xi] Considerations wf/awfiiif/ Function 2~>7 



lie, flu' impression is given that, although it is a part found necessary to survival in the 

 course of natural selection, it is yet one which, in man, does not play the important role 

 it once may have held. 



In view of this it is somewhat singular to find that at any rate one anatomist (Spitzka) 

 looks upon a well-grown insula, and one exposed, the latter condition has been regarded 

 hitherto as a sign of degeneration, and I think rightly so, because it is common in the 

 brains of idiots and then due to opercular deficiency, as indications of high development. 



Experimental physiology and pathology are silent on the functions of the insula: in 

 the anthropoid ape it gives no reaction to electrical excitation, and no attempts have been 

 made to ablate it because its surface is traversed by numerous important branches of the 

 middle cerebral artery, and because it lies immediately over important structures which it 

 would be essential to preserve intact if the operation were to be a truthful record of 

 function. 



Varied conclusions have been drawn concerning the effect of destruction of the insula in 

 the human brain, but the most commonly accepted of these is that it harbours a link in the 

 speech mechanism. Dejerine was the first to insist on this, and many others have followed 

 suit. Thus from Pascal's writing we are given to believe that motor aphasia may result 

 from destruction of the left insular cortex alone, and that it is not essential to this 

 disability that the inferior frontal convolution should be included in the obliteration. The 

 majority of authors, however, are not so openly heterodox, only holding that disorders of 

 speech of an incomplete nature may arise ; for instance, paraphasia, loss of the power to 

 read aloud, dulling of speech comprehension, and even alexia and agraphia, are variously 

 mentioned as sequels of lesions supposed to have been confined to the cortex of the insula. 



The cause of the patent want of unanimity among clinical observers on the effects of 

 insular lesions has to my mind been rightly indicated by von Monakow. The Zurich pro- 

 fessor writes " that an unbiassed perusal of recent records of cases of left-sided lesions of 

 the insula fails to suppress the conclusion that ' insular aphasia ' is a mixed form of speech 

 defect, in which to a greater or less extent all the components of speech are involved, and 

 in which signs of motor aphasia will predominate if the lesion be in the anterior division 

 of the insula, and signs of sensory aphasia if in the posterior 1 ." 



Now these are words which harmonise best with the facts brought to light by histology, 

 and since cases can be' referred to in which the insula has been stripped of its cortex 

 without obvious clinical manifestation several cases of the kind have occurred in my own 

 experience I would go further and say that in those recorded cases of insular lesion in 

 which a positive speech disability has arisen, an unobserved involvement of tracts of fibres 

 pertaining to the frontal operculum, on the one hand, or to the transverse gyri of Heschl, 

 on the other, has been at the bottom of the mischief, an anatomical complication which 

 the vascular supply of the part renders extremely likely, and a complication which from 

 a wide anatomical experience of cases of cerebral softening I know to be particularly common. 



1 Wer in unbefangener Weise die Kraukeugeschichten der neueren Falle mit linksseitigen Inselliision durcliliest, 

 der wird sich der Meinung nicht verschliessen kiinnen, dass es sich bei der Inselaphasie fast nur urn eine geinischte 

 Form von Sprachstorung handelt, bei der rnehr oder weniger alle Sprachqualitaten beeintrachtigt sind (" incomplete" 

 Totalaphasie) und bei der, je naehdem der Liision mehr die vorderen oder rnehr die hinteren Abschuitte der Insel 

 ergreift, bald mehr die Erscheinungen der motorischen Aphasie, bald mehr die der sensorischen (aber beide partiell) 

 vorwiegen. 



c 33 



