Motor Cortical Reorganization Research Articles

Unlocking the power of motor imagery: a comprehensive review on its application in alleviating foot pain.

Motor imagery is a cognitive process that involves mentally simulating movements without physical execution. It has been studied in the context of foot pain to understand the role of motor cortical reorganization and its impact on motor imagery abilities. However, further research is needed to establish consistent evidence regarding the relationship between motor imagery and foot pain. This review analyzed five relevant articles that investigated motor imagery in the context of foot pain. The studies involved participants with various conditions, including leg amputation, chronic leg pain, complex regional pain syndrome, and Achilles tendinopathy. Different methodologies were employed, including motor cortical mapping, foot laterality recognition tasks, EEG recordings, and treatment interventions incorporating motor imagery. The findings indicated that individuals with leg amputation exhibited functional reorganization in upper limb motor cortical maps, with a breakdown in the inhibitory relationship between foot and hand representations. Participants with chronic leg pain demonstrated slower and less accurate performance on foot laterality recognition tasks compared to healthy controls. Complex regional pain syndrome patients displayed distinct motor imagery strategies and responded differently to first-person and third-person perspectives. EEG studies revealed differences in brain activity during motor imagery tasks under pain-free and pain conditions. Treatment interventions incorporating motor imagery showed promising outcomes in improving functional outcomes and reducing pain levels. Motor imagery plays a significant role in foot pain conditions, although the evidence is still emerging. The findings suggest that motor imagery abilities may be affected by leg amputation, chronic pain, and complex regional pain syndrome. Further research is needed to establish standardized protocols for assessing motor imagery, identify specific patient populations that may benefit most from motor imagery interventions, and explore long-term effects. Integrating motor imagery into clinical practice has the potential to enhance rehabilitation approaches and improve outcomes in foot pain management.

Longitudinal changes of motor cortex function during motor recovery after stroke

ABSTRACT Background and purpose Functional magnetic resonance imaging (fMRI) combined with behavioral assessments was used in our study to investigate the dynamic process of motor cortical functional reorganization after infarction. Therefore, we could provide a theoretical basis and build a useful evaluation system for rehabilitation after stroke and various other cerebral injuries. Methods Acute stroke patients with a single lesion in the middle cerebral artery supply area and age- and sex-matched healthy volunteers were recruited. A longitudinal observational study involving 20 patients with stroke was conducted using repeated fMRI. Task-based fMRI data were acquired 3 times over a period of 3 months. The behavioral assessment included dynamometer and finger-tapping tests to evaluate the strength and dexterity of each upper arm. Results Behavioral results: The behavioral assessments demonstrated large improvements in session 2 and session 3. fMRI results: The healthy group showed activation in the contralateral primary sensory-motor cortex (S1M1) when executing tasks with either the left or right hand. Compared with the healthy subjects, the patients demonstrated greater activation in the ipsilateral frontal and parietal cortices and supplementary motor areas (SMAs). Across all sessions, more motor activation was observed in the left infarction group. Conclusions Our results show that motor cortical activation induced by moving the paretic hand changes over time. There were differences in motor functional recovery and motor cortex compensation between the dominant hemisphere and nondominant hemisphere after stroke.

Characterization of Bimanual Cyclical Tasks From Single-Trial EEG-fNIRS Measurements.

Robot-assisted bimanual training is promising to improve motor function and cortical reorganization for hemiparetic stroke patients. Closing the rehabilitation training loop with neurofeedback can help refine training protocols in time for better engagements and outcomes. However, due to the low signal-to-noise ratio (SNR) and non-stationary properties of neural signals, reliable characterization of bimanual training-induced neural activities from single-trial measurement is challenging. In this study, ten human participants were recruited conducting robot-assisted bimanual cyclical tasks (in-phase, 90° out-of-phase, and anti-phase) when concurrent electroencephalography (EEG) and functional near-infrared spectroscopy (fNIRS) were recorded. A unified EEG-fNIRS bimodal signal processing framework was proposed to characterize neural activities induced by three types of bimanual cyclical tasks. In this framework, novel artifact removal methods were used to improve the SNR and the task-related component analysis (TRCA) was introduced to increase the reproducibility of EEG-fNIRS bimodal features. The optimized features were transformed into low-dimensional indicators to reliably characterize bimanual training-induced neural activation. The SVM classification results of three bimanual cyclical tasks revealed a good discrimination ability of EEG-fNIRS bimodal indicators (90.1%), which was higher than that using EEG (74.8%) or fNIRS (82.2%) alone, supporting the proposed method as a feasible technique to characterize neural activities during robot-assisted bimanual training.

