Short-term adaptations in spinal cord circuits evoked by repetitive transcranial magnetic stimulation: possible underlying mechanisms

Repetitive Transcranial Magnetic Stimulation for the Treatment of Spinal Cord Injury: Current Status and Perspective

Spinal cord injury (SCI) can lead to devastating dysfunctions and complications, significantly impacting patients' quality of life and aggravating the burden of disease. Since the main pathological mechanism of SCI is the disruption of neuronal circuits, the primary therapeutic strategy for SCI involves reconstructing and activating circuits to restore neural signal transmission. Repetitive transcranial magnetic stimulation (rTMS), a noninvasive brain stimulation technique, can modulate the function or state of the nervous system by pulsed magnetic fields. Here, we discuss the basic principles and potential mechanisms of rTMS for treating SCI, including promoting the reconstruction of damaged circuits in the spinal cord, activating reorganization of the cerebral cortex and circuits, modulating the balance of inputs to motoneurons, improving the microenvironment and intrinsic regeneration ability in SCI. Based on these mechanisms, we provide an overview of the therapeutic effects of rTMS in SCI patients with motor dysfunction, spasticity and neuropathic pain. We also discuss the challenges and prospectives of rTMS, especially the potential of combination therapy of rTMS and neural progenitor cell transplantation, and the synergistic effects on promoting regeneration, relay formation and functional connectivity. This review is expected to offer a relatively comprehensive understanding and new perspectives of rTMS for SCI treatment.

The effect of the combined application of repetitive transcranial magnetic stimulation and local injection of botulinum neurotoxin versus their individual use in children with spastic diplegic cerebral palsy

BACKGROUND

Botulinum neurotoxin (BoNT) is frequently utilized for localized spasticity in patients with spastic diplegic cerebral palsy (CP), while repetitive transcranial magnetic stimulation (rTMS) offers a potential therapeutic option.

OBJECTIVE

To assess and compare BoNT and rTMS effects among children with spastic diplegic CP on spasticity and motor function. Additionally, investigate the potential advantages of combining these therapeutic modalities.

METHODS

Seventy five children (aged 4-8 years) with moderate spastic diplegia, were allocated to one of three groups (25 children in each group): the rTMS group (received 10 hz rTMS, 1500 pulses, two sessions per week for 3 months), the BoNT group (received single BoNT injection), and the combined BoNT-rTMS group. All groups underwent a 3-month physical therapy program. Baseline and post-3-month assessments included the motor function by using Gross Motor Function Classification System (GMFCS), and spasticity by using Modified Ashworth Scale (MAS), and electromyography (i.e. the ratio between the amplitude of both Hoffman response to muscle response (H/M ratio)).

RESULTS

There were a statistically significant difference between groups regarding H/M ratio and GMFCS where p values were (<0.001 and 0.009) respectively. Multivariate regression analysis favored combination therapy over BoNT alone, showing lower odds ratios for MAS (OR = 0.47, p = .04), GMFCS (OR = 0.171, p < .001), and a negative beta coefficient for H/M ratio (Beta = -0.137, p < .001).

CONCLUSION

BoNT and rTMS reduce CP-related spasticity and improve motor function, however the combined therapy of these modalities demonstrates an additive effect.

Effects of cerebellar transcranial direct current stimulation on the excitability of spinal motor neurons and vestibulospinal tract in healthy individuals

Cerebellar transcranial direct current stimulation (ctDCS) modulates cerebellar cortical excitability in a polarity-dependent manner and affects inhibitory pathways from the cerebellum. The cerebellum modulates spinal reflex excitability via the vestibulospinal tract and other pathways projecting to the spinal motor neurons; however, the effects of ctDCS on the excitability of spinal motor neurons and vestibulospinal tract remain unclear. The experiment involved 13 healthy individuals. ctDCS (sham-ctDCS, anodal-ctDCS, and cathodal-ctDCS) was applied to the cerebellar vermis at 2 mA with an interval of at least 3 days between each condition. We measured the maximal M-wave (Mmax) and maximal H-reflex (Hmax) in the right soleus muscle to assess the excitability of spinal motor neurons. We applied galvanic vestibular stimulation (GVS) for 200 ms at 100 ms before tibial nerve stimulation to measure Hmax conditioned by GVS (GVS-Hmax) and calculated the change rate of Hmax by GVS as the excitability of vestibulospinal tract. We measured the Mmax, Hmax, and GVS-Hmax before, during, and after ctDCS in the sitting posture. No main effects of tDCS condition, main effects of time, or interaction effects were observed in Hmax/Mmax or the change rate of Hmax by GVS. It has been suggested that ctDCS does not affect the excitability of spinal motor neurons and vestibulospinal tract, as measured by neurophysiological methods, such as the H-reflex, in healthy individuals in a sitting posture. Effect of ctDCS on other descending pathways to spinal motor neurons, the neurological mechanism of tDCS and the cerebellar activity during the experiment may have contributed to these results. Therefore, we need to investigate the involvement of the cerebellum in Hmax/Mmax and the change rate of Hmax by GVS under different neuromodulation techniques and postural conditions.

Brain state-dependent repetitive transcranial magnetic stimulation for motor stroke rehabilitation: a proof of concept randomized controlled trial

Background

In healthy subjects, repetitive transcranial magnetic stimulation (rTMS) targeting the primary motor cortex (M1) demonstrated plasticity effects contingent on electroencephalography (EEG)-derived excitability states, defined by the phase of the ongoing sensorimotor μ-oscillation. The therapeutic potential of brain state-dependent rTMS in the rehabilitation of upper limb motor impairment post-stroke remains unexplored.

Objective

Proof-of-concept trial to assess the efficacy of rTMS, synchronized to the sensorimotor μ-oscillation, in improving motor impairment and reducing upper-limb spasticity in stroke patients.

Methods

We conducted a parallel group, randomized double-blind controlled trial in 30 chronic stroke patients (clinical trial registration number: NCT05005780). The experimental intervention group received EEG-triggered rTMS of the ipsilesional M1 [1,200 pulses; 0.33 Hz; 100% of the resting motor threshold (RMT)], while the control group received low-frequency rTMS of the contralesional motor cortex (1,200 pulses; 1 Hz, 115% RMT), i.e., an established treatment protocol. Both groups received 12 rTMS sessions (20 min, 3× per week, 4 weeks) followed by 50 min of physiotherapy. The primary outcome measure was the change in upper-extremity Fugl-Meyer assessment (FMA-UE) scores between baseline, immediately post-treatment and 3 months' follow-up.

Results

Both groups showed significant improvement in the primary outcome measure (FMA-UE) and the secondary outcome measures. This included the reduction in spasticity, measured objectively using the hand-held dynamometer, and enhanced motor function as measured by the Wolf Motor Function Test (WMFT). There were no significant differences between the groups in any of the outcome measures.

Conclusion

The application of brain state-dependent rTMS for rehabilitation in chronic stroke patients is feasible. This pilot study demonstrated that the brain oscillation-synchronized rTMS protocol produced beneficial effects on motor impairment, motor function and spasticity that were comparable to those observed with an established therapeutic rTMS protocol.

Clinical Trial Registration

ClinicalTrials.gov, identifier [NCT05005780].

Trans-spinal magnetic stimulation combined with kinesiotherapy as a new method for enhancing functional recovery in patients with spinal cord injury due to neuromyelitis optica: a case report

BACKGROUND

Experimental studies have shown that repetitive trans-spinal magnetic stimulation (TsMS) decreases demyelination and enables recovery after spinal cord injury (SCI). However, the usefulness of TsMS in humans with SCI remains unclear. Therefore, the main objective of this study is to evaluate the effects of TsMS combined with kinesiotherapy on SCI symptoms. We describe a protocol treatment with TsMS and kinesiotherapy in a patient with SCI due to neuromyelitis optica (NMO)-associated transverse myelitis.

