894 



THE NERVOUS SYSTEM 



(5) The gustatory area is supposed to comprise the anterior portion of the fusiform gyrus 

 and the zone (motor portion) about the anterior extremity of the inferior temporal sulcus. 



(6) The assocaition areas. — The relatively large areas allotted at present to the so-called 

 higher psychic activities are indicated in fig. 703. The great relative extent of these is one of 

 the characteristics of the human brain. They probably merely represent the portions of the 

 cortex of which httle is known, and may eventually be subdivided into more specific areas. 

 They are considered to be connected with the structures below by fewer projection fibres than 

 are the recognised areas named above, while, on the other hand, they are rich in association 

 fibres. By means of the latter they are in intimate connection with the specific areas and have 

 abundant means of correlating and exercising a controlhng influence upon the functions of these 

 areas. According to Flechsig, they consist of — (1) a parietal association area, comprising that 

 part of the parietal cortex between the somsesthetic area and the visual area; (2) an occipito- 

 temporal association area, including the unspecified portions of the temporal lobe and the ad- 

 joining portion of the occipital lobe not included in the visual area; (3) a frontal association 

 area, including all the frontal lobe anterior to the somesthetic and olfactory area. In the 

 folds of the inferior parietal lobule of the parietal association area such intellectual activities 

 as the optic discrimination of words, letters, numbers, and objects generally are supposed to 



Fig. 704. 



-Convex Surface of left Cerebral Hemisphere with Diagrammatic Presenta- 

 tion OF the Areas Suggested as Concerned with Speech. 



Area for coordination of muscles producing speech 

 /* (Broca's convolution) 



' Motor area for hand (graphic) 



Motor area for mouth and larynx 



Auditory word 



images 



Visual word 

 images 



.Portion of 

 visual area 



Auditory area 



Word understanding 



take place, while the superior parietal lobule continued into the posterior part of the prsecuneus 

 is the general region for the perception of form and solidity of objects — the stereognostic centre. 



The insula is suggested as the area in which auditory, olfactory and gustatory impulses 

 are associated with the motor areas beginning in the operculum dorso-laterally adjacent to it. 



Observations of symptoms and the position of lesions accompanying them have made it 

 possible to arrive at some trustworthy conclusions regarding the cortical areas controlling 

 speech. Broca announced in 1861 that the inferior frontal gyrus of the left hemisphere was 

 peculiarly concerned with speech. This area was later confined to the posterior end or opercular 

 portion of this gyrus and the name "Broca's Convolution" was given it. It is now known that 

 Broca's convolution and the adjacent portion of the triangular part of the inferior frontal gyrus 

 as well comprise the motor area or emissive speech area — the area especially devoted to the 

 control of that coordinated action of the muscles concerned which makes possible articulate 

 speech. . Pati ents in whom this area is impaired are unable to give utterance to words though 

 they may understand them both written and spoken, and though they may give utterance toj 

 sound. This inability is known as motor aphasia. Results of observed lesions have further 

 shown that the area in which the auditory images of words are retained (word memories) com- 

 prises the posterior end of the superior temporal gyrus and the adjoining portion of the supra- 

 marginal gyrus. Injury to this area is accompanied by inability to recognise spoken words 

 although the patient hears them and may recognise and understand written words, a phe- 

 nomenon known as "word-deafness" or sensory aphasia. This area may be considered as 

 continuous with the superior portion of the posterior end of the middle temporal gyrus which 

 has been suggested as the area of "word-understanding," or "lalognosis." On the other 

 hand, the area in which visual images of words arc retained is located as the angular gy rus. 

 Injury to this results in an inability to recogni.se printed or written words although the patient 



