How many functional brains in developmental dyslexia? When the history of language delay makes the difference

Clinical manifestations of developmental dyslexia (DD) are greatly variable, suggesting complex underlying mechanisms. It was recently advanced that the characteristics of DD in Italian, a language with shallow orthography, are influenced by a positive history for language delay.

We explored this hypothesis by studying in Italian individuals with DD (i) the brain representation of phonological processing with functional magnetic resonance imaging and (ii) the correlation between the patterns of activation and the presence/absence of previous language delay.

Thirteen individuals with DD and 13 controls participated in the functional magnetic resonance imaging experiment consisting of a rhyme-generation task.

Individuals with DD showed a reduced activation of phonological processing areas of the left hemisphere, such as the middle frontal gyrus, the precuneus, and the inferior parietal lobule, and in particular the superior temporal gyrus. Furthermore, patients with a history of language delay had reduced activation in the left inferior and medial frontal gyrus, that was associated with worse reading and phonological accuracy than patients with normal language development.

Neurofunctional profiles of Italian individuals with DD are correlated to the history of language delay, suggesting that the relatively better behavioral profiles observed in individuals without a history of language delay are associated with a major activation of frontal networks normally involved in phonological working memory.