Epilepsy Information/Diagnosis and Testing

EEG for Seizures: What To Expect During the Test

Medically reviewed by Federica Polidoro, M.D.

Written by Sarah Winfrey

Posted on August 14, 2026

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Key Takeaways

An electroencephalogram, or EEG, is a painless test that records the brain's electrical activity and can help doctors look for answers after a seizure.

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When a seizure happens, it can leave you with a lot of questions. What caused it? Could it happen again? An electroencephalogram (EEG) is one test that can help doctors look for answers.

An EEG is a painless test that records the brain’s electrical activity. Although the electrodes and wires may look intimidating, knowing what to expect can make the experience easier. Here’s how an EEG works, how to prepare, and what the results may tell you about seizures and epilepsy.

What Is an Electroencephalogram?

An electroencephalogram allows doctors to understand what’s happening with the electrical signals in your brain. During the test, a healthcare provider will attach small electrodes to your scalp.

Whenever your brain sends an electrical signal — one of the main ways different parts of your brain communicate — the electrode will send that signal to an EEG machine. This machine will record the patterns, called brain waves. It will display them so you can see them and your provider can look at the patterns to understand your brain activity.

Epilepsy is characterized by seizures that happen when you have abnormal electrical activity in the brain, and EEG is one way to see what’s going on. Note that an EEG doesn’t give doctors a visual image of your brain or show anything other than electrical activity. If the problems you’re experiencing have a different cause, your doctor will need to run additional tests to find out what’s going on.

An EEG may also be used to help diagnose:

Brain damage
Some brain diseases
Brain tumors
Brain inflammation
Some sleep disorders
A stroke

Types of EEG

There are different types of EEG that your doctor can ask you to do. For a routine EEG, you’ll go to a doctor’s office and an EEG specialist will perform the test there.

However, your doctor may want to see your brain activity in different situations. These make up the types of EEG and include:

Ambulatory EEG — In this test, you wear electrodes while you go about your normal, daily activities.
Sleep EEG — This test measures your brain activity specifically while you’re sleeping.
Prolonged EEG — This is the same as a routine EEG except that the test lasts longer.
Video EEG — This test records you on video while the EEG is occurring so doctors can see the effects of your brain activity on your actions or movements.

Your doctor will order one of these if they need additional information. If you have a sleep disorder that may be connected to epilepsy, for example, they may order a sleep EEG. If you have seizures in daily life but not when connected to the EEG machine, they may order an ambulatory EEG.

What To Expect When You Have an EEG

Knowing what to expect when you or your child goes in to have an EEG can make the whole process easier. Here’s what you need to know.

Before an EEG

Your doctor will give you instructions regarding what to do before your EEG. In general, you’ll want to wash your hair the night before the test and avoid all creams, gels, and other hair products on the day you go in. This makes your hair clean and dry for the EEG technologist.

Tell your doctor about any medications you’re taking before the test. They may give you special instructions about these, as well as about what you eat or drink before the test. Your doctor may also ask you to stay awake all night before you go in for your EEG if they need you to be sleep-deprived.

If your doctor gives you instructions not listed here, make sure you follow those specifically. They may have to do with particular information your doctor wants to get during the test.

During an EEG

When you’re called back for an EEG, you’ll be asked to sit comfortably or lie down. The EEG expert will measure your head, then mark where they want to put the electrodes. These are attached with a glue that you may need to wash off later.

Once the electrodes are attached, the test can start. It usually lasts between 20 and 40 minutes, though the whole process can take up to 90 minutes.

You’ll spend at least part of the test relaxed, and your eyes can be open or closed. During the test, the technician may ask you to do certain things. This can involve looking at blinking lights, opening and closing your eyes, or breathing differently, like deeply or faster.

If you know what seizure symptoms feel like, you should let the technician know if you start to feel them. Having a seizure in this situation is rare, but there will be help for you if it happens.

After an EEG

After the EEG, the technician will remove the electrodes. You can usually return to your normal activities right away, although you may need to wash some glue or paste from your hair and scalp. A doctor will review the recording and discuss the results with you at a follow-up visit.

What Does an EEG Tell You About Epilepsy?

Doctors do not use EEG results alone to diagnose epilepsy. They will also consider your or your child’s symptoms, medical history, and family history. An abnormal EEG may show brain wave patterns linked to epilepsy and help doctors learn more about the type of seizures involved.

What if the EEG Is Normal?

A normal EEG does not always rule out epilepsy. The test records brain activity only during the testing period, so it may not catch unusual activity when it happens. If you or your child continues to have possible seizures, tell your doctor. Epilepsy may still be diagnosed based on symptoms and other evidence, or your doctor may recommend more testing.

Ask Your Doctor About an EEG

Talk to your doctor if you think you or your child may have had a seizure or if you have questions about an EEG. They can explain why the test is being ordered, what the results mean, and whether more testing or treatment may be needed.