Krishnan Seetha, Dong Can, Ratigan Heather, Morales-Rodriguez Denisse, Cherian Chery, Sheffield Mark
Department of Neurobiology and Institute for Neuroscience, University of Chicago, Chicago, United States.
Elife. 2025 Jun 17;14:RP105422. doi: 10.7554/eLife.105422.
Contextual fear conditioning (CFC) is a classical laboratory task that tests associative memory formation and recall. Techniques such as multi-photon microscopy and holographic stimulation offer tremendous opportunities to understand the neural underpinnings of these memories. However, these techniques generally require animals to be head-fixed. Few paradigms examine contextual fear in head-fixed mice, and none use freezing-the most common measure of fear in freely moving animals-as the behavioral readout. To address this gap, we developed a CFC paradigm for head-fixed mice using virtual reality (VR). We designed an apparatus to deliver tail shocks while mice navigated a VR environment. We tested three versions of this paradigm and, in all of them, observed increased freezing, particularly on the first trial, in the shock-paired VR compared to a neutral one. These results demonstrate that head-fixed mice can be fear-conditioned in VR and exhibit context-specific freezing behavior. Additionally, using two-photon calcium imaging, we tracked large populations of hippocampal CA1 neurons before, during, and following CFC. As in freely moving mice, CA1 place cells remapped and developed narrower fields following fear conditioning. Thus, our approach enables new opportunities to study the neural mechanisms underlying the formation, recall, and extinction of contextual fear memories.
情境恐惧条件反射(CFC)是一种经典的实验室任务,用于测试联想记忆的形成和回忆。多光子显微镜和全息刺激等技术为理解这些记忆的神经基础提供了巨大的机会。然而,这些技术通常要求动物头部固定。很少有范式研究头部固定小鼠的情境恐惧,并且没有一个使用僵立不动——自由活动动物中最常见的恐惧测量指标——作为行为读数。为了填补这一空白,我们开发了一种使用虚拟现实(VR)的头部固定小鼠的CFC范式。我们设计了一种装置,在小鼠在VR环境中导航时给予尾部电击。我们测试了该范式的三个版本,并且在所有版本中,观察到与中性VR相比,在与电击配对的VR中,尤其是在第一次试验时,僵立不动增加。这些结果表明,头部固定的小鼠可以在VR中形成恐惧条件反射并表现出情境特异性的僵立不动行为。此外,使用双光子钙成像,我们在CFC之前、期间和之后追踪了大量海马CA1神经元。与自由活动的小鼠一样,恐惧条件反射后,CA1位置细胞重新映射并形成了更窄的区域。因此,我们的方法为研究情境恐惧记忆形成、回忆和消退背后的神经机制提供了新的机会。