912) using quantitative Activation Likelihood Estimation (ALE) and Meta-Analytic Connectivity Modeling (MACM) approaches to delineate the functional specificities of six domains: (1) Action Execution, (2) Action Imitation, (3) Motor Imagery, (4) Action Observation, (5) Motor Learning, (6) Motor Preparation. Our results show distinct functional patterns for the different domains with convergence in posterior BA44 (pBA44) for execution, imitation and imagery processing. The functional connectivity network seeding in the motor-based localized cluster of pBA44 differs from the connectivity network seeding in the (language-related) anterior BA44. The two networks implement distinct cognitive functions. We propose that the motor-related network encompassing pBA44 is recruited when processing movements requiring a mental representation of the action itself.

Diagnosis of Conversion Disorder Using Diffusion Tensor Tractography and Transcranial Magnetic Stimulation in a Patient with Mild Traumatic Brain Injury

We report on a patient with mild traumatic brain injury (TBI) who was diagnosed with conversion disorder for severe weakness of an arm, which was demonstrated using diffusion tensor tractography (DTT) and transcranial magnetic stimulation (TMS). A 23-year-old right-handed female suffered from head trauma resulting from a pedestrian car accident. She underwent rehabilitative management for memory impairment and central pain. At 14 months after onset, she complained of severe weakness of her right arm, which was detected in the morning after sleeping (right shoulder abductor: 3/5, elbow flexor: 3/5, wrist extensor: 1/5, finger flexor: 1/5, and finger extensor: 1/5). Electromyography study for peripheral neuropathy performed at 2 weeks after onset of weakness showed no abnormality. On a 14-month DTT configuration, the integrities of the left corticospinal tract (CST), supplementary motor area-corticofugal tract (SMA-CFT), and dorsal premotor cortex (dPMC)-CFT were well-preserved. Significant differences were not observed for the fractional anisotropy (FA), mean diffusivity (MD), and tract volume (TV) values of the CST, SMA-CFT, and dPMC-CFT in both hemispheres between the patient and ten right-handed age- and sex-matched normal subjects (p > 0.05). On a 14-month TMS study, MEPs obtained at the right abductor pollicis brevis muscle showed no abnormality. Using DTT and TMS, conversion disorder was demonstrated in a patient with mild TBI, who showed severe weakness of an arm. Our results suggest the usefulness of an evaluation of the CST and CFTs from the secondary motor areas using DTT, and the CST using TMS for patients who complain of motor weakness due to conversion disorder.

Acupuncture Enhances Communication between Cortices with Damaged White Matters in Poststroke Motor Impairment

Stroke is a leading cause of motor disability. Acupuncture is an effective therapeutic strategy for poststroke motor impairment. However, its mechanism is still elusive. Twenty-two stroke patients having a right-hemispheric subcortical infarct and 22 matched healthy controls were recruited to undergo diffusion tensor imaging (DTI) and functional magnetic resonance imaging (fMRI) scanning. The resting-state fMRI was implemented before and after needling at GB34 (Yanglingquan). The stroke patients presented a substantially reduced fractional anisotropy value in the right superior longitudinal fasciculus (SLF), corticospinal tract, and corpus callosum. The structural integrity of the frontoparietal part of the SLF (SLF-FP) correlated with the motor scores of lower limbs in stroke patients. This corticocortical association bundle originated from the premotor cortex (PM) and the adjacent supplementary motor area (SMA), known as secondary motor areas, and terminated in the supramarginal gyrus (SMG). After acupuncture intervention, the corresponding functional connectivity between the PM/SMA and SMG was enhanced in stroke patients compared with healthy controls. These findings suggested that the integrity of the SLF is a potential neuroimaging biomarker for motor disability of lower limbs following a stroke. Acupuncture could increase the communication between the cortices connected by the impaired white matter tracts, implying the neural mechanism underlying the acupuncture intervention.