CASE PRESENTATION

A 23-year-old white male with NMO spectrum disorders started symptoms in 2014 and included lumbar pain evolving into a mild loss of strength and sensitivity in both lower limbs. Five months later, the symptoms improved spontaneously, and there were no sensorimotor deficits. Two years later, in 2016, the symptoms recurred with a total loss of strength and sensitivity in both lower limbs. Initially, physiotherapy was provided in 15 sessions with goals of motor-sensory recovery and improving balance and functional mobility. Subsequently, TsMS (10 Hz, 600 pulses, 20-seconds inter-trains interval, at 90% of resting motor threshold of the paravertebral muscle) was applied at the 10th thoracic vertebral spinous process before physiotherapy in 12 sessions. Outcomes were assessed at three time points: prior to physiotherapy alone (T-1), before the first session of TsMS combined with kinesiotherapy (T0), and after 12 sessions of TsMS combined with kinesiotherapy (T1). The patient showed a 25% improvement in walking independence, a 125% improvement in balance, and an 18.8% improvement in functional mobility. The Patient Global Impression of Change Scale assessed the patient's global impression of change as 'much improved'.

CONCLUSION

TsMS combined with kinesiotherapy may safely and effectively improve balance, walking independence, and functional mobility of patients with SCI due to NMO-associated transverse myelitis.

Testing spasticity mechanisms in chronic stroke before and after intervention with contralesional motor cortex 1 Hz rTMS and physiotherapy

BACKGROUND

Previous studies showed that repetitive transcranial magnetic stimulation (rTMS) reduces spasticity after stroke. However, clinical assessments like the modified Ashworth scale, cannot discriminate stretch reflex-mediated stiffness (spasticity) from passive stiffness components of resistance to muscle stretch. The mechanisms through which rTMS might influence spasticity are also not understood.

METHODS

We measured the effects of contralesional motor cortex 1 Hz rTMS (1200 pulses + 50 min physiotherapy: 3×/week, for 4-6 weeks) on spasticity of the wrist flexor muscles in 54 chronic stroke patients using a hand-held dynamometer for objective quantification of the stretch reflex response. In addition, we measured the excitability of three spinal mechanisms thought to be related to post-stroke spasticity: post-activation depression, presynaptic inhibition and reciprocal inhibition before and after the intervention. Effects on motor impairment and function were also assessed using standardized stroke-specific clinical scales.

RESULTS

The stretch reflex-mediated torque in the wrist flexors was significantly reduced after the intervention, while no change was detected in the passive stiffness. Additionally, there was a significant improvement in the clinical tests of motor impairment and function. There were no significant changes in the excitability of any of the measured spinal mechanisms.

CONCLUSIONS

We demonstrated that contralesional motor cortex 1 Hz rTMS and physiotherapy can reduce the stretch reflex-mediated component of resistance to muscle stretch without affecting passive stiffness in chronic stroke. The specific physiological mechanisms driving this spasticity reduction remain unresolved, as no changes were observed in the excitability of the investigated spinal mechanisms.

Case report: High-frequency repetitive transcranial magnetic stimulation for treatment of hereditary spastic paraplegia type 11

Hereditary spastic paraplegia (HSP) is a heterogeneous group of inherited neurodegenerative disorders that currently have no cure. HSP type 11 (SPG11-HSP) is a complex form carrying mutations in the SPG11 gene. Neuropathological studies demonstrate that motor deficits in these patients are mainly attributed to axonal degeneration of the corticospinal tract (CST). Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive technique that can induce central nervous system plasticity and promote neurological recovery by modulating the excitability of cortical neuronal cells. Although rTMS is expected to be a therapeutic tool for neurodegenerative diseases, no previous studies have applied rTMS to treat motor symptoms in SPG11-HSP. Here, we report a case of SPG11-HSP with lower extremity spasticity and gait instability, which were improved by applying high-frequency rTMS (HF-rTMS) at the primary motor cortex (M1). Clinical and physiological features were measured throughout the treatment, including the Modified Ashworth Scale (MAS), Berg Balance Scale (BBS), the timed up and go (TUG) test and the 10-meter walk test time (10 MWT). The structure and excitability of the CST were assessed by diffusion tensor imaging (DTI) and transcranial magnetic stimulation (TMS), respectively. After treatment, the patient gained 17 points of BBS, along with a gradual decrease in MAS scores of the bilateral lower extremity. In addition, the TUG test and 10 MWT improved to varying degrees. TMS assessment showed increased motor evoked potential (MEP) amplitude, decreased resting motor threshold (RMT), decreased central motor conduction time (CMCT), and decreased difference in the cortical silent period (CSP) between bilateral hemispheres. Using the DTI technique, we observed increased fractional anisotropy (FA) values and decreased mean diffusivity (MD) and radial diffusivity (RD) values in the CST. It suggests that applying HF-rTMS over the bilateral leg area of M1 (M1-LEG) is beneficial for SPG11-HSP. In this study, we demonstrate the potential of rTMS to promote neurological recovery from both functional and structural perspectives. It may provide a clinical rationale for using rTMS in the rehabilitation of HSP patients.

Motor Neuroplastic Effects of a Novel Paired Stimulation Technology in an Incomplete Spinal Cord Injury Animal Model

Paired stimulation of the brain and spinal cord can remodel the central nervous tissue circuitry in an animal model to induce motor neuroplasticity. The effects of simultaneous stimulation vary according to the extent and severity of spinal cord injury. Therefore, our study aimed to determine the significant effects on an incomplete SCI rat brain and spinal cord through 3 min and 20 min stimulations after 4 weeks of intervention. Thirty-three Sprague Dawley rats were classified into six groups: (1) normal, (2) sham, (3) iTBS/tsDCS, (4) iTBS/ts-iTBS, (5) rTMS/tsDCS, and (6) rTMS/ts-iTBS. Paired stimulation of the brain cortex and spinal cord thoracic (T10) level was applied simultaneously for 3−20 min. The motor evoked potential (MEP) and Basso, Beattie, and Bresnahan (BBB) scores were recorded after every week of intervention for four weeks along with wheel training for 20 min. Three-minute stimulation with the iTBS/tsDCS intervention induced a significant (p < 0.050 *) increase in MEP after week 2 and week 4 treatments, while 3 min iTBS/ts-iTBS significantly improved MEP (p < 0.050 *) only after the week 3 intervention. The 20 min rTMS/ts-iTBS intervention showed a significant change only in post_5 min after week 4. The BBB score also changed significantly in all groups except for the 20 min rTMS/tsDCS intervention. iTBS/tsDCS and rTMS/ts-iTBS interventions induce neuroplasticity in an incomplete SCI animal model by significantly changing electrophysiological (MEP) and locomotion (BBB) outcomes.

Repetitive Transcranial Magnetic Stimulation With H-Coil Coupled With Cycling for Improving Lower Limb Motor Function After Stroke: An Exploratory Study

BACKGROUND/OBJECTIVES

Repetitive transcranial magnetic stimulation (rTMS) has been recognized as a promising intervention for the treatment of post-stroke motor deficits. Here, we explore safety, feasibility, and potential effectiveness of high-frequency rTMS (HF-rTMS) delivered with the Hesed coil (H-coil) during active cycling on paretic lower extremity (LE) motor function in chronic stroke.

