Doing an EEG

What is an EEG?

An EEG, or electroencephalogram, is a recording of brain activity done with a technique called electroencephalography. Brain activity is based on electric signals sent from one neuron to the next. In an EEG, these electric signals are detected and recorded by very small flat metal discs (electrodes) placed on the scalp. The EEG recording shows one line for each electrode, with the line moving up and down to show the changes in activity detected by this electrode. The researcher can read these lines to understand the activity of the brain. The EEG only records the electrical activity produced by the brain and it does not stimulate the brain or cause any pain.

Examples of EEG recordings: In these recordings, each line shows the signal recorded by a single electrode.

What happens during an EEG test?

Set up

An EEG is very safe and rather easy to do. First, the researcher will place a cap (sort of like a swim cap) on your head. This special cap has all the electrodes that record the brain activity embedded in it. The cap will have been dipped into a salt based (electrolyte) liquid (this step helps the electrodes detect the brain signals) before being placed on your head, so your hair will get wet. The researcher will use towels to remove the excess water, so that your clothes don’t get wet. 

When the cap is ready, the researcher will start the computer program that records the activity detected by the electrodes. The researcher might ask you to blink and/or close your eyes for a few seconds to check that all the electrodes are working. If the researcher notices that some electrodes need extra salt based liquid to work, they will inject a bit of the liquid on these electrodes.  

It should take around 10 minutes to complete all these steps and set up the EEG.

During the recording

Once everything is ready, the researcher will explain to you what you will have to do during the recording. For your studies, you will probably do one or several tasks while wearing the cap. The researcher will explain the task in details before it begins. Feel free to ask questions before starting the task.

During the whole recording, it is important that you are relaxed and seated comfortably. It is also important that you try and remain as still as possible, because movements can disturb the cap and the electrodes, and this would lower quality of the recordings. 

The tasks to complete will be different for each study. Maybe you will have to listen to sounds, view images, or complete a task on a computer (like a computer game). If there are several tasks, you will always be able to take breaks between tasks. Depending on the number of activities, the EEG recording can last between 10 minutes to 1 hour.

If you feel uncomfortable at any point during the recording, please do tell the researcher. They will do their best to help you.

Photo of a participant wearing an EEG cap and looking at an image on a phone screen. The computer screen shows the brain activity recorded by the EEG cap.

After the recording

The researcher will tell you when the recording is finished, and they will carefully remove the cap from your head. You will be able to dry your hair with the towels available. However, as the liquid used contains a lot of salt, we recommend you wash your hair when you get home.

As the EEG didn’t stimulate the brain at all (it only recorded its activity), you can leave the appointment freely, you can even drive if you came driving.

How to prepare for an EEG?

You do not have to do anything special to prepare for an EEG, but having clean hair (free from oils, sprays and conditioner) and being rested will help the researcher with the quality of the recordings.

If you are anxious about the EEG, for example you might be uncomfortable about wearing the cap, please do get in touch with the researcher, they may be able to help you by letting you try on the cap before your appointment.

Even if the EEG lasts a long time, it is always very safe. The EEG only records brain activity, but it cannot stimulate the brain at all. The most difficult thing about the EEG is to remain still and relaxed, and to get used to the feeling of the cap.