8oo 



HANDBOOK OF PHYSKILOGV 



NEUROPH^-SIOLOG\' 11 



FIG. I. Motor and sensory 

 representations in the cerebral 

 cortex of rabbit, rat and cat. In 

 the rabbit, the subdivisions so- 

 matic area i (Si) and somatic 

 area 1 1 (Sii) are overlapped to a 

 great extent by the responsive 

 field to antidromic stimulation of 

 the medullary pyramid. The map 

 for the rat shows motor repre- 

 sentations only. [After Brodmann 

 (64),Gulotta(i86),Huber (212), 

 VVoolsey & Fairman (477), Adey 

 & Kerr (5) and Porter (365).] 



ANTIOROMIC- 



PYRAMIDAL 



FIELD 



CAT 



TRUNK 



FORELIMB 



HINDPAW^ 

 HINDLIMB J^ TRUNK' 



FORELIMB^J^^Ili-.v'/ FACE 



(MOTOR K ^mJ.i'-t^n 



hind-limb movements readily obtained (143, 158, 

 249, 348, 349, 443, 470). Much of the excitable corte.x 

 in the carnivore is buried in the cruciate sulcus, and 

 specific attention has been directed to this problem 

 by Stout (413) and others, and more recently by 

 Delgado (116). Leyton & Sherrington (266) had es- 

 timated the buried cortex in the higher apes at about 

 35 per cent of the vv'hole motor region. In the cat, 

 Delgado found that the buried cortex in the cruciate 

 sulcus contains a motor representation of the hind 

 limbs, whereas forelimbs, neck and face are consecu- 

 tively placed from the superior to the inferior part of 

 the presylvian sulcus. 



The primates have a common general plan of 

 cortical motor organization, exemplified by the 

 arrangement found in the monkey, as shown in figure 

 2. Although motor functions may be ascribed, with 

 good reason, to a variety of cortical areas, including 

 certain parts of the temporal and occipital lobes, it 

 would seem useful as a point of departure to focus 

 attention on the three cortical zones from which motor 

 responses can be elicited in the greatest profusion and 

 complexity. The nature of the responses from these 

 areas will be discussed below. 



An area of the frontal lobe lying in front of the 

 central sulcus in gyrencephalic brains forms the 

 Rolandic or precentral motor area. This strip, with a 

 vertically inverted and .sequential representation of 

 body parts, may be considered as a unit jointly with a 



similar but less powerful motor representation in a 

 parallel strip of postcentral cortex yielding weaker 

 and less discrete motor responses. Its representations 

 are essentially contralateral (cf. 357, 482). There is a 

 progressive phyletic increase in the representation of 

 distal segments of the limbs, with a remarkable ex- 

 pansion of the digital representation. 



At its upper end the Rolandic area adjoins the 

 medial border of the hemisphere, and in man the 

 contralateral foot is represented on the medial aspect 

 of the hemisphere in the paracentral lobule. In this 

 region the Rolandic area adjoins a supplementary 

 motor area. As noted by Munk (339) and by Horsley 

 & Schafer (211), stimulation of the cortex within the 

 longitudinal fissure anterior to the primary leg repre- 

 .sentation in the monke\- produced moxements of the 

 contralateral arm and head turning, Griinbaum & 

 Sherrington (184) noted movements of foot and leg, 

 shoulder and chest, thumb and fingers from stimula- 

 tion in this area in anthropoid apes. They considered 

 that the conditions under which these reactions oc- 

 curred separated them from those characterizing the 

 Rolandic 'motor' area. Studies to be reported below 

 (358, 479-481) have indicated a largely bilateral 

 representation of l)ody parts in this supplementary 

 area. 



The third cortical zone which may be in\()l\ed in 

 integration of mo\cments is the second somatic area, 

 located in the monkey on the superior lip of the lateral 



