Brain and Mind Research Institute, The University of Sydney, NSW 2050, Australia.
Rev Neurosci. 2011;22(3):317-33. doi: 10.1515/RNS.2011.025. Epub 2011 May 13.
Laboratory rats learn to fear relatively innocuous stimuli which signal the imminent arrival of an innate source of danger, typically brief but aversive foot shock. Much is now known about the neural substrates underlying the acquisition, consolidation and subsequent expression of this fear. Rats also learn to fear stimuli which signal learned sources of danger but relatively little is known about the neural substrates underlying this form of fear. Two Pavlovian conditioning paradigms used to study this form of fear are second-order conditioning and sensory preconditioning. In second-order conditioning, rats are first exposed to a signaling relationship between one stimulus, such as a tone, and aversive foot shock, and then to a signaling relationship between a second stimulus, such as a light, and the now dangerous tone. In sensory preconditioning, these phases are reversed: rats are first exposed to a signaling relationship between the light and the tone and then to a signaling relationship between the tone and the foot shock. In both paradigms, rats exhibit fear when tested with the light. In this review paper, we describe the evidence for higher-order forms of conditioning, the conditions which promote this learning and its contents. We compare and contrast the substrates of the learning underlying second-order and sensory preconditioning fear with those known to underlie the better studied first-order conditioned fear. We conclude with some comments as to the role of higher-order processes in anxiety disorders.
实验室大鼠学会对相对无害的刺激产生恐惧，这些刺激预示着即将到来的固有危险源，通常是短暂但令人不快的足底电击。现在已经了解了许多关于获得、巩固和随后表达这种恐惧的神经基础。大鼠还学会了对预示着习得性危险源的刺激产生恐惧，但对这种形式的恐惧的神经基础知之甚少。两种用于研究这种恐惧形式的经典条件反射范式是二阶条件反射和感觉前条件反射。在二阶条件反射中，大鼠首先暴露于一个刺激（如音调）与令人不快的足底电击之间的信号关系，然后暴露于第二个刺激（如光）与现在危险的音调之间的信号关系。在感觉前条件反射中，这些阶段是颠倒的：大鼠首先暴露于光与音调之间的信号关系，然后暴露于音调与足底电击之间的信号关系。在这两种范式中，当用灯光测试大鼠时，它们会表现出恐惧。在这篇综述论文中，我们描述了高阶条件反射的证据、促进这种学习的条件及其内容。我们比较和对比了二阶和感觉前条件反射恐惧的学习基础与更深入研究的一阶条件恐惧的学习基础。最后，我们对高阶过程在焦虑障碍中的作用进行了一些评论。
