Determining the anatomical location of the tumor can usually be based on your MRI scan. However, the locations of your vital functional areas may not always be the same as in a healthy person. As a tumor grows, it displaces grey matter, and the buildup of liquid can obscure the MRI. Due to brain plasticity, functions can move as a consequence of tumor growth. In some patients, the cortex re-organizes important functions into adjacent tissues which would not normally be associated with function—allowing for safe resection. NBS mapping is used when the disease is thought to be close to vital areas of the brain, such as those responsible for limb movement or speech production. Brain maps are useful when deciding the treatment option. If neurosurgery is recommended, NBS results help your care team plan the operation. Knowing the locations of vital brain functions prior to surgery helps lower the risk of deficits post-operatively, thus preserving your quality of life.
Speech mapping is a technique to locate the parts of your brain involved in language and speaking. Using NBS to rapidly stimulate part of the cortex, its normal function can be temporarily disturbed. This rapid stimulation technique is called repetitive TMS, or rTMS.
A speech stimulation session
After a system set-up process, you will be shown pictures of everyday objects. Only the objects you can readily name will be retained and shown to you later with stimulation. These pictures form a naming task tailored just for you.
While you are performing your naming task, the clinician will move the stimulation coil over the side of your head. Every time an image changes, the NBS System automatically delivers a burst of stimuli (rTMS). When an area of your brain vital for speech is stimulated like this, it can cause hesitation, loss of fluency or even the inability to speak. Sometimes, you may not be aware of any interference or change yourself.
The mapping session is recorded on video. You can expect a speech mapping to last several hours in total, but you may take breaks, as needed. Any speech interference caused by NBS will only last for a moment and is completely harmless.
What happens after a speech stimulation session?
The clinician performs computer-assisted speech behavior analysis later. You will not need to be present. Matching stimulation locations to speech disturbances allows the physician to determine which areas of the brain need to be preserved so that your ability to speak is not harmed. Speech mapping results are a significant help for patients and doctors when they come to discuss treatment and any possible trade-offs between risks and expected benefits of surgery.
Mapping motor function
Patients are a lot more confident when they go into surgery.
Bernhard Meyer, MD, Professor & Chair,
Department of Neurosurgery, Klinikum rechts der Isar, Technical University of Munich, Germany.
The detailed NBS maps open the door to surgery for many patients who are currently denied surgical treatment and enable more extensive resections - while at the same time leading to better neurological outcomes.
I consider NBS mapping as a very important tool to get the best results in surgery over critical area lesions on the brain.
Indications for use and safety
INDICATION FOR USE
The Nexstim Navigated Brain Stimulation System 5 (NBS System) is indicated for non-invasive mapping of the primary motor cortex of the brain to its cortical gyrus. The NBS System provides information that may be used in the assessment of the primary motor cortex for pre-procedural planning.The NBS System is not intended to be used during a surgical procedure. The NBS System is intended to be used by trained clinical professionals.
Nexstim NEXSPEECH® indicated for noninvasive localization of cortical areas that do not contain essential speech function. Nexstim NEXSPEECH® provides information that may be used in presurgical planning in patients undergoing brain surgery.
Do not use the Nexstim NBS System on:
- persons who have metallic implants anywhere in the head (excluding teeth)
- persons who have any electrical implants
- persons with increased intracranial pressure
- persons with intracardiac lines, intravenous pumps, or dose calculators.
Do not use the Nexstim NBS System without clear benefit or compelling clinical reason on:
- persons with epilepsy
- persons with serious heart disease
- persons with lowered seizure threshold due to acute large infarctions, intracranial hemorrhage, or trauma
- persons with medication that lowers the seizure threshold
- persons with cardiac pacemaker.
Women of childbearing age must be questioned about the possibility of pregnancy before participating, and excluded—if there is a chance that they may be pregnant. Women of childbearing age should not participate without clinical reason.
Risk of seizures
Cortical magnetic stimulation runs the risk of inducing seizures - although they are rare. Single-pulse TMS, which is used in mapping the cortical representation areas of specific muscles, is generally considered a non-significant risk application. However, secondarily generalized or partial motor seizures have been induced in patients with stroke, intracranial brain lesions and major disorders of the central nervous system. The seizures have occurred either during the TMS stimulation or minutes after the end of the stimulation session.