EEG

Alternative names
electroencephalogram; brain wave test

Definition
The brain cells communicate by producing tiny electrical impulses. In the EEG, electrodes are placed on the scalp over multiple areas of the brain to detect and record the electrical impulses within the brain. Certain abnormalities can be detected by observing the characteristic pattern of the recorded brain waves. This procedure does not "read the mind" or detect senility.

How the test is performed
The test is performed by an EEG technician in a specially-designed room that may be in the health care provider's office or in the hospital. You will be asked to lie on your back on the table or in a reclining chair. The technician will apply between 16 and 25 flat metal discs (electrodes) in different positions on your scalp. The discs are held in place with a sticky paste. The electrodes are connected by wires to an amplifier and the recording machine. The recording machine converts the electrical signals into a series of wavy lines which are drawn onto a moving piece of graph paper. You will need to lie still with your eyes closed because movement can alter the results. You may be asked to do certain things during the recording, such as breathe deeply and rapidly for several minutes or look at a very bright flickering light.

How to prepare for the test
You will need to wash your hair the night before the test. No oils, sprays, or lotion should be used on your hair. The health care provider may want you to discontinue some medications before the test. You should avoid all foods containing caffeine for 8 hours before the test. Sometimes it is necessary to sleep during the test, so you may be asked to reduce your sleep time the night before.

Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experience, and level of trust.

How the test will feel
Nothing will be felt during the procedure.

Risks
The procedure is very safe. If you have a seizure disorder, a seizure may be triggered by the flashing lights or hyperventilation. The health care provider is trained to take care of you if this happens.

How the test is performed
The EEG is used to help diagnose the presence and type of seizure disorders, confusion, head injuries, brain tumors, infections, degenerative diseases, and metabolic disturbances that affect the brain. It is also used to evaluate sleep disorders and to investigate periods of unconsciousness. The EEG may be done to confirm brain death in a comatose patient. The procedure cannot be used to "read the mind," measure intelligence, or diagnose mental illness.

Normal values
The brain waves have a normal frequency, amplitude, and characteristics.

What abnormal results mean
Abnormal findings may indicate seizure disorders (epilepsy, convulsions), brain tumor, brain abscess (infection), head injury, encephalitis (inflammation of the brain), hemorrhage (abnormal bleeding caused by a ruptured blood vessel), cerebral infarct (tissue that is dead because of a blockage of the blood supply), narcolepsy (sleep epilepsy), Alzheimer's disease, and cerebral death