EEG (electroencephalogram)


  • A test used to measure the electrical activity of the brain.


  • To distinguish epileptic seizures from other types of spells, such as syncope (fainting) or psychogenic nonepileptic attacks (PNEAs).
  • To reveal the type and location of activity in the brain during a seizure.
  • To determine if anti-epileptic medication dosages need to be adjusted.
  • To evaluate head trauma, brain tumor, brain infection, migraine, stroke, and memory impairment.
  • To study sleep disorders, such as narcolepsy.
  • To serve as an adjunct test of brain death if a person is in a coma.

What to expect:
Prior to the test

    • Before the EEG, tell your doctor if you are taking any medications that may interfere with the brain’s usual electrical activity.  These include antidepressants, muscle relaxants, sleeping aids, stimulants, or seizure medications.  Your doctor may or may not want you to discontinue these prior to the test.
    • Avoid all foods containing caffeine (such as coffee, tea, cola, and chocolate) for 8 hours before the test.
    • Wash your hair the night before.  Avoid using any conditioners, oils, sprays, creams, or styling gels after shampooing.
    • If you are having a sleep-deprived EEG, your doctor may ask you to stay awake or sleep less (only 4 to 5 hours) the night before the test.
    • If you were asked to discontinue your seizure medications or if you are having a sleep-deprived EEG, have someone drive you to and from the test.

During the test

  • The test is performed by an EEG technician and may be done in a hospital or doctor’s office.
  • You will be asked to lie on your back in a bed or sit in a comfortable chair.
  • The EEG technician will apply 16-20 electrodes to your scalp using special glue.
  • The electrodes will then be connected by wires to a computer so the brain’s electrical activity can be recorded.
  • During most of the test, you will be asked to relax with your eyes closed because any movement can alter the results; however, you may be asked by the technician to change your breathing pattern, look at a flashing light, read a paragraph, or perform simple calculations periodically.
  • If you are having a sleep-deprived EEG, you may be given a sedative to help you relax and sleep.

After the test

  • The technician will remove the electrodes and attachments.
  • Depending on your doctor’s instructions, you may return to your hospital room or home following the test.
  • If you were asked to discontinue your seizure medications or if you had a sleep-deprived EEG, be sure to have someone drive you home afterwards.
  • Resume normal activities unless otherwise instructed.
  • You will be instructed by your doctor when to resume your medications if any were discontinued prior to the test.
  • You may notice some electrode glue still in your hair after the EEG.  A few washings with regular shampoo should remove what is left.  A fine tooth comb may also help loosen the glue.

How long will it take?

  • A standard EEG takes 1-2 hours.
  • A sleep-deprived EEG will last 2-3 hours.
  • An ambulatory EEG typically lasts 24 hours.  You will be allowed to go home and resume normal activities while your brain’s activity is continuously recorded.

Will it hurt?

  • An EEG causes no pain or discomfort.  The electrodes only record activity and do not produce any sensation.


  • The doctor or technician will tell you when to expect your results.  They may be given to you over the phone or during an office visit.

Information from the National Institutes of Health, April 2010