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HANDBOOK OF PH^'SIOI.OG^' 



NEUROPHYSIOLOGY 11 



these immediate effects the term 'suppression' should 

 he discarded and the proper term 'inhibition' used 

 (58, 126).] On the other hand, inhibition of sponta- 

 neous movements and of motor after-discharges has 

 also been recorded on stimulation of areas outside 

 the "suppressor" strips of Dusser de Barenne and Mc- 

 CuUoch. Thus, Tower in 1936 (254) obtained such 

 effects l)y stimulation of the frontal, temporal and 

 occipital respiratory inhibitory fields in cats under 

 light ether anesthesia. In the monkey, a quieting 

 effect on spontaneous movements has been produced 

 from a rather diffuse zone of the lateral surface of the 

 frontal lobe, comprising chiefly the intermediate 

 region, areas 8s and 9 (11 i, 126, 172, 173), and from 

 the junctional region of the parietal and occipital 

 lobes with the superior gyrus of the temporal lobes 

 (ill, 126). There was, however, no loss in tone, either 

 in cats or in monkeys, on stimulation of these areas. 

 This is important to note because Tower's frontal 

 field in cats includes the anterior cingulate region, 

 electrical stimulation of which in monkeys under 

 Dial anesthesia by Bailey et at. (23) has been said to 

 pro\oke a "relaxation of existing muscular tension," 

 and in the etherized monkey a "pronounced decrease 

 in the resistance of the nonino\ ing extremity to pas- 

 sive movements to the point of flaccidity" (238). The 

 knee jerk was abolished (238). This was confirmed by 

 Ward (266). These discrepancies were further empha- 

 sized in the reports by C'lark and associates (44, 45) 

 who failed to find any evidence of inhibition of muscu- 

 lar tone by stimulation of the anterior cingulate 

 cortex in unanesthetized dogs (44) or of the frontal 

 eye field (area 8s) in unanesthetized monkeys (45). 

 Kaada (126) has reinvestigated and further analyzed 

 the influence of the cortical "suppressor" areas, par- 

 ticularh' the rostral cingulate region, on spontaneous 

 moxements, posture and tone, cortically induced 

 movements and spinal reflexes in lightly anesthetized 

 cats and monkeys. The presence of an orbitoinsulo- 

 temporal polar field, with quite similar inhibitory 

 effects on respiratory movements as part of the an- 

 terior cingulate cortex, prompted the search for the 

 possible inhibitory influence of this field on the vari- 

 ous other kinds of somatomotor acti\ ities just men- 

 tioned. The results may be summarized as follows. 



a) Effects on spontaneous movements and muscular tone. 

 Spontaneous movements occurring under light anes- 

 thesia such as struggling and shivering and induced 

 'chloralose jerks,' could readily be inhibited by electri- 

 cal excitation of all areas exerting an inhibitory 

 influence on respiratory movements in the monkey, 

 infant chimpanzee, cat and dog (the dotted areas in 



fig. 2.-1 to E). Maximum quieting effect was obtained 

 from the same two medial and basal fields which 

 produced the strongest inhibition of respiration — one 

 around the genu of the corpus callosum on the medial 

 surface, and a second centering around the olfactory 

 tubercle in the posterior orbital, anterior insular, 

 rostral pyriform and adjacent temporal polar cortex 

 of the monkey and the corresponding areas in the 

 cat. .Such movements could be held in abeyance, 

 bilaterally, as long as the stimulus was applied and 

 were usually resumed within a few seconds after 

 cessation of stimulation. Inhibition of movements 

 from these two optimum zones was associated with a 

 widespread muscular relaxation as judged by the 

 diminished resistance to passive movements of the 

 extremities. Pre-existing postures were inhibited. Thus 

 a rigidly extended or raised arm or leg became 

 flaccid and slowh dropped; the knee jerk was abol- 

 ished and the eyelids often closed as when the animal 

 is going to sleep. The feeling of tiredness and sleepi- 

 ness and the tendency to close the eyes on stimulation 

 of the same area in conscious patients should be re- 

 called (see al)o\e). 



From the regions with weaker effects on the respira- 

 tory movements — such as a great portion of the 

 anterior cingulate area, the lower part of the subcal- 

 losal region, the lower precentral region, parts of the 

 orbitoinsulotemporal field, the retrosplenial region, 

 and the separate lateral temporal field of monkeys, 

 cats and dogs — the effect under light anesthesia was 

 mainlv one of arresting spontaneous random and 

 rhythmic movements (fig. 45, C) without loss of 

 muscular tone. The eyes opened and the pupils 

 dilated slighth', gi\ing the animal an "awaking" type 

 of response or appearance of attentive repose or 

 alertness. A similar quieting or "arrest" reaction 

 without any loss of tone has been obtained by weak 

 stimulation of these areas through implanted elec- 

 trodes in unanesthetized cats (118, 119, 126, 130, 131, 

 232, 269) and also from points within the so-called 

 cortical "suppressor" areas 8s, 2s, and 19s in lightly 

 anesthetized cats (fig. 4.4 to C) and the intermediate 

 zone of the lateral frontal cortex in the monkey (126). 

 Frequently the inhibition of mo\ements may outlast 

 the stimulus for some seconds. This prolonged action 

 is associated with a local electrical after-discharge at 

 the site of stimulation with no spread into the motor 

 cortical regions (126, 270). 



/)) Inliihition of motor after-discharges evoked by motor 

 cortex stimulation. Motor after-discharges can be 

 brought to a fairly abrupt halt or prevented, as shown 

 in fiijurc 4/), b\- stimulation of the areas in figure 2.I 



