52 BRAINS OF RATS AND MEN 



characteristic of the most primitive nervous centers. 

 They contain an ample amount of what Child would 

 call "physiologically young tissue,'* that is, tissue 

 which has not matured in rigid molds but is still 

 plastic and readily modifiable (Herrick, 1924, p. 252). 



This does not mean, as Lashley seems to imply, 

 that in these higher correlation centers the tissue is 

 equipotential and that conduction is diffused uni- 

 formly throughout a physiologically homogeneous 

 network of fibers. The anatomical structure of these 

 centers is well known. The neurons involved are in 

 synaptic relation with one another, and the direction 

 of conduction at any moment is probably influenced 

 by the physiological state of the synaptic junctions 

 at that moment. 



These centers possess the apparatus for wide dis- 

 persal of all incoming nervous impulses and for the 

 interaction of one system of such impulses upon 

 another. During the formation of a new habit, 

 definite preformed nervous pathways leading into 

 and out of the correlation center are activated, and 

 within the center new patterns of interaction of these 

 systems may be formed and perpetuated just because 

 the preformed pathways here converge into a tissue 

 lacking such inborn patterns of interneuronic con- 

 nection. After completion of the formation of the 

 habit, definite pathways of nervous discharge through 

 the correlation center have doubtless been estab- 

 lished, and the plasticity of the behavior pattern is 



