220 PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



recognition of external objects. From this point of view word- 

 blindness might be designated as visual agnosia, word-deafness as 

 auditory agnosia, and astereognosis as chiefly a tactile agnosia. 

 The exact localization in the cortex of the areas involved in the 

 auditory and visual associations and perceptions connected with 

 speech has not been established definitely. The question is a 

 complex and difficult one, and those who have had the most ex- 

 perience are perhaps the most cautious in referring word-bhnd- 

 ness or word-deafness to the lesion of circumscribed areas of the 

 cortex.* It may be said, however, with some certainty that the 

 phenomena of sensory aphasia in general are connected with lesions 

 involving the area along the margins of the posterior portion of 

 the lateral fissure (fissure of Sylvius), and extending into the 

 parietal lobe as far as the angular gyrus, and with the cortex 

 within the fissure including the cortex of the island. 



The general facts regarding aphasia illustrate very well the 

 theory or idea usually held among physiologists in regard to the 

 distribution or localization of mental activity in the cerebral cor- 

 tex. The understanding and the use of spoken or written language 

 is, so to speak, a mental whole, both from the standpoint of educa- 

 tion and of use. To express certain concepts implies the use of 

 definite words, and our visual, auditory, and motor experiences 

 are combined in these symbols. Each phase of this complex may 

 be cultivated more or less separately; in the case of the unlettered 

 man, for instance, the written or printed symbols form no part 

 in the associations connected with his verbal concepts. Cor- 

 responding to these facts we have, on the anatomical side, a portion 

 of the brain in which the auditory memories are organized — that 

 is, they are connected in some way with a definite arrangement 

 of nerve cells and their processes, another part in which the 

 visual memories are organized, and other parts in which the 

 motor memories as regards speaking or writing are laid down in 

 some definite form. This mode of representing the relations of 

 the nervous mechanisms to the power of "symbolic thinking and 

 expression"! must be regarded only as an imperfect schema. 

 Careful analysis of the phenomena of aphasia as they are actually 

 presented in patients shows that they do not conform very satis- 

 factorily to any of the classifications that have been proposed. 



The Association Areas. — According to the views presented 

 above, it will be seen that the motor and sense areas occupy only 

 a small portion of the cortex, forming islands, as has been said, 

 surrounded by much larger areas (Fig. 98). Flechsigl has desig- 



* For a general review see Monakow, "Ergebnisse der Physiologie," 1907, 

 p. 334. 



t For a critical discussion, see Head, "Brain." vol. 43, p. 87, 1920. 



i Flechsig, "Gehirn und Seele," Leipzig, 1896; also, "Archives de Neurol- 

 ogie," vol. ii, 1900. 



