Assessment and modulation of neural plasticity in rehabilitation with transcranial magnetic stimulation

Exercise effects on cortical excitability in pain populations: A systematic review and meta-analysis

BACKGROUND

Transcranial Magnetic Stimulation (TMS) studies examining exercise-induced neuroplasticity in pain populations have produced contradictory findings. We conducted a systematic review to explore how exercise impacts cortical excitability in pain populations using TMS metrics. This review aims to summarize the effect sizes and to understand their sources of heterogeneity.

METHODS

We searched multiple databases from inception to December 2022. We included randomized controlled trials (RCTs) with any type of pain population, including acute and chronic pain; exercise interventions were compared to sham exercise or other active interventions. The primary outcomes were TMS metrics, and pain intensity was the secondary outcome. Risk of bias assessment was conducted using the Cochrane tool.

RESULTS

This review included five RCTs (n = 155). The main diagnoses were fibromyalgia and cervical dystonia. The interventions included submaximal contractions, aerobic exercise, physical therapy, and exercise combined with transcranial direct current stimulation. Three studies are considered to have a high risk of bias. All five studies showed significant pain improvement with exercise. The neurophysiological data revealed improvements in cortical excitability measured by motor-evoked potentials; standardized mean difference = 2.06, 95% confidence interval 1.35-2.78, I2 = 19%) but no significant differences in resting motor threshold. The data on intracortical inhibition/facilitation (ICI/ICF) was not systematically analyzed, but one study (n = 45) reported higher ICI and lower ICF after exercise.

CONCLUSIONS

These findings suggest that exercise interventions positively affect pain relief by modifying corticospinal excitability, but their effects on ICI/ICF are still unclear. While the results are inconclusive, they provide a basis for further exploration in this area of research; future studies should focus on establishing standardized TMS measurements and exercise protocols to ensure consistent and reliable findings. A large-scale RCT that examines various exercise interventions and their effects on cortical excitability could offer valuable insights to optimize its application in promoting neuroplasticity in pain populations.

Defining the concept of reserve in the motor domain: a systematic review

A reserve in the motor domain may underlie the capacity exhibited by some patients to maintain motor functionality in the face of a certain level of disease. This form of "motor reserve" (MR) could include cortical, cerebellar, and muscular processes. However, a systematic definition has not been provided yet. Clarifying this concept in healthy individuals and patients would be crucial for implementing prevention strategies and rehabilitation protocols. Due to its wide application in the assessment of motor system functioning, non-invasive brain stimulation (NIBS) may support such definition. Here, studies focusing on reserve in the motor domain and studies using NIBS were revised. Current literature highlights the ability of the motor system to create a reserve and a possible role for NIBS. MR could include several mechanisms occurring in the brain, cerebellum, and muscles, and NIBS may support the understanding of such mechanisms.

Assessing Consciousness through Neurofeedback and Neuromodulation: Possibilities and Challenges

Neurofeedback is a non-invasive therapeutic approach that has gained traction in recent years, showing promising results for various neurological and psychiatric conditions. It involves real-time monitoring of brain activity, allowing individuals to gain control over their own brainwaves and improve cognitive performance or alleviate symptoms. The use of electroencephalography (EEG), such as brain-computer interface (BCI), transcranial direct current stimulation (tDCS), and transcranial magnetic stimulation (TMS), has been instrumental in developing neurofeedback techniques. However, the application of these tools in patients with disorders of consciousness (DoC) presents unique challenges. In this narrative review, we explore the use of neurofeedback in treating patients with DoC. More specifically, we discuss the advantages and challenges of using tools such as EEG neurofeedback, tDCS, TMS, and BCI for these conditions. Ultimately, we hope to provide the neuroscientific community with a comprehensive overview of neurofeedback and emphasize its potential therapeutic applications in severe cases of impaired consciousness levels.

Effects of dorsolateral prefrontal cortex stimulation on network topological attributes in young individuals with high-level perceived stress: A randomized controlled trial

Individuals with high-level perceived stress are at higher risk of developing a psychiatric disorder. While repetitive transcranial magnetic stimulation (rTMS) is effective for improving emotional symptoms, there is little evidence of its effect on perceived stress. This randomized sham-controlled trial investigated the effect of rTMS on ameliorating high-level stress and explored the associated changes in brain network activity. Fifty participants with high-level perceived stress were randomly assigned to either the active or sham rTMS group and received 12 active/sham rTMS sessions over four weeks (three per week). Perceived stress score (PSS), Chinese affective scale (CAS) normal and now statuses, and functional network topology were measured. Our results showed greater improvements in PSS and CAS_Normal scores, and reduced path length in the default mode network after active rTMS. Functional activations of the angular gyrus, posterior insula, and prefrontal cortex were also modulated in the active group. There were significant associations between posterior insula efficiency and PSS scores, and between angular efficiency and CAS_Now scores in the active group. These cumulative findings suggest rTMS as a promising intervention for recovery from high-level perceived stress.

Application of Transcranial Magnetic Stimulation with Electroencephalography in the Evaluation of Brain Function Changes after Stroke

Objective

Based on transcranial magnetic stimulation (TMS) with electroencephalography technology, this study analyzed the rehabilitation mechanism of patients' motor function reconstruction and nerve remodeling after stroke. It revealed the function of the cerebral cortex network at a deeper level and established a set of prognostic marker evaluation indicators for the reconstruction of motor function after stroke.

Methods

Twenty-one patients treated at the Beijing Rehabilitation Hospital of Capital Medical University because of ischemic stroke in the territory supplied by the middle cerebral artery were selected as the experimental group. Neurophysiological evaluation, motor function evaluation, and clinical evaluation were performed 30 and 180 d after the onset of ischemic stroke. In the control group, neurophysiological evaluation was also performed as a reference index to evaluate the changes in cortical patterns after stroke.

Results

The brain topographic map showed the changes in energy or power spectral density (PSD) at 1,000 ms after stimulation as compared with before stimulation, but no difference was detected in these patients. The time-frequency analysis showed that when the left primary motor cortex (M1) area was stimulated using TMS, the PSD values of the left and right M1 and posterior occipital cortex areas produced an 8-40 Hz wave band in patients S1-S11. There was no significant energy change in patients S12-S16.

Conclusions

For patients with different injury types, degrees of injury, and different onset periods, individualized intervention methods should be adopted. The evaluation methods should be as diverse as possible, and the rehabilitation effects of patients should be assessed from multiple perspectives to avoid the limitations of single factors. Possible mechanism: After brain injury, the nervous system can change its structure and function through different ways and maintain it for a certain period of time. This plasticity change will change with the course of the disease.

Post-Stroke Rehabilitation of Distal Upper Limb with New Perspective Technologies: Virtual Reality and Repetitive Transcranial Magnetic Stimulation-A Mini Review

Upper extremity motor impairment is the most common sequelae in patients with stroke. Moreover, its continual nature limits the optimal functioning of patients in the activities of daily living. Because of the intrinsic limitations in the conventional form of rehabilitation, the rehabilitation applications have been expanded to technology-driven solutions, such as Virtual Reality and Repetitive Transcranial Magnetic Stimulation (rTMS). The motor relearning processes are influenced by variables, such as task specificity, motivation, and feedback provision, and a VR environment in the form of interactive games could provide novel and motivating customized training solutions for better post-stroke upper limb motor improvement. rTMS being a precise non-invasive brain stimulation method with good control of stimulation parameters, has the potential to facilitate neuroplasticity and hence a good recovery. Although several studies have discussed these forms of approaches and their underlying mechanisms, only a few of them have specifically summarized the synergistic applications of these paradigms. To bridge the gaps, this mini review presents recent research and focuses precisely on the applications of VR and rTMS in distal upper limb rehabilitation. It is anticipated that this article will provide a better representation of the role of VR and rTMS in distal joint upper limb rehabilitation in patients with stroke.

