Dyslexie und ihre neuronale Signatur

Dyslexia is one of the most common specific developmental disorders. Dyslexics exhibit a profound and persistent reading disorder, frequently accompanied by spelling difficulties. Current theories assume dyslexia to be caused by phonological, auditory or visual deficits, or by deficits in rapid naming and automatisation. Due to the familial risk of this developmental disorder, a genetic origin is being discussed as well. Post-mortem studies revealed ectopias and dysplasias in the language-associated perisylvian cortex of dyslexics. Whether the plana temporalia are symmetrically distributed or asymmetric as in non-dyslexics is still the subject of controversial discussion. In neurofunctional studies dyslexics showed underactivated left-hemispheric parieto-temporal and occipito-temporal structures. However, there was an overactivation of the left and right inferior frontal gyri and of the right-hemispheric occipito-temporal structures. Various eye-tracking studies revealed longer fixations, shorter saccades and more frequent regressions in dyslexics than in normal readers. Neuroanatomic and neurophysiological results are still inconsistent, which is certainly due to the diversity of methodological approaches, to age differences between the participants, small sample sizes, heterogeneous definitions of dyslexia, and to the phenotypic heterogeneity of the disorder itself.