Department of Psychobiology, University of Granada, Campus Cartuja 18071, Spain.
Brain Res. 2013 Oct 2;1533:105-13. doi: 10.1016/j.brainres.2013.08.030. Epub 2013 Aug 22.
Previous experiments have shown that changes in the time of day between taste pre-exposure and conditioning prevent the latent inhibition of conditioning taste aversion. The effect of these changes in circadian context between pre-exposure and conditioning on the magnitude of the learned aversion appears to be similar to the effect of changes in spatial context on this type of learning. To elucidate the brain areas involved in this circadian dependence of latent inhibition of conditioning taste aversion, the effect of excitotoxic lesions of the hippocampus, a region related to spatial-contextual modulation in this learning process, was analyzed. The latent inhibition of conditioning taste aversion in animals with hippocampal lesions, that were pre-exposed and conditioned to the same or different time of day, was compared with the response of animals exposed to either conditions ("same" or "different") but had undergone amygdala lesions or sham lesions. The results showed that selective dorsal hippocampus lesion eliminated the circadian dependence of latent inhibition of taste aversion. A change in the time of day between pre-exposure and conditioning did not prevent latent inhibition in animals with hippocampal lesions. In contrast, this change prevented latent inhibition in the amygdala-lesioned and sham groups. These findings suggest that the hippocampus contains a selective mechanism that modulates the contextual dependency of the latent inhibition of conditioning taste aversion without interfering with the effect of taste pre-exposure itself. This study may help to understand the possible common involvement of the hippocampus in different types of contextual control of associative learning.
先前的实验表明，在味觉前暴露和条件作用之间的时间变化会阻止条件味觉厌恶的潜伏抑制。在预暴露和条件作用之间的昼夜节律背景中这些变化对习得性厌恶的幅度的影响似乎类似于空间背景变化对这种学习类型的影响。为了阐明潜伏抑制的条件味觉厌恶的这种昼夜节律依赖性所涉及的脑区，分析了海马体兴奋毒性损伤的影响，海马体是该学习过程中与空间-上下文调制相关的区域。将具有海马体损伤的动物的条件味觉厌恶的潜伏抑制与暴露于相同或不同时间的预暴露和条件作用的动物的反应进行比较，这些动物接受了“相同”或“不同”条件的暴露，但经历了杏仁核损伤或假手术损伤。结果表明，选择性背侧海马体损伤消除了味觉厌恶潜伏抑制的昼夜节律依赖性。在海马体损伤的动物中，预暴露和条件作用之间的时间变化并没有阻止潜伏抑制。相比之下，这种变化阻止了杏仁核损伤和假手术组的潜伏抑制。这些发现表明，海马体包含一种选择性机制，调节条件味觉厌恶的潜伏抑制的上下文依赖性，而不干扰味觉前暴露本身的效果。这项研究可能有助于理解海马体在不同类型的联想学习的上下文控制中的可能共同参与。
