Electroencephalogram (EEG)

An electroencephalogram (EEG) is a diagnostic tool that detects and measures electrical activity in your brain, helping physicians identify changes in the typical pattern of electrical activity. An EEG is used to diagnose a range of conditions, including:

An EEG is also used to monitor brain activity in brain surgery patients or to check for brain activity in coma patients.

EEG: What to Expect

An EEG may take from 1 to 2 hours. During the test, you may be lying on your back on a bed or table or sitting in a chair. A technician will attach special sensors called electrodes to your head. The sensors will be attached by wires to a computer and will detect your brain’s electrical activity.

During the test, you will need to remain as still as possible, with your eyes closed. The technician may have you perform certain tasks, such as looking at a flashing light or breathing rapidly, in order to see how your brain activity changes.

After the test, the EEG technician will give your test results to your doctor.

EEG: How to Prepare

There are several important steps to take prior to an EEG:

  • If you are taking any medications, be sure to tell your doctor, as some drugs can affect your test results.
  • Avoid all caffeine on the day of the test.
  • Wash your hair the night before or the day of the test. Do not use conditioners, hair spray or other hair products, as they can make it difficult for the electrodes to adhere to your scalp.
  • Depending on the nature of your condition, you may be asked to sleep during your EEG. To help prepare, your doctor may ask you to sleep less or avoid sleep entirely the night before your test.