MATERIALS AND METHODS

Twelve subjects with a first-ever stroke were recruited in this double-blind, placebo controlled, crossover study. Eleven sessions of HF-rTMS (40 2s-trains of 20 Hz at 90% resting leg motor threshold) were delivered over the LE motor areas using the H-coil during active cycling for three weeks. Each subject underwent both real and sham rTMS treatments separated by a four-week washout period, in a random sequence. Vital signs were recorded before and after each rTMS session. Any discomfort related to stimulation and side effects were recorded. LE function was also evaluated with Fugl-Meyer assessment (FMA-LE), spasticity was assessed with modified-Ashworth scale and measures of gait speed and endurance (10-meter and 6-min walk tests, respectively) were recorded.

RESULTS

No participant reported serious adverse effects. During real rTMS, 4 of 12 subjects reported mild side effects including transitory dizziness and muscle twitches on shoulder, so that intensity of stimulation initially set at 90% of RMT was reduced to 80% of RMT on average in these four subjects. Only real treatment was associated with a significant and sustained improvement in FMA-LL (67% responders vs. 9% of the sham). Spasticity significantly ameliorated only after the real rTMS. Real treatment did not offer advantages on walking timed measures when compared with sham.

CONCLUSIONS

This exploratory study suggests that bilateral HF-rTMS combined with cycling is safe and potentially effective in ameliorating paretic LE motor function and spasticity, rather than gait speed or endurance, in chronic stroke.

The role of spinal reciprocal inhibition and intracortical inhibition in functional recovery from stroke

Spinal reciprocal inhibition (RI) and intracortical inhibition are important physiological mechanisms for voluntary movement control and functional recovery of voluntary movement in patients with stroke. Spasticity, which impairs motor performance, is one of the major manifestations of stroke. RI may be involved in reducing spasticity. This might allow finger extension, and, therefore, better hand function by reducing co-contraction with finger extensors. One potential mechanism of functional reorganization of the motor cortex is that pre-existing masking pathways are unmasked by decreased intracortical inhibition. The inhibitory neurotransmitter GABA plays an important role in this process. Changes in RI might be mediated through unmasking of cortical pathways through decreased inhibition, with the neurotransmitter GABA. These changes can be assessed using short-latency intracortical inhibition (SICI) and RI. Functional recovery in the chronic phase of stroke induced by rehabilitation was accompanied by SICI and spinal RI changes. Cortical reorganization and spinal plasticity might play important roles in functional recovery induced by rehabilitation, even in patients with chronic severe hemiparesis. This review aims to provide a focused overview of neuroplasticity of spinal RI and intracortical inhibition associated with functional motor recovery from stroke.

Muscle length and joint angle influence spinal but not corticospinal excitability to the biceps brachii across forearm postures

Forearm rotation (supination/pronation) alters corticospinal excitability to the biceps brachii, but it is unclear whether corticospinal excitability is influenced by joint angle, muscle length, or both. Thus the purpose of this study was to separately examine elbow joint angle and muscle length on corticospinal excitability. Corticospinal excitability to the biceps and triceps brachii was measured using motor evoked potentials (MEPs) elicited via transcranial magnetic stimulation. Spinal excitability was measured using cervicomedullary motor evoked potentials (CMEPs) elicited via transmastoid electrical stimulation. Elbow angles were manipulated with a fixed biceps brachii muscle length (and vice versa) across five unique postures: 1) forearm neutral, elbow flexion 90°; 2) forearm supinated, elbow flexion 90°; 3) forearm pronated, elbow flexion 90°; 4) forearm supinated, elbow flexion 78°; and 5) forearm pronated, elbow flexion 113°. A musculoskeletal model determined biceps brachii muscle length for postures 1-3, and elbow joint angles (postures 4-5) were selected to maintain biceps length across forearm orientations. MEPs and CMEPs were elicited at rest and during an isometric contraction of 10% of maximal biceps muscle activity. At rest, MEP amplitudes to the biceps were largest during supination, which was independent of elbow joint angle. CMEP amplitudes were not different when the elbow was fixed at 90° but were largest in pronation when muscle length was controlled. During an isometric contraction, there were no significant differences across forearm postures for either MEP or CMEP amplitudes. These results highlight that elbow joint angle and biceps brachii muscle length can each independently influence spinal excitability. NEW & NOTEWORTHY Changes in upper limb posture can influence the responsiveness of the central nervous system to artificial stimulations. We established a novel approach integrating neurophysiology techniques with biomechanical modeling. Through this approach, the effects of elbow joint angle and biceps brachii muscle length on corticospinal and spinal excitability were assessed. We demonstrate that spinal excitability is uniquely influenced by joint angle and muscle length, and this highlights the importance of accounting for muscle length in neurophysiological studies.

Voluntary contraction enhances spinal reciprocal inhibition induced by patterned electrical stimulation in patients with stroke

BACKGROUND

Reciprocal inhibition (RI) may be important for recovering locomotion after stroke. Patterned electrical stimulation (PES) can modulate RI in a manner that could be enhanced by voluntary muscle contraction (VC).

OBJECTIVE

To investigate whether VC enhances the PES-induced spinal RI in patients with stroke.

METHODS

Twelve patients with chronic stroke underwent three 20 min tasks, each on different days: (1) PES (10 pulses, 100 Hz every 2 s) applied to the common peroneal nerve; (2) VC consisting of isometric contraction of the affected-side tibialis anterior muscle; (3) PES combined with VC (PES + VC). RI from the tibialis anterior to the soleus muscle was assessed before, immediately after, and 10, 20, and 30 min after the task.

RESULTS

Compared to the baseline, PES + VC significantly increased the changes in reciprocal inhibition at immediately after and 10 min after the task. PES alone significantly increased this change immediately after the task, while VC alone showed no significant increase.

CONCLUSION

VC enhanced the PES-induced plastic changes in RI in patients with stroke. This effect can potentially increase the success rate of newer neurorehabilitative approaches in achieving functional recovery after stroke.

Effects of repetitive transcranial magnetic stimulation and trans-spinal direct current stimulation associated with treadmill exercise in spinal cord and cortical excitability of healthy subjects: A triple-blind, randomized and sham-controlled study

Repetitive transcranial magnetic stimulation (rTMS) over motor cortex and trans-spinal direct current stimulation (tsDCS) modulate corticospinal circuits in healthy and injured subjects. However, their associated effects with physical exercise is still not defined. This study aimed to investigate the effect of three different settings of rTMS and tsDCS combined with treadmill exercise on spinal cord and cortical excitability of healthy subjects. We performed a triple blind, randomized, sham-controlled crossover study with 12 healthy volunteers who underwent single sessions of rTMS (1Hz, 20Hz and Sham) and tsDCS (anodal, cathodal and Sham) associated with 20 minutes of treadmill walking. Cortical excitability was assessed by motor evoked potential (MEP) and spinal cord excitability by the Hoffmann reflex (Hr), nociceptive flexion reflex (NFR) and homosynaptic depression (HD). All measures were assessed before, immediately, 30 and 60 minutes after the experimental procedures. Our results demonstrated that anodal tsDCS/treadmill exercise reduced MEP's amplitude and NFR's area compared to sham condition, conversely, cathodal tsDCS/treadmill exercise increased NFR's area. High-frequency rTMS increased MEP's amplitude and NFR's area compared to sham condition. Anodal tsDCS/treadmill exercise and 20Hz rTMS/treadmill exercise reduced Hr amplitude up to 30 minutes after stimulation offset and no changes were observed in HD measures. We demonstrated that tsDCS and rTMS combined with treadmill exercise modulated cortical and spinal cord excitability through different mechanisms. tsDCS modulated spinal reflexes in a polarity-dependent way acting at local spinal circuits while rTMS probably promoted changes in the presynaptic inhibition of spinal motoneurons. In addition, the association of two neuromodulatory techniques induced long-lasting changes.

