The World of EEGs

The World of EEGs

An electroencephalogram (EEG) is a test that measures and records the electrical activity of the patient’s brain.  Electrodes are attached to the patient’s head and hooked by wires to a computer.  The computer records the brain's electrical activity on the screen or on paper as wavy lines.  Certain conditions, such as seizures, can be seen by the changes in the normal pattern of the brain's electrical activity.

An EEG determines if the patient’s level of alertness or consciousness is normal, if abnormalities exist in one specific part of the brain, if a patient has a tendency to have seizures or convulsions, and if a patient is likely to have a particular kind of epilepsy.

Sometimes a patient may have a tendency to have seizures, but his or her EEG is normal at the particular time it is done. That’s because people with a seizure tendency may have abnormalities that come and go from hour to hour or day to day.   In these cases, a repeat EEG or a longer period of EEG monitoring may be useful.

An EEG may be done to:

  • Diagnose epilepsy and see what type of seizures are occurring.  EEG is the most useful and important test in confirming a diagnosis of epilepsy.
  • Check for problems with loss of consciousness or dementia.
  • Help find out a person's chance of recovery after a change in consciousness.
  • Find out if a person who is in a coma is brain-dead.
  • Help determine a sleep disorder, such as narcolepsy.
  • Watch brain activity while a person is receiving general anesthesia during brain surgery.
  • Help find out if a person has a physical problem (problems in the brain, spinal cord, or nervous system) or a mental health problem.

Types of EEGs:

Ambulatory EEG (or "extended EEG"): A test that measures the electrical activity in the brain and detects abnormalities in the brain waves or electrical activity of the brain.   The EEG is recorded over an extended period of time, usually 24-72 hours.


The Ambulatory EEG provides the physician an extended evaluation period of the patient’s brain patterns while the patient goes about their daily routine at home, school or work.   The patient carries a small, portable recording unit.   The extended monitoring period increases the physician’s chances of finding a true diagnosis.    


Routine EEG: Records electrical impulses from the nerves in the head.  EEG exams are done by putting electrodes (detectors of electricity) on the scalp and seeing what the electrical impulses look like when the patient is awake, asleep, in a room with a flashing light or sometimes when the patient is asked to breathe deeply over and over.  When the EEG is done, no electricity is put in to or taken out of the patient. The electrical signals that the brain produces are simply detected and printed out on a computer screen or a piece of paper.


Video EEG: Uses a regular EEG machine, but adds video monitoring for ambulatory and routine EEG exams.  Using video allows the physician to view electrical activity in the brain and a person's physical activity, and make a comparison between the two.


Long Term EEG: Same process as the ambulatory EEG, but is performed in a hospital setting.

Preparing for the EEG examination


Prior to the test

For the test

During the test

After the test

Wash hair

Don't use any conditioner, hairspray, oil, or other product on your hair after you wash it

No braids or weave

Wear shirt that buttons or zips

NO chewing gum

Return equipment (Ambulatory EEG)

Eat normally

Don't consume any caffeine for at least eight hours

Bring a scarf or hat (Ambulatory EEG)

NO talking-follow the technician’s instructions

Wash hair

Ask your doctor if you need to discontinue any of your medications temporarily


Continue medications (Ambulatory EEG)

Follow up with physician


No tampering with the computer or electrodes


No showers (Ambulatory EEG)