EEG Setup

This EEG recording protocol describes in detail how to obtain clean data.  Read the Brain Vision website and watch the PURSUE capping procedure and the Brain Vision video showing the setup.

Setting up the EEG cap

1. Have the subject read the consent form. If they still agree to be a subject, have them sign the form.

2. Measure the persons head size using a measuring tape. Measure from the bulge of their middle forehead around the back of the skull (you should be able to feel a boney protrusion). Typically we observe skull sizes between 52cm and 60cm, so if you get a result wildly outside this range you are likely measuring incorrectly.

3. Find the cap that is closest to the measured size, with a preference towards the smaller size.

4. Begin attaching electrodes to the selected cap. There should be two separate splitter boxes of electrodes.  Splitter box “1” electrodes should be placed into the green sockets while splitter box “2” electrodes should be placed into yellow sockets. Individual electrodes are labelled 1-32 and should be placed into the respective sockets.

5. After attaching all 64 electrodes, take the black single electrode, labelled ground, and attach it to the black socket on the top of the cap.

Setting up the EEG cap on a participant

1. Plug both electrode bundles into the amplifier. There are two ports on top of the amp where this should be accomplished. Make sure to plug splitter box “1” into the port closest to the front of the amp.

2. Plug the end of the ground electrode into the ground port on the front of the amplifier.

3. Next we will place the cap on the subjects head. We have found it is easiest to let the subject do it themselves with minor assistance on our part making sure it is unwrinkled and correctly placed. The front of the cap should rest on the mid to lower forehead, and ears should be comfortably fit through the ear holes. Make sure the cap is strapped on as tightly as is comfortable.

4. Go to the back of the amp and unplug the wire going into the bottom section of the amp. This is the battery. Plug the top and bottom part of the amp together.

5. Return to the control computer and initiate the experiment. The first few steps can be skipped through fairly quickly, but make sure that the recorder actually opens on step 4 before going to step 5. Step 5 opens up the impedance check, so turn your attention to the EEG monitoring computer. Make sure the measured range is from 0 to 50kohms. The electrodes on the cap should all light up bright red.

6. Return to the subject and begin to fill the ground and reference electrode with a small amount of gel (.3ml should suffice). Each electrode has a tiny hole on the top that you should be able to slide a needle through to squirt gel on the scalp. We have found that it is easier if you squirt some gel onto the scalp then proceed to gently wiggle the tip of the needle on the scalp to move the hair away. If done correctly, the electrode should turn a bright green or yellow. If the electrode remains red try to re-swirl the hair or use a tiny bit more gel. Sometimes leaving the electrode to rest for a while will also reduce the impendence. Make sure both the ground and reference are green or yellow before proceeding.

7. Repeat this last step for each of the remaining 63 electrodes on the cap, making sure each becomes yellow or green. If certain ones are troublesome, leave them alone for a while and try again later.

8. Once all the electrodes are green or yellow, double-check the EEG monitoring computer to ensure that all impedances are below 25kohms before continuing.

9. Once the impedances are all sufficiently low, return to the control computer and proceed to the monitoring step of the setup. The recorder on the monitoring computer should start to display the EEG activity for each electrode on the screen. Make sure no electrodes are recording any absurd noise or interference; the signal should be pretty flat if the subject is motionless.

10. Next we will set up the eye channel electrodes. For one splitter box, plug in all three electrodes. The plus slot electrode goes above the eye near the eyebrow. The minus slot electrode goes below the eye in line with the pupil. The middle slot electrode goes on the middle of the forehead between the eye brows; this is the ground. The other splitter box only uses the outer two slots (no ground). These two electrodes go on both sides of the face on the exterior edge of the eye socket, parallel to the pupil. Because these are not on the cap, it is easiest to squirt a bit of gel on the spot, place the electrode on top and then tape the electrode in place with medical tape.

11. Oftentimes I like to have the subject stand up and come look at the signal. I have them do eye movements, blinks and jaw clenches just to show them how minor muscle activity creates artifacts we don’t want. I also instruct them when the best time to blink would be, normally between individual trials.

12. Have the subject sit back down in the experiment room, with the front legs of their chair on the white tape marking the ground.

13. Return to the control computer and continue through the experiment until you get to the experiment instructions. Read them aloud to the subject and clarify any questions they may have. Then you can start the experiment.

Cleaning the cap

1. Unplug the amplifier from the battery and plug the battery back into the wall. Unplug the two splitter boxes and the ground electrode from the amplifier box. Remove the cap from the subjects head.

2. Remove each electrode from the cap by gripping the plastic and twisting/pulling. Make sure not to grip or yank the wires.

3. Place the electrodes in filtered/distilled water for 10 minutes. Make sure the splitter boxes and plugs are kept away from contact with water! I normally place them in a dry Ziploc bag then zip up the bag.

4. Rinse the cap under warm tap water, cleaning out the gel from the sockets.

5. Remove the electrodes from their bath and, using a toothbrush, scrub the gel off the electrodes.

6. Once all electrodes are free of gel, place the electrodes into Envirocide for 3 minutes.

7. Rinse the electrodes briefly under warm water, then hang up to dry.