Posts Tagged TMS

[ARTICLE] Using Brain Oscillations and Corticospinal Excitability to Understand and Predict Post-Stroke Motor Function – Full Text

What determines motor recovery in stroke is still unknown and finding markers that could predict and improve stroke recovery is a challenge. In this study, we aimed at understanding the neural mechanisms of motor function recovery after stroke using neurophysiological markers by means of cortical excitability (Transcranial Magnetic Stimulation – TMS) and brain oscillations (electroencephalography – EEG). In this cross-sectional study, fifty-five subjects with chronic stroke (62±14 yo, 17 women, 32±42 months post-stroke) were recruited in two sites. We analyzed TMS measures (i.e. motor threshold – MT – of the affected and unaffected sides) and EEG variables (i.e. power spectrum in different frequency bands and different brain regions of the affected and unaffected hemispheres) and their correlation with motor impairment as measured by Fugl-Meyer. Multiple univariate and multivariate linear regression analyses were performed to identify the predictors of good motor function. A significant interaction effect of MT in the affected hemisphere and power in beta bandwidth over the central region for both affected and unaffected hemispheres was found. We identified that motor function positively correlates with beta rhythm over the central region of the unaffected hemisphere, while it negatively correlates with beta rhythm in the affected hemisphere. Our results suggest that cortical activity in the affected and unaffected hemisphere measured by EEG provides new insights on the association between high frequency rhythms and motor impairment, highlighting the role of excess of beta in the affected central cortical region in poor motor function in stroke recovery.

Introduction

Stroke is a leading cause of morbidity, mortality, and disability worldwide (12). Among the sequels of stroke, motor impairment is one of the most relevant, since it conditions the quality of life of patients, it reduces their capability to perform their daily activities and it impairs their autonomy (3). Despite the advancements of the acute stroke therapy, patients require an intensive rehabilitation program that will partially determine the extent of their recovery (4). These rehabilitation programs aim at stimulating cortical plasticity to improve motor performance and functional recovery (5). However, what determines motor improvement is still unknown. Indeed, finding markers that could predict and enhance stroke recovery is still a challenge (6). Different types of biomarkers exist: diagnostic, prognostic, surrogate outcome, and predictive biomarkers (7). The identification of these biomarkers is critical in the management of stroke patients. In the field of stroke research, great attention has been put to biomarkers found in the serum, especially in acute care. However, research on biomarkers of stroke recovery is still limited, especially using neurophysiological tools.

A critical research area in stroke is to understand the neural mechanisms underlying motor recovery. In this context, neurophysiological techniques such as transcranial magnetic stimulation (TMS) and electroencephalography (EEG) are useful tools that could be used to identify potential biomarkers of stroke recovery. However, there is still limited data to draw further conclusions on neural reorganization in human trials using these techniques. A few studies have shown that, in acute and sub-acute stage, stroke patients present increased power in low frequency bands (i.e., delta and theta bandwidths) in both affected and unaffected sides, as well as increased delta/alpha ratio in the affected brain area; these patterns being also correlated to functional outcome (811). Recently, we have identified that, besides TMS-indexed motor threshold (MT), an increased excitability in the unaffected hemisphere, coupled with a decreased excitability in the affected hemisphere, was associated with poor motor function (12), as measured by Fugl-Meyer (FM) [assessing symptoms severity and motor recovery in post-stroke patients with hemiplegia—Fugl-Meyer et al. (13); Gladstone et al. (14)]. However, MT measurement is associated with a poor resolution as it indexes global corticospinal excitability. Therefore, combining this information with direct cortical measures such as cortical oscillations, as measured by EEG, can help us to understand further neural mechanisms of stroke recovery.

To date, there are very few studies looking into EEG and motor recovery. For that reason, we aimed, in the present study, to investigate the relationship between motor impairment, EEG, and TMS variables. To do so, we conducted a prospective multicenter study of patients who had suffered from a stroke, in which we measured functional outcome using FM and performed TMS and EEG recordings. Based on our preliminary work, we expected to identify changes in interhemispheric imbalances on EEG power, especially in frequency bands associated with learning, such as alpha and beta bandwidths. […]

Continue —> Frontiers | Using Brain Oscillations and Corticospinal Excitability to Understand and Predict Post-Stroke Motor Function | Neurology

Figure 1. Topoplots showing the topographic distribution of high-beta bandwidth (25 Hz) for every individual. Red areas represent higher high-beta activity, while blue areas represent lower high-beta activity. Central region (C3 or C4) in red stands for the affected side. For patients with poor motor function, a higher beta activity of the affected central region as compared to the affected side is observed in 16 out of 28 individuals. For patients with good motor function, a similar activity over central regions bilaterally, or higher activity over the unaffected central area can be identified in 21 out of 27 individuals. FM = Fugl-Meyer.

