THE MAIN AFFERENT FIBER SYSTEMS OF 

 THE CEREBRAL CORTEX IN PRIMATES 



STEPHEN POLIAK, M.D. 



Chapter I 



INTRODUCTION 



Without minimizing our knowledge of the organization and func- 

 tion of the cerebral cortex, the need of a thorough, systematic study 

 of the connections of the various cytoarchitectural areas and regions 

 is clear. The cytoarchitectural and myeloarchitectural delimitation 

 of cortical areas and the physiological and pathological investiga- 

 tion of special, circumscribed portions of the cortex, important and 

 indispensable though they be, do not give a fully satisfactory answer 

 concerning the functions of these areas and regions. For that 

 answer the areal and regional connections must be known. To under- 

 stand the distinctive function of the cortex the same fundamental 

 problem encountered in other parts of the nervous system must 

 be solved, namely, that of connections or interrelationships. While 

 other branches of the investigation of the brain — physiology, psy- 

 chology, and pathologj^ — deal preponderantly or even exclusively with 

 the elusive dynamic changes of the nervous substance and their 

 frequently ambiguous manifestations, anatomy has to disclose special 

 structures, neuronic complexes, fiber systems, and agglomerations of 

 nerve cells which serve as the material substratum of these activities. 

 Study of the fiber connections of the forebrain cortex will demon- 

 strate the paths of spread of ner^^ous impulses from the peripheral 

 receptor organs to the cortex, the paths in the cortex itself, and back 

 again from the cortex to the subcortical mechanisms and to various 

 executive organs of the body; thus it \^dll necessarily influence our 

 conception of the organization and function of the brain. 



Our current conception of the structure and function of the cortex 

 is somewhat as follows: The cerebral cortex is a composite organ 

 consisting of numberless nerve cells and fibers arranged for the most 

 part in regular, parallel layers. Though almost everywhere essen- 

 tially the same, these cell layers, as well as those of the intracortical 

 fibers, exhibit, according to locality, considerable variation in the 



