CEREBRAL LOCALIZATION 699 



THE FRONTAL ASSOCIATION AREA 



The preceding localization of the different motor and sensory areas 

 has undoubtedly led us to believe that the cerebral cortex embraces 

 a number of island-like fields which are concerned with particular 

 functions. While this conception is correct, it should not be forgotten 

 that still larger areas are situated in between those already explored, 

 which have not as yet been shown to possess a specific functional 

 value. Guided very largely by the fact that the aphasics may lose 

 their power of word-formation without suffering a decided impair- 

 ment of their intelligence, the clinicians have assumed that thought 

 is quite independent of auditory, visual and other impressions and 

 memories. In accordance with this assumption, it was then believed 

 that the psycho-optic, the psycho-acoustic, and other psychic areas are 

 apportioned severally to the different sense organs, and are amplified by 

 definite areas in which solely the more general psychic activities are 

 situated. 



This at first purely hypothetical center of thought received a firmer 

 morphological basis by the investigations of Flechsig 1 pertaining to the 

 time of myelinization of the fibers of the embryonal brain. It is 

 conceivable that those association areas of the cortex attain their 

 function first which are first placed in possession of myelinated fibers, 

 and thus antecede the others in gaining connection with the outgoing 

 paths of the white matter. By this method Flechsig succeeded in 

 outlining thirty-six different cortical fields which 'he further divided 

 into primary, intermediary and terminal. The first attain their myelin- 

 ated fibers at birth and constitute the primary sense centers, namely, 

 those of smell, cutaneous and muscle sense, sight, hearing and touch. 

 These areas are characterized by large numbers of radial, transverse 

 and projection fibers which eventually make connection with the more 

 distant projection centers apportioned to the different sensations 

 and motor actions. The intermediary fields contain fibers which 

 attain their medullary sheath during the first month of extra-uterine 

 life. The terminal regions possess few transverse fibers, but numerous 

 association paths which unite them with the different projection cen- 

 ters. They form the association areas which amplify the individual 

 primary sensory centers and thus form the memory realms for vision, 

 audition, olfaction, etc. In addition, they form those independent 

 association realms which give rise to the higher psychic concepts. 

 For this reason, they may be regarded as the organs of perception 

 and thought. In this connection it should be stated, however, that 

 many physiologists do not admit that the highest psychical activities 

 are mediated by special and individualized association centers (Munk), 

 but are produced in the association realms belonging to the different 

 primary sensory regions. 



1 Die Legalisation der geist. Vorgange, Leipzig, 1896; also: Sachs. Gesellsch. 

 der Wissensch., Leipzig, 1904. 