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[VIDEO] How TMS Works – YouTube

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[Abstract] TMS measures of motor cortex function after stroke: A meta-analysis

Highlights

    The neurophysiological effects of stroke are localised to the affected motor cortex.There is no clear evidence of imbalanced interhemispheric inhibition after stroke.Facilitating the affected motor cortex may be most beneficial in selected patients.

Abstract

Background

Transcranial magnetic stimulation (TMS) is commonly used to measure the effects of stroke on corticomotor excitability, intracortical function, and interhemispheric interactions. The interhemispheric inhibition model posits that recovery of motor function after stroke is linked to rebalancing of asymmetric interhemispheric inhibition and corticomotor excitability. This model forms the rationale for using neuromodulation techniques to suppress unaffected motor cortex excitability, and facilitate affected motor cortex excitability. However, the evidence base for using neuromodulation techniques to promote post-stroke motor recovery is inconclusive.

Objective

The aim of this meta-analysis was to compare measures of corticomotor excitability, intracortical function, and interhemispheric inhibition, between the affected and unaffected hemispheres of people with stroke, and measures made in healthy adults.

Methods

A literature search was conducted to identify studies that made TMS measures of the motor cortex in adult stroke patients. Two authors independently extracted data, and the quality of included studies was assessed. TMS measures were compared between the affected and unaffected hemispheres of stroke patients, between the affected hemisphere and healthy controls, and between the unaffected hemisphere and healthy controls. Analyses were carried out with data grouped according to the muscle from which responses were recorded, and separately according to time post-stroke (<3 months, and ≥6 months). Meta-analyses were carried out using a random effects model.

Results

There were 844 studies identified, and 112 studies included in the meta-analysis. Results were very similar across muscle groups. Affected hemisphere M1 excitability is lower than unaffected and healthy control M1 excitability after stroke. Affected hemisphere short interval intracortical inhibition (SICI) is lower than unaffected and healthy control SICI early after stroke, and not different in the chronic phase. There were no differences detected between the unaffected hemisphere and healthy controls. There were only seven studies of interhemispheric inhibition that could be included, with no clear effects of hemisphere or time post-stroke.

Conclusions

The neurophysiological effects of stroke are primarily localised to the affected hemisphere, and there is no clear evidence for hyper-excitability of the unaffected hemisphere or imbalanced interhemispheric inhibition. This indicates that facilitating affected M1 excitability directly may be more beneficial than suppressing unaffected M1 excitability for promoting post-stroke recovery.

Source: TMS measures of motor cortex function after stroke: A meta-analysis

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[Abstract] TMS measures of motor cortex function after stroke: A meta-analysis

Highlights

  • The neurophysiological effects of stroke are localised to the affected motor cortex.
  • There is no clear evidence of imbalanced interhemispheric inhibition after stroke.
  • Facilitating the affected motor cortex may be most beneficial in selected patients.

Abstract

Background

Transcranial magnetic stimulation (TMS) is commonly used to measure the effects of stroke on corticomotor excitability, intracortical function, and interhemispheric interactions. The interhemispheric inhibition model posits that recovery of motor function after stroke is linked to rebalancing of asymmetric interhemispheric inhibition and corticomotor excitability. This model forms the rationale for using neuromodulation techniques to suppress unaffected motor cortex excitability, and facilitate affected motor cortex excitability. However, the evidence base for using neuromodulation techniques to promote post-stroke motor recovery is inconclusive.

Objective

The aim of this meta-analysis was to compare measures of corticomotor excitability, intracortical function, and interhemispheric inhibition, between the affected and unaffected hemispheres of people with stroke, and measures made in healthy adults.

Methods

A literature search was conducted to identify studies that made TMS measures of the motor cortex in adult stroke patients. Two authors independently extracted data, and the quality of included studies was assessed. TMS measures were compared between the affected and unaffected hemispheres of stroke patients, between the affected hemisphere and healthy controls, and between the unaffected hemisphere and healthy controls. Analyses were carried out with data grouped according to the muscle from which responses were recorded, and separately according to time post-stroke (<3 months, and ≥ 6 months). Meta-analyses were carried out using a random effects model.

