CHAPTER XGVIII 



THE HIGHER FUNCTIONS OF THE CEREBRUM IN MAN; 



APHASIA 



The study of the higher functions of the cerebrum leads us to the border- 

 land between physiology and psychology, but into this vast and relatively 

 unexplored field we can not venture here, unless just far enough to gain a 

 suitable vantage point from which to understand the pathology of the 

 condition known as aphasia* As we have seen from our studies on cerebral 

 localization, the cerebrum must be regarded as a great sensorimotor gan- 

 glion, whose functional activities are indicated by various movements. 

 These movements may, in general, be classified as objective indications 

 either of feeling and emotion or of intelligence. Although both classes are 

 evident in all animals, it is particularly in the case of man that the evi- 

 dences of intelligent activity are especially prominent, since they include 

 gesticulation and the muscular activities required in spoken and written 

 language. The movements that express emotional conditions are evolved 

 earlier and from lower planes than those of intellectual activity. Thus, 

 very young infants "make faces" when there is reason to believe they 

 feel pain, and, as they develop, their power of expressing emotion is 

 evolved long before they present evidence of intelligent motor activity, 

 and still longer before they can articulate words. 



The phenomenon of human psychic activity which is of greatest im- 

 portance is that of language, and to understand the nature of the cerebral 

 integration required to produce it, we must briefly consider the cerebral 

 processes involved in the intellectual development of the infant. The 

 first step in this development is the storing away in projection centers of 

 memories of the sensations which these centers have received. For ex- 

 ample, when the child looks at a bell, there is stored in the visual center a 

 memory of the shape of the bell, and when the bell moves so as to produce 

 sound, this also is stored as a sound impression in the auditory center. 

 Likewise, when he touches the bell impressions of its hardness and smooth- 

 ness and temperature are stored in the centers for cutaneous sensations. 

 At first each of these memory impressions occupies an isolated position ; 

 but Later, association tracts open up between them, so that the calling 



*Free use of Bolton's article is made in this chapter. 



860 



