212 BRAINS OF RATS AND MEN 



systems. Upon extensive injury to any part of the 

 cortex these associational patterns are more or less im- 

 paired, their normal equilibrium is disordered — a dia- 

 schisis effect (von Monakow). The cortex no longer 

 excites the lower reflex patterns, diverting them now 

 in this direction now in that as the play of intracorti- 

 cal associations shifts in response to momentarily 

 changing external and internal conditions. The older 

 and more stable elements of the action system are, ac- 

 cordingly, reHeved of this sort of distraction, and the 

 subcortical apparatus of simple trial-and-error learn- 

 ing already sketched is free to work out a new stable 

 behavior pattern more directly and rapidly than in 

 the case where normal cortical associations are con- 

 tinually intervening. 



It may be conjectured further than in normal rats 

 the cortical facilitation of the visual conditioned re- 

 flex is brought about by a differential inhibition of the 

 irrelevant random exploratory wanderings and gener- 

 al friskiness by a process of "drainage" or cortical 

 "induction" (p. 59) which tends to concentrate the 

 entire available cortical energy upon the visual cortex 

 when this is activated from the receptive field, that 

 is, by the unequally illuminated maze. In ourselves 

 we would say in a similar situation that cortical ac- 

 tivity converges upon the matter in the focus of atten- 

 tion. In the rat this cortical effect is doubtless tran- 

 sient and evanescent but so effective when operative 

 that the removal of the visual cortex disrupts the habit. 



