13^4 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



This is the body-mind relation; its difficulty lies in its 

 'how'. . . . 



. . . Instead of, as is usual in physiology, leaving that im- 

 passe unmentioned, it seemed better to draw attention to it by 

 the experimental observations in this book's linal chapter. 



Sherrington, C. S. The Integrative Action of the 

 jVervous System. Foreword to 1947 Edition (i^g^- 



INTRODUCTION 



FOR THE p.-IlST CENTURY and a half, the "niind-body' 

 problem has been focused on tlie relationship between 

 the functions of the cerebral mantle and mental 

 processes. The question is often raised as to whether 

 mental processes — especially "complex" mental 

 processes such as ideas, attitudes and thoughts — are 

 radically (incommensurably) different from the 

 physiological and the physical. With regard to ele- 

 mentary sensory and motor events (such as depressing 

 a key when a light is flashed), the scientist proceeds 

 upon the basis that psychological concepts (here 

 the visual field) are inferred from observations and 

 measurements of organism-environment interactions, 

 interactions that can be specified by the use of physio- 

 logical, physical and behavioral methods. Experi- 

 mental evidence is presented here that more complex 

 mental processes — such as thought, attitude, value — 

 can also be studied in this manner: that environ- 

 mental, organismic and behavioral referents for these 

 processes can be specified — that, therefore, the differ- 

 ence between the psychological processes designated 

 as complex and those designated as elementary is not 

 a radical one. 



Coinplex mental processes are most readily inferred 

 from observations of problem-solving behavior. Those 

 portions of the cerebral mantle devoid of any major 

 direct connections with peripheral structures have 

 been consistently linked with problein-solving proc- 

 esses and have, therefore, been of especial interest to 

 students of the mind-body relationship. The designa- 

 tion 'association cortex' has obscured a considerable 

 ignorance concerning the functions of these parts of 

 the brain. The designation was framed within the 

 empiricist tradition as this had evolved up to the 

 latter part of the past century, and presupposes 

 anatomical and physiological evidence for the notion 

 of a transcortical reflex. Data are presented here upon 

 which an alternative conception is proposed. 



Definition of Intrinsic Systems of the Forehrain 



The conception of an 'association cortex' stems from 

 the fact that certain parts of the forehrain have 



obvious major direct connections with peripheral 

 structures while others do not. This difference has 

 been used by Rose & Woolsey (124) in a rigorous 

 classification of the sui:>di\isions of the dorsal thalamus 

 — the foreijrain structiu-e which, as a whole, serves as 

 the final discontinuit\ intercalated between periph- 

 erally initiated neural e\ents and those of the end- 

 brain. These investigators suggest the term 'intrinsic' 

 for those portions of the dorsal thalamus in which no 

 major extrathalamic, extratelencephalic afferents 

 terminate. The intrinsic portions of the thalamus 

 project to those sectors of the cerebral mantle usually 

 referred to as 'association cortex.' As already noted, 

 the term 'association cortex' has its disad\antages: 

 "association" makes the unsupported assumption that 

 in these areas, convergent tracts bring together 

 "sensory' events transmitted from the "receiving areas' 

 of the brain. Throughout this presentation, therefore, 

 the currently less loaded term "intrinsic sectors' will be 

 substituted for "association cortex'; "intrinsic systems' 

 will be used when reference is made to the thalamic 

 projection as well as to the related cortical area. 



The key to an analysis of the ftmctions of the 

 intrinsic systems of the foreijrain is obtained from a 

 study of the organization of the mammalian thalamus. 

 On the basis that some of the nuclear groups within 

 the thalamus bear a fairly consistent relation to one 

 another, an external portion and an internal core of 

 the thalamus can ije distinguished (59). The external 

 portion is composed of the ventral, the posterior 

 (lateral and pulvinar) and the geniculate nuclei 

 (fig. i). In carnivores and primates this external 

 portion is, for a considerable extent, demarcated from 

 the internal core of the dorsal thalamus by an ag- 

 gregation of fibers, the internal medullar\' lamina and 

 its rostral exten.sions surrounding the anterior nuclear 

 group. The internal core of the dorsal thalamus may 

 also be subdi\ided into three large groups; the an- 

 terior, the medial and the central (mid-line and intra- 

 laminar) nuclei. 



Each of the major subdivisions (external and in- 

 ternal) may be further characterized according to the 

 type of its nontelencephalic major afferents (fig. 2). 

 Thus, the ventral and geniculate nuclei of the external 

 division are the terminations of the lars;e topologically 

 discrete 'specific' afferent tracts (e.g. spinothalamic, 

 trigeminal, lemniscal and the brachium conjunctivinii, 

 as well as the otic and optic radiations) of the somatic, 

 gustatory, auditory and visual systems (144). Within 

 the internal core, the anterior nuclei receive an input 

 from the posterior hypothalamus through the mam- 

 millothalainic tract; the central nuclei receive non- 

 specific diffuse afferents by way of the reticular forma- 



