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By Mayo Clinic staff
During the test
You'll feel little or no discomfort during an EEG. The electrodes don't transmit any sensations. They just record your brain waves. If you need to sleep during the EEG, you might be given a sedative beforehand to help you relax. During the test:
- A technician measures your head and marks your scalp with a type of pencil, to indicate where to attach the electrodes. Those spots on your scalp may be scrubbed with a gritty cream to improve the quality of the recording.
- A technician attaches flat metal discs (electrodes) to your scalp using a special adhesive. The electrodes are connected with wires to an instrument that amplifies — makes bigger — the brain waves and records them on computer equipment. Some people wear an elastic cap fitted with electrodes, instead of having the adhesive applied to their scalps. Once the electrodes are in place, an EEG typically takes 30 to 60 minutes.
- You relax in a comfortable position with your eyes closed during the test. At various times, the technician may ask you to open and close your eyes, perform a few simple calculations, read a paragraph, look at a picture, breathe deeply (hyperventilate) for a few minutes, or look at a flashing light.
Your doctor may want you to have a video EEG, which may require you to be admitted to a hospital. During this test, your body motions are captured by a video camera while the EEG simultaneously records your brain waves during a seizure. This may help your doctor pinpoint the location in your brain where seizures begin.
After the test
After the test, the technician removes the electrodes or cap. If no sedative was given, you should feel no side effects after the procedure, and you can return to your normal routine.
If you used a sedative, it may take about an hour to partially recover from the medication. You'll need someone to take you home because it can take up to a day for the full effects of the sedative to wear off. Rest and don't drive for the remainder of the day.
- Aminoff MJ. Electrophysiology. In: Goetz CG. Textbook of Clinical Neurology. 3rd ed. Philadelphia, Pa.: Saunders Elsevier; 2007:477.
- Hirsch LJ, et al. Electroencephalography (EEG) in the diagnosis of seizures and epilepsy. http://www.uptodate.com/home/index.html. Accessed March 23, 2011.
- Aminoff MJ. Electrodiagnostic studies of nervous system disorders: EEG, evoked potentials and EMG. In: Fauci AS, et al. Harrison's Online. 17th ed. New York, N.Y.: The McGraw-Hill Companies; 2008. http://www.accessmedicine.com/content.aspx?aID=2885536. Accessed March 23, 2011.
- Importance of EEG tests. Epilepsy Foundation. http://www.epilepsyfoundation.org/about/quickstart/newlydiagnosed/qstreatment/qstreeg.cfm. Accessed March 23, 2011.
- Neurological diagnostic tests and procedures. National Institute of Neurological Disorders and Stroke. http://www.ninds.nih.gov/disorders/misc/diagnostic_tests.htm. Accessed March 23, 2011.
- Devinsky O. Epilepsy: Patient and Family Guide. 3rd ed. New York, N.Y.: Demos Medical Publishing LLC; 2008:76.
- Sedation analgesia. American Society of Anesthesiologists. http://www.lifelinetomodernmedicine.com/Types-Of-Anesthesia/Sedation-Analgesia.aspx. Accessed March 23, 2011.
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