The population of hippocampal neurons actively coding space continually changes across days as mice repeatedly perform tasks. Many hippocampal place cells become inactive while other previously silent neurons become active, challenging the idea that stable behaviors and memory representations are supported by stable patterns of neural activity. Active cell replacement may disambiguate unique episodes that contain overlapping memory cues, and could contribute to reorganization of memory representations. How active cell replacement affects the evolution of representations of different behaviors within a single task is unknown. We trained mice to perform a delayed nonmatching to place task over multiple weeks, and performed calcium imaging in area CA1 of the dorsal hippocampus using head‐mounted miniature microscopes. Cells active on the central stem of the maze “split” their calcium activity according to the animal's upcoming turn direction (left or right), the current task phase (study or test), or both task dimensions, even while spatial cues remained unchanged. We found that, among reliably active cells, different splitter neuron populations were replaced at unequal rates, resulting in an increasing number of cells modulated by turn direction and a decreasing number of cells with combined modulation by both turn direction and task phase. Despite continual reorganization, the ensemble code stably segregated these task dimensions. These results show that hippocampal memories can heterogeneously reorganize even while behavior is unchanging.

中文翻译：

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小鼠的海马空间记忆表征是异质稳定的

随着小鼠反复执行任务，活跃编码空间的海马神经元群在几天内不断变化。许多海马位置细胞变得不活跃，而其他以前沉默的神经元变得活跃，这挑战了稳定的行为和记忆表征由稳定的神经活动模式支持的想法。主动细胞替换可以消除包含重叠记忆线索的独特情节的歧义，并可能有助于记忆表征的重组。活跃的细胞替换如何影响单个任务中不同行为表示的演变是未知的。我们训练小鼠在数周内执行延迟不匹配放置任务，并使用头戴式微型显微镜在背侧海马 CA1 区域进行钙成像。根据动物即将转向（左或右）、当前任务阶段（研究或测试）或两个任务维度，即使在空间线索保持不变的情况下，迷宫中央干上活跃的细胞也会“分裂”它们的钙活性。我们发现，在可靠活跃的细胞中，不同的分裂神经元群以不相等的速率被替换，导致转向方向调制的细胞数量增加，而转向方向和任务阶段联合调制的细胞数量减少。尽管不断重组，集成代码稳定地分离了这些任务维度。这些结果表明，即使行为不变，海马记忆也可以异质重组。当前任务阶段（学习或测试），或两个任务维度，即使空间线索保持不变。我们发现，在可靠活跃的细胞中，不同的分裂神经元群以不相等的速率被替换，导致转向方向调制的细胞数量增加，而转向方向和任务阶段联合调制的细胞数量减少。尽管不断重组，集成代码稳定地分离了这些任务维度。这些结果表明，即使行为不变，海马记忆也可以异质重组。当前任务阶段（学习或测试），或两个任务维度，即使空间线索保持不变。我们发现，在可靠活跃的细胞中，不同的分裂神经元群以不相等的速率被替换，导致转向方向调制的细胞数量增加，而转向方向和任务阶段联合调制的细胞数量减少。尽管不断重组，集成代码稳定地分离了这些任务维度。这些结果表明，即使行为不变，海马记忆也可以异质重组。导致转向方向调制的单元数量增加，转向方向和任务阶段组合调制的单元数量减少。尽管不断重组，集成代码稳定地分离了这些任务维度。这些结果表明，即使行为不变，海马记忆也可以异质重组。导致转向方向调制的单元数量增加，转向方向和任务阶段组合调制的单元数量减少。尽管不断重组，集成代码稳定地分离了这些任务维度。这些结果表明，即使行为不变，海马记忆也可以异质重组。