Synaptic plasticity and mental health: methods, challenges and opportunities

Activity-dependent synaptic plasticity is a ubiquitous property of the nervous system that allows neurons to communicate and change their connections as a function of past experiences. Through reweighting of synaptic strengths, the nervous system can remodel itself, giving rise to durable memories that create the biological basis for mental function. In healthy individuals, synaptic plasticity undergoes characteristic developmental and aging trajectories. Dysfunctional plasticity, in turn, underlies a wide spectrum of neuropsychiatric disorders including depression, schizophrenia, addiction, and posttraumatic stress disorder. From a mechanistic standpoint, synaptic plasticity spans the gamut of spatial and temporal scales, from microseconds to the lifespan, from microns to the entire nervous system. With the numbers and strengths of synapses changing on such wide scales, there is an important need to develop measurement techniques with complimentary sensitivities and a growing number of approaches are now being harnessed for this purpose. Through hemodynamic measures, structural and tracer imaging, and noninvasive neuromodulation, it is possible to image structural and functional changes that underlie synaptic plasticity and associated behavioral learning. Here we review the mechanisms of neural plasticity and the historical and future trends in techniques that allow imaging of synaptic changes that accompany psychiatric disorders, highlighting emerging therapeutics and the challenges and opportunities accompanying this burgeoning area of study.

Repetitive Peripheral Magnetic Stimulation to Improve Ankle Function and Gait in Cerebral Palsy at Adulthood: An open-label Case Study

Repetitive peripheral magnetic stimulation (rPMS) is noninvasive and painless. It drives plasticity of the primary motor cortex (M1) in children with cerebral palsy (CP) and this improves the ankle function and gait. Our study explored whether rPMS of muscles could influence motricity in an adult CP case. A 30-year-old woman with mixed CP participated in four sessions (S1 to S4, one per week) where rPMS was applied bilaterally on leg and trunk muscles (tibialis anterior-TA, hamstrings, transverse abdominis, paraspinal multifidus). Clinical scores and M1 excitability (probed by transcranial magnetic stimulation) were tested at pre-rPMS at S1 (baseline) and S4, then 40 days later (follow-up). The active ankle dorsiflexion was significantly increased and the plantar flexors resistance to stretch reduced as compared to baseline. The improvement of the ankle function was carried-over to the quality of locomotor patterns. Changes persisted until follow-up and were paralleled by drastic changes of M1 excitability. These original findings of rPMS influence on M1 plasticity and motricity are promising for the functional improvement of adult people living with CP and should be replicated in larger-sampled studies.

Determining the Corticospinal Responses and Cross-Transfer of Ballistic Motor Performance in Young and Older Adults: A Systematic Review and Meta-Analysis

Ballistic motor training induces plasticity changes and imparts a cross-transfer effect. However, whether there are age-related differences in these changes remain unclear. Thus, the purpose of this study was to perform a meta-analysis to determine the corticospinal responses and cross-transfer of motor performance following ballistic motor training in young and older adults. Meta-analysis was performed using a random-effects model. A best evidence synthesis was performed for variables that had insufficient data for meta-analysis. There was strong evidence to suggest that young participants exhibited greater cross-transfer of ballistic motor performance than their older counterparts. This meta-analysis showed no significant age-related differences in motor-evoked potentials (MEPs), short-interval intracortical inhibition (SICI) and surface electromyography (sEMG) for both hands following ballistic motor training.

Effects of transcranial magnetic stimulation on neurobiological changes in Alzheimer's disease (Review)

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by cognitive decline and brain neuronal loss. A pioneering field of research in AD is brain stimulation via electromagnetic fields (EMFs), which may produce clinical benefits. Noninvasive brain stimulation techniques, such as transcranial magnetic stimulation (TMS), have been developed to treat neurological and psychiatric disorders. The purpose of the present review is to identify neurobiological changes, including inflammatory, neurodegenerative, apoptotic, neuroprotective and genetic changes, which are associated with repetitive TMS (rTMS) treatment in patients with AD. Furthermore, it aims to evaluate the effect of TMS treatment in patients with AD and to identify the associated mechanisms. The present review highlights the changes in inflammatory and apoptotic mechanisms, mitochondrial enzymatic activities, and modulation of gene expression (microRNA expression profiles) associated with rTMS or sham procedures. At the molecular level, it has been suggested that EMFs generated by TMS may affect the cell redox status and amyloidogenic processes. TMS may also modulate gene expression by acting on both transcriptional and post‑transcriptional regulatory mechanisms. TMS may increase brain cortical excitability, induce specific potentiation phenomena, and promote synaptic plasticity and recovery of impaired functions; thus, it may re‑establish cognitive performance in patients with AD.

Repetitive transcranial magnetic stimulation and its role in suicidality - A systematic review

BACKGROUND

Repetitive transcranial magnetic stimulation (rTMS) as a brain stimulation modality is approved for the treatment of resistant depression and its efficacy in depression is also well supported in several studies. However, its effect on suicidality is still unclear, unlike electroconvulsive therapy.

METHODOLOGY

This paper provides a systematic review of the literature published till June 2021. Studies that used rTMS as either monotherapy or adjunctive treatment in patients with suicidality, irrespective of their diagnosis, were included. The Preferred Reporting Items for Systematic Reviews and Meta Analyses (PRISMA) guidelines was followed. A total of 20 studies (N = 1584) were included for the qualitative synthesis. The quality of studies was assessed using the Cochrane Risk of Bias tool for Randomised control trials (RCT) and the Newcastle-Ottawa Scale tool for Non-Randomised studies (NRS).

RESULTS

Of the 20 articles selected for qualitative synthesis, 11 were RCTs and 9 were NRS. The results are categorized in domains of type of the study, size of population, type of population, diagnosis, assessment scales, mode of rTMS, stimulus parameters, safety and efficacy.

CONCLUSIONS

The high frequency rTMS at left dorsolateral prefrontal cortex as an adjunct to antidepressant medication is promising in reducing suicidal behaviour in treatment resistant depression. However, role of TMS targeting other areas of stimulation in mitigating suicide risk in other disorders could not be established due to scarcity of such studies. The results should be interpreted cautiously as considerable risk of bias was present in the reviewed studies.

Deficit of Inhibition as a Marker of Neuroplasticity (DEFINE Study) in Rehabilitation: A Longitudinal Cohort Study Protocol

Background: Brain plasticity is an intrinsic property of the nervous system, which is modified during its lifetime. This is one mechanism of recuperation after injuries with an important role in rehabilitation. Evidence suggests that injuries in the nervous system disturb the stability between inhibition and excitability essential for the recuperation process of neuroplasticity. However, the mechanisms involved in this balance are not completely understood and, besides the advancement in the field, the knowledge has had a low impact on the rehabilitation practice. Therefore, the understanding of the relationship between biomarkers and functional disability may help to optimize and individualize treatments and build consistent studies in the future.

Methods: This cohort study, the deficit of inhibition as a marker of neuroplasticity study, will follow four groups (stroke, spinal cord injury, limb amputation, and osteoarthritis) to understand the neuroplasticity mechanisms involved in motor rehabilitation. We will recruit 500 subjects (including 100 age- and sex-matched controls). A battery of neurophysiological assessments, transcranial magnetic stimulation, electroencephalography, functional near-infrared spectroscopy, and magnetic resonance imaging, is going to be used to assess plasticity on the motor cortex before and after rehabilitation. One of the main hypotheses in this cohort is that the level of intracortical inhibition is related to functional deficits. We expect to develop a better understanding of the neuroplasticity mechanisms involved in the rehabilitation, and we expect to build neurophysiological “transdiagnostic” biomarkers, especially the markers of inhibition, which will have great relevance in the scientific and therapeutic improvement in rehabilitation. The relationship between neurophysiological and clinical outcomes will be analyzed using linear and logistic regression models.

