CEREBRAL L0< IUZATION 351 



tion and those relating to the position and movements of the muscles. 

 Pain and temperature sensations ■ !<» no1 seem to have cortical rep 



tation. 



There is of course a close association between sensory and motor cen 

 ters, as is illustrated in the experiment described elsewhere under the 

 head of apesthesia (page 838), in which it will be remembered that the 

 complete section of all the posterior roots <>f an extremity renders the 

 pari as effectively paralyzed for volitional movement as it would 1; 

 been had the motor roots themselves been cut. Afferenl impulses are 

 therefore necessary for the efficient volitional control of the muscular 

 nio\ ements. 



SENSE CENTERS 



Attempts to locate exactly the position on the cerebral cortex win 

 impressions of the projicient sensations vision, hearing, etc. — are re- 

 ceived are of course more or less difficult because of the fact that the 

 experiments have to he performed on dumb animals. Nevertheless Borne 

 information can lie gleaned from the results of ablation and stimulation 

 of various parts of the cortex, ablation causing, for example, definite 

 evidence either of blindness or of deafness, and stimulation causing 

 movements of the eyes or cars similar to those ordinarily observed when 

 these organs are stimulated in the usual way. 



The auditory center is located in the hack part of the superior temporal 

 convolution. Stimulati f this area in animals causes a pricking up 



of the ear on the opposite side as if the animal heard a sound. Clinical 



observation has confirmed this conclusion. 



The visual Ci nti r is located in the occipital lobe. Tt is important • 



peal again that there are two centers uu the cerebral cortex concerned in 

 vision: the frontal visual center, located as we have Been in the frontal 

 lobe, and the so-called visual center itself, located in the occipital I 

 stimulation of the frontal visual center produces a prompter movement 



of the eyes than does stimulation of the occipital center, indicating that 

 the frontal center has the immediate control of the muscular movements, 



whereas the occipital lobe IS probably concerned in the adjust mi 

 the muscular reactions which are necessary in controlling the eye mo 



incuts, bo that the objects may he properly viewed and judgmi 

 formed, by the extent of the movements, of its distanc sition, 



The actual response to stimulation of the occipital i hat 



the lobe on one side is connected with the corresponding half o 

 retina, the fovea centralis being, however, connected with both 



