OnsetDys

Speech comprehension has been proposed to critically rely on oscillatory cortical tracking, that is, phase alignment of neural oscillations to the slow temporal modulations (envelope) of speech. Speech-brain entrainment is readjusted over time as transient events (edges) in speech lead to speech-brain phase realignment. Auditory behavioral research suggests that phonological deficits in dyslexia are linked to difficulty in discriminating speech edges. Importantly, research to date has not specifically examined neural responses to speech edges in dyslexia. In the present study, we used MEG to record brain activity from normal and dyslexic readers while they listened to speech. We computed phase locking values (PLVs) to evaluate phase entrainment between neural oscillations and the speech envelope time-locked to edge onsets. In both groups, we observed that edge onsets induced phase resets in the auditory oscillations tracking speech, thereby enhancing their entrainment to speech. Importantly, dyslexic readers showed weaker PLVs compared to normal readers in left auditory regions from ~0.15 s to ~0.65 s after edge onset. Our results indicate that the neural mechanism that adapts cortical entrainment to the speech envelope is impaired in dyslexia. These findings here are consistent with the temporal sampling theory of developmental dyslexia.言语理解被认为关键依赖于皮层振荡追踪（oscillatory cortical tracking），即神经振荡（neural oscillations）与言语慢时间调制（包络）的相位对齐。言语-脑锁相（speech-brain entrainment）会随时间动态调整，因为言语中的瞬态事件（言语边界）会引发言语-脑相位重对齐（phase realignment）。听觉行为研究表明，发展性阅读障碍（developmental dyslexia）患者的语音缺陷与言语边界辨别困难存在关联。值得注意的是，迄今尚无研究专门考察阅读障碍群体对言语边界的神经响应。本研究采用脑磁图（Magnetoencephalography, MEG）记录正常阅读者与阅读障碍者聆听言语时的脑活动，并计算相位锁定值（phase locking value, PLV），以评估神经振荡与锁时于言语边界起始点的言语包络之间的相位锁相程度。结果显示，两组被试参与言语追踪的听觉振荡均在边界起始点诱发了相位重置，进而增强了其对言语的相位锁相。关键在于，在边界起始后的约0.15秒至0.65秒区间内，阅读障碍组左侧听觉皮层的PLV显著低于正常阅读组。本研究结果表明，将皮层锁相适配于言语包络的神经机制在阅读障碍群体中存在损伤。上述发现与发展性阅读障碍的时间采样理论相一致。