Higuchi Hiroki, Iwaki Sunao, Uno Akira
Automotive Human Factors Research Center, National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba, Ibaraki, 305-8566, Japan.
Automotive Human Factors Research Center, National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba, Ibaraki, 305-8566, Japan.
Neurosci Lett. 2020 Apr 1;723:134841. doi: 10.1016/j.neulet.2020.134841. Epub 2020 Feb 17.
Many studies have confirmed a brain dysfunction in people with developmental dyslexia (DD) in certain brain regions, including the left superior temporal gyrus and the left fusiform gyrus. However, the neurobiological substrates in Japanese-speaking people with dyslexia are not fully understood, mostly due to the uniqueness of the orthographic systems. Since a substantial part of the written Japanese includes the logographic Kanji as well as the phonographic Kana systems, the reading disability might be caused not only by a dysfunction in the phonological system, but also by a dysfunction in the visual recognition system. Previous studies reported altered hierarchical visual word form processing in the left occipitotemporal cortex; however, it remains unclear whether the altered hierarchical visual processing is language stimuli-specific. Therefore, we aimed to investigate whether (a) Japanese-speaking individuals with DD exhibit atypical hierarchical visual processing, and if so, (b) whether the altered hierarchical visual processing is language stimuli-specific or not. The present study investigated the brain activation pattern for the hierarchical component of the Kanji characters and object stimuli in typically developing (TD) adolescents and adolescents with DD using functional magnetic resonance imaging. For the Kanji characters, adolescents with DD showed a greater activation in the left occipital gyrus and right occipital fusiform gyrus, and this hyperactivity was also found for pseudo and artificial Kanji characters. These results imply reliance on an early visual system in Kanji reading in Japanese-speaking adolescents with DD. Additionally, we also investigated the brain activity for object stimuli, and adolescents with DD showed a greater activation in the bilateral occipital gyri compared with the TD adolescents. These results imply an altered hierarchical visual processing characterized by overactivation in the early visual areas, which is a not restricted to language stimulus only.
许多研究已证实，发育性阅读障碍（DD）患者在某些脑区存在脑功能障碍，包括左侧颞上回和左侧梭状回。然而，由于书写系统的独特性，说日语的阅读障碍患者的神经生物学基础尚未完全明确。由于书面日语的很大一部分包括表意文字汉字以及表音文字假名系统，阅读障碍可能不仅由语音系统功能障碍引起，还可能由视觉识别系统功能障碍引起。先前的研究报告了左侧枕颞叶皮质中层次化视觉词形加工的改变；然而，尚不清楚这种改变的层次化视觉加工是否具有语言刺激特异性。因此，我们旨在研究：（a）说日语的DD个体是否表现出非典型的层次化视觉加工，如果是，（b）这种改变的层次化视觉加工是否具有语言刺激特异性。本研究使用功能磁共振成像，调查了典型发育（TD）青少年和DD青少年在汉字和物体刺激的层次成分方面的脑激活模式。对于汉字，DD青少年在左侧枕叶回和右侧枕叶梭状回表现出更大的激活，并且这种过度活跃在假汉字和人造汉字中也被发现。这些结果表明，说日语的DD青少年在阅读汉字时依赖早期视觉系统。此外，我们还研究了物体刺激的脑活动，与TD青少年相比，DD青少年在双侧枕叶回表现出更大的激活。这些结果意味着层次化视觉加工发生了改变，其特征是早期视觉区域过度激活，且不仅限于语言刺激。
