NEURAL CHANGES ASSOCIATED WITH CRITICAL LEARNING PERIODS

在鸟类的声音学习过程中，鸟类会记住同种的歌曲， 听觉反馈来塑造他们的发声这些存储的模型。 通常，歌曲学习仅限于特定物种的敏感期， 这项提议旨在确定神经变化， 鼓励并暂时限制这种学习。一般的做法是 来描述相关的大脑区域在发声时是如何变化的 学习，然后评估这些细胞的功能意义， 通过检查它们如何受到听觉输入的影响来改变 歌曲学习这些研究涉及斑胸草雀（Poephilla guttata）， 一个物种，其歌曲的发展与主要的解剖学和 控制歌曲的大脑通路中的神经化学变化。研究 建议研究伴随着歌曲学习的两个特定神经变化; 大量新的神经元加入到发声运动通路中， N-甲基-D-天冬氨酸类兴奋性氨基酸减少 一个与歌曲发展有关的区域内的受体。在第一盘 的研究，胸苷放射自显影和逆行追踪将是 结合起来评估听觉输入如何在歌曲记忆或 发声练习会影响新神经元的存活， 发声运动通路此外，长效逆行示踪剂将用于 确定是否神经元替换或添加发生在同一个 成年期的神经通路，当歌曲模式稳定时。在第二 实验系列，神经递质受体放射自显影将是 用于确定是否：i）NMDA受体的发育调节 结合与年龄相关的差异的倾向， 声乐学习，2）如果听觉操纵，延迟完成 无论是歌曲记忆还是声乐练习， NMDA受体下降。这种受体亚型与 许多其他依赖经验的发育可塑性的例子 和学习敏感期的特点是各种各样的 行为现象（如语言习得，社会依恋， 这些研究将有助于确定神经机制， 鼓励在这些独特的易感时期学习。

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.