CENTRAL AUTONmilC MECHANISMS 



973 



have been found by HoHnian & Rasmussen (80). 

 Stimulation of the insular cortex in the monkey pro- 

 duced a fall in arterial pressure, inhibition of respira- 

 tion in expiration, decrease in tonus of the stomach 

 and inhibition of gastric peristalsis, the two latter 

 being eliminated by section of the vagi. Stimulation 

 of the insular region in man also gi\es some indication 

 that this area is concerned with \isceral functions 

 (131, 132). 



It has already been mentioned that the cortex has 

 extensive fiber connections, mostly indirect, with the 

 hypothalamus and lower regions of the brain stem. 

 An extensive discussion of these connections is to be 

 found in Mitchell (121), although some of the evi- 

 dence cited has not been substantiated (9). However, 

 the functional connections are rich, and Rossi & 

 Brodal (141) have found corticofugal fibers passing 

 from the cortex to the reticular formation of the pons 

 and medulla, with the motor area as the chief con- 

 tributor. These fibers, descending in the pyramidal 

 tract, provide a nonhypothalamic route for influenc- 

 ing somatomotor and autonomic functions. 



The question arises as to what extent autonomic 

 responses evoked from the cerebral cortex are me- 

 diated through the hypothalamus. Landau (100) 

 approached this problem by stimulation of the corti- 

 cospinal tract in the medulla, producing sweating, 

 changes in arterial pressure and pulse rate, contrac- 

 tion of the bladder and of the stomach, pupillary 

 changes, and piloerection. In his opinion the cortex 

 can influence most autonomic functions by way of the 

 spinal cord, separately from the hypothalamus and 

 its pathways, and he proposes the predominant eflfect 

 on visceral function to be one of facilitation of activity 

 patterns which are essentially determined at spinal 

 and peripheral levels. Wall & Davis {165), by excit- 

 ing the cortex after removal of surface afFerents by 

 section of the trigeminal nerves, found that stimula- 

 tion of the sensorimotor cortex, the anterior part of 

 the gyrus cinguli, the posterior orbital cortex, the 

 anterior part of the insula and the anterior part of 

 the temporal lobe produced arterial pressure changes. 

 Responses elicited from the sensorimotor area were 

 independent of the hypothalamus and could be 

 abolished by section of the pyramid. They also ob- 

 served that the temporal lobe responses did not de- 

 pend upon the hypothalamus. Responses produced by 

 stimulation of the posterior orbital cortex and the 

 insula were abolished by destruction of the hypo- 

 thalamus; however, some respiratory responses 

 remained. 



Some other interesting observations have recently 



been presented by Hoff el al. (79) who found that 

 stimulation of the anterior sigmoid gyrus in cats 

 causes an elevated arterial pressure plus a renal corti- 

 cal ischemia, the latter being prevented by renal 

 denervation. Upon repeated stimulation, fatty de- 

 generation and, later, lower nephron nephrosis 

 occurs due to chronic vasoconstriction. On the other 

 hand, Johnson & Browne (90) found that ablation of 

 autonomic cortical zones had no effect on the arterial 

 pressure in dogs witli chronic renal hypertension, the 

 reason probably being the multiplicity of cortical 

 areas concerned with vasomotor functions. 



The influence of cortical extirpation upon emo- 

 tional responses has already been mentioned, but this 

 is no place for an extensive discussion of this topic 

 which is the subject of Chapters LXIII and LXIX. 

 It will be recalled, however, that decortication in 

 animals has been said to lower the threshold for rage; 

 and since rage phenomena are closely associated with 

 outbursts of autonomic activity, this relationship 

 becomes of interest. However, Rothfield & Harman 

 (142) found that such a lowering of the rage threshold 

 by decortication was depetident upon concomitant 

 interruption of the fornix and postulated that inhibi- 

 tory influences pass from the rhinencephalon to the 

 hypothalamic 'rage integrating center' via the fornix. 

 If confirmed, this will add support to the Papez 

 theory of the anatomical basis for emotions. 



A great deal of detailed work has been done re- 

 cently concerning the activities of the rhinencephalic 

 areas, including the amygdala and piriform lobe, 

 hippocampus, gyrus cinguli and subcallosal regions. 

 The functions of these areas will be thoroughly dis- 

 cussed in Chapters L\T, L\'II and LVTII of this 

 work, and it is sufficient to state here that these areas 

 have important relationships to autonomic function, 

 some of which may be carried out in collaboration 

 with the hypothalamus, as has already been men- 

 tioned. Some similarity of the effects of lesions in the 

 amygdaloid nuclei and lesions in the hypothalamus 

 has been claimed. For instance, Morgane & Kosman 

 (124) have reported that hyperphagia follows bilateral 

 amygdaloidectomy in cats, a finding in variance with 

 that of Anand & Broljeck (5) who found no change in 

 food intake but simply decreased activity. There is a 

 possibility that rhinencephalic structures may be inter- 

 mediary in the activation of the anterior hypophysis 

 through the hypothalamic route. Sawyer {146) found 

 that the release of pituitary gonadotrophin produced 

 by intraventricularly injected histamine in rabbits is 

 probably due to excitation of rhinencephalic path- 

 ways and not to direct action on the adenohypophysis. 