Differences in motor network dynamics during recovery between supra- and infra-tentorial ischemic strokes

Most previous stroke studies have been performed in heterogeneous patient populations. Moreover, the brain network might demonstrate different recovery dynamics according to lesion location. In this study, we investigated variation in motor network alterations according to lesion location. Forty patients with subcortical ischemic stroke were enrolled. Patients were divided into two groups: 21 patients with supratentorial stroke (STS) and 19 patients with infratentorial stroke (ITS). All patients underwent resting-state functional magnetic resonance imaging and behavioral assessment at 2 weeks and 3 months poststroke. Twenty-four healthy subjects participated as a control group. To compare altered connectivity between groups, measures used in previous studies to evaluate interhemispheric balance and global network reorganization were investigated and the relationship between network measures and motor functions were examined. Cortico-cerebellar connectivity was also extracted to investigate its relationship with interhemispheric connectivity. In the STS group, measures related to interhemispheric balance were disrupted compared to the control group 2 weeks poststroke, while this was not found in the ITS group. During recovery, measures related to global network reorganization in the STS group and measures related to interhemispheric balance in the ITS group demonstrated significant changes, respectively. Moreover, motor functions were correlated with altered network measures in both groups. There was an interactive relationship between cortico-cerebellar and interhemispheric cortical connectivity only in the ITS group. Different changes in the motor network were observed depending on the location of stroke lesions. These results might originate from differences in the interactions between cortico-cerebellar and interhemispheric connectivity.

Non-invasive brain stimulation for fine motor improvement after stroke: a meta-analysis

The aim of this study was to determine whether non-invasive brain stimulation (NIBS) techniques improve fine motor performance in stroke. We searched PubMed, EMBASE, Web of Science, SciELO and OpenGrey for randomized clinical trials on NIBS for fine motor performance in stroke patients and healthy participants. We computed Hedges' g for active and sham groups, pooled data as random-effects models and performed sensitivity analysis on chronicity, montage, frequency of stimulation and risk of bias. Twenty-nine studies (351 patients and 152 healthy subjects) were reviewed. Effect sizes in stroke populations for transcranial direct current stimulation and repeated transcranial magnetic stimulation were 0.31 [95% confidence interval (CI), 0.08-0.55; P = 0.010; Tau² , 0.09; I² , 34%; Q, 18.23; P = 0.110] and 0.46 (95% CI, 0.00-0.92; P = 0.05; Tau² , 0.38; I² , 67%; Q, 30.45; P = 0.007). The effect size of non-dominant healthy hemisphere transcranial direct current stimulation on non-dominant hand function was 1.25 (95% CI, 0.09-2.41; P = 0.04; Tau² , 1.26; I² , 93%; Q, 40.27; P < 0.001). Our results show that NIBS is associated with gains in fine motor performance in chronic stroke patients and healthy subjects. This supports the effects of NIBS on motor learning and encourages investigation to optimize their effects in clinical and research settings.

Recovery of an injured corticofugal tract from the supplementary motor area in a patient with traumatic brain injury: A case report

RATIONALE

We report on a patient with traumatic brain injury who showed motor recovery concurrent with recovery of injured corticofugal tracts (CFTs), diagnosed by diffusion tensor tractography (DTT).

PATIENT CONCERNS

Four weeks after onset, when the patient started rehabilitation, he showed severe weakness of both upper and lower extremities [Motricity Index (MI, full score: 100/100): 9/30].

DIAGNOSES

A 29-year-old male patient underwent conservative management for traumatic hemorrhages in both frontal lobes and right thalamus resulting from a car accident.

INTERVENTIONS

The patient participated in a comprehensive rehabilitative management program, including movement therapy, dopaminergic drugs for improvement of apraxia (pramipexole: 2.5mg, amantadine: 300mg, ropinirole: 0.75 mg, and levodopa: 500mg), and neuromuscular electrical stimulation therapy of the right elbow extensors, finger extensors, both knee extensors, and ankle dorsiflexors.

OUTCOMES

After 2 months' intensive rehabilitation, his motor weakness rapidly recovered to the point that he was able to move all 4 extremities against some resistance (MI: 75/75). The right supplementary motor area (SMA)-CFT showed narrowing and partial tearing in the upper portion on 1-month DTT, and became thicker on 3-month DTT. Compared to the 12 normal control subjects, the fractional anisotropy (FA) values of the right corticospinal tract and both dorsal premotor cortex-CFT were more than 1 standard deviation lower than those of normal control subjects on both 1- and 3-month DTTs.

