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HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



We shall discuss these effects separately Iselow (Ex- 

 trapyramidal Motor Responses). More complete 

 transverse lesion at or just above thalamic level in 

 man is seen in cases of severe cortical damage from 

 anoxia, cortical and subcortical degenerative dis- 

 eases such as destructive types of encephalitis or 

 diffuse sclerosis. In such conditions, or following uni- 

 lateral hemispherectomy, the motor status more 

 closely resembles that of the thalamic animal. 



Control of Movement by Cortex {Rolandic Area) 



In the whole of the above discussion the part 

 played by the pyramidal tract in movement has 

 been set aside. Its function is obviously related to 

 the cerebral cortex. Its increasing development in 

 the higher mammals and the corresponding greater 

 severity of symptoms resulting from lesions of it 

 point to increasing importance of a particular aspect 

 of motor function, particularly in relation to prehen- 

 sion in the primates. In subsequent chapters the pat- 

 terns of anatomical representation in the cerebral 

 cortex and their relation to behavior will be discussed 

 fully. Here we shall attempt to outline only the func- 

 tional capacity of cortical mechanisms for movement 

 in relation to the subcortical integration that has 

 been discussed above. 



The most obvious immediate change resulting from 

 complete ablation of the precentral gyrus of one side 

 in the monkey is a flaccid paralysis of the lower part 

 of the face and of both liinbs on the opposite side. 

 From the beginning it is seen that the weakness of 

 lip muscles is only partial and is greater for some 

 movements than others. Within a few hours the ani- 

 mal begins to use proximal muscles of the lower limb. 

 Within 2 or 3 days the affected arm begins to be used 

 in climbing, particularly if the animal is frightened, 

 and the hand and foot may be hooked onto cage 

 wire in clumsy fashion (25). At this time the tendon 

 reflexes are becoming more ample and brisker than 

 those of the other side. After i to 2 weeks, when the 

 animal is laid on the operated side and the fingers 

 or toes of the uppermost side hooked over the ex- 

 aminer's finger and thus pulled upwards, a counter- 

 contraction of the flexors of the limb may be felt in 

 response. If, while so suspended, the animal is sud- 

 denly lowered in space, the fingers (or toes) will be 

 felt to contract as well as the other flexors of the limbs. 

 This is the reaction that is called by us the 'traction 

 response' (22, 30), and by Fulton and his associates 

 (11, 37) the 'grasp reflex.' We prefer to reserve the 



term 'grasp reflex' for a type of reaction triggered by a 

 contactual stimulus (85). 



A few days before the appearance of the 'traction 

 response,' passive stretch of a flexor muscle of the 

 upper limb or an extensor muscle of the lower limb 

 begins to encounter some resistance. At first this is in 

 the proximal muscles and is felt only towards the end 

 of a stretch. This is the beginning of spasticity and is 

 associated with increasing briskness of tendon re- 

 flexes in the same muscle (21). In the course of time 

 the phenomena of 'clasp-knife' melting of spasticity 

 during stretch and clonus of tendon reflexes may 

 appear, but these are a matter of degree of spasticity 

 and are more apparent with capsular lesions. It 

 will be noted that whereas spasticity is a response 

 limited to the muscle that is stretched, the traction 

 reaction is a response in all the flexors of the limb 

 (already tense) in response to increasing stretch of 

 any one of them. The traction response when well 

 developed can be elicited in all the flexor muscles 

 if all of the afferent roots to the limb but one are 

 sectioned. It is felt in the fingers and wrist when 

 only the shoulder fle.xors have afferent innervation, 

 or vice versa. It cannot be elicited from a deafferented 

 muscle. The traction reaction is affected more ob- 

 viously than the tendon reflexes by neck and labyrin- 

 thine posture. 



In the lower limb the appearance of the traction 

 reaction is associated with the appearance of the 

 propriocepti\ e positive supporting reaction, a pillar- 

 like stiffening or tendency to stiffen of the extensors 

 of the limb when the ankle and toes are passively 

 dorsiflexed. In the lower limb this reaction soon 

 becomes even more evident than the traction reac- 

 tion, whereas in the upper limb its development is 

 delayed. The pattern of hemiplegic spasticity in the 

 flexors of the upper limb and the extensors of the 

 lower limb is related to the relative preponderance of 

 these two reactions. 



Within 2 to 3 days of the appearance of the trac- 

 tion reaction, it is apparent that with sufficiently 

 strong motivation, for example food within reaching 

 distance while the other limbs are restrained or teas- 

 ing with some unpleasant object under the same 

 circumstances, the animal will make a plucking 

 movement of the limb to luring the object to his mouth. 

 When the reaction can be facilitated by turning the 

 neck, the animal soon learns to turn the neck in addi- 

 tion to plucking at the objects. The triple flexion re- 

 sponse remains the same, all joints having to l^e flexed 

 in order to flex one. The traction reaction is greatly 

 facilitated b\- laving the animal on the sound side and 



