What is an electroencephalogram (EEG)?
An electroencephalogram (EEG) lets a doctor see the electrical activity of your brain.
You will have small pads or patches attached to different places on your head. These are called electrodes. Wires connect the electrodes to a computer.
The computer records the activity of the brain. This looks like wavy lines on the computer screen or on paper.
Why is an electroencephalogram (EEG) done in children?
The test is often used to diagnose epilepsy. It helps a doctor know what types of seizures a child is having.
An EEG can also check brain activity in people with sleep disorders.
It can also help a doctor know why a person passed out (lost consciousness).
How is an electroencephalogram (EEG) done for children?
- Your child will lie on his or her back on a bed or table. Or your child might relax in a chair with eyes closed.
- A technologist will attach the electrodes to different places on your child's head. Or your child might get a cap with fixed electrodes on it.
- Your child will lie still with eyes closed. He or she will be told not to talk unless it's needed.
- The technologist may ask your child to:
- Breathe deeply and rapidly. This is called hyperventilating.
- Look at a bright, flashing light called a strobe.
- Go to sleep. If your child can't fall asleep, he or she may get medicine to help.
How do you prepare for an electroencephalogram (EEG)?
- Tell your doctor ALL the medicines, vitamins, supplements, and herbal remedies you take. Some may increase the risk of problems during your test. Your doctor will tell you if you should stop taking any of them before the test and how soon to do it.
- Do not eat or drink anything with caffeine in it for 12 hours before the test. This includes cola, energy drinks, and chocolate.
- Shampoo your hair and rinse with clear water the evening before or the morning of the test. Do not put any hair conditioner or oil on after you wash your hair.
- Your doctor may ask you not to sleep the night before the test or to sleep for only about 4 or 5 hours. This is because some types of brain activity can only be seen if you are asleep. If your doctor asks you to get less sleep than normal, plan to have someone drive you to and from the test.
What do the results of an electroencephalogram (EEG) mean?
EEG test results are ready on the same day or the next day.
There are several types of brain waves.
- Alpha waves are present only when you're awake with your eyes closed but you are mentally alert. Alpha waves go away when your eyes are open or you are concentrating.
- Beta waves are normally found when you are alert or have taken high doses of certain medicines, such as benzodiazepines.
- Delta waves are normally found only in young children and in people who are asleep.
- Theta waves are normally found only in young children and in people who are asleep.
Normal: | In adults who are awake, the EEG shows mostly alpha waves and beta waves. |
|---|---|
| The two sides of the brain show similar patterns of electrical activity. | |
| There are no abnormal bursts of electrical activity and no slow brain waves on the EEG tracing. | |
| If flashing lights are used during the test, one area of the brain (the occipital region) may have a brief response after each flash of light. But the brain waves are normal. | |
Abnormal: | The two sides of the brain show different patterns of electrical activity. This may mean that there's a problem in one area or side of the brain. |
| The EEG shows sudden bursts of electrical activity called spikes. Or the test shows sudden slowing of brain waves in the brain. These changes may be caused by a brain tumor, infection, injury, stroke, or epilepsy. When a person has epilepsy, the location and exact pattern of the abnormal brain waves may help show the type of epilepsy or seizures. In many people with epilepsy, the EEG may appear normal between seizures. An EEG by itself does not diagnose or rule out epilepsy or a seizure problem. | |
| The EEG records changes in the brain waves that may not be in just one area of the brain. A problem that affects the whole brain may cause these kinds of changes. This includes drug intoxication, infections (encephalitis), and metabolic disorders (such as diabetic ketoacidosis). These problems change the chemical balance in the body, including the brain. | |
| The EEG shows delta waves or too many theta waves in adults who are awake. This may mean that there is a brain injury or brain illness. Some medicines can also cause this. | |
| The EEG shows no electrical activity in the brain. This is a "flat" or "straight-line" EEG. This means that brain function has stopped. It's usually caused by lack of oxygen or blood flow inside the brain. It may happen when a person has been in a coma. In some cases, severe sedation from drugs can cause a flat EEG. |
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