558 TEXT-BOOK OF PHYSIOLOGY. 



associated with right hemiplegia. In agraphic aphasia the patient is unable 

 to communicate his ideas by writing through an inability to execute the 

 necessary movements, though retaining his mental processes. In this form of 

 aphasia the lesion is in the writing area. These two forms of motor aphasia 

 are not infrequently associated. 



Sensor aphasia or amnesia may be either visual or auditory. In visual 

 aphasia or amnesia the patient is unable to recognize a letter or word, printed 

 or written (though capable of seeing other objects), a condition known as 

 letter- or word-blindness. It is usually associated with lesions in the neighbor- 

 hood of the supra-marginal convolution. In auditory aphasia or amnesia 

 the patient cannot understand articulate or vocal speech, though capable of 

 hearing and understanding other sounds, through an inability to distinguish 

 the associations of words and letters a condition known as word-deafness. 

 It is associated with lesions of the auditory area. 



Paraphasia is an inability to recall the proper words to associate with 

 ideas and necessary to their expression. 



Concept aphasia is the inability to recall the names of objects. It is 

 associated with lesions of the cortex of the mid-temporal or third temporal 

 convolution (Mills). This area is known as the concept or naming area. 



Bilateral Representation. Though highly specialized movements, 

 such as those performed by the arms and hands, legs and feet, have their 

 areas of representation on one side of the cerebrum only, and that opposite 

 to the side of the movement, less highly specialized movements, such as the 

 masticatory, phonatory, respiratory and various trunk movements, which 

 require for their performance the cooperation of muscles on both sides of 

 the body, have their areas of representation on both sides of the cerebrum ; 

 the area of either side exciting to action the muscles on both sides of the 

 body. In the case of specialized movements the representation is unilateral; 

 in the case of the more general movements the representation is bilateral. 



Association Centers. The sensor and motor areas to which specific 

 functions have been assigned do not constitute more than one-third of the 

 total cerebral cortex. There yet remain large regions to which it has been 

 impossible to assign specific functions based on physiologic experiments. 

 Three or four such regions separated by the sensor and motor centers are to 

 be recognized on the lateral and mesial aspects of the hemisphere. In Fig. 

 256 the location, extent, and names of these regions are represented. The 

 fibers which are found in these regions belong almost exclusively to the 

 association system, and become medullated at a later period than do the 

 fibers of the projection system; moreover, from the method of their medulliza- 

 tion it would appear that many of these fibers grow out directly from the 

 sensor centers into these regions and become related to the nerve-cells of 

 their convolutions, while others grow out from adjacent as well as distant 

 convolutions. From histologic and pathologic evidence these regions were 

 termed by Flechsig association centers or areas, implying the idea that 

 through the intervention of their cell mechanisms the sense areas are in- 

 directly associated anatomically and physiologically, and together constitute 

 a mechanism by which sensations are associated and elaborated into concrete 

 forms of knowledge or related to definite forms of movement. 



It has been assumed by Flechsig that the frontal association center, from 



