Archive for category tDCS/rTMS

[ARTICLE] The impact of large structural brain changes in chronic stroke patients on the electric field caused by transcranial brain stimulation – Full Text

Abstract

Transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (TDCS) are two types of non-invasive transcranial brain stimulation (TBS). They are useful tools for stroke research and may be potential adjunct therapies for functional recovery. However, stroke often causes large cerebral lesions, which are commonly accompanied by a secondary enlargement of the ventricles and atrophy. These structural alterations substantially change the conductivity distribution inside the head, which may have potentially important consequences for both brain stimulation methods. We therefore aimed to characterize the impact of these changes on the spatial distribution of the electric field generated by both TBS methods. In addition to confirming the safety of TBS in the presence of large stroke-related structural changes, our aim was to clarify whether targeted stimulation is still possible. Realistic head models containing large cortical and subcortical stroke lesions in the right parietal cortex were created using MR images of two patients. For TMS, the electric field of a double coil was simulated using the finite-element method. Systematic variations of the coil position relative to the lesion were tested. For TDCS, the finite-element method was used to simulate a standard approach with two electrode pads, and the position of one electrode was systematically varied. For both TMS and TDCS, the lesion caused electric field “hot spots” in the cortex. However, these maxima were not substantially stronger than those seen in a healthy control. The electric field pattern induced by TMS was not substantially changed by the lesions. However, the average field strength generated by TDCS was substantially decreased. This effect occurred for both head models and even when both electrodes were distant to the lesion, caused by increased current shunting through the lesion and enlarged ventricles. Judging from the similar peak field strengths compared to the healthy control, both TBS methods are safe in patients with large brain lesions (in practice, however, additional factors such as potentially lowered thresholds for seizure-induction have to be considered). Focused stimulation by TMS seems to be possible, but standard tDCS protocols appear to be less efficient than they are in healthy subjects, strongly suggesting that tDCS studies in this population might benefit from individualized treatment planning based on realistic field calculations.

1. Introduction

Transcranial brain stimulation (TBS) methods are useful tools to induce and to quantify neural plasticity, and as such are increasingly being used in stroke research and as potential adjunct therapies in stroke rehabilitation. The cerebral lesions caused by stroke result in persisting physical or cognitive impairments in around 50% of all survivors (Di Carlo, 2008Leys et al., 2005 ;  Young and Forster, 2007), meaning that new therapies are urgently needed. Transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (TDCS) are two TBS approaches which are being increasingly utilised in stroke research. Single-pulse TMS combined with electromyography (EMG) or electroencephalography (EEG) can be used to assess cortical excitability, for example to index the functional state of the perilesional tissue. The neuromodulatory effects of repetitive TMS protocols (rTMS) may, in association with neuro-rehabilitative treatments, enhance motor recovery (Liew et al., 2014). Similar results have been demonstrated for TDCS. For example, anodal TDCS of the hand area in the primary motor cortex has been shown to improve motor performance of the affected hand (Allman et al., 2016Hummel et al., 2005 ;  Stagg et al., 2012) and anodal TDCS applied over the left frontal cortex enhanced naming accuracy in patients with aphasia (Baker et al., 2010). However, not all studies report a clear-cut positive impact of TBS on the stroke symptoms. Rather, the observed effects are often weak and not consistent across patients, demonstrating the need for a better understanding of the underlying biophysical and physiological mechanisms.

Compared with healthy subjects, several factors might contribute to a change in the neuroplastic response to TBS protocols in stroke patients, including changes in the neural responsiveness to the applied electric fields, as well as differences in the underlying physiology and metabolism (Blicher et al., 2009Blicher et al., 2015 ;  O’Shea et al., 2014). When the lesions are large, they may also substantially alter the generated electric field pattern, meaning that the assumptions on spatial targeting as derived from biophysical modelling and physiological experiments in healthy subjects might no longer be valid. Stroke lesions are often accompanied by secondary macrostructural changes such as cortical atrophy and enlargement of the ventricles (e.g., Skriver et al., 1990), which may further contribute to changes in the field pattern. In addition, the safety of TBS in patients with large lesions needs to be further clarified, as it is possible that the lesions might cause stimulation “hot spots”. In chronic patients, the stroke cavity becomes filled with corticospinal fluid (CSF), which might cause shunting of current, funnelling the generated currents towards the surrounding brain tissue and potentially causing localized areas of dangerously high field strengths.

