stimulation of the brain. neuro-oncology 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. this procedure is considered standard for operations involving gliomas in order to reduce loss of motor function and overall morbidity. 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. patients whose surgeon uses cortical stimulation mapping to assess the anatomy and function of rolandic areas have a greater chance and faster rate of regaining baseline function post-operatively than those who undergo surgeries that avoid this technique. the same may be said for the benefits of mapping language areas with the cortical stimulation technique before a glioma resection. assessing and minimizing the damage of operating on language-involved regions leads to the greater and faster return of overall language function. despite the functional gain from preserving these eloquent cortical areas, benefit-to-risk factors are still considered. 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. vision mapping of the occipital cortex has possible use in the development of a prosthesis for the blind. 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 . 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. electrical stimulation in the occipital lobe has also been known to produce small colored circles usually in the center of the patient's field of vision. visual hallucinations, such as moving geometric patterns and moving colored phosphenes have also been observed with cortical stimulation. electrodes at the occipital cortex surface tend to produce flickering phosphenes, while electrodes inserted deeper within the cortex produce steady colors. the primary visual cortex, which is responsible for generating more complex images, is located deeper within the calcarine fissure of the occipital lobe, so intracortical stimulation is needed to stimulate these areas effectively. intracortical stimulation uses an electrode that goes deeper into the brain to more effectively stimulate the primary visual cortex, as opposed to trying to work only from the surface of the brain, which can cause unintended visual signals, pain, and damage to the nervous tissue. for patients with glaucoma and optic nerve atrophy, existing retinal prostheses are not an option since the optic nerve is damaged, therefore a prosthesis using cortical stimulation is a remaining hope to offer some vision function. a cortical visual prosthesis is a promising subject of research because it targets neurons past the site of disease in most blind patients. however, significant challenges remain such as reproducibility in different patients, long-term effects of electrical stimulation, and the higher complexity of visual organization in the primary visual cortex versus that in the retina. another site of research for a vision prosthesis using cortical stimulation is the optic nerve itself, which contains the nerve fibers responsible for the complete visual field. 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 cortical stimulation mapping vs. transcranial magnetic stimulation 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. the history of beneficial outcomes and the amount of information already established about the csm technique makes it advantageous in clinical and research applications. however, because it has the drawback of being an intraoperative technique, there is growing debate about its status as the preferred method. instead, transcranial magnetic stimulation (tms), a new procedure that does not carry the same amount of surgical risk, is being considered. 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. additionally, because of the increasing body of research focused on investigating the many medical uses of tms, it could eventually have more applications than 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. similarly, tms is also being researched for its possibilities as a long-term and possibly more cost-effective therapeutic alternative for treating chronic psychiatric disorders such as major depression as well as its use as a means of in aiding in stroke recovery. however, although therapeutic tms is promising overall, its success is still unclear and has not been upheld in a number of studies. this is true relating to studies of parkinson's patients who were given long-term tms therapy. although it initially appeared as if these subjects gained improved performance in motor coordination tests, these results are inconsistently reproducible. 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. such results suggest that evidence of the effects of tms are lacking and this technique's neurobiological mechanisms are still not well understood. because of these uncertainties, research on this method is ongoing and much is still to be determined about its exact effect on the activation state of the brain. comparatively, csm, having the advantages of the more researched technique, is often still preferred. safety must also be considered with respect to both methods. so far, food and drug administration (fda) guidelines have only approved the use of tms for the treatment of depression. 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. 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.