Name: non-invasive electrical brain stimulation montages for modulation of human motor function
Uploaded: 2016-02-04T13:00:00
Description: Watch this Scientific Journal Video about Non-Invasive Electrical Brain Stimulation Montages for Modulation of Human Motor Function at JoVE.com

MC and JR are supported by the German Research Foundation (DFG RE 2740/3-1).

Ethics statement: Human studies require written informed consent of participants before study entry. Obtain approval by the relevant ethics committee before recruitment of participants. Make sure studies are in accordance with the Declaration of Helsinki. The representative findings reported here (Figure 4) are based on a study performed in accordance with the Declaration of Helsinki amended by the 59th WMA General Assembly, Seoul, October 2008 and approved by the local Ethics Committee of the Uni...

This protocol describes typical materials and procedural steps for modulation of hand motor function and skill learning using NEBS, specifically unilateral and bilateral M1 stimulation for anodal tDCS, and unilateral tRNS. Before choosing a particular NEBS protocol for a human motor system study, e.g., in the context of motor learning, methodological aspects (safety, tolerability, blinding) as well as conceptual aspects (montage or current type specific effects on a particular brain region) need to be taken into...

Non-invasive electrical brain stimulation (NEBS), the administration of electrical currents to the brain through the intact skull, can modify brain function and behavior1-3. To optimize the therapeutic potential of NEBS strategies understanding the underlying mechanisms leading to neurophysiological and behavioral effects is still needed. Standardization of application across different laboratories and full transparency of stimulation procedures provides the basis for comparability of data which supports reliable interpretation of results and evaluation of the proposed mechanisms of action. Transcranial direct current stimulation (tDCS) or transcranial alternating current stimulation (tACS) differ by parameters of the applied electrical current: tDCS consists of an unidirectional constant current flow between two electrodes (anode and cathode)2-6 while tACS uses an alternating current applied at a specific frequency7. Transcranial random noise stimulation (tRNS) is a special form of tACS that uses an alternating current applied at random frequencies (e.g., 100-640 Hz) resulting in quickly varying stimulation intensities and removing polarity-related effects4,6,7. Polarity is only of relevance if the stimulation setting includes a stimulation offset, e.g., noise spectrum randomly changing around a +1 mA baseline intensity (usually not used). For the purpose of this article, we will focus on work using tDCS and tRNS effects on the motor system, closely following a recent publication from our lab6.
The underlying mechanisms of action of tRNS are even less understood than of tDCS but likely different from the latter. Theoretically, in the conceptual framework of stochastic resonance tRNS introduces stimulation-induced noise to a neuronal system which may provide a signal processing benefit by altering the signal-to-noise ratio4,8,9. TRNS may predominantly amplify weaker signals and could thus optimize task-specific brain activity (endogenous noise9). Anodal tDCS increases cortical excitability indicated by alteration of the spontaneous neuronal firing rate10 or increased motor evoked potential (MEP) amplitudes2 with the effects outlasting the stimulation duration for minutes to hours. Long-lasting increases in synaptic efficacy known as long-term potentiation are thought to contribute to learning and memory. Indeed, anodal tDCS enhances synaptic efficacy of motor cortical synapses repeatedly activated by a weak synaptic input11. In accordance, improved motor function/skill acquisition is often revealed only if stimulation is co-applied with motor training11-13, also suggesting synaptic co-activation as a prerequisite of this activity-dependent process. Nevertheless, causality between increases in cortical excitability (increase in firing rate or MEP amplitude) on one hand and improved synaptic efficacy (LTP or behavioral function such as motor learning) on the other hand has not been demonstrated.
NEBS applied to the primary motor cortex (M1) has attracted increasing interest as safe and effective method to modulate human motor function1. Neurophysiological effects and behavioral outcome may depend on the stimulation strategy (e.g., tDCS polarity or tRNS), electrode size and montage4-6,14,15. Aside from subject-inherent anatomical and physiological factors the electrode montage significantly influences electric field distribution and may result in different patterns of current spreading within the cortex16-18. In addition to the intensity of the applied current the size of the electrodes determines the current density delivered3. Common electrode montages in human motor system studies include (Figure 1): 1) anodal tDCS as unilateral M1 stimulation with the anode positioned on the M1 of interest and the cathode positioned on the contralateral forehead; the basic idea of this approach is upregulation of excitability in the M1 of interest6,13,19-22; 2) anodal tDCS as bilateral M1 stimulation (also referred to as &#34;bihemispheric&#34; or &#34;dual&#34; stimulation) with the anode positioned on the M1 of interest and the cathode positioned on the contralateral M15,6,14,23,24; the basic idea of this approach is maximizing stimulation benefits by upregulation of excitability in the M1 of interest while downregulating excitability in the opposite M1 (i.e., modulation of interhemispheric inhibition between the two M1s); 3) For tRNS, only the above mentioned unilateral M1 stimulation montage has been investigated4,6; with this montage excitability enhancing effects of tRNS have been found for the frequency spectrum of 100-640 Hz4. The choice of brain stimulation strategy and electrode montage represents a critical step for an efficient and reliable use of NEBS in clinical or research settings. Here these three NEBS procedures are described in detail as used in human motor system studies and methodological and conceptual aspects are discussed. Materials for unilateral or bilateral tDCS and unilateral tRNS are the same (Figure 2).
<img alt="Figure 1" src="/files/ftp_upload/53367/53367fig1.jpg" /> 
Figure 1.&#160;Electrode montages and current direction for distinct NEBS strategies.&#160;(A) For unilateral anodal transcranial direct current stimulation (tDCS), the anode is centered over the primary motor cortex of interest and the cathode positioned over the contralateral supra-orbital area. (B) For bilateral motor cortex stimulation, anode and cathode are located each over one motor cortex. The position of the anode determines the motor cortex of interest for anodal tDCS. (C) For unilateral transcranial random noise stimulation (tRNS), one electrode is located over the motor cortex and the other electrode over the contralateral supra-orbital area. The current flow between electrodes is indicated by the black arrow. Anode (+, red), cathode (-, blue), Alternating current (+/-, green). <a href="https://www.jove.com/files/ftp_upload/53367/53367fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

