EEG is the name of a commonly performed investigation that detects abnormalities in the electrical activity of the brain.  An EEG is not a ‘brain scan’.  The EEG is a painless procedure.

Neurons (brain cells) communicate with each other via tiny electric currents.  In an EEG, small flat metal discs (electrodes) are placed on the scalp in order to record the brain’s continuous electrical activity.  These tiny electrical impulses are then transmitted via wires to a recording machine and the information is then displayed, as a series of wavy lines, on a computer screen or paper.

The test is performed by an EEG technician either at your physician’s office or in a hospital.  The EEG technician will ask you to lie on your back on a bed or to sit in a reclining chair where a series of electrodes (usually around 20) will be applied to your scalp.  The electrodes are held in place by way of a sticky paste.  The electrodes only record activity and do not produce any sensations.

• To assist in the evaluation of patients with convulsions or seizures.
• To help establish the diagnosis of epilepsy.
• To evaluate patients with altered mental status, confusion or coma.
• To evaluate patients with head injury.
• To assess patients with various brain disorders.
• To confirm brain death.
• To assess certain sleep disorders.

• Wash your hair the night before the test.
• Do not use conditioner, oils or sprays prior to the test.
• Avoid all caffeine-containing substances prior to the test.
• Do not stop or reduce your medications prior to the test unless instructed to do so by your physician. 

You may be asked to perform several tasks during the recording session.  These are necessary for the correct interpretation of the EEG and also assist in revealing abnormalities that may otherwise go undetected.  These tasks include:

• Opening and closing your eyes.
• Breathing deeply for several minutes.
• Looking at a bright flickering light.

An EEG is interpreted by a neurologist or a neurophysiologist.  If an EEG that is recorded during wakefulness is normal or only reveals nonspecific abnormalities, your physician may request an EEG during sleep.  Similarly, your physician may request a sleep-deprived EEG.  For this, you will be instructed not to sleep the night before the test.  This may at times help to reveal abnormalities that would otherwise go undetected.

It is possible to record the EEG over a period of one or more days, during both daytime activities and sleep, using a small portable EEG recorder which is worn on a waist belt.  This is known as ambulatory EEG monitoring.

In certain circumstances, a patient may need to be admitted to an epilepsy monitoring unit in order to record the brain wave activity while simultaneously maintaining video camera surveillance for several days.  The information is stored on a computer where it can be reviewed at a later time by a neurologist or neurophysiologist.