Effects of intermittent theta burst stimulation on spasticity after spinal cord injury

PURPOSE

Spasticity is a common disorder in patients with spinal cord injury (SCI). The aim of this study was to investigate whether intermittent theta burst stimulation (iTBS), a safe, non-invasive and well-tolerated protocol of excitatory repetitive transcranial magnetic stimulation (rTMS), is effective in modulating spasticity in SCI patients.

METHODS

In this randomized, double-blind, crossover, sham-controlled study, ten subjects with incomplete cervical or thoracic SCI received 10 days of daily sessions of real or sham iTBS. The H/M amplitude ratio of the Soleus H reflex, the amplitude of the motor evoked potentials (MEPs) at rest and during background contraction, as well as Modified Ashworth Scale (MAS) and the Spinal Cord Injury Assessment Tool for Spasticity (SCAT) were compared before and after the stimulation protocols.

RESULTS

Patients receiving real iTBS showed significant increased resting and active MEPs amplitude and a significant reduction of the H/M amplitude ratio. In these patients also the MAS and SCAT scores were significantly reduced after treatment. These changes persisted up to 1 week after the end of the iTBS treatment, and were not observed under the sham-TBS condition.

CONCLUSION

These findings suggest that iTBS may be a promising therapeutic tool for the spasticity in SCI patients.

The effects of patterned electrical stimulation combined with voluntary contraction on spinal reciprocal inhibition in healthy individuals

The aim of this study was to examine the effects of voluntary contraction (VC) on the modulation of reciprocal inhibition induced by patterned electrical stimulation (PES) in healthy individuals. Twelve healthy volunteers participated in this study. PES was applied to the common peroneal nerve with a train of 10 pulses at 100 Hz every 2 s for 20 min. VC comprised repetitive ankle dorsiflexion at a frequency of 0.5 Hz for 20 min. All participants performed the following three tasks: (i) VC alone, (ii) PES alone, and (iii) PES combined with VC (PES+VC). Reciprocal inhibition was assessed using a soleus H-reflex conditioning-test paradigm at the time points of before, immediately after, 10 min after, 20 min after, and 30 min after the tasks. PES+VC increased the amount of reciprocal inhibition, with after-effects lasting up to 20 min. PES alone increased reciprocal inhibition and maintained the after-effects on reciprocal inhibition for 10 min, whereas VC alone increased only immediately after the task. VC could modulate the plastic changes in spinal reciprocal inhibition induced by PES in healthy individuals. PES combined with VC has a potential to modulate impaired reciprocal inhibition and it may facilitate functional recovery and improve locomotion after central nervous system lesions.

Priming Neural Circuits to Modulate Spinal Reflex Excitability

While priming is most often thought of as a strategy for modulating neural excitability to facilitate voluntary motor control, priming stimulation can also be utilized to target spinal reflex excitability. In this application, priming can be used to modulate the involuntary motor output that often follows central nervous system injury. Individuals with spinal cord injury (SCI) often experience spasticity, for which antispasmodic medications are the most common treatment. Physical therapeutic/electroceutic interventions offer an alternative treatment for spasticity, without the deleterious side effects that can accompany pharmacological interventions. While studies of physical therapeutic/electroceutic interventions have been published, a systematic comparison of these approaches has not been performed. The purpose of this study was to compare four non-pharmacological interventions to a sham-control intervention to assess their efficacy for spasticity reduction. Participants were individuals (n = 10) with chronic SCI (≥1 year) who exhibited stretch-induced quadriceps spasticity. Spasticity was quantified using the pendulum test before and at two time points after (immediate, 45 min delayed) each of four different physical therapeutic/electroceutic interventions, plus a sham-control intervention. Interventions included stretching, cyclic passive movement (CPM), transcutaneous spinal cord stimulation (tcSCS), and transcranial direct current stimulation (tDCS). The sham-control intervention consisted of a brief ramp-up and ramp-down of knee and ankle stimulation while reclined with legs extended. The order of interventions was randomized, and each was tested on a separate day with at least 48 h between sessions. Compared to the sham-control intervention, stretching, CPM, and tcSCS were associated with a significantly greater reduction in spasticity immediately after treatment. While the immediate effect was largest for stretching, the reduction persisted for 45 min only for the CPM and tcSCS interventions. tDCS had no immediate or delayed effects on spasticity when compared to sham-control. Interestingly, the sham-control intervention was associated with significant within-session increases in spasticity, indicating that spasticity increases with immobility. These findings suggest that stretching, CPM, and tcSCS are viable non-pharmacological alternatives for reducing spasticity, and that CPM and tcSCS have prolonged effects. Given that the observed effects were from a single-session intervention, future studies should determine the most efficacious dosing and timing strategies.

Effects of repetitive transcranial magnetic stimulation on lower extremity spasticity and motor function in stroke patients

PURPOSE

To investigate the effect of low-frequency repetitive transcranial magnetic stimulation (rTMS) on lower extremity (LE) spasticity, motor function and motor neurone excitability in chronic stroke patients.

METHOD

This study was a randomised sham-controlled cross-over trial with 1-week follow-up. A total of 20 post-stroke patients were randomised to receive active (n = 10) or sham (n = 10) rTMS. Fourteen of them (7 in each group) crossed over to the sham or active rTMS after a washout period of 1 month. Interventions consist of five consecutive daily sessions of active or sham rTMS to the unaffected lower extremity motor area (1000 pulses; 1 Hz; 90% of the tibialis anterior motor threshold). Outcome measures were modified modified ashworth scale (MMAS), the H-reflex, lower extremity section of Fugl-Mayer assessment (LE-FMA) and timed UP and GO (TUG) test. All outcomes were measured at three levels in each intervention period: pre- and post-intervention and 1-week follow-up.

RESULTS

Friedman's test revealed significant improvement in MMAS score only after active rTMS. This improvement lasted for one week after the active rTMS. Repeated measure analysis of variance (ANOVA) showed significant time*intervention interaction for LE-FMA. There are no differences between groups for the MMAS and LE-FMA. No significant change in Hmax/Mmax ratio and TUG test was noted.

CONCLUSION

Low-frequency rTMS over the LE motor area can improve clinical measures of muscle spasticity and motor function. More studies are needed to clarify the changes underlying this improvement in spasticity. Implications for Rehabilitation Spasticity is a common disorder and one of the causes of long-term disability after stroke. Physical therapy modalities, oral medications, focal intervention and surgical procedures have been used for spasticity reduction. Beneficial effect of the repetitive transcranial magnetic stimulation (rTMS) for post-stroke upper extremity spasticity reduction and motor function improvement was demonstrated in previous studies. This study shows amelioration of lower extremity spasticity and motor function improvement after five daily sessions of inhibitory rTMS to the unaffected brain hemisphere which lasted for at least 1 week following the intervention.

Efficacy of QuadroPulse rTMS for improving motor function after spinal cord injury: Three case studies

CONTEXT/OBJECTIVE

To examine the effects of repetitive QuadroPulse transcranial magnetic stimulation (rTMS(QP)) on hand/leg function after spinal cord injury (SCI).

DESIGN

Interventional proof-of-concept study.

SETTING

University laboratory.

PARTICIPANTS

Three adult subjects with cervical SCI. Interventions Repeated trains of magnetic stimuli were applied to the motor cortical hand/leg area. Several exploratory single-day rTMS(QP) protocols were examined. Ultimately we settled on a protocol using three 5-day trials of (1) rTMS(QP) only; (2) exercise only (targeting hand or leg function); and (3) rTMS(QP) combined with exercise.