Local activation of \u03b12 adrenergic receptors is required for vagus nerve stimulation induced motor cortical plasticity

Vagus nerve stimulation (VNS) paired with rehabilitation training is emerging as a potential treatment for improving recovery of motor function following stroke. In rats, VNS paired with skilled forelimb training results in significant reorganization of the somatotopic cortical motor map; however, the mechanisms underlying this form of VNS-dependent plasticity remain unclear. Recent studies have shown that VNS-driven cortical plasticity is dependent on noradrenergic innervation of the neocortex. In the central nervous system, noradrenergic α2 receptors (α2-ARs) are widely expressed in the motor cortex and have been critically implicated in synaptic communication and plasticity. In current study, we examined whether activation of cortical α2-ARs is necessary for VNS-driven motor cortical reorganization to occur. Consistent with previous studies, we found that VNS paired with motor training enlarges the map representation of task-relevant musculature in the motor cortex. Infusion of α2-AR antagonists into M1 blocked VNS-driven motor map reorganization from occurring. Our results suggest that local α2-AR activation is required for VNS-induced cortical reorganization to occur, providing insight into the mechanisms that may underlie the neuroplastic effects of VNS therapy.

Abnormal changes in motor cortical maps in humans with spinal cord injury.

The functional role of motor cortical reorganization following spinal cord injury (SCI) remains largely unknown. Here, we tested motor maps in a hand muscle at rest and during voluntary contraction of the hand with and without voluntary contraction of a proximal arm muscle. Motor map area in participants with SCI decreased during hand voluntary contraction and further decreased during additional contraction of a proximal arm muscle compared with rest. In contrast, motor map area in controls increased during the same motor tasks. Participants with SCI with more severe sensory deficits in the hand showed larger decreases in motor map area. Ten minutes of hand muscle-tendon vibration increased the motor map area during voluntary contraction in SCI participants. These novel findings suggest that abnormal changes in motor cortical maps during voluntary contraction after SCI can be reshaped by sensory input, knowledge that can have implications for rehabilitation. Motor cortical representations reorganize following cervical spinal cord injury (SCI). The functional role of this reorganization remains largely unknown. Using neuronavigated transcranial magnetic stimulation, we examined motor cortical maps during voluntary contraction in humans with chronic cervical SCI and age-matched controls. We constructed motor maps in the first dorsal interosseous (FDI) muscle at rest and during voluntary contraction of the FDI with and without voluntary contraction of the biceps brachi (BB). The role of sensory input into this reorganization was examined by muscle-tendon vibration. We found that, at rest, motor maps were larger in SCI (22.3cm2 ) compared with control (12.6cm2 , P<0.001) participants. Motor map area increased during voluntary contraction of the FDI (120.7%) and further increased during contraction of the BB (143.9%) compared with rest in control subjects; however, motor map area decreased during voluntary contraction of the FDI (69.5%) and further decreased during contraction of the BB (55.5%) in individuals with SCI. SCI participants with larger decreases in map area during voluntary contraction of the FDI were those with larger sensory deficits in the hand and 10min of hand muscle-tendon vibration increased motor map area. These results provide the first evidence of abnormal changes in motor cortical maps in humans with chronic SCI during voluntary contraction, suggesting that sensory input can help to reshape this reorganization.

A novel fully immersive virtual reality environment for upper extremity rehabilitation in patients with stroke.

Given the rising incidence of stroke, several technology-driven methods for rehabilitation have recently been developed. Virtual reality (VR) is a promising therapeutic technology among them. We recently developed a neuroscientifically grounded VR system to aid recovery of motor function poststroke. The developed system provides unilateral and bilateral upper extremity (UE) training in a fully immersive virtual environment that may stimulate and activate mirror neurons (MNs) in the brain necessary for UE rehabilitation. Twenty-three participants were randomized to a VR group (n=12) to receive VR intervention (8 h within 2 weeks) plus 8-h occupational therapy (OT) or a control group (n=11) to receive time-matched OT alone. Treatment effects on motor recovery and cortical reorganization were investigated using the Barthel Index (BI), Fugl-Meyer Upper Extremity (FM-UE), and resting-state fMRI. Both groups significantly improved BI (P < 0.05), reflecting the recovery of UE motor function. The VR group revealed significant improvements on FM-UE scores (P < 0.05) than the control group. Neural activity increased after the intervention, particularly in the brain areas implicating MNs, such as in the primary motor cortex. Overall, results suggested that using a neuroscientifically grounded VR system might offer additional benefits for UE rehabilitation in patients receiving OT.

