>53 6 



HANDBOOK OF l'HYSlol.OGY 



NEUROPHYSIOLOGY III 



.mil between the anterior thalamus and the cingu- 



late gyrus on the other, would seem to suggest the 

 framework within which this forebrain integrative 

 process in emotional behavior may be best understood. 

 Ii is through the latter of these two systems that the 

 anterior nucleus of the thalamus can interact with the 

 'limbic system' circuits receiving so much contem- 

 porary emphasis in the analysis of emotional be- 

 havior (45, [32, 133, 155, 216, 255-260, 311). 



Th 1 .1 nihil S) item 



The early reference by Broca (59) to "le strand 

 lobe limbique' as a common denominator in all 

 mammalian brains, and Papez' (302) subsequent 

 theoretical speculations on a possible anatomical 

 ■mechanism of emotion,' long ago suggested the 

 potential mediating role of the "limbic system' in 

 affective processes. In general terms, Papez' pro- 

 posal focused upon the more medial aspects of the 

 cerebral hemispheres and emphasized the transmit- 

 tal of the 'central emotive process of cortical origin 

 built up in the hippocampal formation' (hippocam- 

 pus, hippocampal gyrus, dentate gyrus and amyg- 

 dala) via the fornix to the mamillary bodies. Lifer- 

 ents from this hypothalamic center were then pre- 

 sumed to course both downward to the brain stem 

 and lower effector mechanisms, and upward through 

 the mammillothalamic tract to the anterior thalamic 

 nuclei, and onward to the cingulate gyrus, Papez' 

 candidate for the 'cortical receptive and association 

 area' lor affective behavior. It was Papez' view 

 "thai the hypothalamus, the anterior thalamic 

 nuclei, the gyrus cinguli, the hippocampus, and 

 their connections constitute ,1 harmonious mecha- 

 nism which may elaborate the functions of central 

 emotion, as well as participate in emotional ex- 

 pression." Certainly, Papez' delimitation of these 

 Structures as bearing an important relationship to 

 emotional behavior, and his concomitant prediction 

 11I symptomatic changes associated with involve- 

 ment ol this 'anatomic circuit," can in the light of 

 subsequent clinical ,\ih\ experimental developments 

 he seen 111 represent a considerable tour de force. 

 The morphological and functional characteristics 

 ui this 'limbic system' have been more precisely 

 defined and elaborated over the two decades since 

 this original proposal, and several systematic attempts 

 have been made in order the obviously complex 

 inter -relationships between these stun inn and othei 



nervous system components rding to both 



anatomicophysiological and behavioral principles 



14-,, 155, 161, 175, 215, 216, 255, 256, 258, 259, 299, 

 311). 



Despite these recent efforts, however, there is no 

 general agreement as to the definition of morpho- 

 logical formations to be subsumed under the several 

 presumably synonymous terms ('rhinencephalon,' 

 visceral brain,' "paleocortex," etc.) used to refer to 

 these groups or systems of functionally related fore- 

 brain structures associated with emotional behavior. 

 Figure 1 illustrates diagrammatically some of the 

 more prominent anatomical interrelationships which 

 characterize the medial aspects of the hemisphere 

 (45, 295, 3201 and which provide at least some basis 

 for considering the functional properties of these 

 "limbic system' structures within three general groups 

 or classes as follows. 



First, the paleocortical or allocortical portions of 

 the system can be distinguished as those surface 

 structures which meet the criteria for 'cortex' sug- 

 gested by Rose & Woolsey (320) (a composition of 

 at least three layers with the superficial layer con- 

 stituting a fiber layer I and which also have clear 

 phylogenetic primacy. These structures include the 

 hippocampus (Amnion's horn and the dentate gyrus), 

 the pyriform lobe (prepyriform cortex, pcriamygda- 

 loid cortex and entorhinal area) and the olfactory 

 bulb and tubercle. 



Secondly, the juxtallocortical portions of the svs- 

 tem define that group of cortical regions which are 

 intermediate in position between the phylogene- 

 tically old paleocortex and the phylogeneticall) 

 young neocortex, most of which have demonstrable 

 anatomical connections with paleocortical structures. 

 Such juxtallocortical regions include the cingulate 

 gyrus or 'limbic cortex' (bo, 349), the presubiculum 

 and the 'frontotemporal' cortex, as recently defined 

 by Pribram & Kxuger (311). 



Finally, a third group of subcortical structures 

 (not meeting the criteria for 'cortex') which have 

 been show rr to lie iiitiin.itelv related both anatomi- 

 cally and functional!) to the paleocortex and jux- 

 tallocortex must be considered as pan of the 'limbic 

 system,' most broadl) defined. These would include 

 the amygdaloid complex, the septal region (septal 

 nuclei and the nucleus of the diagonal band), cer- 

 tain thalamic and hypothalamic nuclei, and possibly 

 even the caudate nucleus .urd midbrain reticular 



formation, 



Unfortunately, most of these structures were 



liiimeilv believed lo be involved irr mechanisms of 

 olfaction and are even presentlv referred to irr rrrost 

 standard didaclic sources as the 'olfactory lirain' 



