P.S. received funding support from CAPES, Brazil. This work was partially supported with a grant from CIMIT. The authors are also grateful to Uri Fligil for his technical assistance and to Olivia Gozel and Noelle Chiavetta for their help in editing this manuscript.

1. Materials
<ol>
	<li>Check that if all materials are available (Figure 1) before starting the following steps.</li>
	<li>There are 3 sizes of neoprene caps, depending on the size of the subjects' head (small, medium and large). The cap has 27 holes representing EEG positions based on the 10/20 system: prefrontal (F8, AF8, Fp2, Fpz, Fp1, AF7, F7), frontal (F4, Fz, F3), central (C3, C1, Cz, C2, C4), parietal (P7, P3, Pz, P4, P8), temporal (T7, T8) and occipital (PO7, O1, Oz, O2, PO8).</li>
	<li>The electrodes have 2 different uses; they can be used for the EEG (six channels) and for tDCS (two channels for sponge-electrodes, the anode and the cathode). In some circumstances, more than two sites of stimulation can be used. In this case four sponge-electrodes will be required and consequently, only 4 channels will remain for EEG recordings.</li>
	<li>The variation of the tDCS electrodes size leads to a variation of focal effects 11. With a decrease of electrode dimension, a more focal stimulation can be achieved. On the other hand, by increasing electrode size it is possible to have a functionally ineffective electrode. The most commonly used proportions are 25 cm2 (5 cm x 5 cm) or 35 cm2 (5 cm x 7 cm). In this paper, sponge-electrodes of 25 cm2 will be used.</li>
	<li>All the electrodes have to be connected to the Control Box device through the wires. This device has to be charged periodically using the Control Box Battery charger. For safety reasons, it is not possible to charge the Control Box during active stimulation.</li>
	<li>The USB for Bluetooth connection is needed to pair the Control Box to the laptop/computer (see below).</li>
</ol>
2. Skin Preparation
<ol>
	<li>Inspect the skin for any pre-existing lesions - avoid electrical stimulation/EEG recording over damaged skin or over skull lesions.</li>
	<li>To increase conductance, move hair away from the site of electrical stimulation/EEG registering and place plastic hair clips to keep hair away, clean the surface of the skin to remove any signs of lotion, dirt, grease, etc. and allow it to dry.</li>
</ol>
3. Head Measurements
<ol>
	<li>Find and mark the localization of the Vertex or Cz (Figure 2), by measuring the distance of nasion to inion and marking halfway using a skin marker 11.</li>
</ol>
4. Electrodes Positioning in the Cap
<ol>
	<li>Put saline solution on the tDCS sponge-electrodes. The sponge-electrodes should be soaked with saline solution 11 before wearing the head cap. For a 25-35 cm2 sponge, approximately 6 ml of solution per side should suffice. It is important to periodically refill the sponge-electrode with saline solution in the case of a prolonged stimulation protocol.</li>
	<li>The EEG and the tDCS electrodes have to be fixed in the cap before the subject is physically wearing it.</li>
	<li>For further details on general tDCS electrodes preparation and positioning see 11.</li>
</ol>
5. Wearing the Cap and Fixing the Control Box on it
<ol>
	<li>Make sure the subject is seated comfortably.</li>
	<li>Place the cap in a way that the Vertex (measured on the head) matches the Cz point on the cap. Important: this is only valid for average size heads. Three different cap sizes are available, if necessary.</li>
	<li>Fill the EEG electrodes with gel using a curved syringe.</li>
	<li>Connect EEG and tDCS electrodes to the Control Box wires. The Control Box has to be fixed to the posterior part of the cap. Use channels 1 and 2 for stimulation and the remaining ones (3 to 8) for EEG recording. Their position in the cap will depend on the desired experimental approach for both recording and stimulation (Table 1). As a demonstration, the classical left anodal tDCS set up will be displayed: anode = M1; cathode = Supraorbital contralateral. For this montage, connect the anode (red sponge-electrode) to the C3 and the cathode (black sponge-electrode) to Fp2.</li>
	<li>Put the reference electrodes to one of the mastoids making sure they do not touch one another and attached them to the wires (CMS, Common Mode Sense and DRL, Driven Right Leg) from the Control Box.</li>
</ol>
6. Stimulation and Recording Set Up
<ol>
	<li>In order to configure parameters of stimulation and check recording, the software needs to be properly installed according to the manufacturer's instruction.</li>
	<li>Press "STIMULATION" in the horizontal bar on upper screen (Figure 3).</li>
	<li>Select the option "EDIT" in the upper screen and choose "tDCS" or "sham" out of other electrical stimulation techniques, such as "transcranial alternating current stimulation (tACS)" and "transcranial random noise stimulation" (tRNS) (Figure 3a). The details of such approaches is out of the scope of this paper and are better discussed elsewhere 12, 13.</li>
	<li>Choose the total duration of the electrical stimulation, usually 20 min (Figure 3b) and at intensity of 2mA. Note: the device is capable of stimulating electrically and recording EEG signals for up to 1 hr, if needed.</li>
	<li>Choose the electrode positioning according to channels (Figure 3c).</li>
	<li>Configure tDCS and EEG channels (Figure 3d) according to the experimental approach (Table 1). The reference electrodes are labeled as DRL and CMS. Be sure to select the right function for each channel. Important: label the active stimulation electrode as "anode" or "cathode" and its reference as "return" (Figure 3d).</li>
	<li>In the bar menu located in the lower part of the screen choose the duration of the ramp down and ramp up period, usually 30 sec (Figure 3e). During this step you will also select the duration of pre- and post EEG recordings (Figure 3f). The EEG recording is not dependent on the stimulation and can be programmed to start before, during or after the end of the tDCS.</li>
	<li>To check electrode impedance press "STIMULATION" in the upper part of the screen and then "MOUNT" in the left side of the screen and then "START IMPEDANCE CHECK" (Figure 4).</li>
</ol>
7. Start the Device
<ol>
	<li>The subject should be relaxed, comfortable and awake during the procedure.</li>
	<li>Press "LAUNCH" in the lower part of the screen (Figure 5a).</li>
	<li>Check if the vertical gray bar is moving forward before (Figure 5b), during (5c) and after (5d) the tDCS.</li>
	<li>Re-check electrode impedances (Figure 5e).</li>
	<li>Press "Abort" to suspend the stimulation at any moment, if needed (Figure 5f).</li>
</ol>
8. Record EEG Data
<ol>
	<li>Press "EEG" in the upper screen to check if the EEG signals are visible and without any artifacts (Figure 6, yellow bracket). The signals can be filtered from 2 to 15 Hz in order to clarify the EEG traces.</li>
	<li>EEG recording will start automatically as soon as the icon LAUNCH is pressed.</li>
	<li>During the stimulation the ongoing EEG can be checked in three different panels, localized at the vertical menu bar (Figure 6).
	<ol>
		<li>Time domain (Figure 6): see the data as it is being received, choosing different time and voltage scales.</li>
		<li>Spectrum (Figure 7): select a channel and visualize the power spectrum online i.e. the screen shows the power of each EEG frequency by real-time Fast Fourier Transform (FFT) analysis.</li>
		<li>Spectrogram (Figure 8): visualize the power spectrogram online by getting the information about the frequency content of the recorded EEG as a function of time (time-frequency analysis).</li>
	</ol>
	</li>
	<li>In any of the aforementioned options the researcher is able to filter the EEG activity (Figure 6, yellow rectangle) into specific frequency bands (Table 2). Most studies addressing the effects of tDCS on EEG activity have used this approach for data analysis (Table 3).</li>
</ol>

