What Is an Electroencephalogram (EEG)?
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Medically reviewed by Smita Patel, DO
An electroencephalogram—or EEG for short—is a diagnostic test that looks at the electrical activity in your brain. An EEG is often used to detect and evaluate epilepsy (a condition that causes frequent seizures), but may also be helpful for other conditions like brain injuries or sleep disorders.
During an EEG, your healthcare provider will attach wires and electrodes to your scalp that transmits information and brain activity to a computer. Generally, a neurologist (or, a doctor who specializes in the brain and spinal cord) will order the test and review the results.
Purpose
An EEG looks at the electrical activity in the brain. A neurologist interprets EEGs and looks at patterns of brainwave activity to diagnose any potential brain abnormalities. EEGs are most often used to evaluate and monitor seizure disorders, like epilepsy. However, your provider may also order an EEG to assess your risk or look for symptoms for the following conditions:
Sleep disorders
Syncope (loss of consciousness)
Encephalitis (brain inflammation)
Brain death
Types of EEG
There are several different types of EEGs that your provider may order and conduct. These include:
Routine EEG: Standard EEG that uses mechanisms like quick breathing or flashing lights to record how your brain responds to stimuli
Ambulatory EEG: A longer test that uses a portable monitor and head electrodes to assess how the brain functions during normal activities
Video EEG: Records a video of the person so that brain activity can be correlated with body movements or behaviors
High-density EEG: Uses more electrodes spaced closer together on the scalp to help pinpoint the exact location of any brain abnormalities or concerns
Sleep-deprived EEG: Occurs after a period of sleep deprivation and can help diagnose seizures and sleep disorders
In most cases, you will likely be receiving a routine or ambulatory EEG. However, if your healthcare provider suspects that you have a specific condition or wants to record videos alongside the EEG, they can employ other types.
How Does It Work?
During an EEG, a trained lab technician will place electrodes on your scalp with an adhesive (sticky) paste. The electrodes collect information about your brain activity for a certain period of time. The electrodes are attached to wires that connect to a computer that helps monitor and analyze your brain waves.
A video monitor is typically set up to record your body movements during the test. During the test, you will be asked to remain still. In some cases, the provider or technician can also request you to close your eyes or sleep. Here's what you can expect to happen before, during, and after the test.
Before the Test
In preparation for the test, you will first be asked to fill out a consent form. A lab technician will then ask questions about your medical history, including any details about possible seizures that you've been experiencing.
Before the test begins, you will sit or recline in a chair or bed. The technician will position your head properly, take measurements of your scalp, and mark the exact locations of where the electrodes will be placed. Once this is done, the technician will usually place about 20 electrodes on your scalp using the adhesive paste.
Some adhesives have a strong odor. If you notice your technician is using a needle, it's important to know that it is a blunt needle only used for the application of glue, and not for pricking your skin. Your technician will also place some electrodes on your arm and chest to record muscle movement and heart activity. You can expect it to take 20 to 40 minutes for the electrodes to be placed properly.
During the Test
During an EEG, the scalp electrodes will transmit information to a computer. You will be asked to remain still and possibly to try to sleep. Keep in mind: the test is completely painless. You may be asked to perform provocation techniques such as looking at a flashing light or taking deep and fast breaths for a few minutes. This can sometimes help activate certain parts of your brain, making the measurement of brain activity easier to record.
The length of the test depends on the type of EEG you're receiving. However, in most cases, an EEG lasts 30 minutes to a couple of hours. If you're receiving an overnight EEG or an ambulatory EEG, the length of your exam will be longer.
After the Test
After the EEG is conducted and your neurologist has gathered the brain activity measurements they need, the technician will begin to remove electrodes from your scalp and clean the adhesive off your hair. Something to keep in mind: you'll likely need to wash your hair after the exam to remove all of the adhesive paste properly.
Once the test is complete, your neurologist can interpret and analyze the results from the EEG. In most cases, your provider will call you or schedule a phone appointment to discuss the results, the need for any additional testing, and referrals to additional specialists, if needed.
Risks and Precautions
It's important to note that for most people, an EEG is a safe procedure. In some cases, the electrodes can feel cold or uncomfortable or you might experience a bit of sensitivity or irritation because of the adhesive paste.
