Learning letter-speech sound (LS) association is the first and critical step for reading development. At the neural level, LS integration is related to left superior temporal cortex (STC) activity and its disruption was previously observed in dyslexia. Whether this disruption is a cause of reading impairment or a consequence of decreased exposure to print remains unclear. We compared brain activity for letters, speech sounds and LS integration in emerging readers with (FHD+, N=50) and without (FHD-, N=35) familial history of dyslexia, out of whom 17 developed dyslexia two years later.
FHD+ and FHD- groups showed opposite pattern of activation in left STC – in FHD- children it was higher for incongruent compared to congruent, whereas in FHD+ it was higher for congruent LS pairs. Higher activation to congruent LS pairs was also characteristic of future dyslexics. The magnitude of incongruency effect in left STC was positively related to early reading skills, but only in FHD- children and (retrospectively in) typical readers. We conclude that neural disruption in LS integration can be identified at initial stages of reading acquisition, suggesting a causal involvement in dyslexia.