CHAPTER XCIV 



THE SENSORY CENTERS OF THE BRAIN 



Sensory experience and the recognition of the quality and location of 

 stimuli acting upon the receptors of the body depends upon the arrival 

 of impulses at certain stations in the brain which correspond to the re- 

 ceptors in question. Knowledge concerning the location of the centers 

 involved in the perception of sensations arising from each kind of recep- 

 tor and from each part of the body has been gained by inference from 

 the anatomical arrangements of the fibers connecting the sense organs 

 with the various parts of the brain and from studies of the reactions of 

 animals which have had certain parts of the brain removed. But this 

 information is of slight value, since we can learn about a sensation di- 

 rectly only through the verbal report of the person who is experiencing 

 it. Consequently the important contributions to the sensory physiology 

 of the brain have come from the clinical study of individuals who have 

 suffered injury in some part of the cerebrum. Gushing 12 induced two 

 patients in whom part of the brain was exposed to allow him to stimulate 

 it while they were in a conscious state. As the result of the stimulation 

 of the postcentral convolution definite sensory impressions were experi- 

 enced, consisting of a . sensation of numbness, deadness, or tactual im- 

 pressions. No muscular groups underwent movement unless the precen- 

 tral convolution was stimulated, when no sensations w r ere experienced 

 by the patient except those which accompanied the change in the posi- 

 tion of the part that was moved. The sensations which were thus shown 

 to be represented on the cortex are those of touch discrimination and 

 those relating to the position and movements of the muscles. A com- 

 prehensive analysis of sensory localization has been made by Head 9 from 

 observations on soldiers suffering from the wounds of war. 



The Sensory Center of the Optic Thalamus 



It has long been recognized that the cerebral cortex is the site of cen- 

 ters concerned in the perception of many qualities of sensation. Ex- 

 periments by Goltz on a dog from which the cortex had been removed, 

 suggested that certain subcortical centers might also give rise to sensa- 

 tion, since this animal responded to various sensory stimuli, and when 

 hungry gave evidence, so far as his actions were concerned, of experienc- 

 ing sensations of hunger. Head's clinical observations have led him to 



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