Sokoliuk Rodika, Degano Giulio, Melloni Lucia, Noppeney Uta, Cruse Damian
School of Psychology, University of Birmingham, Birmingham, United Kingdom.
Centre for Human Brain Health, University of Birmingham, Birmingham, United Kingdom.
Front Hum Neurosci. 2021 Aug 11;15:702768. doi: 10.3389/fnhum.2021.702768. eCollection 2021.
Language comprehension relies on integrating words into progressively more complex structures, like phrases and sentences. This hierarchical structure-building is reflected in rhythmic neural activity across multiple timescales in E/MEG in healthy, awake participants. However, recent studies have shown evidence for this "cortical tracking" of higher-level linguistic structures also in a proportion of unresponsive patients. What does this tell us about these patients' residual levels of cognition and consciousness? Must the listener direct their attention toward higher level speech structures to exhibit cortical tracking, and would selective attention across levels of the hierarchy influence the expression of these rhythms? We investigated these questions in an EEG study of 72 healthy human volunteers listening to streams of monosyllabic isochronous English words that were either unrelated (scrambled condition) or composed of four-word-sequences building meaningful sentences (sentential condition). Importantly, there were no physical cues between four-word-sentences. Rather, boundaries were marked by syntactic structure and thematic role assignment. Participants were divided into three attention groups: from passive listening (passive group) to attending to individual words (word group) or sentences (sentence group). The passive and word groups were initially naïve to the sentential stimulus structure, while the sentence group was not. We found significant tracking at word- and sentence rate across all three groups, with sentence tracking linked to left middle temporal gyrus and right superior temporal gyrus. Goal-directed attention to words did not enhance word-rate-tracking, suggesting that word tracking here reflects largely automatic mechanisms, as was shown for tracking at the syllable-rate before. Importantly, goal-directed attention to sentences relative to words significantly increased sentence-rate-tracking over left inferior frontal gyrus. This attentional modulation of rhythmic EEG activity at the sentential rate highlights the role of attention in integrating individual words into complex linguistic structures. Nevertheless, given the presence of high-level cortical tracking under conditions of lower attentional effort, our findings underline the suitability of the paradigm in its clinical application in patients after brain injury. The neural dissociation between passive tracking of sentences and directed attention to sentences provides a potential means to further characterise the cognitive state of each unresponsive patient.
语言理解依赖于将单词整合到越来越复杂的结构中，如短语和句子。这种层次结构构建在健康、清醒参与者的脑电/脑磁图（E/MEG）中多个时间尺度上的节律性神经活动中有所体现。然而，最近的研究表明，在一部分无反应患者中也存在这种对高级语言结构的“皮层追踪”证据。这对于这些患者的残余认知和意识水平告诉了我们什么？听者是否必须将注意力指向更高层次的言语结构才能表现出皮层追踪，并且层次结构各水平上的选择性注意是否会影响这些节律的表达？我们在一项脑电图研究中对72名健康人类志愿者进行了调查，他们听的是单音节等时英语单词流，这些单词要么是不相关的（打乱条件），要么由构建有意义句子的四字序列组成（句子条件）。重要的是，四字句子之间没有物理线索。相反，边界由句法结构和主题角色分配来标记。参与者被分为三个注意力组：从被动聆听（被动组）到关注单个单词（单词组）或句子（句子组）。被动组和单词组最初对句子刺激结构并不了解，而句子组则了解。我们发现所有三组在单词和句子速率上都有显著的追踪，句子追踪与左中颞回和右上颞回相关。对单词的目标导向性注意并没有增强单词速率追踪，这表明这里的单词追踪在很大程度上反映了自动机制，正如之前在音节速率追踪中所显示的那样。重要的是，相对于单词，对句子的目标导向性注意显著增加了左下额回的句子速率追踪。这种在句子速率上对节律性脑电活动的注意力调节突出了注意在将单个单词整合到复杂语言结构中的作用。然而，鉴于在较低注意力努力条件下存在高级皮层追踪，我们的研究结果强调了该范式在脑损伤后患者临床应用中的适用性。句子的被动追踪和对句子的定向注意之间的神经分离为进一步表征每个无反应患者的认知状态提供了一种潜在方法。
