Problems in the Comparative Study of Brain Waves *

It is the purpose of this discussion to point out certain of the approaches and problems that inhere in the study of that form of nervous activity giving rise to "brain waves," especially as seen from the comparative point of view. Brain waves will be loosely considered as any fluctuating electrical potentials ascribable to the brain or to the highest ganglia of the central nervous system in the absence of apparent external stimulation. It is considered undesiralble for the present purpose to attempt an artificial separation of one portion of the frequency spectrum from others by restricting the term ta those frequencies that appear as waves instead of spikes at a certain speed of the recording tape. It is not intended to present the results of a finished investigation, but simply to call attention to some significant problems raised by our present knowledge of brain waves in lower animals, supplemented by some new records, and to certain bearings which this knowledge has upon existing interpretations of brain waves. In the decade and very little more since it became accepted that rhythmic, oscillatory potentials were a valid and constant feature of the normal, apparently unstimulated cerebral cortex of man and higher animals, a large literature has accumulated on the "electroencephalogram" (EEG) under a great variety of circumstances. After a few early attempts at a fundamental explanatio;n of the phenomenon, which served to indicate the difficulty of the prdblem, attention turnedl to the establishment of empirical correlations useful in clinical application and it is in this area that the principal body of our knowledge lies. These clinical studies have emphasized the sensitivity and objectivity of this sign of the activity of the brain and at the same time its crudity as compared with signs based on behavior, sensation, and introspection. Thus, the EEG provides clear indications of sleep, of light ether anesthesia, and, under the proper circumstances, of thinking as opposed to the resting state, but it is virtually unaffected (by frontal lobotomy (Davis36),