An electroencephalogram (EEG) is a recording of brain activity.
The brain’s cells produce tiny electrical signals when they send messages to each other. During an EEG test, small electrodes are placed on to your scalp.
They pick up your brain’s electrical signals and send them to a machine called an electroencephalograph, which records the signals as wavy lines on to a computer screen or paper.
An EEG is painless, takes 30-45 minutes and rarely causes any side effects.
When an EEG is used
The pattern of electrical activity produced on an EEG can be used to help diagnose a number of conditions that affect the brain.
An EEG is mainly used to diagnose and manage epilepsy (a condition that causes repeated brain seizures). However, it can also be used to investigate other conditions that affect brain function, including:
- brain infections, such as encephalitis
- head injuries
- brain tumours
- bleeding on the brain (hemorrhage)
EEGs can also be used to diagnose and manage sleep disorders such as insomnia.
An EEG can identify areas of the brain that are not working properly. This helps doctors to make decisions about the type of treatment that is most suitable for you.
EEGs are also sometimes used to determine the level of brain function in people who are in a coma.