Results

There were 844 studies identified, and 112 studies included in the meta-analysis. Results were very similar across muscle groups. Affected hemisphere M1 excitability is lower than unaffected and healthy control M1 excitability after stroke. Affected hemisphere short interval intracortical inhibition (SICI) is lower than unaffected and healthy control SICI early after stroke, and not different in the chronic phase. There were no differences detected between the unaffected hemisphere and healthy controls. There were only seven studies of interhemispheric inhibition that could be included, with no clear effects of hemisphere or time post-stroke.

Conclusions

The neurophysiological effects of stroke are primarily localised to the affected hemisphere, and there is no clear evidence for hyper-excitability of the unaffected hemisphere or imbalanced interhemispheric inhibition. This indicates that facilitating affected M1 excitability directly may be more beneficial than suppressing unaffected M1 excitability for promoting post-stroke recovery.

Source: TMS measures of motor cortex function after stroke: A meta-analysis – Brain Stimulation: Basic, Translational, and Clinical Research in Neuromodulation

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[Abstract] Changes in motor cortex excitability for the trained and non-trained hand after long-term unilateral motor training

Highlights

We investigated intracortical facilitation (ICF) in M1 after unilateral long term hand training.

Motor performance improved for both hands but ICF was only altered for the untrained hand.

The ICF-decrease is associated with a transfer of training-induced improvement of performance.


Abstract

Repetitive unilateral upper limb motor training does not only affect behavior but also increases excitability of the contralateral primary motor cortex (M1). The behavioral gain is partially transferred to the non-trained side. Changes in M1 intracortical facilitation (ICF) might as well be observed for both hand sides. We measured ICF of both left and right abductor pollicis brevis muscles (APB) before and after a two-week period of arm ability training (AAT) of the left hand in 13 strongly right handed healthy volunteers. Performance with AAT-tasks improved for both the left trained and right untrained hand. ICF for the untrained hand decreased over training while it remained unchanged for the left trained hand. Decrease of ICF for the right hand was moderately associated with an increase of AAT-performance for the untrained right hand. We conclude that ICF-imbalance between dominant and non-dominant hand is sensitive to long-term motor training: training of the non-dominant hand results in a decrease of ICF of the dominant hand. The ICF-decrease is associated with a transfer of training-induced improvement of performance from the non-dominant to the dominant hand.

Source: Changes in motor cortex excitability for the trained and non-trained hand after long-term unilateral motor training

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[WEB SITE] Transcranial magnetic stimulation Overview – Mayo Clinic

Overview

Transcranial magnetic stimulation (TMS) is a noninvasive procedure that uses magnetic fields to stimulate nerve cells in the brain to improve symptoms of depression. TMS is typically used when other depression treatments haven’t been effective.

How it works

During a TMS session, an electromagnetic coil is placed against your scalp near your forehead. The electromagnet painlessly delivers a magnetic pulse that stimulates nerve cells in the region of your brain involved in mood control and depression. And it may activate regions of the brain that have decreased activity in people with depression.

Though the biology of why rTMS works isn’t completely understood, the stimulation appears to affect how this part of the brain is working, which in turn seems to ease depression symptoms and improve mood.

Treatment for depression involves delivering repetitive magnetic pulses, so it’s called repetitive TMS or rTMS.

Visit Site —> Transcranial magnetic stimulation Overview – Mayo Clinic

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[Abstract] Individual differences in contralateral motor cortex (CMC) plasticity during short-term upper limb immobilisation (ULI) in healthy individuals – A transcranial magnetic stimulation (TMS) study

By decreasing CMC excitability, ULI holds the potential for being explored as a stroke model in healthy individuals for developing rehabilitation strategies ( Furlan et al., 2016 ). Determining the minimum effective restriction time is critical for optimising the immobilisation paradigm and facilitating its application.

Question

How does CMC excitability change over a period of 9 h of ULI?

Methods

Healthy individuals will have their right (dominant) upper limb immobilised for 9 h. CMC excitability will be assessed with TMS immediately before and after 3, 6, and 9 h of immobilisation. The TMS coil will be positioned over the hot spot of the right FDI muscle. Frameless stereotaxy will be used to keep the position of the coil constant across all TMS assessments. Fifteen MEPs will be recorded from the target muscle during each TMS assessment by using a fixed suprathreshold stimulation intensity (sSI). IO curves will also be obtained at each assessment by using 50, 70, 90, 110, and 130% of sSI.