<ol>
	<li>Fregni, F., Pascual-Leone, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Technology+insight:+noninvasive+brain+stimulation+in+neurology-perspectives+on+the+therapeutic+potential+of+rTMS+and+tDCS.">Technology insight: noninvasive brain stimulation in neurology-perspectives on the therapeutic potential of rTMS and tDCS.</a> Nat. Clin. Pract. Neurol. 3, 383-393 (2007).</li><li>Nitsche, M. A., Cohen, L. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transcranial+direct+current+stimulation:+State+of+the+art.">Transcranial direct current stimulation: State of the art.</a> Brain Stimul. 1, 206-223 (2008).</li><li>Nitsche, M. A., Paulus, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sustained+excitability+elevations+induced+by+transcranial+DC+motor+cortex+stimulation+in+humans.">Sustained excitability elevations induced by transcranial DC motor cortex stimulation in humans.</a> Neurology. 57, 1899-1901 (2001).</li><li>Kwon, Y. H., Ko, M. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Primary+motor+cortex+activation+by+transcranial+direct+current+stimulation+in+the+human+brain.">Primary motor cortex activation by transcranial direct current stimulation in the human brain.</a> Neurosci. Lett. 435, 56-59 (2008).</li><li>Ardolino, G., Bossi, B., Barbieri, S., Priori, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Non-synaptic+mechanisms+underlie+the+after-effects+of+cathodal+transcutaneous+direct+current+stimulation+of+the+human+brain.">Non-synaptic mechanisms underlie the after-effects of cathodal transcutaneous direct current stimulation of the human brain.</a> J. Physiol. 568, 653-663 (2005).</li><li>Marshall, L., Kirov, R., Brade, J., M&#246;lle, M., Born, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transcranial+electrical+currents+to+probe+EEG+brain+rhythms+and+memory+consolidation+during+sleep+in+humans.">Transcranial electrical currents to probe EEG brain rhythms and memory consolidation during sleep in humans.</a> PLoS One. 6, 16905 (2011).</li><li>Brunoni, A. R., Nitsche, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Clinical+research+with+transcranial+direct+current+stimulation+(tDCS):+challenges+and+future+directions.">Clinical research with transcranial direct current stimulation (tDCS): challenges and future directions.</a> Brain Stimul. 5, 175-195 (2012).</li><li>Nuwer, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Assessment+of+digital+EEG,+quantitative+EEG,+and+EEG+brain+mapping:+report+of+the+American+Academy+of+Neurology+and+the+American+Clinical+Neurophysiology+Society.">Assessment of digital EEG, quantitative EEG, and EEG brain mapping: report of the American Academy of Neurology and the American Clinical Neurophysiology Society.</a> Neurology. 49, 277-292 (1997).</li><li>Morrell, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=RNS+System+in+Epilepsy+Study+Group.+Responsive+cortical+stimulation+for+the+treatment+of+medically+intractable+partial+epilepsy.">RNS System in Epilepsy Study Group. Responsive cortical stimulation for the treatment of medically intractable partial epilepsy.</a> Neurology. 77, 1295-1304 (2011).</li><li>Ber&#233;nyi, A., Belluscio, M., Mao, D., Buzs&#225;ki, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Closed-loop+control+of+epilepsy+by+transcranial+electrical+stimulation.">Closed-loop control of epilepsy by transcranial electrical stimulation.</a> Science. 337, 735-737 (2012).</li><li>DaSilva, A. F., Volz, M. S., Bikson, M., Fregni, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrode+positioning+and+montage+in+transcranial+direct+current+stimulation.">Electrode positioning and montage in transcranial direct current stimulation.</a> J. Vis. Exp. (51), e2744 (2011).</li><li>Antal, A., Boros, K., Poreisz, C., Chaieb, L., Terney, D., Paulus, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparatively+weak+after-effects+of+transcranial+alternating+current+stimulation+(tACS)+on+cortical+excitability+in+humans.">Comparatively weak after-effects of transcranial alternating current stimulation (tACS) on cortical excitability in humans.</a> Brain Stimul. 1, 97-105 (2008).</li><li>Terney, D., Chaieb, L., Moliadze, V., Antal, A., Paulus, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Increasing+human+brain+excitability+by+transcranial+high-frequency+random+noise+stimulation.">Increasing human brain excitability by transcranial high-frequency random noise stimulation.</a> J. Neurosci. 28, 14147-14155 (2008).</li><li>Boggio, P. S., Rigonatti, S. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+randomized,+double-blind+clinical+trial+on+the+efficacy+of+cortical+direct+current+stimulation+for+the+treatment+of+major+depression.">A randomized, double-blind clinical trial on the efficacy of cortical direct current stimulation for the treatment of major depression.</a> Int. J. Neuropsychopharmacol. 11, 249-254 (2008).</li><li>Loo, C. K., Alonzo, A., Martin, D., Mitchell, P. B., Galvez, V., Sachdev, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transcranial+direct+current+stimulation+for+depression:+3-week,+randomised,+sham-controlled+trial.">Transcranial direct current stimulation for depression: 3-week, randomised, sham-controlled trial.</a> Br. J. Psychiatry. 200, 52-59 (2012).</li><li>Boggio, P. S., Rocha, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Noninvasive+brain+stimulation+with+high-frequency+and+low-intensity+repetitive+transcranial+magnetic+stimulation+treatment+for+posttraumatic+stress+disorder.">Noninvasive brain stimulation with high-frequency and low-intensity repetitive transcranial magnetic stimulation treatment for posttraumatic stress disorder.</a> J. Clin. Psychiatry. 71, 992-999 (2010).</li><li>Goldman, R. L., Borckardt, J. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Prefrontal+cortex+transcranial+direct+current+stimulation+(tDCS)+temporarily+reduces+food+cravings+and+increases+the+self-reported+ability+to+resist+food+in+adults+with+frequent+food+craving.">Prefrontal cortex transcranial direct current stimulation (tDCS) temporarily reduces food cravings and increases the self-reported ability to resist food in adults with frequent food craving.</a> Appetite. 56, 741-746 (2011).</li><li>Boggio, P. S., Zaghi, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modulation+of+risk-taking+in+marijuana+users+by+transcranial+direct+current+stimulation+(tDCS)+of+the+dorsolateral+prefrontal+cortex+(DLPFC).">Modulation of risk-taking in marijuana users by transcranial direct current stimulation (tDCS) of the dorsolateral prefrontal cortex (DLPFC).</a> Drug Alcohol Depend. 112, 220-225 (2010).</li><li>Boggio, P. S., Sultani, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Prefrontal+cortex+modulation+using+transcranial+DC+stimulation+reduces+alcohol+craving:+a+double-blind,+sham-controlled+study.">Prefrontal cortex modulation using transcranial DC stimulation reduces alcohol craving: a double-blind, sham-controlled study.</a> Drug Alcohol Depend. 92, 55-60 (2008).</li><li>Fregni, F., Liguori, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cortical+stimulation+of+the+prefrontal+cortex+with+transcranial+direct+current+stimulation+reduces+cue-provoked+smoking+craving:+a+randomized,+sham-controlled+study.">Cortical stimulation of the prefrontal cortex with transcranial direct current stimulation reduces cue-provoked smoking craving: a randomized, sham-controlled study.