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Updated Technique for Reliable, Easy, and Tolerated Transcranial Electrical Stimulation Including Transcranial Direct Current Stimulation
Chapters
Summary January 3rd, 2020
When administering transcranial direct current stimulation (tDCS), reproducible electrode preparation and placement are vital for a tolerated and effective session. The purpose of this article is to demonstrate updated modern setup procedures for the administration of tDCS and related transcranial electrical stimulation techniques, such as transcranial alternating current stimulation (tACS).
Transcript
The purpose of this video is to demonstrate updated setup procedures for administering transcranial direct current stimulation, tDCS, and related transcranial electrical stimulation techniques, such as transcranial alternating current stimulation, tACS. In this, we demonstrate tDCS using commonly applied montages intended for motor cortex and dorsolateral prefrontal cortex stimulation. The modern tDCS technique explained here avoids tape measurement for determining electrode placement, cumbersome carbon rubber insertion steps, tedious procedures of wetting electrode sponges, and use of rubber bands as headgear.
This process is optimized by using a specialized headgear and a pre-saturated snap connector electrode. For each montage, there is a specific headgear. While some materials will depend on the specific protocol of the study or treatment, there are basic items that are general across modern tDCS applications.
Prior to the tDCS session, make sure all necessary materials are handy. For research trials, before the study begins, the subject must give consent to participate in the study. The consent form includes details about the research protocol, risks, and benefits of the study.
This form is intended to disclose appropriate information to subjects so that they may make a voluntary choice to accept or refuse treatment. It originates from legal and ethical rights, as subjects have to be aware of what happens to their body, and also from ethical responsibilities of a researcher to get the participants involved in their physical and mental well-being. A written consent must be collected from the participants before the stimulation is started.
Setup begins by first measuring the subject's head circumference to determine the appropriate size of the headgear to be used. There are different sizes of headgear depending on the electrode montage. Consult your headgear's user manual to select the appropriate size based on the measurements.
Inspect the skin where the electrode is expected to be placed. If you observe any visible lesions, do not administer tDCS. If possible, expose the scalp by parting the hair with your fingers to ensure that the saline seeps through the hair into the scalp, to enhance contact quality between the electrode and the scalp.
We're employing a single-use, pre-assembled snap sponge electrode. Remove two five-centimeter-by-five-centimeter sponge electrodes from the bag. Electrodes used in tDCS are generally conductive rubber electrodes enclosed in a sponge saturated with electrolyte solution, mostly saline.
Pre-saturated and new electrodes are used to enhance reliability. The fixed-position headgear is used to secure the electrodes over the brain target. To accurately position the sponge electrodes over the M1SO brain region, first position the nasion-representing ring of the strap, located at the bottom portion of the strap, over the nasion.
The nasion is the portion anterior to the brain, located between the forehead and the nose. Next, adjust the top portion of the strap so that it is perpendicular to the bottom portion of the strap. The top portion of the strap is intended to sit approximately above the ear, symmetrically positioned on both sides of the head.
The posterior elastic portion of the strap should be positioned over the inion, the most prominent point of the occipital bone. Ensure that the headgear is snug but not uncomfortably tight. Connect the black cathode connecting cable into the corresponding input black driver of the tDCS device.
Repeat this for the red anode connecting cable for its respective location on the tDCS device. Ensure the connection polarity is correct, as the effects of tDCS are considered polarity specific. In the context of tDCS and electrical stimulation in general, the anode is the positive terminal where positive current enters the body, and the cathode is the negative terminal where positive current exits the body.
In the context of tACS, there is no concept of anode and cathode, as both terminals will act anode and cathode alternatively. Before initiating the tDCS session, make sure the subject is comfortable and awake. Confirm the device is turned on, the cables are properly connected, and the headgear and electrode properly situated.
The impedance meter is a secondary method to ensure good contact, but it does not replace the need to make sure all protocol steps are followed correctly. Check the impedance meter for contact quality. If the subject's overall contact quality is abnormally low, this may indicate improper electrode setup, resulting in high impedance.
If the contact quality continues to be low after adjusting the headgear and/or judiciously supplementing saline, you may press Pre-Stim Tickle, if available on your device, to achieve a better contact quality. Program the tDCS session duration, intensity, or, if applicable to your device, sham condition setting. Note that some stimulators are recommended to be switched on before the contact between the electrodes and the skin is made.
If you're using a tES device for the tDCS session, make sure to select the tDCS waveform setting. Initiate the tDCS by pressing the Start button. In order to reduce any adverse effects, some devices include automatic current ramp up at the start of the stimulation, in which the device ramps up the current slowly for 30 seconds.
At the beginning of the stimulation, subjects will often perceive an itching and/or tingling sensation underneath the electrodes, which then fades out in most cases. Some subjects may experience discomfort during the initial tDCS period. In such cases, the current may be moderately decreased for a temporary period as the subject adjusts.
Then, gradually increase the current back up to the desired level. This feature may depend on the device being used and protocol. The electrodes must not be dehydrated during stimulation to ensure good contact quality.
If the electrodes become dehydrated, you can use a syringe to gradually add more saline to the electrodes. If addition of saline does not improve the contact quality, confirm skin sensation from the subject. At the end of the stimulation session, the device will ramp down from the treatment intensity to zero mA.
Remove the headgear loaded with the electrodes from subject's scalp. Finally, power off the device. This table compares the overall difference between the traditional tDCS application methods and the updated tDCS methods, as explained in this video.
Furthermore, we conducted an experiment in which we measured the setup times using the traditional and modern tDCS methods. For this, we recruited experts and novices in both methods and measured how long each participant took to conduct the setup. The setup was repeated five times, and each trial was timed individually.
The results show that the modern method required significantly less setup time for both expert and novice participants than the traditional method. Using the traditional tDCS method, the average setup time taken by the expert was approximately eight minutes. Using the traditional tDCS method, the average setup time taken by the novice was about 10 1/2 minutes.
Novices made setup errors and were generally unable to achieve an error-free setup, even after five sessions. Using the modern tDCS method, the average setup time taken by the experts was slightly over a minute. Using the modern tDCS method, the average setup time taken by the novices was about 2 1/2 minutes.
Novices were generally able to achieve an error-free setup by the fifth session, and any errors were minor. The modern tDCS method allows electrode placement with comparable precision to an expert operator measuring traditional EEG 10-10 positions. For operator or self-application, the modern tDCS method is highly reliable.
The modern tDCS approach explained here increases setup reliability while decreasing stimulation setup time.
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