THE ASSOCIATION CENTERS 243 



ment. The dissociation of cortical functions in time 

 as well as in space (pp. 80, 259) has been perfected. 



These are the observed facts. A theoretic explana- 

 tion which is consonant with what we know of cor- 

 tical organization might take this form. The estab- 

 lishment of an association or conditioned response in 

 the cortex activates certain associational neurons in a 

 particular pattern. If the reaction is consummated, 

 this pattern is left in a slightly more favorable form 

 for reactivation when the stimuli are repeated (the 

 familiar physiological principle of facilitation of path 

 by use — the organic basis of habit). This is a property 

 of all nervous circuits. But the associational centers 

 are so organized that a similar structural change, or 

 cortical set, may be preserved even in those cases 

 where a cortical association does not eventuate in 

 overt action. The essential feature of the functional 

 pattern will reappear when the neurologic pattern is 

 reactivated in any way, by stimuli either outside or 

 inside the body. 



This is the organic basis (engram) of a cortical 

 memory. What is preserved is not an image in the 

 psychological sense; it is simply a change in the 

 structural organization, static not dynamic (Cole, 

 1925). Its psychological significance is not neces- 

 sarily different from that of the muscular set of a rat 

 or raccoon in Hunter's delayed reaction experiment. 

 And yet this ability to inhibit the overt expression of a 

 reaction and still preserve centrally a permanent rec- 



