An fMRI investigation of hand representation in paraplegic humans

Multisensory integration in humans with spinal cord injury

Although multisensory integration (MSI) has been extensively studied, the underlying mechanisms remain a topic of ongoing debate. Here we investigate these mechanisms by comparing MSI in healthy controls to a clinical population with spinal cord injury (SCI). Deafferentation following SCI induces sensorimotor impairment, which may alter the ability to synthesize cross-modal information. We applied mathematical and computational modeling to reaction time data recorded in response to temporally congruent cross-modal stimuli. We found that MSI in both SCI and healthy controls is best explained by cross-modal perceptual competition, highlighting a common competition mechanism. Relative to controls, MSI impairments in SCI participants were better explained by reduced stimulus salience leading to increased cross-modal competition. By combining traditional analyses with model-based approaches, we examine how MSI is realized during normal function, and how it is compromised in a clinical population. Our findings support future investigations identifying and rehabilitating MSI deficits in clinical disorders.

Effective Connectivity in Spinal Cord Injury-Induced Neuropathic Pain

AIM

The aim of this study was to differentiate the effects of spinal cord injury (SCI) and central neuropathic pain (CNP) on effective connectivity during motor imagery of legs, where CNP is typically experienced.

METHODS

Multichannel EEG was recorded during motor imagery of the legs in 3 groups of people: able-bodied (N = 10), SCI with existing CNP (N = 10), and SCI with no CNP (N = 20). The last group was followed up for 6 months to check for the onset of CNP. Source reconstruction was performed to obtain cortical activity in 17 areas spanning sensorimotor regions and pain matrix. Effective connectivity was calculated using the directed transfer function in 4 frequency bands and compared between groups.

RESULTS

A total of 50% of the SCI group with no CNP developed CNP later. Statistically significant differences in effective connectivity were found between all groups. The differences between groups were not dependent on the frequency band. Outflows from the supplementary motor area were greater for the able-bodied group while the outflows from the secondary somatosensory cortex were greater for the SCI groups. The group with existing CNP showed the least differences from the able-bodied group, appearing to reverse the effects of SCI. The connectivities involving the pain matrix were different between able-bodied and SCI groups irrespective of CNP status, indicating their involvement in motor networks generally.

SIGNIFICANCE

The study findings might help guide therapeutic interventions targeted at the brain for CNP alleviation as well as motor recovery post SCI.

Corticomuscular Connectivity during Walking in Able Bodied and Individuals with Incomplete Spinal Cord Injury

This exploratory study used EEG as mobile imaging method to study cortico-muscular connectivity (CMC) during walking in able-bodied individuals (AB) and individuals with spinal cord injury (iSCI), while walking with and without exoskeleton walking robot (EWR) assistance. We also explored change in CMC after intensive training using EWR assistance in iSCI. Results showed no different in CMC within the AB group during walking with and without robot assistance. However, before training the iSCI subjects showed lower CMC during walking with robot assistance. The intensive 40 hours of walking training with EWR improved the walking function in iSCI participants allowing them to walk with robot assistance set to lower assistance level. This decrease in assistance level and improvement in walking function correlated with increase in CMC, reducing the difference in CMC during walking with and without EWR assistance. The findings suggest that high level of robot assistance and low walking function in iSCI correlates with weaker connectivity between primary motor cortices and lower extremity muscles. Further research is needed to better understand the importance of intention and cortical involvement in training of walking function using EWRs. Clinical Relevance - This study provides innovative data on CMC during walking and how it changes with EWR assistance and with training. This research is important to the clinical field to provide recommendations of how training of walking function can be delivered to maximize cortical engagement and improve rehabilitation outcomes.

Identifying Oscillations under Multi-site Sensory Stimulation for High-level Peripheral Nerve Injured Patients：A Pilot Study

OBJECTIVE

For high-level peripheral nerve injured (PNI) patients with severe sensory dysfunction of upper extremities, identifying the multi-site tactile stimulation is of great importance to provide neurorehabilitation with sensory feedback. In this pilot study, we showed the feasibility of identifying multi-site and multi-intensity tactile stimulation in terms of electroencephalography (EEG).

APPROACH

Three high-level PNI patients and eight non-PNI participants were recruited in this study. Four different sites over the upper arm, forearm, thumb finger and little finger were randomly stimulated at two intensities (both sensory-level) based on the transcutaneous electrical nerve stimulation (TENS). Meanwhile, 64-channel EEG signals were recorded during the passive tactile sense stimulation on each side.

MAIN RESULTS

The spatial-spectral distribution of brain oscillations underlying multi-site sensory stimulation showed dominant power attenuation over the somatosensory and prefrontal cortices in both alpha-band (8-12 Hz) and beta-band (13-30 Hz). But there was no significant difference among different stimulation sites in terms of the averaged power spectral density over the region of interest (ROI). By further identifying different stimulation sites using temporal-spectral features, we found the classification accuracies were all above 89% for the affected arm of PNI patients, comparable to that from their intact side and that from the non-PNI group. When the stimulation site-intensity combinations were treated as eight separate classes, the classification accuracies were ranging from 88.89% to 99.30% for the affected side of PNI subjects, similar to that from their non-affected side and that from the non-PNI group. Other performance metrics, including Specificity, Precision, and F1-Score, also showed a sound identification performance for both PNI patients and non-PNI subjects.