Action Observation for Neurorehabilitation in Apraxia.

Neurorehabilitation and brain stimulation studies of post-stroke patients suggest that action-observation effects can lead to rapid improvements in the recovery of motor functions and long-term motor cortical reorganization. Apraxia is a clinically important disorder characterized by marked impairment in representing and performing skillful movements [gestures], which limits many daily activities and impedes independent functioning. Recent clinical research has revealed errors of visuo-motor integration in patients with apraxia. This paper presents a rehabilitative perspective focusing on the possibility of action observation as a therapeutic treatment for patients with apraxia. This perspective also outlines impacts on neurorehabilitation and brain repair following the reinforcement of the perceptual-motor coupling. To date, interventions based primarily on action observation in apraxia have not been undertaken.

Accurate motor mapping in awake common marmosets using micro-electrocorticographical stimulation and stochastic threshold estimation

Objective. Motor map has been widely used as an indicator of motor skills and learning, cortical injury, plasticity, and functional recovery. Cortical stimulation mapping using epidural electrodes is recently adopted for animal studies. However, several technical limitations still remain. Test-retest reliability of epidural cortical stimulation (ECS) mapping has not been examined in detail. Many previous studies defined evoked movements and motor thresholds by visual inspection, and thus, lacked quantitative measurements. A reliable and quantitative motor map is important to elucidate the mechanisms of motor cortical reorganization. The objective of the current study was to perform reliable ECS mapping of motor representations based on the motor thresholds, which were stochastically estimated by motor evoked potentials and chronically implanted micro-electrocorticographical (µECoG) electrode arrays, in common marmosets. Approach. ECS was applied using the implanted µECoG electrode arrays in three adult common marmosets under awake conditions. Motor evoked potentials were recorded through electromyographical electrodes implanted in upper limb muscles. The motor threshold was calculated through a modified maximum likelihood threshold-hunting algorithm fitted with the recorded data from marmosets. Further, a computer simulation confirmed reliability of the algorithm. Main results. Computer simulation suggested that the modified maximum likelihood threshold-hunting algorithm enabled to estimate motor threshold with acceptable precision. In vivo ECS mapping showed high test-retest reliability with respect to the excitability and location of the cortical forelimb motor representations. Significance. Using implanted µECoG electrode arrays and a modified motor threshold-hunting algorithm, we were able to achieve reliable motor mapping in common marmosets with the ECS system.

Domiciliary VR-Based Therapy for Functional Recovery and Cortical Reorganization: Randomized Controlled Trial in Participants at the Chronic Stage Post Stroke.

BackgroundMost stroke survivors continue to experience motor impairments even after hospital discharge. Virtual reality-based techniques have shown potential for rehabilitative training of these motor impairments. Here we assess the impact of at-home VR-based motor training on functional motor recovery, corticospinal excitability and cortical reorganization.ObjectiveThe aim of this study was to identify the effects of home-based VR-based motor rehabilitation on (1) cortical reorganization, (2) corticospinal tract, and (3) functional recovery after stroke in comparison to home-based occupational therapy.MethodsWe conducted a parallel-group, controlled trial to compare the effectiveness of domiciliary VR-based therapy with occupational therapy in inducing motor recovery of the upper extremities. A total of 35 participants with chronic stroke underwent 3 weeks of home-based treatment. A group of subjects was trained using a VR-based system for motor rehabilitation, while the control group followed a conventional therapy. Motor function was evaluated at baseline, after the intervention, and at 12-weeks follow-up. In a subgroup of subjects, we used Navigated Brain Stimulation (NBS) procedures to measure the effect of the interventions on corticospinal excitability and cortical reorganization.ResultsResults from the system’s recordings and clinical evaluation showed significantly greater functional recovery for the experimental group when compared with the control group (1.53, SD 2.4 in Chedoke Arm and Hand Activity Inventory). However, functional improvements did not reach clinical significance. After the therapy, physiological measures obtained from a subgroup of subjects revealed an increased corticospinal excitability for distal muscles driven by the pathological hemisphere, that is, abductor pollicis brevis. We also observed a displacement of the centroid of the cortical map for each tested muscle in the damaged hemisphere, which strongly correlated with improvements in clinical scales.ConclusionsThese findings suggest that, in chronic stages, remote delivery of customized VR-based motor training promotes functional gains that are accompanied by neuroplastic changes.Trial RegistrationInternational Standard Randomized Controlled Trial Number NCT02699398 (Archived by ClinicalTrials.gov at https://clinicaltrials.gov/ct2/show/NCT02699398?term=NCT02699398&rank=1)

