Verbal short-term memory in developmental dyslexia: the role of the temporoparietal area

Developmental dyslexia (DD) is characterized by difficulties in reading due to a core impairment in phonological awareness. The clinical manifestation also includes a more general auditory verbal short-term memory (vSTM) dysfunction. However, little is known about the behavioral and brain basis of vSTM deficits in children with dyslexia, failing to understand factors that may account for co-occurrence of deficits or substantial heterogeneity within DD. The study identified deficiencies in vSTM within a large cohort of children with DD and examined their neuroanatomical alterations. 81 children with DD and 17 typically developing (TD) children completed an experimental repetition task, which evaluated two components of phrases, namely length (6 and 9 syllable phrases) and meaning (more or less meaningful phrases). In addition, a battery of reading, phonological, and verbal memory tasks was administered to DD children, which were used for preliminary examination of different subtypes of dyslexia. Structural brain T1-weighted MR images were analyzed to investigate the neural correlates of vSTM deficit in children with DD. Behavioral results showed that children with DD had impaired phrase repetition compared to TD, especially when repeating long and non-meaningful phrases. Crucially, lower repetition performance on long or non-meaningful phrases was associated with greater cortical thickness in the left temporoparietal area in children with DD. Finally, two distinct DD subtypes with disproportional deficits in phonology and vSTM were identified, demonstrating different repetition patterns. Those with primary vSTM deficits showed lower repetition performance and decreased cortical thickness in the left precentral gyrus compared to those with primary phonological processing deficits. This study covers topics central to understanding neurocognitive diversity in dyslexia and may suggest that verbal memory ability may be an important area for future intervention.