SIGNIFICANCE

These results suggest that reliable brain oscillations could be evoked and identified well, even though induced tactile sense could not be discerned by the PNI patients. This study have implication for facilitating bidirectional neurorehabilitation systems with sensory feedback.

Differences in sensorimotor and functional recovery between the dominant and non-dominant upper extremity following cervical spinal cord injury

STUDY DESIGN

Post hoc analysis of prospective multi-national, multi-centre cohort study.

OBJECTIVE

Determine whether cerebral dominance influences upper extremity recovery following cervical spinal cord injury (SCI).

SETTING

A multi-national subset of the longitudinal GRASSP dataset (n = 127).

METHODS

Secondary analysis of prospective, longitudinal multicenter study of individuals with cervical SCI (n = 73). Study participants were followed for up to 12 months after a cervical SCI, and the following outcome measures were serially assessed - the Graded Redefined Assessment of Strength, Sensibility, and Prehension (GRASSP) and the International Standards for the Neurological Classification of SCI (ISNCSCI), including upper extremity motor and sensory scores. Observed recovery and relative (percent) recovery were then determined for both the GRASSP and ISNCSCI, based on change from initial to last available assessment.

RESULTS

With the exception of prehension performance (quantitative grasping) following complete cervical SCI, there were no significant differences (p < 0.05) for observed and relative (percent) recovery, between the dominant and non-dominant upper extremities, as measured using GRASSP subtests, ISNCSCI motor scores and ISNCSCI sensory scores.

CONCLUSION

Despite well documented differences between the cerebral hemispheres, cerebral dominance appears to play a limited role in upper extremity recovery following acute cervical SCI.

Maladaptive reorganization following SCI: The role of body representation and multisensory integration

In this review we focus on maladaptive brain reorganization after spinal cord injury (SCI), including the development of neuropathic pain, and its relationship with impairments in body representation and multisensory integration. We will discuss the implications of altered sensorimotor interactions after SCI with and without neuropathic pain and possible deficits in multisensory integration and body representation. Within this framework we will examine published research findings focused on the use of bodily illusions to manipulate multisensory body representation to induce analgesic effects in heterogeneous chronic pain populations and in SCI-related neuropathic pain. We propose that the development and intensification of neuropathic pain after SCI is partly dependent on brain reorganization associated with dysfunctional multisensory integration processes and distorted body representation. We conclude this review by suggesting future research avenues that may lead to a better understanding of the complex mechanisms underlying the sense of the body after SCI, with a focus on cortical changes.

Agonist-antagonist myoneural interface amputation preserves proprioceptive sensorimotor neurophysiology in lower limbs

The brain undergoes marked changes in function and functional connectivity after limb amputation. The agonist-antagonist myoneural interface (AMI) amputation is a procedure that restores physiological agonist-antagonist muscle relationships responsible for proprioceptive sensory feedback to enable greater motor control. We compared results from the functional neuroimaging of individuals (n = 29) with AMI amputation, traditional amputation, and no amputation. Individuals with traditional amputation demonstrated a significant decrease in proprioceptive activity, measured by activation of Brodmann area 3a, whereas functional activation in individuals with AMIs was not significantly different from controls with no amputation (P < 0.05). The degree of proprioceptive activity in the brain strongly correlated with fascicle activity in the peripheral muscles and performance on motor tasks (P < 0.05), supporting the mechanistic basis of the AMI procedure. These results suggest that surgical techniques designed to restore proprioceptive peripheral neuromuscular constructs result in desirable central sensorimotor plasticity.

Divergent Findings in Brain Reorganization After Spinal Cord Injury: A Review

Spinal cord injury (SCI) leads to a general lack of sensory and motor functions below the level of injury and may promote deafferentation-induced brain reorganization. Functional magnetic resonance imaging (fMRI) has been established as an essential tool in neuroscience research and can precisely map the spatiotemporal distribution of brain activity. Task-based fMRI experiments associated with the tongue, upper limbs, or lower limbs have been used as the primary paradigms to study brain reorganization following SCI. A review of the current literature on the subject shows one common trait: while most articles agree that brain networks are usually preserved after SCI, and that is not the case as some articles describe possible alterations in brain activation after the lesion. There is no consensus if those alterations indeed occur. In articles that show alterations, there is no agreement if they are transient or permanent. Besides, there is no consensus on which areas are most prone to activation changes, or on the intensity and direction (increase vs. decrease) of those possible changes. In this article, we present a critical review of the literature and trace possible reasons for those contradictory findings on brain reorganization following SCI. fMRI studies based on the ankle dorsiflexion, upper-limb, and tongue paradigms are used as case studies for the analyses.

Reorganization of the brain in spinal cord injury: a meta-analysis of functional MRI studies

PURPOSE

Reorganization of the brain is considered the key mechanism of functional recovery in patients after spinal cord injury (SCI). This meta-analysis assessed abnormal brain activation in SCI patients to understand the pattern of reorganization in the brain after SCI.

METHODS

Functional magnetic resonance imaging (fMRI) studies that compared SCI patients with controls and were published before August 30, 2018, were extracted from the PubMed, Web of Science, and EMBASE databases. Voxel-wise whole-brain meta-analysis and region-of-interest meta-analysis of group differences were separately performed. Then, meta-regression analysis was conducted with several clinical characteristics as regressors.

