CHAPTER X. 



THE SENSE AREAS AND THE ASSOCIATION AREAS OF 

 THE CORTEX. 



The delimitation of the sensory areas in the cortex is a matter 

 of very considerable difficulty, owing, mainly, to the fact that the 

 determination of the presence or absence of certain states of con- 

 sciousness in the animal or person under observation cannot be 

 made except by indirect means. Moreover, the distinction be- 

 tween what we may call simple sensations and the more complex 

 psychical representations and judgments of which these sensations 

 form a necessary constituent can not be made clearly, even by the 

 individual in whom the reactions occur. We recognize in ourselves 

 different stages in the degree of consciousness aroused by sensory 

 reactions. Our visual and auditory sensations are clearly dif- 

 ferentiated ; but many of the lower senses escape recognition in 

 the individual himself, since the state of consciousness accom- 

 panying them is of a lower order. Our muscular sensations, for in- 

 stance, are so indefinite as to be practically subconscious. They 

 are most important to us in every act of our lives, yet the unin- 

 formed person is unconscious of the existence of such a sensation, 

 and if deprived of it would recognize the defect only in the con- 

 sequent loss of control of the voluntary muscular movements. In 

 the attempts to determine in what part of the brain the various 

 sensations are mediated every possible method of inquiry has been 

 used : the anatomical course of the sensory paths, physiological ex- 

 periments of stimulation and ablation, and observations upon in- 

 dividuals with pathological or traumatic lesions in the brain. In 

 the long run, the study of neuropathological cases in man must give 

 us the last word, because in such cases the estimate of the sensory 

 defect can be made with most accuracy and because in man the 

 specialization of the psychical functions has reached its highest 

 development. The results that have been obtained are perhaps 

 the most definite in the case of the higher senses, vision and hearing, 

 since defects in these senses are recognized most clearly, and the 

 anatomical mechanisms involved have proved to be more accessi- 

 ble to investigation. 



The Body-sense Area. In his early experiments Munk in- 

 sisted that lesions of the cortex involving the Rolandic area are 



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