OUTCOME MEASURES

Hand motor function was assessed by Purdue Pegboard and Complete Minnesota Dexterity tests. Walking function was based on treadmill walking and the Timed Up and Go test. Electromyographic recordings were used for neurophysiological testing of cortical (by single- and double-pulse TMS) and spinal (via tendon taps and electrical nerve stimulation) excitability.

RESULTS

Single-day rTMS(QP) application had no clear effect in the 2 subjects whose hand function was targeted, but improved walking speed in the person targeted for walking, accompanied by increased cortical excitability and reduced spinal excitability. All 3 subjects showed functional improvement following the 5-day rTMS(QP) intervention, an effect being even more pronounced after the five-day combined rTMS(QP) + exercise sessions. There were no rTMS(QP)-associated adverse effects.

CONCLUSION

Our findings suggest a functional benefit of motor cortical rTMS(QP) after SCI. The effect of rTMS(QP) appears to be augmented when stimulation is accompanied by targeted exercises, warranting expansion of this pilot study to a larger subject population.

A pilot study on the effects of low frequency repetitive transcranial magnetic stimulation on lower extremity spasticity and motor neuron excitability in patients after stroke

PURPOSE

To evaluate the effect of low frequency, repetitive transcranial magnetic stimulation (rTMS) on the lower extremity spasticity and motor neuron excitability in patients after stroke.

METHODS

Seven patients after stroke aged 42-78 years were included in this pretest-posttest clinical trial. The rTMS at 1 Hz and duration of 20 min was applied to the intact leg motor cortex for five consecutive sessions. Primary outcome measures were the Modified Modified Ashwoth Scale (MMAS) and the H(max)/M(max) ratio. Measurements were taken at baseline (T0), after the last treatment (5th) session (T1), and at 1 week follow up (T2).

RESULTS

Clinically assessed ankle plantar flexor spasticity (p = 0.05) improved significantly after treatment at T1. Knee extensor spasticity scored 0 after treatment at T1 and T2. The H(max)/M(max) ratio showed no statistically significant improvement after treatment.

CONCLUSION

The pilot data indicate that the inhibitory rTMS of the intact leg motor cortex in patients after stroke may improve the lower extremity spasticity.

The Neurophysiologist Perspective into MS Plasticity

Multiple sclerosis (MS) is a frequent, highly debilitating inflammatory demyelinating disease, starting to manifest in early adulthood and presenting a wide variety of symptoms, which are often resistant to pharmacological treatments. Cortical dysfunctions have been demonstrated to be key components of MS condition, and plasticity of the corticospinal motor system is highly involved in major MS symptoms, such as fatigue, spasticity, or pain. Cortical dysfunction in MS can be studied with neurophysiological tools, such as electroencephalography (EEG) and related techniques (evoked potentials) or transcranial magnetic stimulation (TMS). These techniques are now widely used to provide essential elements of MS diagnosis and can also be used to modulate plasticity. Indeed, the recent development of non-invasive brain stimulation techniques able to induce cortical plasticity, such as repetitive TMS or transcranial direct current stimulation, has brought promising results as add-on treatments. In this review, we will focus on the use of these tools (EEG and TMS) to study plasticity in MS and on the major techniques used to modulate plasticity in MS.

Repetitive transcranial magnetic stimulation and transcranial direct current stimulation in motor rehabilitation after stroke: an update

Stroke is a leading cause of adult motor disability. The number of stroke survivors is increasing in industrialized countries, and despite available treatments used in rehabilitation, the recovery of motor functions after stroke is often incomplete. Studies in the 1980s showed that non-invasive brain stimulation (mainly repetitive transcranial magnetic stimulation [rTMS] and transcranial direct current stimulation [tDCS]) could modulate cortical excitability and induce plasticity in healthy humans. These findings have opened the way to the therapeutic use of the 2 techniques for stroke. The mechanisms underlying the cortical effect of rTMS and tDCS differ. This paper summarizes data obtained in healthy subjects and gives a general review of the use of rTMS and tDCS in stroke patients with altered motor functions. From 1988 to 2012, approximately 1400 publications were devoted to the study of non-invasive brain stimulation in humans. However, for stroke patients with limb motor deficit, only 141 publications have been devoted to the effects of rTMS and 132 to those of tDCS. The Cochrane review devoted to the effects of rTMS found 19 randomized controlled trials involving 588 patients, and that devoted to tDCS found 18 randomized controlled trials involving 450 patients. Without doubt, rTMS and tDCS contribute to physiological and pathophysiological studies in motor control. However, despite the increasing number of studies devoted to the possible therapeutic use of non-invasive brain stimulation to improve motor recovery after stroke, further studies will be necessary to specify their use in rehabilitation.

Noninvasive Neuromodulation in Poststroke Gait Disorders

Walking rehabilitation is one of the primary goals in stroke survivors because of its great potential for recovery and its functional relevance in daily living activities. Although 70% to 80% of people in the chronic poststroke phases are able to walk, impairment of gait often persists, involving speed, endurance, and stability. Walking involves several brain regions, such as the sensorimotor cortex, supplementary motor area, cerebellum, and brainstem, which are approachable by the application of noninvasive brain stimulation (NIBS). NIBS techniques, such as repetitive transcranial magnetic stimulation and transcranial direct current stimulation, have been reported to modulate neural activity beyond the period of stimulation, facilitating neuroplasticity. NIBS methods have been largely applied for improving paretic hand motor function and stroke-associated cognitive deficits. Recent studies suggest a possible effectiveness of these techniques also in the recovery of poststroke gait disturbance. This article is a selective review about functional investigations addressing the mechanisms of lower-limb motor system reorganization after stroke and the application of NIBS for neurorehabilitation.

Descending motor pathways and cortical physiology after spinal cord injury assessed by transcranial magnetic stimulation: a systematic review

We performed here a systematic review of the studies using transcranial magnetic stimulation (TMS) as a research and clinical tool in patients with spinal cord injury (SCI). Motor evoked potentials (MEPs) elicited by TMS represent a highly accurate diagnostic test that can supplement clinical examination and neuroimaging findings in the assessment of SCI functional level. MEPs allows to monitor the changes in motor function and evaluate the effects of the different therapeutic approaches. Moreover, TMS represents a useful non-invasive approach for studying cortical physiology, and may be helpful in elucidating the pathophysiological mechanisms of brain reorganization after SCI. Measures of motor cortex reactivity, e.g., the short interval intracortical inhibition and the cortical silent period, seem to point to an increased cortical excitability. However, the results of TMS studies are sometimes contradictory or divergent, and should be replicated in a larger sample of subjects. Understanding the functional changes at brain level and defining their effects on clinical outcome is of crucial importance for development of evidence-based rehabilitation therapy. TMS techniques may help in identifying neurophysiological biomarkers that can reliably assess the extent of neural damage, elucidate the mechanisms of neural repair, predict clinical outcome, and identify therapeutic targets. Some researchers have begun to therapeutically use repetitive TMS (rTMS) in patients with SCI. Initial studies revealed that rTMS can induce acute and short duration beneficial effects especially on spasticity and neuropathic pain, but the evidence is to date still very preliminary and well-designed clinical trials are warranted. This article is part of a Special Issue entitled SI: Spinal cord injury.

