Electrical Potentials from the Intact Human Brain

Abstract

Berger''s observation of rhythmic action potentials from the intact human brain recorded from electrodes applied to the surface of the head has been repeated. With one electrode on the occiput and the other on the forehead or vertex, for example, the most prominent oscillations occur at frequencies ranging from 8 to 12 per sec. in different individuals and with magnitudes varying from 20 to 80 microvolts. Different individuals present different characteristic frequencies, but the frequency is practically constant for a given individual under the same conditions of experimentation. Smaller oscillations are observed at frequencies of 25 to 50 cycles per sec. with magnitudes of 15 to 30 microvolts. These waves seem to be of brain origin since they do not correspond to simultaneous records of respiration, pulse, and muscle action currents, and they appear to increase in magnitude as electrodes are placed through the skin to the periosteum or over trephine openings in the skull. Furthermore, the large oscillations are of different frequencies in the case of pathological brain tissue and are also varied by visual stimulation, some thought processes, and anesthesia. They appear to be due to the spontaneous beating together of cortical cells in the relatively undisturbed resting state since they disappear when their synchronous activity is disturbed by certain kinds of afferent impulses.