8 BRAINS OF RATS AND MEN 



cited by some retinal image, each of these certainly 

 activates at least ten others (lo^), and each of these 

 in turn ten others (lo^). From each of these last 

 neurons associational fibers go out that may reach 

 the extreme dimensions of the cortex, and at this 

 stage of the process the lo^ neurons in actual function 

 may act upon a considerable part of the entire 

 cerebral cortex, some parts being intensely activated 

 and other parts being so slightly affected as not to 

 reach the threshold of stimulation. 



But the associational process has just begun. 

 From each of these foci of cortical activity, lines of 

 nervous conduction irradiate in definite patterns de- 

 pending on the particular trains of association that 

 are set up, and these lines of transmission may be 

 activated in momentarily changing patterns of un- 

 limited complexity. If for simplicity of computation 

 we limit ourselves to one million of the lo^ neurons 

 already activated in the process, and if we assume 

 that these may be recombined among themselves in 

 all theoretically possible patterns, the total number 

 of such connections would far exceed the io^'^^-^°°° 

 already mentioned as the theoretically possible com- 

 binations in groups of two only. Not all of these 

 theoretic combinations are actually present anatomi- 

 cally, but a large proportion of them certainly are 

 structurally there. 



Of course, in any one series of cortical associations 

 only a minute fraction of the anatomically present 



