Electroencephalogram (EEG) Test for Epilepsy

Why does your doctor want you to have this test?

EEG. Oli Scarff / Staff / Getty Images

An electroencephalogram, or EEG, is one of the available tests used to diagnose epilepsy, and it's used quite commonly when doctors suspect someone has epilepsy.

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.

In addition to diagnosing epilepsy, an EEG can also help doctors identify other brain abnormalities, 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 intimidating due to all the electrodes and wires involved. But the truth is, an EEG is an important — and completely 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.

Before the EEG, your head will be measured and your scalp will be carefully marked by a crayon or washable marker in order to show the places to attach the electrodes.

Next, electrodes will be secured to the scalp using a special glue (don't worry — the glue is made so that it can be washed out of your hair later).

These electrodes are connected by a wire that is routed to a computer. The computer 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 to breathe deeply or rapidly to see how your brain responds.

In some cases, the neurologist might want to record your brain activity while you sleep. Your doctor will tell you about this before the EEG.

The results of your EEG are recorded in a computer, or sometimes on paper, and will be read by the neurologist.

What Will An EEG Tell My Neurologist?

The neurologist is looking for what's called “epileptiform” activity, which is a general term that refers to any patterns due to epilepsy that are noted on the EEG.

These patterns usually will appear as sharp spikes and waves on the graph. The location of these spikes and waves may be able to tell your neurologist where your seizures are occurring, as well as the type of seizures you are having.

How Do I Need To Prepare For an EEG?

There's very little you need to do to prepare for an EEG. That being said, you should take these few steps:

  • Don’t consume alcohol before the procedure.
  • Tell your doctor about 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 epileptiform activity.


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

Chang BS and Lowenstein DH. Epilepsy. New England Journal of Medicine. 2003;349:1257-66.

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