Associated Neurological Specialties and Sleep Disorders Center

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What Is an 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.

The test 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, where the results are recorded.

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 an EEG Performed?


An EEG is used to detect problems in the electrical activity of the brain that may be associated with certain brain disorders. The measurements given by an EEG are used to confirm or rule out various conditions, including:

  • seizure disorders (such as epilepsy)
  • a head injury
  • encephalitis (an inflammation of the brain)
  • a brain tumor
  • encephalopathy (a disease that causes brain dysfunction)
  • memory problems
  • sleep disorders
  • stroke
  • dementia

Are There Risks Associated with an EEG?


There are no risks associated with an EEG. The test is painless and safe.

When someone has epilepsy or another seizure disorder, the stimuli presented during the test (such as a flashing light) may cause a seizure. However, the technician performing the EEG is trained to safely manage the situation should this occur.

How Do I Prepare for an EEG?


Before the test, you should take the following steps:

Wash your hair the night before the EEG, and don’t put any products (such as 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 consuming any food or drinks containing caffeine for at least eight hours prior to the test.

Your doctor may ask you to sleep as little as possible the night before the test if you’re required to sleep during the EEG. You may also be given a sedative to help you to relax and sleep before the test begins.

After the EEG is over, you can continue with your regular routine for the day. 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 has worn off.


What Can I Expect During an EEG?


An EEG measures the electrical impulses in your brain by using several electrodes that are attached to your scalp. An electrode is a conductor through which an electric current enters or leaves. The electrodes transfer information from your brain to a machine that measures and records the data.

An EEG may be given at a hospital, at your doctor’s office, or at a laboratory by a specialized technician. It usually takes 30 to 60 minutes to complete. The test typically involves the following steps:

You’ll be asked to lie down on your back in a reclining chair or on a bed.
The technician will measure your head and mark where the electrodes will be placed. These spots are then scrubbed with a special cream that helps the electrodes get a high-quality reading.
The technician will put a sticky gel adhesive on 16 to 25 electrodes. They will then be attached to various spots on your scalp.
Once the test begins, the electrodes send electrical impulse data from your brain to the recording machine. This machine converts the electrical impulses into visual patterns that can be seen on a screen. These patterns are saved to a computer.
The technician may instruct you to do certain things while the test is in progress. They may ask you to lie still, close your eyes, breathe deeply, or look at stimuli (such as a flashing light or a picture).
After the test is complete, the technician will remove the electrodes from your scalp.

During the test, very little electricity is passed between the electrodes and your skin, so you’ll feel very little to no discomfort.

What Do the EEG Test Results Mean?


A neurologist (someone who specializes in nervous system disorders) interprets the recordings taken 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.

Normal Results

Electrical activity in the brain is seen in an EEG as a pattern of waves. Different levels of consciousness, such as 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 Results

Abnormal EEG results may be due to:

  • epilepsy or another seizure disorder
  • abnormal bleeding or hemorrhage
  • sleep disorder
  • encephalitis (swelling of the brain)
  • a tumor
  • dead tissue due to a blockage of blood flow
  • migraines
  • alcohol or drug abuse
  • head injury

It’s very important to discuss your test results with your doctor. Before you review the results with them, 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.

EEG (Electroencephalogram)