246 BRAINS OF RATS AND MEN 



The stimulus-response physiology when broadly 

 interpreted is an adequate basis for an understanding 

 of most subcortical nervous activities. It also pro- 

 vides the activators for all cortical functions. But the 

 intrinsic processes within the human cortex go beyond 

 these simple principles. In the associational fields we 

 have the machinery for registering in static form the 

 structural modifications (engrams) left by the activa- 

 tion of every cortical associational pathway. Every 

 such associational pattern which has once been acti- 

 vated seems to be preserved, set as on a trigger, ready 

 to be activated when some related or congruous sys- 

 tem of subcortical activities again overflows into the 

 cortical projection centers — the conventional theory 

 of cortical memory. (For further analysis of this 

 situation see Hunter, 1924^, p. 19, and Dashiell, 

 1925.) 



These reactivated cortical patterns (memories) 

 knit in with the lower sensori-motor systems at the 

 moment in action and serve as the "deciders" of con- 

 duct. When many such mnemonic vestiges have been 

 laid down in the structural organization of the cortex, 

 these may be so related that the excitation of one may 

 activate another and so arise trains of cortical activ- 

 ity which, though initiated from the outside, are 

 themselves strictly intrinsic to the cortex and may 

 continue as intracortical processes indefinitely — the 

 conventional theory of free cortical association. 



The cortical areas into which nervous impulses are 



