82 THE BRAIN OF THE TIGER SALAMANDER 



PRINCIPLES OF LOCALIZATION OF FUNCTION 



The gi-eat advances that have been made in the diagnosis and 

 treatment of nervous diseases have been due in large measure to the 

 more accurate mapping of the structural features of the nervous sys- 

 tem and recognition of the specific functions of its several parts. 

 Before a disorder can be successfully treated we must know what it 

 is and where it is. The most notable triumphs in this medical field 

 have been registered with those diseases whose situs can be recog- 

 nized and then subjected to appropriate therapy or surgery. Even a 

 systemic disorder like anemia has localization in blood corpuscles 

 and blood-forming organs; and a general infection, like poliomyelitis, 

 spreads in preferential paths determined by the histochemical struc- 

 ture of the tissue. The stable heritable tissues of the nervous system 

 are most accessible to this kind of inquiry, of diagnosis, and of treat- 

 ment; conquest of the unlocalized disorders has been retarded. 



Some kinds of disorder, particularly those of primary concern to 

 psychiatrists, have resisted all attempts at localization in accordance 

 with conventional principles, and in the field of physiology the con- 

 cept of local reflex arcs has limited application. The various attempts 

 to elaborate a comprehensive account of animal and human behavior 

 in terms of conventional reflexology have broken down. These con- 

 spicuous failures have led some competent authorities to question 

 the over-all significance of localization in space of nervous functions 

 and to search for other principles in the realm of pure dynamics or 

 chemical interaction or some as yet unknown factors which operate 

 quite independently of stable structural patterns. But no nervous 

 tissue is structurally homogeneous or physiologically equipotential. 

 In this connection it is interesting to note that Lashley, the leading 

 advocate of the equipotentiality of the nervous tissues, has given us 

 clear demonstration of point-to-point projection of retinal loci upon 

 the lateral geniculate body and the cerebral cortex of the rat (Lashley, 

 '34, '34a). This is the most refined anatomical localization of func- 

 tion known. In a later communication ('41) he demonstrated a very 

 precise projection of the thalamic nuclei upon the cerebral cortex and 

 added: "A functional interpretation of the spatial arrangement of 

 the thalamo-cortical connections is not justified on anatomic grounds 

 alone for any sensory system." 



Somewhere between the extreme views of rigid localization in spa- 

 tial patterns and a labile physiological equipotentiality a practicable 

 working conception of the meaning of the structural configuration 



