EEG

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Brain

Brain wave monitor

Electroencephalogram; Brain wave test

Brain electrical activity has certain frequencies (the number of waves per second) that are normal for different levels of consciousness. For example, brain waves are faster when you are awake, and slower when you're sleeping. There are also normal patterns to these waves. These frequencies and patterns are what the EEG reader looks for.

Abnormal results on an EEG test may be due to:

• An abnormal structure in the brain (such as a brain tumor)
• Attention problems
• Tissue death due to a blockage in blood flow (cerebral infarction)
• Drug or alcohol abuse
• Head injury
• Inflammation of the brain (encephalitis)
• Hemorrhage (abnormal bleeding caused by a ruptured blood vessel)
• Migraines (in some cases)
• Seizure disorder (such as epilepsy or convulsions)
• Sleep disorder (such as narcolepsy)

Note: A normal EEG does not mean that a seizure did not occur.

Review Date: 03/21/2010
Reviewed By: Linda J. Vorvick, MD, Medical Director, MEDEX Northwest Division of Physician Assistant Studies, University of Washington, School of Medicine; Luc Jasmin, MD, PhD, Department of Neurosurgery at Cedars-Sinai Medical Center, Los Angeles, and Department of Anatomy at UCSF, San Francisco, CA. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org).

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