Electroencephalography (EEG)

An EEG, or electroencephalogram, is a recording of the electrical activity of the brain. During the test, small electrodes (small metal discs) are placed on the head. The electrodes can detect electrical signals between the cells in the brain. A doctor can look at the results from the EEG and get information on how the brain is working.

The brain gets information from all parts of the body. For example, the brain gets information from the eye about light, from the ears about sound, and from the skin about the sensation of touch. The brain also sends information to all parts of the body to control breathing, or how fast the heart beats, etc. This information is sent back and forth from the brain to the body with small electrical messages. The brain’s electrical messages also control thinking and memory. The EEG helps the doctor look at these messages and see if they are working well. The test will also help the doctor diagnose neurological problems.

An EEG is commonly used to diagnose the following conditions:

• Seizures.This is when certain brains cells (neurons) send uncontrolled messages over and over again.
• Epilepsy. This is when a person has one or more seizures and they don’t go away over time.
• Head injuries. These can include concussion or traumatic brain injury.
• Brain tumors. Tumors a growths in the brain. Some are cancer and some are not.
• Inflammation of the brain (encephalitis). This is usually caused by an infection.
• Stroke. A stroke is when the blood supply to your brain is cut off or reduced, causing symptoms such as trouble walking, talking, or a drooping face.
• Sleep problems. Common sleep problems include sleep apnea, insomnia, or restless leg syndrome.

The test usually lasts one to two hours. However, if you have a sleep-related problem, the test may last for several hours while a person sleeps.

An EEG is a noninvasive procedure. It is painless and safe. In rare cases, the test may cause a seizure. This may occur in people with epilepsy or another seizure disorder.

The test is painless and noninvasive (no need to break the skin or physically enter the body). You will be made as comfortable as possible during the test.

If you are scheduled to have an EEG, it is important to follow all instructions to prepare for the test. You may be asked to:

• Wash your hair the night before so that your scalp is clean.
• Avoid putting oil, conditioner, gel, or other products in your hair.
• Avoid coffee, tea, soda, and certain medicines that can affect the brain’s electrical activity.

If you are required to sleep during the test, your doctor may ask you to sleep as little as possible the night before.

A skilled EEG technician will put small metal electrodes on your head. These electrodes do not hurt and do not give a shock. They are stuck to the skin with a special paste. The electrodes sense and record the brain’s electrical messages. The signals appear as little squiggly lines on a computer monitor.

During the test, the technician may ask you to do simple tasks such as opening and closing your eyes and repeating words.

After the test, a neurologist will review the results and send the results to your doctor. A neurologist is a physician with special training in how the brain and nervous system works. You will then schedule an appointment to go over the results with your doctor.

After the EEG, your doctor will discuss the next steps. If the test detects a stroke or infection, you will likely begin treatment immediately following the EEG. It is important you go over the test results with your doctor. Be sure to write down any questions that you may have before your appointment.

• Medline Plus
• KidsHealth