Holahan Matthew R, White Norman M
Department of Psychology, McGill University, Montreal, Québec, Canada H3A 1B1.
Neurobiol Learn Mem. 2002 Mar;77(2):250-75. doi: 10.1006/nlme.2001.4012.
Three conditioned aversive responses were used to infer the existence of an unobservable central state of "conditioned fear," and the roles of certain amygdala subregions in producing these responses were investigated. Rats received tone-shock pairings in one compartment of a shuttle box and no tones or shocks in the other, distinctive, compartment. They were then trained to find food in one arm of a Y-maze. After the final training trial they were exposed to different sets of stimuli in the shuttle box with no shock. Twenty-four hours later rats that had received immediate posttraining exposure to the conditioned stimuli (in the shock-paired compartment) made significantly more correct responses on the Y-maze than rats that had been exposed to the neutral stimuli (in the no-shock compartment) or rats that had received delayed posttraining exposure to the conditioned stimuli. This constitutes a demonstration of posttraining memory modulation by conditioned aversive stimuli. Freezing increased during posttraining exposure to the conditioned stimuli compared to the neutral stimuli. When subsequently allowed to move freely between the two compartments, the rats in all groups also showed significant conditioned avoidance of the compartment containing the conditioned stimuli. In a second experiment the effects of lesions confined to specific parts of the amygdala on the three conditioned responses (memory modulation, freezing, avoidance) were tested. Lesions of the central nucleus impaired all three conditioned responses; lesions of the medial nucleus impaired conditioned modulation and avoidance. These lesions had no effect on freezing during the training trials. Lesions of the lateral and basolateral nuclei attenuated freezing during both training and testing. The findings suggest that the central and medial nuclei of the amygdala may be important parts of neural circuits mediating conditioned responses that constitute conditioned aversive states, but that conditioned freezing may be mediated independently.
使用三种条件性厌恶反应来推断不可观察的“条件性恐惧”中枢状态的存在，并研究杏仁核某些亚区域在产生这些反应中的作用。大鼠在穿梭箱的一个隔室中接受音调 - 电击配对，而在另一个独特的隔室中既不接受音调也不接受电击。然后训练它们在Y型迷宫的一个臂中寻找食物。在最后一次训练试验后，它们在没有电击的情况下在穿梭箱中暴露于不同的刺激组。24小时后，在训练后立即暴露于条件刺激（在电击配对隔室中）的大鼠在Y型迷宫上做出的正确反应明显多于暴露于中性刺激（在无电击隔室中）的大鼠或在训练后延迟暴露于条件刺激的大鼠。这构成了条件性厌恶刺激对训练后记忆调节的证明。与中性刺激相比，在训练后暴露于条件刺激期间，僵住行为增加。当随后允许在两个隔室之间自由移动时，所有组的大鼠也表现出对包含条件刺激的隔室的显著条件性回避。在第二个实验中，测试了局限于杏仁核特定部位的损伤对三种条件反应（记忆调节、僵住、回避）的影响。中央核的损伤损害了所有三种条件反应；内侧核的损伤损害了条件调节和回避。这些损伤在训练试验期间对僵住行为没有影响。外侧核和基底外侧核的损伤在训练和测试期间均减弱了僵住行为。研究结果表明，杏仁核的中央核和内侧核可能是介导构成条件性厌恶状态的条件反应的神经回路的重要组成部分，但条件性僵住可能是独立介导的。