Discussion: By evaluating the reliability of electroencephalography, functional near-infrared spectroscopy, transcranial magnetic stimulation, and magnetic resonance imaging measures as possible biomarkers for neurologic rehabilitation in different neurologic disorders, this study will aid in the understanding of brain plasticity mechanisms in rehabilitation, allowing more effective approaches and screening methods to take place.

The efficacy of repetitive transcranial magnetic stimulation (rTMS) for young individuals with high-level perceived stress: study protocol for a randomized sham-controlled trial

Background

High level of perceived stress may result in negative effects both psychologically and physically on individuals and may predispose onset of mental disorders such as depression, anxiety, and posttraumatic stress disorder. However, there is no suitable intervention for it. Repetitive transcranial magnetic stimulation (rTMS) studies have shown its therapeutic efficacy in treatment resistant patients with stress-related disorders. Here we describe an exploratory study protocol to investigate the effect of the intervention for the individuals with high level of stress.

Method

This is a single blinded, randomized sham-controlled trial, targeting at young healthy adults aging from 18 to 24 years old. Forty eligible volunteers will be recruited and randomly divided into active and sham rTMS group. All subjects will take a set of neuropsychological and biological assessments and MRI scanning before and right after the intervention. During the interventional period, 12-session stimulations will be performed in 4 weeks with three sessions per week. The primary outcome will detect the difference of Chinese 14-item perceived stress scales between active and sham rTMS groups after intervention. Secondary outcomes will examine the differences of other affective measurements, level of cortisol, and MRI-derived neural functional measures between the two groups after intervention.

Discussion

This trial aims to examine the effect of the 12-session rTMS intervention on individuals with high level of perceived stress. Positive or negative findings from any of the outcome measures would further our understanding of the efficacy of the stimulation and its neural impact. If effective, it would provide an evidence for a new treatment for high perceived stress.

Trial registration

Chinese Clinical Trial Registry (ChiCTR1900027662). Registered on 23 November 2019. And all items of the WHO Trial Registry Data set can be found within the protocol.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13063-021-05308-3.

Zakaria H, M. Ragab W, Al Awaji NN, Y. Elzanaty M, R. Elserougy H. Therapeutic Efficacy of Transcutaneous Electrical Nerve Stimulation Acupoints on Motor and Neural Recovery of the Affected Upper Extremity in Chronic Stroke: A Sham-Controlled Randomized Clinical Trial

Inability to use the affected upper extremity (UE) in daily activities is a common complaint in stroke patients. The somatosensory system (central and peripheral) is essential for brain reorganization and plasticity. Neuromuscular electrical stimulation is considered an effective modality for improving UE function in stroke patients. The aim of the current study was to determine the therapeutic effects of transcutaneous electrical nerve stimulation (TENS) acupoints on cortical activity and the motor function of the affected UE in chronic stroke patients. Forty male and female patients diagnosed with stroke agreed to join the study. They were randomly assigned to group 1 (G1) and group 2 (G2). G1 received task-specific training (TST) and sham electrical stimulation while G2 received TST in addition to TENS acupoints. Session duration was 80 min. Both groups received 18 sessions for 6 successive weeks, 3 sessions per week. Evaluation was carried out before and after completion of the treatment program. Outcome measures used were the Fugl-Meyer Assessment of the upper extremity (FMA-UE) and the box and block test (BBT) as measures of the motor function of the affected UE. Brain activity of the motor area (C3) in the ipsilesional hemisphere was measured using a quantitative electroencephalogram (QEEG). The measured parameter was peak frequency. It was noted that the motor function of the affected UE improved significantly post-treatment in both groups, while no significant change was reported in the FMA-UE and BBT scores post-treatment in either G1 or G2. On the other hand, the activity of the motor area C3 improved significantly in G2 only, post-treatment, while G1 showed no significant improvement. There was also significant improvement in the activity of the motor area (C3) in G2 compared to G1 post-treatment. The results of the current study indicate that TST only or combined with TENS acupoints can be considered an effective method for improving motor function of the affected UE in chronic stroke patients, both being equally effective. However, TST combined with TENS acupoints proved better in improving brain plasticity in chronic stroke patients.

Enhancing vs. inhibiting semantic performance with transcranial magnetic stimulation over the anterior temporal lobe: Frequency- and task-specific effects

Accumulating, converging evidence indicates that the anterior temporal lobe (ATL) appears to be the transmodal hub for semantic representation. A series of repetitive transcranial magnetic stimulation (rTMS) investigations utilizing the ‘virtual lesion’ approach have established the brain-behavioural relationship between the ATL and semantic processing by demonstrating that inhibitory rTMS over the ATL induced impairments in semantic performance in healthy individuals. However, a growing body of rTMS studies suggest that rTMS might also be a tool for cognitive enhancement and rehabilitation, though there has been no previous exploration in semantic cognition. Here, we explored a potential role of rTMS in enhancing and inhibiting semantic performance with contrastive rTMS protocols (1 Hz vs. 20 Hz) by controlling practice effects. Twenty-one healthy participants were recruited and performed an object category judgement task and a pattern matching task serving as a control task before and after the stimulation over the ATL (1 Hz, 20 Hz, and sham). A task familiarization procedure was performed prior to the experiment in order to establish a ‘stable baseline’ prior to stimulation and thus minimize practice effect. Our results demonstrated that it is possible to modulate semantic performance positively or negatively depending on the ATL stimulation frequency: 20 Hz rTMS was optimal for facilitating cortical processing (faster RT in a semantic task) contrasting with diminished semantic performance after 1 Hz rTMS. In addition to cementing the importance of the ATL to semantic representation, our findings suggest that 20 Hz rTMS leads to semantic enhancement in healthy individuals and potentially could be used for patients with semantic impairments as a therapeutic tool.

The Ties That Bind: Aberrant Plasticity and Networks Dysfunction in Movement Disorders-Implications for Rehabilitation

Background: Movement disorders encompass various conditions affecting the nervous system. The pathological processes underlying movement disorders lead to aberrant synaptic plastic changes, which in turn alter the functioning of large-scale brain networks. Therefore, clinical phenomenology does not only entail motor symptoms but also cognitive and motivational disturbances. The result is the disruption of motor learning and motor behavior. Due to this complexity, the responsiveness to standard therapies could be disappointing. Specific forms of rehabilitation entailing goal-based practice, aerobic training, and the use of noninvasive brain stimulation techniques could "restore" neuroplasticity at motor-cognitive circuitries, leading to clinical gains. This is probably associated with modulations occurring at both molecular (synaptic) and circuitry levels (networks). Several gaps remain in our understanding of the relationships among plasticity and neural networks and how neurorehabilitation could promote clinical gains is still unclear. Purposes: In this review, we outline first the networks involved in motor learning and behavior and analyze which mechanisms link the pathological synaptic plastic changes with these networks' disruption in movement disorders. Therefore, we provide theoretical and practical bases to be applied for treatment in rehabilitation.

The Neurophysiological Responses of Concussive Impacts: A Systematic Review and Meta-Analysis of Transcranial Magnetic Stimulation Studies

Aim: This systematic review and meta-analysis investigated neurophysiological responses using transcranial magnetic stimulation (TMS) following a concussion or sub-concussion.