Smudging of the Motor Cortex Is Related to the Severity of Low Back Pain.

Cross-sectional design. Here we aimed to determine whether motor cortical reorganization in low back pain (LBP) can be identified using noninvasive surface electromyographic (EMG) recordings of back muscles at different lumbar levels, and whether cortical reorganization is related to clinical features of LBP. Reorganization of motor regions of the brain may contribute to altered motor control, pain, and disability in chronic LBP. However, data have been limited by the need for invasive recordings of back muscle myoelectric activity. The relationship between altered cortical organization and clinical features of LBP remains unclear. In 27 individuals with recurrent, nonspecific LBP and 23 pain-free controls, we mapped the motor cortical representation of the paraspinal muscles using transcranial magnetic stimulation in conjunction with noninvasive surface EMG recordings at L3 and L5 levels. Clinical measures of pain severity, location, and duration were made. The results demonstrate a loss of discrete motor cortical organization of the paraspinal muscles in chronic LBP that can be identified using noninvasive EMG recordings. A loss of discrete cortical organization was clearer when surface electrodes were positioned at L3 rather than L5. A novel finding was that altered motor cortical organization (number of discrete peaks and map volume) was associated with the severity and location of LBP. These data suggest that surface EMG positioned at L3 is appropriate for the identification of changes in the motor cortex in LBP. Furthermore, our data have implications for treatment strategies that aim to restore cortical organization in LBP. 2.

Changes in Expressions of Major Histocompatibility Complex Class I, Paired-Immunoglobulin-Like Receptor B, and Cluster of Differentiation 3ζ in Motor Cortical Representations of the Brachial Plexus After Avulsion in Rats

Major histocompatibility complex class I (MHCI), paired-immunoglobulin-like receptor B (PirB), and cluster of differentiation 3ζ (CD3ζ) negatively regulate neuronal plasticity in developing and adult brains. The aim of this study was to evaluate expressive changes of these factors in motor cortical representations of the brachial plexus (MCRBP) after total brachial plexus root avulsion (tBPRA). A total of 45 rats were randomly and equally divided into 3 groups for evaluating mRNA and protein expression levels of MHCI, PirB, and CD3ζ: 7 days, 3 months, and control. In the 7-day and 3-month groups, expressions were examined at 7 days and 3 months, respectively, after left tBPRA. In the control group, the brachial plexus was uninjured. Three rats from each group were used for examining expressions of MHCI, PirB, and CD3ζ proteins by immunofluorescence labeling, 6 rats for quantification of MHCI, PirB, and CD3ζ mRNAs by real-time quantitative polymerase chain reaction, and the remaining 6 animals for quantification of MHCI, PirB, and CD3ζ proteins by Western blotting. In the original MCRBP, mRNA and protein expression levels of MHCI, PirB, and CD3ζ were down-regulated 7 days postinjury compared with control (P<0.01). Interestingly, mRNA and protein expression levels of these factors were up-regulated at 3 months compared with 7 days (P < 0.01), excepting PirB protein, whose expression was not increasing (P > 0.05). Recovery of protein expressions were initiated from near the border region of the original MCRBP. MHCI, PirB, and CD3ζ may participate in motor cortical reorganization after tBPRA.

