152 THE HUMAN BODY 



Association Areas. The different sensory areas and the motor 

 areas occupy only a small part of the whole cerebral cortex. 

 Most of the frontal lobes and large areas of the parietal and tem- 

 poral lobes are not involved in the immediate reception of im- 

 pulses, nor in their transmission to the Body. These areas are 

 as richly supplied with interconnecting neurons as any part of the 

 cortex. They are assumed, without very positive proof, to be 

 the seat of a function we know the cerebrum to possess, that of 

 association. 



The Nature and Mechanism of Association. At birth the 

 brain of the infant may be compared to a clean page. It bears no 

 impressions of any sort. Such activities as the infant shows are 

 purely reflex. In course of time sense impressions begin to come 

 into the sensory areas of the cortex. These register themselves 

 more or less definitely as memories, and presently the child is in 

 possession of a considerable store of memories of various sorts. 

 He may know the sound of his mother's voice or may recognize 

 her face. As yet, however, there is no connection between these 

 independent impressions. When in the child's mind that voice is 

 associated with that face, so that he knows them as parts of a 

 single whole, he has performed an act of association. From this 

 time throughout his life his memory is not alone of the simple 

 sound of the voice or the appearance of the face but of the mother 

 whom he has learned to know by these associated impressions. 



Acts of association are supposed to be carried on within the 

 association areas of the cortex. We may picture the process in 

 the example cited above somewhat as follows: The impression of 

 the voice is stored in the auditory area; that of the appearance 

 of the face is in the visual area; both these sensory areas have 

 rich communications with neurons of the association areas. By 

 some means impulses from the sensory cells where these impres- 

 sions are stored meet in a cell of an association area. That cell 

 builds from these single related sense impressions, a composite, 

 which is stored in turn as a memory. As additional related in- 

 formation is gained the composite, or concept, is enlarged. 



The union of related impressions into concepts does not nec- 

 essarily involve loss or impairment of the fundamental impres- 

 sions themselves; the child in whose mind is a definite concept 

 of his mother retains also clear memories of her voice and her 



