žAn electroencephalogram (EEG) is a test that detects electrical activity in your brain using small, flat metal discs (electrodes) attached to your scalp. Your brain cells communicate via electrical impulses and are active all the time, even when you’re asleep. This activity shows up as wavy lines on an EEG recording.

žAn EEG is one of the main diagnostic tests for epilepsy. An EEG may also play a role in diagnosing other brain disorders.

How Do I Prepare For an EEG?

žDiscuss any medications you are taking with your doctor prior to your procedure.

žWash your hair the night before the test. Do not use hair cream, oils, or spray afterward.

žAvoid anything with caffeine on the day of the test, because caffeine can affect the test results.

What Happens During the EEG?

žDuring an EEG, you lie down on the examining table or bed while about 20 electrodes are attached to your scalp. You are asked to relax and lie first with your eyes open, then later with them closed. You may be asked to breathe deeply and rapidly or to stare at a flashing light — both of these activities produce changes in the brain-wave patterns. If you are prone to seizures, it is rare that you may experience one during the test. If you are being evaluated for a sleep disorder, EEG may be performed continuously during the night while you are asleep. Such a recording, which may involve an evaluation of other body functions during sleep, such as respiration and pulse, is referred to as polysomnography.

What Happens After an EEG?

žWhen the EEG is done, the electrodes are removed and the glue that held them in place is washed away with acetone and the paste with water. Unless you are actively having seizures or are restricted by your doctor, you may drive home.

žIf you stopped taking anticonvulsant drugs for the EEG, you can usually start taking them again.

A neurologist examines the EEG recording for abnormalities in the brain-wave pattern, which may reflect diseases of the nervous system.

Types of EEG

Routine EEG. This is the basic EEG test that is most often used to diagnose epilepsy and other neurological conditions. It provides a 20 to 40 minute sample of brain activity.

žAmbulatory EEG. If the sample of brain activity gathered from the routine EEG isn’t enough, an ambulatory EEG may be recommended to capture more activity and give a better idea of when seizures occur. This EEG can capture as much as 72 hours worth of brain activity, which is recorded while you go about your normal daily activities outside the doctor’s office.

žSleep EEG. Done to patients who have seizures when asleep or tired.

žUsually done in hospital, using a standard EEG machine before the test, you may be given medication and it lasts for 1 or 2 hours.

ž Video is frequently recorded during the EEG.

ž Your body motions are captured by a video camera while the EEG simultaneously records your brain waves.

žThis combined recording may help your doctor diagnose and treat your condition

Why is the test performed?

žEEG is used to look at your brain activity. It can be used to diagnose or monitor the following health conditions:

• žAbnormal changes in body chemistry that affect the brain
• žBrain diseases, such as Alzheimer disease
• žConfusion
• žFainting spells or periods of memory loss that cannot be explained otherwise
• žHead injuries
• žInfections
• žSeizures
• žTumors
• žEEG is also used to:
• žEvaluate problems with sleep (sleep disorders)
• žMonitor the brain during brain surgery
• žAn EEG may be done to show that the brain has no activity, in the case of someone who is in a deep coma. It can be helpful when trying to decide if a person is brain dead.
• EEG cannot be used to measure intelligence