RESULTS

Sixteen studies that met the inclusion criteria were identified. Compared with control individuals, SCI patients showed increased activation in the sensorimotor cortex in both whole-brain and region-of-interest (ROI) analyses. In addition, whole-brain meta-analysis revealed increased activation in the cerebellum, and this increase was positively correlated with lesion level and injury severity.

CONCLUSION

Our results demonstrated that reorganization occurred mainly in the sensorimotor system of the brain after SCI, implying that brain functions involved in sensorimotor demands can still be preserved in this condition. These findings provide opportunities for future studies in terms of therapeutic strategies and prognosis assessment.

Differences in neuroplasticity after spinal cord injury in varying animal models and humans

Rats have been the primary model to study the process and underlying mechanisms of recovery after spinal cord injury. Two weeks after a severe spinal cord contusion, rats can regain weight-bearing abilities without therapeutic interventions, as assessed by the Basso, Beattie and Bresnahan locomotor scale. However, many human patients suffer from permanent loss of motor function following spinal cord injury. While rats are the most understood animal model, major differences in sensorimotor pathways between quadrupeds and bipeds need to be considered. Understanding the major differences between the sensorimotor pathways of rats, non-human primates, and humans is a start to improving targets for treatments of human spinal cord injury. This review will discuss the neuroplasticity of the brain and spinal cord after spinal cord injury in rats, non-human primates, and humans. A brief overview of emerging interventions to induce plasticity in humans with spinal cord injury will also be discussed.

Cortical Reorganization of Sensorimotor Systems and the Role of Intracortical Circuits After Spinal Cord Injury

The plasticity of sensorimotor systems in mammals underlies the capacity for motor learning as well as the ability to relearn following injury. Spinal cord injury, which both deprives afferent input and interrupts efferent output, results in a disruption of cortical somatotopy. While changes in corticospinal axons proximal to the lesion are proposed to support the reorganization of cortical motor maps after spinal cord injury, intracortical horizontal connections are also likely to be critical substrates for rehabilitation-mediated recovery. Intrinsic connections have been shown to dictate the reorganization of cortical maps that occurs in response to skilled motor learning as well as after peripheral injury. Cortical networks incorporate changes in motor and sensory circuits at subcortical or spinal levels to induce map remodeling in the neocortex. This review focuses on the reorganization of cortical networks observed after injury and posits a role of intracortical circuits in recovery.

Adaptive motor cortex plasticity following grip reconstruction in individuals with tetraplegia

Background:

Tendon transfer is a surgical technique for restoring upper limb motor control in patients with cervical spinal cord injuries (SCI), and offers a rare window into cortical neuroplasticity following regained arm and hand function.

Objective:

Here, we aimed to examine neuroplasticity mechanisms related to re-established voluntary motor control of thumb flexion following tendon transfer.

Methods:

We used functional Magnetic Resonance Imaging (fMRI) to test the hypothesis that restored limb control following tendon transfer is mediated by activation of that limb’s area of the primary motor cortex. We examined six individuals with tetraplegia who underwent right-sided surgical grip reconstruction at Sahlgrenska University Hospital, Sweden. All were right-handed males, with a SCI at the C6 or C7 level, and a mean age of 40 years (range = 31–48). The average number of years elapsed since the SCI was 13 (range = 6–26). Six right-handed gender- and age-matched control subjects were included (mean age 39 years, range = 29–46). Restoration of active thumb flexion in patients was achieved by surgical transfer of one of the functioning elbow flexors (brachioradialis), to the paralyzed thumb flexor (flexor pollicis longus). We studied fMRI responses to isometric right-sided elbow flexion and key pinch, and examined the cortical representations within the left hemisphere somatomotor cortex a minimum of one year after surgery.

Results:

Cortical activations elicited by elbow flexion did not differ in topography between patients and control participants. However, in contrast to control participants, patients’ cortical thumb flexion activations were not topographically distinct from their elbow flexion activations.

Conclusion:

This result speaks against a topographic reorganization in which the thumb region regains thumb control following surgical tendon transfer. Instead, our findings suggest a neuroplastic mechanism in which motor cortex resources previously dedicated to elbow flexion adapt to control the thumb.

Cortical morphometric changes after spinal cord injury

Neuroimaging studies suggest that spinal cord injury (SCI) may lead to significant anatomical alterations in the human sensorimotor system. In particular, voxel-based morphometry (VBM) of cortical volume has revealed a significant gray and white matter atrophy bilaterally in the primary sensory cortex (S1). By contrast, some structural studies failed to detect changes in gray matter volume (GMV) in the primary motor cortex (M1) following SCI, whereas others have reported a substantial decrease of GMV also in M1. In addition to direct degeneration of the sensorimotor cortex, SCI can also lead to atrophy of the non-sensorimotor cortex, such as anterior cingulate cortex, insular cortex, middle frontal gyrus and supplementary motor area. These findings suggest that SCI can cause remote atrophy of brain gray matter in the salient network. Furthermore, pain-related remodelling may occur in SCI. In fact, structural changes in SCI are also related to the presence and degree of below-level pain. We performed a systematic review of the neuroimaging studies showing morphometric cortical changes and subsequent functional reorganization in humans with SCI. Literature search was conducted using PubMed and Embase. We identified 12 articles matching the inclusion criteria and 195 patients were included in these studies. The wide range of disease duration, rehabilitation training, drug intervention, and different research methodology, especially the identification of region of interest and the statistical approach to correct for multiple comparisons, may have contributed to some inconsistencies between the reviewed studies. Nevertheless, neuroimaging biomarkers can assess the extent of neural damage, elucidate the mechanisms of neural repair, and predict clinical outcome. A better understanding of the structural and functional changes that occur at cortical level following SCI may be useful in tracking potential treatment induced changes and identifying potential therapeutic targets, thus developing evidence-based rehabilitation therapies.

