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HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY I 



FIG. 7. Toposcope display sys- 

 tem record of the effect of mental 

 activity on alpha frequency and 

 distribution in a normal subject. 

 Each of the 22 circular areas is 

 the face of a cathode ray tube 

 connected to an electrode pair 

 over the brain. There are thus 22 

 channels. In each circuit there 

 has been introduced a spiral 

 scanning time-base upon which 

 are projected the variations in 

 brilliance proportional to the 

 rhythmic changes of voltage re- 

 sulting from brain activity. In 

 this case the rotation speed of the 

 signals was one-third of the fre- 

 quency of the resting alpha 

 rhythm, which was 8.8 cycles per 

 sec. The duration of each expo- 

 sure was 8 sec. The intrinsic 

 rhythms are seen as white 

 smudges in each indicator tube. 

 The first exposure (.4) shows the 

 alpha distribution and frequency 

 at rest; during the next exposure 

 (B) the subject was asked to 

 begin a series of mental tasks; 

 the immediate effect of the in- 

 structions was to suppress the 

 alpha activity in all but two 

 channels in the right hemisphere 

 where the frequency rose to 9.4 

 cycles per sec. The subsequent 

 exposures were taken during 

 performance of the task and show 

 a gi-adual return to the resting 

 state. During this period the 

 alpha activity decelerated slowly 

 and returned to the left hemis- 

 phere where it remained accel- 

 erated for a longer period than 

 on the right side. The return to 

 the original condition took nearly 

 too sec, but the final frequency 

 was exactly the same as before 

 the activation. [From Walter 

 (61).] 



