291 



mentally demonstrated, in themselves and aside from any philo- 

 sophic theories based upon them, contribute no evidence what- 

 ever to a solution of the problem of a seat of consciousness or of 

 particular mental "faculties." That the proper functioning of 

 a given locus in the cortex is essential to the execution of a 

 given motion or the experience of a given sensation by no means 

 necessarily implies that the consciousness of the act is located 

 there. The latter is an entirely independent problem which 

 must be separately investigated. It is not, then, the facts of 

 cerebral localization which can be called in question so much as 

 the interpretation of these facts. 



The search for a single seat of consciousness, such as psychol- 

 ogists and philosophers have so long sought, is vain. The higher 

 mental processes undoubtedly require the activity of associa- 

 tion centers of the cerebral cortex, and the integrity of the 

 associational mechanism as a whole is essential for their full 

 efficiency. The cerebral cortex differs from the reflex centers of 

 the brain stem chiefly in that all of its parts are interconnected 

 by inconceivably complex systems of associational connections, 

 many of which are probably acquired late in life under the influ- 

 ence of individual experience, and any combination of which 

 may, under appropriate conditions of external excitation and 

 internal physiological state, become involved in any cerebral 

 process whatever. 



Nevertheless, some of these cortical association paths are 

 structurally more highly elaborated than others (Fig. 121, p. 

 267, illustrates the most distinct of these tracts), and certain 

 combinations of cortical functions are, therefore, more likely to 

 follow a given stimulus than others. This associational pattern 

 is doubtless partly innate and partly acquired. That there is a 

 fairly precise anatomical pattern of association tracts can be seen 

 in any good dissection of the cerebral hemisphere, and that the 

 elements of this pattern are related in definite functional systems 

 which are spatially separate is shown by numberless clinical ob- 

 servations in which sharply circumscribed mental defects are 

 found to be associated with definite cerebral lesions. The 

 phenomena of aphasia give the clearest illustrations of these 

 relations. 



The term aphasia has commonly been applied to a variety of 



