Studies of the Brain-Behavioral Relationships of Anatomy and Reading Ability
Torre, Gabrielle-Ann A.
Eden, Guinevere F.
The functional brain bases of reading have been thoroughly studied in children, adolescents, and adults. Yet, the relationships between neuroanatomical measures and reading ability at these ages are far less understood. This dissertation presents two studies designed to test how cortical anatomy is related to individual differences in single real word reading ability in a large sample of typically developing children, adolescents, and adults from the NIH Study of Normal Pediatric Development. First, we asked whether the brain regions that are shown to have less gray matter volume (GMV) in dyslexia have a linear relationship with reading ability in typical readers. We found no such relationships in the eight regions interrogated across the entire sample, either when employing correlations or a multiple regression model. Dividing the sample into three age groups revealed correlations in the oldest group (ages 15-22) in the right superior temporal gyrus (STG) and left fusiform gyrus (FG) with reading ability, but both were sex-specific. Next, we investigated cortical thickness (CT) and surface area (SA) to test their relationships with reading and math ability, as well as whether the relationships for these academic skills overlap. Multiple regressions in the entire sample (focused on fourteen regions representing the areas known to subserve reading or math) revealed that word reading ability, age, and their interactions contributed unique variance to CT of the left supramarginal gyrus (SMG) and left intraparietal sulcus (IPS); also, the interaction between reading and age contributed unique variance to CT of the left FG. Dividing the sample into three age groups to test correlations revealed that CT of the left SMG and FG were positively correlated with single word reading only in the oldest age group. In both approaches, there were no findings for math ability or SA. Altogether, these findings converge on two important findings: First, in a representative sample of typical readers, there are no linear relationships between measures of brain anatomy and real word reading ability. This suggests that dyslexia does not represent the lower-end tail of a normal distribution. Second, greater age/experience brings about a relationship between brain anatomy (GMV and CT) and single real word reading ability. In sum, these findings shed important insights into the brain-behavioral relationships for reading.
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