APHASIA, a-fi'zhi-a, the designation of a disorder of speech due to disturbance of the brain mechanism independently of any muscu lar defect. This mechanism is complex and is usually divisible into two parts, the receptive or sensory and emissive or motor. To the former belong those parts of the brain that store concepts of spoken words or written words; to the latter those parts concerned in co-ordinate speech or In writing. Thus aphasia may be of at least four different and independ ent types. Frequently it is a combination of one or more of these. The zones in the brain that store intellectual auditory impressions are located in the first temporal convolution. Any injury to this part of the speech mechanism may produce auditory aphasia or word deaf ness. A patient thus affected is able to hear words and to speak, but he does not compre hend what is being said to him. He has lost his hearing word memories, and his own lan guage is as a foreign language that he hears but cannot comprehend. In an analogous man ner, if there is disorder of the occipital lobes, about the calcarine fissure, or of its related fibre tracts, a patient may have visual aphasia or word blindness. His own written language might as well be in Arabic, for he has lost all his memory of written words. These types of aphasia are much less common than the true type of motor aphasia or aphemia. In this the trouble is in the third left frontal convolution in the brain, Brocas convolution, or its related fibre tracts, and a patient thus affected has lost the power to say the words he desires to say. He is perfectly able to talk, may repeat words, but knowing in his mind precisely what he wishes to say is unable to express it, not be cause of any failure of the muscular power of the tongue to articulate, but because of the defect in the storage centre or its fibre paths for motor speech. A fourth type is agraphia,
in which the affected patient is unable to write with understanding the words with which he is familiar. The site of the lesion here is un determined. It usually accompanies motor aphasia. There are also forms of combined aphasia in which the fibre tracts from one centre to another are cut off. These make para phasias, and their symptoms are extremely complex. Aphasia in its various forms may differ very widely in its extent. It may be very slight or very profound. It may be temporary or permanent, depending on the nature and extent of the brain injury. Aphasia is most frequently a symptom of haemorrhage from some artery or arteries in the brain; it may be caused by the growth of a tumor or result from an injury. The treatment is that of the causing disease. In the sensory aphasias edu cation of the non-affected areas is of great importance. If there is word blindness, the memory for spoken symbols should be culti vated, and vice-versa.
Baldwin, 'Dictionary of Philosophy and Psychology,' article entitled Speech and Its Defects" (1903); Bastian, 'Aphasia and Other Speech Defects' (1898) ; Elder, 'Aphasia and the Cerebral Speech Mechanism' (with bibliography, 1897) ; Gould and Pyle, 'Cyclopedia of Medicine and Sur ge:7' (Philadelphia 1912) ; Jelliffe and White, 'Diseases of Nervous System' (1917).