Neural Mechanisms of Vocal Imitation in Adult Birds

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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.