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HANDBOOK OF PH'lSIOLOGV 



NEUROPHYSIOLOGY II 



animals, namely the intermediate frontal cortex, parts 

 of the sensory-motor cortex, superior temporal gyrus 

 and paraoccipital region (225). The cortical points 

 from which Bremer & Terzuolo {31, 32) evoked 

 identical EEG eflfects appear likewise to be located 

 within these zones. The cortically induced EEG 

 arousal is readily blocked by anesthetic agents (225; 

 Kaada & Johannessen, unpublished observations). 

 Even in lightly anesthetized animals the effect is 

 rather inconstant and the regions influenced are more 

 or less restricted. The most effective loci are found in 

 the cingulate and temporal polar cortex and in the 

 superior temporal gyrus (225; Kaada & Johannessen, 

 unpublished observations). This is consistent with the 

 finding that these cortical areas are also more effec- 

 tive in inhibiting spontaneous movements (as part 

 of the arousal response) than the frontal, parietal 

 and occipital inhibitory fields (126). 



The cortically induced EEG arousal is not sec- 

 ondary to accompanying respiratory or arterial pres- 

 sure alterations (126). It may further be associated 

 with either facilitation, inhibition or no effect of 

 movements evoked from the motor cortex (126, 232). 

 The response depends on a cortical-subcortical 

 mechanism (126, 231) and, like the behavioral 

 arousal, it is most likely produced \ ia the brain-stem 

 and thalamic reticular .system (126, p. 238; 231). The 

 cortically evoked EEG arousal is present in the 

 encephale isole (31, 32, 126). The primary and sec- 

 ondary components of cortical potentials evoked by 

 sensory stimulation are unaffected during cortically 

 induced EEG arousal, whereas the subsequent 

 'evoked burst potentials' are Ijlocked (126). 



BURST .\UGMENT.4TiON. Occasionally stimulation of 

 points in the anterior cingulate (126, 231), orljital 

 and rostral pyriform cortex and in the olfactory 

 tubercle (126) in animals under light barijiturate 

 narcosis may result in an increase in the burst prom- 

 inence in all cortical areas. The response, which 

 appears to l)e opposite of that characterizing the EEG 

 arousal, is probably mediated \ia the thalamic reticu- 

 lar system which is the only subcortical structure at 

 present known to initiate generalized bursts on 

 stimulation. 



ELECTRICAL AFTER-DiscjHARGES. A characteristic fea- 

 ture of the anterior cingulate, subcallosal and orbito- 

 insulotemporal polar cortex, as well as of the amvg- 

 dala and hippocampus, is a low threshold for elicita- 

 tion of seizure discharges as compared to that of 

 neocortical areas. This was first shown h\ Gibbs & 



Gibbs (go) for motor seizures and by Jung (124), 

 Lennox et al. (152) and Kaada (126) for electrical 

 after-discharges from the hippocampus, amygdaloid 

 region and medial-basal cortical areas, respectivelv. 

 These findings have later been confirmed by a number 

 of investigators (12, 48, 79, 83, 95, 96, 125, 126, 154, 

 '55' '93' 208). The lowest threshold for electrical 

 after-discharges is found in the hippocampus, amyg- 

 dala and pyriform cortex. Details about the various 

 types and preferential pathways of spread are found 

 in the papers just referred to. Of particular interest 

 is the observation that after-discharges elicited from 

 almost any of the areas concerned readily spread into 

 the others, suggesting a close functional relationship 

 between them (12, 48, 126), as also demonstrated by 

 physiological neuronography (192, 203). Mention 

 should further be made of the generalized petit mal- 

 like 3-per-sec. spike and wave formations associated 

 with clinical manifestations of petit mal epilepsy 

 which have been evoked from the anterior cingulate 

 cortex in animals (126, 153, 193). 



The vast literature on the relation of psychomotor 

 seizures or automatism to the temporoinsular region 

 is reviewed elsewhere (65, 84, 127, 168, 187) and will 

 not be discussed further in this connection. Brief men- 

 tion should only be made of the immediate "flatten- 

 ing' (also termed 'suppression') of electrical activity, 

 including spikes, at the onset of the seizure in the 

 majority of patients with temporal automatism 

 (66, 88, 109, 121, 123, 171). Such 'suppression' may 

 be generalized, bitemporal or unilateral. This phe- 

 nomenon, together with the clinical features of 

 automatism, can be reproduced in man at operation 

 by stimulation of the anterior temporal-insular gray 

 matter and the region of the claustroamygdaloid 

 complex and anterior hippocampus (65, 66, 123). 

 Similar effects have been produced from the homol- 

 ogous areas in cats (85, 126) and monkeys (50, 126). 

 It .seems likely that the effect is identical with the 

 'acti\'ation' response (126, 127). 



OTHER ELECTROCORTICOGRAPHIC EFFECTS. \"arioUS 



Other types of effect in the EEG in response to stimu- 

 lation of the areas under discussion have been de- 

 scribed as 'suppression' or 'elimination of strychnine 

 and unelicited spikes' (59, 152), 'suppression of 

 spindles' (59), 'attenuation' (231) and "depression' 

 (126) of electrocortical activity. The functional sig- 

 nificance of all these types of effect is not clear. Experi- 

 mental esidence has been gi\en that the "at- 

 tenuation" response and the 'suppression of spindles,' 

 without any appreciable increase of frequency of the 



