HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



RHiNENCEPHALON. Kaacla (134) observed two opti- 

 mum zones in the anterior rliinencephalic areas yield- 

 ing pressor and depressor responses on electrical 

 stimulation, one in the anterior limbic cortex and a 

 second in the postorbital anterior insula, anterior 

 hippocampal gyrus and neighboring temporal regions 

 in monkeys and in the homologous areas in cats and 

 dogs. Arterial pressure reductions were also produced 

 by stimulation of the amygdaloid and caudate nuclei. 

 Ward (220) stimulated structures in the anterior 

 gyrus cinguli in monkeys and obtained depressor 

 responses with cardiac retardation and in some cases 

 cardiac arrest. Smith (194) in similar experiments had 

 observed pressor responses with or without cardiac 

 acceleration as well as depressor effects, usually as- 

 sociated with more or less pronounced cardiac re- 

 tardation. In man, too, stimulation of the anterior 

 part of the gyrus cinguli results in alteration of the 

 arterial pressure and pulse rate [Pool & Ransohoff 



('77)]- 



Anand & Dua (16) stimulated the gyrus cinguli in 

 conscious cats and monkeys with implanted electrodes. 

 From rostral portions of the gyrus cinguli belonging to 

 the frontal lobe, they usually obtained a rise of ar- 

 terial pressure, whereas stimulation of caudal parts 

 belonging to the temporal lobe caused a fall. They 

 observed both cardiac acceleration and retardation; 

 but since these did not correlate with the arterial 

 pressure responses, the latter probably were manifesta- 

 tions of variations in vasoconstrictor discharge. Hoff- 

 man & Rasmussen (128) observed chiefly depressor 

 responses and inhibition of the gastrointestinal ac- 

 tivity on stimulation on the insular cortex in Macaco 

 mulatta. .Similar effects were obtained on stimulation 

 of the posterior orbital surface and the tip of the tem- 

 poral lobe. Since the cardiovascular effects persisted 

 after vagotomy, they must be attributed to changes 

 in vasoconstrictor tone. 



TEMPORAL LOBE. Stimulation of the human temporal 

 pole has yielded marked rises in arterial pressure 

 [Anand & Dua (14, 15, 16)]. In the monkey, pressor 

 as well as depressor respon.ses have been observed on 

 temporal lobe stimulation [Kaada et al. (135)]. 



EFFERENT PATHWAYS. The pathways for corticofugal 

 excitatory and inhibitory cardiovascular effects are 

 largely unknown. Probably the majority of the cortico- 

 spinal cardiovascular neurons are relaved in or pass 

 through the hypothalamus. However, some efferent 

 neurons might run outside the hypothalamus. Spiegel 



& Hunsicker (195) stimulated the cortex of the cat 

 and obtained arterial pressure and bladder responses 

 which persisted after transverse sections in the medulla 

 oblongata that were designed to interrupt p\ramidal 

 or extrapyramidal tracts. The conclusion was reached 

 that there exist both pyramidal and extrapyramidal 

 pathways for autonomic efferents. In monkeys and 

 chimpanzees, they found that arterial pressure re- 

 sponses arising from stimulation in the sensory motor 

 cortex were completely abolished by pyramid section, 

 but were uninfluenced by lesions in the hypothalamus. 

 Responses elicited from the posterior orbital surface 

 and anterior insula disappeared after destruction of 

 the hypothalamus. The vasomotor pathways from 

 the temporal lobe, however, were found not to pass 

 the hypothalamus. 



The ob.servations of Spiegel & Hunsicker thus sug- 

 gest that autonomic pathways pass through the hypo- 

 thalamus from some areas but not from others. How- 

 ever, observations made with such a rough technique 

 as that employed in the above experiments cannot be 

 credited with any major evidential value. It should 

 also be pointed out that corticospinal pathways pass- 

 ing through the hypothalamus mav well have a pyra- 

 midal or juxtapyramidal course in more caudal re- 

 gions, as for instance the pons and medulla oblongata. 

 This is the case with the sympathetic vasodilator out- 

 flow which in its posthypothalamic course first turns 

 dorsad across the tectum mesencephali and then once 

 more descends \entrad and passes beneath its medul- 

 lary portion in close relation to the psramidal path- 

 way. This vasodilator pathway, which is al.so accom- 

 panied by vasoconstrictor fibers, would therefore 

 have been severed in experiments conducted b\' the 

 methods of Spiegel & Hunsicker. 



The pioneering in\estigations of Magoun el al. 

 have demonstrated that the reticular system in the 

 brain stem contains structures which have a facilita- 

 tory and inhiljiiory influence on both reflexogenic and 

 corticogenic somatic motor phenomena. Bach (20) 

 sought to find out whether stimulation of these retic- 

 ular structures also had inhibitory and facilitatory 

 effects on autonomic responses and whether certain 

 combinations of effects, as for instance inhibition of 

 the patellar reflex with a coincident depressor effect, 

 could be demonstrated; he found that this was not 

 the case. Bach's investigation did not lend weight to 

 the hypothesis which identifies the somatic facilitatixe 

 and inhil:)itory reticular formation with \asopressor 

 or vasodepressor structures. 



In the opinion of Landau (143), the autonomic 



