ONTOGENY OF SONG LEARNING CIRCUITS

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This proposal has two main goals: 1) to better understand the mechanisms of vocal learning; 2) to understand the circuit changes that bring the sensitive period for vocal learning to an end. Vocal learning is one of the most symptomatic traits of our species, yet we know very little about the circuitry that makes it possible. A distinctive set of nuclei and pathways associated with acquisition and production of learned song has been described in songbirds. Unpublished observations from this laboratory indicate that the relation between parts of the avian auditory telencephalon changes towards the end of the sensitive period for vocal learning, with the disappearance of two major projections. Research planned will give a detailed description of the anatomy and time course of these changes in three species of songbird, the zebra finch, canary and swamp sparrow, that differ in the timing of their vocal learning. We will also test the extent to which manipulation of auditory experience, social experience and hormones -- which are known to influence the end of the sensitive period for vocal learning -- can affect the timing of the changes in connectivity observed in the auditory pathways of young zebra finches. Standard anterograde (Biocytin, dextran amines) and retrograde (fluorogold, fluorescent beads and cholera toxin) techniques will be used to map connectivity. The behavioral importance of the auditory regions studied will be tested by placing in them small injections of cytotoxic substances. This work is related to health studies in that it seeks to identify connections and conditions that restrict or favor vocal learning, with the hope that these insights can be of use in humans.