Intracortical microstimulation of human somatosensory cortex

Intracortical microstimulation of the somatosensory cortex offers the potential for creating a sensory neuroprosthesis to restore tactile sensation. Whereas animal studies have suggested that both cutaneous and proprioceptive percepts can be evoked using this approach, the perceptual quality of the stimuli cannot be measured in these experiments. We show that microstimulation within the hand area of the somatosensory cortex of a person with long-term spinal cord injury evokes tactile sensations perceived as originating from locations on the hand and that cortical stimulation sites are organized according to expected somatotopic principles. Many of these percepts exhibit naturalistic characteristics (including feelings of pressure), can be evoked at low stimulation amplitudes, and remain stable for months. Further, modulating the stimulus amplitude grades the perceptual intensity of the stimuli, suggesting that intracortical microstimulation could be used to convey information about the contact location and pressure necessary to perform dexterous hand movements associated with object manipulation.

Alterations in Cortical Sensorimotor Connectivity following Complete Cervical Spinal Cord Injury: A Prospective Resting-State fMRI Study

Functional magnetic resonance imaging (fMRI) studies have demonstrated alterations during task-induced brain activation in spinal cord injury (SCI) patients. The interruption to structural integrity of the spinal cord and the resultant disrupted flow of bidirectional communication between the brain and the spinal cord might contribute to the observed dynamic reorganization (neural plasticity). However, the effect of SCI on brain resting-state connectivity patterns remains unclear. We undertook a prospective resting-state fMRI (rs-fMRI) study to explore changes to cortical activation patterns following SCI. With institutional review board approval, rs-fMRI data was obtained in eleven patients with complete cervical SCI (>2 years post injury) and nine age-matched controls. The data was processed using the Analysis of Functional Neuroimages software. Region of interest (ROI) based analysis was performed to study changes in the sensorimotor network using pre- and post-central gyri as seed regions. Two-sampled t-test was carried out to check for significant differences between the two groups. SCI patients showed decreased functional connectivity in motor and sensory cortical regions when compared to controls. The decrease was noted in ipsilateral, contralateral, and interhemispheric regions for left and right precentral ROIs. Additionally, the left postcentral ROI demonstrated increased connectivity with the thalamus bilaterally in SCI patients. Our results suggest that cortical activation patterns in the sensorimotor network undergo dynamic reorganization following SCI. The presence of these changes in chronic spinal cord injury patients is suggestive of the inherent neural plasticity within the central nervous system.

Imaging of trauma of the spine

The goal of imaging in spine trauma is to gauge the extent of bony, vascular, and neurologic compromise. Neurologic and mechanical stability are key pieces of information that must be efficiently communicated to the referring clinician. From immobilization and steroid therapy, to vascular repair and emergent surgical intervention, clinical outcomes of spine-injured patients depend on timely and well-chosen imaging studies. Multidetector computed tomography (CT) has essentially replaced radiography in clearance of the spine and is the gold standard in evaluation of the bony spinal column. Magnetic resonance imaging (MRI) is typically reserved for patients with neurologic deficits or for obtunded/impaired patients in whom the neurologic exam is not reliable, even in the absence of osseous injury on CT. MRI is the only available imaging modality that is able to clearly depict the internal architecture of the spinal cord, and, as such, has a central role in depicting parenchymal changes resulting from injury. Intramedullary edema and hemorrhage have been shown to correlate with the degree of neurologic deficit and prognosis. Moreover, advanced MRI techniques, such as diffusion and diffusion tensor imaging, have shifted the focus to determining structural and functional integrity of neural structures. Here, we review the role of imaging in spine trauma, as well as the key radiologic features of injury to the spinal column and spinal cord.

Evolution of EEG Motor Rhythms after Spinal Cord Injury: A Longitudinal Study

Spinal cord injury (SCI) does not only produce a lack of sensory and motor function caudal to the level of injury, but it also leads to a progressive brain reorganization. Chronic SCI patients attempting to move their affected limbs present a significant reduction of brain activation in the motor cortex, which has been linked to the deafferentation. The aim of this work is to study the evolution of the motor-related brain activity during the first months after SCI. Eighteen subacute SCI patients were recruited to participate in bi-weekly experimental sessions during at least two months. Their EEG was recorded to analyze the temporal evolution of the event-related desynchronization (ERD) over the motor cortex, both during motor attempt and motor imagery of their paralyzed hands. The results show that the α and β ERD evolution after SCI is negatively correlated with the clinical progression of the patients during the first months after the injury. This work provides the first longitudinal study of the event-related desynchronization during the subacute phase of spinal cord injury. Furthermore, our findings reveal a strong association between the ERD changes and the clinical evolution of the patients. These results help to better understand the brain transformation after SCI, which is important to characterize the neuroplasticity mechanisms involved after this lesion and may lead to new strategies for rehabilitation and motor restoration of these patients.

