244 ANNUAL REPORT SMITHSONIAN INSTITUTION, 195 



sideration of brain function as a whole. Present concepts can be sum- 

 marized most concisely by stating that the general function of the 

 brain is to construct and contain a working model of the outside world, 

 and to test upon this model the effect of the operations that circum- 

 stances suggest are necessary for comfort or survival. The more 

 accurate and detailed the model, the more trustworthy will be the 

 forecast of the results of action, and the better the chances of survival 

 of the organism. In the human brain, the working parts of the model 

 are the circuits that link the nerve cells; since their permutations are 

 of the order of lOi°-<'°° there seems ample scope for detail — and for 

 fantasy. 



The notion of the brain as a signal analyzer and statistical predictor 

 has developed parallel with the design and construction of the various 

 large computing engines sometimes known as electronic brains, but 

 it must be admitted that as yet very little is known of the precise man- 

 ner in which the animal brain composes its models so that they are 

 compact enough to be portable, plastic enough to be changed from 

 second to second, yet durable enough for a lifetime. It may be men- 

 tioned, however, that in man the purely nervous model is totally in- 

 adequate for social life, and is supplemented by external patterns in 

 the form of written records, laws, and so forth. The neurophysiolo- 

 gist, then, would use the term "mind" as meaning the individual's model 

 of his environment and "thought" as a miniature rehearsal for action. 

 Such generalizations are bound to reawaken many ancient philosophi- 

 cal controversies, but have the virtue of promising linkage between 

 brain physiology and other human interests, some of which will be 

 considered later. 



Eeturning to the discoveries in the field of electroencephalography, 

 it was found at an early stage that recognizable perturbations of the 

 electrical patterns occur in diseases of the brain. This observation 

 had the unfortunate effect of distracting attention from fundamental 

 problems, so that most laboratories engaged in this sort of work were 

 soon full of records from epileptics and patients with brain tumors, 

 and, during the war, with head injuries and abscesses. The literature 

 of the subject contains thousands of papers and reports describing 

 empirical correlations between various E. E. G. features and brain 

 diseases, but of these publications only a few dozen are of funda- 

 mental importance, and there is no doubt that the great discoveries are 

 still to be made. 



Records from normal people show a great variety of more or less 

 irregular electrical discharges from all parts of the brain, but in most 

 subjects, when the eyes are shut, the discharges become more rhythmic 

 in the occipital region, where visual impressions are projected. These 

 regular oscillations are known as alpha rhythms and have a frequency 



