What Is An Electroencephalogram (EEG)?
An electroencephalogram (EEG) — also known as electroencephalography — is a noninvasive, painless test to record and evaluate electrical activity in your brain. It can be used to diagnose and plan treatment for epilepsy.
Types of EEG
There are several types of EEG tests, including:
- Ambulatory EEG — Records your brain’s electrical activity over one to three days using a special recorder that you wear while going about your normal daily activities.
- Prolonged EEG — Performed for a longer period of time than a routine test and typically lasts more than one hour.
- Routine EEG — A short recording, typically lasting around 25 minutes.
- Sleep-deprived EEG — Recording of your brain’s electrical activity after sleeping a shortened amount of time the night before.
- Video EEG — Typically performed in the inpatient Epilepsy Monitoring Unit (EMU) over the course of several days, this test combines a recording of your brain's electrical activity with video and audio, so your doctors can see and hear your symptoms during a seizure.
Conditions we diagnose and monitor with EEG
- Behavioral changes
- Coma
- Epilepsy
- Functional seizures
- Loss of consciousness
Why Would I Need EEG?
You may need an EEG to diagnose epilepsy, monitor your brain’s electrical activity in the setting of antiseizure medication changes, or rule out a diagnosis of epilepsy.
Who’s a candidate for EEG?
You may be a candidate for EEG if you have seizures or events that look like or are concerning for seizures. Your care team will recommend the best type of EEG for your needs.
What Are the Risks and Complications of EEG?
EEG is a painless, noninvasive test that rarely causes complications.
However, side effects may include:
- Dizziness from taking a series of deep breaths.
- Hair loss or skin irritation where electrodes were placed on your scalp.
- Triggering a seizure in patients that are sensitive to flashing lights or deep breathing.
What Should I Expect From EEG?
Before: How to prepare for EEG
Your provider will let you know how to prepare for your EEG depending on what type of EEG you’re having. Your test may be performed in the hospital, the Epilepsy Monitoring Unit, or at home while you go about your everyday activities.
Your provider will explain the procedure to you and answer your questions. To prepare for the procedure, you should:
- Tell your provider if you are sensitive or allergic to any medications, iodine, latex, tape, or anesthetic agents (local and general).
- Tell your provider about all medications (prescription and over-the-counter) and herbal or other supplements you are taking.
- Tell your provider if you have any other health conditions. Your care team may need to take certain precautions during the study for your safety.
The night before the procedure, you should:
- Avoid food and drinks containing caffeine for at least eight hours before the test.
- Wash your hair and make sure it's free of conditioners, oils, sprays, or gels. If you have a hair weave, ask your provider or EEG scheduling staff for special instructions on how to prepare.
- Stop taking medications only if directed by your provider. Do not stop taking any medications or change your medication routine without talking to your provider first.
On the day of your procedure, be sure to bring your photo ID and health insurance card(s). Leave valuables such as cash and jewelry at home.
How long does an EEG take?
Routine EEG tests take 20 to 30 minutes and prolonged EEG tests take an hour or longer. Ambulatory EEG tests take several days, and sleep EEG tests may be performed overnight. Additional time is required for the EEG leads to be placed on the scalp.
During your EEG
An EEG is a painless, noninvasive test, so you will not need any type of anesthesia.
During your test:
- You will sit in a chair or lie on a bed.
- Your EEG technician will place more than 20 electrodes at various points on your scalp using a temporary glue to hold them in place. The electrodes are not painful and will record your brain's electrical activity.
- Your technician will start the test. They may ask you to look at bright, flashing lights or take deep breaths.
- The electrodes on your scalp will send signals to an EEG machine, which records your brain waves and displays them on a screen.
After the test is complete, your technician will remove the electrodes from your scalp. Your EEG results will be sent to your doctor, who will review them for abnormalities.
Recovery after EEG
In most cases, you should be able to resume your normal activities immediately after your EEG test.
When to call your provider about complications
It is unlikely that you will experience any complications after your EEG. However, contact your doctor if you have increased seizure activity or any other symptoms that concern you.
Why Choose UPMC for EEG?
When you choose UPMC for your EEG, you will receive:
- Results interpreted by epilepsy specialists — neurologists that specialize in seizures.
By UPMC Editorial Staff. Last reviewed on 2026-03-04.
