An EEG is a test that detects abnormalities in your brain waves, or in the electrical activity of your brain. During the procedure, electrodes consisting of small metal discs with thin wires are pasted onto your scalp. The electrodes detect tiny electrical charges that result from the activity of your brain cells. The charges are amplified and appear as a graph on a computer screen, or as a recording that may be printed out on paper. Your healthcare provider then interprets the reading.
During an EEG, your healthcare provider typically evaluates about 100 pages, or computer screens, of activity. He or she pays special attention to the basic waveform, but also examines brief bursts of energy and responses to stimuli, such as flashing lights.
Evoked potential studies are related procedures that also may be done. These studies measure electrical activity in your brain in response to stimulation of sight, sound, or touch.
The EEG is used to evaluate several types of brain disorders. When epilepsy is present, seizure activity will appear as rapid spiking waves on the EEG.
People with lesions of their brain, which can result from tumors or stroke, may have unusually slow EEG waves, depending on the size and the location of the lesion.
The test can also be used to diagnose other disorders that influence brain activity, such as Alzheimer’s disease, certain psychoses, and a sleep disorder called narcolepsy.
The EEG may also be used to determine the overall electrical activity of the brain (for example, to evaluate trauma, drug intoxication, or extent of brain damage in comatose patients). The EEG may also be used to monitor blood flow in the brain during surgical procedures.
There may be other reasons for your healthcare provider to recommend an EEG.
The EEG has been used for many years and is considered a safe procedure. The test causes no discomfort. The electrodes record activity. They do not produce any sensation. In addition, there is no risk of getting an electric shock.
In rare instances, an EEG can cause seizures in a person with a seizure disorder. This is due to the flashing lights or the deep breathing that may be involved during the test. If you do get a seizure, your healthcare provider will treat it immediately.
Other risks may be present, depending on your specific medical condition. Be sure to discuss any concerns with your healthcare provider before the procedure.
Certain factors or conditions may interfere with the reading of an EEG test. These include:
Ask your healthcare provider to tell you what you should do before your test. Below is a list of common steps that you may be asked to do.
An EEG may be done on an outpatient basis, or as part of your stay in a hospital. Procedures may vary depending on your condition and your healthcare provider’s practices. Talk with your healthcare provider about what you will experience during your test.
Generally, an EEG procedure follows this process:
Once the test is completed, the electrodes will be removed and the electrode paste will be washed off with warm water, acetone, or witch hazel. In some cases, you may need to wash your hair again at home.
If you took any sedatives for the test, you may be required to rest until the sedatives have worn off. You will need to have someone drive you home.
Skin irritation or redness may be present at the locations where the electrodes were placed, but this will wear off in a few hours.
Your healthcare provider will inform you when you may resume any medicines you stopped taking before the test.
Your healthcare provider may give you additional or alternate instructions after the procedure, depending on your particular situation.