Functional neuroanatomy of Japanese writing systems

要旨

Background: Most of the brain imaging studies to date have addressed the skill of writing as a paradigm to examine the neural correlates for complex limb movements. Although these data have enriched our view of the functional organization of the brain for motor aspects of writing, there have been few attempts to discuss their relevance to aphasiology research. Aims: The aim of the present article is two-fold. First, we examined neuroimaging data on writing to provide an overview of the neurophysiological basis subserving the motor aspects of the skill. Second, while taking into consideration the framework provided by these data, we reviewed lesion and functional imaging studies of Japanese to discuss the possible difference in neural correlates that has been assumed for its two orthographic systems, kanji (logogram) and kana (syllabogram). Main Contributions: The fronto-parietal cortical circuit linking the premotor with posterior parietal areas in the left hemisphere seems to constitute a basic neural substrate for the motor act of writing. Lesion and imaging data with Japanese suggest that writing of kana utilises these structures in conjunction with the left perisylvian area for spoken language. In contrast, writing of kanji shares this network for the later phase of motor execution, but recruits the left basal temporal area as an additional device for the generation of motor output. Conclusions: The execution of writing, irrespective of the script type, is achieved by common brain structures used for a wide range of limb movements. Writing of kanji seems to differ from that of kana only in that the former needs the retrieval of visuospatial information of characters as an additional cognitive operation. This difference does not necessarily imply that the two kinds of script have distinct neural substrates.

主題