Results

Fig. 1 shows preliminary MEP data from 5 participants. At the group level there was a depressant effect of immobilisation on CMC excitability. CMC excitability decreased to 63 and 54% of the baseline value after 3 and 6 h of immobilisation, respectively. However, after 9 h, excitability levels increased to 84% of the baseline value, suggesting that CMC excitability might follow a U-shaped curve during ULI. At the individual level there was great variability in CMC excitability among participants over the course of immobilisation, particularly in terms of the position of the deflection point of the excitability curve.

Conclusion

Our data is in line with previous studies reporting inter-individual differences in CMC plasticity after ULI ( Rosenkranz et al., 2014 ). Importantly, our study shows how these differences develop during ULI. This information should be given consideration when seeking for the ideal length of the immobilisation protocol.

Source: P311 Individual differences in contralateral motor cortex (CMC) plasticity during short-term upper limb immobilisation (ULI) in healthy individuals – A transcranial magnetic stimulation (TMS) study – Clinical Neurophysiology

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[Abstract+References] Thirty years of transcranial magnetic stimulation: where do we stand?

Abstract

Experimental Brain ResearchTranscranial magnetic stimulation (TMS) has been first described 30 years ago, and since then has gained enormous attention by neurologists, psychiatrists, neurosurgeons, clinical neurophysiologists, psychologists, and neuroscientist alike. In the early days, it was primarily used to test integrity of the corticospinal tract. Beyond further developments of TMS in diagnostics, mapping and monitoring of the motor system, major other applications expanded into using TMS as research tool in the cognitive neurosciences, and as therapeutic tool in neurological and psychiatric disease by virtue of inducing long-term change in excitability and connectivity of the stimulated brain networks. This mini-review will highlight these developments by reviewing the 10 most frequently cited TMS publications. Despite the tremendous popularity and success of TMS as a non-invasive technique to stimulate the human brain, several aims remain unresolved. This review will end with highlighting those 10 most frequently cited papers that have been published in 2014–2016 to indicate the currently hottest topics in TMS research and major avenues of development.

Source: Thirty years of transcranial magnetic stimulation: where do we stand? | SpringerLink

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[WEB SITE] Researchers study magnetic brain stimulation to improve symptoms after stroke – Fox News

Dr. Marcie Bockbrader adjusts an external brain stimulator on stroke survivor Debbie Hall at The Ohio State University Wexner Medical Center.

In an ongoing multi-center clinical trial, researchers are studying whether transcranial magnetic stimulation and occupational therapy can improve recovery for stroke patients.

For the study, patients are treated with transcranial magnetic stimulation, which stimulates a specific part of the brain using the Transcranial Magnetic Stimulator (TMS) by Nexstim (the technology developer who is funding the study), to help improve activity in the side of the body injured by stroke. The study currently has about 60 participants in 12 centers, but researchers are aiming to recruit 200 patients.

During a stroke, the blood vessel that carries oxygen and nutrients to the brain is blocked by a clot, called an ischemic stroke, or ruptures, known as a hemorrhagic stroke, depriving part of the brain from blood and oxygen. This leads to brain cell death and lasting deficits, which can include changes in speech, as well as vision and memory problems.

A patient may also lose feeling and movement in one side of their body due to decreased activity and function in the side of the brain injured by stroke.

The decrease in activity is similar to “a negative feedback loop, such that the less activity that those neurons have, the harder it is for them to recover function— and the greater the activity on the healthier side of the brain,” principal investigator Dr. Marcie Bockbrader, assistant professor of physical medicine and rehabilitation at The Ohio State University Wexner Medical Center, told FoxNews.com.

“This imbalance actually prevents— to some extent and to some people— the recovery of function on the injured side,” she said.

One therapy to address this imbalance is to physically constrain the healthy side of the body to allow the injured side of the brain and body to express itself.

While not all stroke patients experience this imbalance, a large proportion does. The study authors intend to demonstrate that delivering inhibitory stimulation to the healthy side of the brain combined with occupational therapy sessions, prompts increased activity on the injured side of the brain— and results in better function on the side of the body weakened by stroke.

Previous studies have shown brain stimulation alone does not provide enough benefit, so combining the process with therapy is key, Bockbrader said.

To participate, patients must have had a stroke within three to 12 months of enrollment, and have some one-sided upper-limb deficits but still have some upper-limb function in order to do the occupational therapy exercises.

Bockbrader noted that researchers have been selective and, to avoid confounding variables, can’t accept people with severe deficits, multiple sclerosis and spinal fusion. Patients must be close enough to their study center to go in three times a week to receive their therapies over the six-week course.