Here, using finite-element calculations and individual head models derived from structural MR images, we focused on the impact of a large cortical lesion in chronic stroke on the electric field pattern generated in the brain by TMS and TDCS, respectively. Firstly, we assessed the safety of the stimulation by comparing the achieved field strengths with those estimated for a healthy control. Secondly, we tested how reliably we can accurately target the perilesional tissue, often the desired target for TBS, as reorganisation here is thought to underpin functional recovery (Kwakkel et al., 2004). Finally, we were also interested to see whether any observed changes in the field pattern were specific to a patient with a cortical lesion (which is connected to the CSF layer underneath the skull), or whether similar effects might occur in case of large chronic subcortical lesion. We therefore additionally tested the field distribution in a head model of a patient with a subcortical lesion occurring at a similar position as the cortical lesion.

2. Materials and methods

2.1. Selection of patients

The aim of this study was to characterize the effect of a large chronic cortical stroke lesion on the electric field distribution generated by TBS, and to compare the effects of this lesion to that caused by a large chronic subcortical lesion. MR images of several patients were visually inspected to select two datasets, which had a cortical [P01] and subcortical lesion [P02], respectively, within the same gross anatomical regions.

Patient P01 was a 36 year old female with episodic migraine; she was admitted with left hemiparalysis, fascial palsy and a total NIHSS score of 16 due to a right ICI/MCI occlusion. She was treated with IV thrombolysis and thrombectomy and recanalization was achieved 5 h after symptom onset. One year post-stroke she still suffered from motor impairment (Wolf Motor Function Test [WMFT] score of 30) and was scanned as part of a clinical study investigating the effect of combining Constraint-Induced Movement Therapy and tDCS (Figlewski et al., 2017; Clinical trials NCT01983319, Regional Ethics approval: 1-10-72-268-13). The structural scans showed a cortical lesion in the right parietal lobe (Fig. 1A). The lesion volume, delineated manually with reference to T1- and T2-weighted imaging, was 26,415 mm3.

Fig. 1:Fig. 1.

A) Coronal view of patient P01 with a cortical lesion in the right hemisphere. The top shows the T1-weighted MR image and the bottom the reconstructed head mesh. The view was chosen to include the lesion centre. The lesion is marked by red dashed circles. B) Corresponding view of patient P02 with a large subcortical lesion at a similar location in the right hemisphere. C) Corresponding view of the data set of the healthy control. D) The coil and electrode positions were systematically moved along two directions that were approximately perpendicular to each other. Five positions were manually placed every 2 cm in posterior – anterior direction symmetrically around the centre of the cortical lesion. The same was repeated along the lateral – medial direction. Both lines share the same centre position above the lesion, resulting in 9 positions in total. E) At each position, two coil orientations were tested which resulted in a current flow underneath the coil centre from anterior to posterior (top) and from lateral to medial, respectively (bottom). F) For each position of the yellow “stimulating” electrode, two positions of the blue return electrode were tested. First, the contralateral equivalent of the electrode position above the centre of the cortical lesion was used (top). In addition, a position on the contralateral forehead was tested (bottom).

Patient P02 was a 44 year old female. She woke up with a left hemiparesis and an acute CT scan showed no bleeding. No IV thrombolysis was given due to uncertain timing of symptom onset. An embolic stroke was suspect due to a patent foramen ovale, which was subsequently closed. She was scanned with MRI 9 months post stroke showing a right subcortical infarct, at which time she had a WMFT score of 8. The lesion volume, delineated as for P01, was 56,010 mm3. She was scanned as part of a clinical study investigating the effect of combining tDCS with daily motor training (Allman et al., 2016; Regional Ethics approval: Oxfordshire REC A; 10/H0604/98)….

