Robins Pei L, Gilbert Jessica R, Luber Bruce, Mustafa Nadia, Bharti Eesha, Stout Jeffrey D, Carver Frederick W, Deng Zhi-De
medRxiv. 2025 Jul 21:2025.07.18.25331749. doi: 10.1101/2025.07.18.25331749.
A core function of episodic memory is to distinguish between overlapping experiences by converting similar inputs into distinct, non-overlapping representations-a process termed pattern separation. While anatomical models emphasize the role of specific hippocampal subfields, particularly the dentate gyrus, CA3, and CA1, less is known about how these computations unfold over time and influence memory-based decisions. Here, we use source-localized magnetoencephalography and computational modeling to examine how theta oscillations from the hippocampus as a whole are related to evidence accumulation during mnemonic discrimination. Participants performed the Mnemonic Similarity Task, in which they classified repeat, lure, and foil images as "old," "similar," or "new." We fit a hierarchical Linear Ballistic Accumulator model to behavioral data, estimating trial-by-trial drift rates-a latent index of mnemonic evidence accumulation-and examined whether hippocampal theta power predicted these dynamics. Theta power in the left hippocampus was positively associated with drift toward "new" responses across stimulus conditions, consistent with a novelty-oriented decision bias. In contrast, right hippocampal theta showed negative associations with drift toward familiarity-driven false alarms to foil items, suggesting a complementary mechanism that curtails evidence accumulation based on false familiarity. Both hemispheres showed positive theta-drift associations during correct "similar" responses, implicating bilateral coordination in successful discrimination. Event-related source activity confirmed reliable hippocampal engagement despite the anatomical depth of the source. These findings reveal a dynamic, lateralized mechanism by which hippocampal theta oscillations shape memory-guided decisions, offering new insight into how the brain resolves mnemonic uncertainty in real time.
情景记忆的一个核心功能是通过将相似的输入转换为不同的、不重叠的表征来区分重叠的经历，这一过程称为模式分离。虽然解剖学模型强调特定海马亚区的作用，特别是齿状回、CA3和CA1，但对于这些计算如何随时间展开并影响基于记忆的决策，我们了解得较少。在这里，我们使用源定位脑磁图和计算模型来研究整个海马体的theta振荡如何与记忆辨别过程中的证据积累相关。参与者执行记忆相似性任务，他们将重复、诱饵和陪衬图像分类为“旧的”、“相似的”或“新的”。我们将分层线性弹道累加器模型拟合到行为数据中，估计逐次试验的漂移率——记忆证据积累的一个潜在指标——并检查海马体theta功率是否能预测这些动态。左侧海马体的theta功率与跨刺激条件下向“新”反应的漂移呈正相关，这与以新颖性为导向的决策偏差一致。相比之下，右侧海马体的theta与对陪衬项目基于错误熟悉度的误报向熟悉度驱动的漂移呈负相关，这表明存在一种互补机制，可减少基于错误熟悉度的证据积累。在正确的“相似”反应过程中，两个半球均显示出正的theta-漂移关联，这意味着在成功辨别中存在双侧协调。尽管源位于解剖学深度，但事件相关源活动证实了海马体的可靠参与。这些发现揭示了一种动态的、侧化的机制，通过该机制海马体theta振荡塑造基于记忆的决策，为大脑如何实时解决记忆不确定性提供了新的见解。
