Gao Chenyang, Wu Junjie, Cheng Yao, Ke Yuming, Qu Xingfang, Yang Mingchuan, Hartwigsen Gesa, Chen Luyao
School of Global Education and Development, University of Chinese Academy of Social Sciences, Beijing, China.
Key Research Base of Humanities and Social Sciences of the Ministry of Education, Academy of Psychology and Behavior, Tianjin Normal University, Tianjin, China.
Neuroimage. 2025 Feb 1;306:121014. doi: 10.1016/j.neuroimage.2025.121014. Epub 2025 Jan 9.
Hierarchical syntactic structure processing is proposed to be at the core of the human language faculty. Syntactic processing is supported by the left fronto-temporal language network, including a core area in the inferior frontal gyrus as well as its interaction with the posterior temporal lobe (i.e., "IFG + pTL"). Moreover, during complex syntactic processes, left IFG also interacts with executive control regions, such as the superior parietal lobule (SPL). However, the functional relevance of these network interactions is largely unclear. In particular, it remains to be demonstrated whether the language network plays a specific causal role in comparatively challenging syntactic processes, separable from the interaction between IFG and other general cognitive regions (i.e., "IFG + SPL" in the present study). The present study was designed to address this question. Thirty healthy adult Chinese native speakers underwent four continuous theta-burst stimulation (cTBS) sessions: stimulation over IFG, stimulation over IFG + pTL, stimulation over IFG + SPL, and sham stimulation over IFG + irrelevant region in a pseudo-randomized order. In each session, participants were required to label the syntactic categories of jabberwocky sequences retaining real Chinese function words (e.g., "ムウ" is labeled as a verb phrase (VP): "[ [V]N]", similar to "ziff-ed a wug", where "ziff" and "wug" are nonsense pseudowords, and the whole phrase is a VP). Contrasted with sham cTBS, change percentage of accuracy rates (ΔACCR%), reaction times (ΔRT%), and coefficient of variation (ΔCV%) were calculated and compared across conditions. First-order behavioral results showed a significantly higher ΔCV% after stimulating IFG + pTL compared to stimulating the IFG + SPL, indicating that syntactic processing became more unstable. Second-order representational similarity analysis (RSA) results revealed that cTBS effects on IFG + pTL selectively depended on the hierarchical embedding depth, a key measure of syntactic hierarchical complexity, whereas the effects on IFG + SPL were sensitive to the dependency length, a crucial index reflecting the working memory load. Collectively, these findings reveal the specific causal relevance of the language areas for hierarchical syntactic processing, separable from other general cognitive (such as working memory) capacities. These results shed light on the uniqueness and the specific causal role of the language network for the human language faculty, further supporting the causally separable view of the functional dissociation between the language network and the domain-general/multiple-demand network.
层级句法结构处理被认为是人类语言能力的核心。句法处理由左侧额颞叶语言网络支持，包括额下回的一个核心区域及其与颞叶后部的相互作用（即“IFG + pTL”）。此外，在复杂的句法处理过程中，左侧额下回还与执行控制区域相互作用，如顶上小叶（SPL）。然而，这些网络相互作用的功能相关性在很大程度上尚不清楚。特别是，语言网络在相对具有挑战性的句法处理中是否发挥特定的因果作用，与额下回和其他一般认知区域之间的相互作用（即本研究中的“IFG + SPL”）相分离，仍有待证明。本研究旨在解决这个问题。30名以汉语为母语的健康成年人接受了四次连续的theta爆发刺激（cTBS）：对额下回进行刺激、对额下回 + 颞叶后部进行刺激、对额下回 + 顶上小叶进行刺激，以及对额下回 + 无关区域进行假刺激，刺激顺序为伪随机。在每次刺激过程中，要求参与者对保留真实汉语功能词的胡言乱语序列的句法类别进行标注（例如，“ムウ”被标注为动词短语（VP）：“[[V]N]”，类似于“ziff - ed a wug”，其中“ziff”和“wug”是无意义的假词，整个短语是一个VP）。与假cTBS相比，计算并比较了不同条件下准确率变化百分比（ΔACCR%）、反应时间变化百分比（ΔRT%）和变异系数（ΔCV%）。一阶行为结果显示，与刺激额下回 + 顶上小叶相比，刺激额下回 + 颞叶后部后的ΔCV%显著更高，表明句法处理变得更加不稳定。二阶表征相似性分析（RSA）结果表明，cTBS对额下回 + 颞叶后部的影响选择性地取决于层级嵌入深度，这是句法层级复杂性的一个关键指标，而对额下回 + 顶上小叶的影响对依存长度敏感，依存长度是反映工作记忆负荷的一个关键指标。总的来说，这些发现揭示了语言区域在层级句法处理中的特定因果相关性，与其他一般认知（如工作记忆）能力相分离。这些结果揭示了语言网络对于人类语言能力的独特性和特定因果作用，进一步支持了语言网络与领域通用/多需求网络之间功能分离的因果可分离观点。