LESSONS

Although the tract volume of the right SMA-CFT was more than 1 standard deviation lower than normal control subjects on 1-month DTT, it increased to within 1 standard deviation on 3-month DTT. Recovery of the injured SMA-CFT concurrent with motor recovery was demonstrated in a patient with traumatic brain injury.

Cortical thickness and metabolite concentration in chronic stroke and the relationship with motor function

BACKGROUND

Hemiparesis is one of the most prevalent chronic disabilities after stroke. Biochemical and structural magnetic resonance imaging approaches may be employed to study the neural substrates underpinning upper-extremity (UE) recovery after chronic stroke.

OBJECTIVE

The purposes of this study were to 1) quantify anatomical and metabolic differences in the precentral gyrus, and 2) test the relationships between anatomical and metabolic differences, and hemiparetic arm function in individuals in the chronic stage of stroke recovery. Our hypotheses were: 1) the Stroke group would exhibit reduced precentral gyrus cortical thickness and lower concentrations of total N-acetylaspartate (tNAA) and glutamate+glutamine (Glx) in the ipsilesional motor cortex; and 2) that each of these measures would be associated with UE motor function after stroke.

METHODS

Seventeen individuals with chronic (>6 months) subcortical ischemic stroke and eleven neurologically healthy controls were recruited. Single voxel proton magnetic resonance spectroscopy (H1MRS) was performed to measure metabolite concentrations of tNAA and Glx in the precentral gyrus in both ipsilesional and contralesional hemispheres. Surface-based cortical morphometry was used to quantify precentral gyral thickness. Upper-extremity motor function was assessed using the Wolf Motor Function Test (WMFT).

RESULTS

Results demonstrated significantly lower ipsilesional tNAA and Glx concentrations and precentral gyrus thickness in the Stroke group. Ipsilesional tNAA and Glx concentration and precentral gyrus thickness was significantly lower in the ipsilesional hemisphere in the Stroke group. Parametric correlation analyses revealed a significant positive relationship between precentral gyrus thickness and tNAA concentration bilaterally. Multivariate regression analyses revealed that ipsilesional concentrations of tNAA and Glx predicted the largest amount of variance in WMFT scores. Cortical thickness measures alone did not predict a significant amount of variance in WMFT scores.

CONCLUSION

While stroke impairs both structure and biochemistry in the ipsilesional hemisphere our data suggest that tNAA has the strongest relationship with motor function.

Limb-kinetic apraxia in a patient with mild traumatic brain injury: A case report

RATIONALE

We report on a patient who developed limb-kinetic apraxia (LKA) due to an injured corticofugal tract (CFT) from the secondary motor area following mild traumatic brain injury (TBI), demonstrated on diffusion tensor tractography (DTT).

PATIENT CONCERNS

She was struck in the right leg by a sedan at a crosswalk and fell to the ground. She lost consciousness and experienced post-traumatic amnesia for approximately ten minutes. She was obliged to wear a cast for a left humerus fracture for two months, and she found she could not move her left hand quickly with intention after removal of the cast; consequently her left hand was almost non-functional. When she visited the rehabilitation department of a university hospital two years after the crash, she had mild weakness of the left upper extremity (manual muscle test: 4/5). However, the movements of the left hand were slow, clumsy, and mutilated when executing grasp-release movements of her left hand.

DIAGNOSES

A 44-year-old female suffered head trauma resulting from a pedestrian car accident.

INTERVENTIONS

When she extended all her left fingers, it took approximately eight seconds at her fastest speed to perform the pattern extending from the thumb to little finger sequentially.

OUTCOMES

On two-year DTT, narrowing and partial tearing was observed in the right supplementary motor area (SMA)-CFT.

LESSONS

Injury of the right SMA-CFT was demonstrated in a patient with LKA in a hand following mild TBI. Our results stress the need to evaluate the CFTs from the secondary motor area for patients with unexplained motor execution problems following mild TBI.

