What Is Brain Mapping?

Before epilepsy surgery, your doctor will need critical information about your brain. They may turn to a technique called brain mapping to learn more.

Brain mapping is a procedure that helps doctors figure out which areas of your brain control different functions. Doctors already have a general idea, but brain mapping provides more exact locations.¹

A doctor creates a "map" by stimulating different areas of the brain with a low electrical current. The map reveals which specific regions of the brain are connected to distinct functions like movement, speech, and vision. These areas vary from person to person and can change with:¹

• Tumors
• Seizures
• Other conditions that affect the brain

How does brain mapping help with epilepsy?

Doctors use brain mapping before performing epilepsy surgery. They want to learn more about how your brain functions near the seizure area. This way, they can safely remove brain tissue without impacting parts of the brain that control essential functions.¹

Types of brain mapping

Doctors commonly carry out brain mapping in 1 of 2 ways. Intraoperative brain mapping happens during surgery, while doctors do extraoperative brain mapping outside the operating room. Here is how each procedure works:¹

• Intraoperative: During this procedure, you are awake and can talk but will not feel any pain. The surgeon uses a small electrical tool to probe different areas of the brain and create a map. For example, if you have trouble speaking, the surgeon has probed the language area of your brain.
• Extraoperative: First, doctors create an opening in your skull and place small electrodes on the surface of the brain. After this first surgery, the electrodes record your seizures and map your brain. A few days later, you will have another surgery. Your doctor will use information from the map as a guide in removing abnormal brain tissue while avoiding critical areas.

Recently, scientists have been investigating other types of brain mapping that do not require surgery:^2-4

• Magnetoencephalography (MEG): MEG records magnetic fields cast out by your brain cells (neurons). You will wear a helmet-like scanner on your head, which collects information from 275 sensors every millisecond. The data is then combined with magnetic resonance imaging (MRI) to create a brain map.
• Functional MRI (fMRI): While an MRI allows doctors to capture images of the brain’s structure, an fMRI is more advanced. You will put on a pair of goggles and lie inside a scanner. A technician will then give you simple instructions, like thinking of a specific word. Each task will light up different parts of your brain. This helps surgeons to map out where to perform epilepsy surgery.

What are the possible side effects of brain mapping?

Brain mapping could trigger a seizure in people with epilepsy. That is because the doctor is mapping an area near the origin point of your seizures.¹

During the procedure, your healthcare team will monitor your brainwaves with an electroencephalogram (EEG) to watch for an oncoming seizure. If you start to have a seizure, they could either stop mapping or give you seizure medicine before continuing.¹

Pain is also another potential side effect, although the risk is small. Now and then, an electrode may touch membranes around your brain. This could cause pain or tingling.¹

These are not all the possible side effects of brain mapping. Talk to your doctor about what to expect with brain mapping. You also should call your doctor if you have any changes that concern you about brain mapping.

Things to know about brain mapping

Keep in mind that you will not have complete control over your body during the mapping process. You may unwillingly lift a limb, lose your vision, or even laugh – all triggered by the electrical current. But these changes are temporary, so you don’t have to worry about them.¹