Methods: A systematic searching of relevant databases for peer-reviewed literature quantifying motor evoked potentials from TMS between 1999 and 2019 was performed. A meta-analysis quantified pooled data for measures including motor threshold, motor latency, and motor evoked potential amplitude and for inhibitory measures such as cortical silent period duration, short-interval intracortical inhibition (SICI), and long-interval intracortical inhibition (LICI) ratios.

Results: Fifteen articles met the inclusion criteria. The studies were arbitrarily classified into the groups, based on time post-concussion, “acute” (subjects 0–3 months post-injury, n = 8) and “post-acute” (3 months−2 years post-concussion, n = 7). A TMS quality of study checklist rated studies from moderate to high in methodological quality; however, the risk of bias analysis found that the included studies were categorised as high risk of bias, particularly for a lack of allocation concealment and blinding of participants in the methodologies. A meta-analysis showed no differences in excitability measures, apart from a decreased motor threshold that was observed in the concussed group (SMD −0.28, 95% CI −0.51 to −0.04; P = 0.02) for the post-acute time frame. Conversely, all inhibitory measures showed differences between groups. Cortical silent period duration was found to be significantly increased in the acute (SMD 1.19, 95% CI 0.58–1.81; P < 0.001) and post-acute (SMD 0.55, 95% CI 0.12–0.98; P = 0.01) time frames. The SICI (SMD −1.15, 95% CI −1.95 to −0.34; P = 0.005) and LICI (SMD −1.95, 95% CI −3.04 to −0.85; P = 0.005) ratios were reduced, inferring increased inhibition, for the post-acute time frame.

Conclusion: This systematic review and meta-analysis demonstrates that inhibitory pathways are affected in the acute period post-concussion. However, persistent alterations in cortical excitability remain, with increased intracortical inhibition. While TMS should be considered as a reliable technique to measure the functional integrity of the central nervous system, the high risk of bias and heterogeneity in data suggest that future studies should aim to incorporate standardised methodological techniques, particularly with threshold determination and stimulus intervals for paired-pulse measures.

Role of Single Low Pulse Intensity of Transcranial Magnetic Stimulation Over the Frontal Cortex for Cognitive Function

Background: The principal aim of this study was to measure the effect of online single-pulse transcranial magnetic stimulation (TMS) over the right dorsolateral prefrontal cortex (DLPFC) on cognition via the Cambridge Neuropsychological Test Automated Battery (CANTAB) in healthy individuals.

Methods: In a single-blind, sham-controlled study, we assessed both 50% and 60% of the resting motor threshold (RMT) over the right DLPFC in healthy right-handed (n = 42) adults using cognitive function, such as attention and memory, as a measure via CANTAB.

Results: We observed an improvement in the cognitive function level during the use of online low intensities of 50% and 60% RMT active stimulation of the DLPFC compared to the sham stimulation.

Conclusions: The results showed that low-intensity TMS can indeed effectively modulate cognitive function in DLPFC. Future research is, however, necessary to investigate the potential effects of low-intensity TMS on different brain areas to increase confidence in the observed results.

Low-Frequency Right Repetitive Transcranial Magnetic Stimulation for the Treatment of Depression After Traumatic Brain Injury: A Randomized Sham-Controlled Pilot Study

OBJECTIVE

Major depression is the most common psychiatric sequela of traumatic brain injury (TBI), but effective treatment continues to be a challenge, with few studies providing guidance.

METHODS

In a pilot study, the authors evaluated the effect size of low-frequency right-sided (LFR) repetitive transcranial magnetic stimulation (rTMS), compared with sham treatment, over the right dorsolateral prefrontal cortex (DLPFC) in patients (N=30) with TBI depression and co-occurring neuropsychiatric symptoms, including suicidal thoughts, anxiety, posttraumatic stress disorder, sleep disturbance, behavioral problems, and cognitive dysfunction. Exploratory analyses of diffusion tensor imaging pre- and postintervention were performed to determine the effect size of LFR rTMS on white matter integrity.

RESULTS

Small (Hedge's g=0.19) and highly variable effects of LRF rTMS over right DLPFC in TBI depression were observed. Similarly, the effect of LFR rTMS for treatment of comorbid neuropsychiatric symptoms varied from small to moderate.

CONCLUSIONS

These findings suggest that the observed effects of LFR rTMS over the right DLPFC in TBI depression and co-occurring neuropsychiatric symptoms are small, at best, and, preliminarily, that low-frequency right DLPFC stimulation has limited potential in this patient population. However, studies employing different rTMS parameters (e.g., type, location, frequency, duration) or other participant characteristics (e.g., TBI severity, chronicity, comorbidity, concurrent treatment) may potentially yield different responses.

Entropy Analysis of High-Definition Transcranial Electric Stimulation Effects on EEG Dynamics

A foundation of medical research is time series analysis—the behavior of variables of interest with respect to time. Time series data are often analyzed using the mean, with statistical tests applied to mean differences, and has the assumption that data are stationary. Although widely practiced, this method has limitations. Here we present an alternative statistical approach with sample analysis that provides a summary statistic accounting for the non-stationary nature of time series data. This work discusses the use of entropy as a measurement of the complexity of time series, in the context of Neuroscience, due to the non-stationary characteristic of the data. To elucidate our argument, we conducted entropy analysis on a sample of electroencephalographic (EEG) data from an interventional study using non-invasive electrical brain stimulation. We demonstrated that entropy analysis could identify intervention-related change in EEG data, supporting that entropy can be a useful “summary” statistic in non-linear dynamical systems.

Optogenetic Stimulation Enhanced Neuronal Plasticities in Motor Recovery after Ischemic Stroke

Motor capability recovery after ischemic stroke involves dynamic remodeling processes of neural connectomes in the nervous system. Various neuromodulatory strategies combining direct stimulating interventions with behavioral trainings for motor recovery after ischemic stroke have been developed. However, the effectiveness of these interventions varies widely due to unspecific activation or inhibition of undefined neuronal subtypes. Optogenetics is a functional and structural connection-based approach that can selectively activate or inhibit specific subtype neurons with a higher precision, and it has been widely applied to build up neuronal plasticities of the nervous system, which shows a great potential in restoring motor functions in stroke animal models. Here, we reviewed neurobiological mechanisms of enhanced brain plasticities underlying motor recovery through the optogenetic stimulation after ischemic stroke. Several brain sites and neural circuits that have been previously proven effective for motor function rehabilitation were identified, which would be helpful for a more schematic understanding of effective neuronal connectomes in the motor function recovery after ischemic stroke.

Short Intracortical Inhibition During Voluntary Movement Reveals Persistent Impairment Post-stroke

Objective: Short intracortical inhibition (SICI) is a GABA_A-mediated phenomenon, argued to mediate selective muscle activation during coordinated motor activity. Markedly reduced SICI has been observed in the acute period following stroke and, based on findings in animal models, it has been posited this disinhibitory phenomenon may facilitate neural plasticity and contribute to early motor recovery. However, it remains unresolved whether SICI normalizes over time, as part of the natural course of stroke recovery. Whether intracortical inhibition contributes to motor recovery in chronic stroke also remains unclear. Notably, SICI is typically measured at rest, which may not fully reveal its role in motor control. Here we investigated SICI at rest and during voluntary motor activity to determine: (1) whether GABA_A-mediated inhibition recovers, and (2) how GABA_A-mediated inhibition is related to motor function, in the chronic phase post-stroke.

Methods: We studied 16 chronic stroke survivors (age: 64.6 ± 9.3 years; chronicity: 74.3 ± 52.9 months) and 12 age-matched healthy controls. We used paired-pulse transcranial magnetic stimulation (TMS) to induce SICI during three conditions: rest, submaximal grip, and performance of box-and-blocks. Upper-extremity Fugl-Meyer Assessment and Box-and-Blocks tests were used to evaluate motor impairment in stroke survivors and manual dexterity in all participants, respectively.

