Neural Mechanisms of Vocal Imitation in Adult Birds

人类和动物是如何模仿声音的？这个问题是人类如何学习说一门语言这个更广泛问题的核心，但在人类身上很难回答，因为人类的神经系统相对不受实验研究的影响。由于这个困难，斯特里特博士和他的合作者使用了一种小型鹦鹉虎皮鹦鹉来测试一个特定的模型，以了解声音模仿是如何起作用的。该模型指出，只要雀鸟发出类似于期望（即目标）发声的声音，虎皮鹦鹉大脑中先前确定的高级听觉区域就会向高级声音控制中心发送强化（或奖励）信号。通过试错和选择性强化，系统应该逐渐学会发出目标声音。为了验证这一假设，提出了两种实验。首先，在鸟类“试图”学习记忆声音的过程中，高级听觉区域受损（即化学损伤）。根据假设，这样的损伤应该会阻碍学习。其次，每次鸟儿发出符合实验者设定的某些声学标准的声音时，听觉区域就会受到电刺激。根据这个假设，这应该相当于实验者驱动的选择性强化，随着时间的推移，导致鸟发出的声音与实验者的期望非常吻合。总的来说，这些实验将导致对鹦鹉如何“鹦鹉学舌”的详细机制理解。结合Striedter实验室之前关于声音模仿的行为意义的其他工作，这项工作将导致对鸟类如何以及为什么模仿声音的全面解释。这项工作满足了公众理解鸟类如何以及为什么歌唱的愿望，并进一步推动了神经科学家对理解复杂大脑如何学习复杂事物的更具体的探索。

How do humans and animals imitate sounds? This question is central to the broader question of how humans learn to speak a language, but it is difficult to answer in humans because their nervous systems are relatively impervious to experimental study. Because of this difficulty, Dr. Striedter and his collaborators have used budgerigars, which are small parrots, to test a specific model of how vocal imitation works. The model specifies that a previously identified high-level auditory region in the brain of budgerigars sends a reinforcement (or reward) signal to a high-level vocal control center whenever the bird produced a sound that resembles the desired (i.e. target) vocalization. By trial and error, and selective reinforcement, the system should gradually learn to produce the target sound. To test this hypothesis, two kinds of experiments are proposed. First, the high-level auditory region is lesioned (i.e. chemically damaged) during the time that a bird is "trying" to learn a remembered sound. According to the hypothesis, such a lesion should prevent the learning. Second, the auditory region will be stimulated electrically every time the bird produced a vocalization that matches some acoustic criterion set by the experimenter. According to the hypothesis, this should amount to experimenter-driven selective reinforcement and, over time, cause the bird to produce vocalizations that closely match the experimenter's expectation. Collectively, these experiments will lead to a detailed mechanistic understanding of how parrots "parrot". Combined with other prior work in the Striedter laboratory on the behavioral significance of vocal imitation, this work will lead to a comprehensive account of how and why birds imitate sounds. This work fulfills the public's desire to understand how and why birds sing, and furthers the neuroscientists' more specific quest of understanding how complex brains learn complex things.