Effects of repetitive transcranial magnetic stimulation on recovery of function after spinal cord injury

A major goal of rehabilitation strategies after spinal cord injury (SCI) is to enhance the recovery of function. One possible avenue to achieve this goal is to strengthen the efficacy of the residual neuronal pathways. Noninvasive repetitive transcranial magnetic stimulation (rTMS) has been used in patients with motor disorders as a tool to modulate activity of corticospinal, cortical, and subcortical pathways to promote functional recovery. This article reviews a series of studies published during the last decade that used rTMS in the acute and chronic stages of paraplegia and tetraplegia in humans with complete and incomplete SCI. In the studies, rTMS has been applied over the arm and leg representations of the primary motor cortex to target 3 main consequences of SCI: sensory and motor function impairments, spasticity, and neuropathic pain. Although some studies demonstrated that consecutive sessions of rTMS improve aspects of particular functions, other studies did not show similar effects. We discuss how rTMS parameters and postinjury reorganization in the corticospinal tract, motor cortical, and spinal cord circuits might be critical factors in understanding the advantages and disadvantages of using rTMS in patients with SCI. The available data highlight the limited information on the use of rTMS after SCI and the need to further understand the pathophysiology of neuronal structures affected by rTMS to maximize the potential beneficial effects of this technique in humans with SCI.

The effects of 15 Hz trans-spinal magnetic stimulation on locomotor control in mice with chronic contusive spinal cord injury

The effects of repetitive trans-spinal magnetic stimulation (rTSMS), combined with acrobatic exercise on functional locomotor recovery in chronic spinal-contused mice were tested. The exposure to magnetic stimulation was initiated 3 weeks after injury, when the animals entered chronic stage. The rTSMS was applied for a total of 4 weeks over a 9-week duration trial. Seventeen mice with the spinal cord contusion injured at level T13 were separated into two groups. While one group consisting of 10 animals was exposed to rTSMS (15 Hz), the other seven animals served as controls. Functional recovery measured with Basso mouse scale and horizontal ladder scale showed significantly better functional recovery in rTSMS-treated animals. The progress in recovery continued even after cessation of magnetic stimulation. In vitro experiments revealed that the release of glutamate analog, radioactive D-aspartate from the segments of the spinal cord exposed to rTSMS was significantly elevated. In conclusion, the exposure to rTSMS, applied to injured spinal cord during chronic post-surgery stage remarkably improves the functional recovery. This recovery may be correlated by magnetically induced elevation in the release of major excitatory neurotransmitter, glutamate from injured tissue.

Induction of central nervous system plasticity by repetitive transcranial magnetic stimulation to promote sensorimotor recovery in incomplete spinal cord injury

Cortical and spinal cord plasticity may be induced with non-invasive transcranial magnetic stimulation to encourage long term potentiation or depression of neuronal circuits. Such plasticity inducing stimulation provides an attractive approach to promote changes in sensorimotor circuits that have been degraded by spinal cord injury (SCI). If residual corticospinal circuits can be conditioned appropriately there should be the possibility that the changes are accompanied by functional recovery. This article reviews the attempts that have been made to restore sensorimotor function and to obtain functional benefits from the application of repetitive transcranial magnetic stimulation (rTMS) of the cortex following incomplete spinal cord injury. The confounding issues that arise with the application of rTMS, specifically in SCI, are enumerated. Finally, consideration is given to the potential for rTMS to be used in the restoration of bladder and bowel sphincter function and consequent functional recovery of the guarding reflex.

Benefits of repetitive transcranial magnetic stimulation (rTMS) for spastic subjects: clinical, functional, and biomechanical parameters for lower limb and walking in five hemiparetic patients

Introduction. Spasticity is a disabling symptom resulting from reorganization of spinal reflexes no longer inhibited by supraspinal control. Several studies have demonstrated interest in repetitive transcranial magnetic stimulation in spastic patients. We conducted a prospective, randomized, double-blind crossover study on five spastic hemiparetic patients to determine whether this type of stimulation of the premotor cortex can provide a clinical benefit. Material and Methods. Two stimulation frequencies (1 Hz and 10 Hz) were tested versus placebo. Patients were assessed clinically, by quantitative analysis of walking and measurement of neuromechanical parameters (H and T reflexes, musculoarticular stiffness of the ankle). Results. No change was observed after placebo and 10 Hz protocols. Clinical parameters were not significantly modified after 1 Hz stimulation, apart from a tendency towards improved recruitment of antagonist muscles on the Fügl-Meyer scale. Only cadence and recurvatum were significantly modified on quantitative analysis of walking. Neuromechanical parameters were modified with significant decreases in H max⁡ /M max⁡ and T/M max⁡ ratios and stiffness indices 9 days or 31 days after initiation of TMS. Conclusion. This preliminary study supports the efficacy of low-frequency TMS to reduce reflex excitability and stiffness of ankle plantar flexors, while clinical signs of spasticity were not significantly modified.

Repetitive activation of the corticospinal pathway by means of rTMS may reduce the efficiency of corticomotoneuronal synapses

Low-frequency rTMS applied to the primary motor cortex (M1) may produce depression of motor-evoked potentials (MEPs). This depression is commonly assumed to reflect changes in cortical circuits. However, little is known about rTMS-induced effects on subcortical circuits. Therefore, the present study aimed to clarify whether rTMS influences corticospinal transmission by altering the efficiency of corticomotoneuronal (CM) synapses. The corticospinal transmission to soleus α-motoneurons was evaluated through conditioning of the soleus H-reflex by magnetic stimulation of either M1 (M1-conditioning) or the cervicomedullary junction (CMS-conditioning). The first facilitation of the H-reflex (early facilitation) was determined after M1- and CMS-conditioning. Comparison of the early facilitation before and after 20-min low-frequency (1 Hz) rTMS revealed suppression with M1- (-17 ± 4%; P = 0.001) and CMS-conditioning (-6 ± 2%; P = 0.04). The same rTMS protocol caused a significant depression of compound MEPs, whereas amplitudes of H-reflex and M-wave remained unaffected, indicating a steady level of motoneuronal excitability. Thus, the effects of rTMS are likely to occur at a premotoneuronal site-either at M1 and/or the CM synapse. As the early facilitation reflects activation of direct CM projections, the most likely site of action is the synapse of the CM neurons onto spinal motoneurons.

Transcranial magnetic stimulation after spinal cord injury

OBJECTIVE

To review the basic principles and techniques of transcranial magnetic stimulation (TMS) and provide information and evidence regarding its applications in spinal cord injury clinical rehabilitation.

METHODS

A review of the available current and historical literature regarding TMS was conducted, and a discussion of its potential use in spinal cord injury rehabilitation is presented.

RESULTS

TMS provides reliable information about the functional integrity and conduction properties of the corticospinal tracts and motor control in the diagnostic and prognostic assessment of various neurological disorders. It allows one to follow the evolution of motor control and to evaluate the effects of different therapeutic procedures. Motor-evoked potentials can be useful in follow-up evaluation of motor function during treatment and rehabilitation, specifically in patients with spinal cord injury and stroke. Although studies regarding somatomotor functional recovery after spinal cord injury have shown promise, more trials are required to provide strong and substantial evidence.

CONCLUSIONS

TMS is a promising noninvasive tool for the treatment of spasticity, neuropathic pain, and somatomotor deficit after spinal cord injury. Further investigation is needed to demonstrate whether different protocols and applications of stimulation, as well as alternative cortical sites of stimulation, may induce more pronounced and beneficial clinical effects.