</a> J. Clin. Psychiatry. 69, 32-40 (2008).</li><li>Fregni, F., Gimenes, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+randomized,+sham-controlled,+proof+of+principle+study+of+transcranial+direct+current+stimulation+for+the+treatment+of+pain+in+fibromyalgia.">A randomized, sham-controlled, proof of principle study of transcranial direct current stimulation for the treatment of pain in fibromyalgia.</a> Arthritis Rheum. 54, 3988-3998 (2006).</li><li>Fregni, F., Marcondes, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transient+tinnitus+suppression+induced+by+repetitive+transcranial+magnetic+stimulation+and+transcranial+direct+current+stimulation.">Transient tinnitus suppression induced by repetitive transcranial magnetic stimulation and transcranial direct current stimulation.</a> Eur. J. Neurol. 13, 996-1001 (2006).</li><li>Antal, A., Kriener, N., Lang, N., Boros, K., Paulus, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cathodal+transcranial+direct+current+stimulation+of+the+visual+cortex+in+the+prophylactic+treatment+of+migraine.">Cathodal transcranial direct current stimulation of the visual cortex in the prophylactic treatment of migraine.</a> Cephalalgia. 31, 820-828 (2011).</li><li>Fregni, F., Otachi, P. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+randomized+clinical+trial+of+repetitive+transcranial+magnetic+stimulation+in+patients+with+refractory+epilepsy.">A randomized clinical trial of repetitive transcranial magnetic stimulation in patients with refractory epilepsy.</a> Ann. Neurol. 60, 447-455 (2006).</li><li>Benninger, D. H., Lomarev, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transcranial+direct+current+stimulation+for+the+treatment+of+Parkinson's+disease.">Transcranial direct current stimulation for the treatment of Parkinson's disease.</a> J. Neurol. Neurosurg. Psychiatry. 81, 1105-1111 (2010).</li><li>Boggio, P. S., Nunes, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Repeated+sessions+of+noninvasive+brain+DC+stimulation+is+associated+with+motor+function+improvement+in+stroke+patients.">Repeated sessions of noninvasive brain DC stimulation is associated with motor function improvement in stroke patients.</a> Restor. Neurol. Neurosci. 25, 123-129 (2007).</li><li>Lindenberg, R., Renga, V., Zhu, L. L., Nair, D., Schlaug, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bihemispheric+brain+stimulation+facilitates+motor+recovery+in+chronic+stroke+patients.">Bihemispheric brain stimulation facilitates motor recovery in chronic stroke patients.</a> Neurology. 75, 2176-2184 (2010).</li><li>Fregni, F., Boggio, P. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Anodal+transcranial+direct+current+stimulation+of+prefrontal+cortex+enhances+working+memory.">Anodal transcranial direct current stimulation of prefrontal cortex enhances working memory.</a> Exp. Brain Res. 166, 23-30 (2005).</li><li>Shafi, M. M., Westover, M. B., Fox, M. D., Pascual-Leone, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Exploration+and+modulation+of+brain+network+interactions+with+noninvasive+brain+stimulation+in+combination+with+neuroimaging.">Exploration and modulation of brain network interactions with noninvasive brain stimulation in combination with neuroimaging.</a> Eur. J. Neurosci. 35, 805-825 (2012).</li><li>Wirth, M., Rahman, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+transcranial+direct+current+stimulation+(tDCS)+on+behaviour+and+electrophysiology+of+language+production.">Effects of transcranial direct current stimulation (tDCS) on behaviour and electrophysiology of language production.</a> Neuropsychologia. 49, 3989-3998 (2011).</li><li>Keeser, D., Padberg, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Prefrontal+direct+current+stimulation+modulates+resting+EEG+and+event-related+potentials+in+healthy+subjects:+a+standardized+low+resolution+tomography+(sLORETA)+study.">Prefrontal direct current stimulation modulates resting EEG and event-related potentials in healthy subjects: a standardized low resolution tomography (sLORETA) study.</a> Neuroimage. 55, 644-657 (2011).</li><li>Zaehle, T., Sandmann, P., Thorne, J. D., J&#228;ncke, L., Herrmann, C. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transcranial+direct+current+stimulation+of+the+prefrontal+cortex+modulates+working+memory+performance:+combined+behavioral+and+electrophysiological+evidence.">Transcranial direct current stimulation of the prefrontal cortex modulates working memory performance: combined behavioral and electrophysiological evidence.</a> BMC Neurosci. 12, 979-984 (2011).</li><li>Polan&#237;a, R., Nitsche, M. A., Paulus, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modulating+functional+connectivity+patterns+and+topological+functional+organization+of+the+human+brain+with+transcranial+direct+current+stimulation.">Modulating functional connectivity patterns and topological functional organization of the human brain with transcranial direct current stimulation.</a> Hum. Brain Mapp. 32, 1236-1249 (2011).</li><li>Maeoka, H., Matsuo, A., Hiyamizu, M., Morioka, S., Ando, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Influence+of+transcranial+direct+current+stimulation+of+the+dorsolateral+prefrontal+cortex+on+pain+related+emotions:+a+study+using+electroencephalographic+power+spectrum+analysis.">Influence of transcranial direct current stimulation of the dorsolateral prefrontal cortex on pain related emotions: a study using electroencephalographic power spectrum analysis.</a> Neurosci. Lett. 512, 12-16 (2012).</li><li>Isley, M. R., Edmonds, H. L., Stecker, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=American+Society+of+Neurophysiological+Monitoring.+Guidelines+for+intraoperative+neuromonitoring+using+raw+(analog+or+digital+waveforms)+and+quantitative+electroencephalography:+a+position+statement+by+the+American+Society+of+Neurophysiological+Monitoring.">American Society of Neurophysiological Monitoring. Guidelines for intraoperative neuromonitoring using raw (analog or digital waveforms) and quantitative electroencephalography: a position statement by the American Society of Neurophysiological Monitoring.</a> J. Clin. Monit. Comput. 23, 369-390 (2009).</li><li>Faria, P., Leal, A., Miranda, P. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparing+different+electrode+configurations+using+the+10-10+international+system+in+tDCS:+a+finite+element+model+analysis.">Comparing different electrode configurations using the 10-10 international system in tDCS: a finite element model analysis.</a> Conf Proc. IEEE Eng. Med. Biol. Soc. , 1596-1599 (2009).</li><li>Dmochowski, J. P., Datta, A., Bikson, M., Su, Y., Parra, L. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optimized+multi-electrode+stimulation+increases+focality+and+intensity+at+target.">Optimized multi-electrode stimulation increases focality and intensity at target.</a> J. Neural. Eng. 8, 046011 (2011).</li><li>Flink, R., Pedersen, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Guidelines+for+the+use+of+EEG+methodology+in+the+diagnosis+of+epilepsy.">Guidelines for the use of EEG methodology in the diagnosis of epilepsy.</a> International League Against Epilepsy: commission report. Acta Neurol. Scand. 106, 1-7 (2002).</li></ol>

