Lizarazu, M. . 1 , Lallier, M. 1 , Bourguignon, M. 1 , Carreiras, M. 1, 2 & Molinaro, N. 1, 2
1 BCBL
2 Ikerbasque
Delta, theta and gamma neural oscillations in several brain regions are specifically entrained by the quasi-rhythmic component of the speech envelope. During speech processing, sharp large-amplitude transients (edges) in the speech envelope reset the phase of low-frequency (<8Hz) oscillations in auditory cortices. These resets improve the neural entrainment and enable efficient speech sampling. Numerous studies propose that phonological difficulties in dyslexia arise in part from impaired neural entrainment to low-frequency amplitude modulation during continuous speech. However, there are no previous studies showing how dyslexic readers deal with the low-frequency phase resetting mechanism observed in normal readers around the speech edges. Here, we analyzed MEG data from 20 dyslexic and 20 normal readers while hearing continuous speech. After low-pass filtering MEG data (<8Hz), we extracted trials time-locked to the onsets of the speech edges (from -0.4 to 1 s). Then, Phase-Locking-Value (PLV) across trials was calculated for each participant and sensor. The presence of speech edges induces a synchronization enhancement in bilateral fronto-temporal sensors in normal and dyslexic readers. Interestingly, dyslexic readers present weaker PLVs compared to normal readers after the onset (0.25 - 0.35 s) in left fronto-temporal sensors. Atypical low-frequency phase resetting affects neural entrainment to rhythmic components of the speech envelope and might contribute to the phonological deficit observed in dyslexia.