ON THE FUNCTIONS OF THE CEREBRUM 329 



probably an approximately equal amount in the case of either 

 of these senses. In the uneducated, loss of hearing produces 

 greater cerebral disability than does loss of sight. 



In all cases of acquired deafness or blindness, however, the 

 following results ensue. On the one hand, the patient suffers a 

 permanent loss of one or both of the important avenues of special 

 sensation, and on the other, all kinds and degrees of structural 

 and functional impairment develop in the cerebrum in conse- 

 quence of the deprivation. Not only does secondary atrophy of 

 the particular afferent fibres to the cerebrum result, but the com- 

 plex associational relations between the special projection area or 

 areas and the rest of the cerebrum are seriously affected. The 

 special sensori-memorial images dependent on the lost sense or 

 senses pass more and more into the sphere of the permanently sub- 

 conscious. The physical bases for the evolution of even the most 

 elementary (already experienced) percepts require readjustment to 

 the altered conditions. Finally, the mechanism for the development 

 of new and the correction and continuation of already experienced 

 percepts, which normally involves the majority of, if not all, the 

 projection or sensory areas of the cerebrum, together with their 

 related memorial spheres, becomes imperfect or " maimed." 



In all these types, therefore, both sensory and also extensive 

 and grave associational deprivations exist ; and the cerebrum, 

 as a machine, is maimed not only in its most stable and earliest 

 acquired regions, namely, in one or more centres of projection 

 or sensory areas, but also throughout its intricate, later evolved, 

 and more important (from the psychic aspect) systems of lower 

 association. 



Sense deprivation is, however, followed, in all, or nearly all, 

 early and congenital cases, and in many acquired cases, by still 

 more serious disturbances of the psychic functions than those 

 already indicated. In the former, imperfect evolution of the 

 higher functions of mind is usual if not invariable ; and in both 

 types dissolution of the centre of higher association, with conse- 

 quent dementia, is of common occurrence. In congenital cases 

 involution of the centre of higher association, with resulting 

 dementia, is eventually incited by the stress of prolonged sense 

 deprivation and the consequent abnormal modes of psychic asso- 

 ciation which result. In other words, the abnormally working 

 psychic machine sooner or later breaks down. 



