Program in Neuroscience, Bates College, Lewiston, Maine 04240-6028, USA.
Learn Mem. 2010 Apr 28;17(5):259-66. doi: 10.1101/lm.1755810. Print 2010 May.
Long-term memory for fear of an environment (contextual fear conditioning) emerges later in development (postnatal day; PD 23) than long-term memory for fear of discrete stimuli (PD 17). As contextual, but not explicit cue, fear conditioning relies on the hippocampus; this has been interpreted as evidence that the hippocampus is not fully developed until PD 23. Alternatively, the hippocampus may be functional prior to PD 23, but unable to cooperate with the amygdala for fearful learning. The current experiments investigate this by separating the phases of conditioning across developmental stages. Rats were allowed to learn about the context on one day and to form the fearful association on another. Rats exposed to the context on PD 17 exhibited significant fear only when trained and tested a week later (PD 23, 24), but not on consecutive days (PD 18, 19), demonstrating that rats can learn about a context as early as PD 17. Further experiments clarify that it is associative mechanisms that are developing between PD 18 and 23. Finally, the hippocampus was lesioned prior to training to ensure the task is being solved in a hippocampus-dependent manner. These data provide compelling evidence that the hippocampus is functional for contextual learning as early as PD 17, however, its connection to the amygdala or other relevant brain structures may not yet be fully developed.
长期记忆的恐惧的环境(情景恐惧条件反射)出现在发育后期(产后天;PD 23)比长期记忆的离散刺激的恐惧(PD 17)。作为情景的，但不是明确的线索，恐惧条件反射依赖于海马体;这被解释为证据表明，海马体没有完全发育直到 PD 23。或者，海马体可能是功能性的之前 PD 23，但无法与杏仁核合作的恐惧学习。目前的实验通过在不同的发育阶段分离条件作用的阶段来研究这一点。大鼠被允许在一天内学习环境，并在另一天形成恐惧的联想。在 PD 17 暴露于环境的大鼠仅在训练和测试一周后(PD 23,24)表现出明显的恐惧，而不是在连续的日子(PD 18,19)，这表明大鼠可以早在 PD 17 就了解环境。进一步的实验澄清了在 PD 18 和 23 之间发展的是联想机制。最后，在训练前对海马体进行了损伤，以确保任务是在海马体依赖的方式下解决的。这些数据提供了令人信服的证据，表明海马体早在 PD 17 就对情景学习有了功能性，然而，它与杏仁核或其他相关脑结构的连接可能尚未完全发育。
