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HANDBOOK OF PHVSIOLOGV 



NEtTROPHVSIOLOGY II 



pressure alterations on excitation of the orbital surface 

 of the frontal lobe. Smith (237, 238) evoked similar 

 responses from the rostral portions of the cingulate 

 and hippocampal gyri and Kaada et al. (133) from 

 the anterior insular and temporal polar cortex in 

 monkeys. These findings have been confirmed and 

 further analyzed in various species of animals. Rises 

 as well as falls in arterial pressure have been recorded 

 in the cat, dog and monkey on stimulating the ante- 

 rior cingulate cortex (10, 107, 126, 133, 147, 238- 

 240), the orbital surface (21, 54, 107, 126, 133, 159, 

 215, 240, 241), the anterior insula (i 15, 126, 133), the 

 rostral pyriform (10, 126, 133, 146, 195, 237, 239, 

 263) and adjacent temporal polar cortex (10, 126, 

 133, 195, 263). Similar effects have been obtained in 

 man from the anterior cingulate (198), posterior 

 orbital surface {41, 42, 158) and temporal pole (40, 

 42). 



The two most sensitive regions on the medial and 

 basal surfaces appear to coincide with the optimum 

 zones for inhibition of respiratory movements and 

 gastric motility in the monkey (the areas encircled 

 by broken lines in fig. 65), dog and cat. According to 

 Poirier & Schulmann (195) the low-threshold cardio- 

 vascular temporal zone extends farther backward 

 than indicated on figure 65 and includes about one 

 third of the medioventral portion of the hippocampal 

 gyrus. In the cat and dog the most sensitive spots are 

 similarly found in the pre- and subgenual region and 

 in the orbital and adjacent rostral pyriform cortex 

 and olfactory tubercle. 



Most authors have reported a fall in pressure as the 

 most frequent response from these two zones in the 

 various animals and under a variety of anesthetics. 

 The fall may amount to 1 5 to 30 mm Hg, or even up 

 to 60 mm (126, 240, 263). It occurs almost instan- 

 taneously (fig. 3^) and may or may not be associated 

 with a slowing of the pulse rate. The initial decline 

 may be followed by a secondary small rise above 

 normal. Initial arterial pressure elevations rarely 

 exceed 40 mm Hg and occur after a latency of 2 to 

 8 sec. (fig. 3/I). From the temporal pole rather pro- 

 longed arterial pressure alterations mav be induced 

 (263). 



The character of the response seems to depend on 

 several factors, a) The site of stimulation may be criti- 

 cal. Pressor and depressor points have been located 

 only a few millimeters apart. However, usually one 

 type of response predominates from all points within 

 a given area under the same experimental conditions. 

 In the same animal the orbital surface and olfactory 

 tubercle mav yield opposite effects (215) and the same 



may be true when comparing the posterior orbital 

 surface and the temporal pole (263). b) The level and 

 type of anesthesia are important. Deepening the anes- 

 thesia sometimes seems to favor depressor responses 

 (126); further, under curare (215), light ether (10, 

 241), pentobarbital (21) or thiopental (42, 158) 

 anesthesia, pressor responses predominate on stimu- 

 lation of the orbital surface whereas depressor effects 

 are usually encountered under diallyl barbituric acid 

 (Dial) anesthesia (54, 215). c) Occasionally a fre- 

 Cjuency-conditioned reversal of the arterial pressure 

 effect has been observed (126, 215), but as a rule the 

 direction of the change is independent of the stimulus 

 frequency; both falls and rises may be obtained over 

 a wide frequency' range, with only the degree of the 

 response varying (usually optimum at 30 to 60 cps 

 and prolonged pulse durations of 10 to 20 msec). 

 d) Stimulus strength alterations may also yield re- 

 versals. Hess et al. (107) obtained arterial pressure fall 

 and respiratory inhibition on weak stimulation of the 

 anterior cingulate cortex in cats, whereas stronger 

 stimulation yielded the reverse, e) Animals of different 

 species may react differently. Rises in arterial pressure 

 induced from the orbital surface in animals anes- 

 thetized with diallyl barbituric acid seem to be more 

 readily obtained in the monkey than in the cat (215, 

 241). 



The arterial pressure effects are not secondary to 

 the a.ssociated respiratory changes (42, 126, 215, 238), 

 and there is no constant relationship between the 

 direction of the respiratory and arterial pressure 

 responses (126, 215, 23B). Section of the trigeminal 

 nerves does not alter the arterial pressure responses 

 from the cortical areas concerned (115, 126). Bilateral 

 vagotomy abolishes or greatly reduces the depressor 

 responses from the anterior cingulate (126, 238, 240), 

 the orbitoinsular cortex (126) and temporal pole 

 (126, 237). On the other hand, the pressor responses 

 persist after vagotomy (16, 126, 240). Since some fall 

 in arterial pressure still may be obtained after bilateral 

 vagotomy (115, 126, 215), a dilatation of the periph- 

 eral JDlood vessels through some extravagal route must 

 also be assumed to occur. Peripheral effects have been 

 observed by Delgado & Lixingston (54) who recorded 

 a marked rise in the skin temperature of the limbs on 

 excitation of the posterior orbital surface in monkeys. 

 According to Sachs ft al. (215) arterial pressure 

 changes (and respiratory arrest) produced from the 

 same area persist after bilateral cer\'ical vagotomy, 

 splanchnicectomy and adrenalectomy, and after 

 destruction of the liypothalamic paraventricular 

 nuclei. Piiysostismine prolongs the cardiac inhibition 



