Abstract
Brain abnormalities in the reading network have been repeatedly reported in individuals with developmental dyslexia (DD); however, it is still not totally understood where the structural and functional abnormalities are consistent/inconsistent across languages. In the current multimodal meta-analysis, we found convergent structural and functional alterations in the left superior temporal gyrus across languages, suggesting a neural signature of DD. We found greater reduction in grey matter volume and brain activation in the left inferior frontal gyrus in morpho-syllabic languages (e.g. Chinese) than in alphabetic languages, and greater reduction in brain activation in the left middle temporal gyrus and fusiform gyrus in alphabetic languages than in morpho-syllabic languages. These language differences are explained as consequences of being DD while learning a specific language. In addition, we also found brain regions that showed increased grey matter volume and brain activation, presumably suggesting compensations and brain regions that showed inconsistent alterations in brain structure and function. Our study provides important insights about the etiology of DD from a cross-linguistic perspective with considerations of consistency/inconsistency between structural and functional alterations.
Highlights
Individuals with developmental dyslexia (DD) encounter difficulty in learning to read even with normal intelligence and adequate educational guidance (Peterson& Pennington, 2012)
Multiple deficits have been identified to be associated with DD (Ring & Black, 2018), among which phonological deficit has been well-documented across languages (Gu & Bi, 2020; Snowling & Melby-Lervag, 2016)
In the direct comparison between alphabetic and morpho-syllabic languages, we found greater hypoactivation in DD in alphabetic languages than in morpho-syllabic languages in the left middle temporal gyrus (MTG), right superior temporal gyrus (STG) and left fusiform gyrus, which was verified in the well-matched confirmation analysis, suggesting that the language difference should not be due to differences in age, tasks, and number of 434 studies in the two language groups
Summary
Individuals with developmental dyslexia (DD) encounter difficulty in learning to read even with normal intelligence and adequate educational guidance To identify the common language differences between the structural and functional studies, we conducted a conjunction analysis between the language differences in structural studies and functional studies This produced an overlap of 377 voxels in the left IFG opercular part, with a peak at (-52, 10, 24), indicating greater reduction of both GMV and brain activation in morpho-syllabic languages than in alphabetic languages (Figure 2C). Studies and the structural studies, which was greater reduction of brain activation and GMV in morpho-syllabic languages than in alphabetic languages in the left IFG opercular part (-54, 10, 20) with a cluster of 273 voxels (Figure 2-figure supplement 1C), which is consistent with the original result. Conjunction analysis between the original results and the current functional differences between English and Chinese showed consistent greater reduction of brain activation in DD in morpho-syllabic languages/Chinese than in alphabetic languages/English in the left dorsal IFG (-52, 6, 16) with a cluster size of. Altered myelination and neurotransmitters may contribute to the structural and functional alterations related to basal ganglia (Nord et al, 2019; Wichmann & DeLong, 2012)
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