The application of electrical methods to the study of cerebral function is still in an experimental stage. In 1923 Grant,1using a simple Wheatstone bridge arrangement, reported marked diminution in the electrical resistance of tumor tissue as compared with that of normal brain. Berger2amplified electric potentials set up in the brain and ascribed changes in potential to nervous activity. Foerster and Altenburger3succeeded in recording characteristic changes in potential in several cases of tumor of the brain. Subsequently, electroencephalographic methods have resulted in the accumulation of a considerable amount of data, especially with respect to the epileptic syndromes.4Recently, important contributions to the possibility of localization of tumors by electroencephalography5have been made. However, in only a few instances (notably, those of Foerster and Altenburger,3in Germany, and Walter, in England) have direct records from the cortex been demonstrated. We believed that studies