THE MOTOR AREAS 



633 



In the first place it may be observed, that if the current took effect on the 

 lower parts of the cerebrum, muscular movements should be obtained by appli- 

 cation of the current to widely different regions of the cortex. Since this is not 

 the case, it is merely a question between the cortex and the subjacent white mat- 

 ter. The following facts speak against 

 the latter possibility: 



(1) Under certain circumstances it is 

 possible to stimulate the cortex mechan- 

 ically, but the white matter cannot be 

 so stimulated (Luciani and Tamburini). 

 (2) It requires a stronger current to stimu- 

 late the corona radiata electrically than to 

 stimulate the cortex. (3) On the other 

 hand a muscular contraction caused by 

 continuous stimulation of the cortex ceases 

 decidedly sooner than after stimulation of 

 the corona (Levy). (4) After poisoning 

 with chloral (Franck and Pitres), the cor- 

 tex becomes inexcitable, but movements can 

 still be obtained from the corona. Like- 

 wise the cortex is rendered inexcitable to 

 a depth of 2-3 mm. by painting it with 

 cocain (Carvalho). 



Again when a certain muscular con- 

 traction is aroused first from the cortex 

 and then from the corona and the first 

 two responses are recorded, it is found 

 that the latent period of the first is con- 

 siderably longer than that of the second 

 e. g., cortex, 0.065 second ; corona, 0.045 

 second (Franck). The difference of 0.02 



second is doubtless due to a delay in the excitation process occasioned by the 

 nerve cells (Fig. 283). The facts also that the contraction curve following cor- 

 tical stimulation rises more slowly and is not so regular as that following stimu- 

 lation of the corona, and that cortical stimulation is accompanied by a clonic * 

 contraction, while stimulation of the corona is not, are probably to be explained 

 by the presence of nerve cells. 



Hence it is conceivable that the electrical stimulus acts directly on the large 

 pyramidal cells of the cortex (cf. Fig. 284, right side ISTos. 4, 5, 6) although this 

 would not mean that there might not be other points of attack, as, e. g., the end 

 arborizations of the afferent nerves as well. 



These things being so, we may say that certain definite regions of the 

 cortex stand in a more definite relation to the movements of the body than 

 do other parts of the brain. These regions are described as the motor cortical 

 areas of the cerebrum. 



B. STIMULATION OF THE MOTOR CORTICAL AREAS IN DIFFERENT 



MAMMALS 



It would lead us too far afield to describe here in detail all the results 

 obtained by electrical stimulation of the cortex in the different mammals. 



FIG. 283. Latent period of muscular con- 

 traction induced by stimulation of the 

 cortex (upper tracing), and by stimula- 

 tion of the underlying white substance 

 (lower tracing), after Franck. The 

 time record in each case is in l-100ths 

 of a second. The instant of stimulation 

 is indicated by the vertical line to the 

 left, the beginning of the contraction 

 by the vertical line to the right. 



1 By clonic contraction is meant one whose strength is continually changing (cf. Fig. 291). 



