Normal Values:

Brain electrical activity has a certain number of waves per second (frequencies) that are normal for different levels of consciousness. For example, brain waves are faster when you are awake, and slower when you are sleeping.

There are also normal patterns to these waves. The EEG looks for these frequencies and patterns.

What abnormal results mean:

Abnormal results on an EEG test may be due to:

• Abnormal bleeding (hemorrhage)
• 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
• Migraines (in some cases)
• Seizure disorder (such as epilepsy or convulsions)
• Sleep disorder (such as narcolepsy)
• Swelling of the brain (encephalitis)

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