This work was partially supported by Neuroelectric, Barcelona Spain, which produces the instrument used in this article.

Safety issues
Initially, subjects should be screened for any contraindications for tDCS 11. Check also for skin lesions or diseases, since there is evidence of tDCS induced lesions according to skin integrity. If tDCS is strongly indicated over a lesioned area, it is possible to do it at lower intensity, i.e. 0.5-1.0 mA. However, it is not guaranteed that this will prevent skin irritations or lesions. Thus, the condition of the skin under the electrodes should be inspected before and after tDCS 2.
Impedance and electrodes
Electrode impedances should be as low as possible. This reduces the risk for internal and external noise interference or distorted signals. Impedances should also be rechecked whenever there is any artifact present in the signal 37.
All electrodes must be of good quality with intact surfaces. Reusable electrodes with inconsistent surfaces can create uneven current densities. All surface electrodes should be applied with sufficient conductive gel to ensure low impedances, and the impedances should be checked for artifacts 37.
Closed-loop systems
A closed-loop system is a system capable of diagnosing electrophysiological abnormalities and treating them promptly 8, 10. An illustrative example is the EEG spike detector for an oncoming seizure. This principle has been successfully applied in patients with severe epilepsy. Morrell and colleagues 9 treated 191 subjects with intractable epilepsy using a brain implanted stimulator and observed a significant reduction in seizure frequency as well as improvements in quality of life. Despite the success, invasive procedures are associated with risks and complications such as local infection or unwanted mood or cognitive effects and therefore an alternative, non-invasive approach is desirable. Hence, the present device may represent an interesting option for those patients who need rapid neurophysiological diagnosis and prompt treatment, such as epileptic patients.
The closed-loop system application might not be restricted to patients with epilepsy only. A number of recent studies have suggested that EEG alterations may be markers of various neuropsychiatric diseases 30. Using a combination of tDCS and EEG could also be useful for optimizing the parameters of stimulation. Such algorithms are still undeveloped, but the combination of findings from EEG and tDCS studies may help in such development.
Compared to TMS, which is another non-invasive brain stimulation technique, tDCS is considered much more suitable for therapeutic purposes mainly because of its low cost and relative portability. In addition, having a system that uses a head cap with pre-determined electrode locations can standardize location of stimulation and improve results. Another advantage of this device is the possibility to stimulate more than one site at the same time, which has been found to be clinically superior than conventional stimulation according to some authors 38, 39.
Although the device shows clear advantages, some limitations need to be addressed in order to improve the device for the future. First, the device cannot stimulate and record EEG signals in the same location simultaneously (See Figure 9). Second, the number of channels available to record EEG is low. The usual recommendation is to use at least 16-channels for an adequate EEG study 40 and even more channels for electro-oculography to detect eye movement artifacts. Indeed, in the past few years there has been a tendency to increase the number of channels in EEG/tDCS studies (Table 3). Although the low number of channels might affect sensibility in detecting dynamic changes in cortical excitability, such system may still be useful for finding algorithms for specific electrode locations.

Transcranial direct current stimulation (tDCS) is a technique that uses weak and direct electric currents delivered continuously through the scalp to induce changes in cortical excitability 1, 2. Using motor evoked potentials as a marker of motor cortex excitability, Nitsche and Paulus3 demonstrated that the direction of the tDCS effects over the brain is polarity-specific: cathodal stimulation induces a decrease in cortical excitability, whereas anodal stimulation induces an increase in cortical excitability. This effect on cortical excitability can last for over an hour following stimulation. These tDCS-induced changes in cortical excitability can result in significant behavioral effects. One important issue is the variability of tDCS effects on behavior. There are several reasons to explain this variability. Studies on fMRI 4 and electroencephalography (EEG) 5,6 reveal that although tDCS has the most activating effect on the underlying cortex, the stimulation evokes widespread changes in other regions of the brain. In addition, it has been shown that tDCS effects depend on the state of baseline cortical activity 7. Therefore, given these sources of variability, the use of better surrogates to measure the effects of tDCS is desirable.
In this context, we propose the use of concomitant EEG monitoring to provide real-time data on the impact of tDCS on cortical excitability for several reasons. First, to optimize the stimulation parameters of tDCS. Second, to provide insights into new targets for therapies. Third, to assure safety during brain stimulation, especially in children. Fourth, to aid in the early detection and treatment of seizures in patients with intractable epilepsy i.e. closed-loop system. Finally, this device might also have a potential application in brain-computer interface systems.
Due to the critical role of monitoring cortical excitability changes related to non-invasive brain stimulation, the purpose of this article is to demonstrate how to combine the use of tDCS with EEG by means of a novel device (Starstim&Ograve; - Neuroelectrics Instrument Controller, v 1.0; Rev 2012-08-01, Neurolelectrics, Barcelona, Spain). It should be noted that this article does not provide details of tDCS application. For a complete understanding of the application of this technique we recommend reading the article on tDCS from DaSilva et al. 11

<table border="1">
<tbody>
 <tr>
 <td>Name</td>
 <td>Company</td>
 <td>Catalog Number</td>
 <td>Comments</td>
 </tr>
 <tr>
 <td></td>
 <td></td>
 <td></td>
 <td>Material</td>
 </tr>
 <tr>
 <td>Neoprene HeadCap </td>
 <td>Neuroelectrics</td>
 <td>NE019 </td>
 <td>1</td>
 </tr>
 <tr>
 <td>Neoprene Headband</td>
 <td>Neuroelectrics</td>
 <td>NE020</td>
 <td>1</td>
 </tr>
 <tr>
 <td>Frontal dry electrode front-end</td>
 <td>Neuroelectrics</td>
 <td>NE021</td>
 <td>4</td>
 </tr>
 <tr>
 <td>Gel electrode front-end</td>
 <td>Neuroelectrics</td>
 <td>NE022</td>
 <td>8</td>
 </tr>
 <tr>
 <td>Gel Bottle 60cl</td>
 <td>Neuroelectrics</td>
 <td>NE016</td>
 <td>1</td>
 </tr>
 <tr>
 <td>Stimulation electrode Pi cm2</td>
 <td>Neuroelectrics</td>
 <td>NE024</td>
 <td>8</td>
 </tr>
 <tr>
 <td>Saline solution bottle 100ml</td>
 <td>Neuroelectrics</td>
 <td>NE033</td>
 <td>1</td>
 </tr>
 <tr>
 <td>Sponge electrode fron-end 25 cm2</td>
 <td>Neuroelectrics</td>
 <td>NE026</td>
 <td>4</td>
 </tr>
 <tr>
 <td>Adhesive Electrode Front-end</td>
 <td>Neuroelectrics</td>
 <td>NE025</td>
 <td>25</td>
 </tr>
 <tr>
 <td>USB Bluetooth Dongle</td>
 <td>Neuroelectrics</td>
 <td>NE031</td>
 <td>1</td>
 </tr>
 <tr>
 <td>USB card with software</td>
 <td>Neuroelectrics</td>
 <td>NE015</td>
 <td>1</td>
 </tr>
 <tr>
 <td>Curved Syringe</td>
 <td>Neuroelectrics</td>
 <td>NE014</td>
 <td>1</td>
 </tr>
 <tr>
 <td>microUSB NECBOX charger</td>
 <td>Neuroelectrics</td>
 <td>NE013 </td>
 <td>1</td>
 </tr>
 <tr>
 <td>Electrode cable</td>
 <td>Neuroelectrics</td>
 <td>NE017 10</td>
 <td>1</td>
 </tr>
 <tr>
 <td></td>
 <td></td>
 <td></td>
 <td>Material Name</td>
 </tr>
 <tr>
 <td>StarStim NECBOX </td>
 <td>Neuroelectrics</td>
 <td>NE012 </td>
 <td>1</td>
 </tr>
 </tbody>
</table>

simultaneous eeg monitoring during transcranial direct current stimulation

Transcranial direct current stimulation (tDCS) is a technique that delivers weak electric currents through the scalp. This constant electric current induces shifts in neuronal membrane excitability, resulting in secondary changes in cortical activity. Although tDCS has most of its neuromodulatory effects on the underlying cortex, tDCS effects can also be observed in distant neural networks. Therefore, concomitant EEG monitoring of the effects of tDCS can provide valuable information on the mechanisms of tDCS. In addition, EEG findings can be an important surrogate marker for the effects of tDCS and thus can be used to optimize its parameters. This combined EEG-tDCS system can also be used for preventive treatment of neurological conditions characterized by abnormal peaks of cortical excitability, such as seizures. Such a system would be the basis of a non-invasive closed-loop device. In this article, we present a novel device that is capable of utilizing tDCS and EEG simultaneously. For that, we describe in a step-by-step fashion the main procedures of the application of this device using schematic figures, tables and video demonstrations. Additionally, we provide a literature review on clinical uses of tDCS and its cortical effects measured by EEG techniques.