Continue —> The impact of large structural brain changes in chronic stroke patients on the electric field caused by transcranial brain stimulation

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[Abstract] The treatment of fatigue by non-invasive brain stimulation

Summary

The use of non-invasive brain neurostimulation (NIBS) techniques to treat neurological or psychiatric diseases is currently under development. Fatigue is a commonly observed symptom in the field of potentially treatable pathologies by NIBS, yet very little data has been published regarding its treatment. We conducted a review of the literature until the end of February 2017 to analyze all the studies that reported a clinical assessment of the effects of NIBS techniques on fatigue. We have limited our analysis to repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS). We found only 15 studies on this subject, including 8 tDCS studies and 7 rTMS studies. Of the tDCS studies, 6 concerned patients with multiple sclerosis while 6 rTMS studies concerned fibromyalgia or chronic fatigue syndrome. The remaining 3 studies included patients with post-polio syndrome, Parkinson’s disease and amyotrophic lateral sclerosis. Three cortical regions were targeted: the primary sensorimotor cortex, the dorsolateral prefrontal cortex and the posterior parietal cortex. In all cases, tDCS protocols were performed according to a bipolar montage with the anode over the cortical target. On the other hand, rTMS protocols consisted of either high-frequency phasic stimulation or low-frequency tonic stimulation. The results available to date are still too few, partial and heterogeneous as to the methods applied, the clinical profile of the patients and the variables studied (different fatigue scores) in order to draw any conclusion. However, the effects obtained, especially in multiple sclerosis and fibromyalgia, are really carriers of therapeutic hope.

Source: The treatment of fatigue by non-invasive brain stimulation

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[ARTICLE] Transcranial Direct Current Stimulation Does Not Affect Lower Extremity Muscle Strength Training in Healthy Individuals: A Triple-Blind, Sham-Controlled Study – Full Text

The present study investigated the effects of anodal transcranial direct current stimulation (tDCS) on lower extremity muscle strength training in 24 healthy participants. In this triple-blind, sham-controlled study, participants were randomly allocated to the anodal tDCS plus muscle strength training (anodal tDCS) group or sham tDCS plus muscle strength training (sham tDCS) group. Anodal tDCS (2 mA) was applied to the primary motor cortex of the lower extremity during muscle strength training of the knee extensors and flexors. Training was conducted once every 3 days for 3 weeks (7 sessions). Knee extensor and flexor peak torques were evaluated before and after the 3 weeks of training. After the 3-week intervention, peak torques of knee extension and flexion changed from 155.9 to 191.1 Nm and from 81.5 to 93.1 Nm in the anodal tDCS group. Peak torques changed from 164.1 to 194.8 Nm on extension and from 78.0 to 85.6 Nm on flexion in the sham tDCS group. In both groups, peak torques of knee extension and flexion significantly increased after the intervention, with no significant difference between the anodal tDCS and sham tDCS groups. In conclusion, although the administration of eccentric training increased knee extensor and flexor peak torques, anodal tDCS did not enhance the effects of lower extremity muscle strength training in healthy individuals. The present null results have crucial implications for selecting optimal stimulation parameters for clinical trials.

Introduction

Transcranial direct current stimulation (tDCS) is a non-invasive cortical stimulation procedure in which weak direct currents polarize target brain regions (Nitsche and Paulus, 2000). The application of anodal tDCS to the primary motor cortex of the lower extremity transiently increases corticospinal excitability in healthy individuals (Jeffery et al., 2007Tatemoto et al., 2013) and improves motor function in healthy individuals and patients with stroke (Tanaka et al., 20092011Madhavan et al., 2011Sriraman et al., 2014Chang et al., 2015Montenegro et al., 20152016Angius et al., 2016Washabaugh et al., 2016). Thus, anodal tDCS has a potential to become a new adjunct therapeutic strategy for the rehabilitation of leg motor function and locomotion following a stroke.

Lower leg muscle strength is an important motor function required for patients who have had a stroke to regain activities of daily living (ADL). Lower leg muscle strength correlates with performance in activities, including sit-to-stand, gait, and stair ascent (Bohannon, 2007). Furthermore, lower leg muscle strength training increases muscle strength and improves ADL in patients with stroke (Ada et al., 2006). Therefore, lower leg muscle strength training is one of the important activities rehabilitating patients with stroke to regain their independence in ADL.

