Adult born neurons and the avian song system, zebra finches
Songs serve important functions in many species, and at least one function for zebra finches is the means for the male to attract a female.
Male zebra finches learn their song from a tutor, who is typically the father. The process of learning a song is analogous to language learning, where both the strong motivation to mimic, learn and practice produces greater fluency and precision. When juvenile birds reach adulthood, the song they sing appears crystalized, remaining the same for the remainder of their adult lives. Curiously, during their adulthood, there is ongoing neurogenesis in an area of the brain, HVC, that is instrumental in the production of this song. Despite the fact that adult neurogenesis has been well-documented in this area for decades, it is not well known how nor to what extent these new neurons may benefit song production in the adult.
What is known is that 50% of the adult-born neurons (ABNs) in HVC send their axons to a motor area (RA), which then projects to the motor nuclei conducting the muscles responsible for producing song. It is currently unknown how these adult-born HVC-RA neurons develop and become incorporated into the existing HVC circuit, and Jake Aronowitz has been using injections of retrovirus to label ABNs and thus identify and record the HVC-RA for better understanding of that process.
The identity of the remaining 50% of ABNs in HVC that do not project to area RA is not known. Jake has been leading a project with a team of undergraduates (see below) that strongly suggests the mysterious 50% of HVC ABNs are readily labelled by DARPP-32, a phosphoprotein that is found in neurons with dopamine receptors. What is very clear in these studies is that the HVC-RA neurons do NOT have DARPP-32. Thus, we believe that there are two distinct and identifiable populations of ABNs in HVC. Current and future studies are focused on the DARPP-32+ ABNs in area HVC so that we can better understand their connections with other neurons and role(s) in song production.