Department of Biomedical Sciences, Marquette University, Milwaukee, Wisconsin 53233
Department of Biomedical Sciences, Marquette University, Milwaukee, Wisconsin 53233.
J Neurosci. 2020 Apr 15;40(16):3217-3230. doi: 10.1523/JNEUROSCI.1453-19.2020. Epub 2020 Mar 18.
The PFC, through its high degree of interconnectivity with cortical and subcortical brain areas, mediates cognitive and emotional processes in support of adaptive behaviors. This includes the formation of fear memories when the anticipation of threat demands learning about temporal or contextual cues, as in trace fear conditioning. In this variant of fear learning, the association of a cue and shock across an empty trace interval of several seconds requires sustained cue-elicited firing in the prelimbic cortex (PL). However, it is unknown how and when distinct PL afferents contribute to different associative components of memory. Among the prominent inputs to PL, the hippocampus shares with PL a role in both working memory and contextual processing. Here we tested the necessity of direct hippocampal input to the PL for the acquisition of trace-cued fear memory and the simultaneously acquired contextual fear association. Optogenetic silencing of ventral hippocampal (VH) terminals in the PL of adult male Long-Evans rats selectively during paired trials revealed that direct communication between the VH and PL during training is necessary for contextual fear memory, but not for trace-cued fear acquisition. The pattern of the contextual memory deficit and the disruption of local PL firing during optogenetic silencing of VH-PL suggest that the VH continuously updates the PL with the current contextual state of the animal, which, when disrupted during memory acquisition, is detrimental to the subsequent rapid retrieval of aversive contextual associations. Learning to anticipate threat from available contextual and discrete cues is crucial for survival. The prelimbic cortex is required for forming fear memories when temporal or contextual complexity is involved, as in trace fear conditioning. However, the respective contribution of distinct prelimbic afferents to the temporal and contextual components of memory is not known. We report that direct input from the ventral hippocampus enables the formation of the contextual, but not trace-cued, fear memory necessary for the subsequent rapid expression of a fear response. This finding dissociates the contextual and working-memory contributions of prelimbic cortex to the formation of a fear memory and demonstrates the crucial role for hippocampal input in contextual fear learning.
前额皮质通过与皮质和皮质下脑区的高度互联,介导认知和情绪过程,以支持适应性行为。这包括在预期威胁时形成恐惧记忆,例如在痕迹恐惧条件反射中,需要学习时间或上下文线索。在这种恐惧学习的变体中,在几秒钟的空迹间隔内,线索和冲击的关联需要在额前皮质(PL)中持续引发线索诱发的放电。然而,目前尚不清楚不同的 PL 传入纤维如何以及何时有助于记忆的不同联想成分。在 PL 的主要传入中,海马体与 PL 一起在工作记忆和上下文处理中发挥作用。在这里,我们测试了直接海马体输入到 PL 对于获取痕迹线索恐惧记忆和同时获得的上下文恐惧关联的必要性。成年雄性 Long-Evans 大鼠在配对试验期间选择性地用光遗传学沉默 PL 中的腹侧海马(VH)末梢,结果表明,在训练期间,VH 和 PL 之间的直接通讯对于上下文恐惧记忆是必要的,但对于痕迹线索恐惧的获得则不是。上下文记忆缺陷的模式以及在 VH-PL 光遗传学沉默期间局部 PL 放电的中断表明,VH 不断地将动物的当前上下文状态更新到 PL,当在记忆获取过程中被中断时,会对随后快速检索厌恶的上下文关联造成损害。学习从可用的上下文和离散线索中预测威胁对于生存至关重要。当涉及时间或上下文复杂性时,如在痕迹恐惧条件反射中,前额皮质对于形成恐惧记忆是必需的。然而,不同的前额皮质传入纤维对记忆的时间和上下文成分的各自贡献尚不清楚。我们报告说,来自腹侧海马体的直接输入使形成上下文而非痕迹线索恐惧记忆成为可能,这对于随后快速表达恐惧反应是必需的。这一发现将前额皮质对记忆形成的上下文和工作记忆贡献分离出来,并证明了海马体输入在上下文恐惧学习中的关键作用。