CEREBRAL LOCALIZATION 701 



may be relearned in about the same period of time. Long-standing 

 habits, on the other hand, seemed to be retained, in spite of the injury 

 to this lobe. 



As far as the higher functions of the association regions are con- 

 cerned, much work must still be done to obtain more definite data. 

 For the present, we can go no further than to state that the cortex of 

 the cerebrum is the seat of special sensory and motor projection areas 

 which may be mapped out with varying definiteness. We are also 

 fairly well acquainted with the sensory and motor paths leading to and 

 away from these regions. Around and in between these primary 

 cortical fields certain association areas are situated which are inti- 

 mately connected with the centers to wMch they belong, and in turn 

 also with one another. Their destruction affects first of all the par- 

 ticular sensory or motor function to which they are assigned, and 

 secondly, the functional equiHbrium of the cerebrum as a whole. 

 This constitutes the so-called diaschisis effect of Monakow,^ consisting 

 in a disturbance of the dynamics of the cerebral processes as a whole 

 which, however, is rather transitory in its nature. 



It is conceived that the higher mental concepts are not the product 

 of special areas of the cortex, but are the result of discharges of nervous 

 energy from one center to another as well as to more remote regions 

 of the body. This interaction of nervous energy gives rise to a com- 

 plex product, the analysis of which is at present impossible. This 

 constitutes the so-called dynamic theory of cortical function, in accor- 

 dance with which the different sensory and motor centers of the cere- 

 brum are to be regarded merely as fixed points of action of a complex 

 system of neurons and not as independent generators of mental 

 actions. The result of this reverberation of discharges through the 

 nervous system depends in each case upon the number and kind of 

 neurons involved. Thus, the higher cortical function results in con- 

 sequence of the correlation of its different products, and cannot be 

 ascribed exclusively to one or the other of its constituent areas. 



THE CORPUS CALLOSUM 



The cerebral hemispheres are connected with one another by three 

 tracts of commissural fibers, namely, the anterior commissure, the for- 

 nix, and the corpus callosum. The most conspicuous of these is the 

 corpus callosum which forms the floor of the great longitudinal fissure 

 and may be brought into view by separating the hemispheres. The 

 fibers composing this structure, do not enter the main paths of the 

 internal capsule, but extend directly across from cortex to cortex. 

 According to Ferrier,^ Brown-Sequard,^ Koranyi,^ and others, its divi- 

 sion at the point where it crosses the longitudinal fissure, is not followed 



1 Die Lokalisation des Grosshirns, Wiesbaden, 1914. 



2 Proc. Royal Soc, London, 1875. 



3 Compt. rend. Soc. biol., 1887. 

 ^Pfliiger's Archiv, xlvii, 1896, 35. 



