An electroencephalogram (EEG) is a test that monitors and records the electrical activity of your brain using  electrodes attached to your scalp and connected to a computer. The computer records and shows your brain’s electrical activity as wavy lines on the screen or on paper. Seizures, for example, may be identified by monitoring abnormalities in the usual pattern of the brain’s electrical activity.

Why Is It Done?

An electroencephalogram (EEG) may be performed in order to:

  • Assist in the confirmation of an epilepsy diagnosis and the selection of the appropriate treatment choice depending on seizure type.
  • Identify  a possible brain lesion, such as a tumour, inflammation, or infection.
  • Examine  dementia.
  • Investigate sleep disorders such as narcolepsy.

Preparation for the test

Caffeine-containing foods (such as coffee, tea, cola, and chocolate) should be avoided for at least 8 hours before the test. Eat a modest breakfast before the test since low blood sugar (hypoglycemia) may create an abnormal test result.

Because the electrodes are connected to your scalp, you must have clean hair that is free of sprays, oils, creams, lotions, and other hair preparations. Shampoo and rinse your hair with clean water the night before or the morning of the test. After shampooing, do not use any conditioners or oils on your hair.

Certain types of aberrant electrical activity in the brain may need you to be sleeping throughout the recording. As a consequence, you may be advised to decrease your sleep duration the night before the test to 2 to 3 hours by going to bed later and waking up earlier than normal. 


You will be asked to relax on your back on a bed or examination table, or to close your eyes and relax in a chair. The EEG technician will put 16 to 25 flat metal discs (electrodes) on your skull in various locations, using a sticky adhesive to keep the electrodes in place. Wires link the electrodes to a machine that amplifies and records the electrical activity within the brain. The electrical activity is recorded by the EEG machine as a sequence of wavy lines on a moving sheet of paper or as an image on the computer screen.

If a longer recording is required, the recording may be paused from time to time to enable you to stretch and reposition yourself.

What Does the Test Feels like?

The electroencephalogram (EEG) is a non-invasive test. During the EEG recording, you will not feel anything out of the usual.

To place the electrodes, a substance is used, and some gel may remain in your hair after the test, therefore you will need to wash your hair to remove it.

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