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John R. Kirn






Neurogenesis persists into adulthood in many vertebrates including humans. The avian song system provides a great model to study the properties and functions of adultgenerated neurons. Here we report the first detailed analysis of the functional incorporation of adult-born neurons into the song system and their participation in a learned behavior-song production. New neurons formed in adult zebra finches were labeled with the cell birth dating marker [3H]-thymidine or 5-Bromo-2’-deoxy-uridine (BrdU) and examined 7, 15, 40 and 60 days later for their neuronal activity patterns marked by the expression of the immediate early gene ZENK. We found that song-related activity patterns emerged in adult-born HVC neurons 15 days after their formation. The present study provides the first direct evidence that adult-born neurons are activated by a specific learned motor behavior in awake and behaving birds. In addition, we discovered a culling period between 15 days and 40 days after cell birth when there was a significant decrease in new HVC neuron numbers and this culling occurred after significant song-related activation emerged. This period also coincided with the time when the activity patterns between new neurons and pre-existing cell populations differed the most. Taken together, our results strongly suggest that new neurons contribute to song-related behavior and that an activity-dependent selective culling process may contribute to the functional integration of adult-generated neurons. Our results reveal a cell age-dependent singing-related functional integration of adult-born neurons and contribute to our understanding of the functional significance of adult neurogenesis



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