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What Is an EEG and What Information Does It Provide?

Many patients are referred to a neurologist to have an electroencephalogram (EEG), which records electrical impulses from the nerves in the head. “Electro” refers to the electrical impulses sent from one nerve cell to another. These impulses are the way nerves talk to each other and get information from the brain to the rest of the body. “Encephalo” refers to the head, and “gram” refers to the printed record.

EEG exams are done by putting electrodes (detectors of electricity) on the scalp and seeing what the electrical impulses look like when the patient is awake, asleep, in a room with a flashing light or sometimes when the patient is asked to breathe deeply over and over. When the EEG is done, no electricity is put in to or taken out of the patient. The electrical signals that the brain produces are simply detected and printed out on a computer screen or a piece of paper.

An EEG determines if the patient’s level of alertness or consciousness is normal, if abnormalities exist in one specific part of the brain, if a patient has a tendency to have seizures or convulsions, and if a patient is likely to have a particular kind of epilepsy.

Sometimes a patient may have a tendency to have seizures, but his or her EEG is normal at the particular time it is done. That’s because people with a seizure tendency may have abnormalities that come and go from hour to hour or day to day. In these cases, a repeat EEG or a longer period of EEG monitoring may be useful.

What Can My Child Expect?

Your child will be asked to lie down on a bed or stretcher. The technologist then will:

  • Explain the procedure to you and your child
  • Measure your child’s head
  • Make small marks on the scalp with a washable marker or pen
  • Rub each marked area with a gritty lotion so the electrodes transmit the brain’s electrical signals well
  • Place glue on the electrodes, which are applied to each of the marked spots on the scalp
  • Connect the electrodes to the EEG machine

As the test begins, your child will need to sit or lie as still as possible. He or she may be asked to breathe fast (hyperventilate), look at flashing lights and try to sleep. The test takes about one hour, and your child is usually videotaped. Your child’s physician may order a video EEG to give him or her more time to study the brain waves. The procedure is the same, but may last six hours to several days, depending on the information that is needed and the frequency of your child’s episodes.

Last Update
April 3, 2014
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Last Update
April 3, 2014
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