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Abstract：
The structure of human language is inherently hierarchical. The left posterior inferior frontal gyrus (LpIFG) is proposed to be a core region for constructing syntactic hierarchies. However, it remains unclear whether LpIFG plays a causal role in syntactic processing in Mandarin Chinese and whether its contribution depends on syntactic complexity, working memory, or both. We addressed these questions by applying inhibitory continuous theta-burst stimulation (cTBS) over LpIFG. Thirty-two participants processed sentences containing embedded relative clauses (i.e., complex syntactic processing), syntactically simpler coordinated sentences (i.e., simple syntactic processing), and non-hierarchical word lists (i.e., word list processing) after receiving real or sham cTBS. We found that cTBS significantly increased the coefficient of variation, a representative index of processing stability, in complex syntactic processing (esp., when subject relative clause was embedded) but not in the other two conditions. No significant changes in d\' and reaction time were detected in these conditions. The findings suggest that (a) inhibitory effect of cTBS on the LpIFG might be prominent in perturbing the complex syntactic processing stability but subtle in altering the processing quality; and (b) the causal role of the LpIFG seems to be specific for syntactic processing rather than working memory capacity, further evidencing their separability in LpIFG. Collectively, these results support the notion of the LpIFG as a core region for complex syntactic processing across languages.
摘要：
人类语言的结构本质上是分层的。左后下额回（LpIFG）被认为是构建句法层次结构的核心区域。然而,目前尚不清楚LpIFG是否在普通话句法加工中起因果作用，其贡献是否取决于句法复杂性，工作记忆,或者两者兼而有之。我们通过在LpIFG上应用抑制性连续θ爆发刺激（cTBS）来解决这些问题。32名参与者处理了包含嵌入的相对从句的句子(即，复杂句法处理)，语法上更简单的协调句子(即，简单的句法处理)，和非分层单词列表(即，单词列表处理)在收到真实或假cTBS后。我们发现cTBS显著增加了变异系数，加工稳定性的代表性指标，在复杂的句法处理中(尤指,当主语相对从句被嵌入时)，但不在其他两个条件中。在这些条件下没有检测到d'和反应时间的显著变化。研究结果表明，（a）cTBS对LpIFG的抑制作用可能在扰乱复杂的句法加工稳定性方面很突出，但在改变加工质量方面却很微妙；（b）LpIFG的因果作用似乎特定于句法加工而不是工作记忆能力，进一步证明它们在LpIFG中的可分离性。总的来说，这些结果支持LpIFG作为跨语言复杂句法处理的核心区域的概念。