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			<td height="21" style="height:21px;width:301px;">NEBS device (DC Stimulator plus)</td>
			<td style="width:271px;">Neuroconn</td>
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			<td height="21" style="height:21px;width:301px;">Electrode cables</td>
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			<td height="21" style="height:21px;width:301px;">Conductive-rubber electrodes</td>
			<td style="width:271px;">Neuroconn</td>
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			<td>5x5 cm</td>
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			<td height="21" style="height:21px;width:301px;">Perforated sponge bags</td>
			<td style="width:271px;">Neuroconn</td>
			<td style="width:119px;"></td>
			<td>5x5 cm</td>
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			<td height="21" style="height:21px;width:301px;">Non-conductive rubber sponge cover</td>
			<td style="width:271px;">Amrex-Zetron</td>
			<td style="width:119px;">FG-02-A103</td>
			<td>Rubber pad 3&#34;*3&#34;</td>
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			<td height="21" style="height:21px;width:301px;">NaCl isotonic solution&#160;</td>
			<td style="width:271px;">B. Braun Melsungen AG&#160;</td>
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			<td>Ecoflac, 0,9%</td>
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			<td height="21" style="height:21px;width:301px;">Cotton crepe bandage</td>
			<td style="width:271px;">Paul Hartmann AG</td>
			<td style="width:119px;">931004</td>
			<td>8x5m, textile elasticity</td>
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			<td height="21" style="height:21px;width:301px;">Adhesive tape (Leukofix)</td>
			<td style="width:271px;">BSN medical</td>
			<td style="width:119px;">02122-00</td>
			<td>2,5cm*5m</td>
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			<td height="21" style="height:21px;width:301px;">Skin preparation paste</td>
			<td style="width:271px;">Weaver</td>
			<td style="width:119px;">10-30</td>
			<td></td>
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			<td height="21" style="height:21px;width:301px;">Magnetic stimulator</td>
			<td style="width:271px;">Magstim</td>
			<td style="width:119px;">3010-00</td>
			<td>Magstim 200</td>
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			<td height="21" style="height:21px;width:301px;">EMG conductive paste</td>
			<td style="width:271px;">GE Medical Systems</td>
			<td style="width:119px;">217083</td>
			<td></td>
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			<td height="21" style="height:21px;width:301px;">EMG bipolar electrodes</td>
			<td>e.g., Natus Medical Inc. Viking 4&#160;</td>
			<td style="width:119px;"></td>
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			<td height="21" style="height:21px;width:301px;">EMG amplifier</td>
			<td>e.g., Natus Medical Inc. Viking 4&#160;</td>
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			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:301px;">Cable for EMG signal transmission</td>
			<td>e.g., Natus Medical Inc. Viking 4</td>
			<td style="width:119px;"></td>
			<td></td>
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			<td height="21" style="height:21px;width:301px;">Data acquisition unit&#160;</td>
			<td style="width:271px;">Cambridge Electronic Design (CED)</td>
			<td style="width:119px;">MK1401-3</td>
			<td>AD converter</td>
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			<td height="42" style="height:42px;width:301px;">Computer for signal recording and offline analysis</td>
			<td style="width:271px;"></td>
			<td style="width:119px;"></td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:301px;">Signal 4.0.9</td>
			<td style="width:271px;">Cambridge Electronic Design (CED)</td>
			<td style="width:119px;"></td>
			<td>Software</td>
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		<tr height="21">
			<td height="21" style="height:21px;width:301px;">non-permanent skin marker</td>
			<td style="width:271px;">Edding</td>
			<td style="width:119px;">8020</td>
			<td>1 mm, blue</td>
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non-invasive electrical brain stimulation montages for modulation of human motor function

