I350 



HANDBOOK OF PH\SIOLOGV 



NEUROPHVSIOLOG^■ 11 



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FIG. 3. Inhibition of respira- 

 tory mo\"cments (second line) 

 and arterial pressure alterations 

 ' Jirst line) following excitation of 

 the anterior cingulate cortex in 

 the monkey. Note opposite arte- 

 rial pressure effects in A and B. 

 Ether anesthesia. Time in sec- 

 onds. [From .Smith (238).] 



tigators to obtain respiratory inliibition from several 

 points in the anterior cingulate area is probably due 

 to the limited extent of the optimal zone within this 

 area, a point which has not been seriously considered. 

 The efTect has also been obtained in unanesthetized 

 dogs and cats by stimulation through implanted 

 electrodes (lo, 44, 107, 126). 



The basal respiratory inhibitory fields in cats and 

 dogs occupy part of the orbital gyrus (fig. 2C, D) {21, 

 51, 54, 108, 126, 199, 215, 234, 240, 241, 257) and also 

 include the olfactory tubercle (126), the anterior 

 portion of the pyriform corte.x and the ventral surface 

 of the proreate gyrus which is largely co\ered by the 

 olfactory bulb and tract (126). Posteriorly the border 

 is indistinct and extends into the rostral ends of the 

 anterior ectosylvian and sylvian gyri. Less intense and 

 fickle responses have also been obtained backward 

 along the rhinal fissure onto the tentorial surface of 

 the hemisphere and into the retrosplenial region ( i 26, 

 254). As long as the basal respiratory inhibitory 

 field in the monkey was thought to be restricted to the 

 posterior orbital gyrus (the insula and temporal lobe 

 has not yet been studied), the orbital gsrus of cats and 

 dogs was reasonably considered the homologue of this 

 gyrus of primates (21, 54, 215). Howes'er, the demon- 

 stration in the monkey of an uninterrupted orbito- 

 insulotemporal polar inhibitory field makes it ex- 

 tremely likely that the responsive cortex of the orbital 

 surface of cats and dogs corresponds to the orbito- 

 insulotcmporal polar field of primates (126, p. 84). 



A separate, less active respiratory inhibitory field 

 (apparently the homologue of that found in the 

 superior temporal gyrus in the monkey) is located in 

 the anterior sylvian and ectosylvian gyri (fig. 2C') 

 (126, 254). Complete arrest has only rarely been 

 obtained from this area, the usual response being a 

 slowing of the respiratory rate. 



The usual t\pe of inhibitory response in cats and 



dogs to stimulation of all these areas is similar to that 

 in monkeys, i.e. arrest in expiration. In the author's 

 experience it is not possible in these species to oijtain 

 the prolonged and dramatic inhibition observed in 

 the monkey; escape usually occurs after only 10 to 

 20 sec, even with strong stimulation (126, 240). The 

 optimum stimulus parameters are approximately the 

 same as in the monkey, i.e. a frequency of 40 to 60 

 cps and prolonged pulse durations of 6 to 10 msec. 

 (126, 240). Far more common than in monkeys is a 

 slowing of the rate w-ithout much change in ampli- 

 tude, or a combination of slowing and decreased 

 amplitude (107, 126). Further, stimulation, particu- 

 larly of the orbital gyrus of the cat and dog, frequently 

 results in arrest in inspiration irrespective of whether 

 the stimulus is applied during the inspiratory or 

 expiratory phase (126, 241). Also on central vagal 

 stimulation such 'inspiratory effects" are weaker in 

 monkeys than in dogs, cats and rabbits (276). This 

 feature therefore possibly denotes a species difference. 



The cortical origin of the respiratory effects from 

 the various parts of the medial and basal zones in the 

 monkey, cat and dog has been demonstrated {126). 

 The effects are not due to spread of current to the 

 dura, blood vessels, cranial nerves or to subcortical 

 structures (126). Further, the response from a given 

 area is not initiated by activation of other cortical 

 areas through corticocortical connections. Thus, for 

 instance, the effects obtained from the orbital surface 

 and from the temporal pole in the monkey remain 

 unaltered after section of the imcinate fasciculus ( 1 26, 

 133) which is known to connect the two areas recipro- 

 cally (192, 203). The influence is mediated directly 

 "downstream' l)y corticosubcortical fibers, outside the 

 pyramidal tract and the hippocampus-fornix system 

 (126). The possible subcortical routes are discussed 

 below. 



Man. In man arrest of breathing quite similar to 