Results: At rest, SICI revealed no differences between ipsilesional and contralesional hemispheres of either cortical or subcortical stroke survivors, or healthy controls (P's > 0.05). During box-and-blocks, however, ipsilesional hemisphere SICI was significantly reduced (P = 0.025), especially following cortical stroke (P < 0.001). SICI in the ipsilesional hemisphere during box-and-blocks task was significantly related to paretic hand dexterity (r = 0.56, P = 0.039) and motor impairment (r = 0.56, P = 0.037).

Conclusions: SICI during motor activity, but not rest, reveals persistent impairment in chronic stroke survivors indicating that inhibitory brain circuits responsible for motor coordination do not fully normalize as part of the natural history of stroke recovery. Observation that reduced SICI (i.e., disinhibition) is associated with greater motor impairment and worse dexterity in chronic hemiparetic individuals suggests the response considered to promote neuroplasticity and recovery in the acute phase could be maladaptive in the chronic phase post-stroke.

Transcranial magnetic stimulation for the treatment of anxiety disorder

Anxiety is currently one of the main mood changes and can impair the quality of life of the individual when associated with other neurological or psychiatric disorders. Neuromodulation has been highlighted as a form of treatment of several pathologies, including those involving anxiety symptoms. Among the neuromodulatory options with the potential to improve mood changes, we highlight repetitive transcranial magnetic stimulation (rTMS). rTMS is a viable therapeutical option for neuropsychiatric dysfunctions of high prevalence and is important for the understanding of pathological and neuropsychological adaptation processes. Even with this potential, and high relevance of intervention, we observe the scarcity of literature that covers this subject. The objective of this study was to carry out a survey of the current literature, using scientific databases for the last five years. We found 32 studies reporting the effects of rTMS on anxiety, 7 on anxiety disorders and 25 on anxiety symptoms as comorbidities of neurological or psychiatric disorders. This survey suggests the need for further studies using TMS for anxiety in order to seek strategies that minimize these anxiety effects on the quality of life of the victims of this disorder.

Assessment of neuroplasticity of corticospinal tract induced by antigravity treadmill (AlterG) in cerebral palsy children

The aim of this study was to assess neuroplasticity that occurred in the corticospinal tract (CST) following antigravity treadmill (AlterG) training. AlterG can facilitate walking by having up to an 80% reduction of weight-bearing in patients. Systematic and intensive gait training for sufficient periods of time may lead to neuroplasticity and walking capacity improvement. AlterG gait training was done for eight weeks, 3 sessions per week, and 45 minutes each session. Three cerebral palsy (CP) children participated in this study. The function and structure of CST on the brain's more affected side were evaluated using Transcranial Magnetic Stimulation (TMS) and Diffusion Tensor Imaging (DTI). Also, some common clinical tests were performed to evaluate walking capacity and endurance. DTI features such as fractional anisotropy (FA) and mean diffusivity (MD) as well as some TMS features were extracted to estimate structural changes of the CST. The evaluations were performed before and after 8week AlterG training. The results showed an improvement in the DTI metrics of the CST following AlterG training. Also, TMS parameters were improved and these changes in CST function and structure were concurrent with changes in walking capacity. These results suggest that AlterG training can be used as a therapeutic tool to provide an effective and persistent gait improvement in CP children.

Remodeling of Dendritic Spines in the Avian Vocal Motor Cortex Following Deafening Depends on the Basal Ganglia Circuit

Deafening elicits a deterioration of learned vocalization, in both humans and songbirds. In songbirds, learned vocal plasticity has been shown to depend on the basal ganglia-cortical circuit, but the underlying cellular basis remains to be clarified. Using confocal imaging and electron microscopy, we examined the effect of deafening on dendritic spines in avian vocal motor cortex, the robust nucleus of the arcopallium (RA), and investigated the role of the basal ganglia circuit in motor cortex plasticity. We found rapid structural changes to RA dendritic spines in response to hearing loss, accompanied by learned song degradation. In particular, the morphological characters of RA spine synaptic contacts between 2 major pathways were altered differently. However, experimental disruption of the basal ganglia circuit, through lesions in song-specialized basal ganglia nucleus Area X, largely prevented both the observed changes to RA dendritic spines and the song deterioration after hearing loss. Our results provide cellular evidence to highlight a key role of the basal ganglia circuit in the motor cortical plasticity that underlies learned vocal plasticity.

Enhanced motor function and its neurophysiological correlates after navigated low-frequency repetitive transcranial magnetic stimulation over the contralesional motor cortex in stroke

BACKGROUND

The net effect of altered interhemispheric interactions between homologous motor cortical areas after unilateral stroke has been previously reported to contribute to residual hemiparesis. Using this framework, we hypothesized that navigated 1 Hz repetitive transcranial magnetic stimulation (rTMS) over the contralesional hemisphere would induce a stronger physiological and behavioural response in patients with residual motor deficit than in healthy subjects, because an imbalance in interhemispheric excitability may underlie motor dysfunction.

METHODS

Navigated rTMS was conducted in 8 chronic stroke patients (67.50±13.77 years) and in 8 comparable normal subjects (57.38±9.61 years). We evaluated motor function (Finger tapping, Nine Hole Peg test, Strength Index and Reaction Time) as well as the excitatory and inhibitory function (resting motor threshold, motor evoked potential amplitude, intra-cortical inhibition and facilitation, and silent period) of the stimulated and non-stimulated motor cortex before and after navigated rTMS.

RESULTS

rTMS induced an increase in excitability in the ipsilesional (non-stimulated) motor cortex and led to improved performance in the finger tapping task and pinch force task. These physiological and behavioral effects were more prominent (or robust) in the group of stroke patients than in the control group.

CONCLUSION

Navigated low-frequency rTMS involving precise and consistent targeting of the contralesional hemisphere in stroke patients enhanced the cortical excitability of the ipsilesional hemisphere and the motor response of the hemiparetic hand.

Combining Upper Limb Robotic Rehabilitation with Other Therapeutic Approaches after Stroke: Current Status, Rationale, and Challenges

A better understanding of the neural substrates that underlie motor recovery after stroke has led to the development of innovative rehabilitation strategies and tools that incorporate key elements of motor skill relearning, that is, intensive motor training involving goal-oriented repeated movements. Robotic devices for the upper limb are increasingly used in rehabilitation. Studies have demonstrated the effectiveness of these devices in reducing motor impairments, but less so for the improvement of upper limb function. Other studies have begun to investigate the benefits of combined approaches that target muscle function (functional electrical stimulation and botulinum toxin injections), modulate neural activity (noninvasive brain stimulation), and enhance motivation (virtual reality) in an attempt to potentialize the benefits of robot-mediated training. The aim of this paper is to overview the current status of such combined treatments and to analyze the rationale behind them.

Abnormal EEG Responses to TMS During the Cortical Silent Period Are Associated With Hand Function in Chronic Stroke

BACKGROUND

Abnormal brain excitability influences recovery after stroke at which time a prolonged transcranial magnetic stimulation (TMS)-induced electromyographic silent period is thought to reflect abnormal inhibitory interneuron excitability. Cortical excitability can be probed directly during the silent period using concurrent electroencephalography (EEG) of TMS-evoked responses.

OBJECTIVE

The primary study objectives were to characterize TMS-evoked cortical potentials (TEPs) using EEG and to investigate associations with persistent hand and arm motor dysfunction in individuals with chronic stroke.

METHODS

Thirteen participants with chronic stroke-related mild-moderate arm motor impairment and 12 matched controls completed a single TMS-EEG cortical excitability assessment. TEPs recorded from the vertex during cortical silent period (CSP) assessment and while at rest were used to evaluate differences in cortical excitability between stroke and control participants. Associations between TEPs and CSP duration with measures of upper extremity motor behavior were investigated.

