298 INTRODUCTION TO NEUROLOGY 



cerned with the individually acquired and especially the intelli- 

 gently performed activities as distinguished from the fundamen- 

 tal reflex and instinctive processes whose mechanisms are innate. 

 There is a specific localization of function in the cerebral cortex, 

 in the sense that particular systems of sensory projection fibers 

 terminate in special regions (the sensory projection centers), 

 that from other special regions (the motor projection centers) 

 particular systems of efferent fibers arise for connection with the 

 lower motor centers related to groups of muscles concerned with 

 the bodily movements, and that between these projection centers 

 there are association centers, each of which has fibrous connec- 

 tions of a more or less definite pattern with all other parts of the 

 cortex. The destruction of any part of the cortex or of the 

 fiber tracts connected therewith involves, first, a permanent loss 

 of the particular functions served by the neurons affected, and, 

 in the second place, a transitory disturbance of the cortical 

 equilibrium as a whole (diaschisis effect). Specific mental acts 

 or faculties are not resident in particular cortical areas, but all 

 conscious processes probably require the discharge of nervous 

 energy throughout extensive regions of the cortex, and the char- 

 acter of the consciousness will depend in each case upon the 

 dynamic pattern of this discharge and the sequence of function of 

 its component systems. This pattern is inconceivably complex 

 and only the grosser features are at present open to observation 

 by experiment and pathological studies. 



No cortical area can properly be described as the exclusive 

 center of a particular function. Such "centers" are merely 

 nodal points in an exceedingly complex system of neurons which 

 must act as a whole in order to perform any function whatsoever. 

 Their relation to cerebral functions is analogous to that of the 

 railway stations of a big city to traffic, each drawing from the 

 whole city its appropriate share of passengers and freight; and 

 their great clinical value grows out of just this segregation of 

 fibers of like functional systems in a narrow space, and not to any 

 mysterious power of generating psychic or any other special 

 forces of their own. 



The essence of cortical function is correlation, and a cortical 

 center for the performance of a particular function is a physio- 

 logical absurdity, save in the restricted sense described above, as 



