Second-order fear conditioning has been demonstrated in protocols using discrete and simple stimuli, and much is now known about its behavioral and neural characteristics. In contrast, the mechanisms of second-order conditioning to more complex stimuli, such as contexts, are unknown. To address this gap in our knowledge, we conducted a series of experiments to investigate the neural and behavioral characteristics of second-order context fear conditioning in rats. We found that rats acquire fear to a context in which a first-order conditioned stimulus is presented (Experiment 1); neuronal activity in the basolateral amygdala (BLA) is required for the acquisition (Experiment 2) and extinction (Experiment 3) of second-order context fear; second-order context fear can be reduced by extinction of its first-order conditioned stimulus associate (Experiment 4); and that second-order fear reduced in this way is restored when fear of the first-order conditioned stimulus spontaneously recovers or is reconditioned (Experiment 5). Thus, second-order context fear requires neuronal activity in the BLA, and once established, tracks the level of fear to its first-order conditioned stimulus-associate. These results are discussed with respect to the substrates of second-order fear conditioning in other protocols, and the role of the amygdala in different forms of conditioning.

在使用离散和简单刺激的协议中已经证明了二阶恐惧条件反射，并且现在对其行为和神经特征有很多了解。相比之下，对更复杂刺激（例如上下文）的二级调节机制尚不清楚。为了解决我们知识上的这一差距，我们进行了一系列实验来研究大鼠二阶情境恐惧条件反射的神经和行为特征。我们发现大鼠在呈现一阶条件刺激的环境中会产生恐惧（实验 1）；基底外侧杏仁核 (BLA) 的神经元活动是二阶情境恐惧的获得（实验 2）和消退（实验 3）所必需的；二阶情境恐惧可以通过消除其一阶条件刺激关联来减少（实验 4）；当对一阶条件刺激的恐惧自发恢复或被重新调节时，以这种方式减少的二阶恐惧就会恢复（实验 5）。因此，二阶情境恐惧需要 BLA 中的神经元活动，并且一旦建立，就会将恐惧水平跟踪到其一阶条件刺激相关。这些结果讨论了其他协议中二阶恐惧条件反射的底物，以及杏仁核在不同形式条件反射中的作用。二阶情境恐惧需要 BLA 中的神经元活动，并且一旦建立，就会将恐惧水平跟踪到其一阶条件刺激相关。这些结果讨论了其他协议中二阶恐惧条件反射的底物，以及杏仁核在不同形式条件反射中的作用。二阶情境恐惧需要 BLA 中的神经元活动，并且一旦建立，就会将恐惧水平跟踪到其一阶条件刺激相关。这些结果讨论了其他协议中二阶恐惧条件反射的底物，以及杏仁核在不同形式条件反射中的作用。