tDCS is currently being investigated as a therapeutic instrument for varied neurological conditions, which includes major depression 14, 15, post-traumatic stress disorder 16, craving for food 17, marijuana 18, alcohol 19 and smoking 20, as well as pain 21, tinnitus 22, migraine 23, epilepsy 24, Parkinson's disease 25, 26, stroke rehabilitation 27, 28 and cognitive dysfunction 6, 29. Table 1 shows the evidence-based tDCS electrode montages to be used as treatment for different clinical conditions.
In most cases, clinical improvement after tDCS is mainly attributed to its cortical effects. There are several ways to quantify cortical changes and the most frequently used ones are functional magnetic resonance imaging (fMRI), TMS-indexed cortical excitability and the electroencephalography (EEG). In comparison with fMRI, EEG has poorer spatial resolution, but superior temporal resolution 30, reflecting timing of neuronal activity more accurately. In addition, as compared with TMS-indexed cortical excitability, EEG provides a greater spatial resolution. For instance, using the tDCS/EEG device, it is possible to detect ongoing changes on the raw EEG in response to tDCS. Figure 9 shows the attenuation of cortical activity, mainly on the parietal region, after the tDCS was turned on (channels C3 and C4). Note that during stimulation it is not possible to record brain activity in the same channels used for stimulation.
The effects of tDCS on EEG have been recently studied by several authors (see Table 3), but only one has applied tDCS and EEG concomitantly 31. Most of the studies showed significant EEG changes upon tDCS by analyzing the EEG power spectrum in response to active versus sham-tDCS. Using power spectrum analysis, EEG signals can be decomposed into a sum of pure frequency components using FFT analysis. In this way, the signals can be analyzed in terms of its power spectrum, which provides information on the signal's power at each frequency (Table 2).
Figure 7 shows a representative example of an ongoing EEG activity during tDCS (red bracket on the bottom) and after FFT analysis (red circle). The first peak activity corresponds to theta (5-7 Hz) and the second to alpha (8-10 Hz) band frequencies. The amplitude of EEG peaks is measured in &mu;V2.
Another example comes from the study by Maeoka et al. 36, in which the authors found a local decrease in alpha and an increase in beta band amplitudes after anodal stimulation of the dorsolateral prefrontal cortex combined with emotional stress.
Figure 10 shows an illustrative example of the effects of tDCS on quantitative EEG (power spectrum). The size of frontal alpha amplitude was significantly higher in response to active-tDCS when compared to sham-tDCS of the left dorsolateral prefrontal cortex.
Therefore, using the automatic FFT analysis (Figure 7) the investigator is able to determine and measure the amplitude of the predominant EEG frequency activities (delta, theta, alpha, beta, gamma) during and after tDCS. Depending on the region of stimulation and other experimental conditions, the amplitude of specific EEG frequency bands is expected to change after tDCS (Table 3). Indeed, adding the FFT analysis function to the EEG recording during tDCS offers a unique opportunity to understand the cortical neuromodulatory effects in real time.
Finally, EEG signals can be analyzed with a technique called a time-frequency based, or spectrogram image. This technique has been considered promising for research purposes; however, this type of EEG analysis is still not fully validated for diagnostic intentions and should be interpreted with caution for this purpose 8.
Figure 8 shows an illustrative example of an EEG spectrogram processed by the same device.
<img alt="Figure 1" src="/files/ftp_upload/50426/50426fig1.jpg" /> 
 Figure 1. List of required materials for simultaneous EEG monitoring during tDCS: neoprene cap, Control Box, cables, electrodes, measurement tape, saline solution and Bluetooth USB.
<img alt="Figure 2" src="/files/ftp_upload/50426/50426fig2.jpg" /> 
 Figure 2. Localization of vertex (Cz) on the scalp 11: Measure the distance of nasion to inion and mark halfway using a skin marker.
<img alt="Figure 3" src="/files/ftp_upload/50426/50426fig3.jpg" /> 
 Figure 3. Stimulation Screenshot: a) Electrical stimulation mode (tDCS, tACS, tRNS, sham); b) Total duration of electrical stimulation; c) Electrode positioning according to channels; d) tDCS and EEG channel configuration; e) tDCS ramping duration; f) EEG recording durations.
<img alt="Figure 4" src="/files/ftp_upload/50426/50426fig4.jpg" /> 
 Figure 4. Mount Screenshot: Check electrodes impedance before stimulation begins.
<img alt="Figure 5" src="/files/ftp_upload/50426/50426fig5.jpg" /> 
 Figure 5. Launch Screenshot: a) LAUNCH button; b) Vertical gray bar before tDCS; c) Vertical gray bar during tDCS; d) Vertical gray bar after tDCS; e) Impedance re-checking; f) ABORT button.
<img alt="Figure 6" src="/files/ftp_upload/50426/50426fig6.jpg" /> 
 Figure 6. EEG Time domain: check the baseline ongoing EEG activity and select EEG band frequencies if needed (yellow arrow at the right bottom).
<img alt="Figure 7" src="/files/ftp_upload/50426/50426fig7.jpg" /> 
 Figure 7. EEG power spectrum: check the predominant EEG frequency band (red circle) after automatic Fast Fourier Transform (FFT) analysis over the raw ongoing EEG activity (red rectangle on the bottom).
<img alt="Figure 8" src="/files/ftp_upload/50426/50426fig8.jpg" /> 
 Figure 8. EEG spectrogram: EEG signals (red rectangle on the bottom) can also be transformed into images (red circle) using a technique called time-frequency based.
<img alt="Figure 9" src="/files/ftp_upload/50426/50426fig9.jpg" /> 
 Figure 9. Attenuation of parietal EEG activity in response to anodal tDCS (Anode = C3; Cathode = C4). Note that during stimulation it not possible to record brain activity in the same channels used for stimulation. <a href="https://www.jove.com/files/ftp_upload/50426/50426fig9large.jpg" target="_blank">Click here to view larger figure</a>.
<img alt="Figure 10" src="/files/ftp_upload/50426/50426fig10.jpg" /> 
 Figure 10. tDCS effects on EEG power spectrum: Note differences in frontal alpha (a) and beta (b) amplitude in response to active-tDCS when compared to sham-tDCS over the left dorsolateral prefrontal cortex.
<table border="1">
	<tbody>
		<tr>
			<td>Disease</td>
			<td>Authors</td>
			<td>Anode electrode positioning</td>
			<td>Cathode electrode positioning</td>
		</tr>
		<tr>
			<td>Depression</td>
			<td>Boggio et al., 2008; Loo et al., 2012</td>
			<td>DLPFC</td>
			<td>Supraorbital</td>
		</tr>
		<tr>
			<td>Pain</td>
			<td>Fregni et al., 2006</td>
			<td>M1</td>
			<td>Supraorbital</td>
		</tr>
		<tr>
			<td rowspan="3">Stroke</td>
			<td>Lindenberg et al., 2010</td>
			<td>M1</td>
			<td>M1</td>
		</tr>
		<tr>
			<td rowspan="2">Boggio et al., 2007</td>
			<td>M1 (affected side)</td>
			<td>Supraorbital</td>
		</tr>
		<tr>
			<td>Supraorbital</td>
			<td>MI (non-affected side)</td>
		</tr>
		<tr>
			<td>Tinnitus</td>
			<td>Fregni et al., 2006</td>
			<td>LTA</td>
			<td>Supraorbital</td>
		</tr>
		<tr>
			<td rowspan="2">Parkinson</td>
			<td>Benninger et al., 2010</td>
			<td>M1/DLPFC</td>
			<td>Mastoid</td>
		</tr>
		<tr>
			<td>Fregni et al., 2006</td>
			<td>M1</td>
			<td>Supraorbital</td>
		</tr>
		<tr>
			<td>Migraine</td>
			<td>Antal et al., 2011</td>
			<td>V1</td>
			<td>Oz</td>
		</tr>
		<tr>
			<td>Alcohol abuse</td>
			<td>Boggio et al., 2008</td>
			<td>R/L - DLPFC</td>
			<td>L/R - DLPFC</td>
		</tr>
	</tbody>
</table>
Table 1. tDCS electrode montages in different clinical conditions. Legends: LTA, left temporoparietal area; V1, Visual cortex; DLPFC, Dorsolateral prefrontal cortex; M1, Motor cortex, R, Right; L, Left.
<table border="1">
	<tbody>
		<tr>
			<td>Bands</td>
			<td>Symbol</td>
			<td>Frequency (Hz)</td>
			<td>Best recording site</td>
			<td>More prominent during&hellip;</td>
		</tr>
		<tr>
			<td>Delta</td>
			<td>&delta;</td>
			<td>1-4</td>
			<td>Frontal (adults), Posterior (children)</td>
			<td>Deep stages of sleep (3 and 4)</td>
		</tr>
		<tr>
			<td>Theta</td>
			<td>&theta;</td>
			<td>5-7</td>
			<td>Diffuse in the scalp</td>
			<td>Drowsiness</td>
		</tr>
		<tr>
			<td>Alpha</td>
			<td>&alpha;</td>
			<td>8-12</td>
			<td>Posterior regions</td>
			<td>Awakens, with eyes closed</td>
		</tr>
		<tr>
			<td>Beta</td>
			<td>&beta;</td>
			<td>13-30</td>
			<td>Frontal</td>
			<td>Mental effort, deep sleep</td>
		</tr>
		<tr>
			<td>Gamma</td>
			<td>&gamma;</td>
			<td>31-45</td>
			<td>Somato-sensory cortex</td>
			<td>Short term memory tasks and tactile stimulation</td>
		</tr>
	</tbody>
</table>
Table 2. EEG frequency bands.
<table border="1">
	<tbody>
		<tr>
			<td>Authors</td>
			<td>Anode electrode positioning</td>
			<td>Cathode electrode positioning </td>
			<td>EEG Channels (number)</td>
			<td>Main Findings</td>
		</tr>
		<tr>
			<td>Ardolino et al., 2005</td>
			<td>Fp1</td>
			<td>C4</td>
			<td>4</td>
			<td>Bilateral increase of frontal delta and theta bands.</td>
		</tr>
		<tr>
			<td>Keeser et al., 2011</td>
			<td>F3</td>
			<td>Fp2</td>
			<td>25</td>
			<td>Decrease in frontal and prefrontal delta band.</td>
		</tr>
		<tr>
			<td>Marshall et al., 2011</td>
			<td>F3/F4</td>
			<td>Mastoids</td>
			<td>7</td>
			<td>- Non-REM sleep: frontal decrease of delta band. 
			- REM sleep: global increase of gamma band.</td>
		</tr>
		<tr>
			<td>Wirth et al., 2011</td>
			<td>F3</td>
			<td>Right shoulder</td>
			<td>52</td>
			<td>Global decrease in delta band.</td>
		</tr>
		<tr>
			<td>Zaehle et al., 2011</td>
			<td>F3</td>
			<td>Mastoids</td>
			<td>32</td>
			<td>- Anodal: local increase of theta and alpha bands. 
			- Cathodal: local decrease of theta and alpha bands.</td>
		</tr>
		<tr>
			<td>Jacobson et al., 2011</td>
			<td>Between T4-Fz</td>
			<td>Fp1</td>
			<td>27</td>
			<td>Decrease in right frontal theta band.</td>
		</tr>
		<tr>
			<td>Polania et al., 2011</td>
			<td>C3</td>
			<td>Fp3</td>
			<td>62</td>
			<td>- Global synchronization of all studied bands.</td>
		</tr>
		<tr>
			<td>Maeoka et al., 2012</td>
			<td>F3</td>
			<td>Fp2</td>
			<td>128</td>
			<td>Local increase in beta and decreased alpha bands.</td>
		</tr>
	</tbody>
</table>
Table 3. Studies analyzing the effects of tDCS on EEG recordings.

