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Psychology

Find out more about EEG

The EEG lab

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Location: Department of Psychology Social Sciences Building Level 4, Room D401/402 Tel: +44 (0)20 7040 4211. EEG lab2 is located on the ground floor in room DG08A.

The EEG labs are purpose-built units in the Department of Psychology. EEG enables the measuring of electrical brain activity occurring during all kinds of externally and internally triggered cognitive processes such as sensory perception, selective attention, action preparation, executive control processes, learning, working memory, etc. We employ a 64- / 32-channel EEG setup and all recordings are performed in an acoustically and electrically shielded chamber.

A brief introduction to EEG research

Groups of neurons firing synchronously create electrical potentials that can be measured by electrodes placed on the scalp. When the electrical signals from a given electrode are graphed over a period of time, the resulting representation is called an EEG (electroencephalogram). The EEG ultimately provides information about the time course and location of the neural firing, allowing researchers to draw conclusions about the underlying brain activity and its relation to cognitive functions.

The image below shows EEG traces from commonly used electrodes, all placed on the scalp. Although such information is the basis of the conclusions researchers in the lab make about brain function, a fair amount of analysis must be performed before many interesting conclusions can be made. Very little can be concluded by simply looking at these traces, as one can usually only see noise not related to brain activity (e.g. eye blinks), or alpha waves when a person becomes very sleepy!

Experimental procedure

In order to record the electrical signals indicating brain activity, participants must wear a cap with embedded electrodes. The person above is modeling one such cap, and sometimes participants also wear facial electrodes in order to record eye movements, as such movements affect the readings from the electrodes monitoring brain activity. The facial electrodes and the electrodes in the cap must be filled with a conductive gel (a saline solution that easily washes off skin and out of hair) in order to obtain good electrical signals.

An experiment consists of a participant repeatedly performing a specific cognitive task while one of the lab's computers records the electrical signals from the electrodes. During the experiment, the signals from the electrodes are relayed through the amplifiers to the computer via the wires and connectors that are visible in the back of the head of the participant on the photo.

Data analysis

Since just looking at the raw EEG data does not relay much useful information to the researcher, they must be mathematically transformed in order to answer the questions a given study has posed. The most frequent analysis technique is to average the EEG recordings across multiple trials, where a trial is defined in relation to some event such as a subject response or the appearance of a visual stimulus. Such averaging reduces the effects of electrical signals not related to the brain activity evoked by the event in question. The waveform produced after averaging across trials is called an event related potential (ERP). Below is an example of averaged ERPs in response to tactile stimuli applied to one of the hands recorded over ipsilateral (same side as tactile stimulation) and contralateral (opposite side as tactile stimulation) somatosensory cortex.

EEG lab volunteers

Are you interested in participating in an EEG study? The following description will give you an idea of a typical EEG study in our lab. Please, read this information before participating in a study.

What will you be doing?

Basically you will be sitting in front of a computer screen doing a simple task. For example: On the screen you see a circle flashing in different colours, every time the triangle turns green you press a button (this is a very basic example). In most of our experiments we measure changes in your brain's activity while you are performing the task - that is we measure your electroencephalogram (EEG). In order for us to do this, you need to wear a cap with electrodes on your head during the experiment. We use the same equipment to do this as is used in hospitals for monitoring patients.

How long will it take?

On average an experiment takes about 2 to 3 hours. About half an hour is needed to put the cap on and ensure that a good measurement is possible. Also, you will want to wash your hair afterwards, to remove the left-behind bits of conductive gel from your hair. We have a hand-held shower, clean towels, hair-care products etc. for you to use.

Reward

We pay each participant £7 per hour in cash (or £20 for a 2.5 - 3 hour session). We do not pay for your travelling expenses.

Who are we looking for?

We are looking for healthy people between the age of 18 and 45. The experiments take place in a small cabin and for this reason it is not wise to take part in an experiment if you are claustrophobic. It is important to be fit and well-rested when you take part in an EEG experiment. Also, it helps if you do not use any hair-care products like conditioner, oils or wax in your hair. Finally, if you are wearing contact lenses but also have a pair of spectacles you could wear, it is advisable to bring your spectacles, because some participants complain of dry eyes when they are doing our experiments.

The cap

The electrodes we use to record the EEG are fitted in a cap, which looks like a bathing cap with a lot of wires coming out. To make a good contact between the skin and the electrodes we clean the skin underneath the electrodes with some alcohol and then fill the electrode with a conductive paste (this is a completely harmless saline solution). Some of this paste will be left behind in your hair after we take the cap off, so you will probably want to wash your hair afterwards and we have all the necessary facilities in our lab.

Interested?

If you are interested in taking part or have any further queries, please e-mail Dr Bettina Forster, Dr Corinna Haenschel or the CNRU lab.