274 



BIOPHYSICAL STUDIES ON NERVE AND MUSCLE 



this organ is meager. Thus, while neuroanatomy, which deals with the 

 geography of the brain and the relation of various parts of the brain to 

 certain functions of the whole system, is well advanced, and its daughter, 

 neurosurgery, is in a rapid state of development, physiological studies are 

 necessarily phenomenological because of the complexity of the system under 

 study; and biophysical studies, mainly electrical because of the fast elec- 

 trical responses of the system, tend to be either empirical or theoretical — 

 and hence do not assure a correct understanding of the phenomena under study. 

 As a result of this complexity, the most important advances of the past 

 decade have not been biophysical at all. Three different kinds of study will 

 now be briefly noted: (a) the recording and analysis of gross electrical sig- 

 nals of the brain; (b) the transmission across synapses in the spinal cord; 

 and (c) the electrical behavior of single neurons in the cortex. 

 The method of electroencephalography (EEG) is as follows: 

 Small pellets of solder, or other metal-contact electrodes, preferably non- 

 polarizable,*** are placed on symmetrical points of the scalp and fastened 



delta 



v I 



theta 



alpha 



Hsed 



beta 



4h4H|rWpvHM^ 



Figure 10-6. Components of an Electro- 

 encephalogram. 



there with a binder such as collodion. Twelve to twenty-six leads cover the 

 scalp in localization experiments, overlying each important lobe of the brain, 

 and even different portions of each lobe. Voltages between these and some 

 reference position, such as a lead to the ear lobe, are" fed into standard high- 

 gain amplifiers, and traced by pen recorders. Five or six seconds of record- 

 ing gives patterns (Figure 10-6) which, quite empirically, have been cata- 



***A nonpolarizable electrode is one in which the voltage with respect to some reference 

 remains unchanged when current is passed through the electrode. A silver disk coated with a 

 thin layer of AgCl, which makes contact with the chloride-containing body salts, is non- 

 polarizable in EEG work where the currents are very small (< 10 amp). 



