696 THE CEREBRUM 



a destruction of this region, but no aphasia. It seems, therefore, that 

 we cannot adhere to the old view of Broca, but must regard this 

 particular area merely as a link in the chain of 'the speech circuit. As 

 speech is a skilled act, involving several cerebral regions, Marie^ 

 believes that it cannot be referred to any particular group of cells to 

 the exclusion of another. The latter point will be brought out more 

 clearly during the succeeding discussion upon sensory aphasia. ^ 



Sensory Aphasia. — Speaking, as well as writing, necessitates the 

 presence of distinct concepts which may be memories of visual sensa- 

 tions, auditory sensations, tactile sensations and others. Hence, 

 it may be gathered that speech must be lost whenever these associa- 

 tions are absent, because it then lacks its causative factors. In other 

 words, a person may be in complete possession of the power of articu- 

 lation and phonation, but be quite unable properly to construct those 

 mental pictures or concepts which ordinarily give rise to speech. 

 In this case, therefore, the difficulty lies on the sensory side of the speech 

 circuit. 



We have previously seen that an injury to Wernicke's area of the 

 temporal lobe gives rise to word-deafness, i.e., to an inability of cor- 

 rectly associating sounds or words, in spite of the fact that they are 

 clearly heard. In the same way, a lesion to the parietal realm of the 

 psycho-visual field may give rise to the condition of word-blindness, 

 i.e., to an inability of associating written or printed language. In 

 both cases, of course, the peripheral afferent paths are in perfect condition, 

 and hence, the difficulty must be situated in the auditory and visual 

 centers. Under ordinary conditions, these two centers are the chief 

 contributors to the speech center proper, but not in an equal measure, 

 because the auditory realm is no doubt more directly associated with 

 it than the visual. This is shown especially by the fact that a loss of 

 speech is more frequently associated with word-deafness than with 

 word-blindness. This constitutes the so-called sensory aphasia of 

 Wernicke,^ so designated to differentiate it from the motor aphasia 

 of Broca. A simple word-blindness, on the other hand, rarely leads 

 to sensory aphasia, but presents itself rather as an inability to read 

 (alexia) and an inability to write from copy (agraphia). It may 

 happen, however, that the primary lesion does not remain confined 

 to the psycho-optic realm but also involves the psycho-auditory field, 

 in which case, of course, the aphasia is associated with both conditions, 

 word-deafness and word-blindness, as well as with alexia and agraphia. 

 It should also be added that auditory aphasia is often combined with 

 at least sHght defects in hearing, and visual aphasia, with certain 

 defects in sight (hemianopia). This cannot surprise us, because the 

 lesions involving these areas, are rarely so precisely placed as not to 

 affect neighboring units. 



1 Semaine medicale, Nos. 21, 42 and 48, 1906. 



2 A. Meyer, Harvey Lectures, New York, 1910, 228. 



3 Der aphasische Symptomenkomplex, Breslau, 1874. 



