Princeton Neuroscience Institute, Princeton University, Princeton, New Jersey 08540
Department of Psychology, Columbia University, New York, New York 10027
J Neurosci. 2024 Mar 6;44(10):e0627232023. doi: 10.1523/JNEUROSCI.0627-23.2023.
Everyday life is composed of events organized by changes in contexts, with each event containing an unfolding sequence of occurrences. A major challenge facing our memory systems is how to integrate sequential occurrences within events while also maintaining their details and avoiding over-integration across different contexts. We asked if and how distinct hippocampal subfields come to hierarchically and, in parallel, represent both event context and subevent occurrences with learning. Female and male human participants viewed sequential events defined as sequences of objects superimposed on shared color frames while undergoing high-resolution fMRI. Importantly, these events were repeated to induce learning. Event segmentation, as indexed by increased reaction times at event boundaries, was observed in all repetitions. Temporal memory decisions were quicker for items from the same event compared to across different events, indicating that events shaped memory. With learning, hippocampal CA3 multivoxel activation patterns clustered to reflect the event context, with more clustering correlated with behavioral facilitation during event transitions. In contrast, in the dentate gyrus (DG), temporally proximal items that belonged to the same event became associated with more differentiated neural patterns. A computational model explained these results by dynamic inhibition in the DG. Additional similarity measures support the notion that CA3 clustered representations reflect shared voxel populations, while DG's distinct item representations reflect different voxel populations. These findings suggest an interplay between temporal differentiation in the DG and attractor dynamics in CA3. They advance our understanding of how knowledge is structured through integration and separation across time and context.
日常生活由按上下文变化组织的事件构成，每个事件都包含一个展开的事件序列。我们的记忆系统面临的主要挑战是如何在整合事件内的顺序事件的同时保持其细节，避免在不同的上下文中过度整合。我们想知道，在学习过程中，海马体的不同亚区是否以及如何以分层和并行的方式分别表示事件上下文和子事件的发生。研究招募了女性和男性人类参与者，他们在接受高分辨率 fMRI 扫描的同时，观看了定义为共享颜色框架上叠加的对象序列的顺序事件。重要的是，这些事件被重复以诱导学习。在所有重复中都观察到了事件分割，其指标为事件边界处的反应时间增加。与来自不同事件的项目相比，相同事件中的项目的时间记忆决策更快，这表明事件塑造了记忆。随着学习的进行，海马体 CA3 的多体素激活模式聚类以反映事件上下文，聚类越多，在事件转换期间的行为促进作用越大。相比之下，在齿状回（DG）中，属于同一事件的时间上接近的项目与更分化的神经模式相关联。一个计算模型通过 DG 中的动态抑制来解释这些结果。其他相似性度量支持 CA3 聚类表示反映共享体素群体，而 DG 的独特项目表示反映不同体素群体的观点。这些发现表明，DG 中的时间分化和 CA3 中的吸引子动态之间存在相互作用。它们增进了我们对知识如何通过时间和上下文的整合和分离来构建的理解。