Change of Brain Functional Connectivity in Patients With Spinal Cord Injury: Graph Theory Based Approach

Objective

To investigate the global functional reorganization of the brain following spinal cord injury with graph theory based approach by creating whole brain functional connectivity networks from resting state-functional magnetic resonance imaging (rs-fMRI), characterizing the reorganization of these networks using graph theoretical metrics and to compare these metrics between patients with spinal cord injury (SCI) and age-matched controls.

Methods

Twenty patients with incomplete cervical SCI (14 males, 6 females; age, 55±14.1 years) and 20 healthy subjects (10 males, 10 females; age, 52.9±13.6 years) participated in this study. To analyze the characteristics of the whole brain network constructed with functional connectivity using rs-fMRI, graph theoretical measures were calculated including clustering coefficient, characteristic path length, global efficiency and small-worldness.

Results

Clustering coefficient, global efficiency and small-worldness did not show any difference between controls and SCIs in all density ranges. The normalized characteristic path length to random network was higher in SCI patients than in controls and reached statistical significance at 12%-13% of density (p<0.05, uncorrected).

Conclusion

The graph theoretical approach in brain functional connectivity might be helpful to reveal the information processing after SCI. These findings imply that patients with SCI can build on preserved competent brain control. Further analyses, such as topological rearrangement and hub region identification, will be needed for better understanding of neuroplasticity in patients with SCI.

Cortical reorganization after spinal cord injury: always for good?

Plasticity constitutes the basis of behavioral changes as a result of experience. It refers to neural network shaping and re-shaping at the global level and to synaptic contacts remodeling at the local level, either during learning or memory encoding, or as a result of acute or chronic pathological conditions. 'Plastic' brain reorganization after central nervous system lesions has a pivotal role in the recovery and rehabilitation of sensory and motor dysfunction, but can also be "maladaptive". Moreover, it is clear that brain reorganization is not a "static" phenomenon but rather a very dynamic process. Spinal cord injury immediately initiates a change in brain state and starts cortical reorganization. In the long term, the impact of injury - with or without accompanying therapy - on the brain is a complex balance between supraspinal reorganization and spinal recovery. The degree of cortical reorganization after spinal cord injury is highly variable, and can range from no reorganization (i.e. "silencing") to massive cortical remapping. This variability critically depends on the species, the age of the animal when the injury occurs, the time after the injury has occurred, and the behavioral activity and possible therapy regimes after the injury. We will briefly discuss these dependencies, trying to highlight their translational value. Overall, it is not only necessary to better understand how the brain can reorganize after injury with or without therapy, it is also necessary to clarify when and why brain reorganization can be either "good" or "bad" in terms of its clinical consequences. This information is critical in order to develop and optimize cost-effective therapies to maximize functional recovery while minimizing maladaptive states after spinal cord injury.

Trans-spinal direct current enhances corticospinal output and stimulation-evoked release of glutamate analog, D-2,3-³H-aspartic acid

Trans-spinal direct current (tsDC) stimulation is a modulator of spinal excitability and can influence cortically elicited muscle contraction in a polarity-dependent fashion. When combined with low-frequency repetitive cortical stimulation, cathodal tsDC [tsDC(-)] produces a long-term facilitation of cortically elicited muscle actions. We investigated the ability of this combined stimulation paradigm to facilitate cortically elicited muscle actions in spinal cord-injured and noninjured animals. The effect of tsDC-applied alone or in combination with repetitive spinal stimulation (rSS) on the release of the glutamate analog, D-2,3-(3)H-aspartate (D-Asp), from spinal cord preparations in vitro-was also tested. In noninjured animals, tsDC (-2 mA) reproducibly potentiated cortically elicited contractions of contralateral and ipsilateral muscles tested at various levels of baseline muscle contraction forces. Cortically elicited muscle responses in animals with contusive and hemisectioned spinal cord injuries (SCIs) were similarly potentiated. The combined paradigm of stimulation caused long-lasting potentiation of cortically elicited bilateral muscle contraction in injured and noninjured animals. Additional analysis suggests that at higher baseline forces, tsDC(-) application does not increase the rising slope of the muscle contraction but causes repeated firing of the same motor units. Both cathodal and anodal stimulations induced a significant increase of D-Asp release in vitro. The effect of the combined paradigm of stimulation (tsDC and rSS) on the concentration of extracellular D-Asp was polarity dependent. These results indicate that tsDC can powerfully modulate the responsiveness of spinal cord neurons. The results obtained from the in vitro preparation suggest that the changes in neuronal excitability were correlated with an increased concentration of extracellular glutamate. The combined paradigm of stimulation, used in our experiments, could be noninvasively applied to restore motor control in humans with SCI.

