CHAPTER XX 



THE FUNCTIONS OF THE CEREBRAL CORTEX 



THE greatest diversity of view has prevailed and still prevails 

 regarding the method of cortical function. That the cerebral 

 cortex is concerned in some way with the higher conscious func- 

 tions is clearly shown by a large body of experimental and 

 clinical evidence. 



The partial or complete removal of both cerebral hemispheres 

 has been accomplished in various species of animals, from fishes 

 to apes, and the changes in behavior carefully studied. In 

 fishes and frogs the behavior is but little modified, save for the 

 loss of the sense of smell, if the thalamus is left intact; but if the 

 thalamus also is destroyed, the animal loses all power of sponta- 

 neous movement, of feeding when hungry, etc., though it will still 

 react to some strong stimuli in an apparently normal manner. 

 The fundamental reflexes of the spinal cord and brain stem are 

 but little modified by this operation in frogs, save for the dis- 

 turbance of the olfactory and visual functions. The recent 

 experiments of Burnett have, moreover, shown that frogs in 

 which the cerebral hemispheres alone have been removed are 

 somewhat more excitable than normal frogs (probably due to the 

 loss of cortical inhibitions), and that simple associations easily 

 learned by normal frogs are in this case impossible. 



In the dog the loss of the cerebral hemispheres alone leaves the 

 animal in a state of profound idiocy, though here also all of the 

 primary sensori-motor reflexes (except the olfactory) remain if 

 the thalamus is uninjured, and one such animal operated on by 

 Goltz lived for eighteen months. During this time, however, he 

 had to be artificially fed, for he had lost the ability to recognize 

 food when set before him, nor did he show any of his former signs 

 of intelligence. (These experiments are summarized in Schafer's 

 Physiology, vol. ii, pp. 698 ff., to which the reader is referred for 



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