RESULTS

Significantly increased TEP component peak amplitudes and delayed latencies were observed for stroke participants compared with controls during CSP assessment and while at rest. Delayed early TEP component (P30) peak latencies during CSP assessment were associated with less manual dexterity. CSP duration was prolonged in stroke participants, and correlated with P30 peak latency and paretic arm dysfunction.

CONCLUSIONS

Abnormal cortical excitability directly measured by early TMS-evoked EEG responses during CSP assessment suggests abnormal cortical inhibition is associated with hand dysfunction in chronic stroke. Further investigation of abnormal cortical inhibition in specific brain networks is necessary to characterize the salient neurophysiologic mechanisms contributing to persistent motor dysfunction after stroke.

Optogenetic neuronal stimulation of the lateral cerebellar nucleus promotes persistent functional recovery after stroke

Stroke induces network-wide changes in the brain, affecting the excitability in both nearby and remotely connected regions. Brain stimulation is a promising neurorestorative technique that has been shown to improve stroke recovery by altering neuronal activity of the target area. However, it is unclear whether the beneficial effect of stimulation is a result of neuronal or non-neuronal activation, as existing stimulation techniques nonspecifically activate/inhibit all cell types (neurons, glia, endothelial cells, oligodendrocytes) in the stimulated area. Furthermore, which brain circuit is efficacious for brain stimulation is unknown. Here we use the optogenetics approach to selectively stimulate neurons in the lateral cerebellar nucleus (LCN), a deep cerebellar nucleus that sends major excitatory output to multiple motor and sensory areas in the forebrain. Repeated LCN stimulations resulted in a robust and persistent recovery on the rotating beam test, even after cessation of stimulations for 2 weeks. Furthermore, western blot analysis demonstrated that LCN stimulations significantly increased the axonal growth protein GAP43 in the ipsilesional somatosensory cortex. Our results demonstrate that pan-neuronal stimulations of the LCN is sufficient to promote robust and persistent recovery after stroke, and thus is a promising target for brain stimulation.

Vascular Cognitive Impairment through the Looking Glass of Transcranial Magnetic Stimulation

In the last years, there has been a significant growth in the literature exploiting transcranial magnetic stimulation (TMS) with the aim at gaining further insights into the electrophysiological and neurochemical basis underlying vascular cognitive impairment (VCI). Overall, TMS points at enhanced brain cortical excitability and synaptic plasticity in VCI, especially in patients with overt dementia, and neurophysiological changes seem to correlate with disease process and progress. These findings have been interpreted as part of a glutamate-mediated compensatory effect in response to vascular lesions. Although a single TMS parameter owns low specificity, a panel of measures can support the VCI diagnosis, predict progression, and possibly identify early markers of "brain at risk" for future dementia, thus making VCI a potentially preventable cause of both vascular and degenerative dementia in late life. Moreover, TMS can be also exploited to select and evaluate the responders to specific drugs, as well as to become an innovative rehabilitative tool in the attempt to restore impaired neural plasticity. The present review provides a perspective of the different TMS techniques by further understanding the cortical electrophysiology and the role of distinctive neurotransmission pathways and networks involved in the pathogenesis and pathophysiology of VCI and its subtypes.

Vascular Cognitive Impairment through the Looking Glass of Transcranial Magnetic Stimulation

In the last years, there has been a significant growth in the literature exploiting transcranial magnetic stimulation (TMS) with the aim at gaining further insights into the electrophysiological and neurochemical basis underlying vascular cognitive impairment (VCI). Overall, TMS points at enhanced brain cortical excitability and synaptic plasticity in VCI, especially in patients with overt dementia, and neurophysiological changes seem to correlate with disease process and progress. These findings have been interpreted as part of a glutamate-mediated compensatory effect in response to vascular lesions. Although a single TMS parameter owns low specificity, a panel of measures can support the VCI diagnosis, predict progression, and possibly identify early markers of "brain at risk" for future dementia, thus making VCI a potentially preventable cause of both vascular and degenerative dementia in late life. Moreover, TMS can be also exploited to select and evaluate the responders to specific drugs, as well as to become an innovative rehabilitative tool in the attempt to restore impaired neural plasticity. The present review provides a perspective of the different TMS techniques by further understanding the cortical electrophysiology and the role of distinctive neurotransmission pathways and networks involved in the pathogenesis and pathophysiology of VCI and its subtypes.

Non-invasive electrical brain stimulation: from acute to late-stage treatment of central nervous system damage

Non-invasive brain current stimulation (NIBS) is a promising and versatile tool for inducing neuroplasticity, protection and functional rehabilitation of damaged neuronal systems. It is technically simple, requires no surgery, and has significant beneficial effects. However, there are various technical approaches for NIBS which influence neuronal networks in significantly different ways. Transcranial direct current stimulation (tDCS), alternating current stimulation (ACS) and repetitive transcranial magnetic stimulation (rTMS) all have been applied to modulate brain activity in animal experiments under normal and pathological conditions. Also clinical trials have shown that tDCS, rTMS and ACS induce significant behavioural effects and can – depending on the parameters chosen – enhance or decrease brain excitability and influence performance and learning as well as rehabilitation and protective mechanisms. The diverse phaenomena and partially opposing effects of NIBS are not yet fully understood and mechanisms of action need to be explored further in order to select appropriate parameters for a given task, such as current type and strength, timing, distribution of current densities and electrode position. In this review, we will discuss the various parameters which need to be considered when designing a NIBS protocol and will put them into context with the envisaged applications in experimental neurobiology and medicine such as vision restoration, motor rehabilitation and cognitive enhancement.

Neurophysiologic predictors of motor function in stroke

PURPOSE

Understanding the neural mechanisms of stroke recovery is of paramount importance for neurorehabilitation.

METHODS

For this purpose, we analyzed several TMS and EEG variables and their association with motor recovery. Thirty-five subjects with chronic stroke were recruited. The neurophysiological examination included assessments by transcranial magnetic stimulation (TMS), intra- and inter-hemispheric EEG coherence in different frequency bands (e.g. alpha (8-13 Hz)) as determined by quantitative electroencephalography (qEEG). Motor function was measured by Fugl-Meyer (FM). Multiple univariate and multivariate linear regression analyses were performed to identify the predictors for FM.

RESULTS

Multivariate analyses, showed a significant interaction effect of motor threshold (MT) in the lesioned hemisphere and beta coherence in the unlesioned hemisphere. This interaction suggests that higher beta activity in the unlesioned hemisphere strengthens the negative association between MT and FM scores.

CONCLUSIONS

Our results suggest that MT in the lesioned hemisphere is the strongest predictors of motor recovery after stroke. Moreover, cortical activity in the unlesioned hemisphere measured by qEEG provides additional information, specifying the association between MT and FM scores. Therefore, complementary application of EEG and TMS can help constitute a better model of the lesioned and the unlesioned hemispheres that supports the importance of bihemispheric activity in recovery.

Optogenetic Approaches to Target Specific Neural Circuits in Post-stroke Recovery

Stroke is a leading cause of death and disability in the USA, yet treatment options are very limited. Functional recovery can occur after stroke and is attributed, in part, to rewiring of neural connections in areas adjacent to or remotely connected to the infarct. A better understanding of neural circuit rewiring is thus an important step toward developing future therapeutic strategies for stroke recovery. Because stroke disrupts functional connections in peri-infarct and remotely connected regions, it is important to investigate brain-wide network dynamics during post-stroke recovery. Optogenetics is a revolutionary neuroscience tool that uses bioengineered light-sensitive proteins to selectively activate or inhibit specific cell types and neural circuits within milliseconds, allowing greater specificity and temporal precision for dissecting neural circuit mechanisms in diseases. In this review, we discuss the current view of post-stroke remapping and recovery, including recent studies that use optogenetics to investigate neural circuit remapping after stroke, as well as optogenetic stimulation to enhance stroke recovery. Multimodal approaches employing optogenetics in conjunction with other readouts (e.g., in vivo neuroimaging techniques, behavior assays, and next-generation sequencing) will advance our understanding of neural circuit reorganization during post-stroke recovery, as well as provide important insights into which brain circuits to target when designing brain stimulation strategies for future clinical studies.