Restoring Motor Functions After Stroke: Multiple Approaches and Opportunities

More than 1.5 million people suffer a stroke in Europe per year and more than 70% of stroke survivors experience limited functional recovery of their upper limb, resulting in diminished quality of life. Therefore, interventions to address upper-limb impairment are a priority for stroke survivors and clinicians. While a significant body of evidence supports the use of conventional treatments, such as intensive motor training or constraint-induced movement therapy, the limited and heterogeneous improvements they allow are, for most patients, usually not sufficient to return to full autonomy. Various innovative neurorehabilitation strategies are emerging in order to enhance beneficial plasticity and improve motor recovery. Among them, robotic technologies, brain-computer interfaces, or noninvasive brain stimulation (NIBS) are showing encouraging results. These innovative interventions, such as NIBS, will only provide maximized effects, if the field moves away from the “one-fits all” approach toward a “patient-tailored” approach. After summarizing the most commonly used rehabilitation approaches, we will focus on NIBS and highlight the factors that limit its widespread use in clinical settings. Subsequently, we will propose potential biomarkers that might help to stratify stroke patients in order to identify the individualized optimal therapy. We will discuss future methodological developments, which could open new avenues for poststroke rehabilitation, toward more patient-tailored precision medicine approaches and pathophysiologically motivated strategies.

Interactions Between the Corticospinal Tract and Premotor-Motor Pathways for Residual Motor Output After Stroke

BACKGROUND AND PURPOSE

Brain imaging has continuously enhanced our understanding how different brain networks contribute to motor recovery after stroke. However, the present models are still incomplete and do not fit for every patient. The interaction between the degree of damage of the corticospinal tract (CST) and of corticocortical motor connections, that is, the influence of the microstructural state of one connection on the importance of another has been largely neglected.

METHODS

Applying diffusion-weighted imaging and probabilistic tractography, we investigated cross-network interactions between the integrity of ipsilesional CST and ipsilesional corticocortical motor pathways for variance in residual motor outcome in 53 patients with subacute stroke.

RESULTS

The main finding was a significant interaction between the CST and corticocortical connections between the primary motor and ventral premotor cortex in relation to residual motor output. More specifically, the data indicate that the microstructural state of the connection primary motor-ventral premotor cortex plays only a role in patients with significant damage to the CST. In patients with slightly affected CST, this connection did not explain a relevant amount of variance in motor outcome.

CONCLUSIONS

The present data show that patients with stroke with different degree of CST disruption differ in their dependency on structural premotor-motor connections for residual motor output. This finding might have important implications for future research on recovery prediction models and on responses to treatment strategies.

[The importance of neuronal networks for motor rehabilitation after a stroke]

Every year in Europe 1.5 million patients suffer a new stroke. Despite the further developments in acute therapy with nationwide stroke units, thrombolysis, thrombectomy and post-acute neurorehabilitation, only a small proportion of patients recover to a satisfactory degree allowing them to return to their normal social and professional life. This makes stroke the main cause of long-term disability with a corresponding impact on patient lives, socioeconomics and the healthcare system. Thus, the concepts of neurorehabilitation have to be extended to enhance the effects of rehabilitative treatment strategies. To achieve this, an understanding of the prediction of the course of recovery, the mechanisms underlying functional recovery and factors influencing recovery have to be enhanced for the development towards patient-tailored precision medicine approaches. A central point towards this is the understanding of stroke as a disease, which not only influences the damaged area but also the associated network. This is crucial for the understanding of the stroke-induced deficits, for prediction of recovery and options for interventional treatment strategies, which can target different areas in this network (e.g. primary motor cortex and secondary motor regions) based on individual factors of the patient. The present article discusses the importance of network alterations for motor neurorehabilitation after a stroke and which novel options, concepts and consequences could arise from this for neurorehabilitation.

The role of oligodendrocyte precursor cells expressing the GPR17 receptor in brain remodeling after stroke

