Dyslexia and brain morphology: Relationships between neuroanatomical variation and neurolinguistic tasks

Abstract

This study, in contrast to previous studies of morphological differences between dyslexics and normals, examined the relationship between performance on neurolinguistic tasks and measures of brain morphology in 10 dyslexics, 10 clinic-comparison Attention Deficit Disorder/Hyperactive (ADD/H) children, and 10 normal control children. The dyslexics were found to be significantly deficient on automatic and confrontational naming, word attack (nonword reading), and passage comprehension tasks as compared to the ADD/H and normal groups. Relationships between differences in neurolinguistic function and variations in brain morphology were found only in the dyslexic group. Smaller right frontal width appeared to be related to significantly poorer passage comprehension for the dylexic group. In addition, reversed asymmetry or symmetrical anterior area (L⩾R) was also related to significantly poorer word attack skills for the dyslexic group. These effects were not present for the other two groups. Reversed or symmetrical planum temporale length (L⩽R), despite group membership, was significantly related to lower verbal comprehension on the WISC-R, indicating that the planum temporale are involved in language processing. The results of this study demonstrated that the neurolinguistic functional deficits in dyslexics may be related to significant structural differences in the frontal and temporal lobes. Further, consistent with neurobiological theory, the inclusion of the clinic comparison (ADD/H) children suggests that these structure-function relationships may be unique to the dyslexic syndrome.