ORIGIN AND SIGNIFICANCE OF THE CEREBRAL CORTEX 229 



may be effected and various automatisms set off in accordance 

 with their preformed structure. These subcortical systems are 

 to some extent modifiable by racial and individual experience, 

 but their reactions are chiefly of the determinate or stereotyped 

 character, with a relatively limited range of possible reaction 

 types for any given stimulus complex. 



It is shown by the lower vertebrates which lack the cerebral 

 cortex that these subcortical mechanisms are adequate for all 

 of the ordinary simple processes of life, including some degree 

 of associative memory. But here, when emergencies arise which 

 involve situations too complex to be resolved by these mechan- 

 isms, the animal will pay the inevitable penalty of failure — 

 perhaps the loss of his dinner, or even of his life. 



In the higher mammals with well developed cortex the auto- 

 matisms and simple associations are likewise performed in the 

 main by the subcortical apparatus, but the inadequacy of this 

 apparatus in any particular situation presents, not the certainty 

 of failure, but rather a dilemma. The rapid preformed auto- 

 matisms fail to give relief, or perhaps the situation presents so 

 many complex sensory excitations as to cause mutual interfer- 

 ence and inhibition of all reaction. There is a stasis in the sub- 

 cortical centers. Meanwhile the higher neural resistance of the 

 cortical pathways has been overcome by summation of stimuli 

 and the cortex is excited to function. Here is a mechanism 

 adapted, not for a limited number of predetermined and imme- 

 diate responses, but for a much greater range of combination of 

 the afferent impressions with each other and with memory 

 vestiges of previous reactions and a much larger range of pos- 

 sible modes of response to any given set of afferent impressions. 

 By a process of trial and error, perhaps, the elements necessary 

 to effect the adaptive response may be assembled and the prob- 

 lem solved. 



It is evident here that the physiological factors in the dilemma 

 or problem as this is presented to the cortex are by no means 

 simple sensory impressions, but definitely organized systems of 

 neural discharge, each of which is a physiological resultant of 

 the. reflexes, automatisms, impulses and inhibitions character- 

 istic of its appropriate subcortical centers. The precise form 

 which these subcortical combinations will assume in response to 

 any particular excitation is in large measure determined by the 



