936 THE CENTRAL NERVOUS SYSTEM 



commonly due to a lesion in the left hemisphere alone. The answer to 

 this question is supposed to be partly supplied by the important and 

 curious observation that in left-handed individuals damage to the right 

 inferior frontal convolution may cause aphasia. In the right-handed 

 man the motor areas of the left hemisphere may be supposed to be more 

 highly educated than those of the right hemisphere. The movements 

 of the right side which they initiate or control are stronger and more 

 delicate and precise than those of the left side. It is only necessary to 

 assume that this processs of specialization, of selective training, has 

 been carried on to a still greater extent in the left frontal convolution, 

 that in most men the speech-centre there has taken upon itself the whole, 

 or the greater part, of the labour of clothing ideas in words, leaving to 

 the right centre only its primitive but undeveloped powers. In left- 

 handed persons the speech-centre on the right side may be supposed to 

 share in the general functional development of the right hemisphere. 

 That great capabilities are lying dormant in the right speech-centre of 

 the ordinary right-handed individual is indicated by the fact that after 

 complete destruction of the left inferior frontal convolution the power 

 of speech may be to a considerable extent, though slowly and laboriously 

 regained; and it is said that this second accumulation may be swept 

 away, and without remedy, by a second lesion in the right inferior frontal 

 convolution. But frail is the tenure of life in a person who has twice 

 suffered from such a lesion ; and we do not know whether recovery might 

 not take place to some extent even after destruction of both inferior 

 frontal convolutions, if the patient only lived long enough. 



Recently Marie has reopened the whole question of the relation of 

 aphasia to lesions of the inferior frontal convolution. He believes that 

 the so-called Broca's area has nothing to do with aphasia in the proper 

 sense of the term i.e., it is not a cortical area concerned in ' internal ' 

 speech processes, or in which motor or kinaesthetic ' speech memories ' 

 are stored but simply a ' motor ' area for the movements of articula- 

 tion. He maintains that there is but one form of true aphasia the 

 aphasia of Wernicke which has for its basis a lesion of the so-called 

 zone of Wernicke (the supramarginal and angular gyri, and the posterior 

 portions of the first and second temporal convolutions) . This, according 

 to him, is the true speech-centre. The symptom-complex known as 

 Broca's aphasia, which everybody admits to exist as a distinctly charac- 

 terized clinical condition, is due, he says, to a double lesion. One lesion 

 causes aphemia (loss of the power of co-ordinating the movements 

 needed in the articulation of words without actual paralysis of the 

 muscles), and the other the disturbance of internal speech, and the 

 difficulty of reading and of writing, which constitute the true aphasia. 

 According to Marie, the lesion which causes the aphemia is not even 

 situated in Broca's convolution, but somewhere in a rather badly de- 

 fined region, which he denominates the lenticular zone, since it includes 

 the lenticular as well as the caudate nucleus, in addition to the external 

 and internal capsules and the cortex of the island of Reil. It would be 

 out of place to enter more minutely here upon such controversial 

 matters. The conclusion which emerges most definitely from the dis- 

 cussion is that Broca's localization was based upon a very narrow 

 foundation, and must probably be modified. 



It is generally recognized that in almost all cases of aphasia in which 

 the brain has been studied after death, some lesion of association fibres 

 has been present, and not merely a cortical lesion. Interference with the 

 association fibres causes confusion in the processes of association which 

 are so important in mental activity, and defects of intelligence are there- 

 fore commonly observed in aphasia. 



