A meta-analysis of brain abnormalities in Chinese dyslexic reading



Developmental dyslexia is a neurocognitive disorder characterized by a severe and persistent impairment in the acquisition of literacy. During the last two decades, there was significant advance in the neurobiological understanding of developmental dyslexia. Across many languages and writing systems, neurocognitive research has identified brain regions crucially involved in typical and dyslexic reading using functional magnetic resonance imaging (fMRI), electroencephalography (EEG), magnetoencephalography (MEG), and positron emission tomography (PET). Qualitative narrative reviews and quantitative objective meta-analyses of neuroimaging studies have converged on a generally accepted functional neuroanatomical model of developmental dyslexia. Specifically, altered brain activation in dyslexic readers was consistently reported in left posterior temporo-parietal (TP) cortex (middle temporal gyrus, superior temporal gyrus, supramarginal gyrus and angular gyrus), left occipito-temporal (OT) cortex (inferior temporal gyrus and fusiform gyrus), and left frontal cortex (inferior frontal gyrus and precentral gyrus).
Of specific importance for our neurobiological understanding of developmental dyslexia is the investigation of the brain-behavior relationships across languages and writing systems. The planned project aims at providing such an investigation by means of a meta-analysis of brain abnormalities in Chinese dyslexic reading. Specifically, we will use coordinate-based meta-analysis in order to objectively quantify brain activation abnormalities in Chinese dyslexic readers. Therefore, we will synthesize foci of under- and overactivation in Chinese dyslexic readers relative to Chinese typical readers reported in published fMRI and PET studies. At the moment, there are about 30 existing studies principally eligible for inclusion in the meta-analysis, which is a reasonable number for robust meta-analytic quantification.
The existing evidence, up to now, suggests that the functional neuroanatomy of developmental dyslexia is similar across languages and writing systems, with some orthography-specific peculiarities. Specifically, underactivation (in dyslexic readers relative to typical readers) in core regions of the left hemisphere reading network including OT, TP, and IFG regions in response to reading or reading-related tasks seems to be a universal signature of developmental dyslexia. Therefore, we expect underactivation of the core network also in Chinese dyslexic reading. Consequently, these core regions are language-universal prime candidates to be targeted by intervention programs.
Across alphabetic writing systems, the depth of the orthography has an influence on the relative importance of different underlying cognitive processes required for fluent reading, and, accordingly, on the degree and spatial extent of brain activation clusters of typical readers. Consequently, the brain dysfunctions of dyslexic readers are associated with an emphasis on different parts of the core reading network, reflected in stronger or weaker under- and overactivation relative to typical readers depending on orthographic depth (Martin et al., 2016; Richlan, 2014). In the case of the logographic Chinese writing system, a crucial role is assigned to the left MFG, possibly subserving working memory processes required for the successful recognition of written characters. In line with existing evidence, we expect Chinese dyslexic reading to be associated with underactivation of the left MFG.
Cross-linguistic comparisons have proven to provide extremely valuable information on the neurobiology of reading and developmental dyslexia. The focus, up to now, was largely on the comparison of dysfunctions in the form of reading-related dyslexic underactivation relative to typical readers. In contrast, the patterns of dyslexic overactivation relative to typical readers were hardly compared across languages and writing systems. This is probably because there is larger inter-individual variability with respect to overactivation compared with underactivation in developmental dyslexia and, in turn, less consistency across studies (and activation tasks). The overactivation patterns, however, may be informative on potential compensatory mechanisms supporting language-universal remediation strategies. First evidence (Cao et al., 2017; Hancock et al., 2017; Martin et al., 2016) points to an important role of the precentral gyrus subserving neural compensation across languages and writing systems. Since we will include foci of overactivation in our coordinate-based meta-analysis, the planned project is suitable to shed more light on this issue.
Tatsächlicher Beginn/ -es Ende13/08/2131/12/22