(Electroencephalography, Brain Wave Test)
An electroencephalogram (EEG) detects abnormalities in the brain waves or electrical activity of the brain. During the procedure, electrodes consisting of small metal discs with thin wires are pasted on the scalp. The electrodes detect tiny electrical charges that result from the activity of the 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 doctor then interprets the reading.
Related procedures that may be performed are evoked potential studies. These studies are used to measure electrical activity in the brain in response to stimulation of sight, sound, or touch. Please see this procedure for additional information.
An EEG records patterns of brain activity. Among the basic waveforms are the alpha, beta, theta, and delta rhythms:
During an EEG, typically about 100 pages or computer screens of activity are evaluated. Special attention is paid to the basic waveforms, but brief bursts of energy and responses to stimuli, such as light, are also examined.
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.
Patients with lesions of the 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 doctor 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 only record activity and 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 due to the flashing lights or the deep breathing that may be involved during the test. If this occurs, a doctor will treat the seizure immediately.
There may be other risks depending on your specific medical condition. Be sure to discuss any concerns with your doctor prior to the procedure.
Certain factors or conditions may interfere with the reading of an EEG test. These include, but are not limited to, the following:
An EEG may be performed on an outpatient basis or as part of your stay in a hospital. Procedures may vary depending on your condition and your doctor's practices.
Generally, an EEG procedure follows this process:
Once the test is complete, 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 any sedatives were taken 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 doctor will inform you as to when to resume any medications you stopped taking before the test.
Your doctor may give you additional or alternate instructions after the procedure, depending on your particular situation.
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