CINGULATE, POSTERIOR ORBITAL, ANTERIOR INSULAR AND TEMPORAL POLE CORTEX 



■363 



Since 1950 several papers dealing with the effects of 

 stimulation of these medial and basal cortical regions 

 on the electrocorticogram have appeared. These 

 effects are all apparent immediately at the end of 

 stimulation. This is in contrast to the so-called "sup- 

 pression of electrical activity' with a latency of several 

 minutes {61). As already discussed, the latter has been 

 demonstrated to be identical with the nonspecific 

 phenomenon of "spreading depression' which is not 

 related to any particular cortical area (58, 230). 



The various types of immediate responses obtained 

 will now be described. 



'activation" or "arousal' RESPONSE. As first reported 

 by Sloan & Jasper in 1950 (231), high-frequency 

 electrical stimulation of the anterior cingulate corte.x 

 in cats anesthetized with diallyl barbituric acid may 

 produce a 'desynchronization' of the electrocortical 

 activity of all cortical regions similar to the EEG 

 arousal following stimulation of the brain-stem reticu- 



lar system and peripheral sensory nerves. The most 

 prominent feature of the response is the disappearance 

 of the intermittent 6-to-i2-per-sec. bursts or spindles 

 and their replacement by a high-frequency low-volt- 

 age activity. The same effects were elicited by Kaada 

 (126) on exciting the anterior cingulate, subcallosal, 

 orbitoinsulotemporal polar cortex, the olfactorv path- 

 ways and amygdala in cats, monkeys and chimpanzee 

 (the dotted areas shown in fig. 2). A typical example 

 is given in figure 8. In nonanesthetized animals the 

 EEG responses from these areas appear to be allied 

 to the behavioral arousal induced from the same 

 regions (134; Fangel & Kaada and Kaada & Jo- 

 hannessen, unpublished observations). These findings 

 have recently been confirmed in the monkey (225) 

 and, for the anterior cingulate, in man (233). The 

 same type of EEG response has also been elicited 

 from the cortical regions on the lateral aspect of the 

 hemisphere stimulation of which causes, as described 

 above, similar behavioral arousal in unanesthetized 



Before 

 (5) Before 



6 V('^^^v'^/<V'^,%V'M^^^'< 



(Bj2 sec ofter stim. of orbital gyrus ill 

 (£)2 sec. offer stim of lateroi gyrus (n) 



f/ 



(c)25 sec. oflcr stim 





FIG. 8. Generalized 'arousal' of the EEG on stimulation of the left orbital gyrus of the cat for 

 3 sec. (at arrow I). A: Control. B: Disappearance of intermittent burst potentials with increased 

 frequency of cortical potentials. C: Return to normal after 25 sec. D and E.- Stimulation of the 

 left lateral gyrus at arrow II with the same stimulus parameters failed to produce any effect at the 

 six cortical electrodes. [From Kaada (126).] 



