Magnetoencephalography (mag-NEE-toe-en-sef-uh-low-graf-ee) is a technique that checks brain function. For example, it can assess the magnetic fields that arise from electrical currents in the brain to pinpoint the parts of the brain that cause seizures. It also can help identify the location of important things such as speech or motor function. Magnetoencephalography is often called MEG.

MEG is used to plan surgery for epilepsy and brain tumors. MEG helps surgeons understand specific parts of the brain before operating so that they can treat only the parts of the brain that are affected.

MEG is done in a clinic setting and usually does not require staying in a hospital. Most people have no pain during the test and may go back to their regular activities after the test.

When surgery is needed, it's best that your healthcare team members understand all they can about your brain. MEG is a noninvasive way to understand areas of the brain that cause seizures and areas that affect your brain functions.

MEG also helps your care team identify areas of the brain to avoid. The data that MEG provides makes it easier to plan surgery precisely.

In the future, MEG may be helpful in diagnosing stroke, traumatic brain injury, Parkinson's disease, dementia, chronic pain, brain disease that results from liver disease and other conditions.

You may need to limit food and water intake before the test. You may also need to stop taking your regular medicines before the test. Follow any instructions you get from your care team.

You must wear comfortable clothing without metal buttons, rivets or threads. You may need to change into a gown before the test. Don't wear jewelry, metal accessories, and makeup and hair products because they may contain metallic compounds.

If having equipment around your head makes you nervous, ask your care team about taking a light sedative before the test. Infants and children may receive sedation or anesthesia to help them remain still during MEG. Your healthcare professional can explain your child's needs and options.

The equipment used in MEG testing fits over the head much like a motorcycle helmet. Your care team checks the fit of your head in the machine before doing the test. A member of your care team may give something to put on your head to help position the machine properly. You sit or lie flat while your care team checks the fit.

The MEG test takes place in a room built to block magnetic activity that could make the test less accurate. You are alone in the room during the test. You can talk with the care team members during and after the test.

Usually, MEG tests are painless.

Your healthcare professional may perform an electroencephalogram (EEG) at the same time as the MEG. If so, your care team will place other sensors on your head using a cap or tape.

If you will have an MRI scan as well as MEG, your care team likely will do MEG first to reduce the chance that the strong magnets used in MRI affect the MEG test.

During the test

During MEG, you sit or lie on your back without moving. Sensors in the helmet record magnetic activity in your brain and send information to your care team. Your care team monitors you from a nearby room. Doctors, technicians and engineers analyze the data and map brain activity that causes seizures. Your care team ensures that the system is working properly and gives you instructions.

During some parts of the test, you may be able to read or watch TV. And during other parts of the test, you may need to pay attention to certain stimuli. You also may be asked to open or close your eyes.

MEG tests usually last no more than two hours. Getting set up and taking the test may take four hours. MEG that's done to check your brain during sleep is a key part of most studies.

After the test

If you don't have sedation or anesthesia, you may be able to resume your usual activities right away.

If you or your child got a sedative, you need to wait 30 minutes to 2 hours for the sedative to wear off. You may not want to drive or do other activities right away.

A healthcare professional trained to interpret MEG test results will analyze, interpret and review the test data and send a report to your doctor. Your care team will discuss the test results with you and create a treatment plan that is right for your situation.