Several studies have examined the effect of a single session of tDCS on lower leg muscle strength, although the evidence is inconsistent (Tanaka et al., 20092011Montenegro et al., 20152016Angius et al., 2016Washabaugh et al., 2016). Its effects seem dependent on tDCS protocols, training tasks, muscle groups, and subject populations. Although, most tDCS studies on lower leg muscle strength have focused on the acute effects of a single tDCS application, to the best of our knowledge, no study has examined how lower extremity strength training combined with repeated sessions of tDCS affects lower leg muscle strength. This type of investigation has strong clinical implications for the application of tDCS in rehabilitation for patients with lower leg muscle weakness.

Thus, to examine whether anodal tDCS can enhance the effects of lower extremity muscle strength training, the present study simultaneously applied anodal tDCS and lower extremity muscle strength training to healthy individuals and evaluated their effects on lower extremity muscle strength.

Continue —> Frontiers | Transcranial Direct Current Stimulation Does Not Affect Lower Extremity Muscle Strength Training in Healthy Individuals: A Triple-Blind, Sham-Controlled Study | Perception Science

Figure 1. Experimental setup of the muscle strength training and torque assessment.

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[Abstract+References] Combined Transcranial Direct Current Stimulation and Vision Restoration Training in Subacute Stroke Rehabilitation: A Pilot Study

Abstract

Background

Visual field defects after posterior cerebral artery stroke can be improved by vision restoration training (VRT), but when combined with transcranial direct current stimulation (tDCS), which alters brain excitability, vision recovery can be potentiated in the chronic stage. To date, the combination of VRT and tDCS has not been evaluated in postacute stroke rehabilitation.

Objectives

To determine whether combined tDCS and VRT can be effectively implemented in the early recovery phase following stroke, and to explore the feasibility, safety and efficacy of an early intervention.

Design

Open-label pilot study including a case series of 7 tDCS/VRT versus a convenience sample of 7 control patients (ClinicalTrials.gov ID: NCT02935413).

Setting

Rehabilitation center.

Subjects

Patients with homonymous visual field defects following a posterior cerebral artery stroke.

Methods

Seven homonymous hemianopia patients were prospectively treated with 10 sessions of combined tDCS (2.mA, 10 daily sessions of 20 minutes) and VRT at 66 (±50) days on average poststroke. Visual field recovery was compared with the retrospective data of 7 controls, whose defect sizes and age of lesions were matched to those of the experimental subjects and who had received standard rehabilitation with compensatory eye movement and exploration training.

Results

All 7 patients in the treatment group completed the treatment protocol. The safety and acceptance were excellent, and patients reported occasional skin itching beneath the electrodes as the only minor side effect. Irrespective of their treatment, both groups (treatment and control) showed improved visual fields as documented by an increased mean sensitivity threshold in decibels in standard static perimetry. Recovery was significantly greater (P < .05) in the tDCS/VRT patients (36.73% ± 37.0%) than in the controls (10.74% ± 8.86%).

Conclusion

In this open-label pilot study, tDCS/VRT in subacute stroke was demonstrated to be safe, with excellent applicability and acceptance of the treatment. Preliminary effectiveness calculations show that tDCS/VRT may be superior to standard vision training procedures. A confirmatory, larger-sample, controlled, randomized, and double-blind trial is now underway to compare real-tDCS− versus sham-tDCS−supported visual field training in the early vision rehabilitation phase.

