Why Is an Electroencephalography Performed?

An EEG can determine changes in brain activity that may be useful in diagnosing brain disorders, especially epilepsy. An EEG can't measure intelligence or detect mental illness. An EEG may be helpful for diagnosing or treating the following disorders:

An EEG may 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.

Before the procedure

To prepare for an EEG:

 Wash your hair the night before or the day of the test, but don't use any conditioners, hair creams, sprays or styling gels. Hair products can make it harder for the sticky patches that hold the electrodes to adhere to your scalp.

 Avoid anything with caffeine on the day of the test, because caffeine can affect the test results.

 Take your usual medications unless instructed otherwise.

If you're supposed to sleep during your EEG test, your doctor may ask you to sleep less or even avoid sleep entirely the night before your EEG.

What Happens During an Electroencephalography?

You'll feel little or no discomfort during an EEG. The electrodes don't transmit any sensations. They just record your brain waves.

Here are some things you can expect to happen during an 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 may be scrubbed with a gritty cream to improve the quality of the recording.

 A technician attaches flat metal 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 — makes bigger — the brain waves and records them on computer equipment. Once the electrodes are in place, an EEG typically takes up to 60 minutes. If you need to sleep for the test, it may take up to three hours.

 You relax in a comfortable position with your eyes closed during the test. At various times, the technician may ask you to open and close your eyes, perform a few simple calculations, read a paragraph, look at a picture, breathe deeply (hyperventilate) for a few minutes, or look at a flashing light.

 Video is frequently recorded during the EEG. Your body motions are captured by a video camera while the EEG simultaneously records your brain waves. This combined recording may help your doctor diagnose and treat your condition.