In rare cases, EEGs can sometimes trigger a seizure. If you have an underlying seizure disorder you may experience a seizure during the test. This is useful for diagnosis, and personnel are trained to manage seizures immediately as they happen.
How to Prepare for an EEG
It's normal to be nervous before getting a medical test done. However, knowing how to prepare for an EEG can make this process easier for you. Here are some things to keep in mind:
Hair: Ensure that your hair is clean and that you do not use conditioners, sprays, or oils prior to the EEG. If you have a weave, wig, or hair extensions, talk to your healthcare provider about how to best prepare for the exam.
Clothing: On the day of your test, wear loose, comfortable clothing. You may be asked to change into a hospital gown. Do not wear earrings as they may get in the way of the electrodes during the EEG.
Food and drinks: You are generally allowed to eat breakfast before the study unless instructed otherwise by your healthcare provider. Make sure to avoid caffeine for eight hours prior to the study.
Medications: Take all of your normal medications (if any) as prescribed, and do not miss any doses unless your healthcare provider has specifically instructed you to do so.
Items to bring: Be sure to bring a photo ID and your insurance card. Information about insurance coverage can be obtained ahead of the procedure by speaking with your insurance provider. In many cases, insurance will cover an EEG, but you may have to pay a copay depending on your insurance plan. It's important to note that if you don't have insurance or your insurance doesn't cover an EEG, the cost of an EEG in the U.S. can vary but the current average is just under $1,000.
Emotional support: Typically, you are allowed to bring someone with you to an EEG for emotional support. However, it's best to check with the location before the exam in the chance they don't allow visitors. Plan to also make arrangements for a ride home in the event that you have seizure activity or require sedating seizure medications during the test. You must also have a ride home if you are undergoing a sleep-deprived EEG.
Results
Once the EEG is completed, a neurologist will have the opportunity to evaluate your results. The EEG itself looks like wavy lines on a paper or computer screen. Neurologists are able to interpret patterns in these lines to determine levels of brain activity in sleep and wakefulness, and if there is any evidence of seizure activity or other brain abnormalities. In most cases, your results will be available to you within a few days after the test is done.
If an EEG does not identify seizure activity, it does not necessarily mean that you don't have seizures or epilepsy. It just means that your brain activity didn't record a seizure at the time of the test. In such cases, your neurologist or primary care provider can order an ambulatory EEG for you to take home and wear for several days to assess your brain activity over a longer period of time or request other imaging tests, like a CT scan or MRI.
A Quick Review
An EEG is a painless test that neurologists often use to identify and evaluate your brain activity. In most cases, EEGs help detect and diagnose conditions like epilepsy, but can also be useful to assess symptoms or risks of brain injuries or sleep disorders.
While getting an EEG may seem scary at first, there's nothing to worry about as this is a standard procedure for people who are experiencing seizures or other brain changes. During the test, a technician will place electrodes on your scalp to monitor brain activity over a period of time. These electrodes are directly connected to a computer that helps your neurologist and technician visualize patterns in your brain activity.
Once the test is done, your neurologist will analyze your test results and either provide you with a diagnose or recommend further testing if needed. If you have any concerns about getting an EEG, it's important to talk to your healthcare provider and get those questions addressed prior to test. They can provide you with any additional information you may need and calm worries about the test that you may have.
Frequently Asked Questions
How much does an EEG cost?
According to a study published in 2021, the average out-of-pocket cost for EEG for people with private insurance ranges from $100-$200. This cost has risen over time, with a 190% increase in cost from 2001 to 2016. Without insurance, cost varies widely, with average cost reported to be $972.
What can an EEG show that an MRI cannot?
An EEG is a test that looks at the brain's electrical activity and can show brain activity changes that occur in different states of sleep or wakefulness. It's useful to use an EEG to diagnose brain disorders like seizures. An MRI, however, is an imaging test that shows the anatomy of the brain and takes detailed picture of the brain to detect conditions like tumors, brain bleeds, or structural changes in the brain.
Will an EEG show past seizures?
An EEG only shows brain activity occurring during the test, so it cannot show past seizures. However, one 2020 study found that for those who experienced a new seizure, performing an EEG within 16 hours of the seizure was more likely to identify brain abnormalities in the test results.
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