Non-invasive electrical brain stimulation (NEBS) is used to modulate brain function and behavior, both for research and clinical purposes. In particular, NEBS can be applied transcranially either as direct current stimulation (tDCS) or alternating current stimulation (tACS). These stimulation types exert time-, dose- and in the case of tDCS polarity-specific effects on motor function and skill learning in healthy subjects. Lately, tDCS has been used to augment the therapy of motor disabilities in patients with stroke or movement disorders. This article provides a step-by-step protocol for targeting the primary motor cortex with tDCS and transcranial random noise stimulation (tRNS), a specific form of tACS using an electrical current applied randomly within a pre-defined frequency range. The setup of two different stimulation montages is explained. In both montages the emitting electrode (the anode for tDCS) is placed on the primary motor cortex of interest. For unilateral motor cortex stimulation the receiving electrode is placed on the contralateral forehead while for bilateral motor cortex stimulation the receiving electrode is placed on the opposite primary motor cortex. The advantages and disadvantages of each montage for the modulation of cortical excitability and motor function including learning are discussed, as well as safety, tolerability and blinding aspects.

To investigate the effects of NEBS on the human motor system it is important to consider appropriate outcome measures. One advantage of the motor system is the accessibility of the cortical representations by electrophysiological tools. Motor evoked potentials are frequently used as an indicator of motor cortical excitability. After application of 9 or more minutes of anodal tDCS at a current density of 29 &#181;A/cm2, motor cortical excitability is increased for at least 30 mi...

Watch this Scientific Journal Video about Non-Invasive Electrical Brain Stimulation Montages for Modulation of Human Motor Function at JoVE.com

Non-Invasive Electrical Brain Stimulation Montages for Modulation of Human Motor Function

Non-invasive electrical brain stimulation can modulate cortical function and behavior, both for research and clinical purposes. This protocol describes different brain stimulation approaches for modulation of the human motor system.

Non-invasive electrical brain stimulation (NEBS) is used to modulate brain function and behavior, both for research and clinical purposes. In particular, ...

