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Running EEG

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sydney-smith edited this page Oct 10, 2018 · 3 revisions

Guidelines for Running EEG

T Donoghue, Voytek Lab

This setup guide is for the Brain Products EEG System

Location: SDSC Room B128E

Supplies

The following are required to run an EEG subject:

  • Towels
  • Tape Measure
  • Tape
  • Alcohol Swabs
  • Electrode Gel
  • Syringes
  • Syringe Tips
  • Toothbrushes (for cleaning)


Preparation Prior to Subject Arrival

  • Turn on the presentation computer and log in
  • Check that you have a clean towel ready for the subject after the experiment
  • Check the EEG battery pack(s) is/are charged
  • Check that screen, chair and desk behind the chair are all in the right place
  • Make sure the EEG caps are ready (and dry) for the experiment
  • Check all electrodes are present and ready, lay them out ready to apply to the dummy
  • Prepare syringes and fill with gel
  • Prepare tape for any extra electrodes
  • Open up the presentation software that is needed, made sure programs are ready

EEG Setup

  • Place all the EEG components on the table that sits behind the subject
  • Plug both amplifiers into the control box
  • Plug the two amplifiers into the battery pack
  • Plug the USB cable in between the impedance control box and the computer
  • Plug the fibre optic connectors in between the amplifiers and the USB box
    • Note: You need not do this until after checking impedances, if the wires get in the way
  • Plug the USB cable in between the USB box and the computer

Subject Checks

  • Check if the subjects hair will be okay for the EEG (for example - dreadlocks won’t work)
  • Measure the circumference of the head immediately, so an experimenter can set up the cap.
    • Once you know the circumference, select the right cap. Caps are available in sizes 54, 56, 58 and 60. Round down if possible, so that it is not loose on the subjects head.
    • Check the cap on the subject to make sure it is the right size. It needs to be tight across the scalp, otherwise it won’t hold the electrodes in place.
    • Using the head dummy, plug all the electrodes into the correct locations (always start from the front and work the way back, one electrode set at a time).
  • Ask if the subject if they have any piercings or metal in/on their head
    • If they do, ask if they can remove them
  • Ask the subject if they need the bathroom or a glass of water before starting the experiment
  • Give the subject a brief introduction to the study
  • Get the subject to read and sign the Consent Form
  • Fill out the control sheet, assigning a subject number to use
  • Fill out the subject information form, asking the subject questions as needed
  • Ask the subject to remove any electronic devices from their pockets
  • Make sure to ask the subject if they have any questions about the study, and to tell them about the EEG setup. Show them the syringes used for setup (explain that they are dull), explain what you need to do to apply the EEG cap.

Subject Preparation

  • Ask the subject to sit in the chair, facing the presentation monitor.
  • Measure the location of Cz. This is halfway between the Nasion and Inion and halfway between LPA and RPA. Use a marker the draw a cross on the scalp to locate through the cap (this might not work on all subjects - if the hair is particularly difficult, these measurements can be taken over the top of the cap).
  • Place the cap (with electrodes now inserted) onto the subjects head. Pull it over from the front, and ask the subject to hold the top at their forehead while you position the rest of it. Check the cap around the ears. Make sure the strap is fastened tight to enough to hold the cap in place.
  • Check that the ground and reference electrodes have been added. If they haven’t, add them to the cap and plug them into the control box.
  • Try to locate the mark on the subjects head through the Cz electrode location. Position this electrode over the cross. (Alternately, measure over the cap and position the cap with that).
  • If you are using any extra electrodes, add them now. Clean the area with an alcohol swab, and tape the electrode on. Plug it into the control box.
  • Once Cz is positioned, check that the cap is placed centrally over the head. Look from the front of the participant, to check that it looks straight.

Checking Impedences

  • Turn on the control box, and make sure it’s in impedance mode (by pressing and holding the impedance button).
  • Start the ActiCap control software on the stimulus computer. Drag the ActiCap GUI to the presentation screen. Click on the Impedance tab, and click ‘Start’. Make sure the limits are set to 5 kOhms and 10 kOhms (or set to desired impedance).
  • Start with the reference and ground electrodes. For each electrode use the syringe the push some of the hair out of the way (using either circular or criss-cross motions) and squirt some gel to make the connection. Continue to manipulate the syringe after gel insertion until the connection is good enough.
    • The lights on the screen, and on the electrodes themselves, are colour coded, with green being ‘good impedance’, yellow being ‘almost good enough’ and red being ‘too high’, where what is good enough is set by the experimenter in the ActiCap software.
    • Do not add too much gel - if the gel extends to another electrode it will short the circuit and render the electrodes useless
    • Impedances can be tricky. If an electrode is being a problem continue with other electrodes and prioritize important electrodes to save time. Sometimes moving on and giving an electrode some time to settle can help.
  • Once impedances are finished, syringes can be discarded into the ‘Sharps / Biohazards’ box - not into the garbage.

Running the Experiment

  • Each experiment will have it’s own instructions for running the actual experiment, depending on what software is used for presentation, for EEG recording, whether the experiment has any real-time components, etc. Follow the experiment specific run guides for those steps.

Clean Up / Wrapping Up

  • Once the experiment is complete, disconnect any streams / connections the EEG system has to the computer. Close presentation software. Save anything that needs to be manually saved (saving should be automated).
  • Once everything is disconnected, you can take the cap off the participant and put it straight into the blue clean-up bucket
  • Once the subject has the cap removed, give them a towel and shampoo and show them where the bathroom is to clean up.
  • Thank the subject for participating. They are free to leave whenever after this point.
  • Disconnect the EEG electrodes from the control box. The plug ends up to the boxes should be put into the white ActiCap bag.
    • Take the cap and electrodes to the sink. Clean them both thoroughly
    • Use the toothbrushes to clean up the electrodes and the holes in the cap
    • The cap must never be wrung out - don’t do anything that can stretch it
  • In the EEG room, unplug all the connections. The EEG equipment should be arranged neatly on the desk to the right of the presentation screen.
  • Once clean, the electrodes should be hung up neatly. Make sure to hang them in a way that water can’t trickle down into the connectors or boxes
  • The cap should be laid out so it can dry. If it needs to be dried quickly for another experiment, the hair dryer can be used, but only with cold air.
  • Make sure everything is cleaned up from applying the electrodes, including that the gel is sealed properly.
  • Log out and power down the computer
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