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Electroencephalogram (EEG)


Updated May 16, 2014

An electroencephalogram, or EEG, is one of the available tests used to diagnose epilepsy.

When epilepsy is suspected, one of the more common diagnostic tests used is the electroencephalogram. The electroencephalogram, or EEG, measures and records the electrical activity of the neurons in the brain. An EEG can tell your healthcare provider if there is abnormal electrical activity in the brain and, in some cases, the types of seizures you might be experiencing.

An EEG can also help your healthcare provider identify any other abnormalities existing in the brain, such as a coma, brain death, or the presence of a tumor or a stroke.

What Should I Expect When I Get An EEG?

An EEG may seem a little foreboding due to the electrodes and wires involved, however it is an important -- and painless -- procedure that will help your neurologist identify any abnormal activity occurring in your brain.

EEGs are typically performed in a neurology clinic by a trained technician or in the hospital on an outpatient basis. You are fully awake for this procedure. Your head will be measured and your scalp will be carefully marked by a crayon or washable marker in order to designate the places to attach the electrodes. Next, electrodes will be secured to the scalp using a special adhesive that can be washed out of the hair. These electrodes are connected by a wire that is routed to a computer that will analyze the electrical activity occurring in your brain.

The entire EEG should take between one and two hours. During this time, you may be asked to blink or breath deeply or rapidly to see how your brain responds. In some cases, the neurologist might want to record your brain activity while you sleep. You will be notified of this before the EEG is conducted. The results of your EEG are recorded in a computer, or sometimes paper, and will be read by the neurologist.

What Will An EEG Tell My Neurologist?

The neurologist is looking for “epileptiform” activity, which is a general term that refers to any abnormalities noted on the EEG. These abnormalities will usually appear as sharp spikes and waves on the graph. The location of these spikes and waves may be able to tell your neurologist where seizures are occurring as well as the type of seizures you are having.

How Do I Need To Prepare For an EEG?

There are not a lot of things that you can do for an EEG, other than:
  • Don’t consume alcohol before the procedure.
  • Tell your healthcare provider all of the medications you are taking, since some types of medications may produce an abnormal result.
  • Keep your hair clean before the test, and free of conditioners, gels or anything that can interfere with the recording by the electrodes.
  • Get a good night’s sleep before the procedure. Keep in mind that, in some cases, your neurologist may want you to stay up the night before, since this can increase the likelihood of eliptiform activity.


Kasper J et al. Harrison Principal of Internal Medicine 16th ed.

Chang BS and Lowenstein DH. Epilepsy. N Engl J Med 2003;349:1257-66.

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