What is electroencephalography?

Electroencephalography is a method of detecting and analysing electrical activity in the brain. The procedure, which involves placing several small metal sensors called electrodes on the scalp, is known as an electroencephalogram or EEG.

What does electroencephalography consist of?

An electroencephalogram involves attaching around 20 electrodes to the scalp. Each electrode sends a signal to a machine called an electrocephalograph, which displays the rhythmic fluctuation of the brain’s electrical activity (brainwaves) visually as an undulating line. In this way, it is possibly to monitor brain activity.

In a normal, healthy adult who is in a calm state, the EEG will show regular, oscillating waves (alpha waves). In sleep, the waves become very slow, while if the individual is startled or excited, they become rapid and irregular.

Some conditions are associated with particular patterns. For example, localised areas of brain damage may display slow, irregular delta waves.

Why is electroencephalography done?

Electroencephalography can be used to check for brain damage in patients who have had serious head injuries, and can help in the diagnosis of various conditions, such as brain tumours, sleep disorders, epilepsy, and several degenerative nervous system diseases. It is also useful for assessing if brain death has occurred.

The data obtained by EEGs is limited in that it records small samples of electrical activity from the surface of the brain, and cannot analyse deeper activity such as emotion, making it useless for diagnosing psychiatric illness.

Preparation for electroencephalography

In preparation for an EEG, you should:

• Avoid caffeine on the day – it can affect the results.
• Wash your hair beforehand and don’t use products, including conditioners, gel and hairspray – these can make it harder to stick the electrodes to your scalp.
• If instructed by the doctor, you may have to sleep less or avoid sleep the night before in order to sleep during the EEG.

What to expect during during the test?

An electroencephalogram in non-invasive and doesn’t cause any pain or sensations, so you should be relatively comfortable during the procedure. However, the procedure can take up to an hour. During this time, you may be asked questions or given instructions to see how your brain responds in different ways to different stimuli. You may be asked to do calculations, read something, open and close your eyes, look at a flashing light, or any number of things. You may also be required to go to sleep during the test to analyse your brain at rest.