Importance of EEG Tests
The electroencephalograph (EEG) is a machine that translates the electrical activity of the brain into a series of wavy lines.
An EEG test will likely be ordered to see whether there are any continuing irregularities in your brain's electrical activity that may produce seizures.
Small metal discs with thin wires, called electrodes, are pasted on the scalp. They are connected to a computer which records the results of the test.
The electrodes pick up tiny electrical charges which are produced by activity of nerve cells in the brain. The charges are amplified and recorded on the computer monitor. Changes in electrical activity alter the height of the recording. The result is a series of wavy or jagged lines. The recording may also be read out on paper.
Normal electrical activity in the brain makes a recognizable pattern. Seizures, which are rarely seen in EEG's, produce very specific, abnormal patterns. Even without your having a seizure, doctors can recognize abnormal patterns that are markers for the risk of seizures. The patterns are called different names. Common names for these abnormal patterns are spikes, polyspikes, sharp waves and spike and wave complexes. These patterns can tell your doctor a lot about your seizures, including the part of the brain where your seizures start, and may even suggest which medicine might be best for you.
Having an EEG is a painless, safe procedure. The machine can't read your mind. It has safety features to prevent you from getting an electric shock. It doesn't measure intelligence or reveal mental or emotional illness. It's not used to treat or to cure - just to find out.
How an EEG Works
EEG tests may be given in special laboratories or in hospital outpatient departments. Sometimes the person having the test will be told to stay up late the night before and to avoid caffeine drinks on the morning of the test.
The test itself may be given in a small room separated from the EEG machine and the technologist. This is done to give the person having the test a quiet, relaxing environment.
Some clinics have small TV cameras set up in the test area to videotape the person's movements during the test. The movements recorded on the videotape, when combined with the EEG recording, may give additional clues about the kind of seizure the person is having.
Before the test, the EEG technologist applies the small metal disks to several places on the scalp (hair should be washed on the morning of the test with no additional chemicals, hair sprays, cleansers, cosmetics, or setting gels applied). A special glue is used to attach the electrode disks. It washes out afterwards. Sometimes a cap with the wires already attached is used instead.
Some EEG tests are made with the patient sitting in a chair. Others are performed with the patient lying down on a couch. During the test, the technologist may ask you to breathe deeply through your mouth for a short time. This may produce a slightly dizzy feeling or a numbness in the hands or feet, which goes away when you start breathing normally again.
The technologist may shine a flashing light into your eyes, or ask you to open and close them rapidly a few times. You may be asked to sleep or to make other simple responses, depending on the aims of the test.
Children should be told what to expect during an EEG test, and can be encouraged to "practice" on a doll or stuffed animal beforehand.
The average EEG test may last 35 to 40 minutes; one involving a period of sleep will take longer.
A home monitoring variation of the standard test allows people to go on with normal activities while the recording is being made. The patient wears special headgear with electrodes connected to a recorder worn on the belt. A test like this may take several hours.
After the test, the results will be sent to your personal physician. Sometimes the medical history and other tests suggest that a person has epilepsy, but there is no sign of seizure activity on the EEG. A normal EEG does not rule out epilepsy. There may have been no seizure activity during the relatively short time the test was given, or the seizure activity may be located in such a small area of the brain that the surface electrodes failed to pick it up. When this happens, the physician may order an extended test of several hours or use special electrodes that can pick up fainter signals.
