ELECTROENCEPHALOGRAM 



239 



The /8 activity is a universal feature of all records (Pauline A. Davis 

 [1941]) and is present all over the brain. 



Suppose that a and /3 activities were recorded as a pure sinusoidal 

 wave of frequency 10 and 20 cycles per second, and possessed amplitudes 



\J 



sec 



Normal human EEG 



4llAJli\iW^ 



3 sec 



10~ 

 W Alpha waves 

 nearly continuous 

 10-50/iV 



Alpha modulated 

 100/tv 



D v d v '1M , fy/WVvv\j^^ 



2 sec 



E /*~^~^ v W|JlJj| |lfl/Vv^-^vvvv-v--v _ 



20 ^ 



/3-rhythm 



10/iv 



'Spindles" 



Fig. VI-12. Copies of typical fundamental rhythm patterns found in normal 

 human electroencephalograms. 



equal to 200 and 100 microvolts, respectively. They could be graphi- 

 cally represented as the broken lines in Fig. VI-13. The solid line repre- 

 sents their algebraic sum. This composite curve could then represent 

 an idealized encephalogram. If this composite curve were being 

 recorded as if it were an electroencephalogram, then, by the introduction 

 of an electric filter in the recording circuit which would absorb the /3 

 wave form, the structure of the a rhythm could be obtained. The result- 

 ing wave train would then be similar to that represented by Fig. VI-12, 

 B, except for the slight modulations shown. 



Ever since the original observations by Berger, investigators have 

 attempted to describe and interpret these records. A successful stand- 

 ardized recording has recently been reported by Pauline A. Davis 

 [1941], which also contains a description of a standardized technique on a 

 selected normal individual, a classification of fundamental types of 



