CINGULATE, POSTERIOR ORBITAL, ANTERIOR INSULAR AND TEMPORAL POLE CORTEX 



>349 



region which was found to be continuous with tiie 

 responsive orbitoinsular field. A more detailed study 

 of these respiratory inhibitory zones has appeared 

 (126). The existence of an inhibitory insular (115, 

 132, 263) and temporal polar (10, 93, 115, 156, 195, 

 263) field in monkey and man has been confirmed. 



In 1945 Smith (238) first reported the respiratory 

 inhibitory effect exerted by the anterior cingulate 

 cortex in the monkey. Tower (254), working with 

 lightly etherized cats, had previously included this 

 region in her frontal inhibitory field which also com- 

 prised the entire gyrus proreus. The response from 

 the anterior cingulate has later been studied in the 

 cat (10, 59, 107, 113, 126, 240), dog (44, 126, 147, 

 240), monkey (126, 133, 227, 266) and man (132, 

 156, 198). 



Monkey. In the monkey the iniiibitory area on the 

 medial surface appears to correspond closely to the 

 agranular anterior cingulate region (fig. 2B). The 

 responsive field extends through the subcallosal region 

 towards the ventromedial edge of the frontal lobe 

 where it seems to be continuous with the respiratory 

 inhibitory area of the posterior orbital surface of the 

 frontal lobe (126, 133). There is an area with optimal 

 effects in the region surrounding the genu of the 

 corpus callosum (126). 



On the ventral surface the respiratory inhibitory 

 area (fig. 2B) includes the olfactory tubercle and 

 approximately the posterior one fourth of the cortex 

 of the gyrus rectus and the medial, posterior and 

 lateral orbital gyri. The most sensitive zone is the 

 olfactory tubercle and the posterior orbital gyrus 

 rostral to the lateral olfactory stria (area 13) (126, 

 215). This low-threshold area continues without 

 interruption into the anterior insula (fig. 2.4, B) (115, 

 126, 133, 245, 263) with the most pronounced effects 

 from the limen insulae. Via the 'buried' anterior 

 upper bank of the sylvian fissure, the responsive 

 anterior insular area extends (with a higher threshold) 

 onto the lateral surface of the frontal lobe and in- 

 cludes a small portion of the lower end of the pre- 

 central region (126). This portion represents the 

 area (6B) from which several earlier investigators, 

 stimulating the dorsolateral frontal surface only, had 

 noted respiratory inhibition in the monkey (234, 

 259, 262), chimpanzee (262) and man (38). 



In the temporal lobe of the monkey the region 

 vielding respiratory inhibition (fig. 2) continues 

 unbroken from the anterior insula onto the anterior 

 end of the iiippocampal gyrus (uncal region) and the 

 neighboring cortex of the temporal pole lateral to the 

 rhinal fissure (area 38 or TG in \on Bonin and Bailey's 



terminology) (115, 126, 133). Weak responses in 

 lightly anesthetized animals have also been obtained 

 from a narrow strip extending backward along the 

 rhinal fissure on the ventral surface towards and into 

 the retrosplenial region (126). This is likely the same 

 area from which Showers & Crosby (227) recently 

 obtained respiratory inhibition. The best and most 

 consistent effects result from stimulation of the medial 

 and ventral aspects of the temporal tip (126, 263). 

 According to Poirier & Schulmann (195) the low- 

 threshold respiratory inhibitory area of the medial 

 temporal tip extends farther backward along the 

 hippocampal gyrus and occupies about the medial 

 third of this gyrus at its caudal extremity. Cytoarchi- 

 tecturally this latter area approximately corresponds 

 to the TH field as mapped by von Bonin & Bailey 

 (260). No effects have been obtained from the dentate 

 gyrus (195) or hippocampus proper (126, 195, 263). 



A much weaker but distinct respiratory inhibitory 

 field, separated from the responsive insular and 

 temporal polar areas, has been located in the middle 

 and posterior portion of the superior temporal con- 

 volution in lightly anesthetized monkeys (fig. 2A) 

 (126). The area extends into the 'buried" cortex of 

 the lower bank of the sylvian fi.ssure. 



Respiratory inhibition has also been recorded by 

 stimulating the uncus through implanted electrodes 

 in the conscious monkey (166) and from the orbito- 

 insulotemporal polar region in a conscious infant 

 chimpanzee ( 126). 



The inhibition obtained from all cortical regions 

 outlined above mainly concerns the active phase of 

 the respiratory cycle, i.e. inspiration, with the chest 

 assuming an expiratory position during the period of 

 apnea (fig. 3). The effect occurs almost instanta- 

 neously. The respiratory movements cannot be held 

 in abeyance for more than 25 to 35 sec. despite con- 

 tinuous stimulation, after which period respiratory 

 'escape' occurs. Variations in the stimulus parameters 

 do not alter the character of the response. No fre- 

 quency-conditioned reversal of the respiratory effects 

 has been produced from these areas in monkeys (126). 

 Optimum inhibitory effect is obtained with fre- 

 quencies of 40 to 60 cps and prolonged pulse durations 

 of 10 to 20 msec. (126). 



Cat and dog. As in the monkeys the optimal inhibi- 

 tory zone on the medial surface is found just in front 

 of and below the genu of the corpus callosum (fig. 

 2E) (107, 113, 126, 240). Weaker effects only are 

 evoked from the rest of the anterior cingulate and 

 subcallosal (infralimbic) cortex as depicted by Rose 

 & Woolsey (fig. yE) (126). The failure of some inves- 



