2,6 BRAINS OF RATS AND MEN 



moved progressively forward from midbrain (most 

 fishes), thalamus, and corpus striatum (reptiles and 

 birds), to the cerebral cortex (mammals). This theme 

 has been elaborated by others (e.g., von Monakow, 

 1910). 



The significance of this history for our present 

 purpose lies in the fact that in these progressively 

 elaborated centers of exteroceptive adjustment we 

 see reflected in structure the corresponding enlarge- 

 ment of the behavior patterns. In forms below the 

 mammals these behavior patterns are chiefly of 

 reflex and instinctive types — stable, held in common 

 by all members of a race or species, and modifiable 

 slowly and with difficulty. These animals learn, but 

 for the most part by trial-and-error and only after 

 many repetitions. 



In the mammals, especially the higher species, 

 the picture is radically changed. The cerebral cortex 

 structurally overshadows the rest of the brain and 

 physiologically it dominates behavior. The learning 

 pattern changes from slow fabrication of conditioned 

 reflexes by the method of trial-and-error or by mere 

 repetition of simultaneous excitations to direct attack 

 upon the problem and intentional control of the 

 "trials." The appropriate response may be attained 

 at the first overt trial because the tentative move- 

 ments of inappropriate trials are centrally evaluated 

 (physiologically or psychologically) and inhibited. 

 The explicit or overt behavior is simplified because 



