An electroencephalogram (EEG) is a test that measures and records the electrical activity of your brain. Special sensors (electrodes) are attached to your head and hooked by wires to a computer. The computer records your 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 electroencephalogram (EEG) may be done to:

Diagnose epilepsy and see what type of seizures is 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.

Study sleep disorders, 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.

An electroencephalogram (EEG) is done in by an EEG technologist. The EEG record is read by a doctor who is specially trained to diagnose and treat disorders affecting the nervous system (neurologist).

The patient will be asked to lie on your back on a bed or table or relax in a chair with your eyes closed. The EEG technologist will attach several flat metal discs (electrodes) to different places on your head, using a sticky paste to hold the electrodes in place. A cap with fixed electrodes may be placed on your head instead of individual electrodes. In rare cases, these electrodes may be attached to the scalp with tiny needles.

The electrodes are hooked by wires to a computer that records the electrical activity inside the brain. A machine can show the activity as a series of wavy lines drawn by a row of pens on a moving piece of paper or as an image on the computer screen.

The patient lies still with eyes closed during the recording, and do not talk to the technologist unless need to. The technologist will watch you directly or through a window during the test. The recording may be stopped from time to time to allow you to stretch and reposition yourself.

The technologist may the patient to do different things during the test to record what activity  brain does at that time.

The patient may be asked to breathe deeply and rapidly (hyperventilate). Usually he will take 20 breaths a minute for 3 minutes.

The patient may be asked to look at a bright, flashing light called a strobe. This is called photic or stroboscopic stimulation.

Later you will be asked to go to sleep. If you can't fall asleep, you may be given a sedative to help you fall asleep. If an EEG is being done to check a sleep problem, an all-night recording of your brain's electrical activity may be done.

An EEG takes 1 to 2 hours. After the test, you may do your normal activities. But if you were sleep-deprived or given a sleep medicine, have someone drive you home after the test.

There is no pain with an electroencephalogram (EEG).

If paste is used to hold the electrodes, some paste may stay in your hair after the test, so you will have to wash your hair to remove it. If needle electrodes are used (which is rare), you will feel a brief, sharp prick (about like having a hair pulled out) when each electrode is inserted. If electrodes are placed in your nose, they may cause a tickling feeling and, rarely, some soreness or a small amount of bleeding for 1 to 2 days after the test.

If you are asked to breathe rapidly, you may feel lightheaded or have some numbness in your fingers. This reaction is normal. It will go away a few minutes after you start breathing normally again.