AMYGDALA 



1409 



loid stimulation responses. It therefore appears that 

 the organization of function in the amygdala (and 

 probably in other parts of the rliinencephalon) is of 

 a different order than that typical of certain neo- 

 cortical areas with their mosaic-like representation 

 of specific separate functions (96, 99). Functional 

 representation in the amygdala, and probably in 

 other rhinencephalic structures as well, seems to be of 

 a more global and topographically undifferentiated 

 type. This would not exclude the possibilitv that the 

 cytoarchitectonically defined suljnuclei of the amyg- 

 dala may ha\e their specific tasks in amygdaloid 

 function. It seems however that their contribution is 

 not related to any particular types of amygdaloid 

 responses but rather may contribute in some as yet 

 unknown way to the elaijoration of all functional 

 effects obtained by amygdaloid stimulation. 



Mediation of Amygdaloid Stimulalion Responses 



According to Koikegami and his collaborators 

 (146-152) most vegetative responses, except respira- 

 tory and arterial pressure changes which depend upon 

 the stria terminalis, are mediated via direct ventral 

 amygdalohypothalamic pathways. However, there 

 also is some evidence that respiratory changes may 

 still occur after cutting of the stria terminalis (133) 

 and that arterial pressure responses may even be 

 elicited by direct influence upon the brain stem by- 

 passing the hypothalamus (250). 



Inhibition of spinal reflexes (133), mastication 

 (i 15), sniffing, sneezing and coughing (116), micturi- 

 tion and defecation (114, 136) can also be elicited 

 by stimulation of the stria terminalis or its bed nu- 

 cleus. This suggests that this bundle takes part in 

 mediating these responses, although it does not ex- 

 clude the existence of alternative pathways. 



The extensive projection of the amygdala upon sub- 

 cortical structures as revealed by electrophysiological 

 studies (96) explains how it is possible that such a con- 

 fusingly great number of responses can be elicited by 

 amygdaloid stimulation. Any response produced by 

 stimulation of the amygdala is also known to be elic- 

 itable from stimulation of some other subcortical 

 structure to which the amygdala projects. Figure 8 

 shows these relationships in a diagrammatic way. The 

 work from the schools of Ranson, of Hess and of Ma- 

 goun has demonstrated the highly integrative charac- 



terof these subcortical structures and the topographical 

 organization of function whicii prevails among them. 

 Purposeful patterns of function made up of integrated 

 component functions are elicited from definite areas 

 to the exclusion of others. In the amygdala this type 

 of organization seems to be absent. This is in accord 

 with the fact that the amygdala is ai^le to fire into 

 various subcortical structures regulating different or 

 even antagonistic functions. Thus it ijecomes under- 

 standable that the amygdala can influence one and 

 the same function in opposite ways. Examples of 

 this are numerous, such as facilitation and inhibition 

 of e\oked motor activities, inhibition and activation 

 of respiration, rise and fall in arterial pressure, activa- 

 tion and inhibition of gastrointestinal function, and 

 so forth. 



Dynamic Aspects 



Naquet (190) has drawn attention to some im- 

 portant dynamic aspects of amygdaloid stimulation 

 responses. Stimulation in the unanesthetized animal 

 shows that all the varied effects are not elicited simul- 

 taneously but appear in a patterned time sequence 

 (fig. 10). The immediate effects are quite discrete 

 and often merely consist of a slight change of the 

 respiratory rhythm together with some mild attention 

 response. If stimulation is maintained the delayed 

 responses appear with a latency of 10 to 30 sec. They 

 usually begin with acceleration of respiration, pupil- 

 lary dilatation and sniffing, followed in sequence by 

 some clouding of awareness, contraversion, ipsi- 

 lateral facial clonus, licking, chewing and swallowing 

 with salivation, and finally fearful behavior or micturi- 

 tion or defecation. This sequence of events may vary 

 slightly, but once started it will generally outlast the 

 end of stimulation with a local electrical after-dis- 

 charge conducted to cortical and subcortical areas 

 receiving amygdaloid connections. 



The dynamic aspects of amygdaloid responses are 

 also illustrated by Kaada's observations (133) that 

 facilitation and inhibition of spinal reflexes and 

 cortically induced movements exhibit 'recruitment' 

 and may outlast the end of stimulation as does the 

 local electrical after-discharge. 



It thus appears that the recruiting phenomena 

 shown by electrographic studies (97) have their 

 counterpart in the mode of development of amygda- 



A., anterior part of the amygdala; .4.4., anterior amygdaloid area; BJV., basal nucleus; CMN., corticomedial nuclei; CJV., 

 central nucleus; EC, external capsule where it borders the lateral nucleus; I. A.M., inferoanteromedial part of the amygdala; 

 I.L., inferolateral part of the amygdala; I.M., inferomedial part of the amygdala; L.. lateral part of the amygdala; Z,A'., 

 lateral nucleus; M., medial part of the amygdala; M.A., medioanterior part of the amydgala; .W.V., medial nucleus; PC, 

 periamygdaloid cortex;^'., superior part of the amygdala; .S.A/., superomedial part of the amygdala. 



