CEREBRAL LOCALIZATION 851 



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

 Pain and temperature sensations do not seem to have cortical represen- 

 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 of an extremity renders the 

 part as effectively paralyzed for volitional movement as it would have 

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

 therefore necessary for the efficient volitional control of the muscular 

 movements. 



SENSE CENTERS 



Attempts to locate exactly the position on the cerebral cortex where 

 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 be performed on dumb animals. Nevertheless some 

 information can be 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 ears similar to those ordinarily observed when 

 these organs are stimulated in the usual way. 



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

 convolution. Stimulation of 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 center is located in the occipital lobe. It is important to re- 

 peat again that there are two centers on the cerebral cortex concerned in 

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

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

 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 adjustment of 

 the muscular reactions which are necessary iri controlling the eye move- 

 ments, so that the objects may be properly viewed and judgments 

 formed, by the extent of the movements, of its distance, position, etc. 

 The actual response to stimulation of the occipital centers shows that 

 the lobe on one side is connected with the corresponding half of each 

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



