Electroencephalography (EEG)

Introduction

The electroencephalogram (EEG) is a measure of brain waves. It is a readily available test that provides evidence of how the brain functions over time.

• The EEG is used in the evaluation of brain disorders. Most commonly it is used to show the type and location of the activity in the brain during a seizure. It also is used to evaluate people who are having problems associated with brain function. These problems might include confusion, coma, tumors, long-term difficulties with thinking or memory, or weakening of specific parts of the body (such as weakness associated with a stroke).
• An EEG is also used to determine brain death. It may be used to prove that someone on life-support equipment has no chance of recovery.
• Scientists first captured and recorded brain waves in dogs in 1912. By the 1950s the EEG was used commonly throughout the United States.

Risks

Very few risks are associated with an EEG. You may be asked not to take certain seizure or antidepressant medications 1-2 days before you have an EEG. This may make you more prone to have a seizure, which is exactly what the doctor would like to measure. During an EEG, the doctor may encourage the things that stimulate your seizures, such as deep breathing or flashing lights, so that he or she can see what happens in your brain during your seizures.

EEG Preparation

You should be given instructions when the EEG is scheduled.

· If you routinely take seizure medication to prevent seizures, antidepressants, or stimulants, you may be asked to stop taking these medications 1-2 days before the test.

· You may be told not to consume caffeine before the test.

· You should avoid using hair styling products (hairspray or gel) on the day of the exam.

· It is prudent to have someone take you to the EEG location, especially if you have been asked to stop your seizure medications.

· If you are having a sleep EEG, you may be asked to stay awake the night before the exam.

During the Procedure

A standard noninvasive EEG takes about 1 hour. You will be positioned on a padded bed or table, or in a comfortable chair. To measure the electrical activity in various parts of your brain, a nurse or EEG technician will attach 16-20 electrodes to your scalp. Your brain generates electrical impulses that these electrodes will pick up. To improve the conduction of these impulses to the electrodes, a gel will be applied to them. Then a temporary glue will be used to attach them to your skin. No pain will be involved.

The electrodes only gather the impulses given off by your brain and do not transmit any stimulus to your brain. The technician may tell you to breathe slowly or quickly and may use visual stimuli such as flashing lights to see what happens in your brain when you see these things. The brain's electrical activity is recorded continuously throughout the exam on special EEG paper.

• Sleep EEG: During a specialized sleep EEG, you will be placed in a room that encourages relaxation and asked to fall asleep while your brain's electrical activity is recorded. The sleep EEG will last about 2-3 hours.
• Ambulatory EEG: During a specialized ambulatory (moving from place to place, walking) EEG, the electrodes are placed on your scalp and attached to a portable cassette recorder. You will be allowed to go home and resume normal activities while the EEG continuously records. The ambulatory EEG typically lasts 24 hours.

After the Procedure

After the test is complete, the technician will remove the electrodes. You will be instructed when to resume any medications. You generally will be ready to go home immediately following the test. No recovery time is required. Because you may be at risk for a seizure (especially if your medication has been withheld prior to the EEG), you should have someone take you home, and you should not drive. You should avoid activities that may harm you if a seizure occurs, until you have resumed your seizure medication for an adequate length of time. These precautions do not necessarily apply to the person who was not on any seizure medication prior to the EEG.

Next Steps

The doctor or technician will tell you when and how you will learn the results or your EEG. Probably you will either get a telephone call or have an office visit. If you have not learned the test results within 2-3 weeks and you don't yet have a follow up appointment, call your doctor.

When to Seek Medical Care

If your typical seizure pattern changes, you should notify your doctor. If you experience any changes in mental status, or any new weakness, numbness, or tingling, you should tell the doctor immediately. If you experience new onset seizures, an increase in the usual number of seizures, an altered mental status, or a new loss of function, go to the nearest Emergency Department for treatment.

Results

When the EEG is finished, the results are interpreted by a neurologist (a doctor who specializes in the nervous system). The EEG records your brain waves from various locations in the brain. Each area produces a different brain wave strip for the neurologist to interpret.

· When examining the recordings, the neurologist looks for certain patterns that represent problems in a particular area of the brain. For example, certain types of seizures have specific brain wave patterns that the trained neurologist recognizes. Likewise, a normal brain has a specific brain wave pattern that the trained neurologist recognizes. The neurologist must look at all recorded tracings, decide what is normal and what is not, and determine what the abnormal tracings represent.

· The neurologist forwards the EEG results to the doctor who ordered the test, and you are then notified as arranged.