Department of Psychology, University of York, Heslington, York, UK, YO10 5DD.
Department of Psychology, University of York, Heslington, York, UK, YO10 5DD.
Neuroimage. 2021 Jan 1;224:117405. doi: 10.1016/j.neuroimage.2020.117405. Epub 2020 Sep 28.
Semantic retrieval is flexible, allowing us to focus on subsets of features and associations that are relevant to the current task or context: for example, we use taxonomic relations to locate items in the supermarket (carrots are a vegetable), but thematic associations to decide which tools we need when cooking (carrot goes with peeler). We used fMRI to investigate the neural basis of this form of semantic flexibility; in particular, we asked how retrieval unfolds differently when participants have advanced knowledge of the type of link to retrieve between concepts (taxonomic or thematic). Participants performed a semantic relatedness judgement task: on half the trials, they were cued to search for a taxonomic or thematic link, while on the remaining trials, they judged relatedness without knowing which type of semantic relationship would be relevant. Left inferior frontal gyrus showed greater activation when participants knew the trial type in advance. An overlapping region showed a stronger response when the semantic relationship between the items was weaker, suggesting this structure supports both top-down and bottom-up forms of semantic control. Multivariate pattern analysis further revealed that the neural response in left inferior frontal gyrus reflects goal information related to different conceptual relationships. Top-down control specifically modulated the response in visual cortex: when the goal was unknown, there was greater deactivation to the first word, and greater activation to the second word. We conclude that top-down control of semantic retrieval is primarily achieved through the gating of task-relevant 'spoke' regions.
语义检索具有灵活性，可以使我们专注于与当前任务或上下文相关的特征和关联子集：例如，我们使用分类关系在超市中定位物品（胡萝卜是一种蔬菜），但使用主题关联来决定烹饪时需要哪些工具（胡萝卜需要削皮器）。我们使用 fMRI 研究了这种语义灵活性的神经基础；特别是，我们询问了当参与者对要在概念之间检索的链接类型（分类或主题）有了深入了解时，检索是如何以不同的方式展开的。参与者执行语义关联性判断任务：在一半的试验中，他们被提示搜索分类或主题链接，而在其余的试验中，他们在不知道哪种语义关系将相关的情况下判断关联性。当参与者提前知道试验类型时，左额下回显示出更大的激活。当项目之间的语义关系较弱时，重叠区域显示出更强的反应，这表明该结构支持自上而下和自下而上的语义控制形式。多元模式分析进一步表明，左额下回的神经反应反映了与不同概念关系相关的目标信息。自上而下的控制特别调节了视觉皮层的反应：当目标未知时，第一个词的去激活程度更大，第二个词的激活程度更大。我们得出结论，语义检索的自上而下控制主要是通过门控任务相关的“辐条”区域来实现的。
