The anatomy of the nervous system, from the standpoint of development and function . ch areas the auditory, visual, and olfa< tory impulses impinge, and less accurately that in which the thalamic general bodily sensibility, terminates. Destruction of these areascauses impairment or loss of the corresponding sensations with reference to theopposite side of the body or the opposite half of the field of vision. Total lossof cutaneous sensibility even within circumscribed areas never results from cor-tical lesions; and it seems probable that the thalamic centers are in thems
The anatomy of the nervous system, from the standpoint of development and function . ch areas the auditory, visual, and olfa< tory impulses impinge, and less accurately that in which the thalamic general bodily sensibility, terminates. Destruction of these areascauses impairment or loss of the corresponding sensations with reference to theopposite side of the body or the opposite half of the field of vision. Total lossof cutaneous sensibility even within circumscribed areas never results from cor-tical lesions; and it seems probable that the thalamic centers are in themselvessufficient for a certain low grade, non-discriminative consciousness or awarenessof cutaneous stimulation. This is particularly true of painful sensations, whichseem to be for the most part of thalamic origin (Head, 1918). Furthermore,the various parts of the cerebral cortex are so intimately linked together by as-sociation fibers that when afferent impulses reach a given projection center theymust not only activate this center, but be propagated to other parts of the cortex. Motor speech ccnttr Auditory speech center Visual sPeech ccnlcrFig. 225.—The cortical areas especially concerned with language. as well. In view of these facts it is best to express the known facts of corticallocalization in terms of the relation of particular areas to the known projectionfiber systems. Aphasia.—Some idea of the significance of the so-called association centersmay be obtained from a study of the group of speech defects included under theterm aphasia. In right-handed individuals these result from lesions in theleft hemisphere. Destruction of the triangular and opercular portions of theinferior frontal gyrus usually causes loss of ability to carry out the coordinatedmovements required in speaking, but does not impair the ability to move thetongue or lips (Fig. 225). This defect is known as motor aphasia. Brocascenter, as this particular part of the cortex is sometimes called, is loc
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectnervoussystem, bookye