P023 Motor cortical reorganization and clinical outcomes after stroke: A longitudinal TMS/EEG evaluation

Introduction Since early days after stroke, the brain undergoes a complex reorganization to allow compensatory mechanisms that promote functional recovery. Characterizing specific neurophysiological markers of motor recovery after stroke could improve clinical decision making. Objectives: To track the time-course of motor cortical reorganization in a stroke patients group, and to individuate the neurophysiological markers associated to clinical outcome. Patients & methods Ten patients in the sub-acute phase of ischemic subcortical stroke were evaluated within 20 days and after 40, 60 and 180 days after stroke. For each time-point, cortical reactivity and cortical oscillations changes, evoked by 80 single TMS pulses, were assessed over the motor cortex of the affected and unaffected hemisphere, combining TMS-EEG. These measurements were paralleled with motor and clinical evaluations. Repeated measures ANOVA and Friedman test were used to evaluate changes over time of all measures. Results Our data showed specific cortical oscillatory activity changes in the alpha band, in a specific time point of the longitudinal evaluation only in the affected hemisphere. Stroke patients showed a significant increase in TMS-evoked alpha oscillations, as highlighted by spectral perturbation analysis. Notably, these changes occurred at 60 days after stroke, indicating that crucial mechanisms of cortical reorganization occur in this short-time window. Moreover, a cortical reactivity increase was observed at 40 days after stroke onset in affected hemisphere respect to other times and respect to unaffected hemisphere. These changes coincided with the clinical and behavioural amelioration. Conclusion For the first time, this study demonstrates the possibility to track longitudinally the motor cortical changes following stroke, by means a multimodal approach. These findings could allow, not only to identify neurophysiological markers of stroke pathophysiology, but also to provide new insight into how and when neuromodulatory interventions could drive neuroplasticity in a functional direction.

Motor cortical reorganization and clinical outcomes after stroke: a longitudinal TMS/EEG evaluation

Motor cortical reorganization and clinical outcomes after stroke: a longitudinal TMS/EEG evaluation

P293 Assessment of primary motor cortex plastic changes following the use of a new prosthetic system able to provide somatosensory feedback from the missing hand in an amputee patient: A TMS study

Introduction The cortical representation of a muscle can be significantly modified by plastic reorganization following a limb amputation. These plastic changes are not immutable and can be further modified restoring by the use of prosthesis like new bionic anthropomorphic prosthesis connected to the peripheral nervous system via bidirectional neural interfaces. Transcranial magnetic stimulation (TMS) is a non-invasive technique commonly used to assess topographical reorganization of motor brain areas. Objective The aim of this study is to evaluate the motor cortical reorganization of primary motor cortex with the TMS mapping technique in a left trans-radial amputee patient following the use of a novel prosthetic system able to provide somatosensory feed-back from the lost hand of the user. Materials and methods Cortical motor output was mapped via TMS (intensity 10% above standardized excitability motor Threshold) for each hemisphere at the beginning, after 1 month and 2 month of training with the new prosthetic system. Peripheral responses were recorded from forearm flexor and extensor carpi ulnaris muscles of both limbs. Resting and Active motor threshold were also collected during separate mapping of right and left hemispheres. Results No significant differences were found in the motor thresholds between the two hemispheres before and after implantation. Pre-surgical TMS motor maps showed a slight abnormal interhemispheric asymmetry of motor cortex topography, resulted in a smaller area of representation of muscles governing the stump compared to the area for the intact limb. Following training, post-surgical maps, showed a reduction and a partial reversal of this asymmetry because of an enlargement of the excitable area on the right hemisphere contralateral to the stump, leading towards a more symmetrical muscle representation in the two hemispheres, as in control subjects. Conclusions Our experiment provides a direct and unique evidence of brain plasticity changes occurring in the motor cortex following the use of a prosthetic system able to restore a somatosensory feedback from the missing limb after amputation. Figure options Download full-size image Download high-quality image (378 K) Download as PowerPoint slide Figure options Download full-size image Download high-quality image (399 K) Download as PowerPoint slide

Reduced Phrenic Motoneuron Recruitment during Sustained Inspiratory Threshold Loading Compared to Single-Breath Loading: A Twitch Interpolation Study

