Fear and extinction learning are thought to generate distinct and competing memory representations in the hippocampus. How these memory representations modulate the expression of appropriate behavioral responses remains unclear. To investigate this question, we used cholera toxin B subunit to retrolabel ventral hippocampal (vHPC) neurons projecting to the infralimbic cortex (IL) and basolateral amygdala (BLA) and then quantified c-Fos immediate early gene activity within these populations following expression of either contextual fear recall or contextual fear extinction recall. Fear recall was associated with increased c-Fos expression in vHPC projections to the BLA, whereas extinction recall was associated with increased activity in vHPC projections to IL. A control experiment was performed to confirm that the apparent shift in projection neuron activity was associated with extinction learning rather than mere context exposure. Overall, results indicate that hippocampal contextual fear and extinction memory representations differentially activate vHPC projections to IL and BLA. These findings suggest that hippocampal memory representations orchestrate appropriate behavioral responses through selective activation of projection pathways.

恐惧和消退学习被认为会在海马体中产生独特且相互竞争的记忆表征。这些记忆表征如何调节适当行为反应的表达仍不清楚。为了研究这个问题，我们使用霍乱毒素 B 亚基来逆向标记投射到边缘下皮层 (IL) 和基底外侧杏仁核 (BLA) 的腹侧海马 (vHPC) 神经元，然后在表达以下任一者后量化这些群体中的 c-Fos 立即早期基因活性：情境恐惧回忆或情境恐惧消退回忆。恐惧回忆与 vHPC 投射到 BLA 中的 c-Fos 表达增加相关，而消退回忆则与 vHPC 投射到 IL 中的活动增加相关。进行对照实验以确认投射神经元活动的明显变化与消退学习相关，而不仅仅是与环境暴露相关。总体而言，结果表明海马情境恐惧和消退记忆表征不同地激活 vHPC 对 IL 和 BLA 的投射。这些发现表明，海马记忆表征通过选择性激活投射通路来协调适当的行为反应。