Motor cortex stimulation modulates defective central beta rhythms in patients with neuropathic pain

OBJECTIVE

Motor cortex stimulation therapy (MCS) is increasingly used to control refractory neuropathic pain. Post-movement beta synchronization (PMBS) is defined as a sharp increase in beta-frequency electroencephalographic power following movement offset and may reflect sensorimotor cortex inhibition induced, at least in part, by cortical processing of movement-related sensory afferent inputs. PMBS pattern is then often altered in case of neuropathic pain. The main objective of the present study was to test the hypothesis that implanted MCS modulates PMBS in patients presenting with neuropathic pain.

METHODS

Using a high-resolution, 128-electrode electroencephalographic system, we recorded and compared, before and during MCS, PMBS patterns during brisk, unilateral right and left index finger extension in 8 patients presenting with neuropathic pain.

RESULTS

The pre-operative PMBS patterns were altered in all cases. MCS increased the spatial distribution and amplitude of PMBS in most of cases and restored maximum-intensity of PMBS contralateral to the painful body side. These modifications appeared significantly correlated with the analgesic effect of MCS.

CONCLUSION

This study provides evidence of central beta rhythms neuromodulation induced by MCS.

SIGNIFICANCE

The restoration by MCS of defective cortical inhibition in patients with neuropathic pain is evoked.

Effects of anodal transcranial direct current stimulation over the leg motor area on lumbar spinal network excitability in healthy subjects

In recent years, two techniques have become available for the non-invasive stimulation of human motor cortex: transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS). The effects of TMS and tDCS when applied over motor cortex should be considered with regard not only to cortical circuits but also to spinal motor circuits. The different modes of action and specificity of TMS and tDCS suggest that their effects on spinal network excitability may be different from that in the cortex. Until now, the effects of tDCS on lumbar spinal network excitability have never been studied. In this series of experiments, on healthy subjects, we studied the effects of anodal tDCS over the lower limb motor cortex on (i) reciprocal Ia inhibition projecting from the tibialis anterior muscle (TA) to the soleus (SOL), (ii) presynaptic inhibition of SOL Ia terminals, (iii) homonymous SOL recurrent inhibition, and (iv) SOL H-reflex recruitment curves. The results show that anodal tDCS decreases reciprocal Ia inhibition, increases recurrent inhibition and induces no modification of presynaptic inhibition of SOL Ia terminals and of SOL-H reflex recruitment curves. Our results indicate therefore that the effects of tDCS are the opposite of those previously described for TMS on spinal network excitability. They also indicate that anodal tDCS induces effects on spinal network excitability similar to those observed during co-contraction suggesting that anodal tDCS activates descending corticospinal projections mainly involved in co-contractions.

Transcranial direct current stimulation modulates the spinal plasticity induced with patterned electrical stimulation

OBJECTIVE

Patterned sensory electrical stimulation (PES) has been shown to induce plasticity in spinal reciprocal Ia inhibition of the calf muscles. To study the cortical modulation of spinal plasticity, we examined the effects of giving transcranial direct current stimulation (tDCS) to the motor cortex before PES.

METHODS

Seven healthy volunteers participated in this study. PES involved stimulating the left common peroneal nerve at the fibular head with a train of 10 pulses at 100 Hz every 1.5s for 20 min using an intensity equal to the motor threshold of the tibialis anterior. tDCS was applied for 10 min before PES. For anodal stimulation, the electrode was placed over the motor cortex, and the cathodal electrode over the contralateral supraorbital area. For cathodal stimulation, the electrodes were reversed. Reciprocal inhibition was assessed using a soleus H reflex conditioning-test paradigm.

RESULTS

PES increased disynaptic reciprocal inhibition from the peroneal nerve to the soleus H reflex. When cathodal tDCS was applied before PES, PES no longer increased reciprocal inhibition.

CONCLUSIONS

Applying tDCS before PES modulated the effects of PES on spinal reciprocal inhibition in a polarity specific manner.

SIGNIFICANCE

We suggest that the motor cortex may play a role in spinal plasticity.

Paired associative stimulation induces change in presynaptic inhibition of Ia terminals in wrist flexors in humans

Enhancements in the strength of corticospinal projections to muscles are induced in conscious humans by paired associative stimulation (PAS) to the motor cortex. Although most of the previous studies support the hypothesis that the increase of the amplitude of motor evoked potentials (MEPs) by PAS involves long-term potentiation (LTP)-like mechanism in cortical synapses, changes in spinal excitability after PAS have been reported, suggestive of parallel modifications in both cortical and spinal excitability. In a first series of experiments (experiment 1), we confirmed that both flexor carpi radialis (FCR) MEPs and FCR H reflex recruitment curves are enhanced by PAS. To elucidate the mechanism responsible for this change in the H reflex amplitude, we tested, using the same subjects, the hypothesis that enhanced H reflexes are caused by a down-regulation of the efficacy of mechanisms controlling Ia afferent discharge, including presynaptic Ia inhibition and postactivation depression. To address this question, amounts of both presynaptic Ia inhibition of FCR Ia terminals (D1 and D2 inhibitions methods; experiment 2) and postactivation depression (experiment 3) were determined before and after PAS. Results showed that PAS induces a significant decrease of presynaptic Ia inhibition of FCR terminals, which was concomitant with the facilitation of the H reflex. Postactivation depression was unaffected by PAS. It is argued that enhancement of segmental excitation by PAS relies on a selective effect of PAS on the interneurons controlling presynaptic inhibition of Ia terminals.

Neural interface technology for rehabilitation: exploiting and promoting neuroplasticity

This article reviews neural interface technology and its relationship with neuroplasticity. Two types of neural interface technology are reviewed, highlighting specific technologies that the authors directly work with: (1) neural interface technology for neural recording, such as the micro-ECoG BCI system for hand prosthesis control, and the comprehensive rehabilitation paradigm combining MEG-BCI, action observation, and motor imagery training; (2) neural interface technology for functional neural stimulation, such as somatosensory neural stimulation for restoring somatosensation, and non-invasive cortical stimulation using rTMS and tDCS for modulating cortical excitability and stroke rehabilitation. The close interaction between neural interface devices and neuroplasticity leads to increased efficacy of neural interface devices and improved functional recovery of the nervous system. This symbiotic relationship between neural interface technology and the nervous system is expected to maximize functional gain for individuals with various sensory, motor, and cognitive impairments, eventually leading to better quality of life.

Reduction of spasticity with repetitive transcranial magnetic stimulation in patients with spinal cord injury

OBJECTIVE

Spasticity with increased tone and spasms is frequent in patients after spinal cord injury (SCI). Damage to descending corticospinal pathways that normally exert spinal segmental control is thought to play an important causal role in spasticity. The authors examined whether the modulation of excitability of the primary motor cortex with high-frequency repetitive transcranial magnetic stimulation (rTMS) could modify lower limb spasticity in patients with incomplete SCI.

METHODS

Patients were assessed by the Modified Ashworth Scale, Visual Analogue Scale, and the Spinal Cord Injury Spasticity Evaluation Tool (SCI-SET) and neurophysiologically with measures of corticospinal and segmental excitability by the H(max)/M(max), T reflex, and withdrawal reflex. Fifteen patients received 5 days of daily sessions of active (n = 14) or sham (n = 7) rTMS to the leg motor area (20 trains of 40 pulses at 20 Hz and an intensity of 90% of resting motor threshold for the biceps brachii muscle).

RESULT

A significant clinical improvement in lower limb spasticity was observed in patients following active rTMS but not after sham stimulation.This improvement lasted for at least 1 week following the intervention. Neurophysiological studies did not change.

CONCLUSIONS

High-frequency rTMS over the leg motor area can improve aspects of spasticity in patients with incomplete SCI.

