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Why is an EEG performed?
An electroencephalogram (EEG) (elek-tro-in-SEF-all-oh-gram) is a neurological test that measures the electrical signals within your brain, and records them on a graph. An EEG is used to evaluate the cause of seizures, diagnose comas, and evaluate strokes and sleep disorders. It can also be used to determine the presence and location of brain injuries, abscesses, tumors, intracranial hemorrhages, and to confirm brain death.
What should I do to prepare for an EEG?
To prepare for an EEG:
- Make sure you are well rested and not sleep deprived the night before the exam.
- Inform the doctor of any medications you are taking. You may be advised to stop taking any sleep (and sometimes seizure) medications because they may have an impact on the test results.
- Avoid foods or beverages that contain caffeine.
- Make sure your hair is clean and free of any hair sprays, creams or gels.
Lack of sleep, medications, low blood sugar, and movement of the eyes, tongue, head or body, may affect the results.
What happens during the test?
During the procedure, you relax in a reclining chair or lie on a bed either in a hospital or doctor's office. Electrodes are attached to specific regions of the scalp with a special paste or glue. You will then be asked to relax and lie first with your eyes open, and then closed. You may also be asked to breathe deeply and rapidly, or to stare at flashing lights.
The electrodes pick up the electrical signals produced by the brain and transmit them to an electroencephalograph, which produces graphs on paper or on a computer screen. The procedure takes approximately two hours and is painless. After the exam, the electrodes are removed. Unless your physician restricts you, you may drive home. If you are being evaluated for a sleep disorder, an EEG may be performed continuously during the night while you are asleep.
Does an EEG have risks?
Looking at flashing lights during the test can cause seizures in some people with a seizure disorder.
What are normal results?
A neurologist or other physician will evaluate the type of brainwaves, location and brainwave patterns, and responses to stimulation (such as lights or noise). The basic waveforms are the alpha, beta, theta, and delta rhythms. "Normal" brainwave patterns vary. However, a normal adult in a fully conscious but relaxed state, typically registers regularly recurring oscillating alpha waves that occur at a frequency of 8 to 12 cycles per second. Young children and sleeping adults typically register delta waves of under 4 cycles per second.
What are abnormal results?
Bursts or spikes of electrical activity can be seen in EEG readings of patients with epilepsy or other seizure disorders. The electroencephalograph pattern and location of these waves may also identify the specific type of seizure. The brainwave patterns of other disorders vary widely. Generally, brain wave patterns in patients with brain disease, mental retardation, and brain injury show overall slowing.
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External Source
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US National Library of Medicine
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This article was reviewed and updated June 2007.
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