A flexible hippocampal population code for experience relative to reward

2-photon imaging and behavioral data from hippocampal area CA1 during virtual reality navigation in mice. Included in Sosa, Plitt, & Giocomo (2025), "A flexible hippocampal population code for experience relative to reward," Nature Neuroscience.To reinforce rewarding behaviors, events leading up to and following rewards must be remembered. Hippocampal place cell activity spans spatial and non-spatial episodes, but whether hippocampal activity encodes entire sequences of events relative to reward is unknown. To test this, we performed two-photon imaging of hippocampal CA1 as mice navigated virtual environments with changing hidden reward locations. When the reward moved, a subpopulation of neurons updated their firing fields to the same relative position with respect to reward, constructing behavioral timescale sequences spanning the entire task. Over learning, this reward-relative representation became more robust as additional neurons were recruited, and changes in reward-relative firing often preceded behavioral adaptations following reward relocation. Concurrently, the spatial environment code was maintained through a parallel, dynamic subpopulation rather than through dedicated cell classes. These findings reveal how hippocampal ensembles flexibly encode multiple aspects of experience while amplifying behaviorally relevant information.

本数据集源自小鼠虚拟现实导航任务中海马CA1区（hippocampal CA1）的双光子成像（two-photon imaging）与行为学数据，收录于Sosa、Plitt与Giocomo于2025年发表于《自然-神经科学》（Nature Neuroscience）的论文《适配奖赏关联经验的灵活海马群体编码》。为强化奖赏导向行为，生物体需记忆奖赏发生前后的各类事件。海马体位置细胞的活动可覆盖空间与非空间情境，但目前尚不明确海马活动是否能编码与奖赏相关的完整事件序列。为验证这一科学问题，我们在小鼠导航带有可变隐藏奖赏位置的虚拟环境时，对其海马CA1区开展双光子成像实验。当奖赏位置发生偏移时，有一神经元亚群会将其放电野更新至与奖赏相对的同一位置，从而构建出覆盖整个任务周期的行为时程序列。随着训练进程推进，随着更多神经元被招募，这种与奖赏相关的表征变得愈发稳定；而奖赏位置偏移后，奖赏相关放电模式的变化往往先于行为适应出现。与此同时，空间环境编码并非通过特定细胞类群维持，而是依托并行的动态神经元亚群实现。本研究结果揭示了海马神经元集群如何在放大行为相关信息的同时，灵活编码经验的多个维度。