3i8 BRAINS OF RATS AND MEN 



activated within their field. Each of these may be 

 activated by any one of the numerous associational 

 neuronic systems which traverse its vicinity. These 

 non-specific reserves may be utilized successively by 

 many different associational systems and perhaps 

 play a large part in maintaining cortical tone and sup- 

 plying the energy or driving force so characteristic of 

 some higher cortical functions. 



Thus we have in the cerebral cortex (as elsewhere 

 in the brain) abundant provision of non-specific 

 neurological reserves available on demand for any 

 cortical activity, and in addition an accumulation of 

 an enormous number of specific mnemonic reserves, 

 each of which is a particular pattern of associational 

 neurons of very complex organization. The preserva- 

 tion of these structural alterations (engrams) each of 

 which has resulted from some particular personal ex- 

 perience, and the power to reactivate these structural 

 associational patterns in appropriate new situations 

 with reinforcement from the intrinsic non-specific type 

 II cortical neurons, give to the human cerebral cortex 

 its unique position as the master-tissue of the body. 



Spontaneity, initiative, inventiveness, and what 

 we call "dynamic personality" are physiologically 

 very expensive functions. The immediate source of 

 their energies is largely cortical, and the known 

 structure of the cortex indicates that ample reserves 

 are available on demand for reinforcement of any 

 cortical pattern of associational activity whatever. 



