THE NEURAL CONTROL OF RESPIRATION III5 



also causes simultaneously general changes in muscle 

 tone (107, 188). It is for this reason that the interpreta- 

 tion of respiratory effects with stimulation of the 

 cortex is so diflicult, particularly in the anesthetized 

 and restrained animal. Thus, in the following discus- 

 sion, only the most frequently observed respiratory 

 effects will be mentioned. 



Most easily obtained through cortical stimulation 

 is a respiratory inhibition, with a decrease in the depth 

 of inspiration and a prolongation of expiration. W'ith 

 stronger stimulation, a respiratory arrest can occur in 

 expiration lasting for the entire duration of the 

 stimulus. As shown in figure 3, the corresponding 

 excitable regions are, in the cat, the gyrus orbitalis 

 and gyrus proreus (13, 94, 177), the anterior part of 

 the cingulate gyrus (inferior to the genu corporis 

 callosi) (94, 178), and, with higher stimulus threshold, 

 the sylvian and ectosylvian gyri (6g, 177, 178). In the 

 dog appro.ximately the same zones are described as 

 inhibitory to respiration and in Macaco rhesus or 

 mulatta inhibitory zones are described, inore or less in 

 agreement with these, in the posterior orbital gyrus 

 (13, 54, 107) and in the rostral and deeper portions 

 of the cingulate gyrus (area 24) (107, 195). In man, 

 for the most part, stimulation of the cortex results in an 

 inhibition of respiration, for example from the orbital 

 face of the frontal lobe (39), from the anterior end of 

 the island of Reil (150) and from the columna fornicis 

 (176). 



Less densely located are regions from which a 

 respiratory activation (inspiratory reaction) is ob- 

 tained. The latter consists mostly, although not 

 always, of an increase in respiratory frequency with an 

 increase or decrease in amplitude. The occasionally 

 observed respiratory arrests in inspiration are con- 

 sidered as maximal inspiratory activation and, there- 

 fore, are also included in this group. Respiratory 

 activation is obtained in tlie dog and in the cat from 

 the anterior sigmoid gyrus (107, 177) as well as from 

 the anterior and middle portions of the cingulate 

 gyrus (i 78). In the monkey the region with inspiratory 

 reactions is located in an area rostral to the sulcus 

 precentralis superior which cytoarchitectonically cor- 

 responds to area 6a (107, 177). 



The course of the descending pathways for the 

 cortical control of respiration has as yet been little in- 

 vestigated. For the most part, the connections from 

 the cortical regions activating respiration to the sep- 

 tum and to the hypothalamus are at present being 

 traced (55, 157, 176). 



From the few reports dealing with the cerebellar 

 influence on respiration one may conclude, from 



S.coronaUs 



S.supraatjlvius 



S.ccloatjlviua post. 



SrhiridLlis 



I CAT 



3.ps<;udosqlviu9 

 S.ectosylvias ant. 



S.supraisijlvius 



5.pr<i£34lvlu3 



S.eclostflvias post. 



S.psc udoaijlv ioa 

 5.*jclo3qlvias ojit. 

 S.rhLnalia 



Z DO& 



S.precciitTdlis sup. 

 S.rcntreJis 



'S.svjlvias 

 S-viMCcntraJis vni. 

 S.pj'incipalis 



3 MONKEY 



— InViibltorq cortex 



— Accelerator q cortex. 



FIG. 3. .Xreas ot the cerebral cortex irom which ahcrations 

 of respiratory movements were ehcited by electrical stimulation. 

 The closest stippling and the closest lines indicate the areas from 

 which the responses were most easily obtained. [From Smith 



(177)-] 



ablation experiments on the decerebrate dog (184) 

 and from stimulation experiments on the cat (135, 136), 

 that inhibition of the tonus of the inspiratory muscles 

 and dampening of the chemoreceptor reflexes can be 

 initiated from the anterior lobe. 



Spinal Respiratory Centers and Descending 

 Respiratory Tracts 



Towards the end of the last century investigations 

 were published in which animals were reported to be 



