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Gray matter correlates of reading fluency deficits: SES matters, IQ does not

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Abstract

Brain correlates of reading ability have been intensely investigated. Most studies have focused on single-word reading and phonological processing, but the brain basis of reading fluency remains poorly explored to date. Here, in a voxel-based morphometry study with 8-year-old children, we compared fluent readers (n = 18; seven boys) with dysfluent readers with normal IQ (n = 18; six boys) and with low IQ (n = 18; ten boys). Relative to dysfluent readers, fluent readers had larger gray matter volume in the right superior temporal gyrus and the two subgroups of dysfluent readers did not differ from each other, as shown in frequentist and Bayesian analyses. Pairwise comparisons showed that dysfluent readers of normal and low IQ did not differ in core reading regions and that both subgroups had less gray matter volume than fluent readers in occipito-temporal, parieto-temporal and fusiform areas. We also examined gray matter volume in matched subgroups of dysfluent readers differing only in socioeconomic status (SES): lower-SES (n = 14; seven boys) vs. higher-SES (n = 14; seven boys). Higher-SES dysfluent readers had larger gray matter volume in the right angular gyrus than their lower-SES peers, and the volume of this cluster correlated positively with lexico-semantic fluency. Age, sex, IQ, and gray matter volume of the right angular cluster explained 68% of the variance in the reading fluency of higher-SES dysfluent readers. In sum, this study shows that gray matter correlates of dysfluent reading are independent of IQ, and suggests that SES modulates areas sub-serving lexico-semantic processes in dysfluent readers—two findings that may be useful to inform language/reading remediation programs.

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Availability of data and material

The data that support the findings from this study are available from the corresponding author upon reasonable request.

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Acknowledgements

We thank the research assistants, school administrators, teachers, parents and, very especially, all the children who took part in the study. We are also grateful to Nadine Gaab for insightful discussions.

Funding

Funded by grants from Bial Foundation (BF 2014/304) and the Portuguese Foundation for Science and Technology (CPUP UID/PSI/00050/2013 and SFRH/BD/99622/2014). MRI-related costs were supported by Unilabs Boavista, Portugal.

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Authors

Contributions

CG, MM, and SLC designed the study. MM collected and analyzed the data. CG and SLC supervised data analysis and AMR contributed to data analysis. MM and SLC wrote the manuscript. All authors read and approved the final version of the manuscript.

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Correspondence to São Luís Castro.

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Conflict of interest

The authors declare they have no conflicts of interest.

Ethics approval

All experimental procedures were approved by the ethics committee of the Faculty of Psychology and Education Sciences, University of Porto (reference number FPCEUP 2015.1.23) and conducted in accordance with the Declaration of Helsinki.

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Written informed consent was obtained from all parents and from local school authorities, and children gave their verbal assent at the start of data collection.

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Martins, M., Reis, A.M., Castro, S.L. et al. Gray matter correlates of reading fluency deficits: SES matters, IQ does not. Brain Struct Funct 226, 2585–2601 (2021). https://doi.org/10.1007/s00429-021-02353-1

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  • DOI: https://doi.org/10.1007/s00429-021-02353-1

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