NEURAL CHANGES ASSOCIATED WITH CRITICAL LEARNING PERIODS

在学习鸟类发声的过程中，鸟类会记住同种的歌声并使用 听觉反馈来塑造他们的发声，以适应这些存储的模型。 通常，歌曲学习被限制在特定物种的敏感期， 这项提议旨在识别神经变化，这些变化可能 鼓励和暂时限制这种学习。一般的方法是 描述相关大脑区域在发声过程中的正常变化 然后评估这些细胞的功能意义 通过检查它们如何受到基本听觉输入的影响而发生变化 为了歌曲学习。这些研究涉及斑马雀(Poephilla Guttata)， 一个物种，其歌声发育与主要的解剖和 控制歌曲的大脑通路中的神经化学变化。这些研究 建议检查伴随歌曲学习的两个特定的神经变化； 声带运动通路的新神经元的大量增加，以及 兴奋性氨基酸N-甲基-D-天冬氨酸的下降 与歌曲发育有关的区域内的受体。在第一组中 研究中，胸苷放射自显影和逆行示踪将 结合评估听觉输入在歌曲记忆或 发声练习影响植入神经元的新神经元的存活 发声运动通路。此外，长效逆行示踪剂将用于 确定在同一区域内是否发生神经元替换或增加 成年期的神经通路，此时歌唱模式稳定。在第二个 实验系列，神经递质受体放射自显影将 用于确定是否：i)NMDA受体的发育调节 绑定与年龄相关的倾向的差异相关 发声学习和，2)如果听觉操作延迟完成 无论是背诵歌曲还是发声练习，都同样会影响时间进程 NMDA受体下降。这一受体亚型与 许多其他依赖经验的发育可塑性的例子 和学习。敏感期的特征是各种各样的 行为现象(如语言习得、社交依恋、 印记)，这些研究将有助于定义 鼓励在这些独特的敏感时期学习。

During avian vocal learning, birds memorize conspecific songs and use auditory feedback to shape their vocalizations to these stored models. Often song learning is restricted to species-specific sensitive periods, and this proposal is aimed at identifying neural changes that may encourage and temporally constrain this learning. The general approach is to describe how relevant brain regions normally change during vocal learning, and then to assess the functional significance of these cellular changes by examining how they are influenced by auditory inputs essential to song learning. The studies concern zebra finches (Poephilla guttata), a species whose song development is associated with major anatomical and neurochemical changes within brain pathways controlling song. The studies proposed examine two specific neural changes that accompany song learning; a massive addition of new neurons to the vocal motor path way, and a decline in the N- methyl -D- aspartate class of excitatory amino acid receptor within a region implicated in song development. In the first set of studies, thymidine autoradiography and retrograde tracing will be combined to assess how auditory inputs during either song memorization or vocal practice influence the survival of new neurons inserted into the vocal motor pathway. Also, long-lasting retrograde tracers will be used to determine if neuronal replacement or addition occurs within this same neural pathway in adulthood, when song patterns are stable. In the second experimental series, neurotransmitter receptor autoradiography will be used to determine if: i) the developmental regulation of NMDA receptor binding correlates with age-related differences in the propensity for vocal learning and, 2) if auditory manipulations that delay completion of either song memorization or vocal practice similarly affect the timecourse of NMDA receptor decline. This receptor subtype has been linked to numerous other instances of experience-dependent developmental plasticity and learning. Sensitive periods are characteristic of a wide variety of behavioral phenomenon (e.g. language acquisition, social attachment, imprinting) and these studies will help define neural mechanisms that encourage learning during these periods of unique susceptibility.