Endogenous TGFβ1 Plays a Crucial Role in Functional Recovery After Traumatic Brain Injury Associated with Smad3 Signal in Rats

Transforming growth factor-β 1 (TGFβ1) has a diverse role in astrogliosis and neuronal survival, but the underlying mechanism remains to be elucidated, especially in traumatic brain injury (TBI). Here, we show that the expression of TGFβ1 was increased in the pericontusional region, accompanied with astrogliosis and neuronal loss in TBI rats. Moreover, TGFβ1 knockdown not only reduced the number of neurons and inhibited astrogliosis but also resulted in a significant neurological dysfunction in rats with TBI. Subsequently, Smad3, a key downstream signal of TGFβ1, was involved in pericontusional region after TBI. These findings therefore indicate that TGFβ1 is involved in neuroprotection and astrogliosis, via activation of down stream Smad3 signal in the brain after injury.

Exploring the Evolution of Cortical Excitability Following Acute Stroke

BACKGROUND

Evolution of changes in intracortical excitability following stroke, particularly in the contralesional hemisphere, is being increasingly recognized in relation to maximizing the potential for functional recovery.

OBJECTIVE

The present study utilized a prospective longitudinal design over a 12-month period from stroke onset, to investigate the evolution of intracortical excitability involving both motor cortices and their relationship to recovery, and whether such changes were influenced by baseline stroke characteristics.

METHODS

Thirty-one patients with acute unilateral ischemic stroke were recruited from a tertiary hospital stroke unit. Comprehensive clinical assessments and cortical excitability were undertaken at stroke onset using a novel threshold-tracking paired-pulse transcranial magnetic stimulation technique, and repeated at 3-, 6-, and 12-month follow-up in 17 patients who completed the longitudinal assessment.

RESULTS

Shortly following stroke, short-interval intracortical inhibition (SICI) was significantly reduced in both lesioned and contralesional hemispheres that correlated with degree of recovery over the subsequent 3 months. Over the follow-up period, ipsilesional SICI remained reduced in all patient groups, while SICI over the contralesional hemisphere remained reduced only in the groups with cortical stroke or more baseline functional impairment.

CONCLUSIONS

The current study has demonstrated that evolution of intracortical excitability, particularly over the contralesional hemisphere, may vary between patients with differing baseline stroke and clinical characteristics, suggesting that ongoing contralesional network recruitment may be necessary for those patients who have significant disruptions to the integrity of ipsilesional motor pathways. Results from the present series have implications for the development of neuromodulatory brain stimulation protocols to harness and thereby facilitate stroke recovery.

Movement related slow cortical potentials in severely paralyzed chronic stroke patients

Movement-related slow cortical potentials (SCPs) are proposed as reliable and immediate indicators of cortical reorganization in motor learning. SCP amplitude and latency have been reported as markers for the brain's computational effort, attention and movement planning. SCPs have been used as an EEG signature of motor control and as a main feature in Brain-Machine-Interfaces (BMIs). Some reports suggest SCPs are modified following stroke. In this study, we investigated movement-related SCPs in severe chronic stroke patients with no residual paretic hand movements preceding and during paretic (when they try to move) and healthy hand movements. The aim was to identify SCP signatures related to cortex integrity and complete paralysis due to stroke in the chronic stage. Twenty severely impaired (no residual finger extension) chronic stoke patients, of whom ten presented subcortical and ten cortical and subcortical lesions, underwent EEG and EMG recordings during a cue triggered hand movement (open/close) paradigm. SCP onset appeared and peaked significantly earlier during paretic hand movements than during healthy hand movements. Amplitudes were significantly larger over the midline (Cz, Fz) for paretic hand movements while contralateral (C4, F4) and midline (Cz, Fz) amplitudes were significantly larger than ipsilateral activity for healthy hand movements. Dividing the participants into subcortical only and mixed lesioned patient groups, no significant differences observed in SCP amplitude and latency between groups. This suggests lesions in the thalamocortical loop as the main factor in SCP changes after stroke. Furthermore, we demonstrated how, after long-term complete paralysis, post-stroke intention to move a paralyzed hand resulted in longer and larger SCPs originating in the frontal areas. These results suggest SCP are a valuable feature that should be incorporated in the design of new neurofeedback strategies for motor neurorehabilitation.

Non-Invasive Brain Stimulation for the Treatment of Symptoms Following Traumatic Brain Injury

BACKGROUND

Traumatic brain injury (TBI) is a common cause of physical, psychological, and cognitive impairment, but many current treatments for TBI are ineffective or produce adverse side effects. Non-invasive methods of brain stimulation could help ameliorate some common trauma-induced symptoms.

OBJECTIVE

This review summarizes instances in which repetitive Transcranial Magnetic Stimulation (rTMS) and transcranial Direct Current Stimulation (tDCS) have been used to treat symptoms following a TBI. A subsequent discussion attempts to determine the value of these methods in light of their potential risks.

METHODS

The research databases of PubMed/MEDLINE and PsycINFO were electronically searched using terms relevant to the use of rTMS and tDCS as a tool to decrease symptoms in the context of rehabilitation post-TBI.

RESULTS

Eight case-studies and four multi-subject reports using rTMS and six multi--subject studies using tDCS were found. Two instances of seizure are discussed.

CONCLUSION

There is evidence that rTMS can be an effective treatment option for some post-TBI symptoms, such as depression, tinnitus, and neglect. Although the safety of this method remains uncertain, the use of rTMS in cases of mild TBI without obvious structural damage may be justified. Evidence on the effectiveness of tDCS is mixed, highlighting the need for additional investigations.

Neurostimulation for traumatic brain injury

Traumatic brain injury (TBI) remains a significant public health problem and is a leading cause of death and disability in many countries. Durable treatments for neurological function deficits following TBI have been elusive, as there are currently no FDA-approved therapeutic modalities for mitigating the consequences of TBI. Neurostimulation strategies using various forms of electrical stimulation have recently been applied to treat functional deficits in animal models and clinical stroke trials. The results from these studies suggest that neurostimulation may augment improvements in both motor and cognitive deficits after brain injury. Several studies have taken this approach in animal models of TBI, showing both behavioral enhancement and biological evidence of recovery. There have been only a few studies using deep brain stimulation (DBS) in human TBI patients, and future studies are warranted to validate the feasibility of this technique in the clinical treatment of TBI. In this review, the authors summarize insights from studies employing neurostimulation techniques in the setting of brain injury. Moreover, they relate these findings to the future prospect of using DBS to ameliorate motor and cognitive deficits following TBI.