Watch this Scientific Journal Video about Simultaneous EEG Monitoring During Transcranial Direct Current Stimulation at JoVE.com

Simultaneous EEG Monitoring During Transcranial Direct Current Stimulation

Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that has shown initial therapeutic effects in several neurological conditions. The main mechanism underlying these therapeutic effects is the modulation of cortical excitability. Therefore, online monitoring of cortical excitability would help guide stimulation parameters and optimize its therapeutic effects. In the present article we review the use of a novel device that combines simultaneous tDCS and EEG monitoring in real time.

Transcranial  direct current stimulation (tDCS) is a technique that delivers weak electric  currents through the scalp. This constant electric current ...

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39.4K Views.  Universidade Federal do Rio Grande do Sul. Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that has shown initial therapeutic effects in several neurological conditions. The main mechanism underlying these therapeutic effects is the modulation of cortical excitability. Therefore, online monitoring of cortical excitability would help guide stimulation parameters and optimize its therapeutic effects. In the present article we review the use of a novel device that combines...

Video: Simultaneous EEG Monitoring During Transcranial Direct Current Stimulation

Method for Simultaneous fMRI/EEG Data Collection during a Focused Attention Suggestion for Differential Thermal Sensation

In the present work, we demonstrate a method for concurrent collection of EEG/fMRI data. In our setup, EEG data are collected using a high-density 256-channel sensor net. The EEG amplifier itself is contained in a field isolation containment system (FICS), and MRI clock signals are synchronized with EEG data collection for subsequent MR artifact characterization and removal. We demonstrate this method first for resting state data collection. Thereafter, we demonstrate a protocol for EEG/fMRI data recording, while subjects listen to a tape asking them to visualize that their left hand is immersed in a cold-water bath and referred to, here, as the cold glove paradigm. Thermal differentials between each hand are measured throughout EEG/fMRI data collection using an MR compatible temperature sensor that we developed for this purpose. We collect cold glove EEG/fMRI data along with simultaneous differential hand temperature measurements both before and after hypnotic induction. Between pre and post sessions, single modality EEG data are collected during the hypnotic induction and depth assessment process. Our representative results demonstrate that significant changes in the EEG power spectrum can be measured during hypnotic induction, and that hand temperature changes during the cold glove paradigm can be detected rapidly using our MR compatible differential thermometry device.

We present a protocol for concurrent collection of EEG/fMRI data, and synchronized MR clock signal recording. We demonstrate this method using a unique paradigm whereby subjects receive &#x2018;cold glove&#x2019; instructions during scanning, and EEG/fMRI data are recorded along with hand temperature measurements both before and after hypnotic induction.

In the present work, we demonstrate a method for concurrent collection of EEG/fMRI data. In our setup, EEG data are collected using a high-density ...

