CINGULATE, POSTERIOR ORBITAL, ANTERIOR INSULAR AND TEMPORAL POLE CORTEX 1 347 



and temporal polar regions represent the anterior 

 half of the alio- and juxtallocortical hilar formation. 

 Physiological experiments, particularly in the past i o 

 years, have shown that these areas respond to electri- 

 cal stimulation with a great variety of somatomotor 

 and visceromotor eflfects, thus imputing to it motor 

 functions. This view is consistent with the histological 

 findings that the responsive ancient type of cortex is 

 of the agranular or sparsely granular type which, 

 therefore^ might be expected to possess effector 

 functions (fig. i). 



On the other hand, this ancient type of agranular 

 'motor' cortex on the medial and basal aspects of the 

 cerebral mantle may also be regarded as interposed 

 between the upper and lower ends of the precentral 

 motor cortex of the dorsolateral aspects of the hemi- 

 sphere, joining the latter at the cingulate sulcus on 

 the one side and at the lower precentral and anterior 

 insular region on the other (fig. i). Thus, the physio- 

 logical experiments lend support to von Economo's 

 (261) contention of the existence of a broad zone of 

 'motor' cortex which encircles the entire cerelsral 

 hemisphere in a frontal plane anterior to the central 

 sulcus of primates. 



The hmited space at disposal unfortunately does 

 not allow any anatomical description of the cortical 

 areas concerned. The reader is referred to the fol- 

 lowing more recent publications: cytoarchitecture 

 (reviews: 126, 202; cingulate cortex; 22, 205, 209, 

 238, 260; orbitoinsular cortex: 22, 29, 73, 260; and 

 temporal polar cortex: 22, 260); corticocortical con- 

 nections (cingulate: 23, 167, 203, 204, 228; orbito- 

 insulotemporal cortex: 24, 167, 192, 203, 204); 

 afferent and efferent subcortical projections (re- 

 views: 46, 75, 92, 126, 202; cingulate: 46, 47, 91, 194, 

 201, 228; orbitoinsular: 46, 200, 215, 256, 264, 268; 

 and temporal polar cortex: 4, 39, 195, 200, 224, 244, 

 263); and olfactory pathways (2, 36, 37, 176, 202, 

 205). The subcortical pathways mediating the differ- 

 ent types of responses obtained on stimulation are 

 discussed in the subsequent sections. 



At this point brief mention should be made of the 

 hippocampal-cingulate relationships. Two distinct 

 types of cortex can be distinguished in all mammals 

 within the cingulate gyrus: a posterior granular type 

 and an anteriorly situated agranular type. The 

 cingulate cortex is closely connected with the hippo- 

 campus through the fornix via the maminillary bodies 

 through the anterior thalamic nucleus to the cingulate 

 gyrus. The thalamocingulate projections are derived 

 from all three portions of this nucleus: the antero- 

 medial nucleus, projecting upon the agranular 



anterior cingulate area (Brodmann's area 24); the 

 anteroventral nucleus, projecting upon the granular 

 posterior cingulate area (area 23 j; and the antero- 

 dorsal nucleus, projecting upon the retrosplenial 

 region (areas 29 and 30). [Reviews and references 

 may be found in various pulslications (22, 46, 126, 

 209, 260).] In all these cortical areas (and in the 

 granular prefrontal cortex) (3) the fibers of the cingu- 

 lum bundle originate and run through the white 

 matter in the retrosplenial region to terminate mainly 

 in the subiculum and presubiculum (i, 3, 80, 205) and 

 possibly directly in the hippocampus proper (205, 

 228). Thus the cingulum fibers appear to complete 

 some kind of a 'circuit' between the cingulate cortex 

 and the hippocampus, as first suggested by Papez 

 (184) in 1937 in his much publicized theory on the 

 central mechanism of emotion. 



Along the sulcus cinguli bordering areas 24 and 23, 

 there is the so-called 'cingular belt,' homologous with 

 areas 32 and 31, which Bailey et al. (23) in 1944 found 

 to receive connections from the cortical 'supressor' 

 areas (24s, 8s, 4s, 2S and 19s). Le Gros Clark & 

 Meyer (46) have referred to this beh "as a nodal 

 point of considerable physiological activity," but to 

 the author's knowledge there are no experimental or 

 clinical data that give any clue as to its functional 

 significance and it will therefore not be dealt with any 

 further in this review. 



EFFECTS OF STIMULATION 



Electrical stimulation of the anterior cingulate and 

 orbitoinsulotemporal polar cortex has elicited com- 

 plex somatomotor, autonomic, behavioral and elec- 

 trocorticographic effects which will be described in 

 this order. The effects on respiratory movements will 

 be discussed together with the somatomotor responses 

 as they are subserved by somatomotor nerves inner- 

 vating striated muscles. 



Somatomotor Responses 



INHIBITION OF RESPIRATORY MOVEMENTS. One of the 



more striking effects of stimulation of anterior cingu- 

 late cortex on the medial surface and the orbitoinsulo- 

 temporal polar cortex on the ventral surface of the 

 hemisphere is the profound inhibition of respiratory 

 movements. This effect is part of a more generalized 

 inhibitory influence on spontaneous somatomotor 

 movements exerted by the same cortical areas. 



Slowing or arrest of respiratory movements was 



