1 68 BRAINS OF RATS AND MEN 



ly. He says, "The mere demonstration that animals 

 with a complex cerebrum are capable of learning com- 

 plex problems more rapidly than those at a lower 

 evolutionary level will not answer the question." 

 True; but if it is evident that the complexity of this 

 tissue is commensurate with the complexity and 

 rapidity of the learning processes and that this com- 

 plex issue is essential for such processes, then we do 

 have an answer. He says further: "The preexisting 

 habits of the organism, the number and variety of 

 instinctive responses available, the complexity of or- 

 ganization of existing reacting systems, perhaps the 

 mere number of unemployed association fibers in the 

 nervous system, all may influence the rate of learning, 

 even though the underlying mechanism is the same." 

 But by the very terms of this statement the underly- 

 ing mechanism is not the same, and in so far as this 

 greater complexity of organization is cortical and is 

 essential for higher learning processes we may say 

 that this cortex is "particularly well adapted for 

 learning." And the evidence that in higher mammals 

 the cerebral cortex does perform a necessary function 

 in complex learning is unimpeachable. Even in rats 

 Lashley's experiments show that a definite cortical 

 field does in some way participate in the simplest 

 possible brightness-discrimination habit, and his ex- 

 periments certainly do not preclude an essential cor- 

 tical role in various sorts of more complex habits; in 

 fact, they strongly suggest such a participation. His 