In humans, inspiratory constraints engage cortical networks involving the supplementary motor area. Functional magnetic resonance imaging (fMRI) shows that the spread and intensity of the corresponding respiratory-related cortical activation dramatically decrease when a discrete load becomes sustained. This has been interpreted as reflecting motor cortical reorganization and automatisation, but could proceed from sensory and/or affective habituation. To corroborate the existence of motor reorganization between single-breath and sustained inspiratory loading (namely changes in motor neurones recruitment), we conducted a diaphragm twitch interpolation study based on the hypothesis that motor reorganization should result in changes in the twitch interpolation slope. Fourteen healthy subjects (age: 21–40 years) were studied. Bilateral phrenic stimulation was delivered at rest, upon prepared and targeted voluntary inspiratory efforts (“vol”), upon unprepared inspiratory efforts against a single-breath inspiratory threshold load (“single-breath”), and upon sustained inspiratory efforts against the same type of load (“continuous”). The slope of the relationship between diaphragm twitch transdiaphragmatic pressure and the underlying transdiaphragmatic pressure was −1.1 ± 0.2 during “vol,” −1.5 ± 0.7 during “single-breath,” and −0.6 ± 0.4 during “continuous” (all slopes expressed in percent of baseline.percent of baseline−1) all comparisons significant at the 5% level. The contribution of the diaphragm to inspiration, as assessed by the gastric pressure to transdiaphragmatic pressure ratio, was 31 ± 17% during “vol,” 22 ± 16% during “single-breath” (p = 0.13), and 19 ± 9% during “continuous” (p = 0.0015 vs. “vol”). This study shows that the relationship between the amplitude of the transdiaphragmatic pressure produced by a diaphragm twitch and its counterpart produced by the underlying diaphragm contraction is not unequivocal. If twitch interpolation is interpreted as reflecting motoneuron recruitment, this study supports motor reorganization compatible with “diaphragm sparing” when an inspiratory threshold load becomes sustained.

Combinatorial Motor Training Results in Functional Reorganization of Remaining Motor Cortex after Controlled Cortical Impact in Rats.

Cortical reorganization subsequent to post-stroke motor rehabilitative training (RT) has been extensively examined in animal models and humans. However, similar studies focused on the effects of motor training after traumatic brain injury (TBI) are lacking. We previously reported that after a moderate/severe TBI in adult male rats, functional improvements in forelimb use were accomplished only with a combination of skilled forelimb reach training and aerobic exercise, with or without nonimpaired forelimb constraint. Thus, the current study was designed to examine the relationship between functional motor cortical map reorganization after experimental TBI and the behavioral improvements resulting from this combinatorial rehabilitative regime. Adult male rats were trained to proficiency on a skilled reaching task, received a unilateral controlled cortical impact (CCI) over the forelimb area of the caudal motor cortex (CMC). Three days post-CCI, animals began RT (n = 13) or no rehabilitative training (NoRT) control procedures (n = 13). The RT group participated in daily skilled reach training, voluntary aerobic exercise, and nonimpaired forelimb constraint. This RT regimen significantly improved impaired forelimb reaching success and normalized reaching strategies, consistent with previous findings. RT also enlarged the area of motor cortical wrist representation, derived by intracortical microstimulation, compared to NoRT. These findings indicate that sufficient RT can greatly improve motor function and improve the functional integrity of remaining motor cortex after a moderate/severe CCI. When compared with findings from stroke models, these findings also suggest that more intense RT may be needed to improve motor function and remodel the injured cortex after TBI.

Motor and sensory cortical reorganization after bilateral forearm transplantation: Four-year follow-up fMRI case study

The objective of this study was to characterize the cortical activity pattern of one patient who received bilateral forearm transplants.Using fMRI we acquired motor and sensory brain activity every year after surgery and during three consecutive years while the patient underwent physical rehabilitation.The motor related cortical activity evaluated during the first year showed a sparse pattern involving several brain regions. Over time, the analysis showed a progressive delimitation of the motor-related areas that had significant activity. The results also showed continuous size reductions of the activated cluster in the motor cortex. The activation in the sensory cortex showed significant increases in cluster size over time. The intensity of both motor and sensory cortical activations correlated with the Disabilities of the Arm, Shoulder and Hand questionnaire.Our results show significant cortical reorganization of motor and sensory cortices after transplantation of bilateral forearm transplantation over a four-year period.