Because most health insurance covers only three months’ worth of therapy, researchers have found success recruiting at physical and occupational therapy sites. The study provides free therapy for six weeks for all participants.

“Everybody benefits, whether or not there’s added benefit from brain stimulation. That’s a bonus,” Bockbrader said.

For the double-blind, randomized trial, participants undergo six weeks of the combination of brain stimulation and occupational therapy. Half of the group receives sham stimulation and the other receives active stimulation. Once the data is collected across all the sites, researchers will reveal participants’ information and evaluate their functional ability to use the arm on their weaker side. Bockbrader expects the study to continue for another year or two as they gather data.

“What this would tell us is if the brain stimulation is working more than just therapy alone,” Bockbrader said, “making the neural ‘pop’ that is needed to change and increase their activity on the injured side of the brain … by suppressing the healthy side of the brain.”

The TMS treatment
Once participants are accepted into the study, an MRI scan of the brain is taken to understand the motor areas affected so researchers can target the magnetic pulse. The pulse is strong enough to illicit a twitch in the person’s healthy arm, so researchers know they’re aiming for the part of the healthy side of the brain assisting with motor function of the arm or hand.

“We can get something like 2 millimeter accuracy when we’re delivering 900 stimulation pulses over the course of 15 minutes, so it’s a 3D targeting within the brain based on the individual patient’s motor area for their hand,” Bockbrader said. There is also an orientation rotational component so researchers know the magnet is oriented in a way that maximally stimulates the correct neurons.

Participants sit in a comfortable reclining chair during the treatment. Once their stimulation intensity is determined, the Nexstim device is placed next to the head against the patient’s scalp, and delivers rapid magnetic pulses that go directly to their motorcortex to inhibit activity on the healthy side. A tracker on the patient’s forehead and an infrared sensing system tells the device’s navigation system if the pulses are on target, or if the Nexstim coil needs to be moved.  After 15 minutes, the patient is done and goes on to the occupational therapy session.

The stimulation threshold is dependent on the state of the brain at the time, which means that each time a patient comes in for his appointment, it is recalibrated to get the same amount of motor response each time. Eventually, researchers hope to be able to prescribe individual patients a specific strength of pulse, for a specific duration of time in a particular brain area.

Researchers re-examine patients six months after treatment to see whether the benefits are sustained.

TMS beyond stroke rehabilitation
Researchers hope that future phase III research will show enough evidence that the brain stimulation therapy can be adopted as a way to help people who have persistent deficiencies after a stroke.

The therapy can also potentially be pointed at any part of the brain that needs to be modulated after a stroke.  Noninvasive brain stimulation may also be useful for non-stroke related issues, such as fatigue, attention, and mood, Bockbrader said.

“I also see patients with traumatic brain injury and the protocols are similar across brain injury types…. So you can apply some of the technology to problems that result from brain injuries of different types,” she said.

One unknown is whether the therapy would work when administered beyond a year after stroke incidence.

“Theoretically it seems possible, but until we test… we just don’t know,” Bockbrader said. “[After a year] the spontaneous recovery period from stroke is essentially over, so if we could reinstitute a state of being more receptive through therapies to drive plasticity, that would improve function and drive recovery.”

Once the treatment is approved by the Food and Drug Administration (FDA), Bockbrader expects it would be marketed immediately in the clinical setting.

“From my point of view as a clinician, that’s what’s important— what we do in terms of man on the street,” she said. “Can they get this to help them get better? We want to make it more widely available.”

Source: Researchers study magnetic brain stimulation to improve symptoms after stroke | Fox News

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[Abstract] Neural plasticity during motor learning with motor imagery practice: Review and perspectives

Highlights

• TMS reveals the neural aspects of motor learning with MI.

• Neural plasticity during MI practice may occur at the cortical and spinal level.

• MI training may strengthen synapse efficiency.

• Presynaptic inhibition may decrease after MI training.


Abstract

In the last decade, many studies confirmed the benefits of mental practice with motor imagery. In this review we first aimed to compile data issued from fundamental and clinical investigations and to provide the key-components for the optimization of motor imagery strategy. We focused on transcranial magnetic stimulation studies, supported by brain imaging research, that sustain the current hypothesis of a functional link between cortical reorganization and behavioral improvement. As perspectives, we suggest a model of neural adaptation following mental practice, in which synapse conductivity and inhibitory mechanisms at the spinal level may also play an important role.

Source: Neural plasticity during motor learning with motor imagery practice: Review and perspectives

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