Best Current Practice for Obtaining High Quality EEG Data During Simultaneous fMRI

Simultaneous EEG-fMRI allows the excellent temporal resolution of EEG to be combined with the high spatial accuracy of fMRI. The data from these two modalities can be combined in a number of ways, but all rely on the acquisition of high quality EEG and fMRI data. EEG data acquired during simultaneous fMRI are affected by several artifacts, including the gradient artefact (due to the changing magnetic field gradients required for fMRI), the pulse artefact (linked to the cardiac cycle) and movement artifacts (resulting from movements in the strong magnetic field of the scanner, and muscle activity). Post-processing methods for successfully correcting the gradient and pulse artifacts require a number of criteria to be satisfied during data acquisition. Minimizing head motion during EEG-fMRI is also imperative for limiting the generation of artifacts.
Interactions between the radio frequency (RF) pulses required for MRI and the EEG hardware may occur and can cause heating. This is only a significant risk if safety guidelines are not satisfied. Hardware design and set-up, as well as careful selection of which MR sequences are run with the EEG hardware present must therefore be considered.
The above issues highlight the importance of the choice of the experimental protocol employed when performing a simultaneous EEG-fMRI experiment. Based on previous research we describe an optimal experimental set-up. This provides high quality EEG data during simultaneous fMRI when using commercial EEG and fMRI systems, with safety risks to the subject minimized. We demonstrate this set-up in an EEG-fMRI experiment using a simple visual stimulus. However, much more complex stimuli can be used. Here we show the EEG-fMRI set-up using a Brain Products GmbH (Gilching, Germany) MRplus, 32 channel EEG system in conjunction with a Philips Achieva (Best, Netherlands) 3T MR scanner, although many of the techniques are transferable to other systems.

Simultaneous electroencephalography (EEG) and functional Magnetic Resonance imaging (fMRI) is a powerful neuroimaging tool. However, the inside of an MRI scanner forms a difficult environment for EEG data recording and safety must be considered whenever operating EEG equipment inside a scanner. Here, we present an optimised EEG-fMRI data acquisition protocol.

Simultaneous  EEG-fMRI allows the excellent temporal resolution of EEG to be combined with the  high spatial accuracy of fMRI. The data  from these two ...

Simultaneous Scalp Electroencephalography (EEG), Electromyography (EMG), and Whole-body Segmental Inertial Recording for Multi-modal Neural Decoding

Recent studies support the involvement of supraspinal networks in control of bipedal human walking. Part of this evidence encompasses studies, including our previous work, demonstrating that gait kinematics and limb coordination during treadmill walking can be inferred from the scalp electroencephalogram (EEG) with reasonably high decoding accuracies. These results provide impetus for development of non-invasive brain-machine-interface (BMI) systems for use in restoration and/or augmentation of gait- a primary goal of rehabilitation research. To date, studies examining EEG decoding of activity during gait have been limited to treadmill walking in a controlled environment. However, to be practically viable a BMI system must be applicable for use in everyday locomotor tasks such as over ground walking and turning. Here, we present a novel protocol for non-invasive collection of brain activity (EEG), muscle activity (electromyography (EMG)), and whole-body kinematic data (head, torso, and limb trajectories) during both treadmill and over ground walking tasks. By collecting these data in the uncontrolled environment insight can be gained regarding the feasibility of decoding unconstrained gait and surface EMG from scalp EEG.

Simultaneous Scalp Electroencephalography EEG, Electromyography EMG, and Whole-body Segmental Inertial Recording for Multi-modal Neural Decoding

Development of an effective brain-machine-interface (BMI) system for restoration and rehabilitation of bipedal locomotion requires accurate decoding of user's intent. Here we present a novel experimental protocol and data collection technique for simultaneous non-invasive acquisition of neural activity, muscle activity, and whole-body kinematics during various locomotion tasks and conditions.

Recent  studies support the involvement of supraspinal networks in control of bipedal  human walking. Part of this evidence  encompasses studies, ...

Stimulating the Lip Motor Cortex with Transcranial Magnetic Stimulation

Transcranial magnetic stimulation (TMS) has proven to be a useful tool in investigating the role of the articulatory motor cortex in speech perception. Researchers have used single-pulse and repetitive TMS to stimulate the lip representation in the motor cortex. The excitability of the lip motor representation can be investigated by applying single TMS pulses over this cortical area and recording TMS-induced motor evoked potentials (MEPs) via electrodes attached to the lip muscles (electromyography; EMG). Larger MEPs reflect increased cortical excitability. Studies have shown that excitability increases during listening to speech as well as during&#160;viewing speech-related movements. TMS can be used also to disrupt the lip motor representation. A 15-min train of low-frequency sub-threshold repetitive stimulation has been shown to suppress motor excitability for a further 15-20 min. This TMS-induced disruption of the motor lip representation impairs subsequent performance in demanding speech perception tasks and modulates auditory-cortex responses to speech sounds. These findings are consistent with the suggestion that the motor cortex contributes to speech perception. This article describes how to localize the lip representation in the motor cortex and how to define the appropriate stimulation intensity for carrying out both single-pulse and repetitive TMS experiments.

Transcranial magnetic stimulation (TMS) has proven to be a useful tool in investigating the role of the articulatory motor cortex in speech perception.&#160; This article describes how to record motor evoked potentials (MEPs) from the lip muscles and how to disrupt the motor lip representation using repetitive TMS.

Transcranial magnetic stimulation (TMS) has proven to be a useful tool in investigating the role of the articulatory motor cortex in speech perception. ...

Transcranial Direct Current Stimulation and Simultaneous  Functional Magnetic Resonance Imaging

Transcranial direct current stimulation (tDCS) is a noninvasive brain stimulation technique that uses weak electrical currents administered to the scalp to manipulate cortical excitability and, consequently, behavior and brain function. In the last decade, numerous studies have addressed short-term and long-term effects of tDCS on different measures of behavioral performance during motor and cognitive tasks, both in healthy individuals and in a number of different patient populations. So far, however, little is known about the neural underpinnings of tDCS-action in humans with regard to large-scale brain networks. This issue can be addressed by combining tDCS with functional brain imaging techniques like functional magnetic resonance imaging (fMRI) or electroencephalography (EEG).
In particular, fMRI is the most widely used brain imaging technique to investigate the neural mechanisms underlying cognition and motor functions. Application of tDCS during fMRI allows analysis of the neural mechanisms underlying behavioral tDCS effects with high spatial resolution across the entire brain. Recent studies using this technique identified stimulation induced changes in task-related functional brain activity at the stimulation site&#160;and also in more distant brain regions, which were associated with behavioral improvement. In addition, tDCS administered during resting-state fMRI allowed identification of widespread changes in whole brain functional connectivity.
Future studies using this combined protocol should yield new insights into the mechanisms of tDCS action in health and disease and new options for more targeted application of tDCS in research and clinical settings. The present manuscript describes this novel technique in a step-by-step fashion, with a focus on technical aspects of tDCS administered during fMRI.

Transcranial direct current stimulation (tDCS) is a noninvasive brain stimulation technique. It has successfully been used in basic research and clinical settings to modulate brain function in humans. This article describes the implementation of tDCS and simultaneous functional magnetic resonance imaging (fMRI), to investigate the neural basis of tDCS effects.

Transcranial direct current stimulation (tDCS) is a noninvasive brain stimulation technique that uses weak electrical currents administered to the scalp ...

Modulating Cognition Using Transcranial Direct Current Stimulation of the Cerebellum

Numerous studies have emerged recently that demonstrate the possibility of modulating, and in some cases enhancing, cognitive processes by exciting brain regions involved in working memory and attention using transcranial electrical brain stimulation. Some researchers now believe the cerebellum supports cognition, possibly via a remote neuromodulatory effect on the prefrontal cortex. This paper describes a procedure for investigating a role for the cerebellum in cognition using transcranial direct current stimulation (tDCS), and a selection of information-processing tasks of varying task difficulty, which have previously been shown to involve working memory, attention and cerebellar functioning. One task is called the Paced Auditory Serial Addition Task (PASAT) and the other a novel variant of this task called the Paced Auditory Serial Subtraction Task (PASST). A verb generation task and its two controls (noun and verb reading) were also investigated. All five tasks were performed by three separate groups of participants, before and after the modulation of cortico-cerebellar connectivity using anodal, cathodal or sham tDCS over the right cerebellar cortex. The procedure demonstrates how performance (accuracy, verbal response latency and variability) could be selectively improved after cathodal stimulation, but only during tasks that the participants rated as difficult, and not easy. Performance was unchanged by anodal or sham stimulation. These findings demonstrate a role for the cerebellum in cognition, whereby activity in the left prefrontal cortex is likely dis-inhibited by cathodal tDCS over the right cerebellar cortex. Transcranial brain stimulation is growing in popularity in various labs and clinics. However, the after-effects of tDCS are inconsistent between individuals and not always polarity-specific, and may even be task- or load-specific, all of which requires further study. Future efforts might also be guided towards neuro-enhancement in cerebellar patients presenting with cognitive impairment once a better understanding of brain stimulation mechanisms has emerged.

