Innately aversive experiences produce rapid defensive responses and powerful emotional memories. The midbrain periaqueductal gray (PAG) drives defensive behaviors through projections to brainstem motor control centers, but the PAG has also been implicated in aversive learning, receives information from aversive-signaling sensory systems and sends ascending projections to the thalamus as well as other forebrain structures which could control learning and memory. Here we sought to identify PAG subregions and cell types which instruct memory formation in response to aversive events. We found that optogenetic inhibition of neurons in the dorsolateral subregion of the PAG (dlPAG), but not the ventrolateral PAG (vlPAG), during an aversive event reduced memory formation. Furthermore, inhibition of a specific population of thalamus projecting dlPAG neurons projecting to the anterior paraventricular thalamus (aPVT) reduced aversive learning, but had no effect on the expression of previously learned defensive behaviors. By contrast, inactivation of dlPAG neurons which project to the posterior PVT (pPVT) or centromedial intralaminar thalamic nucleus (CM) had no effect on learning. These results reveal specific subregions and cell types within PAG responsible for its learning related functions.

中文翻译：

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中脑导水管周围灰质调节厌恶记忆形成的功能组织

天生的厌恶体验会产生快速的防御反应和强大的情感记忆。中脑导水管周围灰质 (PAG) 通过投射到脑干运动控制中心来驱动防御行为，但 PAG 也与厌恶学习有关，接收来自厌恶信号感觉系统的信息，并将上行投射发送到丘脑以及其他前脑结构可以控制学习和记忆。在这里，我们试图确定 PAG 亚区和细胞类型，它们指导记忆形成以响应厌恶事件。我们发现，在厌恶事件期间，对 PAG 背外侧亚区 (dlPAG) 神经元的光遗传学抑制，而不是腹外侧 PAG (vlPAG) 神经元的抑制会减少记忆形成。此外，抑制投射到前室旁丘脑 (aPVT) 的丘脑投射 dlPAG 神经元的特定群体减少了厌恶学习，但对先前学习的防御行为的表达没有影响。相比之下，投射到后 PVT (pPVT) 或中心内侧椎板内丘脑核 (CM) 的 dlPAG 神经元的失活对学习没有影响。这些结果揭示了 PAG 中负责其学习相关功能的特定子区域和细胞类型。