Department of Psychology, University of York, York, UK.
York Neuroimaging Centre, Innovation Way, York, UK.
Hum Brain Mapp. 2024 Feb 1;45(2):e26607. doi: 10.1002/hbm.26607.
Language comprehension involves multiple hierarchical processing stages across time, space, and levels of representation. When processing a word, the sensory input is transformed into increasingly abstract representations that need to be integrated with the linguistic context. Thus, language comprehension involves both input-driven as well as context-dependent processes. While neuroimaging research has traditionally focused on mapping individual brain regions to the distinct underlying processes, recent studies indicate that whole-brain distributed patterns of cortical activation might be highly relevant for cognitive functions, including language. One such pattern, based on resting-state connectivity, is the 'principal cortical gradient', which dissociates sensory from heteromodal brain regions. The present study investigated the extent to which this gradient provides an organizational principle underlying language function, using a multimodal neuroimaging dataset of functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) recordings from 102 participants during sentence reading. We found that the brain response to individual representations of a word (word length, orthographic distance, and word frequency), which reflect visual; orthographic; and lexical properties, gradually increases towards the sensory end of the gradient. Although these properties showed opposite effect directions in fMRI and MEG, their association with the sensory end of the gradient was consistent across both neuroimaging modalities. In contrast, MEG revealed that properties reflecting a word's relation to its linguistic context (semantic similarity and position within the sentence) involve the heteromodal end of the gradient to a stronger extent. This dissociation between individual word and contextual properties was stable across earlier and later time windows during word presentation, indicating interactive processing of word representations and linguistic context at opposing ends of the principal gradient. To conclude, our findings indicate that the principal gradient underlies the organization of a range of linguistic representations while supporting a gradual distinction between context-independent and context-dependent representations. Furthermore, the gradient reveals convergent patterns across neuroimaging modalities (similar location along the gradient) in the presence of divergent responses (opposite effect directions).
语言理解涉及跨时间、空间和表示层次的多个分层处理阶段。在处理一个单词时，感觉输入会转化为越来越抽象的表示，这些表示需要与语言语境相结合。因此，语言理解既涉及输入驱动的过程，也涉及依赖语境的过程。虽然神经影像学研究传统上侧重于将单个脑区映射到不同的基础过程，但最近的研究表明，皮质激活的全脑分布式模式可能与认知功能（包括语言）高度相关。基于静息态连接的这样一种模式是“主要皮质梯度”，它将感觉与异模态脑区区分开来。本研究使用来自 102 名参与者在阅读句子期间的功能磁共振成像（fMRI）和脑磁图（MEG）记录的多模态神经影像学数据集，调查了这种梯度在多大程度上为语言功能提供了组织原则。我们发现，大脑对单词的单个表示（单词长度、正字法距离和单词频率）的反应逐渐向梯度的感觉端增加，这些反应反映了视觉、正字法和词汇属性。尽管这些属性在 fMRI 和 MEG 中表现出相反的效应方向，但它们与梯度感觉端的关联在两种神经影像学模式中都是一致的。相比之下，MEG 揭示了反映单词与其语言语境之间关系的属性（语义相似性和句子中的位置）在更大程度上涉及到异模态端的梯度。这种个体单词和语境属性之间的分离在单词呈现的早期和晚期时间窗口中是稳定的，这表明单词表示和语言语境在主要梯度的相反端进行交互处理。总之，我们的研究结果表明，主要梯度是一系列语言表示的组织基础，同时支持上下文独立和上下文依赖的表示之间的逐渐区分。此外，梯度在存在发散反应（相反的效应方向）的情况下，揭示了跨神经影像学模式的收敛模式（梯度上的相似位置）。
