THE NEURAL CONTROL OF RESPIRATION 



less lengthy expirations. Respiratory frequency and 

 minute volume are greatly reduced as a result. One 

 continues to ob.serve this apneustic respiration even 

 when only the most caudal segments of the pons re- 

 main intact. On the other hand, an incision below the 

 striae acusticae, separating the medulla oblongata 

 entirely from the pons, brings about the disappearance 

 of the apneustic respiration. The medullary animal 

 then shows either eupneic respiration, to be sure not 

 always well coordinated, or very deep breaths in regu- 

 lar succession. The latter respiratory form has been 

 described as 'gasping' respiration {126). In many cases 

 transverse sectioning in the upper and lower regions 

 of the pons leads to periodic respiration (102), so that 

 an apneusis is not always observed. 



These ablation experiments have led to the assump- 

 tion of two pontine respiratory centers. In the cranial 

 part of the tegmentum pontis lies a nervous substrate 

 inhibiting respiratory activity, which is called the 

 pneumotaxic center. A more extensi\e region in the 

 middle and caudal pons is called the apneustic center. 

 The latter exerts a strong tonic effect on the bulbar 

 inspiratory center and, therefore, apneustic respira- 

 tion results when the inhibiting expiratory influence 

 of the pneumotaxic center is abolished. In conformity 

 with stimulation and coagulation experiments in the 

 pontine tectum (16, 105), the locus coeruleus may be 

 assumed to represent the bilaterally situated pneumo- 

 taxic center. Its isolated bilateral destruction in the 

 vagotomized cat results in apneusis. In man destruc- 

 tion of these nuclei leads to a severe cerebral dyspnea 

 with large, inspiratorily emphasized respiration, or 

 with periodic respiration (87). Concerning the lo- 

 cation of the apneustic center uniform accounts are, 

 up to the present, not available. Presumably it includes 

 extensive areas of the lateral reticular substance of the 

 pons (139). 



Structures of Higher Brain Stem Involved 

 in Respiratory Regulation 



It was recognized early in the course of investigation 

 of nervous centers that faradic stimulation of the 

 quadrigeminal plate in the rabbit produced an in- 

 spiratory displacement of the respiratory middle po- 

 sition, a restriction of the amplitude on the expiratory 

 side, and a marked increase in frequency — with 

 stronger stimulation showing concomitantly a marked 

 motor effect (132). Inspiratory reactions were particu- 

 larly easy to obtain from the caudal regions of the 

 thalamus situated close to the third ventricle (40). 

 Stimulation in the superior coUiculi was more likely 



to produce an expiratory effect with a decrease in 

 respiratory frequency and a lengthening of the dura- 

 tion of expiration (41). However, a subdivision in this 

 region into zones activating respiration and those in- 

 hibiting respiration resulted first from the systematic 

 electrical probing in the anesthetized and unanes- 

 thetized cat (90, 91, 160); the results of this appear in 

 figure 2. 



In the region of the posterior commissure, electrical 

 stimulation causes an increase in the respiratorv fre- 

 quency and in the respiratory amplitude. The effect 

 of the stimulation increases with the duration of the 

 stimulus, is comparable to the effect of carbon dioxide 

 and shows ventilatory conditioned negative after- 

 effects. From the perifornical region a sort of parox- 

 ysmal tachypnea is obtained which is characterized by 

 the sudden onset of a high respiratory frequency, with 

 hardly increased or actually decreased respiratory 

 amplitude and a displacement of the respiratory mid- 

 position toward the expiratory side. This tachypnea 

 accompanies general affectiNe reactions, such as 

 piloerection, arching of the back, mewing and spit- 

 ting, reactions which are obtained from this same 

 region with stronger stimulation. 



From the interthalamic commissure and from the 

 lateral thalamus — lateral, ventral and caudal to the 

 perifornical activating region — an electrical stimulus 

 always causes a reduction in the respiratory frequency. 

 With stimulation of the interthalamic commis.sure this 

 is, for the most part, caused by a lengthening of the 

 duration of inspiration. With stimulation of the 

 lateral hypothalamus both phases, the inspiratory and 

 the expiratory, are generally lengthened, and the 

 respiratory amplitude is often reduced. In many cases 

 the respiration has a dyspneic character, with in- 

 creased simultaneous widening of the nostrils during 

 inspiration, so that one must consider the possibility 

 of a bronchoconstrictor effect with secondary changes 

 in the respiration (95). 



In connection with the diencephalon and mesen- 

 cephalon one should also mention panting. Excitation 

 of the hypothalamic thermal center leads, in the dog 

 and in the cat, to an increase in the respiratory fre- 

 quency up to 300 per min. which results — in spite of 

 the reduction in respiratory volume — in an increase 

 in the minute volume and an increased excretion of 

 carbon dioxide. Panting can be elicited in the anes- 

 thetized dog by means of high-frequency thermal 

 stimulation. Magoun and coworkers (129) state con- 

 cerning this: "In the telencephalon the responsive 

 region occupies a position between the anterior com- 

 missure and the base of the brain. Throughout the 



