Dejerine's Discovery of the role of the left angular gyrus as the center of reading and writing in 1891 and in 1892 was the beginning of a new field of neuroscience, which I called “Neurogrammatology.” His diagram of neuronal circuit of reading and writing was later revised by Geschwind in 1965 and has been widely accepted. Japanese neuropsychologists, however, have since long been puzzled about the problem of alexia and agraphia of “kanji” which can hardly be explained by Dejerine's diagram. Japanese language has two different types of letters; “kana” (phonogram) and “kanji” (morphogram). The reading and writing disturbances of “kana” in focal brain damage can be very well explained by Dejerine's diagram, but as to “kanji”, the left medial occipital lesion which usually causes alexia without agraphia in western language cause alexia with agraphia of “kanji”. On the other hand, a focal lesion of the left angular gyrus causes only agraphia for “kanji”. As the third type of alexia in Japanese language, we have found cases of alexia and agraphia affecting only “kanji” caused by lesions of the posterior-inferior part of left temporal lobe. Basing upon these clinical observations, we proposed a dual neuronal circuit model of reading and writing in Japanese language .
Then we did PET scan activation studies on the normal subjects and found the two cortical areas of the left cerebral hemisphere which are indispensable for reading: area 37 responsible for semantic reading and area 19 just behind the angular gyrus for phonological reading. The phonological reading circuit is the main stream of reading “kana” and the semantic circuit is requisite for reading “kanji” . As a result, we proposed a new diagram of dual neuronal circuits of reading process of Japanese language as shown in Figure 1 .Le texte complet de cet article est disponible en PDF.
|☆|| Meeting abstract Jules Dejerine: bilingual publication (English version).