CEREBRAL LOCALIZATION 



693 



parts (L), by means of an efferent path through the motor area (M). 

 This entire complex, inclusive, so to speak, of one-half of the center of 

 speech, forms the motor arc of the speech circuit. But, inasmuch as 

 speech results only in consequence of incoming impulses, inclusive 

 of those of pure psychic origin, this circuit can only be completed 

 by bringing it into relation with a sensory or afferent arc. The latter 

 may embrace either the visual, auditory, or any other mechanism. 

 Supposing that we are now dealing with a visual impression, we would 

 say that the stimuli are received upon the retina (R) and are then 

 conveyed to the visual center in the occipital 

 cortex for proper association (F). From 

 here they are conducted to the center of 

 speech by way of definite association fibers. 

 In the chief center they are then remodelled 

 and transferred upon the efferent path by 

 way of which they attain the larynx. Natur- 

 ally, if speech is the outcome of an auditory 

 impression, the organ of Corti and the audi- 

 tory center would have to be substituted for 

 the retina and the visual center, but the 

 motor path remains the same. 



The Location of the Center for Speech. 

 Aphasia. Adult persons are capable of com- 

 municating their mental products to one 

 another by means of mimic movements, 

 speech and writing. The second of these 

 means has been shown by Broca 1 to be lost 

 whenever the base of the left inferior frontal 

 convolution is extensively injured. For this 

 reason, this investigator recognized in this 

 area the cortical regulatory factor of speech, 



or more correctly speaking, of the motor ap- E PosiTI01 * OF THE LESIONS 

 i i i ,. , ,. "HICK GIVE RISE TO SENSORY 



paratus which derives its mnervation from AND MOTOR APHASIA. 



the fifth, seventh and ninth to twelfth cranial R, Receptor; V, association 

 nerves. He designated the aforesaid condi- center; c, speech center; M, 

 tion as cortical motor aphasia, thereby fur- KottSy^EE^i 

 nishing the basis for the commonly accepted realm of motor aphasia, 

 view that the speech center is situated in the 



left inferior frontal convolution. We shall see later on that this locali- 

 zation is not quite correct, because it is restricted to too narrow a 

 sphere. In this connection attention should also be called to the fact 

 that cerebral localization should never be attempted upon a strictly 

 anatomical basis. Function should really be the deciding factor. 



The term aphasia signifies a loss of the power of speech (Fig. 348) . An 

 individual so afflicted is unable to express his ideas in spoken words. 

 The difficulty, however, does not lie in the larynx nor in the paths con- 

 1 In amplification of the observation of Bouillaud, 1825. 



FIG. 348. DIAGRAM OF THE 

 SPEECH CIRCUIT, ILLUSTRATING 



