Wiltgen Brian J, Silva Alcino J
Departments of Neurobiology, Psychology, Psychiatry and the Brain Research Institute, UCLA, Los Angeles, California 90095, USA.
Learn Mem. 2007 Apr 10;14(4):313-7. doi: 10.1101/lm.430907. Print 2007 Apr.
Context memories initially require the hippocampus, but over time become independent of this structure. This shift reflects a consolidation process whereby memories are gradually stored in distributed regions of the cortex. The function of this process is thought to be the extraction of statistical regularities and general knowledge from specific experiences. The current study examined this idea in mice by measuring the specificity of context memories during consolidation. In the first experiment, separate groups of animals were trained with a single shock and tested in the training context or a novel environment 1, 14, 28, or 36 d later. We found a systematic increase in generalization over this period. Initially, mice froze more in the training context, but fear of the novel environment grew over time until animals eventually froze an equivalent amount in both contexts. The second experiment demonstrated that the increase in generalization was due to a loss of detailed information about the context and not fear incubation. In this experiment, mice were exposed to the context and then trained with an immediate shock 1 or 36 d later. Animals trained 1 d after exposure acquired robust context fear that did not generalize across environments. In contrast, mice trained 36 d after exposure froze an equivalent amount in the training context and the novel environment. The same profile was observed in H-ras mutants that exhibit enhanced hippocampal plasticity and learning. These results suggest that context memories are specific early after training when they require the hippocampus, and become more general as they are permanently stored in the cortex.
情境记忆最初需要海马体，但随着时间的推移会变得独立于该结构。这种转变反映了一个巩固过程，即记忆逐渐存储在皮质的分布式区域中。这个过程的功能被认为是从特定经历中提取统计规律和一般知识。当前的研究通过在巩固过程中测量情境记忆的特异性，在小鼠身上检验了这一观点。在第一个实验中，将单独的动物组用单次电击进行训练，并在训练后的第1、14、28或36天在训练情境或新环境中进行测试。我们发现在这段时间内泛化有系统性增加。最初，小鼠在训练情境中冻结反应更多，但对新环境的恐惧随着时间增长，直到动物最终在两种情境中的冻结反应量相当。第二个实验表明泛化的增加是由于关于情境的详细信息丧失，而非恐惧潜伏期延长。在这个实验中，小鼠先接触情境，然后在1天或36天后接受即时电击训练。接触后1天训练的动物获得了强烈的情境恐惧，且不会在不同环境中泛化。相比之下，接触后36天训练的小鼠在训练情境和新环境中的冻结反应量相当。在表现出海马体可塑性和学习能力增强的H-ras突变体中也观察到了相同的情况。这些结果表明，情境记忆在训练后早期需要海马体时是特定的，而在永久存储于皮质中时会变得更具普遍性。
