THE ASSOCIATION CENTERS 



251 



development of such a lower mammal as is pictured 

 on page 153 (Fig. 2S)y ^^e projection centers with 

 their contiguous primitive associational fields are ar- 

 ranged as in Figure 51. In the associational zones 

 there is sensual fusion, not only of present complexes 

 of stimuli, but also of vestiges of previous similar ac- 

 tivities which have been fabricated through facilita- 

 tion of path and the retention of these acquired struc- 

 tural alterations — cortical memories, conscious or un- 

 conscious. 



On the plane of "perceptual-motor learning" 

 (Carr) the relations of the primary projection centers 

 and of the primitive associational field may be con- 

 ceived as diagramed in the figure. The sensory or 

 primitive associational fields, yf' , B\ C, are directly 

 connected by association fibers so that the excitation 

 of one may be communicated to all of the others, and 

 all of them are directly connected with the motor 

 field, M. There are also motor pathways (not indi- 

 cated) passing down from each of the primitive 

 associational fields directly to lower subcortical cen- 

 ters. Simultaneous excitation of associational fields 

 B'y C, may result in the establishment of a B'-C 

 complex with a stable modification of structure by 

 facilitation of path so that later reactivation of B' 

 alone will be followed by activation of C also. We 

 now have an associational memory. Any two or more 

 of the primitive association centers may be thus re- 

 lated. In such a system, repeated experiences with 