The overall goal of this procedure is to demonstrate the localization of the primary motor cortex, and correct placement of electrical brain stimulation electrodes, to modulate the motor system. This method can help answer key questions in the field of neuroplasticity, through the targeted modulation of brain networks that improve motor functions, or counteract motor disabilities. The main advantage of non-evasive electrical brain stimulation is that it is easy to administer even as a bedside technique, without inducing pain or discomfort.This method of brain stimulation can provide insight into the function of the motor system. It can also be applied to other regions of interest, such as the pre-frontal cortex, or the visual cortex. Visual demonstration of the localization of target cortical areas and electrode placement are crucial for the success of these experiments.Otherwise, electrical current flow may not reach the intended brain areas, resulting in a lack of effect, or unexpected findings. Begin by asking the participant to sit comfortably in the chair. Clean the participant's skin by rubbing preparation paste in the regions of the hand where electrodes will be placed.Remove excess with a clean gauze pad. Attach the electromyography, or EMG, surface electrodes in a belly-tendon montage, on the hand muscle of interest, and connect a ground electrode. Then, turn on the magnetic stimulator and charge the capacitor by pressing the corresponding charge button.Place a figure of eight TMS coil on the participant's scalp on the motor cortex region. Hold the TMS coil at a 45 to 50 degree angle, referenced to the inter-hemispheric fissure, with the handle oriented backwards. When the magnetic stimulator is charged, discharge the stimulator by either pressing the trigger button, by stepping on the foot switch, or automatically with a software program.Next, start with a low stimulation intensity, and watch for motor evoked potentials, or MEP's, visible on the EMG amplifier. If no MEP is visible, increase the stimulation intensity, until an MEP is clearly present. Repeat stimulation by pressing the trigger button.Move the coil radially, in one centimeter steps, around the initially stimulated site, to find the spot with the largest MEP response, following the application of single TMS pulses. From there, start moving the coil again to secure the hot spot. Finally, mark the hot spot position, and coil orientation with a non-permanent skin marker.Connect cables to rubber electrodes, and place the electrodes inside the sponge bags. Ensure that the electrode size and sponge bag size match. Soak sponge bags on both sides with isotonic sodium chloride solution, but avoid excessive soaking to prevent salt bridges, or dripping onto the volunteer.Next, find the head markings indicating the motor cortical hot spot, and separate the hair around the area. To improve conductance, clean the skin before electrode placement with a swab soaked with 40 to 50 percent alcohol, or skin preparation paste. Remove excess with a swab, and clean the area again with isotonic sodium chloride solution.Dry the area afterwards. Place one electrode on the head marking for the motor cortex area of interest, and keep the sponge in direct contact with the skin as much as possible. For unilateral stimulation, place the second electrode over the contralateral supra-orbital area.Alternatively, for bilateral stimulation, place the second electrode on the opposite motor cortex, following the head marking ipsilateral to the limb used in the study. Place all of the electrode cables towards the participants back, to avoid disturbance during stimulation, and to ease connection to the non-invasive electrical brain stimulation, or any BS device. Then, cover the head twice, with an elastic bandage, circularly in the mediolateral direction, to stabilize the M1 electrode.Use the remaining bandage to cover the head circularly in the anterior posterior direction, to stabilize both electrodes. Use adhesive tape to fix the end of the bandage, and secure the cables with adhesive tape on the participant's neck, or shirt. Finally, connect the electrode cables to any BS device.Begin by switching on any BS device. Adjust the any BS device settings, regarding stimulation type, intensity, duration, ramping up and down, and frequency spectrum for transcranial random noise stimulation. Next, inform the participant about potential side effects associated with any BS.Then start the stimulation, and check for continuity of stimulation, during ramping up, and throughout the session.If any BS is co-applied with the execution of a motor task, start the testing after stimulation is ramped up, and after the participant is feeling comfortable with stimulation. Finally, after the stimulation session is complete, disinfect the electrodes and sponges with 40 to 50 percent alcohol. Then thoroughly rinse in water, and let the materials dry before storing.This protocol describes multiple approaches for non-invasive electrical brain stimulation, for modulation of the human motor system. Here the time course of cortical excitability is shown over the course of 90 minutes after stimulation of the primary motor cortex. Note that TRNS exerts similar effects on cortical excitability compared to TDCS.Within three days of motor training, motor skill increases significantly over time, in the Sham control group, and is augmented further by each any BS strategy. After watching this video, you should have a good understanding of how to locate the primary motor cortex by TMS, and place electrodes for the different any BS montages. Once mastered, this technique can be completed in 10 to 15 minutes, if it is performed properly.Don't forget that working with magnetic and electrical brain stimulation can be harmful if used improperly, and safety screening of participants should always be done before performing this procedure.

Research

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