AMYGDALA 



1 4' 5 



The study of propagation of amygdaloid seizure 

 activity in animals by the use of the after-discharge 

 method shows a widespread subcortical conduction of 

 such seizures. Thus the basal ganglia, the septal 

 nuclei, the hypothalamus, the subthalamus, the 

 thalamus and the mesencephalon are invaded by the 

 seizure discharge (20, 44, 100, 175). Quite in contrast 

 to this is the limited cortical propagation which is 

 usually restricted to the anterior temporal, insular and 

 uncohippocampal cortex (20, 44, 80, 100, 175). Wide- 

 spread subcortical conduction may even occur with- 

 out any neocortical involvement at all {20, 100, 175). 

 Thus it may be explained why the performance of 

 elaborate automatic activities is still possible during 

 ictal automatism since the neocortex is not, or only 

 slightly, invaded by the seizure discharge, while 

 memory recording and consciousness are interfered 

 with due to conduction of seizure discharge into 

 central integrating structures of the higher brain stem 

 and diencephalon (20, 100, 175, 197). The contrast 

 between the extent of subcortical and cortical in\olve- 

 ment may be related to the fact that recruitment is a 

 common feature of subcortical and rhinencephalic 

 responses to repetitive amygdaloid stimulation, 

 whereas no such recruitment is seen in the neocortex 

 (97) (see p. 1402). However repetiti\e amygdaloid 

 stimulation usually does not lead to any appreciable 

 thalamic invoh'ement. It is a reasonable assumption 

 that this may occur under the influence of maximal 

 or nearly maximal repetitive amygdaloid firing as in 

 a seizure discharge. 



The preferential pathways of propagation of amyg- 

 daloid seizure discharges are to subcortical structures 

 (fig. II), mainly to the hypothalamus, subthalamus 

 and mesencephalic tegmentum. Increasingly labile 

 is the propagation to the thalamus, temporal cortex 

 and the contralateral temporal lobe including the 

 contralateral amygdala (20, 100). Different results 

 however are reported by Creutzfeldt (44) who found 

 preferential spread to the homolateral anterior and 

 basal cortex, and by Faeth et al. (57) who describe a 

 preferential route of propagation to the opposite 

 amygdala and hippocampus and to the ipsilateral 

 temporal cortex. Faeth et al. however stimulated the 

 'amygdala-hippocampal complex' and this may well 

 explain their different results. 



Hallucinations 



Freeman & Williams (67, 68, 253) advanced the 

 theory that the amygdala plays an important role in 

 the emission and regulation of 'sonar' in chiroptera 



Tempore - 

 Insular 

 Cortex, 

 (controlat ) 



AmygdoTa 



(contralat } 

 Thalamus 



Hypothalamus 



Tegmentum 



FIG. II. Preferential pathways of spread of amygdaloid 

 seizure discharges as based on experimental studies in the cat. 

 Note that the most prominent conduction is that into the 

 hypothalamus and mesencephalic tegmentum. [From Gloor 

 (100).] 



and cetacea. They believed that auditory hallucina- 

 tions in man may be related to disturbances in the 

 human counterpart of this 'sonar' apparatus. On this 

 theoretical basis they attempted to cure auditory 

 hallucinations with bilateral excision of the amygdala. 

 There is however not much factual foundation for 

 their hypothesis and it is therefore hardly surprising 

 that no significant number of cures were obtained by 

 this operative procedure. 



FUNCTIONAL SIGNIFICANCE OF AMYGDALA 



A comparison of physiological studies carried out 

 on the amygdala with those performed on other parts 

 of the rhinencephalon reveals a surprising similarity of 

 function between various parts of this system (99). 

 This similarity is especially close within what Pri- 

 bram & Kruger (205) have called the 'second system' 

 of the rhinencephalon which comprises the amygdala, 

 the piriform lobe, the orbitofrontal cortex and the 

 septum. It is not legitimate therefore to divorce the 

 discussion of the functional significance of the amygda- 

 loid complex from that of this anatomically more 

 extensive functional system. 



A fruitful approach to the understanding of the 

 fimctional role of this system is to set the results of 

 bilateral lesions against the background of the sur- 

 prisingly wide spectrum of autonomic and somato- 

 motor functions influenced by rhinencephalic stimu- 

 lation (99). It then becomes at once apparent that 



