| Estimates of the number of people with developmental dyslexia range from 3% to 20% of the population. However, even though dyslexia is the most common kind of learning disability, after a century of study, there is still no agreement on the definition, subtypes, and characteristics of dyslexia. New technology, such as magnetic resonance imaging (MRI) now permits in vivo investigation of the brains of dyslexics that may lead to clearer definitions, establishment of characteristics, and early or more definite diagnosis, thus improving not only future research, but also detection and treatment of this pervasive learning disability.; It is widely accepted that the brain is anatomically and functionally asymmetrical. This anatomical asymmetry is highly correlated with language dominance. Researchers speculate that anomalies of this anatomical asymmetry may be related to disruption in the development of the brain and, thus, may contribute to language processing disorders, including dyslexia.; This study investigated cognitive, behavioral, and anatomic correlates of dyslexia. Sixteen dyslexics and sixteen controls, matched for age, education, sex, and handedness, were given a battery of cognitive, reading and language tests, and a volumetric MRI brain scan. Analysis of performance on three reading measures (phonology, orthography, and semantics) indicated five clinical subgroups. Six gross lobar regions were measured in each hemisphere. The five subgroups differed significantly on every cognitive and behavioral measure. On asymmetry quotients dyslexia subgroups were significantly different (p = .043). Examination of the percentage of TBV of each structure revealed that Controls and Dyslexics were significantly different (p = .018). Dyslexics had a larger percentage of brain volume than did the Controls devoted to: Total Prefrontal (p = .003, 9.30% larger) and Superior Prefrontal (p = .004, 11.48% larger). A Pearson correlation was performed to investigate whether a relationship existed between behavioral measures and either volumes of Total Prefrontal and Total Occipital regions or asymmetry quotients. Although results must be interpreted cautiously because of the possibility of Type 1 error, a significant positive relationship between the left Total Occipital and Word Identification performance existed (R = .452, p = .045). |