Disability, atrophy and cortical reorganization following spinal cord injury

The impact of traumatic spinal cord injury on structural integrity, cortical reorganization and ensuing disability is variable and may depend on a dynamic interaction between the severity of local damage and the capacity of the brain for plastic reorganization. We investigated trauma-induced anatomical changes in the spinal cord and brain, and explored their relationship to functional changes in sensorimotor cortex. Structural changes were assessed using cross-sectional cord area, voxel-based morphometry and voxel-based cortical thickness of T₁-weighted images in 10 subjects with cervical spinal cord injury and 16 controls. Cortical activation in response to right-sided (i) handgrip; and (ii) median and tibial nerve stimulation were assessed using functional magnetic resonance imaging. Regression analyses explored associations between cord area, grey and white matter volume, cortical activations and thickness, and disability. Subjects with spinal cord injury had impaired upper and lower limb function bilaterally, a 30% reduced cord area, smaller white matter volume in the pyramids and left cerebellar peduncle, and smaller grey matter volume and cortical thinning in the leg area of the primary motor and sensory cortex compared with controls. Functional magnetic resonance imaging revealed increased activation in the left primary motor cortex leg area during handgrip and the left primary sensory cortex face area during median nerve stimulation in subjects with spinal cord injury compared with controls, but no increased activation following tibial nerve stimulation. A smaller cervical cord area was associated with impaired upper limb function and increased activations with handgrip and median nerve stimulation, but reduced activations with tibial nerve stimulation. Increased sensory deficits were associated with increased activations in the left primary sensory cortex face area due to median nerve stimulation. In conclusion, spinal cord injury leads to cord atrophy, cortical atrophy of primary motor and sensory cortex, and cortical reorganization of the sensorimotor system. The degree of cortical reorganization is predicted by spinal atrophy and is associated with significant disability.

Functional reorganization of the brain in humans following spinal cord injury: evidence for underlying changes in cortical anatomy

Loss of somatosensory drive results in functional reorganization of the primary somatosensory cortex (SI). While the phenomenon of functional cortical reorganization is well established, it remains unknown whether in humans, functional reorganization results from changes in brain anatomy, or simply reflects an unmasking of already existing dormant synapses. In 20 subjects with complete thoracic spinal cord injuries (SCIs) and 23 controls, we used functional and structural magnetic resonance imaging to determine whether SI reorganization was associated with changes in SI anatomy. SCI resulted in a significant SI reorganization, with the little finger representation moving medially toward the lower body representation (i.e., area of sensory loss). Furthermore, although SCI was associated with gray matter volume loss in the lower body representation, this loss was minimized as reorganization increased. That is, the greater the medial shift in little finger representation, the greater the gray matter preservation in the lower body representation. In addition, in the region of greatest SI reorganization (little finger), fractional anisotropy was correlated with SI reorganization. That is, as SI reorganization increased, the extent of aligned structures decreased. Finally, although thalamocortical fibers remained unchanged, the ease and direction of water movement within the little finger representation was altered, being directed more toward the midline in SCI subjects. These data show that SI reorganization following SCI is associated with changes in SI anatomy and provide compelling evidence that SI reorganization in humans results from the growth of new lateral connections, and not simply from the unmasking of already existing lateral connections.

Rewiring of hindlimb corticospinal neurons after spinal cord injury

Little is known about the functional role of axotomized cortical neurons that survive spinal cord injury. Large thoracic spinal cord injuries in adult rats result in impairments of hindlimb function. Using retrograde tracers, we found that axotomized corticospinal axons from the hindlimb sensorimotor cortex sprouted in the cervical spinal cord. Mapping of these neurons revealed the emergence of a new forelimb corticospinal projection from the rostral part of the former hindlimb cortex. Voltage-sensitive dye (VSD) imaging and blood-oxygen-level-dependent functional magnetic resonance imaging (BOLD fMRI) revealed a stable expansion of the forelimb sensory map, covering in particular the former hindlimb cortex containing the rewired neurons. Therefore, axotomized hindlimb corticospinal neurons can be incorporated into the sensorimotor circuits of the unaffected forelimb.

Reorganization and preservation of motor control of the brain in spinal cord injury: a systematic review

Reorganization of brain function in people with CNS damage has been identified as one of the fundamental mechanisms involved in the recovery of sensorimotor function. Spinal cord injury (SCI) brain mapping studies during motor tasks aim for assessing the reorganization and preservation of brain networks involved in motor control. Revealing the activation of cortical and subcortical brain areas in people with SCI can indicate principal patterns of brain reorganization when the neurotrauma is distal to the brain. This review assessed brain activation after SCI in terms of intensity, volume, and somatotopic localization, as well as preservation of activation during attempted and/or imagined movements. Twenty-five studies meeting the inclusion criteria could be identified in Medline (1980 to January 2008). Relevant characteristics of studies (level of lesion, time after injury, motor task) and mapping techniques varied widely. Changes in brain activation were found in both cortical and subcortical areas of individuals with SCI. In addition, several studies described a shift in the region of brain activation. These patterns appeared to be dynamic and influenced by the level, completeness, and time after injury, as well as extent of clinical recovery. In addition, several aspects of reorganization of brain function following SCI resembled those reported in stroke. This review demonstrates that brain networks involved in different demands of motor control remain responsive even in chronic paralysis. These findings imply that therapeutic strategies aimed at restoring spinal cord function, even in people with chronic SCI, can build on preserved competent brain control.

Cortical reorganization in NT3-treated experimental spinal cord injury: Functional magnetic resonance imaging

Functional magnetic resonance imaging (fMRI) studies were performed for visualizing ongoing brain plasticity in Neurotrophin-3 (NT3)-treated experimental spinal cord injury (SCI). In response to the electrical stimulation of the forepaw, the NT3-treated animals showed extensive activation of brain structures that included contralateral cortex, thalamus, caudate putamen, hippocampus, and periaqueductal gray. Quantitative analysis of the fMRI data indicated significant changes both in the volume and center of activations in NT3-treated animals relative to saline-treated controls. A strong activation in both ipsi- and contralateral periaqueductal gray and thalamus was observed in NT3-treated animals. These studies indicate ongoing brain reorganization in the SCI animals. The fMRI results also suggest that NT3 may influence nociceptive pathways.

