What is Electroencephalogram (EEG)?
An electroencephalogram (EEG) is a test used to evaluate the electrical activity in the brain. Brain cells communicate with each other through electrical impulses. An EEG can be used to help detect potential problems associated with this activity.
An EEG tracks and records brain wave patterns. Small flat metal discs called electrodes are attached to the scalp with wires. The electrodes analyze the electrical impulses in the brain and send signals to a computer that records the results.
The electrical impulses in an EEG recording look like wavy lines with peaks and valleys. These lines allow doctors to quickly assess whether there are abnormal patterns. Any irregularities may be a sign of seizures or other brain disorders.
Why is Electroencephalogram (EEG) performed?
An EEG can determine changes in brain activity that might be useful in diagnosing brain disorders, especially epilepsy or another seizure disorder. An EEG might also be helpful for diagnosing or treating the following disorders:
- Brain tumor
- Brain damage from head injury
- Brain dysfunction that can have a variety of causes (encephalopathy)
- Inflammation of the brain (encephalitis)
- Sleep disorders
An EEG might also be used to confirm brain death in someone in a persistent coma. A continuous EEG is used to help find the right level of anesthesia for someone in a medically induced coma.
What should I know before receiving Electroencephalogram (EEG)?
There are no risks associated with an EEG. The test is painless and safe.
Some EEGs do not include lights or other stimuli. If an EEG does not produce any abnormalities, stimuli such as strobe lights, or rapid breathing may be added to help induce any abnormalities.
When someone has epilepsy or another seizure disorder, the stimuli presented during the test (such as a flashing light) may cause a seizure. The technician performing the EEG is trained to safely manage any situation that might occur.
How to prepare for Electroencephalogram (EEG)?
Before the test, you should take the following steps:
- Wash your hair the night before the EEG, and don’t put any products (like sprays or gels) in your hair on the day of the test.
- Ask your doctor if you should stop taking any medications before the test. You should also make a list of your medications and give it to the technician performing the EEG.
- Avoid eating or drinking anything containing caffeine for at least eight hours before the test.
Your doctor may ask you to sleep as little as possible the night before the test if you have to sleep during the EEG. You may also be given a sedative to help you relax and sleep before the test begins.
After the EEG is over, you can continue with your regular routine. However, if you were given a sedative, the medication will remain in your system for a little while. This means that you’ll have to bring someone with you so they can take you home after the test. You’ll need to rest and avoid driving until the medication wears off.
What happens during Electroencephalogram (EEG)?
A technician measures your head and marks your scalp with a special pencil to indicate where to attach the electrodes. Those spots on your scalp might be scrubbed with a gritty cream to improve the quality of the recording.
A technician attaches discs (electrodes) to your scalp using a special adhesive. Sometimes, an elastic cap fitted with electrodes is used instead. The electrodes are connected with wires to an instrument that amplifies the brain waves and records them on computer equipment.
Once the electrodes are in place, an EEG typically takes up to 60 minutes. Testing for certain conditions require you to sleep during the test. In that case, the test can be longer.
You relax in a comfortable position with your eyes closed during the test. At various times, the technician might ask you to open and close your eyes, perform a few simple calculations, read a paragraph, look at a picture, breathe deeply for a few minutes, or look at a flashing light.
Video is routinely recorded during the EEG. Your body motions are captured by a video camera while the EEG records your brain waves. This combined recording can help your doctor diagnose and treat your condition.
Ambulatory EEGs (aEEGs), which allow for longer monitoring outside an office or hospital setting, are in limited use. This test can record brain activity over several days, which increases the chances of catching seizure activity. However, compared to inpatient video-EEG monitoring, an ambulatory EEG is not as good at determining the difference between epileptic seizures and nonepileptic seizures.
What happens after Electroencephalogram (EEG)?
The technician removes the electrodes or cap. If you had no sedative, you should feel no side effects after the procedure, and you can return to your normal routine.
If you used a sedative, it will take time for the medication to begin to wear off. Arrange to have someone drive you home. Once home, rest and don’t drive for the rest of the day.
If you have any questions about the Electroencephalogram (EEG), please consult with your doctor to better understand your instructions.
Explanation of results
What do my results mean?
A neurologist (someone who specializes in nervous system disorders) interprets the recordings from the EEG and then sends the results to your doctor. Your doctor may schedule an appointment to go over the test results with you.
Electrical activity in the brain appears in an EEG as a pattern of waves. Different levels of consciousness, like sleeping and waking, have a specific range of frequencies of waves per second that are considered normal. For example, the wave patterns move faster when you’re awake than when you’re asleep. The EEG will show if the frequency of waves or patterns are normal. Normal activity typically means you don’t have a brain disorder.
Abnormal EEG results may be due to:
- Epilepsy or another seizure disorder
- Abnormal bleeding or hemorrhage
- Sleep disorder
- Encephalitis (swelling of the brain)
- Dead tissue due to a blockage of blood flow
- Alcohol or drug abuse
- Head injury
It’s very important to discuss your test results with your doctor. Before you review the results, it may be helpful to write down any questions you might want to ask. Be sure to speak up if there’s anything about your results that you don’t understand.
Depending on the laboratory and hospital, the normal range for Electroencephalogram (EEG) may vary. Please discuss with your doctor any questions you may have about your test results.
Hello Health Group does not provide medical advice, diagnosis or treatment.
EEG (Electroencephalogram). https://www.healthline.com/health/eeg#uses. Accessed October 16, 2018.
EEG (electroencephalogram). https://www.mayoclinic.org/tests-procedures/eeg/about/pac-20393875. Accessed October 16, 2018.
Review Date: November 4, 2018 | Last Modified: November 4, 2018