Physiology of repetitive transcranial magnetic stimulation of the human brain

During the last two decades, transcranial magnetic stimulation (TMS) has rapidly become a valuable method to investigate noninvasively the human brain. In addition, repetitive TMS (rTMS) is able to induce changes in brain activity that last after stimulation. Therefore, rTMS has therapeutic potential in patients with neurologic and psychiatric disorders. It is, however, unclear by which mechanism rTMS induces these lasting effects on the brain. The effects of rTMS are often described as LTD- or LTP-like, because the duration of these alterations seems to implicate changes in synaptic plasticity. In this review we therefore discuss, based on rTMS experiments and knowledge about synaptic plasticity, whether the physiologic basis of rTMS-effects relates to changes in synaptic plasticity. We present seven lines of evidence that strongly suggest a link between the aftereffects induced by rTMS and the induction of synaptic plasticity. It is, nevertheless, important to realize that at present it is impossible to demonstrate a direct link between rTMS on the one hand and synaptic plasticity on the other. Therefore, we provide suggestions for future, innovating research, aiming to investigate both the local effects of rTMS on the synapse and the effects of rTMS on other, more global levels of brain organization. Only in that way can the aftereffects of rTMS on the brain be completely understood.

Impact of transcranial direct current stimulation on spinal network excitability in humans

Transcranial direct current stimulation (tDCS) when applied over the motor cortex, modulates excitability dependent on the current polarity. The impact of this cortical modulation on spinal cord network excitability has rarely been studied. In this series of experiments, performed in healthy subjects, we show that anodal tDCS increases disynaptic inhibition directed from extensor carpi radialis (ECR) to flexor carpi radialis (FCR) with no modification of presynaptic inhibition of FCR Ia terminals and FCR H-reflex recruitment curves. We also show that cathodal tDCS does not modify spinal network excitability. Our results suggest that the increase of disynaptic inhibition observed during anodal tDCS relies on an increase of disynaptic interneuron excitability and that tDCS over the motor cortex in human subjects induces effects on spinal network excitability. Our results highlight the fact that the effects of tDCS should be considered in regard to spinal motor circuits and not only to cortical circuits.

Electrophysiological outcomes after spinal cord injury

Electrophysiological measures can provide information that complements clinical assessments such as the American Spinal Injury Association sensory and motor scores in the evaluation of outcomes after spinal cord injury (SCI). The authors review and summarize the literature regarding tests that are most relevant to the study of SCI recovery--in particular, motor evoked potentials and somatosensory evoked potentials (SSEPs). In addition, they discuss the role of other tests, including F-wave nerve conductance tests and electromyography, sympathetic skin response, and the Hoffman reflex (H-reflex) test as well as the promise of dermatomal SSEPs and the electrical perceptual threshold test, newer quantitative tests of sensory function. It has been shown that motor evoked potential amplitudes improve with SCI recovery but latencies do not. Somatosensory evoked potentials are predictive of ambulatory capacity and hand function. Hoffman reflexes are present during spinal shock despite the loss of tendon reflexes, but their amplitudes increase with time after injury. Further, H-reflex modulation is reflective of changes in spinal excitability. While these tests have produced data that is congruent with clinical evaluations, they have yet to surpass clinical evaluations in predicting outcomes. Continuing research using these methodologies should yield a better understanding of the mechanisms behind SCI recovery and thus provide potentially greater predictive and evaluative power.

Changes in soleus H-reflex modulation after treadmill training in children with cerebral palsy

In healthy children, short latency leg muscle reflexes are profoundly modulated throughout the step cycle in a functionally meaningful way and contribute to the electromyographic (EMG) pattern observed during gait. With maturation of the corticospinal tract, the reflex amplitudes are depressed via supraspinal inhibitory mechanisms. In the soleus muscle the rhythmic part of the modulation pattern is present in children with cerebral palsy (CP), but the development of tonic depression with increasing age, as seen in healthy children, is disturbed. Treadmill training clinically improves the walking pattern in children with CP. Presuming that short latency reflexes contribute significantly to the walking pattern, a change in the modulation may occur after training. The aim of this study was to assess whether treadmill training also improves the soleus reflex modulation during gait in children with CP. Seven children with CP underwent brief treadmill training for 10 min a day over 10 consecutive days; all of them were functional walkers. Soleus Hoffmann (H-) reflexes were investigated during walking on a treadmill before the first, and one day after the last, training session. Treadmill training led to a considerable clinical improvement in gait velocity. After 10 days of training, soleus H-reflexes during gait were almost completely depressed during the swing phase. The complete suppression of the soleus H-reflex during the swing phase, which is also exhibited by healthy subjects, could reflect an improvement towards a functionally more useful pattern. In conclusion, treadmill training can induce changes in the modulation of short latency reflexes during gait.

Quadriceps activity and movement reactions in response to unpredictable sagittal support-surface translations in women with patellofemoral pain

Patellofemoral pain (PFP) may be related to unfavorable knee joint loading. Delayed and/or reduced activity of vastus medialis obliquus (VMO) and different movement patterns have been identified in individuals with PFP in some studies, whereas other studies have failed to show a difference compared to non-affected controls. The discrepancy between study results may depend on the different tasks that have been investigated. No previous study has investigated these variables in postural responses to unpredictable perturbations in PFP. Whole body three dimensional kinematics and surface EMG of quadriceps muscles activation was studied in postural responses to unpredictable support surface translations in 17 women with PFP who were pain free at the time of testing, and 17 matched healthy controls. The results of the present study showed earlier onset of VMO activity and associated changes in kinematics to anterior platform translation in the PFP subjects. We suggest that the relative timing between the portions quadriceps muscles may be task specific and part of an adapted response in attempt to reduce knee joint loading. This learned response appears to remain even when the pain is no longer present.

Repetitive transcranial magnetic stimulation of the motor cortex ameliorates spasticity in multiple sclerosis

OBJECTIVE

To investigate whether repetitive transcranial magnetic stimulation (rTMS) can modify spasticity.

METHODS

We used high-frequency (5 Hz) and low-frequency (1 Hz) rTMS protocols in 19 remitting patients with relapsing-remitting multiple sclerosis and lower limb spasticity.

RESULTS

A single session of 1 Hz rTMS over the leg primary motor cortex increased H/M amplitude ratio of the soleus H reflex, a reliable neurophysiologic measure of stretch reflex. Five hertz rTMS decreased H/M amplitude ratio of the soleus H reflex and increased corticospinal excitability. Single sessions did not induce any effect on spasticity. A significant improvement of lower limb spasticity was observed when rTMS applications were repeated during a 2-week period. Clinical improvement was long-lasting (at least 7 days after the end of treatment) when the patients underwent 5 Hz rTMS treatment during a 2-week protocol. No effect was obtained after a 2-week sham stimulation.

CONCLUSIONS

Repetitive transcranial magnetic stimulation may improve spasticity in multiple sclerosis.

Changes to somatosensory detection and pain thresholds following high frequency repetitive TMS of the motor cortex in individuals suffering from chronic pain

Research has shown that transcranial magnetic stimulation (TMS) results in a transient reduction in the experience of chronic pain. The present research aimed to investigate whether a single session of high frequency TMS is able to change the sensory thresholds of individuals suffering from chronic pain. Detection and pain thresholds for cold and heat sensations were measured before and after 20Hz repetitive TMS (rTMS) administered over the motor cortex. A significant decrease in temperature for cold detection and pain thresholds and a significant increase in temperature for heat pain thresholds were evident following a single session of rTMS. In contrast, no change in detection and pain thresholds was obtained following sham rTMS. The finding that rTMS can have a direct effect on sensory thresholds in individuals suffering from chronic pain has implications for the therapeutic use of rTMS in the relief of chronic pain.