Patient Basics: Electroencephalogram (EEG)

An EEG (electroencephalogram) is a test that records the brain’s electrical activity, often called brain waves. Small metal discs (electrodes) are attached to the scalp and pick up tiny signals that brain cells send to each other. The test is painless and sends no electricity into your head. It is the main test doctors use to look for seizures and epilepsy.

Key points

• An EEG is like an EKG for the brain. It shows how the brain is working, not what it looks like.
• Doctors use it to check for seizures and epilepsy, unexplained spells or confusion, and some sleep problems.
• Come with clean, dry hair and no conditioner, oils or styling products.
• A routine EEG takes about an hour. Some EEGs last overnight or several days.
• A normal EEG doesn’t rule out epilepsy, because seizure activity may not happen during the recording.

Why an EEG is done

Doctors order an EEG to:

• Find out whether a spell, blackout or strange episode was a seizure
• Diagnose epilepsy and identify the type, which guides the choice of medicine
• Check how well seizure treatment is working
• Look into confusion, memory problems or changes in alertness
• Check brain activity after a head injury, stroke, infection or loss of oxygen
• Monitor people in a coma or under deep sedation in intensive care, and help confirm brain death
• Study sleep, as part of an overnight sleep study

An EEG isn’t a brain scan. CT and MRI scans show pictures of the brain’s structure, such as a tumor or a stroke. An EEG shows the brain’s activity from moment to moment.

Types of EEG

• Routine EEG. Recorded in a clinic or hospital for 20 to 40 minutes.
• Sleep-deprived EEG. You sleep less the night before, which makes seizure activity more likely to show up.
• Ambulatory EEG. Electrodes stay on while you wear a small recorder at home for 1 to 3 days.
• Video EEG. EEG and video are recorded together, often over several days in a hospital epilepsy unit, to capture your usual episodes.

Before the test

• Wash your hair the night before or the morning of the test. Don’t use conditioner, hair oil, spray or gel.
• Ask ahead about braids, weaves or extensions, which can get in the way.
• Take your usual medicines unless your doctor tells you otherwise. Don’t stop seizure medicine on your own.
• Eat as usual. Low blood sugar can change the results.
• Some labs ask you to skip coffee, tea, cola and energy drinks for 8 hours before.
• If you’re asked to sleep less the night before, arrange for someone to drive you home.
• Bring a list of your medicines. For a child, bring a favorite toy or blanket.

What happens during an EEG

You lie on a bed or sit in a reclining chair. A technologist measures your head and marks spots on your scalp with a washable pencil. They gently scrub each spot and attach about 20 electrodes with a sticky paste, or fit a stretchy cap that holds them. Thin wires carry the signals to a computer that records them as wavy lines.

You’ll rest with your eyes closed and keep as still as you can. Blinking, chewing and moving can blur the recording. During the test, you may be asked to:

• Open and close your eyes
• Breathe deeply and quickly for about 3 minutes
• Look at a light that flashes at different speeds
• Fall asleep, if you can

Deep breathing and flashing lights can bring out abnormal brain waves. A video camera may record you at the same time so the doctor can match any movement with the brain waves. The whole visit usually takes about 60 to 90 minutes.

Afterward

The electrodes are removed, and the paste is cleaned off with warm water. Some may stay in your hair until you wash it at home. You can go back to normal activities right away. If you were short on sleep or were given a sedative, don’t drive until you’ve rested.

Possible risks

An EEG is very low-risk. The electrodes only record signals. In people with epilepsy, flashing lights, fast breathing or lack of sleep can sometimes set off a seizure. This happens in a controlled setting with trained staff, and it can help with diagnosis. The paste or glue can irritate the skin a little.

Your EEG results

A neurologist reads the recording, which can take a few days. Brain waves are grouped by speed. Faster waves are normal when you’re awake and alert. Slower waves are normal in sleep and in young children.

An abnormal EEG may show:

• Sudden spikes or sharp waves, which suggest a tendency to have seizures
• An actual seizure, if one happens during the test
• Slowing in one area, which can point to an injury, stroke or tumor there
• Slowing throughout the brain, which can come from medicines, infection, low blood sugar, liver or kidney problems, or other illness

Many people with epilepsy have a normal EEG between seizures. If your doctor still suspects seizures, you may need a repeat EEG, a longer recording or video EEG. Results are always read together with your symptoms and other tests, such as an MRI.

When to call your doctor

Ask when you’ll get your results. Call if you have new or more frequent spells, or side effects from seizure medicine. If you have epilepsy, follow your state’s driving rules and your doctor’s advice until your seizures are under control.

Call 911 for a seizure that lasts more than 5 minutes, seizures that happen one after another, a seizure in water, a first-ever seizure, or a seizure with an injury or trouble breathing.

Common questions about EEG tests

Does an EEG hurt?

No. The electrodes only listen to the brain’s own signals, and nothing is sent into your head. The skin scrub may feel a little rough, and lying still for a long time can be tiring. Most children handle the test well, especially if they can nap during it.

Can an EEG detect anxiety, ADHD or other mental health conditions?

No. An EEG isn’t used to diagnose anxiety, depression, ADHD or autism. These are diagnosed through talking with a clinician and checklists of symptoms. An EEG may be ordered when someone with these conditions also has spells that could be seizures.

Can an EEG show a brain tumor or stroke?

It may show slowing in the area of a tumor or stroke, but it can’t show what is causing it. An MRI or CT scan is the test for finding tumors, strokes and other structural problems. Doctors often order both tests to understand the full picture.

Questions to ask your doctor

• What are you looking for with this EEG?
• Which type of EEG do I need, and how long will it take?
• Should I take my medicines or skip sleep before the test?
• What happens if the result is normal but my spells continue?
• When can I drive?

Learn more

• EEG (MedlinePlus, U.S. National Library of Medicine)

This guide is general information and doesn’t replace advice from your own doctor. Last updated October 2026.