What is it?
An electroencephalogram (EEG) is a test to detect problems in the electrical activity of the brain. Brain cells communicate with each other by producing tiny electrical impulses. In an EEG, this faint electrical activity is measured by putting electrodes on the scalp.
How is the test performed?
A technician will apply flat metal disks (electrodes) in different positions on the scalp. The disks are held in place with a sticky paste. The electrodes are connected by wires to an amplifier and a recording machine.
The recording machine converts the electrical impulses into patterns that can be seen on a computer screen, as well as stored on a computer disk. Patients need to lie still with their eyes closed because any movement can alter the results.
Patients may be asked to do certain things during the recording, such as breathe deeply and rapidly for several minutes or look at a bright flashing light.
Your health care provider will provide information on what to do to prepare for the test.
What can the test tell my doctor?
This test can be performed to help evaluate:
-- Head injuries
-- Degenerative diseases, such as Alzheimer’s disease
-- Abnormal change in body chemistry that can affect the brain
-- Periods of unconsciousness
-- Sleep disorders
-- Attention problems
-- Cerebral infarction (tissue that is dead because of a blockage of the blood supply)
-- Encephalitis (inflammation of the brain)
-- Hemorrhage (abnormal bleeding caused by a ruptured blood vessel)
The EEG may be done to show that the brain has no activity in the case of someone in a deep coma. It can be helpful when trying to decide if someone is brain dead.
Brain electrical activity has certain frequencies (the number of waves per second) that are normal for different levels of consciousness. For example, brain waves are faster when you are awake, and slower when you're sleeping. There are also normal patterns to these waves. These frequencies and patterns are what the EEG reader looks for.
The procedure is very safe. This test causes no discomfort. Although having electrodes pasted onto your skin may feel strange, they only record activity and do not produce any sensation. No significant electricity passes from the electrode into your skin.
If patients have a seizure disorder, a seizure may be triggered by flashing lights or by fast breathing (hyperventilation) that is done during the test. The health care provider performing the EEG is trained to help if this happens.