Functional magnetic resonance imaging in rodents: Methodology and application to spinal cord injury

Functional MRI (fMRI) on spinal cord-injured rodents at 4 and 8 weeks post injury (PI) is described. The paradigm for fMRI, based on electrical stimulation of rat paws, was automated using an in-house designed microprocessor-based controller that was interfaced to a stimulator. The MR images were spatially normalized to the Paxinos and Watson atlas using publicly available digital images of the cryosections. In normal uninjured animals, the activation was confined to the contralateral somatosensory cortex. In contrast, in injured animals, extensive activation, which included structures such as ipsilateral cortex, thalamus, hippocampus, and the caudate putamen, was observed at 4 and 8 weeks PI. Quantitative cluster analysis was carried out to calculate the volumes and centers of activation in individual brain structures. Based on this analysis, significant increase in activation between 4 and 8 weeks was observed only in the ipsilateral caudate putamen and thalamus. These studies suggest extensive and ongoing brain reorganization in spinal cord-injured animals.

Event-related beta EEG-changes during passive and attempted foot movements in paraplegic patients

A number of electroencephalographic (EEG) studies report on motor event-related desynchronization and synchronization (ERD/ERS) in the beta band, i.e. a decrease and increase of spectral amplitudes of central beta rhythms in the range from 13 to 35 Hz. Following an ERD that occurs shortly before and during the movement, bursts of beta oscillations (beta ERS) appear within a 1-s interval after movement offset. Such a post-movement beta ERS has been reported after voluntary hand movements, passive movements, movement imagination, and also after movements induced by functional electrical stimulation. The present study compares ERD/ERS patterns in paraplegic patients (suffering from a complete spinal cord injury) and healthy subjects during attempted (active) and passive foot movements. The aim of this work is to address the question, whether patients do have the same focal beta ERD/ERS pattern during attempted foot movement as healthy subjects do. The results showed midcentral-focused beta ERD/ERS patterns during passive, active, and imagined foot movements in healthy subjects. This is in contrast to a diffuse and broad distributed ERD/ERS pattern during attempted foot movements in patients. Only one patient showed a similar ERD/ERS pattern. Furthermore, no significant ERD/ERS patterns during passive foot movement in the group of the paraplegics could be found.

Alterations in Burst Firing of Thalamic VPL Neurons and Reversal by Nav1.3 Antisense After Spinal Cord Injury

We recently showed that spinal cord contusion injury (SCI) at the thoracic level induces pain-related behaviors and increased spontaneous discharges, hyperresponsiveness to innocuous and noxious peripheral stimuli, and enlarged receptive fields in neurons in the ventral posterolateral (VPL) nucleus of the thalamus. These changes are linked to the abnormal expression of Nav1.3, a rapidly repriming voltage-gated sodium channel. In this study, we examined the burst firing properties of VPL neurons after SCI. Adult male Sprague–Dawley rats underwent contusion SCI at the T9 level. Four weeks later, when Nav1.3 protein was upregulated within VPL neurons, extracellular unit recordings were made from VPL neurons in intact animals, those with SCI, and in SCI animals after receiving lumbar intrathecal injections of Nav1.3 antisense or mismatch oligodeoxynucleotides for 4 days. After SCI, VPL neurons with identifiable peripheral receptive fields showed rhythmic oscillatory burst firing with changes in discrete burst properties, and alternated among single-spike, burst, silent, and spindle wave firing modes. Nav1.3 antisense, but not mismatch, partially reversed alterations in burst firing after SCI. These results demonstrate several newly characterized changes in spontaneous burst firing properties of VPL neurons after SCI and suggest that abnormal expression of Nav1.3 contributes to these phenomena.

Stroke recovery and its imaging

Functional imaging of stroke recovery is a unique source of information that might be useful in the development of restorative treatments. Several features of brain function change spontaneously after stroke. Current studies define many of the most common events. Key challenges for the future are to develop standardized approaches to help address certain questions, determine the psychometric qualities of these measures, and define the clinical usefulness of these methods.

Brain motor system function after chronic, complete spinal cord injury

Most therapies under development to restore motor function after spinal cord injury (SCI) assume intact brain motor functions. To examine this assumption, 12 patients with chronic, complete SCI and 12 controls underwent functional MRI during attempted, and during imagined, right foot movement, each at two force levels. In patients with SCI, many features of normal motor system function were preserved, however, several departures from normal were apparent: (i) volume of activation was generally much reduced, e.g. 4-8% of normal in primary sensorimotor cortex, in the setting of twice normal variance in signal change; (ii) abnormal activation patterns were present, e.g. increased pallido-thalamocortical loop activity during attempted movement and abnormal processing in primary sensorimotor cortex during imagined movement; and (iii) modulation of function with change in task or in force level did not conform to patterns seen in controls, e.g. in controls, attempted movement activated more than imagined movement did within left primary sensorimotor cortex and right dorsal cerebellum, while imagined movement activated more than attempted movement did in dorsolateral prefrontal cortex and right precentral gyrus. These modulations were absent in patients with SCI. Many features of brain motor system function during foot movement persist after chronic complete SCI. However, substantial derangements of brain activation, poor modulation of function with change in task demands and emergence of pathological brain events were present in patients. Because brain function is central to voluntary movement, interventions that aim to improve motor function after chronic SCI likely also need to attend to these abnormalities of brain function.