Following stroke-induced neuronal damage, quiescent oligodendrocyte precursors (OPCs) are activated to proliferate and later to differentiate to myelin-producing cells. GPR17, a receptor transiently expressed on early OPCs, has emerged as a target to implement stroke repair through stimulation of OPC maturation. However, being GPR17 completely downregulated in myelin-producing oligodendrocytes, its actual role in determining the final fate of OPCs after cerebral ischemia is still uncertain. Here, to univocally define the spatiotemporal changes and final fate of GPR17-expressing OPCs, we induced ischemia by middle cerebral artery occlusion (MCAo) in reporter GPR17iCreERT2:CAG-eGreen florescent protein (GFP) mice, in which, upon tamoxifen treatment, cells expressing GPR17 become green and traceable for their entire life. Starting from 3 days and up to 2 weeks after MCAo, GFP+ cells markedly accumulated in regions surrounding the ischemic lesion; several of them proliferated, as shown by co-labeling of the DNA synthesis marker 5-Bromo-2'-deoxyuridine (BrdU). Almost all GFP+/BrdU+ cells expressed the OPC early marker neural/glial antigen 2 (NG2), indicating that they were still precursors. Accumulation of GFP+ cells was also because of OPC recruitment from surrounding areas, as suggested in vivo by acquisition of typical features of migrating OPCs, shown in vitro in presence of the chemoattractant PDGF-AA and confirmed by transplantation of GFP+-OPCs in wild-type MCAo mice. Eight weeks after MCAo, only some of these precociously recruited cells had undergone maturation as shown by NG2 loss and acquisition of mature myelinating markers like GSTpi. A pool of recruited GFP+-OPCs was kept at a precursor stage to likely make it available for further insults. Thus, very early after ischemia, GFP+-OPCs proliferate and migrate toward the lesion; however, most of these cells remain undifferentiated, suggesting functional roles other than myelination.

Restoring brain function after stroke - bridging the gap between animals and humans

Stroke is the leading cause of complex adult disability in the world. Recovery from stroke is often incomplete, which leaves many people dependent on others for their care. The improvement of long-term outcomes should, therefore, be a clinical and research priority. As a result of advances in our understanding of the biological mechanisms involved in recovery and repair after stroke, therapeutic opportunities to promote recovery through manipulation of poststroke plasticity have never been greater. This work has almost exclusively been carried out in preclinical animal models of stroke with little translation into human studies. The challenge ahead is to develop a mechanistic understanding of recovery from stroke in humans. Advances in neuroimaging techniques now enable us to reconcile behavioural accounts of recovery with molecular and cellular changes. Consequently, clinical trials can be designed in a stratified manner that takes into account when an intervention should be delivered and who is most likely to benefit. This approach is expected to lead to a substantial change in how restorative therapeutic strategies are delivered in patients after stroke.

Spontaneous and Therapeutic-Induced Mechanisms of Functional Recovery After Stroke

With increasing rates of survival throughout the past several years, stroke remains one of the leading causes of adult disability. Following the onset of stroke, spontaneous mechanisms of recovery at the cellular, molecular, and systems levels ensue. The degree of spontaneous recovery is generally incomplete and variable among individuals. Typically, the best recovery outcomes entail the restitution of function in injured but surviving neural matter. An assortment of restorative therapies exists or is under development with the goal of potentiating restitution of function in damaged areas or in nearby ipsilesional regions by fostering neuroplastic changes, which often rely on mechanisms similar to those observed during spontaneous recovery. Advancements in stroke rehabilitation depend on the elucidation of both spontaneous and therapeutic-driven mechanisms of recovery. Further, the implementation of neural biomarkers in research and clinical settings will enable a multimodal approach to probing brain state and predicting the extent of post-stroke functional recovery. This review will discuss spontaneous and therapeutic-induced mechanisms driving post-stroke functional recovery while underscoring several potential restorative therapies and biomarkers.

Does neuroimaging help to deliver better recovery of movement after stroke?

PURPOSE OF REVIEW

This review examines recent brain imaging studies that might contribute to delivering better recovery of motor function after stroke.

RECENT FINDINGS

Most recent studies characterize differences in structural and functional organization of the poststroke brain in relation to impairment, or measure alterations in brain organization as the result of one form of therapy or another. These studies have not altered clinical practice. New approaches can test specific models of motor recovery after stroke. Firstly, anatomical assessment of key motor pathways, particularly corticospinal tract, may be useful in predicting long-term outcomes if used in combination with early clinical scores. Secondly, assessment of neuronal oscillations with electro or magneto-encephalography may provide a novel way of assessing the balance between excitatory and inhibitory cortical processes and thereby provide biomarkers of the potential for experience-dependent plasticity.

SUMMARY

Most recent studies are observational and do not test a plausible model of motor recovery after stroke. Brain imaging studies of stroke recovery need to consider how to provide tools to aid prediction of long-term outcome or response to treatment, or describe potential therapeutic targets for novel recovery promoting interventions, if they are to be clinically useful.

