CEREBRAL LOCALIZATION 



697 



Strictly speaking, however, the condition of sensory aphasia 

 must result in consequence of any lesion producing a loss of the intel- 

 lectual recognition of external objects through any one of our senses, 

 at least, of those which ordinarily give rise to concepts employed in 

 speech. On this account, the different association centers may really 

 be regarded as subsidiary or tributary centers to the speech center. 

 This failure of intellectual recognition has been designated as agnosia; 

 hence, word-deafness is really auditory agnosia, and word-blindness, 

 visual agnosia, while stereognosis is tactile agnosia. Thus, practically 

 any agnosia may give rise to defects in expressing our ideas in words 

 or deeds. The location and extent of these sensory lesions determine 

 the intensity of the aphasia or agraphia; and hence, these conditions 



FIG. 349. THE SPEECH CIRCUIT PROJECTED TO SHOW THE LOCATION OF LESIONS WHICH 



MAY GIVE RISE TO APHASIA. 



E, Eye; Y, visual association area; SC, speech center; M, motor points; L, larynx. 

 Sensory aphasia follows injuries to the association center (A) its transcortical connecting 

 path (E) or the receiving side of the center for speech (C). Motor aphasia may be 

 produced by an injury to the motor neurones of the center for speech (D) or its con- 

 necting path (E) with the motor area. 



may be either complete or incomplete. At all events, sensory apha- 

 sics suffer in most instances a greater deterioration of their mental 

 faculties than the simple motor aphasics, because their primary as- 

 sociation spheres are more directly involved. For the present, there- 

 fore, we must adhere to the belief that the speech circuit consists of 

 a number of distinct centers, the several activities of which are com- 

 bined into the single product of speech. This circuit may be broken 

 at different points, namely, at (a) the tributary association center, (6) 

 the association path connecting this lower center with the chief center, 

 (c) the chief center on its ingoing or sensory side, (d) the chief center 

 on its outgoing or efferent side, and (e) the association path connecting 

 the latter with the motor area. Injuries at points a, b, and c, must 

 give rise to sensory aphasia and injuries at points d and e, to motor 

 aphasia. 