Corticospinal Excitability in Patients With Chronic Low Back Pain

OBJECTIVE

This study was designed to investigate corticospinal excitability of lumbar muscles using transcranial magnetic stimulation (TMS) in patients with chronic low back pain and correlate this with self-rated measures of disability and pain.

METHODS

Twenty-four patients with chronic low back pain and 11 healthy control subjects were used in this study. TMS was delivered through an angled double-cone coil, with its cross-over on the vertex and a posterior-to-anterior current flow in the brain. Electromyographic (EMG) recordings were made from erector spinae (ES) muscles at the fourth lumbar level. Motor cortical excitability was assessed using motor threshold (MTh) for motor evoked potentials (MEPs) and threshold for silent period (SP) during facilitation of the back muscles. Latency, duration, and area of MEPs and SPs were also measured.

RESULTS

The latency, duration, and size of MEPs and SPs did not differ between the left and right ES muscles in either the patients or the control subjects and also did not differ between the patients and the control subjects. However, there was a significantly higher MTh and threshold for the SP in the patients as compared with the control subjects; the full significance of this requires further investigation. Interestingly, there was a positive correlation between the self-rated measure of disability (the Oswestry Disability Index score) and both the MTh and the threshold for the SP in the patients. There was also a positive correlation between the self-rated index of back pain and the threshold for the SP in the patients. This finding of an association between clinical and neurophysiologic measures reinforces the need for further research to establish the clinical relevance of these rises in MTh and SP threshold.

CONCLUSIONS

In summary, this study has revealed that corticospinal excitability, driving ES muscles close to the site of pain, is lowered in patients with chronic low back pain.

Reduction of the hand representation in the ipsilateral primary motor cortex following unilateral section of the corticospinal tract at cervical level in monkeys

BACKGROUND

After sub-total hemi-section of cervical cord at level C7/C8 in monkeys, the ipsilesional hand exhibited a paralysis for a couple of weeks, followed by incomplete recovery of manual dexterity, reaching a plateau after 40-50 days. Recently, we demonstrated that the level of the plateau was related to the size of the lesion and that progressive plastic changes of the motor map in the contralesional motor cortex, particularly the hand representation, took place following a comparable time course. The goal of the present study was to assess, in three macaque monkeys, whether the hand representation in the ipsilesional primary motor cortex (M1) was also affected by the cervical hemi-section.

RESULTS

Unexpectedly, based on the minor contribution of the ipsilesional hemisphere to the transected corticospinal (CS) tract, a considerable reduction of the hand representation was also observed in the ipsilesional M1. Mapping control experiments ruled out the possibility that changes of motor maps are due to variability of the intracortical microstimulation mapping technique. The extent of the size reduction of the hand area was nearly as large as in the contralesional hemisphere in two of the three monkeys. In the third monkey, it represented a reduction by a factor of half the change observed in the contralesional hemisphere. Although the hand representation was modified in the ipsilesional hemisphere, such changes were not correlated with a contribution of this hemisphere to the incomplete recovery of the manual dexterity for the hand affected by the lesion, as demonstrated by reversible inactivation experiments (in contrast to the contralesional hemisphere). Moreover, despite the size reduction of M1 hand area in the ipsilesional hemisphere, no deficit of manual dexterity for the hand opposite to the cervical hemi-section was detected.

CONCLUSION

After cervical hemi-section, the ipsilesional motor cortex exhibited substantial reduction of the hand representation, whose extent did not match the small number of axotomized CS neurons. We hypothesized that the paradoxical reduction of hand representation in the ipsilesional hemisphere is secondary to the changes taking place in the contralesional hemisphere, possibly corresponding to postural adjustments and/or re-establishing a balance between the two hemispheres.

Somatotopy and movement representation sites following cortical stroke

Stroke has been associated with many changes in motor system function, but there has been limited study of changes in somatotopic organization. This was examined in a group of patients with cortical stroke affecting primary sensorimotor cortex. In 17 patients with good outcome after cortical stroke involving precentral and/or postcentral gyri, plus 14 controls, four functional MRI evaluations of brain activity were obtained: finger, shoulder, and face motor tasks plus a sensory task, passive finger motion. For each, coordinates for contralateral primary sensorimotor cortex activation site were determined, as was a measure of inter-hemispheric balance. The normal motor somatotopy measured in controls was largely preserved after stroke. The main difference found between controls and patients was that the face was lateral to finger motor activation in all controls, but face was centered medial to finger in 43% of patients. Among patients, smaller infarct volume was associated with more ventral, and larger infarct with more dorsal, contralateral primary sensorimotor cortex activation. On the other hand, better behavioral outcome was associated with a more posterior, and poorer outcome with more anterior, activation. Larger infarct and poorer behavioral outcome were each associated with a change in inter-hemispheric balance towards the non-stroke hemisphere. Shifts in contralateral movement representation site did not correlate with changes in inter-hemispheric balance. Motor somatotopy is generally preserved after injury to primary sensorimotor cortex. Greater injury and larger behavioral deficits are associated with distinct effects on movement representation sites. Changes in motor organization within and between hemispheres arise independently after stroke.