Electroencephalogram (EEG) and 24-hour Ambulatory EEG

What is an EEG?

An EEG records the electrical activity of the brain.  Highly sensitive monitoring equipment records the activity through electrodes that are placed at measured intervals on the patient’s scalp for the duration of the EEG test.

Will an EEG Hurt and How Long Will it Take?

An EEG is not painful.  The head is measured and electrodes are placed on the scalp with water-based glue or gel.  The EEG procedure itself usually takes about 60 minutes. 

Why Would My Doctor Order an EEG?

EEG tests assist physicians in the diagnosis of a variety of neurological disorders, from common headaches and dizziness to seizure disorders, strokes, and degenerative brain disease. EEG testing is also used to look for organic causes of psychiatric symptoms and disabilities in children.

What is a 24-hour Ambulatory EEG?

The 24-hour ambulatory EEG test uses a small digital recorder. Electrodes are applied to the scalp, as with any EEG test, but the patient is sent home with the electrodes in place. A diary is used by the patient to record the activities of the day and any symptoms that may occur during the 24-hour period of EEG testing. The patient returns to the testing center the next day to have the electrodes removed and turn in the diary.

What is a Sleep EEG?

Physicians may want to observe brain patterns that occur during sleep.  For a sleep EEG, the patient may be asked to stay awake during most of the night prior to the EEG appointment.  This should help induce sleep at the time of the EEG test.

Before Your EEG Test

Prepare for your EEG test as instructed. Wash and dry your hair but do not use any hair styling products. Your scalp and hair should be clean and free of excess oil. Take your routine medications unless told not to. You may be asked to sleep during the EEG test. To help you do this, you should go to bed at midnight the night before the EEG test and wake up at 4:00 a.m. the next morning. This should help induce sleep at the time of your EEG procedure.

During Your EEG Test

During your EEG test, you will sit in a reclining chair or lie down on an exam table in a softly lit room. The technologist will measure certain points on your head. He or she will use a special pencil to mark the spots where the electrodes will be placed on your scalp for the EEG test. You may be asked to do the following:

  • Relax, and open and close your eyes
  • Breathe rapidly and deeply for a few minutes
  • Sense a flashing light through your closed eyes
  • Relax and go to sleep

After Your EEG Test

When your EEG test is done, all of the electrodes will be removed. At home, wash your hair to remove any remaining glue. You can get right back to your normal routine. If you stopped taking any medications before the EEG test, ask your doctor when you can restart them. Your doctor will let you know when the results of your EEG test are ready.


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