SENSORIMOTOR CORTICAL ACTIVITIES 



807 



CORTICAL ABLATION STUDIES OF 

 ROLANDIC MOTOR AREA 



The neurological deficit following resection of 

 cortical motor areas becomes greater at progressively 

 higher levels of the phylogenetic scale. Walker & 

 Fulton (459) have examined the effects of hemide- 

 cortication in carnivores and a series of primates, in- 

 cluding the monkey, baboon and chimpanzee. 

 Whereas the hemidecorticated cat is able to walk on 

 the first postoperative day, this operation produces 

 severe paralysis with persistent paralysis and reflex 

 changes in higher primates. Walker & Fulton discuss 

 two possible explanations for these differences. Either 

 there is greater bilateral motor representation in the 

 lower animals or there is greater encephalization of 

 function in the primates. Although there is evidence 

 for the ipsilateral control of movements in rabbits, 

 cats, dogs and monkeys, an extensive comparative 

 study is lacking; and Walker & Fulton conclude that 

 the differences arising from hemidecortication are 

 more probably attributable to increasing encephaliza- 

 tion in higher mammals where the more extensive 

 and more complex cerebral cortex may assume func- 

 tions controlled at subcortical levels in lower mam- 

 mals. 



Phyletic differences in the degree of spasticity in- 

 duced by cortical resection have been stressed by 

 Walker & Fulton, and since this is a dominant aspect 

 of the postoperative picture, a discussion of its 

 mechanisms of origin will be found in Chapters 

 XXXII by Denny-Brown, XXXIV by Patton & 

 Amassian and XXXV by Jung & Hassler. 



Removal of the excitable areas of frontal and parie- 

 tal lobes in primates from monkey to man reveals the 

 increasing significance of the role of the cortex in 

 motor functions, both by reason of the increasingly 

 profound paresis immediately after ablation in higher 

 primates and also from the decreasing extent of ulti- 

 mate recovery following such resections. Attention 

 will be directed first to the effects following removal 

 of the primary motor area. 



Proceeding from earlier investigation (cf. ;520, 

 321-324, 394, 449), Fulton & Keller (162) removed 

 the foot area in the precentral gyrus of the young 

 chimpanzee after defining its margins by faradic 

 stimulation. A profound monoplegia ensued for 24 

 hours with complete areflexia, but the knee jerk then 

 reappeared and with it a faint withdrawal respon.se 

 on vigorously pinching the plantar surface. By the 

 second day the withdrawal response was more obvi- 

 ous. The paresis was at all times flaccid in the digits 



and remained so for 9 mos. Movement began to re- 

 appear at the hip after 4 or 5 days, followed by knee 

 and ankle mo\ements, but the digits tended to re- 

 main permanently paralyzed. Fulton & Keller then 

 studied a series of other primates with lesions sharply 

 restricted to the posterior part of area 4, including 

 monkeys, baboons and gibbons, and coniirmed the 

 presence of a flaccid paralysis. 



Denny-Brown & Botterell (118) made subtotal 

 lesions of area 4 and found that muscles of the fingers 

 may go through moderate spasticity in the course of 

 recovery of motor power, e\'en though more proximal 

 muscles are flaccid. Travis (425) observed after pre- 

 central motor lesions in the macaque an immediate 

 severe voluntary impairment, hypotonia and dimin- 

 ished tendon reflexes. No ipsilateral deficits were ob- 

 served. In contrast to Fulton & Keller's findings in 

 the chimpanzee, recovery was as rapid in distal as in 

 proximal joints, with impairments persisting in both. 

 Within 2 to 12 weeks these animals were able to pick 

 up small stationary objects by apposition of thumb and 

 index finger but never again at faster than half the 

 initial speed. Atrophy of about 10 per cent appeared 

 in contralateral liinbs during the period of greatest 

 disuse and completely disappeared after maximal 

 functional recovery. 



Lesions of the precentral agranular cortex in the 

 macaque were found to interfere especially with 

 skilled acts, as measured by time scores (369). 

 Posterior lesions produced a greater defect than an- 

 terior lesions (the latter extending anteriorly to the 

 arcuate sulcus). Visual discrimination and delayed 

 response were unaffected. Bilateral ablation exacer- 

 bated the effects of a unilateral lesion. Pribram et al. 

 (369) concluded that the motor defect in precentral 

 ablation is not due to the loss of an act through ex- 

 cision of the locus of a "habit', but rather that a sco- 

 toma of action results. Hopping and placing reactions 

 (38, 475) and their abolition by lesions in the motor 

 cortex are described elsewhere. 



Much additional information is to be found in the 

 comprehensive reviews of Hines (199, 203) and 

 Penfield & Rasmussen (358 j. 



Hahnuki Response 



Historically, concepts concerning this sign have 

 changed since the original proposals of Babinski (cf. 

 259) who noted that in certain patients with nervous 

 system disorders, plantar stimulation caused an ex- 

 tension of the toes, especially the great toe, followed 

 by abduction of one or more toes ('fanning'), and 