References

  1. Roux, F. Perimetric visual field and functional MRI correlation: Implications for image-guided surgery in occipital brain tumours. J Neurol Neurosurg Psychiatry. 2001;71:505–514.
  2. Gray, C., French, J., Bates, D., Cartlidgen, Venables, G., James, O. Recovery of visual fields in acute stroke: Homonymous hemianopia associated with adverse prognosis. Age Ageing. 1989;18:419–421.
  3. Zhang, X., Kedar, S., Lynn, M., Newman, N., Biousse, V. Natural history of homonymous hemianopia. Neurology. 2006;66:901–905.
  4. Romano, J. Progress in rehabilitation of hemianopic visual field defects. Cerebrovasc Dis. 2009;27:187–190.
  5. Pöppel, E., Held, R., Frost, D. Residual visual function after brain wounds involving the central visual pathways in man. Nature. 1973;243:295–296.
  6. Weiskrantz, L., Warrington, E., Sanders, M., Marshall, J. Visual capacity in the hemianopic field following a restricted occipital ablation. Brain. 1974;97:709–728.
  7. Wüst, S., Kasten, E., Sabel, B. Blindsight after optic nerve injury indicates functionality of spared fibers. J Cogn Neurosci. 2002;14:243–253.
  8. Sabel, B.A., Fedorov, A., Naue, N., Borrmann, A., Herrmann, C., Gall, C. Non-invasive alternating current stimulation improves vision in optic neuropathy. Restor Neurol Neurosci. 2011;29:493–505.
  9. Sabel, B.A., Henrich-Noack, P., Fedorov, A., Gall, C. Vision restoration after brain and retina damage: The “residual vision activation theory”. Prog Brain Res. 2011;192:199–262.
  10. Bola, M., Gall, C., Sabel, B.A. “Sightblind”: Perceptual deficits in the “intact” visual field.Front Neurol. 2013;4:80.
  11. Bola, M., Gall, C., Moewes, C., Fedorov, A., Hinrichs, H., Sabel, B.A. Brain functional connectivity network breakdown and restoration in blindness. Neurology. 2014;83:542–551.
  12. Bola, M., Sabel, B.A. Dynamic reorganization of brain functional networks during cognition.NeuroImage. 2015;114:398–413.
  13. Bridge, H., Thomas, O., Jbabdi, S., Cowey, A. Changes in connectivity after visual cortical brain damage underlie altered visual function. Brain. 2008;131:1433–1444.
  14. Kasten, E., Wüst, S., Behrens-Baumann, W., Sabel, B.A. Computer-based training for the treatment of partial blindness. Nature Med. 1998;4:1083–1087.
  15. Gall, C., Antal, A., Sabel, B.A. Non-invasive electrical brain stimulation induces vision restoration in patients with visual pathway damage. Graefes Arch Clin Exp Ophthalmol. 2013;251:1041–1043.
  16. Eysel, U.T., Schweigart, G., Mittmann, T. et al, Reorganization in the visual cortex after retinal and cortical damage. Restor Neurol Neurosci. 1999;15:153–164.
  17. Poggel, D., Kasten, E., Sabel, B.A. Attentional cueing improves vision restoration therapy in patients with visual field defects. Neurology. 2004;63:2069–2076.
  18. Kasten, E., Bunzenthal, U., Sabel, B.A. Visual field recovery after vision restoration therapy (VRT) is independent of eye movements: An eye tracker study. Behav Brain Res. 2006;175:18–26.
  19. Nitsche, M.A., Schauenburg, A., Lang, N. et al, Facilitation of implicit motor learning by weak transcranial direct current stimulation of the primary motor cortex in the human. J Cogn Neurosci. 2003;15:619–626.
  20. Nitsche, M.A., Cohen, L.G., Wassermann, E.M. et al, Transcranial direct current stimulation: State of the art 2008. Brain Stimul. 2008;1:206–223.
  21. Antal, A., Kincses, T., Nitsche, M.A., Bartfai, O., Paulus, W. Excitability changes induced in the human primary visual cortex by transcranial direct current stimulation: Direct electrophysiological evidence. Invest Ophthalmol Vis Sci. 2004;45:702.
  22. Kraft, A., Roehmel, J., Olma, M., Schmidt, S., Irlbacher, K., Brandt, S. Transcranial direct current stimulation affects visual perception measured by threshold perimetry. Exp Brain Res. 2010;207:283–290.
  23. Plow, E.B., Obretenova, S.N., Halko, M.A. et al, Combining visual rehabilitative training and noninvasive brain stimulation to enhance visual function in patients with hemianopia: A comparative case study. PM R. 2011;3:825–835.
  24. Plow, E., Obretenova, S., Fregni, F., Pascual-Leone, A., Merabet, L.B. Comparison of visual field training for hemianopia with active versus sham transcranial direct cortical stimulation.Neurorehabil Neural Repair. 2012;26:616–626.
  25. Plow, E., Obretenova, S., Jackson, M., Merabet, L.B. Temporal profile of functional visual rehabilitative outcomes modulated by transcranial direct current stimulation.Neuromodulation. 2012;15:367–373.
  26. Hummel, F., Celnik, P., Pascual-Leone, A. et al, Controversy: Noninvasive and invasive cortical stimulation show efficacy in treating stroke patients. Brain Stimul. 2008;1:370–382.
  27. Alber, R., Cardoso, A.M., Nafee, T. Effects of non-invasive brain stimulation in cerebral stroke related vision loss. Princip Pract Clin Res. 2015;1:15–20.
  28. Rossi, S., Hallett, M., Rossini, P., Pascual-Leone, A. Safety, ethical considerations, and application guidelines for the use of transcranial magnetic stimulation in clinical practice and research. Clin Neurophysiol. 2009;120:2008–2039.
  29. Anops [computer program]. Version 2.9.6. Aachen, Germany: LinguAdapt.
  30. Bowen, D.J., Kreuter, M., Spring, B. et al, How we design feasibility studies. Am J Prev Med. 2009;36:452–457.

