In 1959, Wilder Penfield and Lamar Roberts published a book dealing with their experience in electrically stimulating small portions of the brain during neurosurgical procedures designed to relieve epilepsy. Penfield was one of the great pioneers of neurosurgery. Among his many accomplishments and innovations was the beginning of the use of surgical excisions for the relief of certain forms of epilepsy. In some patients, a small scar, tumor, vascular malformation, infection, or other abnormality is the cause of seizures. Although many of these seizures can be controlled with medication, a few cannot, and in these remaining cases, it may be possible and worthwhile to remove the epileptogenic area of the cortex. Obviously, if the removal of this area of cortex leaves the patient with a severe functional impairment, the treatment will have been worse than the disease. Therefore, if the epileptogenic lesion is in primary motor cortex, or in some other area which is important in an essential function, this surgery is not performed. One of the areas which obviously must be avoided during such surgery is any portion of the brain which is necessary for language functioning. One of the first challenges facing Penfield in the development of this type of surgery, therefore, was to find a method to determine what portion of the brain was responsible for these basic functions, including language.

The technique that Penfield developed was to stimulate tiny portions of the brain electrically during the neurosurgical procedure. Because the brain itself has no pain receptors, it is possible to undertake neurosurgical procedures under local anesthesia when the patient is lightly sedated.