（图片来源：http://699pic.com/tupian-100475742.html）

我们的长辈经常告诫我们：“不听老人言，吃亏在眼前。”这句话真是千真万确的生存法则之一， 因为通过后天学习其他个体不愉快的经历，对于学习者的生存是低风险的。毕竟，如果我们可以避免潜在的风险，为什么还要去体验痛苦、失望和失败呢？！比如说，一只兔子看见自己的小伙伴被狼吃了，如果它下次看见狼还大摇大摆的向狼靠近，那结果可想而知，所以要想生存下去，下次发现狼在附近，最好躲起来或者跑掉。因此，在漫漫进化长河中，通过学习令他人恐惧事情来避免自己下次陷入这种危险的可能，是十分重要的一种生存能力。

但是患有自闭症（Autism Spectrum Disorder，ASD）的群体缺乏这种后天对于恐惧的事情的学习能力，研究表明ASD个体大脑的杏仁核会出现功能异常。“杏仁核”，是指在大脑海马的末端，一个呈杏仁状的区域，这个区域对于后天恐惧学习具有很重要的作用。在中央杏仁核的外面是外侧杏仁核（Lateral Amygdala,LA）,这个区域可以感知信息，并将信息传递给其它杏仁核区域，比如内侧杏仁核（Medial Amygdala,MeA）。MeA区域除了接受来自LA的信息外，还可以接受大量来自嗅觉系统的投射，从而对个体的社会行为产生影响。因此科学家Twining等人推测：LA-MeA神经投射对于个体的后天恐惧学习很重要。

这些科学家通过让正常的或者杏仁核部分区域受到抑制的无经验的大鼠A观察处于条件恐惧实验的另一只大鼠B后的反应来确定上述推测的正确性。条件恐惧实验是指：一种特定的声音作为环境因素中的条件刺激，每当响起后，就对大鼠B进行足部电击，而受到电击后大鼠发出的味道、信息素、声音、姿势甚至面部恐怖表情就属于社会因素。正常的大鼠A看到受到电击后大鼠表现出的一系列的社会因素后，当大鼠A仅仅再次听到这种特定的声音后，表现出的反应就如同它们亲身经历了电击一样，说明后天的恐怖学习成功。接下来，科学家设计下面的实验：①当把正常的大鼠A换成大脑一边的LA和另一边的MeA同时受到抑制的大鼠a时，发现后天恐怖学习能力受损。②他们使用药物遗传学仅抑制可以投射到MeA区域的LA区域的大鼠aa,发现后天恐怖学习能力受损。③对大鼠aa的LA区域进行电刺激，发现大鼠aa的学习能力增强。上述实验结果初步表明LA-MeA是后天恐惧学习的基础，那这一投射路径是否在ASD个体中损坏呢？

（图片来源：Twining, R.C., Vantrease, J.E., Love, S., Padival, M. & Rosenkranz, J.ANat. Neurosci. 20, 459–469 (2016).）

科学家发现ASD模型大鼠的LA-MeA投射很弱，如果提高ASD模型大鼠MeA的兴奋或者对来自LA区域的反应，其后天恐惧学习能力明显提高。因此说明LA-MeA投射路径确实在ASD个体中有所损坏，也同时再次表明LA-MeA投射路径对于后天恐惧学习很重要。

当我们在日常生活中听到别人的痛苦经历，往往表现出的感同身受的情绪可能来自于杏仁核LA-MeA的投射，这种情绪可以帮助我们避免受到别人曾经经历的痛苦，让我们可以更好的适应社会。所以有时候无所畏惧并不是强大的表现，适当的听从老人言才是机智的选择！

1.论文标题：An intra-amygdala circuit specifically regulates social fear learning

原文摘要：Adaptive social behavior requires transmission and reception of salient social information. Impairment of this reciprocity is a cardinal symptom of autism. The amygdala is a critical mediator of social behavior and is implicated in social symptoms of autism. Here we found that a specific amygdala circuit, from the lateral nucleus to the medial nucleus (LA–MeA), is required for using social cues to learn about environmental cues that signal imminent threats. Disruption of the LA–MeA circuit impaired valuation of these environmental cues and subsequent ability to use a cue to guide behavior. Rats with impaired social guidance of behavior due to knockout of Nrxn1, an analog of autism-associated gene NRXN, exhibited marked LA–MeA deficits. Chemogenetic activation of this circuit reversed these impaired social behaviors. These findings identify an amygdala circuit required to guide emotional responses to socially significant cues and identify an exploratory target for disorders associated with social impairments.

全文链接：http://www.nature.com/neuro/journal/v20/n3/abs/nn.4481.html

2、论文标题：Plastic Synaptic Networks of the Amygdala for the Acquisition, Expression, and Extinction of Conditioned Fear

原文摘要：The last 10 years have witnessed a surge of interest for the mechanisms underlying the acquisition and extinction of classically conditioned fear responses. In part, this results from the realization that abnormalities in fear learning mechanisms likely participate in the development and/or maintenance of human anxiety disorders. The simplicity and robustness of this learning paradigm, coupled with the fact that the underlying circuitry is evolutionarily well conserved, make it an ideal model to study the basic biology of memory and identify genetic factors and neuronal systems that regulate the normal and pathological expressions of learned fear. Critical advances have been made in determining how modified neuronal functions upon fear acquisition become stabilized during fear memory consolidation and how these processes are controlled in the course of fear memory extinction. With these advances came the realization that activity in remote neuronal networks must be coordinated for these events to take place. In this paper, we review these mechanisms of coordinated network activity and the molecular cascades leading to enduring fear memory, and allowing for their extinction. We will focus on Pavlovian fear conditioning as a model and the amygdala as a key component for the acquisition and extinction of fear responses.

全文链接：http://physrev.physiology.org/content/90/2/419.short

3、论文标题：Social learning of fear

原文摘要：Research across species highlights the critical role of the amygdala in fear conditioning. However, fear conditioning, involving direct aversive experience, is only one means by which fears can be acquired. Exploiting aversive experiences of other individuals through social fear learning is less risky. Behavioral research provides important insights into the workings of social fear learning, and the neural mechanisms are beginning to be understood. We review research suggesting that an amygdala-centered model of fear conditioning can help to explain social learning of fear through observation and instruction. We also describe how observational and instructed fear is distinguished by involvement of additional neural systems implicated in social-emotional behavior, language and explicit memory, and propose a modified conditioning model to account for social fear learning. A better understanding of social fear learning promotes integration of biological principles of learning with cultural evolution.

全文链接：http://www.nature.com/neuro/journal/v10/n9/abs/nn1968.html