CHAPTER XCV 

 CEREBRAL LOCALIZATION 



Of much greater practical importance than the experiments in which 

 the entire cerebrum is removed, as described in the last chapter, are 

 those in which various parts of it are destroyed or stimulated. From 

 the results conclusions may be drawn regarding the important subject 

 of cerebral localization. The effects produced by removal or stimulation of 

 different parts of the cerebral cortex vary considerably, some parts of the 

 cortex being set apart for the control of the motor mechanism of the 

 body, others for the reception and interpretation of afferent stimuli, 

 while others, and these by far the most extensive, are concerned in the 

 correlation or association of the sensory and motor centers. It may 

 be stated in general that: (1) The precentral region of the cerebrum 

 contains the centers of higher thought. (2) The ascending frontal con- 

 volution immediately in front of the precentral sulcus contains the 

 chief motor centers, a center being distinguishable for each muscular 

 grouping of the body. (3) The postcentral convolution has to do with 

 the centers for the immediate reception of sensory stimuli, the so-called 

 sensory centers. (4) A large area occupying most of the parietal lobe 

 and part of the occipital is undoubtedly associational in its function, 

 since from it no response can be obtained by .stimulation, etc. (5) Be- 

 'hind this, in the occipital lobe, there is a center having to do with the 

 reception of visual impulses. (6) In the upper convolution of the tem- 

 poro-sphenoidal lobe, is a similar center for hearing. 



These centers have been differentiated from one another by anatomical, 

 experimental and clinical research. At present we shall confine ourselves 

 to the experimental results. These are obtained by ablation and stimula- 

 tion, and in considering the results it will be convenient to divide the 

 centers into motor, sensory, and nonreactive. 



ABLATION OF THE MOTOR CENTERS 



Removal of the cortex from the area which controls the movements of 

 a definite part of the body say, the arm will be found to produce an 

 immediate and profound muscular paralysis. The animal does not use 

 the paralyzed extremity for any purpose whatsoever, and yet the mus- 



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