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HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



that this appeared to result from a perturbation of 

 function of the pyramidal tract. He recognized that 

 the sign occurred in patients with intact pyramidal 

 tracts, and that its anatomical basis might be obscure. 

 Less cautious clinical observers ha\'e regarded the 

 sign as pathognomonic of a lesion of the pyramidal 

 tract. Nathan & Smith (345) examined the phe- 

 nomenon following cordotomy and with histological 

 control, and concluded that there is no relation be- 

 tween the anatomic state of the corticospinal tracts 

 and the form of the plantar response. 



Fulton & Keller (162) have investigated the 

 Babinski response on a comparative basis in a series 

 of primates. In the chimpanzee the reaction shows 

 two phases, as in the human, with an initial digital 

 extension, particularly in the great toe, followed by 

 a phase of lateral deviation and fanning. The second 

 phase is more obxious after bilateral removal of the 

 foot areas and is augmented when the premotor area 

 is encroached upon. The Babinski response persists 

 indefinitely in the chimpanzee. In the gibbon, which 

 they regard as intermediate between the baboon and 

 the chimpanzee in encephalization, the Babinski re- 

 sponse is well-developed for 3 weeks following area 4 

 ablation and then gradually disappears with the re- 

 turn of volitional use. Removal of the leg area on one 

 or both sides of the motor cortex failed to produce the 

 reflex in the macaque, mangabey, patas monkey or 

 guenon. Only when the lower lumbar segments were 

 freed completely from higher control by hemisection 

 of the spinal cord was the Babinski response noted. 

 In the baboon, on the other hand, removal of the 

 cortical leg area produced the response, and motor 

 recovery in the baboon was slower than in the inon- 

 keys. Fulton & Keller concluded that 'cortical dom- 

 inance' is more highly developed in the baboon than 

 in the other old world monkeys studied. The gibbon 

 shows still higher cortical dominance, with an even 

 more obvious Babinski sign, and an even slower re- 

 turn of motor functions. 



Recovery After Ablation 



The nature of compensation and recovery of func- 

 tion postoperatively has attracted considerable atten- 

 tion. A phenomenon of bilateral compensation for 

 the effects of unilateral lesions of area 4 has been de- 

 scribed, such that if area 4 of the remaining hemi- 

 sphere is removed after a delay of 3 or 4 mos., none 

 of the usual signs of pyramidal tract injury appear 

 (2). Similar compensations occur in the absence of 

 callosal connections but are prevented if the sensory 



cortex of areas 3, i and 2 are also removed. The pre- 

 motor cortex may also participate in the process of 

 compensation. 



Kennard (230, 231) has studied extensively the in- 

 fluence of age on the processes of recovery of motor 

 functions. The possibility of reorganization of these 

 functions has been found to diminish progressively 

 with age. While ablation of areas 4 and 6 in the infant 

 monkey is followed by a quite substantial recovery, 

 similar intervention in adult monkeys produces more 

 dramatic and permanent motor defects. Participation 

 of the intact cortex in the recovery processes has been 

 postulated since ablation of either parietal areas i, 

 2, 3, 5 and 7, or frontal areas 9, 10, 11 and 12 increases 

 the pre-existing motor deficit. Murphy & Arana (340) 

 found no evidence of reorganization in adjacent corti- 

 cal areas after excision of the arm area. They suggest 

 that the postoperative recovery of functions may in- 

 vohe subcortical mechanisms. Glees & Cole (177) 

 have made repeated small lesions in the motor cortex 

 of the macaque and mangabey. Small lesions of area 4 

 in the thumb and hand zones produced paralysis 

 with a considerable degree of recovery and return of 

 motor skill. Stimulation of adjacent cortex after re- 

 covery gave hand movements not previously present 

 in these areas. Undercutting of these responsive areas 

 caused a recurrence of paralysis and loss of motor 

 skill. They consider that the motor cortex does not 

 function as a mosaic but has a tendency, when a 

 lesion occurs, to act in a less differentiated and more 

 primitive manner which they ascribe to the pluri- 

 segmental connections of area 4 as revealed in their 

 concurrent histological studies. 



EFFECTS ON PH.XSIC AND TONIC MUSCULAR ACTIVITIES 

 OF STIMULATION AND ABLATION OF CORTICAL AREAS 

 OTHER THAN PRIMARY' MOTOR AREA. THEIR 



CONNECTIONS 



Supplementary Motor Areas 



Following the early observation of movement from 

 stimulation of the medial surface of the hemisphere 

 (see page 800), the name 'supplementary motor area' 

 has been applied by Penfield and his associates to 

 this region within the longitudinal fissure in the su- 

 perior and intermediate frontal region (358-360). A 

 variety of responses follow stimulation here in man, 

 including raising of the opposite arm, turning of the 

 head, bilateral synergic contraction of the leg and 

 trunk, movements of the eyes and pupillary changes. 