Optogenetic neuronal stimulation promotes functional recovery after stroke

Clinical and research efforts have focused on promoting functional recovery after stroke. Brain stimulation strategies are particularly promising because they allow direct manipulation of the target area's excitability. However, elucidating the cell type and mechanisms mediating recovery has been difficult because existing stimulation techniques nonspecifically target all cell types near the stimulated site. To circumvent these barriers, we used optogenetics to selectively activate neurons that express channelrhodopsin 2 and demonstrated that selective neuronal stimulations in the ipsilesional primary motor cortex (iM1) can promote functional recovery. Stroke mice that received repeated neuronal stimulations exhibited significant improvement in cerebral blood flow and the neurovascular coupling response, as well as increased expression of activity-dependent neurotrophins in the contralesional cortex, including brain-derived neurotrophic factor, nerve growth factor, and neurotrophin 3. Western analysis also indicated that stimulated mice exhibited a significant increase in the expression of a plasticity marker growth-associated protein 43. Moreover, iM1 neuronal stimulations promoted functional recovery, as stimulated stroke mice showed faster weight gain and performed significantly better in sensory-motor behavior tests. Interestingly, stimulations in normal nonstroke mice did not alter motor behavior or neurotrophin expression, suggesting that the prorecovery effect of selective neuronal stimulations is dependent on the poststroke environment. These results demonstrate that stimulation of neurons in the stroke hemisphere is sufficient to promote recovery.

Differential effects of motor cortical excitability and plasticity in young and old individuals: a Transcranial Magnetic Stimulation (TMS) study

Aging is associated with changes in the motor system that, over time, can lead to functional impairments and contribute negatively to the ability to recover after brain damage. Unfortunately, there are still many questions surrounding the physiological mechanisms underlying these impairments. We examined cortico-spinal excitability and plasticity in a young cohort (age range: 19–31) and an elderly cohort (age range: 47–73) of healthy right-handed individuals using navigated transcranial magnetic stimulation (nTMS). Subjects were evaluated with a combination of physiological [motor evoked potentials (MEPs), motor threshold (MT), intracortical inhibition (ICI), intracortical facilitation (ICF), and silent period (SP)] and behavioral [reaction time (RT), pinch force, 9 hole peg task (HPT)] measures at baseline and following one session of low-frequency (1 Hz) navigated repetitive TMS (rTMS) to the right (non-dominant) hemisphere. In the young cohort, the inhibitory effect of 1 Hz rTMS was significantly in the right hemisphere and a significant facilitatory effect was noted in the unstimulated hemisphere. Conversely, in the elderly cohort, we report only a trend toward a facilitatory effect in the unstimulated hemisphere, suggesting reduced cortical plasticity and interhemispheric communication. To this effect, we show that significant differences in hemispheric cortico-spinal excitability were present in the elderly cohort at baseline, with significantly reduced cortico-spinal excitability in the right hemisphere as compared to the left hemisphere. A correlation analysis revealed no significant relationship between cortical thickness of the selected region of interest (ROI) and MEPs in either young or old subjects prior to and following rTMS. When combined with our preliminary results, further research into this topic could lead to the development of neurophysiological markers pertinent to the diagnosis, prognosis, and treatment of neurological diseases characterized by monohemispheric damage and lateralized motor deficits.

Noninvasive and painless magnetic stimulation of nerves improved brain motor function and mobility in a cerebral palsy case

Motor deficits in cerebral palsy disturb functional independence. This study tested whether noninvasive and painless repetitive peripheral magnetic stimulation could improve motor function in a 7-year-old boy with spastic hemiparetic cerebral palsy. Stimulation was applied over different nerves of the lower limbs for 5 sessions. We measured the concurrent aftereffects of this intervention on ankle motor control, gait (walking velocity, stride length, cadence, cycle duration), and function of brain motor pathways. We observed a decrease of ankle plantar flexors resistance to stretch, an increase of active dorsiflexion range of movement, and improvements of corticospinal control of ankle dorsiflexors. Joint mobility changes were still present 15 days after the end of stimulation, when all gait parameters were also improved. Resistance to stretch was still lower than prestimulation values 45 days after the end of stimulation. This case illustrates the sustained effects of repetitive peripheral magnetic stimulation on brain plasticity, motor function, and gait. It suggests a potential impact for physical rehabilitation in cerebral palsy.

Motor cortex excitability in acute cerebellar infarct

Limited evidence to date has demonstrated changes in excitability that develops over the contralateral motor cortex after a cerebellar infarct. As such, the present study investigated changes in excitability over the contra- (contraM1) and ipsilateral motor cortices (ipsiM1), in patients with acute cerebellar infarct, to determine whether the changes may have functional relevance. Paired-pulse transcranial magnetic stimulation, combined with detailed clinical assessment, was undertaken in ten patients presenting with acute unilateral cerebellar infarct. Studies were undertaken within 1 week of ictus and followed longitudinally at 3-, 6-, and 12-month periods. Comparisons were made with 15 age-matched controls. Immediately following a stroke, short-interval intracortical inhibition (SICI) was significantly reduced over the contraM1 in all patients (P = 0.01), while reduced over the ipsiM1 in those with severe functional impairment (P = 0.01). Moreover, ipsiM1 SICI correlated with impairment (r = 0.69, P = 0.03), such that less SICI was observed in those patients with most impairment. Cortical excitability changes persisted over the follow-up period in the context of clinical improvement. Following an acute cerebellar infarct, excitability abnormalities develop over both motor cortices, more prominently in patients with severe functional impairment. The cortical changes, particularly over the ipsilateral motor cortex, may represent a functionally relevant plastic process that may guide future therapeutic strategies to better facilitate recovery.

Anodal transcranial direct current stimulation alters elbow flexor muscle recruitment strategies

BACKGROUND

Transcranial direct current stimulation (tDCS) is known to reliably alter motor cortical excitability in a polarity dependent fashion such that anodal stimulation increases cortical excitability and cathodal stimulation inhibits cortical excitability. However, the effect of tDCS on agonist and antagonist volitional muscle activation is currently not known.

OBJECTIVE

This study investigated the effect of motor cortical anodal tDCS on EMG/force relationships of biceps brachii (agonist) and triceps brachii (antagonist) using surface electromyography (EMG).

METHODS

Eighteen neurologically intact adults (9 tDCS and 9 controls) participated in this study. EMG/force relationships were established by having subjects perform submaximal isometric contractions at several force levels (12.5%, 25%, 37.5%, and 50% of maximum).

RESULTS

Results showed that anodal tDCS significantly affected the EMG/force relationship of the biceps brachii muscle. Specifically, anodal tDCS increased the magnitude of biceps brachii activation at 37.5% and 50% of maximum. Anodal tDCS also resulted in an increase in the peak force and EMG values during maximal contractions as compared to the control condition. EMG analyses of other elbow muscles indicated that the increase in biceps brachii activation after anodal tDCS was not related to alterations in synergistic or antagonistic muscle activity.

CONCLUSIONS

Our results indicate that anodal tDCS significantly affects the voluntary EMG/force relationship of the agonist muscles without altering the coactivation of the antagonistic muscles. The most likely explanation for the observed greater EMG per unit force after anodal tDCS appears to be related to alterations in motor unit recruitment strategies.

Applications of transcranial magnetic stimulation and magnetic seizure therapy in the study and treatment of disorders related to cerebral aging

Transcranial magnetic stimulation (TMS) can be used to probe cortical function and treat neuropsychiatric illnesses. TMS has demonstrated neuroplastic effects akin to long-term potentiation and long-term depression, and therapeutic applications are in development for post-stroke recovery, Alzheimer's disease, and depression in seniors. Here, we discuss two new directions of TMS research relevant to cerebral aging and cognition. First, we introduce a paradigm for enhancing cognitive reserve, based on our research in sleep deprivation. Second, we discuss the use of magnetic seizure therapy (MST) to spare cognitive functions relative to conventional electroconvulsive therapy, and as a means of providing a more potent antidepressant treatment when subconvulsive TMS has shown modest efficacy in seniors. Whether in the enhancement of cognition as a treatment goal, or in the reduction of amnesia as a side effect, these approaches to the use of TMS and MST merit further exploration regarding their clinical potential.