Learning to associate written letters with speech sounds is crucial for the initial phase of acquiring reading skills. However, little is known about the cortical reorganization for supporting letter-speech sound learning, particularly the brain dynamics during the learning of grapheme-phoneme associations. In the present study, we trained 30 Finnish participants (mean age: 24.33 years, SD: 3.50 years) to associate novel foreign letters with familiar Finnish speech sounds on two consecutive days (first day ∼ 50 minutes; second day ∼ 25 minutes), while neural activity was measured using magnetoencephalography (MEG). Two sets of audiovisual stimuli were used for the training in which the grapheme-phoneme association in one set (Learnable) could be learned based on the different learning cues provided, but not in the other set (Control). The learning progress was tracked at a trial-by-trial basis and used to segment different learning stages for the MEG source analysis. The learning-related changes were examined by comparing the brain responses to Learnable and Control uni/multi-sensory stimuli, as well as the brain responses to learning cues at different learning stages over the two days. We found dynamic changes in brain responses related to multi-sensory processing when grapheme-phoneme associations were learned. Further, changes were observed in the brain responses to the novel letters during the learning process. We also found that some of these learning effects were observed only after memory consolidation the following day. Overall, the learning process modulated the activity in a large network of brain regions, including the superior temporal cortex and the dorsal (parietal) pathway. Most interestingly, middle- and inferior- temporal regions were engaged during multi-sensory memory encoding after the cross-modal relationship was extracted from the learning cues. Our findings highlight the brain dynamics and plasticity related to the learning of letter-speech sound associations and provide a more refined model of grapheme-phoneme learning in reading acquisition.

中文翻译：

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成人学习字素-音素关联期间大脑活动的快速变化

学习将书面字母与语音联系起来对于获得阅读技能的初始阶段至关重要。然而，对于支持字母-语音声音学习的皮层重组知之甚少，尤其是在学习字素-音素关联过程中的大脑动力学。在本研究中，我们训练了 30 名芬兰参与者（平均年龄：24.33 岁，SD：3.50 岁）连续两天（第一天 ~ 50 分钟；第二天 ~ 25 分钟）将新的外文字母与熟悉的芬兰语语音联系起来，而神经活动是使用脑磁图（MEG）测量的。两组视听刺激用于训练，其中一组（可学习）中的字素-音素关联可以根据提供的不同学习线索学习，但不能在另一组（控制）中学习。学习进度在逐个试验的基础上进行跟踪，并用于对 MEG 源分析的不同学习阶段进行细分。通过比较大脑对可学习和控制单/多感官刺激的反应，以及大脑对两天内不同学习阶段的学习线索的反应，来检查与学习相关的变化。当学习字素-音素关联时，我们发现与多感官处理相关的大脑反应的动态变化。此外，在学习过程中观察到大脑对新字母的反应发生了变化。我们还发现，只有在第二天的记忆巩固后才能观察到其中一些学习效果。总体而言，学习过程调节了大脑区域大型网络中的活动，包括上颞叶皮层和背侧（顶叶）通路。最有趣的是，在从学习线索中提取跨模态关系后，在多感官记忆编码过程中参与了中颞区和下颞区。我们的研究结果突出了与学习字母-语音声音关联相关的大脑动力学和可塑性，并提供了一个更精细的阅读习得中的字素-音素学习模型。