8io 



HANDBOOK OF PHVSIOLOOV 



NEUROPHVSIOLOGV II 



sentation within it (cf. 15, 54, 474). Evidence for the 

 existence of such an area in man has been found also 

 (357' 35^)- Some form of sensation, referred to parts 

 of the lower or upper extremities, was produced by 

 cortical stimulation in the region located on the su- 

 perior lip of the lateral sulcus. These sensations fre- 

 quently took, according to Penfield & Rasmussen 

 (358), the form of a 'desire' to make a specific move- 

 ment. From the same general area, stimulation has 

 yielded both movements and inhibition of inter- 

 current movements. These results have been frag- 

 mentary and, according to Penfield & Rasmussen, 

 the evidence does not yet justify the concept of an 

 extensive and precise motor representation largely 

 coincident with the second sensory area. In the mon- 

 key, however, such a motor representation has been 

 described in detail by Sugar et al. (414). According to 

 these authors, the somatic arrangement of motor 

 points is roughly that of the second sensory cortex, 

 which lies a little more posteriorly, overlapping this 

 motor representation. The face region is antero- 

 superior and extends onto the lateral aspect of the 

 hemisphere. The foot region lies posteroinferiorly. 

 The hand region is b\' far the largest and lies between 

 the other two. With stimuli at 4 per sec. movements 

 were elicited with distal movements of limb parts 

 greater than proximal. A separate second motor area, 

 located posteriorly to the face area, has also been de- 

 scribed by Garol in the cat (165). Ablation of the 

 cortex, which in man would include the second 

 somatic area, was not followed by either sensory or 

 motor paralysis (358).^ Intracortical connections of 

 this area, as defined by strychninography (157), do 

 not tlirow light on its possiljle functions. 



Premiitor Cortex (Area 6) 



Architectural differences have led to the definition 

 of the anterior portion of the agranular cortex as 

 area 6 (cf. 444, 445). Rotation of the head and trunk 

 to the opposite side, as well as synergic movement of 

 flexion and extension of contralateral arm and limb, 

 have been observed in man b\' stimulating area 6 

 after removal of area 4 (150). Contractions of proxi- 

 mal muscles of the extremities, as well as synergic 



' In a paper by Orbach & Chow (347a), the performance 

 of the rhesus monkey on six somesthetic discriminations has 

 been tested after removal of sensory somatic areas I and II 

 and areas 5 and 7 of Brodmann. Lesions restricted to somatic 

 area II seemed to be without effect on these tests and do not 

 exacerbate, even if combined with removal of areas 5 and 7, 

 the loss which appears after lesion of sensory area I. 



movements, have also been seen in the chimpanzee 

 (201). Intenuption of both pyramidal tracts does not 

 suppress the motor responses obtained from the 

 macaque monkey. Those obtained from the anterior 

 portion of area 6 were described as "flexor synergies 

 with . . . grasping and deviation of the head and 

 trunk to the opposite side" (cf. 204). It would appear, 

 therefore, that mo\ement evoked from area 6 might 

 be mediated exclusively by extrapyramidal pathways. 

 However, according to Foerster (150) and Fulton 

 (161), .some of them take place via the motor area 

 as indicated by the effects of surgical section between 

 these two areas. No discontinuity of responses be- 

 tween area 4 and 6 has been observed, however, by 

 C:iark & Ward (92) in the unanesthetized monkey. 

 Changes in autonomic functions, induced by stimula- 

 tion of this cortical region, are uncertain (232). 

 Further information will be found in the works of 

 \arious authors (160, 161, 204, 483) and in Chapter 

 XXX\' h\ June; & Hassler in this work. 



Lesions of the upper part of area 6 cause changes 

 both of movement and of reflexes in the arm and leg 

 (373, 374). A soft plastic rigidity appears with both 

 lengthening and shortening reactions and a powerful 

 involuntary "sjrasp" reflex. The grasp reflex involves a 

 slow flexion of the digits in response to contact with 

 the palmar and plantar surfaces, and fluctuates in 

 intensit\' with intercurrent visual and auditory stimuli. 

 This reflex tends to disappear 2 to 3 weeks after a uni- 

 lateral ablation but reappears in an exaggerated form 

 following; removal of area 6 in the second hemisphere. 

 Bilateral resection of area 6 in the monkey is followed 

 by severe defects in manual dexterit\- and postural 

 adjustments. 



Although a Baljinski sign with extension of the great 

 toe does not appear after a lesion in area 6 in the mon- 

 key, lateral desiation of the toes with 'fanning' is ob- 

 served. Removal of area 6 secondarily to ablation of 

 area 4 exaggerates these reflex disturbances with tiie 

 appearance of the full Babinski response and a marked 

 spastic hemiplegia. 



The results of Jacobsen (218) indicate that area 6 

 plays a role in adaptive motor activities. Unilateral 

 lesions do not impair fine adaptive movements but 

 disorganize them as a pattern of response to a specific 

 situation when assessed by trials with a problem box. 

 However, recovery by postoperative training is pos- 

 sible. Some concept of the complexity- of the inter- 

 relationships between pre- and postcentral motor 

 areas may be gained from the studies of Welch & 

 Kennard (472). Following ablation of areas 4 and 6 on 

 the left side in an immature chimpanzee, a right 



