阅读能力个体差异的神经机制研究进展

The Neural Substrates Underlying the Individual Differences of Reading Abilities

阅读是人脑的高级功能之一,也是现代社会人们生活中不可缺少的一部分。由于文字短暂的进化史,人类缺乏专门的基因和神经模块负责文字加工,阅读需要经过多年的专门学习和系统训练,这一过程也带来了阅读能力的显著个体差异。随着功能影像技术的发展,研究者在阅读的认知神经科学领域取得了较大进展,并逐步揭示了阅读能力的个体差异,特别是正常群体内部个体差异的认知和神经机制。本文首先概述阅读所涉及的基本认知过程及神经机制,然后从脑功能和脑结构方面,综述近年来对阅读能力个体差异的认知神经机制研究的主要发现,并进一步讨论建立个体神经水平差异与阅读能力之间因果关系的几种重要的研究方法及有关成果。文章最后对阅读能力个体差异的未来研究方向提出几点建议。

Reading is an indispensible part of human life in the modem era. Due to the relatively short history of written languages in human evolution, it is generally believed that the human is unlikely to have developed specialized genes or neural cireuitries to process written languages. Probably due to this reason, fluent reading involves years＇ of formal education and training, and there are significant individual differences in reading abilities. With the development of noninvasive functional imaging techniques in the last two decades, researchers have made major progresses in understanding the neural substrates of individual differences in reading abilities. The present paper aims at reviewing the cognitive process and neural mechanisms of reading as well as some of the exciting advances in understanding the neural basis of individual differences. Existing studies have revealed at least three brain regions involved in reading, including the temporooccipital cortex, the temporoparietal cortex and the inferior frontal cortex. Consistent with the dual-route model suggested by the behavioral, neuropsychological, and computational studies, the left supramarginal gyms, posterior superior temporal gyms, and dorsal inferior frontal gyrus are mainly involved in assembled phonology, i.e., the indirect route, which transforms visual words into phonology through grapheme-to-phoneme correspondences （ GPC）. In contrast, the ventral part of the lateral temporal cortex and the inferior frontal gyrus are mainly involved in the addressed phonology, i.e., the direct route, which achieves phonological access via the direct associations between the visual forms of words and their sounds. Furthermore, existing studies have shown that the many neural measures are associated with individual differences in reading abilities, including brain activity levels, gray matter volume, white matter integrity and functional connectivity among multiple brain regions, which is modulated by the characteristics of different writing systems. In particular, increased activity in left-hemisphere middle temporal and inferior frontal gyri and decreased activity in right inferotemporal cortical areas are associated with better reading abilities. Whereas the cortical thickness of the temporoparietal area is positively correlated with the reading of irregular words, the gray matter volume in the left middle frontal gyms is correlated with Chinese word reading. In contrast, the cortical thickness in the left mid-fusiform gyrus was positively correlated with performance on reading abilities of both Chinese characters and English words, suggesting its common role in the reading of different writing systems. Using diffusion tensor imaging （DTI） to measure the white matter integrity indexed by fractional anisotropy （FA）, it has been shown that the FA of left tempoj＇oparietal area, left frontal lobe and corpus callosum was associated with reading ability. Functional connectivity studies further suggested that the connection strength between the left temporoparietal region and the Broca area is positively correlated with reading ability. Finally, resting-state functional connectivity （RSFC） within the reading network has also been linked to reading abilities in native language （L1） and second language （L2）.