Transcranial direct current stimulation (tDCS) over the cerebellum exerts a remote effect on the prefrontal cortex, which can modulate cognition and performance. This was demonstrated using two information-processing tasks of varying complexity, whereby only cathodal tDCS improved performance when the task was difficult, but not easy.

Numerous studies have emerged recently that demonstrate the possibility of modulating, and in some cases enhancing, cognitive processes by exciting brain ...

Functional Near Infrared Spectroscopy of the Sensory and Motor Brain Regions with Simultaneous Kinematic and EMG Monitoring During Motor Tasks

There are several advantages that functional near-infrared spectroscopy (fNIRS) presents in the study of the neural control of human movement. It is relatively flexible with respect to participant positioning and allows for some head movements during tasks. Additionally, it is inexpensive, light weight, and portable, with very few contraindications to its use. This presents a unique opportunity to study functional brain activity during motor tasks in individuals who are typically developing, as well as those with movement disorders, such as cerebral palsy. An additional consideration when studying movement disorders, however, is the quality of actual movements performed and the potential for additional, unintended movements. Therefore, concurrent monitoring of both blood flow changes in the brain and actual movements of the body during testing is required for appropriate interpretation of fNIRS results. Here, we show a protocol for the combination of fNIRS with muscle and kinematic monitoring during motor tasks. We explore gait, a unilateral multi-joint movement (cycling), and two unilateral single-joint movements (isolated ankle dorsiflexion, and isolated hand squeezing). The techniques presented can be useful in studying both typical and atypical motor control, and can be modified to investigate a broad range of tasks and scientific questions.

Monitoring brain activity during upright motor tasks is of great value when investigating the neural source of movement disorders. Here, we demonstrate a protocol that combines functional near infrared spectroscopy with continuous monitoring of muscle and kinematic activity during 4 types of motor tasks.

There are several advantages that functional near-infrared spectroscopy (fNIRS) presents in the study of the neural control of human movement. It is ...

Neuronavigation-guided Repetitive Transcranial Magnetic Stimulation for Aphasia

Repetitive transcranial magnetic stimulation (rTMS) is widely used for several neurological conditions, as it has gained acknowledgement for its potential therapeutic effects. Brain excitability is non-invasively modulated by rTMS, and rTMS to the language areas has proved its potential effects on treatment of aphasia. In our protocol, we aim to artificially induce virtual aphasia in healthy subjects by inhibiting Brodmann area 44 and 45 using neuronavigational TMS (nTMS), and F3 of the International 10-20 EEG system for conventional TMS (cTMS). To measure the degree of aphasia, changes in reaction time to a picture naming task pre- and post-stimulation are measured and compare the delay in reaction time between nTMS and cTMS. Accuracy of the two TMS stimulation methods is compared by averaging the Talairach coordinates of the target and the actual stimulation. Consistency of stimulation is demonstrated by the error range from the target. The purpose of this study is to demonstrate use of nTMS and to describe the benefits and limitations of the nTMS compared to those of cTMS.

This study is designed to test the hypothesis that neuronavigational system-guided transcranial magnetic stimulation has higher accuracy for targeting the intended target as demonstrated by eliciting a greater degree of virtual aphasia in healthy subjects, measured by delay in reaction time to picture naming.

Repetitive transcranial magnetic stimulation (rTMS) is widely used for several neurological conditions, as it has gained acknowledgement for its potential ...

Concurrent Electroencephalography Recording During Transcranial Alternating Current Stimulation (tACS)

Oscillatory brain activities are considered to reflect the basis of rhythmic changes in transmission efficacy across brain networks and are assumed to integrate cognitive neural processes. Transcranial alternating current stimulation (tACS) holds the promise to elucidate the causal link between specific frequencies of oscillatory brain activity and cognitive processes. Simultaneous electroencephalography (EEG) recording during tACS would offer an opportunity to directly explore immediate neurophysiological effects of tACS. However, it is not trivial to measure EEG signals during tACS, as tACS creates a huge artifact in EEG data. Here we explain how to set up concurrent tACS-EEG experiments. Two necessary considerations for successful EEG recording while applying tACS are highlighted. First, bridging of the tACS and EEG electrodes via leaking EEG gel immediately saturates the EEG amplifier. To avoid bridging via gel, the viscosity of the EEG gel is the most important parameter. The EEG gel must be viscous to avoid bridging, but at the same time sufficiently fluid to create contact between the tACS electrode and the scalp. Second, due to the large amplitude of the tACS artifact, it is important to consider using an EEG system with a high resolution analog-to-digital (A/D) converter. In particular, the magnitude of the tACS artifact can exceed 100 mV at the vicinity of a stimulation electrode when 1 mA tACS is applied. The resolution of the A/D converter is of importance to measure good quality EEG data from the vicinity of the stimulation site. By following these guidelines for the procedures and technical considerations, successful concurrent EEG recording during tACS will be realized.

Concurrent Electroencephalography Recording During Transcranial Alternating Current Stimulation tACS

In this article we explain how to set up a concurrent transcranial alternating current stimulation and EEG experiment.

Oscillatory brain activities are considered to reflect the basis of rhythmic changes in transmission efficacy across brain networks and are assumed to ...

Repetitive Transcranial Magnetic Stimulation to the Unilateral Hemisphere of Rat Brain

Previous rodent models of repetitive transcranial magnetic stimulation (rTMS) adopted whole-brain stimulation instead of unilateral hemispheric rTMS, which is unlike the protocols used for human subjects. We report a successful application of rTMS to the unilateral hemisphere of rat brain. The rTMS was delivered with a low-frequency (1 Hz), high-frequency (20 Hz), or sham stimulation protocol to one side of the brain by using a small 25-mm figure-8 coil. We placed the center of the coil 1 cm lateral to the vertex on the biauricular line and angulated the coil 45&#176; to the ground to minimize a potential direct effect of rTMS on the contralateral cortex. We also used an in-house water cooling system to enable repetitive magnetic stimulation for more than 20 min, even at a 20-Hz stimulation frequency. Increases in the transcriptions of immediate early genes (Arc, Junb, and Egr2) were greater after rTMS than after sham stimulation. After 5 consecutive days of 20-min 1-Hz rTMS, bdnf mRNA expression was significantly higher in stimulated cortex than in contralateral side. The model presented herein will elucidate the molecular mechanisms of rTMS by allowing analysis of the inter-hemispheric difference in its effect.

We applied repetitive transcranial magnetic stimulation (rTMS) to the unilateral hemisphere of rat brain, by placing a 25-mm figure-8 coil 1 cm lateral to the vertex on the biauricular line and angulating the coil by 45&#176;. An in-house water cooling system was used for rTMS for more than 20 min.

Previous rodent models of repetitive transcranial magnetic stimulation (rTMS) adopted whole-brain stimulation instead of unilateral hemispheric rTMS, ...