242 BRAINS OF RATS AND MEN 



tion of an orienting attitude of the body during the 

 delay. The raccoons retained the memory of the stim- 

 ulus for twenty-five seconds (possibly by unobserved 

 motor cues), and the six-year-old children could re- 

 act perfectly after more than twenty-five minutes. 



These observations might well be extended with 

 critical study of the motor cues and other observable 

 phenomena during the delay. If rats can execute the 

 delayed reactions only with the aid of overt motor 

 cues or an enduring "set" of the body musculature 

 c*nd children can react perfectly after a delay of 

 twenty-five minutes, it is suggested that there is 

 probably some internal apparatus which preserves the 

 cue — an apparatus not available to the rats and the 

 youngest children. 



The association centers of the cerebral cortex pro- 

 vide such a mechanism, and the known structure of 

 the cortex supports this interpretation. The estab- 

 lishment of an association or conditioned reflex of the 

 type used by Hunter is possible in the absence of the 

 cortex, as has already been pointed out; but to hold 

 the association, as it were, in suspense, without re- 

 leasing it into motor channels is apparently beyond 

 the capacity of the rat even with the aid of his cortex. 

 The cortical activities cannot be far dissociated in 

 time from the subcortical. The more complex and 

 more impressionable human cortex makes such asso- 

 ciations more quickly, and it cg.n retain them without 

 the necessity of consummating them as overt move- 



