262 BRAINS OF RATS AND MEN 



non-specific tonic reinforcement is largely striatal and 

 the specific phasic activation involved in intentional 

 control of behavior is almost exclusively cortical. 

 Cortical reinforcement or facilitation as seen in man 

 is of very different type from that of the corpus 

 striatum, and it employs a quite different mechanism. 



So important is the combined dynamogenic effect 

 of cortical and striatal reinforcement of lower activi- 

 ties that in all mammals complete destruction of both 

 of these parts of the cerebral hemispheres leaves the 

 animal in a state of profound depression and stupor, 

 with perhaps decerebrate restlessness due to loss of 

 the inhibitions to be mentioned immediately. 



9. The cerebral cortex from its inception exerts 

 more or less inhibitory influence upon subcortical 

 functions. In the simpler learning processes of rats 

 there seems to be a differential activation of some key 

 factor of a subcortical learning process (as of the 

 visual component in a brightness-discrimination re- 

 action) which in effect draws off all available cortical 

 energy, leaving other and irrelevant sensori-motor 

 processes relatively enfeebled so that they are sub- 

 ordinated. The effect is the same as if a specific in- 

 hibitory action were exerted by the cortex upon the 

 inappropriate movements. This theoretic interpreta- 

 tion has no direct experimental support, though it 

 seems constant with the known facts. It may be sug- 

 gested, further, that all inhibition is in reality a dif- 

 ferential activation, the mechanism being in some 