Influence of contralateral homologous cortices on motor cortical reorganization after brachial plexus injuries in rats

Brachial plexus injuries induce corresponding cortical representations to be occupied by adjacent cortices. The purpose of this study was to clarify if contralateral homologous motor regions of adjacent cortices influence occupation of deafferented motor cortex. 36 rats were divided into 3 groups of 12 each. In group 1, total brachial plexus root avulsion (tBPRA) was made on the left side. In group 2, rats underwent left tBPRA combined with corpus callosum transection (CCX). In group 3, only CCX was performed. 6 rats in each group were used for intracortical microstimulation (ICMS) to map representations of motor cortex in the right hemisphere at 7 days and the other 6 rats, at 3 months. 18 more rats without any operation underwent ICMS, with 6 each taken to serve as normal control for motor cortical representations' changes caused by different surgery. Results showed that in groups 1 and 2, sites for motor cortical representations of vibrissae, of neck and of the hindlimb was statistically more than that of control, respectively, and statistically more sites were found at 3 months than at 7 days, respectively. At the two time points, sites for vibrissa cortices and that for the hindlimb were statistically more in group 2 than in group 1, respectively. CCX alone did not induce change of site number for motor cortical representations. We conclude that after tBPRA, contralateral homologous motor cortices may, to some extent, prevent neighboring cortices from encroachment on motor cortical representations of the brachial plexus.

Cortical Stimulation Concurrent With Skilled Motor Training Improves Forelimb Function and Enhances Motor Cortical Reorganization Following Controlled Cortical Impact

Background. Electrical and magnetic brain stimulation can improve motor function following stroke in humans, rats, and nonhuman primates, especially when paired with rehabilitative training (RT). Previously, we found in rodent stroke models that epidural electrical cortical stimulation (CS) of the ipsilesional motor cortex (MC) combined with motor RT enhances motor function and motor cortical plasticity. It was unknown whether CS following experimental traumatic brain injury (TBI) would have similar effects. Objective. To test the effects of CS combined with motor training after moderate/severe TBI on behavioral outcome and motor cortical organization. Methods. Following unilateral controlled cortical impact (CCI) over the caudal forelimb area of the MC in adult male rats, forelimb reach training was administered daily for 9 weeks concurrently with subthreshold, 100-Hz monopolar CS or no-stimulation control procedures. The rate and magnitude of behavioral improvements and changes in forelimb movement representations in the injured MC as revealed by intracortical microstimulation were measured. Results. CCI resulted in severe motor impairments persisting throughout the 9 weeks of training in both groups, but CS-treated animals had significantly greater behavioral improvements. CS also increased wrist motor cortical representation, one of the main movements used in the training task, when compared with RT alone. However, the overall recovery level was modest, leaving animals still extremely impaired. Conclusions. These data suggest that CS may be useful for improving rehabilitation efficacy after TBI but also raise the possibility that the CS parameters that are highly effective following stroke are suboptimal after moderate/severe TBI.

Enduring Poststroke Motor Functional Improvements by a Well–Timed Combination of Motor Rehabilitative Training and Cortical Stimulation in Rats

Background. In animal stroke models, peri-infarct cortical stimulation (CS) combined with rehabilitative reach training (RT) enhances motor functional outcome and cortical reorganization, compared with RT alone. It was unknown whether the effects of CS + RT (a) persist long after treatment, (b) can be enhanced by forcing greater use of the paretic limb, and (C) vary with treatment onset time. Objective. To test the endurance, time sensitivity, and the potential for augmentation by forced forelimb use of CS + RT treatment effects following ischemic stroke. Methods. Adult rats that were proficient in skilled reaching received unilateral ischemic motor cortical lesions. RT was delivered for 3 weeks alone or concurrently with 100-Hz cathodal epidural CS, delivered at 50% of movement thresholds. In study 1, this treatment was initiated at 14 days postinfarct, with some subgroups receiving an overlapping period of continuous constraint of the nonparetic forelimb to force use of the paretic limb. The function of the paretic limb was assessed weekly for 9 to 10 months posttreatment. In study 2, rats underwent CS, RT, and the combination during the chronic postinfarct period. Results. Early onset CS + RT resulted in greater functional improvements than RT alone. The CS-related gains persisted for 9 to 10 months posttreatment and were not significantly influenced by forced use of the paretic limb. When treatment onset was delayed until 3 months post-infarct, RT alone improved function, but CS + RT was no more effective than RT alone. Conclusion. CS can enhance the persistence, as well as the magnitude of RT-driven functional improvements, but its effectiveness in doing so may vary with time postinfarct.