Medical Encyclopedia

 

Medical Encyclopedia

Other encyclopedia topics:  A-Ag  Ah-Ap  Aq-Az  B-Bk  Bl-Bz  C-Cg  Ch-Co  Cp-Cz  D-Di  Dj-Dz  E-Ep  Eq-Ez  F  G  H-Hf  Hg-Hz  I-In  Io-Iz  J  K  L-Ln  Lo-Lz  M-Mf  Mg-Mz  N  O  P-Pl  Pm-Pz  Q  R  S-Sh  Si-Sp  Sq-Sz  T-Tn  To-Tz  U  V  W  X  Y  Z  0-9 

EEG

Contents of this page:

Illustrations

Brain
Brain
Brain wave monitor
Brain wave monitor

Alternative Names    Return to top

Electroencephalogram; Brain wave test

Definition    Return to top

An electroencephalogram (EEG) is a test to detect problems in the electrical activity of the brain.

How the Test is Performed    Return to top

Brain cells communicate with each other by producing tiny electrical impulses. In an EEG, this faint electrical activity is measured by putting electrodes on the scalp.

The test is performed by an EEG technician in your health care provider's office, at a hospital, or at an independent laboratory. You will be asked to lie on your back on a bed or in a reclining chair.

The technician will apply between 16 and 25 flat metal disks (electrodes) in different positions on your scalp. The disks are held in place with a sticky paste. The electrodes are connected by wires to an amplifier and a recording machine.

The recording machine converts the electrical impulses into patterns that can be seen on a computer screen, as well as stored on a computer disk. Before computers, the activity was printed on paper. In either case, the electical activity looks like a series of wavy lines. You will need to lie still with your eyes closed because any movement can alter the results.

You may be asked to do certain things during the recording, such as breathe deeply and rapidly for several minutes or look at a bright flashing light.

How to Prepare for the Test    Return to top

You will need to wash your hair the night before the test. Do not use any oils, sprays, or conditioner on your hair before this test.

Your health care provider may want you to stop taking certain medications before the test. Do not change or stop medications without first talking to your health care provider.

You should avoid all foods containing caffeine for 8 hours before the test.

Sometimes it is necessary to sleep during the test, so you may be asked to reduce your sleep time the night before. If you're asked to sleep as little as possible before the test, don't consume any caffeine, energy drinks, or other products that help you stay awake.

How the Test Will Feel    Return to top

This test causes no discomfort. Although having electrodes pasted onto your skin may feel strange, they only record activity and do not produce any sensation. No significant electricity passes from the electrode into your skin.

Why the Test is Performed    Return to top

EEG is used to help diagnose if you're having seizures and if so, what type. An EEG is also used to find the causes of confusion, and to evaluate head injuries, tumors, infections, degenerative diseases such as Alzheimer's disease, and abnormal changes in body chemistry that affect the brain.

It is also used to evaluate problems with sleep ( sleep disorders) and to investigate periods of unconsciousness. The EEG may be done to show that the brain has no activity, in the case of someone in a deep coma. It can be helpful when trying to decide if someone is brain dead.

EEG can not be used to measure intelligence.

Normal Results    Return to top

Brain electical 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.

What Abnormal Results Mean    Return to top

Abnormal results on an EEG test may be due to:

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

Risks    Return to top

The procedure is very safe. However, the flashing lights or fast breathing (hyperventilation) required during the test may trigger seizures in those with seizure disorders. The health care provider performing the EEG is trained to take care of you if this happens.

It may be difficult to get the paste out of your hair, but it should come out after a few washings with regular shampoo.

References    Return to top

Foldvary-Schaefer N, Wyllie E. Epilepsy. In: Goetz, CG, ed. Textbook of Clinical Neurology. 3rd ed. Philadelphia, PA: Saunders Elsevier; 2007: chap 52.

Update Date: 3/2/2009

Updated by: David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc. Previously reviewed By: Daniel B. Hoch, PhD, MD, Assistant Professor of Neurology, Harvard Medical School, Department of Neurology, Massachusetts General Hospital (5/29/2008)

A.D.A.M. Logo

The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed physician should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. Copyright 1997-2009, A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.