Cortical stimulation mapping
[1] It remains one of the earliest methods of analyzing the brain and has allowed researchers to study the relationship between cortical structure and systemic function.
These findings, which were repeated by Harvey Cushing through the early 1900s, show that the Rolandic fissure is the point of separation between the motor and sensory cortices.
[5] Cushing took work that had previously been done on animals, specifically chimpanzees and orangutans, and was able to utilize cortical stimulation mapping to account for the differences between these species and humans.
However, an advantage of subdural electrode grids is that they can be left in the brain for multiple days, and allow functional testing during stimulation outside the operating room.
[4] Patients who undergo the procedure with an awake craniotomy instead of general anesthesia have better preservation of language function, a prediction of their seizure-free outcome based on corticography, a shorter hospitalization (which corresponds to a reduced cost of care), a decreased usage of invasive monitors, and decreased number of postoperative complications due to anesthesia such as nausea and vomiting.
[4] Cortical stimulation mapping is used for somatotopy to determine the areas of the cerebral cortex that connect through nerve fibers with different body parts.
When the precentral gyrus of the frontal lobe is stimulated, specific muscles in the body will contract based on the location of the brain that receives the electric signal.
[1] During stimulation various language tasks are used to check brain function such as reading sentences, auditory comprehension, and spontaneous speech such as naming objects.
Sensation has been tested in patients through the stimulation of the postcentral gyrus, with a drop in amplitude of sensory responses occurring towards the central sulcus.
Once the focal point of the seizures is determined, this information allows aids neurosurgeons with knowing what portions of the brain could potentially be resected without any negative post-operative neurological deficits.
[11] Through the technique of CSM, generally using awake craniotomies, the neurosurgeon has the ability to monitor the functioning of the patient during the resection and stimulation of the brain.
Cortical stimulation mapping may be used in neuro-oncology as a tool to identify the areas of a patient's brain that are critical for functions such as the language and motor pathways.
Pre-surgical planning allows for the physician to avoid these high-risk areas as much as possible during a tumor resection, minimizing potential loss of function and development of sequelae.
More complete tumor resection has been shown to possibly expand the life expectancy of glioma patients; however, increasing the amount of brain tissue removed may also cause a debilitating decrease in function.
As such, cortical stimulation mapping aids in determining the maximum amount of tissue that can be removed while still maintaining the patient's quality of life.
Electrical stimulation in the occipital lobe has been found to cause visual illusions called phosphenes such as light, colors, or shadows, which were observed in the early experiments of Penfield and Jasper .
[1] The first recorded production of artificial sight was in experiments done by Brindley and Dobelle, where they were able to allow blind patients to 'see' small characters through cortical stimulation.
A cortical visual prosthesis is a promising subject of research because it targets neurons past the site of disease in most blind patients.
Research is still ongoing in this area and the small size of the optic nerve and the high density of nerve fibers are continuing challenges to this approach [18] Cortical stimulation mapping (CSM) is considered the gold standard for mapping functional regions of the brain to create a presurgical plan that maximizes the patient's functional outcome.
[3] The history of beneficial outcomes and the amount of information already established about the CSM technique makes it advantageous in clinical and research applications.
Transcranial magnetic stimulation has been gaining increasing interest as an alternative tool for studying the relationships between specific cortical areas and brain function, particularly because its non-invasive nature is advantageous over CSM.
For example, this procedure been successfully used to measure the speed of conduction in central motor pathways, making it a useful tool for those studying multiple sclerosis.
[24] The same type of results are seen in studies in schizophrenia where it has been shown that cognitive performance in schizophrenic patients treated with TMS is highly variable.
[26] Although this technique has no known lasting side effects except for a few reported cases of induced seizures, it is still treated with caution due to its relative novelty in clinical use.
[27] CSM has gained U.S. FDA approval for its uses regarding cortical stimulation mapping, especially in cases of seizure and glioma treatments, and for aiding in the placement of electrodes within the brain.
