Flexing the principal gradient of the cerebral cortex to suit changing semantic task demands

Understanding how thought emerges from the topographical structure of the cerebral cortex is a primary goal of cognitive neuroscience. Recent work has revealed a principal gradient of intrinsic connectivity capturing the separation of sensory-motor cortex from transmodal regions of the default mode network (DMN); this is thought to facilitate memory-guided cognition. However, studies have not explored how this dimension of connectivity changes when conceptual retrieval is controlled to suit the context. We used gradient decomposition of informational connectivity in a semantic association task to establish how the similarity in connectivity across brain regions changes during familiar and more original patterns of retrieval. Multivoxel activation patterns at opposite ends of the principal gradient were more divergent when participants retrieved stronger associations; therefore when long-term semantic information is sufficient for ongoing cognition, regions supporting heteromodal memory are functionally separated from sensory-motor experience. In contrast, when less related concepts were linked, this dimension of connectivity was reduced in strength as semantic control regions separated from the DMN to generate more flexible and original responses. We also observed fewer dimensions within the neural response towards the apex of the principal gradient when strong associations were retrieved, reflecting less complex or varied neural coding across trials and participants. In this way, the principal gradient explains how semantic cognition is organised in the human cerebral cortex: the separation of DMN from sensory-motor systems is a hallmark of the retrieval of strong conceptual links that are culturally shared.

认知神经科学的核心目标之一在于洞察思维如何从大脑皮层的拓扑结构中涌现。近期研究揭示了内在连接性中的主要梯度，该梯度捕捉了感觉运动皮层与默认模式网络（DMN）跨模态区域之间的分离；这一发现被认为有助于记忆引导的认知过程。然而，现有研究尚未探讨当概念检索被调控以适应具体情境时，这一连接性维度如何发生变化。我们通过在语义联想任务中对信息连接性进行梯度分解，确立了在熟悉的和更为新颖的检索模式中，大脑区域间连接性相似性的变化情况。在主要梯度两端的多体素激活模式在参与者检索更强关联时表现出更大的差异性；因此，当长期语义信息足以支持持续的认知时，支持异模态记忆的区域在功能上与感觉运动经验分离。相反，当联系较弱的概念时，这一连接性维度在强度上降低，因为语义控制区域从DMN中分离出来，以产生更为灵活和原创的响应。我们还观察到，在检索到强关联时，主要梯度顶端的神经反应维度减少，反映了在试验和参与者之间神经编码的复杂性和多样性降低。以这种方式，主要梯度解释了语义认知在人类大脑皮层中的组织方式：DMN与感觉运动系统之间的分离是检索文化共享的强烈概念链接的显著标志。