Before the participant arrives
Each participant must be sent an email with screening questions to ensure that they can participant in the experiment. When someone signs up for a tDCS time slot on Sona, an email is automatically sent to the Lupyan Lab google group. When you see such an email, log into the Sona system, click the “modify” button for that time slot, and use the option to “contact all participants” towards the bottom of the screen. The text of the email can be found on Dropbox in the “Consent forms” folder under the name “tDCS email instructions.” After you’ve emailed the participant, find the time slot on the google calendar and mark it as “emailed.”
Setting up the tDCS equipment
Get everything you will need out of the file drawer and ready to go.
- tape measure
- tDCS machine
Make sure you have enough saline solution. If not, more can be found in the cabinet by the door.
Turn on the machine briefly to make sure the low battery indicator is not lit. If it is, replace the batteries (in file drawer or in charger) and put the used ones in the charger.
Each side of the sponges should be soaked in saline. About 12mL per sponge should be good. Sponges should be completely soaked for safety and efficacy, but not be excessively wet such that they drip all over the participant. Insert electrodes into sponges (as shown in picture).
When the participant arrives
Screening and Consent
When the participant arrives, ask him/her if they received the email with the screening questions, and explain that we also need a written copy of their answers to the questions. Ask the participant to fill out the screening form. If they say yes to any of the questions, they are not able to participate. Screening forms of persons who did not participate should be destroyed. Screening forms of persons who do participate should be kept with their data.
Give the participant the consent form and explain the nature of the study. Make sure to highlight: that we will be using a technique called Transcranial Direct Current Stimulation which passes a small amount of electric current over their scalp to stimulate a certain part of their brain, that they will experience an itchy or tingling sensation but should not experience any pain, and that the current can be lessened or the experiment stopped at any time if they are in any discomfort. Ask them to look over the form and ask any questions they may have, point out the two places on the consent form where they should sign, and witness the form by signing on the last page.
Preparing the participant
Make sure the participant is seated comfortably at the table. Use the tape measurer to measure their head in cm. You can ask the participant to help you hold the tape in place as you measure. Start at the nasion (place where nose meets the forehead), wrap around to the inion (bone at back of head), and back around to the nasion. [PICTURE] Use this measurement to select appropriate cap (small: 49.5-54cm; medium: 54.5-57cm; or large: 57.5-62cm).
Place cap on participant’s head such that the N is located over their nasion. You can ask the participant to hold the cap in place as you pull it on. Using the color diagram of the 10/20 system, locate the appropriate area for the experiment. Use dry erase marker to draw on participant’s scalp where the area of interest is (pro tip: red markers will make it easier to locate your markings.) [PICTURE] As you are drawing on the scalp, you should also make sure that the participant doesn’t have any cuts or irritation there and remove any bobby pins or clips. You can pull hair out of the way using hair ties we keep on hand.
Remove the cap—this was just for marking the area of interest. It should not be left on the head because we don’t want it to be ruined by repeated contact with saline solution or to interfere with the stimulation process. Now place rubber strap over the head so that longer piece wraps around head and shorter piece straps under chin. You can adjust straps so that it fits comfortably but snugly, and that it will be position to hold sponge/electrode in place over area of interest. Depending on the cortical area you intend to stimulate, the strap may need to be placed at an angle on the head. For example, in order for the sponge/electrode to be placed over Wernicke’s area, the strap needs to be higher on the left than right side of the head. Practicing on Susan, the Styrofoam head, can help you become more efficient at adjusting the straps so you can do more quickly on a real head.
Turn the machine on before placing the sponges/electrodes on the participant. The operator’s manual recommends never turning the power on or off while it is connected to the participant. Check to make sure duration dial on machine is set to 20 and intensity is set to 1.75. Select either Sham On or Sham Off depending on condition: if in sham condition then turn on, if in anodal or cathodal condition then turn off. Turn relax slider to full current.
Place the sponges/electrodes in their respective positions (scalp/cheek) based on condition: if participant is in anodal condition (a) place anode electrode (red wire) on scalp and cathode on cheek; if in cathodal condition (c) place cathode electrode (black wire) on scalp and anode on cheek; if in sham condition (s) place either. Make sure sponge is against scalp—pull hair out of the way. It is okay if hair is over the electrode, just not under.
Running the Experiment
It is now time to give the participant a bit of a pre-stim tickle. Explain that you are going to give them a brief stimulation so they know what to expect. Explain again to participant that if they feel uncomfortable at any time, they just need to let you know, and you can decrease the stimulation or stop it. Press the pre-stim tickle button.
Press start button. The active light will flash for about 30 seconds while the current ramps up. It will then remain lit once it reaches full current and the timer will appear in the duration window. Stimulation will continue until the 20 minutes have elapsed and then the machine will automatically ramp back down.
Some participants will take longer than 20 minutes to complete the behavioral task. If the stimulation finishes before they finish the task, that’s okay, simply leave the apparatus on their head until they finish. Note approximately where they are in the task when stimulation ended in the relevant subject info sheet column. You don’t need to alert them to it either—in fact many participants will not be aware of the sensation once they become engaged in the task.
If the participant complains about the intensity of the current, you can use the relax slider to slowly lower the current. If they experience too much discomfort or fear, press the abort button. NB: It is better to press the abort button then to turn off the machine. Do not touch the sponges or electrodes until the current has ramped all the way down. Even pressing abort doesn’t immediately stop current, and so you will need to wait until current is at 0 before touching anything.
The machine will ramp the current back down after the allotted time has passed. When the participant has finished the task(s) and the current is back to 0, remove sponges from participant. Do not turn off the machine, however, until you have taken the sponges off the participant.
After the Experiment
- Have the subject complete any associated surveys.
- Have the subject complete the tDCS Safety Monitoring sheet.
- Give the subject credit in Sona.
- Note the contact quality and time left on the clock at the end of experiment/1st experiment in the appropriate column of the subject info sheet.
- File the subject's paperwork in the file cabinet--there should be one file for the consent forms for each study and another for the all of the screening and safety monitoring paperwork.