Electroencephalogram (EEG)

The most common type, a routine EEG may be one of the first tests done to check for epilepsy or another disorder. This test might also be used after a diagnosis to monitor your condition or changes in medication.

During an evoked potential test, a trigger is used to provoke a seizure or seizure-like activity in your brain so that it can be recorded. Triggers may include looking at flashing lights or taking quick breaths. Your care team is there to provide treatment right away if you have a seizure during the test.

A prolonged EEG lasts several hours and records your brain activity while you’re awake and asleep. It may be done in a health care center or while you’re at home. Testing over a longer period increases the chances of abnormal activity being recorded.

Your care team may take a video recording of you during your EEG. This helps your doctor see your movements and behavior during abnormal brain activity. A long-term video EEG takes place in a health care center for several days. You might need a long-term test to determine if you have epilepsy or another condition, or to record how often you have seizures, see how well antiseizure drugs are working, or assess whether you’re a candidate for epilepsy surgery.

An ambulatory EEG takes place over a few days while you’re at home and doing your usual activities. If you have seizures, an ambulatory EEG can help your doctor learn how often they occur, whether you need medication, or if your current medication can be tapered. Sometimes ambulatory EEGs are recorded on video with equipment you set up at home.

Stereoelectroencephalography (stereo-EEG) requires minimally invasive surgery to create small holes in your skull so that electrodes can be placed temporarily into your brain tissue. This type of EEG is done if you have epilepsy that hasn’t responded to medications. Placing electrodes in your brain can help your doctor determine where your seizures begin and whether you’re a candidate for epilepsy surgery. A stereo-EEG can also map the areas of your brain to help plan surgery.

When you arrive for your EEG, you’ll lie on a reclining chair or bed. A member of your care team will place several small discs called electrodes on your scalp, using medical glue to hold them in place. You’ll lie still as the electrodes pick up your brain activity and a machine records it as wavy lines on a screen. For an evoked potential EEG, you might need to take deep, fast breaths or to look at flashing lights. The test may be recorded on video.

A routine or evoked potential EEG takes around 20 to 40 minutes, while a prolonged EEG takes an hour or longer. If you’re having a long-term video EEG, the test will take several days, and you’ll stay in the hospital during that time.

For an ambulatory EEG, you can go home after the electrodes are attached to your scalp. You’ll be given a recorder to wear and optional video equipment to observe and track any seizures. You can do your daily activities during the test, which lasts one to three days.

A stereo-EEG is done in a hospital under general anesthesia, so you’ll be asleep during the surgery. After the anesthesia takes effect, your care team will place a frame on your head to keep it stable and secure. Your surgeon makes small incisions in your scalp and will drill tiny holes in your skull. Small electrodes will then be placed through the holes to reach brain areas where your seizures may begin. Imaging tests may be done before and during the procedure to offer guidance. Afterward, your care team will remove the head frame and put a bandage or soft wrap around your head. Your care team will take brain scans to see the exact locations of the electrodes. Surgery can last several hours.

Afterward, you’ll go to an epilepsy monitoring unit where the electrodes will be connected to a device that records your brain activity. A computer creates 3D images that show where your seizures begin and spread. You’ll be in the hospital for about a week or longer for this type of EEG while seizure activity is recorded. When monitoring is complete, your doctor will remove the electrodes and close the incisions with stitches under local anesthesia. You’ll be awake but numb during this procedure.