240 THE BIOPHYSICAL PROBLEM OF NERVE CONDUCTION 



electroencephalogram patterns, and a system of evaluation as to the 

 degree of normality and abnormality. 



.10 



Time in seconds 



Fig. VI-13. A synthetic encephalogram. Hypothetical a waves, 200-microvoIt 

 amplitude, 10-cycle frequency, superimposed on /3 waves, 100-microvolt amplitude 

 and 20-cycle frequency. Note similarity of composite graph (a + 0) with electroen- 

 cephalogram A in Fig. VI-12. 



A selected normal individual is defined as one whose medical history 

 reveals only the ordinary childhood diseases, who has had no psychiatric 

 problem necessitating care, and whose behavior has been normal at 

 home, at school, at work, and at play. He must be known to be free of 

 drugs, even as common a one as aspirin, for several days before the 

 recording. 



Upon examination, the person must be free from apprehension in rela- 

 tion to the procedure, comfortably relaxed but thoroughly awake with 

 eyes closed, and on a bed in a diffusely lighted room. 



The recording apparatus may be an ink-writing oscillograph with 

 amplifiers and broad-band filters. An available two-channel commer- 

 cial form is shown in Fig. VI-14. The speed of the recording tape is 

 about 3 cm/sec. Sensitivity is 1-cm deflection of the oscillograph pens 

 per 100 millivolts. Tuned electric filters may be used in the circuit. 

 The 10-cycle filter has a broad peak at 10 cycles, and will pass 9, 8, and^ 

 cycles on one side and 11, 12, and 13 cycles on the other side; the 

 higher- and lower-frequency filters have comparable breadth. 



A three-pen recording can be obtained simultaneously. The three 

 matched amplifying systems are balanced with push-pull input stages, 

 non-interfering and independent of one another. 



As an example of cranial recording the " multiple monopolar method " 



