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Electroencephalogram (EEG)

An electroencephalogram (EEG) is a test that measures and records the electrical activity of the brain. An EEG uses sensors, or electrodes, attached to the head and connected by wires to a computer.

Why an EEG is done

An EEG is done to:

  • detect abnormalities in the electrical activity of the brain
  • test for epilepsy
  • identify the location of a suspected brain tumour, inflammation, infection, bleeding, head injury or disease in the brain
  • monitor the brain during brain surgery

How an EEG is done

An EEG may be done in a hospital, medical clinic or doctor's office. It takes 1–2 hours, but may be longer if the person needs to sleep during the test.

  • Some special preparation is required before EEG:
    • If the person is on any medication, they may have to stop taking it before the test.
    • Avoid foods that contain caffeine, such as cola and chocolate, for at least 8 hours before the test.
    • Eat a small meal shortly before the test because low blood sugar may produce abnormal results.
    • The person’s hair should be clean and free of sprays, oils, creams, lotions and any other hair product because the electrodes will be attached to the person’s scalp.
      • The person’s hair should be shampooed and rinsed with clear water the night before or the morning of the test. Do not apply any hair conditioners or oils after shampooing.
  • The person will lie on a bed or examination table or relax in a chair with their eyes closed. They need to be still and not speak during the test.
  • 16–25 electrodes (flat metal discs) will be attached to different places on the person’s head.
    • A sticky paste may be used to hold the electrodes in place.
      • Some paste may remain in the hair after the test, so the person may have to wash their hair to remove it.
    • The person may wear a cap with fixed electrodes.
  • The electrodes are connected by wires to a machine that amplifies and records the electrical activity inside the brain.
  • The machine records the electrical activity as a series of wavy lines drawn by a row of pens on a moving piece of paper or as an image on a computer screen.
  • The recording may be stopped from time to time to allow the person a break to stretch and reposition themselves.
  • The person may be asked to do certain tasks to observe how the brain responds to different forms of stimulation. These tasks may include:
    • breathing deeply and rapidly
    • looking at a bright, flashing light called a strobe
    • sleeping

Special considerations for children

Being prepared for a test or procedure can reduce anxiety, increase cooperation and help the child develop coping skills. Parents and caregivers can help prepare children by explaining to them what will happen, including what they will see, feel and hear during the test.

  • An EEG is a painless test.
  • Bring the child’s favourite toy or security item, such as a blanket or pillow.
  • Parents may be asked to hold younger children during the test to get a better recording.
  • If the child is asked to breathe rapidly, they may feel light-headed or have some numbness in their fingers.

The preparation you can provide for an EEG depends on the age and experience of the child. See the following for more age-specific information on helping children cope with tests and treatment.

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