ELECTROENCEPHALOGRA M 



241 



recommended by Pauline A. Davis will be described. Figure VI-15 

 shows the arrangement of the electrode contacts. The lobe of the ear is 

 used as a reference point since it is electrically much less active than 

 points on the cranium. 



Fig. VI-14. A commercially available two-channel portable research electroen- 

 cephalograph. Motion-picture camera in foreground, facing the two-channel oscillo- 

 graph fluorescent screens. Mechanical two-pen recorder right end of display. Input 

 amplifier. Sensitivity, 1 mm per microvolt. Voltage gain 20 million. Frequency 

 range 1-10,000 cycles. Output amplifier. Power gain 4 X 10 w times. Cathode- 

 ray screen, 5 in. Camera, 35-mm film. Power supply, 115 volts, 60 cycles, 400 

 watts. (By courtesy of the Electro-Medical Laboratory, Inc., Holliston, Mass.) 



The electrodes are solder pellets covered with electrocardiogram 

 paste. They are fastened to the head by covering them with collodion. 

 The contact resistance should be 



less than 10,000 ohms. 



In the encephalogram records 

 examined by Pauline A. Davis 

 [1941] it was found that the pat- 

 tern of the occipital area in normal 

 people was the most stable, and 

 that if an a: frequency were present 

 it was more pronounced than from 

 any other area. The temporal 

 area usually showed less a activ- 

 ity than the motor area. The 

 frontal electroencephalogram was 

 found to be distorted by the 



Frontal 



Occipital 

 Multiple monopolar 



Fig. VI-15. Placements on head rep- 

 resent multiple monopolar recording 

 technique. The numbers represent the 

 amplifier channels. (By courtesy of 

 Pauline A. Davis [1941].) 



potentials generated by eye movements and muscle potentials. 



A standard procedure is to determine the a index, which is the per- 