Source: Combined Transcranial Direct Current Stimulation and Vision Restoration Training in Subacute Stroke Rehabilitation: A Pilot Study – PM&R

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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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[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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[ARTICLE] Notes on Human Trials of Transcranial Direct Current Stimulation between 1960 and 1998 – Full Text

Background: Transcranial direct current stimulation (tDCS) is investigated to modulate neuronal function including cognitive neuroscience and neuropsychiatric therapies. While cases of human stimulation with rudimentary batteries date back more than 200 years, clinical trials with current controlled stimulation were published intermittently since the 1960s. The modern era of tDCS only started after 1998.

Objectives: To review methods and outcomes of tDCS studies from old literature (between 1960 and 1998) with intention of providing new insight for ongoing tDCS trials and development of tDCS protocols especially for the purpose of treatment.

Methods: Articles were identified through a search in PubMed and through the reference list from its selected articles. We included only non-invasive human studies that provided controlled direct current and were written in English, French, Spanish or Portuguese before the year of 1998, the date in which modern stimulation paradigms were implemented.

Results: Fifteen articles met our criteria. The majority were small-randomized controlled clinical trials that enrolled a mean of approximately 26 subjects (Phase II studies). Most of the studies (around 83%) assessed the role of tDCS in the treatment of psychiatric conditions, in which the main outcomes were measured by means of behavioral scales and clinical observation, but the diagnostic precision and the quality of outcome monitoring, including adverse events, were deficient by modern standards. Compared to modern tDCS dose, the stimulation intensities used (0.1–1 mA) were lower, however as the electrodes were typically smaller (e.g., 1.26 cm2), the average electrode current density (0.2 mA/cm2) was approximately 4× higher. The number of sessions ranged from one to 120 (median 14). Notably, the stimulation session durations of several minutes to 11 h (median 4.5 h) could markedly exceed modern tDCS protocols. Twelve studies out of 15 showed positive results. Only mild side effects were reported, with headache and skin alterations the most common.

Conclusion: Most of the studies identified were for psychiatric indications, especially in patients with depression and/or schizophrenia and majority indicated some positive results. Variability in outcome is noted across trials and within trials across subjects, but overall results were reported as encouraging, and consistent with modern efforts, given some responders and mild side effects. The significant difference with modern dose, low current with smaller electrode size and interestingly much longer stimulation duration may worth considering.

Introduction

Transcranial direct current stimulation (tDCS) consists of applying a weak direct current on the scalp, a portion of which crosses the skull (Datta et al., 2009) and induces cortical changes (Fregni and Pascual-Leone, 2007; Nitsche et al., 2008). The investigation of the application of electricity over the brain dates back to at least 200 years, when Giovanni Aldini (Zaghi et al., 2010) recommended galvanism for patients with deafness, amaurosis and “insanity”, reporting good results with this technique especially when used in patients with “melancholia”. Aldini also used tDCS in patients with symptoms of personality disorders and supposedly reported complete rehabilitation following transcranial administration of electric current (Parent, 2004).

