Electroencephalogram (EEG)

What is an EEG?

An electroencephalogram (EEG) is a test used to evaluate the electrical activity in the brain. Brain cells communicate with each other through electrical impulses. An EEG can be used to help detect potential problems associated with this activity.

The test tracks and records brain wave patterns. Small, flat metal discs called electrodes are attached to the scalp with wires. The electrodes analyze the electrical impulses in the brain and send signals to a computer, where the results are recorded.

The electrical impulses in an EEG recording look like wavy lines with peaks and valleys. These lines allow doctors to quickly assess whether there are abnormal patterns. Any irregularities may be a sign of seizures or other brain disorders.

Why is an EEG performed?

An EEG is used to detect problems in the electrical activity of the brain that may be associated with certain brain disorders. The measurements given by an EEG are used to confirm or rule out various conditions, including:

  • seizure disorders (such as epilepsy)
  • passing out episodes
  • a head injury
  • encephalitis (an inflammation of the brain)
  • encephalopathy (a disease that causes brain dysfunction)
  • memory problems
  • dementia
  • Or it can be performed to assess any unusual sensation such as dizziness, lightheadedness, tingling, numbness, visual disturbances, abnormal smell or a change in behavior such as unusual movements of the limbs or face.

Risk associated with EEG:

There are no risks associated with an EEG. The test is painless and safe.

When someone has epilepsy or another seizure disorder, the stimuli presented during the test (such as a flashing light) may cause a seizure. However, our technician performing the EEG is trained to safely manage the situation should this occur.

How do you prepare for the test?

Before the test, you should take the following steps:

  • Wash your hair the night before the EEG, and don’t put any products (such as sprays or gels) in your hair on the day of the test.
  • Ask your doctor if you should stop taking any medications before the test. You should also make a list of your medications and give it to the technician performing the EEG.
  • Avoid consuming any food or drinks containing caffeine for at least eight hours prior to the test.
  • Your doctor may ask you to sleep fewer hours than usual the night before the test if you’re required to sleep during the EEG.

After the EEG is over, you can continue with your regular routine for the day. However, if you were given a sedative, the medication will remain in your system for a little while. This means that you’ll have to bring someone with you so they can take you home after the test. You’ll need to rest and avoid driving until the medication has worn off.


An EEG measures the electrical impulses in your brain by using several electrodes that are attached to your scalp. An electrode is a conductor through which an electric current enters or leaves. The electrodes transfer information from your brain to a machine that measures and records the data.

An EEG usually takes 30 to 60 minutes to complete. The test typically involves the following steps:

  • You’ll be asked to lie down on your back in a reclining chair or on a bed.
  • The technician will measure your head and mark where the electrodes will be placed. These spots are then scrubbed with a special cream that helps the electrodes get a high-quality reading.
  • The technician will put a sticky gel adhesive on 16 to 25 electrodes. They will then be attached to various spots on your scalp.
  • Once the test begins, the electrodes send electrical impulse data from your brain to the recording machine. This machine converts the electrical impulses into visual patterns that can be seen on a screen. These patterns are saved to a computer.
  • The technician may instruct you to do certain things while the test is in progress. They may ask you to lie still, close your eyes, breathe deeply, or look at stimuli (such as a flashing light or a picture).
  • After the test is complete, the technician will remove the electrodes from your scalp.

During the test, no electricity is passed between the electrodes and your skin, so you’ll feel no discomfort.

Normal Results

Electrical activity in the brain is seen in an EEG as a pattern of waves. Different levels of consciousness, such as sleeping and waking, have a specific range of frequencies of waves per second that are considered normal. For example, the wave patterns move faster when you’re awake than when you’re asleep. The EEG will show if the frequency of waves or patterns are normal. Normal activity typically means you don’t have a brain disorder.

Abnormal Results

Abnormal EEG results may be due to:

  • epilepsy or another seizure disorder
  • abnormal bleeding or hemorrhage
  • sleep disorder
  • encephalitis (swelling of the brain)
  • a tumor
  • dead tissue due to a blockage of blood flow
  • migraines
  • alcohol or drug abuse
  • head injury
  • dementia

It’s very important to discuss your test results with your doctor. Before you review the results with them, it may be helpful to write down any questions you might want to ask. Be sure to speak up if there’s anything about your results that you don’t understand.