Central perception of position sense involves a distributed neural network - Evidence from lesion-behavior analyses

It is well established that proprioceptive inputs from the periphery are important for the constant update of arm position for perception and guiding motor action. The degree to which we are consciously aware of the position of our limb depends on the task. Our understanding of the central processing of position sense is rather limited, largely based on findings in animals and individual human case studies. The present study used statistical lesion-behavior analysis and an arm position matching task to investigate position sense in a large sample of subjects after acute stroke. We excluded subjects who performed abnormally on clinical testing or a robotic visually guided reaching task with their matching arm in order to minimize the potential confound of ipsilesional impairment. Our findings revealed that a number of regions are important for processing position sense and include the posterior parietal cortex, the transverse temporal gyrus, and the arcuate fasciculus. Further, our results revealed that position sense has dissociable components - spatial variability, perceived workspace area, and perceived workspace location. Each component is associated with unique neuroanatomical correlates. These findings extend the current understanding of the neural processing of position sense and identify some brain areas that are not classically associated with proprioception.

Structural connectivity analyses in motor recovery research after stroke

Structural connectivity analyses by means of diffusion‐weighted imaging have substantially advanced the understanding of stroke‐related network alterations and their implications for motor recovery processes and residual motor function. Analyses of the corticospinal tract, alternate corticofugal pathways as well as intrahemispheric and interhemispheric corticocortical connections have not only been related to residual motor function in cross‐sectional studies, but have also been evaluated to predict functional recovery after stroke in longitudinal studies. This review will consist of an update on the available literature about structural connectivity analyses after ischemic motor stroke, followed by an outlook of possible future directions of research and applications.

Combinations of stroke neurorehabilitation to facilitate motor recovery: perspectives on Hebbian plasticity and homeostatic metaplasticity

Motor recovery after stroke involves developing new neural connections, acquiring new functions, and compensating for impairments. These processes are related to neural plasticity. Various novel stroke rehabilitation techniques based on basic science and clinical studies of neural plasticity have been developed to aid motor recovery. Current research aims to determine whether using combinations of these techniques can synergistically improve motor recovery. When different stroke neurorehabilitation therapies are combined, the timing of each therapeutic program must be considered to enable optimal neural plasticity. Synchronizing stroke rehabilitation with voluntary neural and/or muscle activity can lead to motor recovery by targeting Hebbian plasticity. This reinforces the neural connections between paretic muscles and the residual motor area. Homeostatic metaplasticity, which stabilizes the activity of neurons and neural circuits, can either augment or reduce the synergic effect depending on the timing of combination therapy and types of neurorehabilitation that are used. Moreover, the possibility that the threshold and degree of induced plasticity can be altered after stroke should be noted. This review focuses on the mechanisms underlying combinations of neurorehabilitation approaches and their future clinical applications. We suggest therapeutic approaches for cortical reorganization and maximal functional gain in patients with stroke, based on the processes of Hebbian plasticity and homeostatic metaplasticity. Few of the possible combinations of stroke neurorehabilitation have been tested experimentally; therefore, further studies are required to determine the appropriate combination for motor recovery.

Stochastic process for white matter injury detection in preterm neonates

Preterm births are rising in Canada and worldwide. As clinicians strive to identify preterm neonates at greatest risk of significant developmental or motor problems, accurate predictive tools are required. Infants at highest risk will be able to receive early developmental interventions, and will also enable clinicians to implement and evaluate new methods to improve outcomes. While severe white matter injury (WMI) is associated with adverse developmental outcome, more subtle injuries are difficult to identify and the association with later impairments remains unknown. Thus, our goal was to develop an automated method for detection and visualization of brain abnormalities in MR images acquired in very preterm born neonates. We have developed a technique to detect WMI in T1-weighted images acquired in 177 very preterm born infants (24–32 weeks gestation). Our approach uses a stochastic process that estimates the likelihood of intensity variations in nearby pixels; with small variations being more likely than large variations. We first detect the boundaries between normal and injured regions of the white matter. Following this we use a measure of pixel similarity to identify WMI regions. Our algorithm is able to detect WMI in all of the images in the ground truth dataset with some false positives in situations where the white matter region is not segmented accurately.