Separating The Influences Of Late Talking And Dyslexia On Brain Structure

Being a late talker constitutes a risk factor for later neurodevelopmental disorders; however, its neurobiological basis remains unexplored. We aimed to determine the unique and mutual correlates of late talking and developmental dyslexia on brain structure and behavioral outcomes in a large sample of 8- to 10-year-old children in a between-groups design (N = 120). Brain structure was examined using voxel-based morphometry (to measure gray matter volume) and surface-based morphometry (to measure gray matter volume, cortical thickness, surface area, and curvature of the cortex). Behaviorally, late talking and dyslexia are independently connected to language and literacy skills, and late talkers have difficulties in grammar, phonological awareness, and reading accuracy. Children with dyslexia show impairments in all of the above, as well as in vocabulary, spelling, reading speed, and rapid automatized naming. Neuroanatomically, dyslexia is related to lower total intracranial volume and total surface area. Late talking is related to reduced cortical thickness in the left posterior cingulate gyrus and the right superior temporal gyrus, which are structures belonging to the dorsal speech articulatory-phonetic perception system. Finally, a cumulative effect of late talking and dyslexia was found on the left fusiform gray matter volume. This might explain inconsistencies in previous neuroanatomical studies of dyslexia.