Ambulatory EEG

Why do I need Ambulatory EEG Monitoring?

Epilepsy is a disease of the brain caused by abnormal electrical activity.  Ambulatory EEG monitoring enables your doctor to observe your EEG over a prolonged period of time.  Ambulatory monitoring can help diagnose your seizure type and provides important information regarding the best treatment for your seizures.

What will happen when I am set up for monitoring?

Placement of the EEG wires for monitoring

EEG wires will be attached to your head with a special glue so that the electrodes will stay attached for several days.  Sometimes, the electrodes can cause some itching to occur and you can take medication to help the itching.  Do not scratch your head with the electrodes in place.  Benadryl 25 mg to 50 mg can be used for itching.  This can be obtained over the counter at your local pharmacy.


Please do not eat potato chips or other snack foods or chew gum, since this will interfere with the EEG – it generates a lot of “noise” on the graph which makes it impossible to detect anything else.


You should wear comfortable clothing while your ambulatory EEG is being performed.  Sweat pants and a loose fitting top with buttons down the front are suggested.  Tight fitting sleeves and pull over tops will not be permitted.  Do not attempt to pull a shirt or other clothing over your head during the ambulatory EEG.  The electrodes may become dislodged and the quality of the recording will be affected.

What do I need to do before my test?

Assemble enough comfortable, appropriate clothes to wear.  Most patients wear street clothes or a sweat suit during the day and warm pajamas and socks at night.  Remember that the tops should button and be loose fitting.

Before the test, bathe and wash your hair well.  Do not leave any hair products in your hair and remove any braids or hair extensions.  This will facilitate comfortable placement of the electrodes

What is Ambulatory EEG Monitoring?

EEG is the abbreviation for electroencephalography.  The electroencephalograph is a machine that translates the electrical activity of the brain into a series of wavy lines (a graph) on a computer called the EEG record. An EEG measures the electrical activity of the brain, sometimes referred to as brain waves.  This test is performed to see how the different parts of your brain function.  It records a graph of your brain waves. It can tell us what may be causing your episodes and help with deciding the best treatment for you. The doctor can see seizure activity as well as sleep stages during your EEG.

Digital analysis is a procedure that can give additional information about any problems that may be found. Analysis and examination of the data obtained allows your doctor to see one of the many ways that your brain functions.

EEG is not a treatment of any kind.  No electricity is transferred to your brain.  The EEG only detects activity in the brain. If you have a seizure during the test, you should behave as you normally would during a seizure.  Family and friends should follow your usual first aid or emergency procedures.

The ambulatory EEG is a very expensive (~$20,000) piece of equipment that allows us to monitor a 24 hour period of brain waves but allows you to continue with most of your daily activities.  Do not get it wet.  Do not allow the box to get hit or banged against other objects.  Do not attempt to adjust anything on the device and do not adjust the wires.  You will be held responsible for any damages.

How does an Ambulatory EEG work?

Small, non-invasive metal cups called electrodes (usually 16 to 32 in number) are pasted on the scalp, after careful measurement by a trained technologist.  The paste or glue is to keep the electrodes firmly in place.  If the electrodes are moved, then the quality of the recording will be poor.  The electrodes pick up very small changes in brain electrical activity.  The activity is amplified and recorded on the computer.  It is then translated into a complicated graph. During this procedure, the EEG is recorded for a prolonged period, allowing you to have a comprehensive EEG at home. You will need to keep a diary with exact times to correlate behavior with events on the EEG. Do not forget to use the button to mark the time of your events.  This helps to determine the cause of any seizures.

How will I get my results?

After the technologist completes your study the doctor will review the study and discuss it with you at your next visit.  If there are issues regarding the EEG of immediate concern, the doctor will contact you for further testing or discuss the findings with you on the phone.  Do not ask the EEG technologist to interpret or explain your results.  The EEG technologist will contact the physician if your EEG shows something that may be of immediate concern. 

Neurodiagnostic Testing of the Brain, Spine & Nerves