STRUCTURE AND FUNCTIONS OF THE CEREBRUM 153 



face. The paths of communication between the cells where are 

 stored the primary sense impressions and those where the resulting 

 concepts are formed seem to remain always very easy of passage. 

 The sound of the mother's voice calls up the entire concept of the 

 mother with great clearness, even though years may have elapsed 

 since it was heard. 



Since concepts are stored as memories they may serve in their 

 turn as bases for more complex associations; these again by be- 

 coming memories may contribute to the associative process, and 

 so the complex structure of the mind is built up, resting at bot- 

 tom always upon primary sense impressions. 



The act of association is essentially one*of combining related 

 memories; the formed associations become memories in their turn. 

 For these reasons the term associative memory is used as more 

 truly describing the nature of associative processes than the older 

 expression " the association of ideas." 



The use of a memory in forming one association does not inter- 

 fere with its use in the formation of others. This ability of the 

 cerebrum to use memories over and over again is a very valuable 

 property since it enables us to make the utmost of all our knowl- 

 edge. 



Development of the Cortex. The increase in intellectual 

 power which accompanies the growth of the child is not the re- 

 sult of any increase in the number of nerve-cells, for the child 

 is born with his full number. It is, however, based upon their 

 continuous development; this development consisting chiefly of 

 greater and greater branching with correspondingly richer synaptic 

 connections. At birth scarcely any cortical cells are sufficiently 

 developed to be functional. The sensory areas first become so. 

 The association areas reach their highest point of development at 

 about the thirty-fifth year. At this age the anatomical progress of 

 the brain comes to an end ; all possible paths of association have 

 been laid down. This does not mean, however, that all possible 

 associations have been formed. These continue to be formed so 

 long as the brain continues active. It is probably true, however, 

 that with advancing years there is a diminution in the freedom 

 of associative activity; the brain no longer accomplishes daring 

 feats of thought, such as constitute creative genius, but plods 

 along in the ruts established by its earlier activities. This fact 