These earliest studies used rudimentary batteries and so were constant voltage, where the resulting current depends on a variable body resistance. Over the 20th century, direct voltage continued to be used but most testing involved pulsed stimulation, starting with basic devices where a mechanical circuit that intermittently connected and broke the circuit between the battery and the subject and evolving to modern current control circuits including Cranial Electrotherapy Stimulation and its variants (Guleyupoglu et al., 2013). Interest in direct current stimulation (or tDCS) resurged with the studies of Priori et al. (1998) and Nitsche and Paulus (2000) that demonstrated weak direct current could change cortical response to Transcranial Magnetic Stimulation, thereby indicating that tDCS could change cortical “excitability”. Testing for clinical and cognitive modification soon followed (Fregni et al., 2005, 2006). Developments and challenges in tDCS research, including applications in the treatment of neuro-psychiatrics disease since 1998 have been reviewed in detailed elsewhere (Brunoni et al., 2012).

This historical note aims to explore earlier data on human trial using current controlled stimulation (tDCS) before 1998 with the goal of informing ongoing understanding and development of tDCS protocols. As expected, we found variability in the quality of trial design, data collection and reporting in these earlier studies. Nonetheless, many clinical findings are broadly consistent with modern efforts, including some encouraging results but also variability across subjects. We also describe a significant difference in dose with lower current, smaller electrodes and much longer durations (up to 11 h) than used in modern tDCS.

Figure 2. Summary of study parameters on human trials using transcranial direct current stimulation (tDCS) in old literature (from 1960 to 1998). Models of commonly used montages of tDCS in early studies (A); red: anode electrode(s), blue: cathode electrode(s). Total number of subjects in each group of patients participating in studies using aforementioned montages (B.1) and leading countries conducting tDCS studies in early stage with number of published articles (B.2).

Continue —> Frontiers | Notes on Human Trials of Transcranial Direct Current Stimulation between 1960 and 1998 | Frontiers in Human Neuroscience

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[Abstract] The effect of transcranial direct current stimulation on motor sequence learning and upper limb function after stroke

Introduction

Transcranial direct current stimulation (tDCS) is a safe and non-invasive brain stimulation technique with the potential to improve upper limb function after stroke. Ipsilesional primary motor cortex (M1) excitability can be increased with anodal tDCS, contralesional M1 excitability can be decreased with cathodal tDCS or both anodal and cathodal tDCS can be used simultaneously on both cortices (bihemispheric). The impact of these different electrode arrangements on the efficacy of tDCS, and whether any of the changes are due to callosal connections between cortices, is unclear.

Objectives

This study aimed to investigate the effect of tDCS electrode arrangement on motor sequence learning and upper limb function in chronic stroke survivors.

Patients and methods

21 stroke survivors (range 3–124 months post-stroke, 34–81 years of age) with upper limb impairment received 20 min of 1 mA tDCS (0.04 mA·cm−2) during performance of a motor sequence learning task which involved movement of a computer mouse with the paretic arm to circular targets on a monitor in a repeating pattern. Four tDCS conditions were studied in a repeated-measures design; (i) anodal to the ipsilesional M1, (ii) cathodal to the contralesional M1, (iii) bihemispheric and (iv) sham. Upper limb function was assessed before and after tDCS, using the Jebsen–Taylor hand function test (JTT). Changes in transcallosal inhibition (TCI) were assessed using transcranial magnetic stimulation (ipsilateral silent period duration).

Results

There was no effect of tDCS condition on performance of the motor sequence learning task. Performance on the JTT improved significantly after unilateral tDCS (anodal or cathodal) compared to sham (p < 0.05), but not after bihemispheric (Fig. 1). There was no effect on TCI (p > 0.5), and no relationship between changes in TCI and upper limb function.

Conclusions

Unilateral, but not bihemispheric, tDCS improves upper limb function. The response to tDCS does not appear to be driven by changes in TCI. These results have implications for the use of tDCS for upper limb rehabilitation.

Source: P244 The effect of transcranial direct current stimulation on motor sequence learning and upper limb function after stroke – Clinical Neurophysiology

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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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